WorldWideScience

Sample records for atlantic meridional overturning

  1. The Atlantic Meridional Overturning Circulation's Response to Variable Buoyancy Forcing

    Science.gov (United States)

    Butler, Edward; Oliver, Kevin; Hirschi, Joël

    2014-05-01

    The Meridional Overturning Circulation (MOC) is a large-scale global circulation of water (and heat) throughout the world's ocean. It is an integral part of the climate system, responsible for significant anomalous warming of the North Atlantic region. Much of our current understanding of the MOC is based on equilibrium theories. However, the MOC is not a steady circulation and exhibits variability across a broad range of timescales. We examine the transient response of global ocean overturning, with particular emphasis on the Atlantic MOC (AMOC), to periodic variations in the North Atlantic meridional density gradient on decadal, centennial, and millennial timescales within the Nucleus for European Modelling of the Ocean (NEMO) model framework. We use the ORCA2 global ocean configuration of NEMO (with realistic topography and a horizontal resolution of 2°) and impose periodic variations in air temperature over the North Atlantic. In response, we see large oscillations in the strength of the AMOC which peak in magnitude at 128-year timescales. A scaling relationship of the form Ψ ~ ΔρH2 (in which Δρ is a measure of meridional density gradient and H is the depth scale of maximal overturning) is found to hold for the AMOC in these transient simulations with strongest correlations observed at centennial timescales. We explore the validity of this scaling relationship across a broad range of spatial and temporal scales and discuss its validity in a global context.

  2. Surface changes in the North Atlantic meridional overturning circulation during the last millennium

    OpenAIRE

    Wanamaker, Alan D.; Butler, Paul G.; James D Scourse; Heinemeier, Jan; Eiríksson, Jón; Knudsen, Karen Luise; Richardson, Christopher A.

    2012-01-01

    Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local rad...

  3. Surface changes in the North Atlantic meridional overturning circulation during the last millennium.

    Science.gov (United States)

    Wanamaker, Alan D; Butler, Paul G; Scourse, James D; Heinemeier, Jan; Eiríksson, Jón; Knudsen, Karen Luise; Richardson, Christopher A

    2012-01-01

    Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector. PMID:22692542

  4. Role of the Southern Ocean in setting the Atlantic stratification and meridional overturning circulation

    OpenAIRE

    Kamenkovich, Igor; Radko, Timour

    2011-01-01

    This study examines the importance of the Southern Ocean (SO) stratification in determining the upper cell of the Atlantic meridional overturning circulation (MOC) and stratification. Main results are based on a suite of idealized numerical simulations of the Atlantic with the prescribed density structure at the Atlantic southern boundary, intended to explore the importance of various factors. The results demonstrate that the density distribution at the SO-Atlantic boundary is the...

  5. Surface changes in the North Atlantic meridional overturning circulation during the last millennium

    DEFF Research Database (Denmark)

    Wanamaker, A.D.; Butler, P.G.; Scourse, J.D.;

    2012-01-01

    decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning...

  6. Frequency-dependent effects of the Atlantic meridional overturning on the tropical Pacific Ocean

    NARCIS (Netherlands)

    Raa, L.A. te; Oldenborgh, G.J. van; Dijkstra, H.A.; Philip, S.Y.

    2009-01-01

    Using the ECHAM5/MPI-OM model, we study the relation between the variations in the Atlantic meridional overturning circulation (AMOC) and both the Pacific sea surface temperature (SST) and the El Niño-Southern Oscillation (ENSO) amplitude. In a 17-member 20C3M/SRES-A1b ensemble for 1950–2100 the Pac

  7. Multi-spatial variability modes of the Atlantic Meridional Overturning Circulation

    Institute of Scientific and Technical Information of China (English)

    ZHOU Tianjun

    2003-01-01

    The multi-spatial variability modes of the Atlantic Meridional Overturning Circulation (MOC) are identified in the natural coupled simulation of two climate models, the MOC either oscillates at decadal scales with strong cross- equatorial flow or fluctuates locally at interannual scales with weaker cross-equatorial flow. Former studies mainly emphasize the paleo-environmental and paleo-climatic impacts of the meridional overturning states transition; this analysis indicates the existence of the multi-spatial variability modes of the MOC at interannual to decadal scales. Further analysis indicates that the conventionally used MOC index, which is defined as the maximum zonal mean meridional stream-function of the North Atlantic, cannot properly describe the multi-spatial variability characteristics of the MOC.

  8. Response of the South Atlantic circulation to an abrupt collapse of the Atlantic meridional overturning circulation

    Energy Technology Data Exchange (ETDEWEB)

    Laurian, Audine [University of Hawai' i at Manoa, International Pacific Research Center, School of Ocean and Earth Science and Technology, Honolulu, HI (United States); Drijfhout, Sybren S. [Royal Netherlands Meteorological Institute, De Bilt (Netherlands)

    2011-08-15

    The South Atlantic response to a collapse of the North Atlantic meridional overturning circulation (AMOC) is investigated in the ECHAM5/MPI-OM climate model. A reduced Agulhas leakage (about 3.1 Sv; 1 Sv = 10{sup 6} m{sup 3} s{sup -1}) is found to be associated with a weaker Southern Hemisphere (SH) supergyre and Indonesian throughflow. These changes are due to reduced wind stress curl over the SH supergyre, associated with a weaker Hadley circulation and a weaker SH subtropical jet. The northward cross-equatorial transport of thermocline and intermediate waters is much more strongly reduced than Agulhas leakage in relation with an AMOC collapse. A cross-equatorial gyre develops due to an anomalous wind stress curl over the tropics that results from the anomalous sea surface temperature gradient associated with reduced ocean heat transport. This cross-equatorial gyre completely blocks the transport of thermocline waters from the South to the North Atlantic. The waters originating from Agulhas leakage flow somewhat deeper and most of it recirculates in the South Atlantic subtropical gyre, leading to a gyre intensification. This intensification is consistent with the anomalous surface cooling over the South Atlantic. Most changes in South Atlantic circulation due to global warming, featuring a reduced AMOC, are qualitatively similar to the response to an AMOC collapse, but smaller in amplitude. However, the increased northward cross-equatorial transport of intermediate water relative to thermocline water is a strong fingerprint of an AMOC collapse. (orig.)

  9. Carbon Cycle Variability Due to the Atlantic Meridional Overturning Circulation

    Science.gov (United States)

    McKinley, G. A.; Breeden, M.

    2014-12-01

    The North Atlantic is the most intense region of CO2 uptake by the world oceans. Though characterization of the mean sink is robust across methodologies [1], a detailed understanding of variability remains lacking, seriously complicating interpretation of observations [2,3]. We investigate the causes of decadal scale variability in the North Atlantic carbon cycle using a regional numerical simulation driven by realistic climate for 1948-2013 and preindustrial atmospheric pCO2. Modeled decadal-timescale variability in air-sea CO2 fluxes and surface ocean pCO2 are dominantly controlled by basin-averaged sea surface temperature (SST). This SST signal is composed of two parts: the Atlantic Multidecadal Oscillation (AMO), associated with the model AMOC, and a positive trend. AMO dominates long-term pCO2 variability, with positive AMO leading to pCO2 declines in the subpolar gyre and pCO2 increases in the subtropical gyre. Decomposition of pCO2 into chemical (pCO2-chem) and temperature (pCO2-SST) drivers is instructive. Maximum positive AMO causes subpolar pCO2-SST to increase by ~10 uatm, but also for pCO2-chem to decline by ~20 uatm. Reduced subpolar pCO2-chem is due to reduced supply of dissolved inorganic carbon (DIC) by winter deep mixing and to enhanced DIC horizontal divergence. On net, positive AMO substantially depresses subpolar North Atlantic pCO2. AMO had maximum negative amplitude in the 1980s and maximum positive amplitude in the mid-2000s, which coincides with the observed record of surface ocean pCO2 [2]. This model suggests that the changing sign of AMO drove trends in the natural component of surface ocean pCO2 of approximately -7 uatm / decade in the subpolar gyre since the 1980s. This trend is significant in comparison to observed changes in surface ocean pCO2 [3], and thus impacts our understanding of the changing ocean carbon sink in this critical region. [1] Schuster et at 2013 [2] McKinley et al. 2011, McKinley and Fay 2013 [3] Metzl et al. 2010

  10. Support of Publication Costs, Atlantic Meridional Overturning Circulation Special Issue of Deep Sea Research II Journal

    Energy Technology Data Exchange (ETDEWEB)

    Amy Honchar

    2012-11-12

    The contribution of funds from DOE supported publication costs of a special issue of Deep Sea Research arising from presentations at the First U.S. Atlantic Meridional Overturning Circulation (AMOC) Meeting held 4-6 May, 2009 to review the US implementation plan and its coordination with other monitoring activities. The special issue includes a total of 16 papers, including publications from three DOE-supported investigators (ie Sevellec, F., and A.V. Fedorov; Hu et. al., and Wan et. al.,). The special issue addresses DOE interests in understanding and simulation/modeling of abrupt climate change.

  11. Changes of the surface cell of the Atlantic and Indian Meridional overturning circulations

    OpenAIRE

    Pérez Hernández, María Dolores

    2014-01-01

    [EN]This research thesis focuses on the Meridional Overturning Circulations (MOC) of both the Atlantic and Indian Oceans (AMOC and IMOC). The MOC plays a very important role in the ocean and the climate systems. The MOC connects the flow of the different world oceans, distributing heat and other properties through the different latitudes. The AMOC at 26.5o N transports 1.33 ± 0.14PW, this is about half of the total heat carried together by the climate system form the Equator towards hi...

  12. Deep water provenance and dynamics of the (de)glacial Atlantic meridional overturning circulation

    Science.gov (United States)

    Lippold, Jörg; Gutjahr, Marcus; Blaser, Patrick; Christner, Emanuel; de Carvalho Ferreira, Maria Luiza; Mulitza, Stefan; Christl, Marcus; Wombacher, Frank; Böhm, Evelyn; Antz, Benny; Cartapanis, Olivier; Vogel, Hendrik; Jaccard, Samuel L.

    2016-07-01

    Reconstructing past modes of ocean circulation is an essential task in paleoclimatology and paleoceanography. To this end, we combine two sedimentary proxies, Nd isotopes (εNd) and the 231Pa/230Th ratio, both of which are not directly involved in the global carbon cycle, but allow the reconstruction of water mass provenance and provide information about the past strength of overturning circulation, respectively. In this study, combined 231Pa/230Th and εNd down-core profiles from six Atlantic Ocean sediment cores are presented. The data set is complemented by the two available combined data sets from the literature. From this we derive a comprehensive picture of spatial and temporal patterns and the dynamic changes of the Atlantic Meridional Overturning Circulation over the past ∼25 ka. Our results provide evidence for a consistent pattern of glacial/stadial advances of Southern Sourced Water along with a northward circulation mode for all cores in the deeper (>3000 m) Atlantic. Results from shallower core sites support an active overturning cell of shoaled Northern Sourced Water during the LGM and the subsequent deglaciation. Furthermore, we report evidence for a short-lived period of intensified AMOC in the early Holocene.

  13. Interdecadal North-Atlantic meridional overturning circulation variability in EC-EARTH

    Energy Technology Data Exchange (ETDEWEB)

    Wouters, Bert; Drijfhout, Sybren; Hazeleger, Wilco

    2012-12-15

    The Atlantic meridional overturning circulation (AMOC) in a 600 years pre-industrial run of the newly developed EC-EARTH model features marked interdecadal variability with a dominant time-scale of 50-60 years. An oscillation of approximately 2 Sverdrup (1 Sv = 10{sup 6} m{sup 3} s{sup -1}) is identified, which manifests itself as a monopole causing the overturning to simultaneously strengthen (/weaken) and deepen (/shallow) as a whole. Eight years before the AMOC peaks, density in the Labrador-Irminger Sea region reaches a maximum, triggering deep water formation. This density change is caused by a counterclockwise advection of temperature and salinity anomalies at lower latitudes, which we relate to the north-south excursions of the subpolar-subtropical gyre boundary and variations in strength and position of the subpolar gyre and the North Atlantic Current. The AMOC fluctuations are not directly forced by the atmosphere, but occur in a delayed response of the ocean to forcing by the North Atlantic Oscillation, which initiates ''intergyre''-gyre fluctuations. Associated with the AMOC is a 60-year sea surface temperature variability in the Atlantic, with a pattern and timescale showing similarities with the real-world Atlantic Multidecadal Variability. This good agreement with observations lends a certain degree of credibility that the mechanism that is described in this article could be seen as representative of the real climate system. (orig.)

  14. Mechanisms for decadal scale variability in a simulated Atlantic meridional overturning circulation

    Energy Technology Data Exchange (ETDEWEB)

    Medhaug, I.; Eldevik, T.; Furevik, T. [University of Bergen, Geophysical Institute, Bergen (Norway); Bjerknes Centre for Climate Research, Bergen (Norway); Langehaug, H.R. [Nansen Environmental and Remote Sensing Center, Bergen (Norway); Bjerknes Centre for Climate Research, Bergen (Norway); Bentsen, M. [Uni Bjerknes Centre, Uni Research, Bergen (Norway); Bjerknes Centre for Climate Research, Bergen (Norway)

    2012-07-15

    Variability in the Atlantic Meridional Overturning Circulation (AMOC) has been analysed using a 600-year pre-industrial control simulation with the Bergen Climate Model. The typical AMOC variability has amplitudes of 1 Sverdrup (1 Sv = 10{sup 6} m{sup 3} s{sup -1}) and time scales of 40-70 years. The model is reproducing the observed dense water formation regions and has very realistic ocean transports and water mass distributions. The dense water produced in the Labrador Sea (1/3) and in the Nordic Seas, including the water entrained into the dense overflows across the Greenland-Scotland Ridge (GSR; 2/3), are the sources of North Atlantic Deep Water (NADW) forming the lower limb of the AMOC's northern overturning. The variability in the Labrador Sea and the Nordic Seas convection is driven by decadal scale air-sea fluxes in the convective region that can be related to opposite phases of the North Atlantic Oscillation. The Labrador Sea convection is directly linked to the variability in AMOC. Linkages between convection and water mass transformation in the Nordic Seas are more indirect. The Scandinavian Pattern, the third mode of atmospheric variability in the North Atlantic, is a driver of the ocean's poleward heat transport (PHT), the overall constraint on northern water mass transformation. Increased PHT is both associated with an increased water mass exchange across the GSR, and a stronger AMOC. (orig.)

  15. Glacial climate sensitivity to different states of the Atlantic Meridional overturning circulation : results from the IPSL model

    OpenAIRE

    Kageyama, M.; J. Mignot; D. Swingedouw; Marzin, C.; Alkama, R.; O. Marti

    2009-01-01

    Numerous records from the North Atlantic and the surrounding continents have shown rapid and large amplitude climate variability during the last glacial period. This variability has often been associated to changes in the Atlantic Meridional Overturning Circulation (AMOC). Rapid climate change on the same time scales has also been reconstructed for sites far away from the North Atlantic, such as the tropical Atlantic, the East Pacific and Asia. The mechanisms explaining these climatic respons...

  16. Impact of the Indonesian Throughflow on the Atlantic Meridional Overturning Circulation

    Science.gov (United States)

    Le Bars, Dewi; Dijkstra, Henk

    2014-05-01

    Understanding the mechanisms controlling the strength and variability of the Atlantic Meridional Overturning Circulation (AMOC) is one of the main topics of climate science and in particular physical oceanography. Current simple representations of the global ocean overturning separates the surface return flow to the Atlantic basin into a cold water path through the Drake Passage and a warm water path through the Indonesian Throughflow and Agulhas leakage. The relative importance of these two paths has been investigated in non-eddying ocean models. In these models the Agulhas retroflection cannot be modelled properly, which leads to an important overestimation of the Agulhas leakage. Furthermore, it seems that the in these models the relation between the meridional density gradient and the overturning strength is greatly simplified and changes significantly when eddies are resolved (Den Toom et al. 2013). As a result, the impact of the Pacific-Indian Oceans exchange through the Indonesian Throughflow on the AMOC is still unknown. To investigate this question we run a state-of-the-art ocean model, the Parallel Ocean Program (POP), globally, at eddy resolving resolution (0.1º). Using climatological forcing from the CORE dataset we perform two simulations of 110 years, a control experiment with realistic coastlines and one in which the Indonesian Passages are closed. Results show that, for a closed Indonesian Throughflow, the Indian Ocean cools down but its salinity increases. The Agulhas leakage reduces also by 3Sv (Le Bars et al. 2013) and the net effect on the south Atlantic is a cooling down and decrease salinity. The anomalies propagate slowly northward and a significant decrease of the AMOC is found at 26ºN after 50 years. This decrease AMOC also leads to reduced northward heat flux in the Atlantic. These processes are investigated with a detailed analysis of the heat and freshwater balances in the Atlantic-Arctic region and in the region south of 34ºS where

  17. Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review

    Science.gov (United States)

    Buckley, Martha W.; Marshall, John

    2016-03-01

    This is a review about the Atlantic Meridional Overturning Circulation (AMOC), its mean structure, temporal variability, controlling mechanisms, and role in the coupled climate system. The AMOC plays a central role in climate through its heat and freshwater transports. Northward ocean heat transport achieved by the AMOC is responsible for the relative warmth of the Northern Hemisphere compared to the Southern Hemisphere and is thought to play a role in setting the mean position of the Intertropical Convergence Zone north of the equator. The AMOC is a key means by which heat anomalies are sequestered into the ocean's interior and thus modulates the trajectory of climate change. Fluctuations in the AMOC have been linked to low-frequency variability of Atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses. On intra-annual timescales, variability in AMOC is large and primarily reflects the response to local wind forcing; meridional coherence of anomalies is limited to that of the wind field. On interannual to decadal timescales, AMOC changes are primarily geostrophic and related to buoyancy anomalies on the western boundary. A pacemaker region for decadal AMOC changes is located in a western "transition zone" along the boundary between the subtropical and subpolar gyres. Decadal AMOC anomalies are communicated meridionally from this region. AMOC observations, as well as the expanded ocean observational network provided by the Argo array and satellite altimetry, are inspiring efforts to develop decadal predictability systems using coupled atmosphere-ocean models initialized by ocean data.

  18. Reduced interdecadal variability of Atlantic Meridional Overturning Circulation under global warming

    Science.gov (United States)

    Cheng, Jun; Liu, Zhengyu; Zhang, Shaoqing; Liu, Wei; Dong, Lina; Liu, Peng; Li, Hongli

    2016-03-01

    Interdecadal variability of the Atlantic Meridional Overturning Circulation (AMOC-IV) plays an important role in climate variation and has significant societal impacts. Past climate reconstruction indicates that AMOC-IV has likely undergone significant changes. Despite some previous studies, responses of AMOC-IV to global warming remain unclear, in particular regarding its amplitude and time scale. In this study, we analyze the responses of AMOC-IV under various scenarios of future global warming in multiple models and find that AMOC-IV becomes weaker and shorter with enhanced global warming. From the present climate condition to the strongest future warming scenario, on average, the major period of AMOC-IV is shortened from ˜50 y to ˜20 y, and the amplitude is reduced by ˜60%. These reductions in period and amplitude of AMOC-IV are suggested to be associated with increased oceanic stratification under global warming and, in turn, the speedup of oceanic baroclinic Rossby waves.

  19. Variations of the Atlantic meridional overturning circulation in control and transient simulations of the last millennium

    Directory of Open Access Journals (Sweden)

    D. Hofer

    2011-02-01

    Full Text Available The variability of the Atlantic meridional overturing circulation (AMOC strength is investigated in control experiments and in transient simulations of up to the last millennium using the low-resolution Community Climate System Model version 3. In the transient simulations the AMOC exhibits enhanced low-frequency variability that is mainly caused by infrequent transitions between two semi-stable circulation states which amount to a 10 percent change of the maximum overturning. One transition is also found in a control experiment, but the time-varying external forcing significantly increases the probability of the occurrence of such events though not having a direct, linear impact on the AMOC. The transition from a high to a low AMOC state starts with a reduction of the convection in the Labrador and Irminger Seas and goes along with a changed barotropic circulation of both gyres in the North Atlantic and a gradual strengthening of the convection in the Greenland-Iceland-Norwegian (GIN Seas. In contrast, the transition from a weak to a strong overturning is induced by decreased mixing in the GIN Seas. As a consequence of the transition, regional sea surface temperature (SST anomalies are found in the midlatitude North Atlantic and in the convection regions with an amplitude of up to 3 K. The atmospheric response to the SST forcing associated with the transition indicates a significant impact on the Scandinavian surface air temperature (SAT in the order of 1 K. Thus, the changes of the ocean circulation make a major contribution to the Scandinavian SAT variability in the last millennium.

  20. Observed decline of the Atlantic Meridional Overturning Circulation 2004 to 2012

    Directory of Open Access Journals (Sweden)

    D. A. Smeed

    2013-09-01

    Full Text Available The Atlantic Meridional Overturning Circulation (AMOC has been observed continuously at 26° N since April 2004. The AMOC and its component parts are monitored by combining a transatlantic array of moored instruments with submarine-cable based measurements of the Gulf Stream and satellite derived Ekman transport. The time series has recently been extended to October 2012 and the results show a downward trend since 2004. From April~2008 to March 2012 the AMOC was an average of 2.7 Sv weaker than in the first four years of observation (95% confidence that the reduction is 0.3 Sv or more. Ekman transport reduced by about 0.2 Sv and the Gulf Stream by 0.5 Sv but most of the change (2.0 Sv is due to the mid-ocean geostrophic flow. The change of the mid-ocean geostrophic flow represents a strengthening of the subtropical gyre above the thermocline. The increased southward flow of warm waters is balanced by a decrease in the southward flow of Lower North Atlantic Deep Water below 3000 m. The transport of Lower North Atlantic Deep Water slowed by 7% per year (95% confidence that the rate of slowing is greater than 2.5% per year.

  1. Wind effect on the Atlantic meridional overturning circulation via sea ice and vertical diffusion

    Science.gov (United States)

    Yang, Haijun; Wang, Kun; Dai, Haijin; Wang, Yuxing; Li, Qing

    2016-06-01

    Effects of wind and fresh water on the Atlantic meridional overturning circulation (AMOC) are investigated using a fully coupled climate model. The AMOC can change significantly when perturbed by either wind stress or freshwater flux in the North Atlantic. This study focuses on wind stress effect. Our model results show that the wind forcing is crucial in maintaining the AMOC. Reducing wind forcing over the ocean can cause immediately weakening of the vertical salinity diffusion and convection in the mid-high latitudes Atlantic, resulting in an enhancement of vertical salinity stratification that restrains the deep water formation there, triggering a slowdown of the thermohaline circulation. As the thermohaline circulation weakens, the sea ice expands southward and melts, providing the upper ocean with fresh water that weakens the thermohaline circulation further. The wind perturbation experiments suggest a positive feedback between sea-ice and thermohaline circulation strength, which can eventually result in a complete shutdown of the AMOC. This study also suggests that sea-ice variability may be also important to the natural AMOC variability on decadal and longer timescales.

  2. On the relation between Meridional Overturning Circulation and sea-level gradients in the Atlantic

    Directory of Open Access Journals (Sweden)

    H. Kienert

    2012-04-01

    Full Text Available On the basis of model simulations, we examine what information on changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC can be extracted from associated changes in sea surface height (SSH, specifically from a broad Atlantic north-south gradient as has been suggested previously in the literature. Since a relation between AMOC and SSH changes can only be used as an AMOC diagnostic if it is valid independently of the specific forcing, we consider three different forcing types: increase of CO2 concentration, freshwater fluxes to the northern convection sites and the modification of Southern Ocean winds. We concentrate on a timescale of 100 yr. We find approximately linear and numerically similar relations between a sea-level difference within the Atlantic and the AMOC for freshwater as well as wind forcing. However, the relation is more complex in response to atmospheric CO2 increase, which precludes this sea-level difference as an AMOC diagnostic under climate change. Finally, we show qualitatively to what extent changes in SSH and AMOC strength that are caused by simultaneous application of different forcings correspond to the sum of the changes due to the individual forcings, a potential prerequisite for more complex SSH-based AMOC diagnostics.

  3. The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

    Energy Technology Data Exchange (ETDEWEB)

    Frankignoul, Claude [Universite Pierre et Marie Curie, Paris 6, LOCEAN/IPSL, Paris Cedex 05 (France); Deshayes, Julie; Curry, Ruth [Woods Hole Oceanographic Institution, Woods Hole, MA (United States)

    2009-11-15

    An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during 1963-2003. The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1,500 m reproduce well those derived from the available record of hydrographic measurements. In the model, the variability of the Atlantic meridional overturning circulation (MOC) is primarily driven by changes in deep water formation taking place in the Irminger Sea and, to a lesser extent, the Labrador Sea. Both are strongly influenced by the North Atlantic Oscillation (NAO). The modeled interannual to decadal salinity changes in the subpolar basins are mostly controlled by circulation-driven anomalies of freshwater flux convergence, although surface salinity restoring to climatology and other boundary fluxes each account for approximately 25% of the variance. The NAO plays an important role: a positive NAO phase is associated with increased precipitation, reduced northward salt transport by the wind-driven intergyre gyre, and increased southward flows of freshwater across the Greenland-Scotland ridge. Since the NAO largely controlled deep convection in the subpolar gyre, fresher waters are found near the sinking region during convective events. This markedly differs from the active influence on the MOC that salinity exerts at decadal and longer timescales in most coupled models. The intensification of the MOC that follows a positive NAO phase by about 2 years does not lead to an increase in the northward salt transport into the subpolar domain at low frequencies because it is cancelled by the concomitant intensification of the subpolar gyre which shifts the subpolar front eastward and reduces the northward salt transport by the North Atlantic Current waters. This differs again from most coupled models, where the gyre

  4. Stochastically-driven multidecadal variability of the Atlantic meridional overturning circulation in CCSM3

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young-Oh [Woods Hole Oceanographic Institution, Physical Oceanography Department, Woods Hole, MA (United States); Frankignoul, Claude [Universite Pierre et Marie Curie, LOCEAN/IPSL, Paris (France)

    2012-03-15

    The Atlantic meridional overturning circulation (AMOC) in the last 250 years of the 700-year-long present-day control integration of the Community Climate System Model version 3 with T85 atmospheric resolution exhibits a red noise-like irregular multi-decadal variability with a persistence longer than 10 years, which markedly contrasts with the preceding {proportional_to}300 years of very regular and stronger AMOC variability with {proportional_to}20 year periodicity. The red noise-like multi-decadal AMOC variability is primarily forced by the surface fluxes associated with stochastic changes in the North Atlantic Oscillation (NAO) that intensify and shift northward the deep convection in the Labrador Sea. However, the persistence of the AMOC and the associated oceanic anomalies that are directly forced by the NAO forcing does not exceed about 5 years. The additional persistence originates from anomalous horizontal advection and vertical mixing, which generate density anomalies on the continental shelf along the eastern boundary of the subpolar gyre. These anomalies are subsequently advected by the mean boundary current into the northern part of the Labrador Sea convection region, reinforcing the density changes directly forced by the NAO. As no evidence was found of a clear two-way coupling with the atmosphere, the multi-decadal AMOC variability in the last 250 years of the integration is an ocean-only response to stochastic NAO forcing with a delayed positive feedback caused by the changes in the horizontal ocean circulation. (orig.)

  5. Expert judgements on the response of the Atlantic meridional overturning circulation to climate change

    International Nuclear Information System (INIS)

    We present results from detailed interviews with 12 leading climate scientists about the possible effects of global climate change on the Atlantic Meridional Overturning Circulation (AMOC). The elicitation sought to examine the range of opinions within the climatic research community about the physical processes that determine the current strength of the AMOC, its future evolution in a changing climate and the consequences of potential AMOC changes. Experts assign different relative importance to physical processes which determine the present-day strength of the AMOC as well as to forcing factors which determine its future evolution under climate change. Many processes and factors deemed important are assessed as poorly known and insufficiently represented in state-of-the-art climate models. All experts anticipate a weakening of the AMOC under scenarios of increase of greenhouse gas concentrations. Two experts expect a permanent collapse of the AMOC as the most likely response under a 4xCO2 scenario. Assuming a global mean temperature increase in the year 2100 of 4 K, eight experts assess the probability of triggering an AMOC collapse as significantly different from zero, three of them as larger than 40%. Elicited consequences of AMOC reduction include strong changes in temperature, precipitation distribution and sea level in the North Atlantic area. It is expected that an appropriately designed research program, with emphasis on long-term observations and coupled climate modeling, would contribute to substantially reduce uncertainty about the future evolution of the AMOC

  6. Detectability of changes to the Atlantic meridional overturning circulation in the Hadley Centre Climate Models

    International Nuclear Information System (INIS)

    The Atlantic meridional overturning circulation (MOC) is responsible for a climatically significant northward heat transport that is expected to decrease in response to anthropogenic global warming. Here, simulations from an ensemble of UK Met Office Hadley Centre Climate Models (HadGEM1, HadGEM2 and a 22 member perturbed physics ensemble of HadCM3-like models) are used to evaluate detection times for different MOC observing strategies. Six different detection statistics are compared, including direct observations of the MOC at two latitudes (26 N and 50 N) and several multivariate detection variables based on an optimal fingerprint of MOC change previously identified using HadCM3 (Vellinga and Wood in Geophys Res Lett 31(14):L14203, 2004). Using these models, and assuming perfectly observed conditions, we find no evidence to suggest that detection times would be significantly reduced by measuring the MOC at 50 N instead of (or in addition to) measurements at 26 N. Our results suggest that complementary observations of hydrographic properties in the North Atlantic may help reduce MOC detection times, but the benefits are not universal across models, nor as large as previously suggested. In addition, detection times calculated using optimal fingerprint methods are sensitive to the model-dependent estimates of covariances describing internal climate variability. This last result presents a strong case for deriving fingerprints of MOC change using dynamical/physical arguments, rather than statistical methods, in order to promote more robust results across a range of models. (orig.)

  7. Variability of the Atlantic meridional overturning circulation in the last millennium and two IPCC scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Ortega, Pablo; Montoya, Marisa; Gonzalez-Rouco, Fidel [Universidad Complutense de Madrid, Ciudad Universitaria, Dpto. Astrofisica y Ciencias de la Atmosfera/Instituto de Geociencias, Facultad de Ciencias Fisicas, Madrid (Spain); Universidad Complutense de Madrid, Ciudad Universitaria, Instituto de Geociencias (UCM-CSIC), Facultad de Ciencias Fisicas, Madrid (Spain); Mignot, Juliette [IPSL/LOCEAN, UPMC/CNRS/IRD/MNHN, Universite Pierre et Marie Curie, Paris Cedex 05 (France); Legutke, Stephanie [Deutsches Klimarechenzentrum (DKRZ), Hamburg (Germany)

    2012-05-15

    The variability of the Atlantic meridional overturning circulation (AMOC) is investigated in several climate simulations with the ECHO-G atmosphere-ocean general circulation model, including two forced integrations of the last millennium, one millennial-long control run, and two future scenario simulations of the twenty-first century. This constitutes a new framework in which the AMOC response to future climate change conditions is addressed in the context of both its past evolution and its natural variability. The main mechanisms responsible for the AMOC variability at interannual and multidecadal time scales are described. At high frequencies, the AMOC is directly responding to local changes in the Ekman transport, associated with three modes of climate variability: El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the East Atlantic (EA) pattern. At low frequencies, the AMOC is largely controlled by convection activity south of Greenland. Again, the atmosphere is found to play a leading role in these variations. Positive anomalies of convection are preceded in 1 year by intensified zonal winds, associated in the forced runs to a positive NAO-like pattern. Finally, the sensitivity of the AMOC to three different forcing factors is investigated. The major impact is associated with increasing greenhouse gases, given their strong and persistent radiative forcing. Starting in the Industrial Era and continuing in the future scenarios, the AMOC experiences a final decrease of up to 40% with respect to the preindustrial average. Also, a weak but significant AMOC strengthening is found in response to the major volcanic eruptions, which produce colder and saltier surface conditions over the main convection regions. In contrast, no meaningful impact of the solar forcing on the AMOC is observed. Indeed, solar irradiance only affects convection in the Nordic Seas, with a marginal contribution to the AMOC variability in the ECHO-G runs. (orig.)

  8. The impact of multidecadal Atlantic meridional overturning circulation variations on the Southern Ocean

    Science.gov (United States)

    Zhang, Liping; Delworth, Thomas L.; Zeng, Fanrong

    2016-05-01

    The impact of multidecadal variations of the Atlantic meridional overturning circulation (AMOC) on the Southern Ocean (SO) is investigated in the current paper using a coupled ocean-atmosphere model. We find that the AMOC can influence the SO via fast atmosphere teleconnections and subsequent ocean adjustments. A stronger than normal AMOC induces an anomalous warm SST over the North Atlantic, which leads to a warming of the Northern Hemisphere troposphere extending into the tropics. This induces an increased equator-to-pole temperature gradient in the Southern Hemisphere (SH) upper troposphere and lower stratosphere due to an amplified tropical upper tropospheric warming as a result of increased latent heat release. This altered gradients leads to a poleward displacement of the SH westerly jet. The wind change over the SO then cools the SST at high latitudes by anomalous northward Ekman transports. The wind change also weakens the Antarctic bottom water (AABW) cell through changes in surface heat flux forcing. The poleward shifted westerly wind decreases the long term mean easterly winds over the Weddell Sea, thereby reducing the turbulent heat flux loss, decreasing surface density and therefore leading to a weakening of the AABW cell. The weakened AABW cell produces a temperature dipole in the SO, with a warm anomaly in the subsurface and a cold anomaly in the surface that corresponds to an increase of Antarctic sea ice. Opposite conditions occur for a weaker than normal AMOC. Our study here suggests that efforts to attribute the recent observed SO variability to various factors should take into consideration not only local process but also remote forcing from the North Atlantic.

  9. The East Greenland Spill Jet as an important component of the Atlantic Meridional Overturning Circulation

    Science.gov (United States)

    von Appen, Wilken-Jon; Koszalka, Inga M.; Pickart, Robert S.; Haine, Thomas W. N.; Mastropole, Dana; Magaldi, Marcello G.; Valdimarsson, Héðinn; Girton, James; Jochumsen, Kerstin; Krahmann, Gerd

    2014-10-01

    The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean's role in climate.

  10. Seasonal to interannual variability in density around the Canary Islands and their influence on the Atlantic meridional overturning circulation at 26°N

    OpenAIRE

    Duchez, Aurelie; Frajka-Williams, Eleanor; Castro, Natalia; Hirschi, Joel; Coward, Andrew

    2014-01-01

    The meridional interior flow obtained from the RAPID array is determined by horizontal density fluctuations at the eastern and western boundary of 26°N. The physical causes of these density variations are responsible for fluctuations in the Atlantic Meridional Overturning Circulation (AMOC) and through it, the meridional heat transport of the Atlantic. In this modelling study, a high resolution ocean model is used to investigate the source and origin of the AMOC variability associated with th...

  11. Reconstructing global overturning from meridional density gradients

    Science.gov (United States)

    Butler, E. D.; Oliver, K. I. C.; Hirschi, J. J.-M.; Mecking, J. V.

    2016-04-01

    Despite the complexity of the global ocean system, numerous attempts have been made to scale the strength of the meridional overturning circulation (MOC), principally in the North Atlantic, with large-scale, basin-wide hydrographic properties. In particular, various approaches to scaling the MOC with meridional density gradients have been proposed, but the success of these has only been demonstrated under limited conditions. Here we present a scaling relationship linking overturning to twice vertically-integrated meridional density gradients via the hydrostatic equation and a "rotated" form of the geostrophic equation. This provides a meridional overturning streamfunction as a function of depth for each basin. Using a series of periodically forced experiments in a global, coarse resolution configuration of the general circulation model NEMO, we explore the timescales over which this scaling is temporally valid. We find that the scaling holds well in the upper Atlantic cell (at 1000 m) for multi-decadal (and longer) timescales, accurately reconstructing the relative magnitude of the response for different frequencies and explaining over 85 % of overturning variance on timescales of 64-2048 years. Despite the highly nonlinear response of the Antarctic cell in the abyssal Atlantic, between 76 and 94 % of the observed variability at 4000 m is reconstructed on timescales of 32 years (and longer). The scaling law is also applied in the Indo-Pacific. This analysis is extended to a higher resolution, stochastically forced simulation for which correlations of between 0.79 and 0.99 are obtained with upper Atlantic MOC variability on timescales >25 years. These results indicate that meridional density gradients and overturning are linked via meridional pressure gradients, and that both the strength and structure of the MOC can be reconstructed from hydrography on multi-decadal and longer timescales provided that the link is made in this way.

  12. An abrupt slowdown of Atlantic Meridional Overturning Circulation during 1915–1935 induced by solar forcing in a coupled GCM

    OpenAIRE

    Lin, P.; Song, Y.; Yu, Y.; Liu, H.

    2014-01-01

    In this study, we explore an abrupt change of Atlantic Meridional Overturning Circulation (AMOC) apparent in the historical run simulated by the second version of the Flexible Global Ocean–Atmosphere–Land System model – Spectral Version 2 (FGOALS-s2). The abrupt change is noted during the period from 1915 to 1935, in which the maximal AMOC value is weakened beyond 6 Sv (1 Sv = 106 m3 s−1). The abrupt signal first occurs at high latitudes (north of 46° N), then shifts ...

  13. Ocean science: Vagaries of Atlantic overturning

    Science.gov (United States)

    Haine, Thomas W. N.

    2016-07-01

    A weakening of the Atlantic meridional overturning circulation has emerged from noise after years of painstaking measurements. Three independent lines of evidence suggest that an anthropogenic influence on this overturning is not yet detectable.

  14. On the Nordic Seas' role in the Atlantic Meridional Overturning Circulation

    International Nuclear Information System (INIS)

    In the present climate, the North Atlantic thermohaline circulation (THC) plays a fundamental role in the global transport of heat at high latitudes. The response of the North Atlantic Ocean-Nordic Seas THC to surface forcing and basin geometries in an idealized one-hemisphere basin is analyzed to better understand the processes that are fundamental to the modeled circulation. Focusing on the dynamics of the Nordic Seas, analytical and numerical modeling highlight the relevance of a sill (Greenland-Scotland Ridge) in setting the properties of the water masses formed in and exported from a marginal sea. Finally, the influence of the convective activity in the Greenland Sea for the overflow, and thus the overturning, is assessed using hydrographic data (from 1950 to present), a regional ocean model, and a unique tracer release experiment. Greenland Sea Gyre water is estimated to contribute less than 1 Sv, and there is no evidence for causality between changes in the Greenland Sea and the overflow (author)

  15. Glacial climate sensitivity to different states of the Atlantic Meridional Overturning Circulation: results from the IPSL model

    Directory of Open Access Journals (Sweden)

    M. Kageyama

    2009-09-01

    Full Text Available Paleorecords from distant locations on the globe show rapid and large amplitude climate variations during the last glacial period. Here we study the global climatic response to different states of the Atlantic Meridional Overturning Circulation (AMOC as a potential explanation for these climate variations and their possible connections. We analyse three glacial simulations obtained with an atmosphere-ocean coupled general circulation model and characterised by different AMOC strengths (18, 15 and 2 Sv resulting from successive ~0.1 Sv freshwater perturbations in the North Atlantic. These AMOC states suggest the existence of a freshwater threshold for which the AMOC collapses. A weak (18 to 15 Sv AMOC decrease results in a North Atlantic and European cooling. This cooling is not homogeneous, with even a slight warming over the Norwegian Sea. Convection in this area is active in both experiments, but surprisingly stronger in the 15 Sv simulation, which appears to be related to interactions with the atmospheric circulation and sea-ice cover. Far from the North Atlantic, the climatic response is not significant. The climate differences for an AMOC collapse (15 to 2 Sv are much larger and of global extent. The timing of the climate response to this AMOC collapse suggests teleconnection mechanisms. Our analyses focus on the North Atlantic and surrounding regions, the tropical Atlantic and the Indian monsoon region. The North Atlantic cooling associated with the AMOC collapse induces a cyclonic atmospheric circulation anomaly centred over this region, which modulates the eastward advection of cold air over the Eurasian continent. This can explain why the cooling is not as strong over western Europe as over the North Atlantic. In the Tropics, the southward shift of the Inter-Tropical Convergence Zone appears to be strongest over the Atlantic and Eastern Pacific and results from an adjustment of the atmospheric and oceanic heat transports. Finally, the

  16. Coupling of the distribution of silicon isotopes to the meridional overturning circulation of the North Atlantic Ocean

    Science.gov (United States)

    Brzezinski, Mark A.; Jones, Janice L.

    2015-06-01

    The distribution of silicon isotopes within silicic acid, δ30Si(OH)4, was examined along a section in the North Atlantic from the Cape Verde Islands off Africa to Cape Cod, Massachusetts in North America. Surface water displayed elevated δ30Si(OH)4 associated with biological fractionation of Si during silica production. Below 300 m variations in δ30Si(OH)4 were closely tied to the distribution of water masses as diagnosed through optimum multiparameter analysis, confirming a tight relationship between δ30Si(OH)4 and the meridional overturning circulation in the Atlantic. A linear relationship between δ30Si(OH)4 and the inverse of silicic acid concentration supported control of Si isotope distribution by conservative mixing of end member water masses of different isotopic composition in the Atlantic. There was a suggestion of a weak local minimum in δ30Si(OH)4 in deep waters above the Trans-Atlantic Geotraverse hydrothermal zone on the mid-Atlantic Ridge consistent with the light δ30Si(OH)4 of hydrothermal waters. The lightest δ30Si(OH)4 values were observed in the deep western and deep eastern basins where Antarctic Bottom Water (AABW) dominated. The heaviest values in subsurface waters occurred in North Atlantic Deep Water due to strong ventilation and the contribution of heavy northern source waters that are influenced by the Arctic Ocean. The concept of a silicon isotope bipole is introduced to explain how the isotopic differences between the northern and southern end-member water masses arise, and how they influence Si isotope distributions. Northern end-member water masses are heavy due to the influence of the Arctic Ocean. Bottom topography prevents light deep waters from entering the Arctic and the further removal of light isotopes through local biological productivity results in extremely heavy δ30Si(OH)4 within the Arctic. Light AABW dominates the southern end member. The Southern Ocean silicic acid trap distills heavier isotopes of Si out of the

  17. An abrupt slowdown of Atlantic Meridional Overturning Circulation during 1915–1935 induced by solar forcing in a coupled GCM

    Directory of Open Access Journals (Sweden)

    P. Lin

    2014-06-01

    Full Text Available In this study, we explore an abrupt change of Atlantic Meridional Overturning Circulation (AMOC apparent in the historical run simulated by the second version of the Flexible Global Ocean–Atmosphere–Land System model – Spectral Version 2 (FGOALS-s2. The abrupt change is noted during the period from 1915 to 1935, in which the maximal AMOC value is weakened beyond 6 Sv (1 Sv = 106 m3 s−1. The abrupt signal first occurs at high latitudes (north of 46° N, then shifts gradually to middle latitudes (∼35° N three to seven years later. The weakened AMOC can be explained in the following. The weak total solar irradiance (TIS during early twentieth century decreases pole-to-equator temperature gradient in the upper stratosphere. The North polar vortex is weakened, which forces a negative North Atlantic Oscillation (NAO phase during 1905–1914. The negative phase of NAO induces anomalous easterly winds in 50–70° N belts, which decrease the release of heat fluxes from ocean to atmosphere and induce surface warming over these regions. Through the surface ice–albedo feedback, the warming may lead to continuously melting sea ice in Baffin Bay and Davis Strait, which results in freshwater accumulation. This can lead to salinity and density reductions and then an abrupt slowdown of AMOC. Moreover, due to increased TIS after 1914, the enhanced Atlantic northward ocean heat transport from low to high latitudes induces an abrupt warming of sea surface temperature or upper ocean temperature in mid–high latitudes, which can also weaken the AMOC. The abrupt change of AMOC also appears in the PiControl run, which is associated with the lasting negative NAO phases due to natural variability.

