WorldWideScience

Sample records for monsoon experiment capmex

  1. Aerosol and Cloud Properties during the Cloud Cheju ABC Plume -Asian Monsoon Experiment (CAPMEX) 2008: Linking between Ground-based and UAV Measurements

    Science.gov (United States)

    Kim, S.; Yoon, S.; Venkata Ramana, M.; Ramanathan, V.; Nguyen, H.; Park, S.; Kim, M.

    2009-12-01

    Cheju Atmospheric Brown Cloud (ABC) Plume-Monsoon Experiment (CAPMEX), comprehsensive ground-based measurements and a series of data-gathering flights by specially equipped autonomous unmanned aerial vehicles (AUAVs) for aerosol and cloud, had conducted at Jeju (formerly, Cheju), South Korea during August-September 2008, to improve our understanding of how the reduction of anthropogenic emissions in China (so-called “great shutdown” ) during and after the Summer Beijing Olympic Games 2008 effcts on the air quliaty and radiation budgets and how atmospheric brown clouds (ABCs) influences solar radiation budget off Asian continent. Large numbers of in-situ and remote sensing instruments at the Gosan ABC observatory and miniaturized instruments on the aircraft measure a range of properties such as the quantity of soot, size-segregated aerosol particle numbers, total particle numbers, size-segregated cloud droplet numbers (only AUAV), aerosol scattering properties (only ground), aerosol vertical distribution, column-integrated aerosol properties, and meteorological variables. By integrating ground-level and high-elevation AUAV measurements with NASA-satellite observations (e.g., MODIS, CALIPSO), we investigate the long range transport of aerosols, the impact of ABCs on clouds, and the role of biogenic and anthropogenic aerosols on cloud condensation nuclei (CCN). In this talk, we will present the results from CAPMEX focusing on: (1) the characteristics of aerosol optical, physical and chemical properties at Gosan observatory, (2) aerosol solar heating calculated from the ground-based micro-pulse lidar and AERONET sun/sky radiometer synergy, and comparison with direct measurements from UAV, and (3) aerosol-cloud interactions in conjunction with measurements by satellites and Gosan observatory.

  2. Winter/Summer Monsoon Experiment

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Winter/Summer Monsoon Experiment (MONEX) was conducted during the First Global GARP (Global Atmospheric Research Program) Experiment (FGGE). An international...

  3. Monsoon Convection during the South China Sea Monsoon Experiment Observed from Shipboard Radar and the TRMM Satellite

    Science.gov (United States)

    Rickenbach, Tom; Cifelli, Rob; Halverson, Jeff; Kucera, Paul; Atkinson, Lester; Fisher, Brad; Gerlach, John; Harris, Kathy; Kaufman, Cristina; Liu, Ching-Hwang; hide

    1999-01-01

    A main goal of the recent South China Sea Monsoon Experiment (SCSMEX) was to study convective processes associated with the onset of the Southeast Asian summer monsoon. The NASA TOGA C-band scanning radar was deployed on the Chinese research vessel Shi Yan #3 for two 20 day cruises, collecting dual-Doppler measurements in conjunction with the BMRC C-Pol dual-polarimetric radar on Dongsha Island. Soundings and surface meteorological data were also collected with an NCAR Integrated Sounding System (ISS). This experiment was the first major tropical field campaign following the launch of the Tropical Rainfall Measuring Mission (TRMM) satellite. These observations of tropical oceanic convection provided an opportunity to make comparisons between surface radar measurements and the Precipitation Radar (PR) aboard the TRMM satellite in an oceanic environment. Nearly continuous radar operations were conducted during two Intensive Observing Periods (IOPS) straddling the onset of the monsoon (5-25 May 1998 and 5-25 June 1998). Mesoscale lines of convection with widespread regions of both trailing and forward stratiform precipitation were observed during the active monsoon periods in a southwesterly flow regime. Several examples of mesoscale convection will be shown from ship-based and spacebome radar reflectivity data during times of TRMM satellite overpasses. Further examples of pre-monsoon convection, characterized by isolated cumulonimbus and shallow, precipitating congestus clouds, will be discussed. A strong waterspout was observed very near the ship from an isolated cell in the pre-monsoon period, and was well documented with photography, radar, sounding, and sounding data.

  4. Monsoon Convective During the South China Sea Monsoon Experiment: Observations from Ground-Based Radar and the TRMM Satellite

    Science.gov (United States)

    Cifelli, Rob; Rickenbach, Tom; Halverson, Jeff; Keenan, Tom; Kucera, Paul; Atkinson, Lester; Fisher, Brad; Gerlach, John; Harris, Kathy; Kaufman, Cristina

    1999-01-01

    A main goal of the recent South China Sea Monsoon Experiment (SCSMEX) was to study convective processes associated with the onset of the Southeast Asian summer monsoon. The NASA TOGA C-band scanning radar was deployed on the Chinese research vessel Shi Yan #3 for two 20 day cruises, collecting dual-Doppler measurements in conjunction with the BMRC C-Pol dual-polarimetric radar on Dongsha Island. Soundings and surface meteorological data were also collected with an NCAR Integrated Sounding System (ISS). This experiment was the first major tropical field campaign following the launch of the Tropical Rainfall Measuring Mission (TRMM) satellite. These observations of tropical oceanic convection provided an opportunity to make comparisons between surface radar measurements and the Precipitation Radar (PR) aboard the TRMM satellite in an oceanic environment. Nearly continuous radar operations were conducted during two Intensive Observing Periods (IOPS) straddling the onset of the monsoon (5-25 May 1998 and 5-25 June 1998). Mesoscale lines of convection with widespread regions of both trailing and forward stratiform precipitation were observed following the onset of the active monsoon in the northern South China Sea region. The vertical structure of the convection during periods of strong westerly flow and relatively moist environmental conditions in the lower to mid-troposphere contrasted sharply with convection observed during periods of low level easterlies, weak shear, and relatively dry conditions in the mid to upper troposphere. Several examples of mesoscale convection will be shown from the ground (ship)-based and spaceborne radar data during times of TRMM satellite overpasses. Examples of pre-monsoon convection, characterized by isolated cumulonimbus and shallow, precipitating congestus clouds, will also be discussed.

  5. Some heat and moisture budgets over Bay of Bengal during MONSOON 17 experiment

    International Nuclear Information System (INIS)

    Bhaskar Rao, D.V.

    1985-12-01

    Heat and moisture budgets have been estimated for the period 13-18 August 1977 over Bay of Bengal using data collected from USSR ships during MONSOON 77 experiment. The divergence, relative vorticity and vertical p-velocity fields are derived. The apparent heat source and moisture sink are obtained for the period. The vertical-time sections of the derived fields are presented and the distributions are compared for undisturbed conditions during the period of study. The results show strong convective motions during the disturbed period indicating the importance of convection in the monsoon depressions. (author)

  6. Assessment of CORDEX-South Asia experiments for monsoonal precipitation over Himalayan region for future climate

    Science.gov (United States)

    Choudhary, A.; Dimri, A. P.

    2018-04-01

    Precipitation is one of the important climatic indicators in the global climate system. Probable changes in monsoonal (June, July, August and September; hereafter JJAS) mean precipitation in the Himalayan region for three different greenhouse gas emission scenarios (i.e. representative concentration pathways or RCPs) and two future time slices (near and far) are estimated from a set of regional climate simulations performed under Coordinated Regional Climate Downscaling Experiment-South Asia (CORDEX-SA) project. For each of the CORDEX-SA simulations and their ensemble, projections of near future (2020-2049) and far future (2070-2099) precipitation climatology with respect to corresponding present climate (1970-2005) over Himalayan region are presented. The variability existing over each of the future time slices is compared with the present climate variability to determine the future changes in inter annual fluctuations of monsoonal mean precipitation. The long-term (1970-2099) trend (mm/day/year) of monsoonal mean precipitation spatially distributed as well as averaged over Himalayan region is analyzed to detect any change across twenty-first century as well as to assess model uncertainty in simulating the precipitation changes over this period. The altitudinal distribution of difference in trend of future precipitation from present climate existing over each of the time slices is also studied to understand any elevation dependency of change in precipitation pattern. Except for a part of the Hindu-Kush area in western Himalayan region which shows drier condition, the CORDEX-SA experiments project in general wetter/drier conditions in near future for western/eastern Himalayan region, a scenario which gets further intensified in far future. Although, a gradually increasing precipitation trend is seen throughout the twenty-first century in carbon intensive scenarios, the distribution of trend with elevation presents a very complex picture with lower elevations

  7. Predictability experiments for the Asian summer monsoon: impact of SST anomalies on interannual and intraseasonal variability

    International Nuclear Information System (INIS)

    Molteni, Franco; Corti, Susanna; Ferranti, Laura; Slingo, Julia M.

    2003-07-01

    The effects of SST anomalies on the interannual and intraseasonal variability of the Asian summer monsoon have been studied by multivariate statistical analyses of 850-hPa wind and rainfall fields simulated in a set of ensemble integrations of the ECMWF atmospheric GCM, referred to as the PRISM experiments. The simulations used observed SSTs (PRISM-O), covering 9 years characterised by large variations of the ENSO phenomenon in the 1980's and the early 1990's. A parallel set of simulations was also performed with climatological SSTs (PRISM-C), thus enabling the influence of SST forcing on the modes of interannual and intraseasonal variability to be investigated. As in observations, the model's interannual variability is dominated by a zonally-oriented mode which describes the north-south movement of the tropical convergence zone (TCZ). This mode appears to be independent of SST forcing and its robustness between the PRISM-O and PRISM-C simulations suggests that it is driven by internal atmospheric dynamics. On the other hand, the second mode of variability, which again has a good correspondence with observed patterns, shows a clear relationship with the ENSO cycle. Since the mode related to ENSO accounts for only a small part of the total variance, the notion of a quasi-linear superposition of forced and unforced modes of variability may not provide an appropriate interpretation of monsoon interannual variability. Consequently, the possibility of a non-linear influence has been investigated by exploring the relationship between interannual and intraseasonal variability. As in other studies, a common mode of interannual and intraseasonal variability has been found, in this case describing the north-south transition of the TCZ associated with monsoon active/break cycles. Although seasonal-mean values of the Principal Component (PC) timeseries associated with the leading intraseasonal mode shows no significant correlation with ENSO, the 2-dimensional probability

  8. Predictability experiments for the Asian summer monsoon: Impact of SST anomalies on interannual and intraseasonal variability

    International Nuclear Information System (INIS)

    Molteni, F.; Corti, S.; Ferranti, L.; Slingo, J.M.

    2002-04-01

    The effects of SST anomalies on the interannual and intraseasonal variability of the Asian summer monsoon have been studied by multivariate statistical analyses of 850-hPa wind and rainfall yields simulated in a set of ensemble integrations of the ECMWF atmospheric GCM, referred to as the PRISM experiments. The simulations used observed SSTs (PRISM-O), covering 9 years characterised by large variations of the ENSO phenomenon in the 1980's and the early 1990's. A parallel set of simulations was also performed with climatological SSTs (PRISM-C), thus enabling the influence of SST forcing on the modes of interannual and intraseasonal variability to be investigated. As in observations, the model's interannual variability is dominated by a zonally-oriented mode which describes the north-south movement of the tropical convergence zone (TCZ). This mode appears to be independent of SST forcing and its robustness between the PRISM-O and PRISM-C simulations suggests that it is driven by internal atmospheric dynamics. On the other hand, the second mode of variability, which again has a good correspondence with observed patterns, shows a clear relationship with the ENSO cycle. Since the mode related to ENSO accounts for only a small part of the total variance, the notion of a quasi-linear superposition of forced and unforced modes of variability may not provide an appropriate interpretation of monsoon interannual variability. Consequently, the possibility of a non-linear influence has been investigated by exploring the relationship between interannual and intraseasonal variability. As in other studies, a common mode of interannual and intraseasonal variability has been found, in this case describing the north-south transition of the TCZ associated with monsoon active/break cycles. Although seasonal-mean values of the Principal Component (PC) timeseries associated with the leading intraseasonal mode shows no significant correlation with ENSO, the 2-dimensional probability

  9. Diagnosing GCM errors over West Africa using relaxation experiments. Part I: summer monsoon climatology and interannual variability

    Science.gov (United States)

    Pohl, Benjamin; Douville, Hervé

    2011-10-01

    The CNRM atmospheric general circulation model Arpege-Climat is relaxed towards atmospheric reanalyses outside the 10°S-32°N 30°W-50°E domain in order to disentangle the regional versus large-scale sources of climatological biases and interannual variability of the West African monsoon (WAM). On the one hand, the main climatological features of the monsoon, including the spatial distribution of summer precipitation, are only weakly improved by the nudging, thereby suggesting the regional origin of the Arpege-Climat biases. On the other hand, the nudging technique is relatively efficient to control the interannual variability of the WAM dynamics, though the impact on rainfall variability is less clear. Additional sensitivity experiments focusing on the strong 1994 summer monsoon suggest that the weak sensitivity of the model biases is not an artifact of the nudging design, but the evidence that regional physical processes are the main limiting factors for a realistic simulation of monsoon circulation and precipitation in the Arpege-Climat model. Sensitivity experiments to soil moisture boundary conditions are also conducted and highlight the relevance of land-atmosphere coupling for the amplification of precipitation biases. Nevertheless, the land surface hydrology is not the main explanation for the model errors that are rather due to deficiencies in the atmospheric physics. The intraseasonal timescale and the model internal variability are discussed in a companion paper.

  10. Diagnosing GCM errors over West Africa using relaxation experiments. Part I: summer monsoon climatology and interannual variability

    Energy Technology Data Exchange (ETDEWEB)

    Pohl, Benjamin [Meteo-France/CNRS, CNRM/GAME, Toulouse (France); CNRS/Universite de Bourgogne, Centre de Recherches de Climatologie, Dijon (France); Douville, Herve [Meteo-France/CNRS, CNRM/GAME, Toulouse (France)

    2011-10-15

    The CNRM atmospheric general circulation model Arpege-Climat is relaxed towards atmospheric reanalyses outside the 10 S-32 N 30 W-50 E domain in order to disentangle the regional versus large-scale sources of climatological biases and interannual variability of the West African monsoon (WAM). On the one hand, the main climatological features of the monsoon, including the spatial distribution of summer precipitation, are only weakly improved by the nudging, thereby suggesting the regional origin of the Arpege-Climat biases. On the other hand, the nudging technique is relatively efficient to control the interannual variability of the WAM dynamics, though the impact on rainfall variability is less clear. Additional sensitivity experiments focusing on the strong 1994 summer monsoon suggest that the weak sensitivity of the model biases is not an artifact of the nudging design, but the evidence that regional physical processes are the main limiting factors for a realistic simulation of monsoon circulation and precipitation in the Arpege-Climat model. Sensitivity experiments to soil moisture boundary conditions are also conducted and highlight the relevance of land-atmosphere coupling for the amplification of precipitation biases. Nevertheless, the land surface hydrology is not the main explanation for the model errors that are rather due to deficiencies in the atmospheric physics. The intraseasonal timescale and the model internal variability are discussed in a companion paper. (orig.)

  11. Hydrographic Conditions in the Gulf of Carpentaria During Australian Monsoon Experiment

    Science.gov (United States)

    Inoue, M.; Steinberg, C.; Wolanski, E.; Ridd, P.

    2002-12-01

    Gulf of Carpentaria located in the northern Australia, is a shallow wide basin with the deepest bottom depths of approximately 60 m. It is connected to Arafura Sea to the north and west, and to the Torres Strait to the east. Hydrographic surveys of the Gulf of Carpentaria were carried out in January and March, 1987 as part of Australian Monsoon Experiment. During the January survey, Tropical Cyclone (TC) Irma was formed in the Gulf of Carpentaria. An east-west CTD section at 13o52'S was occupied twice, one prior to and during, and the other after the formation of TC Irma. In addition, two post-Irma east-west sections were occupied at 12o40'S and 11o30'S. The pre-cyclone section indicates a well-defined stratified two-layer system, while the post-cyclone sections show deepening of the surface warm layer due to significant mixing by TC Irma. Overall, significant cooling of near surface warm water on the order of more than 1oC was observed. Significant heat loss estimated for the water column has presumably contributed toward the development of TC Irma. In February 1987, TC Jason was formed in the gulf. During the March survey, two east-west CTD sections were occupied at 11o30'S and 13o52'S. The March survey reveals notable warming of the bottom water. Detailed discussion of the CTD data from the two cruises will be presented.

  12. Predictability experiments for the Asian summer monsoon impact of SST anomalies on interannual and intraseasonal variability

    CERN Document Server

    Molteni, F; Ferranti, L; Slingo, J M

    2003-01-01

    The effects of SST anomalies on the interannual and intraseasonal variability of the Asian summer monsoon have been studied by multivariate statistical analyses of 850-hPa wind and rainfall fields simulated in a set of ensemble integrations of the ECMWF atmospheric GCM, referred to as the PRISM experiments. The simulations used observed SSTs (PRISM-O), covering 9 years characterised by large variations of the ENSO phenomenon in the 1980's and the early 1990's. A parallel set of simulations was also performed with climatological SSTs (PRISM-C), thus enabling the influence of SST forcing on the modes of interannual and intraseasonal variability to be investigated. As in observations, the model's interannual variability is dominated by a zonally-oriented mode which describes the north-south movement of the tropical convergence zone (TCZ). This mode appears to be independent of SST forcing and its robustness between the PRISM-O and PRISM-C simulations suggests that it is driven by internal atmospheric dynamics. O...

  13. Intercomparison and analyses of the climatology of the West African monsoon in the West African monsoon modeling and evaluation project (WAMME) first model intercomparison experiment

    Energy Technology Data Exchange (ETDEWEB)

    Xue, Yongkang; Sales, Fernando De [University of California, Los Angeles, CA (United States); Lau, W.K.M.; Schubert, Siegfried D.; Wu, Man-Li C. [NASA, Goddard Space Flight Center, Greenbelt, MD (United States); Boone, Aaron [Centre National de Recherches Meteorologiques, Meteo-France Toulouse, Toulouse (France); Feng, Jinming [University of California, Los Angeles, CA (United States); Chinese Academy of Sciences, Institute of Atmospheric Physics, Beijing (China); Dirmeyer, Paul; Guo, Zhichang [Center for Ocean-Land-Atmosphere Interactions, Calverton, MD (United States); Kim, Kyu-Myong [University of Maryland Baltimore County, Baltimore, MD (United States); Kitoh, Akio [Meteorological Research Institute, Tsukuba (Japan); Kumar, Vadlamani [National Center for Environmental Prediction, Camp Springs, MD (United States); Wyle Information Systems, Gaithersburg, MD (United States); Poccard-Leclercq, Isabelle [Universite de Bourgogne, Centre de Recherches de Climatologie UMR5210 CNRS, Dijon (France); Mahowald, Natalie [Cornell University, Ithaca, NY (United States); Moufouma-Okia, Wilfran; Rowell, David P. [Met Office Hadley Centre, Exeter (United Kingdom); Pegion, Phillip [NASA, Goddard Space Flight Center, Greenbelt, MD (United States); National Center for Environmental Prediction, Camp Springs, MD (United States); Schemm, Jae; Thiaw, Wassila M. [National Center for Environmental Prediction, Camp Springs, MD (United States); Sealy, Andrea [The Caribbean Institute for Meteorology and Hydrology, St. James (Barbados); Vintzileos, Augustin [National Center for Environmental Prediction, Camp Springs, MD (United States); Science Applications International Corporation, Camp Springs, MD (United States); Williams, Steven F. [National Center for Atmospheric Research, Boulder, CO (United States)

    2010-07-15

    This paper briefly presents the West African monsoon (WAM) modeling and evaluation project (WAMME) and evaluates WAMME general circulation models' (GCM) performances in simulating variability of WAM precipitation, surface temperature, and major circulation features at seasonal and intraseasonal scales in the first WAMME experiment. The analyses indicate that models with specified sea surface temperature generally have reasonable simulations of the pattern of spatial distribution of WAM seasonal mean precipitation and surface temperature as well as the averaged zonal wind in latitude-height cross-section and low level circulation. But there are large differences among models in simulating spatial correlation, intensity, and variance of precipitation compared with observations. Furthermore, the majority of models fail to produce proper intensities of the African Easterly Jet (AEJ) and the tropical easterly jet. AMMA Land Surface Model Intercomparison Project (ALMIP) data are used to analyze the association between simulated surface processes and the WAM and to investigate the WAM mechanism. It has been identified that the spatial distributions of surface sensible heat flux, surface temperature, and moisture convergence are closely associated with the simulated spatial distribution of precipitation; while surface latent heat flux is closely associated with the AEJ and contributes to divergence in AEJ simulation. Common empirical orthogonal functions (CEOF) analysis is applied to characterize the WAM precipitation evolution and has identified a major WAM precipitation mode and two temperature modes (Sahara mode and Sahel mode). Results indicate that the WAMME models produce reasonable temporal evolutions of major CEOF modes but have deficiencies/uncertainties in producing variances explained by major modes. Furthermore, the CEOF analysis shows that WAM precipitation evolution is closely related to the enhanced Sahara mode and the weakened Sahel mode, supporting

  14. Influence of the monsoon trough on air-sea interaction in the head of the Bay of Bengal during the southwest monsoon of 1990 (monsoon trough boundary layer experiment - 90)

    Digital Repository Service at National Institute of Oceanography (India)

    Sarma, Y.V.B.; Seetaramayya, P.; Murty, V.S.N.; Rao, D.P.

    programme reveals considerable temporal variability in sea-level pressure, sea-surface temperature (SST) and the fluxes of heat and momentum at the air-sea interface. This variability is related closely to the north-south movement of the monsoon trough...

  15. Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006

    Directory of Open Access Journals (Sweden)

    S. Janicot

    2008-09-01

    Full Text Available The AMMA (African Monsoon Multidisciplinary Analysis program is dedicated to providing a better understanding of the West African monsoon and its influence on the physical, chemical and biological environment regionally and globally, as well as relating variability of this monsoon system to issues of health, water resources, food security and demography for West African nations. Within this framework, an intensive field campaign took place during the summer of 2006 to better document specific processes and weather systems at various key stages of this monsoon season. This campaign was embedded within a longer observation period that documented the annual cycle of surface and atmospheric conditions between 2005 and 2007. The present paper provides a large and regional scale overview of the 2006 summer monsoon season, that includes consideration of of the convective activity, mean atmospheric circulation and synoptic/intraseasonal weather systems, oceanic and land surface conditions, continental hydrology, dust concentration and ozone distribution. The 2006 African summer monsoon was a near-normal rainy season except for a large-scale rainfall excess north of 15° N. This monsoon season was also characterized by a 10-day delayed onset compared to climatology, with convection becoming developed only after 10 July. This onset delay impacted the continental hydrology, soil moisture and vegetation dynamics as well as dust emission. More details of some less-well-known atmospheric features in the African monsoon at intraseasonal and synoptic scales are provided in order to promote future research in these areas.

  16. Deployment and Performance of an X-Band Dual-Polarization Radar during the Southern China Monsoon Rainfall Experiment

    Directory of Open Access Journals (Sweden)

    Zhao Shi

    2017-12-01

    Full Text Available An X-band dual-polarization radar (XPRAD was deployed in Guangdong province as part of the Southern China Monsoon Rainfall Experiment (SCMREX during the storm season in 2016. This paper presents a comprehensive assessment of XPRAD observations during SCMREX with emphasis on data processing and rainfall products. The differential phase-based attenuation correction and radar calibration using self-consistency of dual-polarization observables are presented. It is found that the standard deviation of the Z d r bias is less than 0.2 dB based on ‘light rain at low angle’ and ‘dry aggregate snow’ observations. Cross-comparison with two standard S-band China New Generation Weather Radars (CINRAD shows that the bias of Z h has a mean value less than 1.5 dBZ and a standard deviation less than 0.5 dBZ. In addition, fifteen rainfall events that occurred during the intensive observing period (IOP are analyzed to demonstrate the rainfall estimation performance of XPRAD. In particular, rainfall accumulations at 1-, 2- and 3-h scales derived using R( K d p and R( Z h , Z d r relations are evaluated using national level rain gauge data and CINRAD-based rainfall estimation. The results show that both R( K d p - and R( Z h , Z d r -based products agree well with the rain gauge observations and CINRAD estimation. The difference between R ( K d p and R ( Z h , Z d r is not significant, although R ( K d p shows slightly better performance than R ( Z h , Z d r .

  17. The Indian Monsoon

    Indian Academy of Sciences (India)

    The word 'monsoon' is derived from the Arabic word 'mausam' for season and the distinguishing attribute of ... lance, the word monsoon is used for the rainfall in the rainy season. In this article, I discuss the ..... [1] C S Ramage, Monsoon meteorology, International Geophysics Series,. Academic Press, San Diego, California ...

  18. Assessment of the performance of CORDEX-South Asia experiments for monsoonal precipitation over the Himalayan region during present climate: part I

    Science.gov (United States)

    Ghimire, S.; Choudhary, A.; Dimri, A. P.

    2018-04-01

    Analysis of regional climate simulations to evaluate the ability of 11 Coordinated Regional Climate Downscaling Experiment in South Asia experiments (CORDEX-South Asia) along with their ensemble to produce precipitation from June to September (JJAS) over the Himalayan region have been carried out. These suite of 11 combinations come from 6 regional climate models (RCMs) driven with 10 initial and boundary conditions from different global climate models and are collectively referred here as 11 CORDEX South Asia experiments. All the RCMs use a similar domain and are having similar spatial resolution of 0.44° ( 50 km). The set of experiments are considered to study precipitation sensitivity associated with the Indian summer monsoon (ISM) over the study region. This effort is made as ISM plays a vital role in summertime precipitation over the Himalayan region which acts as driver for the sustenance of habitat, population, crop, glacier, hydrology etc. In addition, so far the summer monsoon precipitation climatology over the Himalayan region has not been studied with the help of CORDEX data. Thus this study is initiated to evaluate the ability of the experiments and their ensemble in reproducing the characteristics of summer monsoon precipitation over Himalayan region, for the present climate (1970-2005). The precipitation climatology, annual precipitation cycles and interannual variabilities from each simulation have been assessed against the gridded observational dataset: Asian Precipitation-Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources for the given time period. Further, after the selection of the better performing experiment the frequency distribution of precipitation was also studied. In this study, an approach has also been made to study the degree of agreement among individual experiments as a way to quantify the uncertainty among them. The experiments though show a wide variation among themselves and individually over

  19. The Indian Monsoon

    Indian Academy of Sciences (India)

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    and led to the expectation that the impact of the monsoon on the ... a lead time of 10 days to a month for rainfall, temperature, etc., ... trying to predict, such as clouds or a monsoon depression (in ... occur because (i) the models are not perfect (involving many ... ally at many centres in the world, long-range predictions are.

  20. The Indian Monsoon

    Indian Academy of Sciences (India)

    Pacific Oceans, on subseasonal scales of a few days and on an interannual scale. ... over the Indian monsoon zone2 (Figure 3) during the summer monsoon .... each 500 km ×500 km grid over the equatorial Indian Ocean, Bay of Bengal and ...

  1. Energetics and monsoon bifurcations

    Science.gov (United States)

    Seshadri, Ashwin K.

    2017-01-01

    Monsoons involve increases in dry static energy (DSE), with primary contributions from increased shortwave radiation and condensation of water vapor, compensated by DSE export via horizontal fluxes in monsoonal circulations. We introduce a simple box-model characterizing evolution of the DSE budget to study nonlinear dynamics of steady-state monsoons. Horizontal fluxes of DSE are stabilizing during monsoons, exporting DSE and hence weakening the monsoonal circulation. By contrast latent heat addition (LHA) due to condensation of water vapor destabilizes, by increasing the DSE budget. These two factors, horizontal DSE fluxes and LHA, are most strongly dependent on the contrast in tropospheric mean temperature between land and ocean. For the steady-state DSE in the box-model to be stable, the DSE flux should depend more strongly on the temperature contrast than LHA; stronger circulation then reduces DSE and thereby restores equilibrium. We present conditions for this to occur. The main focus of the paper is describing conditions for bifurcation behavior of simple models. Previous authors presented a minimal model of abrupt monsoon transitions and argued that such behavior can be related to a positive feedback called the `moisture advection feedback'. However, by accounting for the effect of vertical lapse rate of temperature on the DSE flux, we show that bifurcations are not a generic property of such models despite these fluxes being nonlinear in the temperature contrast. We explain the origin of this behavior and describe conditions for a bifurcation to occur. This is illustrated for the case of the July-mean monsoon over India. The default model with mean parameter estimates does not contain a bifurcation, but the model admits bifurcation as parameters are varied.

  2. Monsoon onset over Kerala and pre monsoon rainfall peak

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Shenoi, S.S.C.; Shankar, D.

    and the monsoon onset date over Kerala was found to be 0.72, which was statistically significant. Thus, as is felt that the pre monsoon rainfall estimate from the satellite data can be used for predicting the monsoon onset over Kerala coast. The results...

  3. Measuring the monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Nair, R.R.

    that are constant enough to be used for navigation. But the monsoon also acts as a sign of the climatic times. Although its timing is remarkably regular, the intensity of its effects varies considerably from year to year. On top of natural variations in the strength...

  4. Tropical and Monsoonal Studies.

    Science.gov (United States)

    1988-01-01

    Duiing the cold surge event the balance of the 200 mb zonal momentum budget is between the zonal advecton of momentum and the coriolis, aceration ...over the South China Sea in the Malaysia ACKNOWLEDGEMENTS region during the winter monsoon, December 1973. Pure AppL Geophys., 115, 1303-1334. We wish

  5. The Indian Monsoon

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 13; Issue 3. The Indian Monsoon - Links to Cloud systems over the Tropical Oceans. Sulochana Gadgil. Series Article Volume 13 Issue 3 March 2008 pp 218-235. Fulltext. Click here to view fulltext PDF. Permanent link:

  6. Foretelling the Monsoon

    Indian Academy of Sciences (India)

    Relation between the continental TCZ and the TCZ over Equatorial Indian Ocean · Understanding year-to year (interannual) variation of the monsoon · Slide 40 · IMPACT OF EL NINO/LA NINA · Slide 42 · Variation of ISMR anomalies ( i.e. difference from the average value) normalized by std. deviation from 1979-2004.

  7. The Monsoon Erosion Pump and the Indian Monsoon since Eocene

    Science.gov (United States)

    Giosan, L.

    2017-12-01

    Lack of consensus on the Neogene establishment and evolution of the Indian Monsoon is remarkable after half a century of research. Conflicting interpretations point toward the possibility of periodic decoupling between monsoon winds and monsoon precipitation. Here I introduce the concept of a monsoon erosion pump based on terrestrial and oceanic records reconstructed from recent NGHP and IODP drilling and spanning the last 34 million years in the Bay of Bengal, Arabian and Andaman Seas. From millennial to orbital to tectonic timescales, these records suggest that vegetation land cover interacts and modulates the regime of erosion and weathering under perennial but variable monsoonal rain conditions. Under this new proposed paradigm the Indian monsoon exhibits two distinct flavours during the Neogene that can be largely explained by its heartbeat, or astronomical forcing, mediated by the global glacial state and interacting with the paleogeography of South Asia.

  8. Did Aboriginal vegetation burning affect the Australian summer monsoon?

    Science.gov (United States)

    Balcerak, Ernie

    2011-08-01

    For thousands of years, Aboriginal Australians burned forests, creating grasslands. Some studies have suggested that in addition to changing the landscape, these burning practices also affected the timing and intensity of the Australian summer monsoon. Different vegetation types can alter evaporation, roughness, and surface reflectivity, leading to changes in the weather and climate. On the basis of an ensemble of experiments with a global climate model, Notaro et al. conducted a comprehensive evaluation of the effects of decreased vegetation cover on the summer monsoon in northern Australia. They found that although decreased vegetation cover would have had only minor effects during the height of the monsoon season, during the premonsoon season, burning-induced vegetation loss would have caused significant decreases in precipitation and increases in temperature. Thus, by burning forests, Aboriginals altered the local climate, effectively extending the dry season and delaying the start of the monsoon season. (Geophysical Research Letters, doi:10.1029/2011GL047774, 2011)

  9. Forecasting Monsoon Precipitation Using Artificial Neural Networks

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This paper explores the application of Artificial Intelligent (AI) techniques for climate forecast. It pres ents a study on modelling the monsoon precipitation forecast by means of Artificial Neural Networks (ANNs). Using the historical data of the total amount of summer rainfall over the Delta Area of Yangtze River in China, three ANNs models have been developed to forecast the monsoon precipitation in the corre sponding area one year, five-year, and ten-year forward respectively. Performances of the models have been validated using a 'new' data set that has not been exposed to the models during the processes of model development and test. The experiment results are promising, indicating that the proposed ANNs models have good quality in terms of the accuracy, stability and generalisation ability.

  10. Effects of increased CO{sub 2} levels on monsoons

    Energy Technology Data Exchange (ETDEWEB)

    Cherchi, Annalisa; Masina, Simona; Navarra, Antonio [Centro Euro-Mediterraneo per i Cambiamenti Climatici and Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy); Alessandri, Andrea [Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna (Italy)

    2011-07-15

    Increased atmospheric carbon dioxide concentration provided warmer atmospheric temperature and higher atmospheric water vapor content, but not necessarily more precipitation. A set of experiments performed with a state-of-the-art coupled general circulation model forced with increased atmospheric CO{sub 2} concentration (2, 4 and 16 times the present-day mean value) were analyzed and compared with a control experiment to evaluate the effect of increased CO{sub 2} levels on monsoons. Generally, the monsoon precipitation responses to CO{sub 2} forcing are largest if extreme concentrations of carbon dioxide are used, but they are not necessarily proportional to the forcing applied. In fact, despite a common response in terms of an atmospheric water vapor increase to the atmospheric warming, two out of the six monsoons studied simulate less or equal summer mean precipitation in the 16 x CO{sub 2} experiment compared to the intermediate sensitivity experiments. The precipitation differences between CO{sub 2} sensitivity experiments and CTRL have been investigated specifying the contribution of thermodynamic and purely dynamic processes. As a general rule, the differences depending on the atmospheric moisture content changes (thermodynamic component) are large and positive, and they tend to be damped by the dynamic component associated with the changes in the vertical velocity. However, differences are observed among monsoons in terms of the role played by other terms (like moisture advection and evaporation) in shaping the precipitation changes in warmer climates. The precipitation increase, even if weak, occurs despite a weakening of the mean circulation in the monsoon regions (''precipitation-wind paradox''). In particular, the tropical east-west Walker circulation is reduced, as found from velocity potential analysis. The meridional component of the monsoon circulation is changed as well, with larger (smaller) meridional (vertical) scales. (orig.)

  11. Pleistocene Indian Monsoon Rainfall Variability

    Science.gov (United States)

    Yirgaw, D. G.; Hathorne, E. C.; Giosan, L.; Collett, T. S.; Sijingeo, A. V.; Nath, B. N.; Frank, M.

    2014-12-01

    The past variability of the Indian Monsoon is mostly known from records of wind strength over the Arabian Sea. Here we investigate proxies for fresh water input and runoff in a region of strong monsoon precipitation that is a major moisture source for the east Asian Monsoon. A sediment core obtained by the IODP vessel JOIDES Resolution and a gravity core from the Alcock Seamount complex in the Andaman Sea are used to examine the past monsoon variability on the Indian sub-continent and directly over the ocean. The current dataset covers the last glacial and deglacial but will eventually provide a Pleistocene record. We utilise the ecological habitats of G. sacculifer and N. dutertrei to investigate the freshwater-induced stratification with paired Mg/Ca and δ18O analyses to estimate seawater δ18O (δ18Osw). During the last 60 kyrs, Ba/Ca ratios and δ18Osw values generally agree well between the two cores and suggest the weakest surface runoff and monsoon during the LGM and strongest monsoon during the Holocene. The difference in δ18O between the species, interpreted as a proxy for upper ocean stratification, implies stratification developed around 37 ka and remained relatively constant during the LGM, deglacial and Holocene. To investigate monsoon variability for intervals in the past, single shell Mg/Ca and δ18O analyses have been conducted. Mg/Ca ratios from individual shells of N. dutertrei suggest relatively small changes in temperature. However, individual N. dutertrei δ18O differ greatly between the mid-Holocene and samples from the LGM and a nearby core top. The mid-Holocene individuals have a greater range and large skew towards negative values indicating greater fresh water influence.

  12. Circulation characteristics of a monsoon depression during ...

    Indian Academy of Sciences (India)

    M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

    ciated with organized convective processes in a monsoon depression. The objective is to ..... the errors are large and the performance of the high-resolution ... Ramage C S 1971 Monsoon meteorology (London: Academic. Press) 45–46.

  13. On breaks of the Indian monsoon

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    quadrapole is a basic feature of weak spells of the intraseasonal variation over the Asia-west Pacific region. ... (Earth Planet. Sci.), 112 .... be useful to define the break monsoon (and active ... monsoon zone, different scientists have used the.

  14. Large-Scale Control of the Arabian Sea Summer Monsoon Inversion and Low Clouds: A New Perspective

    Science.gov (United States)

    Wu, C. H.; Wang, S. Y.; Hsu, H. H.; Hsu, P. C.

    2016-12-01

    The Arabian Sea undergoes a so-called summer monsoon inversion that reaches the maximum intensity in August associated with a large amount of low-level clouds. The formation of inversion and low clouds was generally thought to be a local system influenced by the India-Pakistan monsoon advancement. New empirical and numerical evidence suggests that, rather than being a mere byproduct of the nearby monsoon, the Arabian Sea monsoon inversion is coupled with a broad-scale monsoon evolution connected across the Africa Sahel, South Asia, and the East Asia-western North Pacific (WNP). Several subseasonal variations occur in tandem: The eastward expansion of the Asian-Pacific monsoonal heating likely suppresses the India-Pakistan monsoon while enhancing low-level thermal inversion of Arabian Sea; the upper-tropospheric anticyclone in South Asia weakens in August smoothing zonal contrast in geopotential heights (10°N-30°N); the subtropical WNP monsoon trough in the lower troposphere that signals the revival of East Asian summer monsoon matures in August; the Sahel rainfall peaks in August accompanied by an intensified tropical easterly jet. The occurrence of the latter two processes enhances upper-level anticyclones over Africa and WNP and this, in turn, induces subsidence in between over the Arabian Sea. Numerical experiments demonstrate the combined effect of the African and WNP monsoonal heating on the enhancement of the Arabian Sea monsoon inversion. Connection is further found in the interannual and decadal variations between the East Asian-WNP monsoon and the Arabian Sea monsoon inversion. In years with reduced low clouds of Arabian Sea, the East Asian midlatitude jet stream remains strong in August while the WNP monsoon trough appears to be weakened. The Arabian Sea inversion (ridge) and WNP trough pattern which forms a dipole structure, is also found to have intensified since the 21st century.

  15. Meteorological results of monsoon-88 Expedition (pre-monsoon period)

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Krishnamurthy, L.; Babu, M.T.

    Mean atmospheric circulation, moisture budget and net heat exchange were studied during a pre-monsoon period (18th March to 3rd May, 1988), making use of the data collected on board "Akademik Korolev" in the central equatorial and southern Arabian...

  16. Asian monsoon variability, cyclicities, and forcing mechanisms

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    in monsoonal intensity from 5 to 2Ma. Uplift of the Himalayas and the Tibetan Plateau occurred coeval with the increase in strength of the Asian Monsoon between 9.5 and 5Ma. Variability of monsoon on glacial and interglacial time scale Multi proxy based... in the Western Ghats of India 131 Fig. 3. Multi proxy monsoon reconstructions show that summer monsoon strength was stronger during interglacials (shaded intervals) as compared to glacials 0 2 4 6 8 10 12 14 16 18 20 0 100 200 300 400 0 50...

  17. Revisiting Asian monsoon formation and change associated with Tibetan Plateau forcing: I. Formation

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Guoxiong; Liu, Yimin; Duan, Anmin; Bao, Qing [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing (China); Dong, Buwen [University of Reading, Department of Meteorology, National Centre for Atmospheric Science, Reading (United Kingdom); Liang, Xiaoyun [China Meteorological Administration, National Climate Center, Beijing (China); Yu, Jingjing [China Meteorological Administration, National Meteorological Information Center, Beijing (China)

    2012-09-15

    Numerical experiments with different idealized land and mountain distributions are carried out to study the formation of the Asian monsoon and related coupling processes. Results demonstrate that when there is only extratropical continent located between 0 and 120 E and between 20/30 N and the North Pole, a rather weak monsoon rainband appears along the southern border of the continent, coexisting with an intense intertropical convergence zone (ITCZ). The continuous ITCZ surrounds the whole globe, prohibits the development of near-surface cross-equatorial flow, and collects water vapor from tropical oceans, resulting in very weak monsoon rainfall. When tropical lands are integrated, the ITCZ over the longitude domain where the extratropical continent exists disappears as a consequence of the development of a strong surface cross-equatorial flow from the winter hemisphere to the summer hemisphere. In addition, an intense interaction between the two hemispheres develops, tropical water vapor is transported to the subtropics by the enhanced poleward flow, and a prototype of the Asian monsoon appears. The Tibetan Plateau acts to enhance the coupling between the lower and upper tropospheric circulations and between the subtropical and tropical monsoon circulations, resulting in an intensification of the East Asian summer monsoon and a weakening of the South Asian summer monsoon. Linking the Iranian Plateau to the Tibetan Plateau substantially reduces the precipitation over Africa and increases the precipitation over the Arabian Sea and the northern Indian subcontinent, effectively contributing to the development of the South Asian summer monsoon. (orig.)

  18. Monsoonal reversal of remote sensing biases in latent heat flux over eastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Muraleedharan, P.M.; Pankajakshan, T.; Sathe, P.V.; Murty, V.S.N.; Santosh, K.R.

    The Arabian Sea is a unique basin where a number of atmospheric and oceanographic processes occur due to the contrasting climatic conditions, which it experiences. The drastic monsoonal variability occurring in the boundary layer adversely affects...

  19. Annual monsoon rains recorded by Jurassic dunes.

    Science.gov (United States)

    Loope, D B; Rowe, C M; Joeckel, R M

    2001-07-05

    Pangaea, the largest landmass in the Earth's history, was nearly bisected by the Equator during the late Palaeozoic and early Mesozoic eras. Modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality, but direct evidence for annual rainfall periodicity has been lacking. In the Mesozoic era, about 190 million years ago, thick deposits of wind-blown sand accumulated in dunes of a vast, low-latitude desert at Pangaea's western margin. These deposits are now situated in the southwestern USA. Here we analyse slump masses in the annual depositional cycles within these deposits, which have been described for some outcrops of the Navajo Sandstone. Twenty-four slumps, which were generated by heavy rainfall, appear within one interval representing 36 years of dune migration. We interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains, with the other four having been the result of winter storms. The slumped lee faces of these Jurassic dunes therefore represent a prehistoric record of yearly rain events.

  20. Potential modulations of pre-monsoon aerosols during El Niño: impact on Indian summer monsoon

    Science.gov (United States)

    Fadnavis, S.; Roy, Chaitri; Sabin, T. P.; Ayantika, D. C.; Ashok, K.

    2017-10-01

    The potential role of aerosol loading on the Indian summer monsoon rainfall during the El Niño years are examined using satellite-derived observations and a state of the art fully interactive aerosol-chemistry-climate model. The Aerosol Index (AI) from TOMS (1978-2005) and Aerosol Optical Depth (AOD) from MISR spectroradiometer (2000-2010) indicate a higher-than-normal aerosol loading over the Indo-Gangetic plain (IGP) during the pre-monsoon season with a concurrent El Niño. Sensitivity experiments using ECHAM5-HAMMOZ climate model suggests that this enhanced loading of pre-monsoon absorbing aerosols over the Indo-Gangetic plain can reduce the drought during El Niño years by invoking the `Elevated-Heat-Pump' mechanism through an anomalous aerosol-induced warm core in the atmospheric column. This anomalous heating upshot the relative strengthening of the cross-equatorial moisture inflow associated with the monsoon and eventually reduces the severity of drought during El Niño years. The findings are subject to the usual limitations such as the uncertainties in observations, and limited number of El Niño years (during the study period).

  1. The Summer Monsoon of 1987.

    Science.gov (United States)

    Krishnamurti, T. N.; Bedi, H. S.; Subramaniam, M.

    1989-04-01

    In this paper we have examined the evolution of a number of parameters we believe were important for our understanding of the drought over India during the summer of 1987. The list of parameters includes monthly means or anomalies of the following fields: sea surface temperatures, divergent circulations, outgoing longwave radiation, streamfunction of the lower and upper troposphere, and monthly precipitation (expressed as a percentage departure from a long-term mean). The El Niño related warm sea surface temperature anomaly and a weaker warm sea surface temperature anomaly over the equatorial Indian Ocean provide sustained convection, as reflected by the negative values of the outgoing longwave radiation. With the seasonal heating, a pronounced planetary-scale divergent circulation evolved with a center along the western Pacific Ocean. The monsoonal divergent circulation merged with that related to the El Niño, maintaining most of the heavy rainfall activity between the equatorial Pacific Ocean and east Asia. Persistent convective activity continued south of India during the entire monsoon season. Strong Hadley type overturnings with rising motions over these warm SST anomaly regions and descent roughly near 20° to 25°S was evident as early as April 1987. The subtropical high pressure areas near 20° to 25°S showed stronger than normal circulations. This was revealed by the presence of a counterclockwise streamfunction anomaly at 850 mb during April 1987. With the seasonal heating, this anomaly moved northwards and was located over the Arabian Sea and India. This countermonsoon circulation anomaly at the low levels was associated with a weaker than normal Somali jet and Arabian Sea circulation throughout this summer. The monsoon remained active along northeast India, Bangladesh, northern lndochina, and central China during the summer monsoon season. This was related to the eastward shift of the divergent circulation. An eastward shift of the upper tropospheric

  2. Characteristics of monsoon low level jet (MLLJ)

    Indian Academy of Sciences (India)

    Temperature and wind data are used to describe variation in the strength of the Monsoon Low Level Jet (MLLJ) from an active phase of the monsoon to a break phase. Also estimated are the characteristics of turbulence above and below MLLJ.

  3. Sensible climates in monsoon Asia.

    Science.gov (United States)

    Ono, H S; Kawamura, T

    1991-06-01

    This study identifies characteristics of the geographical distribution of sensible climates and their diurnal and annual variations, and presents a classification of bioclimates in monsoon Asia by using Kawamura's discomfort index formula. During the hottest month, tropical areas and areas in central and South China are uncomfortable for humans throughout the day and night, and temperate zones in lowlands are uncomfortable during the daytime. Tropical zones are uncomfortable all year long and temperate zones in lowlands are uncomfortable during summer. Four climatic types were distinguished in monsoon Asia. Climatic type I, hyperthermal throughout the year, occurs in the tropics south of latitude 20 degrees N. Climatic type II, hyperthermal in the hottest month and comfortable in the coldest month, extends over latitudes from 20 degrees to 30 degrees N except in the highlands. Climatic type III, hyperthermal in the hottest month and hypothermal in the coldest month, encompasses temperate zones of East Asia and subtropical arid areas of northwestern India. Climatic type V, comfortable in the hottest month and hypothermal in coldest month, occurs near the southeast coast of the Soviet Union and in the highlands of the Himalayas.

  4. Global monsoons in the mid-Holocene and oceanic feedback

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Z.; Kutzbach, J. [Center for Climatic Research, University of Wisconsin-Madison, 1225 W. Dayton Street, Madison, WI 53706 (United States); Harrison, S.P. [Max Planck Institute for Biogeochemistry, P.O. Box 100164, 07701 Jena (Germany); Otto-Bliesner, B. [National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307 (United States)

    2004-03-01

    The response of the six major summer monsoon systems (the North American monsoon, the northern Africa monsoon, the Asia monsoon, the northern Australasian monsoon, the South America monsoon and the southern Africa monsoon) to mid-Holocene orbital forcing has been investigated using a coupled ocean-atmosphere general circulation model (FOAM), with the focus on the distinct roles of the direct insolation forcing and oceanic feedback. The simulation result is also found to compare well with the NCAR CSM. The direct effects of the change in insolation produce an enhancement of the Northern Hemisphere monsoons and a reduction of the Southern Hemisphere monsoons. Ocean feedbacks produce a further enhancement of the northern Africa monsoon and the North American monsoon. However, ocean feedbacks appear to weaken the Asia monsoon, although the overall effect (direct insolation forcing plus ocean feedback) remains a strengthened monsoon. The impact of ocean feedbacks on the South American and southern African monsoons is relatively small, and therefore these regions, especially the South America, experienced a reduced monsoon regime compared to present. However, there is a strong ocean feedback on the northern Australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region. A new synthesis is made for mid-Holocene paleoenvironmental records and is compared with the model simulations. Overall, model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations. (orig.)

  5. Interactions Between Asian Air Pollution and Monsoon System: South Asia (ROSES-2014 ACMAP)

    Science.gov (United States)

    Pan, Xiaohua; Chin, Mian; Tao, Zhining; Kim, Dongchul; Bian, Huisheng; Kucsera, Tom

    2018-01-01

    Asia's rapid economic growth over the past several decades has brought a remarkable increase in air pollution levels in that region. High concentrations of aerosols (also known as particulate matter or PM) from pollution sources pose major health hazards to half of the world population in Asia including South Asia. How do pollution and dust aerosols regulate the monsoon circulation and rainfall via scattering and absorbing solar radiation, changing the atmospheric heating rates, and modifying the cloud properties? We conducted a series of regional model experiments with NASA-Unified Weather Research and Forecast (NUWRF) regional model with coupled aerosol-chemistry-radiation-microphysics processes over South Asia for winter, pre-monsoon, and monsoon seasons to address this question. This study investigates the worsening air quality problem in South Asia by focusing on the interactions between pollution and South Asian monsoon, not merely focusing on the increase of pollutant emissions.

  6. BOBMEX: The Bay of Bengal Monsoon Experiment

    Digital Repository Service at National Institute of Oceanography (India)

    Bhat, G.S.; Gadgil, S.; Kumar, P.V.H.; Kalsi, S.R.; Madhusoodanan, P.; Murty, V.S.N.; Rao, C.V.K.P.; RameshBabu, V.; Rao, L.V.G.; Rao, R.R.; Ravichandran, M.; Reddy, K.G.; Rao, P.Sanjeeva; Sengupta, D.; Sikka, D.R.; Swain, J.; Vinayachandran, P.N.

    . However, unforeseen difficulties were faced in pro- curing radiosondes for one of the ships. Hence, radio- sondes (Vaisala model RS80-15G) were launched only from SK. More than 90 ascents covering active and weak phases of convection are available. The fre...- diosonde processor adjusted the calibration constants to take care of these minor differences. Before each launch, the radio- sonde humidity sensor was tested in a 100% RH chamber. The RH measured by the radio- sonde increased quickly to 90% within a few...

  7. Seasonally asymmetric transition of the Asian monsoon in response to ice age boundary conditions

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Hiroaki; Kuroki, Harumitsu; Kamae, Youichi [University of Tsukuba, Graduate School of Life and Environmental Sciences, Tsukuba, Ibaraki (Japan); Ohba, Masamichi [Central Research Institute of Electric Power Industry, Environmental Science Research Laboratory, Abiko (Japan)

    2011-12-15

    Modulation of a monsoon under glacial forcing is examined using an atmosphere-ocean coupled general circulation model (AOGCM) following the specifications established by Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) to understand the air-sea-land interaction under different climate forcing. Several sensitivity experiments are performed in response to individual changes in the continental ice sheet, orbital parameters, and sea surface temperature (SST) in the Last Glacial Maximum (LGM: 21 ka) to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon. Comparison of the model results in the LGM with the pre-industrial (PI) simulation shows that the Arabian Sea and Bay of Bengal are characterized by enhancement of pre-monsoon convection despite a drop in the SST encompassing the globe, while the rainfall is considerably suppressed in the subsequent monsoon period. In the LGM winter relative to the PI, anomalies in the meridional temperature gradient (MTG) between the Asian continents minus the tropical oceans become positive and are consistent with the intensified pre-monsoon circulation. The enhanced MTG anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude, showing an opposing view to a warmer future climate. It is also evident that a latitudinal gradient in the SST across the equator plays an important role in the enhancement of pre-monsoon rainfall. As for the summer, the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the Asian continent, which is consistent with the reduction of MTG involved in the attenuated monsoon. The surplus pre-monsoon convection causes a decrease in the SST through increased heat loss from the ocean surface; in other words, negative ocean feedback is also responsible for the subsequent weakening of summer

  8. GMMIP (v1.0) contribution to CMIP6: Global Monsoons Model Inter-comparison Project

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Tianjun; Turner, Andrew G.; Kinter, James L.; Wang, Bin; Qian, Yun; Chen, Xiaolong; Wu, Bo; Wang, Bin; Liu, Bo; Zou, Liwei; He, Bian

    2016-10-10

    The Global Monsoons Model Inter-comparison Project (GMMIP) has been endorsed by the panel of Coupled Model Inter-comparison Project (CMIP) as one of the participating model inter-comparison projects (MIPs) in the sixth phase of CMIP (CMIP6). The focus of GMMIP is on monsoon climatology, variability, prediction and projection, which is relevant to four of the “Grand Challenges” proposed by the World Climate Research Programme. At present, 21 international modeling groups are committed to joining GMMIP. This overview paper introduces the motivation behind GMMIP and the scientific questions it intends to answer. Three tiers of experiments, of decreasing priority, are designed to examine (a) model skill in simulating the climatology and interannual-to-multidecadal variability of global monsoons forced by the sea surface temperature during historical climate period; (b) the roles of the Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation in driving variations of the global and regional monsoons; and (c) the effects of large orographic terrain on the establishment of the monsoons. The outputs of the CMIP6 Diagnostic, Evaluation and Characterization of Klima experiments (DECK), “historical” simulation and endorsed MIPs will also be used in the diagnostic analysis of GMMIP to give a comprehensive understanding of the roles played by different external forcings, potential improvements in the simulation of monsoon rainfall at high resolution and reproducibility at decadal timescales. The implementation of GMMIP will improve our understanding of the fundamental physics of changes in the global and regional monsoons over the past 140 years and ultimately benefit monsoons prediction and projection in the current century.

  9. Observational Analysis of Two Contrasting Monsoon Years

    Science.gov (United States)

    Karri, S.; Ahmad, R.; Sujata, P.; Jose, S.; Sreenivas, G.; Maurya, D. K.

    2014-11-01

    The Indian summer monsoon rainfall contributes about 75 % of the total annual rainfall and exhibits considerable interannual variations. The agricultural economy of the country depends mainly on the monsoon rainfall. The long-range forecast of the monsoon rainfall is, therefore of significant importance in agricultural planning and other economic activities of the country. There are various parameters which influence the amount of rainfall received during the monsoon. Some of the important parameters considered by the Indian Meteorological Department (IMD) for the study of monsoon are Outgoing Longwave Radiation (OLR), moisture content of the atmosphere, zonal wind speed, low level vorticity, pressure gradient etc. Compared to the Long Period Average (LPA) value of rain fall, the country as a whole received higher amount of rainfall in June, 2013 (34 % more than LPA). The same month showed considerable decrease next year as the amount of rainfall received was around 43 % less compared to LPA. This drastic difference of monsoon prompted to study the behaviour of some of the monsoon relevant parameters. In this study we have considered five atmospheric parameters as the indicators of monsoon behaviour namely vertical relative humidity, OLR, aerosol optical depth (AOD), wind at 850 hPa and mean sea level pressure (MSLP). In the initial analysis of weekly OLR difference for year 2013 and 2014 shows positive values in the month of May over north-western parts of India (region of heat low). This should result in a weaker monsoon in 2014. This is substantiated by the rainfall data received for various stations over India. Inference made based on the analysis of RH profiles coupled with AOD values is in agreement with the rainfall over the corresponding stations.

  10. Influence of inland aerosol loading on the monsoon over Indian subcontinent

    Science.gov (United States)

    Satyanarayana, M.; Krishnakumar, V.; Mahadevan Pillai, V. P.; Radhakrishnan, S. R.; Raghunath, K.

    2008-12-01

    The monsoon water cycle is the lifeline to over 60% of the world's population. The study on the behavioral change of Indian monsoon due to aerosol loading will help for the better understanding of Indian Monsoon. Aerosol system influences the atmosphere in two ways; it affects directly the radiation budget and indirectly provides condensation nuclei required for the clouds. The precipitation of the clouds in the monsoon season depends on the microphysical properties of the clouds. The effect of aerosol on cirrus clouds is being looked into through this work as an effort to study the role of aerosol on Indian Monsoon. The microphysical properties of high altitude clouds were obtained from the ground based lidar experiments at a low latitude station in the Indian subcontinent. Measurements during the Indian monsoon period from the inland station National Atmospheric Research Laboratory (NARL) Gadanki (13.5_ N, 79.2_ E), Tirupati, India were used for the investigation. The depolarization characteristics of the cirrus clouds were measured and the correlation between the depolarization and the precipitation characteristics were studied. The results obtained over a period of one year from January 1998 to December 1998 were presented.

  11. The East Asian Atmospheric Water Cycle and Monsoon Circulation in the Met Office Unified Model

    Science.gov (United States)

    Rodríguez, José M.; Milton, Sean F.; Marzin, Charline

    2017-10-01

    In this study the low-level monsoon circulation and observed sources of moisture responsible for the maintenance and seasonal evolution of the East Asian monsoon are examined, studying the detailed water budget components. These observational estimates are contrasted with the Met Office Unified Model (MetUM) climate simulation performance in capturing the circulation and water cycle at a variety of model horizontal resolutions and in fully coupled ocean-atmosphere simulations. We study the role of large-scale circulation in determining the hydrological cycle by analyzing key systematic errors in the model simulations. MetUM climate simulations exhibit robust circulation errors, including a weakening of the summer west Pacific Subtropical High, which leads to an underestimation of the southwesterly monsoon flow over the region. Precipitation and implied diabatic heating biases in the South Asian monsoon and Maritime Continent region are shown, via nudging sensitivity experiments, to have an impact on the East Asian monsoon circulation. By inference, the improvement of these tropical biases with increased model horizontal resolution is hypothesized to be a factor in improvements seen over East Asia with increased resolution. Results from the annual cycle of the hydrological budget components in five domains show a good agreement between MetUM simulations and ERA-Interim reanalysis in northern and Tibetan domains. In simulations, the contribution from moisture convergence is larger than in reanalysis, and they display less precipitation recycling over land. The errors are closely linked to monsoon circulation biases.

  12. Relationship between summer monsoon rainfall and cyclogenesis ...

    Indian Academy of Sciences (India)

    relationship between Indian Ocean Dipole Mode. Index (IODMI) and the ... 2013) in the cyclogenesis over north Indian Ocean ..... Indian summer monsoon; J. Climate 17 3141–3155. ... Murakami H, Wang B and Kitoh A 2011 Future change.

  13. The Red Sea outflow regulated by the Indian monsoon

    Science.gov (United States)

    Aiki, Hidenori; Takahashi, Keiko; Yamagata, Toshio

    2006-08-01

    To investigate why the Red Sea water overflows less in summer and more in winter, we have developed a locally high-resolution global OGCM with transposed poles in the Arabian peninsula and India. Based on a series of sensitivity experiments with different sets of idealized atmospheric forcing, the present study shows that the summer cessation of the strait outflow is remotely induced by the monsoonal wind over the Indian Ocean, in particular that over the western Arabian Sea. During the southwest monsoon (May-September), thermocline in the Gulf of Aden shoals as a result of coastal Ekman upwelling induced by the predominantly northeastward wind in the Gulf of Aden and the Arabian Sea. Because this shoaling is maximum during the southwest summer monsoon, the Red Sea water is blocked at the Bab el Mandeb Strait by upwelling of the intermediate water of the Gulf of Aden in late summer. The simulation also shows the three-dimensional evolution of the Red Sea water tongue at the mid-depths in the Gulf of Aden. While the tongue meanders, the discharged Red Sea outflow water (RSOW) (incoming Indian Ocean intermediate water (IOIW)) is always characterized by anticyclonic (cyclonic) vorticity, as suggested from the potential vorticity difference.

  14. Impacts of Aerosol-Monsoon Interaction on Rainfall and Circulation over Northern India and the Himalaya Foothills

    Science.gov (United States)

    Lau, William K. M.; Kim, Kyu-Myong; Shi, Jainn-Jong; Matsui, T.; Chin, M.; Tan, Qian; Peters-Lidard, C.; Tao, W. K.

    2016-01-01

    The boreal summer of 2008 was unusual for the Indian monsoon, featuring exceptional heavy loading of dust aerosols over the Arabian Sea and northern-central India, near normal all- India rainfall, but excessive heavy rain, causing disastrous flooding in the Northern Indian Himalaya Foothills (NIHF) regions, accompanied by persistent drought conditions in central and southern India. Using NASA Unified-physics Weather Research Forecast (NUWRF) model with fully interactive aerosol physics and dynamics, we carried out three sets of 7-day ensemble model forecast experiments: 1) control with no aerosol, 2) aerosol radiative effect only and 3) aerosol radiative and aerosol-cloud-microphysics effects, to study the impacts of aerosol monsoon interactions on monsoon variability over the NIHF during the summer of 2008. Results show that aerosol-radiation interaction (ARI), i.e., dust aerosol transport, and dynamical feedback processes induced by aerosol-radiative heating, plays a key role in altering the large scale monsoon circulation system, reflected by an increased north-south tropospheric temperature gradient, a northward shift of heavy monsoon rainfall, advancing the monsoon onset by 1-5 days over the HF, consistent with the EHP hypothesis (Lau et al. 2006). Additionally, we found that dust aerosols, via the semi-direct effect, increase atmospheric stability, and cause the dissipation of a developing monsoon onset cyclone over northeastern India northern Bay of Bengal. Eventually, in a matter of several days, ARI transforms the developing monsoon cyclone into mesoscale convective cells along the HF slopes. Aerosol-Cloud-microphysics Interaction (ACI) further enhances the ARI effect in invigorating the deep convection cells and speeding up the transformation processes. Results indicate that even in short-term (up to weekly) numerical forecasting of monsoon circulation and rainfall, effects of aerosol-monsoon interaction can be substantial and cannot be ignored.

  15. Future projection of mean and variability of the Asian Summer Monsoon and Indian Ocean Climate systems

    Energy Technology Data Exchange (ETDEWEB)

    Annamalai, H. [Univ. of Hawaii, Honolulu, HI (United States)

    2014-09-15

    The overall goal of this project is to assess the ability of the CMIP3/5 models to simulate the Indian-Ocean monsoon systems. The PI along with post-docs investigated research issues ranging from synoptic systems to long-term trends over the Asian monsoon region. The PI applied diagnostic tools such as moist static energy (MSE) to isolate: the moist and radiative processes responsible for extended monsoon breaks over South Asia, precursors in the ENSO-monsoon association, reasons for the drying tendency over South Asia and the possible effect on tropical Indian Ocean climate anomalies influencing certain aspects of ENSO characteristics. By diagnosing various observations and coupled model simulations, we developed working hypothesis and tested them by carrying out sensitivity experiments with both linear and nonlinear models. Possible physical and dynamical reasons for model sensitivities were deduced. On the teleconnection front, the ability of CMIP5 models in representing the monsoon-desert mechanism was examined recently. Further more, we have applied a suite of diagnostics and have performed an in depth analysis on CMIP5 integrations to isolate the possible reasons for the ENSO-monsoon linkage or lack thereof. The PI has collaborated with Dr. K.R. Sperber of PCMDI and other CLIVAR Asian-Australian monsoon panel members in understanding the ability of CMIP3/5 models in capturing monsoon and its spectrum of variability. The objective and process-based diagnostics aided in selecting models that best represent the present-day monsoon and its variability that are then employed for future projections. Two major highlights were an invitation to write a review on present understanding monsoons in a changing climate in Nature Climate Change, and identification of an east-west shift in observed monsoon rainfall (more rainfall over tropical western Pacific and drying tendency over South Asia) in the last six decades and attributing that shift to SST rise over the tropical

  16. Aerosol and monsoon climate interactions over Asia: AEROSOL AND MONSOON CLIMATE INTERACTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhanqing [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Lau, W. K. -M. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Ramanathan, V. [Department of Atmospheric and Climate Sciences, University of California, San Diego California USA; Wu, G. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Ding, Y. [National Climate Center, China Meteorological Administration, Beijing China; Manoj, M. G. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Liu, J. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Qian, Y. [Pacific Northwest National Laboratory, Richland Washington USA; Li, J. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Zhou, T. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Fan, J. [Pacific Northwest National Laboratory, Richland Washington USA; Rosenfeld, D. [Institute of Earth Sciences, Hebrew University, Jerusalem Israel; Ming, Y. [Geophysical Fluid Dynamic Laboratory, NOAA, Princeton New Jersey USA; Wang, Y. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena California USA; Huang, J. [College of Atmospheric Sciences, Lanzhou University, Lanzhou China; Wang, B. [Department of Atmospheric Sciences, University of Hawaii, Honolulu Hawaii USA; School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing China; Xu, X. [Chinese Academy of Meteorological Sciences, Beijing China; Lee, S. -S. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Cribb, M. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Zhang, F. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Yang, X. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Zhao, C. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Takemura, T. [Research Institute for Applied Mechanics, Kyushu University, Fukuoka Japan; Wang, K. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Xia, X. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Yin, Y. [School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing China; Zhang, H. [National Climate Center, China Meteorological Administration, Beijing China; Guo, J. [Chinese Academy of Meteorological Sciences, Beijing China; Zhai, P. M. [Chinese Academy of Meteorological Sciences, Beijing China; Sugimoto, N. [National Institute for Environmental Studies, Tsukuba Japan; Babu, S. S. [Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram India; Brasseur, G. P. [Max Planck Institute for Meteorology, Hamburg Germany

    2016-11-15

    Asian monsoons and aerosols have been studied extensively which are intertwined in influencing the climate of Asia. This paper provides a comprehensive review of ample studies on Asian aerosol, monsoon and their interactions. The region is the primary source of aerosol emissions of varies species, influenced by distinct weather and climatic regimes. On continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulation. The atmospheric thermodynamic state may also be altered by the aerosol serving as cloud condensation nuclei or ice nuclei. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of numerous monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcings of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

  17. A numerical study of the South China Sea Warm Current during winter monsoon relaxation

    Science.gov (United States)

    Zhang, Cong; Ding, Yang; Bao, Xianwen; Bi, Congcong; Li, Ruixiang; Zhang, Cunjie; Shen, Biao; Wan, Kai

    2018-03-01

    Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current (SCSWC) in the northern South China Sea (NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea (SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.

  18. Understanding the Unusual 2017 Monsoon and Floods in South Asia

    Science.gov (United States)

    Akanda, A. S.; Palash, W.; Hasan, M. A.; Nusrat, F.

    2017-12-01

    Driven primarily by the South Asian Monsoon, the Ganges-Brahmaputra-Meghna (GBM) river basin system collectively drains intense precipitation for an area of more than 1.5 million square kilometers during the wet summer season. Bangladesh, being the lowest riparian country in the system, experiences recurrent floods and immense suffering to its population. The 2017 monsoon season was quite unusual in terms of the characteristics of the precipitation received in the basin. The monsoon was spread out over a much larger time span (April-October) compared to the average monsoon season (June-September). Although the monsoon does not typically start until June in Bangladesh, the 2017 season started much earlier in April with unusually heavy precipitation in the Meghna basin region and caused major damage to agriculture in northeastern Bangladesh. The rainfall continued in several record-breaking pulses, compared to the typical one or two large waves. One of the largest pulses occurred in early August with very high in intensity and volume, causing ECMWF to issue a major warning about widespread flooding in Bangladesh, Northern India, and Eastern Nepal. This record flood event impacted over 40 million people in the above regions, causing major damage to life and infrastructure. Although the Brahmaputra rose above the danger level several times this season, the Ganges was unusually low, thus sparing downstream areas from disastrous floods. However, heavy precipitation continued until October, causing urban flooding in Dhaka and Chittagong - and worsening sanitation and public health conditions in southern Bangladesh - currently undergoing a terrible humanitarian crisis involving Rohingya refugees from the Myanmar. Despite marked improvement in flood forecasting systems in recent years, the 2017 floods identified critical gaps in our understanding of the flooding phenomena and limitations of dissemination in these regions. In this study, we investigate 1) the unusual

  19. Monsoon signatures in recent corals from the Laccadive Islands

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.A.S.

    X-radiographs of the coral (Porites sp.) collected from several atolls of Lakshadweep show alternate bands of low and high density, formed in non-monsoon period and monsoon period, respectively. The results reveal annual density variations as well...

  20. Hydrography of the Wadge bank - premonsoon and monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    RamaRaju, V.S.; Rao, T.V.N.; RameshBabu, V.; Anto, A.F.

    The hydrography of the Wadge Bank during premonsoon and monsoon seasons is presented. The thermocline slopes downward towards the central region. Upwelling is prominent in the entire region during monsoon and is observed only in the western...

  1. The monsoon system: Land-sea breeze or the ITCZ?

    Science.gov (United States)

    Gadgil, Sulochana

    2018-02-01

    For well over 300 years, the monsoon has been considered to be a gigantic land-sea breeze driven by the land-ocean contrast in surface temperature. In this paper, this hypothesis and its implications for the variability of the monsoon are discussed and it is shown that the observations of monsoon variability do not support this popular theory of the monsoon. An alternative hypothesis (whose origins can be traced to Blanford's (1886) remarkably perceptive analysis) in which the basic system responsible for the Indian summer monsoon is considered to be the Intertropical Convergence Zone (ITCZ) or the equatorial trough, is then examined and shown to be consistent with the observations. The implications of considering the monsoon as a manifestation of the seasonal migration of the ITCZ for the variability of the Indian summer monsoon and for identification of the monsoonal regions of the world are briefly discussed.