  18. Climate and vegetation changes around the Atlantic Ocean resulting from changes in the meridional overturning circulation during deglaciation

    Directory of Open Access Journals (Sweden)

    D. Handiani

    2012-07-01

    Full Text Available The Bølling-Allerød (BA, starting ~ 14.5 ka BP is one of the most pronounced abrupt warming periods recorded in ice and pollen proxies. The leading explanation of the cause of this warming is a sudden increase in the rate of deepwater formation in the North Atlantic Ocean and the resulting effect on the heat transport by the Atlantic Meridional Overturning Circulation (AMOC. In this study, we used the University of Victoria (UVic Earth System-Climate Model (ESCM to run simulations, in which a freshwater perturbation initiated a BA-like warming period. We found that under present climate conditions, the AMOC intensified when freshwater was added to the Southern Ocean. However, under Heinrich event 1 (HE1, ~ 16 ka BP climate conditions, the AMOC only intensified when freshwater was extracted from the North Atlantic Ocean, possibly corresponding to an increase in evaporation or a decrease in precipitation in this region. The intensified AMOC led to a warming in the North Atlantic Ocean and a cooling in the South Atlantic Ocean, resembling the bipolar seesaw pattern typical of the last glacial period.

    In addition to the physical response, we also studied the simulated vegetation response around the Atlantic Ocean region. Corresponding with the bipolar seesaw hypothesis, the rainbelt associated with the Intertropical Convergence Zone (ITCZ shifted northward and affected the vegetation pattern in the tropics. The most sensitive vegetation area was found in tropical Africa, where grass cover increased and tree cover decreased under dry climate conditions. An equal but opposite response to the collapse and recovery of the AMOC implied that the change in vegetation cover was transient and robust to an abrupt climate change such as during the BA period, which is also supported by paleovegetation data. The results are in agreement with paleovegetation records from Western tropical Africa, which also show a reduction in forest cover during this

  19. Glacial climate sensitivity to different states of the Atlantic Meridional Overturning Circulation: results from the IPSL model

    Directory of Open Access Journals (Sweden)

    M. Kageyama

    2009-03-01

    Full Text Available Numerous records from the North Atlantic and the surrounding continents have shown rapid and large amplitude climate variability during the last glacial period. This variability has often been associated to changes in the Atlantic Meridional Overturning Circulation (AMOC. Rapid climate change on the same time scales has also been reconstructed for sites far away from the North Atlantic, such as the tropical Atlantic, the East Pacific and Asia. The mechanisms explaining these climatic responses to the state of the AMOC are far from being completely understood, especially in a glacial context. Here we study three glacial simulations characterised by different AMOC strengths: 18, 15 and 2 Sv. With these simulations, we analyse the global climate sensitivity to a weak (18 to 15 Sv and a strong (15 to 2 Sv decrease in the AMOC strength.

    A weak decrease in the AMOC is associated, in our model simulations, to the classical North Atlantic and European cooling, but this cooling is not homogeneous over this region. We investigate the reasons for a lesser cooling (or even slight warming in some cases over the Norwegian Sea and Northwestern Europe. It appears that the convection site in this area is active in both simulations, but that convection is unexpectedly stronger in the 15 Sv simulation. Due to the large variability of the atmosphere, it is difficult to definitely establish what is the origin of this climatic difference, but it appears that the atmospheric circulation anomaly helps sustaining the activity of this convection sites. Far from the North Atlantic, the climatic response is of small amplitude, the only significant change appearing in summer over the tropical Atlantic, where the Inter-Tropical Convergence Zone (ITCZ shifts southward.

    The climate differences between the 15 Sv and 2 Sv simulations are much larger and our analyses focus on three areas: the North Atlantic and surrounding regions, the Tropics and the Indian

  20. Dynamics of the Atlantic meridional overturning circulation and Southern Ocean in an ocean model of intermediate complexity

    Science.gov (United States)

    McCreary, Julian P.; Furue, Ryo; Schloesser, Fabian; Burkhardt, Theodore W.; Nonaka, Masami

    2016-04-01

    A steady-state, variable-density, 2-layer, ocean model (VLOM) is used to investigate basic dynamics of the Atlantic meridional overturning circulation and Southern Ocean. The domain consists of idealized (rectangular) representations of the Atlantic, Southern, and Pacific Oceans. The model equations represent the depth-averaged, layer-1 response (except for one solution in which they represent the depth-integrated flow over both layers). To allow for overturning, water can cross the bottom of layer 1 at the velocity we =wd +wm +wn , the three parts representing: interior diffusion wd that increases the layer-1 thickness h throughout the basin, mixed-layer entrainment wm that ensures h is never less than a minimum value hm , and diapycnal (cooling) processes external to the basin wn that adjust h to hn . For most solutions, horizontal mixing has the form of Rayleigh damping with coefficient ν , which we interpret to result from baroclinic instability through the closure, V∗ = - (ν /f2) ∇P , where ∇P = ∇(1/2 g‧h2) is the depth-integrated pressure gradient, g‧ is the reduced-gravity coefficient, and ν is a mixing coefficient; with this interpretation, the layer-1 flow corresponds to the sum of the Eulerian-mean and eddy-mean (V∗) transport/widths, that is, the "residual" circulation. Finally, layer-1 temperature cools polewards in response to a surface heat flux Q, and the cooling can be strong enough in the Southern Ocean for g‧ = 0 south of a latitude y0 , in which case layer 1 vanishes and the model reduces to a single layer 2. Solutions are obtained both numerically and analytically. The analytic approach splits fields into interior and boundary-layer parts, from which a coupled set of integral constraints can be derived. The set allows properties of the circulation (upwelling-driven transport out of the Southern Ocean M , downwelling transport in the North Atlantic, transport of the Antarctic Circumpolar Current) and stratification (Atlantic

  1. On the Nordic Seas’ role in the Atlantic Meridional Overturning Circulation

    OpenAIRE

    Iovino, Doroteaciro

    2007-01-01

    In the present climate, the North Atlantic thermohaline circulation (THC) plays a fundamental role in the global transport of heat at high latitudes. The response of the North Atlantic Ocean-Nordic Seas THC to surface forcing and basin geometries in an idealized one-hemisphere basin is analyzed to better understand the processes that are fundamental to the modeled circulation. Focusing on the dynamics of the Nordic Seas, analytical and numerical modeling highlight the releva...

  2. Sediment 231Pa/230Th as a recorder of the rate of the Atlantic meridional overturning circulation: insights from a 2-D model

    Directory of Open Access Journals (Sweden)

    S. E. Allen

    2009-11-01

    Full Text Available A two dimensional scavenging-circulation model is used to investigate the patterns of sediment 231Pa/230Th generated by the Atlantic Meridional Overturning Circulation (AMOC and further advance the application of this proxy for ocean paleocirculation studies. The scavenging parameters and the geometry of the overturning circulation cell have been chosen so that the model generates meridional sections of dissolved 230Th and 231Pa consistent with published water column profiles and an additional 12 previously unpublished profiles measured in the North and Equatorial Atlantic. The processes that generate the meridional sections of dissolved and particulate 230Th, dissolved and particulate 231Pa, dissolved and particulate 231Pa/230Th, and sediment 231Pa/230Th are discussed in detail. The results indicate that the relationship between sediment 231Pa/230Th at any given site and the overturning circulation is very complex. They clearly show that constraining past changes in the strength and geometry of the AMOC requires an extensive data set and they suggest strategies to maximize information from a limited number of samples.

  3. Sediment 231Pa/230Th as a recorder of the rate of the Atlantic meridional overturning circulation: insights from a 2-D model

    Directory of Open Access Journals (Sweden)

    S. E. Allen

    2010-03-01

    Full Text Available A two dimensional scavenging model is used to investigate the patterns of sediment 231Pa/230Th generated by the Atlantic Meridional Overturning Circulation (AMOC and further advance the application of this proxy for ocean paleocirculation studies. The scavenging parameters and the geometry of the overturning circulation cell have been chosen so that the model generates meridional sections of dissolved 230Th and 231Pa consistent with published water column profiles and an additional 12 previously unpublished profiles measured in the North and Equatorial Atlantic. The processes that generate the meridional sections of dissolved and particulate 230Th, dissolved and particulate 231Pa, dissolved and particulate 231Pa/230Th, and sediment 231Pa/230Th are discussed in detail. The results indicate that the relationship between sediment 231Pa/230Th at any given site and the overturning circulation is very complex. They clearly show that constraining past changes in the strength and geometry of the AMOC requires an extensive data set and they suggest strategies to maximize information from a limited number of samples.

  4. The contribution of eastern-boundary density variations to the Atlantic meridional overturning circulation at 26.5° N

    Directory of Open Access Journals (Sweden)

    M. P. Chidichimo

    2009-11-01

    Full Text Available We study the contribution of eastern-boundary density variations to sub-seasonal and seasonal anomalies of the strength and vertical structure of the Atlantic Meridional Overturning Circulation (AMOC at 26.5° N, by means of the RAPID/MOCHA mooring array between April 2004 and October 2007. The major density anomalies are found in the upper 500 m, and they are often coherent down to 1400 m. The densities have 13-day fluctuations that are apparent down to 3500 m. The two strategies for measuring eastern-boundary density – a tall offshore mooring (EB1 and an array of moorings on the continental slope (EBH – show little correspondence in terms of amplitude, vertical structure, and frequency distribution of the resulting basin-wide integrated transport fluctuations, implying that there are significant transport contributions between EB1 and EBH. Contrary to the original planning, measurements from EB1 cannot serve as backup or replacement for EBH: density needs to be measured directly at the continental slope to compute the full-basin density gradient. Fluctuations in density at EBH generate transport variability of 2 Sv rms in the AMOC, while the overall AMOC variability is 4.9 Sv rms. There is a pronounced deep-reaching seasonal cycle in density at the eastern boundary, which is apparent between 100 m and 1400 m, with maximum positive anomalies in spring and maximum negative anomalies in autumn. These changes drive anomalous southward upper mid-ocean flow in spring, implying maximum reduction of the AMOC, and vice-versa in autumn. The amplitude of the seasonal cycle of the AMOC arising from the eastern-boundary densities is 5.2 Sv peak-to-peak, dominating the 7.0 Sv peak-to-peak seasonal cycle of the total AMOC. Our analysis suggests that the seasonal cycle in density may be forced by the strong near-coastal seasonal cycle in wind stress curl.

  5. Observed and simulated estimates of the meridional overturning circulation at 26.5° N in the Atlantic

    Directory of Open Access Journals (Sweden)

    P. Heimbach

    2009-07-01

    Full Text Available Daily timeseries of the meridional overturning circulation (MOC estimated from the UK/US RAPID/MOCHA array at 26.5° N in the Atlantic are used to evaluate the MOC as simulated in two global circulation models: (i an 8-member ensemble of the coupled climate model ECHAM5/MPI-OM, and (ii the ECCO-GODAE state estimate. In ECHAM5/MPI-OM, we find that the observed and simulated MOC have a similar variability and time-mean within the 99 percent confidence interval. In ECCO-GODAE, we find that the observed and simulated MOC show a significant correlation within the 99 percent confidence interval. To investigate the contribution of the different transport components, the MOC is decomposed into Florida Current, Ekman and upper mid-ocean geostrophic transports. In both models, the mid-ocean transport is closely approximated by the residual of the MOC minus Florida Current and Ekman transports. As the models conserve volume by definition, future comparisons of the RAPID/MOCHA mid-ocean transport should be done against the residual transport in the models. The similarity in the variance and the correlation between the RAPID/MOCHA, and respectively ECHAM5/MPI-OM and ECCO-GODAE MOC estimates at 26.5° N is encouraging in the context of estimating (natural variability in climate simulations and its use in climate change signal-to-noise detection analyses. Enhanced confidence in simulated hydrographic and transport variability will require longer observational time series.

  6. The Influence of Glacial Ice Sheets on Atlantic Meridional Overturning Circulation Through Atmospheric Circulation Change under Glacial Climate

    Science.gov (United States)

    Sherriff-Tadano, S.; Abe-Ouchi, A.; Yoshimori, M.; Oka, A.; Chan, W. L.

    2014-12-01

    It is well known that glacial ice sheets (Laurentide, Fennoscandian and Antarctic ice sheets) exert a large influence on the climate including the atmospheric circulation. Moreover, recent climate modeling studies suggest that glacial ice sheets have a large impact on the Atlantic meridional overturning circulation (AMOC). However, the process by which the ice sheets impact on the AMOC is not yet fully understood. On the other hand, recent studies showed that surface wind changes play a crucial role on changes to the AMOC under glacial climate. Therefore, in this study, we investigate in detail, the process by which the ice sheet modifies the AMOC through surface wind change. Here we conduct numerical experiments using an atmospheric general circulation model (AGCM) and an ocean general circulation model (OGCM) separately. Our method consists of 2 steps. First, from AGCM experiments, we evaluate the effect of glacial ice sheets on the surface wind. Second, from OGCM experiments, we evaluate the influence of the wind stress change on the AMOC by applying the surface wind change as a boundary condition, while leaving other boundary conditions (surface heat and water fluxes) unchanged. In addition, we conduct several sensitivity experiments. Using the AGCM, we explore individual ice sheet effect, ice sheet topography effect and albedo effect on surface wind change. Moreover, using the OGCM, we change the surface wind gradually or apply the surface wind change only at a specific region in order to explore the wind change effect in detail. We find that glacial ice sheets largely intensify the AMOC by surface wind change under glacial climate. Compare to other regions, it reveals that the wind change at the North Atlantic (NA) is a key region. There, the northern glacial ice sheet topography intensifies the Icelandic Low and anti-cyclonic circulation over the Laurentide ice sheet. However, this wind effect is effective only when the NA is not widely covered by sea ice

  7. Influence of runoff, high frequency atmospheric forcing and model resolution on deep water mass formation regions and Atlantic Meridional Overturning Circulation, from a numerical model.

    Science.gov (United States)

    Garcia Quintana, Yarisbel; Courtois, Peggy; Hu, Xianmin; Pennelly, Clark; Myers, Paul G.

    2016-04-01

    Water mass formation regions act as windows to the deep ocean where surface waters are transformed to intermediate and deep waters. Within the North Atlantic, Labrador Sea Water (LSW) is convectively produced in the Labrador Sea while in the Nordic Seas the source waters for Denmark Strait Overflow Water (DSOW) and Iceland-Scotland Overflow Water (NEADW) are formed. They are the main components of the North Atlantic Deep Water (NADW) which forms the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). We explore the changes of the LSW formation rates and in AMOC strength as consequence of runoff glacial melt, high frequency atmospheric forcing influence and variations in model's resolution. We use 1/4° resolution Arctic and Northern Hemisphere Atlantic (ANHA4) configuration from the Nucleus for European Modelling of the Ocean (NEMO) model. A nest using ANHA4 and the Adaptive Grid Refinement in FORTRAN (AGRIF) package was used to increase the resolution to 1/12° in the sub-polar gyre. The formation rate is calculated based upon a kinematic subduction approach where the exchange through the dynamic mixed layer base is calculated based on shallowing and deepening in the mixed layer, and convergence of horizontal transport into or out of the mixed layer. Lastly we use a Lagrangian tool (Ariane) to track the path of the DSOW and the NEADW from their formation source.

  8. Abrupt Climate Change and the Atlantic Meridional Overturning Circulation: sensitivity and non-linear response to Arctic/sub-Arctic freshwater pulses. Collaborative research. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Hill, Christopher [MIT (Massachusetts Inst. of Technology), Cambridge, MA (United States)

    2015-06-15

    This project investigated possible mechanisms by which melt-water pulses can induce abrupt change in the Atlantic Meridional Overturning Circulation (AMOC) magnitude. AMOC magnitude is an important ingredient in present day climate. Previous studies have hypothesized abrupt reduction in AMOC magnitude in response to influxes of glacial melt water into the North Atlantic. Notable fresh-water influxes are associated with the terminus of the last ice age. During this period large volumes of melt water accumulated behind retreating ice sheets and subsequently drained rapidly when the ice weakened sufficiently. Rapid draining of glacial lakes into the North Atlantic is a possible origin of a number of paleo-record abrupt climate shifts. These include the Younger-Dryas cooling event and the 8,200 year cooling event. The studies undertaken focused on whether the mechanistic sequence by which glacial melt-water impacts AMOC, which then impacts Northern Hemisphere global mean surface temperature, is dynamically plausible. The work has implications for better understanding past climate stability. The work also has relevance for today’s environment, in which high-latitude ice melting in Greenland appears to be driving fresh water outflows at an accelerating pace.

  9. Pulling the Meridional Overturning Circulation From the South DESC0005100

    Energy Technology Data Exchange (ETDEWEB)

    Cessi, Paola [Univ. of California, San Diego, CA (United States); Wolfe, Christopher L. [Scripps Inst. of Oceanography, San Diego, CA (United States)

    2015-11-25

    This project concerned the Atlantic Meridional Overturning Circulation (AMOC), its stability, variability and sensitivity to atmospheric forcing, both mechanical (wind-stress) and thermodynamical (heat and freshwater surface fluxes). The focus of the study is the interhemispheric cell in the largely adiabatic regime, where the flow is characterized by a descending branch in the high latitudes of the North Atlantic and the upwelling branch in the Antarctic Circumpolar Current (ACC) region of the Southern Ocean. These two end points are connected by shared isopycnals along which the flow takes place. The approach is to systematically study the amplitude and frequency of the AMOC’s response to localized buoyancy with an ocean-only model in both coarse and high-resolution configurations, analyzed with innovative diagnostics, focused on the “residual overturning circulation” (ROC), which is the proper measure of the transport of heat and other tracers.

  10. Probabilistic hindcasts and projections of the coupled climate, carbon cycle and Atlantic meridional overturning circulation system: a Bayesian fusion of century-scale observations with a simple model

    Science.gov (United States)

    Urban, Nathan M.; Keller, Klaus

    2010-10-01

    How has the Atlantic Meridional Overturning Circulation (AMOC) varied over the past centuries and what is the risk of an anthropogenic AMOC collapse? We report probabilistic projections of the future climate which improve on previous AMOC projection studies by (i) greatly expanding the considered observational constraints and (ii) carefully sampling the tail areas of the parameter probability distribution function (pdf). We use a Bayesian inversion to constrain a simple model of the coupled climate, carbon cycle and AMOC systems using observations to derive multicentury hindcasts and projections. Our hindcasts show considerable skill in representing the observational constraints. We show that robust AMOC risk estimates can require carefully sampling the parameter pdfs. We find a low probability of experiencing an AMOC collapse within the 21st century for a business-as-usual emissions scenario. The probability of experiencing an AMOC collapse within two centuries is 1/10. The probability of crossing a forcing threshold and triggering a future AMOC collapse (by 2300) is approximately 1/30 in the 21st century and over 1/3 in the 22nd. Given the simplicity of the model structure and uncertainty in the forcing assumptions, our analysis should be considered a proof of concept and the quantitative conclusions subject to severe caveats.

  11. Effects of reduced vertical mixing under sea ice on Atlantic meridional overturning circulation (AMOC) in a global ice-ocean model

    Science.gov (United States)

    Kim, Sang Yeob; Lee, Ho Jin; Park, Jae-Hun; Kim, Young Ho

    2015-06-01

    Most open ocean and climate models assume a constant background mixing; however, vertical mixing should be reduced under the sea ice in polar region because the sea-ice cover acts as an insulator against the momentum transfer between the atmosphere and ocean. Using a global Ocean General Circulation Model (OGCM), we show that the Atlantic meridional overturning circulation (AMOC) can be substantially affected by reduced vertical mixing under the sea ice. When the background diffusivity under the sea ice is reduced by 1 order less than that in ice-free regions, the volume transport of the AMOC in the upper 3000 m is increased by up to 14% accordingly. The numerical experiment suggests that the reduced background diffusivity makes waters denser in the Arctic Ocean and the denser water is transported into the Nordic Seas to push up the isopycnal surfaces over the Greenland- Iceland-Scotland Ridge. Consequently, the AMOC is enhanced by overflows of the denser water crossing the Denmark Strait.

  12. The global Meridional Overturning Circulation's response to variable buoyancy forcing

    OpenAIRE

    Butler, Edward D.

    2015-01-01

    The meridional overturning circulation (MOC) is a large-scale circulation throughout the global ocean and plays a significant role in the complex global climate system. However, our traditional understanding of the processes driving the MOC has been questioned in recent years. In particular, it has been suggested that surface buoyancy forcing plays little energetic role in driving the MOC. Furthermore, doubt has also been cast over the relationship between meridional overturning and meridiona...

  13. Simulated Atlantic Meridional Overturning Circulation in the 20th century with an ocean model forced by reanalysis-based atmospheric data sets

    Science.gov (United States)

    He, Yan-Chun; Drange, Helge; Gao, Yongqi; Bentsen, Mats

    2016-04-01

    Global ocean hindcast simulations for the period 1871-2009 have been run with the ocean-sea ice component of the Norwegian Earth System Model (NorESM-O), forced by an adjusted version of the Twentieth Century Reanalysis version 2 data set (20CRv2 data set), as well as by the commonly used second version of atmospheric forcing data set for the Coordinated Ocean-ice Reference Experiments phase-II (CORE-II) for the period 1948-2007 (hereafter CORE.v2 data set). The simulated Atlantic Meridional Overturning Circulation (AMOC) in the 20CR and the CORE simulations have comparable variability as well as mean strength during the last three decades of the integration. The simulated AMOC undergoes, however, distinctly different evolutions during the period 1948-1970, with a sharply declining strength in CORE but a gradual increase in 20CR. Sensitivity experiments suggest that differences in the wind forcing between CORE and 20CR have major impact on the simulated AMOCs during this period. It is furthermore found that differences in the air temperature between the two data sets do contribute to the differences in AMOC, but to a much lesser degree than the wind. An additional factor for the diverging AMOC in the two decades following 1948 is the inevitable switching of atmospheric forcing fields in 1948 in the CORE.v2-based runs due to the cyclic spin-up procedure of the ocean model. The latter is a fundamental issue for any ocean hindcast simulation. The ocean initial state mainly influence the actual value but to a lesser degree also the temporal evolution (variability) of AMOC. It may take about two decades for the AMOC to adjust to a new atmospheric state during the spin-up, although a dynamically balanced ocean initial state tends to reduce the adjustment time and the magnitude of the deviation, implying that an ocean model run with atmospheric forcing fields extending back in time, like 20CRv2, can be used to extend the reliable duration of CORE-type of simulations.

  14. Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

    NARCIS (Netherlands)

    den Toom, M.; Dijkstra, H.A.

    2011-01-01

    An important expression of the non-linear character of the ocean’s meridional overturning circulation (MOC) is the scaling of its amplitude with the magnitude of the vertical mixing coefficient (diffusivity) of heat and salt. This paper extends recent work that indicated that the Atlantic and Pacifi

  15. Enhancement of the southward return flow of the Atlantic Meridional Overturning Circulation by data assimilation and its influence in an assimilative ocean simulation forced by CORE-II atmospheric forcing

    Science.gov (United States)

    Fujii, Yosuke; Tsujino, Hiroyuki; Toyoda, Takahiro; Nakano, Hideyuki

    2015-08-01

    This paper examines the difference in the Atlantic Meridional Overturning Circulation (AMOC) mean state between free and assimilative simulations of a common ocean model using a common interannual atmospheric forcing. In the assimilative simulation, the reproduction of cold cores in the Nordic Seas, which is absent in the free simulation, enhances the overflow to the North Atlantic and improves AMOC with enhanced transport of the deeper part of the southward return flow. This improvement also induces an enhanced supply of North Atlantic Deep Water (NADW) and causes better representation of the Atlantic deep layer despite the fact that correction by the data assimilation is applied only to temperature and salinity above a depth of 1750 m. It also affects Circumpolar Deep Water in the Southern Ocean. Although the earliest influence of the improvement propagated by coastal waves reaches the Southern Ocean in 10-15 years, substantial influence associated with the arrival of the renewed NADW propagates across the Atlantic Basin in several decades. Although the result demonstrates that data assimilation is able to improve the deep ocean state even if there is no data there, it also indicates that long-term integration is required to reproduce variability in the deep ocean originating from variations in the upper ocean. This study thus provides insights on the reliability of AMOC and the ocean state in the Atlantic deep layer reproduced by data assimilation systems.

  16. The role of the northward-directed (subsurface limb of the Atlantic Meridional Overturning Circulation during the 8.2 ka Event

    Directory of Open Access Journals (Sweden)

    A. D. Tegzes

    2014-02-01

    Full Text Available The so-called "8.2 ka Event" has been widely regarded as a major climate perturbation over the Holocene. It is most readily identifiable in the oxygen-isotope records from Greenland ice cores as an approximately 160 yr-long cold interval between 8250–8090 yr BP. The prevailing view has been that the cooling over Greenland, and potentially over the northern North Atlantic at least, was triggered by the catastrophic final drainage of the Agassiz-Ojibway proglacial lake as part of the remnant Laurentide Ice Sheet collapsed over Hudson Bay at around 8420 ± 80 yr BP. The consequent freshening of surface waters in the northern North Atlantic Ocean and the Nordic Seas resulted in weaker overturning, hence reduced northward heat transport. Here we present proxy records from site JM97-MD95-2011 on the mid-Norwegian Margin indicating a (sharp decline in the strength of the eastern branch of the Atlantic Inflow into the Nordic Seas immediately following a uniquely large drop in (subsurface ocean temperatures coeval with the lake outbursts. We propose that the final drainage of Lake Agassiz-Ojibway was accompanied by a major iceberg discharge from Hudson Bay, which resulted in the cooling of the northward-directed northern Gulf Stream-North Atlantic Drift-Norwegian Atlantic Current system. Since our current-strength proxy records from the mid-Norwegian Margin do not evidence an exceptionally strong reduction in the main branch of the Atlantic Inflow into the Nordic Seas at the time, we argue that a chilled northward-directed (subsurface-current system and an already colder background climate state could be the main factors responsible for the 8.2 ka climate perturbation.

  17. Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation

    NARCIS (Netherlands)

    Yang, Qian; Dixon, Timothy H.; Myers, Paul G.; Bonin, Jennifer; Chambers, Don; Van Den Broeke, M. R.

    2016-01-01

    The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), for

  18. Mechanisms Determining the Winter Atmospheric Response to the Atlantic Overturning Circulation

    OpenAIRE

    Gastineau, Guillaume; L’Hévéder, B.; Codron, Francis; Frankignoul, Claude

    2016-01-01

    International audience In climate models, an intensification of the Atlantic meridional overturning circulation (AMOC) precedes a warming in the North Atlantic subpolar basin by a few years. In the IPSL-CM5A-LR model, this warming may explain the atmospheric response to the AMOC observed in winter, which resembles a negative phase of the North Atlantic Oscillation (NAO). To firmly establish the causality links between the ocean and the atmosphere and illustrate the underlying mechanisms in...

  19. Dynamical Attribution of Recent Variability in Atlantic Overturning

    Science.gov (United States)

    Pillar, Helen; Heimbach, Patrick; Johnson, Helen; Marshall, David

    2016-04-01

    Attributing observed variability of the Atlantic Meridional Overturning Circulation (AMOC) to past changes in surface forcing is challenging but essential for detecting any influence of anthropogenic forcing and reducing uncertainty in future climate predictions. Here we obtain quantitative estimates of wind and buoyancy-driven AMOC variations at 25N by projecting observed atmospheric anomalies onto model-based dynamical patterns of AMOC sensitivity to surface wind, thermal and freshwater forcing over the preceding 15 years. We show that local wind forcing dominates AMOC variability on short timescales, whereas subpolar heat fluxes dominate on decadal timescales. The reconstructed transport time series successfully reproduces most of the interannual variability observed by the RAPID-MOCHA array. However, the apparent decadal trend in the RAPID-MOCHA time series is not captured, requiring improved model representation of ocean adjustment to subpolar heat fluxes over at least the past two decades, and highlighting the importance of sustained monitoring of the high latitude North Atlantic.

  20. Hydrographic biases in global coupled climate models and their relation to the meridional overturning circulation

    Science.gov (United States)

    Plancherel, Yves

    2015-01-01

    Comparison of the volumetric θ/S distribution of models participating in the Climate Model Intercomparison Project 3 (CMIP3) indicates that these models differ widely in their ability to represent the thermohaline properties of water masses. Relationships between features of the quasi-equilibrium hydrographic mean state of these models and aspects of their overturning circulations are investigated. This is achieved quantitatively with the help of seven diagnostic hydrographic stations. These few stations were specifically selected to provide a minimalist schematic of the global water mass system. Relationships between hydrographic conditions in the North Atlantic measured with a subset of these stations suggest that hydrographic properties in the subpolar North Atlantic are set by the circulation field of each model, pointing towards deficiencies in the models ability to resolve the Gulf Stream-North Atlantic Current system as a major limitation. Since diapycnal mixing and viscosity parameterizations differ across CMIP3 models and exert a strong control on the overturning, it is likely that these architectural differences ultimately explain the main across-model differences in overturning circulation, temperature and salinity in the North Atlantic. The analysis of properties across the quasi-equilibrium states of the CMIP3 models agrees with previously reported relationships between meridional steric height gradients or horizontal density contrasts at depth and the strength of the deep water cell. Robust relationships are also found in the Southern Ocean linking measures of vertical stratification with the strength of the abyssal circulations across the CMIP3 models. Consistent correlations between aspects of the quasi-equilibrium hydrography in the Southern Ocean and the sensitivity of the abyssal cell to increasing radiative forcing by 2100 were found. Using these relations in conjunction with modern hydrographic observations to interpolate the fate of the

  1. "What Controls the Structure and Stability of the Ocean Meridional Overturning Circulation: Implications for Abrupt Climate Change?"

    Energy Technology Data Exchange (ETDEWEB)

    Fedorov, Alexey [Yale University

    2013-11-23

    The central goal of this research project is to understand the properties of the ocean meridional overturning circulation (MOC) – a topic critical for understanding climate variability and stability on a variety of timescales (from decadal to centennial and longer). Specifically, we have explored various factors that control the MOC stability and decadal variability in the Atlantic and the ocean thermal structure in general, including the possibility abrupt climate change. We have also continued efforts on improving the performance of coupled ocean-atmosphere GCMs.

  2. The Shallow Meridional Overturning Circulation in the Northern Indian Ocean and Its Interannual Variability

    Institute of Scientific and Technical Information of China (English)

    HU Ruijin; LIU Qinyu; WANG Qi; J. Stuart GODFREY; MENG Xiangfeng

    2005-01-01

    The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years (1987-1996). It is shown that the shallow meridional overturning circulation has a prominent seasonal reversal characteristic. In winter, the flow is northward in the upper layer and returns southward at great depth. In summer, the deep northward inflow upwells north of the equator and returns southward in the Ekman layer. In the annual mean, the northward inflow returns through two branches: one is a southward flow in the Ekman layer, the other is a flow that sinks near 10°N and returns southward between 500 m and 1000 m. There is significant interannual variability in the shallow meridional overturning circulation, with a stronger (weaker) one in 1989 (1991) and with a period of about four years. The interannual variability of the shallow meridional overturning circulation is intimately related to that of the surface wind stress. Several indices are proposed to describe the anomaly of this circulation associated with the cross-equatorial part.

  3. Revisiting annual mean and seasonal cycle of deep meridional overturning circulation of the Indian Ocean

    Science.gov (United States)

    Wang, Weiqiang; Xie, Qiang; Li, Sha; Zhu, Xiuhua

    2014-05-01

    The annual mean and seasonal cycle of the deep meridional overturning circulation (MOC) of the Indian Ocean is being revisited here using GECCO synthesis. Resulting from ocean general circulation models, the annual mean deep MOC of the Indian Ocean are generally weak with inflow in the bottom layer and outflow in the intermediate and upper layer mixing with strong Indonesian Throughflow. For seasonal cycle of deep MOC, two significant and seasonal reversed counter-rotating deep cells over full depth of water column, roughly separated by 20S, are revealed during boreal summer and winter. The coincidences of the latitude 20S with where the maximum climatological wind curl for most of seasons reveals intimate relations between the deep meridional overturning and surface winds. Dynamical decompositions on annual mean and complete seasonal cycle of the meridional overturning show varying relative contribution of each dynamical component at different time scale. For annual mean deep MOC, Ekman dynamics is found to be dominant in the region of north of 25S, particularly in upper 3000m, whereas south of 25S external and vertical shear components show remarkable "seamount" features and are compensated with much larger strengths because of topo-modulated strong western boundary topography. At seasonal time scale, dominant role of Ekman dynamics and secondary role of external mode are found in the deep cell north of 20S in January and July. However in transition seasons, vertical shear is responsible for major part of meridional overturning and Ekman dynamics has comparable contribution north of Equator.

  4. Response of the meridional overturning circulation to variable buoyancy forcing in a double hemisphere basin

    Energy Technology Data Exchange (ETDEWEB)

    Lucas, Marc A. [National Oceanography Centre, University of Southampton, School of Ocean and Earth Science, Southampton (United Kingdom); Collecte Localisation Satellite, Ramonville Saint Agne (France); Hirschi, J.J.M. [National Oceanography Centre, University of Southampton, School of Ocean and Earth Science, Southampton (United Kingdom); Marotzke, J. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany)

    2010-04-15

    We consider how a highly idealized double-hemisphere basin responds to a zonally constant restoring surface temperature profile that oscillates in time, with periods ranging from 0.5 to 32,000 years. In both hemispheres, the forcing is similar but can be either in phase or out of phase. The set-up is such that the Northern Hemisphere always produces the densest waters. The model's meridional overturning circulation (MOC) exhibits a strong response in both hemispheres on decadal to multi-millennial timescales. The amplitude of the oscillations reaches up to 140% of the steady-state maximum MOC and exhibits resonance-like behaviour, with a maximum at centennial to millennial forcing periods. When the forcing is in phase between the Northern and Southern Hemispheres, there is a marked decrease in the amplitude of the MOC response as the forcing period is increased beyond the resonance period. In this case the resonance-like behaviour is identical to the one we found earlier in a single-hemisphere model and occurs for the same reasons. When the forcing is out of phase between the Northern and Southern Hemispheres, the amplitude of the MOC response is substantially greater for long forcing periods (millennial and longer), particularly in the Southern Hemisphere. This increased MOC amplitude occurs because for an out of phase forcing, either the northern or the southern deep water source is always active, leading to generally colder bottom waters and thus greater stratification in the opposite hemisphere. This increased stratification in turn stabilises the water column and thus reduces the strength of the weaker overturning cell. The interaction of the two hemispheres leads to response timescales of the deep ocean at half the forcing period. Our results suggest a possible explanation for the half-precessional time scale observed in the deep Atlantic Ocean palaeo-temperature record. (orig.)

  5. Inferring the zonal distribution of measured changes in the meridional overturning circulation

    Directory of Open Access Journals (Sweden)

    A. de Boer

    2006-10-01

    Full Text Available Recently, hydrographic measurements have been used to argue that the meridional overturning circulation at 25° N has decreased by 30% over the last 50 years. Here, we show that the most likely interpretation consistent with this approach (i.e., with the dynamic method together with a level-of-no-motion assumption and Ekman dynamics, is that any decrease in strength of the deep western boundary current must have been compensated, not by a basin-wide increase in upper layer southward flow, but by changes in the nonlinear region, immediately outside of the Florida Straits.

  6. Eastern Pacific cooling and Atlantic overturning circulation during the last deglaciation.

    Science.gov (United States)

    Kienast, Markus; Kienast, Stephanie S; Calvert, Stephen E; Eglinton, Timothy I; Mollenhauer, Gesine; François, Roger; Mix, Alan C

    2006-10-19

    Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean-atmosphere feedbacks or by changes in the Atlantic thermohaline circulation. North Atlantic cold periods during Heinrich events and millennial-scale cold events (stadials) have been linked with climatic changes in the tropical Atlantic Ocean and South America, as well as the Indian and East Asian monsoon systems, but not with tropical Pacific sea surface temperatures. Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements. Our data show a temperature drop of approximately 1 degrees C, synchronous (within dating uncertainties) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1, and a smaller temperature drop of approximately 0.5 degrees C synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event. Both cold events coincide with maxima in surface ocean productivity as inferred from 230Th-normalized carbon burial fluxes, suggesting increased upwelling at the time. From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation, we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans' thermohaline circulation, although possibly amplified by tropical ocean-atmosphere interaction as suggested before. PMID:17051216

  7. Simulation of meridional overturning in the upper layer of the South China Sea with an idealized bottom topography

    Institute of Scientific and Technical Information of China (English)

    WANG Dongxiao; LIU Xiongbin; WANG Wenzhi; DU Yan; ZHOU Weidong

    2004-01-01

    The large-scale upper circulations and meridional overturning in the upper layer of the South China Sea (SCS) with idealized bottom topography in winter and summer are investigated. Simulations with the GFDL general circulation model are carried out under the conditions of open or enclosed boundary regarding transport in the Luzon Strait. The intrusion area of Kuroshio, its impact on the meridional overturning in the upper layer of the SCS and seasonal characteristic of this impact are explored, respectively. The model is forced by climatological wind stress and relaxed to monthly mean climatological temperature and salinity. The resultant meridional overturning is non-enclosed, with transporting from north to south in the surface and returning to north at the depth of about 500 m in winter, about 200 m in summer, with amplitudes of 105 m3/s. It shows the transporting path of intermediate water of the SCS and offers an idealized reference for further study on dynamics of wind-driven and thermohaline circulation of the SCS.

  8. Stratification-dependent mixing may increase sensitivity of Atlantic overturning to global warming

    International Nuclear Information System (INIS)

    Full text: We use the earth system model of intermediate complexity CLIMBER-3 to investigate the effect of stratification-dependent mixing on the stability of the Atlantic Meridional Overturning Circulation (AMOC) under an idealized CO2 increase scenario. The vertical diffusivity κ of the ocean is parameterized as κ ∼ N-α, where N is the local buoyancy frequency. For all parameter values 0 ≤ α ≤ 3, we find the AMOC to decrease in response to increased CO2 concentrations. The sensitivity of the AMOC is significantly stronger for α ≥ αcr ∼ 1.5, also after stabilization of the CO2 concentration. This threshold behavior is explained by a halt of dense water formation in the subpolar gyre, which is caused by a positive feedback between stratification and mixing anomalies. Our findings indicate that climate models using time-invariant vertical mixing may underestimate the sensitivity of the AMOC to global warming. (author)

  9. The shallow meridional overturning circulation in the South China Sea and the related internal water movement

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ningning; LAN Jian; MA Jie; CUI Fengjuan

    2016-01-01

    The structure of the annual-mean shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) and the related water movement are investigated, using simple ocean data assimilation (SODA) outputs. The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale, which consists of downwelling in the northern SCS, a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow, with a strength of about 1×106 m3/s. The formation mechanisms of its branches are studied separately. The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m. The annual-mean Ekman transport across 18°N is about 1.2×106 m3/s. An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework. An annual subduction rate of about 0.66×106 m3/s is obtained between 17° and 20°N, of which 87% is due to vertical pumping and 13% is due to lateral induction. The subduction rate implies that the subdution contributes significantly to the downwelling branch. The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 11°N within the western boundary current before returning northward. The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents. Significant upwelling mainly occurs off the Vietnam coast in the southern SCS. An upper bound for the annual-mean net upwelling rate between 10° and 15°N is 0.7×106 m3/s, of which a large portion is contributed by summer upwelling, with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.

  10. North Atlantic 20th century multidecadal variability in coupled climate models: sea surface temperature and ocean overturning circulation

    Science.gov (United States)

    Medhaug, I.; Furevik, T.

    2011-06-01

    Output from a total of 24 state-of-the-art Atmosphere-Ocean General Circulation Models is analyzed. The models were integrated with observed forcing for the period 1850-2000 as part of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. All models show enhanced variability at multi-decadal time scales in the North Atlantic sector similar to the observations, but with a large intermodel spread in amplitudes and frequencies for both the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC). The models, in general, are able to reproduce the observed geographical patterns of warm and cold episodes, but not the phasing such as the early warming (1930s-1950s) and the following colder period (1960s-1980s). This indicates that the observed 20th century extreme in temperatures are due to primarily a fortuitous phasing of intrinsic climate variability and not dominated by external forcing. Most models show a realistic structure in the overturning circulation, where more than half of the available models have a mean overturning transport within the observed estimated range of 13-24 Sverdrup. Associated with a stronger than normal AMOC, the surface temperature is increased and the sea ice extent slightly reduced in the North Atlantic. Individual models show potential for decadal prediction based on the relationship between the AMO and AMOC, but the models strongly disagree both in phasing and strength of the covariability. This makes it difficult to identify common mechanisms and to assess the applicability for predictions.

  11. Compensation between meridional flow components of the Atlantic MOC at 26° N

    Science.gov (United States)

    Frajka-Williams, E.; Meinen, C. S.; Johns, W. E.; Smeed, D. A.; Duchez, A.; Lawrence, A. J.; Cuthbertson, D. A.; McCarthy, G. D.; Bryden, H. L.; Baringer, M. O.; Moat, B. I.; Rayner, D.

    2016-04-01

    From ten years of observations of the Atlantic meridional overturning circulation (MOC) at 26° N (2004-2014), we revisit the question of flow compensation between components of the circulation. Contrasting with early results from the observations, transport variations of the Florida Current (FC) and upper mid-ocean (UMO) transports (top 1000 m east of the Bahamas) are now found to compensate on sub-annual timescales. The observed compensation between the FC and UMO transports is associated with horizontal circulation and means that this part of the correlated variability does not project onto the MOC. A deep baroclinic response to wind-forcing (Ekman transport) is also found in the lower North Atlantic Deep Water (LNADW; 3000-5000 m) transport. In contrast, co-variability between Ekman and the LNADW transports does contribute to overturning. On longer timescales, the southward UMO transport has continued to strengthen, resulting in a continued decline of the MOC. Most of this interannual variability of the MOC can be traced to changes in isopycnal displacements on the western boundary, within the top 1000 m and below 2000 m. Substantial trends are observed in isopycnal displacements in the deep ocean, underscoring the importance of deep boundary measurements to capture the variability of the Atlantic MOC.

  12. The modern and glacial overturning circulation in the Atlantic ocean in PMIP coupled model simulations

    Directory of Open Access Journals (Sweden)

    S. L. Weber

    2007-01-01

    Full Text Available This study analyses the response of the Atlantic meridional overturning circulation (AMOC to LGM forcings and boundary conditions in nine PMIP coupled model simulations, including both GCMs and Earth system Models of Intermediate Complexity. Model results differ widely. The AMOC slows down considerably (by 20–40% during the LGM as compared to the modern climate in four models, there is a slight reduction in one model and four models show a substantial increase in AMOC strength (by 10–40%. It is found that a major controlling factor for the AMOC response is the density contrast between Antarctic Bottom Water (AABW and North Atlantic Deep Water (NADW at their source regions. Changes in the density contrast are determined by the opposing effects of changes in temperature and salinity, with more saline AABW as compared to NADW consistently found in all models and less cooling of AABW in all models but one. In only two models is the AMOC response during the LGM directly related to the response in net evaporation over the Atlantic basin. Most models show large changes in the ocean freshwater transports into the basin, but this does not seem to affect the AMOC response. Finally, there is some dependence on the accuracy of the control state.

  13. Changes in ocean meridional overturning circulation over glacial termination I - The global record of marine C-14 paleoreservoir ages 23 - 13 cal. ka

    International Nuclear Information System (INIS)

    Dramatic climate changes occurred during early last deglacial times, 19.0-14.5 cal. ka. They were linked to most fundamental recent changes in ocean circulation, which likely contributed to major shifts in CO2 transfer from ocean to atmosphere. Marine radiocarbon (C-14) paleoreservoir ages provide unique new insights into the fate of paleo-water masses associated with changes in meridional overturning circulation (MOC). These ages are monitored at an ever growing number of key locations in all three oceans by means of a new C-14 plateau tuning technique. Opposite trends in paleoreservoir ages indicate a short-lasting phase of deep and intermediate-water formation in the North Pacific 17.5 to less than 14.6 cal. ka. This event was coeval with a brief northward reversal of Denmark Strait Overflow waters in the North Atlantic, the source region of modern global MOC, and a dramatic cooling of North Atlantic and Eurasian climate (Heinrich-1 event)

  14. Meridional overturning transports at 30°S in the Indian and Pacific Oceans in 2002-2003 and 2009

    Science.gov (United States)

    Hernández-Guerra, Alonso; Talley, Lynne D.

    2016-08-01

    The meridional circulation and transports at 30°S in the Pacific and Indian Oceans for the years 2002-2003 and 2009 are compared, using GO-SHIP hydrographic section data with an inverse box model and several choices of constraints. Southward heat transport across the combined Indian-Pacific sections, reflecting net heating north of these sections, doubled from -0.7 ± 0.2 PW in 2002-2003 to -1.4 ± 0.1 PW in 2009 (negative sign is southward), with the increase concentrated in the Indian Ocean (∼0.6 PW compared with ∼0.2 PW in the Pacific), and was insensitive to model choices for the Indonesian Throughflow. Diagnosed net evaporation also more than doubled in the Indian Ocean, from 0.21-0.27 Sv in 2002-2003 to 0.51-0.58 in 2009, with a smaller but significant increase in net evaporation in the Pacific, from 0.06-0.08 Sv to 0.16-0.32 Sv. These increased heat and freshwater exports coincided with Indian Ocean warming, a shift in the Indian's shallow gyre overturning transport to lower densities, and an increase in southward Agulhas Current transport from 75 Sv in 2002 to 92 Sv in 2009. The Indian's deep overturn weakened from about 11 Sv in 2002 to 7 Sv in 2009. In contrast, the Pacific Ocean overturning circulation was nearly unchanged from 2003 to 2009, independent of model within the uncertainties. The East Australian Current transport decreased only slightly, from -52 Sv to -46 Sv. The southward Pacific Deep Water transport was at a higher density than the southward Indian Deep Water transport in both years and all models, similar to prior results. Estimated diapycnal diffusivity and velocity are strongly enhanced near the ocean bottom and are higher farther up in the water column in the Indian than in the Pacific, likely extending the reach of Indian Ocean overturning up to shallower depths than in the Pacific. The horizontal distribution of transports in the Pacific at all depths changed notably from 2003 to 2009, despite the stability of its meridional

  15. North Atlantic 20th century multidecadal variability in coupled climate models: sea surface temperature and ocean overturning circulation

    Directory of Open Access Journals (Sweden)

    I. Medhaug

    2011-06-01

    Full Text Available Output from a total of 24 state-of-the-art Atmosphere-Ocean General Circulation Models is analyzed. The models were integrated with observed forcing for the period 1850–2000 as part of the Intergovernmental Panel on Climate Change (IPCC Fourth Assessment Report. All models show enhanced variability at multi-decadal time scales in the North Atlantic sector similar to the observations, but with a large intermodel spread in amplitudes and frequencies for both the Atlantic Multidecadal Oscillation (AMO and the Atlantic Meridional Overturning Circulation (AMOC. The models, in general, are able to reproduce the observed geographical patterns of warm and cold episodes, but not the phasing such as the early warming (1930s–1950s and the following colder period (1960s–1980s. This indicates that the observed 20th century extreme in temperatures are due to primarily a fortuitous phasing of intrinsic climate variability and not dominated by external forcing. Most models show a realistic structure in the overturning circulation, where more than half of the available models have a mean overturning transport within the observed estimated range of 13–24 Sverdrup. Associated with a stronger than normal AMOC, the surface temperature is increased and the sea ice extent slightly reduced in the North Atlantic. Individual models show potential for decadal prediction based on the relationship between the AMO and AMOC, but the models strongly disagree both in phasing and strength of the covariability. This makes it difficult to identify common mechanisms and to assess the applicability for predictions.

  16. Mechanisms of meridional transport processes in the tropical Atlantic; Mechanismen meridionaler Transportprozesse im tropischen Atlantik

    Energy Technology Data Exchange (ETDEWEB)

    Kroeger, J.

    2001-07-01

    Meridional transport processes of water masses and tracers in the subtropical and tropical Atlantic are investigated using a regional eddy resolving model of the wind driven and thermohaline circulation. Analytical emphasis is on float simulations in the model which, complementary to Eulerian means, represent the Lagrangian view and give further insight into the spreading and pathways of characteristic water masses in this area. In the tropics and subtropics shallow 3-dimensional circulation cells are superimposed on the northward warm water transfer within the deep reaching thermohaline overturning cell (MOC) as part of the global ''Conveyor Belt''. Under present-day climate conditions the model shows that the equatorial thermocline is exclusively ventilated by subsurface flow within the tropical-subtropical cell (STC) of the South Atlantic. Only with a prescribed ''Conveyor-off''-Mode the STC of the North Atlantic contributes to this ventilation process with equal amounts. Throughout the year the interhemispheric transport of surface and central water masses of South Atlantic origin into the Caribbean Sea is dominated by zonal detours to the east as a consequence of the interplay of several retroflection events occuring in the North Atlantic. The eulerian mean flow field in the deep layer postulates the interhemispheric mass transport into the South Atlantic to be confined entirely to the western boundary, whereas Lagrangian means indicate intermittent eastward excursions along the equator, related to seasonally alternating zonal currents due to long Rossby waves. It was suggested that the observed characteristic eastward maximum of tracer concentrations along the equator is a consequence of rectifying effects of single or interacting equatorial waves. The model does not validate this hypothesis. The response to transport anomalies of subpolar origin and long periodicity is subject to different time-scales in both

  17. Holocene North Atlantic Overturning in an atmosphere-ocean-sea ice model compared to proxy-based reconstructions

    Science.gov (United States)

    Blaschek, M.; Renssen, H.; Kissel, C.; Thornalley, D.

    2015-11-01

    Climate and ocean circulation in the North Atlantic region changed over the course of the Holocene, partly because of disintegrating ice sheets and partly because of an orbital-induced insolation trend. In the Nordic Seas, this impact was accompanied by a rather small, but significant, amount of Greenland ice sheet melting. We have employed the EMIC LOVECLIM and compared our model simulations with proxy-based reconstructions of δ13C, sortable silt, and magnetic susceptibility (κ) used to infer changes in past ocean circulation over the last 9000 years. The various reconstructions exhibit different long-term evolutions suggesting changes in either the overturning of the Atlantic in total or of subcomponents of the ocean circulation, such as the overflow waters across the Greenland-Scotland ridge. Thus, the question arises whether these reconstructions are consistent with each other or not. A comparison with model results indicates that δ13C, employed as an indicator of overturning, agrees well with the long-term evolution of the modeled Atlantic meridional overturning circulation (AMOC). The model results suggest that different long-term trends in subcomponents of the AMOC, such as Iceland-Scotland overflow water, are consistent with proxy-based reconstructions and allow some of the reconstructions to be reconciled with the modeled and reconstructed (from δ13C) AMOC evolution. We find a weak early Holocene AMOC, which recovers by 7 kyr B.P. and shows a weak increasing trend of 88 ± 1 mSv/kyr toward present, with relatively low variability on centennial to millennial timescales.

  18. Warm and Saline Events Embedded in the Meridional Circulation of the Northern North Atlantic

    Science.gov (United States)

    Hakkinen, Sirpa; Rhines, Peter B.; Worthen, Denise L.

    2011-01-01

    Ocean state estimates from 1958 to 2005 from the Simple Ocean Assimilation System (SODA) system are analyzed to understand circulation between subtropical and subpolar Atlantic and their connection with atmospheric forcing. This analysis shows three periods (1960s, around 1980, and 2000s) with enhanced warm, saline waters reaching high latitudes, alternating with freshwater events originating at high latitudes. It complements surface drifter and altimetry data showing the subtropical -subpolar exchange leading to a significant temperature and salinity increase in the northeast Atlantic after 2001. The warm water limb of the Atlantic meridional overturning cell represented by SODA expanded in density/salinity space during these warm events. Tracer simulations using SODA velocities also show decadal variation of the Gulf Stream waters reaching the subpolar gyre and Nordic seas. The negative phase of the North Atlantic Oscillation index, usually invoked in such variability, fails to predict the warming and salinization in the early 2000s, with salinities not seen since the 1960s. Wind stress curl variability provided a linkage to this subtropical/subpolar gyre exchange as illustrated using an idealized two ]layer circulation model. The ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal. In this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax; hence, the polar front moves westward, opening an enhanced northward access of the subtropical waters in the eastern boundary current.

  19. Links Between the Deep Western Boundary Current, Labrador Sea Water Formation and Export, and the Meridional Overturning Circulation

    Science.gov (United States)

    Myers, Paul G.; Kulan, Nilgun

    2010-05-01

    Based on an isopyncal analysis of historical data, 3-year overlapping triad fields of objectively analysed temperature and salinity are produced for the Labrador Sea, covering 1949-1999. These fields are then used to spectrally nudge an eddy-permitting ocean general circulation model of the sub-polar gyre, otherwise forced by inter annually varying surface forcing based upon the Coordinated Ocean Reference Experiment (CORE). High frequency output from the reanalysis is used to examine Labrador Sea Water formation and its export. A number of different apprpoaches are used to estimate Labrador Sea Water formation, including an instanteous kinematic approach to calculate the annual rate of water mass subduction at a given density range. Historical transports are computed along sections at 53 and 56N for several different water masses for comparison with recent observations, showing a decline in the stength of the deep western boundary current with time. The variability of the strength of the meridional overturning circulation (MOC) from the reanalysis is also examined in both depth and density space. Linkages between MOC variability and water mass formation variability is considered.

  20. Two-signed feedback of cross-isthmus moisture transport on glacial overturning controlled by the Atlantic warm pool

    Directory of Open Access Journals (Sweden)

    H. J. de Boer

    2011-11-01

    Full Text Available This paper studies the control of the Atlantic Warm Pool (AWP on atmospheric moisture transport across the Central American isthmus as a potential feedback on rapid glacial climate fluctuations. Defined as a region of the Atlantic with surface temperatures above 28.5 °C, the modern AWP expands from the tropical Northwest Atlantic up to the Gulf of Mexico during boreal summer. Due to enhanced deep convection over these warm waters, changes in AWP area cause inverse changes in the strength of the Caribbean low level jet. This low level jet drives atmospheric moisture transport from the Atlantic across the Central American isthmus towards the Pacific. Changes in cross-isthmus moisture transport, potentially related to the AWP, may therefore have affected North Atlantic salinity and the partly density driven Atlantic Meridional Overturning Circulation (AMOC during the glacial. Based on available proxy evidence we hypothesize that the AWP evolved independent of extratropical North Atlantic temperatures during most of the last glacial, except during periods of AMOC collapse when intense extratropical North Atlantic cooling may have limited eastward AWP expansion. We investigate the implications of this hypothesis for cross-isthmus moisture transport by simulating the coupled ocean-atmosphere response to AMOC collapse and the atmospheric sensitivity to additional variations in AWP area. Our simulations suggest that a decrease in AWP area may increase cross-isthmus moisture transport, whereas extratropical North Atlantic cooling beside a persistent AWP may decrease cross-isthmus moisture transport. Interpretation of these effects throughout an idealized Bond Cycle suggests a positive feedback of reduced cross-isthmus moisture transport in response to Greenland cooling prior to AMOC collapse. During AMOC collapse, when AWP expansion is proposed to have been inhibited, this positive feedback turns negative as enhanced cross-isthmus moisture transport may

  1. The relation between AMOC, gyre circulation, and meridional heat transports in the North Atlantic in model simulations of the last millennium

    Science.gov (United States)

    Jungclaus, Johann; Moreno-Chamarro, Eduardo; Lohmann, Katja

    2016-04-01

    While it is clear that the Atlantic Meridional Overturning Circulation (AMOC) is responsible for meridional heat transfer from the South Atlantic and the tropics to the North Atlantic, the majority of the heat transport in the northern North Atlantic and the Nordic seas is carried by the gyre system. However, the detailed mechanisms determining the interaction between and the temporal modulation of the components of the northward heat transport system are not clear. Long-term climate records and model simulations can help to identify important processes and to provide background for the changes that are presently observed. Multi-centennial proxy records from the subpolar North Atlantic and the Nordic Seas indicate, for example, an out-of-phase behavior of sea surface temperature and gyre circulation between the two regions with consequences for regional climate. Paleoceanographic evidence from Fram Strait shows a pronounced modulation of heat transfer to the Arctic by the Atlantic Water layer during the last 2000 years and reconstructions from the Subpolar North Atlantic suggest a role of ocean circulation in the transition between the Medieval Climate Anomaly and the Little Ice Age. Here we explore a small ensemble of last millennium simulations, carried out with the Max Planck Institute Earth System Model, and analyze mechanisms connecting the AMOC and gyre circulation and their relation to external forcing. Our results support the important role of the Subpolar Gyre strength and the related meridional mass and temperature fluxes. We find that the modulation of the northward heat transport into the Nordic Seas and the Arctic has pronounced impact on sea-ice distribution, ocean-atmosphere interaction, and the surface climate in Scandinavia and Western Europe.

  2. Observations and Modeling of the Atlantic Meridional Mode during the Atlantic hurricane season

    Science.gov (United States)

    Smirnov, D.; Vimont, D. J.

    2009-12-01

    An observational and modeling study is conducted to investigate the vertical structure of the Atlantic Meridional Mode (AMM) during the Atlantic hurricane season months based on an AMM index derived by Chiang and Vimont (2004). The analysis shows that the SST anomaly structure that is typically associated with the AMM is accompanied by a slackening (intensification) of trade winds in the Northern (Southern) Hemisphere where SST anomalies are positive (negative). However, the accompanying air temperature anomalies are limited to the boundary layer. Furthermore, the AMM is shown to be associated with an anomalous baroclinic circulation in the northern subtropical Atlantic, with an anomalous lower-level cyclonic circulation residing under an anomalous upper-level anticyclone during a positive AMM. Initializing the atmospheric GCM CAM3.1 coupled to a slab ocean with AMM-like SST anomalies yields an atmospheric circulation that is highly similar to observational analyses. This suggests that the SST anomalies are forcing the atmospheric anomalies, and not vice versa. The anomalous atmospheric circulations of the lower and upper-levels act in tandem to reduce shear over the main development region (MDR), reiterating that a positive AMM favors increased hurricane activity in the MDR. A closer inspection of the monthly evolution of shear shows that the response increases three-fold from September to November within the MDR. However, the origin of the SST anomalies, which is vital in improving seasonal hurricane activity predictions, remains unclear.

  3. Anthropogenic CO2 uptake, transport, storage, and dynamical controls in the ocean imposed by the meridional overturning circulation: A modeling study

    Science.gov (United States)

    Nakano, H.; Ishii, M.; Rodgers, K. B.; Tsujino, H.; Yamanaka, G.

    2015-10-01

    Using an ocean carbon cycle model embedded in an ocean general circulation model, we examine how the budget of anthropogenic CO2 (Cant) is controlled by ocean dynamics. To complement recent studies showing only vertically integrated budgets, we provide a step-by-step description by making use of three different coarse grainings of the full vertical resolution of the ocean model in our budget analysis. For the 11 subdomains of the global ocean, these coarse grainings are (1) a one-layer (vertically integrated) budget, (2) a three-layer budget, and (3) an 11-layer budget. We largely focus on the Pacific circulation. We identify and quantify substantial carbon transport associated with the subtropical cells (STCs), which are dominant contributors to the meridional overturning circulation in the upper ocean in the tropics and subtropics, as playing a fundamental role in governing the ocean interior distribution of Cant. The upper branch of the STCs transports Cant-rich water from the tropics to the subtropics, contributing to the precondition for the high Cant inventory in mode waters. The lower branch of the STCs carries about two thirds of the transported Cant back to the tropics, while it largely excludes Subtropical Mode Waters. This work implies that the reemergence of Cant through recirculation within the STCs may lead to a reduced capacity for further Cant uptake via gas exchange into the surface ocean, potentially contributing to a positive carbon-climate feedback.

  4. An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation

    Directory of Open Access Journals (Sweden)

    R. Marsh

    2013-02-01

    Full Text Available The key physical parameters of the "eb_go_gs" configuration of GENIE, an Earth system Model of Intermediate Complexity (EMIC, are tuned using a multi-objective genetic algorithm. An ensemble of 90 parameter sets is tuned using two ocean and two atmospheric state variables as targets. These are "Pareto-optimal", representing a range of trade-offs between the four tuning targets. For the leading five parameter sets, simulations are further evaluated alongside a simulation with untuned "default" parameters, comparing selected variables and diagnostics that describe the state of the atmosphere, ocean and sea ice. One of these parameter sets is selected for further analysis of the objective function (error landscape in the vicinity of its tuned values. "Cliffs" along some dimensions motivate closer inspection of corresponding variations in the Atlantic meridional overturning circulation (AMOC. This reveals that bifurcations in the AMOC are highly sensitive to parameters that are not commonly associated with MOC stability. Specifically, the state of the AMOC is sensitive to parameters governing the wind-driven circulation and atmospheric heat transport. Five optimal parameter sets are recommended for future use of GENIE in the configuration presented here.

  5. Oxygen variability and meridional oxygen supply in the tropical North East Atlantic oxygen minimum zone

    Science.gov (United States)

    Hahn, Johannes; Brandt, Peter; Greatbatch, Richard J.; Krahmann, Gerd; Körtzinger, Arne

    2013-04-01

    The oxygen minimum zone (OMZ) of the tropical North East Atlantic (TNEA) is located between the oxygen-rich equatorial region and the Cape Verde Frontal Zone at about 20°N in a depth range of 300 - 700 m. Its horizontal extent is predominantly defined by the North Equatorial Current and by the equatorial zonal current system ventilating the region to the north and south of the OMZ, respectively. The interior of the OMZ is characterized by a sluggish flow regime, where mesoscale eddies play a major role in the ventilation. In this study we focus on the oxygen variability in the TNEA as well as the eddy driven lateral ventilation of the TNEA OMZ across its southern boundary. During recent years an intense measurement program was executed along 23°W cutting meridionally through the TNEA OMZ. Hydrographic and velocity data has been acquired from ship sections and moorings, together covering the latitude range between 6°S and 14°N with particularly high meridional resolution of shipboard and high temporal resolution of moored observations. Based on shipboard data we derived a meridional section of oxygen variance, which reveals numerous local maxima of oxygen variability. Exemplary, strong oxygen variability is observed at the upper (300m, 5° - 12°N) and the southern boundary (400m - 700m, 5°N - 8°N) of the OMZ, whereas the interior of the OMZ is characterized by weak variability. An application of the extended Osborn-Cox model shows that the strong oxygen variability at the southern boundary is mainly generated by mesoscale eddies. The strong variability at the upper boundary is generated by mesoscale eddies as well as microscale turbulence. We apply two methods to estimate the meridional oxygen flux: 1) a flux gradient parameterization and 2) a correlation of oxygen and velocity mooring time series. From the analysis of the 5°N mooring data we find a northward oxygen flux directed towards the OMZ at its core depth, that is mainly due to variability of

  6. An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation

    Directory of Open Access Journals (Sweden)

    R. Marsh

    2013-10-01

    Full Text Available The key physical parameters for the "eb_go_gs" configuration of version 2.7.4 of GENIE, an Earth system model of intermediate complexity (EMIC, are tuned using a multi-objective genetic algorithm. An ensemble of 90 parameter sets is tuned using two ocean and two atmospheric state variables as targets. These are "Pareto-optimal", representing a range of trade-offs between the four tuning targets. For the leading five parameter sets, simulations are evaluated alongside a simulation with untuned "default" parameters, comparing selected variables and diagnostics that describe the state of the atmosphere, ocean and sea ice. Further experiments are undertaken with these selected parameter sets to compare equilibrium climate sensitivities and transient climate responses. The pattern of warming under doubled CO2 is strongly shaped by changes in the Atlantic meridional overturning circulation (AMOC, while the pattern and rate of warming under rising CO2 is closely linked to changing sea ice extent. One of the five tuned parameter sets is identified as marginally optimal, and the objective function (error landscape is further analysed in the vicinity of the tuned values of this parameter set. "Cliffs" along some dimensions motivate closer inspection of corresponding variations in the AMOC. This reveals that bifurcations in the AMOC are highly sensitive to parameters that are not typically associated with MOC stability. Specifically, the state of the AMOC is sensitive to parameters governing the wind-driven circulation and atmospheric heat transport. For the GENIE configuration presented here, the marginally optimal parameter set is recommended for single simulations, although the leading five parameter sets may be used in ensemble mode to admit a constrained degree of parametric uncertainty in climate prediction.

  7. Potential for seasonal prediction of the Atlantic sea surface temperatures using the RAPID array at 26°N

    OpenAIRE

    Duchez, Aurélie; Courtois, Peggy; Harris, Elizabeth; Josey, Simon; Kanzow, Torsten; Marsh, Robert; Smeed, David; Hirschi, Joël Jean-Marie

    2015-01-01

    The Atlantic meridional overturning circulation (AMOC) plays a critical role in the climate system and is responsible for much of the meridional heat transported by the ocean. In this paper, the potential of using AMOC observations from the 26 ? N RAPID array to predict North Atlantic sea surface temperatures is investigated for the first time. Using spatial correlations and a composite method, the AMOC anomaly is used as a precursor of North Atlantic sea-surface temperature anomalies (SSTAs...

  8. 10-years of Atlantic Overturning observations: variability revealed on sub-annual, seasonal, annual and multi-annual timescales

    Science.gov (United States)

    McCarthy, Gerard; Johns, William; Meinen, Chris; Baringer, Molly; Rayner, Darren; Moat, Ben; Smeed, David

    2015-04-01

    The RAPID/MOCHA/WBTS project has been measuring the Atlantic Overturning circulation (AMOC) at 26.5 N in the North Atlantic since 2004. The joint UK-US project has recently reached the 10 year milestone. Here we present some of the key results from the first 10 years of the program. The first year's measurements revealed a sub-annual variability that encompassed all previous ship-based, hydrographic estimates of the AMOC, thus showing that a perceived decline could be encompassed in short-term variability. Seasonal variability in the AMOC was larger than expected with a 6 Sv range, with the largest single component derived from wind-stress curl induced density fluctuations at the eastern boundary. Interannual variability, far larger than that present in state of the art climate models, was seen in 2009/10. A 30% reduction lasted 18 months and cooled the subtropical North Atlantic significantly. The existence of continuous heat transport measurements enabled us to show that the main cause of the cooling was a reduction in ocean heat convergence rather than air-sea fluxes. The winter of 2010/11 revealed a second consecutive winter of low AMOC: a double dip. Whether ocean re-emergence or the change in AMOC circulation was the cause of the SST tripole pattern pattern that emerged in the winter of 2010/11 is a topic of ongoing research. Nonetheless, this SST pattern was shown to be sufficient to push the atmosphere into a second consecutive negative wintertime North Atlantic Oscillation (NAO) and increased predictability of this negative NAO. Most recently a multi-year decline in the AMOC has been observed. This 0.5 Sv/year decline is much larger than the long-term decline predicted due to anthropogenic climate change. The decline first reported on the 8.5-year timeseries has continued in the 10-year timeseries. The magnitude of the decline is so large as to suggest it may be decadal variability. A decline in the AMOC is consistent with a declining phase of the Atlantic

  9. North Atlantic multidecadal variability in coupled climate models - Mechanisms and responses

    OpenAIRE

    Medhaug, Iselin

    2011-01-01

    Global atmosphere-ocean general circulation models have been used to investigate mechanisms controlling the North Atlantic low-frequency variability, with the focus on the Atlantic Meridional Overturning Circulation, the Subpolar Gyre dynamics and the North Atlantic basin scale sea surface temperatures, called the Atlantic Multidecadal Oscillation. The understanding of the dynamics of, and mechanisms behind the variability in these components of the climate system are of great ...

  10. Distribution and composition of suspended matter at meridional section in the western Atlantic

    Science.gov (United States)

    Politova, N. V.; Artem'ev, V. A.; Zernova, V. V.

    2015-11-01

    The results of the study of suspended particulate matter of the surface waters in the Western Atlantic from the moderate latitudes of the northern hemisphere to the subtropics of the southern hemisphere, its distribution of quantity, and its composition are considered. The dominant influence of climatic zonality, where maximum contents and a biogenic component of suspended matter are confined to the eutrophic and mesotrophic segments of the ocean, as well as the influence of circumcontinental zonality, especially manifest in the distribution of the lithogenic fraction of suspended matter, are recorded.

  11. On multidecadal and quasi-decadal North Atlantic variability

    OpenAIRE

    Alvarez-Garcia, F.; Latif, Mojib; Biastoch, Arne

    2008-01-01

    Observed sea surface temperatures (SSTs) in the North Atlantic from 1958 through 2000, as well as data from an ocean model simulation driven with the atmospheric variability observed during the same period, are examined using multichannel singular spectrum analysis. The two leading oscillatory modes are associated with a multidecadal and a quasi-decadal period. The former is connected to a basinwide uniform SST pattern and changes in the deep North Atlantic meridional overturning circulation....

  12. Tropical versus high latitude freshwater influence on the Atlantic circulation

    OpenAIRE

    Goelzer, H.; J. Mignot; Levermann, A; Rahmstorf, S.

    2006-01-01

    We investigate the model sensitivity of the Atlantic meridional overturning circulation (AMOC) to anomalous freshwater flux in the tropical and northern Atlantic. Forcing in both locations leads to the same qualitative response: a positive freshwater anomaly induces a weakening of the AMOC and a negative freshwater anomaly strengthens the AMOC. Strong differences arise in the temporal characteristics and amplitude of the response. The advection of the tropical anomaly up to the deep water for...

  13. Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard-Oeschger events

    Science.gov (United States)

    Gottschalk, Julia; Skinner, Luke C.; Misra, Sambuddha; Waelbroeck, Claire; Menviel, Laurie; Timmermann, Axel

    2015-12-01

    The glacial climate system transitioned rapidly between cold (stadial) and warm (interstadial) conditions in the Northern Hemisphere. This variability, referred to as Dansgaard-Oeschger variability, is widely believed to arise from perturbations of the Atlantic Meridional Overturning Circulation. Evidence for such changes during the longer Heinrich stadials has been identified, but direct evidence for overturning circulation changes during Dansgaard-Oeschger events has proven elusive. Here we reconstruct bottom water [CO32-] variability from B/Ca ratios of benthic foraminifera and indicators of sedimentary dissolution, and use these reconstructions to infer the flow of northern-sourced deep water to the deep central sub-Antarctic Atlantic Ocean. We find that nearly every Dansgaard-Oeschger interstadial is accompanied by a rapid incursion of North Atlantic Deep Water into the deep South Atlantic. Based on these results and transient climate model simulations, we conclude that North Atlantic stadial-interstadial climate variability was associated with significant Atlantic overturning circulation changes that were rapidly transmitted across the Atlantic. However, by demonstrating the persistent role of Atlantic overturning circulation changes in past abrupt climate variability, our reconstructions of carbonate chemistry further indicate that the carbon cycle response to abrupt climate change was not a simple function of North Atlantic overturning.

  14. Impact of tropical Pacific variability on the mean North Atlantic thermohaline circulation

    OpenAIRE

    Semenov, Vladimir; Latif, Mojib

    2006-01-01

    A series of 500 years long coupled general circulation model simulations has been performed, in which the sea surface temperatures (SSTs) in different tropical oceans have been prescribed from climatology. A statistically significant reduction by about one Sverdrup of the meridional overturning circulation (MOC) in the North Atlantic was found when the tropical Pacific SSTs do not vary interannually. Anomalously low salinities originating in the tropical Atlantic due to increased precipitatio...

  15. The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability

    Directory of Open Access Journals (Sweden)

    C. F. Schleussner

    2014-02-01

    By decomposing the GMT variance into contributions of the AMOC and Northern Hemisphere sea-ice extent using a graph-theoretical statistical approach, we find the AMOC to contribute 8% to GMT variability in the ensemble mean. Our results highlight the importance of AMOC sea-ice feedbacks that explain 5% of the GMT variance, while the contribution solely related to the AMOC is found to be about 3%. As a consequence of multi-decadal AMOC variability, we report substantial variations in North Atlantic deep-ocean heat content with trends of up to 0.7 × 1022 J decade−1 that are of the order of observed changes over the last decade and consistent with the reduced GMT warming trend over this period. Although these temperature anomalies are largely density-compensated by salinity changes, we find a robust negative correlation between the AMOC and North Atlantic deep-ocean density with density lagging the AMOC by 5 to 11 yr in most models. While this would in principle allow for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean system, our results are inconclusive about the role of this feedback in the model ensemble.

  16. A multi-decadal meridional displacement of the Subpolar Front in the Newfoundland Basin

    Directory of Open Access Journals (Sweden)

    I. Núñez-Riboni

    2011-02-01

    Full Text Available Observations since the 1950s show a multi-decadal cycle of a meridional displacement of the Subpolar Front (SPF in the Newfoundland Basin (NFB in the North Atlantic. The SPF displacement is associated with corresponding variations in the path of the North Atlantic Current. We use the ocean general circulation model MPIOM with enhanced horizontal and vertical resolutions and forced with NCEP/NCAR reanalysis data to study the relation of the SPF displacement to Labrador Sea Water (LSW volume, atmospheric forcing and intensities of the Subpolar Gyre (SPG and Meridional Overturning Circulation (MOC. The simulations indicate that the SPF displacement is associated with a circulation anomaly between the SPG and the subtropical gyre (STG, an inter-gyre gyre with a multi-decadal time scale. Contributions of wind stress curl (WSC and LSW volume changes to the inter-gyre gyre are similar between 35 and 55° N (excluding the western boundary current. An anticyclonic inter-gyre gyre is related to negative WSC and LSW anomalies and to a SPF north of its climatological position, indicating an expanding STG. A cyclonic inter-gyre gyre is related to positive WSC and LSW anomalies and a SPF south of its climatological position, indicating an expanding SPG. Therefore, the mean latitudinal position of the SPF in the NFB could be an indicator of the amount of LSW in the inter-gyre region. Spreading of LSW anomalies intensifies the MOC, suggesting our SPF index as predictor of the MOC intensity at multi-decadal time scales. The meridional displacement of the SPF has a pronounced influence on the meridional heat transport, both on its gyre and overturning components.

  17. A multi-decadal meridional displacement of the Subpolar Front in the Newfoundland Basin

    Directory of Open Access Journals (Sweden)

    I. Núñez-Riboni

    2012-02-01

    Full Text Available Observations since the 1950s show a multi-decadal cycle of a meridional displacement of the Subpolar Front (SPF in the Newfoundland Basin (NFB in the North Atlantic. The SPF displacement is associated with corresponding variations in the path of the North Atlantic Current. We use the ocean general circulation model MPIOM with enhanced horizontal and vertical resolutions and forced with NCEP/NCAR reanalysis data to study the relation of the SPF displacement to atmospheric forcing, intensities of the subpolar gyre (SPG and Meridional Overturning Circulation (MOC, and Labrador Sea Water (LSW volume. The simulations indicate that the SPF displacement is associated with a circulation anomaly between the SPG and the subtropical gyre (STG, an inter-gyre gyre with a multi-decadal time scale. A sensitivity experiment indicates that both wind stress curl (WSC and heat fluxes (which match LSW changes contribute to the circulation anomalies in the frontal region and to the SPF displacement. An anticyclonic inter-gyre gyre is related to negative WSC and LSW anomalies and to a SPF north of its climatological position, indicating an expanding STG. A cyclonic inter-gyre gyre is related to positive WSC and LSW anomalies and a SPF south of its climatological position, indicating an expanding SPG. Therefore, the mean latitudinal position of the SPF in the NFB (a "SPF index" could be an indicator of the amount of LSW in the inter-gyre region. Spreading of LSW anomalies intensifies the MOC, suggesting our SPF index as predictor of the MOC intensity at multi-decadal time scales. The meridional displacement of the SPF has a pronounced influence on the meridional heat transport, both on its gyre and overturning components.

  18. Late Glacial – Holocene climate variability and sedimentary environments on northern continental shelves Zonal and meridional Atlantic Water advection

    OpenAIRE

    Sørensen, Steffen Aagaard

    2011-01-01

    The overall objective for this PhD-study was to further advance the understanding of the oceanographic variability and development in the Nordic Seas during the Late Glacial and the Holocene and towards the present. The focus is specifically on the poleward Atlantic Water advection along the continental margins of Norway, into the SW Barents Sea and along the West Spitsbergen slope. Four high resolution sediment cores retrieved from northern continental shelve allowed examination of spatial a...

  19. Decadal predictions of the North Atlantic CO2 uptake

    Science.gov (United States)

    Li, Hongmei; Ilyina, Tatiana; Müller, Wolfgang A.; Sienz, Frank

    2016-03-01

    As a major CO2 sink, the North Atlantic, especially its subpolar gyre region, is essential for the global carbon cycle. Decadal fluctuations of CO2 uptake in the North Atlantic subpolar gyre region are associated with the evolution of the North Atlantic Oscillation, the Atlantic meridional overturning circulation, ocean mixing and sea surface temperature anomalies. While variations in the physical state of the ocean can be predicted several years in advance by initialization of Earth system models, predictability of CO2 uptake has remained unexplored. Here we investigate the predictability of CO2 uptake variations by initialization of the MPI-ESM decadal prediction system. We find large multi-year variability in oceanic CO2 uptake and demonstrate that its potential predictive skill in the western subpolar gyre region is up to 4-7 years. The predictive skill is mainly maintained in winter and is attributed to the improved physical state of the ocean.

  20. Decadal predictions of the North Atlantic CO2 uptake.

    Science.gov (United States)

    Li, Hongmei; Ilyina, Tatiana; Müller, Wolfgang A; Sienz, Frank

    2016-01-01

    As a major CO2 sink, the North Atlantic, especially its subpolar gyre region, is essential for the global carbon cycle. Decadal fluctuations of CO2 uptake in the North Atlantic subpolar gyre region are associated with the evolution of the North Atlantic Oscillation, the Atlantic meridional overturning circulation, ocean mixing and sea surface temperature anomalies. While variations in the physical state of the ocean can be predicted several years in advance by initialization of Earth system models, predictability of CO2 uptake has remained unexplored. Here we investigate the predictability of CO2 uptake variations by initialization of the MPI-ESM decadal prediction system. We find large multi-year variability in oceanic CO2 uptake and demonstrate that its potential predictive skill in the western subpolar gyre region is up to 4-7 years. The predictive skill is mainly maintained in winter and is attributed to the improved physical state of the ocean. PMID:27026490

  1. Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean

    Science.gov (United States)

    Böning, Claus W.; Behrens, Erik; Biastoch, Arne; Getzlaff, Klaus; Bamber, Jonathan L.

    2016-07-01

    The Greenland ice sheet has experienced increasing mass loss since the 1990s. The enhanced freshwater flux due to both surface melt and outlet glacier discharge is assuming an increasingly important role in the changing freshwater budget of the subarctic Atlantic. The sustained and increasing freshwater fluxes from Greenland to the surface ocean could lead to a suppression of deep winter convection in the Labrador Sea, with potential ramifications for the strength of the Atlantic meridional overturning circulation. Here we assess the impact of the increases in the freshwater fluxes, reconstructed with full spatial resolution, using a global ocean circulation model with a grid spacing fine enough to capture the small-scale, eddying transport processes in the subpolar North Atlantic. Our simulations suggest that the invasion of meltwater from the West Greenland shelf has initiated a gradual freshening trend at the surface of the Labrador Sea. Although the freshening is still smaller than the variability associated with the episodic `great salinity anomalies', the accumulation of meltwater may become large enough to progressively dampen the deep winter convection in the coming years. We conclude that the freshwater anomaly has not yet had a significant impact on the Atlantic meridional overturning circulation.

  2. Vertical density gradient in the eastern North Atlantic during the last 30,000 years

    Energy Technology Data Exchange (ETDEWEB)

    Rogerson, M.; Ramirez, J. [University of Hull, Geography Department, Hull (United Kingdom); Bigg, G.R. [University of Sheffield, Department of Geography, Sheffield (United Kingdom); Rohling, E.J. [University of Southampton, National Oceanography Centre, School of Ocean and Earth Science, Southampton (United Kingdom)

    2012-08-15

    Past changes in the density and momentum structure of oceanic circulation are an important aspect of changes in the Atlantic Meridional Overturning Circulation and consequently climate. However, very little is known about past changes in the vertical density structure of the ocean, even very extensively studied systems such as the North Atlantic. Here we exploit the physical controls on the settling depth of the dense Mediterranean water plume derived from the Strait of Gibraltar to obtain the first robust, observations-based, probabilistic reconstruction of the vertical density gradient in the eastern North Atlantic during the last 30,000 years. We find that this gradient was weakened by more than 50%, relative to the present, during the last Glacial Maximum, and that changes in general are associated with reductions in AMOC intensity. However, we find only a small change during Heinrich Event 1 relative to the Last Glacial Maximum, despite strong evidence that overturning was substantially altered. This implies that millennial-scale changes may not be reflected in vertical density structure of the ocean, which may be limited to responses on an ocean-overturning timescale or longer. Regardless, our novel reconstruction of Atlantic density structure can be used as the basis for a dynamical measure for validation of model-based AMOC reconstructions. In addition, our general approach is transferrable to other marginal sea outflow plumes, to provide estimates of oceanic vertical density gradients in other locations. (orig.)

  3. Local and remote impacts of a tropical Atlantic salinity anomaly

    Energy Technology Data Exchange (ETDEWEB)

    Mignot, Juliette; Frankignoul, Claude [UPMC/CNRS/IRD/MNHN, Universite Pierre et Marie Curie, IPSL/LOCEAN, Paris (France)

    2010-12-15

    The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean-atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector after ten years. It has the form of a robust wave-like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the Amazonian basin. Meanwhile, the salt anomaly is carried northward by the mean oceanic circulation. It is traced up to the convection sites and then on its return path at depth towards lower latitudes. Consistent with the density increase, deep convection is enhanced after the arrival of the salt anomaly and the Atlantic meridional overturning circulation (AMOC) intensifies about 20 years after the beginning of the perturbation. The adjustment of the tropical Atlantic to the AMOC intensification then modifies its initial response to the freshwater forcing, leading to a weaker cooling in the northern tropical Atlantic than in the southern tropical Atlantic, a slight northward shift of the tropical Atlantic precipitation pattern and an intensification of the North Brazil current. On the other hand, no significant anomalous precipitations are found in the Pacific. The initial remote atmospheric response is also modulated, by an NAO-like response to the AMOC intensification. (orig.)

  4. Dynamics and Variability of the Circulation in the North-Atlantic Subpolar Seas

    OpenAIRE

    Chafik, Léon

    2014-01-01

    This thesis deals with the dynamics and circulation in the northern North Atlantic and the Nordic Seas, processes of crucial importance for the mild climate of Scandinavia and Northern Europe. High-resolution ADCP scans of currents from Greenland to Scotland in the top 400 m demonstrate that the Reykjanes Ridge is a very effective separator of flow towards the Nordic and Labrador Seas, respectively. It was found that the meridional overturning circulation has weakened by ~1.7 Sv (1 Sv = 106 m...

  5. The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

    OpenAIRE

    Kandiano, E. S.; H. A. Bauch; K. Fahl; J. P. Helmke; Röhl, U.; Pérez-Folgado, M.; Cacho, I.

    2012-01-01

    Temporal and spatial patterns in eastern North Atlantic sea surface temperatures (SST) were reconstructed for marine isotope stage (MIS) 11c using a submeridional transect of five sediment cores. The SST reconstructions are based on planktic foraminiferal abundances and alkenone indices, and are supported by benthic and planktic stable isotope measurements, as well as by ice-rafted debris content in polar and middle latitudes. Additionally, the larger-scale dynamics of the precipitation regim...