  2. Modelling the Asian summer monsoon using CCAM

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Kim Chi; McGregor, John L. [CSIRO Marine and Atmospheric Research, Aspendale, VIC (Australia)

    2009-02-15

    A ten-year mean (1989-1998) climatology of the Asian summer monsoon is studied using the CSIRO Conformal-Cubic Atmospheric Model (CCAM) to downscale NCEP reanalyses. The aim of the current study is to validate the model results against previous work on this topic, in order to identify model strengths and weaknesses in simulating the Asian summer monsoon. The model results are compared with available observations and are presented in two parts. In the first part, the mean summer rainfall, maximum and minimum temperatures and winds are compared with the observations. The second part focuses on validation of the monsoon onset. The model captures the mean characteristics such as the cross-equatorial flow of low-level winds over the Indian Ocean and near the Somali coast, rainfall patterns, onset indices, northward movements, active-break and revival periods. (orig.)

  3. Mechanism of ENSO influence on the South Asian monsoon rainfall in global model simulations

    Science.gov (United States)

    Joshi, Sneh; Kar, Sarat C.

    2018-02-01

    Coupled ocean atmosphere global climate models are increasingly being used for seasonal scale simulation of the South Asian monsoon. In these models, sea surface temperatures (SSTs) evolve as coupled air-sea interaction process. However, sensitivity experiments with various SST forcing can only be done in an atmosphere-only model. In this study, the Global Forecast System (GFS) model at T126 horizontal resolution has been used to examine the mechanism of El Niño-Southern Oscillation (ENSO) forcing on the monsoon circulation and rainfall. The model has been integrated (ensemble) with observed, climatological and ENSO SST forcing to document the mechanism on how the South Asian monsoon responds to basin-wide SST variations in the Indian and Pacific Oceans. The model simulations indicate that the internal variability gets modulated by the SSTs with warming in the Pacific enhancing the ensemble spread over the monsoon region as compared to cooling conditions. Anomalous easterly wind anomalies cover the Indian region both at 850 and 200 hPa levels during El Niño years. The locations and intensity of Walker and Hadley circulations are altered due to ENSO SST forcing. These lead to reduction of monsoon rainfall over most parts of India during El Niño events compared to La Niña conditions. However, internally generated variability is a major source of uncertainty in the model-simulated climate.

  4. Prediction of a thermodynamic wave train from the monsoon to the Arctic following extreme rainfall events

    Science.gov (United States)

    Krishnamurti, T. N.; Kumar, Vinay

    2017-04-01

    This study addresses numerical prediction of atmospheric wave trains that provide a monsoonal link to the Arctic ice melt. The monsoonal link is one of several ways that heat is conveyed to the Arctic region. This study follows a detailed observational study on thermodynamic wave trains that are initiated by extreme rain events of the northern summer south Asian monsoon. These wave trains carry large values of heat content anomalies, heat transports and convergence of flux of heat. These features seem to be important candidates for the rapid melt scenario. This present study addresses numerical simulation of the extreme rains, over India and Pakistan, and the generation of thermodynamic wave trains, simulations of large heat content anomalies, heat transports along pathways and heat flux convergences, potential vorticity and the diabatic generation of potential vorticity. We compare model based simulation of many features such as precipitation, divergence and the divergent wind with those evaluated from the reanalysis fields. We have also examined the snow and ice cover data sets during and after these events. This modeling study supports our recent observational findings on the monsoonal link to the rapid Arctic ice melt of the Canadian Arctic. This numerical modeling suggests ways to interpret some recent episodes of rapid ice melts that may require a well-coordinated field experiment among atmosphere, ocean, ice and snow cover scientists. Such a well-coordinated study would sharpen our understanding of this one component of the ice melt, i.e. the monsoonal link, which appears to be fairly robust.

  5. Anomalous behaviour of the Indian summer monsoon 2009

    Indian Academy of Sciences (India)

    The Indian subcontinent witnessed a severe monsoon drought in the year 2009. India as a whole received. 77% of its long period average during summer monsoon season (1 June to 30 September) of 2009, which is the third highest deficient all India monsoon season rainfall year during the period 1901–2009. Therefore,.

  6. Origins of the Asian-Australian monsoons related to Cenozoic plate movement and Tibetan Plateau uplift - A modeling study

    Science.gov (United States)

    Liu, X.; Dong, B.; Yin, Z. Y.; Smith, R. S.; Guo, Q.

    2017-12-01

    The origin of monsoon is a subject that has attracted much attention in the scientific community and even today it is still controversial. According to geological records, there is conflicting evidence regarding the timings of establishment of the monsoon climates in South Asia, East Asia, and northern Australia. Additionally, different explanations for the monsoon origins have been derived from various numerical simulations. To further investigate the origin and evolution of the Asian and Australian monsoons, we designed a series of numerical experiments using a coupled atmospheric-oceanic general circulation model. Since the Indian-Australian plate has shifted its position significantly during the Cenozoic, together with the large-scale uplift of the Tibetan Plateau (TP), in these experiments we considered the configurations of ocean-land masses and large topographic features based on geological evidence of plate motion and TP uplift in 5 typical Cenozoic geological periods: mid-Paleocene ( 60Ma), late-Eocene ( 40Ma), late-Oligocene ( 25Ma), late-Miocene ( 10Ma), and present day. These experiments allowed us to examine the combined effects of the changes in the land-ocean configuration due to plate movement and TP uplift, they also provided insight into the effects of the high CO2 levels during the Eocene. The simulations revealed that during the Paleocene, the Indian Subcontinent was still positioned in the Southern Hemisphere (SH) and, therefore, its climate behaved as the SH tropical monsoon. By the late Eocene, it moved into the tropical Northern Hemisphere, which allowed the establishment of the South Asian monsoon. In contrast, the East Asian and Australian monsoon did not exist in the late Oligocene. These monsoon systems were established in the Miocene and then enhanced thereafter. Establishments of the low-latitude monsoons in South Asia and Australia were entirely determined by the position of the Indian-Australian plate and not related to the TP uplift

  7. Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October-December) season

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y; Maneesha, K.

    peak monsoon (October–November) season and concluded that the frequency of cyclones is modulated by negative and positive IOD rather than El-Nino and La-Nina. In this study, the relationship between southwest monsoon rainfall (June–September) and TNDC... Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October–December) season Y Sadhuram∗ and K Maneesha CSIR–National Institute of Oceanography, 176, Lawsons Bay Colony, Visakhapatnam 530 017, India...

  8. Does SW Monsoon Influence Total Suspended Matter Flux into the Arabian Sea?

    Digital Repository Service at National Institute of Oceanography (India)

    Raghavan, B.R.; Chauhan, O.S.

    Seasonal enhancement in the flux of total suspended matter (TSM) has been attributed to climatology of the SW monsoon (SWM) in time-series trap experiments conducted in the Arabian Sea. To determine the influence of climate on TSM flux, synoptic...

  9. Distribution and sources of particulate organic matter in the Indian monsoonal estuaries during monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Sarma, V.V.S.S.; Krishna, M.S.; Prasad, V.R.; Kumar, B.S.K.; Naidu, S.A.; Rao, G.D.; Viswanadham, R.; Sridevi, T.; Kumar, P.P.; Reddy, N.P.C.

    The distribution and sources of particulate organic carbon (POC) and nitrogen (PN) in 27 Indian estuaries were examined during the monsoon using the content and isotopic composition of carbon and nitrogen. Higher phytoplankton biomass was noticed...

  10. Reanalysis of the Indian summer monsoon: four dimensional data assimilation of AIRS retrievals in a regional data assimilation and modeling framework

    Science.gov (United States)

    Attada, Raju; Parekh, Anant; Chowdary, J. S.; Gnanaseelan, C.

    2018-04-01

    This work is the first attempt to produce a multi-year downscaled regional reanalysis of the Indian summer monsoon (ISM) using the National Centers for Environmental Prediction (NCEP) operational analyses and Atmospheric Infrared Sounder (AIRS) version 5 temperature and moisture retrievals in a regional model. Reanalysis of nine monsoon seasons (2003-2011) are produced in two parallel setups. The first set of experiments simply downscale the original NCEP operational analyses, whilst the second one assimilates the AIRS temperature and moisture profiles. The results show better representation of the key monsoon features such as low level jet, tropical easterly jet, subtropical westerly jet, monsoon trough and the spatial pattern of precipitation when AIRS profiles are assimilated (compared to those without AIRS data assimilation). The distribution of temperature, moisture and meridional gradients of dynamical and thermodynamical fields over the monsoon region are better represented in the reanalysis that assimilates AIRS profiles. The change induced by AIRS data on the moist and thermodynamic conditions results in more realistic rendering of the vertical shear associated with the monsoon, which in turn leads to a proper moisture transport and the moist convective feedback. This feedback benefits the representation of the regional monsoon characteristics, the monsoon dynamics and the moist convective processes on the seasonal time scale. This study emphasizes the use of AIRS soundings for downscaling of ISM representation in a regional reanalysis.

  11. Reanalysis of the Indian summer monsoon: four dimensional data assimilation of AIRS retrievals in a regional data assimilation and modeling framework

    KAUST Repository

    Attada, Raju

    2017-07-04

    This work is the first attempt to produce a multi-year downscaled regional reanalysis of the Indian summer monsoon (ISM) using the National Centers for Environmental Prediction (NCEP) operational analyses and Atmospheric Infrared Sounder (AIRS) version 5 temperature and moisture retrievals in a regional model. Reanalysis of nine monsoon seasons (2003–2011) are produced in two parallel setups. The first set of experiments simply downscale the original NCEP operational analyses, whilst the second one assimilates the AIRS temperature and moisture profiles. The results show better representation of the key monsoon features such as low level jet, tropical easterly jet, subtropical westerly jet, monsoon trough and the spatial pattern of precipitation when AIRS profiles are assimilated (compared to those without AIRS data assimilation). The distribution of temperature, moisture and meridional gradients of dynamical and thermodynamical fields over the monsoon region are better represented in the reanalysis that assimilates AIRS profiles. The change induced by AIRS data on the moist and thermodynamic conditions results in more realistic rendering of the vertical shear associated with the monsoon, which in turn leads to a proper moisture transport and the moist convective feedback. This feedback benefits the representation of the regional monsoon characteristics, the monsoon dynamics and the moist convective processes on the seasonal time scale. This study emphasizes the use of AIRS soundings for downscaling of ISM representation in a regional reanalysis.

  12. Assessment of Land Surface Models in a High-Resolution Atmospheric Model during Indian Summer Monsoon

    KAUST Repository

    Attada, Raju

    2018-04-17

    Assessment of the land surface models (LSMs) on monsoon studies over the Indian summer monsoon (ISM) region is essential. In this study, we evaluate the skill of LSMs at 10 km spatial resolution in simulating the 2010 monsoon season. The thermal diffusion scheme (TDS), rapid update cycle (RUC), and Noah and Noah with multi-parameterization (Noah-MP) LSMs are chosen based on nature of complexity, that is, from simple slab model to multi-parameterization options coupled with the Weather Research and Forecasting (WRF) model. Model results are compared with the available in situ observations and reanalysis fields. The sensitivity of monsoon elements, surface characteristics, and vertical structures to different LSMs is discussed. Our results reveal that the monsoon features are reproduced by WRF model with all LSMs, but with some regional discrepancies. The model simulations with selected LSMs are able to reproduce the broad rainfall patterns, orography-induced rainfall over the Himalayan region, and dry zone over the southern tip of India. The unrealistic precipitation pattern over the equatorial western Indian Ocean is simulated by WRF–LSM-based experiments. The spatial and temporal distributions of top 2-m soil characteristics (soil temperature and soil moisture) are well represented in RUC and Noah-MP LSM-based experiments during the ISM. Results show that the WRF simulations with RUC, Noah, and Noah-MP LSM-based experiments significantly improved the skill of 2-m temperature and moisture compared to TDS (chosen as a base) LSM-based experiments. Furthermore, the simulations with Noah, RUC, and Noah-MP LSMs exhibit minimum error in thermodynamics fields. In case of surface wind speed, TDS LSM performed better compared to other LSM experiments. A significant improvement is noticeable in simulating rainfall by WRF model with Noah, RUC, and Noah-MP LSMs over TDS LSM. Thus, this study emphasis the importance of choosing/improving LSMs for simulating the ISM phenomena

  13. Assessment of Land Surface Models in a High-Resolution Atmospheric Model during Indian Summer Monsoon

    Science.gov (United States)

    Attada, Raju; Kumar, Prashant; Dasari, Hari Prasad

    2018-04-01

    Assessment of the land surface models (LSMs) on monsoon studies over the Indian summer monsoon (ISM) region is essential. In this study, we evaluate the skill of LSMs at 10 km spatial resolution in simulating the 2010 monsoon season. The thermal diffusion scheme (TDS), rapid update cycle (RUC), and Noah and Noah with multi-parameterization (Noah-MP) LSMs are chosen based on nature of complexity, that is, from simple slab model to multi-parameterization options coupled with the Weather Research and Forecasting (WRF) model. Model results are compared with the available in situ observations and reanalysis fields. The sensitivity of monsoon elements, surface characteristics, and vertical structures to different LSMs is discussed. Our results reveal that the monsoon features are reproduced by WRF model with all LSMs, but with some regional discrepancies. The model simulations with selected LSMs are able to reproduce the broad rainfall patterns, orography-induced rainfall over the Himalayan region, and dry zone over the southern tip of India. The unrealistic precipitation pattern over the equatorial western Indian Ocean is simulated by WRF-LSM-based experiments. The spatial and temporal distributions of top 2-m soil characteristics (soil temperature and soil moisture) are well represented in RUC and Noah-MP LSM-based experiments during the ISM. Results show that the WRF simulations with RUC, Noah, and Noah-MP LSM-based experiments significantly improved the skill of 2-m temperature and moisture compared to TDS (chosen as a base) LSM-based experiments. Furthermore, the simulations with Noah, RUC, and Noah-MP LSMs exhibit minimum error in thermodynamics fields. In case of surface wind speed, TDS LSM performed better compared to other LSM experiments. A significant improvement is noticeable in simulating rainfall by WRF model with Noah, RUC, and Noah-MP LSMs over TDS LSM. Thus, this study emphasis the importance of choosing/improving LSMs for simulating the ISM phenomena in

  14. Assessment of Land Surface Models in a High-Resolution Atmospheric Model during Indian Summer Monsoon

    KAUST Repository

    Attada, Raju; Kumar, Prashant; Dasari, Hari Prasad

    2018-01-01

    Assessment of the land surface models (LSMs) on monsoon studies over the Indian summer monsoon (ISM) region is essential. In this study, we evaluate the skill of LSMs at 10 km spatial resolution in simulating the 2010 monsoon season. The thermal diffusion scheme (TDS), rapid update cycle (RUC), and Noah and Noah with multi-parameterization (Noah-MP) LSMs are chosen based on nature of complexity, that is, from simple slab model to multi-parameterization options coupled with the Weather Research and Forecasting (WRF) model. Model results are compared with the available in situ observations and reanalysis fields. The sensitivity of monsoon elements, surface characteristics, and vertical structures to different LSMs is discussed. Our results reveal that the monsoon features are reproduced by WRF model with all LSMs, but with some regional discrepancies. The model simulations with selected LSMs are able to reproduce the broad rainfall patterns, orography-induced rainfall over the Himalayan region, and dry zone over the southern tip of India. The unrealistic precipitation pattern over the equatorial western Indian Ocean is simulated by WRF–LSM-based experiments. The spatial and temporal distributions of top 2-m soil characteristics (soil temperature and soil moisture) are well represented in RUC and Noah-MP LSM-based experiments during the ISM. Results show that the WRF simulations with RUC, Noah, and Noah-MP LSM-based experiments significantly improved the skill of 2-m temperature and moisture compared to TDS (chosen as a base) LSM-based experiments. Furthermore, the simulations with Noah, RUC, and Noah-MP LSMs exhibit minimum error in thermodynamics fields. In case of surface wind speed, TDS LSM performed better compared to other LSM experiments. A significant improvement is noticeable in simulating rainfall by WRF model with Noah, RUC, and Noah-MP LSMs over TDS LSM. Thus, this study emphasis the importance of choosing/improving LSMs for simulating the ISM phenomena

  15. The Diurnal Cycle of the Boundary Layer, Convection, Clouds, and Surface Radiation in a Coastal Monsoon Environment (Darwin Australia)

    Energy Technology Data Exchange (ETDEWEB)

    May, Peter T.; Long, Charles N.; Protat, Alain

    2012-08-01

    The diurnal variation of convection and associated cloud and radiative properties remains a significant issue in global NWP and climate models. This study analyzes observed diurnal variability of convection in a coastal monsoonal environment examining the interaction of convective rain clouds, their associated cloud properties, and the impact on the surface radiation and corresponding boundary layer structure during periods where convection is suppressed or active on the large scale. The analysis uses data from the Tropical Warm Pool International Cloud Experiment (TWP-ICE) as well as routine measurements from the Australian Bureau of Meteorology and the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program. Both active monsoonal and large-scale suppressed (buildup and break) conditions are examined and demonstrate that the diurnal variation of rainfall is much larger during the break periods and the spatial distribution of rainfall is very different between the monsoon and break regimes. During the active monsoon the total net radiative input to the surface is decreased by more than 3 times the amount than during the break regime - this total radiative cloud forcing is found to be dominated by the shortwave (SW) cloud effects because of the much larger optical thicknesses and persistence of long-lasting anvils and cirrus cloud decks associated with the monsoon regime. These differences in monsoon versus break surface radiative energy contribute to low-level air temperature differences in the boundary layer over the land surfaces.

  16. Dirtier Air from a Weaker Monsoon

    Science.gov (United States)

    Chin, Mian

    2012-01-01

    The level of air pollution in China has much increased in the past decades, causing serious health problems. Among the main pollutants are aerosols, also known as particulate matter: tiny, invisible particles that are suspended in the air. These particles contribute substantially to premature mortality associated with cardiopulmonary diseases and lung cancer1. The increase of the aerosol level in China has been commonly attributed to the fast rise in pollutant emissions from the rapid economic development in the region. However, writing in Geophysical Research Letters, Jianlei Zhu and colleagues2 tell a different side of the story: using a chemical transport model and observation data, they show that the decadal scale weakening of the East Asian summer monsoon has also contributed to the increase of aerosol concentrations in China. The life cycle of atmospheric aerosols starts with its emission or formation in the atmosphere. Some aerosol components such as dust, soot and sea salt are emitted directly as particles to the atmosphere, but others are formed there by way of photochemical reactions. For example, sulphate and nitrate aerosols are produced from their respective precursor gases, sulphur dioxide and nitrogen oxides. Aerosol particles can be transported away from their source locations by winds or vertical motion of the air. Eventually, they are removed from the atmosphere by means of dry deposition and wet scavenging by precipitation. Measurements generally show that aerosol concentrations over Asia are lowest during the summer monsoon season3, because intense rainfall efficiently removes them from the air. The East Asian summer monsoon extends over subtropics and mid-latitudes. Its rainfall tends to concentrate in rain belts that stretch out for many thousands of kilometres and affect China, Korea, Japan and the surrounding area. Observations suggest that the East Asian summer monsoon circulation and precipitation have been in decline since the 1970s4. In

  17. Transport of sulfonamide antibiotics in crop fields during monsoon season.

    Science.gov (United States)

    Park, Jong Yol; Ruidisch, Marianne; Huwe, Bernd

    2016-11-01

    Previous studies have documented the occurrence of veterinary sulfonamide antibiotics in groundwater and rivers located far from pollution sources, although their transport and fate is relatively unknown. In mountainous agricultural fields, the transport behaviour can be influenced by climate, slope and physico-chemical properties of the sulfonamides. The objective of this research is to describe the transport behaviour of three sulfonamide antibiotics (sulfamethoxazole, sulfadimethoxine and sulfamethazine) in sloped agricultural fields located in the Haean catchment, South Korea. During dry and monsoon seasons, a solute transport experiment was conducted in two typical sandy loam agricultural fields after application of antibiotics and potassium bromide as conservative tracers. Field measurement and modelling revealed that frequency and amount of runoff generation indicate a relation between slope and rain intensity during monsoon season. Since the steepness of slope influenced partitioning of precipitation between runoff and subsurface flow, higher loss of sulfonamide antibiotics and bromide by runoff was observed at the steeper sloped field. Bromide on topsoil rapidly infiltrated at high infiltration rates. On the contrary, the sulfonamides were relatively retarded in the upper soil layer due to adsorption onto soil particles. Presence of furrows and ridges affected the distribution of sulfonamide antibiotics in the subsurface due to gradient from wetter furrows to drier ridges induced by topography. Modelling results with HydroGeoSphere matched with background studies that describe physico-chemical properties of the sulfonamides interaction between soil and the antibiotic group, solute transport through vadose zone and runoff generation by storm events.

  18. Automated software configuration in the MONSOON system

    Science.gov (United States)

    Daly, Philip N.; Buchholz, Nick C.; Moore, Peter C.

    2004-09-01

    MONSOON is the next generation OUV-IR controller project being developed at NOAO. The design is flexible, emphasizing code re-use, maintainability and scalability as key factors. The software needs to support widely divergent detector systems ranging from multi-chip mosaics (for LSST, QUOTA, ODI and NEWFIRM) down to large single or multi-detector laboratory development systems. In order for this flexibility to be effective and safe, the software must be able to configure itself to the requirements of the attached detector system at startup. The basic building block of all MONSOON systems is the PAN-DHE pair which make up a single data acquisition node. In this paper we discuss the software solutions used in the automatic PAN configuration system.

  19. Development of summer monsoon and onset of continuous rains over central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    rains happening during the last phase of monsoon development as a consequence of and after (2-5 weeks) the establishment of monsoon circulation or monsoon front. Summer monsoon front, as the term 'monsoon' originally meant, is to be delineated from...

  20. Recent changes in the summer monsoon circulation and their impact on dynamics and thermodynamics of the Arabian Sea

    Science.gov (United States)

    Pratik, Kad; Parekh, Anant; Karmakar, Ananya; Chowdary, Jasti S.; Gnanaseelan, C.

    2018-05-01

    The present study examines changes in the low-level summer monsoon circulation over the Arabian Sea and their impact on the ocean dynamics using reanalysis data. The study confirms intensification and northward migration of low-level jet during 1979 to 2015. Further during the study period, an increase in the Arabian Sea upper ocean heat content is found in spite of a decreasing trend in the net surface heat flux, indicating the possible role of ocean dynamics in the upper ocean warming. Increase in the anti-cyclonic wind stress curl associated with the change in the monsoon circulation induces downwelling over the central Arabian Sea, favoring upper ocean warming. The decreasing trend of southward Ekman transport, a mechanism transporting heat from the land-locked north Indian Ocean to southern latitudes, also supports increasing trend of the upper ocean heat content. To reinstate and quantify the role of changing monsoon circulation in increasing the heat content over the Arabian Sea, sensitivity experiment is carried out using ocean general circulation model. In this experiment, the model is forced by inter-annual momentum forcing while rest of the forcing is climatological. Experiment reveals that the changing monsoon circulation increases the upper ocean heat content, effectively by enhancing downwelling processes and reducing southward heat transport, which strongly endorses our hypothesis that changing ocean dynamics associated with low-level monsoon circulation is causing the increasing trend in the heat content of the Arabian Sea.

  1. Teleconnections associated with the intensification of the Australian monsoon during El Nino Modoki events

    International Nuclear Information System (INIS)

    Taschetto, A S; Gupta, A Sen; Ummenhofer, C C; England, M H; Haarsma, R J

    2010-01-01

    In this study we investigate the teleconnection between the central-western Pacific sea surface temperature (SST) warming, characteristic of El Nino Modoki events, and Australian rainfall using observations and atmospheric general circulation model experiments. During Modoki events, wet conditions are generally observed over northwestern Australia at the peak of the monsoon season (i.e. January and February) while dry conditions occur in the shoulder-months (i.e. December and March). This results in a shorter but more intense monsoon season over northwestern Australia relative to the climatology. We show that, apart from the well-known displacement of the Walker circulation, the anomalous warming in the central-western equatorial Pacific also induces a westward-propagating disturbance associated with a Gill-type mechanism. This in turn generates an anomalous cyclonic circulation over northwestern Australia that reinforces the climatological mean conditions during the peak of the monsoon season. The anomalous circulation leads to convergence of moisture and increased precipitation over northern Australia. This response, however, only occurs persistently during austral summer when the South Pacific Convergence Zone is climatologically strengthened, phase-locking the Gill-type response to the seasonal cycle. The interaction between the interannual SST variability during El Nino Modoki events and the evolution of the seasonal cycle intensifies deep convection in the central-west Pacific, driving a Gill-type response to diabatic heating. The intensified monsoonal rainfall occurs strongly in February due to the climatological wind conditions that are normally cyclonic over northwestern Australia.

  2. Sensitivity of convective precipitation to soil moisture and vegetation during break spell of Indian summer monsoon

    Science.gov (United States)

    Kutty, Govindan; Sandeep, S.; Vinodkumar; Nhaloor, Sreejith

    2017-07-01

    Indian summer monsoon rainfall is characterized by large intra-seasonal fluctuations in the form of active and break spells in rainfall. This study investigates the role of soil moisture and vegetation on 30-h precipitation forecasts during the break monsoon period using Weather Research and Forecast (WRF) model. The working hypothesis is that reduced rainfall, clear skies, and wet soil condition during the break monsoon period enhance land-atmosphere coupling over central India. Sensitivity experiments are conducted with modified initial soil moisture and vegetation. The results suggest that an increase in antecedent soil moisture would lead to an increase in precipitation, in general. The precipitation over the core monsoon region has increased by enhancing forest cover in the model simulations. Parameters such as Lifting Condensation Level, Level of Free Convection, and Convective Available Potential Energy indicate favorable atmospheric conditions for convection over forests, when wet soil conditions prevail. On spatial scales, the precipitation is more sensitive to soil moisture conditions over northeastern parts of India. Strong horizontal gradient in soil moisture and orographic uplift along the upslopes of Himalaya enhanced rainfall over the east of Indian subcontinent.

  3. Monsoon Rainfall and Landslides in Nepal

    Science.gov (United States)

    Dahal, R. K.; Hasegawa, S.; Bhandary, N. P.; Yatabe, R.

    2009-12-01

    A large number of human settlements on the Nepal Himalayas are situated either on old landslide mass or on landslide-prone areas. As a result, a great number of people are affected by large- and small-scale landslides all over the Himalayas especially during monsoon periods. In Nepal, only in the half monsoon period (June 10 to August 15), 70, 50 and 68 people were killed from landslides in 2007, 2008 and 2009, respectively. In this context, this paper highlights monsoon rainfall and their implications in the Nepal Himalaya. In Nepal, monsoon is major source of rainfall in summer and approximately 80% of the annual total rainfall occurs from June to September. The measured values of mean annual precipitation in Nepal range from a low of approximately 250 mm at area north of the Himalaya to many areas exceeding 6,000 mm. The mean annual rainfall varying between 1500 mm and 2500 mm predominate over most of the country. In Nepal, the daily distribution of precipitation during rainy season is also uneven. Sometime 10% of the total annual precipitation can occur in a single day. Similarly, 50% total annual rainfall also can occur within 10 days of monsoon. This type of uneven distribution plays an important role in triggering many landslides in Nepal. When spatial distribution of landslides was evaluated from record of more than 650 landslides, it is found that more landslides events were concentrated at central Nepal in the area of high mean annual rainfall. When monsoon rainfall and landslide relationship was taken into consideration, it was noticed that a considerable number of landslides were triggered in the Himalaya by continuous rainfall of 3 to 90 days. It has been noticed that continuous rainfall of few days (5 days or 7 days or 10 days) are usually responsible for landsliding in the Nepal Himalaya. Monsoon rains usually fall with interruptions of 2-3 days and are generally characterized by low intensity and long duration. Thus, there is a strong role of

  4. Onset, active and break periods of the Australian monsoon

    International Nuclear Information System (INIS)

    Shaik, Hakeem A; Cleland, Samuel J

    2010-01-01

    Four operational techniques of monsoon monitoring the Australian monsoon at Darwin have been developed in the Darwin Regional Specialised Meteorological Centre. Two techniques used the rainfall only criteria and look into the onset of wet season rainfall/monsoon rainfall. The other two techniques are based purely on Darwin wind data. The data used for the study ranges from 14 to 21 years. The main purpose of the study is to develop near-real time monitoring tools for the Australian monsoon at Darwin. The average date of onset of the monsoon ranges from 19 December to 30 December. The average date of monsoon onset is 28 December. In eleven out of twenty-one years the onset date remained within three days range between the two rainfall techniques, whereas it is eleven out of fourteen years between the wind techniques. The median number of active monsoon spells in a wet season is 3 for the rainfall techniques and 6 for the wind techniques. The average length of each active monsoon spell is around 4 days for all of the techniques. The date of onset of the monsoon has shown negative correlation with the Southern Oscillation Index (SOI) that is late onset is found to occur in El Nino years while early onset is more likely in La Nina years.

  5. Sea surface temperature variability over North Indian Ocean - A study of two contrasting monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Sathyendranath, S.; Viswambharan, N.K.; Rao, L.V.G.

    Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali...

  6. Asian Eocene monsoons as revealed by leaf architectural signatures

    Science.gov (United States)

    Spicer, Robert A.; Yang, Jian; Herman, Alexei B.; Kodrul, Tatiana; Maslova, Natalia; Spicer, Teresa E. V.; Aleksandrova, Galina; Jin, Jianhua

    2016-09-01

    The onset and development of the Asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations, coupled with a diversity of definitions and metrics characterizing monsoon phenomena, have generated much debate. Failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the Inter-tropical Convergence Zone (ITCZ) from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics. Here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils. Leaf form adapts to the prevailing climate, particularly under the extreme seasonal stresses imposed by monsoons, so it is likely that fossil leaves carry a unique signature of past monsoon regimes. Leaf form trait spectra obtained from fossils from Eocene basins in southern China were compared with those seen in modern leaves growing under known climate regimes. The fossil leaf trait spectra, including those derived from previously published fossil floras from northwestern India, were most similar to those found in vegetation exposed to the modern Indonesia-Australia Monsoon (I-AM), which is largely a product of seasonal migrations of the ITCZ. The presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in Eocene time across southern Asia the characteristics of the modern topographically-enhanced South Asia Monsoon had yet to develop. By the Eocene leaves in South Asia had become well adapted to an I-AM type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the Eocene. No fossil trait spectra typical of exposure to the modern East Asia monsoon were seen, suggesting the effects of this system in southern

  7. Dependence of Indian monsoon rainfall on moisture fluxes across the Arabian Sea and the impact of coupled model sea surface temperature biases

    Energy Technology Data Exchange (ETDEWEB)

    Levine, Richard C. [Met Office Hadley Centre, Devon (United Kingdom); Turner, Andrew G. [University of Reading, NCAS-Climate, Department of Meteorology, Reading (United Kingdom)

    2012-06-15

    The Arabian Sea is an important moisture source for Indian monsoon rainfall. The skill of climate models in simulating the monsoon and its variability varies widely, while Arabian Sea cold sea surface temperature (SST) biases are common in coupled models and may therefore influence the monsoon and its sensitivity to climate change. We examine the relationship between monsoon rainfall, moisture fluxes and Arabian Sea SST in observations and climate model simulations. Observational analysis shows strong monsoons depend on moisture fluxes across the Arabian Sea, however detecting consistent signals with contemporaneous summer SST anomalies is complicated in the observed system by air/sea coupling and large-scale induced variability such as the El Nino-Southern Oscillation feeding back onto the monsoon through development of the Somali Jet. Comparison of HadGEM3 coupled and atmosphere-only configurations suggests coupled model cold SST biases significantly reduce monsoon rainfall. Idealised atmosphere-only experiments show that the weakened monsoon can be mainly attributed to systematic Arabian Sea cold SST biases during summer and their impact on the monsoon-moisture relationship. The impact of large cold SST biases on atmospheric moisture content over the Arabian Sea, and also the subsequent reduced latent heat release over India, dominates over any enhancement in the land-sea temperature gradient and results in changes to the mean state. We hypothesize that a cold base state will result in underestimation of the impact of larger projected Arabian Sea SST changes in future climate, suggesting that Arabian Sea biases should be a clear target for model development. (orig.)

  8. Early forecasting of Indian Summer Monsoon: case study 2016

    Science.gov (United States)

    Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

    2017-04-01

    The prior knowledge of dates of onset and withdrawal of monsoon is of vital importance for the population of the Indian subcontinent. In May 2016 before monsoon season, India recorded its highest-ever temperature of 51C. Hot waves have decimated crops, killed livestock and left 330 million people without enough water. At the end of monsoon season the floods in Indian this year have also broken previous records. Severe and devastating rainfall poured down, triggering dams spilling and floods. Such extreme conditions pose the vital questions such as: When will the monsoon come? When will the monsoon withdraw? More lead time in monsoon forecast warning is crucial for taking appropriate decisions at various levels - from the farmer's field (e.g. plowing day, seeding) to the central government (e.g. managing water and energy resources, food procurement policies). The Indian Meteorological Department issues forecasts of onset of monsoon for Kerala state in South India on May 15-th. It does not give such predictions for the other 28 states of the country. Our study concerns the central part of India. We made the monsoon forecast using our recently developed method which focuses on Tipping elements of the Indian monsoon [1]. Our prediction relies on observations of near-surface air temperature and relative humidity from both the ERA-40 and NCEP/NCAR reanalyses. We performed both of our forecasts for the onset and withdrawal of monsoon for the central part of India, the Eastern Ghats (20N,80E). We predicted the monsoon arrival to the Eastern Ghats (20N,80E) on the 13th of June with a deviation of +/-4 days. The prediction was made on May 6-th, 2016 [2], that is 40 days in advance of the date of the forecast. The actual monsoon arrival was June 17-th. In this day near-surface air temperature and relative humidity overcame the critical values and the monsoon season started, that was confirmed by observations of meteorological stations located around the EG-region. We

  9. Evaporation over the Arabian Sea during two contrasting monsoons

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Sadhuram, Y.

    monsoon rainfall. It is noticed that in general, the sea surface temperatures are higher in 1983 throughout the monsoon season than in 1979 in the Arabian Sea excepting western region. The mean rates of evaporation on a seasonal scale are found to be equal...

  10. Reconciling societal and scientific definitions for the monsoon

    Science.gov (United States)

    Reeve, Mathew; Stephenson, David

    2014-05-01

    Science defines the monsoon in numerous ways. We can apply these definitions to forecast data, reanalysis data, observations, GCMs and more. In a basic research setting, we hope that this work will advance science and our understanding of the monsoon system. In an applied research setting, we often hope that this work will benefit a specific stakeholder or community. We may want to inform a stakeholder when the monsoon starts, now and in the future. However, what happens if the stakeholders cannot relate to the information because their perceptions do not align with the monsoon definition we use in our analysis? We can resolve this either by teaching the stakeholders or learning from them about how they define the monsoon and when they perceive it to begin. In this work we reconcile different scientific monsoon definitions with the perceptions of agricultural communities in Bangladesh. We have developed a statistical technique that rates different scientific definitions against the people's perceptions of when the monsoon starts and ends. We construct a probability mass function (pmf) around each of the respondent's answers in a questionnaire survey. We can use this pmf to analyze the time series of monsoon onsets and withdrawals from the different scientific definitions. We can thereby quantitatively judge which definition may be most appropriate for a specific applied research setting.

  11. The monsoon system: Land–sea breeze or the ITCZ?

    Indian Academy of Sciences (India)

    Sulochana Gadgil

    2018-01-27

    Jan 27, 2018 ... ocean contrast is one of the main drivers of the monsoon rainfall, in the 5th Assessment Report of the Inter-governmental Panel on Climate Change. (IPCC Climate Change 2013), the likely enhance- ment of monsoon rainfall has been attributed to increased land–sea contrast, and more abundant.

  12. Impact of Climate Change on India's Monsoonal Climate: Present ...

    Indian Academy of Sciences (India)

    Expected Future Changes in Rainfall and Temperature over India under IPCC SRES A1B GHG Scenarios · Expected Future Change in Monsoon Rainfall and Annual Surface Temp for 2020's, 2050's and 2080's · Likely Future Paradox of Monsoon-ENSO Links · High-Resolution Regional Climate Change Scenarios.

  13. Gridded daily Indian monsoon rainfall for 14 seasons: Merged ...

    Indian Academy of Sciences (India)

    Indian monsoon is an important component of earth's climate system. Daily rainfall data for longer period is vital to study components and processes related to Indian monsoon. Daily observed gridded rainfall data covering both land and adjoining oceanic regions are required for numerical model vali- dation and model ...

  14. Influence of savanna fire on Australian monsoon season precipitation and circulation as simulated using a distributed computing environment

    Science.gov (United States)

    Lynch, Amanda H.; Abramson, David; Görgen, Klaus; Beringer, Jason; Uotila, Petteri

    2007-10-01

    Fires in the Australian savanna have been hypothesized to affect monsoon evolution, but the hypothesis is controversial and the effects have not been quantified. A distributed computing approach allows the development of a challenging experimental design that permits simultaneous variation of all fire attributes. The climate model simulations are distributed around multiple independent computer clusters in six countries, an approach that has potential for a range of other large simulation applications in the earth sciences. The experiment clarifies that savanna burning can shape the monsoon through two mechanisms. Boundary-layer circulation and large-scale convergence is intensified monotonically through increasing fire intensity and area burned. However, thresholds of fire timing and area are evident in the consequent influence on monsoon rainfall. In the optimal band of late, high intensity fires with a somewhat limited extent, it is possible for the wet season to be significantly enhanced.

  15. Comparison of East Asian winter monsoon indices

    Directory of Open Access Journals (Sweden)

    Gao Hui

    2007-01-01

    Full Text Available Four East Asian winter monsoon (EAWM indices are compared in this paper. In the research periods, all the indices show similar interannual and decadal-interdecadal variations, with predominant periods centering in 3–4 years, 6.5 years and 9–15 years, respectively. Besides, all the indices show remarkable weakening trends since the 1980s. The correlation coefficient of each two indices is positive with a significance level of 99%. Both the correlation analyses and the composites indicate that in stronger EAWM years, the Siberian high and the higher-level subtropical westerly jet are stronger, and the Aleutian low and the East Asia trough are deeper. This circulation pattern is favorable for much stronger northwesterly wind and lower air temperature in the subtropical regions of East Asia, while it is on the opposite in weaker EAWM years. Besides, EAWM can also exert a remarkable leading effect on the summer monsoon. After stronger (weaker EAWM, less (more summer precipitation is seen over the regions from the Yangtze River valley of China to southern Japan, while more (less from South China Sea to the tropical western Pacific.

  16. Prediction and Monitoring of Monsoon Intraseasonal Oscillations over Indian Monsoon Region in an Ensemble Prediction System using CFSv2

    Science.gov (United States)

    Borah, Nabanita; Sukumarpillai, Abhilash; Sahai, Atul Kumar; Chattopadhyay, Rajib; Joseph, Susmitha; De, Soumyendu; Nath Goswami, Bhupendra; Kumar, Arun

    2014-05-01

    An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using NCEP Climate Forecast System model version2 at T126 horizontal resolution. The EPS is formulated by producing 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001-2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio becomes unity by about18 days and the predictability error saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are observed even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of amplitude of large scale MISO as well as the initial conditions related to the different phases of MISO. Categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lead.

  17. Weakening of the North American monsoon with global warming

    Science.gov (United States)

    Pascale, Salvatore; Boos, William R.; Bordoni, Simona; Delworth, Thomas L.; Kapnick, Sarah B.; Murakami, Hiroyuki; Vecchi, Gabriel A.; Zhang, Wei

    2017-11-01

    Future changes in the North American monsoon, a circulation system that brings abundant summer rains to vast areas of the North American Southwest, could have significant consequences for regional water resources. How this monsoon will change with increasing greenhouse gases, however, remains unclear, not least because coarse horizontal resolution and systematic sea-surface temperature biases limit the reliability of its numerical model simulations. Here we investigate the monsoon response to increased atmospheric carbon dioxide (CO2) concentrations using a 50-km-resolution global climate model which features a realistic representation of the monsoon climatology and its synoptic-scale variability. It is found that the monsoon response to CO2 doubling is sensitive to sea-surface temperature biases. When minimizing these biases, the model projects a robust reduction in monsoonal precipitation over the southwestern United States, contrasting with previous multi-model assessments. Most of this precipitation decline can be attributed to increased atmospheric stability, and hence weakened convection, caused by uniform sea-surface warming. These results suggest improved adaptation measures, particularly water resource planning, will be required to cope with projected reductions in monsoon rainfall in the American Southwest.

  18. Glacial to Holocene swings of the Australian-Indonesian monsoon

    Science.gov (United States)

    Mohtadi, Mahyar; Oppo, Delia W.; Steinke, Stephan; Stuut, Jan-Berend W.; de Pol-Holz, Ricardo; Hebbeln, Dierk; Lückge, Andreas

    2011-08-01

    The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region. However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java. We show that glacial-interglacial variations in the Australian-Indonesian winter monsoon were in phase with the Indian summer monsoon system, consistent with their modern linkage through cross-equatorial surface winds. Likewise, millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea. On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive, we infer that (austral) summer monsoon rainfall was highest during the Bølling-Allerød period and the past 2,500 years. Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator. We suggest that the Australian-Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere.

  19. NAMMA LIDAR ATMOSPHERIC SENSING EXPERIMENT (LASE) V1

    Data.gov (United States)

    National Aeronautics and Space Administration — NASA's Lidar Atmospheric Sensing Experiment (LASE) system using the DIAL (Differential Absorption Lidar) system was operated during the NASA African Monsoon...

  20. A Holocene Record of Monsoon Intensity From Speleothems in Flores, Indonesia

    Science.gov (United States)

    Griffiths, M. L.; Drysdale, R.; Gagan, M.; Ayliffe, L.; Zhao, J.; St. Pierre, E.; Hantoro, W.; Suwargadi, B.

    2007-12-01

    The Australasian monsoon is among the largest monsoon systems on Earth. The affected region experiences a marked seasonal cycle in winds and precipitation, similar to its Northern Hemisphere counterparts (e.g., Asian monsoons). The Australasian monsoon is the life blood of the millions of people of the Indonesian archipelago. Since the climate is the dominating factor controlling food production, it is of great significance and urgency that we gain a firmer grasp on the parameters that control variations in monsoon intensity. Precise uranium series dating of two actively growing speleothems measuring ~1.25 (LR06-B1) and ~1.61 (LR06-B3) meters in length from Liang Luar cave (Flores, eastern Indonesia), reveal basal ages of ~12,846±103 and 23,605±171 years respectively. In previous studies, stable isotope ratios (δ18O and δ13C) and trace element concentrations in speleothems have revealed past environmental change (e.g., Burns et al., 2001; Wang et al., 2001; Fleitmann et al., 2004; Drysdale et al., 2004).In monsoon-affected regions, the δ18O signal recorded in stalagmites seems to be dominated by the amount of precipitation (so-called `amount effect'), whereby more negative (positive) δ18O values indicate enhanced (diminished) precipitation. Preliminary results from LR06-B1 indicate that δ18O values show a general increase in monsoon intensity from the beginning of the record to ~2000 years BP: this more or less follows insolation changes over the Australian continent.Comparison of our record with D4 from Dongge Cave reveals an anticorrelation during the Holocene, further supporting the hypothesis that tropical monsoon intensity is largely controlled by changes in insolation in both the Northern and Southern Hemisphere. Examination of our δ13C record demonstrates a high-frequency signal superimposed on low- frequency variability which correlates with the reconstructed sunspot cycle: higher (lower) sunspot numbers, and hence increased solar activity

  1. SPATIO-TEMPORAL ESTIMATION OF INTEGRATED WATER VAPOUR OVER THE MALAYSIAN PENINSULA DURING MONSOON SEASON

    Directory of Open Access Journals (Sweden)

    S. Salihin

    2017-10-01

    Full Text Available This paper provides the precise information on spatial-temporal distribution of water vapour that was retrieved from Zenith Path Delay (ZPD which was estimated by Global Positioning System (GPS processing over the Malaysian Peninsular. A time series analysis of these ZPD and Integrated Water Vapor (IWV values was done to capture the characteristic on their seasonal variation during monsoon seasons. This study was found that the pattern and distribution of atmospheric water vapour over Malaysian Peninsular in whole four years periods were influenced by two inter-monsoon and two monsoon seasons which are First Inter-monsoon, Second Inter-monsoon, Southwest monsoon and Northeast monsoon.

  2. Persistence of radon-222 flux during monsoon at a geothermal zone in Nepal

    International Nuclear Information System (INIS)

    Girault, Frederic; Koirala, Bharat Prasad; Perrier, Frederic; Richon, Patrick; Rajaure, Sudhir

    2009-01-01

    The Syabru-Bensi hydrothermal zone, Langtang region (Nepal), is characterized by high radon-222 and CO 2 discharge. Seasonal variations of gas fluxes were studied on a reference transect in a newly discovered gas discharge zone. Radon-222 and CO 2 fluxes were measured with the accumulation chamber technique, coupled with the scintillation flask method for radon. In the reference transect, fluxes reach exceptional mean values, as high as 8700 ± 1500 g m -2 d -1 for CO 2 and 3400 ± 100 x 10 -3 Bq m -2 s -1 for radon. Gases fluxes were measured in September 2007 during the monsoon and during the dry winter season, in December 2007 to January 2008 and in December 2008 to January 2009. Contrary to expectations, radon and its carrier gas fluxes were similar during both seasons. The integrated flux along this transect was approximately the same for radon, with a small increase of 11 ± 4% during the wet season, whereas it was reduced by 38 ± 5% during the monsoon for CO 2 . In order to account for the persistence of the high gas emissions during monsoon, watering experiments have been performed at selected radon measurement points. After watering, radon flux decreased within 5 min by a factor of 2-7 depending on the point. Subsequently, it returned to its original value, firstly, by an initial partial recovery within 3-4 h, followed by a slow relaxation, lasting around 10 h and possibly superimposed by diurnal variations. Monsoon, in this part of the Himalayas, proceeds generally by brutal rainfall events separated by two- or three-day lapses. Thus, the recovery ability shown in the watering experiments accounts for the observed long-term persistence of gas discharge. This persistence is an important asset for long-term monitoring, for example to study possible temporal variations associated with stress accumulation and release.

  3. Decadal Monsoon-ENSO Relationships Reexamined

    Science.gov (United States)

    Yun, Kyung-Sook; Timmermann, Axel

    2018-02-01

    The strength of the El Niño-Southern Oscillation (ENSO)-Indian summer monsoon rainfall (ISMR) relationship shows considerable decadal fluctuations, which have been previously linked to low-frequency climatic processes such as shifts in ENSO's center of action or the Atlantic Multidecadal Oscillation. However, random variability can also cause similar variations in the relationship between climate phenomena. Here we propose a statistical test to determine whether the observed time-evolving correlations between ENSO and ISMR are different from those expected from a simple stochastic null hypothesis model. The analysis focuses on the time evolution of moving correlations, their expected variance, and probabilities for rapid transitions. The results indicate that the time evolution of the observed running correlation between these climate modes is indistinguishable from a system in which the ISMR signal can be expressed as a stochastically perturbed ENSO signal. This challenges previous deterministic interpretations. Our results are further corroborated by the analysis of climate model simulations.

  4. Response of the Asian summer monsoon to changes in El Niño properties

    Science.gov (United States)

    Annamalai, H.; Liu, P.

    2005-04-01

    Diagnostics from observed precipitation and National Centers for Environmental Prediction-National Center for Atmospheric Research re-analysis products reveal that after the 1976-77 climate shift in the Pacific there was a dramatic change in the response of the Indian summer monsoon (ISM) to El Niño, particularly during the months of July and August. Based on 1950-75 (PRE76) and 1977-2001 (POST76) El Niño composites: the western North Pacific monsoon (WNPM) was stronger than normal in both periods; the ISM was weaker than normal during the entire monsoon season in PRE76, but in POST76 was weaker only during the onset and withdrawal phases. In terms of observed sea surface temperature (SST) during July-August, the major differences between the two periods are the presence of cold SST anomalies over the Indo-Pacific warm pool and the intensity of warm SST anomalies in the central Pacific in POST76. The effect of these differences on the ISM is investigated in a suite of experiments with an Atmospheric General Circulation Model (AGCM) that has a realistic monsoon precipitation climatology.Separate ten-member ensemble simulations with the AGCM were conducted for PRE76 and POST76 El Niño events with SST anomalies inserted as follows: (i) tropical Indo-Pacific (TIP), (ii) tropical Pacific only (TPO), and (iii) tropical Indian Ocean only (TIO). Qualitatively, TPO solutions reproduce the observed differences in the monsoon response in both periods. Specifically, during July-August of POST76 the cold SST anomalies in conjunction with remote subsidence suppress precipitation (3-5 mm day-1) over the maritime continent and equatorial central Indian Ocean. Inclusion of Indian Ocean SST anomalies in the TIP runs further suppresses precipitation over the entire equatorial Indian Ocean. The low-level anticyclonic circulation anomalies that develop as a Rossby-wave response to these convective anomalies increase the south-westerlies over the northern Indian Ocean, and favour a

  5. The Aerosol-Monsoon Climate System of Asia

    Science.gov (United States)

    Lau, William K. M.; Kyu-Myong, Kim

    2012-01-01

    In Asian monsoon countries such as China and India, human health and safety problems caused by air-pollution are worsening due to the increased loading of atmospheric pollutants stemming from rising energy demand associated with the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon rain associated with flash flood or prolonged drought, has caused major loss of human lives, and damages in crop and properties with devastating societal impacts on Asian countries. Historically, air-pollution and monsoon research are treated as separate problems. However a growing number of recent studies have suggested that the two problems may be intrinsically intertwined and need to be studied jointly. Because of complexity of the dynamics of the monsoon systems, aerosol impacts on monsoons and vice versa must be studied and understood in the context of aerosol forcing in relationship to changes in fundamental driving forces of the monsoon climate system (e.g. sea surface temperature, land-sea contrast etc.) on time scales from intraseasonal variability (weeks) to climate change ( multi-decades). Indeed, because of the large contributions of aerosols to the global and regional energy balance of the atmosphere and earth surface, and possible effects of the microphysics of clouds and precipitation, a better understanding of the response to climate change in Asian monsoon regions requires that aerosols be considered as an integral component of a fully coupled aerosol-monsoon system on all time scales. In this paper, using observations and results from climate modeling, we will discuss the coherent variability of the coupled aerosol-monsoon climate system in South Asia and East Asia, including aerosol distribution and types, with respect to rainfall, moisture, winds, land-sea thermal contrast, heat sources and sink distributions in the atmosphere in seasonal, interannual to climate change time scales. We will show examples of how elevated

  6. Validation of the HIRHAM-Simulated Indian Summer Monsoon Circulation

    Directory of Open Access Journals (Sweden)

    Stefan Polanski

    2010-01-01

    Full Text Available The regional climate model HIRHAM has been applied over the Asian continent to simulate the Indian monsoon circulation under present-day conditions. The model is driven at the lateral and lower boundaries by European reanalysis (ERA40 data for the period from 1958 to 2001. Simulations with a horizontal resolution of 50 km are carried out to analyze the regional monsoon patterns. The focus in this paper is on the validation of the long-term summer monsoon climatology and its variability concerning circulation, temperature, and precipitation. Additionally, the monsoonal behavior in simulations for wet and dry years has been investigated and compared against several observational data sets. The results successfully reproduce the observations due to a realistic reproduction of topographic features. The simulated precipitation shows a better agreement with a high-resolution gridded precipitation data set over the central land areas of India and in the higher elevated Tibetan and Himalayan regions than ERA40.

  7. Prediction of monsoon rainfall with a nested grid mesoscale limited ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    At the India Meteorological Department (IMD), New Delhi, a 12-level limited area ... namurti et al (1995, 1998) noted that the Florida .... intensifies into monsoon depression giving rise to .... available to us on rainfall over the sea is the INSAT.

  8. Retrieval of vertical wind profiles during monsoon from satellite ...

    Indian Academy of Sciences (India)

    Complex EOF analysis; cloud motion vector winds; wind profiles; retrieval; monsoon. Proc. Indian Acad. Sci. .... The data gaps are removed using simple linear interpolation .... retrieved via standard linear regression using the two independent ...

  9. Spatial monsoon variability with respect to NAO and SO

    Indian Academy of Sciences (India)

    the negative phase of ESI tendency, almost all subdivisions of India show ... to affect the Indian summer monsoon rainfall indi- ... Monthly composite picture of ESI during (a) positive (28 years) and (b) negative (25 years) tendency of ESI.

  10. Air sea interaction during summer monsoon period of 1979

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.

    The present study highlights the utility of satellite derived parameters like SST, precipitation, CMV winds in the lower troposphere etc. in supplementing the in-situ observations. This information can lead to a better understanding of the monsoon...

  11. Unusual rainfall shift during monsoon period of 2010 in Pakistan ...

    African Journals Online (AJOL)

    Arslan

    2013-09-04

    Sep 4, 2013 ... Key words: Indus River, monsoon, flooding in 2010, rainfall pattern, Climate ... data was plotted in excel sheet with upper and lower limits defined .... Houze Jr, Rasmussen R, Medina K, Brodzik S, Romatschke SU (2011).

  12. Dinoflagellates in a mesotrophic, tropical environment influenced by monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    DeCosta, P.M.; Anil, A.C.; Patil, J.S.; Hegde, S.; DeSilva, M.S.; Chourasia, M.

    The changes in dinoflagellate community structure in both e the water column and sediment in a mesotrophic, tropical port environment were investigated in this study. Since the South West Monsoon (SWM) is the main source of climatic variation...

  13. quantitative precipitation forecasts during the Indian Summer Monsoon

    Indian Academy of Sciences (India)

    65

    the Indian Summer Monsoon: Contiguous Rain Area (CRA) Approach ... 1Centre for Australian Weather and Climate Research, Melbourne, Australia ... are evaluated over India using the Contiguous Rainfall Area (CRA) verification technique.

  14. Spatio-temporal variability of summer monsoon rainfall over Orissa ...

    Indian Academy of Sciences (India)

    decreasing trends in rainfall and number of rainy days over some parts of southwest Orissa during. June and ..... the recent trends and associated physical processes. 3. Results and ... depends on the activity of the monsoon trough. To.

  15. The INCOMPASS project field and modelling campaign: Interaction of Convective Organization and Monsoon Precipitation, Atmosphere, Surface and Sea

    Science.gov (United States)

    Turner, Andrew; Bhat, Ganapati; Evans, Jonathan; Madan, Ranju; Marsham, John; Martin, Gill; Mitra, Ashis; Mrudula, Gm; Parker, Douglas; Pattnaik, Sandeep; Rajagopal, En; Taylor, Christopher; Tripathi, Sachchida

    2017-04-01

    also include initial results from nested high-resolution modelling experiments of the 2016 monsoon, at a resolution of 4km in comparison with bespoke regional forecasts run throughout the field campaign.

  16. Recent change of the global monsoon precipitation (1979-2008)

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Bin [University of Hawaii at Manoa, Department of Meteorology, Honolulu, HI (United States); University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Liu, Jian [Chinese Academy of Sciences, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Nanjing (China); Kim, Hyung-Jin [Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, Yokohama, Kanagawa (Japan); Webster, Peter J. [Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, GA (United States); Yim, So-Young [University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States)

    2012-09-15

    The global monsoon (GM) is a defining feature of the annual variation of Earth's climate system. Quantifying and understanding the present-day monsoon precipitation change are crucial for prediction of its future and reflection of its past. Here we show that regional monsoons are coordinated not only by external solar forcing but also by internal feedback processes such as El Nino-Southern Oscillation (ENSO). From one monsoon year (May to the next April) to the next, most continental monsoon regions, separated by vast areas of arid trade winds and deserts, vary in a cohesive manner driven by ENSO. The ENSO has tighter regulation on the northern hemisphere summer monsoon (NHSM) than on the southern hemisphere summer monsoon (SHSM). More notably, the GM precipitation (GMP) has intensified over the past three decades mainly due to the significant upward trend in NHSM. The intensification of the GMP originates primarily from an enhanced east-west thermal contrast in the Pacific Ocean, which is coupled with a rising pressure in the subtropical eastern Pacific and decreasing pressure over the Indo-Pacific warm pool. While this mechanism tends to amplify both the NHSM and SHSM, the stronger (weaker) warming trend in the NH (SH) creates a hemispheric thermal contrast, which favors intensification of the NHSM but weakens the SHSM. The enhanced Pacific zonal thermal contrast is largely a result of natural variability, whilst the enhanced hemispherical thermal contrast is likely due to anthropogenic forcing. We found that the enhanced global summer monsoon not only amplifies the annual cycle of tropical climate but also promotes directly a ''wet-gets-wetter'' trend pattern and indirectly a ''dry-gets-drier'' trend pattern through coupling with deserts and trade winds. The mechanisms recognized in this study suggest a way forward for understanding past and future changes of the GM in terms of its driven mechanisms. (orig.)

  17. Transient coupling relationships of the Holocene Australian monsoon

    Science.gov (United States)

    McRobie, F. H.; Stemler, T.; Wyrwoll, K.-H.

    2015-08-01

    The northwest Australian summer monsoon owes a notable degree of its interannual variability to interactions with other regional monsoon systems. Therefore, changes in the nature of these relationships may contribute to variability in monsoon strength over longer time scales. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Niño-related proxy records, have been qualitative, relying on 'curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9000 years. The resulting networks demonstrate the existence of coupling relationships between regional monsoon systems on millennial time scales, but also highlight the transient nature of teleconnections during this period. In the context of the northwest Australian summer monsoon, we recognise a shift in coupling relationships from strong interhemispheric links with East Asian and ITCZ-related proxy records in the mid-Holocene to significantly weaker coupling in the later Holocene. Although the identified links cannot explain the underlying physical processes leading to coupling between regional monsoon systems, this method provides a step towards understanding the role that changes in teleconnections play in millennial-to orbital-scale climate variability.

  18. Causal evidence between monsoon and evolution of rhizomyine rodents.

    Science.gov (United States)

    López-Antoñanzas, Raquel; Knoll, Fabien; Wan, Shiming; Flynn, Lawrence J

    2015-03-11

    The modern Asian monsoonal systems are currently believed to have originated around the end of the Oligocene following a crucial step of uplift of the Tibetan-Himalayan highlands. Although monsoon possibly drove the evolution of many mammal lineages during the Neogene, no evidence thereof has been provided so far. We examined the evolutionary history of a clade of rodents, the Rhizomyinae, in conjunction with our current knowledge of monsoon fluctuations over time. The macroevolutionary dynamics of rhizomyines were analyzed within a well-constrained phylogenetic framework coupled with biogeographic and evolutionary rate studies. The evolutionary novelties developed by these rodents were surveyed in parallel with the fluctuations of the Indian monsoon so as to evaluate synchroneity and postulate causal relationships. We showed the existence of three drops in biodiversity during the evolution of rhizomyines, all of which reflected elevated extinction rates. Our results demonstrated linkage of monsoon variations with the evolution and biogeography of rhizomyines. Paradoxically, the evolution of rhizomyines was accelerated during the phases of weakening of the monsoons, not of strengthening, most probably because at those intervals forest habitats declined, which triggered extinction and progressive specialization toward a burrowing existence.

  19. Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

    Directory of Open Access Journals (Sweden)

    L. Thomas

    2018-05-01

    Full Text Available Thermodynamic soundings for pre-monsoon and monsoon seasons from the Indian subcontinent are analysed to document differences between convective environments. The pre-monsoon environment features more variability for both near-surface moisture and free-tropospheric temperature and moisture profiles. As a result, the level of neutral buoyancy (LNB and pseudo-adiabatic convective available potential energy (CAPE vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher lifting condensation levels (LCLs. LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity, arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCLs and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way the Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.

  20. On the recent warming in the subcloud layer entropy and vertically integrated moist static energy over South Asian Monsoon region.

    Science.gov (United States)

    Konduru, R.; Gupta, A.; Matsumoto, J.; Takahashi, H. G.

    2017-12-01

    In order to explain monsoon circulation, surface temperature gradients described as most traditional concept. However, it cannot explain certain important aspects of monsoon circulation. Later, convective quasi-equilibrium framework and vertically integrated atmospheric energy budget has become recognized theories to explain the monsoon circulation. In this article, same theories were analyzed and observed for the duration 1979-2010 over south Asian summer monsoon region. With the help of NCEP-R2, NOAA 20th Century, and Era-Interim reanalysis an important feature was noticed pertained to subcloud layer entropy and vertical moist static energy. In the last 32 years, subcloud layer entropy and vertically integrated moist static energy has shown significant seasonal warming all over the region with peak over the poleward flank of the cross-equatorial cell. The important reason related to the warming was found to be increase in surface enthalpy fluxes. Instead, other dynamical contributions pertained to the warming was also observed. Increase in positive anomalies of vertical advection of moist static energy over northern Bay of Bengal, Central India, Peninsular India, Eastern Arabian Sea, and Equatorial Indian Ocean was found to be an important dynamic factor contributing for warming of vertically integrated moist static energy. Along with it vertical moist stability has also supported the argument. Similar interpretations were perceived in the AMIP simulation of CCSM4 model. Further modeling experiments on this warming will be helpful to know the exact mechanism behind it.

  1. Warm pool thermodynamics from the Arabian Sea Monsoon Experiment (ARMEX)

    Digital Repository Service at National Institute of Oceanography (India)

    Sengupta, D.; Parampil, S.R.; Bhat, G.S.; Murty, V.S.N.; RameshBabu, V.; Sudhakar, T.; Premkumar, K.; Pradhan, Y.

    in the Lakshadweep group (Fig 1). We examine the role of surface heat flux, penetrative radiation, and lateral advection in subseasonal SST evolution, with the help of available observations and a simple heat balance. The data and methodology is outlined in the next... section. In Section 3 we present the results of the heat balance cal- culations, and discuss possible sources of uncertainty in the estimates. The main results and their implications are discussed in Section 4. 2. The ARMEX premonsoon warm pool in 2005...

  2. Vegetation Variability And Its Effect On Monsoon Rainfall Over South East Asia: Observational and Modeling Results

    Science.gov (United States)

    Sarkar, S.; Peters-Lidard, C.; Chiu, L.; Kafatos, M.

    2005-12-01

    Increasing population and urbanization have created stress on developing nations. The quickly shifting patterns of vegetation change in different parts of the world have given rise to the pertinent question of feedback on the climate prevailing on local to regional scales. It is now known with some certainty, that vegetation changes can affect the climate by influencing the heat and water balance. The hydrological cycle particularly is susceptible to changes in vegetation. The Monsoon rainfall forms a vital link in the hydrological cycle prevailing over South East Asia This work examines the variability of vegetation over South East Asia and assesses its impact on the monsoon rainfall. We explain the role of changing vegetation and show how this change has affected the heat and energy balance. We demonstrate the role of vegetation one season earlier in influencing rainfall intensity over specific areas in South East Asia and show the ramification of vegetation change on the summer rainfall behavior. The vegetation variability study specifically focuses on India and China, two of the largest and most populous nations. We have done an assessment to find out the key meteorological and human induced parameters affecting vegetation over the study area through a spatial analysis of monthly NDVI values. This study highlights the role of monsoon rainfall, regional climate dynamics and large scale human induced pollution to be the crucial factors governing the vegetation and vegetation distribution. The vegetation is seen to follow distinct spatial patterns that have been found to be crucial in its eventual impact on monsoon rainfall. We have carried out a series of sensitivity experiments using a land surface hydrologic modeling scheme. The vital energy and water balance parameters are identified and the daily climatological cycles are examined for possible change in behavior for different boundary conditions. It is found that the change from native deciduous forest

  3. Aerosol-Water Cycle Interaction: A New Challenge in Monsoon Climate Research

    Science.gov (United States)

    Lau, William K. M.

    2006-01-01

    Long recognized as a major environmental hazard, aerosol is now known to have strong impacts on both regional and global climate. It has been estimated that aerosol may reduce by up to 10% of the seasonal mean solar radiation reaching the earth surface, producing a global cooling effect that opposes global warming (Climate Change 2001). This means that the potential perils that humans have committed to global warming may be far greater than what we can detect at the present. As a key component of the Earth climate system, the water cycle is profoundly affected by the presence of aerosols in the atmosphere. Through the so-called "direct effect", aerosol scatters and/or absorbs solar radiation, thus cooling the earth surface and changing the horizontal and vertical radiational heating contrast in the atmosphere. The heating contrast drives anomalous atmospheric circulation, resulting in changes in convection, clouds, and rainfall. Another way aerosol can affect the water cycle is through the so-called "indirect effects", whereby aerosol increases the number of cloud condensation nuclei, prolongs life time of clouds, and inhibits the growth of cloud drops to raindrops. This leads to more clouds, and increased reflection of solar radiation, and further cooling at the earth surface. In monsoon regions, the response of the water cycle to aerosol forcing is especially complex, not only because of presence of diverse mix of aerosol species with vastly different radiative properties, but also because the monsoon is strongly influenced by ocean and land surface processes, land use, land change, as well as regional and global greenhouse warming effects. Thus, sorting out the impacts of aerosol forcing, and interaction with the monsoon water cycle is a very challenging problem. In this talk, I will offer some insights into how aerosols may impact the Asian monsoon based on preliminary results from satellite observations and climate model experiments. Specifically, I will

  4. Modelling Monsoons: Understanding and Predicting Current and Future Behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Turner, A; Sperber, K R; Slingo, J M; Meehl, G A; Mechoso, C R; Kimoto, M; Giannini, A

    2008-09-16

    The global monsoon system is so varied and complex that understanding and predicting its diverse behaviour remains a challenge that will occupy modellers for many years to come. Despite the difficult task ahead, an improved monsoon modelling capability has been realized through the inclusion of more detailed physics of the climate system and higher resolution in our numerical models. Perhaps the most crucial improvement to date has been the development of coupled ocean-atmosphere models. From subseasonal to interdecadal timescales, only through the inclusion of air-sea interaction can the proper phasing and teleconnections of convection be attained with respect to sea surface temperature variations. Even then, the response to slow variations in remote forcings (e.g., El Nino-Southern Oscillation) does not result in a robust solution, as there are a host of competing modes of variability that must be represented, including those that appear to be chaotic. Understanding the links between monsoons and land surface processes is not as mature as that explored regarding air-sea interactions. A land surface forcing signal appears to dominate the onset of wet season rainfall over the North American monsoon region, though the relative role of ocean versus land forcing remains a topic of investigation in all the monsoon systems. Also, improved forecasts have been made during periods in which additional sounding observations are available for data assimilation. Thus, there is untapped predictability that can only be attained through the development of a more comprehensive observing system for all monsoon regions. Additionally, improved parameterizations - for example, of convection, cloud, radiation, and boundary layer schemes as well as land surface processes - are essential to realize the full potential of monsoon predictability. Dynamical considerations require ever increased horizontal resolution (probably to 0.5 degree or higher) in order to resolve many monsoon features

  5. Indian monsoon variability on millennial-orbital timescales.

    Science.gov (United States)

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F M

    2016-04-13

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ(18)O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ(18)O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales.

  6. Testing a flexible method to reduce false monsoon onsets.

    Directory of Open Access Journals (Sweden)

    Mathew Alexander Stiller-Reeve

    Full Text Available To generate information about the monsoon onset and withdrawal we have to choose a monsoon definition and apply it to data. One problem that arises is that false monsoon onsets can hamper our analysis, which is often alleviated by smoothing the data in time or space. Another problem is that local communities or stakeholder groups may define the monsoon differently. We therefore aim to develop a technique that reduces false onsets for high-resolution gridded data, while also being flexible for different requirements that can be tailored to particular end-users. In this study, we explain how we developed our technique and demonstrate how it successfully reduces false onsets and withdrawals. The presented results yield improved information about the monsoon length and its interannual variability. Due to this improvement, we are able to extract information from higher resolution data sets. This implies that we can potentially get a more detailed picture of local climate variations that can be used in more local climate application projects such as community-based adaptations.

  7. Global monsoon precipitation responses to large volcanic eruptions

    Science.gov (United States)

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-01-01

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do. PMID:27063141

  8. Global monsoon precipitation responses to large volcanic eruptions.

    Science.gov (United States)

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-04-11

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do.

  9. Asian monsoons in a late Eocene greenhouse world.

    Science.gov (United States)

    Licht, A; van Cappelle, M; Abels, H A; Ladant, J-B; Trabucho-Alexandre, J; France-Lanord, C; Donnadieu, Y; Vandenberghe, J; Rigaudier, T; Lécuyer, C; Terry, D; Adriaens, R; Boura, A; Guo, Z; Soe, Aung Naing; Quade, J; Dupont-Nivet, G; Jaeger, J-J

    2014-09-25

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

  10. Carbon dioxide emissions from Indian monsoonal estuaries

    Science.gov (United States)

    Sarma Vedula, VSS

    2012-07-01

    The oceans act as a net sink for atmospheric CO2, however, the role of coastal bodies on global CO2 fluxes remains unclear due to lack of data. The estimated absorption of CO2 from the continental shelves, with limited data, is 0.22 to 1.0 PgC/y, and of CO2 emission by estuaries to the atmosphere is 0.27 PgC/y. The estimates from the estuaries suffer from large uncertainties due to large variability and lack of systematic data collection. It is especially true for Southeast Asian estuaries as the biogeochemical cycling of material are different due to high atmospheric temperature, seasonality driven by monsoons, seasonal discharge etc. In order to quantify CO2 emissions from the Indian estuaries, samples were collected at 27 estuaries all along the Indian coast during discharge wet and dry periods. The emissions of CO2 to the atmosphere from Indian estuaries were 4-5 times higher during wet than dry period. The pCO2 ranged between ~300 and 18492 microatm which were within the range of world estuaries. The mean pCO2 and particulate organic carbon (POC) showed positive relation with rate of discharge suggesting availability of high quantities of organic matter that led to enhanced microbial decomposition. The annual CO2 fluxes from the Indian estuaries, together with dry period data available in the literature, amounts to 1.92 TgC which is >10 times less than that from the European estuaries. The low CO2 fluxes from the Indian estuaries are attributed to low flushing rates and less human settlements along the banks of the Indian estuaries.