  6. Evidence for external forcing of the Atlantic Multidecadal Oscillation since the termination of the Little Ice Age

    Science.gov (United States)

    Faurschou Knudsen, Mads; Holm Jacobsen, Bo; Seidenkrantz, Marit-Solveig; Olsen, Jesper

    2014-05-01

    Variations in North Atlantic sea-surface temperatures (SSTs) are particularly prominent on multidecadal timescales. These changes, which exert a strong influence on climate in the North Atlantic region, are dominated by the alternation between warm and cold SST anomalies on a timescale of 60-80 years, a phenomenon known as the Atlantic Multidecadal Oscillation (AMO). The forcing mechanism pacing the AMO remains subject to considerable debate. One school of thought holds that the AMO is driven by internal ocean variability and related to multidecadal fluctuations in the Atlantic meridional overturning circulation (AMOC). In contrast, a recent model study concluded that the combined external forcing due to solar variability and volcanic eruptions has dictated the pace and phasing of the AMO over the past 600 years, as the combined solar and volcanic forcing is highly correlated to the AMO in the model with the forcing leading this AMO by ~5 years. Identifying the relative roles of internal ocean variability and external forcing agents in driving multi-decadal SST variability in the North Atlantic is important, in particular because the AMO purportedly influence climate variables of key importance to society, such as precipitation and hurricane activity. In the present study, we examine the relationship between the AMO and potential external forcing agents over the past 450 years based on statistical analyses of available high-resolution proxy data. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation (AMOC) is important for linking external forcing with North Atlantic sea

  7. Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing

    Science.gov (United States)

    Morrison, Adele K.; Hogg, Andrew M.; Ward, Marshall L.

    2011-07-01

    The sensitivity of the Southern Ocean overturning to altered surface buoyancy forcing is investigated in a series of eddy-permitting, idealised simulations. The modelled response indicates that heat and freshwater fluxes in the Southern Hemisphere mid-latitudes may play a significant role in setting the strength of the overturning circulation. Enhanced buoyancy fluxes act to increase the meridional overturning up to a limit approaching the wind-driven Ekman transport. The sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile, buoyancy forcing and upwelling region. The numerical simulations provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes, instead of, or in addition to, changes in wind stress.

  8. Changes in extreme regional sea surface height due to an abrupt weakening of the Atlantic MOC

    Directory of Open Access Journals (Sweden)

    S.-E. Brunnabend

    2014-04-01

    Full Text Available As an extreme scenario of dynamical sea level changes, regional sea surface height (SSH changes that occur in the North Atlantic due to an abrupt weakening of the Atlantic Meridional Overturning Circulation (AMOC are simulated. Two versions of the same ocean-only model are used to study the effect of ocean model resolution on these SSH changes: a high-resolution (HR strongly eddying version and a low-resolution (LR version in which the effect of eddies are parameterized. The weakening of the AMOC is induced in both model versions by applying strong freshwater perturbations around Greenland. A rapid decrease of the AMOC in the HR version induces much shorter return times of several specific regional and coastal extremes in North Atlantic SSH than in the LR version. This effect is caused by a change in main eddy pathways associated with a change in separation latitude of the Gulf Stream.

  9. The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature.

    Science.gov (United States)

    Yamamoto, Ayako; Palter, Jaime B

    2016-01-01

    Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air-sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline. PMID:26975331

  10. Abundance, distribution and size structure of zooplankton along a 20° west meridional transect of the northeast Atlantic Ocean in July

    Science.gov (United States)

    Gallienne, C. P.; Robins, D. B.; Woodd-Walker, R. S.

    Zooplankton distribution, abundance and size structure were characterised on leg 2 of the PRIME cruise in the northeast Atlantic during July 1996. Latitudinal sampling was carried out from 60°N to 37°N along a meridian at approximately 20°W. Zooplankton were characterised using an Optical Plankton Counter (OPC), and from traditional depth-integrated net hauls for taxonomy and carbon. The former method allows zooplankton to be described in terms of biovolume and size. There was good agreement between the two methods for abundance and a good correlation between OPC biovolume and carbon analysis. These data also showed compatibility with concurrent acoustic measurements of zooplankton. Results for the cruise compared to recent studies in the region, show that, overall abundance was generally low, although most of the previous studies were closer to spring bloom conditions. The size structure over latitude shows that mean size fluctuated, but there was a general trend of decreasing mean size from the north of the transect to about 47°N. Further statistical treatment of the OPC data, using principal component analysis, showed that zooplankton size structure changed at five positions along the transect. Three of these coincided with changes in physical structure, one each side of the front at 48°N and the third on the outer edge of an eddy. The other two occurred in regions of high-surface chlorophyll concentration.

  11. Reorganization of the North Atlantic Oscillation during early Holocene deglaciation

    Science.gov (United States)

    Wassenburg, Jasper A.; Dietrich, Stephan; Fietzke, Jan; Fohlmeister, Jens; Jochum, Klaus Peter; Scholz, Denis; Richter, Detlev K.; Sabaoui, Abdellah; Spötl, Christoph; Lohmann, Gerrit; Andreae, Meinrat O.; Immenhauser, Adrian

    2016-08-01

    The North Atlantic Oscillation is the dominant atmospheric pressure mode in the North Atlantic region and affects winter temperature and precipitation in the Mediterranean, northwest Europe, Greenland, and Asia. The index that describes the sea-level pressure difference between Iceland and the Azores is correlated with a dipole precipitation pattern over northwest Europe and northwest Africa. How the North Atlantic Oscillation will develop as the Greenland ice sheet melts is unclear. A potential past analogue is the early Holocene, during which melting ice sheets around the North Atlantic freshened surface waters, affecting the strength of the meridional overturning circulation. Here we present a Holocene rainfall record from northwest Africa based on speleothem δ18O and compare it against a speleothem-based rainfall record from Europe. The two records are positively correlated during the early Holocene, followed by a shift to an anti-correlation, similar to the modern record, during the mid-Holocene. On the basis of our simulations with an Earth system model, we suggest the shift to the anti-correlation reflects a large-scale atmospheric and oceanic reorganization in response to the demise of the Laurentide ice sheet and a strong reduction of meltwater flux to the North Atlantic, pointing to a potential sensitivity of the North Atlantic Oscillation to the melting of ice sheets.

  12. Surface salinity variability in the northern North Atlantic during recent decades

    Science.gov (United States)

    HäKkinen, Sirpa

    2002-12-01

    The sea surface salinity (SSS) variability in the North Atlantic is investigated using numerical model simulations for the last 50 years based on atmospheric forcing variability from the Comprehensive Atmosphere Ocean Data Set (COADS) and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. The focus here is the SSS variability in the subpolar region. The seasonality of the subpolar surface salinity variability is prominent with the maximum standard deviation (SD) occurring in the summer/fall period so that the amplitude of the summer SSS anomalies far exceed those of the wintertime. The interannual SSS variability in the subpolar gyre can be attributed mainly to excess ice melt, while the longer-term (decadal) variability is associated with meridional overturning variability. In these two hindcasts, the deep mixing (which drives overturning changes) is forced by heat flux variability so that weak subpolar heat loss and subsequent weak overturning are usually manifested in fresh surface conditions in the subpolar gyre within 2 years. This is because the role of deep convection is to mix down the net fresh water input received by the high latitudes. Hence, at the lack of widespread deep mixing, a signal of slowing down overturning, the fresh water input that would be expected based on climatology would accumulate at the surface.

  13. Deglacial diatom production in the tropical North Atlantic driven by enhanced silicic acid supply

    Science.gov (United States)

    Hendry, Katharine R.; Gong, Xun; Knorr, Gregor; Pike, Jennifer; Hall, Ian R.

    2016-03-01

    Major shifts in ocean circulation are thought to be responsible for abrupt changes in temperature and atmospheric CO2 during the last deglaciation, linked to variability in meridional heat transport and deep ocean carbon storage. There is also widespread evidence for shifts in biological production during these times of deglacial CO2 rise, including enhanced diatom production in regions such as the tropical Atlantic. However, it remains unclear as to whether this diatom production was driven by enhanced wind-driven upwelling or density-driven vertical mixing, or by elevated thermocline concentrations of silicic acid supplied to the surface at a constant rate. Here, we demonstrate that silicic acid supply at depth in the NE Atlantic was enhanced during the abrupt climate events of the deglaciation. We use marine sediment archives to show that an increase in diatom production during abrupt climate shifts could only occur in regions of the NE Atlantic where the deep supply of silicic acid could reach the surface. The associated changes are indicative of enhanced regional wind-driven upwelling and/or weakened stratification due to circulation changes during phases of weakened Atlantic meridional overturning. Globally near-synchronous pulses of diatom production and enhanced thermocline concentrations of silicic acid suggest that widespread deglacial surface-driven breakdown of stratification, linked to changes in atmospheric circulation, had major consequences for biological productivity and carbon cycling.

  14. Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions.

    Science.gov (United States)

    Swingedouw, Didier; Ortega, Pablo; Mignot, Juliette; Guilyardi, Eric; Masson-Delmotte, Valérie; Butler, Paul G; Khodri, Myriam; Séférian, Roland

    2015-01-01

    While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Here we show that the subset of CMIP5 historical climate simulations that produce such bidecadal variability exhibits a robust synchronization, with a maximum in Atlantic Meridional Overturning Circulation (AMOC) 15 years after the 1963 Agung eruption. The mechanisms at play involve salinity advection from the Arctic and explain the timing of Great Salinity Anomalies observed in the 1970s and the 1990s. Simulations, as well as Greenland and Iceland paleoclimate records, indicate that coherent bidecadal cycles were excited following five Agung-like volcanic eruptions of the last millennium. Climate simulations and a conceptual model reveal that destructive interference caused by the Pinatubo 1991 eruption may have damped the observed decreasing trend of the AMOC in the 2000s. Our results imply a long-lasting climatic impact and predictability following the next Agung-like eruption. PMID:25818017

  15. Persistent positive North Atlantic oscillation mode dominated the Medieval Climate Anomaly.

    Science.gov (United States)

    Trouet, Valérie; Esper, Jan; Graham, Nicholas E; Baker, Andy; Scourse, James D; Frank, David C

    2009-04-01

    The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña-like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA. PMID:19342585

  16. Low-frequency variability of meridional transport in the divergence zone of the North Atlantic subtropical and subpolar gyres. The WOCE section A2; Niederfrequente Variabilitaet meridionaler Transporte in der Divergenzzone des nordatlantischen Subtropen- und Subpolarwirbels. Der WOCE-Schnitt A2

    Energy Technology Data Exchange (ETDEWEB)

    Lorbacher, K.

    2000-07-01

    The subinertial, climate relevant variability of the large-scale ocean circulation in the northern North Atlantic and its integral key parameters such as the advective transports of mass (volume), heat and freshwater are determined from observations alone using the hydrographic data from seven realisations of the so-called '48 N'-section between the English Channel and the Grand Banks of Newfoundland. The data consist of five available sets of the WOCE/A2-section during the Nineties for the years 1993, 1994, 1996, 1997, 1998 and of two previous transatlantic cruises in April of 1957 and 1982. The realisations of the WOCE/A2-section were carried out in the same season (May to July), except for the cruise in October 1994. The '48 N'-section follows the divergence zone of the mainly wind-driven subtropical gyre and the more complex, with respect to the forcing, subpolar gyre. In the central Westeuropean and Newfoundland Basins the section runs a few degrees south of the line of zero wind stress curl (curl{sub z}{tau}). In the West, the WOCE/A2-section turns northwest to cross the boundary current regime perpendicularly. Therefore, this quasi-zonal hydrographic section covers all large-scale circulation elements on the regional scale that contribute essentially to the ocean circulation on the global scale - the Meridional Overturning Circulation (MOC). The transport estimates are given as the sum of the three transport components of a quasi-steady, large-scale ocean circulation: The ageostrophic Ekman-, and the two geostrophic components, the depth-independent, barotropic or Sverdrup- and the baroclinic component. To maintain the mass balance over the plane of the section the compensation of each component is assumed. In the case of the baroclinic component the balance is achieved through a suitable choice for a surface of 'no-motion'. The absolute meridional velocity as a function of the zonal distance along the section and depth is

  17. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates

    Directory of Open Access Journals (Sweden)

    M. Sarnthein

    2009-06-01

    Full Text Available A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern-Hemisphere Glaciation (NHG and of pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic and continue until today (Zachos et al., 2001. The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3 and 2.7 Ma (glacial MIS G6/4 (Lisiecki and Raymo, 2005. Various models (sensu Driscoll and Haug, 1998 and paleoceanographic records (intercalibrated using orbital age control suggest clear linkages between the onset of NHG and the three steps in the final closure of the Central American Seaways (CAS, deduced from rising salinity differences between Caribbean and the East Pacific. Each closing event led to an enhanced North Atlantic meridional overturning circulation and this strengthened the poleward transport of salt and heat (warmings of +2–3°C (Bartoli et al., 2005. Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia (Lunt et al., 2007, which probably led to an enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS, and an increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, new evidence shows that the closing of the CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC. Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~2 psu from 3.25/3.16–3.00 Ma, right after the first but still reversible attempt of closing the CAS.

  18. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates*

    Science.gov (United States)

    Sarnthein, M.; Prange, M.; Schmittner, A.; Schneider, B.; Weinelt, M.

    2009-01-01

    A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern Hemisphere Glaciation (NHG) and pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic, that and continue until today. The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3) and 2.7 Ma (glacial MIS G6/4). Various models and paleoceanographic records (intercalibrated using orbital age control) suggest clear linkages between the onset of NHG and three steps in the final closure of the Central American Seaways (CAS), deduced from rising salinity differences between Caribbean and East Pacific. Each closing event led to enhanced North Atlantic meridional overturning circulation and strengthened the poleward transport of salt and heat (warmings of +2-3°C). Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia, which led to enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS), and increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, the closing of CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC). Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~1 psu from 3.16-3.00 Ma, right after the first but still reversible attempt of closing the CAS.

  19. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates

    Science.gov (United States)

    Sarnthein, M.; Bartoli, G.; Prange, M.; Schmittner, A.; Schneider, B.; Weinelt, M.; Andersen, N.; Garbe-Schönberg, D.

    2009-06-01

    A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern-Hemisphere Glaciation (NHG) and of pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic and continue until today (Zachos et al., 2001). The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3) and 2.7 Ma (glacial MIS G6/4) (Lisiecki and Raymo, 2005). Various models (sensu Driscoll and Haug, 1998) and paleoceanographic records (intercalibrated using orbital age control) suggest clear linkages between the onset of NHG and the three steps in the final closure of the Central American Seaways (CAS), deduced from rising salinity differences between Caribbean and the East Pacific. Each closing event led to an enhanced North Atlantic meridional overturning circulation and this strengthened the poleward transport of salt and heat (warmings of +2-3°C) (Bartoli et al., 2005). Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia (Lunt et al., 2007), which probably led to an enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS), and an increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, new evidence shows that the closing of the CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC). Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~2 psu from 3.25/3.16-3.00 Ma, right after the first but still reversible attempt of closing the CAS.

  20. Overturning to the oil sector

    International Nuclear Information System (INIS)

    In only 11 months, the Mines and Energy Sector, especially with concerning to oil politics and to Ecopetrol it has given a total overturn, not only new economic conditions settled down to attract investment in the sector, the politics advanced in the activation of the environmental licenses and the consultations with the community. As for Ecopetrol bottom changes were made that guarantee their passive of pensions, disabling this way a fiscal bomb and the countable system was changed that will make that Ecopetrol counts the raw as a capitalization on the part of the Colombians guaranteeing an appropriate return to the petroleum that is given in administration

  1. Characteristics of Solar Meridional Flows

    Science.gov (United States)

    Basu, Sarbani; Antia, H. M.

    2011-01-01

    We have done a ring-diagram analysis of MDI full-disc data to determine the properties of solar meridional flow in the outer 2% of the Sun over the solar cycle 23. The meridional flows show a migrating pattern with higher-velocity flows migrating toward the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of the sunspot butterfly diagram and the zonal flows in the shallow layers. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that during the two minima. We also find that the dominant component of the meridional flows during solar maxima was much lower than that during the minima of solar cycles 23 and 24.

  2. Variability of the North Atlantic Current over the Common Era

    Science.gov (United States)

    Moffa Sanchez, P.; Hall, I. R.; Born, A.; Thornalley, D. J.; Barker, S.; Richter, T.

    2014-12-01

    Over the last 2000 years, the climate of the North Atlantic region was punctuated by centennial oscillations, which despite their small magnitude had important societal impacts, particularly in NW Europe. The most favoured explanations for this climate variability invoke changes in external forcings (such as solar activity and explosive volcanism) amplified by ocean and atmosphere feedbacks, mainly involving the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic Oscillation. However, the scarcity of highly resolved archives has hampered our understanding of the involvement of the ocean-atmosphere interactions in these climatic oscillations. We present a subdecadally resolved temperature and salinity record derived from paired Mg/Ca-δ18O measurements on planktonic foraminifera from a marine sediment core located in the pathway of the North Atlantic Current. Our findings show a strong centennial co-variability of the temperature and salinity of the surface limb of the AMOC with solar irradiance (Moffa-Sánchez et al. 2014- NGS). Climate model results from this study show a similar correlation over the last millennium and we infer that the hydrographic changes were linked to the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic, also known as blocking event, modifies the flow of the westerly winds. To further explore the response of the upper limb of the AMOC to solar forcing found in Moffa-Sánchez et al. 14, we synthesize new and available proxy-data from the North Atlantic Current in combination with analysis from CMIP5 simulations of the last millennium.

  3. No inter-gyre pathway for sea-surface temperature anomalies in the North Atlantic

    Science.gov (United States)

    Foukal, Nicholas P.; Lozier, M. Susan

    2016-04-01

    Recent Lagrangian analyses of surface drifters have questioned the existence of a surface current connecting the Gulf Stream (GS) to the subpolar gyre (SPG) and have cast doubt on the mechanism underlying an apparent pathway for sea-surface temperature (SST) anomalies between the two regions. Here we use modelled Lagrangian trajectories to determine the fate of surface GS water and satellite SST data to analyse pathways of GS SST anomalies. Our results show that only a small fraction of the surface GS water reaches the SPG, the water that does so mainly travels below the surface mixed layer, and GS SST anomalies do not propagate into the SPG on interannual timescales. Instead, the inter-gyre heat transport as part of the Atlantic Meridional Overturning Circulation must be accomplished via subsurface pathways. We conclude that the SST in the SPG cannot be predicted by tracking SST anomalies along the GS.

  4. Subsurface North Atlantic warming as a trigger of rapid cooling events: evidence from the early Pleistocene (MIS 31-19)

    Science.gov (United States)

    Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

    2015-04-01

    Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ18O measurements of Neogloboquadrina pachyderma (sinistral - sin.), deep-dwelling planktonic foraminifera, to estimate the subsurface temperatures and seawater δ18O from a sediment core from Gardar Drift, in the subpolar North Atlantic. Carbon isotopes of benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and seawater δ18O suggest increased subsurface temperatures and salinities during ice-rafting, likely due to northward subsurface transport of subtropical waters during periods of weaker Atlantic Meridional Overturning Circulation (AMOC). Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of IRD. Subsurface accumulation of warm waters would have resulted in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. The release of heat stored at the subsurface to the atmosphere would have helped to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during Marine Isotope Stage (MIS) 3.

  5. Low-frequency storminess signal at Bermuda linked to cooling events in the North Atlantic region

    Science.gov (United States)

    Hengstum, Peter J.; Donnelly, Jeffrey P.; Kingston, Andrew W.; Williams, Bruce E.; Scott, David B.; Reinhardt, Eduard G.; Little, Shawna N.; Patterson, William P.

    2015-02-01

    North Atlantic climate archives provide evidence for increased storm activity during the Little Ice Age (150 to 600 calibrated years (cal years) B.P.) and centered at 1700 and 3000 cal years B.P., typically in centennial-scale sedimentary records. Meteorological (tropical versus extratropical storms) and climate forcings of this signal remain poorly understood, although variability in the North Atlantic Oscillation (NAO) or Atlantic Meridional Overturning Circulation (AMOC) are frequently hypothesized to be involved. Here we present records of late Holocene storminess and coastal temperature change from a Bermudian submarine cave that is hydrographically circulated with the coastal ocean. Thermal variability in the cave is documented by stable oxygen isotope values of cave benthic foraminifera, which document a close linkage between regional temperature change and NAO phasing during the late Holocene. However, erosion of terrestrial sediment into the submarine cave provides a "storminess signal" that correlates with higher-latitude storminess archives and broader North Atlantic cooling events. Understanding the driver of this storminess signal will require higher-resolution storm records to disentangle the contribution of tropical versus extratropical cyclones and a better understanding of cyclone activity during hemispheric cooling periods. Most importantly, however, the signal in Bermuda appears more closely correlated with proxy-based evidence for subtle AMOC reductions than NAO phasing.

  6. Potential for seasonal prediction of Atlantic sea surface temperatures using the RAPID array at 26°N

    Science.gov (United States)

    Duchez, A.; Courtois, P.; Harris, E.; Josey, S. A.; Kanzow, T.; Marsh, R.; Smeed, D. A.; Hirschi, J. J.-M.

    2016-05-01

    The Atlantic meridional overturning circulation (AMOC) plays a critical role in the climate system and is responsible for much of the meridional heat transported by the ocean. In this paper, the potential of using AMOC observations from the 26°N RAPID array to predict North Atlantic sea surface temperatures is investigated for the first time. Using spatial correlations and a composite method, the AMOC anomaly is used as a precursor of North Atlantic sea-surface temperature anomalies (SSTAs). The results show that the AMOC leads a dipolar SSTA with maximum correlations between 2 and 5 months. The physical mechanism explaining the link between AMOC and SSTA is described as a seesaw mechanism where a strong AMOC anomaly increases the amount of heat advected north of 26°N as well as the SSTA, and decreases the heat content and the SSTA south of this section. In order to further understand the origins of this SSTA dipole, the respective contributions of the heat advected by the AMOC versus the Ekman transport and air-sea fluxes have been assessed. We found that at a 5-month lag, the Ekman component mainly contributes to the southern part of the dipole and cumulative air-sea fluxes only explain a small fraction of the SSTA variability. Given that the southern part of the SSTA dipole encompasses the main development region for Atlantic hurricanes, our results therefore suggest the potential for AMOC observations from 26°N to be used to complement existing seasonal hurricane forecasts in the Atlantic.

  7. Thermal evolution of the western South Atlantic and the adjacent continent during Termination 1

    Directory of Open Access Journals (Sweden)

    C. M. Chiessi

    2014-12-01

    Full Text Available During Termination 1, millennial-scale weakening events of the Atlantic meridional overturning circulation (AMOC supposedly produced major changes in sea surface temperatures (SST of the western South Atlantic, and in mean air temperatures (MAT over southeastern South America. It was suggested, for instance, that the Brazil Current (BC would strengthen (weaken and the North Brazil Current (NBC would weaken (strengthen during slowdown (speed-up events of the AMOC. This anti-phase pattern was claimed to be a necessary response to the decreased North Atlantic heat piracy during periods of weak AMOC. However, the thermal evolution of the western South Atlantic and the adjacent continent is largely unknown and a compelling record of the BC-NBC anti-phase behavior remains elusive. Here we address this issue, presenting high temporal resolution SST and MAT records from the BC and southeastern South America, respectively. We identify a warming in the western South Atlantic during Heinrich Stadial 1 (HS1, which is followed first by a drop and then by increasing temperatures during the Bølling–Allerød, in-phase with an existing NBC record. Additionally, a similar SST evolution is shown by a southernmost eastern South Atlantic record, suggesting a South Atlantic-wide pattern in SST evolution during most of Termination 1. Over southeastern South America, our MAT record shows a two-step increase during Termination 1, synchronous with atmospheric CO2 rise (i.e., during the second half of HS1 and during the Younger Dryas, and lagging abrupt SST changes by several thousand years. This delay corroborates the notion that the long duration of HS1 was fundamental to drive the Earth out of the last glacial.

  8. Mechanisms of the Internally Generated Decadal-to-Multidecadal Variability in the Atlantic

    Science.gov (United States)

    Chen, H.; Schneider, E. K.

    2011-12-01

    This study investigates the mechanisms of the internally generated decadal-to-multidecadal time scale SST variability in the Atlantic, including the North Atlantic Tripole variability, the Atlantic Multidecadal Variability and the Tropical Atlantic Variability, on the basis of a 300-year 1990 control simulation (CONTROL) made with CCSM3 and in an interactive ensemble version of CCSM3 (IE-CCSM3: 6 copies of AGCM coupled to the OGCM through the flux coupler). The structures, amplitudes and time scales of these three low frequency modes from CONTROL have properties similar to the observed variability, indicating that CCSM3 is appropriate for studying their mechanisms. These modes are closely related to the variability of the Atlantic Meridional Overturning Circulation (AMOC) on decadal time scales, suggesting that all of these types of variability may be manifestations of a single decadal "mode" of variability. To understand the low frequency modes and their interaction with each other, and the interaction among different oceanic regions, we isolate weather noise forcing from other mechanisms, including the coupled feedback, the gyre circulations, wave dynamics, and AMOC. The weather noise surface fluxes, including the net heat flux, wind stress and freshwater flux, are obtained from CONTROL by removing the SST forced surface fluxes, which are averaged from an ensemble of six AGCMs forced by the CONTROL SST. The IE-CCSM3 simulations in which the specified weather noise forcing is restricted to specific regions or in which the effects of the different specified surface fluxes are isolated are carried out to determine the contributions to the Atlantic decadal modes by region and by forcing type. Our results from the weather noise forced IE-CCSM3 simulations demonstrate that weather noise is responsible for most of decadal variability in the Atlantic and reveal the interactions between the three modes.

  9. An experimental study of the Atlantic variability on interdecadal timescales

    Directory of Open Access Journals (Sweden)

    M. Vincze

    2012-06-01

    Full Text Available A series of laboratory experiments has been carried out to model the basic dynamics of the multidecadal variability observed in North Atlantic sea surface temperature (SST records. According to the minimal numerical sector model introduced by te Raa and Dijkstra (2002, the three key components to excite such a low-frequency variability are rotation, meridional temperature gradient and additive thermal noise in the surface heat forcing. If these components are present, periodic perturbations of the overturning background flow are excited, leading to thermal Rossby mode like propagation of anomalous patches in the SST field. Our tabletop scale setup was built to capture this phenomenon, and to test whether the aforementioned three components are indeed sufficient to generate a low-frequency variability in the system. The results are compared to those of the numerical models, as well as to oceanic SST reanalysis records. To the best of our knowledge, the experiment described here is the very first to investigate the dynamics of the North Atlantic multidecadal variability in a laboratory-scale setup.

  10. The Sun's Shallow Meridional Circulation

    CERN Document Server

    Hathaway, David H

    2011-01-01

    The Sun's global meridional circulation is evident as a slow poleward flow at its surface. This flow is observed to carry magnetic elements poleward - producing the Sun's polar magnetic fields as a key part of the 11-year sunspot cycle. Current theories for the sunspot cycle assume that this surface flow is part of a circulation which sinks inward at the poles and turns equatorward at depths below 100 Mm. Here we use the advection of the Sun's convection cells by the meridional flow to map the flow velocity in latitude and depth. Our measurements show the largest cells clearly moving equatorward at depths below 35 Mm - the base of the Sun's surface shear layer. This surprisingly shallow return flow indicates the need for substantial revisions to solar/stellar dynamo theory.

  11. Model Sensitivity to North Atlantic Freshwater Forcing at 8.2 Ka

    Science.gov (United States)

    Morrill, Carrie; Legrande, Allegra Nicole; Renssen, H.; Bakker, P.; Otto-Bliesner, B. L.

    2013-01-01

    We compared four simulations of the 8.2 ka event to assess climate model sensitivity and skill in responding to North Atlantic freshwater perturbations. All of the simulations used the same freshwater forcing, 2.5 Sv for one year, applied to either the Hudson Bay (northeastern Canada) or Labrador Sea (between Canada's Labrador coast and Greenland). This freshwater pulse induced a decadal-mean slowdown of 10-25%in the Atlantic Meridional Overturning Circulation (AMOC) of the models and caused a large-scale pattern of climate anomalies that matched proxy evidence for cooling in the Northern Hemisphere and a southward shift of the Intertropical Convergence Zone. The multi-model ensemble generated temperature anomalies that were just half as large as those from quantitative proxy reconstructions, however. Also, the duration of AMOC and climate anomalies in three of the simulations was only several decades, significantly shorter than the duration of approx.150 yr in the paleoclimate record. Possible reasons for these discrepancies include incorrect representation of the early Holocene climate and ocean state in the North Atlantic and uncertainties in the freshwater forcing estimates.

  12. Meridional Considerations of the Centrifugal Compressor Development

    Directory of Open Access Journals (Sweden)

    C. Xu

    2012-01-01

    Full Text Available Centrifugal compressor developments are interested in using optimization procedures that enable compressor high efficiency and wide operating ranges. Recently, high pressure ratio and efficiency of the centrifugal compressors require impeller design to pay attention to both the blade angle distribution and the meridional profile. The geometry of the blades and the meridional profile are very important contributions of compressor performance and structure reliability. This paper presents some recent studies of meridional impacts of the compressor. Studies indicated that the meridional profiles of the impeller impact the overall compressor efficiency and pressure ratio at the same rotational speed. Proper meridional profiles can improve the compressor efficiency and increase the overall pressure ratio at the same blade back curvature.

  13. Meridional Considerations of the Centrifugal Compressor Development

    OpenAIRE

    Xu, C.; Amano, R. S.

    2012-01-01

    Centrifugal compressor developments are interested in using optimization procedures that enable compressor high efficiency and wide operating ranges. Recently, high pressure ratio and efficiency of the centrifugal compressors require impeller design to pay attention to both the blade angle distribution and the meridional profile. The geometry of the blades and the meridional profile are very important contributions of compressor performance and structure reliability. This paper presents some ...

  14. Western boundary circulation in the tropical Atlantic at 11°S revisited

    Science.gov (United States)

    Hummels, Rebecca; Brandt, Peter; Dengler, Marcus; Fischer, Jürgen

    2015-04-01

    The tropical Atlantic Ocean plays an important role for climate variability in the Atlantic region. A key region within the tropical Atlantic is the western boundary, where the variability of the North Brazil Undercurrent (NBUC) and the Deep Western Boundary Current (DWBC) supposedly exhibit variations of the meridional overturning circulation (AMOC) and the subtropical cells (STCs) on different time scales. The strength of boundary current fluctuation recently found in observational and modeling studies largely vary; however, the evidence of such fluctuations from direct observations is outstanding. Currently, the western boundary current system off the coast of Brazil at 11°S is investigated with a mooring array and ship based observations including direct current as well as hydrographic measurements. Together with several research cruises acquired between 1990 and 2004 and a similar mooring array installed between 2000 and 2004 at the same location, the new observational program aims at investigating interannual to decadal variability of the western boundary current system, its relation to AMOC and STC variability and its impact on tropical Atlantic variability. Here we present results from the first two research cruises in 2013 and 2014 as well as the first 10.5 months of moored observations in comparison to the observations a decade ago. It appears that the average transports of the NBUC and the DWBC have not changed significantly between the two observational periods. DWBC eddies, that were assumed to disappear with a weakening AMOC, are still present with similar characteristics. Observed patterns of water mass property changes on decadal timescale are associated with both, isopycnal heave and real water-mass modification of the temperature-salinity relationship.

  15. Atlantic Equatorial Deep Jets

    OpenAIRE

    Didwischus, Sven-Helge; Brandt, Peter; Greatbatch, Richard John

    2012-01-01

    The Equatorial Deep Jets (EDJ) are a dominant signal in the deep Atlantic at the equator. EDJs are vertical alternating zonal currents with a vertical wavelength of only a few hundred meters. They are found from below the Equatorial Undercurrent down to about 2500m. They were also observed in the Pacific and Indian Ocean. The EDJs are focused on the equator and have a meridional extent of about 1.5°S to 1.5°N. In the Atlantic, EDJs oscillate at a period of about 4.5 years as could be shown by...

  16. Simulated cold events in the northern North Atlantic during the last millennium

    Science.gov (United States)

    Moreno-Chamarro, Eduardo; Zanchettin, Davide; Lohmann, Katja; Jungclaus, Johann

    2014-05-01

    southward fresh water transport through the Denmark Strait reduce the sea-surface salinity and trigger reduced deep ocean mixing in the Labrador Sea. The consequent weakening of the Atlantic Meridional Overturning Circulation peaks well after the minimum of SST anomalies, allowing us to exclude, in contrast to former suggestions, the overturning circulation as a major triggering factor of such cold events. Cold SSTs and the weakened atmospheric circulation over the Labrador Sea force reduced ocean heat losses in the ocean basin, being the main cause of the cold anomalies over Greenland. The simulated climatic anomaly further entails sea-ice expansion along the eastern coast of Greenland. This would have reduced the trade and fishery in the region, thus increasing the stress on the Norse society during the time of its settlement demise over Greenland.

  17. A volcanically triggered regime shift in the subpolar North Atlantic ocean as a possible origin of the Little Ice Age

    Directory of Open Access Journals (Sweden)

    C. F. Schleussner

    2012-12-01

    Full Text Available Among the climatological events of the last millennium, the Northern Hemisphere Medieval Climate Anomaly (MCA, succeeded by the Little Ice Age (LIA are of exceptional importance. The origin of these regional climate anomalies remains however a subject of debate and besides external influences like solar and volcanic activity, internal dynamics of the climate system might have also played a dominant role. Here, we present transient last millennium simulations of the fully-coupled model Climber 3α forced with stochastically reconstructed wind fields. Our results indicate that short-lived volcanic eruptions might have triggered a cascade of sea-ice – ocean feedbacks in the North Atlantic, ultimately leading to a persistent regime shift in the ocean circulation. We find that an increase in the Nordic Sea sea-ice extent on decadal timescales as a consequence of major volcanic eruptions leads to a spin-up of the subpolar gyre (SPG and a weakened Atlantic Meridional Overturning Circulation, eventually causing a persistent, basin-wide cooling. These results highlight the importance of regional climate feedbacks such as a regime shift in the subpolar gyre circulation for past and future climate.

  18. A volcanically triggered regime shift in the subpolar North Atlantic Ocean as a possible origin of the Little Ice Age

    Directory of Open Access Journals (Sweden)

    C. F. Schleussner

    2013-06-01

    Full Text Available Among the climatological events of the last millennium, the Northern Hemisphere Medieval Climate Anomaly succeeded by the Little Ice Age are of exceptional importance. The origin of these regional climate anomalies remains a subject of debate and besides external influences like solar and volcanic activity, internal dynamics of the climate system might have also played a dominant role. Here, we present transient last millennium simulations of the fully coupled model of intermediate complexity Climber 3α forced with stochastically reconstructed wind-stress fields. Our results indicate that short-lived volcanic eruptions might have triggered a cascade of sea ice–ocean feedbacks in the North Atlantic, ultimately leading to a persistent regime shift in the ocean circulation. We find that an increase in the Nordic Sea sea-ice extent on decadal timescales as a consequence of major volcanic eruptions in our model leads to a spin-up of the subpolar gyre and a weakened Atlantic meridional overturning circulation, eventually causing a persistent, basin-wide cooling. These results highlight the importance of regional climate feedbacks such as a regime shift in the subpolar gyre circulation for understanding the dynamics of past and future climate.

  19. North Atlantic subpolar and subtropical gyres variability during the last 2000 years: a contribution to the THOR project.

    Science.gov (United States)

    Bouinot, Thomas; Cortijo, Elsa; Govin, Aline; Mulder, Thierry; Gonthier, Eliane

    2010-05-01

    Recent oceanographic measurements showed that the Atlantic Meridional Overturning Circulation (AMOC) underwent fluctuations in decadal period of time over the past. The causes of these fluctuations are still poorly understood, and available observations are too limited in time (few decades only) to investigate the detailed mechanisms. The Gulf Stream (GS), which actively transports heat from low to high latitudes, mainly in the first few hundred meters of the water column, could play an important role in the natural variability of the AMOC. This study aims at better constraining the variability of North Atlantic surface and subsurface waters over the last 2000 years, in order to improve our understanding of the links between AMOC oscillations and variations in the upper Atlantic heat content. This work is part of the European THOR (Thermohaline Overturning - at Risk?) project. Three cores are considered in key areas of the North Atlantic: (1) IMAGES core MD08-3182 (52°41.99'N, 35°56.15'W, 3757m) is located in the main pathway of the Gulf Stream in the Charlie Gibbs Fracture Zone, a key location for monitoring the subpolar gyre dynamics. (2) IMAGES core MD99-2203 (34°58.38N, 75°12.06'W-620m) off Cape Hatteras is well located to record the past variability of the GS. (3) Core CADI2KS12 (36°42.79'N, 08°31.39'W-1120m), from the Gulf of Cádiz, monitors the return current of the subtropical gyre. All cores are radiocarbon dated by AMS. In each core, the upper water column characteristics are reconstructed by complementary geochemical analysis: paired measurements of oxygen isotopic composition and trace elements ratio (Mg/Ca) in planktonic foraminifera are combined to reconstruct the seawater temperature and oxygen isotopic composition. Both surface and deep-dwelling species are considered to obtain temperature and oxygen isotopic composition records of the first few hundred meters of the water column. We will present our first results of the variability of the

  20. Meridional circulation in the Sun and stars

    CERN Document Server

    Kitchatinov, L L

    2016-01-01

    Mean-field hydrodynamics advanced to clear explanations for the origin and properties of the global meridional flow in stellar convection zones. Qualitative arguments and analysis of basic equations both show that the meridional circulation is driven by non-conservative centrifugal and buoyancy forces and results from a slight disbalance between these two drivers. The deviations from the thermal wind balance are relatively large near the boundaries of convection zones. Accordingly, the meridional flow attains its largest velocities in the boundary layers and decreases inside the convection zone. This picture, however, is neither supported nor dismissed by the conflicting results of recent helioseismic soundings or 3D numerical experiments. The relevant physics of the differential temperature and its possible relation to the solar oblateness are briefly discussed.

  1. Evolution of the deep Atlantic water masses since the last glacial maximum based on a transient run of NCAR-CCSM3

    Science.gov (United States)

    Marson, Juliana M.; Mysak, Lawrence A.; Mata, Mauricio M.; Wainer, Ilana

    2016-08-01

    During the last deglaciation (from approximately 21 to 11 thousand years ago), the high latitudes of the Atlantic Ocean underwent major changes. Besides the continuous warming, the polar and subpolar ocean surface received a large amount of meltwater from the retracting ice sheets. These changes in temperature and salinity affected deep waters, such as the Antarctic Bottom Water (AABW) and the North Atlantic Deep Water (NADW), which are formed in the Southern Ocean and in the northern North Atlantic, respectively. In this study, we present the evolution of the physical properties and distribution of the AABW and the NADW since the last glacial maximum using the results of a transient simulation with NCAR-CCSM3. In this particular model scenario with a schematic freshwater forcing, we find that modern NADW, with its characteristic salinity maximum at depth, was absent in the beginning of the deglaciation, while its intermediate version—Glacial North Atlantic Intermediate Water (GNAIW)—was being formed. GNAIW was a cold and relatively fresh water mass that dominated intermediate depths between 60 and 20°N. At this time, most of the deep and abyssal Atlantic basin was dominated by AABW. Within the onset of the Bølling-Allerød period, at nearly 15 thousand years ago (ka), GNAIW expanded southwards when the simulated Meridional Overturning Circulation overshoots. The transition between GNAIW and NADW ocurred after that, when AABW was fresh enough to allow NADW to sink deeper in the water column. When the NADW appears (~11 ka), AABW retracts and is constrained to lie near the bottom.

  2. Modelling the Seasonal Overturning Circulation in the Red Sea

    KAUST Repository

    Yao, Fengchao

    2015-04-01

    The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using 50-year, high-resolution MIT general circulation model simulations. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated, and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. For the winter overturning circulation, the climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24°N. The overturning is accomplished through a cyclonic recirculation and a cross-basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model\\'s winter overturning circulation.

  3. Atlantic forcing of Amazonian climates in the last ice age

    Science.gov (United States)

    Bush, M. B.; Mosblech, N.; Valencia, B. G.; Hodell, D. A.; Gosling, W. D.; Van Calsteren, P. W.; Thomas, L. E.; Curtis, J. H.

    2011-12-01

    An absence of study sites means that the relative influence of orbitally driven presession cycles and millenial scale variability upon ice-age Amazonian precipitation is unknown. Here we present a continuous isotopic (δO18 and C13) record spanning the period from ~93-8 ka, from the aseasonal forests of Amazonian Ecuador. The variability in δO18 depletion is probably related to the relative strength of evapotranspired moisture (less depleted) and tropical Atlantic moisture carried across the basin by the South American Low Level Jet (more depleted). Times of strengthened South American Low Level Jet probably correspond to increased overall moisture availability and hence elevated precipitation. The occurrence of markedly depleted δO18 signatures during Heinrich events suggests a strong influence of the Atlantic Ocean on this system, and that these northern hemispheric stadials induced wet episodes in western Amazonia. Weakening of the Atlantic Meridional Overturning Circulation (AMOC) has been suggested to strengthen the South American Low Level Jet. The isotopic records reveal strong cohesion with previously published records from southern Brazil. A precessional influence amplifies the north Atlantic signal between c. 93 ka and 50 ka. However, after c. 50 ka the precessional signal weakens, perhaps sugesting that at a critical size the Laurentide ice mass exerted a strong influence on Neotropical climates suppressing the weaker forcing associated with precession. Contrary to long-standing expectation, the Last Glacial Maximum (21 ± 2 ka) does not stand out as time of aridity in this record. However, between c. 35 ka and 18 ka there is a drift toward less depleted rainfall. One hypothesis to account for this observation is that the climate was becoming more seasonal as the Intertropical Convergence Zone (ITCZ) formed further south than its modern location. The resulting weakened influence of the South American Summer Monsoon (SASM) would probably reduce wet

  4. Initializing decadal climate predictions over the North Atlantic region

    Science.gov (United States)

    Matei, Daniela Mihaela; Pohlmann, Holger; Jungclaus, Johann; Müller, Wolfgang; Haak, Helmuth; Marotzke, Jochem

    2010-05-01

    Decadal climate prediction aims to predict the internally-generated decadal climate variability in addition to externally-forced climate change signal. In order to achieve this it is necessary to start the predictions from the current climate state. In this study we investigate the forecast skill of the North Atlantic decadal climate predictions using two different ocean initialization strategies. First we apply an assimilation of ocean synthesis data provided by the GECCO project (Köhl and Stammer, 2008) as initial conditions for the coupled model ECHAM5/MPI-OM. Hindcast experiments are then performed over the period 1952-2001. An alternative approach is one in which the subsurface ocean temperature and salinity are diagnosed from an ensemble of ocean model runs forced by the NCEP-NCAR atmospheric reanalyzes for the period 1948-2007, then nudge into the coupled model to produce initial conditions for the hindcast experiments. An anomaly coupling scheme is used in both approaches to avoid the hindcast drift and the associated initial shock. Differences between the two assimilation approaches are discussed by comparing them with the observational data in key regions and processes. We asses the skill of the initialized decadal hindcast experiments against the prediction skill of the non-initialized hindcasts simulation. We obtain an overview of the regions with the highest predictability from the regional distribution of the anomaly correlation coefficients and RMSE for the SAT. For the first year the hindcast skill is increased over almost all ocean regions in the NCEP-forced approach. This increase in the hindcast skill for the 1 year lead time is somewhat reduced in the GECCO approach. At lead time 5yr and 10yr, the skill enhancement is still found over the North Atlantic and North Pacific regions. We also consider the potential predictability of the Atlantic Meridional Overturning Circulation (AMOC) and Nordic Seas Overflow by comparing the predicted values to

  5. Construction of the adjoint MIT ocean general circulation model and application to Atlantic heat transport sensitivity

    Science.gov (United States)

    Marotzke, Jochem; Giering, Ralf; Zhang, Kate Q.; Stammer, Detlef; Hill, Chris; Lee, Tong

    1999-12-01

    We first describe the principles and practical considerations behind the computer generation of the adjoint to the Massachusetts Institute of Technology ocean general circulation model (GCM) using R. Giering's software tool Tangent-Linear and Adjoint Model Compiler (TAMC). The TAMC's recipe for (FORTRAN-) line-by-line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input. Then, the sensitivity of 1993 annual mean heat transport across 29°N in the Atlantic, to the hydrography on January 1, 1993, is calculated from a global solution of the GCM. The "kinematic sensitivity" to initial temperature variations is isolated, showing how the latter would influence heat transport if they did not affect the density and hence the flow. Over 1 year the heat transport at 29°N is influenced kinematically from regions up to 20° upstream in the western boundary current and up to 5° upstream in the interior. In contrast, the dynamical influences of initial temperature (and salinity) perturbations spread from as far as the rim of the Labrador Sea to the 29°N section along the western boundary. The sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model. Perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east-west density difference. Our results support the notion that boundary monitoring of meridional mass and heat transports is feasible.

  6. Trends of anthropogenic CO2 storage in North Atlantic water masses

    Directory of Open Access Journals (Sweden)

    P. Lherminier

    2010-01-01

    Full Text Available A high-quality inorganic carbon system database spanning over three decades (1981–2006 and comprising 13 cruises has allowed applying the φCT° method and coming up with accurate estimates of the anthropogenic CO2 (Cant stored in the main water masses of the North Atlantic. In the studied region, strong convective processes convey surface properties, like Cant, into deeper ocean layers and confer this region an added oceanographic interest from the point of view of air-sea CO2 exchanges. Commonly, a tendency for decreasing Cant storage rates towards the deep layers has been observed. In the Iberian Basin, the deep waters (North Atlantic Deep Water have low Cant values and negligible Cant storage rates, while the North Atlantic Central Water in the upper layers shows the largest Cant concentrations and capacity to increase its storage on a yearly basis (1.13±0.14 μmol kg−1 yr−1. This unmatched Cant storage capacity of the warm upper limb of the Meridional Overturning Circulation weakens towards the Irminger basin (0.68±0.06 μmol kg−1 yr−1 due to the lowering of the buffering capacity. The mid and deep waters in the Irminger Sea show rather homogeneous Cant storage rates (between 0.33 and 0.45 μmol kg−1 yr−1, whereas in the Iceland basin these layers seem to have been less affected by Cant. The Cant storage rates in the study region during the 1991–1997 high NAO (North Atlantic Oscillation phase are ~48% higher than during the 1997–2006 low NAO phase that followed. This result suggests that a net decrease in the strength of the North Atlantic sink of atmospheric CO2has taken place during the present decade. The changes in deep-water ventilation together with a detrimental renewal of the main water masses are likely the main driving processes causing this weakening of the North Atlantic CO2sink.

  7. Meridional circulation in turbulent protoplanetary disks

    CERN Document Server

    Fromang, Sebastien; Masset, Frederic

    2011-01-01

    Based on viscous disk theory, a number of recent studies have suggested the existence of a large scale meridional circulation in protoplanetary disks. Such a flow could account for the presence of crystalline silicates, among which Calcium and Aluminium-rich Inclusions (CAIs), at large distances from the sun. This paper aims at examining whether such large scale flows exist in turbulent protoplanetary disks. High resolution global hydrodynamical and magnetohydrodynamical numerical simulations of turbulent protoplanetary disks are used to infer the properties of the flow in such disks. By performing hydrodynamic simulations using explicit viscosity, we demonstrate that our numerical setup does not suffer from any numerical artifact. The aforementioned meridional circulation is readily recovered in viscous and laminar disks. In MHD simulations, the magneto-rotational instability drives turbulence in the disks. Averaging out the turbulent fluctuations over long timescale, the results fail to show any large scale...

  8. Meridional circulation in turbulent protoplanetary disks

    OpenAIRE

    Fromang, Sebastien; Lyra, Wladimir; Masset, Frederic

    2011-01-01

    Based on the viscous disk theory, a number of recent studies have suggested there is large scale meridional circulation in protoplanetary disks. Such a flow could account for the presence of crystalline silicates, including calcium- and aluminum-rich inclusions (CAIs), at large distances from the sun. This paper aims at examining whether such large-scale flows exist in turbulent protoplanetary disks. High-resolution global hydrodynamical and magnetohydrodynamical (MHD) numerical simulations o...

  9. Modes of winter precipitation variability in the North Atlantic

    Energy Technology Data Exchange (ETDEWEB)

    Zorita, E. [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Hydrophysik; Saenz, J.; Fernandez, J.; Zubillaga, J. [Bilbao Univ. (Spain)

    2001-07-01

    The modes of variability of winter precipitation in the North Atlantic sector are identified by Empirical Orthogonal Functions Analysis in the NCEP/NCAR global reanalysis data sets. These modes are also present in a gridded precipitation data set over the Western Europe. The large-scale fields of atmospheric seasonal mean circulation, baroclinic activity, evaporation and humidity transport that are connected to the rainfall modes have been also analyzed in order to investigate the physical mechanisms that are causally linked to the rainfall modes. The results indicate that the leading rainfall mode is associated to the North Atlantic oscillation and represents a meridional redistribution of precipitation in the North Atlantic through displacements of the storm tracks. The second mode is related to evaporation anomalies in the Eastern Atlantic that precipitate almost entirely in the Western Atlantic. The third mode seems to be associated to meridional transport of water vapor from the Tropical Atlantic. (orig.)

  10. Southern Meridional Atmospheric Circulation Associated with IOD

    Institute of Scientific and Technical Information of China (English)

    LIU Na; CHEN Hongxia

    2006-01-01

    Using the monthly wind and sea surface temperature (SST) data, southern meridional atmospheric circulation cells associated with the Indian Ocean Dipole Mode (IOD) events in the Indian Ocean are for the first time described and examined. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. During the four different phases of the positive IOD events, the anomalous meridional Hadley circulation over the western Indian Ocean shows that the air rises in the tropics, flows poleward in the upper troposphere, sinks in the subtropics, and returns back to the tropics in the lower troposphere. The anomalous Hadley circulation over the eastern Indian Ocean is opposite to that over the western Indian Ocean. During positive IOD events, the meridional Hadley circulation over the eastern Indian Ocean is weakened while it is strengthened over the western Indian Ocean. Correlation analysis between the IOD index and the indices of the Hadley cells also proves that, the atmospheric circulation patterns are evident in every IOD event over the period of record.

  11. Changing surface water conditions for the last 500 ka in the Southeast Atlantic: Implications for variable influences of Agulhas leakage and Benguela upwelling

    Science.gov (United States)

    Petrick, Benjamin F.; McClymont, Erin L.; Marret, Fabienne; Meer, Marcel T. J.

    2015-09-01

    The Southeast Atlantic Ocean is an important component of global ocean circulation, as it includes heat and salt transfer into the Atlantic through the Agulhas leakage as well as the highly productive Benguela upwelling system. Here we reconstruct sea surface temperatures (SSTs) from Ocean Drilling Program (ODP) Site 1087 in the Southeast Atlantic to investigate surface ocean circulation patterns during the late Pleistocene (0-500 ka). The UK'37 index and dinoflagellate cyst assemblages are used to reconstruct SSTs, δDalkenone is used to reconstruct changes in sea surface salinity, and mass accumulation rates of alkenones and chlorine pigments are quantified to detect changing marine export productivity. The greatest amplitude of SST warming precedes decreases in benthic δ18O and therefore occurs early in the transition from glacials to interglacials. The δDalkenone, as a salinity indicator, increases before SSTs, suggesting that the pattern of Agulhas leakage is more complex than suggested by SST proxies. Marine isotope stage (MIS) 10 shows an anomalous pattern: it is marked by a pronounced increase in chlorine concentration, which may be related to enhanced/expanded Benguela upwelling reaching the core site. We find no evidence of an absence of Agulhas leakage throughout the record, suggesting that there is no Agulhas cutoff even during MIS 10. Finally, the ODP Site 1087 record shows an increasing strength of Agulhas leakage towards the present day, which may have impacted the intensity of the Atlantic meridional overturning circulation. As a result, the new analyses from ODP Site 1087 demonstrate a complex interaction between influences of the Benguela upwelling and the Agulhas leakage through the late Pleistocene, which are inferred here to reflect changing circulation patterns in the Southern Ocean and in the atmosphere.

  12. Mixing and diffusion in intermittent overturning turbulence

    Science.gov (United States)

    Redondo, Jose M.; Mahjoub, Otman B.; Gonzalez-Nieto, Pilar L.; Lawry, Andrew

    2014-05-01

    The improvements in experimental methods and high resolution image analysis are nowadays able to detect subtle changes in the structure of the turbulence over a wide range of temporal and spatial scales [1], we compare the scaling shown by different mixing fronts driven by buoyancy that form a Rayleigh-Taylor mixing front. We use PIV and density front tracking in several experimental configurations akin to geophysical overturning [2-7]. We parametrize the role of unstable stratification by means of the Atwood number and compare both the scaling and the multifractal and the maximum local fractal structure functions of the different markers used to visualize the front. Both reactive and passive scalar tracers are used to investigate the mixing structure and the intermittency of the flow. Different initial conditions are compared and the mixing efficiency of the overal turbulent process evaluated [6-7]. An interesting approach, relating the Multi-Fractal dimension spectra, the intermittency and the spectral exponent is to find relationships that may be used to parameterise the sub-grid turbulence in terms of generalized diffusivities [4 ] that take into account the topology and the self-similarity of the Mixing RT and RM flows. As an example, a relationship between the diffusivity, the exponent β, the intermittency μ, and D(i), may be found for the volume fraction or the concentration, at the same time other locally measured parameters such as the enstrophy or the gradient alignment as well as their multi-fractal structures may turn out to be physically relevant indicators of the local turbulence and the mixing. Several methods of deriving local eddy diffusivity and local entrainment should give more realistic estimates of the spatial/temporal non-homogeneities (and intermittencies in the Kolmogorov 62 sense obtained as spatial correlations of the turbulent dissipation, or from structure functions) and these values may be used to parameterise turbulence at a variety

  13. Review experience on overturning prevention of NPP buildings in Switzerland

    International Nuclear Information System (INIS)

    Buildings with high ratios of the building height to the width of their foundations show a great potential for overturning. This problem occurs under large horizontal actions like Safe Shutdown Earthquake (SSE) or Aircraft Impact (AI). There are different concepts to prevent overturning under these actions. During the design process one concept has to be chosen and investigated. Therefore, calculations need to be done, which can be static or dynamic and linear or non-linear. In most concepts the resistance and the activation potential of the foundation soil are important for the overturning stability. Therefore, the definition of nominal values and design values of the soil has to be done carefully. In most of the cases field testing is required due to non-existing data of the soil. Namely the transmission of tensile forces to the underlying soil or rock has to be supported by experimental verification of the system's behaviour. This paper shows in the first place different possibilities of overturning prevention, which were used at NPP buildings in Switzerland. In the second place a case study of a recently investigated NPP site is presented. Thereby, the potentials and the limitations of static and linear dynamic analysis are discussed and special experiences with non-linear dynamic analysis for earthquake and aircraft scenarios are presented. (authors)

  14. A Linearized Convective Overturning Model for Prediction of Thunderstorm Movement.

    Science.gov (United States)

    Marroquin, Adrian; Raymond, David J.

    1982-01-01

    A linearized model of convective overturning in shear for prediction of storm propagation is presented. Good correspondence between the model and observation is found for a number of case studies of real storms. Supercell storms, however, are an exception-the tendency to move to the right of the mean winds is not reproduced.

  15. Seasonal overturning circulation in the Red Sea: 2. Winter circulation

    KAUST Repository

    Yao, Fengchao

    2014-04-01

    The shallow winter overturning circulation in the Red Sea is studied using a 50 year high-resolution MITgcm (MIT general circulation model) simulation with realistic atmospheric forcing. The overturning circulation for a typical year, represented by 1980, and the climatological mean are analyzed using model output to delineate the three-dimensional structure and to investigate the underlying dynamical mechanisms. The horizontal model circulation in the winter of 1980 is dominated by energetic eddies. The climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24N. The overturning is accomplished through a cyclonic recirculation and a cross-basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model\\'s winter overturning circulation. The simulated water exchange is not hydraulically controlled in the Strait of Bab el Mandeb; instead, the exchange is limited by bottom and lateral boundary friction and, to a lesser extent, by interfacial friction due to the vertical viscosity at the interface between the inflow and the outflow. Key Points Sinking occurs in a narrow boundary layer along the eastern boundary Surface western boundary current switches into an eastern boundary current Water exchange in the Strait of Bab el Mandeb is not hydraulically controlled © 2014. American Geophysical Union. All Rights Reserved.

  16. Optimization of Meridional Flow Channel Design of Pump Impeller

    OpenAIRE

    Miyauchi Sunao; Horiguchi Hironori; Fukutomi Jun-ichirou; Takahashi Akihiro

    2004-01-01

    The meridional flow channel design of a pump impeller affects its performance. However, since so many design parameters exist, a new design method is proposed in which a meridional and blade-to-blade flow channel is designed by the parallel use of the circulation distribution provided by the designer. Thus, an optimization method was used to design an axis-symmetrical meridional flow channel from the circulation distribution. In addition, the inverse design method proposed by Zangeneh et al. ...

  17. Currents, Geostrophic, Aviso, 0.25 degrees, Global, Meridional

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Aviso Meridional Geostrophic Current is inferred from Sea Surface Height Deviation, climatological dynamic height, and basic fluid mechanics.

  18. Acoustic streaming and Sun's meridional circulation

    Science.gov (United States)

    Valverde, Jose Manuel

    2016-09-01

    A vast number of physical processes involving oscillations of a bounded viscous fluid are relevantly influenced by acoustic streaming. When this happens a steady circulation of fluid develops in a thin boundary adjacent to the interface. Some examples are refracted sound waves, a fluid inside a spherical cavity undergoing torsional oscillations or a pulsating liquid droplet. Steady streaming around circular interfaces consists of a hemispherically symmetric recirculation of fluid from the equatorial plane to the polar axes closely resembling the meridional circulation pattern observed in the Sun's convection zone that determines the solar cycle. In this paper, it is argued that the acoustic pulsations exhibited by the Sun would lead to acoustic streaming in the boundary of the convection zone. A simple estimation using a typical dominant frequency of 3 mHz and the observed surface oscillation amplitude yields a steady streaming velocity us ∼ 10 m s‑1, which is on the order of the meridional circulation velocity observed in the Sun's convection zone.

  19. Creating a National Coalition to Address Tractor Overturn Fatalities.

    Science.gov (United States)

    Tinc, P J; Ayers, P D; May, J J; Purschwitz, M A; Sorensen, J A

    2015-04-01

    Tractor overturns continue to be the leading cause of death on U.S. farms. While rollover protective structures (ROPS) are effective in preventing these fatalities, they are underutilized due to a number of barriers. Past programs in the U.S. and abroad have targeted this area of agricultural safety; however, a national program is not yet in place for U.S. farmers. This study seeks to build a national partnership to address tractor overturn fatalities by increasing the number of tractors with ROPS. A diverse, multisector steering committee has been organized and is working together using Whole System in a Room methods. This method brings together partners from nine stakeholder groups to identify and commit to a collaborative solution to the issue. PMID:26204786

  20. Could massive Arctic sea ice export to the North Atlantic be the real cause of abrupt climate change during the last deglaciation?

    Science.gov (United States)

    Coletti, A. J.; Condron, A.

    2015-12-01

    Using a coupled ocean-sea ice model (MITgcm), we investigate whether the break-up and mobilization of thick, multiyear, Arctic sea ice might have supplied enough freshwater to the Nordic Seas to reduce North Atlantic Deep Water (NADW) formation and weaken the Atlantic Meridional Overturning Circulation (AMOC). Numerical simulations of a Last Glacial Maximum (LGM) environment show the potential for sea ice to grow to ~30m thick, storing ~1.41x105 km3 of freshwater as sea ice in the Arctic (this is ~10 times the volume of freshwater stored in the modern-day Arctic). Releasing this volume of sea ice from the Arctic in 1-yr is equivalent to a high-latitude freshwater forcing of ~4.5 Sv, which is comparable (or larger) in magnitude to most meltwater floods emanating from land-based glacial lakes (e.g. Agassiz) during the last deglaciation. Opening of the Bering Strait and Barents Sea are two plausible mechanisms that may have initiated sea ice mobilization. Opening Bering Strait increases sea ice transport through the Fram Strait by 7% and results in a 22% weakening of AMOC for 2000 years and a >3°C warming in the Arctic basin at 800 m depth. Opening Barents Sea to simulate a collapse of the Fennoscandian ice sheet has little impact on Arctic sea ice and freshwater export to the North Atlantic, but weakens AMOC ~8%. In a simulation with both straits open there is a transition to near-modern sea ice circulation pattern and a 24% reduction in AMOC. Experiments with the Bering Strait open and sea ice artificially capped to 10 m show barely any difference to those when sea ice can grow to ~30m, suggesting that changes in topography have a much greater impact on AMOC than the freshwater forcing from sea ice melting in the Nordic Seas.

  1. Extreme air-sea interaction over the North Atlantic subpolar gyre during the winter of 2013-2014 and its sub-surface legacy

    Science.gov (United States)

    Grist, Jeremy P.; Josey, Simon A.; Jacobs, Zoe L.; Marsh, Robert; Sinha, Bablu; Van Sebille, Erik

    2016-06-01

    Exceptionally low North American temperatures and record-breaking precipitation over the British Isles during winter 2013-2014 were interconnected by anomalous ocean evaporation over the North Atlantic subpolar gyre region (SPG). This evaporation (or oceanic latent heat release) was accompanied by strong sensible heat loss to the atmosphere. The enhanced heat loss over the SPG was caused by a combination of surface westerly winds from the North American continent and northerly winds from the Nordic Seas region that were colder, drier and stronger than normal. A distinctive feature of the air-sea exchange was that the enhanced heat loss spanned the entire width of the SPG, with evaporation anomalies intensifying in the east while sensible heat flux anomalies were slightly stronger upstream in the west. The immediate impact of the strong air-sea fluxes on the ocean-atmosphere system included a reduction in ocean heat content of the SPG and a shift in basin-scale pathways of ocean heat and atmospheric freshwater transport. Atmospheric reanalysis data and the EN4 ocean data set indicate that a longer-term legacy of the winter has been the enhanced formation of a particularly dense mode of Subpolar Mode Water (SPMW)—one of the precursors of North Atlantic Deep Water and thus an important component of the Atlantic Meridional Overturning Circulation. Using particle trajectory analysis, the likely dispersal of newly-formed SPMW is evaluated, providing evidence for the re-emergence of anomalously cold SPMW in early winter 2014/2015.

  2. A spatial cluster analysis of tractor overturns in Kentucky from 1960 to 2002

    Science.gov (United States)

    Saman, D.M.; Cole, H.P.; Odoi, A.; Myers, M.L.; Carey, D.I.; Westneat, S.C.

    2012-01-01

    Background: Agricultural tractor overturns without rollover protective structures are the leading cause of farm fatalities in the United States. To our knowledge, no studies have incorporated the spatial scan statistic in identifying high-risk areas for tractor overturns. The aim of this study was to determine whether tractor overturns cluster in certain parts of Kentucky and identify factors associated with tractor overturns. Methods: A spatial statistical analysis using Kulldorff's spatial scan statistic was performed to identify county clusters at greatest risk for tractor overturns. A regression analysis was then performed to identify factors associated with tractor overturns. Results: The spatial analysis revealed a cluster of higher than expected tractor overturns in four counties in northern Kentucky (RR = 2.55) and 10 counties in eastern Kentucky (RR = 1.97). Higher rates of tractor overturns were associated with steeper average percent slope of pasture land by county (p = 0.0002) and a greater percent of total tractors with less than 40 horsepower by county (ptractor overturns exist in Kentucky and identifies factors associated with overturns. This study provides policymakers a guide to targeted county-level interventions (e.g., roll-over protective structures promotion interventions) with the intention of reducing tractor overturns in the highest risk counties in Kentucky. ?? 2012 Saman et al.

  3. The global warming in the North Atlantic Sector and the role of the ocean

    Science.gov (United States)

    Hand, R.; Keenlyside, N. S.; Greatbatch, R. J.; Omrani, N. E.

    2014-12-01

    This work presents an analysis of North Atlantic ocean-atmosphere interaction in a warming climate, based on a long-term earth system model experiment forced by the RCP 8.5 scenario, the strongest greenhouse gas forcing used in the climate projections for the 5th Assessement report of the Intergovernmental Panel on Climate Change). In addition to a global increase in SSTs as a direct response to the radiative forcing, the model shows a distinct change of the local sea surface temperature (SST hereafter) patterns in the Gulf Stream region: The SST front moves northward by several hundred kilometers, likely as a response of the wind-driven part of the oceanic surface circulation, and becomes more zonal. As a consequence of a massive slowdown of the Atlantic Meridional Overturning Circulation, the northeast North Atlantic only shows a moderate warming compared to the rest of the ocean. The feedback of these changes on the atmosphere was studied in a set of sensitivity experiments based on the SST climatology of the coupled runs. The set consists of a control run based on the historical run, a run using the full SST from the coupled RCP 8.5 run and two runs, where the SST signal was deconstructed into a homogenous mean warming part and a local pattern change. In the region of the precipitation maximum in the historical run the future scenario shows an increase of absolute SSTs, but a significant decrease in local precipitation, low-level convergence and upward motion. Since warmer SSTs usually cause the opposite, this indicates that the local response in that region is connected to the (with respect to the historical run) weakened SST gradients rather than to the absolute SST. Consistently, the model shows enhanced precipitation north of this region, where the SST gradients are enhanced. However, the signal restricts to the low and mid-troposphere and does not reach the higher model levels. There is little evidence for a large-scale response to the changes in the Gulf

  4. Interannual to Decadal Climate Predictability in the North Atlantic: A Multi-Model-Ensemble Study

    OpenAIRE

    Collins, M.; Hadley Centre, Met Office, Exeter, United Kingdom; Botzet, M.; Max-Planck-Institut für Meteorologie, Hamburg, Germany; Carril, A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Drange, H.; Nansen Environmental and Remote Sensing Center, and Bjerknes Centre for Climate Research, Bergen, Norway; Jouzeau, A.; CERFACS, Toulouse, France; Latif, M.; Max-Planck-Institut für Meterologie, Hamburg, and Leibniz-Institut für Meereswissenschaften, Kiel, Germany; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Otteraa, O. H.; Nansen Environmental and Remote Sensing Center, and Bjerknes Centre for Climate Research, Bergen, Norway; Pohlmann, H.; Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada; Sorteberg, A.; Bjerknes Centre for Climate Research, Bergen, Norway; Sutton, R.; Centre for Global Atmospheric Modelling, Reading, United Kingdom; Terray, L.; CERFACS, Toulouse, France

    2006-01-01

    Ensemble experiments are performed with five coupled atmosphere–ocean models to investigate the potential for initial-value climate forecasts on interannual to decadal time scales. Experiments are started from similar model-generated initial states, and common diagnostics of predictability are used. We find that variations in the ocean meridional overturning circulation (MOC) are potentially predictable on interannual to decadal time scales, a more consistent picture of the surfac...

  5. Mechanisms of internally generated decadal-to-multidecadal variability of SST in the Atlantic Ocean in a coupled GCM

    Science.gov (United States)

    Chen, Hua; Schneider, Edwin K.; Wu, Zhiwei

    2016-03-01

    Mechanisms of the internally generated decadal-to-multidecadal variability of SST in the Atlantic Ocean are investigated in a long control simulation of the Community Climate System Model version 3 with constant external forcing. The interactive ensemble (IE) coupling strategy, with an ensemble of atmospheric GCMs (AGCM) coupled to an ocean model, a sea-ice model and a land model, is used to diagnose the roles of various processes in the coupled GCM (CGCM). The noise components of heat flux, wind stress and fresh water flux of the control simulation, determined from the CGCM surface fluxes by subtracting the SST-forced surface fluxes, estimated as the ensemble mean of AGCM simulations, are applied at the ocean surface of the IE in different regions and in different combinations. The IE simulations demonstrate that the climate variability in the control simulation is predominantly forced by noise. The local noise forcing is found to be responsible for the SST variability in the Atlantic Ocean, with noise heat flux and noise wind stress playing a critical role. The control run Atlantic multidecadal variability (AMV) index is decomposed into interannual, decadal and multidecadal modes based on the ensemble empirical mode decomposition. The AMV multidecadal mode, a combination of 50- and 100-year modes, is examined in detail. The North Atlantic Oscillation (NAO) pattern in the atmosphere, dominated by the noise component, forces the multidecadal mode through noise heat flux and noise wind stress. The noise wind stress forcing on the multidecadal mode is associated with ocean dynamics, including gyre adjustment and the Atlantic Meridional Overturning Circulation (AMOC). The AMV decadal mode is also found to be related to noise NAO forcing. The associated ocean dynamics are connected with both noise heat flux and noise wind stress, but the AMOC related to the decadal mode is more likely to be forced by noise heat flux. For both multidecadal and decadal modes, the

  6. Tropical North Atlantic subsurface warming events as a fingerprint for AMOC variability during Marine Isotope Stage 3

    Science.gov (United States)

    Parker, Andrew O.; Schmidt, Matthew W.; Chang, Ping

    2015-11-01

    The role of Atlantic Meridional Overturning Circulation (AMOC) as the driver of Dansgaard-Oeschger (DO) variability that characterized Marine Isotope Stage 3 (MIS 3) has long been hypothesized. Although there is ample proxy evidence suggesting that DO events were robust features of glacial climate, there is little data supporting a link with AMOC. Recently, modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical North Atlantic can be used to fingerprint a weakened AMOC during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics. To determine if AMOC variability played a role during the DO cycles of MIS 3, we present new, high-resolution Mg/Ca and δ18O records spanning 24-52 kyr from the near-surface dwelling planktonic foraminifera Globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera Globorotalia truncatulinoides in Southern Caribbean core VM12-107 (11.33°N, 66.63°W, 1079 m depth). Our subsurface Mg/Ca record reveals abrupt increases in Mg/Ca ratios (the largest equal to a 4°C warming) during the interstadial-stadial transition of most DO events during this period. This change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core. Additionally, our data support the conclusion reached by a recently published study from the Florida Straits that AMOC did not undergo significant reductions during Heinrich events 2 and 3. This record presents some of the first high-resolution marine sediment derived evidence for variable AMOC during MIS 3.

  7. Technical Note: Is radiation important for the high amplitude variability of the MOC in the North Atlantic?

    Directory of Open Access Journals (Sweden)

    D. Nof

    2007-09-01

    Full Text Available Radiation is of fundamental importance to climate modeling and it is customary to assume that it is also important for the variability of North Atlantic Deep Water (NADW formation and the meridional overturning cell (MOC. Numerous articles follow this scenario and incorporate radiation into the calculation. Using relatively old heat-flux maps based on measurements taken in the nineteen sixties, Sandal and Nof (2007 recently suggested that, even though the radiation terms are of the same order as the other heat-flux terms, they are not important for the variability of the NADW and the MOC. They proposed that only sensible and latent heat fluxes are important for the long-term variability of the convection, i.e., for processes such as Heinrich events, which supposedly correspond to turning convection on-and-off in the Atlantic.

    Here, we place this suggestion on a firmer ground by presenting new and accurate up-to-date heat flux maps that also suggest that the radiation is of no major consequence to the NADW variability. Also, we attribute the relative importance of sensible and latent heat fluxes and the contrasting negligible role of radiation to the fact that the latent and sensible heat fluxes are primarily proportional to the difference between the sea surface and the air temperature whereas the radiation is primarily proportional to the sea surface temperature, i.e., radiation is approximately independent of the atmospheric temperature. Due the small heat capacity ratio of air/water (1/4, the difference between the ocean temperature and the air temperature varies dramatically between the state of active and inactive MOC, whereas the ocean temperature by itself varies very modestly between a state of active and inactive convection.

  8. Regime shifts in the Arctic North Atlantic during the Neoglacial revealed by seabirds and precipitation isotopes on Bjørnøya, Svalbard

    Science.gov (United States)

    D'Andrea, William J.; Hormes, Anne; Bakke, Jostein; Nicolaisen, Line

    2016-04-01

    The northeastern North Atlantic Ocean, and the Norwegian and Greenland Seas are subject to large hydrographic changes. These variations can influence oceanic heat transport to the Arctic, meridional overturning circulation, and atmospheric circulation patterns and thereby impact global climate patterns. Marine records suggest that numerous large-scale changes in the hydrography of the northern North Atlantic took place during the middle to late Holocene. We report a record of nitrogen and hydrogen isotope measurements from a lake sediment core from Bjørnøya, Svalbard (74.38°N, 19.02°E) that documents major regime shifts in the climate of the northern North Atlantic during the past 6,000 years. Bjørnøya is the nesting ground for one of the largest seabird populations in the North Atlantic. As top predators in the marine ecosystem, seabirds (and their guano) are enriched in 15N; during spring and summer months they deliver isotopically enriched nitrogen to nesting areas. We developed a record of seabird population changes on Bjørnøya based on the nitrogen isotope composition of sediments in a core collected from lake Ellasjøen. The record reveals multiple multicentennial scale changes in δ15N values (varying between ~8-12‰) that track past changes in the size of seabird populations. From the same sediment core, we also developed a record of δD of precipitation, using δD values of sedimentary n-alkanes. Past intervals with the largest inferred bird populations correspond with the most enriched δD of precipitation, which we interpret to represent a more Atlantic climate. Periods with reduced seabird populations correspond with intervals with more negative δD of precipitation and representing a more Arctic climate. Together, the nitrogen and hydrogen isotope records signify regime shifts in the oceanography, marine ecosystem, and atmospheric circulation of the northern North Atlantic that are related to variations in the strength of the subpolar gyre.

  9. Meridional Transport in the Atmospheres of Earth and Mars

    CERN Document Server

    Soto, Alejandro

    2015-01-01

    As we continue to discover terrestrial exoplanets, many with orbital and planetary characteristics drastically different from anything encountered in our solar system, we are likely to encounter 'exotic' atmospheric transport processes. As an example, we show an analysis of meridional transport from simulations Mars. These simulations provide insight into the differences in meridional transport between Earth and Mars, particularly through the role of a condensation flow. The differences between Earth and Mars are a reminder that there may be a wide variety of meridional transport processes at work across the range of observed terrestrial planets.

  10. Zonal drifts of irregularities imparted by meridional winds.

    Science.gov (United States)

    Waldman, H.; Da Rosa, A. V.

    1973-01-01

    In a uniform ionosphere, meridional winds cause only meridional motions of irregularities. It is shown, however, that, if F-region irregularities are considered in a real ionosphere in which there is a highly conductive E-layer, zonal motions occur. During the day a substantial westward drift takes place, while at night the drift is eastward but smaller, owing to the much smaller E-layer conductivity. Thus, the effect of meridional winds is to impart a net westward drift to small irregularities in the ionization, provided such irregularities persist long enough.

  11. Impact of the seasonal cycle on the decadal predictability of the North Atlantic volume and heat transport under global warming

    Science.gov (United States)

    Fischer, Matthias; Müller, Wolfgang A.; Domeisen, Daniela I. V.; Baehr, Johanna

    2016-04-01

    The North Atlantic ocean circulation is projected to change considerably with future climate change. Here, we investigate whether changes in the North Atlantic meridional overturning circulation (AMOC) and the meridional heat transport (OHT) result in changes in their decadal predictability. In MPI-ESM-LR, we generate two hindcast ensembles with 20 start dates and 10 ensemble members per start date for (i) the present climate state in the CMIP5 historical simulation extended with RCP4.5 starting in 1995 and (ii) a future climate state in RCP4.5 starting in 2045. These two hindcast ensembles are compared against the historical simulation and RCP4.5 as control simulation, respectively, using the anomaly correlation coefficient (ACC) and the Brier skill score (BSS) decomposition in combination with reliability diagrams. The analysis is performed for yearly means and multiyear seasonal means of the AMOC and the OHT. Our results show a decrease in predictability of the AMOC and the OHT from the present climate state to the future climate state in RCP4.5. Both, changes in the AMOC and the OHT decadal predictability are largest at latitudes where the mean seasonal cycle of both AMOC and OHT is projected to change. For example around 25°N, the AMOC shows a reduction in the seasonal amplitude of about 0.5 Sv and a shift of up to 5 months in concert with a reduction in predictable lead times from up to 10 years to 2 years in the ACC. For the OHT, we find a reduction in the seasonal amplitude of about 0.1 PW and a shift of up to 5 months in concert with a reduction in predictable lead time from up to 4 years to 2 years in the ACC around 25°N. Similarly, the BSS and reliability diagrams show a reduction in skill from the present climate state to the future climate state. For multiyear seasonal means, summer months dominate the predictability in the present and future climate. Even though the changes in the decadal predictability of AMOC and OHT are small in general, their

  12. On the relationship between the Meridional Mode and the equatorial SST anomalies

    Science.gov (United States)

    Martín-Rey, Marta; Lazar, Alban

    2016-04-01

    The tropical Atlantic climate is dominated by two modes of variability at inter-annual time scales, the Equatorial Mode (EM) and the Meridional Mode (MM). They are characterized by specific Sea Surface Temperature anomalies (SSTA) distributions, respectively with a maximum over the central-eastern equator during boreal summer, and with an inter-hemispheric gradient during boreal spring. Although their structures, air-sea interactions and impacts have been widely studied, the processes associated to their development, and their connections, still remain a challenge. In the present work, we present a classification of MM events, regarding to their connections with the successive equatorial summer SSTA, associated with an EM or neutral conditions. The MM-I events display SSTA in North Tropical Atlantic (NTA) followed by a same sign summer equatorial SSTA. The MM-II events are related to NTA SSTA and successive equatorial summer SSTA of opposite sign. For both types, the spring north-eastern trades anomalies could generate SSTA impacting on the equatorial SSTA. Nevertheless, it is evidenced that the anomalous wind pattern shown along the equatorial band and South Tropical Atlantic is crucial to give rise, or not, to an EM. In order to further analyse the air-sea interactions and oceanic processes at work in the two different MM types, sensitivity experiments with different wind forcings are performed with the NEMO OGCM.

  13. Evaluation of overturning capacity of low level radioactive waste drum during earthquake. Part 1. Overturning capacity experiment by shaking table and its numerical analysis

    International Nuclear Information System (INIS)

    In the Niigataken Chuuetsu-oki earthquake in 2007 a lot of low level radioactive waste drums heaped up three layers or four layers at storage building were overturned on the storage-building floor in Kashiwazaki-Kariwa nuclear power plant. In this research shaking table test of the same type three layered and four layered waste drum models as overturned low level radioactive waste drums in Kashiwazaki-Kariwa nuclear power plant is carried out to clarify the mechanism of overturning drums and overturning capacity during earthquake. By this experiment the limit acceleration which is minimum value of input acceleration at storage building floor when three layered or four layered waste drums overturn is researched. Next effect of counter measure against overturn such as pallets connecting and drums binding by belt is examined. Numerical simulation of these experiments is conducted successfully by two-dimensional distinct element method and it is shown that analytical evaluation of overturning capacity by our method is available. (author)

  14. Meridional Transport in the Atmospheres of Earth and Mars

    OpenAIRE

    Soto, Alejandro

    2015-01-01

    As we continue to discover terrestrial exoplanets, many with orbital and planetary characteristics drastically different from anything encountered in our solar system, we are likely to encounter 'exotic' atmospheric transport processes. As an example, we show an analysis of meridional transport from simulations Mars. These simulations provide insight into the differences in meridional transport between Earth and Mars, particularly through the role of a condensation flow. The differences betwe...

  15. Characteristics of Solar Meridional Flows during Solar Cycle 23

    Science.gov (United States)

    Basu, Sarbani; Antia, H. M.

    2010-07-01

    We have analyzed available full-disk data from the Michelson Doppler Imager on board SOHO using the "ring diagram" technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius. We find that the dominant component of meridional flows during solar maximum was much lower than that during the minima at the beginning of cycles 23 and 24. There were differences in the flow velocities even between the two minima. The meridional flows show a migrating pattern with higher-velocity flows migrating toward the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of sunspot butterfly diagram and the zonal flows in the shallow layers. A high-latitude band in meridional flow appears around 2004, well before the current activity minimum. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that during the two minima. The different components of the flow have different time dependences, and the dependence is different at different depths.

  16. Characteristics of solar meridional flows during solar cycle 23

    CERN Document Server

    Basu, Sarbani

    2010-01-01

    We have analyzed available full-disc data from the Michelson Doppler Imager (MDI) on board SoHO using the "ring diagram" technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius. We find that the dominant component of meridional flows during solar maximum was much lower than that during the minima at the beginning of cycles 23 and 24. There were differences in the flow velocities even between the two minima. The meridional flows show a migrating pattern with higher-velocity flows migrating towards the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of sunspot butterfly diagram and the zonal flows in the shallow layers. A high latitude band in meridional flow appears around 2004, well before the current activity minimum. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that...

  17. Agulhas ring injection into the South Atlantic during glacials and interglacials

    Directory of Open Access Journals (Sweden)

    V. Zharkov

    2008-09-01

    Full Text Available Recent proxies suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA. This brought about a dramatic increase in the salt-influx (from the Indian Ocean into the SA helping re-start the then-collapsed meridional overturning cell (MOC, leading to the termination of the Younger Dryas (YD. Here, we propose a mechanism through which large variations in ring production take place.

    Using nonlinear analytical solutions for eddy shedding, we show that there are restricted possibilities for ring detachment when the coast is oriented in the north-south direction. We define a critical coastline angle below which there is rings shedding and above which there is almost no shedding. In the case of the Agulhas region, the particular shape of the African continent implies that rings can be produced only when the retroflection occurs beyond a specific latitude where the angle is critical. During glaciation, the wind stress curl (WSC vanished at a latitude lower than that of the critical angle, which prohibited the retroflection from producing rings. When the latitude at which the WSC vanishes migrated poleward towards its present day position, the corresponding coastline angle decreased below the critical angle and allowed for a vigorous production of rings.

    Simple process-oriented numerical simulations (using the Bleck and Boudra model are in satisfactory agreement with our results and enable us to affirm that, during the glacials, the behavior of the Agulhas Current (AC was similar to that of the modern East Australian Current (EAC, for which the coastline slant is supercritical.

  18. The Circum-Pacific Teleconnection Pattern in Meridional Wind in the High Troposphere

    Institute of Scientific and Technical Information of China (English)

    WANG Huijun

    2005-01-01

    The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR reanalysis data. The CPTP is found to be composed of the North Pacific-North American teleconnection pattern (PNA), the South Pacific-South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.

  19. Palaeoclimate: The dynamics of cold events

    Science.gov (United States)

    Meissner, Katrin J.

    2015-12-01

    The last glacial period and deglaciation were marked by abrupt, millennial-scale climate changes. Changes in the North Atlantic meridional overturning circulation were important contributors to rapid climate variability, but did not act alone.

  20. Passive tracers and active dynamics - a model study of hydrography and circulation in the northern North Atlantic

    OpenAIRE

    Mauritzen, C.; Hjøllo, Solfrid Sætre; Sandø, Anne Britt

    2006-01-01

    A long-standing problem in oceanography has been to understand the relationship between what can be measured in the ocean, such as hydrography, and what cannot, such as the strength and structure of the complete Meridional Overturning Circulation (MOC) of the world oceans, commonly considered the main oceanic long-term modifier of Earth’s climate. With the aid of a 50 year simulation from a numerical ice-ocean model we have investigated this relationship in the area of the...

  1. Reduced North Atlantic deep water coeval with the glacial Lake Agassiz freshwater outburst.

    Science.gov (United States)

    Kleiven, Helga Kikki Flesche; Kissel, Catherine; Laj, Carlo; Ninnemann, Ulysses S; Richter, Thomas O; Cortijo, Elsa

    2008-01-01

    An outstanding climate anomaly 8200 years before the present (B.P.) in the North Atlantic is commonly postulated to be the result of weakened overturning circulation triggered by a freshwater outburst. New stable isotopic and sedimentological records from a northwest Atlantic sediment core reveal that the most prominent Holocene anomaly in bottom-water chemistry and flow speed in the deep limb of the Atlantic overturning circulation begins at approximately 8.38 thousand years B.P., coeval with the catastrophic drainage of Lake Agassiz. The influence of Lower North Atlantic Deep Water was strongly reduced at our site for approximately 100 years after the outburst, confirming the ocean's sensitivity to freshwater forcing. The similarities between the timing and duration of the pronounced deep circulation changes and regional climate anomalies support a causal link. PMID:18063758

  2. North Atlantic Deep Water Production during the Last Glacial Maximum

    Science.gov (United States)

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Noble, Taryn L.; Mulitza, Stefan; Chiessi, Cristiano M.; Bayon, Germain

    2016-06-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial-interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.