  11. Assessment of two versions of regional climate model in simulating the Indian Summer Monsoon over South Asia CORDEX domain

    Science.gov (United States)

    Pattnayak, K. C.; Panda, S. K.; Saraswat, Vaishali; Dash, S. K.

    2018-04-01

    This study assess the performance of two versions of Regional Climate Model (RegCM) in simulating the Indian summer monsoon over South Asia for the period 1998 to 2003 with an aim of conducting future climate change simulations. Two sets of experiments were carried out with two different versions of RegCM (viz. RegCM4.2 and RegCM4.3) with the lateral boundary forcings provided from European Center for Medium Range Weather Forecast Reanalysis (ERA-interim) at 50 km horizontal resolution. The major updates in RegCM4.3 in comparison to the older version RegCM4.2 are the inclusion of measured solar irradiance in place of hardcoded solar constant and additional layers in the stratosphere. The analysis shows that the Indian summer monsoon rainfall, moisture flux and surface net downward shortwave flux are better represented in RegCM4.3 than that in the RegCM4.2 simulations. Excessive moisture flux in the RegCM4.2 simulation over the northern Arabian Sea and Peninsular India resulted in an overestimation of rainfall over the Western Ghats, Peninsular region as a result of which the all India rainfall has been overestimated. RegCM4.3 has performed well over India as a whole as well as its four rainfall homogenous zones in reproducing the mean monsoon rainfall and inter-annual variation of rainfall. Further, the monsoon onset, low-level Somali Jet and the upper level tropical easterly jet are better represented in the RegCM4.3 than RegCM4.2. Thus, RegCM4.3 has performed better in simulating the mean summer monsoon circulation over the South Asia. Hence, RegCM4.3 may be used to study the future climate change over the South Asia.

  12. Diatom community dynamics in a tropical, monsoon-influenced environment: West coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    DeCosta, P.M.; Anil, A.C.

    Diatom communities are influenced by environmental perturbations, such as the monsoon system that impact the niche opportunities of species. To discern the influence of the monsoon system on diatom community structure, we sampled during two...

  13. Changes of extreme precipitation and nonlinear influence of climate variables over monsoon region in China

    KAUST Repository

    Gao, Tao; Wang, Huixia Judy; Zhou, Tianjun

    2017-01-01

    of precipitation extremes over monsoon regions in China (MRC). However, research on monsoon extremes in China and their associations with climate variables is limited. In this study, we examine the space-time variations of extreme precipitation across the MRC

  14. Influence of monsoon upwelling on the planktonic foraminifera off Oman during Late Quaternary

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    Planktonic foraminifer abundances, fluxes, test sizes, and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western Arabian Sea. The influence of monsoon driven upwelling...

  15. Environmental status of groundwater affected by chromite ore processing residue (COPR) dumpsites during pre-monsoon and monsoon seasons.

    Science.gov (United States)

    Matern, Katrin; Weigand, Harald; Singh, Abhas; Mansfeldt, Tim

    2017-02-01

    Chromite ore processing residue (COPR) is generated by the roasting of chromite ores for the extraction of chromium. Leaching of carcinogenic hexavalent chromium (Cr(VI)) from COPR dumpsites and contamination of groundwater is a key environmental risk. The objective of the study was to evaluate Cr(VI) contamination in groundwater in the vicinity of three COPR disposal sites in Uttar Pradesh, India, in the pre-monsoon and monsoon seasons. Groundwater samples (n = 57 pre-monsoon, n = 70 monsoon) were taken in 2014 and analyzed for Cr(VI) and relevant hydrochemical parameters. The site-specific ranges of Cr(VI) concentrations in groundwater were Rania), <0.005 to 115 mg L -1 (Chhiwali), and <0.005 to 2.0 mg L -1 (Godhrauli). Maximum levels of Cr(VI) were found close to the COPR dumpsites and significantly exceeded safe drinking water limits (0.05 mg L -1 ). No significant dependence of Cr(VI) concentration on monsoons was observed.

  16. Evaluation of global climate models for Indian monsoon climatology

    International Nuclear Information System (INIS)

    Kodra, Evan; Ganguly, Auroop R; Ghosh, Subimal

    2012-01-01

    The viability of global climate models for forecasting the Indian monsoon is explored. Evaluation and intercomparison of model skills are employed to assess the reliability of individual models and to guide model selection strategies. Two dominant and unique patterns of Indian monsoon climatology are trends in maximum temperature and periodicity in total rainfall observed after 30 yr averaging over India. An examination of seven models and their ensembles reveals that no single model or model selection strategy outperforms the rest. The single-best model for the periodicity of Indian monsoon rainfall is the only model that captures a low-frequency natural climate oscillator thought to dictate the periodicity. The trend in maximum temperature, which most models are thought to handle relatively better, is best captured through a multimodel average compared to individual models. The results suggest a need to carefully evaluate individual models and model combinations, in addition to physical drivers where possible, for regional projections from global climate models. (letter)

  17. Observations of barrier layer formation in the Bay of Bengal during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Vinayachandran, P.N.; Murty, V.S.N.; RameshBabu, V.

    monsoon, J. Geophys. Res., 107(C12), 8018, doi:10.1029/2001JC000831, 2002. 1. Introduction [2] Several monsoon lows and depressions, that contrib- ute substantially to the summer monsoon rainfall of the Indian subcontinent, form over the Bay of Bengal... August–September, 1990,Murtyetal.[1996]foundthatthemixedlayerbasedon a temperature criterion is deeper than that using density. The regionwithrelativelyfreshwaterwithhighSSTappearstobe an excellent breeding ground for the formation of monsoon depressions...

  18. New spatial and temporal indices of Indian summer monsoon rainfall

    Science.gov (United States)

    Dwivedi, Sanjeev; Uma, R.; Lakshmi Kumar, T. V.; Narayanan, M. S.; Pokhrel, Samir; Kripalani, R. H.

    2018-02-01

    The overall yearly seasonal performance of Indian southwest monsoon rainfall (ISMR) for the whole Indian land mass is presently expressed by the India Meteorological Department (IMD) by a single number, the total quantum of rainfall. Any particular year is declared as excess/deficit or normal monsoon rainfall year on the basis of this single number. It is well known that monsoon rainfall also has high interannual variability in spatial and temporal scales. To account for these aspects in ISMR, we propose two new spatial and temporal indices. These indices have been calculated using the 115 years of IMD daily 0.25° × 0.25° gridded rainfall data. Both indices seem to go in tandem with the in vogue seasonal quantum index. The anomaly analysis indicates that the indices during excess monsoon years behave randomly, while for deficit monsoon years the phase of all the three indices is the same. Evaluation of these indices is also studied with respect to the existing dynamical indices based on large-scale circulation. It is found that the new temporal indices have better link with circulation indices as compared to the new spatial indices. El Nino and Southern Oscillation (ENSO) especially over the equatorial Pacific Ocean still have the largest influence in both the new indices. However, temporal indices have much better remote influence as compared to that of spatial indices. Linkages over the Indian Ocean regions are very different in both the spatial and temporal indices. Continuous wavelet transform (CWT) analysis indicates that the complete spectrum of oscillation of the QI is shared in the lower oscillation band by the spatial index and in the higher oscillation band by the temporal index. These new indices may give some extra dimension to study Indian summer monsoon variability.

  19. 20th century intraseasonal Asian monsoon dynamics viewed from Isomap

    Directory of Open Access Journals (Sweden)

    A. Hannachi

    2013-10-01

    Full Text Available The Asian summer monsoon is a high-dimensional and highly nonlinear phenomenon involving considerable moisture transport towards land from the ocean, and is critical for the whole region. We have used daily ECMWF reanalysis (ERA-40 sea-level pressure (SLP anomalies on the seasonal cycle, over the region 50–145° E, 20° S–35° N, to study the nonlinearity of the Asian monsoon using Isomap. We have focused on the two-dimensional embedding of the SLP anomalies for ease of interpretation. Unlike the unimodality obtained from tests performed in empirical orthogonal function space, the probability density function, within the two-dimensional Isomap space, turns out to be bimodal. But a clustering procedure applied to the SLP data reveals support for three clusters, which are identified using a three-component bivariate Gaussian mixture model. The modes are found to appear similar to active and break phases of the monsoon over South Asia in addition to a third phase, which shows active conditions over the western North Pacific. Using the low-level wind field anomalies, the active phase over South Asia is found to be characterised by a strengthening and an eastward extension of the Somali jet. However during the break phase, the Somali jet is weakened near southern India, while the monsoon trough in northern India also weakens. Interpretation is aided using the APHRODITE gridded land precipitation product for monsoon Asia. The effect of large-scale seasonal mean monsoon and lower boundary forcing, in the form of ENSO, is also investigated and discussed. The outcome here is that ENSO is shown to perturb the intraseasonal regimes, in agreement with conceptual ideas.

  20. Monsoon effect simulation on typhoon rainfall potential - Typhoon Morakot (2009

    Directory of Open Access Journals (Sweden)

    Yi-Ling Chang

    2017-01-01

    Full Text Available A record breaking extreme precipitation event produced 3000 mm day-1 of accumulated rainfall over southern Taiwan in August 2009. The interactions between Typhoon Morakot and the prevailing southwesterly (SW monsoon are the primary mechanism for this heavy precipitation during 5 - 13 August 2009. This extreme precipitation could be produced by the abundant moisture from the SW monsoon associated with the interaction between typhoon and monsoon wind fields, leading to severe property damage. The accurate mapping of extreme precipitation caused from the interaction between a monsoon and typhoon is critical for early warning in Taiwan. This study simulates the heavy rainfall event is based on the Weather Research and Forecast system model (WRF using the three nested domain configuration. Using data assimilation with a virtual meteorological field using the 3D-Var system, such as wind field to alter the SW monsoon strength in the initial condition, the impacts of intensified convergence and water vapor content on the accumulated rainfall are analyzed to quantize the intensification of typhoon rainfall potential. The results showed a positive correlation between the enhanced precipitation and the intensity of low-level wind speed convergence as well as water vapor content. For the Typhoon Morakot case study the rainfall for could attain approximately 2 × 104 mm at 6 hours interval in the southern Taiwan area when 10 × 10-6 s-1 convergence intensified at 850 hPa level around the southern part of the Taiwan Strait. These results suggest that low-level wind speed, convergence and water vapor content play key roles in the typhoon rainfall potential coupled with the SW monsoon.

  1. Wet scavenging of organic and elemental carbon during summer monsoon and winter monsoon seasons

    Science.gov (United States)

    Sonwani, S.; Kulshrestha, U. C.

    2017-12-01

    In the era of rapid industrialization and urbanization, atmospheric abundance of carbonaceous aerosols is increasing due to more and more fossil fuel consumption. Increasing levels of carbonaceous content have significant adverse effects on air quality, human health and climate. The present study was carried out at Delhi covering summer monsoon (July -Sept) and winter monsoon (Dec-Jan) seasons as wind and other meteorological factors affect chemical composition of precipitation in different manner. During the study, the rainwater and PM10 aerosols were collected in order to understand the scavenging process of elemental and organic carbon. The Rain water samples were collected on event basis. PM10 samples were collected before rain (PR), during rain (DR) and after rain (AR) during 2016-2017. The collected samples were analysed by the thermal-optical reflectance method using IMPROVE-A protocol. In PM10, the levels of organic carbon (OC) and its fractions (OC1, OC2, OC3 and OC4) were found significantly lower in the AR samples as compared to PR and DR samples. A significant positive correlation was noticed between scavenging ratios of organic carbon and rain intensity indicating an efficient wet removal of OC. In contrast to OCs, the levels of elemental carbon and its fractions (EC1, EC2, and EC3) in AR were not distinct during PR and DR. The elemental carbon showed very week correlation with rain intensity in Delhi region which could be explained on the basis of hydrophobic nature of freshly emitted carbon soot. The detailed results will be discussed during the conference.

  2. International Conference on Aerosols, Clouds and the Indian Monsoon

    Science.gov (United States)

    Singh, Ramesh P.; Tare, Vinod; Tripathi, S. N.

    2005-06-01

    In recent years, dense haze and fog problems in the northern parts of India have affected the 460 million people living in the Indo-Gangetic basin. Substantial Indian research activities related to aerosols, clouds, and monsoon are taking place in the central and southern parts of India. To attract attention to the problems, a three-day International Conference on Aerosols, Clouds and Indian Monsoon was recently held at the Indian Institute of Technology, Kanpur, in the central part of the Indo-Gangetic basin. About 120 delegates from India, Germany, Greece, Japan, Taiwan, and the United States attended the conference.

  3. Orbital forcing of the late Pleistocene boreal summer monsoon: Links to North Atlantic cold events and El Nino; Southern Oscillation. Geologica Ultraiectina (313)

    NARCIS (Netherlands)

    Ziegler, M.

    2009-01-01

    This thesis revolves about the timing of precession-related variations in the boreal summer monsoon and the impact of North Atlantic cold events and the El Nino Southern Oscillation on this timing. Transient climate modelling experiments indicate that the intensity of the Northern Hemisphere summer

  4. Understanding the West African monsoon variability and its remote effects: an illustration of the grid point nudging methodology

    Science.gov (United States)

    Bielli, Soline; Douville, Hervé; Pohl, Benjamin

    2010-07-01

    General circulation models still show deficiencies in simulating the basic features of the West African Monsoon at intraseasonal, seasonal and interannual timescales. It is however, difficult to disentangle the remote versus regional factors that contribute to such deficiencies, and to diagnose their possible consequences for the simulation of the global atmospheric variability. The aim of the present study is to address these questions using the so-called grid point nudging technique, where prognostic atmospheric fields are relaxed either inside or outside the West African Monsoon region toward the ERA40 reanalysis. This regional or quasi-global nudging is tested in ensembles of boreal summer simulations. The impact is evaluated first on the model climatology, then on intraseasonal timescales with an emphasis on North Atlantic/Europe weather regimes, and finally on interannual timescales. Results show that systematic biases in the model climatology over West Africa are mostly of regional origin and have a limited impact outside the domain. A clear impact is found however on the eddy component of the extratropical circulation, in particular over the North Atlantic/European sector. At intraseasonal timescale, the main regional biases also resist to the quasi-global nudging though their magnitude is reduced. Conversely, nudging the model over West Africa exerts a strong impact on the frequency of the two North Atlantic weather regimes that favor the occurrence of heat waves over Europe. Significant impacts are also found at interannual timescale. Not surprisingly, the quasi-global nudging allows the model to capture the variability of large-scale dynamical monsoon indices, but exerts a weaker control on rainfall variability suggesting the additional contribution of regional processes. Conversely, nudging the model toward West Africa suppresses the spurious ENSO teleconnection that is simulated over Europe in the control experiment, thereby emphasizing the relevance

  5. Understanding the West African monsoon variability and its remote effects: an illustration of the grid point nudging methodology

    Energy Technology Data Exchange (ETDEWEB)

    Bielli, Soline; Douville, Herve; Pohl, Benjamin [CNRM/GMGEC/UDC, Meteo-France, Toulouse Cedex 01 (France)

    2010-07-15

    General circulation models still show deficiencies in simulating the basic features of the West African Monsoon at intraseasonal, seasonal and interannual timescales. It is however, difficult to disentangle the remote versus regional factors that contribute to such deficiencies, and to diagnose their possible consequences for the simulation of the global atmospheric variability. The aim of the present study is to address these questions using the so-called grid point nudging technique, where prognostic atmospheric fields are relaxed either inside or outside the West African Monsoon region toward the ERA40 reanalysis. This regional or quasi-global nudging is tested in ensembles of boreal summer simulations. The impact is evaluated first on the model climatology, then on intraseasonal timescales with an emphasis on North Atlantic/Europe weather regimes, and finally on interannual timescales. Results show that systematic biases in the model climatology over West Africa are mostly of regional origin and have a limited impact outside the domain. A clear impact is found however on the eddy component of the extratropical circulation, in particular over the North Atlantic/European sector. At intraseasonal timescale, the main regional biases also resist to the quasi-global nudging though their magnitude is reduced. Conversely, nudging the model over West Africa exerts a strong impact on the frequency of the two North Atlantic weather regimes that favor the occurrence of heat waves over Europe. Significant impacts are also found at interannual timescale. Not surprisingly, the quasi-global nudging allows the model to capture the variability of large-scale dynamical monsoon indices, but exerts a weaker control on rainfall variability suggesting the additional contribution of regional processes. Conversely, nudging the model toward West Africa suppresses the spurious ENSO teleconnection that is simulated over Europe in the control experiment, thereby emphasizing the relevance

  6. On the response of Indian summer monsoon to aerosol forcing in CMIP5 model simulations

    Science.gov (United States)

    Sanap, S. D.; Pandithurai, G.; Manoj, M. G.

    2015-11-01

    The Indo-Gangetic plains (IGP), which hosts 1/7th of the world population, has undergone significant anomalous changes in hydrological cycle in recent decades. In present study, the role of aerosols in the precipitation changes over IGP region is investigated using Coupled Model Inter-comparison Project-5 (CMIP5) experiments with adequate representation of aerosols in state-of-the art climate models. The climatological sea surface temperature experiments are used to explore the relative impact of the aerosols. The diagnostic analysis on representation of aerosols and precipitation over Indian region was investigated in CMIP5 models. After the evaluation, multi-model ensemble was used for further analysis. It is revealed from the analysis that aerosol-forcing plays an important role in observed weakening of the monsoon circulation and decreased precipitation over the IGP region. The significant cooling of the continental Indian region (mainly IGP) caused by the aerosols leads to reduction in land sea temperature contrast, which further leads to weakening of monsoon overturning circulation and reduction in precipitation.

  7. Revisiting Asian monsoon formation and change associated with Tibetan Plateau forcing: II. Change

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yimin; Wu, Guoxiong; Duan, Anmin; Bao, Qing [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing (China); Hong, Jieli; Zhou, Linjiong [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Dong, Buwen [University of Reading, Department of Meteorology, National Centre for Atmospheric Science, Reading (United Kingdom)

    2012-09-15

    Data analysis based on station observations reveals that many meteorological variables averaged over the Tibetan Plateau (TP) are closely correlated, and their trends during the past decades are well correlated with the rainfall trend of the Asian summer monsoon. However, such correlation does not necessarily imply causality. Further diagnosis confirms the existence of a weakening trend in TP thermal forcing, characterized by weakened surface sensible heat flux in spring and summer during the past decades. This weakening trend is associated with decreasing summer precipitation over northern South Asia and North China and increasing precipitation over northwestern China, South China, and Korea. An atmospheric general circulation model, the HadAM3, is employed to elucidate the causality between the weakening TP forcing and the change in the Asian summer monsoon rainfall. Results demonstrate that a weakening in surface sensible heating over the TP results in reduced summer precipitation in the plateau region and a reduction in the associated latent heat release in summer. These changes in turn result in the weakening of the near-surface cyclonic circulation surrounding the plateau and the subtropical anticyclone over the subtropical western North Pacific, similar to the results obtained from the idealized TP experiment in Part I of this study. The southerly that normally dominates East Asia, ranging from the South China Sea to North China, weakens, resulting in a weaker equilibrated Sverdrup balance between positive vorticity generation and latent heat release. Consequently, the convergence of water vapor transport is confined to South China, forming a unique anomaly pattern in monsoon rainfall, the so-called ''south wet and north dry.'' Because the weakening trend in TP thermal forcing is associated with global warming, the present results provide an effective means for assessing projections of regional climate over Asia in the context of global

  8. Indian Ocean and Indian summer monsoon: relationships without ENSO in ocean-atmosphere coupled simulations

    Science.gov (United States)

    Crétat, Julien; Terray, Pascal; Masson, Sébastien; Sooraj, K. P.; Roxy, Mathew Koll

    2017-08-01

    The relationship between the Indian Ocean and the Indian summer monsoon (ISM) and their respective influence over the Indo-Western North Pacific (WNP) region are examined in the absence of El Niño Southern Oscillation (ENSO) in two partially decoupled global experiments. ENSO is removed by nudging the tropical Pacific simulated sea surface temperature (SST) toward SST climatology from either observations or a fully coupled control run. The control reasonably captures the observed relationships between ENSO, ISM and the Indian Ocean Dipole (IOD). Despite weaker amplitude, IODs do exist in the absence of ENSO and are triggered by a boreal spring ocean-atmosphere coupled mode over the South-East Indian Ocean similar to that found in the presence of ENSO. These pure IODs significantly affect the tropical Indian Ocean throughout boreal summer, inducing a significant modulation of both the local Walker and Hadley cells. This meridional circulation is masked in the presence of ENSO. However, these pure IODs do not significantly influence the Indian subcontinent rainfall despite overestimated SST variability in the eastern equatorial Indian Ocean compared to observations. On the other hand, they promote a late summer cross-equatorial quadrupole rainfall pattern linking the tropical Indian Ocean with the WNP, inducing important zonal shifts of the Walker circulation despite the absence of ENSO. Surprisingly, the interannual ISM rainfall variability is barely modified and the Indian Ocean does not force the monsoon circulation when ENSO is removed. On the contrary, the monsoon circulation significantly forces the Arabian Sea and Bay of Bengal SSTs, while its connection with the western tropical Indian Ocean is clearly driven by ENSO in our numerical framework. Convection and diabatic heating associated with above-normal ISM induce a strong response over the WNP, even in the absence of ENSO, favoring moisture convergence over India.

  9. Dynamics and composition of the Asian summer monsoon anticyclone

    NARCIS (Netherlands)

    Gottschaldt, Klaus Dirk; Schlager, Hans; Baumann, Robert; Sinh Cai, Duy; Eyring, Veronika; Graf, Phoebe; Grewe, V.; Jöckel, Patrick; Jurkat-Witschas, Tina; Voigt, Christiane; Zahn, Andreas; Ziereis, Helmut

    2018-01-01

    This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth

  10. Characteristics of monsoon waves off Uran, west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Nayak, B.U.; Chandramohan, P.; Mandal, S.

    's and the spectral methods for determining various wave parameters. Monsoon wave climate was stronger with the occurrence of the highest significant wave height of 2.45 m and the corresponding maximum wave height of 3.9 m in July. Significant wave height varied from...

  11. Simulation of Indian summer monsoon using the Japan ...

    Indian Academy of Sciences (India)

    Simulation of Indian summer monsoon using the Japan Meteorological Agency's seasonal ensemble prediction system. Kailas Sonawane1,∗. , O P Sreejith1, D R Pattanaik1,. Mahendra Benke1, Nitin Patil2 and D S Pai1. 1India Meteorological Department, Pune 411 005, India. 2Interdisciplinary Programme in Climate ...

  12. Monsoon sensitivity to aerosol direct radiative forcing in the ...

    Indian Academy of Sciences (India)

    to the total, scattering aerosols and black carbon aerosols. ... acts as an internal damping mechanism spinning down the regional hydrological cycle and leading to sig- ... tion and emission of longwave radiation. ... effect of aerosols over India, where the emission of .... that aerosol effects on monsoon water cycle dynam-.

  13. Dynamics and composition of the Asian summer monsoon anticyclone

    Science.gov (United States)

    Gottschaldt, Klaus-Dirk; Schlager, Hans; Baumann, Robert; Sinh Cai, Duy; Eyring, Veronika; Graf, Phoebe; Grewe, Volker; Jöckel, Patrick; Jurkat-Witschas, Tina; Voigt, Christiane; Zahn, Andreas; Ziereis, Helmut

    2018-04-01

    This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth System Model Validation (ESMVal) campaign in September 2012. Observed and simulated tracer-tracer relations reflect photochemical O3 production as well as in-mixing from the lower troposphere and the tropopause layer. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from those in the rest of the year, and the measurements reflect the main processes acting throughout the monsoon season. Net photochemical O3 production is significantly enhanced in the ASMA, where uplifted precursors meet increased NOx, mainly produced by lightning. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank and then transported in the southern fringe around the interior region. Radial transport barriers of the circulation are effectively overcome by subseasonal dynamical instabilities of the anticyclone, which occur quite frequently and are of paramount importance for the trace gas composition of the ASMA. Both the isentropic entrainment of O3-rich air and the photochemical conversion of uplifted O3-poor air tend to increase O3 in the ASMA outflow.

  14. Predicting monsoon rainfall and pressure indices from sea surface temperature

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.

    The relationship between the sea surface temperature (SST) in the Indian Ocean and monsoon rainfall has been examined by using 21 years data set (1967-87) of MOHSST.6 (Met. Office Historical Sea Surface Temperature data set, obtained from U.K. Met...

  15. Retrieval of vertical wind profiles during monsoon from satellite ...

    Indian Academy of Sciences (India)

    large number of radiosonde observations of wind profiles over the Indian Ocean during the monsoon months. It has been found that the first ... include several sources of both systematic and random errors. Among them cloud top height .... highly correlated with the pseudo-winds at levels between 850mb and 600mb (r ј 0:8) ...

  16. Fluvial hydrology and geomorphology of Monsoon-dominated Indian rivers

    Directory of Open Access Journals (Sweden)

    Vishwas S. Kale

    2005-11-01

    Full Text Available The Indian rivers are dominantly monsoon rainfed. As a result, their regime characteristics are dictated by the spatio-temporal variations in the monsoon rainfall. Although the rivers carry out most of the geomorphic work during 4-5 months of the monsoon season, the nature and magnitude of response to variations in the discharge and sediment load varies with the basin size and relief characteristics. Large monsoon floods play a role of great importance on all the rivers. This paper describes the hydrological and geomorphological characteristics of the two major fluvial systems of the Indian region, namely the Himalayan fluvial system and the Peninsular fluvial system. Large number of studies published so far indicate that there are noteworthy differences between the two river systems, with respect to river hydrology, channel morphology, sediment load and behaviour. The nature of alterations in the fluvial system due to increased human interference is also briefly mentioned. This short review demonstrates that there is immense variety of rivers in India. This makes India one of the best places to study rivers and their forms and processes.

  17. Multi-model ensemble schemes for predicting northeast monsoon ...

    Indian Academy of Sciences (India)

    drought occurred. Some of these are extreme north- east monsoon years with significantly less rain- fall (1982, 1988, 1989 and 2005), and in some years, more than normal rainfall occurred (1987,. 1993, 1996, 1997 and 1998). Some of these typ- ical years may also be characterized as El Ni˜no year (1987), La Ni˜na year ...

  18. Long range prediction of Indian summer monsoon rainfall

    Indian Academy of Sciences (India)

    to the performance of summer monsoon rain- fall over India. Variations in the total amount of rainfall have strong socio-economic consequences. Parthasarathy et al .... deviation of rainfall for training period 1961–1995, are 838.4 mm and 89.3 mm respectively. The period. 1949–1960 and 1996–2005 is used for independent.

  19. Moisture source for summer monsoon rainfall over India

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Rao, D.P.

    Southwest monsoon plays a vital role in India's economy as the major income comes from agriculture. What could be the moisture source for this copious amount of rainfall over the Indian sub-continent?. This has been studied in detail and noticed...

  20. Surface temperature pattern of the Indian Ocean before summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Gopinathan, C.K.; Rao, D.P.

    , suggests that the position of the warmer areas in the Bay of Bengal in May is an indicator of the subsequent summer rainfall over India. The statistical method adopted for the long range forcasting of the Indian summer monsoon gives very little...

  1. Seasonal prediction of Indian summer monsoon: Sensitivity to ...

    Indian Academy of Sciences (India)

    In the present study, the assessment of the Community Atmosphere Model (CAM) developed at National Centre for Atmospheric Research (NCAR) for seasonal forecasting of Indian Summer Monsoon (ISM) with different persistent SST is reported. Towards achieving the objective, 30-year model climatology has been ...

  2. Global surface temperature in relation to northeast monsoon rainfall ...

    Indian Academy of Sciences (India)

    is observed that the meridional gradient in surface air temperature anomalies between Europe and ... Surface air tempera- ture is one of the factors that influence monsoon variability. The distribution of surface air temper- ature over land and sea determines the locations ..... Asia, north Indian Ocean, northeast Russia and.

  3. Summer monsoon intraseasonal oscillation over eastern Arabian Sea

    Indian Academy of Sciences (India)

    Significant power is seen in the 8–15-day time scale in TWV during onset and retreat of the summer ... Intraseasonal oscillation; wavelet analysis; Indian summer monsoon. J. Earth .... be caused by synoptic scale systems, in conformity with the ...

  4. Unusual rainfall shift during monsoon period of 2010 in Pakistan ...

    African Journals Online (AJOL)

    Floods due to “blocking event” in the jet stream during 2010 caused intense rainfall and flash floods in northern Pakistan which resulted to riverine flooding in southern Pakistan. In the beginning of July 2010, changes in summer monsoon rainfall patterns caused the most severe flooding in Pakistan history. Process control ...

  5. Tropospheric biennial oscillation and South Asian summer monsoon ...

    Indian Academy of Sciences (India)

    20

    suggested that the Indo-Pacific SST displays strong impact on TBO as compared to .... and model display clear biennial signals with above 95% confidence level .... Ascending motion and low level convergence over the monsoon core ..... Indian and western Pacific oceans during the northern winter as revealed by a self-.

  6. Seasonal forecasting of Bangladesh summer monsoon rainfall using ...

    Indian Academy of Sciences (India)

    In this paper, the development of a statistical forecasting method for summer ... 2008 summer monsoon rainfall based on the model were also found to be in good agreement with the ..... nificant on the basis of a one-tailed test of Student's.

  7. Seasonal behaviour of tidal inlets in a tropical monsoon area

    NARCIS (Netherlands)

    Lam, N.T.; Stive, M.J.F.; Verhagen, H.J.; Wang, Z.B.

    2008-01-01

    Morphodynamics of a tidal inlet system on a micro-tidal coast in a tropical monsoon influenced region is modelled and discussed. Influences of river flow and wave climate on the inlet morphology are investigated with the aid of process-based state-of-the-art numerical models. Seasonal and episodic

  8. Increased particle flux to the deep ocean related to monsoons

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, R.R.; Ittekkot, V.; Manganini, S.J.; Ramaswamy, V.; Haake, B.; Degens, E.T.; Desai, B.N.; Honjo, S.

    . To assess the impact of monsoon-driven processes on the downward particle flux variations in the open ocean we deployed three moored arrays consisting of six time-series sediment traps at selected locations in the western, central and eastern parts...

  9. Monsoon regime in the Indian Ocean and zooplankton variability

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, V.R.

    and the estuaries in order to show how the monsoon exerts its influence on zooplankton from different types of environment. In the open ocean, the semi-annually reversing system of currents exert profound influence on the shifting of zooplankton populations and its...

  10. The Global Monsoon as Seen through the Divergent Atmospheric Circulation.

    Science.gov (United States)

    Trenberth, Kevin E.; Stepaniak, David P.; Caron, Julie M.

    2000-11-01

    A comprehensive description is given of the global monsoon as seen through the large-scale overturning in the atmosphere that changes with the seasons, and it provides a basis for delimiting the monsoon regions of the world. The analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions, as given by the monthly mean fields for 1979-93 reanalyses from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) and European Centre for Medium-Range Weather Forecasts (ECMWF), which are able to reproduce the dominant modes. A complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year. The first mode, which depicts the global monsoon, has a simple vertical structure with a maximum in vertical motion at about 400 mb, divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb, and convergence in the lower troposphere with a maximum at 925 mb (ECMWF) or 850 mb (NCEP). However, this mode has a rich three-dimensional spatial structure that evolves with the seasons. It accounts for 60% of the annual cycle variance of the divergent mass circulation and dominates the Hadley circulation as well as three overturning transverse cells. These include the Pacific Walker circulation; an Americas-Atlantic Walker circulation, both of which comprise rising motion in the west and sinking in the east; and a transverse cell over Asia, the Middle East, North Africa, and the Indian Ocean that has rising motion in the east and sinking toward the west. These exist year-round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak Hadley cell. The annual cycle of the two Hadley cells reveals peak strength in early February and early August in both reanalyses.A second monsoon mode, which accounts for

  11. An Assessment of Monsoon Triggered Landslides in Western Nepal

    Science.gov (United States)

    Sudan Acharya, Madhu

    2010-05-01

    Due to heavy monsoon rain, rugged topography and very young mountains, frequent slope failures and soil erosion are very common in Nepal but in most of cases the natural slopes are disturbed by men to construct a road through it and the situation further aggravated by the Monsoon rain. Summer usually tests the disaster response capacity of Nepal, when the monsoons trigger water induced disasters. This year Nepal's Western regions were most severely affected by floods and landslides. Every year, sadly, it is the same story of mostly poor people living in remote villages succumbing to landslides and flooding and those who survive facing hardships brought on by the disaster. The tail end of the monsoon in October has triggered flood and landslides in Nepal which affected a total of 14 districts in the mid and far-west regions, of which Kailali, Bardiya, Banke, Dadeldhura, Accham and Kanchapur district are most affected. The affected areas are geographically scattered and remote, and are therefore difficult to access. In this year (2009), flood and landslides have claimed 62 lives, affecting more than 152,000 individuals from 27,000 families. More than 4,000 families are displaced and are taking shelter in schools, open space and forest areas with no protection from the external elements. In the above context the prevention and mitigation measures for landslides is a great challenge for Nepal. Nepal has been investing its huge amount of resources to stabilize landslides and roadside slope failures, still then it has become unmanageable during Monsoon time. Considering the above facts, an assessment of landslides which were occurred during the Monsoon (July-October 2009), along Khodpe - Jhota - Chainpur road in far western region of Nepal has been carried out based on the field observation of various landslides. The paper presents the causes and mechanisms of failures of different landslides which are mostly triggered by Monsoon rain. It also suggests some low cost

  12. Modeling and forecasting rainfall patterns of southwest monsoons in North-East India as a SARIMA process

    Science.gov (United States)

    Narasimha Murthy, K. V.; Saravana, R.; Vijaya Kumar, K.

    2018-02-01

    Weather forecasting is an important issue in the field of meteorology all over the world. The pattern and amount of rainfall are the essential factors that affect agricultural systems. India experiences the precious Southwest monsoon season for four months from June to September. The present paper describes an empirical study for modeling and forecasting the time series of Southwest monsoon rainfall patterns in the North-East India. The Box-Jenkins Seasonal Autoregressive Integrated Moving Average (SARIMA) methodology has been adopted for model identification, diagnostic checking and forecasting for this region. The study has shown that the SARIMA (0, 1, 1) (1, 0, 1)4 model is appropriate for analyzing and forecasting the future rainfall patterns. The Analysis of Means (ANOM) is a useful alternative to the analysis of variance (ANOVA) for comparing the group of treatments to study the variations and critical comparisons of rainfall patterns in different months of the season.

  13. Large-scale control of the Arabian Sea monsoon inversion in August

    Science.gov (United States)

    Wu, Chi-Hua; Wang, S.-Y. Simon; Hsu, Huang-Hsiung

    2017-12-01

    The summer monsoon inversion in the Arabian Sea is characterized by a large amount of low clouds and August as the peak season. Atmospheric stratification associated with the monsoon inversion has been considered a local system influenced by the advancement of the India-Pakistan monsoon. Empirical and numerical evidence from this study suggests that the Arabian Sea monsoon inversion is linked to a broader-scale monsoon evolution across the African Sahel, South Asia, and East Asia-Western North Pacific (WNP), rather than being a mere byproduct of the India-Pakistan monsoon progression. In August, the upper-tropospheric anticyclone in South Asia extends sideways corresponding with the enhanced precipitation in the subtropical WNP, equatorial Indian Ocean, and African Sahel while the middle part of this anticyclone weakens over the Arabian Sea. The increased heating in the adjacent monsoon systems creates a suppression effect on the Arabian Sea, suggesting an apparent competition among the Africa-Asia-WNP monsoon subsystems. The peak Sahel rainfall in August, together with enhanced heating in the equatorial Indian Ocean, produces a critical effect on strengthening the Arabian Sea thermal inversion. By contrast, the WNP monsoon onset which signifies the eastward expansion of the subtropical Asian monsoon heating might play a secondary or opposite role in the Arabian Sea monsoon inversion.

  14. What drives the global summer monsoon over the past millennium?

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jian [Chinese Academy of Sciences, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Nanjing (China); Wang, Bin [University of Hawaii at Manoa, Department of Meteorology, Honolulu, HI (United States); University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Yim, So-Young; Lee, June-Yi [University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Jhun, Jong-Ghap [Seoul National University, School of Earth and Environmental Sciences/Research Institute of Oceanography, Seoul (Korea, Republic of); Ha, Kyung-Ja [Pusan National University, Division of Earth Environmental System, Busan (Korea, Republic of)

    2012-09-15

    The global summer monsoon precipitation (GSMP) provides a fundamental measure for changes in the annual cycle of the climate system and hydroclimate. We investigate mechanisms governing decadal-centennial variations of the GSMP over the past millennium with a coupled climate model's (ECHO-G) simulation forced by solar-volcanic (SV) radiative forcing and greenhouse gases (GHG) forcing. We show that the leading mode of GSMP is a forced response to external forcing on centennial time scale with a globally uniform change of precipitation across all monsoon regions, whereas the second mode represents internal variability on multi-decadal time scale with regional characteristics. The total amount of GSMP varies in phase with the global mean temperature, indicating that global warming is accompanied by amplification of the annual cycle of the climate system. The northern hemisphere summer monsoon precipitation (NHSMP) responds to GHG forcing more sensitively, while the southern hemisphere summer monsoon precipitation (SHSMP) responds to the SV radiative forcing more sensitively. The NHSMP is enhanced by increased NH land-ocean thermal contrast and NH-minus-SH thermal contrast. On the other hand, the SHSMP is strengthened by enhanced SH subtropical highs and the east-west mass contrast between Southeast Pacific and tropical Indian Ocean. The strength of the GSMP is determined by the factors controlling both the NHSMP and SHSMP. Intensification of GSMP is associated with (a) increased global land-ocean thermal contrast, (b) reinforced east-west mass contrast between Southeast Pacific and tropical Indian Ocean, and (c) enhanced circumglobal SH subtropical highs. The physical mechanisms revealed here will add understanding of future change of the global monsoon. (orig.)

  15. Characteristics of monsoonal circulation over the western Pacific

    Energy Technology Data Exchange (ETDEWEB)

    Shen, J; Chen, E

    1980-01-01

    In this article the meteorological observations on ships four times daily in the area between 0 to 46/sup 0/N, 90 to 155/sup 0/E has been utilized. The grid 2 x 2 degrees along coastal waters, and 5 x 5 degrees over the open sea have been used. Here the monsoon currents over the western Pacific are calculated and analyzed and a brief discussion is given. The following three criteria were obtained: (1) The monsoon current over the western Pacific between winter and summer changed almost in opposite directions with April and October being the transitional months. In general the wind direction change from summer to winter went from the coastal waters to the open sea. (2) After the discussion about the duration and the prevailing wind directions, the following was determined: during the winter monsoon period, the 25/sup 0/N latitudinal line may be regarded as the boundary from October to March when the winter wind directions inclined N (NW or N) to the north of that line; but to the south of it NE winds prevailed. However, the durations were quite different in different regions, ranging from five to nine months. Owing to the topographic influence of the Taiwan Strait, the duration of the NE wind lasted nine months. The 25/sup 0/N line may also be applied for summer monsoons; over the eastern open ocean from the Gulf of the Bohai Sea and the Japanese islands the southerly winds lasted about nine months, but in the Taiwan Strait they lasted only two months. (3) During the winter monsoon period, the region of strong winds which encircled the continent was over the open ocean to the east of the Japanese islands and the Philippines. However, it was not as near to the shore line as in the winter season, and the frequency of strong winds was somewhat more on the southern side of the 25/sup 0/N line.

  16. Changes in Water-Food-Energy Nexus in India and its consistency with changes in Monsoon

    Science.gov (United States)

    Barik, B.; Ghosh, S.; Pathak, A.

    2017-12-01

    Meeting the growing demand for food, water, and energy for a densely populated country like India is a major challenge. Green Revolution helped to maintain the food security, with Government policies such as distribution of electricity at a subsidised rate, resulting in an unregulated withdrawal of groundwater. Thus, the depleting groundwater went unnoticed as the high agricultural productivity overshadowed it. Here we present a comprehensive analysis which assess the present status of the water-food-energy nexus in India. We find that with the growth of population and consequent increase in the food demands, the food production has also increased, and this has been made possible with the intensification of irrigation. However, during the recent decade (after 1996), the increase in food production has not been sufficient to meet its growing demands, precipitating a decline in the per-capita food availability. Also, there has been a decline in the groundwater storage in India during the last decade, as derived from the Gravity Recovery and Climate Experiment (GRACE) data. Regional studies reveal contrasting trends, where North-western India and the middle Ganga basin show a decrease in the groundwater storage as opposed to an increasing storage over western-central India. We also find that, after a drought, the groundwater storage drops but is unable to recover to its original condition even after good monsoon years. The groundwater storage reveals a very strong negative correlation with the electricity consumption for agricultural usage, which may also be considered as a proxy for groundwater pumped for irrigation in a region. The electricity usage for agricultural purposes has an increasing trend and, interestingly, it does not have any correlation with the monsoon rainfall. This reveals an important finding that the irrigation has been intensified irrespective of rainfall. This also resulted in a decreasing correlation between the food production and monsoon

  17. The effect of the Asian Monsoon to the atmospheric boundary layer over the Tibetan Plateau

    Science.gov (United States)

    Li, Maoshan; Su, Zhongbo; Chen, Xuelong; Zheng, Donghai; Sun, Fanglin; Ma, Yaoming; Hu, Zeyong

    2016-04-01

    Modulation of the diurnal variations in the convective activities associated with day-by-day changes of surface flux and soil moisture was observed in the beginning of the monsoon season on the central Tibetan plateau (Sugimoto et al., 2008) which indicates the importance of land-atmosphere interactions in determining convective activities over the Tibetan plateau. Detailed interaction processes need to be studied by experiments designed to evaluate a set of hypotheses on mechanisms and linkages of these interactions. A possible function of vegetation to increase precipitation in cases of Tibetan High type was suggested by Yamada and Uyeda (2006). Use of satellite derived plateau scale soil moisture (Wen et al., 2003) enables the verification of these hypotheses (e.g. Trier et al. 2004). To evaluate these feedbacks, the mesoscale WRF model will be used because several numerical experiments are being conducted to improve the soil physical parameterization in the Noah land surface scheme in WRF so that the extreme conditions on the Tibetan plateau could be adequately represented (Van der Velde et al., 2009) such that the impacts on the structure of the atmospheric boundary layer can be assessed and improved. The Tibetan Observational Research Platform (TORP) operated by the Institute of Tibetan Plateau (Ma et al., 2008) will be fully utilized to study the characteristics of the plateau climate and different aspects of the WRF model will be evaluated using this extensive observation platform (e.g. Su et al., 2012). Recently, advanced studies on energy budget have been done by combining field and satellite measurements over the Tibetan Plateau (e.g. Ma et al., 2005). Such studies, however, were based on a single satellite observation and for a few days over an annual cycle, which are insufficient to reveal the relation between the land surface energy budget and the Asian monsoon over the Tibetan plateau. Time series analysis of satellite observations will provide the

  18. Significance of High Resolution GHRSST on prediction of Indian Summer Monsoon

    KAUST Repository

    Jangid, Buddhi Prakash

    2017-02-24

    In this study, the Weather Research and Forecasting (WRF) model was used to assess the importance of very high resolution sea surface temperature (SST) on seasonal rainfall prediction. Two different SST datasets available from the National Centers for Environmental Prediction (NCEP) global model analysis and merged satellite product from Group for High Resolution SST (GHRSST) are used as a lower boundary condition in the WRF model for the Indian Summer Monsoon (ISM) 2010. Before using NCEP SST and GHRSST for model simulation, an initial verification of NCEP SST and GHRSST are performed with buoy measurements. It is found that approximately 0.4 K root mean square difference (RMSD) in GHRSST and NCEP SST when compared with buoy observations available over the Indian Ocean during 01 May to 30 September 2010. Our analyses suggest that use of GHRSST as lower boundary conditions in the WRF model improve the low level temperature, moisture, wind speed and rainfall prediction over ISM region. Moreover, temporal evolution of surface parameters such as temperature, moisture and wind speed forecasts associated with monsoon is also improved with GHRSST forcing as a lower boundary condition. Interestingly, rainfall prediction is improved with the use of GHRSST over the Western Ghats, which mostly not simulated in the NCEP SST based experiment.

  19. Particle size distribution properties in mixed-phase monsoon clouds from in situ measurements during CAIPEEX

    Science.gov (United States)

    Patade, Sachin; Prabha, T. V.; Axisa, D.; Gayatri, K.; Heymsfield, A.

    2015-10-01

    A comprehensive analysis of particle size distributions measured in situ with airborne instrumentation during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) is presented. In situ airborne observations in the developing stage of continental convective clouds during premonsoon (PRE), transition, and monsoon (MON) period at temperatures from 25 to -22°C are used in the study. The PRE clouds have narrow drop size and particle size distributions compared to monsoon clouds and showed less development of size spectra with decrease in temperature. Overall, the PRE cases had much lower values of particle number concentrations and ice water content compared to MON cases, indicating large differences in the ice initiation and growth processes between these cloud regimes. This study provided compelling evidence that in addition to dynamics, aerosol and moisture are important for modulating ice microphysical processes in PRE and MON clouds through impacts on cloud drop size distribution. Significant differences are observed in the relationship of the slope and intercept parameters of the fitted particle size distributions (PSDs) with temperature in PRE and MON clouds. The intercept values are higher in MON clouds than PRE for exponential distribution which can be attributed to higher cloud particle number concentrations and ice water content in MON clouds. The PRE clouds tend to have larger values of dispersion of gamma size distributions than MON clouds, signifying narrower spectra. The relationships between PSDs parameters are presented and compared with previous observations.

  20. Significance of High Resolution GHRSST on prediction of Indian Summer Monsoon

    KAUST Repository

    Jangid, Buddhi Prakash; Kumar, Prashant; Attada, Raju; Kumar, Raj

    2017-01-01

    In this study, the Weather Research and Forecasting (WRF) model was used to assess the importance of very high resolution sea surface temperature (SST) on seasonal rainfall prediction. Two different SST datasets available from the National Centers for Environmental Prediction (NCEP) global model analysis and merged satellite product from Group for High Resolution SST (GHRSST) are used as a lower boundary condition in the WRF model for the Indian Summer Monsoon (ISM) 2010. Before using NCEP SST and GHRSST for model simulation, an initial verification of NCEP SST and GHRSST are performed with buoy measurements. It is found that approximately 0.4 K root mean square difference (RMSD) in GHRSST and NCEP SST when compared with buoy observations available over the Indian Ocean during 01 May to 30 September 2010. Our analyses suggest that use of GHRSST as lower boundary conditions in the WRF model improve the low level temperature, moisture, wind speed and rainfall prediction over ISM region. Moreover, temporal evolution of surface parameters such as temperature, moisture and wind speed forecasts associated with monsoon is also improved with GHRSST forcing as a lower boundary condition. Interestingly, rainfall prediction is improved with the use of GHRSST over the Western Ghats, which mostly not simulated in the NCEP SST based experiment.

  1. Air pollution episodes associated with East Asian winter monsoons

    Energy Technology Data Exchange (ETDEWEB)

    Hien, P.D., E-mail: pdhien@gmail.com [Vietnam Atomic Energy Agency, 59 Ly Thuong Kiet str. Hanoi (Viet Nam); Loc, P.D.; Dao, N.V. [National Hydro-Meteorological Center, 62-A2 Nguyen Chi Thanh str. Hanoi (Viet Nam)

    2011-11-01

    A dozen multi-day pollution episodes occur from October to February in Hanoi, Vietnam due to prolonged anticyclonic conditions established after the northeast monsoon surges (cold surges). These winter pollution episodes (WPEs) account for most of the 24-h PM{sub 10} exceedances and the highest concentrations of gaseous pollutants in Hanoi. In this study, WPEs were investigated using continuous air quality monitoring data and information on upper-air soundings and air mass trajectories. The 24-h pollutant concentrations are lowest during cold surges; concurrently rise thereafter reaching the highest levels toward the middle of a monsoon cycle, then decline ahead of the next cold surge. Each monsoon cycle usually proceeds through a dry phase and a humid phase as Asiatic continental cold air arrives in Hanoi through inland China then via the East China Sea. WPEs are associated with nighttime radiation temperature inversions (NRTIs) in the dry phase and subsidence temperature inversions (STIs) in the humid phase. In NRTI periods, the rush hour pollution peak is more pronounced in the evening than in the morning and the pollution level is about two times higher at night than in daytime. In STI periods, broad morning and evening traffic peaks are observed and pollution is as high at night as in daytime. The close association between pollution and winter monsoon meteorology found in this study for the winter 2003-04 may serve as a basis for advance warning of WPEs and for forecasting the 24-h pollutant concentrations. - Highlights: {yields} Dozen pollution episodes from Oct. to Feb in Hanoi associated with anticyclones after monsoon surges. {yields} 24-h concentrations of PM{sub 10}, SO{sub 2}, NO{sub 2}, CO rise after surge and decline ahead of the next. {yields} Episodes caused by nighttime radiation and subsidence inversions in dry and humid monsoon phases. {yields} Distinct diurnal variations of pollutant concentrations observed in the two periods. {yields} Close

  2. The Eurasian ice sheet reinforces the East Asian summer monsoon during the interglacial 500 000 years ago

    Directory of Open Access Journals (Sweden)

    Qiuzhen Yin

    2008-05-01

    Full Text Available Deep-sea and ice-core records show that interglacial periods were overall less "warm" before about 420 000 years ago than after, with relatively higher ice volume and lower greenhouse gases concentration. This is particularly the case for the interglacial Marine Isotope Stage 13 which occurred about 500 000 years ago. However, by contrast, the loess and other proxy records from China suggest an exceptionally active East Asian summer monsoon during this interglacial. A three-dimension Earth system Model of Intermediate complexity was used to understand this seeming paradox. The astronomical forcing and the remnant ice sheets present in Eurasia and North America were taken into account in a series of sensitivity experiments. Expectedly, the seasonal contrast is larger and the East Asian summer monsoon is reinforced compared to Pre-Industrial time when Northern Hemisphere summer is at perihelion. Surprisingly, the presence of the Eurasian ice sheet was found to reinforce monsoon, too, through a south-eastwards perturbation planetary wave. The trajectory of this wave is influenced by the Tibetan plateau.

  3. Reduced connection between the East Asian Summer Monsoon and Southern Hemisphere Circulation on interannual timescales under intense global warming

    Science.gov (United States)

    Yu, Tianlei; Guo, Pinwen; Cheng, Jun; Hu, Aixue; Lin, Pengfei; Yu, Yongqiang

    2018-03-01

    Previous studies show a close relationship between the East Asian Summer Monsoon (EASM) and Southern Hemisphere (SH) circulation on interannual timescales. In this study, we investigate whether this close relationship will change under intensive greenhouse-gas effect by analyzing simulations under two different climate background states: preindustrial era and Representative Concentration Pathway (RCP) 8.5 stabilization from the Community Climate System Model Version 4 (CCSM4). Results show a significantly reduced relationship under stabilized RCP8.5 climate state, such a less correlated EASM with the sea level pressure in the southern Indian Ocean and the SH branch of local Hadley Cell. Further analysis suggests that the collapse of the Atlantic Meridional Overturning Circulation (AMOC) due to this warming leads to a less vigorous northward meridional heat transport, a decreased intertropical temperature contrast in boreal summer, which produces a weaker cross-equatorial Hadley Cell in the monsoonal region and a reduced Interhemispheric Mass Exchange (IME). Since the monsoonal IME acts as a bridge connecting EASM and SH circulation, the reduced IME weakens this connection. By performing freshwater hosing experiment using the Flexible Global Ocean—Atmosphere—Land System model, Grid-point Version 2 (FGOALS-g2), we show a weakened relationship between the EASM and SH circulation as in CCSM4 when AMOC collapses. Our results suggest that a substantially weakened AMOC is the main driver leading to the EASM, which is less affected by SH circulation in the future warmer climate.

  4. Predictor-Year Subspace Clustering Based Ensemble Prediction of Indian Summer Monsoon

    Directory of Open Access Journals (Sweden)

    Moumita Saha

    2016-01-01

    Full Text Available Forecasting the Indian summer monsoon is a challenging task due to its complex and nonlinear behavior. A large number of global climatic variables with varying interaction patterns over years influence monsoon. Various statistical and neural prediction models have been proposed for forecasting monsoon, but many of them fail to capture variability over years. The skill of predictor variables of monsoon also evolves over time. In this article, we propose a joint-clustering of monsoon years and predictors for understanding and predicting the monsoon. This is achieved by subspace clustering algorithm. It groups the years based on prevailing global climatic condition using statistical clustering technique and subsequently for each such group it identifies significant climatic predictor variables which assist in better prediction. Prediction model is designed to frame individual cluster using random forest of regression tree. Prediction of aggregate and regional monsoon is attempted. Mean absolute error of 5.2% is obtained for forecasting aggregate Indian summer monsoon. Errors in predicting the regional monsoons are also comparable in comparison to the high variation of regional precipitation. Proposed joint-clustering based ensemble model is observed to be superior to existing monsoon prediction models and it also surpasses general nonclustering based prediction models.

  5. Do differences in future sulfate emission pathways matter for near-term climate? A case study for the Asian monsoon

    Science.gov (United States)

    Bartlett, Rachel E.; Bollasina, Massimo A.; Booth, Ben B. B.; Dunstone, Nick J.; Marenco, Franco; Messori, Gabriele; Bernie, Dan J.

    2018-03-01

    Anthropogenic aerosols could dominate over greenhouse gases in driving near-term hydroclimate change, especially in regions with high present-day aerosol loading such as Asia. Uncertainties in near-future aerosol emissions represent a potentially large, yet unexplored, source of ambiguity in climate projections for the coming decades. We investigated the near-term sensitivity of the Asian summer monsoon to aerosols by means of transient modelling experiments using HadGEM2-ES under two existing climate change mitigation scenarios selected to have similar greenhouse gas forcing, but to span a wide range of plausible global sulfur dioxide emissions. Increased sulfate aerosols, predominantly from East Asian sources, lead to large regional dimming through aerosol-radiation and aerosol-cloud interactions. This results in surface cooling and anomalous anticyclonic flow over land, while abating the western Pacific subtropical high. The East Asian monsoon circulation weakens and precipitation stagnates over Indochina, resembling the observed southern-flood-northern-drought pattern over China. Large-scale circulation adjustments drive suppression of the South Asian monsoon and a westward extension of the Maritime Continent convective region. Remote impacts across the Northern Hemisphere are also generated, including a northwestward shift of West African monsoon rainfall induced by the westward displacement of the Indian Ocean Walker cell, and temperature anomalies in northern midlatitudes linked to propagation of Rossby waves from East Asia. These results indicate that aerosol emissions are a key source of uncertainty in near-term projection of regional and global climate; a careful examination of the uncertainties associated with aerosol pathways in future climate assessments must be highly prioritised.

  6. Predicting onset and withdrawal of Indian Summer Monsoon in 2016: results of Tipping elements approach

    Science.gov (United States)

    Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

    2017-04-01

    The monsoon is the season of rain caused by a global seasonal reverse in winds direction and a change in pressure distribution. The Southwest winds bring summer monsoon to India. The economy of India is able to maintain its GDP in the wake of a good monsoon. However, if monsoon gets delayed by even two weeks, it can spell disaster because the high population depending on agriculture - 70% of its people directly related to farming. Agriculture, in turn, is dependent on the monsoon. Although the rainy season happens annually between June and September, the time of monsoon season's onset and withdrawal varies within a month from year to year. The important feature of the monsoon is that it starts and ends suddenly. Hence, despite enormous progress having been made in predicting monsoon since 1886, it remains a significant scientific challenge. To make predictions of monsoon timing in 2016, we applied our recently developed method [1]. Our approach is based on a teleconnection between the Eastern Ghats (EG) and North Pakistan (NP) - Tipping Elements of Indian Summer Monsoon. Both our predictions - for monsoon onset and withdrawal - were made for the Eastern Ghats region (EG-20N,80E) in the central part of India, while the Indian Meteorological Department forecasts monsoon over Kerala - a state at the southern tip of the Indian subcontinent. Our prediction for monsoon onset was published on May 6-th, 2016 [2]. We predicted the monsoon arrival to the EG on the 13th of June with a deviation of +/-4 days. In fact, monsoon onset was on June 17-th, that was confirmed by information from meteorological stations located around the EG-region. Hence, our prediction of monsoon onset (made 40 days in advance) was correct. We delivered the prediction of monsoon withdrawal on July 27, 2016 [3], announcing the monsoon withdrawal from the EG on October 5-th with a deviation of +/-5 days. The actual monsoon withdrawal started on October 10-th when the relative humidity in the region

  7. Monsoon oscillations regulate fertility of the Red Sea

    KAUST Repository

    Raitsos, Dionysios E.

    2015-02-16

    Tropical ocean ecosystems are predicted to become warmer, more saline, and less fertile in a future Earth. The Red Sea, one of the warmest and most saline environments in the world, may afford insights into the function of the tropical ocean ecosystem in a changing planet. We show that the concentration of chlorophyll and the duration of the phytoplankton growing season in the Red Sea are controlled by the strength of the winter Arabian monsoon (through horizontal advection of fertile waters from the Indian Ocean). Furthermore, and contrary to expectation, in the last decade (1998-2010) the winter Red Sea phytoplankton biomass has increased by 75% during prolonged positive phases of the Multivariate El Niño-Southern Oscillation Index. A new mechanism is reported, revealing the synergy of monsoon and climate in regulating Red Sea greenness. © 2015 The Authors.

  8. Monsoon oscillations regulate fertility of the Red Sea

    KAUST Repository

    Raitsos, Dionysios E.; Yi, Xing; Platt, Trevor; Racault, Marie-Fanny; Brewin, Robert J. W.; Pradhan, Yaswant; Papadopoulos, Vassilis P.; Sathyendranath, Shubha; Hoteit, Ibrahim

    2015-01-01

    Tropical ocean ecosystems are predicted to become warmer, more saline, and less fertile in a future Earth. The Red Sea, one of the warmest and most saline environments in the world, may afford insights into the function of the tropical ocean ecosystem in a changing planet. We show that the concentration of chlorophyll and the duration of the phytoplankton growing season in the Red Sea are controlled by the strength of the winter Arabian monsoon (through horizontal advection of fertile waters from the Indian Ocean). Furthermore, and contrary to expectation, in the last decade (1998-2010) the winter Red Sea phytoplankton biomass has increased by 75% during prolonged positive phases of the Multivariate El Niño-Southern Oscillation Index. A new mechanism is reported, revealing the synergy of monsoon and climate in regulating Red Sea greenness. © 2015 The Authors.

  9. Dynamics and Composition of the Asian Summer Monsoon Anticyclone

    Science.gov (United States)

    Gottschaldt, K. D.; Schlager, H.; Baumann, R.; Bozem, H.; Cai, D. S.; Eyring, V.; Hoor, P. M.; Graf, P.; Joeckel, P.; Jurkat, T.; Voigt, C.; Grewe, V.; Zahn, A.; Ziereis, H.

    2017-12-01

    This study places trace gas observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) obtained with the HALO research aircraft during the ESMVal campaign into the context of regional, intra-annual variability by hindcasts with the EMAC model. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from the rest of the year. Air uplifted from the lower troposphere to the tropopause layer dominates the eastern part of the ASMA's interior, while the western part is characterized by subsidence down to the mid-troposphere. Soluble compounds are being washed out when uplifted by convection in the eastern part, where lightning simultaneously replenishes reactive nitrogen in the upper troposphere. Net photochemical ozone production is significantly enhanced in the ASMA, contrasted by an ozone depleting regime in the mid-troposphere and more neutral conditions in autumn and winter. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank, and then transported in the southern fringe around the interior region. Observed and simulated tracer-tracer relations reflect photochemical O3 production, as well as in-mixing from the lower troposphere and the tropopause layer. The simulation additionally shows entrainment of clean air from the equatorial region by northerly winds at the western ASMA flank. Although the in situ measurements were performed towards the end of summer, the main ingredients needed for their interpretation are present throughout the monsoon season.Subseasonal dynamical instabilities of the ASMA effectively overcome horizontal transport barriers, occur quite frequently, and are of paramount importance for the trace gas composition of the ASMA and its outflow into regions around the world.

  10. Monsoon and primary acute angle closure in malaysia.

    Science.gov (United States)

    Ch'ng, T W; Mosavi, S A A; Noor Azimah, A A; Azlan, N Z; Azhany, Y; Liza-Sharmini, A T

    2013-10-01

    Acute angle closure (AAC) without prompt treatment may lead to optic neuropathy. Environmental factor such as climate change may precipitate pupillary block, the possible mechanism of AAC. To determine the association of northeast monsoon and incidence of AAC in Malaysia. A retrospective study was conducted on AAC patients admitted to two main tertiary hospitals in Kelantan, Malaysia between January 2001 and December 2011. The cumulative number of rainy day, amount of rain, mean cloud cover and 24 hours mean humidity at the estimated day of attack were obtained from the Department of Meteorology, Malaysia. A total 73 cases of AAC were admitted with mean duration of 4.1SD 2.0 days. More than half have previous history of possibility of AAC. There was higher incidence of AAC during the northeast monsoon (October to March). There was also significant correlation of number of rainy day (r=0.718, pclimate as the potential risk factor. Prompt treatment to arrest pupillary block and reduction of the intraocular pressure is important to prevent potential glaucomatous damage. Public awareness of AAC and accessibility to treatment should be part of preparation to face the effect of northeast monsoon.

  11. Atmospheric water budget over the South Asian summer monsoon region

    Science.gov (United States)

    Unnikrishnan, C. K.; Rajeevan, M.

    2018-04-01

    High resolution hybrid atmospheric water budget over the South Asian monsoon region is examined. The regional characteristics, variability, regional controlling factors and the interrelations of the atmospheric water budget components are investigated. The surface evapotranspiration was created using the High Resolution Land Data Assimilation System (HRLDAS) with the satellite-observed rainfall and vegetation fraction. HRLDAS evapotranspiration shows significant similarity with in situ observations and MODIS satellite-observed evapotranspiration. Result highlights the fundamental importance of evapotranspiration over northwest and southeast India on atmospheric water balance. The investigation shows that the surface net radiation controls the annual evapotranspiration over those regions, where the surface evapotranspiration is lower than 550 mm. The rainfall and evapotranspiration show a linear relation over the low-rainfall regions (forcing (like surface net radiation). The lead and lag correlation of water budget components show that the water budget anomalies are interrelated in the monsoon season even up to 4 months lead. These results show the important regional interrelation of water budget anomalies on south Asian monsoon.

  12. Effects of large-scale deforestation on precipitation in the monsoon regions: remote versus local effects.

    Science.gov (United States)

    Devaraju, N; Bala, Govindasamy; Modak, Angshuman

    2015-03-17

    In this paper, using idealized climate model simulations, we investigate the biogeophysical effects of large-scale deforestation on monsoon regions. We find that the remote forcing from large-scale deforestation in the northern middle and high latitudes shifts the Intertropical Convergence Zone southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, and South Asia) and moderate precipitation increases in the Southern Hemisphere monsoon regions (South Africa, South America, and Australia). The magnitude of the monsoonal precipitation changes depends on the location of deforestation, with remote effects showing a larger influence than local effects. The South Asian Monsoon region is affected the most, with 18% decline in precipitation over India. Our results indicate that any comprehensive assessment of afforestation/reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation alongside the large local impacts on temperatures.

  13. The classification of PM10 concentrations in Johor Based on Seasonal Monsoons

    Science.gov (United States)

    Hamid, Hazrul Abdul; Hanafi Rahmat, Muhamad; Aisyah Sapani, Siti

    2018-04-01

    Air is the most important living resource in life. Contaminated air could adversely affect human health and the environment, especially during the monsoon season. Contamination occurs as a result of human action and haze. There are several pollutants present in the air where one of them is PM10. Secondary data was obtained from the Department of Environment from 2010 until 2014 and was analyzed using the hourly average of PM10 concentrations. This paper examined the relation between PM10 concentrations and the monsoon seasons (Northeast Monsoon and Southwest Monsoon) in Larkin and Pasir Gudang. It was expected that the concentration of PM10 would be higher during the Southwest Monsoon as it is a dry season. The data revealed that the highest PM10 concentrations were recorded between 2010 to 2014 during this particular monsoon season. The characteristics of PM10 concentration were compared using descriptive statistics based on the monsoon seasons and classified using the hierarchical cluster analysis (Ward Methods). The annual average of PM10 concentration during the Southwest Monsoon had exceeded the standard set by the Malaysia Ambient Air Quality Guidelines (50 μg/m3) while the PM10 concentration during the Northeast Monsoon was below the acceptable level for both stations. The dendrogram displayed showed two clusters for each monsoon season for both stations excepted for the PM10 concentration during the Northeast Monsoon in Larkin which was classified into three clusters due to the haze in 2010. Overall, the concentration of PM10 in 2013 was higher based on the clustering shown for every monsoon season at both stations according to the characteristics in the descriptive statistics.

  14. Understanding the Asian summer monsoon response to greenhouse warming: the relative roles of direct radiative forcing and sea surface temperature change

    Science.gov (United States)

    Li, Xiaoqiong; Ting, Mingfang

    2017-10-01

    Future hydroclimate projections from state-of-the-art climate models show large uncertainty and model spread, particularly in the tropics and over the monsoon regions. The precipitation and circulation responses to rising greenhouse gases involve a fast component associated with direct radiative forcing and a slow component associated with sea surface temperature (SST) warming; the relative importance of the two may contribute to model discrepancies. In this study, regional hydroclimate responses to greenhouse warming are assessed using output from coupled general circulation models in the Coupled Model Intercomparison Project-Phase 5 (CMIP5) and idealized atmospheric general circulation model experiments from the Atmosphere Model Intercomparison Project. The thermodynamic and dynamic mechanisms causing the rainfall changes are examined using moisture budget analysis. Results show that direct radiative forcing and SST change exert significantly different responses both over land and ocean. For most part of the Asian monsoon region, the summertime rainfall changes are dominated by the direct CO2 radiative effect through enhanced monsoon circulation. The response to SST warming shows a larger model spread compared to direct radiative forcing, possibly due to the cancellation between the thermodynamical and dynamical components. While the thermodynamical response of the Asian monsoon is robust across the models, there is a lack of consensus for the dynamical response among the models and weak multi-model mean responses in the CMIP5 ensemble, which may be related to the multiple physical processes evolving on different time scales.

  15. High sensitivity of Indian summer monsoon to Middle East dust absorptive properties.

    Science.gov (United States)

    Jin, Qinjian; Yang, Zong-Liang; Wei, Jiangfeng

    2016-07-28

    The absorptive properties of dust aerosols largely determine the magnitude of their radiative impacts on the climate system. Currently, climate models use globally constant values of dust imaginary refractive index (IRI), a parameter describing the dust absorption efficiency of solar radiation, although it is highly variable. Here we show with model experiments that the dust-induced Indian summer monsoon (ISM) rainfall differences (with dust minus without dust) change from -9% to 23% of long-term climatology as the dust IRI is changed from zero to the highest values used in the current literature. A comparison of the model results with surface observations, satellite retrievals, and reanalysis data sets indicates that the dust IRI values used in most current climate models are too low, tending to significantly underestimate dust radiative impacts on the ISM system. This study highlights the necessity for developing a parameterization of dust IRI for climate studies.

  16. Impact of cloud radiative heating on East Asian summer monsoon circulation

    International Nuclear Information System (INIS)

    Guo, Zhun; Zhou, Tianjun; Wang, Minghuai; Qian, Yun

    2015-01-01

    The impacts of cloud radiative heating on the East Asian Summer Monsoon (EASM) over southeastern China (105°–125°E, 20°–35°N) are addressed by using the Community Atmosphere Model version 5 (CAM5). Sensitivity experiments demonstrate that the radiative heating of clouds leads to a positive effect on the local EASM circulation over southeastern China. Without the radiative heating of clouds, the EASM circulation and precipitation would be much weaker than that in normal conditions. The longwave heating of clouds dominates the changes of EASM circulation. The positive effect of clouds on EASM circulation is explained by the thermodynamic energy equation, i.e. the different heating rate between cloud base and cloud top enhances the convective instability over southeastern China, which consequently enhances updraft. The strong updraft would further result in a southward meridional wind above the center of the updraft through Sverdrup vorticity balance. (letter)

  17. Effect of climate change on seasonal monsoon in Asia and its impact on the variability of monsoon rainfall in Southeast Asia

    Directory of Open Access Journals (Sweden)

    Yen Yi Loo

    2015-11-01

    Full Text Available Global warming and climate change is one of the most extensively researched and discussed topical issues affecting the environment. Although there are enough historical evidence to support the theory that climate change is a natural phenomenon, many research scientists are widely in agreement that the increase in temperature in the 20th century is anthropologically related. The associated effects are the variability of rainfall and cyclonic patterns that are being observed globally. In Southeast Asia the link between global warming and the seasonal atmospheric flow during the monsoon seasons shows varying degree of fuzziness. This study investigates the impact of climate change on the seasonality of monsoon Asia and its effect on the variability of monsoon rainfall in Southeast Asia. The comparison of decadal variation of precipitation and temperature anomalies before the 1970s found general increases which were mostly varying. But beyond the 1970s, global precipitation anomalous showed increases that almost corresponded with increases in global temperature anomalies for the same period. There are frequent changes and a shift westward of the Indian summer monsoon. Although precipitation is observed to be 70% below normal levels, in some areas the topography affects the intensity of rainfall. These shifting phenomenon of other monsoon season in the region are impacting on the variability of rainfall and the onset of monsoons in Southeast Asia and is predicted to delay for 15 days the onset of the monsoon in the future. The variability of monsoon rainfall in the SEA region is observed to be decadal and the frequency and intensity of intermittent flooding of some areas during the monsoon season have serious consequences on the human, financial, infrastructure and food security of the region.

  18. Modeling the Influences of Aerosols on Pre-Monsoon Circulation and Rainfall over Southeast Asia

    Science.gov (United States)

    Lee, D.; Sud, Y. C.; Oreopoulos, L.; Kim, K.-M.; Lau, W. K.; Kang, I.-S.