  3. Whatever happened to the 'mad, bad' scientist? Overturning the stereotype.

    Science.gov (United States)

    Haynes, Roslynn D

    2016-01-01

    The cluster of myths relating to the pursuit of knowledge has perpetuated the archetype of the alchemist/scientist as sinister, dangerous, possibly mad and threatening to society's values. Shelley's Frankenstein provided imagery and a vocabulary universally invoked in relation to scientific discoveries and technological innovation. The reasons for the longevity of this seemingly antiquated, semiotic imagery are discussed. In the twenty-first century, this stereotype has been radically revised, even overturned. Scientists are now rarely objects of fear or mockery. Mathematicians, both real-life and fictional, are discussed here as being representative of scientists now depicted empathically. This article examines possible sociological reasons for this reversal; what the revisionist image suggests about society's changed attitudes to science; and what might be the substitute fears and sources of horror. PMID:24916194

  4. Estimates of volume, heat and freshwater budgets for the Arctic Mediterranean and North Atlantic in relation to the main physical processes: Insight from the EU-NACLIM observations

    Science.gov (United States)

    Rudels, Bert; Hansen, Bogi; Karstensen, Johannes; McCarthy, Gerard; Quadfasel, Detlef

    2016-04-01

    The EU NACLIM (North Atlantic Climate) project aims to understand the forcing of the North Atlantic circulation and its importance for the climate of northwestern Europe. NACLIM comprises extensive modelling studies of the atmosphere, ocean and climate, but here mainly the oceanographic observations are presented. The core observation areas are the North Atlantic Subpolar Gyre and the Greenland-Scotland Ridge, separating the North Atlantic from the Arctic Mediterranean Sea. These are the areas, where the waters of the lower limb of the Meridional Overturning Circulation (MOC) are formed and sink into the deep North Atlantic to return southward, mainly in the Deep Western Boundary Current (DWBC). The exchanges across the Greenland-Scotland Ridge, both the northward flowing Atlantic and the returning dense waters, have been monitored over decades, as have the circulation in the Subpolar gyre and the convection and mode water formation in the Labrador Sea. These studies are extended southward to the RAPID array located in the Subtropical gyre at 26oN to capture the MOC further south, and northward into the Arctic Mediterranean Sea and the formation area of the densest water in the DWBC. In the Subtropical gyre the ocean circulation is mainly forced by the wind, while in the Subpolar gyre the atmospheric influence, in addition to wind forcing, also has a large thermodynamic component, changing the characteristics of the water masses and the density structure of the gyre. The importance of cooling and freshwater input increases in the Arctic Mediterranean Sea. Variability and a recent declining trend of the MOC strength have been observed in the Subtropical gyre at the RAPID array. By contrast, both the northward flow across the Greenland-Scotland Ridge and the overflows have remained steady during the observation periods. An increased atmospheric freshwater flux does not appear to affect the dense water formation in the Arctic Mediterranean, mainly because the low

  5. Upper-level circulation in the South Atlantic Ocean

    Science.gov (United States)

    Peterson, Ray G.; Stramma, Lothar

    In this paper we present a literature survey of the South Atlantic's climate and its oceanic upper-layer circulation and meridional heat transport. The opening section deals with climate and is focused upon those elements having greatest oceanic relevance, i.e., distributions of atmospheric sea level pressure, the wind fields they produce, and the net surface energy fluxes. The various geostrophic currents comprising the upper-level general circulation are then reviewed in a manner organized around the subtropical gyre, beginning off southern Africa with the Agulhas Current Retroflection and then progressing to the Benguela Current, the equatorial current system and circulation in the Angola Basin, the large-scale variability adn interannual warmings at low latitudes, the Brazil Current, the South Atlantic Current, and finally to the Antarctic Circumpolar Current system in which the Falkland (Malvinas) Current is included. A summary of estimates of the meridional heat transport at various latitudes in the South Atlantic ends the survey.

  6. OPTIMIZATION METHOD ON IMPELLER MERIDIONAL CONTOUR AND 3D BLADE

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    An optimization method for 3D blade and meridional contour of centrifugal or mixed-flow impeller based on the 3D viscous computational fluid dynamics (CFD) analysis is proposed. The blade is indirectly parameterized using the angular momentum and calculated by inverse design method. The design variables are separated into two categories: the meridional contour design variables and the blade design variables. Firstly, only the blade is optimized using genetic algorithm with the meridional contour remained constant. The artificial neural network (ANN) techniques with the training sample data schemed according to design of experiment theory are adopted to construct the response relation between the blade design variables and the impeller performance. Then, based on the ANN approximated relation between the meridional contour design variables and impeller performance, the meridional contour is optimized. Fewer design variables and less calculation effort is required in this method that may be widely used in the optimization of three-dimension impellers. An optimized impeller in a mixed-flow pump, where the head and the efficiency are enhanced by 12.9% and 4.5% respectively, confirms the validity of this newly proposed method.

  7. An overturn-cyclic regime of the thermochemical two-mantle evolution

    Science.gov (United States)

    Kotelkin, V.; Lobkovsky, L.

    2009-04-01

    , spreads over the entire surrounding convective cell. In other words, an avalanche or a plume does not have own outer boundary, and its role is played by boundary of the surrounding convective cell. Thus, plume tectonics is incorporated into plate tectonics via common outer boundaries. On the contrary, during slow convection, chemical processes slow down or, if the temperature is insufficient, stop altogether and thermal convection is maintained solely. So chemical processes lead to a nonlinear impulsive regime of convection, they significantly affect the intermittent pattern of mantle convection, facilitating the overcoming of the 670-km endothermic phase barrier. The numerical experiment shows that regional avalanches are observed with the frequency of the geological Bertrand cycles (175 Myr). This result explains the modern seismic tomography data. The main result of our thermochemical modeling is the phenomena of mantle overturn. In case of critical density stratification between upper and lower mantle a new phenomena of self-organization of mantle convection was observed in numerical experiments which can be described as a one global mantle sink overturn flow (superavalanche). As the result this single sink leads to closure of oceans and assembling of continents. The stabilization of sink positions explains the asymmetry of the Earth and fixed placement (opposite sinks) of the Pacific Ocean. The cyclicity of sink formation results in migration of oceans of the atlantic type and supercontinent constructions, it explains the Wilson cycles. To reach critical stratification and realize the overturn-cyclic regime special condition of initial unstable equilibrium state of the mantle is necessary. Such initial state corresponds to new astrophysical data (Hf-W chronometry), i.e. the short time of hot planet accumulation. From the unstable initial state the mantle convection begins with power mantle overturn, and it repeats several times. A considerable time (650-900 Myr) is

  8. Regime shifts in the northern North Atlantic during the past 6,000 years: A record of seabird population size and precipitation isotopes on Bjørnøya, Svalbard

    Science.gov (United States)

    D'Andrea, W. J.; Hormes, A.; Bakke, J.; Nicolaisen, L.

    2015-12-01

    The northeastern North Atlantic Ocean, and the Norwegian and Greenland Seas are subject to large hydrographic changes. These variations can influence oceanic heat transport to the Arctic, meridional overturning circulation, and atmospheric circulation patterns and thereby impact global climate patterns. Marine records suggest that numerous large-scale changes in the hydrography of the northern North Atlantic took place during the middle to late Holocene. Here, we report a record of nitrogen and hydrogen isotope measurements from a lake sediment core from Bjørnøya, Svalbard (74.38°N, 19.02°E) that documents major regime shifts in the climate of the northern North Atlantic during the past 6,000 years. Bjørnøya is the nesting ground for one of the largest seabird populations in the North Atlantic. As top predators in the marine ecosystem, seabirds (and their guano) are enriched in 15N; during spring and summer months they deliver this isotopically enriched nitrogen to their nesting area. We developed a record of seabird population changes on Bjørnøya based on the bulk nitrogen isotope composition of sediments in a core collected from lake Ellasjøen. The record reveals multiple multicentennial scale changes in δ15N values (varying between ~8-12‰) that track past changes in the size of seabird populations. From the same sediment core, we also developed a record of δD of precipitation, by measuring δD values of sedimentary n-alkanes. Past intervals with the largest inferred bird populations correspond with the most enriched δD of precipitation, which we interpret to represent a more Atlantic climate. Periods with reduced seabird populations correspond with intervals having more negative δD of precipitation and representing a more Arctic climate. Together, the nitrogen and hydrogen isotope records signify regime shifts in the oceanography, marine ecosystem, and atmospheric circulation of the northern North Atlantic that are related to variations in the

  9. Frequency and severity of injuries to operators during overturns of farm tractors.

    Science.gov (United States)

    Cole, H P; Myers, M L; Westneat, S C

    2006-05-01

    Previous estimates of operator death from farm tractor overturn events range from 0.03 to 0.68. This study provided population-based estimates of the denominator of total farm tractor overturns and the frequency of six classes of overturn injury outcomes for tractors with and without rollover protective structures (ROPS). A 40-item telephone survey collected information from a random sample of 6,063 (8.0%) Kentucky farms about each farm's most recent overturn. A total of 551 (9.1%) farms reported overturns, and 5,512 (90.1%) reported no overturns. Injury outcomes for 443 overturns of non-ROPS tractors and 89 ROPS tractors were distributed as follows: no or minor injury (non-ROPS: 70.43%; ROPS: 82.02%), outpatient treatment (non-ROPS: 21.90%; ROPS: 9.00%), hospital admission (non-ROPS: 15.35%; ROPS: 3.37%), temporary disability (non-ROPS: 13.54%; ROPS: 14.61%), permanent disability (non-ROPS: 3.16%; ROPS: 0.00%), and death (non-ROPS: 5.42%; ROPS: 1.12%). (Percents total to more than 100 because some operators treated as outpatients were subsequently hospitalized, disabled, or died.) The observed 0.054 probability of death from overturn of non-ROPS tractors in this sample was corrected for the proportion of farms that went out of business prior to the survey and thus were excluded from the sampling frame. The adjusted 0.08 probability of death from overturn of a non-ROPS tractor is five times smaller than the NIOSH estimate of 0.40. The discrepancy lies in the much larger denominator of all non-fatal and fatal overturns than assumed previously. PMID:16724789

  10. Meridional Circulation in Solar and Stellar Convection Zones

    CERN Document Server

    Featherstone, Nicholas A

    2015-01-01

    We present a series of 3-D nonlinear simulations of solar-like convection, carried out using the Anelastic Spherical Harmonic (ASH) code, that are designed to isolate those processes that drive and shape meridional circulations within stellar convection zones. These simulations have been constructed so as to span the transition between solar-like differential rotation (fast equator/slow poles) and ``anti-solar' differential rotation (slow equator/fast poles). Solar-like states of differential rotation, arising when convection is rotationally constrained, are characterized by a very different convective Reynolds stress than anti-solar regimes, wherein convection only weakly senses the Coriolis force. We find that the angular momentum transport by convective Reynolds stress plays a central role in establishing the meridional flow profiles in these simulations. We find that the transition from single-celled to multi-celled meridional circulation profiles in strong and weak regimes of rotational constraint is lin...

  11. Estudios sobre la vegetacion del estado de Parana (Brasil meridional)

    OpenAIRE

    de Bolòs, Oriol; Cervi, Armando Carlos; Hatschbach, G. (Gert)

    1991-01-01

    BOLOS, O. DE, A.C. CERVI & G. HATSCHBACH (1991). Estudios sobre la vegetación del estado de Paraná (Brasil meridional). Collect. Bot. (Barcelona) 20: 79-182. Aportación al conocimiento de la vegetación del estado de Paraná en el Brasil meridional (Serra do Mar, Planaltos, valle del Iguacú). Se describen numerosas asociaciones vegetales agrupadas en las clases siguientes: Pistio-Eichhornietea (comunidades de cormófitas flotantes). Xyrido-Typhetea (vegetación herbácea helofítica). Polypodio-Til...

  12. A 20th-century reanalysis forced ocean model to recover North Atlantic climate variability from 1870-2007

    Science.gov (United States)

    Mueller, W.; Matei, D.; Bersch, M.; Jungclaus, J.; Lohmann, K.; Marotzke, J.

    2012-04-01

    The MPI ocean model MPIOM is forced with the NOAA 20th-century reanalysis to examine North Atlantic climate variability for the period 1870-2007. Ocean model results are compared with a gridded observational data base (CLISAP) for the later period (1950-2007, NCEP-period hereafter) and selected reconstructions for the earlier period (1870-1949, preNCEP-period). During the NCEP-period the forced MPIOM provides coherent decadal variability of temperature and salinity in the North Atlantic compared with observations. The Labrador Sea water properties follow the observed shift during the 1960s and 1990s and reversal afterwards. Sea water properties within the sub-polar gyre also capture observed decadal variability. The modeled Atlantic meridional overturning circulation (AMOC) at 26°N exhibits a time-mean maximum of ~17 Sv, which is within the current uncertainty range of the RAPID observations. During the first decades of the preNCEP-period sea water properties are substantially different compared to the NCEP-period. Salinity within the sub-polar gyre drops to -0.4PSU during from 1880-1910 and strongly increase afterwards. Similarly the AMOC strength is reduced to 12SV and increased to 17SV from the 1920s to the 1940s. This drop is found independent of the initialization of the forcing components suggesting responsible atmospheric forcing fields. Examination of the atmospheric forcing fields yields a weakened pressure gradient and respective geostrophic flow component over the northern European area during the preNCEP period. In association a weaker heat transport is found towards the Arctic area with considerable lower temperatures during the preNCEP period than for the NCEP period. Sea ice thickness and extent is largely increased within the preNCEP period throughout the Arctic and the Nordic Seas. Consequently more sea ice is transported along the Greenland current exporting large amount of fresh water into the Irminger and Labrador Sea. This fresh water release

  13. Meridional circulation and the lithium abundance gap in F stars

    International Nuclear Information System (INIS)

    The effect of meridional circulation on the time evolution of superficial abundances of helium, lithium, and beryllium in F stars is calculated in detail. It is shown that, as long as the presence of convection zones is assumed not to modify global meridional circulation patterns, the maximum equatorial rotational velocity allowing the settling of Li and He decreases rapidly with T(eff), going from 50 km/s at 7250 K to only 5 km/s at 6400 K. It is also shown that, for stars of the age of the Hyades with T(eff) less than 7000 K and rotational velocities larger than about 25 km/s, meridional circulation is rapid enough to bring to the surface matter that originally was deep enough to have been depleted of its Li through nuclear burning. Observational tests are suggested to distinguish between this scenario and the gravitational settling model or turbulent diffusion model. It is shown how the Li/Be ratio varies in the presence of transport by meridional circulation. 48 references

  14. Unipolar outflows and global meridional circulations in rotating accretion flows

    CERN Document Server

    Igumenshchev, I V

    1999-01-01

    Using two-dimensional simulations of non-radiative viscous rotating black hole accretion flows, we show that the flows with alpha~0.1-0.3 self-organize to form stationary unipolar or bipolar outflows accompanied by global meridional circulations. The required energy comes, with efficiency implications are discussed.

  15. Multi-Centennial Record of North Atlantic Freshwater Variability since the Little Ice Age Archived in Coralline Algal Ba/Ca

    Science.gov (United States)

    Chan, P. T. W.; Halfar, J.; Adey, W.; Zack, T.

    2014-12-01

    Declining Arctic sea-ice cover in recent decades has driven large-scale freshwater transport into the North Atlantic, possibly influencing the strength of the Meridional Overturning Circulation and even global climate. However, due to the lack of long-term oceanographic observations, little is known about the natural freshwater variability of the Northwestern Atlantic. Crustose coralline algae Clathromorphum compactum are extremely long-lived shallow marine calcareous plants that are abundant along the subarctic eastern Canadian coastline. They are particularly well-suited as recorders of paleoclimate signals due to the formation of annual growth increments, allowing for the precise calendar dating and geochemical sampling of hard tissue. Here, we provide the first annually-resolved multi-centennial record of coralline algal Ba/Ca from Labrador, Canada, as a proxy for North Atlantic freshwater variability extending well into the Little Ice Age (LIA) (1665 AD). Barium-to-calcium ratios (Ba/Ca) from coralline algae have previously been used as an indicator of freshwater runoff. This is because barium-rich clay sediments are transported by terrestrial runoff into coastal waters, and barium is released from the clay minerals upon encountering more alkaline elements present in seawater. We observe higher algal barium concentrations during the LIA, followed by a steady decline to recent times. In addition, coralline algal Ba/Ca shows significant positive relationships to Hudson Strait runoff, as well as Canadian Arctic and North Atlantic sea-ice extent. This suggests that more riverine Ba is transported from the Hudson Strait into the Labrador Sea during periods of increased sea-ice cover. Multiyear sea-ice can block incoming solar radiation thereby diminishing the effects of nutrient scavenging by phytoplankton, resulting in a more conservative transport of Ba into northern Labrador. However as sea-ice continues to thin, more sunlight is able to penetrate through the

  16. A flux-transport dynamo with a multi-cell meridional circulation

    Science.gov (United States)

    Bonanno, A.; Elstner, D.; Belvedere, G.; Rüdiger, G.

    2005-04-01

    We discuss the effect of a non-trivial meridional circulation pattern on a flux-transport type of solar dynamo. The critical value of the turbulent helicity and the periods are calculated as a function of the meridional flow strength. We found that the dynamo mechanism is mainly determined by the global topology of the meridional flow. In particular the equatorwards migration in the butterfly diagram can be easily obtained by the combined action of two cells of meridional circulation.

  17. Meridional flow velocities on solar-like stars with known activity cycles

    CERN Document Server

    Baklanova, Dilyara

    2014-01-01

    The direct measurements of the meridional flow velocities on stars are impossible today. To evaluate the meridional flow velocities on solar-like stars with stable activity periods, we supposed that during the stellar Hale cycle the matter on surfaces of stars passes the meridional way equivalent to $2\\pi R_\\star$. We present here the dependence of the mean meridional flow velocity on Rossby number, which is an effective parameter of the stellar magnetic dynamo.

  18. The Neutral Density Temporal Residual Mean overturning circulation

    Science.gov (United States)

    Stewart, A. L.; Thompson, A. F.

    2015-06-01

    Diagnosis of the ocean's overturning circulation is essential to closing global budgets of heat, salt and biogeochemical tracers. This diagnosis is sensitive to the choice of density variable used to distinguish water masses and identify transformations between them. The oceanographic community has adopted neutral density for this purpose because its isopycnal slopes are approximately aligned with neutral slopes, along which ocean flows tend to be confined. At high latitudes there are often no tenable alternatives because potential density varies non-monotonically with depth, regardless of the reference pressure. However, in many applications the use of isoneutral fluxes is impractical due to the high computational cost of calculating neutral density. Consequently neutral density-related diagnostics are typically not available as output from ocean models. In this article the authors derive a modified Temporal Residual Mean (TRM) approximation to the isoneutral mass fluxes, referred to as the Neutral Density Temporal Residual Mean (NDTRM). The NDTRM may be calculated using quantities that are routinely offered as diagnostic output from ocean models, making it several orders of magnitude faster than explicitly computing isoneutral mass fluxes. The NDTRM is assessed using a process model of the Antarctic continental shelf and slope. The onshore transport of warm Circumpolar Deep Water in the model ocean interior approximately doubles when diagnosed using neutral density, rather than potential density. The NDTRM closely approximates these explicitly-computed isoneutral mass fluxes. The NDTRM also exhibits a much smaller error than the traditional TRM in regions of large isoneutral temperature and salinity gradients, where nonlinearities in the equation of state diabatically modify the neutral density.

  19. Born Sensitivity Kernels in Spherical Geometry for Meridional Flows

    Science.gov (United States)

    Jackiewicz, Jason; Boening, Vincent; Roth, Markus; Kholikov, Shukur

    2016-05-01

    Measuring meridional flows deep in the solar convection zone is challenging because of their small amplitudes compared to other background signals. Typically such inferences are made using a ray theory that is best suited for slowly-varying flows. The implementation of finite-frequency Born theory has been shown to be more accurate for modeling flows of complex spatial structure in the near-surface region. Only until recently were such functions available in spherical geometry, which is necessary for applications to meridional flows. Here we compare these sensitivity kernels with corresponding ray kernels in a forward and inverse problem using numerical simulations. We show that they are suitable for inverting travel-time measurements and are more sensitive to small-scale variations of deep circulations.

  20. Meridional Circulation in Solar and Stellar Convection Zones

    OpenAIRE

    Featherstone, Nicholas A.; Miesch, Mark S.

    2015-01-01

    We present a series of 3-D nonlinear simulations of solar-like convection, carried out using the Anelastic Spherical Harmonic (ASH) code, that are designed to isolate those processes that drive and shape meridional circulations within stellar convection zones. These simulations have been constructed so as to span the transition between solar-like differential rotation (fast equator/slow poles) and ``anti-solar' differential rotation (slow equator/fast poles). Solar-like states of differential...

  1. Southern Ocean overturning, export production and climate variability over the past 1 Myr

    Science.gov (United States)

    Jaccard, S.; Hayes, C. T.; Martinez Garcia, A.; Galbraith, E. D.; Anderson, R. F.; Sigman, D. M.; Haug, G. H.

    2011-12-01

    Recently developed XRF core-scanning methods permit paleoceanographic reconstructions on time-scales similar to ice core temperature and atmospheric carbon dioxide measurements. We have investigated distribution of carbonate and biogenic barium (bioBa) - a proxy for integrated organic carbon export - in a sedimentary archive retrieved from the deep South Atlantic (ODP 1094, 53°S, 6°E, 2807 m) covering the past 1 Myr. These measurements are complemented with high-resolution, 230Th-normalized opal, bioBa and chlorin flux determinations spanning the last 150 kyrs. Our multi-proxy approach reveals that export production and biogenic carbonate preservation were tightly linked to atmospheric pCO2 reconstructions over the last 1 Myr. In particular, lukewarm interglacials (i.e. MIS 13-19) show generally lower organic matter export and reduced carbonate preservation when compared to more recent interglacials. This supports the critical contribution of Southern Ocean deglacial upwelling to modulate the partitioning of CO2 between the ocean interior and the atmosphere over the last million years, and immediately suggests that the moderate pCO2 increases during the lukewarm interglacials were due to a reduced dynamic range of Southern Ocean overturning. Changes in the vertical structure of the Southern Ocean water-column do not only prove to be crucial for the transitions from glacial to interglacial climate states. The decrease in upwelling following peak interglacial conditions leads the climate system to progressively converge towards colder, glacial conditions. Once a pCO2 threshold value of about 225 ppmv is reached, export production tends to stabilize around very low values, consistent with more strongly stratified conditions. This threshold also marks the abrupt inception of iron-rich mineral dust generation and deposition downwind of major South American dust sources, thereby catalyzing export production in the Subantarctic Zone of the Southern Ocean, to the north

  2. The Investigation of EM Scattering from the Time-Varying Overturning Wave Crest Model by the IEM

    Directory of Open Access Journals (Sweden)

    Xiao Meng

    2016-01-01

    Full Text Available Investigation of the electromagnetic (EM scattering of time-varying overturning wave crests is a worthwhile endeavor. Overturning wave crest is one of the reasons of sea spike generation, which increases the probability of false radar alarms and reduces the performance of multitarget detection in the environment. A three-dimensional (3D time-varying overturning wave crest model is presented in this paper; this 3D model is an improvement of the traditional two-dimensional (2D time-varying overturning wave crest model. The integral equation method (IEM was employed to investigate backward scattering radar cross sections (RCS at various incident angles of the 3D overturning wave crest model. The super phenomenon, where the intensity of horizontal polarization scattering is greater than that of vertical polarization scattering, is an important feature of sea spikes. Simulation results demonstrate that super phenomena may occur in some time samples as variations in the overturning wave crest.

  3. The Miocene Atlantic Ocean

    Science.gov (United States)

    Müller, R. D.; Herold, N.; Huber, M.

    2012-04-01

    warm Tethys outflow. An interesting model result concerns the importance of the geometry of reconstructed gateways. Regarding the Panama gateway we find only a small eastward throughflow, in contrast in contrast with other published estimates. The difference appears to be related to the exact orientation of the reconstructed gateway. A gateway oriented in a zonal direction results in a natural extension of the equatorial countercurrent, whereas a more meridionally oriented gateway, as in our reconstruction, largely prohibits such a current, emphasizing the effect of subtle model boundary conditions. A decreased northern hemisphere ocean heat transport in the Miocene compared to the present is a result of a significant weakening of North Atlantic Deep Water formation. Modelled flow into the Arctic Ocean is consistent with the idea of an enclosed estuarine sea. Coupled with a relatively deeper Greenland-Scotland Ridge it permits substantial Miocene ocean warming. Determining how this warming varied under changes in modelled bathymetry may elucidate ways in which near ice-free Arctic conditions were sustainable.

  4. A Procedure for Accurately Measuring the Shaker Overturning Moment During Random Vibration Tests

    Science.gov (United States)

    Nayeri, Reza D.

    2011-01-01

    Motivation: For large system level random vibration tests, there may be some concerns about the shaker's capability for the overturning moment. It is the test conductor's responsibility to predict and monitor the overturning moment during random vibration tests. If the predicted moment is close to the shaker's capability, test conductor must measure the instantaneous moment at low levels and extrapolate to higher levels. That data will be used to decide whether it is safe to proceed to the next test level. Challenge: Kistler analog formulation for computing the real-time moment is only applicable to very limited cases in which we have 3 or 4 load cells installed at shaker interface with hardware. Approach: To overcome that limitation, a simple procedure was developed for computing the overturning moment time histories using the measured time histories of the individual load cells.

  5. Paisatge i conflictes territorials a les comarques meridionals de Catalunya

    OpenAIRE

    Saladié Gil, Sergi

    2016-01-01

    Aquesta tesi doctoral analitza el paper del paisatge en els conflictes territorials que els darrers quinze anys han tingut lloc a les comarques meridionals de Catalunya, i reflexiona sobre la seva capacitat com a condicionador dels conflictes. Per assolir aquest objectiu, la investigació s’ha centrat en diversos aspectes clau. Primer, la tesi fa un repàs teòric als conceptes de conflicte territorial i paisatge, així com a les polítiques de paisatge desplegades a Catalunya els darrers anys....

  6. Instability of Meridional Axial System in f(R) Gravity

    CERN Document Server

    Sharif, M

    2015-01-01

    We analyze dynamical instability of non-static reflection axial stellar structure by taking into account generalized Euler's equation in metric $f(R)$ gravity. Such an equation is obtained by contracting Bianchi identities of usual anisotropic and effective stress-energy tensors, which after using radial perturbation technique gives modified collapse equation. In the realm of $R+\\epsilon R^n$ gravity model, we investigate instability constraints at Newtonian and post-Newtonian approximations. We find that instability of meridional axial self-gravitating system depends upon static profile of structure coefficients while $f(R)$ extra curvature terms induce stability to the evolving celestial body.

  7. Bed inventory overturn in a circulating fluid bed riser with pant-leg structure

    Energy Technology Data Exchange (ETDEWEB)

    Jinjing Li; Wei Wang; Hairui Yang; Junfu Lv; Guangxi Yue [Tsinghua University, Beijing (China). Key Laboratory for Thermal Science and Power Engineering of Ministry of Education

    2009-05-15

    The special phenomenon, nominated as bed inventory overturn, in circulating fluid bed (CFB) riser with pant-leg structure was studied with model calculation and experimental work. A compounded pressure drop mathematic model was developed and validated with the experimental data in a cold experimental test rig. The model calculation results agree well with the measured data. In addition, the intensity of bed inventory overturn is directly proportional to the fluidizing velocity and is inversely proportional to the branch point height. The results in the present study provide significant information for the design and operation of a CFB boiler with pant-leg structure. 15 refs., 10 figs., 1 tab.

  8. On the secondary meridional circulation associated with the quasi-biennial oscillation

    OpenAIRE

    Choi, Wookap; Lee, Hyunah; Grant, William B.; Park, Jae H.; HOLTON, JAMES R.; Lee, Kwang-Mog; Naujokat, Barbara

    2002-01-01

    Concentrations and distributions of stratospheric aerosol, hydrogen fluoride and ozone from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) are used to investigate features associated with transport by the secondary meridional circulation induced by the quasi-biennial oscillation (QBO). The points of maxima in the divergence and convergence of the QBO-induced meridional velocity at the equator are identified from the meridional gradients of the tra...

  9. Is a deep one-cell meridional circulation essential for the flux transport Solar Dynamo?

    OpenAIRE

    Hazra, Gopal; Karak, Bidya Binay; Choudhuri, Arnab Rai

    2013-01-01

    The solar activity cycle is successfully modeled by the flux transport dynamo, in which the meridional circulation of the Sun plays an important role. Most of the kinematic dynamo simulations assume a one-cell structure of the meridional circulation within the convection zone, with the equatorward return flow at its bottom. In view of the recent claims that the return flow occurs at a much shallower depth, we explore whether a meridional circulation with such a shallow return flow can still r...

  10. The role of meridional motions for the solar dynamo

    Science.gov (United States)

    Elstner, D.; Rüdiger, G.

    The dynamo equation is solved for the solar convection zone with the given (“observed”) rotation law and positive α-effect. If the latter exists in the entire convection zone the resulting dynamo shows strong toroidal field belts in the polar region migrating equatorwards. The same happens for α concentrated at the bottom of the convection zone but then we get too many belts with higher amplitude. The cycle period is always too short. Including meridional circulation which is directed equatorwards at the bottom of the convection zone (where the eddy diffusivity is reduced), the amplitude of the toroidal field grows and the butterfly diagram reaches low-latitudes. The cycle time approaches the solar value. The dynamo regime is highly sensitive to the interplay between flow and diffusivity at the bottom of the convection zone. Stationary solutions are not very seldom. For less active stars a slight increase of the cycle period with the rotation period is observed in agreement with the decrease of the meridional flow for faster rotation.

  11. Measuring Photospheric Rotational and Meridional Flows Using Magnetic Feature Tracking

    Science.gov (United States)

    Lamb, Derek

    2016-05-01

    Long-lived rotational and meridional flows are important ingredients of the solar cycle. Using magnetic field images to measure these flows on the solar surface has typically been performed by cross-correlating thin longitudinal strips or square patches across sufficiently long time gaps. Here, I use one month of SDO/HMI line-of-sight magnetic field observations, combined with the SWAMIS magnetic feature tracking algorithm to measure the motion of individual features in these magnetograms. By controlling for perturbations due to short-lived flows and due to false motions from feature interactions, I effectively isolate the long-lived flows traced by the magnetic features. This allows me to produce high-fidelity differential rotation measurements with well-characterized variances and covariances of the fit parameters. I also produce medium-fidelity measurements of the much weaker meridional flow that is broadly consistent with previous results, showing a peak flow of 16.7 m/s at 45 degrees latitude. This work shows that measuring the motions of individual features in photospheric magnetograms can produce high precision results in relatively short time spans, which suggests that high resolution non-longitudinally averaged photospheric velocity residual measurements could be produced to compare with coronal results, and to provide other diagnostics of the solar dynamo. This work has been partially supported by NASA Grants NNX11AP03G and NNX14AJ67G.

  12. Neural network analysis of overturning response under near-fault type excitation

    Science.gov (United States)

    Gerolymos, Nikos; Apostolou, Marios; Gazetas, George

    2005-12-01

    Under strong seismic excitation, a rigid block will uplift from its support and undergo rocking oscillations which may lead to (complete) overturning. Numerical and analytical solutions to this highly nonlinear vibration problem are first highlighted in the paper and then utilized to demonstrate how sensitive the overturning behavior is not only to the intensity and frequency content of the base motion, but also to the presence of strong pulses, to their detailed sequence, and even to their asymmetry. Five idealised pulses capable of representing “rupture-directivity” and “fling” affected ground motions near the fault, are utilized to this end: the one-cycle sinus, the one-cycle cosinus, the Ricker wavelet, the truncated (T)-Ricker wavelet, and the rectangular pulse “Overturning-Acceleration Amplification” and “Rotation” spectra are introduced and presented. Artificial neural network modeling is then developed as an alternative numerical solution. The neural network analysis leads to closed-form expressions for predicting the overturning failure or survival of a rigid block, as a function of its geometric properties and the characteristics of the excitation time history. The capability of the developed neural network modeling is validated through comparisons with the numerical solution. The derived analytical expressions could also serve as a tool for assessing the destructiveness of near-fault ground motions, for structures sensitive to rocking with foundation uplift.

  13. Seasonal overturning circulation in the Red Sea: 1. Model validation and summer circulation

    KAUST Repository

    Yao, Fengchao

    2014-04-01

    The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using high-resolution MIT general circulation model simulations. In the first part of this study, the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated, and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. In addition, during late summer two processes associated, respectively, with latitudinally differential heating and increased salinity in the southern Red Sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation. Dynamically, the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the Strait of Bab el Mandeb. Unlike some previous studies, the three-layer summer exchange flows in the Strait of Bab el Mandeb do not appear to be hydraulically controlled.

  14. An analytical framework for understanding tropical Meridional Modes

    CERN Document Server

    Martinez-Villalobos, Cristian

    2016-01-01

    A theoretical framework is developed for understanding the transient growth and propagation characteristics of thermodynamically coupled, meridional mode-like structures in the tropics. The model consists of a Gill-Matsuno type steady atmosphere under the longwave approximation coupled via a wind-evaporation-sea surface temperature (WES) feedback to a "slab" ocean model. When projected onto basis functions for the atmosphere the system simplifies to a non-normal set of equations that describes the evolution of individual sea surface temperature (SST) modes, with clean separation between symmetric and anti-symmetric modes. The following major findings result from analysis of the system: (i) a transient growth process exists whereby specific SST modes propagate toward lower order modes at the expense of the higher-order modes; (ii) the same dynamical mechanisms govern the evolution of symmetric and anti-symmetric SST modes except for the lowest-order wave number, where for symmetric structures the atmospheric K...

  15. Instability of meridional axial system in f(R) gravity

    Energy Technology Data Exchange (ETDEWEB)

    Sharif, M.; Yousaf, Z. [University of the Punjab, Department of Mathematics, Lahore (Pakistan)

    2015-05-15

    We analyze the dynamical instability of a non-static reflection axial stellar structure by taking into account the generalized Euler equation in metric f(R) gravity. Such an equation is obtained by contracting the Bianchi identities of the usual anisotropic and effective stress-energy tensors, which after using a radial perturbation technique gives a modified collapse equation. In the realm of the R + εR{sup n} gravity model, we investigate instability constraints at Newtonian and post-Newtonian approximations. We find that the instability of a meridional axial self-gravitating system depends upon the static profile of the structure coefficients, while f(R) extra curvature terms induce the stability of the evolving celestial body. (orig.)

  16. Is the Butterfly diagram due to meridional motions?

    Science.gov (United States)

    Rüdiger, G.; Elstner, D.

    2002-07-01

    The dynamo equation is solved for the solar convection zone with the given (``observed'') rotation law and positive \\alf-effect. If the latter exists in the entire convection zone the resulting dynamo shows strong toroidal field belts in the polar region migrating equatorwards. The same happens for alpha concentrated at the bottom of the convection zone but then we get too many belts with higher amplitude. The cycle period is always too short. Including meridional circulation which is directed equatorwards at the bottom of the convection zone (where the eddy diffusivity is reduced), the amplitude of the toroidal field grows and the butterfly diagram reaches low-latitudes. The cycle time approaches the solar value. The dynamo regime is highly sensitive to the interplay between flow and diffusivity at the bottom of the convection zone. Stationary solutions are not very seldom.

  17. Meridional Circulation in Solar and Stellar Convection Zones

    Science.gov (United States)

    Featherstone, Nicholas A.; Miesch, Mark S.

    2015-05-01

    We present a series of 3D nonlinear simulations of solar-like convection, carried out using the Anelastic Spherical Harmonic code, that are designed to isolate those processes that drive and shape meridional circulations (MCs) within stellar convection zones. These simulations have been constructed so as to span the transition between solar-like differential rotation (DR; fast equator/slow poles) and “anti-solar” DR (slow equator/fast poles). Solar-like states of DR, which arise when convection is rotationally constrained, are characterized by a very different convective Reynolds stress (RS) than anti-solar regimes, wherein convection only weakly senses the Coriolis force. We find that the angular momentum transport by convective RS plays a central role in establishing the meridional flow profiles in these simulations. We find that the transition from single-celled to multi-celled MC profiles in strong and weak regimes of rotational constraint is linked to a change in the convective RS, which is a clear demonstration of gyroscopic pumping. Latitudinal thermal variations differ between these different regimes, with those in the solar-like regime conspiring to suppress a single cell of MC, whereas the cool poles and warm equator established in the anti-solar states tend to promote single-celled circulations. Although the convective angular momentum transport becomes radially inward at mid-latitudes in anti-solar regimes, it is the MC that is primarily responsible for establishing a rapidly rotating pole. We conclude with a discussion of how these results relate to the Sun, and suggest that the Sun may lie near the transition between rapidly rotating and slowly rotating regimes.

  18. Meridional Circulation From Differential Rotation in an Adiabatically Stratified Solar/Stellar Convection Zone

    CERN Document Server

    Dikpati, Mausumi

    2013-01-01

    Meridional circulation in stellar convection zones is not generally well observed, but may be critical for MHD dynamos. Coriolis forces from differential rotation (DR) play a large role in determining what the meridional circulation is. Here we consider whether a stellar DR that is constant on cylinders concentric with the rotation axis can drive a meridional circulation.Conventional wisdom says that it can not. Using two related forms of governing equations that respectively estimate the longitudinal components of the curl of meridional mass flux and the vorticity, we show that such DR will drive a meridional flow. This is because to satisfy anelastic mass conservation, non-spherically symmetric pressure contours must be present for all DRs, not just ones that depart from constancy on cylinders concentric with the rotation axis. Therefore the fluid is always baroclinic if DR is present, because, in anelastic systems, the perturbation pressure must satisfy a Poisson type equation, as well as an equation of st...

  19. Pulsation-driven mean zonal and meridional flows in rotating massive stars

    CERN Document Server

    Lee, Umin; Neiner, Coralie

    2015-01-01

    Zonal and meridional axisymmetric flows can deeply impact the rotational and chemical evolution of stars. Therefore, momentum exchanges between waves propagating in stars, differential rotation, and meridional circulation must be carefully evaluated. In this work, we study axisymmetric mean flows in rapidly and initially uniformly rotating massive stars driven by small amplitude non-axisymmetric $\\kappa$-driven oscillations. We treat them as perturbations of second-order of the oscillation amplitudes and derive their governing equations as a set of coupled linear ordinary differential equations. This allows us to compute 2-D zonal and meridional mean flows driven by low frequency $g$- and $r$-modes in slowly pulsating B (SPB) stars and $p$-modes in $\\beta$ Cephei stars. Oscillation-driven mean flows usually have large amplitudes only in the surface layers. In addition, the kinetic energy of the induced 2-D zonal rotational motions is much larger than that of the meridional motions. In some cases, meridional f...

  20. Causes of a fresher, colder northern North Atlantic in late 20th century in a coupled model

    Science.gov (United States)

    Hu, Aixue; Meehl, Gerald A.; Han, Weiqing

    2007-05-01

    Observational evidence indicates that in the northern North Atlantic, especially in the Labrador Sea, almost the whole column of the ocean water is fresher, and colder in late 20th century than in 1950-1960s. Here we analyze a four-member ensemble of the 20th century simulations from a coupled climate model to examine the possible causes for these observed changes. The model simulations resemble the observed changes in the northern North Atlantic. The simulated results show that a decreased meridional freshwater divergence and an increased meridional heat divergence associated with a weaker thermohaline circulation in the North Atlantic are the primary causes for the freshening and cooling in the northern North Atlantic. The increased precipitation less evaporation tends to enforce the freshening, but the reduced sea ice flux into this region tends to weaken it. On the other hand, the surface warming induced by a higher atmospheric CO 2 concentration tends to heat up the northern North Atlantic, but is overcome by the cooling from increased meridional heat divergence.

  1. The Sliding and Overturning Analysis of Spent Fuel Storage Rack Based on Dynamic Analysis Model

    OpenAIRE

    Liu, Yu; Lu, Daogang; Wang, Yuanpeng; LIU, HONGDA

    2016-01-01

    Spent fuel rack is the key equipment for the storage of spent fuel after refueling. In order to investigate the performance of the spent fuel rack under the earthquake, the phenomena including sliding, collision, and overturning of the spent fuel rack were studied. An FEM model of spent fuel rack is built to simulate the transient response under seismic loading regarding fluid-structure interaction by ANSYS. Based on D’Alambert’s principle, the equilibriums of force and momentum were establis...

  2. The Sliding and Overturning Analysis of Spent Fuel Storage Rack Based on Dynamic Analysis Model

    Directory of Open Access Journals (Sweden)

    Yu Liu

    2016-01-01

    Full Text Available Spent fuel rack is the key equipment for the storage of spent fuel after refueling. In order to investigate the performance of the spent fuel rack under the earthquake, the phenomena including sliding, collision, and overturning of the spent fuel rack were studied. An FEM model of spent fuel rack is built to simulate the transient response under seismic loading regarding fluid-structure interaction by ANSYS. Based on D’Alambert’s principle, the equilibriums of force and momentum were established to obtain the critical sliding and overturning accelerations. Then 5 characteristic transient loadings which were designed based on the critical sliding and overturning accelerations were applied to the rack FEM model. Finally, the transient displacement and impact force response of rack with different gap sizes and the supporting leg friction coefficients were analyzed. The result proves the FEM model is applicable for seismic response of spent fuel rack. This paper can guide the design of the future’s fluid-structure interaction experiment for spent fuel rack.

  3. Bed-inventory Overturn Mechanism for Pant-leg Circulating Fluidized Bed Boilers

    CERN Document Server

    Wang, Zhe; Yang, Zhiwei; West, Logan; Li, Zheng

    2011-01-01

    A numerical model was established to investigate the lateral mass transfer as well as the mechanism of bed-inventory overturn inside a pant-leg circulating fluidized bed (CFB), which are of great importance to maintain safe and efficient operation of the CFB. Results show that the special flow structure in which the solid particle volume fraction along the central line of the pant-leg CFB is relative high enlarges the lateral mass transfer rate and make it more possible for bed inventory overturn. Although the lateral pressure difference generated from lateral mass transfer inhibits continuing lateral mass transfer, providing the pant-leg CFB with self-balancing ability to some extent, the primary flow rate change due to the outlet pressure change often disable the self-balancing ability by continually enhancing the flow rate difference. As the flow rate of the primary air fan is more sensitive to its outlet pressure, it is easier to lead to bed inventory overturn. While when the solid particle is easier to c...

  4. Rocking motion of structures under earthquakes. Overturning of 2-DOF system

    International Nuclear Information System (INIS)

    In recent years, huge earthquakes happen, for example, The South Hyogo prefecture Earthquake in 1995, The Mid Niigata Prefecture Earthquake in 2004, The Iwate-Miyagi Nairiku Earthquake in 2008. In The Niigataken Chuetsu-oki Earthquake in 2007, hundreds of drums fell down and water spilled out. A lot of studies about rocking behavior of rigid body had been performed from 1960's. However, these studies were only for a specific condition of the structure size or input vibration characteristics. Therefore, generalizes fall condition for earthquake is required. This paper deals with the analytical and the experimental study of the rocking vibration of 1-DOF rocking system, 2-DOF vibration-rocking system and 2-DOF rocking system under earthquakes. In this study, the equation of motion for each rocking systems are developed. The numerical model of 2-DOF rocking system is evaluated by free rocking experiment. In this paper, 'Overturning Map' which can distinguish whether structures falls or not is proposed. The overturning map of each rocking systems excited by the artificial earthquake wave calculated from the design spectrum is shown. As the result, overturning condition of structures is clarified. (author)

  5. On the variability of Florida Straits and wind driven transports at 26° N in the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    T. Kanzow

    2010-04-01

    Full Text Available Since April 2004 the RAPID array has made continuous measurements of the Atlantic Meridional Overturning Circulation (AMOC at 26° N. Two key components of this system are Ekman transport zonally integrated across 26° N and western boundary current transport in the Florida Straits. Whilst measurements of the AMOC as a whole are somewhat in their infancy, this study investigates what useful information can be extracted on the variability of the Ekman and Florida Straits transports using the decadal timeseries already available. Analysis is also presented for Sverdrup transports zonally integrated across 26° N. The seasonal cycles of Florida Straits, Ekman and Sverdrup transports are quantified at 26° N using harmonic analysis of annual and semi-annual constituents. Whilst Sverdrup transport shows clear semi-annual periodicity, calculations of seasonal Florida Straits and Ekman transports show substantial interannual variability due to variability at non-seasonal frequencies; the mean seasonal cycle for these transports only emerges from decadal length observations. The Florida Straits and Ekman mean seasonal cycles project on the AMOC with a combined peak-to-peak seasonal range of 3.5 Sv. The combined seasonal range for heat transport is 0.40 PW. The Florida Straits seasonal cycle possesses a smooth annual periodicity in contrast with previous studies suggesting a more asymmetric structure. No clear evidence is found to support significant changes in the Florida Straits seasonal cycle at sub-decadal periods. Whilst evidence of wind driven Florida Straits transport variability is seen at sub-seasonal and annual periods, model runs from the 1/4° eddy-permitting ocean model NEMO are used to identify an important contribution from internal oceanic variability at sub-annual and interannual periods. The Ekman transport seasonal cycle possesses less symmetric structure, due in part to different seasonal transport regimes east and west of 50 to 60

  6. Numerical simulation of the sensitivity of the Pacific subtropical-tropical meridional cell to global warming

    Institute of Scientific and Technical Information of China (English)

    ZHOU Tianjun; YU Yongqiang; LIU Hailong; LI Wei; YU Rucong

    2006-01-01

    Sensitivity of the Pacific subtropical-tropical meridional cell to global warming is examined by using a global ocean-atmosphere coupled model developed at LASG/IAP. Results indicate that associated with the increasing of atmospheric carbon dioxide, the most prominent signals of global warming locate at high latitudes, and the change of middle and low latitudes, in particular the surface wind, is relatively weak, which leads to a weak response of the Pacific subtropical-tropical meridional cell. At the time of atmospheric carbon dioxide doubling, the change of the meridional cell strength is smaller than the amplitude of natural variability.

  7. Meridional equatorial electrojet current in the American sector

    Directory of Open Access Journals (Sweden)

    R. G. Rastogi

    Full Text Available Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H is associated with a simultaneous increase of eastward geomagnetic field (Y. It is shown that during the counter electrojet period when ∆H is negative, ∆Y also becomes negative. Thus, the diurnal variation of ∆Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej. At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej, a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.

    Key words. Geomagnetism and paleomagnetism (dynamo theories · Ionosphere (equatorial ionosphere; ionosphere disturbances

  8. A global hybrid coupled model based on Atmosphere-SST feedbacks

    CERN Document Server

    Cimatoribus, Andrea A; Dijkstra, Henk A

    2011-01-01

    A global hybrid coupled model is developed, with the aim of studying the effects of ocean-atmosphere feedbacks on the stability of the Atlantic meridional overturning circulation. The model includes a global ocean general circulation model and a statistical atmosphere model. The statistical atmosphere model is based on linear regressions of data from a fully coupled climate model on sea surface temperature both locally and hemispherically averaged, being the footprint of Atlantic meridional overturning variability. It provides dynamic boundary conditions to the ocean model for heat, freshwater and wind-stress. A basic but consistent representation of ocean-atmosphere feedbacks is captured in the hybrid coupled model and it is more than ten times faster than the fully coupled climate model. The hybrid coupled model reaches a steady state with a climate close to the one of the fully coupled climate model, and the two models also have a similar response (collapse) of the Atlantic meridional overturning circulati...

  9. North Atlantic, ITCZ, and Monsoonal Climate Links

    Science.gov (United States)

    Haug, G. H.; Deplazes, G.; Peterson, L. C.; Brauer, A.; Mingram, J.; Dulski, P.; Sigman, D. M.

    2008-12-01

    Major element chemistry and color data from sediment cores in the anoxic Cariaco Basin off Venezuela record with (sub)annual resolution large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the last 80 ka. These data suggest a direct connection between the position of the ITCZ over northern South America, the strength of trade winds, and the temperature gradient to the high northern latitudes, ENSO, and monsoonal climate in Asia. The mechanisms behind these decadal-scale ITCZ-monsoon swings can be further explored at major climate transitions such as the onset of Younger Dryas cooling at ~12.7 ka, one of the most abrupt climate changes observed in ice core, lake and marine records in the North Atlantic realm and much of the Northern Hemisphere. Annually laminated sediments from ideally record the dynamics of abrupt climate changes since seasonal deposition immediately responds to climate and varve counts accurately estimate the time of change. We compare sub-annual geochemical data from a lake in Western Germany, which provides one of the best-dated records currently available for this climate transition, with the new the Cariaco Basin record and a new and higher resolution record from Lake Huguang Maar in China, and the Greenland ice core record. The Lake Meerfelder Maar record indicates an abrupt increase in storminess, occurring from one year to the next at 12,678 ka BP, coincident with other observed climate changes in the region. We interpret this shift of the wintertime winds to signify an abrupt change in the North Atlantic westerlies to a stronger and more zonal jet. The observed wind shift provides the atmospheric mechanism for the strong temporal link between North Atlantic overturning and European climate during the last deglaciation, tightly coupled to ITCZ migrations observed in the Cariaco Basin sediments, and a stronger east Asian Monsoon winter monsoon as seen in lake Huguang Maar, when cave stalagmite oxygen isotope data

  10. Decade time scale variability of ventilation in the North Atlantic: High-precision measurements of bomb radiocarbon in banded corals

    OpenAIRE

    Druffel, Ellen R. M.

    1989-01-01

    The first high-precision radiocarbon measurements for the upper ocean are presented for banded corals from two sites in the North Atlantic Ocean. The striking dissimilarities between the post-1950 records at Bermuda in the Sargasso Sea and the Florida Straits in the Gulf Stream illustrate the different mixing processes in the upper ocean at each site. Convective overturn associated with 18° degree water formation during late winter in the northern Sargasso Sea facilitates storage of considera...

  11. Decade time scale variability of ventilation in the North Atlantic: High-precision measurements of bomb radiocarbon in banded corals

    OpenAIRE

    Druffel, ER

    1989-01-01

    The first high-precision radiocarbon measurements for the upper ocean are presented for banded corals from two sites in the North Atlantic Ocean. The striking dissimilarities between the post-1950 records at Bermuda in the Sargasso Sea and the Florida Straits in the Gulf Stream illustrate the different mixing processes in the upper ocean at each site. Convective overturn associated with 18 ø degree water formation during late winter in the northern Sargasso Sea f...

  12. Wind Diffusivity Current, METOP ASCAT, 0.25 degrees, Global, Near Real Time, Meridional

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NOAA CoastWatch distributes near real time Ekman current (in zonal, meridional, and modulus sets) and Ekman upwelling data. This data begins with wind velocity...

  13. Wind Stress, METOP ASCAT, 0.25 degrees, Global, Near Real Time, Meridional

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NOAA CoastWatch distributes near real time wind stress data in zonal, meridional, modulus, and wind stress curl sets. This data begins with wind velocity...

  14. Wind Stress, QuikSCAT SeaWinds, 0.25 degrees, Global, Science Quality, Meridional

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NOAA CoastWatch distributes science quality wind stress data in zonal, meridional, modulus, and wind stress curl sets. This data begins with wind velocity...

  15. Currents, HF Radio-derived, SF Bay, 1 hr, Meridional, EXPERIMENTAL

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The data is the 1 hour average of the meridional component of ocean surface currents derived from High Frequency Radio-derived measurements. THIS IS AN EXPERIMENTAL...

  16. Variational inference of differential equations of vibrations of piezoceramic shell with meridional polarization

    Directory of Open Access Journals (Sweden)

    I. O. Lastivka

    2014-07-01

    Full Text Available A construction of one embodiment of refined theory of piezoceramic shell with the meridional polarization was proposed, a system of differential equations of membrane vibrations and the boundary conditions using the variational Reissner principle was obtained.

  17. Northern and southern water masses in the equatorial Atlantic: Distribution of nutrients on the WOCE A6 and A7 lines

    Digital Repository Service at National Institute of Oceanography (India)

    Oudot, C.; Morin, P.; Baurand, F.; Wafar, M.V.M.; Le Corre, P.

    In the framework of the WOCE Hydrographic Program, two trans-Atlantic CTDO/tracer sections with closely-spaced stations, along 7 degrees 30'N and 4 degrees 30'S (WHP Lines A6 and A7), and two meridional sections, along 3 degrees 50'W and 35 degrees...

  18. Ocean-atmosphere interaction in the seasonal to decadal variations of tropical Atlantic climate

    Science.gov (United States)

    Okumura, Yuko

    The tropical Atlantic ocean and atmosphere display distinct seasonal cycles with considerable year-to-year variations superimposed. The present study investigates processes and mechanisms important for tropical Atlantic climate and its variability, using numerical models and observational data, with an emphasis on ocean-atmosphere interaction. For the seasonal cycle, topics of particular interest are the rapid development of the monsoon-cold tongue complex in boreal summer and the oceanic response to the secondary acceleration of equatorial easterly winds in November; for interannual-to-decadal variability, they are the effect of the November thermocline shoaling on the equatorial zonal mode and the atmospheric response to the meridional sea surface temperature (SST) dipole mode. Atmospheric model experiments indicate that interaction between the equatorial cold tongue and the West African monsoon is essential for the rapid seasonal transition from boreal spring to summer. Mechanisms are identified for the summertime acceleration of equatorial easterly wind, which contributes to rapid equatorial cooling by forcing upwelling and thermocline shoaling. Analysis of high-resolution satellite/in-situ data reveals the equatorial SST change associated with the November easterly wind acceleration and thermocline shoaling. This overlooked climatic feature is further shown to give rise to a new mode of tropical Atlantic variability---Atlantic Nino II---which resembles the boreal summer zonal mode but peaks in November--December, and is statistically independent of the preceding summer events. Atlantic Nino II significantly affects interannual rainfall variations in the coastal Congo-Angola region, and evolves into the meridional mode in the following spring, affecting rainfall variations in northeast Brazil. It thus fills an important climate predictability gap in time, during the season for which the local variability was otherwise poorly understood. The atmospheric model

  19. Meridional lenticular astigmatism associated with bilateral concurrent uveal metastases in renal cell carcinoma

    OpenAIRE

    Priluck JC; Grover S; Chalam KV

    2012-01-01

    Joshua C Priluck, Sandeep Grover, KV ChalamDepartment of Ophthalmology, University of Florida College of Medicine, Jacksonville, FL, USAPurpose: To demonstrate a case illustrating meridional lenticular astigmatism as a result of renal cell carcinoma uveal metastases.Methods: Case report with images.Results: Clinical findings and diagnostic testing of a patient with acquired meridional lenticular astigmatism are described. The refraction revealed best-corrected visual acuity of 20/20&ndash...

  20. Interpreting the implied meridional oceanic energy transport in AMIP

    Energy Technology Data Exchange (ETDEWEB)

    Randall, D.A. [Colorado State Univ., Fort Collins, CO (United States); Gleckler, P.J. [Lawrence Livermore National Lab., CA (United States)

    1993-09-01

    The Atmospheric Model Intercomparison Project (AMIP) was outlined in Paper No. CLIM VAR 2.3 (entitled {open_quote}The validation of ocean surface heat fluxes in AMIP`) of these proceedings. Preliminary results of AMIP subproject No. 5 were also summarized. In particular, zonally averaged ocean surface heat fluxes resulting from various AMIP simulations were intercompared, and to the extent possible they were validated with uncertainties in observationally-based estimates of surface heat fluxes. The intercomparison is continued in this paper by examining the Oceanic Meridional Energy Transport (OMET) implied by the net surface heat fluxes of the AMIP simulations. As with the surface heat fluxes of the AMIP simulations. As with the surface heat fluxes, the perspective here will be very cursory. The annual mean implied ocean heat transport can be estimated by integrating the zonally averaged net ocean surface heat flux, N{sub sfc}, from one pole to the other. In AGCM simulations (and perhaps reality), the global mean N{sub sfc} is typically not in exact balance when averaged over one or more years. Because of this, an important assumption must be made about changes in the distribution of energy in the oceans. Otherwise, the integration will yield a non-zero transport at the endpoint of integration (pole) which is not physically realistic. Here the authors will only look at 10-year means of the AMIP runs, and for simplicity they assume that any long term imbalance in the global averaged N{sub sfc} will be sequestered (or released) over the global ocean. Tests have demonstrated that the treatment of how the global average energy imbalance is assumed to be distributed is important, especially when the long term imbalances are in excess of 10 W m{sup {minus}2}. However, this has not had a substantial impact on the qualitative features of the implied heat transport of the AMIP simulations examined thus far.

  1. Interpreting the implied meridional oceanic energy transport in AMIP

    International Nuclear Information System (INIS)

    The Atmospheric Model Intercomparison Project (AMIP) was outlined in Paper No. CLIM VAR 2.3 (entitled open-quote The validation of ocean surface heat fluxes in AMIP') of these proceedings. Preliminary results of AMIP subproject No. 5 were also summarized. In particular, zonally averaged ocean surface heat fluxes resulting from various AMIP simulations were intercompared, and to the extent possible they were validated with uncertainties in observationally-based estimates of surface heat fluxes. The intercomparison is continued in this paper by examining the Oceanic Meridional Energy Transport (OMET) implied by the net surface heat fluxes of the AMIP simulations. As with the surface heat fluxes of the AMIP simulations. As with the surface heat fluxes, the perspective here will be very cursory. The annual mean implied ocean heat transport can be estimated by integrating the zonally averaged net ocean surface heat flux, Nsfc, from one pole to the other. In AGCM simulations (and perhaps reality), the global mean Nsfc is typically not in exact balance when averaged over one or more years. Because of this, an important assumption must be made about changes in the distribution of energy in the oceans. Otherwise, the integration will yield a non-zero transport at the endpoint of integration (pole) which is not physically realistic. Here the authors will only look at 10-year means of the AMIP runs, and for simplicity they assume that any long term imbalance in the global averaged Nsfc will be sequestered (or released) over the global ocean. Tests have demonstrated that the treatment of how the global average energy imbalance is assumed to be distributed is important, especially when the long term imbalances are in excess of 10 W m-2. However, this has not had a substantial impact on the qualitative features of the implied heat transport of the AMIP simulations examined thus far

  2. The Effect of Transient Eddy on Interannual Meridional Displacement of Summer East Asian Subtropical Jet

    Institute of Scientific and Technical Information of China (English)

    XIANG Yang; YANG Xiuqun

    2012-01-01

    Using ERA-40 reanalysis daily data for the period 1958-2002.this study investigated the effect of transient eddy (TE) on the interannual meridional displacement of summer East Asian subtropical jet (EASJ)by conducting a detailed dynamical diagnosis.The summer EASJ axis features a significant interannual coherent meridional displacement.Associated with such a meridional displacement,the TE vorticity forcing anomalies are characterized by a meridional dipole pattern asymmetric about the climatological EASJ axis.The TE vorticity forcing anomalies yield barotropic zonal wind tendencies with a phase meridionally leading the zonal wind anomalies,suggesting that they act to reinforce further meridional displacement of the EASJ and favor a positive feedback in the TE and time-mean flow interaction.However,The TE thermal forcing anomalies induce baroclinic zonal wind tendencies that reduce the vertical shear of zonal wind and atmospheric baroclinicity and eventually suppress the TE activity,favoring a negative feedback in the TE and time-mean flow interaction.Although the two types of TE forcing tend to have opposite feedback roles,the TE vorticity forcing appears to be dominant in the TE effect on the time-mean flow.

  3. Pulsation-driven mean zonal and meridional flows in rotating massive stars

    Science.gov (United States)

    Lee, Umin; Mathis, Stéphane; Neiner, Coralie

    2016-04-01

    Zonal and meridional axisymmetric flows can deeply impact the rotational and chemical evolution of stars. Therefore, momentum exchanges between waves propagating in stars, differential rotation, and meridional circulation must be carefully evaluated. In this work, we study axisymmetric mean flows in rapidly and initially uniformly rotating massive stars driven by small amplitude non-axisymmetric κ-driven oscillations. We treat them as perturbations of second order of the oscillation amplitudes and derive their governing equations as a set of coupled linear ordinary differential equations. This allows us to compute 2D zonal and meridional mean flows driven by low frequency g and r modes in slowly pulsating B stars and p modes in β Cephei stars. Oscillation-driven mean flows usually have large amplitudes only in the surface layers. In addition, the kinetic energy of the induced 2D zonal rotational motions is much larger than that of the meridional motions. In some cases, meridional flows have a complex radial and latitudinal structure. We find pulsation-driven and rotation-driven meridional flows can have similar amplitudes. These results show the importance of taking wave - mean flow interactions into account when studying the evolution of massive stars.

  4. Southern Ocean overturning across streamlines in an eddying simulation of the Antarctic Circumpolar Current

    Directory of Open Access Journals (Sweden)

    A. M. Treguier

    2007-12-01

    Full Text Available An eddying global model is used to study the characteristics of the Antarctic Circumpolar Current (ACC in a streamline-following framework. Previous model-based estimates of the meridional circulation were calculated using zonal averages: this method leads to a counter-intuitive poleward circulation of the less dense waters, and underestimates the eddy effects. We show that on the contrary, the upper ocean circulation across streamlines agrees with the theoretical view: an equatorward mean flow partially cancelled by a poleward eddy mass flux. Two model simulations, in which the buoyancy forcing above the ACC changes from positive to negative, suggest that the relationship between the residual meridional circulation and the surface buoyancy flux is not as straightforward as assumed by the simplest theoretical models: the sign of the residual circulation cannot be inferred from the surface buoyancy forcing only. Among the other processes that likely play a part in setting the meridional circulation, our model results emphasize the complex three-dimensional structure of the ACC (probably not well accounted for in streamline-averaged, two-dimensional models and the distinct role of temperature and salinity in the definition of the density field. Heat and salt transports by the time-mean flow are important even across time-mean streamlines. Heat and salt are balanced in the ACC, the model drift being small, but the nonlinearity of the equation of state cannot be ignored in the density balance.

  5. Statistical Aspects of Tropical Cyclone Activity in the North Atlantic Basin, 1945-2010

    Science.gov (United States)

    Wilson, Robert M.

    2012-01-01

    Examined are statistical aspects of the 715 tropical cyclones that formed in the North Atlantic basin during the interval 1945-2010. These 715 tropical cyclones include 306 storms that attained only tropical storm strength, 409 hurricanes, 179 major or intense hurricanes, and 108 storms that struck the US coastline as hurricanes. Comparisons made using 10-year moving average (10-yma) values between tropical cyclone parametric values and surface air and ENSO-related parametric values indicate strong correlations to exist, in particular, against the Armagh Observatory (Northern Ireland) surface air temperature, the Atlantic Multi-decadal Oscillation (AMO) index, the Atlantic Meridional Mode (AMM) index, and the North Atlantic Oscillation (NAO) index, in addition to the Oceanic Ni o index (ONI) and Quasi-Biennial Oscillation (QBO) indices. Also examined are the decadal variations of the tropical cyclone parametric values and a look ahead towards the 2012 hurricane season and beyond.

  6. Searching for overturning convection in penumbral filaments: slit spectroscopy at 0.2 arcsec resolution

    CERN Document Server

    Rubio, L R Bellot; Langhans, K

    2010-01-01

    Recent numerical simulations of sunspots suggest that overturning convection is responsible for the existence of penumbral filaments and the Evershed flow, but there is little observational evidence of this process. Here we carry out a spectroscopic search for small-scale convective motions in the penumbra of a sunspot located 5 deg away from the disk center. The position of the spot is very favorable for the detection of overturning downflows at the edges of penumbral filaments. Our analysis is based on measurements of the Fe I 709.0 nm line taken with the Littrow spectrograph of the Swedish 1 m Solar Telescope under excellent seeing conditions. We compute line bisectors at different intensity levels and derive Doppler velocities from them. The velocities are calibrated using a nearby telluric line, with systematic errors smaller than 150 m/s. Deep in the photosphere, as sampled by the bisectors at the 80%-88% intensity levels, we always observe blueshifts or zero velocities. The maximum blueshifts reach 1.2...

  7. Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning

    Science.gov (United States)

    Abernathey, Ryan P.; Cerovecki, Ivana; Holland, Paul R.; Newsom, Emily; Mazloff, Matt; Talley, Lynne D.

    2016-08-01

    Ocean overturning circulation requires a continuous thermodynamic transformation of the buoyancy of seawater. The steeply sloping isopycnals of the Southern Ocean provide a pathway for Circumpolar Deep Water to upwell from mid depth without strong diapycnal mixing, where it is transformed directly by surface fluxes of heat and freshwater and splits into an upper and lower branch. While brine rejection from sea ice is thought to contribute to the lower branch, the role of sea ice in the upper branch is less well understood, partly due to a paucity of observations of sea-ice thickness and transport. Here we quantify the sea-ice freshwater flux using the Southern Ocean State Estimate, a state-of-the-art data assimilation that incorporates millions of ocean and ice observations. We then use the water-mass transformation framework to compare the relative roles of atmospheric, sea-ice, and glacial freshwater fluxes, heat fluxes, and upper-ocean mixing in transforming buoyancy within the upper branch. We find that sea ice is a dominant term, with differential brine rejection and ice melt transforming upwelled Circumpolar Deep Water at a rate of ~22 × 106 m3 s-1. These results imply a prominent role for Antarctic sea ice in the upper branch and suggest that residual overturning and wind-driven sea-ice transport are tightly coupled.

  8. SOLAR MERIDIONAL FLOW IN THE SHALLOW INTERIOR DURING THE RISING PHASE OF CYCLE 24

    International Nuclear Information System (INIS)

    Solar subsurface zonal- and meridional-flow profiles during the rising phase of solar cycle 24 are studied using the time-distance helioseismology technique. The faster zonal bands in the torsional-oscillation pattern show strong hemispheric asymmetries and temporal variations in both width and speed. The faster band in the northern hemisphere is located closer to the equator than the band in the southern hemisphere and migrates past the equator when the magnetic activity in the southern hemisphere is reaching maximum. The meridional-flow speed decreases substantially with the increase of magnetic activity, and the flow profile shows two zonal structures in each hemisphere. The residual meridional flow, after subtracting a mean meridional-flow profile, converges toward the activity belts and shows faster and slower bands like the torsional-oscillation pattern. More interestingly, the meridional-flow speed above latitude 30° shows an anti-correlation with the poleward-transporting magnetic flux, slower when the following-polarity flux is transported and faster when the leading-polarity flux is transported. It is expected that this phenomenon slows the process of magnetic cancellation and polarity reversal in high-latitude areas

  9. On the seasonal cycles and variability of Florida Straits, Ekman and Sverdrup transports at 26° N in the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    C. P. Atkinson

    2010-10-01

    Full Text Available Since April 2004 the RAPID array has made continuous measurements of the Atlantic Meridional Overturning Circulation (AMOC at 26° N. Two key components of this system are Ekman transport zonally integrated across 26° N and western boundary current transport in the Florida Straits. Whilst measurements of the AMOC as a whole are somewhat in their infancy, this study investigates what useful information can be extracted on the variability of the Ekman and Florida Straits transports using the decadal timeseries already available. Analysis is also presented for Sverdrup transports zonally integrated across 26° N.

    The seasonal cycles of Florida Straits, Ekman and Sverdrup transports are quantified at 26° N using harmonic analysis of annual and semi-annual constituents. Whilst Sverdrup transport shows clear semi-annual periodicity, calculations of seasonal Florida Straits and Ekman transports show substantial interannual variability due to contamination by variability at non-seasonal frequencies; the mean seasonal cycle for these transports only emerges from decadal length observations. The Florida Straits and Ekman mean seasonal cycles project on the AMOC with a combined peak-to-peak seasonal range of 3.5 Sv. The combined seasonal range for heat transport is 0.40 PW.

    The Florida Straits seasonal cycle possesses a smooth annual periodicity in contrast with previous studies suggesting a more asymmetric structure. No clear evidence is found to support significant changes in the Florida Straits seasonal cycle at sub-decadal periods. Whilst evidence of wind driven Florida Straits transport variability is seen at sub-seasonal and annual periods, a model run from the 1/4° eddy-permitting ocean model NEMO is used to identify an important contribution from internal oceanic variability at sub-annual and interannual periods. The Ekman transport seasonal cycle possesses less symmetric structure, due in part to different seasonal transport

  10. South Atlantic Shrimp System

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The SEFSC, in cooperation with the South Atlantic states, collects South Atlantic shrimp data from dealers and fishermen. These data are collected to provide catch,...

  11. 2005 Atlantic Hurricanes Poster

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The 2005 Atlantic Hurricanes poster features high quality satellite images of 15 hurricanes which formed in the Atlantic Basin (includes Gulf of Mexico and...

  12. Differential rotation and meridional circulation in global models of solar convection

    CERN Document Server

    Miesch, M S

    2008-01-01

    In the outer envelope of the Sun and in other stars, differential rotation and meridional circulation are maintained via the redistribution of momentum and energy by convective motions. In order to properly capture such processes in a numerical model, the correct spherical geometry is essential. In this paper I review recent insights into the maintenance of mean flows in the solar interior obtained from high-resolution simulations of solar convection in rotating spherical shells. The Coriolis force induces a Reynolds stress which transports angular momentum equatorward and also yields latitudinal variations in the convective heat flux. Meridional circulations induced by baroclinicity and rotational shear further redistribute angular momentum and alter the mean stratification. This gives rise to a complex nonlinear interplay between turbulent convection, differential rotation, meridional circulation, and the mean specific entropy profile. I will describe how this drama plays out in our simulations as well as i...

  13. The mean-field solar dynamo with double cell meridional circulation pattern

    CERN Document Server

    Pipin, V V

    2013-01-01

    The paper addresses the question whether the dynamo remains of the solar type if it is coupled with the two-cell in radius meridional circulation pattern. The answer is positive for a wide class of dynamo models that take into account the subsurface rotational shear. We show that the Gleisberg-type cycles, representing variations of 11-year on the centure time scale, can be generated due to a nonlinear resonance between the dynamo wave, and the large-scale magnetic field amplification in the middle of the convection zone as a result of the convergent meridional shearing flows. The conditions of such resonant interaction depends on the speed of the meridional flow and other details of the model.

  14. Escleroplastia meridional: A propósito de un caso en 1999 Meridional scleroplasty: With regard to a case in 1999

    Directory of Open Access Journals (Sweden)

    Enrique J. Machado Fernández

    2000-06-01

    Full Text Available En este artículo se presenta un caso reciente de rechazo al aloplante utilizado para escleroplastia meridional. Se refieren las características del cuadro clínico presentado y su tratamiento. Además, se expresan consideraciones basadas en datos estadísticos y hallazgos anatomopatológicos que fundamentan la suspensión de la práctica de esta técnica en el Centro de Microcirugía Ocular.In present paper, authors present a recent case of rejection to allograft used to meridional scleroplasty. Festures of clinical picture and its treatment are related. Furthermore, we express statistical data based on considerations and anatomic-pathologic findings supporting suspension of practice of this technique in Center of Microsurgery of Eye.

  15. Monthly Climatology of Thermospheric Zonal and Meridional Winds Obtained from a Kalman Filter Model

    Science.gov (United States)

    Scherliess, L.; Lomidze, L.

    2015-12-01

    Knowledge of the thermospheric neutral wind and its meridional and zonal components is critical for an improved understanding of the low- and mid-latitude F-region dynamics and morphology. To date, the reliable estimation of the wind and its components remains a challenge because of difficulties in both measurement and modeling. Previous methods that use ionospheric measurements to deduce winds provide their values only in the direction of the magnetic meridian. We will present the monthly climatology of the zonal and meridional components of thermospheric neutral wind at low and mid-latitudes obtained by a Kalman Filter technique. First, the climatology of the magnetic meridional wind is obtained by assimilating monthly maps of F-region ionosphere peak parameters (NmF2 and hmF2), obtained from COSMIC radio occultation data, into the Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model. The model provides the 3-D electron density throughout the ionosphere, together with the magnetic meridional wind. Next, the estimation of the global zonal and meridional wind components is performed using the newly developed Thermospheric Wind Assimilation Model (TWAM). TWAM combines magnetic meridional wind data obtained from GAIM-FP with a physics-based 3-D thermospheric neutral wind model using an implicit Kalman Filter technique. The ionospheric drag and ion diffusion velocities, needed for the wind calculation, are also taken from the GAIM-FP model. We present the monthly climatology of our wind estimation and compare individual horizontal wind components to their corresponding empirical model values and to measurements made by interferometers.

  16. Improvements in launchings and recipients of PIG in Malha de Gasodutos Nordeste Meridional; Melhorias nos lancamentos e recebedores de PIG da Malha de Gasodutos Nordeste Meridional

    Energy Technology Data Exchange (ETDEWEB)

    Maciel, Jairo A.C.; Lemos, Francisco A.C.; Lima, Artur W.R. de S. [PETROBRAS Transporte S.A. (TRANSPETRO), Rio de Janeiro, RJ (Brazil)

    2012-07-01

    This paper describes the study that resulted in the preparation of a project for improvement of launchers and receivers of PIG in facilities maintained and operated by PETROBRAS S.A. (TRANSPETRO) in the Malha de Gasodutos Nordeste Meridional (Malha NEM). The improvements are part of the component in cleaner production system and reduce the risks of accidents and the costs of hazardous waste management.

  17. Angular momentum fluxes caused by Lambda-effect and meridional circulation structure of the Sun

    CERN Document Server

    Pipin, V V

    2016-01-01

    Using mean-field hydrodynamic models of the solar angular momentum balance we show that the non-monotonic latitudinal dependence of the radial angular momentum fluxes caused by Lambda-effect can affect the number of the meridional circulation cells stacking in radial direction in the solar convection zone. In particular, our results show the possibility of a complicated triple-cell meridional circulation structure. This pattern consists of two large counterclockwise circulation cells (the N-hemisphere) and a smaller clockwise cell located at low latitudes at the bottom of the convection zone.

  18. More uneven distributions overturn benefits of higher precipitation for crop yields

    Science.gov (United States)

    Fishman, Ram

    2016-02-01

    Climate change is expected to lead to more uneven temporal distributions of precipitation, but the impacts on human systems are little studied. Most existing, statistically based agricultural climate change impact projections only account for changes in total precipitation, ignoring its intra-seasonal distribution, and conclude that in places that will become wetter, agriculture will benefit. Here, an analysis of daily rainfall and crop yield data from across India (1970-2003), where a fifth of global cereal supply is produced, shows that decreases in the number of rainy days have robust negative impacts that are large enough to overturn the benefits of increased total precipitation for the yields of most major crops. As an illustration, the net, mid 21st century projection for rice production shifts from +2% to -11% when changes in distribution are also accounted for, independently of additional negative impacts of rising temperatures.

  19. Study of the overturning length scales at the Spanish planetary boundary layer

    Science.gov (United States)

    López, Pilar; Cano, José L.

    2016-03-01

    The focus of this paper is to analyse the behaviour of the maximum Thorpe displacement (dT)max and the Thorpe scale LT at the atmospheric boundary layer (ABL), extending previous research with new data and improving our studies related to the novel use of the Thorpe method applied to ABL. The maximum Thorpe displacements vary between -900 and 950 m for the different field campaigns. The Thorpe scale LT ranges between 0.2 and 680 m for the different data sets which cover different stratified mixing conditions (turbulence shear-driven and convective regions). We analyse the relationship between (dT)max and the Thorpe scale LT and we deduce that they verify a power law. We also deduce that there is a difference in exponents of the power laws for convective conditions and shear-driven conditions. These different power laws could identify overturns created under different mechanisms.

  20. A flow law for ilmenite in dislocation creep: Implications for lunar cumulate mantle overturn

    Science.gov (United States)

    Dygert, Nick; Hirth, Greg; Liang, Yan

    2016-01-01

    We present results from new deformation experiments and a dislocation creep flow law for synthetic ilmenite. The flow law predicts an effective viscosity more than 3 orders of magnitude lower than dry olivine at mantle stresses and temperatures. Using the flow law, we predict that lunar ilmenite-bearing cumulates (IBC) will be weakened by the presence of low-viscosity ilmenite. Dense, low-viscosity IBC are expected to flow into the lunar interior by a process known as cumulate mantle overturn. Low-viscosity IBC that sink to the core-mantle boundary may be dynamically stable with respect to upwelling. A hot, stable layer of IBC surrounding the lunar core would suppress the development of a core dynamo. A layer of partially molten IBC can also explain the inferred zone of seismic attenuation around the lunar core, as well as a low-viscosity layer suggested by tidal dissipation.

  1. The effect of mechanical stirring on horizontal convection

    OpenAIRE

    R. Tailleux; Rouleau, L

    2010-01-01

    An important experimental result, as yet poorly understood, is that mechanical stirring can significantly enhance the strength of horizontal convection. A contentious issue is whether this necessarily implies that the mechanical stirring replaces the buoyancy forcing as the main source of energy driving the observed overturning circulation, as has been suggested for the Atlantic meridional overturning circulation (AMOC). In this paper, rigorous energetics considerations and idealized numerica...

  2. 40 CFR 142.311 - What procedures allow the Administrator to object to a proposed small system variance or overturn...

    Science.gov (United States)

    2010-07-01

    ... Administrator to object to a proposed small system variance or overturn a granted small system variance for a... REGULATIONS IMPLEMENTATION Variances for Small System Epa Review and Approval of Small System Variances § 142.311 What procedures allow the Administrator to object to a proposed small system variance or...

  3. Modulation of extremes in the Atlantic region by modes of climate variability/change: A mechanistic coupled regional model study

    Energy Technology Data Exchange (ETDEWEB)

    Saravanan, Ramalingam

    2015-01-09

    During the course of this project, we have accomplished the following: 1) Explored the parameter space of component models to minimize regional model bias 2) Assessed the impact of air-sea interaction on hurricanes, focusing in particular on the role of the oceanic barrier layer 3) Contributed to the activities of the U.S. CLIVAR Hurricane Working Group 4) Assessed the impact of lateral and lower boundary conditions on extreme flooding events in the U.S. Midwest in regional model simulations 5) Analyzed the concurrent impact of El Niño-Southern Oscillation and Atlantic Meridional Mode on Atlantic Hurricane activity using observations and regional model simulations

  4. Aerosol interactions with African/Atlantic climate dynamics

    International Nuclear Information System (INIS)

    Mechanistic relationships exist between variability of dust in the oceanic Saharan air layer (OSAL) and transient changes in the dynamics of Western Africa and the tropical Atlantic Ocean. This study provides evidence of possible interactions between dust in the OSAL region and African easterly jet–African easterly wave (AEJ–AEW) system in the climatology of boreal summer, when easterly wave activity peaks. Synoptic-scale changes in instability and precipitation in the African/Atlantic intertropical convergence zone are correlated with enhanced aerosol optical depth (AOD) in the OSAL region in response to anomalous 3D overturning circulations and upstream/downstream thermal anomalies at above and below the mean-AEJ level. Upstream and downstream anomalies are referred to the daily thermal/dynamical changes over the West African monsoon region and the Eastern Atlantic Ocean, respectively. Our hypothesis is that AOD in the OSAL is positively correlated with the downstream AEWs and negatively correlated with the upstream waves from climatological perspective. The similarity between the 3D pattern of thermal/dynamical anomalies correlated with dust outbreaks and those of AEWs provides a mechanism for dust radiative heating in the atmosphere to reinforce AEW activity. We proposed that the interactions of OSAL dust with regional climate mainly occur through coupling of dust with the AEWs. (paper)

  5. Aerosol interactions with African/Atlantic climate dynamics

    Science.gov (United States)

    Hosseinpour, F.; Wilcox, E. M.

    2014-07-01

    Mechanistic relationships exist between variability of dust in the oceanic Saharan air layer (OSAL) and transient changes in the dynamics of Western Africa and the tropical Atlantic Ocean. This study provides evidence of possible interactions between dust in the OSAL region and African easterly jet-African easterly wave (AEJ-AEW) system in the climatology of boreal summer, when easterly wave activity peaks. Synoptic-scale changes in instability and precipitation in the African/Atlantic intertropical convergence zone are correlated with enhanced aerosol optical depth (AOD) in the OSAL region in response to anomalous 3D overturning circulations and upstream/downstream thermal anomalies at above and below the mean-AEJ level. Upstream and downstream anomalies are referred to the daily thermal/dynamical changes over the West African monsoon region and the Eastern Atlantic Ocean, respectively. Our hypothesis is that AOD in the OSAL is positively correlated with the downstream AEWs and negatively correlated with the upstream waves from climatological perspective. The similarity between the 3D pattern of thermal/dynamical anomalies correlated with dust outbreaks and those of AEWs provides a mechanism for dust radiative heating in the atmosphere to reinforce AEW activity. We proposed that the interactions of OSAL dust with regional climate mainly occur through coupling of dust with the AEWs.

  6. Atmospheric and Surface Contributions to Planetary Albedo and their Relationship to the Total Meridional Energy Transport

    Science.gov (United States)

    Donohoe, A.; Battisti, D. S.

    2010-12-01

    The meridional distribution of incident solar radiation and planetary albedo both contribute to the equator-to-pole gradient in absorbed solar radiation (ASR) in the observed climate system. While the former component is determined by the Earth-Sun geometry and composes 60% of the equator-to-pole gradient in ASR, the latter component makes a significant (40%) contribution to the ASR gradient and is potentially a function of climate state due to its dependence on both atmospheric and surface albedo. In turn, the equator-to-pole gradient in planetary albedo is found to be primarily (86% -89%) dictated by atmospheric albedo with meridional gradients in surface albedo playing a much smaller role in forcing the climate system on the equator-to-pole scale. Simulations of the pre-industrial climate system using the CMIP3 coupled models show large differences in the equator-to-pole gradient in planetary albedo which are mainly due to differences in the simulated cloud distribution, with surface processes playing a much smaller role. The inter-model spread in total meridional heat transport is also primarily (85% of the inter-model spread) due to differences in the simulated cloud distribution. Further model simulations demonstrate that the surface albedo changes associated with moving from the present climate to an ice free climate have a small effect on the equator-to-pole gradient of ASR as compared to the uncertainty in simulated cloud distributions, and hence a small effect on the meridional heat transport.

  7. Importance of Meridional Circulation in Flux Transport Dynamo: Possibility of Maunder-like Grand Minimum

    CERN Document Server

    Karak, Bidya Binay

    2010-01-01

    Meridional circulation is an important ingredient in flux transport dynamo model. We have studied its importance on the period, amplitude of solar cycle and also on producing Maunder-like grand minima in this model. First, we model the periods of last 23 sunspot cycles by varying the meridional circulation speed. We find that most of the cycle amplitudes also get modeled up to some extent when the dynamo is in diffusion-dominated regime. Next, we propose that at the beginning of the Maunder minimum the amplitude of meridional circulation dropped to a low value and then after a few years it increased again. Several independent studies also favor this assumption. With this assumption, a diffusion-dominated dynamo is able to reproduce many important features of Maunder minimum remarkably well. If the dynamo is in diffusion-dominated regime, then the slower meridional circulation means that the poloidal field gets more time to diffuse away from the tachocline, making the dynamo weaker. This consequence helps to m...

  8. Is a deep one-cell meridional circulation essential for the flux transport Solar Dynamo?

    CERN Document Server

    Hazra, Gopal; Choudhuri, Arnab Rai

    2014-01-01

    The solar activity cycle is successfully modeled by the flux transport dynamo, in which the meridional circulation of the Sun plays an important role. Most of the kinematic dynamo simulations assume a one-cell structure of the meridional circulation within the convection zone, with the equatorward return flow at its bottom. In view of the recent claims that the return flow occurs at a much shallower depth, we explore whether a meridional circulation with such a shallow return flow can still retain the attractive features of the flux transport dynamo (such as proper butterfly diagram, proper phase relation between the toroidal and poloidal fields). We consider additional cells of the meridional circulation below the shallow return flow---both the case of multiple cells radially stacked above one another and the case of more complicated cell patterns. As long as there is an equatorward flow in low latitudes at the bottom of the convection zone, we find that the solar behavior is approximately reproduced. Howeve...