    2014-01-01

    We conduct several sets of simulations with a version of NASA's Goddard Earth Observing System, version 5, (GEOS-5) Atmospheric Global Climate Model (AGCM) equipped with a two-moment cloud microphysical scheme to understand the role of biomass burning aerosol (BBA) emissions in Southeast Asia (SEA) in the pre-monsoon period of February-May. Our experiments are designed so that both direct and indirect aerosol effects can be evaluated. For climatologically prescribed monthly sea surface temperatures, we conduct sets of model integrations with and without biomass burning emissions in the area of peak burning activity, and with direct aerosol radiative effects either active or inactive. Taking appropriate differences between AGCM experiment sets, we find that BBA affects liquid clouds in statistically significantly ways, increasing cloud droplet number concentrations, decreasing droplet effective radii (i.e., a classic aerosol indirect effect), and locally suppressing precipitation due to a deceleration of the autoconversion process, with the latter effect apparently also leading to cloud condensate increases. Geographical re-arrangements of precipitation patterns, with precipitation increases downwind of aerosol sources are also seen, most likely because of advection of weakly precipitating cloud fields. Somewhat unexpectedly, the change in cloud radiative effect (cloud forcing) at surface is in the direction of lesser cooling because of decreases in cloud fraction. Overall, however, because of direct radiative effect contributions, aerosols exert a net negative forcing at both the top of the atmosphere and, perhaps most importantly, the surface, where decreased evaporation triggers feedbacks that further reduce precipitation. Invoking the approximation that direct and indirect aerosol effects are additive, we estimate that the overall precipitation reduction is about 40% due to the direct effects of absorbing aerosols, which stabilize the atmosphere and reduce

  19. Comparative Study of Monsoon Rainfall Variability over India and the Odisha State

    Directory of Open Access Journals (Sweden)

    K C Gouda

    2017-10-01

    Full Text Available Indian summer monsoon (ISM plays an important role in the weather and climate system over India. The rainfall during monsoon season controls many sectors from agriculture, food, energy, and water, to the management of disasters. Being a coastal province on the eastern side of India, Odisha is one of the most important states affected by the monsoon rainfall and associated hydro-meteorological systems. The variability of monsoon rainfall is highly unpredictable at multiple scales both in space and time. In this study, the monsoon variability over the state of Odisha is studied using the daily gridded rainfall data from India Meteorological Department (IMD. A comparative analysis of the behaviour of monsoon rainfall at a larger scale (India, regional scale (Odisha, and sub-regional scale (zones of Odisha is carried out in terms of the seasonal cycle of monsoon rainfall and its interannual variability. It is seen that there is no synchronization in the seasonal monsoon category (normal/excess/deficit when analysed over large (India and regional (Odisha scales. The impact of El Niño, La Niña, and the Indian Ocean Dipole (IOD on the monsoon rainfall at both scales (large scale and regional scale is analysed and compared. The results show that the impact is much more for rainfall over India, but it has no such relation with the rainfall over Odisha. It is also observed that there is a positive (negative relation of the IOD with the seasonal monsoon rainfall variability over Odisha (India. The correlation between the IAV of monsoon rainfall between the large scale and regional scale was found to be 0.46 with a phase synchronization of 63%. IAV on a sub-regional scale is also presented.

  20. Aerosol and rainfall variability over the Indian monsoon region: distributions, trends and coupling

    Directory of Open Access Journals (Sweden)

    R. Gautam

    2009-09-01

    Full Text Available Aerosol solar absorption over the Indian monsoon region has a potential role of modulating the monsoon circulation and rainfall distribution as suggested by recent studies based on model simulations. Prior to the onset of the monsoon, northern India is influenced by significant dust transport that constitutes the bulk of the regional aerosol loading over the Gangetic-Himalayan region. In this paper, a multi-sensor characterization of the increasing pre-monsoon aerosol loading over northern India, in terms of their spatial, temporal and vertical distribution is presented. Aerosol transport from the northwestern arid regions into the Indo-Gangetic Plains and over the foothills of the Himalayas is found to be vertically extended to elevated altitudes (up to 5 km as observed from the space-borne lidar measurements (CALIPSO. In relation with the enhanced pre-monsoon aerosol loading and the associated solar absorption effects on tropospheric temperature anomalies, this paper investigates the monsoon rainfall variability over India in recent past decades from an observational viewpoint. It is found that the early summer monsoon rainfall over India is on the rise since 1950s, as indicated by historical rainfall data, with over 20% increase for the period 1950–2004. This large sustained increase in the early summer rainfall is led by the observed strengthening of the pre-monsoon tropospheric land-sea thermal gradient over the Indian monsoon region as indicated by microwave satellite measurements (MSU of tropospheric temperatures from 1979–2007. Combined analysis of changes in tropospheric temperatures and summer monsoon rainfall in the past three decades, suggest a future possibility of an emerging rainfall pattern of a wetter monsoon over South Asia in early summer followed by a drier period.

  1. Evidence for eddy formation in the eastern Arabian Sea during the northeast monsoon

    Science.gov (United States)

    Bruce, John G.; Johnson, Donald R.; Kindle, John C.

    1994-01-01

    The seasonal formation of a large (500-800 km diameter) anticyclonic eddy in the upper 300-400 m of the eastern Arabian Sea during the northest monsoon period (December-April) is indicated fom hydrographic and satellite altimetry sea level observations, as well as from numerical model experiments. The center of the eddy circulation is approximately 10 deg N, 70 deg E, just to the west of the north-south Laccadive Island chain. In this paper the eddy is called the Laccadive High (LH). In some ways it is like a mirrorlike counterpart to the Great Whirl that develops during the southwest monsoon of the Somali coast (western Arabian Sea). The LH occurs at the same latitude but on the opposite side of the basin during the reversed monsoon. It is different from the Great Whirl, however, in its formation process, its intensity, and its decay. The hydrographic data obtained from surveys all during a single season give sufficiently close station spacing to allow reasonable contouring of the geopotential surfaces and of the properties within and around the LH region with minimum time aliasing. The Geostat altimeter record extends over 4 years, during which the seasonal variability of the LH indicates a dynamic relief of approximately 15-20 cm, which is in good agreement with the hydrographics observations. The altimetry time series also suggests a westward translation of the LH by January with a subsequent dissipation in midbasin. The model used is a wind-forced three-layer primitive equation model which depicts a LH agreement with the timing, position, and amplitude of both the hydrographic and altimetric measurements. The numerical simulation includes a passive tracer located in the Western Bay of Bengal; the western advection of the tracer around the south coasts of Sri Lanka and India in December and January is consistent with the appearance of low-salinity water observed to extend into the Arabian Sea during this period. The modeling studies suggest that both local and

  2. South Asian summer monsoon variability during the last ~54 kyrs inferred from surface water salinity and river run off proxies

    Digital Repository Service at National Institute of Oceanography (India)

    Gebregiorgis, D.; Hathorne, E.C.; Sijinkumar, A.V.; Nath, B.N.; Nurnberg, D.; Frank, M.

    ; Viswambharan and Mohanakumar, 2014). Decadal to centennial scale variations in monsoon precipitation have been in phase with temperature fluctuations in northern high latitudes(Fleitmann et al., 2003). Monsoonal changes on millennial to longer time...

  3. Late holocene primary productivity and sea surface temperature variations in the northeastern Arabian Sea: Implications for winter monsoon variability.

    Digital Repository Service at National Institute of Oceanography (India)

    Boll, A.; Luckge, A.; Munz, P.; Forke, S.; Schulz, H.; Ramaswamy, V.; Rixen, T.; Gaye, B.; Emeis, K.-C.

    changes in winter monsoon strength with winds from the northeast that drive convective mixing and high surface ocean productivity in the northeastern Arabian Sea. To establish a high-resolution record of winter monsoon variability for the late Holocene, we...

  4. The abrupt onset of the modern South Asian monsoon winds

    Digital Repository Service at National Institute of Oceanography (India)

    Betzler, C.; Eberli, G.P.; Kroon, D.; Wright, J.D.; Swart, P.K.; Nath, B.N.; Alvarez-Zarikian, C.A.; Alonso-Garcia, M.; Bialik, O.M.; Blattler, C.L.; Guo, J.; Haffen, S.; Horozal, S.; Inoue, M.; Jovane, L.; Lanci, L.; Laya, J.C.; Mee, A.L.H.; Ludmann, T.; Nakakuni, M.; Niino, K.; Petruny, L.M.; Pratiwi, S.D.; Reijmer, J.J.G.; Reolid, J.; Slagle, A.L.; Sloss, C.R.; Su, X.; Yao, Z.; Young, J.R.

    :29838 | DOI: 10.1038/srep29838 www.nature.com/scientificreports The abrupt onset of the modern South Asian Monsoon winds Christian Betzler1, Gregor P. Eberli2, Dick Kroon3, James D. Wright4, Peter K. Swart2, Bejugam Nagender Nath5, Carlos A. Alvarez....betzler@uni-hamburg.de) Received: 25 April 2016 accepted: 21 June 2016 Published: 20 July 2016 OPEN www.nature.com/scientificreports/ 2Scientific RepoRts | 6:29838 | DOI: 10.1038/srep29838 control, and we propose that the post Miocene Climate Optimum cooling, together...

  5. Extended Range Prediction of Indian Summer Monsoon: Current status

    Science.gov (United States)

    Sahai, A. K.; Abhilash, S.; Borah, N.; Joseph, S.; Chattopadhyay, R.; S, S.; Rajeevan, M.; Mandal, R.; Dey, A.

    2014-12-01

    The main focus of this study is to develop forecast consensus in the extended range prediction (ERP) of monsoon Intraseasonal oscillations using a suit of different variants of Climate Forecast system (CFS) model. In this CFS based Grand MME prediction system (CGMME), the ensemble members are generated by perturbing the initial condition and using different configurations of CFSv2. This is to address the role of different physical mechanisms known to have control on the error growth in the ERP in the 15-20 day time scale. The final formulation of CGMME is based on 21 ensembles of the standalone Global Forecast System (GFS) forced with bias corrected forecasted SST from CFS, 11 low resolution CFST126 and 11 high resolution CFST382. Thus, we develop the multi-model consensus forecast for the ERP of Indian summer monsoon (ISM) using a suite of different variants of CFS model. This coordinated international effort lead towards the development of specific tailor made regional forecast products over Indian region. Skill of deterministic and probabilistic categorical rainfall forecast as well the verification of large-scale low frequency monsoon intraseasonal oscillations has been carried out using hindcast from 2001-2012 during the monsoon season in which all models are initialized at every five days starting from 16May to 28 September. The skill of deterministic forecast from CGMME is better than the best participating single model ensemble configuration (SME). The CGMME approach is believed to quantify the uncertainty in both initial conditions and model formulation. Main improvement is attained in probabilistic forecast which is because of an increase in the ensemble spread, thereby reducing the error due to over-confident ensembles in a single model configuration. For probabilistic forecast, three tercile ranges are determined by ranking method based on the percentage of ensemble members from all the participating models falls in those three categories. CGMME further

  6. Why is Bay of Bengal warmer than Arabian Sea during the summer monsoon?

    Digital Repository Service at National Institute of Oceanography (India)

    Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.

    the summer monsoon. In the Arabian Sea, the winds associated with the summer monsoon are stronger and favour the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively...

  7. The value of C sub(e) for the Arabian Sea during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, A.S.; Sadhuram, Y.; Krishna, V.V.G.

    We estimate, from the moisture budget the bulk aerodynamic coefficient for latent heat flux (C sub(e)) during the monsoon season over the central Arabian Sea. The average value of C sub(e) under active monsoon conditions was found to be 2.25 x 10...

  8. Recent trends in pre-monsoon daily temperature extremes over India

    Indian Academy of Sciences (India)

    e-mail: kotha@tropmet.res.in. Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season ... change in day-to-day magnitude of fluctuations of pre-monsoon maximum and minimum tempera- tures. ... by high exceedence counts during drought periods.

  9. Residual estuarine circulation in the Mandovi, a monsoonal estuary: A three-dimensional model study

    Digital Repository Service at National Institute of Oceanography (India)

    Vijith, V.; Shetye, S.R.; Baetens, K.; Luyten, P.; Michael, G.S.

    -dependence is forced by the Indian Summer Monsoon (ISM) and hence the estuary is referred to as a monsoonal estuary. In this paper, we use a three-dimensional, open source, hydrodynamic, numerical model to reproduce the observed annual salinity field in the Mandovi. We...

  10. Late Holocene anti-phase change in the East Asian summer and winter monsoons

    Science.gov (United States)

    Kang, Shugang; Wang, Xulong; Roberts, Helen M.; Duller, Geoff A. T.; Cheng, Peng; Lu, Yanchou; An, Zhisheng

    2018-05-01

    Changes in East Asian summer and winter monsoon intensity have played a pivotal role in the prosperity and decline of society in the past, and will be important for future climate scenarios. However, the phasing of changes in the intensity of East Asian summer and winter monsoons on millennial and centennial timescales during the Holocene is unclear, limiting our ability to understand the factors driving past and future changes in the monsoon system. Here, we present a high resolution (up to multidecadal) loess record for the last 3.3 ka from the southern Chinese Loess Plateau that clearly demonstrates the relationship between changes in the intensity of the East Asian summer and winter monsoons, particularly at multicentennial scales. At multimillennial scales, the East Asian summer monsoon shows a steady weakening, while the East Asian winter monsoon intensifies continuously. At multicentennial scales, a prominent ∼700-800 yr cycle in the East Asian summer and winter monsoon intensity is observed, and here too the two monsoons are anti-phase. We conclude that multimillennial changes are driven by Northern Hemisphere summer insolation, while multicentennial changes can be correlated with solar activity and changing strength of the Atlantic meridional overturning circulation.

  11. Monsoon wind and maritime trade: A case study of historical evidence from Orissa, India

    Digital Repository Service at National Institute of Oceanography (India)

    Tripati, S.; Raut, L.N.

    Monsoon plays a predominant role in the daily life of the people of South Asia. The use of monsoon wind in the Indian Ocean for maritime trade was a boon to the sailing ships to reach overseas countries. It is believed that Hippalus discovered...

  12. Modelling the impacts of deforestation on monsoon rainfall in West Africa

    International Nuclear Information System (INIS)

    Abiodun, B J; Pal, J S; Afiesimama, E A; Gutowski, W J; Adedoyin, A

    2010-01-01

    The study found that deforestation causes more monsoon moisture to be retained in the mid-troposphere, thereby reducing the northward transport of moisture needed for rainfall over West Africa. Hence, deforestation has dynamical impacts on the West African monsoon and rainfall.

  13. SST and OLR relationship during Indian summer monsoon: a coupled climate modelling perspective

    Science.gov (United States)

    Chaudhari, Hemantkumar S.; Hazra, Anupam; Pokhrel, Samir; Chakrabarty, Chandrima; Saha, Subodh Kumar; Sreenivas, P.

    2018-04-01

    The study mainly investigates sea surface temperature (SST) and outgoing longwave radiation (OLR) relationships in coupled climate model. To support the analysis, high-level cloud and OLR relationship is also investigated. High-level cloud and OLR relationship depicts significant negative correlation over the entire monsoon regime. Coupled climate model is able to produce the same. SST and OLR relationship in observation also depicts significant negative relationship, in particular, over the Equatorial Eastern Indian Ocean (EIO) region. Climate Forecast System version 2 (CFSv2) is able to portray the negative relationship over EIO region; however, it is underestimated as compared to observation. Significant negative correlations elucidate that local SSTs regulate the convection and further it initiates Bjerknes feedback in the central Indian Ocean. It connotes that SST anomalies during monsoon period tend to be determined by oceanic forcing. The heat content of the coastal Bay of Bengal shows highest response to EIO SST by a lag of 1 month. It suggests that the coastal region of the Bay of Bengal is marked by coastally trapped Kelvin waves, which might have come from EIO at a time lag of 1 month. Sea surface height anomalies, depth at 20 °C isotherms and depth at 26 isotherms also supports the above hypothesis. Composite analysis based on EIO index and coupled climate model sensitivity experiments also suggest that the coastal Bay of Bengal region is marked by coastally trapped Kelvin waves, which are propagated from EIO at a time lag of 1 month. Thus, SST and OLR relationship pinpoints that the Bay of Bengal OLR (convection) is governed by local ocean-atmospheric coupling, which is influenced by the delayed response from EIO brought forward through oceanic planetary waves at a lag of 1 month. These results have utmost predictive value for seasonal and extended range forecasting. Thus, OLR and SST relationship can constitute a pivotal role in investigating the

  14. On the role of convective systems over the northwest Pacific and monsoon activity over the Indian subcontinent

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Babu, A; Reason, C.

    been examined in relation to breaks in monsoon conditions over the Indian sub-continent during contrasting monsoon years. A see-saw nature of convection between the NWP and north Indian Ocean was found during the years with excess monsoon rainfall...

  15. Fine-scale responses of phytoplankton to freshwater influx in a tropical monsoonal estuary following the onset of southwest monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Pednekar, S.M.; Matondkar, S.G.P.; Gomes, H.R.; Goes, J.I.; Parab, S.G.; Kerkar, V.

    of seawater which have a significant impact on circulation, salinity (Shetye et al 2007; Vijith et al 2009) as well as water column turbidity caused by the dis- turbance of bottom sediments (Devassy and Goes 1988). On account of this free mixing of coastal.... By the first week of October (PostM Influence of SW monsoon in phytoplankton–freshwater influx 549 phase), rainfall had reduced to occasional and spo- radic showers and salinity values began rising to between3and7psu. 3.3 Nitrate Nitrate variation across...

  16. Diagnosis of the Asian summer monsoon variability and the climate prediction of monsoon precipitation via physical decomposition

    Science.gov (United States)

    Lim, Young-Kwon

    This study investigates the space-time evolution of the dominant modes that constitute the Asian summer monsoon (ASM), and, as an ultimate goal, the climate prediction of the ASM rainfall. Precipitation and other synoptic variables during the prominent life cycle of the ASM (May 21 to September 17) are used to show the detailed features of dominant modes, which are identified as the seasonal cycle, the ISO defined by the 40--50 day intraseasonal oscillation including the Madden-Julian oscillation, and the El Nino mode. The present study reveals that the ISO is the second largest component of the ASM rainfall variation. Correlation analysis indicates that ISO explains a larger fraction of the variance of the observed precipitation (without climatology) than the ENSO mode. The dominant ISO signal faithfully explains the northward propagation of the ISO toward the Asian continent causing intraseasonal active/break periods. The interannual variation of the ISO strength suggests that the ENSO exerts some influence on the ISO. The composite convective ISO anomaly and Kelvin-Rossby wave response over the Indian Ocean shows that the ISO tends to be stronger during the early stage of the ASM than normal in El Nino (La Nina) years, indicating greater (smaller) possibility of ISO-related extreme rainfall over India, Bangladesh, and the Bay of Bengal. The ENSO mode reveals that the following factors affect the evolution of the ASM system in El Nino (La Nina) years. (1) The anomalous sea surface temperature and sea level pressure over the Indian Ocean during the early stage of the ASM weaken (enhance) the meridional pressure gradient. (2) As a result, the westerly jet and the ensuing moisture transport toward India and the Bay of Bengal become weak (strong) and delayed (expedited), providing a less (more) favorable condition for regional monsoon onsets. (3) The Walker circulation anomaly results in an enhanced subsidence (ascent) and drought (flood) over the Maritime continent

  17. Relative role of pre-monsoon conditions and intraseasonal oscillations in determining early-vs-late indian monsoon intensity in a GCM

    Science.gov (United States)

    Ghosh, Rohit; Chakraborty, Arindam; Nanjundiah, Ravi S.

    2018-01-01

    The aim of this paper is to identify relative roles of different land-atmospheric conditions, apart from sea surface temperature (SST), in determining early vs. late summer monsoon intensity over India in a high resolution general circulation model (GCM). We find that in its early phase (June-July; JJ), pre-monsoon land-atmospheric processes play major role to modulate the precipitation over Indian region. These effects of pre-monsoon conditions decrease substantially during its later phase (August-September; AS) for which the interannual variation is mainly governed by the low frequency northward propagating intraseasonal oscillations. This intraseasonal variability which is related to mean vertical wind shear has a significant role during the early phase of monsoon as well. Further, using multiple linear regression, we show that interannual variation of early and late monsoon rainfall over India is best explained when all these land-atmospheric parameters are taken together. Our study delineates the relative role of different processes affecting early versus later summer monsoon rainfall over India that can be used for determining its subseasonal predictability.

  18. Monsoon signatures in trace gas records from Cape Rama, India

    International Nuclear Information System (INIS)

    Bhattacharya, S.K.; Jani, R.A.; Borole, D.V.; Francey, R.J.; Allison, C.E.; Masarie, K.A.

    2002-01-01

    Concentrations of trace gases CO 2 , CH 4 , CO, N 2 O and H 2 , and the stable carbon and oxygen isotopic composition of CO 2 have been measured in air samples collected from Cape Rama, a coastal station on the west coast of India, since 1993. The data show clear signatures of continental and oceanic air mass resulting in complex seasonal variation of trace gas characteristics. The regional atmospheric circulation in the Indian Ocean and Arabian Sea undergoes biannual reversal in low-level winds associated with the yearly migration of the inter-tropical convergence zone (ITCZ). From June to September, the wind is from the equatorial Indian Ocean to the Indian subcontinent (southwest monsoon) and brings in pristine marine air. From December to February, dry continental winds blow from the northeast and transport continental emissions to the ocean (northeast monsoon). Detailed transport and chemical modelling will be necessary to interpret these records, however the potential to identify and constrain the regional trace gas emissions appears to be high. (author)

  19. Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

    Directory of Open Access Journals (Sweden)

    R. R. Kuechler

    2018-01-01

    Full Text Available The Pliocene is regarded as a potential analogue for future climate with conditions generally warmer-than-today and higher-than-preindustrial atmospheric CO2 levels. Here we present the first orbitally resolved records of continental hydrology and vegetation changes from West Africa for two Pliocene time intervals (5.0–4.6 Ma, 3.6–3.0 Ma, which we compare with records from the last glacial cycle (Kuechler et al., 2013. Our results indicate that changes in local insolation alone are insufficient to explain the full degree of hydrologic variations. Generally two modes of interacting insolation forcings are observed: during eccentricity maxima, when precession was strong, the West African monsoon was driven by summer insolation; during eccentricity minima, when precession-driven variations in local insolation were minimal, obliquity-driven changes in the summer latitudinal insolation gradient became dominant. This hybrid monsoonal forcing concept explains orbitally controlled tropical climate changes, incorporating the forcing mechanism of latitudinal gradients for the Pliocene, which probably increased in importance during subsequent Northern Hemisphere glaciations.

  20. Community level perceptions of the monsoon onset, withdrawal and climatic trends in Bangladesh

    Science.gov (United States)

    Reeve, M. A.; Abu Syed, M. D.; Hossain, P. R.; Maainuddi, G.; Mamnun, N.

    2012-04-01

    A structured questionnaire study was carried out in 6 different regions in Bangladesh in order to give insight into how the different communities define the monsoon. The respondents were asked how they define the monsoon onset and withdrawal, and by how much these can vary from year to year. They were also asked about how they perceive changes in onset and withdrawal dates and total monsoonal rainfall during the past 20 years. Bangladesh is a developing country with a large proportion of the population living in rural areas and employed in the agricultural sector. It is foreseen that these communities will be most affected by changes in the climate. These groups were considered to be the main stakeholders when considering climate change, due to the direct influence the monsoon has on their livelihood and the food supply for the entire nation. Agricultural workers were therefore the main group targeted in this study. The main aim of the study was to create a framework for defining the monsoon in order to increase the usability of results in future impact-related studies. Refining definitions according to the perceptions of the main stakeholders helps to achieve this goal. Results show that rainfall is the main parameter used in defining the monsoon onset and withdrawal. This is possibly intuitive, however the monsoon onset was considered to be considerably earlier than previous scientific studies. This could be due to pre-monsoonal rainfall, however the respondents defined this type of rainfall separately to what they called the monsoon. The monsoon is considered to start earliest in the Sylhet region in northeast Bangladesh.

  1. Atmospheric circulation characteristics associated with the onset of Asian summer monsoon

    Science.gov (United States)

    Li, Chongyin; Pan, Jing

    2006-12-01

    The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer monsoon is found to occur first over the southwestern part of the South China Sea (SCS) and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump (from 25° 28°N to around 30°N) occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere (500 200 hPa) and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet.

  2. Coupling of Community Land Model with RegCM4 for Indian Summer Monsoon Simulation

    Science.gov (United States)

    Maurya, R. K. S.; Sinha, P.; Mohanty, M. R.; Mohanty, U. C.

    2017-11-01

    Three land surface schemes available in the regional climate model RegCM4 have been examined to understand the coupling between land and atmosphere for simulation of the Indian summer monsoon rainfall. The RegCM4 is coupled with biosphere-atmosphere transfer scheme (BATS) and the National Center for Atmospheric Research (NCAR) Community Land Model versions 3.5, and 4.5 (CLM3.5 and CLM4.5, respectively) and model performance is evaluated for recent drought (2009) and normal (2011) monsoon years. The CLM4.5 has a more distinct category of surface and it is capable of representing better the land surface characteristics. National Centers for Environmental Prediction (NCEP) and Department of Energy (DOE) reanalysis version 2 (NNRP2) datasets are considered as driving force to conduct the experiments for the Indian monsoon region (30°E-120°E; 30°S-50°N). The NNRP2 and India Meteorological Department (IMD) gridded precipitation data are used for verification analysis. The results indicate that RegCM4 simulations with CLM4.5 (RegCM4-CLM4.5) and CLM3.5 (RegCM4-CLM3.5) surface temperature (at 2 ms) have very low warm biases ( 1 °C), while with BATS (RegCM4-BATS) has a cold bias of about 1-3 °C in peninsular India and some parts of central India. Warm bias in the RegCM4-BATS is observed over the Indo-Gangetic plain and northwest India and the bias is more for the deficit year as compared to the normal year. However, the warm (cold) bias is less in RegCM4-CLM4.5 than other schemes for both the deficit and normal years. The model-simulated maximum (minimum) surface temperature and sensible heat flux at the surface are positively (negatively) biased in all the schemes; however, the bias is higher in RegCM4-BATS and lower in RegCM4-CLM4.5 over India. All the land surface schemes overestimated the precipitation in peninsular India and underestimated in central parts of India for both the years; however, the biases are less in RegCM4-CLM4.5 and more in RegCM4-CLM3.5 and Reg

  3. Study on coral annual banding for the investigation of Asian monsoon; Asian monsoon to sango nenrin kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, A. [Geological Survey of Japan, Tsukuba (Japan); Kawabata, H. [Tohoku University, Sendai (Japan)

    1998-07-01

    A coral skeleton is sampled at Kenya`s Malindi National Marine Park situated west of the Seychelles, and it offers information about the Afro-Asian monsoon. An X-ray profile of the specimen discloses the seasonal variation in the density of the coral skeleton. The oxygen isotopic ratio, which is generally affected by the seawater oxygen isotopic ratio composition which is dependent on the surface layer water temperature and fresh water, is found dominated, in the coral skeleton, practically by the surface layer water temperature. Accordingly, the oxygen isotopic ratio represents the seasonal and annual variations in the surface layer water temperature. It is inferred that the emergence of Ba/Ca ratio peaks in December into January reflects the presence of Ba from rivers, and there are indications that the Somali current has transported water to the coral sampling area from the Galana River which is the greatest river in Kenya. Five of the Ba/Ca ratio peaks coincide with peaks in the UV fluorescent band, which is attributed to the presence of terrigenous organic matters. The ENSO and Asian monsoon phenomena are estimated on the basis of the findings described above. 11 refs., 6 figs.

  4. The effect of regional changes in anthropogenic aerosols on rainfall of the East Asian Summer Monsoon

    Directory of Open Access Journals (Sweden)

    L. Guo

    2013-02-01

    Full Text Available The response of East Asian Summer Monsoon (EASM precipitation to long term changes in regional anthropogenic aerosols (sulphate and black carbon is explored in an atmospheric general circulation model, the atmospheric component of the UK High-Resolution Global Environment Model v1.2 (HiGAM. Separately, sulphur dioxide (SO2 and black carbon (BC emissions in 1950 and 2000 over East Asia are used to drive model simulations, while emissions are kept constant at year 2000 level outside this region. The response of the EASM is examined by comparing simulations driven by aerosol emissions representative of 1950 and 2000. The aerosol radiative effects are also determined using an off-line radiative transfer model. During June, July and August, the EASM was not significantly changed as either SO2 or BC emissions increased from 1950 to 2000 levels. However, in September, precipitation is significantly decreased by 26.4% for sulphate aerosol and 14.6% for black carbon when emissions are at the 2000 level. Over 80% of the decrease is attributed to changes in convective precipitation. The cooler land surface temperature over China in September (0.8 °C for sulphate and 0.5 °C for black carbon due to increased aerosols reduces the surface thermal contrast that supports the EASM circulation. However, mechanisms causing the surface temperature decrease in September are different between sulphate and BC experiments. In the sulphate experiment, the sulphate direct and the 1st indirect radiative effects contribute to the surface cooling. In the BC experiment, the BC direct effect is the main driver of the surface cooling, however, a decrease in low cloud cover due to the increased heating by BC absorption partially counteracts the direct effect. This results in a weaker land surface temperature response to BC changes than to sulphate changes. The resulting precipitation response is also weaker, and the responses of the monsoon circulation

  5. Enhancement of vegetation-rainfall feedbacks on the Australian summer monsoon by the Madden-Julian Oscillation

    Science.gov (United States)

    Notaro, Michael

    2018-01-01

    A regional climate modeling analysis of the Australian monsoon system reveals a substantial modulation of vegetation-rainfall feedbacks by the Madden Julian Oscillation (MJO), both of which operate at similar sub-seasonal time scales, as evidence that the intensity of land-atmosphere interactions is sensitive to the background atmospheric state. Based on ensemble experiments with imposed modification of northern Australian leaf area index (LAI), the atmospheric responses to LAI anomalies are composited for negative and positive modes of the propagating MJO. In the regional climate model (RCM), northern Australian vegetation feedbacks are characterized by evapotranspiration (ET)-driven rainfall responses, with the moisture feedback mechanism dominating over albedo and roughness feedback mechanisms. During November-April, both Tropical Rainfall Measuring Mission and RCM data reveal MJO's pronounced influence on rainfall patterns across northern Australia, tropical Indian Ocean, Timor Sea, Arafura Sea, and Gulf of Carpentaria, with the MJO dominating over vegetation feedbacks in terms of regulating monsoon rainfall variability. Convectively-active MJO phases support an enhancement of positive vegetation feedbacks on monsoon rainfall. While the MJO imposes minimal regulation of ET responses to LAI anomalies, the vegetation feedback-induced responses in precipitable water, cloud water, and rainfall are greatly enhanced during convectively-active MJO phases over northern Australia, which are characterized by intense low-level convergence and efficient precipitable water conversion. The sub-seasonal response of vegetation-rainfall feedback intensity to the MJO is complex, with significant enhancement of rainfall responses to LAI anomalies in February during convectively-active MJO phases compared to minimal modulation by the MJO during prior and subsequent calendar months.

  6. Aspect of ECMWF downscaled Regional Climate Modeling in simulating Indian summer monsoon rainfall and dependencies on lateral boundary conditions

    Science.gov (United States)

    Ghosh, Soumik; Bhatla, R.; Mall, R. K.; Srivastava, Prashant K.; Sahai, A. K.

    2018-03-01

    Climate model faces considerable difficulties in simulating the rainfall characteristics of southwest summer monsoon. In this study, the dynamical downscaling of European Centre for Medium-Range Weather Forecast's (ECMWF's) ERA-Interim (EIN15) has been utilized for the simulation of Indian summer monsoon (ISM) through the Regional Climate Model version 4.3 (RegCM-4.3) over the South Asia Co-Ordinated Regional Climate Downscaling EXperiment (CORDEX) domain. The complexities of model simulation over a particular terrain are generally influenced by factors such as complex topography, coastal boundary, and lack of unbiased initial and lateral boundary conditions. In order to overcome some of these limitations, the RegCM-4.3 is employed for simulating the rainfall characteristics over the complex topographical conditions. For reliable rainfall simulation, implementations of numerous lower boundary conditions are forced in the RegCM-4.3 with specific horizontal grid resolution of 50 km over South Asia CORDEX domain. The analysis is considered for 30 years of climatological simulation of rainfall, outgoing longwave radiation (OLR), mean sea level pressure (MSLP), and wind with different vertical levels over the specified region. The dependency of model simulation with the forcing of EIN15 initial and lateral boundary conditions is used to understand the impact of simulated rainfall characteristics during different phases of summer monsoon. The results obtained from this study are used to evaluate the activity of initial conditions of zonal wind circulation speed, which causes an increase in the uncertainty of regional model output over the region under investigation. Further, the results showed that the EIN15 zonal wind circulation lacks sufficient speed over the specified region in a particular time, which was carried forward by the RegCM output and leads to a disrupted regional simulation in the climate model.

  7. Predicting summer monsoon of Bhutan based on SST and teleconnection indices

    Science.gov (United States)

    Dorji, Singay; Herath, Srikantha; Mishra, Binaya Kumar; Chophel, Ugyen

    2018-02-01

    The paper uses a statistical method of predicting summer monsoon over Bhutan using the ocean-atmospheric circulation variables of sea surface temperature (SST), mean sea-level pressure (MSLP), and selected teleconnection indices. The predictors are selected based on the correlation. They are the SST and MSLP of the Bay of Bengal and the Arabian Sea and the MSLP of Bangladesh and northeast India. The Northern Hemisphere teleconnections of East Atlantic Pattern (EA), West Pacific Pattern (WP), Pacific/North American Pattern, and East Atlantic/West Russia Pattern (EA/WR). The rainfall station data are grouped into two regions with principal components analysis and Ward's hierarchical clustering algorithm. A support vector machine for regression model is proposed to predict the monsoon. The model shows improved skills over traditional linear regression. The model was able to predict the summer monsoon for the test data from 2011 to 2015 with a total monthly root mean squared error of 112 mm for region A and 33 mm for region B. Model could also forecast the 2016 monsoon of the South Asia Monsoon Outlook of World Meteorological Organization (WMO) for Bhutan. The reliance on agriculture and hydropower economy makes the prediction of summer monsoon highly valuable information for farmers and various other sectors. The proposed method can predict summer monsoon for operational forecasting.

  8. Multi-decadal modulation of the El Nino-Indian monsoon relationship by Indian Ocean variability

    International Nuclear Information System (INIS)

    Ummenhofer, Caroline C; Sen Gupta, Alexander; Li Yue; Taschetto, Andrea S; England, Matthew H

    2011-01-01

    The role of leading modes of Indo-Pacific climate variability is investigated for modulation of the strength of the Indian summer monsoon during the period 1877-2006. In particular, the effect of Indian Ocean conditions on the relationship between the El Nino-Southern Oscillation (ENSO) and the Indian monsoon is explored. Using an extended classification for ENSO and Indian Ocean dipole (IOD) events for the past 130 years and reanalyses, we have expanded previous interannual work to show that variations in Indian Ocean conditions modulate the ENSO-Indian monsoon relationship also on decadal timescales. El Nino events are frequently accompanied by a significantly reduced Indian monsoon and widespread drought conditions due to anomalous subsidence associated with a shift in the descending branch of the zonal Walker circulation. However, for El Nino events that co-occur with positive IOD (pIOD) events, Indian Ocean conditions act to counter El Nino's drought-inducing subsidence by enhancing moisture convergence over the Indian subcontinent, with an average monsoon season resulting. Decadal modulations of the frequency of independent and combined El Nino and pIOD events are consistent with a strengthened El Nino-Indian monsoon relationship observed at the start of the 20th century and the apparent recent weakening of the El Nino-Indian monsoon relationship.

  9. Multi-decadal modulation of the El Nino-Indian monsoon relationship by Indian Ocean variability

    Energy Technology Data Exchange (ETDEWEB)

    Ummenhofer, Caroline C; Sen Gupta, Alexander; Li Yue; Taschetto, Andrea S; England, Matthew H, E-mail: c.ummenhofer@unsw.edu.au [Climate Change Research Centre, University of New South Wales, Sydney (Australia)

    2011-07-15

    The role of leading modes of Indo-Pacific climate variability is investigated for modulation of the strength of the Indian summer monsoon during the period 1877-2006. In particular, the effect of Indian Ocean conditions on the relationship between the El Nino-Southern Oscillation (ENSO) and the Indian monsoon is explored. Using an extended classification for ENSO and Indian Ocean dipole (IOD) events for the past 130 years and reanalyses, we have expanded previous interannual work to show that variations in Indian Ocean conditions modulate the ENSO-Indian monsoon relationship also on decadal timescales. El Nino events are frequently accompanied by a significantly reduced Indian monsoon and widespread drought conditions due to anomalous subsidence associated with a shift in the descending branch of the zonal Walker circulation. However, for El Nino events that co-occur with positive IOD (pIOD) events, Indian Ocean conditions act to counter El Nino's drought-inducing subsidence by enhancing moisture convergence over the Indian subcontinent, with an average monsoon season resulting. Decadal modulations of the frequency of independent and combined El Nino and pIOD events are consistent with a strengthened El Nino-Indian monsoon relationship observed at the start of the 20th century and the apparent recent weakening of the El Nino-Indian monsoon relationship.

  10. Picophytoplankton as Tracers of Environmental Forcing in a Tropical Monsoonal Bay.

    Science.gov (United States)

    Mitbavkar, Smita; Patil, Jagadish S; Rajaneesh, K M

    2015-10-01

    In order to better understand the picophytoplankton (PP) dynamics in tropical monsoon influenced coastal regions, samples were collected daily (June-September 2008: monsoon, December 2008: post-monsoon and April 2009: pre-monsoon) from a fixed station in Dona Paula Bay, India. Eight PP abundance peaks comprising Prochlorococcus-like cells, picoeukaryotes, and three groups of Synechococcus occurred. The chlorophyll biomass and PP abundance were negatively influenced by reduced solar radiation, salinity and water transparency due to precipitation and positively influenced by the stabilized waters during precipitation break/non-monsoon periods. Responses to environmental conditions differed with PP groups, wherein the presence of Synechococcus-PEI (phycoerythrin) throughout the year suggested its ability to tolerate salinity and temperature variations and low light conditions. Synechococcus-PEII appearance toward monsoon end and non-monsoon during high water transparency suggests its tidal advection from offshore waters. Dominance of Synechococcus-PC (phycocyanin) at intermediate salinities under low water transparency during MON and high salinities in PrM coinciding with high nitrate concentrations implies a greater influence of light quality or nutrients. Cyanobacteria and not picoeukaryotes were the dominant picophytoplankton in terms of numbers as well as biomass. This study suggests that PP could be used as tracers of environmental forcing driven by tides and freshwater influx and also highlights the importance of high-frequency samplings in dynamic coastal regions through which transient responses can be captured.

  11. Global warming and South Indian monsoon rainfall-lessons from the Mid-Miocene.

    Science.gov (United States)

    Reuter, Markus; Kern, Andrea K; Harzhauser, Mathias; Kroh, Andreas; Piller, Werner E

    2013-04-01

    Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3-4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall.

  12. Contrasting sedimentation patterns in two semi-enclosed mesotidal bays along the west and south coasts of Korea controlled by their orientation to the regional monsoon climate

    Science.gov (United States)

    Hong, Seok Hwi; Chun, Seung Soo; Chang, Tae Soo; Jang, Dae Geon

    2017-08-01

    Sedimentation patterns of tidal flats along the Korean west coast have long been known to be largely controlled by the monsoon climate. On the other hand, much less is known about the effect of the monsoon on sedimentation in coastal embayments with mouths of different geographic orientations. Good examples are Hampyeong and Yeoja bays along the west and south coasts, respectively. Both have narrow entrances, but their mouths open toward the northwest and the south, respectively. With mean tidal ranges of 3.46 and 3.2 m, respectively, the two bays experience similar tidal regimes and are hence excellent candidates to compare the effect of different exposure to the same regional monsoon climate on their respective sediment distribution patterns. The winter monsoon, in particular, is characterized by strong northwesterly winds that directly impact the west coast, but blow offshore along the south coast. For the purpose of this study, surficial sediment samples were collected from intertidal and subtidal flats of the two bays, both in summer and winter. Grain-size analyses were carried out by sieving (sand fraction) and Sedigraph (mud fraction). In the case of Yeoja Bay, the sediments consist mostly of mud (mean grain sizes of 5.4 to 8.8 phi). Seasonal changes are very subtle, the sediments being slightly coarser in summer when silt-dominated sediments are supplied by two streams to the northern parts of the bay in response to heavy rainfall. With the exception of the deeper tidal channels, Yeoja Bay is characterized by a thick mud blanket the year round, which is modulated by processes associated with the summer monsoon that predominantly blows from the east. Textural parameters suggest severely restricted sediment mixing on the subtidal and intertidal flats, the overall low energy situation preventing sands from reaching the tidal flats. The sediments of Hampyeong Bay, by contrast, are characterized by a distinct shoreward fining trend. Mean grain sizes average

  13. Initial results from the StratoClim aircraft campaign in the Asian Monsoon in summer 2017

    Science.gov (United States)

    Rex, M.

    2017-12-01

    The Asian Monsoon System is one of the Earth's largest and most energetic weather systems. Monsoon rainfall is critical to feeding over a billion people in Asia and the monsoon circulation affects weather patterns over the entire northern hemisphere. The Monsoon also acts like an enormous elevator, pumping vast amounts of air and pollutants from the surface up to the tropopause region at levels above 16km altitude, from where air can ascend into the stratosphere, where it spreads globally. Thus the monsoon affects the chemical composition of the global tropopause region and the stratosphere, and hence plays a key role for the composition of the UTS. Dynamically the monsoon circulation leads to the formation of a large anticyclone at tropopause levels above South Asia - the Asian Monsoon Anticyclone (AMA). Satellite images show a large cloud of aerosols directly above the monsoon, the Asian Tropopause Aerosol Layer (ATAL). In July to August 2017 the international research project StratoClim carried out the first in-situ aircraft measurements in the AMA and the ATAL with the high altitude research aircraft M55-Geophysica. Around 8 scientific flights took place in the airspaces of Nepal, India and Bangladesh and have horizontally and vertically probed the AMA and have well characterized the ATAL along flight patterns that have been carefully designed by a theory, modelling and satellite data analysing team in the field. The aircraft campaign has been complemented by launches of research balloons from ground stations in Nepal, Bangladesh, China and Palau. The presentation will give an overview of the StratoClim project, the aircraft and balloon activities and initial results from the StratoClim Asian Monsoon campaign in summer 2017.

  14. Why the Australian Monsoon Strengthened During the Cold Last Glacial Maximum?

    Science.gov (United States)

    Yan, M.; Wang, B.; Liu, J.; Ning, L.

    2017-12-01

    The multi-model ensemble simulation suggests that the global monsoon and most sub-monsoons are weakened during the Last Glacial Maximum (LGM) due to the lower green-house gases concentration, the presence of the ice-sheets and the weakened seasonal distribution of insolation. In contrast, the Australian monsoon is strengthened during the LGM. The precipitation there increases in austral summer and decreases in austral winter, so that the annual range or monsoonality increases. The strengthened monsoonality is mainly due to the decreased precipitation in austral winter, which is primarily caused by circulation changes, although the reduced atmospheric water vapor also has a moderate contribution. On the other hand, the strengthened Australian summer monsoon rainfall is likely caused by the change of land-sea thermal contrast due to the alteration of land-sea configuration and by the asymmetric change in sea surface temperature (SST) over Indo-Pacific warm pool region. The strengthened land-sea thermal contrast and Western Pacific-Eastern Indian Ocean thermal gradients in the pre-summer monsoon season triggers a cyclonic wind anomaly that is maintained to the monsoon season, thereby increasing summer precipitation. The increased summer precipitation is associated with the increased cloud cover over the land and decreased cloud cover over the ocean. This may weaken the land-sea thermal contrast, which agrees with the paleoclimate reconstruction. The biases between different models are likely related to the different responses of SST over the North Atlantic Ocean in the pre-summer monsoon season.

  15. Heavy Rainfall Associated with a Monsoon Depression in South China: Structure Analysis

    Institute of Scientific and Technical Information of China (English)

    JIANG Jianying; JIANG Jixi; BU Yalin; LIU Nianqing

    2008-01-01

    A heavy rainfall associated with the deepening of a monsoon depression happened in the summer of 2005.This process was first diagnostically analyzed and the 3D structure of the monsoon depression was discussed,then this structure was compared with those of the monsoon depression in South Asia and the low vortex in the Meiyu front. The results showed that the heavy rainfall directly resulted from a monsoon depression in South China, and the large-scale environment provided a favorable background for the deepening of the monsoon depression. The 3D structure of the monsoon depression was as follows. In the horizontal direction,there existed a convective cloud band to the south of the monsoon depression, which lay in a convectively instable area, with a relatively strong ascending motion in the mid and low levels of the troposphere, and the ascending motion matched well with a moist tongue, a convergence area, and a band of positive vorticity in the mid and low levels of the troposphere. In the vertical direction, the depression had an obviously cyclonic circulation in the mid and low levels of the troposphere, but no circulation from above 300 hPa. The monsoon depression corresponded to convergence and positive vorticity in the low levels, but to divergence and negative vortieity in the upper levels. The upward draft of the depression could reach the upper levels of the troposphere in the west of the depression, while the descending motion lay in the east. There was a low-level jet to the south of the depression, while the upper-level jet was not obvious. The depression was vertically warm in the upper levels and cold in the low levels, and the axis of the depression tilted southeastward with height, whose characteristics were different not only from the monsoon depression in South Asia but also from the low vortex in the Meiyu front.

  16. The northwestern Indian Ocean during the monsoons of 1979: distribution, abundance, and feeding of zooplankton

    Energy Technology Data Exchange (ETDEWEB)

    Smith, S.L.

    1982-01-01

    Upwelling induced by the separation of the Somali Current from the coast of east Africa is associated with low surface temperatures, high concentrations of nitrate, and blooms of phytoplankton. Coefficients of concordance, based upon 17 taxa of zooplankton collected at 33 stations in the southwest monsoon and 15 stations in the northeast monsoon, were consistently larger for the southwest monsoon and indicative of a general response of the zooplankton in the northwestern Indian Ocean. The largest coefficients of concordance in the southwest monsoon were among adult females of Paracalanus denudatus, Paracalanus parvus, and Paracalanus aculeatus and of Calanoides carinatus and Eucalanus spp. Coefficients of concordance among copepodids of six taxa had a trend similar to adult females in the southwest monsoon. During the southwest monsoon, total biomass of zooplankton was significantly greater within areas of upwelling than outside; adult females and copepodids of C. carinatus and Eucalanus spp. were significantly more abundant within the upwelling regions, along with adult females of Clausocalanus furcatus and Clausocalanus minor. The upwelling regions, which are associated with a reproductively active population of the large-bodied C. carinatus, are the primary features affecting distributions of zooplankton during the southwest monsoon and the main difference between monsoons. The ontogenetic migration of C. carinatus is essentially an annual life-history strategy and therefore on the same temporal scale as the reversals in the monsoonal winds and associated upwelling. The ability of C. carinatus to ingest readily the diatoms that dominate the upwelling regions and to store lipid is crucial to its dominance of the areas of upwelling both in numbers and biomass.

  17. Using idealized snow forcing to test teleconnections with the Indian summer monsoon in the Hadley Centre GCM

    Energy Technology Data Exchange (ETDEWEB)

    Turner, A.G. [University of Reading, NCAS-Climate, Walker Institute for Climate System Research, Department of Meteorology, Reading (United Kingdom); Slingo, J.M. [University of Reading, NCAS-Climate, Walker Institute for Climate System Research, Department of Meteorology, Reading (United Kingdom); Met Office, Exeter (United Kingdom)

    2011-05-15

    Anomalous heavy snow during winter or spring has long been regarded as a possible precursor of deficient Indian monsoon rainfall during the subsequent summer. However previous work in this field is inconclusive, in terms of the mechanism that communicates snow anomalies to the monsoon summer, and even the region from which snow has the most impact. In this study we explore these issues in coupled and atmosphere-only versions of the Hadley Centre model. A 1050-year control integration of the HadCM3 coupled model, which well represents the seasonal cycle of snow cover over the Eurasian continent, is analysed and shows evidence for weakened monsoons being preceded by strong snow forcing (in the absence of ENSO) over either the Himalaya/Tibetan Plateau or north/west Eurasia regions. However, empirical orthogonal function (EOF) analysis of springtime interannual variability in snow depth shows the leading mode to have opposite signs between these two regions, suggesting that competing mechanisms may be possible. To determine the dominant region, ensemble integrations are carried out using HadAM3, the atmospheric component of HadCM3, and a variety of anomalous snow forcing initial conditions obtained from the control integration of the coupled model. Forcings are applied during spring in separate experiments over the Himalaya/Tibetan Plateau and north/west Eurasia regions, in conjunction with climatological SSTs in order to avoid the direct effects of ENSO. With the aid of idealized forcing conditions in sensitivity tests, we demonstrate that forcing from the Himalaya region is dominant in this model via a Blanford-type mechanism involving reduced surface sensible heat and longwave fluxes, reduced heating of the troposphere over the Tibetan Plateau and consequently a reduced meridional tropospheric temperature gradient which weakens the monsoon during early summer. Snow albedo is shown to be key to the mechanism, explaining around 50% of the perturbation in sensible

  18. Black carbon and West African Monsoon precipitation. Observations and simulations

    International Nuclear Information System (INIS)

    Huang, J.; Adams, A.; Zhang, C.; Wang, C.

    2009-01-01

    We have recently investigated large-scale co-variability between aerosol and precipitation and other meteorological variables in the West African Monsoon (WAM) region using long term satellite observations and reanalysis data. In this study we compared the observational results to a global model simulation including only direct radiative forcing of black carbon (BC). From both observations and model simulations we found that in boreal cold seasons anomalously high African aerosols are associated with significant reductions in cloud amount, cloud top height, and surface precipitation. These results suggest that the observed precipitation reduction in the WAM region is caused by radiative effect of BC. The result also suggests that the BC effect on precipitation is nonlinear. (orig.)

  19. Simulated sensitivity of tropical cyclone track to the moisture in an idealized monsoon gyre

    Science.gov (United States)

    Yan, Ziyu; Ge, Xuyang; Guo, Bingyao

    2017-12-01

    In this study, the sensitivity of tropical cyclone (TC) track to the moisture condition in a nearby monsoon gyre (MG) is investigated. Numerical simulations reveal that TC track is highly sensitive to the spatial distribution of relative humidity (RH). In an experiment conducted with higher (lower) RH in the eastern (western) semicircle of an MG, the TC experiences a sharp northward turning. In contrast, when the RH pattern is reversed, the simulated TC does not show a sharp northward turning. The RH distribution modulates the intensity and structure of both the TC and MG, so that when the TC is initially embedded in a moister environment, convection is enhanced in the outer core, which favors an expansion of the outer core size. A TC with a larger outer size has greater beta-effect propagation, favoring a faster westward translational speed. Meanwhile, higher RH enhances the vorticity gradient within the MG and promotes a quicker attraction between the TC and MG centers through vorticity segregation process. These cumulative effects cause the TC to collocate with the MG center. Once the coalescence process takes place, the energy dispersion associated with the TC and MG is enhanced, which rapidly strengthens southwesterly flows on the eastern flanks. The resulting steering flow leads the TC to take a sharp northward track.

  20. Inter-decadal change in potential predictability of the East Asian summer monsoon

    Science.gov (United States)

    Li, Jiao; Ding, Ruiqiang; Wu, Zhiwei; Zhong, Quanjia; Li, Baosheng; Li, Jianping

    2018-05-01

    The significant inter-decadal change in potential predictability of the East Asian summer monsoon (EASM) has been investigated using the signal-to-noise ratio method. The relatively low potential predictability appears from the early 1950s through the late 1970s and during the early 2000s, whereas the potential predictability is relatively high from the early 1980s through the late 1990s. The inter-decadal change in potential predictability of the EASM can be attributed mainly to variations in the external signal of the EASM. The latter is mostly caused by the El Niño-Southern Oscillation (ENSO) inter-decadal variability. As a major external signal of the EASM, the ENSO inter-decadal variability experiences phase transitions from negative to positive phases in the late 1970s, and to negative phases in the late 1990s. Additionally, ENSO is generally strong (weak) during a positive (negative) phase of the ENSO inter-decadal variability. The strong ENSO is expected to have a greater influence on the EASM, and vice versa. As a result, the potential predictability of the EASM tends to be high (low) during a positive (negative) phase of the ENSO inter-decadal variability. Furthermore, a suite of Pacific Pacemaker experiments suggests that the ENSO inter-decadal variability may be a key pacemaker of the inter-decadal change in potential predictability of the EASM.

  1. Improvement in the Modeled Representation of North American Monsoon Precipitation Using a Modified Kain–Fritsch Convective Parameterization Scheme

    KAUST Repository

    Luong, Thang

    2018-01-22

    A commonly noted problem in the simulation of warm season convection in the North American monsoon region has been the inability of atmospheric models at the meso-β scales (10 s to 100 s of kilometers) to simulate organized convection, principally mesoscale convective systems. With the use of convective parameterization, high precipitation biases in model simulations are typically observed over the peaks of mountain ranges. To address this issue, the Kain–Fritsch (KF) cumulus parameterization scheme has been modified with new diagnostic equations to compute the updraft velocity, the convective available potential energy closure assumption, and the convective trigger function. The scheme has been adapted for use in the Weather Research and Forecasting (WRF). A numerical weather prediction-type simulation is conducted for the North American Monsoon Experiment Intensive Observing Period 2 and a regional climate simulation is performed, by dynamically downscaling. In both of these applications, there are notable improvements in the WRF model-simulated precipitation due to the better representation of organized, propagating convection. The use of the modified KF scheme for atmospheric model simulations may provide a more computationally economical alternative to improve the representation of organized convection, as compared to convective-permitting simulations at the kilometer scale or a super-parameterization approach.

  2. Factors controlling the temporal and spatial variations in Synechococcus abundance in a monsoonal estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Rajaneesh, K.M.; Mitbavkar, S.

    salinity preferences with phycoerythrin-rich cells at salinities >2 (Synechococcus-PEI), >20 (Synechococcus-PEII) and <1 (Synechococcus-PEIII) whereas phycocyanin-rich (Synechococcus-PC) dominant at lower salinities. Downstream stratification during monsoon...

  3. Deglaciation in the tropical Indian Ocean driven by interplay between the regional monsoon and global teleconnections

    Digital Repository Service at National Institute of Oceanography (India)

    Saraswat, R.; Lea, D.W.; Nigam, R.; Mackensen, A.; Naik, Dinesh K.

    High resolution climate records of the ice age terminations from monsoon-dominated regions reveal the interplay of regional and global driving forces. Speleothem records from Chinese caves indicate that glacial terminations were interrupted...

  4. Attenuation of surface waves due to monsoon rains: A model study for the north Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Vethamony, P.; Kumar, B.P.; Sarma, Y.V.B.

    The dynamic interaction of intense rain with waves based on momentum exchange is applied to a second generation wave model to predict wave attenuation during monsoon. The scheme takes into account the characteristics of rain and wave parameters...

  5. Variability of the date of monsoon onset over Kerala (India) of the ...

    Indian Academy of Sciences (India)

    P N Preenu

    2017-07-25

    Jul 25, 2017 ... Nansen Environmental Research Centre India, 6A Oxford Business Centre, Kochi, Kerala 682 016, India. ... Monsoon onset over Kerala (India) which occurs every year is a ...... for delayed MOK years and figure 12 gives the.

  6. Relationships between Indian summer monsoon rainfall and ice cover over selected oceanic regions

    Digital Repository Service at National Institute of Oceanography (India)

    Gopinathan, C.K.

    The variations in oceanic ice cover at selected polar regions during 1973 to 1987 have been analysed in relation to the seasonal Indian summer monsoon rainfall. The ice cover over the Arctic regions in June has negative relationship (correlation...

  7. Vertical distribution of mesozooplankton in the central and eastern Arabian Sea during the winter monsoons

    Digital Repository Service at National Institute of Oceanography (India)

    Padmavati, G.; Haridas, P.; Nair, K.K.C.; Gopalakrishnan, T.C.; Shiney, P.; Madhupratap, M.

    The vertical distribution of mesozooplankton in the central and eastern Arabian Sea was investigated during the winter monsoon in 1995. Samples were analysed from discrete depth zones defined according to oxygen and temperature profiles of the water...

  8. Monsoon oscillations of the Findlater Jet and coastal winds of India

    Digital Repository Service at National Institute of Oceanography (India)

    Pankajakshan, T.; Zhao, C.; Muraleedharan, P.M.; Rao, G.S.P.; Sugimori, Y.

    Intraseasonal variability (ISV) of the Low Level Jet (LLJ) and its effects on coastal winds during the Indian summer monsoon are examined using National Centre for Environmental Prediction / National Centre for Atmospheric Research (NCEP) reanalyses...

  9. Seasonal variations in the fouling diatom community structure from a monsoon influenced tropical estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Mitbavkar, S.; Anil, A.C.

    Seasonal variations in the fouling diatom community from a monsoon influenced tropical estuary were investigated. The community composition did not differ significantly between stainless steel and polystyrene substrata due to dominance by Navicula...

  10. Bacterial domination over Archaea in ammonia oxidation in a monsoon-driven tropical estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Vipindas, P.V.; Anas, A.; Jasmin, C.; Lallu, K.R.; Fausia, K.H.; Balachandran, K.K.; Muraleedharan, K.R.; Nair, S.

    Autotrophic ammonia oxidizing microorganisms,which are responsible for the rate-limiting step of nitrification in most aquatic systems, have not been studied in tropical estuaries. Cochin estuary (CE) is one of the largest, productive, and monsoon...

  11. Driving forces of Indian summer monsoon on Milankovitch and sub-Milankovitch time scales: A review

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    A scientific consensus exists that tectonic evolution of Himalaya is the main cause of monsoon initiation and evolution in southeast Asia. Several forcing factors such as tectonic, solar insolation, latent heat transport, albedo of the earth surface...

  12. Spectral characteristics of the nearshore waves off Paradip, India during monsoon and extreme events

    Digital Repository Service at National Institute of Oceanography (India)

    Aboobacker, V.M.; Vethamony, P.; Sudheesh, K.; Rupali, S.P.

    and directional wave energy spectra distinctly separate out the wave conditions that prevailed off Paradip in the monsoon, fair weather and extreme weather events during the above period. Frequency-energy spectra during extreme events are single peaked...

  13. Influence of orographically enhanced SW monsoon flux on coastal processes along the SE Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Chauhan, O.S.; Raghavan, B.R.; Singh, K.; Rajawat, A; Ajai; Kader, U.S.A; Nayak, S.

    The Arabian Sea has an excess evaporation over precipitation regime. The southeast Arabian Sea is, however, anomalous because it has ~2800–4800 mm rainfall during the southwest monsoon (SWM). Despite a high rainfall, the fluvial influence on supply...

  14. Interactions between trophic levels in upwelling and non-upwelling regions during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Malik, A; Fernandes, C.E.G.; Gonsalves, M.J.B.D.; Subina, N.S.; Mamatha, S.S.; Krishna, K.S.; Varik, S.; RituKumari; Gauns, M.; Cejoice, R.P.; Pandey, S.S.; Jineesh, V.K.; Kamaleson, A; Vijayan, V.; Mukherjee, I.; Subramanyan, S.; Nair, S.; Ingole, B.S.; LokaBharathi, P.A

    Coastal upwelling is a regular phenomenon occurring along the southwest coast of India during summer monsoon (May–September). We hypothesize that there could be a shift in environmental parameters along with changes in the network of interactions...

  15. Seasonal variations in abundance, biomass and grazing rates of microzooplankton in a tropical monsoonal estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Gauns, M.; Mochemadkar, S.; Patil, S.; Pratihary, A.K.; Naqvi, S.W.A.; Madhupratap, M.

    Seasonal abundance, composition and grazing rates of microzooplankton (20–200 µm) in the Zuari estuary were investigated to evaluate their importance in food web dynamics of a tropical monsoonal estuary. Average abundances of microzooplankton...

  16. Monsoonal impact on planktonic standing stock and abundance in a tropical estuary (Cochin backwaters - India)

    Digital Repository Service at National Institute of Oceanography (India)

    Madhu, N.V.; Jyothibabu, R; Balachandran, K.K.; Honey, U.K.; Martin, G.D.; Vijay, J.G.; Shiyas, C.A.; Gupta, G.V.M.; Achuthankutty, C.T.

    and post monsoon seasons, but became low during premonsoon season (<5). Hence, it is suggested that during the periods of fresh water dominance, the trophic food web of Cochin estuarine system is characterized by substantial amount of unconsumed carbon...

  17. Variations in phytoplankton community in a monsoon-influenced tropical estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Patil, J.S.; Anil, A.C.

    . The break period in monsoon altered the phytoplankton community leading to mixed species bloom of large-sized diatoms and harmful dinoflagellates (Gymnodinium catenatum and Cochlodinium polykrikoides) under high-saline, nutrient-poor, non...

  18. Upper ocean stratification and circulation in the northern Bay of Bengal during southwest monsoon of 1991

    Science.gov (United States)

    Gopalakrishna, V. V.; Murty, V. S. N.; Sengupta, D.; Shenoy, Shrikant; Araligidad, Nilesh

    2002-03-01

    During the southwest monsoon (July) of 1991 a large plume (300×250 km 2) of warm (>29°C) and less saline (Continental Shelf Research 19 (1999) 1437, Journal of Geophysical Research 106 (C1) (2001) 1067).

  19. Foraminiferal production and monsoonal upwelling in the Arabian sea: evidence from sediment traps

    Digital Repository Service at National Institute of Oceanography (India)

    Curry, W.B.; Ostermann, D.R.; Guptha, M.V.S.; Ittekkot, V.

    Planktonic foraminifera collected in sediment traps in the Arabian Sea during 1986 and 1987 responded to the southern Asian monsoon with changes in productivity, relative abundance of species and isotopic shell chemistry. Most species...

  20. Ecology of benthic production during southwest monsoon in an estuarine complex of Goa

    Digital Repository Service at National Institute of Oceanography (India)

    Parulekar, A.H.; Dwivedi, S.N.

    Qualitative and quantitative differences in the spatial temporal distribution and production of benthic macrofauna in pre- and post-monsoon were observed and the differences are discussed in relation to the environmental factors The fauna...

  1. Living coccolithophores during the northeast monsoon from the Equatorial Indian Ocean: Implications on hydrography

    Digital Repository Service at National Institute of Oceanography (India)

    Guptha, M.V.S.; Mergulhao, L.P.; Murty, V.S.N.; Shenoy, D.M.

    suggested a prevalence of oligotrophic conditions or lack of supply of nutrients into the upper mixed layer (approx. 50 m thick) during the northeast monsoon. However, the relatively higher abundance of Florisphaera profunda at 4 degrees S indicated...

  2. RAMA: The Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (including supplement)

    Digital Repository Service at National Institute of Oceanography (India)

    McPhaden, M.J.; Meyers, G.; Ando, K.; Masumoto, Y.; Murty, V.S.N.; Ravichandran, M.; Syamsudin, F.; Vialard, J.; Yu, L.; Yu, W.

    -atmosphere interactions, and intense seasonal rains over the Indian subcontinent, Southeast Asia, East Africa, and Australia. Recurrence of these monsoon rains is critical to agricultural production that supports a third of the world’s population. The Indian Ocean also...

  3. Importance of monsoon rainfall in mass fluxes of filtered and unfiltered mercury in Gwangyang Bay, Korea

    International Nuclear Information System (INIS)

    Jang, Jiyi; Han, Seunghee

    2011-01-01

    We investigated the effects of the East Asian Summer Monsoon (EASM), which brings approximately half of Korea's annual rainfall in July, on the concentration and particle-water partitioning, and sources of Hg in coastal waters. Surface seawater samples were collected from eight sites in Gwangyang Bay, Korea, during the monsoon (July, 2009) and non-monsoon dry (April and November, 2009) seasons and the concentrations of suspended particulate matter, chlorophyll-a, and unfiltered and filtered Hg were determined. We found significant (p 0.05) between the monsoon (459 ± 141 pmol g -1 ) and the dry season (346 ± 30 pmol g -1 ), which resulted in decreased particle-water partition coefficients of Hg in the monsoon season compared to the values in the dry season: 5.7 ± 0.1 in April, 5.3 ± 0.1 in July, and 5.8 ± 0.1 in November. The annual Hg input to Gwangyang Bay was estimated at 64 ± 6.6 mol yr -1 and 27 ± 1.9 mol yr -1 for unfiltered and filtered Hg, respectively. The Hg discharged from rivers was a major source of Hg in Gwangyang Bay: the river input contributed 83 ± 13% of total input of unfiltered and 73 ± 6.0% of filtered Hg. On a monthly basis, unfiltered Hg input was 17 ± 11 mol month -1 in the monsoon season and 3.2 ± 0.70 mol month -1 in the dry season, while filtered Hg input was 7.1 ± 4.1 mol month -1 in the monsoon and 1.3 ± 0.26 mol month -1 in the dry. Consequently, the EASM resulted in an unfiltered Hg input 5.3 times greater than the mean dry month input and a filtered Hg input 5.5 times greater than the mean dry month input, which is mainly attributable to enhanced river water discharge during the monsoon season. - Research Highlights: → Filtered mercury concentration increased in the monsoon month in coastal water. → The monsoon rain increased unfiltered Hg input 5.5 times greater than the dry month. → The monsoon rain increased filtered Hg input 5.3 times greater than the dry month.

  4. Glacial-interglacial water cycle, global monsoon and atmospheric methane changes

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Zhengtang; Wu, Haibin [Chinese Academy of Sciences, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Beijing (China); Zhou, Xin [Chinese Academy of Sciences, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Beijing (China); University of Science and Technology of China, School of Earth and Space Sciences and Institute of Polar Environment, Hefei (China)

    2012-09-15

    The causes of atmospheric methane (CH{sub 4}) changes are still a major contention, in particular with regards to the relative contributions of glacial-interglacial cycles, monsoons in both hemispheres and the late Holocene human intervention. Here, we explore the CH{sub 4} signals in the Antarctic EPICA Dome C and Vostok ice records using the methods of timeseries analyses and correlate them with insolation and geological records to address these issues. The results parse out three distinct groups of CH{sub 4} signals attributable to different drivers. The first group ({proportional_to}80% variance), well tracking the marine {delta}{sup 18}O record, is attributable to glacial-interglacial modulation on the global water cycle with the effects shared by wetlands at all latitudes, from monsoonal and non-monsoonal regions in both hemispheres. The second group ({proportional_to}15% variance), centered at the {proportional_to}10-kyr semi-precession frequency, is linkable with insolation-driven tropical monsoon changes in both hemispheres. The third group ({proportional_to}5% variance), marked by millennial frequencies, is seemingly related with the combined effect of ice-volume and bi-hemispheric insolation changes at the precession bands. These results indicate that bi-hemispheric monsoon changes have been a constant driver of atmospheric CH{sub 4}. This mechanism also partially explains the Holocene CH{sub 4} reversal since {proportional_to}5 kyr BP besides the human intervention. In the light of these results, we propose that global monsoon can be regarded as a system consisting of two main integrated components, one primarily driven by the oscillations of Inter-Tropical Convergence Zone (ITCZ) in response to the low-latitude summer insolation changes, anti-phase between the two hemispheres (i.e. the ITCZ monsoon component); and another modulated by the glacial-interglacial cycles, mostly synchronous at the global scale (i.e. the glacial-interglacial monsoon

  5. Asian summer monsoon prediction in ECMWF System 4 and NCEP CFSv2 retrospective seasonal forecasts

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hye-Mi; Webster, Peter J.; Curry, Judith A.; Toma, Violeta E. [Georgia Institute of Technology, School of Earth and Atmospheric Science, Atlanta, GA (United States)

    2012-12-15

    The seasonal prediction skill of the Asian summer monsoon is assessed using retrospective predictions (1982-2009) from the ECMWF System 4 (SYS4) and NCEP CFS version 2 (CFSv2) seasonal prediction systems. In both SYS4 and CFSv2, a cold bias of sea-surface temperature (SST) is found over the equatorial Pacific, North Atlantic, Indian Oceans and over a broad region in the Southern Hemisphere relative to observations. In contrast, a warm bias is found over the northern part of North Pacific and North Atlantic. Excessive precipitation is found along the ITCZ, equatorial Atlantic, equatorial Indian Ocean and the maritime continent. The southwest monsoon flow and the Somali Jet are stronger in SYS4, while the south-easterly trade winds over the tropical Indian Ocean, the Somali Jet and the subtropical northwestern Pacific high are weaker in CFSv2 relative to the reanalysis. In both systems, the prediction of SST, precipitation and low-level zonal wind has greatest skill in the tropical belt, especially over the central and eastern Pacific where the influence of El Nino-Southern Oscillation (ENSO) is dominant. Both modeling systems capture the global monsoon and the large-scale monsoon wind variability well, while at the same time performing poorly in simulating monsoon precipitation. The Asian monsoon prediction skill increases with the ENSO amplitude, although the models simulate an overly strong impact of ENSO on the monsoon. Overall, the monsoon predictive skill is lower than the ENSO skill in both modeling systems but both systems show greater predictive skill compared to persistence. (orig.)

  6. Monsoon rainfall behaviour in recent times on local/regional scale in India

    International Nuclear Information System (INIS)

    Singh, Surender; Rao, V.U.M.; Singh, Diwan

    2002-08-01

    An attempt has been made here to investigate the local/regional monsoon rainfall behaviour in the meteorological sub-division no. 13 comprising the areas of Haryana, Delhi and Chandigarh in India. The monthly monsoon rainfall data of 30 years (1970-99) of different locations in the region were used for the investigation. All locations except Delhi received more rainfall in monsoon season during the decade (1990-99) showing general increasing trend in the rainfall behaviour in recent times. The mean monsoon rainfall at various locations ranged between 324.8 mm at Sirsa and 974.9 mm at Chandigarh. The major amount of monsoon rainfall occurred during the month of July and August in the entire region. Monthly mean rainfall ranged between 37.5 to 144.9 mm (June), 130.6 to 298.2 mm (July), 92.6 to 313.6 mm (August) and 44.0 to 149.4mm (September) at different locations. All the locations in the region exhibited overall increasing trend in monsoon rainfall over the period under study. All locations in the region received their lowest monsoon rainfall in the year 1987 which was a drought year and the season's rainfall ranged between 56.1 mm (Sirsa) and 290.0 mm (Delhi) during this year. Many of the locations observed clusters of fluctuations in their respective monsoon rainfall. The statistical summaries of historical data series (1970-99) gave rainfall information on various time scale. Such information acquires value through its influence on the decision making of the ultimate users. (author)

  7. A mechanism for land-ocean contrasts in global monsoon trends in a warming climate

    Energy Technology Data Exchange (ETDEWEB)

    Fasullo, J. [National Center for Atmospheric Research, CAS/NCAR, Boulder, CO (United States)

    2012-09-15

    A central paradox of the global monsoon record involves reported decreases in rainfall over land during an era in which the global hydrologic cycle is both expected and observed to intensify. It is within this context that this work develops a physical basis for both interpreting the observed record and anticipating changes in the monsoons in a warming climate while bolstering the concept of the global monsoon in the context of shared feedbacks. The global-land monsoon record across multiple reanalyses is first assessed. Trends that in other studies have been taken as real are shown to likely be spurious as a result of changes in the assimilated data streams both prior to and during the satellite era. Nonetheless, based on satellite estimates, robust increases in monsoon rainfall over ocean do exist and a physical basis for this land-ocean contrast remains lacking. To address the contrast's causes, simulated trends are therefore assessed. While projections of total rainfall are inconsistent across models, the robust land-ocean contrast identified in observations is confirmed. A feedback mechanism is proposed rooted in the facts that land areas warm disproportionately relative to ocean, and onshore flow is the chief source of monsoonal moisture. Reductions in lower tropospheric relative humidity over land domains are therefore inevitable and these have direct consequences for the monsoonal convective environment including an increase in the lifting condensation level and a shift in the distribution of convection generally towards less frequent and potentially more intense events. The mechanism is interpreted as an important modulating influence on the ''rich-get-richer'' mechanism. Caveats for regional monsoons exist and are discussed. (orig.)

  8. Monsoonal response to mid-holocene orbital forcing in a high resolution GCM

    Directory of Open Access Journals (Sweden)

    J. H. C. Bosmans

    2012-04-01

    Full Text Available In this study, we use a sophisticated high-resolution atmosphere-ocean coupled climate model, EC-Earth, to investigate the effect of Mid-Holocene orbital forcing on summer monsoons on both hemispheres. During the Mid-Holocene (6 ka, there was more summer insolation on the Northern Hemisphere than today, which intensified the meridional temperature and pressure gradients. Over North Africa, monsoonal precipitation is intensified through increased landward monsoon winds and moisture advection as well as decreased moisture convergence over the oceans and more convergence over land compared to the pre-industrial simulation. Precipitation also extends further north as the ITCZ shifts northward in response to the stronger poleward gradient of insolation. This increase and poleward extent is stronger than in most previous ocean-atmosphere GCM simulations. In north-westernmost Africa, precipitation extends up to 35° N. Over tropical Africa, internal feedbacks completely overcome the direct warming effect of increased insolation. We also find a weakened African Easterly Jet. Over Asia, monsoonal precipitation during the Mid-Holocene is increased as well, but the response is different than over North-Africa. There is more convection over land at the expense of convection over the ocean, but precipitation does not extend further northward, monsoon winds over the ocean are weaker and the surrounding ocean does not provide more moisture. On the Southern Hemisphere, summer insolation and the poleward insolation gradient were weaker during the Mid-Holocene, resulting in a reduced South American monsoon through decreased monsoon winds and less convection, as well as an equatorward shift in the ITCZ. This study corroborates the findings of paleodata research as well as previous model studies, while giving a more detailed account of Mid-Holocene monsoons.

  9. Evaluation of CFSV2 Forecast Skill for Indian Summer Monsoon Sub-Seasonal Characteristics

    Science.gov (United States)

    S, S. A.; Ghosh, S.

    2015-12-01

    Prediction of sub seasonal monsoon characteristics of Indian Summer Monsoon (ISM) is highly crucial for agricultural planning and water resource management. The Climate forecast System version 2 (CFS V2), the state of the art coupled climate model developed by NCEP, is currently being employed for the seasonal and extended range forecasts of ISM. Even though CFSV2 is a fully coupled ocean- atmosphere- land model with advanced physics, increased resolution and refined initialisation, its ISM forecasts, in terms of seasonal mean and variability needs improvement. Numerous works have been done for verifying the CFSV2 forecasts in terms of the seasonal mean, its mean and variability, active and break spells, and El Nino Southern Oscillation (ENSO) - monsoon interactions. Most of these works are based on either rain fall strength or rainfall based indices. Here we evaluate the skill of CFS v2 model in forecasting the various sub seasonal features of ISM, viz., the onset and withdrawal days of monsoon that are determined using circulation based indices, the Monsoon Intra Seasonal Oscillations (MISO), and Indian Ocean and Pacific Ocean sea surface temperatures. The MISO index, we use here, is based on zonal wind at 850 hPa and Outgoing Long wave Radiation (OLR) anomalies. With this work, we aim at assessing the skill of the model in simulating the large scale circulation patterns and their variabilities within the monsoon season. Variabilities in these large scale circulation patterns are primarily responsible for the variabilities in the seasonal monsoon strength and its temporal distribution across the season. We find that the model can better forecast the large scale circulation and than the actual precipitation. Hence we suggest that seasonal rainfall forecasts can be improved by the statistical downscaling of CFSV2 forecasts by incorporating the established relationships between the well forecasted large scale variables and monsoon precipitation.

  10. Long range forecasting of summer monsoon rainfall from SST in the central equatorial Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y; Murthy, T.V.R.

    of summer monsoon rainfall from SST in the central equatorial Indian ocean Y. Sadhuram and T. V. Ramana Murthy National Institute of Oceanography, Regional Centre, 176, Lawson's Bay Colony, . Visakhapatnam-530017 ABSTRACT Severalprediction tedmiques have... and droughts associated with strong and weak monsoons greatly influence the economy of the country. Most of the droughts and floods are associated with EI-Nino and La- Nina respectively (Webster andYang3 and krishna Kumar et al\\. The relationship between ENSO...

  11. Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India)

    Science.gov (United States)

    Reuter, M.; Piller, W. E.; Harzhauser, M.; Kroh, A.

    2013-09-01

    Climate change has an unknown impact on tropical cyclones and the Asian monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as a recorder of tropical cyclone activity along the NW Indian coast during the late Oligocene warming period (~ 27-24 Ma). Proxy data providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system at the Oligocene-Miocene boundary. The vast shell concentrations are comprised of a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deeper to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished, each recording a relative storm wave base. (1) A shallow storm wave base is shown by nearshore molluscs, reef corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclinid foraminifers, Eupatagus echinoids and corallinacean algae; and (3) a deep storm wave base is represented by an Amussiopecten bivalve-Schizaster echinoid assemblage. These wave base depth estimates were used for the reconstruction of long-term tropical storm intensity during the late Oligocene. The development and intensification of cyclones over the recent Arabian Sea is primarily limited by the atmospheric monsoon circulation and strength of the associated vertical wind shear. Therefore, since the topographic boundary conditions for the Indian monsoon already existed in the late Oligocene, the reconstructed long-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~ 26 Ma followed by a period of monsoon weakening during the peak of the late

  12. African monsoon multidisciplinary analysis - An international research project and field campaign

    OpenAIRE

    Redelsperger, J. L.; Thorncroft, C. D.; Diedhiou, Arona; Lebel, Thierry; Parker, D. J.; Polcher, J.

    2006-01-01

    African Monsoon Multidisciplinary Analysis (AMMA) is an international project to improve our knowledge and understanding of the West African monsoon (WAM) and its variability with an emphasis on daily-to-interannual time scales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on West African nations. Recognizing the societal need to develop strategies that reduce the socioeconomic impacts of the vari...

  13. Vertical structure of atmospheric boundary layer over Ranchi during the summer monsoon season

    Science.gov (United States)

    Chandra, Sagarika; Srivastava, Nishi; Kumar, Manoj

    2018-04-01

    Thermodynamic structure and variability in the atmospheric boundary layer have been investigated with the help of balloon-borne GPS radiosonde over a monsoon trough station Ranchi (Lat. 23°45'N, Long. 85°43'E, India) during the summer monsoon season (June-September) for a period of 2011-2013. Virtual potential temperature gradient method is used for the determination of mixed layer height (MLH). The MLH has been found to vary in the range of 1000-1300 m during the onset, 600-900 m during the active and 1400-1750 m during the break phase of monsoon over this region. Inter-annual variations noticed in MLH could be associated with inter-annual variability in convection and rainfall prevailing over the region. Along with the MLH, the cloud layer heights are also derived from the thermodynamic profiles for the onset, active and break phases of monsoon. Cloud layer height varied a lot during different phases of the monsoon. For the determination of boundary-layer convection, thermodynamic parameter difference (δθ = θ es- θ e) between saturated equivalent potential temperature (θ es ) and equivalent potential temperature (θ e) is used. It is a good indicator of convection and indicates the intense and suppressed convection during different phases of monsoon.

  14. Sensible and latent heat forced divergent circulations in the West African Monsoon System

    Science.gov (United States)

    Hagos, S.; Zhang, C.

    2008-12-01

    Field properties of divergent circulation are utilized to identify the roles of various diabatic processes in forcing moisture transport in the dynamics of the West African Monsoon and its seasonal cycle. In this analysis, the divergence field is treated as a set of point sources and is partitioned into two sub-sets corresponding to latent heat release and surface sensible heat flux at each respective point. The divergent circulation associated with each set is then calculated from the Poisson's equation using Gauss-Seidel iteration. Moisture transport by each set of divergent circulation is subsequently estimated. The results show different roles of the divergent circulations forced by surface sensible and latent heating in the monsoon dynamics. Surface sensible heating drives a shallow meridional circulation, which transports moisture deep into the continent at the polar side of the monsoon rain band and thereby promotes the seasonal northward migration of monsoon precipitation during the monsoon onset season. In contrast, the circulation directly associated with latent heating is deep and the corresponding moisture convergence is within the region of precipitation. Latent heating also induces dry air advection from the north. Neither effect promotes the seasonal northward migration of precipitation. The relative contributions of the processes associated with latent and sensible heating to the net moisture convergence, and hence the seasonal evolution of monsoon precipitation, depend on the background moisture.

  15. Simulation of the anthropogenic aerosols over South Asia and their effects on Indian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Zhenming [Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Beijing (China); National Climate Center, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Kang, Shichang [Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Beijing (China); Chinese Academy of Sciences, State Key Laboratory of Cryospheric Science, Lanzhou (China); Zhang, Dongfeng [Shanxi Meteorological Bureau, Taiyuan (China); Zhu, Chunzi [Nanjing University of Information Science Technology, College of Atmospheric Science, Nanjing (China); Wu, Jia; Xu, Ying [National Climate Center, Beijing (China)

    2011-05-15

    A regional climate model coupled with a chemistry-aerosol model is employed to simulate the anthropogenic aerosols including sulfate, black carbon and organic carbon and their direct effect on climate over South Asia. The model is driven by the NCAR/NCEP re-analysis data. Multi-year simulations with half, normal and double emission fluxes are conducted. Results show that the model performs well in reproducing present climate over the region. Simulations of the aerosol optical depth and surface concentration of aerosols are also reasonable although to a less extent. The negative radiative forcing is found at the top of atmosphere and largely depended on emission concentration. Surface air temperature decreases by 0.1-0.5 C both in pre-monsoon and monsoon seasons. The range and intensity of cooling areas enlarge while aerosol emission increases. Changes in precipitation are between -25 and 25%. Different diversifications of rainfall are showed with three emission scenarios. The changes of precipitation are consistent with varieties of monsoon onset dates in pre-monsoon season. In the regions of increasing precipitation, monsoon onset is advanced and vice versa. In northeast India and Myanmar, aerosols lead the India summer monsoon onset advancing 1-2 pentads, and delaying by 1-2 pentads in central and southeast India. These changes are mainly caused by the anomaly of local Hadley circulations and enhancive precipitation. Tibetan Plateau played a crucial role in the circulation changes. (orig.)

  16. Regional trends in early-monsoon rainfall over Vietnam and CCSM4 attribution

    Science.gov (United States)

    Li, R.; Wang, S. S.-Y.; Gillies, R. R.; Buckley, B. M.; Yoon, J.-H.; Cho, C.

    2018-04-01

    The analysis of precipitation trends for Vietnam revealed that early-monsoon precipitation has increased over the past three decades but to varying degrees over the northern, central and southern portions of the country. Upon investigation, it was found that the change in early-monsoon precipitation is associated with changes in the low-level cyclonic airflow over the South China Sea and Indochina that is embedded in the large-scale atmospheric circulation associated with a "La Niña-like" anomalous sea surface temperature pattern with warming in the western Pacific and Indian Oceans and cooling in the eastern Pacific. The Community Climate System Model version 4 (CCSM4) was subsequently used for an attribution analysis. Over northern Vietnam an early-monsoon increase in precipitation is attributed to changes in both greenhouse gases and natural forcing. For central Vietnam, the observed increase in early-monsoon precipitation is reproduced by the simulation forced with greenhouse gases. However, over southern Vietnam the early-monsoon precipitation increase is less definitive where aerosols were seen to be preponderant but natural forcing through the role of the Interdecadal Pacific Oscillation may well be a factor that is not resolved by CCSM4. Increased early-monsoonal precipitation over the coastal lowland and deltas has the potential to amplify economic and human losses.

  17. Effect of increasing greenhouse gases on Indian monsoon rainfall as downscaled from the ECHAM coupled model

    International Nuclear Information System (INIS)

    Singh, S.V.; Storch, H.V.

    1994-01-01

    It is more or less accepted that the increasing anthropogenic gases will result in global warming through the greenhouse effect. The major influence of this will be felt in the form of ice melts and rising sea levels. The influence on regional climates like monsoons is not very clear. Since the monsoons arise due to surface heating, one would expect that global warming will lead to more vigorous monsoons. The expected change in a climate parameter can be studied by analyzing the historical data and then extrapolating in time. Alternatively, one can use the state-of-the-art coupled GCMs which are able to simulate the earth's climate with reasonable accuracy. Both methods have some limitations. The first method cannot adequately consider the nonlinearity, and the second method may not be efficient for regional scales. So that the projections can be trusted, the regional features should be well simulated. None of the current models are able to simulate the Indian monsoon satisfactorily. Therefore it is desirable to infer the expected change in monsoons from other large and near global scale features which are better simulated. This approach, which depends on the concurrent association between a large-scale modeled feature and a regional scale, is known as downscaling, after Storch et al., and is adopted here to project the Indian monsoon rainfall for the next 100 years from the ECHAM T21 coupled model

  18. A vigorous Mesoamerican monsoon during the Last Glacial Maximum driven by orbital and oceanic forcing

    Science.gov (United States)

    Lachniet, M. S.; Asmerom, Y.; Bernal, J. P.; Polyak, V.; Vazquez-Selem, L. V.

    2012-12-01

    The external forcings on global monsoon strength include summer orbital insolation and ocean circulation changes, both of which are key control knobs on Earth's climate. However, few records of the North American Monsoon (NAM) are available to test its sensitivity to variations in the precession-dominated insolation signal and Atlantic Meridional Overturning Circulation (AMOC) for the Last Glacial Maximum (LGM; 21 ± 3 cal ka BP) and deglacial periods. In particular, well-dated and high-resolution records from the southern sector of the NAM, referred to informally as the Mesoamerican monsoon to distinguish it from the more northerly 'core' NAM, are needed to better elucidate paleoclimate change in North America. Here, we present a 22 ka (ka = kilo years) rainfall history from absolutely-dated speleothems from tropical southwestern Mexico that documents a vigorous LGM summer monsoon, in contradiction to previous interpretations, and that the monsoon collapsed during the Heinrich stadial 1 and Younger Dryas cold events. We conclude that a strong Mesoamerican monsoon requires both a large ocean-to-land temperature contrast, driven as today by summer insolation, and a proximal latitudinal position of the Intertropical Convergence Zone, forced by active AMOC.

  19. Prediction of Indian Summer-Monsoon Onset Variability: A Season in Advance.

    Science.gov (United States)

    Pradhan, Maheswar; Rao, A Suryachandra; Srivastava, Ankur; Dakate, Ashish; Salunke, Kiran; Shameera, K S

    2017-10-27

    Monsoon onset is an inherent transient phenomenon of Indian Summer Monsoon and it was never envisaged that this transience can be predicted at long lead times. Though onset is precipitous, its variability exhibits strong teleconnections with large scale forcing such as ENSO and IOD and hence may be predictable. Despite of the tremendous skill achieved by the state-of-the-art models in predicting such large scale processes, the prediction of monsoon onset variability by the models is still limited to just 2-3 weeks in advance. Using an objective definition of onset in a global coupled ocean-atmosphere model, it is shown that the skillful prediction of onset variability is feasible under seasonal prediction framework. The better representations/simulations of not only the large scale processes but also the synoptic and intraseasonal features during the evolution of monsoon onset are the comprehensions behind skillful simulation of monsoon onset variability. The changes observed in convection, tropospheric circulation and moisture availability prior to and after the onset are evidenced in model simulations, which resulted in high hit rate of early/delay in monsoon onset in the high resolution model.

  20. Effect of Floodplain Inundation on River Pollution in Taiwan's Strong Monsoonal Climate

    Science.gov (United States)

    Hester, E. T.; Lin, A. Y. C.

    2017-12-01

    River-floodplain interaction provides important benefits such as flood mitigation, provision of ecological habitat, and improved water quality. Human actions have historically reduced such interaction and associated benefits by diking, floodplain fill, and river regulation. In response, floodplain restoration has become popular in North America and Europe, but is less practiced in Asia. In Taiwan, unusually strong monsoons and steep terrain alter floodplain dynamics relative to elsewhere around the world, and provide a unique environment for floodplain management. We used numerical models of flow, transport, and reaction in river channels and floodplains to quantify the effect of river-floodplain interaction on water quality in Taiwan's strong monsoon and high topographic relief. We conducted sensitivity analyses of parameters such as river slope, monsoon severity, reservoir operation mode, degree of floodplain reconnection, contaminant reaction rate, and contaminant reaction type on floodplain connectivity and contaminant mitigation. We found significant differences in floodplain hydraulics and residence times in Taiwan's steep monsoonal environment relative to the shallower non-monsoonal environment typical of the eastern USA, with significant implications for water quality. For example, greater flashiness of floodplain inundation in Taiwan provides greater challenges for reconnecting sufficient floodplain volume to handle monsoonal runoff. Yet longer periods when floodplains are reliably dry means that such lands may have greater value for seasonal use such as parks or agriculture. The potential for floodplain restoration in Taiwan is thus significant, but qualitatively different than in the eastern USA.

  1. MONSOONS MUDE AND GOLD MUSONLAR GEMİ VE ALTIN

    Directory of Open Access Journals (Sweden)

    Paul LUNDE

    2009-12-01

    Full Text Available The “global economy” of the Middle Ages was created by linking the Indian Ocean trading networks with those of the Mediterranean Sea and its African and European hinterlands. These products, together with ceramics, textiles and sugar provided from Egypt and Syria, reached European markets almost exclusively through the Italian maritime republics of Amalfi, Pisa, Genoa and Venice. Especially the direction of the monsoon winds in the Indian Ocean and the course of the Venice trade ships were at the same direction. Thereby, Venice trade ships set out toward the end of August and made their way slowly through the Adriatic and the Aegean to Cyprus and Alexandria, timing their arrival there to coincide with the availability of monsoon-borne and by this way the products which are ned carried through Europe. İt is important to emphasize this subject that North Europe economy depends on this Monsoons where they became at Indian Ocean. As a maritime republic dedicated itself to the international trade, Venice was an anomaly in a feudal Europe that measured wealth by land, not money. Therefor this idea were encouraging their believing about ending the monopoly of the Muslim trade at the Indian Ocean. Ortaçağın global ekonomisini Hint Okyanusu ticaret hattı ile Akdeniz, Afrika ve Avrupa Hinterlantları arasındaki ticaret bağlantısı teşkil ediyordu. Avrupa ekonomisindeki gelişmelere paralel olarak Batı dünyasının gereksinim duyduğu ve Mısır ile Suriye’den tedarik edilen şeker, tekstil, seramik gibi ürünler Amalfi, Pisa, Ceneviz ve Venedik gibi İtalyan Cumhuriyetleri aracılığıyla Avrupa pazarlarına taşınmaktaydı. Özellikle Hint Okyanusu üzerindeki muson rüzgârlarının yönleriyle Venedik ticaret gemilerinin rotaları aynı doğrultudaydı. Bu suretle Ağustos ayının sonuna doğru İtalya’dan ayrılan gemiler, Adriyatik, Ege ve Kıbrıs rotasından İskenderiye’ye ulaştığı esnada musonlarla kar

  2. Improving GEFS Weather Forecasts for Indian Monsoon with Statistical Downscaling

    Science.gov (United States)

    Agrawal, Ankita; Salvi, Kaustubh; Ghosh, Subimal

    2014-05-01

    Weather forecast has always been a challenging research problem, yet of a paramount importance as it serves the role of 'key input' in formulating modus operandi for immediate future. Short range rainfall forecasts influence a wide range of entities, right from agricultural industry to a common man. Accurate forecasts actually help in minimizing the possible damage by implementing pre-decided plan of action and hence it is necessary to gauge the quality of forecasts which might vary with the complexity of weather state and regional parameters. Indian Summer Monsoon Rainfall (ISMR) is one such perfect arena to check the quality of weather forecast not only because of the level of intricacy in spatial and temporal patterns associated with it, but also the amount of damage it can cause (because of poor forecasts) to the Indian economy by affecting agriculture Industry. The present study is undertaken with the rationales of assessing, the ability of Global Ensemble Forecast System (GEFS) in predicting ISMR over central India and the skill of statistical downscaling technique in adding value to the predictions by taking them closer to evidentiary target dataset. GEFS is a global numerical weather prediction system providing the forecast results of different climate variables at a fine resolution (0.5 degree and 1 degree). GEFS shows good skills in predicting different climatic variables but fails miserably over rainfall predictions for Indian summer monsoon rainfall, which is evident from a very low to negative correlation values between predicted and observed rainfall. Towards the fulfilment of second rationale, the statistical relationship is established between the reasonably well predicted climate variables (GEFS) and observed rainfall. The GEFS predictors are treated with multicollinearity and dimensionality reduction techniques, such as principal component analysis (PCA) and least absolute shrinkage and selection operator (LASSO). Statistical relationship is

  3. How autumn Eurasian snow anomalies affect east asian winter monsoon: a numerical study

    Science.gov (United States)

    Luo, Xiao; Wang, Bin

    2018-03-01

    Previous studies have found that snow Eurasian anomalies in autumn can affect East Asian winter monsoon (EAWM), but the mechanisms remain controversial and not well understood. The possible mechanisms by which Eurasian autumn snow anomalies affect EAWM are investigated by numerical experiments with a coupled general circulation model and its atmospheric general circulation model component. The leading empirical orthogonal function mode of the October-November mean Eurasian snow cover is characterized by a uniform anomaly over a broad region of central Eurasia (40°N-65°N, 60°E-140°E). However, the results from a 150-ensemble mean simulation with snow depth anomaly specified in October and November reveal that the Mongolian Plateau and Vicinity (MPV, 40°-55°N, 80°-120°E) is the key region for autumn snow anomalies to affect EAWM. The excessive snow forcing can significantly enhance EAWM and the snowfall over the northwestern China and along the EAWM front zone stretching from the southeast China to Japan. The physical process involves a snow-monsoon feedback mechanism. The excessive autumn snow anomalies over the MPV region can persist into the following winter, and significantly enhance winter snow anomalies, which increase surface albedo, reduce incoming solar radiation and cool the boundary layer air, leading to an enhanced Mongolian High and a deepened East Asian trough. The latter, in turn, strengthen surface northwesterly winds, cooling East Asia and increasing snow accumulation over the MPV region and the southeastern China. The increased snow covers feedback to EAWM system through changing albedo, extending its influence southeastward. It is also found that the atmosphere-ocean coupling process can amplify the delayed influence of Eurasian snow mass anomaly on EAWM. The autumn surface albedo anomalies, however, do not have a lasting "memory" effect. Only if the albedo anomalies are artificially extended into December and January, will the EAWM be

  4. Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

    KAUST Repository

    Jin, Q.; Wei, J.; Yang, Z.-L.; Pu, B.; Huang, J.

    2015-01-01

    © Author(s) 2015. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust-ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day-1 (∼10 % of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan

  5. Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

    KAUST Repository

    Jin, Q.

    2015-06-11

    The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust–ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44mmday1 ( 10% of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan Plateau. This study demonstrates

  6. Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

    KAUST Repository

    Jin, Q.

    2015-09-02

    © Author(s) 2015. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust-ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day-1 (∼10 % of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan

  7. Study on the association of green house gas (CO2) with monsoon rainfall using AIRS and TRMM satellite observations

    Science.gov (United States)

    Singh, R. B.; Janmaijaya, M.; Dhaka, S. K.; Kumar, V.

    Monsoon water cycle is the lifeline to over 60 per cent of the world's population. Throughout history, the monsoon-related calamities of droughts and floods have determined the life pattern of people. The association of Green House Gases (GHGs) particularly Carbon dioxide (CO2) with monsoon has been greatly debated amongst the scientific community in the past. The effect of CO2 on the monsoon rainfall over the Indian-Indonesian region (8-30°N, 65°-100°E) is being investigated using satellite data. The correlation coefficient (Rxy) between CO2 and monsoon is analysed. The Rxy is not significantly positive over a greater part of the study region, except a few regions. The inter-annual anomalies of CO2 is identified for playing a secondary role to influencing monsoon while other phenomenon like ENSO might be exerting a much greater influence.

  8. Investigating synoptic-scale monsoonal disturbances in an idealized moist model

    Science.gov (United States)

    Clark, S.; Ming, Y.

    2017-12-01

    Recent studies have highlighted the potential utility of a theory for a "moisture-dynamical" instability in explaining the time and spatial scales of intra-seasonal variability associated with the Indian summer monsoon. These studies suggest that a localized region in the subtropics with mean low-level westerly winds and mean temperature increasing poleward will allow the formation of westward propagating precipitation anomalies associated with moist Rossby-like waves. Here we test this theory in an idealized moist model with realistic radiative transfer by inducing a local poleward-increasing temperature gradient by placing a continent with simplified hydrology in the subtropics. We experiment with different treatments of land-surface hydrology, ranging from the extreme (treating land as having the same heat capacity as the slab ocean used in the model, and turning off evaporation completely over land) to the more realistic (bucket hydrology, with a decreased heat capacity over land), and different continental shapes, ranging from a zonally-symmetric continent, to Earth-like continental geometry. Precipitation rates produced by the simulations are analyzed using space-time spectral analysis, and connected to variability in the winds through regression analysis. The observed behavior is discussed with respect to predictions from the theory.

  9. A tripolar pattern as an internal mode of the East Asian summer monsoon

    Science.gov (United States)

    Hirota, Nagio; Takahashi, Masaaki

    2012-11-01

    A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59 %, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area.

  10. A tripolar pattern as an internal mode of the East Asian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Hirota, Nagio; Takahashi, Masaaki [University of Tokyo, Atmosphere and Ocean Research Institute, Chiba (Japan)

    2012-11-15

    A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59 %, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area. (orig.)

  11. Rainfall variability, climate change and regionalization in the African monsoon region

    International Nuclear Information System (INIS)

    Fontaine, Bernard; Roucou, Pascal; Vigaud, Nicolas; Camara, Moctar; Konare, Abdourahamane; Sanda, Seidou Ibrah; Diedhiou, Arona; Janicot, Serge

    2012-01-01

    This summary recalls some results at the end of the AMMA international experiment (2003-2010) in terms of variability of the African monsoon at the intra-seasonal to multi-decadal scales and of climate prospective. The results confirmed the weight of surface temperatures and marine tele-connections for inter-annual and decadal fluctuations and stressed the importance of atmospheric variability. They also described the dominant modes of intra-seasonal variability as their interactions with the surface. Several hypotheses involving memory effects related to soil water and vegetation, particularly in boreal spring and autumn have also been made. Prospective analysis from model output suggests rainfall surplus around 2050 over the Eastern-central Sahel and relative deficit to the West. Phase 2 of AMMA (2010-2020) will focus more on aspects that have a high social impact in direct collaboration with meteorological services predictability, prediction scores, operational indicators, evaluation of the part of anthropogenic forcing in the current and future variations. (authors)

  12. Condensation heating of the Asian summer monsoon and the subtropical anticyclone in the Eastern Hemisphere

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y.M.; Wu, G.X.; Liu, H.; Liu, P. [Chinese Academy of Sciences, Beijing (China). Inst. of Atmospheric Physics

    2001-02-01

    The effects of condensation heating on the formation of the subtropical anticyclone in the Eastern Hemisphere (EH) are studied by means of theoretical analysis and numerical simulation. The complete vorticity equation is employed for the analysis. It is found that, due to the vertical gradient of strong condensation heating, the distribution of cyclone and anticyclone in the upper troposphere is out of phase with that in the middle and lower troposphere. This is confirmed by a series of numerical experiments. The horizontal gradient of the condensation heating also affects the configuration of the subtropical anticyclone. It is concluded that condensation heating is a key factor for the formation and location of the summer subtropical anticyclone in the EH. The latent heating released by the Asian monsoon rainfall contributes to the formation of the 200 hPa South Asian anticyclone on the western side of the heating center and the 500 hPa western Pacific subtropical anticyclone on the eastern side of the center. Such configurations are modified to some extent by surface sensible heating and orography. The circulation in mid-latitudes is also affected by the latent heating in the subtropical area through the propagation of Rossby waves. (orig.)

  13. First observations of Gigantic Jets from Monsoon Thunderstorms over India

    Science.gov (United States)

    Singh, Rajesh; Maurya, Ajeet; Chanrion, Olivier; Neubert, Torsten; Cummer, Steven; Mlynarczyk, Janusz; Bór, József; Siingh, Devendraa; Cohen, Morris; Kumar, Sushil

    2016-04-01

    Gigantic Jets are electric discharges from thunderstorm cloud tops to the bottom of the ionosphere at ~80 km altitude. After their first discovery in 2001, relatively few observations have been reported. Most of these are from satellites at large distances and a few tens from the ground at higher spatial resolution. Here we report the first Gigantic Jets observed in India from two thunderstorm systems that developed over the land surface from monsoon activity, each storm producing two Gigantic Jets. The jets were recorded by a video camera system at standard video rate (20 ms exposure) at a few hundred km distance. ELF measurements suggest that the jets are of the usual negative polarity and that they develop in less than 40 ms, which is faster than most jets reported in the past. The jets originate from the leading edge of a slowly drifting convective cloud complex close to the highest regions of the clouds and carry ~25 Coulomb of charge to the ionosphere. One jet has a markedly horizontal displacement that we suggest is caused by a combination of close-range cloud electric fields at inception, and longer-range cloud fields at larger distances during full development. The Gigantic Jets are amongst the few that have been observed over land.

  14. Ganges Valley Aerosol Experiment (GVAX) Final Campaign Report

    Energy Technology Data Exchange (ETDEWEB)

    Kotamarthi, VR [Argonne National Laboratory

    2013-12-01

    In general, the Indian Summer Monsoon (ISM) as well as the and the tropical monsoon climate is influenced by a wide range of factors. Under various climate change scenarios, temperatures over land and into the mid troposphere are expected to increase, intensifying the summer pressure gradient differential between land and ocean and thus strengthening the ISM. However, increasing aerosol concentration, air pollution, and deforestation result in changes to surface albedo and insolation, potentially leading to low monsoon rainfall. Clear evidence points to increasing aerosol concentrations over the Indian subcontinent with time, and several hypotheses regarding the effect on monsoons have been offered. The Ganges Valley Aerosol Experiment (GVAX) field study aimed to provide critical data to address these hypotheses and contribute to developing better parameterizations for tropical clouds, convection, and aerosol-cloud interactions. The primary science questions for the mission were as follows:

  15. Role of Ocean Initial Conditions to Diminish Dry Bias in the Seasonal Prediction of Indian Summer Monsoon Rainfall: A Case Study Using Climate Forecast System

    Science.gov (United States)

    Koul, Vimal; Parekh, Anant; Srinivas, G.; Kakatkar, Rashmi; Chowdary, Jasti S.; Gnanaseelan, C.

    2018-03-01

    Coupled models tend to underestimate Indian summer monsoon (ISM) rainfall over most of the Indian subcontinent. Present study demonstrates that a part of dry bias is arising from the discrepancies in Oceanic Initial Conditions (OICs). Two hindcast experiments are carried out using Climate Forecast System (CFSv2) for summer monsoons of 2012-2014 in which two different OICs are utilized. With respect to first experiment (CTRL), second experiment (AcSAL) differs by two aspects: usage of high-resolution atmospheric forcing and assimilation of only ARGO observed temperature and salinity profiles for OICs. Assessment of OICs indicates that the quality of OICs is enhanced due to assimilation of actual salinity profiles. Analysis reveals that AcSAL experiment showed 10% reduction in the dry bias over the Indian land region during the ISM compared to CTRL. This improvement is consistently apparent in each month and is highest for June. The better representation of upper ocean thermal structure of tropical oceans at initial stage supports realistic upper ocean stability and mixing. Which in fact reduced the dominant cold bias over the ocean, feedback to air-sea interactions and land sea thermal contrast resulting better representation of monsoon circulation and moisture transport. This reduced bias of tropospheric moisture and temperature over the Indian land mass and also produced better tropospheric temperature gradient over land as well as ocean. These feedback processes reduced the dry bias in the ISM rainfall. Study concludes that initializing the coupled models with realistic OICs can reduce the underestimation of ISM rainfall prediction.

  16. Changes in the in-phase relationship between the Indian and subsequent Australian summer monsoons during the past five decades

    Directory of Open Access Journals (Sweden)

    J.-Y. Yu

    2007-10-01

    Full Text Available This study examines the decadal changes in the in-phase relationship between Indian summer monsoon and the subsequent Australian summer monsoon using observational data from 1950–2005. The in-phase relationship is the tendency for a strong Indian summer monsoon to be followed by a strong Australian summer monsoon and vice versa. It is found that the in-phase relationship was weak during the late 1950s and early 1960s, strengthened to a maximum in the early 1970s just before the 1976/77 Pacific climate shift, then declined until the late 1990s. Pacific SST anomalies are noticed to have strong persistence from boreal to austral summer, providing the memory to connect the Indian and subsequent Australian summer monsoon. The simultaneous correlation between the Pacific SST anomalies and the Indian summer monsoon is always strong. It is the weakening and strengthening of the simultaneous correlation between the Australian summer monsoon and the Pacific SST anomalies that contributes to the decadal variations of the in-phase monsoon relation. This study suggests that the interaction between the Australian monsoon and the Pacific Ocean is crucial to tropical climate variability and has experienced significant changes over the past five decades.

  17. Simulation of boreal Summer Monsoon Rainfall using CFSV2_SSiB model: sensitivity to Land Use Land Cover (LULC)

    Science.gov (United States)

    Chilukoti, N.; Xue, Y.

    2016-12-01

    The land surface play a vital role in determining the surface energy budget, accurate representation of land use and land cover (LULC) is necessary to improve forecast. In this study, we have investigated the influence of surface vegetation maps with different LULC on simulating the boreal summer monsoon rainfall. Using a National Centres for Environmental Prediction (NCEP) Coupled Forecast System version 2(CFSv2) model coupled with Simplified Simple Biosphere (SSiB) model, two experiments were conducted: one with old vegetation map and one with new vegetation map. The significant differences between new and old vegetation map were in semi-arid and arid areas. For example, in old map Tibetan plateau classified as desert, which is not appropriate, while in new map it was classified as grasslands or shrubs with bare soil. Old map classified the Sahara desert as a bare soil and shrubs with bare soil, whereas in new map it was classified as bare ground. In addition to central Asia and the Sahara desert, in new vegetation map, Europe had more cropped area and India's vegetation cover was changed from crops and forests to wooded grassland and small areas of grassland and shrubs. The simulated surface air temperature with new map shows a significant improvement over Asia, South Africa, and northern America by some 1 to 2ºC and 2 to 3ºC over north east China and these are consistent with the reduced rainfall biases over Africa, near Somali coast, north east India, Bangladesh, east China sea, eastern Pacific and northern USA. Over Indian continent and bay of Bengal dry rainfall anomalies that is the only area showing large dry rainfall bias, however, they were unchanged with new map simulation. Overall the CFSv2(coupled with SSiB) model with new vegetation map show a promising result in improving the monsoon forecast by improving the Land -Atmosphere interactions. To compare with the LULC forcing, experiment was conducted using the Global Forecast System (GFS) simulations

  18. Planetary boundary layer height over the Indian subcontinent: Variability and controls with respect to monsoon

    Science.gov (United States)

    Sathyanadh, Anusha; Prabhakaran, Thara; Patil, Chetana; Karipot, Anandakumar

    2017-10-01

    Planetary boundary layer (PBL) height characteristics over the Indian sub-continent at diurnal to seasonal scales and its controlling factors in relation to monsoon are investigated. The reanalysis (Modern Era Retrospective analysis for Research and Applications, MERRA) PBL heights (PBLH) used for the study are validated against those derived from radiosonde observations and radio occultation air temperature and humidity profiles. The radiosonde observations include routine India Meteorological Department observations at two locations (coastal and an inland) for one full year and campaign based early afternoon radiosonde observations at six inland locations over the study region for selected days from May-September 2011. The temperature and humidity profiles from radio occultations spread over the sub-continent at irregular timings during the year 2011. The correlations and root mean square errors are in the range 0.74-0.83 and 407 m-643 m, respectively. Large pre-monsoon, monsoon and post-monsoon variations in PBL maximum height (1000 m-4000 m), time of occurrence of maximum height (11:00 LST-17:00 LST) and growth rate (100 to 400 m h- 1) are noted over the land, depending on geographical location and more significantly on the moisture availability which influences the surface sensible and latent heat fluxes. The PBLH variations associated with active-break intra-seasonal monsoon oscillations are up to 1000 m over central Indian locations. Inter relationship between the PBLH and the controlling factors, i.e. Evaporative Fraction, net radiation, friction velocity, surface Richardson number, and scalar diffusivity fraction, show significant variation between dry and wet PBL regimes, which also varies with geographical location. Evaporative fraction has dominant influence on the PBLH over the region. Enhanced entrainment during monsoon contributes to reduction in PBLH, whereas the opposite effect is noted during dry period. Linear regression, cross wavelet and

  19. Seasonal and Intraseasonal Variability of Mesoscale Convective Systems over the South Asian Monsoon Region

    Energy Technology Data Exchange (ETDEWEB)

    Virts, Katrina S.; Houze, Robert A.

    2016-12-01

    Seasonal and intraseasonal differences in mesoscale convective systems (MCSs) over South Asia are examined using A-Train satellites, a ground-based lightning network, and reanalysis fields. Pre-monsoon (April-May) MCSs occur primarily over Bangladesh and the eastern Bay of Bengal. During the monsoon (June-September), small MCSs occur over the Meghalaya Plateau and northeast Himalayan notch, while large and connected MCSs are most widespread over the Bay of Bengal. Monsoon MCSs produce less lightning and exhibit more extensive stratiform and anvil reflectivity structures in CloudSat observations than do pre-monsoon MCSs. During the monsoon season, Bay of Bengal and Meghalaya Plateau MCSs vary with the 30-60 day northward-propagating intraseasonal oscillation, while northeast Himalayan notch MCSs are associated with weak large-scale anomalies but locally enhanced CAPE. During intraseasonal active periods, a zone of enhanced large and connected MCSs, precipitation, and lightning extends from the northeastern Arabian Sea southeast over India and the Bay of Bengal, flanked by suppressed anomalies. Spatial variability is observed within this enhancement zone: lightning is most enhanced where MCSs are less enhanced, and vice versa. Reanalysis composites indicate that Bay of Bengal MCSs are associated with monsoon depressions, which are frequent during active monsoon periods, while Meghalaya Plateau MCSs are most frequent at the end of break periods, as anomalous southwesterly winds strengthen moist advection toward the terrain. Over both regions, MCSs exhibit more extensive stratiform and anvil regions and less lightning when the large-scale environment is moister, and vice versa.

  20. The effect of El-Niño on South Asian Monsoon and agricultural production

    Science.gov (United States)

    Mukherjee, A.

    2015-12-01

    Mukherjee A, Wang S.Y.Abstract:The South Asian Monsoon has a prominent and significant impact on South Asian countries like India, Bangladesh, Nepal, Pakistan, Sri Lanka and it is one of the most studied phenomena in the world. The monsoon is historically known to be influenced by El Niño-Southern Oscillation (ENSO). The inter-annual and inter-decadal variability of seasonal precipitation over India strongly depends upon the ENSO phasing. The average southwest monsoon rainfall received during the years with El Niño was found to be less compared to normal years and the average rainfall during the northeast monsoon is higher in coastal Andhra Pradesh. ENSO is anti-correlated with Indian summer monsoon (ISM). The last prominent effect of ENSO on India's monsoon occurred in 2009 with 23% reduction in annual rainfall, reducing summer sown crops such as rice, sugar cane etc. and pushing up food prices. Climatic resources endowment plays a major role in planning agricultural production in tropical and sub-tropical environment especially under rain-fed agriculture, and so contingent crop planning drawn on this relationship would help to mitigate the effects of ENSO episodes in the region. The unexplored area in this domain of research is the changes in the frequency and intensity of ENSO due to global warming and its impact on ENSO prediction and agricultural management practices. We analyze the last 30 years datasets of Pacific SST, and precipitation and air temperature over Southeast Asia to examine the evolution of ENSO teleconnections with ISM, as well as making estimates of drought indices such as Palmer Drought Severity Index. This research can lead toward better crop management strategies in the South Asian monsoon region.

  1. Identification of tipping elements of the Indian Summer Monsoon using climate network approach

    Science.gov (United States)

    Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

    2015-04-01

    Spatial and temporal variability of the rainfall is a vital question for more than one billion of people inhabiting the Indian subcontinent. Indian Summer Monsoon (ISM) rainfall is crucial for India's economy, social welfare, and environment and large efforts are being put into predicting the Indian Summer Monsoon. For predictability of the ISM, it is crucial to identify tipping elements - regions over the Indian subcontinent which play a key role in the spatial organization of the Indian monsoon system. Here, we use climate network approach for identification of such tipping elements of the ISM. First, we build climate networks of the extreme rainfall, surface air temperature and pressure over the Indian subcontinent for pre-monsoon, monsoon and post-monsoon seasons. We construct network of extreme rainfall event using observational satellite data from 1998 to 2012 from the Tropical Rainfall Measuring Mission (TRMM 3B42V7) and reanalysis gridded daily rainfall data for a time period of 57 years (1951-2007) (Asian Precipitation Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources, APHRODITE). For the network of surface air temperature and pressure fields, we use re-analysis data provided by the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR). Second, we filter out data by coarse-graining the network through network measures, and identify tipping regions of the ISM. Finally, we compare obtained results of the network analysis with surface wind fields and show that occurrence of the tipping elements is mostly caused by monsoonal wind circulation, migration of the Intertropical Convergence Zone (ITCZ) and Westerlies. We conclude that climate network approach enables to select the most informative regions for the ISM, providing realistic description of the ISM dynamics with fewer data, and also help to identify tipping regions of the ISM. Obtained tipping elements deserve a

  2. Regional simulation of Indian summer monsoon intraseasonal oscillations at gray-zone resolution

    Science.gov (United States)

    Chen, Xingchao; Pauluis, Olivier M.; Zhang, Fuqing

    2018-01-01

    Simulations of the Indian summer monsoon by the cloud-permitting Weather Research and Forecasting (WRF) model at gray-zone resolution are described in this study, with a particular emphasis on the model ability to capture the monsoon intraseasonal oscillations (MISOs). Five boreal summers are simulated from 2007 to 2011 using the ERA-Interim reanalysis as the lateral boundary forcing data. Our experimental setup relies on a horizontal grid spacing of 9 km to explicitly simulate deep convection without the use of cumulus parameterizations. When compared to simulations with coarser grid spacing (27 km) and using a cumulus scheme, the 9 km simulations reduce the biases in mean precipitation and produce more realistic low-frequency variability associated with MISOs. Results show that the model at the 9 km gray-zone resolution captures the salient features of the summer monsoon. The spatial distributions and temporal evolutions of monsoon rainfall in the WRF simulations verify qualitatively well against observations from the Tropical Rainfall Measurement Mission (TRMM), with regional maxima located over Western Ghats, central India, Himalaya foothills, and the west coast of Myanmar. The onset, breaks, and withdrawal of the summer monsoon in each year are also realistically captured by the model. The MISO-phase composites of monsoon rainfall, low-level wind, and precipitable water anomalies in the simulations also agree qualitatively with the observations. Both the simulations and observations show a northeastward propagation of the MISOs, with the intensification and weakening of the Somali Jet over the Arabian Sea during the active and break phases of the Indian summer monsoon.

  3. Clouds vertical properties over the Northern Hemisphere monsoon regions from CloudSat-CALIPSO measurements

    Science.gov (United States)

    Das, Subrata Kumar; Golhait, R. B.; Uma, K. N.

    2017-01-01

    The CloudSat spaceborne radar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) space-borne lidar measurements, provide opportunities to understand the intriguing behavior of the vertical structure of monsoon clouds. The combined CloudSat-CALIPSO data products have been used for the summer season (June-August) of 2006-2010 to present the statistics of cloud macrophysical (such as cloud occurrence frequency, distribution of cloud top and base heights, geometrical thickness and cloud types base on occurrence height), and microphysical (such as ice water content, ice water path, and ice effective radius) properties of the Northern Hemisphere (NH) monsoon region. The monsoon regions considered in this work are the North American (NAM), North African (NAF), Indian (IND), East Asian (EAS), and Western North Pacific (WNP). The total cloud fraction over the IND (mostly multiple-layered cloud) appeared to be more frequent as compared to the other monsoon regions. Three distinctive modes of cloud top height distribution are observed over all the monsoon regions. The high-level cloud fraction is comparatively high over the WNP and IND. The ice water content and ice water path over the IND are maximum compared to the other monsoon regions. We found that the ice water content has little variations over the NAM, NAF, IND, and WNP as compared to their macrophysical properties and thus give an impression that the regional differences in dynamics and thermodynamics properties primarily cause changes in the cloud frequency or coverage and only secondary in the cloud ice properties. The background atmospheric dynamics using wind and relative humidity from the ERA-Interim reanalysis data have also been investigated which helps in understanding the variability of the cloud properties over the different monsoon regions.

  4. On the link between extreme floods and excess monsoon epochs in South Asia

    Energy Technology Data Exchange (ETDEWEB)

    Kale, Vishwas [University of Pune, Department of Geography, Pune (India)

    2012-09-15

    This paper provides a synoptic view of extreme monsoon floods on all the nine large rivers of South Asia and their association with the excess (above-normal) monsoon rainfall periods. Annual maximum flood series for 18 gauging stations spread over four countries (India, Pakistan, Bangladesh and Nepal) and long-term monsoon rainfall data were analyzed to ascertain whether the extreme floods were clustered in time and whether they coincided with multi-decade excess monsoon rainfall epochs at the basin level. Simple techniques, such as the Cramer's t-test, regression and Mann-Kendall (MK) tests and Hurst method were used to evaluate the trends and patterns of the flood and rainfall series. MK test reveals absence of any long-term tendency in all the series. However, the Cramer's t test and Hurst-Mandelbrot rescaled range statistic provide evidence that both rainfall and flood time series are persistent. Using the Cramer's t-test the excess monsoon epochs for each basin were identified. The excess monsoon periods for different basins were found to be highly asynchronous with respect to duration as well as the beginning and end. Three main conclusions readily emerge from the analyses. Extreme floods (>90th percentile) in South Asia show a tendency to cluster in time. About three-fourth of the extreme floods have occurred during the excess monsoon periods between {proportional_to}1840 and 2000 AD, implying a noteworthy link between the two. The frequency of large floods was higher during the post-1940 period in general and during three decades (1940s, 1950s and 1980s) in particular. (orig.)

  5. Realism of modelled Indian summer monsoon correlation with the tropical Indo-Pacific affects projected monsoon changes.

    Science.gov (United States)

    Li, Ziguang; Lin, Xiaopei; Cai, Wenju

    2017-07-10

    El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) tend to exert an offsetting impact on Indian summer monsoon rainfall (ISMR), with an El Niño event tending to lower, whereas a positive IOD tending to increase ISMR. Simulation of these relationships in Phase Five of the Coupled Model Intercomparison Project has not been fully assessed, nor is their impact on the response of ISMR to greenhouse warming. Here we show that the majority of models simulate an unrealistic present-day IOD-ISMR correlation due to an overly strong control by ENSO. As such, a positive IOD is associated with an ISMR reduction in the simulated present-day climate. This unrealistic present-day correlation is relevant to future ISMR projection, inducing an underestimation in the projected ISMR increase. Thus uncertainties in ISMR projection can be in part induced by present-day simulation of ENSO, the IOD, their relationship and their rainfall correlations.

  6. Evolution of the Large Scale Circulation, Cloud Structure and Regional Water Cycle Associated with the South China Sea Monsoon During May-June, 1998

    Science.gov (United States)

    Lau, William K.-M.; Li, Xiao-Fan

    2001-01-01

    In this paper, changes in the large-scale circulation, cloud structures and regional water cycle associated with the evolution of the South China Sea (SCS) monsoon in May-June 1998 were investigated using data from the Tropical Rainfall Measuring Mission (TRMM) and field data from the South China Sea Monsoon Experiment (SCSMEX). Results showed that both tropical and extratropical processes strongly influenced the onset and evolution of the SCS monsoon. Prior to the onset of the SCS monsoon, enhanced convective activities associated with the Madden and Julian Oscillation were detected over the Indian Ocean, and the SCS was under the influence of the West Pacific Anticyclone (WPA) with prevailing low level easterlies and suppressed convection. Establishment of low-level westerlies across Indo-China, following the development of a Bay of Bengal depression played an important role in building up convective available potential energy over the SCS. The onset of SCS monsoon appeared to be triggered by the equatorward penetration of extratropical frontal system, which was established over the coastal region of southern China and Taiwan in early May. Convective activities over the SCS were found to vary inversely with those over the Yangtze River Valley (YRV). Analysis of TRMM microwave and precipitation radar data revealed that during the onset phase, convection over the northern SCS consisted of squall-type rain cell embedded in meso-scale complexes similar to extratropical systems. The radar Z-factor intensity indicated that SCS clouds possessed a bimodal distribution, with a pronounced signal (less than 30dBz) at a height of 2-3 km, and another one (less than 25 dBz) at the 8-10 km level, separated by a well-defined melting level indicated by a bright band at around 5-km level. The stratiform-to-convective cloud ratio was approximately 1:1 in the pre-onset phase, but increased to 5:1 in the active phase. Regional water budget calculations indicated that during the

  7. Detecting human impacts on the flora, fauna, and summer monsoon of Pleistocene Australia

    Directory of Open Access Journals (Sweden)

    G. H. Miller

    2007-08-01

    Full Text Available The moisture balance across northern and central Australia is dominated by changes in the strength of the Australian Summer Monsoon. Lake-level records that record changes in monsoon strength on orbital timescales are most consistent with a Northern Hemisphere insolation control on monsoon strength, a result consistent with recent modeling studies. A weak Holocene monsoon relative to monsoon strength 65–60 ka, despite stronger forcing, suggests a changed monsoon regime after 60 ka. Shortly after 60 ka humans colonized Australia and all of Australia's largest mammals became extinct. Between 60 and 40 ka Australian climate was similar to present and not changing rapidly. Consequently, attention has turned toward plausible human mechanisms for the extinction, with proponents for over-hunting, ecosystem change, and introduced disease. To differentiate between these options we utilize isotopic tracers of diet preserved in eggshells of two large, flightless birds to track the status of ecosystems before and after human colonization. More than 800 dated eggshells of the Australian emu (Dromaius novaehollandiae, an opportunistic, dominantly herbivorous feeder, provide a 140-kyr dietary reconstruction that reveals unprecedented reduction in the bird's food resources about 50 ka, coeval in three distant regions. These data suggest a tree/shrub savannah with occasionally rich grasslands was converted abruptly to the modern desert scrub. The diet of the heavier, extinct Genyornis newtoni, derived from >550 dated eggshells, was more restricted than in co-existing Dromaius, implying a more specialized feeding strategy. We suggest that generalist feeders, such as Dromaius, were able to adapt to a changed vegetation regime, whereas more specialized feeders, such as Genyornis, became extinct. We speculate that ecosystem collapse across arid and semi-arid zones was a consequence of systematic burning by early humans

  8. Interaction of Convective Organization and Monsoon Precipitation, Atmosphere, Surface and Sea (INCOMPASS)

    Science.gov (United States)

    Turner, A. G.; Bhat, G. S.; Evans, J. G.; Madan, R.; Marsham, J. H.; Martin, G.; Mitra, A. K.; Mrudula, G.; Parker, D. J.; Pattnaik, S.; Rajagopal, E. N.; Taylor, C.; Tripathi, S. N.

    2016-12-01

    INCOMPASS will build on a field and aircraft measurement campaign from the 2016 monsoon onset to better understand and predict monsoon rainfall. The monsoon supplies the majority of water in South Asia, however modelling and forecasting the monsoon from days to the season ahead is limited by large model errors that develop quickly. Likely problems lie in physical parametrizations such as convection, the boundary layer and land surface. At the same time, lack of detailed observations prevents more thorough understanding of monsoon circulation and its interaction with the land surface; a process governed by boundary layer and convective cloud dynamics. From May to July 2016, INCOMPASS used a modified BAe-146 jet aircraft operated by the UK Facility for Airborne Atmospheric Measurements (FAAM), for the first project of this scale in India. The India and UK team flew around 100 hours of science sorties from bases in northern and southern India. Flights from Lucknow in the northern plains took measurements to the west and southeast to allow sampling of the complete contrast from dry desert air to the humid environment over the north Bay of Bengal. These routes were repeated in the pre-monsoon and monsoon phases, measuring contrasting surface and boundary layer structures. In addition, flights from the southern base in Bengaluru measured contrasts from the Arabian Sea, across the intense rains of the Western Ghats mountains, over the rain shadow in southeast India and over the southern Bay of Bengal. Flight planning was performed with the aid of forecasts from a new UK Met Office 4km limited area model. INCOMPASS also installed a network of surface flux towers, as well as operating a cloud-base ceilometer and performing intensive radiosonde launches from a supersite in Kanpur. This presentation will outline preliminary results from the field campaign including new observations of the surface, boundary layer structure and atmospheric profiles together with detailed

  9. The role of potential vorticity anomalies in the Somali Jet on Indian Summer Monsoon Intraseasonal Variability

    Science.gov (United States)

    Rai, P.; Joshi, M.; Dimri, A. P.; Turner, A. G.

    2018-06-01

    The climate of the Indian subcontinent is dominated by rainfall arising from the Indian summer monsoon (ISM) during June to September. Intraseasonal variability during the monsoon is characterized by periods of heavy rainfall interspersed by drier periods, known as active and break events respectively. Understanding and predicting such events is of vital importance for forecasting human impacts such as water resources. The Somali Jet is a key regional feature of the monsoon circulation. In the present study, we find that the spatial structure of Somali Jet potential vorticity (PV) anomalies varies considerably during active and break periods. Analysis of these anomalies shows a mechanism whereby sea surface temperature (SST) anomalies propagate north/northwestwards through the Arabian Sea, caused by a positive feedback loop joining anomalies in SST, convection, modification of PV by diabatic heating and mixing in the atmospheric boundary layer, wind-stress curl, and ocean upwelling processes. The feedback mechanism is consistent with observed variability in the coupled ocean-atmosphere system on timescales of approximately 20 days. This research suggests that better understanding and prediction of monsoon intraseasonal variability in the South Asian monsoon may be gained by analysis of the day-to-day dynamical evolution of PV in the Somali Jet.

  10. On the shortening of Indian summer monsoon season in a warming scenario

    Science.gov (United States)

    Sabeerali, C. T.; Ajayamohan, R. S.

    2018-03-01

    Assessing the future projections of the length of rainy season (LRS) has paramount societal impact considering its potential to alter the seasonal mean rainfall over the Indian subcontinent. Here, we explored the projections of LRS using both historical and Representative Concentration Pathways 8.5 (RCP8.5) simulations of the Coupled Model Intercomparison Project Phase5 (CMIP5). RCP8.5 simulations project shortening of the LRS of Indian summer monsoon by altering the timing of onset and withdrawal dates. Most CMIP5 RCP8.5 model simulations indicate a faster warming rate over the western tropical Indian Ocean compared to other regions of the Indian Ocean. It is found that the pronounced western Indian Ocean warming and associated increase in convection results in warmer upper troposphere over the Indian Ocean compared to the Indian subcontinent, reducing the meridional gradient in upper tropospheric temperature (UTT) over the Asian summer monsoon (ASM) domain. The weakening of the meridional gradient in UTT induces weakening of easterly vertical wind shear over the ASM domain during first and last phase of monsoon, facilitate delayed (advanced) monsoon onset (withdrawal) dates, ensues the shortening of LRS of the Indian summer monsoon in a warming scenario.

  11. Deep learning for predicting the monsoon over the homogeneous regions of India

    Science.gov (United States)

    Saha, Moumita; Mitra, Pabitra; Nanjundiah, Ravi S.

    2017-06-01

    Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the homogeneous regions of India. An ensemble regression tree model is used for monsoon prediction using the identified climatic predictors. The proposed model provides forecast of the monsoon at a long lead time which supports the government to implement appropriate policies for the economic growth of the country. The monsoon of the central, north-east, north-west, and south-peninsular India regions are predicted with errors of 4.1%, 5.1%, 5.5%, and 6.4%, respectively. The identified predictors show high skill in predicting the regional monsoon having high variability. The proposed model is observed to be competitive with the state-of-the-art prediction models.

  12. The effect of monsoon variability on fish landing in the Sadeng Fishing Port of Yogyakarta, Indonesia

    Science.gov (United States)

    Subarna, D.

    2018-03-01

    The volume of landing fish of the Sadeng Fishing Port within certain months showed an increase from year to year, especially during June, July and August (JJA). While in other months the fish production was low. The purpose of this research was to understand the influence of monsoon variability on fish landing in the Sadeng Fishing Port. Data were analyzed descriptively as spatial and temporal catch. Data were namely catch fish production collected from fishing port, while satellite and HYCOM model during 2011–2012 period were selected. The wind data, sea surface temperature (SST) and chlorophyll-a were analyzed from ASCAT and MODIS sensors during the Southeast Monsoon. The result showed the wind from the southeasterly provide wind stress at sea level and caused Ekman Transport to move away water mass from the sea shore. The lost water mass in the ocean surface was replaced by cold water from deeper layer which was rich in nutrients. The distribution of chlorophyll-a during the Southeast Monsoon was relatively higher in the southern coast of Java than during the Northwest monsoon. The SST showed approximately 25.3 °C. The abundance of nutrients indicated by the distribution of chlorophyll-a around the coast during the Southeast Monsoon, will enhance the arrival of larger fish. Thus, it can be understood that during June, July, and August the catch production is higher than the other months.

  13. Is the negative IOD during 2016 the reason for monsoon failure over southwest peninsular India?

    Science.gov (United States)

    Sreelekha, P. N.; Babu, C. A.

    2018-01-01

    The study investigates the mechanism responsible for the deficit rainfall over southwest peninsular India during the 2016 monsoon season. Analysis shows that the large-scale variation in circulation pattern due to the strong, negative Indian Ocean Dipole phenomenon was the reason for the deficit rainfall. Significant reduction in the number of northward-propagating monsoon-organized convections together with fast propagation over the southwest peninsular India resulted in reduction in rainfall. On the other hand, their persistence for longer time over the central part of India resulted in normal rainfall. It was found that the strong convection over the eastern equatorial Indian Ocean creates strong convergence over that region. The combined effect of the sinking due to the well-developed Walker circulation originated over the eastern equatorial Indian Ocean and the descending limb of the monsoon Hadley cell caused strong subsidence over the western equatorial Indian Ocean. The tail of this large-scale sinking extended up to the southern parts of India. This hinders formation of monsoon-organized convections leading to a large deficiency of rainfall during monsoon 2016 over the southwest peninsular India.

  14. Radiative effects of black carbon aerosols on Indian monsoon: a study using WRF-Chem model

    Science.gov (United States)

    Soni, Pramod; Tripathi, Sachchida Nand; Srivastava, Rajesh

    2018-04-01

    The Weather Research and Forecasting model with Chemistry (WRF-Chem) is utilized to examine the radiative effects of black carbon (BC) aerosols on the Indian monsoon, for the year 2010. Five ensemble simulations with different initial conditions (1st to 5th December, 2009) were performed and simulation results between 1st January, 2010 to 31st December, 2010 were used for analysis. Most of the BC which stays near the surface during the pre-monsoon season gets transported to higher altitudes with the northward migration of the Inter Tropical Convergence Zone (ITCZ) during the monsoon season. In both the seasons, strong negative SW anomalies are present at the surface along with positive anomalies in the atmosphere, which results in the surface cooling and lower tropospheric heating, respectively. During the pre-monsoon season, lower troposphere heating causes increased convection and enhanced meridional wind circulation, bringing moist air from Indian Ocean and Bay of Bengal to the North-East India, leading to increased rainfall there. However, during the monsoon season, along with cooling over the land regions, a warming over the Bay of Bengal is simulated. This differential heating results in an increased westerly moisture flux anomaly over central India, leading to increased rainfall over northern parts of India but decreased rainfall over southern parts. Decreased rainfall over southern India is also substantiated by the presence of increased evaporation over Bay of Bengal and decrease over land regions.

  15. Decoupling of monsoon activity across the northern and southern Indo-Pacific during the Late Glacial

    Science.gov (United States)

    Denniston, R. F.; Asmerom, Y.; Polyak, V. J.; Wanamaker, A. D.; Ummenhofer, C. C.; Humphreys, W. F.; Cugley, J.; Woods, D.; Lucker, S.

    2017-11-01

    Recent studies of stalagmites from the Southern Hemisphere tropics of Indonesia reveal two shifts in monsoon activity not apparent in records from the Northern Hemisphere sectors of the Austral-Asian monsoon system: an interval of enhanced rainfall at ∼19 ka, immediately prior to Heinrich Stadial 1, and a sharp increase in precipitation at ∼9 ka. Determining whether these events are site-specific or regional is important for understanding the full range of sensitivities of the Austral-Asian monsoon. We present a discontinuous 40 kyr carbon isotope record of stalagmites from two caves in the Kimberley region of the north-central Australian tropics. Heinrich stadials are represented by pronounced negative carbon isotopic anomalies, indicative of enhanced rainfall associated with a southward shift of the intertropical convergence zone and consistent with hydroclimatic changes observed across Asia and the Indo-Pacific. Between 20 and 8 ka, however, the Kimberley stalagmites, like the Indonesian record, reveal decoupling of monsoon behavior from Southeast Asia, including the early deglacial wet period (which we term the Late Glacial Pluvial) and the abrupt strengthening of early Holocene monsoon rainfall.

  16. Simulation of monsoon intraseasonal variability in NCEP CFSv2 and its role on systematic bias

    Science.gov (United States)

    Goswami, Bidyut B.; Deshpande, Medha; Mukhopadhyay, P.; Saha, Subodh K.; Rao, Suryachandra A.; Murthugudde, Raghu; Goswami, B. N.

    2014-11-01

    We have evaluated the simulation of Indian summer monsoon and its intraseasonal oscillations in the National Centers for Environmental Prediction climate forecast system model version 2 (CFSv2). The dry bias over the Indian landmass in the mean monsoon rainfall is one of the major concerns. In spite of this dry bias, CFSv2 shows a reasonable northward propagation of convection at intraseasonal (30-60 day) time scale. In order to document and understand this dry bias over the Indian landmass in CFSv2 simulations, a two pronged investigation is carried out on the two major facets of Indian summer monsoon: one, the air-sea interactions and two, the large scale vertical heating structure in the model. Our analysis shows a possible bias in the co-evolution of convection and sea surface temperature in CFSv2 over the equatorial Indian Ocean. It is also found that the simulated large scale vertical heat source (Q1) and moisture sink (Q2) over the Indian region are biased relative to observational estimates. Finally, this study provides a possible explanation for the dry precipitation bias over the Indian landmass in the simulated mean monsoon on the basis of the biases associated with the simulated ocean-atmospheric processes and the vertical heating structure. This study also throws some light on the puzzle of CFSv2 exhibiting a reasonable northward propagation at the intraseasonal time scale (30-60 day) despite a drier monsoon over the Indian land mass.

  17. Changes of extreme precipitation and nonlinear influence of climate variables over monsoon region in China

    KAUST Repository

    Gao, Tao

    2017-07-19

    The El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO) and Pacific decadal oscillation (PDO) are well understood to be major drivers for the variability of precipitation extremes over monsoon regions in China (MRC). However, research on monsoon extremes in China and their associations with climate variables is limited. In this study, we examine the space-time variations of extreme precipitation across the MRC, and assess the time-varying influences of the climate drivers using Bayesian dynamic linear regression and their combined nonlinear effects through fitting generalized additive models. Results suggest that the central-east and south China is dominated by less frequent but more intense precipitation. Extreme rainfalls show significant positive trends, coupled with a significant decline of dry spells, indicating an increasing chance of occurrence of flood-induced disasters in the MRC during 1960–2014. Majority of the regional indices display some abrupt shifts during the 1990s. The influences of climate variables on monsoon extremes exhibit distinct interannual or interdecadal variations. IOD, ENSO and AMO have strong impacts on monsoon and extreme precipitation, especially during the 1990s, which is generally consistent with the abrupt shifts in precipitation regimes around this period. Moreover, ENSO mainly affects moderate rainfalls and dry spells, while IOD has a more significant impact on precipitation extremes. These findings could be helpful for improving the forecasting of monsoon extremes in China and the evaluations of climate models.

  18. The role of potential vorticity anomalies in the Somali Jet on Indian Summer Monsoon Intraseasonal Variability

    Science.gov (United States)

    Rai, P.; Joshi, M.; Dimri, A. P.; Turner, A. G.

    2017-08-01

    The climate of the Indian subcontinent is dominated by rainfall arising from the Indian summer monsoon (ISM) during June to September. Intraseasonal variability during the monsoon is characterized by periods of heavy rainfall interspersed by drier periods, known as active and break events respectively. Understanding and predicting such events is of vital importance for forecasting human impacts such as water resources. The Somali Jet is a key regional feature of the monsoon circulation. In the present study, we find that the spatial structure of Somali Jet potential vorticity (PV) anomalies varies considerably during active and break periods. Analysis of these anomalies shows a mechanism whereby sea surface temperature (SST) anomalies propagate north/northwestwards through the Arabian Sea, caused by a positive feedback loop joining anomalies in SST, convection, modification of PV by diabatic heating and mixing in the atmospheric boundary layer, wind-stress curl, and ocean upwelling processes. The feedback mechanism is consistent with observed variability in the coupled ocean-atmosphere system on timescales of approximately 20 days. This research suggests that better understanding and prediction of monsoon intraseasonal variability in the South Asian monsoon may be gained by analysis of the day-to-day dynamical evolution of PV in the Somali Jet.

  19. Asian Summer Monsoon Rainfall associated with ENSO and its Predictability

    Science.gov (United States)

    Shin, C. S.; Huang, B.; Zhu, J.; Marx, L.; Kinter, J. L.; Shukla, J.

    2015-12-01

    The leading modes of the Asian summer monsoon (ASM) rainfall variability and their seasonal predictability are investigated using the CFSv2 hindcasts initialized from multiple ocean analyses over the period of 1979-2008 and observation-based analyses. It is shown that the two leading empirical orthogonal function (EOF) modes of the observed ASM rainfall anomalies, which together account for about 34% of total variance, largely correspond to the ASM responses to the ENSO influences during the summers of the developing and decaying years of a Pacific anomalous event, respectively. These two ASM modes are then designated as the contemporary and delayed ENSO responses, respectively. It is demonstrated that the CFSv2 is capable of predicting these two dominant ASM modes up to the lead of 5 months. More importantly, the predictability of the ASM rainfall are much higher with respect to the delayed ENSO mode than the contemporary one, with the predicted principal component time series of the former maintaining high correlation skill and small ensemble spread with all lead months whereas the latter shows significant degradation in both measures with lead-time. A composite analysis for the ASM rainfall anomalies of all warm ENSO events in this period substantiates the finding that the ASM is more predictable following an ENSO event. The enhanced predictability mainly comes from the evolution of the warm SST anomalies over the Indian Ocean in the spring of the ENSO maturing phases and the persistence of the anomalous high sea surface pressure over the western Pacific in the subsequent summer, which the hindcasts are able to capture reasonably well. The results also show that the ensemble initialization with multiple ocean analyses improves the CFSv2's prediction skill of both ENSO and ASM rainfall. In fact, the skills of the ensemble mean hindcasts initialized from the four different ocean analyses are always equivalent to the best ones initialized from any individual ocean

  20. Modelling the distribution of domestic ducks in Monsoon Asia

    Science.gov (United States)

    Van Bockel, Thomas P.; Prosser, Diann; Franceschini, Gianluca; Biradar, Chandra; Wint, William; Robinson, Tim; Gilbert, Marius

    2011-01-01

    Domestic ducks are considered to be an important reservoir of highly pathogenic avian influenza (HPAI), as shown by a number of geospatial studies in which they have been identified as a significant risk factor associated with disease presence. Despite their importance in HPAI epidemiology, their large-scale distribution in Monsoon Asia is poorly understood. In this study, we created a spatial database of domestic duck census data in Asia and used it to train statistical distribution models for domestic duck distributions at a spatial resolution of 1km. The method was based on a modelling framework used by the Food and Agriculture Organisation to produce the Gridded Livestock of the World (GLW) database, and relies on stratified regression models between domestic duck densities and a set of agro-ecological explanatory variables. We evaluated different ways of stratifying the analysis and of combining the prediction to optimize the goodness of fit of the predictions. We found that domestic duck density could be predicted with reasonable accuracy (mean RMSE and correlation coefficient between log-transformed observed and predicted densities being 0.58 and 0.80, respectively), using a stratification based on livestock production systems. We tested the use of artificially degraded data on duck distributions in Thailand and Vietnam as training data, and compared the modelled outputs with the original high-resolution data. This showed, for these two countries at least, that these approaches could be used to accurately disaggregate provincial level (administrative level 1) statistical data to provide high resolution model distributions.

  1. Soil 137Cs background values in monsoon region of china

    International Nuclear Information System (INIS)

    Zhang Mingli; Yang Hao; Wang Xiaolei; Wang Yihong; Xu Congan; Yang Jiudong; Rong Jing

    2009-01-01

    Land degradation,, which is resulted from the soil erosion, is one of the major environmental problems. It severely affects the food supplies, environmental safety and the sustainable development in China. Some areas in the monsoon region are suffering from the acute soil erosion. To find out the degree of soil erosion, the proven technique of 137 Cs tracer is definitely one of the best methods, and the key is to ascertain the accuracy of soil 137 Cs background value. The distributions of 137 Cs were explored in soil profiles by detecting the 137 Cs of soil cores from the Yimeng mountain area in Shandong Province, hills in the southern area of Jiangsu Province and Dianchi catchment in Yunnan Province, respectively. We found that the depth of 137 Cs distribution is not the same in the soils of various areas. But the 137 Cs activity shows an exponential distribution in the uncultivated soil and demonstrates a strong correlation with the soil depth, while the 137 Cs activity proves uniform in the soil plowing layer of the cultivated land. The study shows the 137 Cs background values of three areas: 1737.1 Bq/m 2 in Yimeng mountain area, 1847.6 Bq/m 2 in southern area of hills in Jiangsu, 918.0 Bq/m 2 in Dianchi catchment. The certainty of 137 Cs background value can technically support the use of 137 Cs technique to study the spatial pattern of soil erosion, deposition and the land degradation, which provides the support for the sustainable utilization of soil resource, the assessment of economical benefit and loss and the evaluation of water and soil conservation measures. (authors)

  2. A strengthened East Asian Summer Monsoon during Pliocene warmth: Evidence from 'red clay' sediments at Pianguan, northern China

    Science.gov (United States)

    Yang, Shiling; Ding, Zhongli; Feng, Shaohua; Jiang, Wenying; Huang, Xiaofang; Guo, Licheng

    2018-04-01

    The Pliocene epoch (5.3-2.6 Ma) is the most recent geological interval in which atmospheric CO2 levels were similar to those of the present day (∼400 ppmv). This epoch is therefore considered to be the best ancient analog for predicting a future anthropogenic greenhouse world. In order to determine the response of the East Asian Summer Monsoon (EASM) rainbelt during Pliocene warmth, a 71.9 m-thick aeolian 'red clay' sequence at Pianguan was investigated. Rock magnetic experiments suggest that magnetite of pseudo-single domain size is the dominant remanence carrier in the 'red clay' sequence. Magnetostratigraphic data, constrained by lithostratigraphy, show that the polarity zones of the 'red clay' section correlate with those between subchrons C2An.2r and C3An.2n of the geomagnetic polarity time scale (GPTS), yielding an age range of 6.9-2.9 Ma. The 'red clay' deposits exhibit enhanced weathering intensity over two time intervals, namely 5.23-4.3 Ma and 3.7-2.9 Ma, as evidenced by their well-developed pedogenic characteristics, as well as their high free to total Fe2O3 ratios and high redness (a∗) values, which in turn indicate an increased summer monsoon intensity during most of the Pliocene. Furthermore, the pedogenic characteristics of the well-weathered Pliocene soils were compared with those of paleosol unit S5 (one of the best-developed soil units found in Pleistocene loess) from the Yulin, Luochuan and Lantian sections, which constitute a north-south transect across the Chinese Loess Plateau (CLP). The Pliocene soils at Pianguan show a pedogenic development similar to the S5 (∼0.5 Ma) at Luochuan in the central Plateau, which is located some 3.7° latitude south of Pianguan, but this development is much stronger than that observed at Yulin in the north, and weaker than that seen at Lantian in the south. This may imply a more northerly penetration (∼400 km) of the monsoon rainbelt during Pliocene warmth compared with the Pleistocene interglacial

  3. Widespread Lake Highstands in the Southernmost Andean Altiplano during Heinrich Event 1: Implications for the South American Summer Monsoon

    Science.gov (United States)

    Chen, C. Y.; McGee, D.; Quade, J.

    2014-12-01

    Speleothem-based oxygen isotope records provide strong evidence of anti-phased behavior of the northern and southern hemisphere summer monsoons during Heinrich events, but we lack rigorous constraints on the amount of wetting or drying occurring in monsoon regions. Studies centered on shoreline deposits of closed-basin lakes are well suited for establishing such quantitative controls on water balance changes by providing unequivocal evidence of lake volume variations. Here we present new dating constraints on the highstands of several high-altitude (3800-4350 m) paleolakes in the southern Andean Altiplano, an outlying arid region of the Atacama Desert stretching across the Chilean-Bolivian-Argentinian border east of the Andes (20-25°S). These lakes once occupied the closed basins where only phreatic playas, dry salars, and shallow ponds exist today. Initial U-Th dating of massive shoreline tufas reveals that these deposits are dateable to within ±150 to 300 yrs due to high U concentrations and low initial Th content (as indicated by high 230Th/232Th). Our U-Th and 14C dates show that lake highstands predominantly occur between 18.5 and 14.5 kyrs BP, coinciding with Heinrich Event 1 (HE1) and the expansion of other nearby lakes, such as Lake Titicaca. Because of their (1) location at the modern-day southwestern edge of the summer monsoon, (2) intact shoreline preservation, and (3) precise age control, these lakes may uniquely enable us to reconstruct the evolution of water balance (P-E) changes associated with HE1. Hydrologic modeling constrained by temperature estimates provided by local glacial records is used to provide bounds for past precipitation changes. We also examine North Atlantic cooling as the mechanism for these changes by comparing a compilation of S. American lake level records with various hosing experiments and transient climate simulations at HE1. Our results lend us confidence in expanding our U-Th work to other shoreline tufas in the

  4. Delivery of halogenated very short-lived substances from the west Indian Ocean to the stratosphere during the Asian summer monsoon

    Directory of Open Access Journals (Sweden)

    A. Fiehn

    2017-06-01

    Full Text Available Halogenated very short-lived substances (VSLSs are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical west Indian Ocean in July and August 2014, we measured the VSLSs, methyl iodide (CH3I and for the first time bromoform (CHBr3 and dibromomethane (CH2Br2, in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian particle dispersion model FLEXPART with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during the Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the west Indian Ocean surface to the stratosphere for July 2000–2015. We found that the west Indian Ocean is a strong source for CHBr3 (910 pmol m−2 h−1, very strong source for CH2Br2 (930 pmol m−2 h−1, and an average source for CH3I (460 pmol m−2 h−1. The atmospheric transport from the tropical west Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime, convection above the Indian Ocean lifts oceanic air masses and VSLSs towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLSs towards India and the Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2. The entrainment of CHBr3 and CH3I from the west Indian Ocean to the stratosphere during the

  5. Variations of Indian monsoon precipitation during the last 32 kyr reflected in the surface hydrography of the Western Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Govil, P.; Naidu, P.D.

    sub-continent. To increase the accuracy of monsoon forecasting one need to understand the variability of monsoon rainfall at different time scales from decadal, centennial and millennial time scales. Several researchers have studied...

  6. Variability of wind stress and currents at selected locations over the north Indian Ocean during 1977 and 1979 summer monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    Gopalakrishna, V.V.; Sadhuram, Y.; RameshBabu, V.; Rao, M.V.

    Intra-seasonal variability of wind stress, wind stress curl and currents at different locations over the northern Indian Ocean during two contrasting monsoon seasons has been investigated making use of the time series data collected during MONSOON...

  7. On the relationship between Indian monsoon withdrawal and Iran's fall precipitation onset

    Science.gov (United States)

    Babaeian, Iman; Rezazadeh, Parviz

    2017-09-01

    Indian monsoon is the most prominent of the world's monsoon systems which primarily affects synoptic patterns of India and adjacent countries such as Iran in interaction with large-scale weather systems. In this article, the relationship between the withdrawal date of the Indian monsoon and the onset of fall precipitation in Iran has been studied. Data included annual time series of withdrawal dates of the Indian monsoon prepared by the Indian Institute for Tropical Meteorology, and time series of the first date of 25 mm accumulated precipitation over Iran's synoptic weather stations in a 10-day period which is the basis for the cultivation date. Both time series were considered in Julian calendar with the starting date on August 1. The studied period is 1960-2014 which covers 55 years of data from 36 meteorological stations in Iran. By classifying the withdrawal dates of the Indian monsoon in three stages of late, normal, and early withdrawals, its relation with the onset of fall precipitation in western, southwestern, southern, eastern, central, and northern regions of Iran was studied. Results demonstrated that in four out of the six mentioned regions, the late withdrawal of the Indian monsoon postpones the onset of fall precipitation over Iran. No significant relation was found between the onset of fall precipitation in central region of Iran and the monsoon's withdrawal date. In the western, southwestern, southern, and eastern regions of Iran, the late monsoon delays the onset of fall's precipitation; while in the south Caspian Sea coastal area, it causes the early onset of autumnal precipitation. The lag in onset of fall precipitation in Iran which is coordinated with the late withdrawal of monsoon is accompanied with prolonged subtropical high settling over Iran's plateau that prevents the southward movement of polar jet frontal systems. Such conditions enhance northerly wind currents over the Caspian Sea which, in turn, increase the precipitation in Caspian

  8. Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

    Directory of Open Access Journals (Sweden)

    F. Ploeger

    2017-06-01

    Full Text Available Pollution transport from the surface to the stratosphere within the Asian monsoon circulation may cause harmful effects on stratospheric chemistry and climate. Here, we investigate air mass transport from the monsoon anticyclone into the stratosphere using a Lagrangian chemistry transport model. We show how two main transport pathways from the anticyclone emerge: (i into the tropical stratosphere (tropical pipe, and (ii into the Northern Hemisphere (NH extratropical lower stratosphere. Maximum anticyclone air mass fractions reach around 5 % in the tropical pipe and 15 % in the extratropical lowermost stratosphere over the course of a year. The anticyclone air mass fraction correlates well with satellite hydrogen cyanide (HCN and carbon monoxide (CO observations, confirming that pollution is transported deep into the tropical stratosphere from the Asian monsoon anticyclone. Cross-tropopause transport occurs in a vertical chimney, but with the pollutants transported quasi-horizontally along isentropes above the tropopause into the tropics and NH.

  9. Variability of mixed layer depth in the northern Indian Ocean during 1977 and 1979 summer monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    Gopalakrishna, V.V.; Sadhuram, Y.; RameshBabu, V.

    quantitatively making use of time-series data collected during MONSOON-77 and MONEX-79 programmes. After the onset of monsoon (June/July 1977) over the central Arabian Sea, wind stress together with possible sinking processes on account of negative wind stress...

  10. Different orbital rhythms in the Asian summer monsoon records from North and South China during the Pleistocene

    NARCIS (Netherlands)

    Ao, H.; Dekkers, M.J.; Xiao, G.; Yang, X.; Qin, L.; Liu, X; Qiang, X.; Chang, H.; Zhao, H.

    2012-01-01

    Here we construct a Pleistocene astronomical timescale for the Nihewan fluvio–lacustrine sediments (North China), via tuning a stacked summer monsoon index generated from grain size and low-field magnetic susceptibility records to orbital obliquity and precession. Combining the summer monsoon

  11. Dynamics of size-fractionated phytoplankton biomass in a monsoonal estuary: Patterns and drivers for seasonal and spatial variability

    Science.gov (United States)

    Rajaneesh, K. M.; Mitbavkar, Smita; Anil, Arga Chandrashekar

    2018-07-01

    Phytoplankton size-fractionated biomass is an important determinant of the type of food web functioning in aquatic ecosystems. Knowledge about the effect of seasonal salinity gradient on the size-fractionated biomass dynamics is still lacking, especially in tropical estuaries experiencing monsoon. The phytoplankton size-fractionated chlorophyll a biomass (>3 μm and 3 μm size-fraction was the major contributor to the total phytoplankton chlorophyll a biomass with the ephemeral dominance of biomass concentration of both size-fractions showed signs of recovery with increasing salinity downstream towards the end of the monsoon season. In contrast, the chlorophyll a biomass response was size-dependent during the non-monsoon seasons with the sporadic dominance (>50%) of biomass during high water temperature episodes from downstream to middle estuary during pre-monsoon and at low salinity and high nutrient conditions upstream during post-monsoon. These conditions also influenced the picophytoplankton community structure with picoeukaryotes dominating during the pre-monsoon, phycoerythrin containing Synechococcus during the monsoon and phycocyanin containing Synechococcus during the post-monsoon. This study highlights switching over of dominance in size-fractionated phytoplankton chlorophyll a biomass at intra, inter-seasonal and spatial scales which will likely govern the estuarine trophodynamics.

  12. Evaporation-precipitation changes in the eastern Arabian Sea for the last 68 ka: Implications on monsoon variability

    Digital Repository Service at National Institute of Oceanography (India)

    Govil, P.; Naidu, P.D.

    from MIS 4 to MIS 3 was marked with a conspicuous shift from higher to lower delta sup(18)Ow values, which reflects a decrease in the evaporation precipitation budget in the EAS, perhaps due to the strengthening of southwest monsoon. Monsoon...

  13. Role of the Indian Ocean on the southern oscillation, atmospheric circulation indices and monsoon rainfall over India

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Wells, N.C.

    Oscillation and ENSO is also examined. Indian monsoon rainfall is strongly and positively correlated with the SST of November month (0.77; statistically significant at 99% level) of the preceding calendar year. Monsoon indices (M1, U200) are strongly...

  14. Summer cooling in the east central Arabian Sea - a process of dynamic response to the southwest monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    RameshBabu, V.; Sastry, J.S.

    The cooling of the east central Arabian Sea during summer monsoon season is examined using data sets of MONEX '79 and MONSOON '77 programmes. These studies have revealed that downward transfer of heat due to the mixing of warm surface and cold sub...

  15. Model Interpretation of Climate Signals: Application to the Asian Monsoon Climate

    Science.gov (United States)

    Lau, William K. M.

    2002-01-01

    This is an invited review paper intended to be published as a Chapter in a book entitled "The Global Climate System: Patterns, Processes and Teleconnections" Cambridge University Press. The author begins with an introduction followed by a primer of climate models, including a description of various modeling strategies and methodologies used for climate diagnostics and predictability studies. Results from the CLIVAR Monsoon Model Intercomparison Project (MMIP) were used to illustrate the application of the strategies to modeling the Asian monsoon. It is shown that state-of-the art atmospheric GCMs have reasonable capability in simulating the seasonal mean large scale monsoon circulation, and response to El Nino. However, most models fail to capture the climatological as well as interannual anomalies of regional scale features of the Asian monsoon. These include in general over-estimating the intensity and/or misplacing the locations of the monsoon convection over the Bay of Bengal, and the zones of heavy rainfall near steep topography of the Indian subcontinent, Indonesia, and Indo-China and the Philippines. The intensity of convection in the equatorial Indian Ocean is generally weaker in models compared to observations. Most important, an endemic problem in all models is the weakness and the lack of definition of the Mei-yu rainbelt of the East Asia, in particular the part of the Mei-yu rainbelt over the East China Sea and southern Japan are under-represented. All models seem to possess certain amount of intraseasonal variability, but the monsoon transitions, such as the onset and breaks are less defined compared with the observed. Evidences are provided that a better simulation of the annual cycle and intraseasonal variability is a pre-requisite for better simulation and better prediction of interannual anomalies.

  16. Characteristics of monsoon inversions over the Arabian Sea observed by satellite sounder and reanalysis data sets

    Directory of Open Access Journals (Sweden)

    S. Dwivedi

    2016-04-01

    Full Text Available Monsoon inversion (MI over the Arabian Sea (AS is one of the important characteristics associated with the monsoon activity over Indian region during summer monsoon season. In the present study, we have used 5 years (2009–2013 of temperature and water vapour measurement data obtained from satellite sounder instrument, an Infrared Atmospheric Sounding Interferometer (IASI onboard MetOp satellite, in addition to ERA-Interim data, to study their characteristics. The lower atmospheric data over the AS have been examined first to identify the areas where MIs are predominant and occur with higher strength. Based on this information, a detailed study has been made to investigate their characteristics separately in the eastern AS (EAS and western AS (WAS to examine their contrasting features. The initiation and dissipation times of MIs, their percentage occurrence, strength, etc., has been examined using the huge database. The relation with monsoon activity (rainfall over Indian region during normal and poor monsoon years is also studied. WAS ΔT values are  ∼  2 K less than those over the EAS, ΔT being the temperature difference between 950 and 850 hPa. A much larger contrast between the WAS and EAS in ΔT is noticed in ERA-Interim data set vis-à-vis those observed by satellites. The possibility of detecting MI from another parameter, refractivity N, obtained directly from another satellite constellation of GPS Radio Occultation (RO (COSMIC, has also been examined. MI detected from IASI and Atmospheric Infrared Sounder (AIRS onboard the NOAA satellite have been compared to see how far the two data sets can be combined to study the MI characteristics. We suggest MI could also be included as one of the semipermanent features of southwest monsoon along with the presently accepted six parameters.

  17. From monsoon to marine productivity in the Arabian Sea: insights from glacial and interglacial climates

    Science.gov (United States)

    Le Mézo, Priscilla; Beaufort, Luc; Bopp, Laurent; Braconnot, Pascale; Kageyama, Masa

    2017-07-01

    The current-climate Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from palaeo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for eight contrasted climates from the last glacial-interglacial cycle. We show that there is no straightforward correlation between boreal summer productivity of the Arabian Sea and summer monsoon strength across the different simulated climates. Locally, productivity is fuelled by nutrient supply driven by Ekman dynamics. Upward transport of nutrients is modulated by a combination of alongshore wind stress intensity, which drives coastal upwelling, and by a positive wind stress curl to the west of the jet axis resulting in upward Ekman pumping. To the east of the jet axis there is however a strong downward Ekman pumping due to a negative wind stress curl. Consequently, changes in coastal alongshore stress and/or curl depend on both the jet intensity and position. The jet position is constrained by the Indian summer monsoon pattern, which in turn is influenced by the astronomical parameters and the ice sheet cover. The astronomical parameters are indeed shown to impact wind stress intensity in the Arabian Sea through large-scale changes in the meridional gradient of upper-tropospheric temperature. However, both the astronomical parameters and the ice sheets affect the pattern of wind stress curl through the position of the sea level depression barycentre over the monsoon region (20-150° W, 30° S-60° N). The combined changes in monsoon intensity and pattern lead to some higher glacial productivity during the summer season, in agreement with some palaeo-productivity reconstructions.

  18. Impacts of interannual variation of the East Asian winter monsoon on aerosol concentrations over eastern China

    Science.gov (United States)

    Zhu, J.; Liao, H.; Li, J.; Feng, J.

    2012-04-01

    China has been experiencing increased concentrations of aerosols, commonly attributed to the large increases in emissions associated with the rapid economic development. We apply a global three-dimensional Goddard Earth Observing System chemical transport model (GEOS-Chem) driven by the NASA/GEOS-4 assimilated meteorological data to quantify the impacts of East Asian winter monsoon (EAWM) on the aerosol concentrations over eastern China. We found that the simulated aerosol concentrations over eastern China have strong interannual variation and negative correlations with the strength of EAWM. Model results show that, accounting for sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols, the winter surface layer PM2.5 concentration averaged over eastern China (110°-125°E, 20°-45°N) can be 17.97% (4.78 µg m-3) higher in the weak monsoon years than that in the strong monsoon years. Regionally, the weakening of EAWM is shown to be able to increase PM2.5 concentration in the middle and lower reach of the Yellow River by 12 µg m-3. This point indicates that climate change associated with variation of EAWM has an essential influence on worsening air quality over eastern China. The possible causes of higher aerosol concentrations in the weak monsoon years may be attributed to the changing in wind fields and planetary boundary layer height between the weak and strong monsoon years. Sensitivity studies are performed to identify the role of chemical reaction associated with temperature and humidity on the higher aerosol concentrations in the weak monsoon years over eastern China.

  19. ENSO, IOD and Indian Summer Monsoon in NCEP climate forecast system

    Energy Technology Data Exchange (ETDEWEB)

    Pokhrel, Samir; Chaudhari, H.S.; Saha, Subodh K.; Dhakate, Ashish; Yadav, R.K.; Salunke, Kiran; Mahapatra, S.; Rao, Suryachandra A. [Indian Institute of Tropical Meteorology, Pashan, Pune (India)

    2012-11-15

    El Nino-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Indian Summer Monsoon rainfall features are explored statistically and dynamically using National Centers for Environment Prediction (NCEP) Climate Forecast System (CFSv1) freerun in relation to observations. The 100 years of freerun provides a sufficiently long homogeneous data set to find out the mean state, periodicity, coherence among these climatic events and also the influence of ENSO and IOD on the Indian monsoon. Differences in the occurrence of seasonal precipitation between the observations and CFS freerun are examined as a coupled ocean-atmosphere system. CFS simulated ENSO and IOD patterns and their associated tropical Walker and regional Hadley circulation in pure ENSO (PEN), pure IOD (PIO) and coexisting ENSO-IOD (PEI) events have some similarity to the observations. PEN composites are much closer to the observation as compared to PIO and PEI composites, which suggest a better ENSO prediction and its associated teleconnections as compared to IOD and combined phenomenon. Similar to the observation, the model simulation also show that the decrease in the Indian summer monsoon rainfall during ENSO phases is associated with a descending motion of anomalous Walker circulation and the increase in the Indian summer monsoon rainfall during IOD phase is associated with the ascending branch of anomalous regional Hadley circulation. During co-existing ENSO and IOD years, however, the fate of Indian summer monsoon is dictated by the combined influence of both of them. The shift in the anomalous descending and ascending branches of the Walker and Hadley circulation may be somewhat attributed to the cold (warm) bias over eastern (western) equatorial Indian Ocean basin, respectively in the model. This study will be useful for identifying some of the limitations of the CFS model and consequently it will be helpful in improving the model to unravel the realistic coupled ocean-atmosphere interactions

  20. The West African monsoon: Contribution of the AMMA multidisciplinary programme to the study of a regional climate system.

    Science.gov (United States)

    Lebel, T.; Janicot, S.; Redelsperger, J. L.; Parker, D. J.; Thorncroft, C. D.

    2015-12-01

    The AMMA international project aims at improving our knowledge and understanding of the West African monsoon and its variability with an emphasis on daily-to-interannual timescales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on water resources, health and food security for West African nations. The West African monsoon (WAM) has a distinctive annual cycle in rainfall that remains a challenge to understand and predict. The location of peak rainfall, which resides in the Northern Hemisphere throughout the year, moves from the ocean to the land in boreal spring. Around the end of June there is a rapid shift in the location of peak rainfall between the coast and around 10°N where it remains until about the end of August. In September the peak rainfall returns equatorward at a relatively steady pace and is located over the ocean again by November. The fact that the peak rainfall migrates irregularly compared to the peak solar heating is due to the interactions that occur between the land, the atmosphere and the ocean. To gain a better understanding of this complex climate system, a large international research programme was launched in 2002, the biggest of its kind into environment and climate ever attempted in Africa. AMMA has involved a comprehensive field experiment bringing together ocean, land and atmospheric measurements, on timescales ranging from hourly and daily variability up to the changes in seasonal activity over a number of years. This presentation will focus on the description of the field programme and its accomplishments, and address some key questions that have been recently identified to form the core of AMMA-Phase 2.

  1. ANALYSIS OF LOW-FREQUENCY OSCILLATIONS FOR THE SOUTH CHINA SEA SUMMER MONSOON IN 1998

    Institute of Scientific and Technical Information of China (English)

    徐国强; 朱乾根

    2003-01-01

    With NCEP/NCAR reanalysis daily data and SST for 1998, the paper investigates the features of summer monsoon low-frequency oscillation (LFO) over the South China Sea (SCS). Results show that SCS summer monsoon onset is enhanced because of its LFO. Low-frequency (LF) low-level convergence (divergence) region of SCS is in the LF positive (negative) rainfall area. LFO of the SCS region migrates from south to north in the meridian and from west to east in zonal direction. LF divergence of SCS is vertically compensating to each other between high and low level.

  2. Lower tropospheric ozone over India and its linkage to the South Asian monsoon

    Science.gov (United States)

    Lu, Xiao; Zhang, Lin; Liu, Xiong; Gao, Meng; Zhao, Yuanhong; Shao, Jingyuan

    2018-03-01

    Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks to both human health and crops, and potentially affects global ozone distribution through frequent deep convection in tropical regions. Our current understanding of the processes controlling seasonal and long-term variations in lower tropospheric ozone over this region is rather limited due to spatially and temporally sparse observations. Here we present an integrated process analysis of the seasonal cycle, interannual variability, and long-term trends of lower tropospheric ozone over India and its linkage to the South Asian monsoon using the Ozone Monitoring Instrument (OMI) satellite observations for years 2006-2014 interpreted with a global chemical transport model (GEOS-Chem) simulation for 1990-2010. OMI observed lower tropospheric ozone over India averaged for 2006-2010, showing the highest concentrations (54.1 ppbv) in the pre-summer monsoon season (May) and the lowest concentrations (40.5 ppbv) in the summer monsoon season (August). Process analyses in GEOS-Chem show that hot and dry meteorological conditions and active biomass burning together contribute to 5.8 Tg more ozone being produced in the lower troposphere in India in May than January. The onset of the summer monsoon brings ozone-unfavorable meteorological conditions and strong upward transport, which all lead to large decreases in the lower tropospheric ozone burden. Interannually, we find that both OMI and GEOS-Chem indicate strong positive correlations (r = 0.55-0.58) between ozone and surface temperature in pre-summer monsoon seasons, with larger correlations found in high NOx emission regions reflecting NOx-limited production conditions. Summer monsoon seasonal mean ozone levels are strongly controlled by monsoon strengths. Lower ozone concentrations are found in stronger monsoon seasons mainly due to less ozone net chemical production. Furthermore, model simulations over 1990-2010 estimate a mean annual trend of 0

  3. Increases in aerosol concentrations over eastern China due to the decadal-scale weakening of the East Asian summer monsoon

    Science.gov (United States)

    Zhu, Jianlei; Liao, Hong; Li, Jianping

    2012-05-01

    China has been experiencing increased concentrations of aerosols, commonly attributed to the large increases in emissions associated with the rapid economic development. We show by using a chemical transport model driven by the assimilated meteorological fields that the observed decadal-scale weakening of the East Asian summer monsoon also contributed to the increases in aerosols in China. We find that the simulated aerosol concentrations have strong negative correlations with the strength of the East Asian Summer monsoon. Accounting for sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols, the summer surface-layer PM2.5 concentration averaged over eastern China (110°-125°E, 20°-45°N) can be 17.7% higher in the weakest monsoon years than in the strongest monsoon years. The weakening of the East Asian Summer monsoon increases aerosol concentrations mainly by the changes in atmospheric circulation (the convergence of air pollutants) in eastern China.

  4. Prediction of monthly rainfall on homogeneous monsoon regions of India based on large scale circulation patterns using Genetic Programming

    Science.gov (United States)

    Kashid, Satishkumar S.; Maity, Rajib

    2012-08-01

    SummaryPrediction of Indian Summer Monsoon Rainfall (ISMR) is of vital importance for Indian economy, and it has been remained a great challenge for hydro-meteorologists due to inherent complexities in the climatic systems. The Large-scale atmospheric circulation patterns from tropical Pacific Ocean (ENSO) and those from tropical Indian Ocean (EQUINOO) are established to influence the Indian Summer Monsoon Rainfall. The information of these two large scale atmospheric circulation patterns in terms of their indices is used to model the complex relationship between Indian Summer Monsoon Rainfall and the ENSO as well as EQUINOO indices. However, extracting the signal from such large-scale indices for modeling such complex systems is significantly difficult. Rainfall predictions have been done for 'All India' as one unit, as well as for five 'homogeneous monsoon regions of India', defined by Indian Institute of Tropical Meteorology. Recent 'Artificial Intelligence' tool 'Genetic Programming' (GP) has been employed for modeling such problem. The Genetic Programming approach is found to capture the complex relationship between the monthly Indian Summer Monsoon Rainfall and large scale atmospheric circulation pattern indices - ENSO and EQUINOO. Research findings of this study indicate that GP-derived monthly rainfall forecasting models, that use large-scale atmospheric circulation information are successful in prediction of All India Summer Monsoon Rainfall with correlation coefficient as good as 0.866, which may appears attractive for such a complex system. A separate analysis is carried out for All India Summer Monsoon rainfall for India as one unit, and five homogeneous monsoon regions, based on ENSO and EQUINOO indices of months of March, April and May only, performed at end of month of May. In this case, All India Summer Monsoon Rainfall could be predicted with 0.70 as correlation coefficient with somewhat lesser Correlation Coefficient (C.C.) values for different

  5. Cloud-edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds

    Science.gov (United States)

    Kumar, Bipin; Bera, Sudarsan; Prabha, Thara V.; Grabowski, Wojceich W.

    2017-03-01

    A direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud-edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX). Evaporation at the cloud-edges initiates mixing at small scale and gradually introduces larger-scale fluctuations of the temperature, moisture, and vertical velocity due to droplet evaporation. Our focus is on early evolution of simulated fields that show intriguing similarities to the CAIPEEX cloud observations. A strong dilution at the cloud edge, accompanied by significant spatial variations of the droplet concentration, mean radius, and spectral width, are found in both the DNS and in observations. In DNS, fluctuations of the mean radius and spectral width come from the impact of small-scale turbulence on the motion and evaporation of inertial droplets. These fluctuations decrease with the increase of the volume over which DNS data are averaged, as one might expect. In cloud observations, these fluctuations also come from other processes, such as entrainment/mixing below the observation level, secondary CCN activation, or variations of CCN activation at the cloud base. Despite large differences in the spatial and temporal scales, the mixing diagram often used in entrainment/mixing studies with aircraft data is remarkably similar for both DNS and cloud observations. We argue that the similarity questions applicability of heuristic ideas based on mixing between two air parcels (that the mixing diagram is designed to properly represent) to the evolution of microphysical properties during turbulent mixing between a cloud and its environment.

  6. South American climate during the Last Glacial Maximum: Delayed onset of the South American monsoon

    Science.gov (United States)

    Cook, K. H.; Vizy, E. K.

    2006-01-01

    The climate of the Last Glacial Maximum (LGM) over South America is simulated using a regional climate model with 60-km resolution, providing a simulation that is superior to those available from global models that do not resolve the topography and regional-scale features of the South American climate realistically. LGM conditions on SST, insolation, vegetation, and reduced atmospheric CO2 on the South American climate are imposed together and individually. Remote influences are not included. Annual rainfall is 25-35% lower in the LGM than in the present day simulation throughout the Amazon basin. A primary cause is a 2-3 month delay in the onset of the rainy season, so that the dry season is about twice as long as in the present day. The delayed onset occurs because the low-level inflow from the tropical Atlantic onto the South American continent is drier than in the present day simulation due to reduced evaporation from cooler surface waters, and this slows the springtime buildup of moist static energy that is needed to initiate convection. Once the monsoon begins in the Southern Hemisphere, LGM rainfall rates are similar to those in the present day. In the Northern Hemisphere, however, rainfall is lower throughout the (shortened) rainy season. Regional-scale structure includes slight precipitation increases in the Nordeste region of Brazil and along the eastern foothills of the Andes, and a region in the center of the Amazon basin that does not experience annual drying. In the Andes Mountains, the signal is complicated, with regions of significant rainfall increases adjacent to regions with reduced precipitation.

  7. Summer monsoon onset-induced changes of autotrophic pico- and nanoplankton in the largest monsoonal estuary along the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Mohan, A.P.; Jyothibabu, R; Jagadeesan, L.; Lallu, K.R; Karnan, C.

    to the microbial food web of the northwestern Indian Ocean.Deep sea research part II. 40: 773–782. Callieri, C., E. Amicucci, R. Bertoni, and L. Voros. 1996. Fluorometric characterization of two picocyanobacteria strains from different underwater light quality.... 2014. Waning of plankton food web in the upstream region of the Cochin backwaters during the Southwest Monsoon. Indian Journal of Marine Sciences (In Press). Jyothibabu, R., N. V. Madhu, L. Jagadeesan, A. Anjusha, A. P. Mohan , N.Ullas, N. Sudheesh...

  8. Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    Science.gov (United States)

    Qian, Y.; Flanner, M.; Leung, R.; Wang, W.

    2012-04-01

    The Tibetan Plateau (TP) has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. In this modeling study a series of numerical experiments with a global climate model are designed to simulate radiative effect of black carbon (BC) and dust in snow, and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow on the snowpack over the TP and subsequent impacts on the Asian monsoon climate and hydrological cycle. Simulations results show a large BC content in snow over the TP, especially the southern slope. Because of the high aerosol content in snow and large incident solar radiation in the low latitude and high elevation, the TP exhibits the largest surface radiative flux changes induced by aerosols (e.g. BC, Dust) in snow compared to any other snow-covered regions in the world. Simulation results show that the aerosol-induced snow albedo perturbations generate surface radiative flux changes of 5-25 W m-2 during spring, with a maximum in April or May. BC-in-snow increases the surface air temperature by around 1.0oC averaged over the TP and reduces spring snowpack over the TP more than pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates). The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1-4 times larger for BC-in-snow than CO2 increase during April-July, indicating that BC-in-snow more efficiently accelerates snowmelt because the increased net solar radiation induced by reduced albedo melts the snow more efficiently than snow melt due to warming in the air. The TP also influences the South (SAM) and East (EAM) Asian monsoon through its dynamical and thermal forcing. Simulation results show that during boreal spring

  9. Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Yun; Flanner, M G; Leung, Lai-Yung R; Wang, Weiguo

    2011-03-02

    The Tibetan Plateau (TP), the highest and largest plateau in the world, has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. The snowpack and glaciers over the TP provide fresh water to billions of people in Asian countries, but the TP glaciers have been retreating extensively at a speed faster than any other part of the world. In this study a series of experiments with a global climate model are designed to simulate black carbon (BC) and dust in snow and their radiative forcing and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow, respectively, on the snowpack over the TP, as well as their subsequent impacts on the Asian monsoon climate and hydrological cycle. Results show a large BC content in snow over the TP, especially the southern slope, with concentration larger than 100 µk/kg. Because of the high aerosol content in snow and large incident solar radiation in the low latitude and high elevation, the TP exhibits the largest surface radiative forcing induced by aerosols (e.g. BC, Dust) in snow compared to other snow-covered regions in the world. The aerosol-induced snow albedo perturbations generate surface radiative forcing of 5-25 W m-2 during spring, with a maximum in April or May. BC-in-snow increases the surface air temperature by around 1.0°C averaged over the TP and reduces snowpack over the TP more than that induced by pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere during spring. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates). The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1-4 times larger for BC-in-snow than CO2 increase during April-July, indicating that BC-in-snow more efficiently

  10. The Glacial-Interglacial summer monsoon recorded in southwest Sulawesi speleothems: Evidence for sea level thresholds driving tropical monsoon strength

    Science.gov (United States)

    Kimbrough, A. K.; Gagan, M. K.; Dunbar, G. B.; Krause, C.; Di Nezio, P. N.; Hantoro, W. S.; Cheng, H.; Edwards, R. L.; Shen, C. C.; Sun, H.; Cai, B.; Rifai, H.

    2016-12-01

    Southwest Sulawesi lies within the Indo-Pacific Warm Pool (IPWP), at the center of atmospheric convection for two of the largest circulation cells on the planet, the meridional Hadley Cell and zonal Indo-Pacific Walker Circulation. Due to the geographic coincidence of these circulation cells, southwest Sulawesi serves as a hotspot for changes in tropical Pacific climate variability and Australian-Indonesian summer monsoon (AISM) strength over glacial-interglacial (G-I) timescales. The work presented here spans 386 - 127 ky BP, including glacial terminations IV ( 340 ky BP) and both phases of TIII (TIII 248 ky BP and TIIIa 217 ky BP). This record, along with previous work from southwest Sulawesi spanning the last 40 kyr, reveals coherent climatic features over three complete G-I cycles. The multi-stalagmite Sulawesi speleothem δ18O record demonstrates that on G-I timescales, the strength of the AISM is most sensitive to changes in sea level and its impact on the regional distribution of land and shallow ocean. Stalagmite δ18O and trace element (Mg/Ca) data indicate a rapid increase in rainfall at glacial terminations and wet interglacials. TIV, TIII, TIIIa, and TI are each characterized by an abrupt 3‰ decrease in δ18O that coincides with sea level rise and flooding of the Sunda and Sahul shelves. Strong evidence for a sea level (flooding/exposure) threshold is found throughout the southwest Sulawesi record. This is most clearly demonstrated over the period 230 - 212 ky BP (MIS 7d-7c), when a sea level fall to only -80 to -60 m for 10 kyr results in a weakened AISM and glacial conditions, followed by a full termination. Taken together, both glaciations and glacial terminations imply a sea level threshold driving the AISM between two primary levels of intensity (`interglacial' & `glacial'). These massive, sea-level driven shifts in AISM strength are superimposed on precession-scale variability associated with boreal fall insolation at the equator, indicating

  11. On the relationship between Indian summer monsoon withdrawal and Indo-Pacific SST anomalies before and after 1976/1977 climate shift

    Energy Technology Data Exchange (ETDEWEB)

    Sabeerali, C.T.; Rao, Suryachandra A. [Indian Institute of Tropical Meteorology, Pune (India); Ajayamohan, R.S. [University of Victoria, Canadian Centre for Climate Modelling and Analysis, Victoria, BC (Canada); Murtugudde, Raghu [University of Maryland, Earth System Science Interdisciplinary Center, College Park, MD (United States)

    2012-08-15

    A clear shift in the withdrawal dates of the Indian Summer Monsoon is observed in the long term time series of rainfall data. Prior (posterior) to the 1976/1977 climate shift most of the withdrawal dates are associated with a late (an early) withdrawal. As a result, the length of the rainy season (LRS) over the Indian land mass has also undergone similar changes (i.e., longer (shorter) LRS prior (posterior) to the climate shift). In this study, probable reasons for this significant shift in withdrawal dates and the LRS are investigated using reanalysis/observed datasets and also with the help of an atmospheric general circulation model. Reanalysis/observational datasets indicate that prior to the climate shift the sea surface temperature (SST) anomalies in the eastern equatorial Pacific Ocean and the Arabian Sea exerted a strong influence on both the withdrawal and the LRS. After the climate shift, the influence of the eastern equatorial Pacific Ocean SST has decreased and surprisingly, the influence of the Arabian Sea SST is almost non-existent. On the other hand, the influence of the southeastern equatorial Indian Ocean has increased significantly. It is observed that the upper tropospheric temperature gradient over the dominant monsoon region has decreased and the relative influence of the Indian Ocean SST variability on the withdrawal of the Indian Summer Monsoon has increased in the post climate shift period. Sensitivity experiments with the contrasting SST patterns on withdrawal dates and the LRS in the pre- and post- climate shift scenarios, confirm the observational evidences presented above. (orig.)

  12. Coastal processes at the southern tip of India during summer monsoon 2005

    Digital Repository Service at National Institute of Oceanography (India)

    Smitha, B.R; VimalKumar, K.G.; Sanjeevan, V.N.

    . Analysis indicates that the system is in harmony with the southwest monsoon winds, maximum during July with horizontal SST gradient of 4 degrees C and 1.17m/ day of vertical velocity. The role of local wind forcing is verified by comparing the isothermal...

  13. Aerosol properties over the Arabian Sea during the north east monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Suresh, T.; Dulac, F; Leon, G.F; Desa, E.

    440, 670, 870, 936, 940 and 1020 mm, in the Arabian Sea between 15.4-17.86 degrees N and 73.28-69.3 degrees E, during the North East monsoon period of 1-10 December, 1998. The aerosol optical properties derived from these data showed variations from...

  14. Climate and land use controls over terrestrial water use efficiency in monsoon Asia.

    Science.gov (United States)

    Hanqin Tian; Chaoqun Lu; Guangsheng Chen; Xiaofeng Xu; Mingliang Liu; et al

    2011-01-01

    Much concern has been raised regarding how and to what extent climate change and intensive human activities have altered water use efficiency (WUE, amount of carbon uptake per unit of water use) in monsoon Asia. By using a process-based ecosystem model [dynamic land ecosystem model (DLEM)], we examined effects of climate change, land use/cover change, and land...

  15. Anomalous circulation in the eastern equatorial Indian Ocean during southwest monsoon of 1994

    Digital Repository Service at National Institute of Oceanography (India)

    Unnikrishnan, A.S.; Murty, V.S.N.; Babu, M.T.; Gopinathan, C.K.; Charyulu, R.J.K.

    and an eastward flow, constituting the southwest monsoon current (SWMC), in the vicinity of the equator characterise the upper ocean circulation. While low salinity waters (33.5 -34.75) in the upper layer are advected westward from 88 E via the westward flow...

  16. Variability of the Date of Monsoon Onset over Kerala (India) of the ...

    Indian Academy of Sciences (India)

    19

    Nansen Environmental Research Centre India,6A Oxford Business Centre, Kochi - ... Monsoon Onset over Kerala (India) which occurs every year is a major ... Decadal variability in DMOK. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

  17. Monsoon control on trace metal fluxes in the deep Arabian Sea

    Indian Academy of Sciences (India)

    Monsoon control on trace metal fluxes in the deep Arabian Sea ... at marine boundaries and surface ocean processes: Forcings and feedbacks Volume 115 ... Annual Al fluxes at shallow and deep trap depths were 0.47 and 0.46 gm−2 in the ...

  18. Vertical Distribution of Temperature in Transitional Season II and West Monsoon in Western Pacific

    Science.gov (United States)

    Pranoto, Hikari A. H.; Kunarso; Soeyanto, Endro

    2018-02-01

    Western Pacific is the water mass intersection from both the Northern Pacific and Southern Pacific ocean. The Western Pacific ocean is warm pool area which formed by several warm surface currents. As a warm pool area and also the water mass intersection, western Pacific ocean becomes an interesting study area. The object of this study is to describe the temperature vertical distribution by mooring buoy and temporally in transitional season II (September - November 2014) and west monsoon (December 2014 - February 2015) in Western Pacific. Vertical temperature and wind speed data that was used in this study was recorded by INA-TRITON mooring instrument and obtained from Laboratory of Marine Survey, BPPT. Supporting data of this study was wind vector data from ECMWF to observe the relation between temperature distribution and monsoon. The quantitative approach was used in this study by processing temperature and wind data from INA-TRITON and interpreted graphically. In the area of study, it was found that in transitional season II the range of sea surface temperature to 500-meter depth was about 8.29 - 29.90 °C while in west monsoon was 8.12 - 29.45 °C. According to the research result, the sea SST of western Pacific ocean was related to monsoonal change with SST and wind speed correlation coefficient was 0.78. While the deep layer temperature was affected by water mass flow which passes through the western Pacific Ocean.

  19. Changes in the Asian monsoon climate during 1700-1850 induced by preindustrial cultivation.

    Science.gov (United States)

    Takata, Kumiko; Saito, Kazuyuki; Yasunari, Tetsuzo

    2009-06-16

    Preindustrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an atmospheric general circulation model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked and was consistent with the observational changes derived from examining the Himalayan ice cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/use change was the major source of disturbances to the climate during that period. This report will set forward quantitative examination of the actual impacts of land cover/use changes on Asian monsoons, relative to the impact of greenhouse gases and aerosols, viewed in the context of global warming on the interannual, decadal, and centennial time scales.

  20. Two millennia of Mesoamerican monsoon variability driven by Pacific and Atlantic synergistic forcing

    Science.gov (United States)

    Lachniet, Matthew S.; Asmerom, Yemane; Polyak, Victor; Bernal, Juan Pablo

    2017-01-01

    The drivers of Mesoamerican monsoon variability over the last two millennia remain poorly known because of a lack of precisely-dated and climate-calibrated proxy records. Here, we present a new high resolution (∼2 yrs) and precisely-dated (± 4 yr) wet season hydroclimate reconstruction for the Mesoamerican sector of the North American Monsoon over the past 2250 years based on two aragonite stalagmites from southwestern Mexico which replicate oxygen isotope variations over the 950-1950 CE interval. The reconstruction is quantitatively calibrated to instrumental rainfall variations in the Basin of Mexico. Comparisons to proxy indices of ocean-atmosphere circulation show a synergistic forcing by the North Atlantic and El Niño/Southern Oscillations, whereby monsoon strengthening coincided with a La Niña-like mode and a negative North Atlantic Oscillation, and vice versa for droughts. Our data suggest that weak monsoon intervals are associated with a strong North Atlantic subtropical high pressure system and a weak Intertropical convergence zone in the eastern Pacific Ocean. Population expansions at three major highland Mexico civilization of Teotihuacan, Tula, and Aztec Tenochtitlan were all associated with drought to pluvial transitions, suggesting that urban population growth was favored by increasing freshwater availability in the semi-arid Mexican highlands, and that this hydroclimatic change was controlled by Pacific and Atlantic Ocean forcing.

  1. Atlantic and Pacific Ocean synergistic forcing of the Mesomerican monsoon over the last two millennia

    Science.gov (United States)

    Lachniet, M. S.; Asmerom, Y.; Polyak, V. J.; Bernal, J. P.

    2015-12-01

    We present a new replicated, high resolution (~2 yrs) and precisely-dated (± 4 yr) wet season hydroclimate reconstruction for the Mesoamerican sector of the North American Monsoon over the past 2250 years. Our new reconstruction is based on two aragonite stalagmites from southwestern Mexico which replicate oxygen isotope variations over the 950-1950 CE interval, and are calibrated to instrumental rainfall variations in the Basin of Mexico. Such data complement existing dendroclimatic reconstructions of early wet season and winter drought severity. Comparisons to indices of ocean-atmosphere circulation show a combined forcing by the North Atlantic Oscillation and the El Niño/Southern Oscillation. Monsoon strengthening coincided with synergistic forcing of a La Niña-like mode and a negative North Atlantic Oscillation, and vice versa for droughts. Although drought is commonly invoked as an stressor leading to societal change, the role of intensified monsoon onto cultural development is rarely explored. We observe that prominent transitions from drought to pluvial conditions are associated with population increases in three of the major highland Mexico civilizations of Teotihuacan, Tula Grande, and the Aztecs. These data suggest a role for ocean-atmosphere dynamics arising from the Atlantic and Pacific Oceans on Mesoamerican monsoon strength.

  2. A Stalagmite record of Holocene Indonesian-Australian summer monsoon variability from the Australian tropics

    Science.gov (United States)

    Denniston, Rhawn F.; Wyrwoll, Karl-Heinz; Polyak, Victor J.; Brown, Josephine R.; Asmerom, Yemane; Wanamaker, Alan D.; LaPointe, Zachary; Ellerbroek, Rebecca; Barthelmes, Michael; Cleary, Daniel; Cugley, John; Woods, David; Humphreys, William F.

    2013-10-01

    Oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave KNI-51, located in the eastern Kimberley region of tropical Western Australia, represent the first absolute-dated, high-resolution speleothem record of the Holocene Indonesian-Australian summer monsoon (IASM) from the Australian tropics. Stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic Holocene IASM which strengthened in the early Holocene, decreased in strength by 4 ka, with a further decrease from ˜2 to 1 ka, before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka. The relationships between the KNI-51 IASM reconstruction and those from published speleothem time series from Flores and Borneo, in combination with other data sets, appear largely inconsistent with changes in the position and/or organization of the Intertropical Convergence Zone (ITCZ). Instead, we argue that the El Niño/Southern Oscillation (ENSO) may have played a dominant role in driving IASM variability since at least the middle Holocene. Given the muted modern monsoon rainfall responses to most El Niño events in the Kimberley, an impact of ENSO on regional monsoon precipitation over northwestern Australia would suggest non-stationarity in the long-term relationship between ENSO forcing and IASM rainfall, possibly due to changes in the mean state of the tropical Pacific over the Holocene.

  3. Pre-monsoon living planktonic foraminifera from the Southeastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Guptha, M.V.S.; Naidu, P.D.; Muralinath, A.S.

    LOGICAL SoCIETY OF INDIA Vol. 36, Dec. 1990, pp. 654 to 660 Pre-Monsoon Living Planktonic Foraminifera from the Southeastern Arabian Sea M. V. S. GUPTHA.. P. DIVAKAR NAlDU AND A. S. MURALINATH Nalional Institute of Oceanography, Dona Paula, Goa 403004...

  4. Variability of the date of monsoon onset over Kerala (India) of the ...

    Indian Academy of Sciences (India)

    P N Preenu

    2017-07-25

    Jul 25, 2017 ... Sci. (2017) 126:76 c Indian Academy of Sciences ... Nansen Environmental Research Centre India, 6A Oxford Business Centre, Kochi, Kerala 682 016, India. .... definition of the large scale monsoon onset (over. India and not ...

  5. Effect of freshwater influx on phytoplankton in the Mandovi estuary (Goa, India) during monsoon season: Chemotaxonomy

    Digital Repository Service at National Institute of Oceanography (India)

    Parab, S.G.; Matondkar, S.G.P.; Gomes, H.R.; Goes, J.I.

    for an increase in nitrate levels upto 26 mu M from less than 1 mu M during pre-monsoon and enhancement of chlorophyll a (chl a) as high as 14 mu g·L sup(-1) during the same period. The phytoplankton population was observed through both chemotaxonomy...

  6. Cyclicity in the Late Holocene monsoonal changes from the western Bay of Bengal: Foraminiferal approach.

    Digital Repository Service at National Institute of Oceanography (India)

    Rana, S.S.; Nigam, R.

    .; Imbrie, J.; Hays, J.; Kukla, G.; Saltzman, B.. NATO ASI Ser. C: Math. Phys. Sci.; 126: 349-366. Sarkar, A., Ramesh, R., Somayajulu, B.L.K., Agnihotri, R., Jull, A.J.T., Burr, G.S. 2000. High resolution Holocene monsoon record from the eastern Arabian Sea...

  7. Wind stress, curl and vertical velocity in the Bay of Bengal during southwest monsoon, 1984

    Digital Repository Service at National Institute of Oceanography (India)

    Babu, M.T.; Heblekar, A.K.; Murty, C.S.

    Wind distribution observed during southwest monsoon of 1984 has used to derive the mean wind stress for the season at every 1 degree square grid and curl over the Bay of Bengal. Two regions of maximum wind stress are present over the Bay of Bengal...

  8. Apparent relationship between thermal regime in Antarctic waters and Indian summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Menon, H.B.; RameshBabu, V.; Sastry, J.S.

    ) charts for the Indian Ocean sector of the Southern Ocean during 2 contrasting years (1977 and 1979) of summer monsoon over India. The results suggest an apparent relationship between the thermal regimes in the Antarctic waters of the Indian Ocean sector...

  9. Hydrography and circulation in the western Bay of Bengal during the northeast monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Shetye, S.R.; Gouveia, A.D.; Shankar, D.; Shenoi, S.S.C.; Vinayachandran, P.N.; Sundar, D.; Michael, G.S.; Nampoothiri, G.

    , the transport is 7.7 x 10 sup(6) m sup(3) s sup(-1) . Recent model studies lead us to conclude that the EICC during the northeast monsoon is driven by winds along the east coast of India and Ekman pumping in the interior bay. In the south, Ekman pumping over...

  10. Decoupled warming and monsoon precipitation in East Asia over the last deglaciation

    NARCIS (Netherlands)

    Peterse, F.; Prins, M.A.; Beets, C.J.; Troelstra, S.R.; Zheng, H.B.; Gu, Z.Y.; Schouten, S.; Sinninghe Damsté, J.S.

    2011-01-01

    Our understanding of the continental climate development in East Asia is mainly based on loess-paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes (delta O-18) of stalagmites from several Chinese caves. Based on these records, it is thought that East Asian

  11. Trace metal dynamics in zooplankton from the Bay of Bengal during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Rejomon, G.; DineshKumar, P.K.; Nair, M.; Muraleedharan, K.R.

    Trace metal (Fe, Co, Ni, Cu, Zn, Cd, and Pb) concentrations in zooplankton from the mixed layer were investigated at 8 coastal and 20 offshore stations in the western Bay of Bengal during the summer monsoon of 2003. The ecotoxicological importance...

  12. A new criterion for identifying breaks in monsoon conditions over the Indian subcontinent

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Dessai, U.R.P.

    in the months of July and August were of 3-4 days duration (49%). Breaks identified by our method were in general consistent with those identified by the conventional methods. Further, the correlation between the seasonal monsoon rainfall and break (active) days...

  13. Hydrographic characteristics of central Bay of Bengal waters during southwest monsoon of 1983

    Digital Repository Service at National Institute of Oceanography (India)

    Somayajulu, Y.K.; Murty, T.V.R.; PrasannaKumar, S.; Sastry, J.S.

    to postmonsoon. The loss of energy from the sea surface to the atmosphere by evaporational cooling due to strong monsoonal winds and reduction in the incoming solar radiation by clouds may result in a net loss of energy (cooling). During premonsoon the isotherms...

  14. Indian monsoon variability at different time scales: Marine and terrestrial proxy records

    Digital Repository Service at National Institute of Oceanography (India)

    Patnaik, R.; Gupta, A; Naidu, P.D.; Yadav, R.R.; Bhattacharyya, A; Kumar, M.

    Here, we present a review of the work done in India during 2007-2011 on various proxy records of monsoon variability preserved in the marine (Central Indian Basin, western, northern and eastern Arabian Sea and the Bay of Bengal) and terrestrial...

  15. Heat content variations in the northeastern Arabian sea during a weak spell of 1986 summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Gopalakrishna, V.V.; Sarma, M.S.S.; Sadhuram, Y.; RameshBabu, V.

    Based on time series measurements of temperature and surface meteorological parameters taken at a stationary location (10 degrees N;67 degrees E) in the northeastern Arabian Sea during a weak spell of 1986 monsoon from 29th August to 5th September...

  16. A model perspective on orbital forcing of monsoons and Mediterranean climate using EC-Earth

    NARCIS (Netherlands)

    Bosmans, J.H.C.

    2014-01-01

    This thesis focuses on orbitally forced changes of monsoons and Mediterranean climate. Changes in the shape of the Earths orbit around the Sun and its rotational axis govern the seasonal and latitudinal distribution of incoming solar radiation on time scales of thousands to millions of years. The

  17. Assessment of Unusual Gigantic Jets observed during the Monsoon season: First observations from Indian Subcontinent

    DEFF Research Database (Denmark)

    Singh, Rajesh; Maurya, Ajeet K.; Chanrion, Olivier

    2017-01-01

    observations. Here we report first observations of Gigantic Jets in Indian subcontinent over the Indo-Gangetic plains during the monsoon season. Two storms each produced two jets with characteristics not documented so far. Jets propagated similar to 37 km up remarkably in similar to 5 ms with velocity...

  18. Organized convection over southwest peninsular India during the pre-monsoon season

    Science.gov (United States)

    Sreelekha, P. N.; Babu, C. A.

    2018-03-01

    The paper addresses observational aspects of widespread rain associated with the organized convection that forms over the southwest peninsular India during the pre-monsoon season. The evolution of the cloud band over the equatorial region, its northward propagation, development of cross equatorial flow near the Somalia coast, and appearance of equatorial westerly wind resemble closely to that of the monsoon organized convection. Low-level convergence, cyclonic vorticity, and ascending motion are other major characteristics of the cloud bands associated with the pre-monsoon organized convection which exhibits similarity with that of monsoon. The ascending motion plays vital role on the formation of cloud band that produces widespread rainfall persisting for more than a week. The vertical shear of meridional winds is found to co-exist with precipitation over the Arabian Sea off the southwest peninsular India. The velocity potential values derived from the winds at 850 and 200 hPa levels confirm the rising motion on the basis of low-level convergence and upper level divergence. Also, shifting of ascending limb of the local Hadley circulation to the north of the equator is observed during the days of the presence of organized convection over the southwest peninsular region. Noticeable shift in the Walker circulation rising limb is also identified during the same time.

  19. The Indian summer monsoon rainfall: interplay of coupled dynamics, radiation and cloud microphysics

    Directory of Open Access Journals (Sweden)

    P. K. Patra

    2005-01-01

    Full Text Available The Indian summer monsoon rainfall (ISMR, which has a strong connection to agricultural food production, has been less predictable by conventional models in recent times. Two distinct years 2002 and 2003 with lower and higher July rainfall, respectively, are selected to help understand the natural and anthropogenic influences on ISMR. We show that heating gradients along the meridional monsoon circulation are reduced due to aerosol radiative forcing and the Indian Ocean Dipole in 2002. An increase in the dust and biomass-burning component of the aerosols through the zonal monsoon circulation resulted in reduction of cloud droplet growth in July 2002. These conditions were opposite to those in July 2003 which led to an above average ISMR. In this study, we have utilized NCEP/NCAR reanalyses for meteorological data (e.g. sea-surface temperature, horizontal winds, and precipitable water, NOAA interpolated outgoing long-wave radiation, IITM constructed all-India rainfall amounts, aerosol parameters as observed from the TOMS and MODIS satellites, and ATSR fire count maps. Based on this analysis, we suggest that monsoon rainfall prediction models should include synoptic as well as interannual variability in both atmospheric dynamics and chemical composition.

  20. A note on Arabian Sea warm pool and its possible relation with monsoon onset over Kerala

    Digital Repository Service at National Institute of Oceanography (India)

    Chacko, K.V.; HareeshKumar, P.V.; RameshKumar, M.R.; Mathew, B.; Bannur, V.M.

    The possible relation of the Arabian Sea Warm Pool (ASWP) with monsoon onset over Kerala is studied by utilizing the TRMM Microwave Imager data during the period 2007-2011 (5 years). The ASWP is a part of the Indian Ocean warm pool and forms...

  1. Impact of East Asian Summer Monsoon on Surface Ozone Pattern in China

    Science.gov (United States)

    Li, Shu; Wang, Tijian; Huang, Xing; Pu, Xi; Li, Mengmeng; Chen, Pulong; Yang, Xiu-Qun; Wang, Minghuai

    2018-01-01

    Tropospheric ozone plays a key role in regional and global atmospheric and climate systems. In East Asia, ozone can be affected both in concentration level and spatial pattern by typical monsoon climate. This paper uses three different indices to identify the strength of East Asian summer monsoon (EASM) and explores the possible impact of EASM intensity on the ozone pattern through synthetic and process analysis. The difference in ozone between three strong and three weak monsoon years was analyzed using the simulations from regional climate model RegCM4-Chem. It was found that EASM intensity can significantly influence the spatial distribution of ozone in the lower troposphere. When EASM is strong, ozone in the eastern part of China (28°N - 42° N) is reduced, but the inverse is detected in the north and south. The surface ozone difference ranges from -7 to 7 ppbv during the 3 months (June to August) of the EASM, with the most obvious difference in August. Difference of the 3 months' average ozone ranges from -3.5 to 4 ppbv. Process analysis shows that the uppermost factor controlling ozone level during summer monsoon seasons is the chemistry process. Interannual variability of EASM can impact the spatial distribution of ozone through wind in the lower troposphere, cloud cover, and downward shortwave radiation, which affect the transport and chemical formation of ozone. The phenomenon should be addressed when considering the interaction between ozone and the climate in East Asia region.

  2. Variations in swells along Eastern Arabian Sea during the summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Johnson, G.; SanilKumar, V.; Sanjiv, P.C.; Singh, J.; Pednekar, P.S.; AshokKumar, K.; Dora, G.U.; Gowthaman, R.

    A study was carried out to find the variation in wave characteristics along the eastern Arabian Sea and the influence of swells in the nearshore waves at 3 locations during summer monsoon in 2010. Percentage of swells in the measured waves was 75...

  3. Transport of regional pollutions to UTLS during Asian Summer Monsoon - A CTM study

    Science.gov (United States)

    Li, Qian; Bian, Jianchun; Lu, Daren

    2013-04-01

    We use a 3-D global Chemical Transport Model (CTM) GEOS-Chem to simulate the observed Asian Summer Monsoon transport of biomass burning tracers HCN and CO from local emissions to UTLS. By analyzing the satellite observations, we focus on the distribution and spatial-temporal variation of HCN and CO concentration in UTLS. The model simulations capture well the main features of distribution of HCN and CO compared with satellite observations. Recent studies (Li et al., 2009; Randel et al., 2010) indicated that regional emissions may play an important role controlling the distribution and variation of HCN in tropical UTLS during Asian Summer Monsoon seasons, mainly due to the local dynamical uplift of Asian Summer Monsoon. By using GEOS-Chem simulations, we will analyze the UTLS distribution and variation of HCN and CO from emissions of different regions including S.E. Asia, Boreal Asia, Indonesia and Australia, Africa, Europe, Northern America and Southern America. According to the amount and seasonal variability of emissions, the contribution of biomass burning and biofuel burning emissions of different regions to the highly concentrated HCN and CO in UTLS during Asian Summer Monsoon seasons will be discussed, individually.

  4. Improvement of Statistical Typhoon Rainfall Forecasting with ANN-Based Southwest Monsoon Enhancement

    Directory of Open Access Journals (Sweden)

    Tsung-Yi Pan

    2011-01-01

    Full Text Available Typhoon Morakot 2009, with significant southwest monsoon flow, produced a record-breaking rainfall of 2361 mm in 48 hours. This study hopes to improve a statistical typhoon rainfall forecasting method used over the mountain region of Taiwan via an artificial neural network based southwest monsoon enhancement (ANNSME model. Rainfall data collected at two mountain weather stations, ALiShan and YuShan, are analyzed to establish the relation to the southwest monsoon moisture flux which is calculated at a designated sea area southwest of Taiwan. The results show that the moisture flux, with southwest monsoon flow, transported water vapor during the landfall periods of Typhoons Mindulle, Bilis, Fungwong, Kalmaegi, Haitaing and Morakot. Based on the moisture flux, a linear regression is used to identify an effective value of moisture flux as the threshold flux which can enhance mountain rainfall in southwestern Taiwan. In particular, a feedforward neural network (FNN is applied to estimate the residuals from the linear model to the differences between simulated rainfalls by a typhoon rainfall climatology model (TRCM and observations. Consequently, the ANNSME model integrates the effective moisture flux, linear rainfall model and the FNN for residuals. Even with very limited training cases, our results indicate that the ANNSME model is robust and suitable for improvement of TRCM rainfall prediction. The improved prediction of the total rainfall and of the multiple rainfall peaks is important for emergency operation.

  5. Characteristics of monsoon low level jet (MLLJ) as an index of ...

    Indian Academy of Sciences (India)

    R.Narasimhan(krishtel emaging) 1461 1996 Oct 15 13:05:22

    level jet or the. Monsoon Low Level Jet (MLLJ) stream over penin- sular India. They have investigated the occurrence of significant low-level wind maximum in the ver- tical and had defined it in accordance with the fol- lowing criteria following Fay ...

  6. Global energetics and local physics as drivers of past, present and future monsoons

    Science.gov (United States)

    Biasutti, Michela; Voigt, Aiko; Boos, William R.; Braconnot, Pascale; Hargreaves, Julia C.; Harrison, Sandy P.; Kang, Sarah M.; Mapes, Brian E.; Scheff, Jacob; Schumacher, Courtney; Sobel, Adam H.; Xie, Shang-Ping

    2018-06-01

    Global constraints on momentum and energy govern the variability of the rainfall belt in the intertropical convergence zone and the structure of the zonal mean tropical circulation. The continental-scale monsoon systems are also facets of a momentum- and energy-constrained global circulation, but their modern and palaeo variability deviates substantially from that of the intertropical convergence zone. The mechanisms underlying deviations from expectations based on the longitudinal mean budgets are neither fully understood nor simulated accurately. We argue that a framework grounded in global constraints on energy and momentum yet encompassing the complexities of monsoon dynamics is needed to identify the causes of the mismatch between theory, models and observations, and ultimately to improve regional climate projections. In a first step towards this goal, disparate regional processes must be distilled into gross measures of energy flow in and out of continents and between the surface and the tropopause, so that monsoon dynamics may be coherently diagnosed across modern and palaeo observations and across idealized and comprehensive simulations. Accounting for zonal asymmetries in the circulation, land/ocean differences in surface fluxes, and the character of convective systems, such a monsoon framework would integrate our understanding at all relevant scales: from the fine details of how moisture and energy are lifted in the updrafts of thunderclouds, up to the global circulations.

  7. Breeding in the monsoon : semi-annual reproduction in the Seychelles warbler (Acrocephalus sechellensis)

    NARCIS (Netherlands)

    Komdeur, Jan; Daan, Serge

    2005-01-01

    Despite the absence of pronounced changes in day length, there is considerable climatological seasonality in the tropics. Its expression can be complex like in the monsoon climate of the Indian Ocean Islands. The land mass distribution on both sides of the equator leads to seasonal changes in

  8. Studies on MODIS NDVI and its relation with the south west monsoon, western ghats, India

    Science.gov (United States)

    Lakshmi Kumar, Tv; Barbosa, Humberto; Uma, R.; Rao, Koteswara

    2012-07-01

    Eleven years (2000 to 2010) of Normalized Difference Vegetation Index (NDVI) data, derived from Moderate Imaging Spectroradiometer (MODIS) Terra with 250m resolution are used in the present study to discuss the changes in the trends of vegetal cover. The interannual variability of NDVI over western ghats (number of test sites are 17) showed increasing trend and the pronounced changes are resulted due to the monsoon variability in terms of its distribution (wide spread/fairly wide spread/scattered/isolated) and activity (vigorous/normal/weak) and are studied in detail. The NDVI progression is observed from June with a minimum value of 0.179 and yielded to maximum at 0.565 during September/October, on average. The study then relates the NDVI with the no of light, moderate and heavy rainfall events via statistical techniques such as correlation and regression to understand the connection in between the ground vegetation and the south west monsoon. The results of the study inferred i) NDVI, Antecedent Precipitation Index (API) are in good agreement throughout the monsoon which is evidenced by correlation as well as by Morlett Wavelet Analysis, ii) NDVI maintained good correlation with no of Light Rainy and Moderate Rainy alternatively but not with no of Heavy Rainy days, iii) Relation of NDVI with Isolated, Scattered distributions and active monsoons is substantial and iv) Phenological stages captured the Rate of Green Up during the crop season over western ghats.

  9. Impacts of half a degree additional warming on the Asian summer monsoon rainfall characteristics

    Science.gov (United States)

    Lee, Donghyun; Min, Seung-Ki; Fischer, Erich; Shiogama, Hideo; Bethke, Ingo; Lierhammer, Ludwig; Scinocca, John F.

    2018-04-01

    This study investigates the impacts of global warming of 1.5 °C and 2.0 °C above pre-industrial conditions (Paris Agreement target temperatures) on the South Asian and East Asian monsoon rainfall using five atmospheric global climate models participating in the ‘Half a degree Additional warming, Prognosis and Projected Impacts’ (HAPPI) project. Mean and extreme precipitation is projected to increase under warming over the two monsoon regions, more strongly in the 2.0 °C warmer world. Moisture budget analysis shows that increases in evaporation and atmospheric moisture lead to the additional increases in mean precipitation with good inter-model agreement. Analysis of daily precipitation characteristics reveals that more-extreme precipitation will have larger increase in intensity and frequency responding to the half a degree additional warming, which is more clearly seen over the South Asian monsoon region, indicating non-linear scaling of precipitation extremes with temperature. Strong inter-model relationship between temperature and precipitation intensity further demonstrates that the increased moisture with warming (Clausius-Clapeyron relation) plays a critical role in the stronger intensification of more-extreme rainfall with warming. Results from CMIP5 coupled global climate models under a transient warming scenario confirm that half a degree additional warming would bring more frequent and stronger heavy precipitation events, exerting devastating impacts on the human and natural system over the Asian monsoon region.

  10. Landslides Induced by 2015 Gorkha Earthquake and Their Continuous Evolution Post 2015 and 2016-Monsoon

    Science.gov (United States)

    Spear, B.; Haritashya, U. K.; Kargel, J. S.

    2017-12-01

    Gorkha Nepal has been a hot bed of landslide activity since the 7.8 magnitude earthquake that occurred on April 25th 2015. Even though previous studies have mapped and analyzed the landslides that were directly related to the earthquake, this research maps and analyzes the landslides that occurred during monsoon or after monsoon season in 2015 and 2016. Specifically, our objectives included monitoring post-earthquake landslide evolution and reactivation. We also observed landslides which occurred in the steep side slopes of various small rivers and threatened to block the flow of river. Consequently, we used Landsat, Sentinel, ASTER and images available at Google Earth Engine to locate, map, and analyze these landslides. Our preliminary result indicates 5,270 landslides, however 957 of these landslides occurred significantly after the earthquake. Of the 957 landslides, 508 of them occurred during the monsoon season of 2015 and 48 in the 2016 monsoon season. As well as locating and mapping these landslides, we were able to identify that there were 22 landslides blocking rivers and 24 were reactivated. Our result and landslide density maps clearly identifies zones that are prone to landslides. For example, the steepest areas, such as the Helambu or Langtang region, have a very high concentration of landslides since the earthquake. Furthermore, landslides with the largest area were often nearby each other in very steep regions. This research can be used to determine which areas in the Gorkha Nepal region are safe to use and which areas are high risk.

  11. Influence of eastern Arabian Sea on summer monsoon rainfall over west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    RameshBabu, V.; Rao, M.S.; Rao, M.V.

    and distant nature. In order to realise the model results and the influence of Arabian sea in the context of long range forecasting of monsoon rainfall, we have examined the correlation between the rainfall over west coast of India and premonsoon thermal...

  12. A lidar study of atmospheric aerosols during two contrasting monsoon seasons

    Energy Technology Data Exchange (ETDEWEB)

    Devara, P.C.S.; Raj, P.E. [Indian Institute of Tropical Meteorology (India)

    1998-10-01

    The vertical profiles of the boundary-layer aerosols obtained with a bistatic argon ion lidar system at the Indian Institute of Tropical Meteorology (IITM), Pune, India, during two contrasting, successive south-west (summer) monsoon seasons of 1987 (weak monsoon year) and 1988 (active monsoon year) have been examined. The concurrent meteorological parameters such as temperature, relative humidity and rainfall over Pune have also been studied. It is noticed that the aerosol columnar content (integration of vertical profile throughout the height range) is greater during the active monsoon months and less during the weak monsoon months. Thus the monsoon season total rainfall during 1987 and 1988, apart from other meteorological parameters, shows close correspondence with the aerosol columnar content over the experimental station. A brief description of the lidar experimental setup and the database is given. The observed association between the aerosol columnar content and the monsoon activity is explained in terms of the environmental and meteorological conditions prevailing over Pune. [Spanish] Los perfiles verticales de los aerosoles de la capa fronteriza obtenidos mediante un sistema de Lidar biestatico de iones de argon en el Instituto de Meteorologia Tropical (IITM) en Pune, India, durante dos estaciones contrastantes y suscesivas del monzon del SW (verano) de 1987 (ano de monzon debil) y 1988 (ano activo de monzon) han sido estudiados. Los parametros meteorologicos concurrentes tales como temperatura, humedad relativa y lluvia en Pune, han sido tambien estudiados. Se observa que el contenido columnar de aerosoles (integracion del perfil vertical en toda la gama de alturas) es mayor durante los meses del monzon activo y menor en los meses del monzon debil. De manera que, el total de la lluvia monzonica durante 1987 y 1988, aparte de otros parametros meteorologicos, muestran una correspondencia intima con el contenido columnar de a erosoles sobre la estacion

  13. Predicting Indian Summer Monsoon onset through variations of surface air temperature and relative humidity

    Science.gov (United States)

    Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

    2015-04-01

    Indian Summer Monsoon (ISM) rainfall has an enormous effect on Indian agriculture, economy, and, as a consequence, life and prosperity of more than one billion people. Variability of the monsoonal rainfall and its onset have a huge influence on food production, agricultural planning and GDP of the country, which on 22% is determined by agriculture. Consequently, successful forecasting of the ISM onset is a big challenge and large efforts are being put into it. Here, we propose a novel approach for predictability of the ISM onset, based on critical transition theory. The ISM onset is defined as an abrupt transition from sporadious rainfall to spatially organized and temporally sustained rainfall. Taking this into account, we consider the ISM onset as is a critical transition from pre-monsoon to monsoon, which take place in time and also in space. It allows us to suggest that before the onset of ISM on the Indian subcontinent should be areas of critical behavior where indicators of the critical transitions can be detected through an analysis of observational data. First, we identify areas with such critical behavior. Second, we use detected areas as reference points for observation locations for the ISM onset prediction. Third, we derive a precursor for the ISM onset based on the analysis of surface air temperature and relative humidity variations in these reference points. Finally, we demonstrate the performance of this precursor on two observational data sets. The proposed approach allows to determine ISM onset in advance in 67% of all considered years. Our proposed approach is less effective during the anomalous years, which are associated with weak/strong monsoons, e.g. El-Nino, La-Nina or positive Indian Ocean Dipole events. The ISM onset is predicted for 23 out of 27 normal monsoon years (85%) during the past 6 decades. In the anomalous years, we show that time series analysis in both areas during the pre-monsoon period reveals indicators whether the

  14. On the relationship between the Indian summer monsoon rainfall and the EQUINOO in the CFSv2

    Science.gov (United States)

    Vishnu, S.; Francis, P. A.; Ramakrishna, S. S. V. S.; Shenoi, S. S. C.

    2018-03-01

    Several recent studies have shown that positive (negative) phase of Equatorial Indian Ocean Oscillation (EQUINOO) is favourable (unfavourable) to the Indian summer monsoon. However, many ocean-atmosphere global coupled models, including the state-of-the-art Climate Forecast System (CFS) version 2 have difficulty in reproducing this link realistically. In this study, we analyze the retrospective forecasts by the CFS model for the period 1982-2010 with an objective to identify the reasons behind the failure of the model to simulate the observed links between Indian summer monsoon and EQUINOO. It is found that, in the model hindcasts, the rainfall in the core monsoon region was mainly due to westward propagating synoptic scale systems, that originated from the vicinity of the tropical convergence zone (TCZ). Our analysis shows that unlike in observations, in the CFS, majority of positive (negative) EQUINOO events are associated with El Niño (La Niña) events in the Pacific. In addition to this, there is a strong link between EQUINOO and Indian Ocean Dipole (IOD) in the model. We show that, during the negative phase of EQUINOO/IOD, northward propagating TCZs remained stationary over the Bay of Bengal for longer period compared to the positive phase of EQUINOO/IOD. As a result, compared to the positive phase of EQUINOO/IOD, during a negative phase of EQUINOO/IOD, more westward propagating synoptic scale systems originated from the vicinity of TCZ and moved on to the core monsoon region, which resulted in higher rainfall over this region in the CFS. We further show that frequent, though short-lived, westward propagating systems, generated near the vicinity of TCZ over the Bay moved onto the mainland were responsible for less number of break monsoon spells during the negative phase of EQUINOO/IOD in the model hindcasts. This study underlines the necessity for improving the skill of the coupled models, particularly CFS model, to simulate the links between EQUINOO/IOD and

  15. Impact assessment of El Nino and La Nina episodes on local/regional monsoon rainfall in India

    International Nuclear Information System (INIS)

    Singh, Sureuder; Rao, V.U.M.; Shigh, Diwan

    2002-08-01

    Large scale atmospheric circulation's and climatic anomalies have been shown to have a significant impact on seasonal weather over many parts of the world. In the present paper an attempt has been made to examine regional monsoon dynamics in relation with El Nino and La Nina episodes. The investigation was earned out for the meteorological sub- division's comprising the areas of Haryana, Delhi and Chandigarh in India. The monthly monsoon rainfall data of different locations in the region and corresponding data on El Nino and La Nina episodes for the period of 30 years (1970-99) were used for this investigation. During the El Nino episodes, various locations experienced excess rainfall in monsoon ranged between 11 and 22 percent. Under the influence of La Nina episodes, the probability of excess monsoon rainfall at different locations in the sub-division ranged between 13 and 25 percent. However, many locations viz., Hisar, Bhiwani, Gurgaon, Delhi and Chandigarh received deficient monsoon rainfall which was contrary to the global belief of the association between SST anomalies and rainfall distribution. No significant association was observed between El Nino and La Nina and monsoon rainfall at different locations in the entire sub-division. However, there was a strong relationship between these SST anomalies and all India monsoon rainfall over the period under study (1970-99). (author)

  16. Distribution of coccolithophores as a potential proxy in paleoceanography: The case of the Oman Sea monsoonal pattern

    Directory of Open Access Journals (Sweden)

    Mojtahedin Elham

    2015-02-01

    Full Text Available High abundances of coccoliths have been observed in surface sediment samples from near the coasts of the Oman Sea in February 2011. At the end of the NE monsoon, the locally observed high Gephyrocapsa oceanica production is hypothesized to respond to local injections of nutrient-rich deep water into the surface water due to sea-surface cooling leading to convection. The most abundant coccolithophore species are G. oceanica followed by Emiliania huxleyi, Helicosphaera carteri, Calcidiscus leptoporus. Some species, such as Gephyrocapsa muellerae, Gephyrocapsa ericsonii, Umbilicosphaera sibogae, Umbellosphaera tenuis and Florisphaera profunda, are rare. The G. oceanica suggested a prevalence of upwelling conditions or high supply of nutrients in the Oman Sea (especially West Jask at the end of the NE monsoon. E. huxleyi showed low relative abundances at the end of the NE monsoon. Due to the location of the Oman Sea in low latitudes with high temperatures, we have observed low abundances of G. muellerae in the study area. Additionally, we have identified low abundances of G. ericsonii at the end of the NE monsoon. Helicosphaera carteri showed a clear negative response with decreasing amounts (relative abundances at the end of the NE monsoon. C. leptoporus, U. sibogae and U. tenuis have very low relative abundances in the NE monsoon and declined extremely at the end of the NE monsoon. F. profunda, which is known to inhabit the lower photic zone (<100 m depht was rarely observed in the samples.

  17. Distribution of coccolithophores as a potential proxy in paleoceanography: The case of the Oman Sea monsoonal pattern

    Science.gov (United States)

    Mojtahedin, Elham; Hadavi, Fatemeh; Lak, Razyeh

    2015-02-01

    High abundances of coccoliths have been observed in surface sediment samples from near the coasts of the Oman Sea in February 2011. At the end of the NE monsoon, the locally observed high Gephyrocapsa oceanica production is hypothesized to respond to local injections of nutrient-rich deep water into the surface water due to sea-surface cooling leading to convection. The most abundant coccolithophore species are G. oceanica followed by Emiliania huxleyi, Helicosphaera carteri, Calcidiscus leptoporus. Some species, such as Gephyrocapsa muellerae, Gephyrocapsa ericsonii, Umbilicosphaera sibogae, Umbellosphaera tenuis and Florisphaera profunda, are rare. The G. oceanica suggested a prevalence of upwelling conditions or high supply of nutrients in the Oman Sea (especially West Jask) at the end of the NE monsoon. E. huxleyi showed low relative abundances at the end of the NE monsoon. Due to the location of the Oman Sea in low latitudes with high temperatures, we have observed low abundances of G. muellerae in the study area. Additionally, we have identified low abundances of G. ericsonii at the end of the NE monsoon. Helicosphaera carteri showed a clear negative response with decreasing amounts (relative abundances) at the end of the NE monsoon. C. leptoporus, U. sibogae and U. tenuis have very low relative abundances in the NE monsoon and declined extremely at the end of the NE monsoon. F. profunda, which is known to inhabit the lower photic zone (<100 m depht) was rarely observed in the samples.

  18. Distributional patterns of anemophilous tree pollen indicating the pathways of Indian monsoon through Qinghai–Tibetan Plateau

    Directory of Open Access Journals (Sweden)

    Zhi-Yong Zhang

    2017-10-01

    Full Text Available The distribution pattern of vegetation on Qinghai–Tibetan Plateau is fundamentally influenced by the plateau climate, which is mainly controlled by Indian monsoon during summer. The long distance transportation of pollen (mostly anemophilous taxa produced by trees on the plateau has been recorded by modern pollen samples in previous studies, and hypothesized to be a good indicator of monsoon dynamics. Here we use 270 surface pollen samples from Qinghai–Tibetan Plateau to test the distribution patterns of the anemophilous tree pollen. Meanwhile factors related to Indian monsoon affecting pollen transportation are simulated and analyzed. Results show that depositional patterns of anemophilous tree pollen, especially Abies, Pinus, Quercus and Betula are completely controlled by the pathways of Indian monsoon. This is reflected by climatic indicators of the atmospheric pressure pattern over June–July–August, by the precipitation pattern over June–July–August and by the topographic feature of the plateau. The spatial interpolation of thin plate spline results also display two depositional centers (ca. 30°N, 95°E and 30°N, 105°E of the anemophilous tree pollen. In contrast to previous conclusion that pollen distributional pattern is determined by mean annual precipitation, we argue that Indian monsoon is the essential controller because of the synchronization between timing of monsoon wind and timing of plants flowering. Our finding strongly suggests that distributional pattern of anemophilous tree pollen on the plateau is a good proxy of Indian monsoon.

  19. Regime shift of Indian summer monsoon rainfall to a persistent arid state: external forcing versus internal variability

    Science.gov (United States)

    Srivastava, Ankur; Pradhan, Maheswar; Goswami, B. N.; Rao, Suryachandra A.

    2017-11-01

    The high propensity of deficient monsoon rainfall over the Indian sub-continent in the recent 3 decades (seven deficient monsoons against 3 excess monsoon years) compared to the prior 3 decades has serious implications on the food and water resources in the country. Motivated by the need to understand the high occurrence of deficient monsoon during this period, we examine the change in predictability of the Indian summer monsoon (ISM) and its teleconnections with Indo-Pacific sea surface temperatures between the two periods. The shift in the tropical climate in the late 1970s appears to be one of the major reasons behind this. We find an increased predictability of the ISM in the recent 3 decades owing to reduced `internal' interannual variability (IAV) due to the high-frequency modes, while the `external' IAV arising from the low-frequency modes has remained largely the same. The Indian Ocean Dipole-ISM teleconnection has become positive during the monsoon season in the recent period thereby compensating for the weakened ENSO-ISM teleconnection. The central Pacific El-Niño and the Indian Ocean (IO) warming during the recent 3 decades are working together to realise enhanced ascending motion in the equatorial IO between 70°E and 100°E, preconditioning the Indian monsoon system prone to a deficient state.

  20. The link between Tibetan Plateau monsoon and Indian summer precipitation: a linear diagnostic perspective

    Science.gov (United States)

    Ge, Fei; Sielmann, Frank; Zhu, Xiuhua; Fraedrich, Klaus; Zhi, Xiefei; Peng, Ting; Wang, Lei

    2017-12-01

    The thermal forcing of the Tibetan Plateau (TP) is analyzed to investigate the formation and variability of Tibetan Plateau Summer Monsoon (TPSM), which affects the climates of the surrounding regions, in particular the Indian summer monsoon precipitation. Dynamic composites and statistical analyses indicate that the Indian summer monsoon precipitation is less/greater than normal during the strong/weak TPSM. Strong (weak) TPSM is associated with an anomalous near surface cyclone (anticyclone) over the western part of the Tibetan Plateau, enhancing (reducing) the westerly flow along its southern flank, suppressing (favoring) the meridional flow of warm and moist air from the Indian ocean and thus cutting (providing) moisture supply for the northern part of India and its monsoonal rainfall. These results are complemented by a dynamic and thermodynamic analysis: (i) A linear thermal vorticity forcing primarily describes the influence of the asymmetric heating of TP generating an anomalous stationary wave flux. Composite analysis of anomalous stationary wave flux activity (after Plumb in J Atmos Sci 42:217-229, 1985) strongly indicate that non-orographic effects (diabatic heating and/or interaction with transient eddies) of the Tibetan Plateau contribute to the generation of an anomalous cyclone (anti-cyclone) over the western TP. (ii) Anomalous TPSM generation shows that strong TPSM years are related to the positive surface sensible heating anomalies over the eastern TP favoring the strong diabatic heating in summer. While negative TPSM years are associated with the atmospheric circulation anomalies during the preceding spring, enhancing northerly dry-cold air intrusions into TP, which may weaken the condensational heat release in the middle and upper troposphere, leading to a weaker than normal summer monsoon over the TP in summer.

  1. Monsoonal influence on variation of hydrochemistry and isotopic signatures: Implications for associated arsenic release in groundwater

    Science.gov (United States)

    Majumder, Santanu; Datta, Saugata; Nath, Bibhash; Neidhardt, Harald; Sarkar, Simita; Roman-Ross, Gabriela; Berner, Zsolt; Hidalgo, Manuela; Chatterjee, Debankur; Chatterjee, Debashis

    2016-04-01

    The present study examines the groundwater and surface water geochemistry of two different geomorphic domains within the Chakdaha block, West Bengal, in an attempt to decipher potential influences of groundwater abstraction on the hydrochemical evolution of the aquifer, the effect of different water inputs (monsoon rain, irrigation and downward percolation from surface water impoundments) to the groundwater system and concomitant As release. A low-land flood plain and a natural levee have been selected for this purpose. Although the stable isotopic signatures of oxygen (δ18O) and hydrogen (δ2H) are largely controlled by local precipitation, the isotopic composition falls sub-parallel to the Global Meteoric Water Line (GMWL). The Cl/Br molar ratio indicates vertical recharge into the wells within the flood plain area, especially during the post-monsoon season, while influences of both evaporation and vertical mixing are visible within the natural levee wells. Increase in mean DOC concentrations (from 1.33 to 6.29 mg/L), from pre- to post-monsoon season, indicates possible inflow of organic carbon to the aquifer during the monsoonal recharge. Concomitant increase in AsT, Fe(II) and HCO3- highlights a possible initial episode of reductive dissolution of As-rich Fe-oxyhydroxides. The subsequent sharp increase in the mean As(III) proportions (by 223%), particularly in the flood plain samples during the post-monsoon season, which is accompanied by a slight increase in mean AsT (7%) may refer to anaerobic microbial degradation of DOC coupled with the reduction of As(V) to As(III) without triggering additional As release from the aquifer sediments.

  2. Non-linear regime shifts in Holocene Asian monsoon variability: potential impacts on cultural change and migratory patterns

    Science.gov (United States)

    Donges, J. F.; Donner, R. V.; Marwan, N.; Breitenbach, S. F. M.; Rehfeld, K.; Kurths, J.

    2015-05-01

    The Asian monsoon system is an important tipping element in Earth's climate with a large impact on human societies in the past and present. In light of the potentially severe impacts of present and future anthropogenic climate change on Asian hydrology, it is vital to understand the forcing mechanisms of past climatic regime shifts in the Asian monsoon domain. Here we use novel recurrence network analysis techniques for detecting episodes with pronounced non-linear changes in Holocene Asian monsoon dynamics recorded in speleothems from caves distributed throughout the major branches of the Asian monsoon system. A newly developed multi-proxy methodology explicitly considers dating uncertainties with the COPRA (COnstructing Proxy Records from Age models) approach and allows for detection of continental-scale regime shifts in the complexity of monsoon dynamics. Several epochs are characterised by non-linear regime shifts in Asian monsoon variability, including the periods around 8.5-7.9, 5.7-5.0, 4.1-3.7, and 3.0-2.4 ka BP. The timing of these regime shifts is consistent with known episodes of Holocene rapid climate change (RCC) and high-latitude Bond events. Additionally, we observe a previously rarely reported non-linear regime shift around 7.3 ka BP, a timing that matches the typical 1.0-1.5 ky return intervals of Bond events. A detailed review of previously suggested links between Holocene climatic changes in the Asian monsoon domain and the archaeological record indicates that, in addition to previously considered longer-term changes in mean monsoon intensity and other climatic parameters, regime shifts in monsoon complexity might have played an important role as drivers of migration, pronounced cultural changes, and the collapse of ancient human societies.

  3. Indian monsoon variations during three contrasting climatic periods: the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

    Science.gov (United States)

    Zorzi, Coralie; Fernanda Sanchez Goñi, Maria; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2016-04-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  4. Bacterioplankton activity in the surface waters of the Arabian Sea during and after the 1994 SW monsoon

    Science.gov (United States)

    Pomroy, Alan; Joint, Ian

    1999-03-01

    Bacterial biomass and production were measured on two cruises to the northwestern Arabian Sea in 1994; the first cruise took place towards the end of the SW monsoon in September, and the second cruise during the inter-monsoon period in November and December. Although phytoplankton production was significantly higher during the monsoon, bacterial numbers showed little difference. Bacteria were most abundant in the euphotic zone and highest bacterial numbers were measured during the monsoon period in the Gulf of Oman and the shelf waters off southern Oman; in these regions, numbers ranged from 0.9 to 1.6×10 9 bacteria l -1. On both cruises, bacteria were less abundant in the euphotic zone of the central Arabian Sea and typically ca 0.8×10 9 cells l -1 were present. The majority of bacteria (80-95%) were small cocci that were larger (median diameter 0.40 μm) during the monsoon period than the inter-monsoon, when the cells had a diameter of 0.36 μm; there was no comparable change in cell dimensions of bacteria present as rods. Bacterial production was measured by the incorporation of 3H-thymidine and 3H-leucine. On both cruises, uptake rates were highest on the Omani shelf and decreased offshore. In the central Arabian Sea, thymidine incorporation rates were similar in the monsoon and inter-monsoon periods, but higher rates of leucine incorporation were measured during the monsoon period. Bacterial production was a relatively small proportion of phytoplankton production in both periods sampled; bacterial production was equivalent to between 10 and 30% of the daily primary production in the Arabian Sea.

  5. Impact of geographic variations of the convective and dehydration center on stratospheric water vapor over the Asian monsoon region

    Directory of Open Access Journals (Sweden)

    K. Zhang

    2016-06-01

    Full Text Available The Asian monsoon region is the most prominent moisture center of water vapor in the lower stratosphere (LS during boreal summer. Previous studies have suggested that the transport of water vapor to the Asian monsoon LS is controlled by dehydration temperatures and convection mainly over the Bay of Bengal and Southeast Asia. However, there is a clear geographic variation of convection associated with the seasonal and intra-seasonal variations of the Asian monsoon circulation, and the relative influence of such a geographic variation of convection vs. the variation of local dehydration temperatures on water vapor transport is still not clear. Using satellite observations from the Aura Microwave Limb Sounder (MLS and a domain-filling forward trajectory model, we show that almost half of the seasonal water vapor increase in the Asian monsoon LS are attributable to geographic variations of convection and resultant variations of the dehydration center, of which the influence is comparable to the influence of the local dehydration temperature increase. In particular, dehydration temperatures are coldest over the southeast and warmest over the northwest Asian monsoon region. Although the convective center is located over Southeast Asia, an anomalous increase of convection over the northwest Asia monsoon region increases local diabatic heating in the tropopause layer and air masses entering the LS are dehydrated at relatively warmer temperatures. Due to warmer dehydration temperatures, anomalously moist air enters the LS and moves eastward along the northern flank of the monsoon anticyclonic flow, leading to wet anomalies in the LS over the Asian monsoon region. Likewise, when convection increases over the Southeast Asia monsoon region, dry anomalies appear in the LS. On a seasonal scale, this feature is associated with the monsoon circulation, convection and diabatic heating marching towards the northwest Asia monsoon region from June to August. The

  6. Forced decadal changes in the East Asian summer monsoon: the roles of greenhouse gases and anthropogenic aerosols

    Science.gov (United States)

    Tian, Fangxing; Dong, Buwen; Robson, Jon; Sutton, Rowan

    2018-02-01

    Since the mid-1990s precipitation trends over eastern China display a dipole pattern, characterized by positive anomalies in the south and negative anomalies in the north, named as the Southern-Flood-Northern-Drought (SFND) pattern. This work investigates the drivers of decadal changes of the East Asian summer monsoon (EASM), and the dynamical mechanisms involved, by using a coupled climate model (specifically an atmospheric general circulation model coupled to an ocean mixed layer model) forced by changes in (1) anthropogenic greenhouse gases (GHG), (2) anthropogenic aerosol (AA) and (3) the combined effects of both GHG and AA (All Forcing) between two periods across the mid-1990s. The model experiment forced by changes in All Forcing shows a dipole pattern of response in precipitation over China that is similar to the observed SFND pattern across the mid-1990s, which suggests that anthropogenic forcing changes played an important role in the observed decadal changes. Furthermore, the experiments with separate forcings indicate that GHG and AA forcing dominate different parts of the SFND pattern. In particular, changes in GHG increase precipitation over southern China, whilst changes in AA dominate in the drought conditions over northern China. Increases in GHG cause increased moisture transport convergence over eastern China, which leads to increased precipitation. The AA forcing changes weaken the EASM, which lead to divergent wind anomalies over northern China and reduced precipitation.

  7. Seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in the southern South China Sea under the influence of the East Asian monsoon

    Science.gov (United States)

    Zhou, L.; Tan, Y.; Huang, L.; Hu, Z.; Ke, Z.

    2015-11-01

    To examine seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in oligotrophic tropical waters under the influence of seasonal reversing monsoon, dilution experiments were conducted during the summer of 2009 (21 May to 9 June) and winter 2010 (9 to 18 November) in the southern South China Sea (SSCS). The results showed that environmental variables, phytoplankton biomass, phytoplankton growth rate (μ), microzooplankton grazing rate (m), and correlationship (coupling) between the μ and m, rather than the microzooplankton grazing impact on phytoplankton (m/μ) significantly varied between the two seasons. Higher relative preference index (RPI) for the larger-sized (> 3 μm) phytoplankton than pico-phytoplankton (intermittent arrivals of the northeast winter monsoon could lead to the low μ and m, and the decoupling between the μ and m in the SSCS, through influencing nutrient supply to the surface water, and inducing surface seawater salinity decrease. The low m/μ (waters such as that of the SSCS.

  8. Multifaceted intra-seasonal modes over the East Asia-western North Pacific summer monsoon region

    Science.gov (United States)

    Ha, K. J.; Oh, H.

    2017-12-01

    Intra-seasonal monsoon prediction is the most imperative task due to high impact on 2/3 of world populations' daily life, but there remains an enduring challenge in climate science. The present study aims to provide a physical understanding of the sources for prediction of dominant intra-seasonal modes in the East Asian-western North Pacific summer monsoon (EA-WNPSM): preMeiyu&Baiu, Changma&Meiyu, WNPSM, and monsoon gyre modes classified by the self-organizing map analysis. The preMeiyu-Baiu mode is strongly linked to both the anomalous low-level convergence and vertical wind shear through baroclinic instability, and the Changma&Meiyu mode has a strengthened tropic-subtropics connection along the western north Pacific subtropical high, which induces vertical destabilization and strong convective instability. The WNPSM and monsoon gyre modes are characterized by anomalous southeasterly flow of warm and moist air from western north Pacific monsoon, and low-level easterly flow, respectively. Prominent difference in response to the ENSO leads to different effects of the Indian Ocean and western Pacific thermal state, and consequently, the distinct moisture supply and instability variations for the EASM intra-seasonal modes. We attempt to determine the predictability sources for the four modes in the EA-WNPSM using physical-empirical model. The selected predictors are based on the persistent and tendency signals of the SST/2m air temperature and sea level pressure fields, which reflect the asymmetric response to the ENSO and the ocean and land surface anomalous conditions. For the preMeiyu&Baiu mode, the SST cooling tendency over the WNP, which persists into summer, is the distinguishing contributor which is causative of north-south thermal contrast. Since the Changma&Meiyu mode is strongly related to the WNP subtropical high, a major precursor is the persistent SST difference between the Indian Ocean and the western Pacific. The WNPSM mode is mostly affected by the

  9. The impact of monsoon intraseasonal variability on renewable power generation in India

    International Nuclear Information System (INIS)

    Dunning, C M; Turner, A G; Brayshaw, D J

    2015-01-01

    India is increasingly investing in renewable technology to meet rising energy demands, with hydropower and other renewables comprising one-third of current installed capacity. Installed wind-power is projected to increase 5-fold by 2035 (to nearly 100GW) under the International Energy Agency's New Policies scenario. However, renewable electricity generation is dependent upon the prevailing meteorology, which is strongly influenced by monsoon variability. Prosperity and widespread electrification are increasing the demand for air conditioning, especially during the warm summer. This study uses multi-decadal observations and meteorological reanalysis data to assess the impact of intraseasonal monsoon variability on the balance of electricity supply from wind-power and temperature-related demand in India. Active monsoon phases are characterized by vigorous convection and heavy rainfall over central India. This results in lower temperatures giving lower cooling energy demand, while strong westerly winds yield high wind-power output. In contrast, monsoon breaks are characterized by suppressed precipitation, with higher temperatures and hence greater demand for cooling, and lower wind-power output across much of India. The opposing relationship between wind-power supply and cooling demand during active phases (low demand, high supply) and breaks (high demand, low supply) suggests that monsoon variability will tend to exacerbate fluctuations in the so-called demand-net-wind (i.e., electrical demand that must be supplied from non-wind sources). This study may have important implications for the design of power systems and for investment decisions in conventional schedulable generation facilities (such as coal and gas) that are used to maintain the supply/demand balance. In particular, if it is assumed (as is common) that the generated wind-power operates as a price-taker (i.e., wind farm operators always wish to sell their power, irrespective of price) then investors

  10. The impact of monsoon intraseasonal variability on renewable power generation in India

    Science.gov (United States)

    Dunning, C. M.; Turner, A. G.; Brayshaw, D. J.

    2015-06-01

    India is increasingly investing in renewable technology to meet rising energy demands, with hydropower and other renewables comprising one-third of current installed capacity. Installed wind-power is projected to increase 5-fold by 2035 (to nearly 100GW) under the International Energy Agency's New Policies scenario. However, renewable electricity generation is dependent upon the prevailing meteorology, which is strongly influenced by monsoon variability. Prosperity and widespread electrification are increasing the demand for air conditioning, especially during the warm summer. This study uses multi-decadal observations and meteorological reanalysis data to assess the impact of intraseasonal monsoon variability on the balance of electricity supply from wind-power and temperature-related demand in India. Active monsoon phases are characterized by vigorous convection and heavy rainfall over central India. This results in lower temperatures giving lower cooling energy demand, while strong westerly winds yield high wind-power output. In contrast, monsoon breaks are characterized by suppressed precipitation, with higher temperatures and hence greater demand for cooling, and lower wind-power output across much of India. The opposing relationship between wind-power supply and cooling demand during active phases (low demand, high supply) and breaks (high demand, low supply) suggests that monsoon variability will tend to exacerbate fluctuations in the so-called demand-net-wind (i.e., electrical demand that must be supplied from non-wind sources). This study may have important implications for the design of power systems and for investment decisions in conventional schedulable generation facilities (such as coal and gas) that are used to maintain the supply/demand balance. In particular, if it is assumed (as is common) that the generated wind-power operates as a price-taker (i.e., wind farm operators always wish to sell their power, irrespective of price) then investors in

  11. Heat budget parameters for the southwestern Arabian Sea during monsoon - 88 experiment

    Digital Repository Service at National Institute of Oceanography (India)

    RameshBabu, V.; Gopalakrishna, V.V.; Sastry, J.S.

    . The cooling in the upper layers is partly accountEd. by the surface heat exchange processes and the subsurface heat gain suggests the influence of sinking motion in the study area wherein the dynamic topography field is predominantly characterised...

  12. Southwest monsoon influences the water quality and waste assimilative capacity in the Mandovi estuary (Goa state, India)

    Digital Repository Service at National Institute of Oceanography (India)

    VishnuRadhan, R.; Sagayadoss, J.; Seelan, E.; Vethamony, P.; Shirodkar, P.V.; Zainudin, Z.; Shirodkar, S.

    The monsoon-dominated Mandovi estuary is located in Goa state – a global tourist destination along the centralwest coast of India. In addition to factor analyses of water quality data, the water quality index (WQI), trophic state index (TSI...

  13. Reconstruction of late Quaternary monsoon oscillations based on clay mineral proxies using sediment cores from the western margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.; Schneider, R.R.

    sites were from the hinterland rocks and soils. Careful evaluations of several factors that could complicate the clay distribution in marine environment indicate that the clay mineral parameters can be used as proxies for the intensity of summer monsoon...

  14. Interdecadal modulation of El Niño teleconnection on monsoon Asia climate over the past five centuries

    Science.gov (United States)

    Li, J.; Xie, S. P.

    2017-12-01

    The El Niño influence on monsoon Asia climate weakened during the mid-20th century and strenthened substantially after the late 1970s. Exploring the nature of such an interdecadal variation is constrained by short instrumental records. Here we synthesize the Indo-Pacific tree-rings and coral records to reconstruct monsoon Asia temperature and moisture change during the past five centuries, and show that the interdecadal modulation of El Niño teleconnection on monsoon Asia climate is a robust feature beyond the instrumenal era. Comparison with proxy El Niño records indicates that the El Niño-monsoon Asia climate teleconnection is controlled by interdecadal changes in ENSO variance, with strong (weak) teleconnection in periods of high (low) variance, respectively.

  15. The crucial role of ocean-atmosphere coupling on the Indian monsoon anomalous response during dipole events

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan, R.; Swapna, P.; Ayantika, D.C.; Mujumdar, M. [Indian Institute of Tropical Meteorology, Climate and Global Modelling Division, Pune (India); Sundaram, Suchithra [Indian Institute of Tropical Meteorology, Climate and Global Modelling Division, Pune (India); Universite Catholique de Louvain, Institut d' Astronomie de Geophysique G. Lemaitre, Louvain-La-Neuve (Belgium); Kumar, Vinay [Indian Institute of Tropical Meteorology, Climate and Global Modelling Division, Pune (India); Florida State University, Department of Meteorology, Tallahassee, FL (United States)

    2011-07-15

    This paper examines an issue concerning the simulation of anomalously wet Indian summer monsoons like 1994 which co-occurred with strong positive Indian Ocean Dipole (IOD) conditions in the tropical Indian Ocean. Contrary to observations it has been noticed that standalone atmospheric general circulation models (AGCM) forced with observed SST boundary condition, consistently depicted a decrease of the summer monsoon rainfall during 1994 over the Indian region. Given the ocean-atmosphere coupling during IOD events, we have examined whether the failure of standalone AGCM simulations in capturing wet Indian monsoons like 1994 can be remedied by including a simple form of coupling that allows the monsoon circulation to dynamically interact with the IOD anomalies. With this view, we have performed a suite of simulations by coupling an AGCM to a slab-ocean model with spatially varying mixed-layer-depth (MLD) specified from observations for the 1994 IOD; as well as four other cases (1983, 1997, 2006, 2007). The specification of spatially varying MLD from observations allows us to constrain the model to observed IOD conditions. It is seen that the inclusion of coupling significantly improves the large-scale circulation response by strengthening the monsoon cross-equatorial flow; leading to precipitation enhancement over the subcontinent and rainfall decrease over south-eastern tropical Indian Ocean - in a manner broadly consistent with observations. A plausible physical mechanism is suggested to explain the monsoonal response in the coupled frame-work. These results warrant the need for improved monsoon simulations with fully coupled models to be able to better capture the observed monsoon interannual variability. (orig.)

  16. Response of the Asian summer monsoons to idealized precession and obliquity forcing in a set of GCMs

    Science.gov (United States)

    Bosmans, J. H. C.; Erb, M. P.; Dolan, A. M.; Drijfhout, S. S.; Tuenter, E.; Hilgen, F. J.; Edge, D.; Pope, J. O.; Lourens, L. J.

    2018-05-01

    We examine the response of the Indian and East Asian summer monsoons to separate precession and obliquity forcing, using a set of fully coupled high-resolution models for the first time: EC-Earth, GFDL CM2.1, CESM and HadCM3. We focus on the effect of insolation changes on monsoon precipitation and underlying circulation changes, and find strong model agreement despite a range of model physics, parameterization, and resolution. Our results show increased summer monsoon precipitation at times of increased summer insolation, i.e. minimum precession and maximum obliquity, accompanied by a redistribution of precipitation and convection from ocean to land. Southerly monsoon winds over East Asia are strengthened as a consequence of an intensified land-sea pressure gradient. The response of the Indian summer monsoon is less straightforward. Over south-east Asia low surface pressure is less pronounced and winds over the northern Indian Ocean are directed more westward. An Indian Ocean Dipole pattern emerges, with increased precipitation and convection over the western Indian Ocean. Increased temperatures occur during minimum precession over the Indian Ocean, but not during maximum obliquity when insolation is reduced over the tropics and southern hemisphere during northern hemisphere summer. Evaporation is reduced over the northern Indian Ocean, which together with increased precipitation over the western Indian Ocean dampens the increase of monsoonal precipitation over the continent. The southern tropical Indian Ocean as well as the western tropical Pacific (for precession) act as a moisture source for enhanced monsoonal precipitation. The models are in closest agreement for precession-induced changes, with more model spread for obliquity-induced changes, possibly related to a smaller insolation forcing. Our results indicate that a direct response of the Indian and East Asian summer monsoons to insolation forcing is possible, in line with speleothem records but in

  17. A Centennial Episode of Weak East Asian Summer Monsoon in the Midst of the Medieval Warming

    Science.gov (United States)

    Jin, C.; Liu, J.; Wang, B.; Wang, Z.; Yan, M.

    2017-12-01

    Recent paleo-proxy evidences suggested that the East Asian summer monsoon (EASM) was generally strong (i.e., northern China wet and southern China dry) during the Medieval Warm Period (MWP, 9th to the mid-13th century), however, there was a centennial period (around 11th century) during which the EASM was weak. This study aims to explore the causes of this centennial weak EASM episode and in general, what controls the centennial variability of the EASM in the pre-industrial period of AD 501-1850. With the Community Earth System Model (CESM), a suit of control and forced experiments were conducted for the past 2000 years. The model run with all external forcings simulates a warm period of EA from AD 801-1250 with a generally increased summer mean precipitation over the northern EA; however, during the 11th century (roughly from AD 980 to AD 1100), the EASM is significantly weaker than the other periods during the MWP. We find that on the multi-decadal to centennial time scale, a strong EASM is associated with a La Nina-like Indo-Pacific warming and the opposite is also true. This sea surface temperature (SST) anomaly pattern represents the leading EOF mode of centennial SST variations, and it is primarily forced by the solar radiation and volcanic activity, whereas the land use/land cover and greenhouse gases as well as internal dynamics play a negligible role. During the MWP, the solar forcing plays a dominate role in supporting the SST variation as the volcanic activity is weak. The weakening of the EASM during the AD 980-1100 is attributed to the relatively low solar radiation, which leads to a prevailing El Nino-like Indo-Pacific cooling with strongest cooling occurring in the equatorial western Pacific. The suppressed convection over the equatorial western Pacific directly induces a Philippine Sea anticyclone anomaly, which increases southern China precipitation, meanwhile suppresses Philippine Sea precipitation, exciting a meridional teleconnection that

  18. Spatial distribution of aerosol black carbon over India during pre-monsoon season

    Science.gov (United States)

    Beegum, S. Naseema; Moorthy, K. Krishna; Babu, S. Suresh; Satheesh, S. K.; Vinoj, V.; Badarinath, K. V. S.; Safai, P. D.; Devara, P. C. S.; Singh, Sacchidanand; Vinod; Dumka, U. C.; Pant, P.

    Aerosol black carbon (BC) mass concentrations ([BC]), measured continuously during a mutli-platform field experiment, Integrated Campaign for Aerosols gases and Radiation Budget (ICARB, March-May 2006), from a network of eight observatories spread over geographically distinct environments of India, (which included five mainland stations, one highland station, and two island stations (one each in Arabian Sea and Bay of Bengal)) are examined for their spatio-temporal characteristics. During the period of study, [BC] showed large variations across the country, with values ranging from 27 μg m -3 over industrial/urban locations to as low as 0.065 μg m -3 over the Arabian Sea. For all mainland stations, [BC] remained high compared to highland as well as island stations. Among the island stations, Port Blair (PBR) had higher concentration of BC, compared to Minicoy (MCY), implying more absorbing nature of Bay of Bengal aerosols than Arabian Sea. The highland station Nainital (NTL), in the central Himalayas, showed low values of [BC], comparable or even lower than that of the island station PBR, indicating the prevalence of cleaner environment over there. An examination of the changes in the mean temporal features, as the season advances from winter (December-February) to pre-monsoon (March-May), revealed that: (a) Diurnal variations were pronounced over all the mainland stations, with an afternoon low and a nighttime high; (b) At the islands, the diurnal variations, though resembled those over the mainlands, were less pronounced; and (c) In contrast to this, highland station showed an opposite pattern with an afternoon high and a late night or early morning low. The diurnal variations at all stations are mainly caused by the dynamics of local Atmospheric Boundary Layer (ABL). At the entire mainland as well as island stations (except HYD and DEL), [BC] showed a decreasing trend from January to May. This is attributed to the increased convective mixing and to the

  19. Contrasting predictability of summer monsoon rainfall ISOs over the northeastern and western Himalayan region: an application of Hurst exponent

    Science.gov (United States)

    Mukherjee, Sandipan

    2017-09-01

    Due to heterogeneous nonlinear forcing of complex geomorphological features, predictability of monsoon rainfall 10-90-day intra-seasonal oscillations (ISO) over the complex terrain of northeastern and western Himalayan region (NEH and WH) remained poorly quantified. Using 72 and 61 number of station observations of monsoon rainfall ISOs of NEH and WH, respectively, this study attempts to investigate variation in the regional scale predictability of monsoon rainfall ISOs with respect to changing geomorphological features and monsoon rainfall characteristics. In view of the bimodal nonlinear dynamical structure of monsoon rainfall ISO, the fractal dynamical Hurst exponent-based predictability indices are estimated as an indicator of predictability for station observations of NEH and WH, and relationships with elevations, slopes, aspects, and average numbers of occurrences of long (short) spell of active (break) phases are investigated. Results show 10-90-day ISOs are anti-persistent throughout the IHR, although, predictability of 10-90-day ISOs is higher over the NEH region than WH. Predictabilities of ISOs are found to decrease with increasing elevation and slope for both NEH and WH regions. Predictabilities of ISOs over both regions are also found to increase linearly as the number of occurrences of monsoon rainfall ISO phases (active/break) increases.

  20. Seasonal modulation of the Asian summer monsoon between the Medieval Warm Period and Little Ice Age: a multi model study

    Science.gov (United States)

    Kamae, Youichi; Kawana, Toshi; Oshiro, Megumi; Ueda, Hiroaki

    2017-12-01

    Instrumental and proxy records indicate remarkable global climate variability over the last millennium, influenced by solar irradiance, Earth's orbital parameters, volcanic eruptions and human activities. Numerical model simulations and proxy data suggest an enhanced Asian summer monsoon during the Medieval Warm Period (MWP) compared to the Little Ice Age (LIA). Using multiple climate model simulations, we show that anomalous seasonal insolation over the Northern Hemisphere due to a long cycle of orbital parameters results in a modulation of the Asian summer monsoon transition between the MWP and LIA. Ten climate model simulations prescribing historical radiative forcing that includes orbital parameters consistently reproduce an enhanced MWP Asian monsoon in late summer and a weakened monsoon in early summer. Weakened, then enhanced Northern Hemisphere insolation before and after June leads to a seasonally asymmetric temperature response over the Eurasian continent, resulting in a seasonal reversal of the signs of MWP-LIA anomalies in land-sea thermal contrast, atmospheric circulation, and rainfall from early to late summer. This seasonal asymmetry in monsoon response is consistently found among the different climate models and is reproduced by an idealized model simulation forced solely by orbital parameters. The results of this study indicate that slow variation in the Earth's orbital parameters contributes to centennial variability in the Asian monsoon transition.[Figure not available: see fulltext.

  1. Role of aerosols on the Indian Summer Monsoon variability, as simulated by state-of-the-art global climate models

    Science.gov (United States)

    Cagnazzo, Chiara; Biondi, Riccardo; D'Errico, Miriam; Cherchi, Annalisa; Fierli, Federico; Lau, William K. M.

    2016-04-01

    Recent observational and modeling analyses have explored the interaction between aerosols and the Indian summer monsoon precipitation on seasonal-to-interannual time scales. By using global scale climate model simulations, we show that when increased aerosol loading is found on the Himalayas slopes in the premonsoon period (April-May), intensification of early monsoon rainfall over India and increased low-level westerly flow follow, in agreement with the elevated-heat-pump (EHP) mechanism. The increase in rainfall during the early monsoon season has a cooling effect on the land surface that may also be amplified through solar dimming (SD) by more cloudiness and aerosol loading with subsequent reduction in monsoon rainfall over India. We extend this analyses to a subset of CMIP5 climate model simulations. Our results suggest that 1) absorbing aerosols, by influencing the seasonal variability of the Indian summer monsoon with the discussed time-lag, may act as a source of predictability for the Indian Summer Monsoon and 2) if the EHP and SD effects are operating also in a number of state-of-the-art climate models, their inclusion could potentially improve seasonal forecasts.

  2. The role of bias in simulation of the Indian monsoon and its relationship to predictability

    Science.gov (United States)

    Kelly, P.

    2016-12-01

    Confidence in future projections of how climate change will affect the Indian monsoon is currently limited by- among other things-model biases. That is, the systematic error in simulating the mean present day climate. An important priority question in seamless prediction involves the role of the mean state. How much of the prediction error in imperfect models stems from a biased mean state (itself a result of many interacting process errors), and how much stems from the flow dependence of processes during an oscillation or variation we are trying to predict? Using simple but effective nudging techniques, we are able to address this question in a clean and incisive framework that teases apart the roles of the mean state vs. transient flow dependence in constraining predictability. The role of bias in model fidelity of simulations of the Indian monsoon is investigated in CAM5, and the relationship to predictability in remote regions in the "free" (non-nudged) domain is explored.

  3. Trends of rainfall regime in Peninsular Malaysia during northeast and southwest monsoons

    Science.gov (United States)

    Chooi Tan, Kok

    2018-04-01

    The trends of rainfall regime in Peninsular Malaysia is mainly affected by the seasonal monsoon. The aim of this study is to investigate the impact of northeast and southwest monsoons on the monthly rainfall patterns over Badenoch Estate, Kedah. In addition, the synoptic maps of wind vector also being developed to identify the wind pattern over Peninsular Malaysia from 2007 – 2016. On the other hand, the archived daily rainfall data is acquired from Malaysian Meteorological Department. The temporal and trends of the monthly and annual rainfall over the study area have been analysed from 2007 to 2016. Overall, the average annual precipitation over the study area from 2007 to 2016 recorded by rain gauge is 2562.35 mm per year.

  4. Monsoon variability in the Himalayas under the condition of global warming

    International Nuclear Information System (INIS)

    Duan Keqin; Yao Tandong

    2003-01-01

    An ice core-drilling program was carried out at the accumulation area of Dasuopu glacier (28deg23'N, 85deg43'E, 7100 m a.s.l.) in the central Himalayas in 1997. The ice core was analyzed continuously for stable isotopes (δ 18 O), and major ions throughout the core. Cycles indicated by δ 18 O, cations were identified and counted as seasonal fluctuations as annual increment from maximum to maximum values. Reconstructed 300-year annual net accumulation (water equivalent) from the core, with a good correlation to Indian monsoon, reflects a major precipitation trend in the central Himalayas. The accumulation trend, separated from the time series, shows a strong negative correlation to Northern Hemisphere temperature. Generally, as northern hemisphere temperature increases 0.1degC, the accumulation decreases about 80 mm, reflecting monsoon rainfall in the central Himalayas has decreased over the past decades in the condition of global warming. (author)

  5. On the unstable ENSO-Western North Pacific Monsoon relation during the 20th Century

    Science.gov (United States)

    Vega Martín, Inmaculada; Gallego Puyol, David; Ribera Rodriguez, Pedro; Gómez Delgado, Francisco de Paula; Peña-Ortiz, Cristina

    2017-04-01

    The concept of the Western North Pacific Summer Monsoon (WNPSM) appeared for the first time in 1987. Unlike the Indian Summer Monsoon and the East Asian summer monsoon, the WNPSM is an oceanic monsoon driven essentially by the meridional gradient of sea surface temperature. Its circulation is characterized by a northwest-southeast oriented monsoon trough with intense precipitation and low-level southwesterlies and upper-tropospheric easterlies in the region [100°-130° E, 5°-15°N]. Although this monsoon is mainly oceanic, it modulates the precipitation of densely populated areas such as the Philippines. To date, the WNPSM has been quantified by the so-called Western North Pacific Monsoon Index (WNPMI), an index based on wind anomalies over large domains of the Western Pacific. The requirement of continuous observed wind over remote oceanic areas to compute the WNPMI has limited its availability to the 1949-2014 period. In this work we have extended the index by almost 100 years by using historical observations of wind direction taken aboard ships. Our Western North Pacific Directional Index (WNPDI), is defined as the sum of the persistence of the low-level westerly winds in [5°-15°N, 100°-130°E] and easterly winds in [20°-30°N, 110°-140°E]. The new WNPDI index is highly correlated to the existent WNPMI for the concurrent period (1948-2014). (r=+0.88, p<0.01), indicating that the new approach based in the use of wind direction alone (a variable that can be considered instrumental even before the 20th Century), captures most of the monsoonal signal. Previous studies found that, during the second part of the 20th Century the WNPSM exhibited two basic characteristics: first a large interannual variability and second, a significant relation between the WNPSM and the El Niño/Southern Oscillation (ENSO) in a way in which a strong (weak) WNPSM tends to occur during the El Niño (La Niña) developing year or/and La Niña (El Niño) decaying year. The analysis of

  6. Failure of CMIP5 climate models in simulating post-1950 decreasing trend of Indian monsoon

    Science.gov (United States)

    Saha, Anamitra; Ghosh, Subimal; Sahana, A. S.; Rao, E. P.

    2014-10-01

    Impacts of climate change on Indian Summer Monsoon Rainfall (ISMR) and the growing population pose a major threat to water and food security in India. Adapting to such changes needs reliable projections of ISMR by general circulation models. Here we find that, majority of new generation climate models from Coupled Model Intercomparison Project phase5 (CMIP5) fail to simulate the post-1950 decreasing trend of ISMR. The weakening of monsoon is associated with the warming of Southern Indian Ocean and strengthening of cyclonic formation in the tropical western Pacific Ocean. We also find that these large-scale changes are not captured by CMIP5 models, with few exceptions, which is the reason of this failure. Proper representation of these highlighted geophysical processes in next generation models may improve the reliability of ISMR projections. Our results also alert the water resource planners to evaluate the CMIP5 models before using them for adaptation strategies.

  7. The Abrupt Onset of the Modern South Asian Monsoon Winds (iodp Exp. 359)

    Science.gov (United States)

    Betzler, C.; Eberli, G. P.; Kroon, D.; Wright, J. D.; Swart, P. K.; Nath, B. N.; Reijmer, J.; Alvarez Zarikian, C. A.

    2016-12-01

    The South Asian Monson (SAM) is one of the most extreme features in Earth's climate system, yet its initiation and variations are not well established. The SAM is a seasonal reversal of winds accompanied by changes in precipitation with heavy rain during the summer monsoon. It is one of the most intense annually recurring climatic elements and of immense importance in supplying moisture to the Indian subcontinent thus affecting human population and vegetation, as well as marine biota in the surrounding seas. The seasonal precipitation change is one of the SAM elements most noticed on land, whereas the reversal of the wind regime is the dominating driver of circulation in the central and northern Indian Ocean realm. New data acquired during International Ocean Discovery Program Expedition 359 from the Inner Sea of the Maldives provide a previously unread archive that reveals an abrupt onset of the SAM-linked ocean circulation pattern and its relationship to the long term Neogene climate cooling. In particular it registers ocean current fluctuations and changes of intermediate water mass properties for the last 25 myrs that are directly related to the monsoon. Dating the deposits of SAM wind-driven currents yields an age of 12.9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of sedimentary organic matter. A weaker `proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

  8. Interhemispheric Changes in Atlantic Ocean Heat Content and Their Link to Global Monsoons

    Science.gov (United States)

    Lopez, H.; Lee, S. K.; Dong, S.; Goni, G. J.

    2015-12-01

    This study tested the hypothesis whether low frequency decadal variability of the South Atlantic meridional heat transport (SAMHT) influences decadal variability of the global monsoons. A multi-century run from a state-of-the-art coupled general circulation model is used as basis for the analysis. Our findings indicate that multi-decadal variability of the South Atlantic Ocean plays a key role in modulating atmospheric circulation via interhemispheric changes in Atlantic Ocean heat content. Weaker SAMHT produces anomalous ocean heat divergence over the South Atlantic resulting in negative ocean heat content anomaly about 15 years later. This, in turn, forces a thermally direct anomalous interhemispheric Hadley circulation in the atmosphere, transporting heat from the northern hemisphere (NH) to the southern hemisphere (SH) and moisture from the SH to the NH, thereby intensify (weaken) summer (winter) monsoon in the NH and winter (summer) monsoon in the SH. Results also show that anomalous atmospheric eddies, both transient and stationary, transport heat northward in both hemispheres producing eddy heat flux convergence (divergence) in the NH (SH) around 15-30°, reinforcing the anomalous Hadley circulation. The effect of eddies on the NH (SH) poleward of 30° is opposite with heat flux divergence (convergence), which must be balanced by sinking (rising) motion, consistent with a poleward (equatorward) displacement of the jet stream and mean storm track. The mechanism described here could easily be interpreted for the case of strong SAMHT, with the reverse influence on the interhemispheric atmospheric circulation and monsoons. Overall, SAMHT decadal variability leads its atmospheric response by about 15 years, suggesting that the South Atlantic is a potential predictor of global climate variability.

  9. Interannual Variability, Global Teleconnection, and Potential Predictability Associated with the Asian Summer Monsoon

    Science.gov (United States)

    Lau, K. M.; Kim, K. M.; Li, J. Y.

    2001-01-01

    In this Chapter, aspects of global teleconnections associated with the interannual variability of the Asian summer monsoon (ASM) are discussed. The basic differences in the basic dynamics of the South Asian Monsoon and the East Asian monsoon, and their implications on global linkages are discussed. Two teleconnection modes linking ASM variability to summertime precipitation over the continental North America were identified. These modes link regional circulation and precipitation anomalies over East Asia and continental North America, via coupled atmosphere-ocean variations over the North Pacific. The first mode has a large zonally symmetrical component and appears to be associated with subtropical jetstream variability and the second mode with Rossby wave dispersion. Both modes possess strong sea surface temperature (SST) expressions in the North Pacific. Results show that the two teleconnection modes may have its origin in intrinsic modes of sea surface temperature variability in the extratropical oceans, which are forced in part by atmospheric variability and in part by air-sea interaction. The potential predictability of the ASM associated with SST variability in different ocean basins is explored using a new canonical ensemble correlation prediction scheme. It is found that SST anomalies in tropical Pacific, i.e., El Nino, is the most dominant forcing for the ASM, especially over the maritime continent and eastern Australia. SST anomalies in the India Ocean may trump the influence from El Nino in western Australia and western maritime continent. Both El Nino, and North Pacific SSTs contribute to monsoon precipitation anomalies over Japan, southern Korea, northern and central China. By optimizing SST variability signals from the world ocean basins using CEC, the overall predictability of ASM can be substantially improved.

  10. Pre and Post-monsoon Seasonal Variation of some Heavy Metal ...

    African Journals Online (AJOL)

    ADOWIE PERE

    ABSTRACT: The concentration of heavy metals (Fe, As and Cu) was examine in riverbed sediments of Gomti river, Lucknow at selected sites in pre and post monsoon season for three consecutive years (2009-11). The concentration was ranged between (As: 0.07-0.7, Fe: 7462.00-7977.00, Cu: 10.98-36.73 μg g-1) in ...

  11. Impact of convection over the equatorial trough on the summer monsoon activity over India

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Shenoi, S.S.C.; Schulz, J.

    . There have been studies (Cadet and Olory Togbe, 1981; Sadhuram and Sastry, 1987) on the role of Equatorial Trough (ET) as well as Southern Hemispheric Equatorial Trough (SHET) on the rainfall over central India. Most of these studies are related... the ET, WET and EET behave in a similar fashion during different monsoon and El Nino conditions ? c) What role do the synoptic systems play during the BM over the Indian subcontinent? 2. Data and Methodology The pentad precipitation data used...

  12. Possible teleconnections between East and South Asian summer monsoon precipitation in projected future climate change

    Science.gov (United States)

    Woo, Sumin; Singh, Gyan Prakash; Oh, Jai-Ho; Lee, Kyoung-Min

    2018-01-01

    The present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010-2039), mid-(2040-2069) and far-(2070-2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40 km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea-Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850 hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea-Japan, while precipitation variations over Korea-Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea-Japan and Southern China with the wind (at 850 hPa) and MSLP fields indicate that the major parts of the moisture over Korea-Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity.

  13. Spatio-Temporal Variation and Monsoon Effect on the Temperature Lapse Rate of a Subtropical Island

    Directory of Open Access Journals (Sweden)

    Ching-An Chiu

    2014-01-01

    Full Text Available Temperature lapse rate (TLR has been widely used in the prediction of mountain climate and vegetation and in many ecological models. The aims of this paper are to explore the spatio-temporal variations and monsoon effects on the TLR in the subtropical island of Taiwan with its steep Central Mountain Region (CMR. A TLR analysis using the 32-year monthly mean air temperatures and elevations from 219 weather stations (sea level to 3852 m a.s.l. was performed based on different geographical regions and monsoon exposures. The results revealed that the average TLR for all of Taiwan is -5.17°C km-1, with a general tendency to be steeper in summer and shallower in winter. The results are also shallower than the typical or global average TLR of -6.5°C km-1. During the prevailing northeast monsoon season (winter, the TLR exhibits a contrast between the windward side (steeper, -5.97°C km-1 and the leeward side (shallower, -4.51°C km-1. From the diagnosis on spatial characteristics of monthly cloud amount and vertical atmospheric profiles, this contrasting phenomenon may be explained by the warming effect of onshore stratus clouds (500 - 2500 m depth on cold and dry Siberian monsoon air on the windward side of the CMR. On the southwestern leeward side of the CMR, the low-level (1500 m, the weak ventilation atmosphere and temperature inversion make the TLR shallower than on the windward side.

  14. Impact of atmospheric circulation types on southwest Asian dust and Indian summer monsoon rainfall

    Science.gov (United States)

    Kaskaoutis, D. G.; Houssos, E. E.; Solmon, F.; Legrand, M.; Rashki, A.; Dumka, U. C.; Francois, P.; Gautam, R.; Singh, R. P.

    2018-03-01

    This study examines the meteorological feedback on dust aerosols and rainfall over the Arabian Sea and India during the summer monsoon using satellite data, re-analysis and a regional climate model. Based on days with excess aerosol loading over the central Ganges basin during May - September, two distinct atmospheric circulation types (weather clusters) are identified, which are associated with different dust-aerosol and rainfall distributions over south Asia, highlighting the role of meteorology on dust emissions and monsoon rainfall. Each cluster is characterized by different patterns of mean sea level pressure (MSLP), geopotential height at 700 hPa (Z700) and wind fields at 1000 hPa and at 700 hPa, thus modulating changes in dust-aerosol loading over the Arabian Sea. One cluster is associated with deepening of the Indian/Pakistan thermal low leading to (i) increased cyclonicity and thermal convection over northwestern India and Arabian Peninsula, (ii) intensification of the southwest monsoon off the Horn of Africa, iii) increase in dust emissions from Rub-Al-Khali and Somalian deserts, (iv) excess dust accumulation over the Arabian Sea and, (v) strengthening of the convergence of humid air masses and larger precipitation over Indian landmass compared to the other cluster. The RegCM4.4 model simulations for dust-aerosol and precipitation distributions support the meteorological fields and satellite observations, while the precipitation over India is positively correlated with the aerosol loading over the Arabian Sea on daily basis for both weather clusters. This study highlights the key role of meteorology and atmospheric dynamics on dust life cycle and rainfall over the monsoon-influenced south Asia.

  15. Impact of Monsoon to Aquatic Productivity and Fish Landing at Pesawaran Regency Waters

    Science.gov (United States)

    Kunarso; Zainuri, Muhammad; Ario, Raden; Munandar, Bayu; Prayogi, Harmon

    2018-02-01

    Monsoon variability influences the productivity processes in the ocean and has different responses in each waters. Furthermore, variability of marine productivity affects to the fisheries resources fluctuation. This research has conducted using descriptive method to investigate the consequences of monsoon variability to aquatic productivity, sea surface temperature (SST), fish catches, and fish season periods at Pesawaran Regency waters, Lampung. Variability of aquatic productivity was determined based on chlorophyll-a indicator from MODIS satellite images. Monsoon variability was governed based on wind parameters and fish catches from fish landing data of Pesawaran fish market. The result showed that monsoon variability had affected to aquatic productivity, SST, and fish catches at Pesawaran Regency waters. Maximum wind speed and lowest SST occurred twice in a year, December to March and August to October, which the peaks were on January (2.55 m/s of wind speed and 29.66°C of SST) and September (2.44 m/s of wind speed and 29.06°C of SST). Also, Maximum aquatic productivity happened on January to March and July to September, which it was arisen simultaneously with maximum wind speed and the peaks was 0.74 mg/m3 and 0.78 mg/m3, on February and August respectively. The data showed that fish catches decreased along with strong wind speed and low SST. However, when weak wind speed and high SST occurred, fish catches increased. The correlation between Catch per Unit Effort (CPUE) with SST, wind speed, and chlorophyll-a was at value 0.76, -0.67, and -0.70, respectively. The high rate fish catches in Pesawaran emerged on March-May and September-December.

  16. Indian Summer Monsoon Rainfall: Implications of Contrasting Trends in the Spatial Variability of Means and Extremes

    Science.gov (United States)

    Ghosh, Subimal; Vittal, H.; Sharma, Tarul; Karmakar, Subhankar; Kasiviswanathan, K. S.; Dhanesh, Y.; Sudheer, K. P.; Gunthe, S. S.

    2016-01-01

    India’s agricultural output, economy, and societal well-being are strappingly dependent on the stability of summer monsoon rainfall, its variability and extremes. Spatial aggregate of intensity and frequency of extreme rainfall events over Central India are significantly increasing, while at local scale they are spatially non-uniform with increasing spatial variability. The reasons behind such increase in spatial variability of extremes are poorly understood and the trends in mean monsoon rainfall have been greatly overlooked. Here, by using multi-decadal gridded daily rainfall data over entire India, we show that the trend in spatial variability of mean monsoon rainfall is decreasing as exactly opposite to that of extremes. The spatial variability of extremes is attributed to the spatial variability of the convective rainfall component. Contrarily, the decrease in spatial variability of the mean rainfall over India poses a pertinent research question on the applicability of large scale inter-basin water transfer by river inter-linking to address the spatial variability of available water in India. We found a significant decrease in the monsoon rainfall over major water surplus river basins in India. Hydrological simulations using a Variable Infiltration Capacity (VIC) model also revealed that the water yield in surplus river basins is decreasing but it is increasing in deficit basins. These findings contradict the traditional notion of dry areas becoming drier and wet areas becoming wetter in response to climate change in India. This result also calls for a re-evaluation of planning for river inter-linking to supply water from surplus to deficit river basins. PMID:27463092

  17. Tibet, the Himalaya, Asian monsoons and biodiversity – In what ways are they related?

    Directory of Open Access Journals (Sweden)

    Robert A. Spicer

    2017-10-01

    Full Text Available Prevailing dogma asserts that the uplift of Tibet, the onset of the Asian monsoon system and high biodiversity in southern Asia are linked, and that all occurred after 23 million years ago in the Neogene. Here, spanning the last 60 million years of Earth history, the geological, climatological and palaeontological evidence for this linkage is reviewed. The principal conclusions are that: 1 A proto-Tibetan highland existed well before the Neogene and that an Andean type topography with surface elevations of at least 4.5 km existed at the start of the Eocene, before final closure of the Tethys Ocean that separated India from Eurasia. 2 The Himalaya were formed not at the start of the India–Eurasia collision, but after much of Tibet had achieved its present elevation. The Himalaya built against a pre-existing proto-Tibetan highland and only projected above the average height of the plateau after approximately 15 Ma. 3 Monsoon climates have existed across southern Asia for the whole of the Cenozoic, and probably for a lot longer, but that they were of the kind generated by seasonal migrations of the Inter-tropical Convergence Zone. 4 The projection of the High Himalaya above the Tibetan Plateau at about 15 Ma coincides with the development of the modern South Asia Monsoon. 5 The East Asia monsoon became established in its present form about the same time as a consequence of topographic changes in northern Tibet and elsewhere in Asia, the loss of moisture sources in the Asian interior and the development of a strong winter Siberian high as global temperatures declined. 6 New radiometric dates of palaeontological finds point to southern Asia's high biodiversity originating in the Paleogene, not the Neogene.

  18. A glimpse of the Quaternary monsoon history from India and adjoining seas

    Digital Repository Service at National Institute of Oceanography (India)

    Saraswat, R.; Nigam, R.; Correge, T.

    /plain; charset=UTF-8 1    Author version: Palaeogeogr. Palaeoclimatol. Palaeoecol., vol.397; 2014; 1-6 A glimpse of the Quaternary monsoon history from India and adjoining seas Rajeev Saraswat1, Rajiv Nigam1, Thierry Correge2 1 National... and radionuclide (210Pb) analyses to understand past environmental changes from the sediment cores collected from mudflat regions of central west coast of India. A significant shift in sediment characteristics is observed post 1980, probably in response...

  19. Afghanistan Reveals the Source of Atmospheric Nitrogen during North Western Monsoons

    Directory of Open Access Journals (Sweden)

    Ayse Ozlem Goral

    2014-10-01

    Full Text Available Chemical analysis of soil samples collected from Afghanistan have shown that those regions having capability of generating wind-induced dust at northern and south western territories have the capability of supplying nitrates and nitrites in addition to crustal materials. Together with all the other essential elements Afghan soil samples has the potential of controlling so far unexplained phytoplankton bloom and excess nitrate and nitrites during the course of NWM (North Western Monsoons over the surface waters of Arabian Sea

  20. Afghanistan Reveals the Source of Atmospheric Nitrogen during North Western Monsoons

    International Nuclear Information System (INIS)

    Goral, A.O.

    2014-01-01

    Chemical analysis of soil samples collected from Afghanistan have shown that those regions having capability of generating wind-induced dust at northern and south western territories have the capability of supplying nitrates and nitrites in addition to crustal materials. Together with all the other essential elements Afghan soil samples has the potential of controlling so far unexplained phytoplankton bloom and excess nitrate and nitrites during the course of NWM (North Western Monsoons) over the surface waters of Arabian Sea. (author)

  1. The East Asian Summer Monsoon at mid-Holocene: results from PMIP3 simulations

    Directory of Open Access Journals (Sweden)

    W. Zheng

    2013-02-01

    Full Text Available Ten Coupled General Circulation Models (CGCMs participated in the third phase of Paleoclimate Modelling Intercomparison Project (PMIP3 are assessed for the East Asian Summer Monsoon (EASM in both the pre-Industrial (PI, 0 ka and mid-Holocene (MH, 6 ka simulations. Results show that the PMIP3 model median captures well the large-scale characteristics of the EASM, including the two distinct features of the Meiyu rainbelt and the stepwise meridional displacement of the monsoonal rainbelt. At mid-Holocene, the PMIP3 model median shows significant warming (cooling during boreal summer (winter over Eurasia continent that are dominated by the changes of insolation. However, the PMIP3 models fail to simulate a warmer annual mean and winter surface air temperature (TAS over eastern China as derived from proxy records. The EASM at MH are featured by the changes of large-scale circulation over Eastern China while the changes of precipitation are not significant over its sub-domains of the Southern China and the lower reaches of Yangzi River. The inter-model differences for the monsoon precipitation can be associated with different configurations of the changes in large-scale circulation and the water vapour content, of which the former determines the sign of precipitation changes. The large model spread for the TAS over Tibetan Plateau has a positive relationship with the precipitation in the lower reaches of Yangzi River, yet this relationship does not apply to those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation. Except that the PMIP3 model median captured the warming of annual mean TAS over Tibetan Plateau, no significant improvements can be concluded when compared with the PMIP2 models results.

  2. Future projections of active-break spells of Indian summer monsoon in a climate change perspective

    Science.gov (United States)

    Sudeepkumar, B. L.; Babu, C. A.; Varikoden, Hamza

    2018-02-01

    The effect of global climate change on Indian summer monsoon has been analysed with special emphasis on active-break cycle. The changes in intensity and duration of active and break monsoon conditions towards the end of the century are studied by using 850 hPa zonal circulations. The analysis is carried out using twenty year climatology of historical period (1986-2005) and future projections (2080-2099) simulated as part of Coupled Model Intercomparison Project phase 5 (CMIP5). Models are compared with NCEP/NCAR reanalysis data. The models that effectively capture the circulation pattern of monsoon (JJAS) are considered for assessing the future climate in RCP 4.5 scenario. They are CanESM2, CNRM-CM5, GFDL-ESM2M, MIROC5 and MPI-ESM-LR. During the southwest monsoon period, the ensemble mean of models projects a strengthening of the wind speed towards north (north of 15°N) and weakening to the southern region (especially south of 12°N) which facilitates wetting of northern Indian regions and drying of southern peninsular regions. In the case of active-break conditions, the active spells are found to be strengthening over northern India and weakening over the peninsular India, the break spells intensify over southern tip of peninsular India indicating intense breaks. Increased propensity of short intense active days and decreased propensity of long active days are also projected by the models. The number of break spells does not show any significant changes.

  3. Role of North Indian Ocean Air-Sea Interaction in Summer Monsoon Intraseasonal Oscillation

    Science.gov (United States)

    Zhang, L.; Han, W.; Li, Y.

    2017-12-01

    Air-sea coupling processes over the North Indian Ocean associated with Indian summer monsoon intraseasonal oscillation (MISO) are analyzed. Observations show that MISO convection anomalies affect underlying sea surface temperature (SST) through changes in surface shortwave radiation (via cloud cover change) and surface latent heat flux (associated with surface wind speed change). In turn, SST anomalies determine the changing rate of MISO precipitation (dP/dt): warm (cold) SST anomalies cause increasing (decreasing) precipitation rate through increasing (decreasing) surface convergence. Air-sea interaction gives rise to a quadrature relationship between MISO precipitation and SST anomalies. A local air-sea coupling model (LACM) is established based on these observed physical processes, which is a damped oscillatory system with no external forcing. The period of LACM is proportional to the square root of mean state mixed layer depth , assuming other physical parameters remain unchanged. Hence, LACM predicts a relatively short (long) MISO period over the North Indian Ocean during the May-June monsoon developing (July-August mature) phase when is shallow (deep). This result is consistent with observed MISO statistics. An oscillatory external forcing of a typical 30-day period is added to LACM, representing intraseasonal oscillations originated from the equatorial Indian Ocean and propagate into the North Indian Ocean. The period of LACM is then determined by both the inherent period associated with local air-sea coupling and the period of external forcing. It is found that resonance occurs when , amplifying the MISO in situ. This result explains the larger MISO amplitude during the monsoon developing phase compared to the mature phase, which is associated with seasonal cycle of . LACM, however, fails to predict the observed small MISO amplitude during the September-October monsoon decaying phase, when is also shallow. This deficiency might be associated with the

  4. Indian Summer Monsoon Rainfall: Implications of Contrasting Trends in the Spatial Variability of Means and Extremes.

    Directory of Open Access Journals (Sweden)

    Subimal Ghosh

    Full Text Available India's agricultural output, economy, and societal well-being are strappingly dependent on the stability of summer monsoon rainfall, its variability and extremes. Spatial aggregate of intensity and frequency of extreme rainfall events over Central India are significantly increasing, while at local scale they are spatially non-uniform with increasing spatial variability. The reasons behind such increase in spatial variability of extremes are poorly understood and the trends in mean monsoon rainfall have been greatly overlooked. Here, by using multi-decadal gridded daily rainfall data over entire India, we show that the trend in spatial variability of mean monsoon rainfall is decreasing as exactly opposite to that of extremes. The spatial variability of extremes is attributed to the spatial variability of the convective rainfall component. Contrarily, the decrease in spatial variability of the mean rainfall over India poses a pertinent research question on the applicability of large scale inter-basin water transfer by river inter-linking to address the spatial variability of available water in India. We found a significant decrease in the monsoon rainfall over major water surplus river basins in India. Hydrological simulations using a Variable Infiltration Capacity (VIC model also revealed that the water yield in surplus river basins is decreasing but it is increasing in deficit basins. These findings contradict the traditional notion of dry areas becoming drier and wet areas becoming wetter in response to climate change in India. This result also calls for a re-evaluation of planning for river inter-linking to supply water from surplus to deficit river basins.

  5. Linking the South Atlantic Meridional Overturning Circulation and the Global Monsoons

    Science.gov (United States)

    Lopez, H.; Dong, S.; Goni, G. J.; Lee, S. K.

    2016-02-01

    This study tested the hypothesis whether low frequency decadal variability of the South Atlantic meridional heat transport (SAMHT) influences decadal variability of the global monsoons. A multi-century run from a state-of-the-art coupled general circulation model is used as basis for the analysis. Our findings indicate that multi-decadal variability of the South Atlantic Ocean plays a key role in modulating atmospheric circulation via interhemispheric changes in Atlantic Ocean heat content. Weaker SAMHT produces anomalous ocean heat divergence over the South Atlantic resulting in negative ocean heat content anomaly about 15 years later. This, in turn, forces a thermally direct anomalous interhemispheric Hadley circulation in the atmosphere, transporting heat from the northern hemisphere (NH) to the southern hemisphere (SH) and moisture from the SH to the NH, thereby intensify (weaken) summer (winter) monsoon in the NH and winter (summer) monsoon in the SH. Results also show that anomalous atmospheric eddies, both transient and stationary, transport heat northward in both hemispheres producing eddy heat flux convergence (divergence) in the NH (SH) around 15-30°, reinforcing the anomalous Hadley circulation. Overall, SAMHT decadal variability leads its atmospheric response by about 15 years, suggesting that the South Atlantic is a potential predictor of global climate variability.

  6. Plant-pollinator interactions in tropical monsoon forests in Southeast Asia.

    Science.gov (United States)

    Kato, Makoto; Kosaka, Yasuyuki; Kawakita, Atsushi; Okuyama, Yudai; Kobayashi, Chisato; Phimminith, Thavy; Thongphan, Daovorn

    2008-11-01

    Forests with different flora and vegetation types harbor different assemblages of flower visitors, and plant-pollinator interactions vary among forests. In monsoon-dominated East and Southeast Asia, there is a characteristic gradient in climate along latitude, creating a broad spectrum of forest types with potentially diverse pollinator communities. To detect a geographical pattern of plant-pollinator interactions, we investigated flowering phenology and pollinator assemblages in the least-studied forest type, i.e., tropical monsoon forest, in the Vientiane plain in Laos. Throughout the 5-year study, we observed 171 plant species blooming and detected flower visitors on 145 species. Flowering occurred throughout the year, although the number of flowering plant species peaked at the end of dry season. The dominant canopy trees, including Dipterocarpaceae, bloomed annually, in contrast to the supra-annual general flowering that occurs in Southeast Asian tropical rain forests. Among the 134 native plant species, 68 were pollinated by hymenopterans and others by lepidopterans, beetles, flies, or diverse insects. Among the observed bees, Xylocopa, megachilids, and honeybees mainly contributed to the pollination of canopy trees, whereas long-tongued Amegilla bees pollinated diverse perennials with long corolla tubes. This is the first community-level study of plant-pollinator interactions in an Asian tropical monsoon forest ecosystem.

  7. Wind profiler observations of a monsoon low-level jet over a tropical Indian station

    Directory of Open Access Journals (Sweden)

    M. C. R. Kalapureddy

    2007-11-01

    Full Text Available Three-year high-resolution wind observations of the wind profiler have been utilized to characterize the diurnal and seasonal features of the monsoon Low-Level Jet (LLJ over a tropical station, Gadanki (13.5° N, 79.2° E, with a focus on the diurnal variability of low-level winds. The Boreal summer monsoon winds show a conspicuously strong westerly LLJ with average wind speed exceeding 20 m s−1. The L-band wind profiler measurements have shown an advantage of better height and time resolutions over the conventional radiosonde method for diurnal wind measurements. An interesting diurnal oscillation of LLJ core has been observed. It is varying in the height range of 1.8±0.6 km with the maximum and minimum intensity noticed during the early morning and afternoon hours, respectively. The jet core (wind maxima height is observed to coincide with the inversion height. Strong wind shears are normally located beneath the LLJ core. The sole wind profiler observations are capable of identifying the monsoon phases, such as onset, break and active spells, etc. The mutual influence between the LLJ and the boundary layer has been discussed. One notices that the observed LLJ diurnal structures depend on the local convective activity, wind shears and turbulence activity associated with boundary layer winds. The day-to-day change in the LLJ structure depends on the latitudinal position of the LLJ core.

  8. Southern Indian Ocean SST as a modulator for the progression of Indian summer monsoon

    Science.gov (United States)

    Shahi, Namendra Kumar; Rai, Shailendra; Mishra, Nishant

    2018-01-01

    This study explores the possibility of southern Indian Ocean (SIO) sea surface temperature (SST) as a modulator for the early phase of Indian summer monsoon and its possible physical mechanism. A dipole-like structure is obtained from the empirical orthogonal function (EOF) analysis which is similar to an Indian Ocean subtropical dipole (IOSD) found earlier. A subtropical dipole index (SDI) is defined based on the SST anomaly over the positive and negative poles. The regression map of rainfall over India in the month of June corresponding to the SDI during 1983-2013 shows negative patterns along the Western Ghats and Central India. However, the regression pattern is insignificant during 1952-1982. The multiple linear regression models and partial correlation analysis also indicate that the SDI acts as a dominant factor to influence the rainfall over India in the month of June during 1983-2013. The similar result is also obtained with the help of composite rainfall over the land points of India in the month of June for positive (negative) SDI events. It is also observed that the positive (negative) SDI delays (early) the onset dates of Indian monsoon over Kerala during the time domain of our study. The study is further extended to identify the physical mechanism of this impact, and it is found that the heating (cooling) in the region covering SDI changes the circulation pattern in the SIO and hence impacts the progression of monsoon in India.

  9. Multi-Satellite Synergy for Aerosol Analysis in the Asian Monsoon Region

    Science.gov (United States)

    Ichoku, Charles; Petrenko, Maksym

    2012-01-01

    Atmospheric aerosols represent one of the greatest uncertainties in environmental and climate research, particularly in tropical monsoon regions such as the Southeast Asian regions, where significant contributions from a variety of aerosol sources and types is complicated by unstable atmospheric dynamics. Although aerosols are now routinely retrieved from multiple satellite Sensors, in trying to answer important science questions about aerosol distribution, properties, and impacts, researchers often rely on retrievals from only one or two sensors, thereby running the risk of incurring biases due to sensor/algorithm peculiarities. We are conducting detailed studies of aerosol retrieval uncertainties from various satellite sensors (including Terra-/ Aqua-MODIS, Terra-MISR, Aura-OMI, Parasol-POLDER, SeaWiFS, and Calipso-CALIOP), based on the collocation of these data products over AERONET and other important ground stations, within the online Multi-sensor Aerosol Products Sampling System (MAPSS) framework that was developed recently. Such analyses are aimed at developing a synthesis of results that can be utilized in building reliable unified aerosol information and climate data records from multiple satellite measurements. In this presentation, we will show preliminary results of. an integrated comparative uncertainly analysis of aerosol products from multiple satellite sensors, particularly focused on the Asian Monsoon region, along with some comparisons from the African Monsoon region.

  10. High carbon dioxide uptake by subtropical forest ecosystems in the East Asian monsoon region

    Science.gov (United States)

    Yu, Guirui; Chen, Zhi; Piao, Shilong; Peng, Changhui; Ciais, Philippe; Wang, Qiufeng; Li, Xuanran; Zhu, Xianjin

    2014-01-01

    Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20°N and 40°N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m−2 yr−1 (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe–Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr−1, which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor. PMID:24639529

  11. Objective spatiotemporal proxy-model comparisons of the Asian monsoon for the last millennium

    Science.gov (United States)

    Anchukaitis, K. J.; Cook, E. R.; Ammann, C. M.; Buckley, B. M.; D'Arrigo, R. D.; Jacoby, G.; Wright, W. E.; Davi, N.; Li, J.

    2008-12-01

    The Asian monsoon system can be studied using a complementary proxy/simulation approach which evaluates climate models using estimates of past precipitation and temperature, and which subsequently applies the best understanding of the physics of the climate system as captured in general circulation models to evaluate the broad-scale dynamics behind regional paleoclimate reconstructions. Here, we use a millennial-length climate field reconstruction of monsoon season summer (JJA) drought, developed from tree- ring proxies, with coupled climate simulations from NCAR CSM1.4 and CCSM3 to evaluate the cause of large- scale persistent droughts over the last one thousand years. Direct comparisons are made between the external forced response within the climate model and the spatiotemporal field reconstruction. In order to identify patterns of drought associated with internal variability in the climate system, we use a model/proxy analog technique which objectively selects epochs in the model that most closely reproduce those observed in the reconstructions. The concomitant ocean-atmosphere dynamics are then interpreted in order to identify and understand the internal climate system forcing of low frequency monsoon variability. We examine specific periods of extensive or intensive regional drought in the 15th, 17th, and 18th centuries, many of which are coincident with major cultural changes in the region.

  12. Primary sand-dune plant community and soil properties during the west-coast India monsoon

    Directory of Open Access Journals (Sweden)

    Willis A.

    2016-06-01

    Full Text Available A seven-station interrupted belt transect was established that followed a previously observed plant zonation pattern across an aggrading primary coastal dune system in the dry tropical region of west-coast India. The dominant weather pattern is monsoon from June to November, followed by hot and dry winter months when rainfall is scarce. Physical and chemical soil characteristics in each of the stations were analysed on five separate occasions, the first before the onset of monsoon, three during and the last post-monsoon. The plant community pattern was confirmed by quadrat survey. A pH gradient decreased with distance from the shoreline. Nutrient concentrations were deficient, increasing only in small amounts until the furthest station inland. At that location, there was a distinct and abrupt pedological transition zone from psammite to humic soils. There was a significant increase over previous stations in mean organic matter, ammonium nitrate and soil-water retention, although the increase in real terms was small. ANOVA showed significant variation in electrical conductivity, phosphorus, calcium, magnesium and sodium concentrations over time. There was no relationship between soil chemistry characteristics and plant community structure over the transect. Ipomoea pes-caprae and Spinifex littoreus were restricted to the foredunes, the leguminous forb Alysicarpus vaginalis and Perotis indica to the two stations furthest from the strand. Ischaemum indicum, a C4 perennial grass species adopting an ephemeral strategy was, in contrast, ubiquitous to all stations.

  13. Tidal Influence on the Diel Vertical Migration Pattern of Zooplankton in a Tropical Monsoonal Estuary

    KAUST Repository

    Vineetha, G.

    2015-04-03

    Monsoonal estuaries, located along the coastline of the Indian subcontinent, differ from other estuaries by their time dependence on the salinity characteristics. Effective sustenance and retention of the mesozooplankton community in the estuarine habitats is often determined by their dominant behavioral patterns: diel vertical migration (DVM) and tidal vertical migration (TVM). The modes of these endogenous rhythms often vary among estuaries based on the river runoff and tidal characteristics. The present study is a pioneering attempt to depict the vertical migration pattern of zooplankton along a diel and tidal scale in a tropical, microtidal, monsoonal estuary. We observed that in spite of the prominent asymmetry in the magnitude of the river runoff between the seasons, most of the zooplankton groups exhibited strong DVM, with a clear increase in biomass and abundance in surface waters during night. The peak increase in biomass and abundance at night always synchronized with the slack periods in the tidal cycles, which differed from the general concepts of downward migration during ebb tide and upward migration during flood tide in estuarine systems. The weak currents during the slack period might have favored the effective vertical migration of the mesozooplankton community in this monsoonal estuarine system. © 2015 Society of Wetland Scientists

  14. Influence of monsoonal winds on chlorophyll-α distribution in the Beibu Gulf.

    Directory of Open Access Journals (Sweden)

    Chunyan Shen

    Full Text Available The influence of seasonal, monsoonal winds on the temporal and spatial variability of chlorophyll-a (chl-a in the Beibu Gulf is studied based on long-term satellite data of sea surface winds, chl-a concentration and sea surface temperature (SST and in-situ observations for the years from 2002 to 2014. The analysis results indicated that under northeasterly monsoonal winds, chl-a concentrations were substantially elevated in most area of the Beibu Gulf, with a high chl-a concentration (>2 mg m-3 patch extending southwestward from the coastal water of the northeastern Gulf, consistent with the winter wind pattern. Meanwhile, the spatial distribution of high chl-a concentration is correlated with low SST in the northeastern Gulf. In the southern Gulf, there was generally low chl-a, except in the coastal waters southwest of Hainan Island. Here, the upwelling cold water prevails outside the mouth of the Beibu Gulf, driven by the southwesterly monsoonal winds and the runoff from the Changhua River, as implied by low observed SST. Correlation analysis indicated the chl-a concentration was strongly modulated by wind speed (r = 0.63, p0.7, p<0.001. Integrated analysis also showed that stratification is weak and mixing is strong in winter as affected by the high wind speed, which suggests that the wind-induced mixing is a dominant mechanism for entrainment of nutrients and the spatial distribution of chl-a in winter.

  15. First detection of ammonia (NH3 in the Asian summer monsoon upper troposphere

    Directory of Open Access Journals (Sweden)

    M. Höpfner

    2016-11-01

    Full Text Available Ammonia (NH3 has been detected in the upper troposphere by the analysis of averaged MIPAS (Michelson Interferometer for Passive Atmospheric Sounding infrared limb-emission spectra. We have found enhanced amounts of NH3 within the region of the Asian summer monsoon at 12–15 km altitude. Three-monthly, 10° longitude  ×  10° latitude average profiles reaching maximum mixing ratios of around 30 pptv in this altitude range have been retrieved, with a vertical resolution of 3–8 km and estimated errors of about 5 pptv. These observations show that loss processes during transport from the boundary layer to the upper troposphere within the Asian monsoon do not deplete the air entirely of NH3. Thus, ammonia might contribute to the so-called Asian tropopause aerosol layer by the formation of ammonium aerosol particles. On a global scale, outside the monsoon area and during different seasons, we could not detect enhanced values of NH3 above the actual detection limit of about 3–5 pptv. This upper bound helps to constrain global model simulations.

  16. Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

    Directory of Open Access Journals (Sweden)

    L. Giosan

    2017-12-01

    Full Text Available Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.

  17. Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

    Science.gov (United States)

    Giosan, Liviu; Ponton, Camilo; Usman, Muhammed; Blusztajn, Jerzy; Fuller, Dorian Q.; Galy, Valier; Haghipour, Negar; Johnson, Joel E.; McIntyre, Cameron; Wacker, Lukas; Eglinton, Timothy I.

    2017-12-01

    Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.

  18. The representation of low-level clouds during the West African monsoon in weather and climate models

    Science.gov (United States)

    Kniffka, Anke; Hannak, Lisa; Knippertz, Peter; Fink, Andreas

    2016-04-01

    The West African monsoon is one of the most important large-scale circulation features in the tropics and the associated seasonal rainfalls are crucial to rain-fed agriculture and water resources for hundreds of millions of people. However, numerical weather and climate models still struggle to realistically represent salient features of the monsoon across a wide range of scales. Recently it has been shown that substantial errors in radiation and clouds exist in the southern parts of West Africa (8°W-8°E, 5-10°N) during summer. This area is characterised by strong low-level jets associated with the formation of extensive ultra-low stratus clouds. Often persisting long after sunrise, these clouds have a substantial impact on the radiation budget at the surface and thus the diurnal evolution of the planetary boundary layer (PBL). Here we present some first results from a detailed analysis of the representation of these clouds and the associated PBL features across a range of weather and climate models. Recent climate model simulations for the period 1991-2010 run in the framework of the Year of Tropical Convection (YOTC) offer a great opportunity for this analysis. The models are those used for the latest Assessment Report of the Intergovernmental Panel on Climate Change, but for YOTC the model output has a much better temporal resolution, allowing to resolve the diurnal cycle, and includes diabatic terms, allowing to much better assess physical reasons for errors in low-level temperature, moisture and thus cloudiness. These more statistical climate model analyses are complemented by experiments using ICON (Icosahedral non-hydrostatic general circulation model), the new numerical weather prediction model of the German Weather Service and the Max Planck Institute for Meteorology. ICON allows testing sensitivities to model resolution and numerical schemes. These model simulations are validated against (re-)analysis data, satellite observations (e.g. CM SAF cloud and

  19. Stratospheric Influence on Summer Monsoon and Associated Planetary Wave Breaking and Mixing in the Subtropical Tropopause Region

    Science.gov (United States)

    Lubis, S. W.; Nakamura, N.

    2017-12-01

    Previous studies have shown that the monsoonal circulation plays an important role in planetary wave breaking (PWB). The highest frequency of breaking events occurs just downstream (east) of the monsoon region in summer. PWB induces mixing of potential vorticity (PV) and hence, alter the horizontal mixing in the atmosphere. Here, the authors hypothesize that the stratospheric easterlies in the boreal summer also play a significant role in the PWB and mixing associated with the summer monsoon. If the stratospheric winds were westerly in boreal summer, the frequency of PWB would be decreased due to more waves penetrating in the stratosphere, resulting in less horizontal PWB and thus reduced mixing in the subtropical tropopause region. The hypothesis is examined by using a set of idealized moist GFDL simulations. The monsoon circulation is produced by adding a land-sea contrast with a Gaussian-shaped mountains positioned in the midlatitudes. Other key ingredients for the monsoon, including albedo, oceanic warm pool, and Q-flux, were also ideally imposed in all simulations. Our control simulation produces a summer monsoon-like circulation similar to the observation. In particular, the thermally forced monsoonal circulation forms a prominent closed upper-level anticyclone that dominates the summertime upper-level flow. Associated with this circulation is an upward-bulging tropopause that forms a large reservoir of anomalously low PV. Consistent with previous studies, the well-defined tropospheric jet lies just poleward of the upper-level anticyclone, and acts as a dynamical barrier between the low-PV reservoir over the monsoonal region and the high-PV reservoir in the extratropics. This barrier disappears just northeast of the monsoon area in the jet exit region, allowing more quasi-planetary waves to break in this region. Repetitive wave breaking further weakens the PV gradient, leading to the formation of the surf zone and stronger mixing in this region. To quantify

  20. The Indian Summer Monsoon onset revisited: new approach based on the analysis of historical wind observations

    Science.gov (United States)

    Ordoñez, Paulina; Gallego, David; Ribera, Pedro; Peña-Ortiz, Cristina; Garcia-Herrera, Ricardo; Vega, Inmaculada; Gómez, Francisco de Paula

    2016-04-01

    The Indian Summer Monsoon onset is one of the meteorological events most anticipated in the world. Due to its relevance for the population, the India Meteorological Department has dated the onset over the southern tip of the Indian Peninsula (Kerala) since 1901. The traditional method to date the onset was based in the judgment of skilled meteorologist and because of this, the method was considered subjective and not adequate for the study of long-term changes in the onset. A new method for determining the monsoon onset based solely on objective criteria has been in use since 2006. Unfortunately, the new method relies -among other variables- on OLR measurements. This requirement impedes the construction of an objective onset series before the satellite era. An alternative approach to establish the onset by objective methods is the use of the wind field. During the last decade, some works have demonstrated that the changes in the wind direction in some areas of the Indian Ocean can be used to determine the monsoon onset rather precisely. However, this method requires precise wind observations over a large oceanic area which has limited the periods covered for such kind of indices to those of the reanalysis products. In this work we present a new approach to track the Indian monsoon onset based solely on historical wind direction measurements taken onboard ships. Our new series provides an objective record of the onset since the last decade of the 19th century and perhaps more importantly, it can incorporate any new historical wind record not yet known in order to extend the series length. The new series captures quite precisely the rapid precipitation increase associated to the monsoon onset, correlates well with previous approaches and it is robust against anomalous (bogus) onsets. Although no significant trends in the onset date were detected, a tendency to later than average onsets during the 1900-1925 and 1970-1990 periods and earlier than average onsets between

  1. Prediction of summer monsoon rainfall over India using the NCEP climate forecast system

    Energy Technology Data Exchange (ETDEWEB)

    Pattanaik, D.R. [India Meteorological Department (IMD), New Delhi (India); Kumar, Arun [Climate Prediction Center, National Centre for Environmental Prediction (NCEP)/NWS/NOAA, Camp Springs, MD (United States)

    2010-03-15

    The performance of a dynamical seasonal forecast system is evaluated for the prediction of summer monsoon rainfall over the Indian region during June to September (JJAS). The evaluation is based on the National Centre for Environmental Prediction's (NCEP) climate forecast system (CFS) initialized during March, April and May and integrated for a period of 9 months with a 15 ensemble members for 25 years period from 1981 to 2005. The CFS's hindcast climatology during JJAS of March (lag-3), April (lag-2) and May (lag-1) initial conditions show mostly an identical pattern of rainfall similar to that of verification climatology with the rainfall maxima (one over the west-coast of India and the other over the head Bay of Bengal region) well simulated. The pattern correlation between verification and forecast climatology over the global tropics and Indian monsoon region (IMR) bounded by 50 E-110 E and 10 S-35 N shows significant correlation coefficient (CCs). The skill of simulation of broad scale monsoon circulation index (Webster and Yang; WY index) is quite good in the CFS with highly significant CC between the observed and predicted by the CFS from the March, April and May forecasts. High skill in forecasting El Nino event is also noted for the CFS March, April and May initial conditions, whereas, the skill of the simulation of Indian Ocean Dipole is poor and is basically due to the poor skill of prediction of sea surface temperature (SST) anomalies over the eastern equatorial Indian Ocean. Over the IMR the skill of monsoon rainfall forecast during JJAS as measured by the spatial Anomaly CC between forecast rainfall anomaly and the observed rainfall anomaly during 1991, 1994, 1997 and 1998 is high (almost of the order of 0.6), whereas, during the year 1982, 1984, 1985, 1987 and 1989 the ACC is only around 0.3. By using lower and upper tropospheric forecast winds during JJAS over the regions of significant CCs as predictors for the All India Summer Monsoon

  2. On the Feasibility of Tracking the Monsoon History by Using Ancient Wind Direction Records

    Science.gov (United States)

    Gallego, D.; Ribera, P.; Peña-Ortiz, C.; Vega, I.; Gómez, F. D. P.; Ordoñez-Perez, P.; Garcia-Hererra, R.

    2015-12-01

    In this work, we use old wind direction records to reconstruct indices for the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). Since centuries ago, ships departing from the naval European powers circumnavigated Africa in their route to the Far East. Most of these ships took high-quality observations preserved in logbooks. We show that wind direction observations taken aboard ships can be used to track the seasonal wind reversal typical of monsoonal circulations. The persistence of the SW winds in the 20W-17W and 7N-13N region is highly correlated with the WAM strength and Sahel's precipitation. It has been possible to build a WAM index back to the 19th Century. Our results show that in the Sahel, the second half of the 19thCentury was significantly wetter than present day. The relation of the WAM with the ENSO cycle, and the Atlantic Multidecadal Oscillation was low and instable from the 1840s to the 1970s, when they abruptly suffered an unprecedented reinforcement which last up to the present day. The persistence of the SSW wind in the 60E-80E and 8N-12N area has been used to track the ISM onset since the 1880s. We found evidences of later than average onset dates during the 1900-1925 and 1970-1990 periods and earlier than average onset between 1940 and 1965. A significant relation between the ISM onset and the PDO restricted to shifts from negative to positive PDO phases has been found. The most significant contribution of our study is the fact that we have shown that it is possible to build consistent monsoon indices of instrumental character using solely direct observations of wind direction. Our indices have been generated by using data currently available in the ICOADS 2.5 database, but a large amount of wind observations for periods previous to the 20thcentury still remain not explored in thousands of logbooks preserved in British archives. The interest of unveil these data to track the monsoons for more than 200 -or even 300 years- it is

  3. Pre- and post-monsoonal changes in grain size and heavy minerals in the sediments from Kalbadevi Bay, Ratnagiri, west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Valsangkar, A.B.; Fernandes, D.

    to the monsoonal effects, where higher sand is derived from the shallow depths due to the wave action. It appears that the sand deposited during the monsoon period does not get compacted and therefore removed during transition period, thereby resulting... particles of magnetite are removed from the Bay after the monsoon due to current action and deposited to the deeper part of the shelf. The offshore non-magnetite heavy minerals in Kalbadevi Bay are predominantly ilmenite. The distribution...

  4. Past 100 Ky surface salinity-gradient response in the eastern Arabian Sea to the summer monsoon variation recorded by delta super(18)O of G. sacculifer

    Digital Repository Service at National Institute of Oceanography (India)

    Chodankar, A.R.; Banakar, V.K.; Oba, T.

    tongue may therefore provide a potential tool for understanding the past variation in the intensity of Indian summer monsoons. In response to past fluctuations in the summer- and winter-monsoon intensity, the salinities in both the basins have oscillated... glacial cycle. Mar. Geol. Bassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackleton, N.J., Lancelot, Y., 1994. The astronomical theory the Bay of Bengal, suggesting weakest summer monsoons. On the other hand, the lowest contrast indicating...

  5. Possible Influences of Air Pollution, Dust and Sandstorms on the Indian Monsoon

    Science.gov (United States)

    Lau, William K. M.; Kim, Kyu-Myong; Hsu, Christina N.; Holben, Brent N.

    2010-01-01

    In Asian monsoon countries, such as China and India, human health and safety problems caused by air pollution are becoming increasingly serious, due to the increased loading of atmospheric pollutants from waste gas emissions and from rising energy demand associated with the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon rain associated with flash floods or prolonged drought, has caused major loss of human life and damage to crops and.property with devastating societal impacts. Historically, air-pollution and monsoons research are treated as separate problems. However recent studies have suggested that the two problems may be intrinsically linked and need to be studied jointly. Fundamentally, aerosols can affect precipitation through radiative effects cif suspended particles in the atmosphere (direct effect) and/or by interfering and changing: the cloud and precipitation formation processes (indirect effect). Based on their optical properties, aerosols can be classified into two types.: those that absorb solar radiation, and those that do not. Both types of aerosols scatter sunlight and reduce the amount of solar radiation from reaching the Earth's surface, causing it to cool. The surface cooling increases atmospheric stability and reduces convection potential, Absorbing aerosols, however, in addition to cooling the surface, can heat the atmosphere. The heating of the atmosphere may reduce the amount of low clouds by increased evaporation in cloud drops. The heating, however, may induce rising motion, enhance low-level moisture, convergence and, hence, increases rainfall, The latent heating from enhanced rainfall may excite feedback processes in the large-scale circulation, further amplify.the initial response to aerosol heating and producing more rain. Additionally, aerosols can increase the concentration of cloud condensation nuclei (CCN), increase cloud amount and decrease coalescence and collision rates, leading to

  6. Multi-scale forcing and the formation of subtropical desert and monsoon

    Directory of Open Access Journals (Sweden)

    G. X. Wu

    2009-09-01

    Full Text Available This study investigates three types of atmospheric forcing across the summertime subtropics that are shown to contribute in various ways to the occurrence of dry and wet climates in the subtropics. To explain the formation of desert over the western parts of continents and monsoon over the eastern parts, we propose a new mechanism of positive feedback between diabatic heating and vorticity generation that occurs via meridional advection of planetary vorticity and temperature. Monsoon and desert are demonstrated to coexist as twin features of multi-scale forcing, as follows. First, continent-scale heating over land and cooling over ocean induce the ascent of air over the eastern parts of continents and western parts of oceans, and descent over eastern parts of oceans and western parts of continents. Second, local-scale sea-breeze forcing along coastal regions enhances air descent over eastern parts of oceans and ascent over eastern parts of continents. This leads to the formation of the well-defined summertime subtropical LOSECOD quadruplet-heating pattern across each continent and adjacent oceans, with long-wave radiative cooling (LO over eastern parts of oceans, sensible heating (SE over western parts of continents, condensation heating (CO over eastern parts of continents, and double dominant heating (D: LO+CO over western parts of oceans. Such a quadruplet heating pattern corresponds to a dry climate over the western parts of continents and a wet climate over eastern parts. Third, regional-scale orographic-uplift-heating generates poleward ascending flow to the east of orography and equatorward descending flow to the west. The Tibetan Plateau (TP is located over the eastern Eurasian continent. The TP-forced circulation pattern is in phase with that produced by continental-scale forcing, and the strongest monsoon and largest deserts are formed over the Afro-Eurasian Continent. In contrast, the Rockies and the Andes are located over the western

  7. Multi-scale forcing and the formation of subtropical desert and monsoon

    Directory of Open Access Journals (Sweden)

    G. X. Wu

    2009-09-01

    Full Text Available This study investigates three types of atmospheric forcing across the summertime subtropics that are shown to contribute in various ways to the occurrence of dry and wet climates in the subtropics. To explain the formation of desert over the western parts of continents and monsoon over the eastern parts, we propose a new mechanism of positive feedback between diabatic heating and vorticity generation that occurs via meridional advection of planetary vorticity and temperature. Monsoon and desert are demonstrated to coexist as twin features of multi-scale forcing, as follows.

    First, continent-scale heating over land and cooling over ocean induce the ascent of air over the eastern parts of continents and western parts of oceans, and descent over eastern parts of oceans and western parts of continents. Second, local-scale sea-breeze forcing along coastal regions enhances air descent over eastern parts of oceans and ascent over eastern parts of continents. This leads to the formation of the well-defined summertime subtropical LOSECOD quadruplet-heating pattern across each continent and adjacent oceans, with long-wave radiative cooling (LO over eastern parts of oceans, sensible heating (SE over western parts of continents, condensation heating (CO over eastern parts of continents, and double dominant heating (D: LO+CO over western parts of oceans. Such a quadruplet heating pattern corresponds to a dry climate over the western parts of continents and a wet climate over eastern parts. Third, regional-scale orographic-uplift-heating generates poleward ascending flow to the east of orography and equatorward descending flow to the west.

    The Tibetan Plateau (TP is located over the eastern Eurasian continent. The TP-forced circulation pattern is in phase with that produced by continental-scale forcing, and the strongest monsoon and largest deserts are formed over the Afro-Eurasian Continent. In contrast, the Rockies and the Andes are

  8. An oxygen isotope record from Lake Xiarinur in Inner Mongolia since the last deglaciation and its implication for tropical monsoon change

    Science.gov (United States)

    Sun, Qing; Chu, Guoqiang; Xie, Manman; Zhu, Qingzeng; Su, Youliang; Wang, Xisheng

    2018-04-01

    We present a high-resolution oxygen isotope record from authigenic carbonate (δ18Ocarb) from Lake Xiarinur (Inner Mongolia) since the last deglaciation. The lake is located at the modern northern limit of the monsoon, and is therefore sensitive to the extension of the East Asian summer monsoon. Based on calibration against the instrumental record, the δ18Ocar variation has been interpreted as changes in atmospheric circulation pattern on decadal time scales. On longer time scales, the δ18Ocarb in lake sediments could be mainly regulated by the relative contribution of nearby (remote) water-vapor sources associated with subtropical (tropical) monsoon through changes in the distance from sources to the site of precipitation. Increased remote water vapors from tropical monsoon would lead to lighter isotope value in our study site. Through time the δ18Ocarb record in Lake Xiarinur indicate a notable weak tropical monsoon during the Younger Dryas, a gradual increasing monsoon from the early Holocene and weakening monsoon after the middle Holocene. Oxygen isotope records from lakes and stalagmite in the Asian monsoon region across different localities show a general similar temporal pattern since the last deglaciation, and highlight a fundamental role of the tropical monsoon.

  9. Soil Microbial Activity Responses to Fire in a Semi-arid Savannah Ecosystem Pre- and Post-Monsoon Season

    Science.gov (United States)

    Jimenez, J. R.; Raub, H. D.; Jong, E. L.; Muscarella, C. R.; Smith, W. K.; Gallery, R. E.

    2017-12-01

    Extracellular enzyme activities (EEA) of soil microorganisms can act as important proxies for nutrient limitation and turnover in soil and provide insight into the biochemical requirements of microbes in terrestrial ecosystems. In semi-arid ecosystems, microbial activity is influenced by topography, disturbances such as fire, and seasonality from monsoon rains. Previous studies from forest ecosystems show that microbial communities shift to similar compositions after severe fires despite different initial conditions. In semi-arid ecosystems with high spatial heterogeniety, we ask does fire lead to patch intensification or patch homogenization and how do monsoon rains influence the successional trajectories of microbial responses? We analyzed microbial activity and soil biogeochemistry throughout the monsoon season in paired burned and unburned sites in the Santa Rita Experimental Range, AZ. Surface soil (5cm) from bare-ground patches, bole, canopy drip line, and nearby grass patches for 5 mesquite trees per site allowed tests of spatiotemporal responses to fire and monsoon rain. Microbial activity was low during the pre-monsoon season and did not differ between the burned and unburned sites. We found greater activity near mesquite trees that reflects soil water and nutrient availability. Fire increased soil alkalinity, though soils near mesquite trees were less affected. Soil water content was significantly higher in the burned sites post-monsoon, potentially reflecting greater hydrophobicity of burned soils. Considering the effects of fire in these semi-arid ecosystems is especially important in the context of the projected changing climate regime in this region. Assessing microbial community recovery pre-, during, and post-monsoon is important for testing predictions about whether successional pathways post-fire lead to recovery or novel trajectories of communities and ecosystem function.

  10. Centennial- to decadal-scale monsoon precipitation variations in the upper Hanjiang River region, China over the past 6650 years

    Science.gov (United States)

    Tan, Liangcheng; Cai, Yanjun; Cheng, Hai; Edwards, Lawrence R.; Gao, Yongli; Xu, Hai; Zhang, Haiwei; An, Zhisheng

    2018-01-01

    The upper Hanjiang River region is the recharge area of the middle route of South-to-North Water Transfer Project. The region is under construction of the Hanjiang-Weihe River Water Transfer Project in China. Monsoon precipitation variations in this region are critical to water resource and security of China. In this study, high-resolution monsoon precipitation variations were reconstructed in the upper Hanjiang River region over the past 6650 years from δ18O and δ13C records of four stalagmites in Xianglong cave. The long term increasing trend of stalagmite δ18O record since the middle Holocene is consistent with other speleothem records from monsoonal China. This trend follows the gradually decreasing Northern Hemisphere summer insolation, which indicates that solar insolation may control the orbital-scale East Asian summer monsoon (EASM) variations. Despite the declined EASM intensity since the middle Holocene, local precipitation may not have decreased remarkably, as revealed by the δ13C records. A series of centennial- to decadal-scale cyclicity was observed, with quasi-millennium-, quasi-century-, 57-, 36- and 22-year cycles by removing the long-term trend of stalagmite δ18O record. Increased monsoon precipitation during periods of 4390-3800 a BP, 3590-2960 a BP, 2050-1670 a BP and 1110-790 a BP had caused four super-floods in the upper reach of Hanjiang River. Dramatically dry climate existed in this region during the 5.0 ka and 2.8 ka events, coinciding with notable droughts in other regions of monsoonal China. Remarkably intensified and southward Westerly jet, together with weakened summer monsoon, may delay the onset of rainy seasons, resulting in synchronous decreasing of monsoon precipitation in China during the two events. During the 4.2 ka event and the Little Ice Age, the upper Hanjiang River region was wet, which was similar to the climate conditions in central and southern China, but was the opposite of drought observed in northern China. We

  11. South Asian summer monsoon variability during the last ˜54 kyrs inferred from surface water salinity and river runoff proxies

    Science.gov (United States)

    Gebregiorgis, D.; Hathorne, E. C.; Sijinkumar, A. V.; Nath, B. Nagender; Nürnberg, D.; Frank, M.

    2016-04-01

    The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and δ18O analyses and to estimate seawater δ18O (δ18Osw). The difference between surface and thermocline temperatures (ΔT) and δ18Osw (Δδ18Osw) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our Δδ18Osw time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the δ18Osw and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at ∼18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum δ18Osw values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation

  12. The 9.2 ka event in Asian summer monsoon area: the strongest millennial scale collapse of the monsoon during the Holocene

    Science.gov (United States)

    Zhang, Wenchao; Yan, Hong; Dodson, John; Cheng, Peng; Liu, Chengcheng; Li, Jianyong; Lu, Fengyan; Zhou, Weijian; An, Zhisheng

    2018-04-01

    Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric 14C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).

  13. Quasi-biweekly oscillations of the South Asian monsoon and its co-evolution in the upper and lower troposphere

    Science.gov (United States)

    Ortega, Sebastián; Webster, Peter J.; Toma, Violeta; Chang, Hai-Ru

    2017-11-01

    The Upper Tropospheric Quasi-Biweekly Oscillation (UQBW) of the South Asian monsoon is studied using the potential vorticity field on the 370 K isentrope. The UQBW is shown to be a common occurrence in the upper troposphere during the monsoon, and its typical evolution is described. We suggest that the UQBW is a phenomenon of both the middle and tropical latitudes, owing its existence to the presence of the planetary-scale upper-tropospheric monsoon anticyclone. The UQBW is first identified as Rossby waves originating in the northern flank of the monsoon anticyclone. These Rossby waves break when reaching the Pacific Ocean, and their associated cyclonic PV anomalies move southward to the east of Asia and then westward across the Indian Ocean and Africa advected by the monsoon anticyclone. A strong correlation, or co-evolution, between the UQBW and quasi-biweekly oscillations in the lower troposphere (QBW) is also found. In particular, analysis of vertically-integrated horizontal moisture transport, 850 hPa geopotential, and outgoing long-wave radiation show that the UQBW is usually observed at the same time as, and co-evolves with, the lower tropospheric QBW over South Asia. We discuss the nature of the UQBW, and its possible physical link with the QBW.

  14. Mineralogical evidence of reduced East Asian summer monsoon rainfall on the Chinese loess plateau during the early Pleistocene interglacials

    Science.gov (United States)

    Meng, Xianqiang; Liu, Lianwen; Wang, Xingchen T.; Balsam, William; Chen, Jun; Ji, Junfeng

    2018-03-01

    The East Asian summer monsoon (EASM) is an important component of the global climate system. A better understanding of EASM rainfall variability in the past can help constrain climate models and better predict the response of EASM to ongoing global warming. The warm early Pleistocene, a potential analog of future climate, is an important period to study EASM dynamics. However, existing monsoon proxies for reconstruction of EASM rainfall during the early Pleistocene fail to disentangle monsoon rainfall changes from temperature variations, complicating the comparison of these monsoon records with climate models. Here, we present three 2.6 million-year-long EASM rainfall records from the Chinese Loess Plateau (CLP) based on carbonate dissolution, a novel proxy for rainfall intensity. These records show that the interglacial rainfall on the CLP was lower during the early Pleistocene and then gradually increased with global cooling during the middle and late Pleistocene. These results are contrary to previous suggestions that a warmer climate leads to higher monsoon rainfall on tectonic timescales. We propose that the lower interglacial EASM rainfall during the early Pleistocene was caused by reduced sea surface temperature gradients across the equatorial Pacific, providing a testable hypothesis for climate models.

  15. Effects of volcanic eruptions on China's monsoon precipitation over the past 700 years

    Science.gov (United States)

    Zhuo, Z.; Gao, C.

    2013-12-01

    Tropical volcanic eruptions were found to affect precipitation especially in Asia and Africa monsoon region. However, studies with different types of eruptions suggested different impacts as well as the spatial patterns. In this study, we combined the Monsoon Asia Drought Atlas (MADA, [Cook et al., 2010]) and the Chinese Historical Drought Disaster Index (CHDDI) compiled from the historic meteorological records to study the effect of volcanic eruptions on China's monsoon precipitation over the past 700 years. Histories of past volcanism were compiled from the IVI2[Gao et al., 2008] and Crowley2013[Crowley and Unterman, 2013] reconstructions. Volcanic events were classified into 2×Pinatubo, 1×Pinatubo , ≥5 Tg sulfate aerosols injection in the northern hemisphere (NH) stratosphere for IVI2; and NH sulfate flux more than 20/15/10/5 kg km-2 for Crowley2013. In both cases, average MADA show a drying trend over mainland China from year zero(0) to year three(+3) after the eruption; and the more sulfate aerosol injected into the NH stratosphere or the larger the sulfate flux, the more severe this drying trend seem to reveal. In comparison, a wetting trend was found in the eruption year with Southern Hemisphere (SH) only injections. Superposed epoch analysis with a 10,000 Monte Carlo resampling procedure showed that 97.9% (96.9%) of the observed MADA values are statistically significant at the 95% (99%) confidence level. The drying is probably caused by a reduction of the latent heat flux due to volcanic aerosol' cooling effect, leading to the weakening of south Asian monsoon and decrease of moisture vapor over tropical oceans, which contribute to a reduced moisture flux over china. Spatial distribution of the average MADA show a southward movement of the driest areas in eastern China from year zero to year three after the 1×Pinatubo and 2×Pinatubo eruptions, whereas part of north china experienced unusual wetting condition. This is in good agreement with CHDDI, which

  16. Monsoonal Responses to External Forcings over the Past Millennium: A Model Study (Invited)

    Science.gov (United States)

    Liu, J.; Wang, B.

    2009-12-01

    The climate variations related to Global Monsoon (GM) and East Asian summer monsoon (EASM) rainfall over the past 1000 years were investigated by analysis of a pair of millennium simulations with the coupled climate model named ECHO-G. The free run was generated using fixed external (annual cycle) forcing, while the forced run was obtained using time-varying solar irradiance variability, greenhouse gases (CO2 and CH4) concentration and estimated radiative effect of volcanic aerosols. The model results indicate that the centennial-millennial variation of the GM and EASM is essentially a forced response to the external radiative forcings (insolation, volcanic aerosols, and greenhouse gases). The GM strength responds more directly to the effective solar forcing (insolation plus radiative effect of the volcanoes) when compared to responses of the global mean surface temperature on centennial timescale. The simulated GM precipitation in the forced run exhibits a significant quasi-bi-centennial oscillation. Weak GM precipitation was simulated during the Little Ice Age (1450-1850) with three weakest periods concurring with the Spörer, Maunder, and Dalton Minimum of solar activity. Conversely, strong GM was simulated during the model Medieval Warm Period (ca. 1030-1240). Before the industrial period, the natural variation in effective solar forcing reinforces the thermal contrasts both between the ocean and continent and between the northern and southern hemispheres, resulting in millennium-scale variation and the quasi-bi-centennial oscillation of the GM. The prominent upward trend in the GM precipitation occurring in the last century and the remarkably strengthening of the global monsoon in the period of 1961-1990 appear unprecedented and owed possibly in part to the increase of atmospheric carbon dioxide concentration. The EASM has the largest meridional extent (5oN-55oN) among all the regional monsoons on globe. Thus, the EASM provides an unique opportunity for

  17. Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

    Science.gov (United States)

    Konda, Gopinadh; Chowdary, J. S.; Srinivas, G.; Gnanaseelan, C.; Parekh, Anant; Attada, Raju; Rama Krishna, S. S. V. S.

    2018-06-01

    In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

  18. Short-Range Prediction of Monsoon Precipitation by NCMRWF Regional Unified Model with Explicit Convection

    Science.gov (United States)

    Mamgain, Ashu; Rajagopal, E. N.; Mitra, A. K.; Webster, S.

    2018-03-01

    There are increasing efforts towards the prediction of high-impact weather systems and understanding of related dynamical and physical processes. High-resolution numerical model simulations can be used directly to model the impact at fine-scale details. Improvement in forecast accuracy can help in disaster management planning and execution. National Centre for Medium Range Weather Forecasting (NCMRWF) has implemented high-resolution regional unified modeling system with explicit convection embedded within coarser resolution global model with parameterized convection. The models configurations are based on UK Met Office unified seamless modeling system. Recent land use/land cover data (2012-2013) obtained from Indian Space Research Organisation (ISRO) are also used in model simulations. Results based on short-range forecast of both the global and regional models over India for a month indicate that convection-permitting simulations by the high-resolution regional model is able to reduce the dry bias over southern parts of West Coast and monsoon trough zone with more intense rainfall mainly towards northern parts of monsoon trough zone. Regional model with explicit convection has significantly improved the phase of the diurnal cycle of rainfall as compared to the global model. Results from two monsoon depression cases during study period show substantial improvement in details of rainfall pattern. Many categories in rainfall defined for operational forecast purposes by Indian forecasters are also well represented in case of convection-permitting high-resolution simulations. For the statistics of number of days within a range of rain categories between `No-Rain' and `Heavy Rain', the regional model is outperforming the global model in all the ranges. In the very heavy and extremely heavy categories, the regional simulations show overestimation of rainfall days. Global model with parameterized convection have tendency to overestimate the light rainfall days and

  19. Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

    KAUST Repository

    Konda, Gopinadh; Chowdary, Jasti S.; Srinivas, G; Gnanaseelan, C; Parekh, Anant; Attada, Raju; Rama Krishna, S S V S

    2018-01-01

    In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

  20. Improvements of ENSO-monsoon relationship in CMIP5 models through statistical downscaling over India.

    Science.gov (United States)

    Akhter, J.; Das, L.; Deb, A.

    2017-12-01

    Present study has assessed the skills of global climate models (GCMS) from coupled model inter-comparison project phase five (CMIP5) in simulating ENSO-monsoon relationships over seven homogeneous zones of India. Observational sea surface temperature (SST) data has revealed that there has been a significant negative correlation between zonal precipitation and Nino 3.4 index over North Mountainous India, North West India, North Central India, West Peninsular India and South Peninsular India. First and third principal component (PC) of zonal precipitation explaining 44.4% and 14.2% variance respectively has also shown significant anti-correlation with Nino 3.4. Analysis with CMIP5 models revealed that majority of GCMs have failed to reproduce both magnitude and phase of such relationships mainly due to poor simulation of Nino 3.4 index. Therefore, an attempt has been made to improve the results through empirical orthogonal function (EOF) based statistical downscaling of CMIP5 GCMs. To downscale Nino 3.4 index, an optimal predictor combination of PCs extracted from EOF fields of large scale GCM predictors like Geo-potential height, u and v wind, Specific and relative humidity and air temperature at pressure levels 500, 850 and 1000 hpa, mean sea level pressure and atmospheric vapor content has been utilized. Results indicated improvements of downscaled CMIP5 models in simulating ENSO-monsoon relationship for zone wise precipitation. Multi-model ensemble (MME) of downscaled GCMs has better skill than individuals GCM. Therefore, downscaled MME may be used more reliably to investigate future ENSO-monsoon relationship under various warming scenarios

  1. East Asian Monsoon and paleoclimatic data analysis: a vegetation point of view

    Directory of Open Access Journals (Sweden)

    J. Guiot

    2008-06-01

    Full Text Available First we review several syntheses of paleodata (pollen, lake-levels showing the climate variations in China and Mongolia from the last glacial maximum to Present and in particular the precipitation increase at mid Holocene related to enhanced monsoon. All these results concur to a much enhanced monsoon on most of China during the first half of the Holocene. Second we present, in some details, a temporal study of a core (Lake Bayanchagan, Inner Mongolia located in an arid region at the edge of the present East Asian Monsoon (EAM influence and then sensitive to climatic change. This study involves pollen data together with other macro-remains and stable isotope curve to obtain a robust climate reconstruction. This study shows a long wet period between 11 000 and 5000 years BP divided in two parts, a warmer one from 11 000 and 8000 (marked by large evapotranspiration and a cooler one more favourable to forest expansion. Third, we present a spatial study based on pollen data only and covering all China and Mongolia at 6000 years BP, but using a mechanistic modelling approach, in an inverse mode. It has the advantage to take into account environmental context different from the present one (lower atmospheric CO2, different seasonality. This study shows temperature generally cooler than present one in southern China, but a significant warming was found over Mongolia, and a slightly higher in northeast China. Precipitation was generally higher than today in southern, northeast China, and northern Mongolia, but lower or similar to today in northwest China and north China. Enhanced EAM was then found in the southern half of China and in northeast China.

  2. Regional-scale relationships between aerosol and summer monsoon circulation, and precipitation over northeast Asia

    Science.gov (United States)

    Yoon, Soon-Chang; Kim, Sang-Woo; Choi, Suk-Jin; Choi, In-Jin

    2010-08-01

    We investigated the regional-scale relationships between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the regional-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001-2008, the increase of almost 40-50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anticyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies in July over the period 2001-2008, we found negative correlations over the areas encompassed by 105-115°E and 30-35°N and by 120-140°E and 35-40°N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation.

  3. Monsoon-driven variability in the southern Red Sea and the exchange with the Indian Ocean

    Science.gov (United States)

    Sofianos, S. S.; Papadopoulos, V. P.; Abualnaja, Y.; Nenes, A.; Hoteit, I.

    2016-02-01

    Although progress has been achieved in describing and understanding the mean state and seasonal cycle of the Red Sea dynamics, their interannual variability is not yet well evaluated and explained. The thermohaline characteristics and the circulation patterns present strong variability at various time scales and are affected by the strong and variable atmospheric forcing and the exchange with the Indian Ocean and the gulfs located at the northern end of the basin. Sea surface temperature time-series, derived from satellite observations, show considerable trends and interannual variations. The spatial variability pattern is very diverse, especially in the north-south direction. The southern part of the Red Sea is significantly influenced by the Indian Monsoon variability that affects the sea surface temperature through the surface fluxes and the circulation patterns. This variability has also a strong impact on the lateral fluxes and the exchange with the Indian Ocean through the strait of Bab el Mandeb. During summer, there is a reversal of the surface flow and an intermediate intrusion of a relatively cold and fresh water mass. This water originates from the Gulf of Aden (the Gulf of Aden Intermediate Water - GAIW), is identified in the southern part of the basin and spreads northward along the eastern Red Sea boundary to approximately 24°N and carried across the Red Sea by basin-size eddies. The GAIW intrusion plays an important role in the heat and freshwater budget of the southern Red Sea, especially in summer, impacting the thermohaline characteristics of the region. It is a permanent feature of the summer exchange flow but it exhibits significant variation from year to year. The intrusion is controlled by a monsoon-driven pressure gradient in the two ends of the strait and thus monsoon interannual variability can laterally impose its signal to the southern Red Sea thermohaline patterns.

  4. Performance of Regional Climate Model in Simulating Monsoon Onset Over Indian Subcontinent

    Science.gov (United States)

    Bhatla, R.; Mandal, B.; Verma, Shruti; Ghosh, Soumik; Mall, R. K.

    2018-06-01

    The performance of various Convective Parameterization Schemes (CPSs) of Regional Climate Model version 4.3 (RegCM-4.3) for simulation of onset phase of Indian summer monsoon (ISM) over Kerala was studied for the period of 2001-2010. The onset date and its associated spatial variation were simulated using RegCM-4.3 four core CPS, namely Kuo, Tiedtke, Emanuel and Grell; and with two mixed convection schemes Mix98 (Emanuel over land and Grell over ocean) and Mix99 (Grell over land and Emanuel over ocean) on the basis of criteria given by the India Meteorological Department (IMD) (Pai and Rajeevan in Indian summer monsoon onset: variability and prediction. National Climate Centre, India Meteorological Department, 2007). It has been found that out of six CPS, two schemes, namely Tiedtke and Mix99 simulated the onset date properly. The onset phase is characterized with several transition phases of atmosphere. Therefore, to study the thermal response or the effect of different sea surface temperature (SST), namely ERA interim (ERSST) and weekly optimal interpolation (OI_WK SST) on Indian summer monsoon, the role of two different types of SST has been used to investigate the simulated onset date. In addition, spatial atmospheric circulation pattern during onset phase were analyzed using reanalyze dataset of ERA Interim (EIN15) and National Oceanic and Atmospheric Administration (NOAA), respectively, for wind and outgoing long-wave radiation (OLR) pattern. Among the six convective schemes of RegCM-4.3 model, Tiedtke is in good agreement with actual onset dates and OI_WK SST forcing is better for simulating onset of ISM over Kerala.

  5. Characterization of non-methane hydrocarbons in Asian summer monsoon outflow observed by the CARIBIC aircraft

    Directory of Open Access Journals (Sweden)

    A. K. Baker

    2011-01-01

    Full Text Available Between April and December 2008 the CARIBIC commercial aircraft conducted monthly measurement flights between Frankfurt, Germany and Chennai, India. These flights covered the period of the Asian summer monsoon (June–September, during which enhancements in a number of atmospheric species were observed in the upper troposphere over southwestern Asia. In addition to in situ measurements of trace gases and aerosols, whole air samples were collected during the flights, and these were subsequently analyzed for a suite of trace gases that included a number of C2–C8 non-methane hydrocarbons. Non-methane hydrocarbons are relatively short-lived compounds and the large enhancements in their mixing ratios in the upper troposphere over southwestern Asia during the monsoon, sometimes more than double their spring and fall means, provides qualitative evidence for the influence of convectively uplifted boundary layer air. The particularly large enhancements of the combustion tracers benzene and ethyne, along with the similarity of their ratios with carbon monoxide and emission ratios from the burning of household biofuels, indicate a strong influence of biofuel burning to NMHC emissions in this region. Conversely, the ratios of ethane and propane to carbon monoxide, along with the ratio between i-butane and n-butane, indicate a significant source of these compounds from the use of fossil fuels, and comparison to previous campaigns suggests that this source could be increasing. Photochemical aging patterns of NMHCs showed that the CARIBIC samples were collected in two distinctly different regions of the monsoon circulation: a southern region where air masses had been recently influenced by low level contact and a northern region, where air parcels had spent substantial time in transit in the upper troposphere before being probed. Estimates of age using ratios of individual NMHCs have ranges of 3–6 days in the south and 9–12 days in

  6. Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

    KAUST Repository

    Konda, Gopinadh

    2018-05-22

    In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

  7. Reforecasting the 1972-73 ENSO Event and the Monsoon Drought Over India

    Science.gov (United States)

    Shukla, J.; Huang, B.; Shin, C. S.

    2016-12-01

    This paper presents the results of reforcasting the 1972-73 ENSO event and the Indian summer monsoon drought using the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), initialized with the Eu­ropean Centre for Medium-Range Weather Forecasts (ECMWF) global ocean reanalysis version 4, and observation-based land and atmosphere reanalyses. The results of this paper demonstrate that if the modern day climate models were available during the 1970's, even with the limited observations at that time, it should have been possible to predict the 1972-73 ENSO event and the associated monsoon drought. These results further suggest the necessity of continuing to develop realistic models of the climate system for accurate and reliable seasonal predictions. This paper also presents a comparison of the 1972-73 El Niño reforecast with the 1997-98 case. As the strongest event during 1958-78, the 1972-73 El Niño is distinguished from the 1997-98 one by its early termination. Initialized in the spring season, the forecast system predicted the onset and development of both events reasonably well, although the reforecasts underestimate the ENSO peaking magnitudes. On the other hand, the reforecasts initialized in spring and fall of 1972 persistently predicted lingering wind and SST anomalies in the eastern equatorial Pacific during the spring of 1973. Initialized in fall of 1997, the reforecast also grossly overestimates the peaking westerly wind and warm SST anomalies in the 1997-98 El Niño.In 1972-73, both the Eastern Pacific SST anomalies (for example Nino 3 Index) and the summer monsoon drought over India and the adjoining areas were predicted remarkably well. In contrast, the Eastern Pacific SST anomalies for the 1997-98 event were predicted well, but the normal summer monsoon rainfall over India of 1997 was not predicted by the model. This case study of the 1972-73 event is part of a larger, comprehensive reforecast project

  8. A ˜50 ka record of monsoonal variability in the Darjeeling foothill region, eastern Himalayas

    Science.gov (United States)

    Ghosh, Ruby; Bera, Subir; Sarkar, Anindya; Paruya, Dipak Kumar; Yao, Yi-Feng; Li, Cheng-Sen

    2015-04-01

    Pollen, phytoliths and δ 13C signatures of soil organic matter from two fluvial sedimentary sequences of the Darjeeling foothill region, eastern Himalayas are used to portray palaeoclimatic oscillations and their impact on regional plant communities over the last ˜50 ka. Quantitative palaeoclimate estimation using coexistence approach on pollen data and other proxies indicate significant oscillations in precipitation during the late part of MIS 3 (46.4-25.9 ka), early and middle part of MIS 2 (25.9-15.6 ka), and 5.4 to 3.5 ka. Middle to late MIS 3 (ca 46.4-31 ka.) was characterized by a comparatively low monsoonal activity and slightly higher temperature than that during ca 31 ka onwards. Simultaneous expansion of deciduous trees and chloridoid grasses also imply a drier and warmer phase. Between 31 and 22.3 ka (late MIS 3 to mid-MIS 2), higher precipitation and a slightly cooler temperature led to an increase in evergreen elements over deciduous taxa and wet-loving panicoid grasses over dry-loving chloridoid grasses than earlier. After ca 22.3 ka, shrinking of forest cover, expansion of C4 chloridoid grasses, Asteraceae and Cheno-ams in the vegetation with lowering of temperature and precipitation characterized the onset of the LGM which continued till 18.3 ka. End of the LGM is manifested by a restoration in the forest cover and in the temperature and precipitation regime. Later, during 5.4 to 4.3 ka, a strong monsoonal activity supported a dense moist evergreen forest cover that subsequently declined during 4.3 to 3.5 ka. A further increase in deciduous elements and non-arboreals might be a consequence of reduced precipitation and higher temperature during this phase. A comparison between monsoonal rainfall, MAT and palaeoatmospheric CO2 with floral dynamics since last ˜50 ka indicates that these fluctuations in plant succession were mainly driven by monsoonal variations.

  9. Hydrography and circulation off the west coast of India during the southwest monsoon 1987

    Digital Repository Service at National Institute of Oceanography (India)

    Shetye, S.R.; Gouveia, A.D.; Shenoi, S.S.C.; Sundar, D.; Michael, G.S.; Almeida, A.M.; Santanam, K.

    Marine Research [48,2 Figure I. Dynamic topography (dyn.cm) ofsea surface in the Arabian Sea relative to 800 db for the period July, August, September 1963. Reproduced from Duing (1970). \\ Goa, India, initiated a program to study the coastal processes off... aJ.: West coast ofIndia during Southwest Monsoon 369 --_.~ i ~"/~-,~ ! f'" l,~ I ~'" -1"' r~ t- f r- l ..gHl I 1.......-~11.... • ( i D~U:.! ~------~3'QGoO Figure 8. (a) Vertical section of temperature (0C) along leg M; (b) Vertical section...

  10. Recently studied sedimentary records from the eastern Arabian Sea: Implications to Holocene monsoonal variability

    Digital Repository Service at National Institute of Oceanography (India)

    Agnihotri, R.; Kurian, S.

    stream_size 72460 stream_content_type text/plain stream_name Earth_Sci_India_1_258.pdf.txt stream_source_info Earth_Sci_India_1_258.pdf.txt Content-Encoding UTF-8 Content-Type text/plain; charset=UTF-8 Agnihotri http://www....earthscienceindia.info/Agnihotri.htm 1 of 14 10/15/2008 9:41 AM Earth Science India Vol.1 (IV), October, 2008, pp. 258-287 http://www.earthscienceindia.info/ Recently studied sedimentary records from the eastern Arabian Sea: Implications to Holocene monsoonal variability Rajesh...

  11. Waves in shallow water off west coast of India during the onset of summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    SanilKumar, V.; Philip, C.S.; Nair, T.N.B.

    and narrowness parameter varies from 0 to 1, and will have smaller values for narrower spectra. Spectral peaked- ness parameter will have higher values for narrow spectra. ε= radicalBigg 1− m 2 2 m0m4 (1) ν= radicalBiggm 0m2 m21 −1 (2) Qp = 2m2 0 integraldisplay.... Mandal, J. C. and Halder, S. R.: Sea breeze like cloud-free zones during monsoon months, Mausam, 43, 163–168, 1992. Massel, S. R.: On the largest wave height in water of constant depth, Ocean Eng., 23, 553–573, 1996. Miles, J.: On the generation...

  12. Stable isotopic characteristic of Taiwan's precipitation: A case study of western Pacific monsoon region

    Science.gov (United States)

    Peng, Tsung-Ren; Wang, Chung-Ho; Huang, Chi-Chao; Fei, Li-Yuan; Chen, Chen-Tung Arthur; Hwong, Jeen-Lian

    2010-01-01

    The stable oxygen and hydrogen isotopic features of precipitation in Taiwan, an island located at the western Pacific monsoon area, are presented from nearly 3,500 samples collected during the past decade for 20 stations. Results demonstrate that moisture sources from diverse air masses with different isotopic signals are the main parameter in controlling the precipitation's isotope characteristics. The air mass from polar continental (Pc) region contributes the precipitation with high deuterium excess values (up to 23‰) and relatively enriched isotope compositions (e.g., - 3.2‰ for δ 18O) during the winter with prevailing northeasterly monsoon. By contrast, air masses from equatorial maritime (Em) and tropical maritime (Tm) supply the precipitation with low deuterium excess values (as low as about 7‰) and more depleted isotope values (e.g., - 8.9‰ and - 6.0‰ for δ 18O of Tm and Em, respectively) during the summer with prevailing southwesterly monsoon. Thus seasonal differences in terms of δ 18O, δD, and deuterium excess values are primarily influenced by the interactions among various precipitation sources. While these various air masses travel through Taiwan, secondary evaporation effects further modify the isotope characteristics of the inland precipitation, such as raindrop evaporation (reduces the deuterium excess of winter precipitation) and moisture recycling (increases the deuterium excess of summer precipitation). The semi-quantitative estimations in terms of evaluation for changes in the deuterium excess suggest that the raindrop evaporation fractions for winter precipitation range 7% to 15% and the proportions of recycling moisture in summer precipitation are less than 5%. Additionally, the isotopic altitude gradient in terms of δ 18O for summer precipitation is - 0.22‰/100 m, greater than - 0.17‰/100 m of winter precipitation. The greater isotopic gradient in summer can be attributed to a higher temperature vs. altitude gradient

  13. Fine particulate matter in the tropical environment: monsoonal effects, source apportionment, and health risk assessment

    OpenAIRE

    M. F. Khan; M. F. Khan; M. T. Latif; M. T. Latif; W. H. Saw; N. Amil; N. Amil; M. S. M. Nadzir; M. S. M. Nadzir; M. Sahani; N. M. Tahir; N. M. Tahir; J. X. Chung

    2016-01-01

    The health implications of PM2.5 in the tropical region of Southeast Asia (SEA) are significant as PM2.5 can pose serious health concerns. PM2.5 concentration and sources here are strongly influenced by changes in the monsoon regime from the south-west quadrant to the north-east quadrant in the region. In this work, PM2.5 samples were collected at a semi-urban area using a high-volume air sampler at different seasons on 24 h basis. Analysis of trace elements and water-sol...

  14. Atmospheric 210Pb changes during monsoon in east and west coast of Peninsular Malaysia

    International Nuclear Information System (INIS)

    Siti Munirah Johari; Che Abdul Rahim Mohamed

    2013-01-01

    Full-text: 210 Pb is widely used as an atmospheric tracer as its parent, 222 Rn is continuously produced in the atmosphere from soil emanation. This study was conducted to observe the changes of 210 Pb activity based on temporal and spatial factor using PM10 samples. PM10 were sampled by Malaysian Meteorological Department in four station consist of two station from both east and west coast of Peninsular Malaysia in 2007. Activity level of 210 Pb was determined using the Tennelec XLB-5 Gross Alpha-Beta Counter, Canberra, after the ingrowth of 210 Pb by the outgrowth of 210 Bi. Basically, the analysed result showed that three to four significant peaks during northeast monsoon, southwest monsoon and inter monsoon. For east coast which comprises Kuantan and Mersing stations, the highest 210 Pb activity in Kuantan was in April and June with 45.73 ± 3.66 mBq/ kg and 48.20 ± 3.33 mBq/ kg, respectively. While in Mersing, 210 Pb activity showed the highest in April and July with 45.77 ± 2.67 mBq/ kg and 44.21 ± 2.42 mBq/ kg, respectively. As for the west coast, it comprises Setiawan and Chuping stations. Setiawan station showed the highest 210 Pb activity in October and July with 48.90 ± 2.52 mBq/ kg and 44.09 ± 2.34 mBq/ kg, respectively. Chuping showed the highest 210 Pb activity in March and October with 39.96 ± 1.94 mBq/ kg and 14.98 ± 0.80 mBq/ kg, respectively. It shows that 210 Pb activity in Chuping is much lower than in Setiawan because of its location is in a rural area. This study showed that during southwest monsoon from May to September, it clearly showed that 210 Pb activity is higher in west coast than in east coast as wind sources come from southwest of Peninsular Malaysia. (author)

  15. Nutrient biogeochemistry of the eastern Arabian Sea during the southwest monsoon retreat

    Digital Repository Service at National Institute of Oceanography (India)

    George, R; Muraleedharan, K.R; Martin, G.D.; Sabu, P.; Gerson, V.J.; Dineshkumar, P.K.; Nair, S.M.; Chandramohanakumar, N.; Nair, K.K.C.

    and adjoining southeastern Arabian Sea. Curr Sci 96:364–375 Jyothibabu R, Madhu NV, Jayalakshmi KV, Balachandran KK, Shiyas CA, Martin GD, Nair KKC (2006) Impact of freshwater influx on microzooplankton mediated food web in a tropical estuary (Cochin backwaters... ARTICLE Nutrient biogeochemistry of the eastern Arabian Sea during the southwest monsoon retreat Rejomon George • K. R. Muraleedharan • G. D. Martin • P. Sabu • Vijay John Gerson • P. K. Dineshkumar • S. M. Nair • N. Chandramohanakumar • K. K. C. Nair...

  16. Enhanced Global Monsoon in Present Warm Period Due to Natural and Anthropogenic Forcings

    Directory of Open Access Journals (Sweden)

    Jing Chai

    2018-04-01

    Full Text Available In this study, we investigate global monsoon precipitation (GMP changes between the Present Warm Period (PWP, 1900–2000 and the Little Ice Age (LIA, 1250–1850 by performing millennium sensitivity simulations using the Community Earth System Model version 1.0 (CESM1. Three millennium simulations are carried out under time-varying solar, volcanic and greenhouse gas (GHG forcing, respectively, from 501 to 2000 AD. Compared to the global-mean surface temperature of the cold LIA, the global warming in the PWP caused by high GHG concentration is about 0.42 °C, by strong solar radiation is 0.14 °C, and by decreased volcanic activity is 0.07 °C. The GMP increases in these three types of global warming are comparable, being 0.12, 0.058, and 0.055 mm day−1, respectively. For one degree of global warming, the GMP increase induced by strong GHG forcing is 2.2% °C−1, by strong solar radiation is 2.8% °C−1, and by decreased volcanic forcing is 5.5% °C−1, which means that volcanic forcing is most effective in terms of changing the GMP among these three external forcing factors. Under volcanic inactivity-related global warming, both monsoon moisture and circulation are enhanced, and the enhanced circulation mainly occurs in the Northern Hemisphere (NH. The circulation, however, is weakened in the other two cases, and the GMP intensification is mainly caused by increased moisture. Due to large NH volcanic aerosol concentration in the LIA, the inter-hemispheric thermal contrast of PWP global warming tends to enhance NH monsoon circulation. Compared to the GHG forcing, solar radiation tends to warm low-latitude regions and cause a greater monsoon moisture increase, resulting in a stronger GMP increase. The finding in this study is important for predicting the GMP in future anthropogenic global warming when a change in natural solar or volcanic activity occurs.

  17. Apparent Trends in Productivity of Monsoon Asia from 1982 to 2002

    Science.gov (United States)

    Alexandrov, G. A.; Yamagata, Y.

    2005-12-01

    The rapid economic growth of Monsoon Asia raises concerns about the future of carbon stored in the terrestrial ecosystems of the region, especially in connection with climate change. The regional carbon budget for 1980s suggests that Monsoon Asia as a whole acted as source [Tian et al., 2003], although some parts of the region acted as sink. Here we provide some evidence from satellite data that productivity of the region changed in the manner that suggests similar conclusion. Comparing the period 1982-1992 and the period 1992-2002, we found that the productivity of the territory generally decreased in the forest zone and increased in the non-forest zone of the region. The productivity of a territory strongly depends on the area covered with photosynthetically active vegetation (PAV) and, therefore, we introduce a grid variable, FPAV, which stands for the fraction of a grid cell covered with PAV. (Grid, here, means geographic grid of half-degree resolution.) Deciduous plants are leafless during the dormant season, and so FPAV may vary on seasonal basis. The amplitude enlarges with the ratio between deciduous and evergreen species. The minimal value of FPAV gives the fraction of a grid cell covered with evergreen vegetation. The maximal value gives the fraction of the cell that covered either with deciduous or evergreen vegetation and, thus, tells us which fraction of t