  9. The two-core longitudinal structure of meridional wind in the middle/natmosphere

    Czech Academy of Sciences Publication Activity Database

    Kozubek, Michal

    Göttingen: European Geosciences Union, 2016. EGU2016-2500. ISSN 1607-7962. [EGU General Assembly 2016. 17.04.2016-22.04.2016, Vienna] Institutional support: RVO:68378289 Keywords : middle atmosphere * meridional wind Subject RIV: DG - Athmosphere Sciences, Meteorology http://meetingorganizer.copernicus.org/EGU2016/EGU2016-2500.pdf

  10. On the configurations of the Atlantic Niño phenomenon under negative AMO phases

    Science.gov (United States)

    Martin-Rey, Marta; Rodríguez de Fonseca, Belen; Polo, Irene; Losada, Teresa; Lazar, Alban

    2016-04-01

    An air-sea coupled mode of inter-annual variability akin to ENSO emerges in the tropical Atlantic basin, named as Atlantic Niño. The teleconnections of the Atlantic Niño phenomenon have changed during recent decades, coinciding with an alteration of its spatial configuration. Previous studies have suggested that the background state could favour particular atmospheric forcings and could also contribute to generate different variability modes. Here, we demonstrate that two different Atlantic Niño patterns coexist in the tropical Atlantic basin during certain decades, coinciding with a negative phase of the Atlantic Multidecadal Oscillation (AMO). The leading mode, Basin-Wide (BW) Atlantic Niño, is characterized by positive SST anomalies covering the entire tropical Atlantic and the second mode, Dipolar (D) Atlantic Niño, presents an equatorial warming flanked by negative SST anomalies in north and south Tropical Atlantic. These modes are driven by different wind patterns, controlled by the Subtropical High Pressure Systems. The BW-Atlantic Niño is preceded by a weakening of both Azores and Sta Helena High, which induces a general reduction of the tropical trades and anomalous wind convergence in the equatorial band. On the other hand, the D-Atlantic Niño is associated with a strengthening of Azores High and a weakening of Sta Helena High, given rise to a meridional Sea Level Pressure (SLP) gradient that intensifies the subtropical trades and generate anomalous trans-equatorial winds along the equatorial band. Both modes seem to be forced by an ENSO-like signal emanating from the Pacific, but with different atmospheric response over the Atlantic. It could be attributed to the changes in the mean state during negative AMO phases. For these decades, shallower thermocline conditions, together with an increase of the oceanic variability (SST and thermocline) in the tropical Atlantic could contribute to the generation of both Atlantic Niño modes. Furthermore, a

  11. Weak response of the Atlantic thermohaline circulation to an increase of atmospheric carbon dioxide in IAP/LASG Climate System Model

    Institute of Scientific and Technical Information of China (English)

    ZHOU Tianjun; YU Rucong; LIU Xiying; GUO Yufu; YU Yongqiang; ZHANG Xuehong

    2005-01-01

    Response of the Atlantic thermohaline circula- tion (THC) to global warming is examined by using the climate system model developed at IAP/LASG. The evidence indicates that the gradually warming climate associated with the increased atmospheric carbon dioxide leads to a warmer and fresher sea surface water at the high latitudes of the North Atlantic Ocean, which prevents the down-welling of the surface water. The succedent reduction of the pole-to- equator meridional potential density gradient finally results in the decrease of the THC in intensity. When the atmospheric carbon dioxide is doubled, the maximum value of the Atlantic THC decreases approximately by 8%. The associated poleward oceanic heat transport also becomes weaker. This kind of THC weakening centralizes mainly in the northern part of the North Atlantic basin, indicating briefly a local scale adjustment rather than a loop oscillation with the whole Atlantic "conveyor belt" decelerating.

  12. Thermohaline feedbacks in ocean-climate models of varying complexity

    NARCIS (Netherlands)

    den Toom, M.

    2013-01-01

    The Atlantic Meridional Overturning Circulation (AMOC) is considered an important component of the climate system, because of its significant contribution to the heat budget of the Northern Hemisphere. Theoretical models indicate that the AMOC has non-linear dynamics, which result in a strong sensit

  13. A Review of ENSO Influence on the North Atlantic. A Non-Stationary Signal

    Directory of Open Access Journals (Sweden)

    Belén Rodríguez-Fonseca

    2016-06-01

    Full Text Available The atmospheric seasonal cycle of the North Atlantic region is dominated by meridional movements of the circulation systems: from the tropics, where the West African Monsoon and extreme tropical weather events take place, to the extratropics, where the circulation is dominated by seasonal changes in the jetstream and extratropical cyclones. Climate variability over the North Atlantic is controlled by various mechanisms. Atmospheric internal variability plays a crucial role in the mid-latitudes. However, El Niño-Southern Oscillation (ENSO is still the main source of predictability in this region situated far away from the Pacific. Although the ENSO influence over tropical and extra-tropical areas is related to different physical mechanisms, in both regions this teleconnection seems to be non-stationary in time and modulated by multidecadal changes of the mean flow. Nowadays, long observational records (greater than 100 years and modeling projects (e.g., CMIP permit detecting non-stationarities in the influence of ENSO over the Atlantic basin, and further analyzing its potential mechanisms. The present article reviews the ENSO influence over the Atlantic region, paying special attention to the stability of this teleconnection over time and the possible modulators. Evidence is given that the ENSO–Atlantic teleconnection is weak over the North Atlantic. In this regard, the multidecadal ocean variability seems to modulate the presence of teleconnections, which can lead to important impacts of ENSO and to open windows of opportunity for seasonal predictability.

  14. Ocean impact on decadal Atlantic climate variability revealed by sea-level observations

    Science.gov (United States)

    McCarthy, Gerard D.; Haigh, Ivan D.; Hirschi, Joël J.-M.; Grist, Jeremy P.; Smeed, David A.

    2015-05-01

    Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with decadal climate fluctuations, such as Indian and Sahel rainfall, European summer precipitation, Atlantic hurricanes and variations in global temperatures. It is widely believed that ocean circulation drives the phase changes of the AMO by controlling ocean heat content. However, there are no direct observations of ocean circulation of sufficient length to support this, leading to questions about whether the AMO is controlled from another source. Here we provide observational evidence of the widely hypothesized link between ocean circulation and the AMO. We take a new approach, using sea level along the east coast of the United States to estimate ocean circulation on decadal timescales. We show that ocean circulation responds to the first mode of Atlantic atmospheric forcing, the North Atlantic Oscillation, through circulation changes between the subtropical and subpolar gyres--the intergyre region. These circulation changes affect the decadal evolution of North Atlantic heat content and, consequently, the phases of the AMO. The Atlantic overturning circulation is declining and the AMO is moving to a negative phase. This may offer a brief respite from the persistent rise of global temperatures, but in the coupled system we describe, there are compensating effects. In this case, the negative AMO is associated with a continued acceleration of sea-level rise along the northeast coast of the United States.

  15. Enhanced Atlantic sea-level rise relative to the Pacific under high carbon emission rates

    Science.gov (United States)

    Krasting, J. P.; Dunne, J. P.; Stouffer, R. J.; Hallberg, R. W.

    2016-03-01

    Thermal expansion of the ocean in response to warming is an important component of historical sea-level rise. Observational studies show that the Atlantic and Southern oceans are warming faster than the Pacific Ocean. Here we present simulations using a numerical atmospheric-ocean general circulation model with an interactive carbon cycle to evaluate the impact of carbon emission rates, ranging from 2 to 25 GtC yr-1, on basin-scale ocean heat uptake and sea level. For simulations with emission rates greater than 5 GtC yr-1, sea-level rise is larger in the Atlantic than Pacific Ocean on centennial timescales. This basin-scale asymmetry is related to the shorter flushing timescales and weakening of the overturning circulation in the Atlantic. These factors lead to warmer Atlantic interior waters and greater thermal expansion. In contrast, low emission rates of 2 and 3 GtC yr-1 will cause relatively larger sea-level rise in the Pacific on millennial timescales. For a given level of cumulative emissions, sea-level rise is largest at low emission rates. We conclude that Atlantic coastal areas may be particularly vulnerable to near-future sea-level rise from present-day high greenhouse gas emission rates.

  16. Chemical differentiation, thermal evolution, and catastrophic overturn on Venus: Predictions and geologic observations

    Science.gov (United States)

    Head, James W.; Parmentier, E. M.; Hess, P. C.

    1993-01-01

    Observations from Magellan show that: (1) the surface of Venus is generally geologically young, (2) there is no evidence for widespread recent crustal spreading or subduction, (3) the crater population permits the hypothesis that the surface is in production, and (4) relatively few impact craters appear to be embayed by volcanic deposits suggesting that the volcanic flux has drastically decreased as a function of time. These observations have led to consideration of hypotheses suggesting that the geological history of Venus may have changed dramatically as a function of time due to general thermal evolution, and/or thermal and chemical evolution of a depleted mantle layer, perhaps punctuated by catastrophic overturn of upper layers or episodic plate tectonics. We have previously examined the geological implications of some of these models, and here we review the predictions associated with two periods of Venus history. Stationary thick lithosphere and depleted mantle layer, and development of regional to global development of regional to global instabilities, and compare these predictions to the geological characteristics of Venus revealed by Magellan.

  17. Impacts of non-canonical El Niño patterns on Atlantic hurricane activity

    Science.gov (United States)

    Larson, S.; Lee, S.; Wang, C.; Chung, E.; Enfield, D. B.

    2012-12-01

    The impact of non-canonical El Niño patterns, typically characterized by warmer than normal sea surface tempera- tures (SSTs) in the central tropical Pacific, on Atlantic tropical cyclone (TC) is explored by using composites of key Atlantic TC indices and tropospheric vertical wind shear over the Atlantic main development region (MDR). The highlight of our major findings is that, while the canonical El Niño pattern has a strong suppressing influence on Atlantic TC activity, non-canonical El Niño patterns con- sidered in this study, namely central Pacific warming, El Niño Modoki, positive phase Trans-Niño, and positive phase Pacific meridional mode, all have insubstantial impact on Atlantic TC activity. This result becomes more conclu- sive when the impact of MDR SST is removed from the Atlantic TC indices and MDR wind shear by using the method of linear regression. Further analysis suggests that the tropical Pacific SST anomalies associated with the non- canonical El Niño patterns are not strong enough to cause a substantial warming of the tropical troposphere in the Atlantic region, which is the key factor that increases the wind shear and atmospheric static stability over the MDR. During the recent decades, the non-canonical El Niños have been more frequent while the canonical El Niño has been less frequent. If such a trend continues in the future, it is expected that the suppressing effect of El Niño on Atlantic TC activity will diminish and thus the MDR SST will play a more important role in controlling Atlantic TC activity in the coming decades.

  18. Meteorological conditions, physiochemical properties, thermal-oxygen stratification, water overturn and water balance of Lake Gardno on Wolin Island

    Directory of Open Access Journals (Sweden)

    Tylkowski Jacek

    2015-09-01

    Full Text Available The main research problem of the paper is aimed at determining the proper functioning of Lake Gardno within the period 2012-2014 considered as hydrological years in reference to the physiochemical properties of its waters, water balance, thermal regime and water overturn. Lake Gardno is a representative of non-run-off lake geo-eco-systems; it is situated within the Southern Baltic Sea Coastland at the cliff shore of Wolin Island. The paper analyses how weather conditions affect the specifics of water supplies provided to the lake and seasonal dynamics of its waters, their chemical, thermal and aerobic properties. It also specifies their overturn and balance with a particular emphasis on their supplies together with fog deposits.

  19. Meridional Flow in the Solar Convection Zone II: Helioseismic Inversions of GONG Data

    CERN Document Server

    Jackiewicz, J; Kholikov, S

    2015-01-01

    Meridional flow is thought to play a very important role in the dynamics of the solar convection zone; however, because of its relatively small amplitude, precisely measuring it poses a significant challenge. Here we present a complete time-distance helioseismic analysis of about two years of ground-based GONG Doppler data to retrieve the meridional circulation profile for modest latitudes, in an attempt to corroborate results from other studies. We use an empirical correction to the travel times due to an unknown center-to-limb systematic effect. The helioseismic inversion procedure is first tested and reasonably validated on artificial data from a large-scale numerical simulation, followed by a test to broadly recover the solar differential rotation found from global seismology. From GONG data, we measure poleward photospheric flows at all latitudes with properties that are comparable with earlier studies, and a shallow equatorward flow about $65$\\,Mm beneath the surface, in agreement with recent findings f...

  20. Three-dimensional simulation of equatorial spread-F with meridional wind effects

    Directory of Open Access Journals (Sweden)

    J. Krall

    2009-05-01

    Full Text Available The NRL SAMI3 three-dimensional simulation code is used to examine the effect of meridional winds on the growth and suppression of equatorial spread F (ESF. The simulation geometry conforms to a dipole field geometry with field-line apex heights from 200 to 1600 km at the equator, but extends over only 4 degrees in longitude. The full SAMI3 ionosphere equations are included, providing ion dynamics both along and across the field. The potential is solved in two dimensions in the equatorial plane under a field-line equipotential approximation. By selectively including terms in the potential equation, the reduced growth predicted by Maruyama (1988 and the stabilization predicted by Zalesak and Huba (1991 are separately realized. We find that ESF is stabilized by a sufficiently large constant meridional wind (60 m/s in our example.

  1. A frozen record of density-driven crustal overturn in lava lakes: The example of Kilauea Iki 1959

    Science.gov (United States)

    Stovall, W.K.; Houghton, B.F.; Harris, A.J.L.; Swanson, D.A.

    2009-01-01

    Lava lakes are found at basaltic volcanoes on Earth and other planetary bodies. Density-driven crustal foundering leading to surface renewal occurs repeatedly throughout the life of a lava lake. This process has been observed and described in a qualitative sense, but due to dangerous conditions, no data has been acquired to evaluate the densities of the units involved. Kilauea Iki pit crater in Hawai'i houses a lava lake erupted during a 2 month period in 1959. Part of the surface of the Kilauea Iki lake now preserves the frozen record of a final, incomplete, crustal-overturn cycle. We mapped this region and sampled portions of the foundering crust, as well as overriding and underlying lava, to constrain the density of the units involved in the overturn process. Overturn is driven by the advance of a flow front of fresh, low-density lava over an older, higher density surface crust. The advance of the front causes the older crust to break up, founder, and dive downwards into the lake to expose new, hot, low-density lava. We find density differences of 200 to 740 kg/m3 between the foundering crust and over-riding and under-lying lava respectively. In this case, crustal overturn is driven by large density differences between the foundering and resurfacing units. These differences lead, inevitably, to frequent crustal renewal: simple density differences between the surface crust and underlying lake lava make the upper layers of the lake highly unstable. ?? Springer-Verlag 2008.

  2. North Atlantic Temperature Anomaly

    OpenAIRE

    Vukcevic, M.A.

    2009-01-01

    The author postulates the existence of a high correlation between North Atlantic Temperature Anomaly and the variations of magnetic field over the Hudson Bay region. Post-glacial uplift and convection in the underlying mantle uplift (as reflected in changes of the area's magnetic intensity) are making significant contribution to the Atlantic basin climate change.

  3. Meridional flow in the solar convection zone. I. Measurements from gong data

    Energy Technology Data Exchange (ETDEWEB)

    Kholikov, S. [National Solar Observatories, Tucson, AZ 85719 (United States); Serebryanskiy, A. [Ulugh Beg Astronomical Institute, Uzbek Academy of Science, Tashkent 100052 (Uzbekistan); Jackiewicz, J., E-mail: kholikov@noao.edu [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)

    2014-04-01

    Large-scale plasma flows in the Sun's convection zone likely play a major role in solar dynamics on decadal timescales. In particular, quantifying meridional motions is a critical ingredient for understanding the solar cycle and the transport of magnetic flux. Because the signal of such features can be quite small in deep solar layers and be buried in systematics or noise, the true meridional velocity profile has remained elusive. We perform time-distance helioseismology measurements on several years worth of Global Oscillation Network Group Doppler data. A spherical harmonic decomposition technique is applied to a subset of acoustic modes to measure travel-time differences to try to obtain signatures of meridional flows throughout the solar convection zone. Center-to-limb systematics are taken into account in an intuitive yet ad hoc manner. Travel-time differences near the surface that are consistent with a poleward flow in each hemisphere and are similar to previous work are measured. Additionally, measurements in deep layers near the base of the convection zone suggest a possible equatorward flow, as well as partial evidence of a sign change in the travel-time differences at mid-convection zone depths. This analysis on an independent data set using different measurement techniques strengthens recent conclusions that the convection zone may have multiple 'cells' of meridional flow. The results may challenge the common understanding of one large conveyor belt operating in the solar convection zone. Further work with helioseismic inversions and a careful study of systematic effects are needed before firm conclusions of these large-scale flow structures can be made.

  4. Topside plasma bubbles, seen as He+ density depletions, and thermosphere meridional wind influence

    International Nuclear Information System (INIS)

    Complete text of publication follows. The study deals with the evaluation of the possible contribution of the thermosphere meridional/transequatorial winds in the diurnal occurrence probability of the equatorial and low-latitudinal plasma bubbles. It is suggested, that the plasma bubbles, produced by Rayleigh-Taylor instability at the bottomside of ionosphere and transported up by buoyancy to the topside ionosphere and plasmasphere, could be strong affected by meridional (poleward) wind during a generation due to inhibiting the growth of Rayleigh-Taylor instability and flux tube integrated conductivity. He+ density depletions, considered as originating from equatorial plasma bubbles phenomena, or as possible fossil bubble signatures, are studied here. He+ density depletions (or subtroughs) are usually observed during a high solar activity at the topside ionospheric altitudes deeply inside the plasmasphere (L∼1.3-3). The diurnal He+ density depletion statistics, obtained from ISS-b satellite data (1978-79) for the different months and averaged for the periods around the solstices and equinoxes, was compared with the velocity variations of the meridional thermosphere wind, calculated in the different models. The best amplitude correlation was found in the longitudinal region of 0 deg - 60 deg W for winter solstice (R=0.72), when the model calculation of Maruyama (1996) was used. The magnetic meridional component of the thermosphere wind was calculated in this model for declination angle of 20 deg. He+ density depletion distribution as function of latitude-longitude, longitudinal statistics and the map of the magnetic declination angle, calculated from IGRF 1975, were involved for further analyses. It was concluded that the significant modulation effect is determined by season and declination angle of the earth magnetic field in the equatorial region.

  5. Is a deep one-cell meridional circulation essential for the flux transport solar dynamo?

    International Nuclear Information System (INIS)

    The solar activity cycle is successfully modeled by the flux transport dynamo, in which the meridional circulation of the Sun plays an important role. Most of the kinematic dynamo simulations assume a one-cell structure of the meridional circulation within the convection zone, with the equatorward return flow at its bottom. In view of the recent claims that the return flow occurs at a much shallower depth, we explore whether a meridional circulation with such a shallow return flow can still retain the attractive features of the flux transport dynamo (such as a proper butterfly diagram, the proper phase relation between the toroidal and poloidal fields). We consider additional cells of the meridional circulation below the shallow return flow—both the case of multiple cells radially stacked above one another and the case of more complicated cell patterns. As long as there is an equatorward flow in low latitudes at the bottom of the convection zone, we find that the solar behavior is approximately reproduced. However, if there is either no flow or a poleward flow at the bottom of the convection zone, then we cannot reproduce solar behavior. On making the turbulent diffusivity low, we still find periodic behavior, although the period of the cycle becomes unrealistically large. In addition, with a low diffusivity, we do not get the observed correlation between the polar field at the sunspot minimum and the strength of the next cycle, which is reproduced when diffusivity is high. On introducing radially downward pumping, we get a more reasonable period and more solar-like behavior even with low diffusivity.

  6. Interannual Meridional Displacement of the East Asian Upper-tropospheric Jet Stream in Summer

    Institute of Scientific and Technical Information of China (English)

    LIN Zhongda; LU Riyu

    2005-01-01

    On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-JulyAugust, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.

  7. Sub-Surface Meridional flow, Vorticity and the life time of Solar Active Regions

    OpenAIRE

    Maurya, R. A.; Ambastha, A.

    2010-01-01

    Solar sub-surface fluid topology provides an indirect approach to examine the internal characteristics of active regions (ARs). Earlier studies have revealed the prevalence of strong flows in the interior of ARs having complex magnetic fields. Using the Doppler data obtained by the Global Oscillation Network Group (GONG) project for a sample of 74 ARs, we have discovered the presence of steep gradients in meridional velocity at depths ranging from 1.5 to 5 Mm in flare productive ARs. The samp...

  8. Noves aportacions al coneixement de la flora vascular de les comarques meridionals de Catalunya. IV

    OpenAIRE

    Guardiola, Moisès; Molero, Julià; Sáez, Llorenç; López Alvarado, Javier; Ríos, Ana I.; Bagaria Morató, Guillem; Carreras i Raurell, Jordi

    2012-01-01

    En aquest treball aportem dades de 30 plantes vasculars trobades a les muntanyes Catalanídiques centrals i meridionals catalanes. Campanula fastigiata Duf. ex A. DC., Centunculus minimus L., Cephalaria syriaca (L.) Roem. & Schult, Orobanche clausonis Pomel i Rosa andegavensis Bastard, suposen novetats per a aquest territori. S’hi presenten també dades de plantes molt poc citades en aquest territori o a Catalunya: Athyrium filix-femina (L.) Roth, Chaenorhinum rubrifolium (DC.) Fourr. subsp. ru...

  9. Inter-comparison of stratospheric mean-meridional circulation and eddy mixing among six reanalysis datasets

    OpenAIRE

    Miyazaki, K.; Iwasaki, T.; Y. Kawatani; Kobayashi, C.; Sugawara, S.; Hegglin, M.

    2015-01-01

    The stratospheric mean-meridional circulation (MMC) and eddy mixing are compared among six meteorological reanalysis datasets: NCEP-NCAR, NCEP-CFSR, ERA-40, ERA-Interim, JRA-25, and JRA-55 for the period 1979–2012. The reanalysis datasets produced using advanced systems (i.e., NCEP-CFSR, ERA-Interim, and JRA-55) generally reveal a weaker MMC and stronger eddy mixing in the Northern Hemisphere (NH) compared with those produced using older s...

  10. Agrobiodiversity of cactus pear (Opuntia, Cactaceae) in the Meridional Highlands Plateau of Mexico

    OpenAIRE

    Juan Antonio Reyes-Agüero; Juan Rogelio Aguirre Rivera

    2011-01-01

    Mexico is characterized by a remarkable richness of Opuntia, mostly at the Meridional Highlands Plateau; it is also here where the greatest richness of Opuntia variants occurs. Most of these variants have been maintained in homegardens; however, the gathering process which originated these homegardens has been disrupted over the past decades, as a result of social change and the destruction of large wild nopaleras. If the variants still surviving in homegardens are lost, these will be hard to...

  11. Meridional flow in the solar convection zone. I. Measurements from gong data

    International Nuclear Information System (INIS)

    Large-scale plasma flows in the Sun's convection zone likely play a major role in solar dynamics on decadal timescales. In particular, quantifying meridional motions is a critical ingredient for understanding the solar cycle and the transport of magnetic flux. Because the signal of such features can be quite small in deep solar layers and be buried in systematics or noise, the true meridional velocity profile has remained elusive. We perform time-distance helioseismology measurements on several years worth of Global Oscillation Network Group Doppler data. A spherical harmonic decomposition technique is applied to a subset of acoustic modes to measure travel-time differences to try to obtain signatures of meridional flows throughout the solar convection zone. Center-to-limb systematics are taken into account in an intuitive yet ad hoc manner. Travel-time differences near the surface that are consistent with a poleward flow in each hemisphere and are similar to previous work are measured. Additionally, measurements in deep layers near the base of the convection zone suggest a possible equatorward flow, as well as partial evidence of a sign change in the travel-time differences at mid-convection zone depths. This analysis on an independent data set using different measurement techniques strengthens recent conclusions that the convection zone may have multiple 'cells' of meridional flow. The results may challenge the common understanding of one large conveyor belt operating in the solar convection zone. Further work with helioseismic inversions and a careful study of systematic effects are needed before firm conclusions of these large-scale flow structures can be made.

  12. Meridional transport of salt in the global ocean from an eddy-resolving model

    Science.gov (United States)

    Treguier, A. M.; Deshayes, J.; Le Sommer, J.; Lique, C.; Madec, G.; Penduff, T.; Molines, J.-M.; Barnier, B.; Bourdalle-Badie, R.; Talandier, C.

    2014-04-01

    The meridional transport of salt is computed in a global eddy-resolving numerical model (1/12° resolution) in order to improve our understanding of the ocean salinity budget. A methodology is proposed that allows a global analysis of the salinity balance in relation to surface water fluxes, without defining a "freshwater anomaly" based on an arbitrary reference salinity. The method consists of a decomposition of the meridional transport into (i) the transport by the time-longitude-depth mean velocity, (ii) time-mean velocity recirculations and (iii) transient eddy perturbations. Water is added (rainfall and rivers) or removed (evaporation) at the ocean surface at different latitudes, which creates convergences and divergences of mass transport with maximum and minimum values close to ±1 Sv. The resulting meridional velocity effects a net transport of salt at each latitude (±30 Sv PSU), which is balanced by the time-mean recirculations and by the net effect of eddy salinity-velocity correlations. This balance ensures that the total meridional transport of salt is close to zero, a necessary condition for maintaining a quasi-stationary salinity distribution. Our model confirms that the eddy salt transport cannot be neglected: it is comparable to the transport by the time-mean recirculation (up to 15 Sv PSU) at the poleward and equatorial boundaries of the subtropical gyres. Two different mechanisms are found: eddy contributions are localized in intense currents such as the Kuroshio at the poleward boundary of the subtropical gyres, while they are distributed across the basins at the equatorward boundaries. Closer to the Equator, salinity-velocity correlations are mainly due to the seasonal cycle and large-scale perturbations such as tropical instability waves.

  13. Solar heating of the oceans-diurnal, seasonal and meridional variation

    OpenAIRE

    Woods, John D; Barkmann, Wolfgang; Horch, Alexander

    1984-01-01

    Solar heating is an important factor in modelling the upper boundary layer of the ocean. It influences not only the temperature, but also the depth of the mixed layer and must be taken into account in circulation dynamics. The study reported in this paper was designed to reveal the principal features of the global climatology of solar heating in the ocean, with such applications in mind. The meridional, seasonal and diurnal variations of the vertical distribution of solar heating inside the o...

  14. Critical embedment depth of a rigid retaining wall against overturning in unsaturated soils considering intermediate principal stress and strength nonlinearity

    Institute of Scientific and Technical Information of China (English)

    张常光; 陈新栋; 范文

    2016-01-01

    The overturning stability is vital for the retaining wall design of foundation pits, where the surrounding soils are usually unsaturated due to water draining. Moreover, the intermediate principal stress does affect the unsaturated soil strength; meanwhile, the relationship between the unsaturated soil strength and matric suction is nonlinear. This work is to present closed-form equations of critical embedment depth for a rigid retaining wall against overturning by means of moment equilibrium. Matric suction is considered to be distributed uniformly and linearly with depth. The unified shear strength formulation for unsaturated soils under the plane strain condition is adopted to characterize the intermediate principal stress effect, and strength nonlinearity is described by a hyperbolic model of suction angle. The result obtained is orderly series solutions rather than one specific answer; thus, it has wide theoretical significance and good applicability. The validity of this present work is demonstrated by comparing it with a lower bound solution. The traditional overturning designs for rigid retaining walls, in which the saturated soil mechanics neglecting matric suction or the unsaturated soil mechanics based on the Mohr-Coulomb criterion are employed, are special cases of the proposed result. Parametric studies about the intermediate principal stress, matric suction and its distributions along with two strength nonlinearity methods on a new defined critical buried coefficient are discussed.

  15. Flux Transport Solar Dynamos with Shallow Meridional Flow and Turbulent Pumping

    Science.gov (United States)

    Nandi, Dibyendu; Hazra, Soumitra

    2016-07-01

    The large-scale solar magnetic cycle is sustained by a dynamo mechanism in which the induction of the toroidal component of the magnetic field by differential rotation and the regeneration of the poloidal component are crucial processes. In the Sun, the Babcock-Leighton mechanism, i.e., the (near-surface) redistribution of the flux of tilted bipolar sunspot pairs is thought to be the main source of the solar poloidal field. The poloidal field so generated must be transported to the solar interior where the toroidal field is generated and stored - presumably near the base of the solar convection zone. Traditionally, flux transport dynamo models have relied on a deep meridional circulation to achieve this transport. However, recent observations claim that the meridional circulation could be much shallower that previously thought. We explore the question whether flux transport dynamos can function with a shallow meridional flow and present an alternative paradigm for flux transport dynamics in solar-stellar interiors sustained by turbulent pumping.

  16. Agrobiodiversity of cactus pear (Opuntia, Cactaceae in the Meridional Highlands Plateau of Mexico

    Directory of Open Access Journals (Sweden)

    Juan Antonio Reyes-Agüero

    2011-08-01

    Full Text Available Mexico is characterized by a remarkable richness of Opuntia, mostly at the Meridional Highlands Plateau; it is also here where the greatest richness of Opuntia variants occurs. Most of these variants have been maintained in homegardens; however, the gathering process which originated these homegardens has been disrupted over the past decades, as a result of social change and the destruction of large wild nopaleras. If the variants still surviving in homegardens are lost, these will be hard to recover, that is, the millenary cultural heritage from the human groups that populated the Mexican Meridional Highland Plateau will be lost forever. This situation motivated the preparation of a catalogue that records the diversity of wild and cultivated Opuntia variants living in the meridional Highlands Plateau. To this end, 379 samples were obtained in 29 localities, between 1998 and 2003. The information was processed through Twinspan. All specimens were identified and preserved in herbaria. Botanical keys and descriptions were elaborated. The catalogue includes information on 126 variants comprising 18 species. There were species with only one variant (Opuntia atropes, O. cochinera, O. jaliscana, O. leucotricha, O. rzedowskii and O. velutina, two (O. durangensis, O. lindheimeri, O. phaeacantha and O. robusta, five (O. joconostle and O. lasiacantha, seven (O. chavena, 12 (O. hyptiacantha and O. streptacantha, 15 (O. ficus-indica, 22 (O. albicarpa, and up to 34 (O. megacantha. Additionally, 267 common cactus pear names were related to those variants.

  17. Solar wave-field simulation for testing prospects of helioseismic measurements of deep meridional flows

    CERN Document Server

    Hartlep, Thomas; Kosovichev, Alexander G; Mansour, Nagi N

    2012-01-01

    The meridional flow in the Sun is an axisymmetric flow that is generally poleward directed at the surface, and is presumed to be of fundamental importance in the generation and transport of magnetic fields. Its true shape and strength, however, is debated. We present a numerical simulation of helioseismic wave propagation in the whole solar interior in the presence of a prescribed, stationary, single-cell, deep meridional circulation serving as a test-bed for helioseismic measurement techniques. A deep-focusing time-distance helioseismology technique is applied to the artificial data showing that it can in fact be used to measure the effects of the meridional flow very deep in the solar convection zone. It is shown that the ray-approximation which is commonly used for interpretation of helioseismology measurements remains a reasonable approximation even for the very long distances between 12 and 42 degrees corresponding to depths between 52 and 195 Mm considered here. From the measurement noise we extrapolate...

  18. Causes and impacts of changes in the stratospheric meridional circulation in a chemistry-climate model

    Energy Technology Data Exchange (ETDEWEB)

    Garny, Hella

    2011-05-13

    The stratospheric meridional circulation is projected to be subject to changes due to enhanced greenhouse-gas concentrations in the atmosphere. This study aims to diagnose and explain long-term changes in the stratospheric meridional circulation using the chemistry-climate model E39CA. The diagnosed strengthening of the circulation is found to be driven by increases in tropical sea surface temperatures which lead to a strengthening and upward shift of the subtropical jets. This enables enhanced vertical propagation of large scale waves into the lower stratosphere, and therefore stronger local wave forcing of the meridional circulation in the tropical lower stratosphere. The impact of changes in transport on the ozone layer is analysed using a newly developed method that allows the separation of the effects of transport and chemistry changes on ozone. It is found that future changes of mean stratospheric ozone concentrations are largely determined by changes in chemistry, while changes in transport of ozone play a minor role. (orig.)

  19. Wind Diffusivity Current, QuikSCAT SeaWinds, 0.25 degrees, Global, Science Quality, Meridional

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NOAA CoastWatch distributes science quality Ekman current (in zonal, meridional, and modulus sets) and Ekman upwelling data. This data begins with wind velocity...

  20. Two-dimensional model for an αΩ-dynamo with meridional circulation and an associated Hamilton-Jacobi equation

    Science.gov (United States)

    Popova, E. P.

    2015-08-01

    A two-dimensional model for an αΩ-dynamo is constructed, taking into account meridional flows. A Hamilton-Jacobi equation for the resulting system of magnetic-field generation equatons is constructed using an asymptotic method analogous to the WKB method. This equation makes it possible to analytically study the influence of meridional flows on the duration of the solar magnetic-activity cycle and the evolution of magnetic waves.

  1. Atlantic Equatorial Deep Jets: Space–Time Structure and Cross-Equatorial Fluxes

    OpenAIRE

    Send, Uwe; Eden, Carsten; Schott, Friedrich

    2002-01-01

    The so-called equatorial stacked jets are analyzed with ship-board observations and moored time series from the Atlantic Ocean. The features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator. Mode-filtering gives clear views of the jets in meridional sections, the typical extent being ±1° in latitude. The vertical structure can be well described (explaining 82% of the variance) by N−1-stretched cosines, with a Gaussia...

  2. North Atlantic climatic changes reflected in the Late Quaternary foraminiferal abundance record of the Andaman Sea, north-eastern Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Sijinkumar, A.V.; Nath, B.N.; Clemens, S.

    tempera- ture and Indian monsoon intensity through a physical mechanism af- fecting the meridional gradient of upper tropospheric temperaturethe East Asian monsoon and the North Atlantic climate for the last gla- cial period (Dykoski et al., 2005... in the Andaman Sea area. Mar. Geol. 11, 159–173. Goswami, B.N., Madhusoodanan, M.S., Neema, C.P., Sengupta, D., 2006. A physical mech- anism for North Atlantic SST influence on the Indian summer monsoon. Geophys. Res. Lett. 33, L02706. http://dx.doi.org/10...

  3. Response of the Water Cycle of West Africa and Atlantic to Radiative Forcing by Saharan Dust

    Science.gov (United States)

    Lau, K. M.; Kim, Kyu-Myong; Sud, Yogesh C.; Walker, Gregory L.

    2010-01-01

    The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence in support of the "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feed back triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Easter Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean. region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while long wave has the opposite response. The elevated dust layer warms the air over Nest Africa and the eastern Atlantic. The condensation heating associated with the induced deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface energy fluxes, resulting in cooling of the Nest African land and the eastern Atlantic, and a warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

  4. Air-sea interactions and oceanic processes in the development of different Atlantic Niño patterns

    Science.gov (United States)

    Martin-Rey, Marta; Polo, Irene; Rodríguez-Fonseca, Belén; Lazar, Alban

    2016-04-01

    Atlantic Niño is the leading mode of inter-annual variability of the tropical Atlantic basin at inter-annual time scales. A recent study has put forward that two different Atlantic Niño patterns co-exist in the tropical Atlantic basin during negative phases of the Atlantic Multidecadal Oscillation. The leading mode, Basin-Wide (BW) Atlantic Niño is characterized by an anomalous warming extended along the whole tropical basin. The second mode, the Dipolar (D) Atlantic Niño presents positive Sea Surface Temperature (SST) anomalies in the central-eastern equatorial band, surrounded by negative ones in the North and South tropical Atlantic. The BW Atlantic Niño is associated with a weakening of both Azores and Sta Helena High, which reduces the tropical trades during previous autumn-winter. On the other hand, the D-Atlantic Niño is related to a strengthening of the Azores and a weakening of Helena High given rise to a meridional Sea Level Pressure (SLP) gradient that originates an intensification of the subtropical trades and anomalous westerlies along the equatorial band. This different wind forcing suggests that different oceanic processes could act in the development of the BW and D Atlantic Niño patterns. For this reason, an inter-annual simulation with the ocean NEMO model has been performed and the heat budget analysis has been analysed for each Atlantic Niño mode. The results suggest that the two Atlantic Nino configurations have different timing. The heat budget analysis reveals that BW Atlantic Nino SST pattern is due to anomalous air-sea heat fluxes in the south tropical and western equatorial Atlantic during the autumn-winter, while vertical processes are responsible of the warming in the central and eastern part of the basin during late-winter and spring. For the D-Atlantic Nino, the subtropical cooling is attributed to turbulent heat fluxes, the equatorial SST signal is mainly forced by vertical entrainment. The role of the oceanic waves in the

  5. Remote influences on freshwater flux variability in the Atlantic warm pool region

    Science.gov (United States)

    Zhang, Liping; Wang, Chunzai

    2012-10-01

    The understanding of freshwater flux variability is both scientifically and socially important. Local freshwater flux response to a large Atlantic warm pool (AWP) is excessive freshwater or negative Evaporation minus Precipitation (EmP) anomalies, whereas the response is deficient to a small AWP. However, the EmP anomalies in the AWP region are also influenced by the SST anomalies in the tropical eastern Pacific and in the tropical South Atlantic. These remote influences operate through the inter-basin mode represented by the SST gradient between the tropical North Atlantic and eastern Pacific and the Atlantic meridional mode (AMM) defined as the SST gradient between the tropical North and South Atlantic. When either of these two modes is in the negative phase, the EmP and sea surface salinity anomalies in the AWP region can be positive although the AWP is large. This indicates that the remote influences of the inter-basin mode and/or the AMM can overwhelm the local effect and induce an opposite freshwater response. Additionally, although ENSO and the AMM sometimes coincide with AWP variability, an El Niño in the preceding winter or a positive AMM in the spring does not necessarily follow a large AWP in the summer.

  6. Impact of the North Atlantic sea surface temperature tripole on the East Asian summer monsoon

    Science.gov (United States)

    Zuo, Jinqing; Li, Weijing; Sun, Chenghu; Xu, Li; Ren, Hong-Li

    2013-07-01

    A strong (weak) East Asian summer monsoon (EASM) is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive (negative) SST anomalies in the northwestern North Atlantic and negative (positive) SST anomalies in the subpolar and tropical ocean. The mechanisms responsible for this linkage are diagnosed in the present study. It is shown that a barotropic wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer. This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains, which has a substantial effect on the EASM. Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing. Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation (NAO), the relationships between these two factors and the EASM are also examined. It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole, which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO. The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.

  7. Atlantic Salmon Telemetry Monitoring

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Annual telemetry data are collected as part of specific projects (assessments within watersheds) or as opportunistic efforts to characterize Atlantic salmon smolt...

  8. Probabilistic safety verification for the overturning of a service water pump house against 'over pressure wave'

    International Nuclear Information System (INIS)

    The Atucha II Nuclear Power Plant is being built in a riverside site located about 100 km north of the city of Buenos Aires. When completed it will become Argentina's third operating station. The Service Water Pump House of the 740 MW Natural Uranium NPP is supplied directly by the Parana de las Palmas River, which is a navigable waterway with heavy fluvial traffic that links the River Plate Estuary with ports along the Parana River, including Rosario, Argentina's third city. Although dolphins were built to protect the water intake structures from direct impact from ships or barges, an accidental escape of gas or flammable material outside the protected area that may result in an explosion with a subsequent pressure wave, could not be precluded. Thus, the water intake structures had to be designed against this event. In addition, concern with the margin of safety against foundation instability due to the overturning moment associated to the induced pressures, made an evaluation of the conditional probability of failure for this loading condition, desirable. The task placed still uncommon demands on the Project Engineers, who were required to provide estimates of the Pump House reliability. In the process, it became necessary to introduce assumptions concerning the unspecified variability of the loads which, according to current international practice, were defined in the form of 'deterministic' design criteria. It seems appropriate to underline these deficiencies in current standards, as well as in aspects of the dynamic of soils that are responsible for a quite large model uncertainty. On the basis of available information, it may be established that the probability of occurrence of a pressure wave at the site is less than 10-3 per year. Accordingly, the probability of failure of the foundation due to a pressure wave does not exceed 1.5 -8 per year, value that is considered admissible by current standards. The use of triangular probability density functions for

  9. The role of barotropic and baroclinic waves in oceanic teleconnections

    OpenAIRE

    Bora, Sagar

    2013-01-01

    Buoyancy forcing in the high latitudes and variability in North Atlantic Deep Water formation leads to weakening of the Meridional Overturning Circulation (MOC). Perturbations at the high latitudes of the North Atlantic are adjusted via coastally trapped waves, equatorial Kelvin waves and westward propagating Rossby waves. This thesis works towards understanding the importance of oceanic teleconnections in transmitting variability through wave mechanisms. The effect of mesh resolution on off-...

  10. Tierra y familia en la España meridional, siglos XIII-XIX.

    OpenAIRE

    Igor Goicovic Donoso

    2011-01-01

    Las siete contribuciones recopiladas por Francisco García Gon-zález en el texto Tierra y familia en la España meridional, siglos XIII-XIX, nos sitúan frente a la historia social a partir de dos inflexiones epistemológicas íntimamente relacionadas en la historia: tierra y familia. Efectivamente, la diada tierra-familia, durante el Antiguo Régimen europeo, se convirtió en un factor explicativo de buena parte de los procesos de articulación de la sociedad. Así, la relación de los sujetos co...

  11. Overturning anti-miscegenation laws: news media coverage of the Lovings' legal case against the state of Virginia.

    Science.gov (United States)

    Hoewe, Jennifer; Zeldes, Geri Alumit

    2012-01-01

    This study fills a gap in scholarship by exploring historical news coverage of interracial relationships. It examines coverage by The New York Times, Washington Post and Times-Herald, and Chicago Tribune of the progression of the landmark civil rights case of Loving v. Virginia, in which the Supreme Court overturned Virginia's anti-miscegenation law, which prohibited marriage between any White and non-White person. An analysis of the frames and sources used in these publications' news stories about the case indicate all three publications' coverage favored the Lovings. PMID:22834052

  12. 76 FR 1153 - Atlantic Grid Operations A LLC, Atlantic Grid Operations B LLC, Atlantic Grid Operations C LLC...

    Science.gov (United States)

    2011-01-07

    ... Energy Regulatory Commission Atlantic Grid Operations A LLC, Atlantic Grid Operations B LLC, Atlantic Grid Operations C LLC, Atlantic Grid Operations D LLC and Atlantic Grid Operations E LLC; Notice of... (Commission) Rules of Practice and Procedure, 18 CFR 385.207, and Order No. 679,\\1\\ Atlantic Grid Operations...

  13. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution ocean model

    Science.gov (United States)

    Topper, R. P. M.; Meijer, P. Th.

    2015-02-01

    A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations of the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic-Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is shallower and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin, a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic-Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which

  14. Meridional motions and Reynolds stress from SDO/AIA coronal bright points data

    CERN Document Server

    Sudar, Davor; Skokić, Ivica; Beljan, Ivana Poljančić; Brajša, Roman

    2016-01-01

    Context. It is possible to detect and track coronal bright points (CBPs) in SDO/AIA images. Combination of high resolution and high cadence provides a wealth of data that can be used to determine velocity flows on the solar surface with very high accuracy. Aims. We derived a very accurate solar rotation profile and investigated meridional flows, torsional oscillations and horizontal Reynolds stress based on $\\approx$6 months of SDO/AIA data. Methods. We used a segmentation algorithm to detect CBPs in SDO/AIA images. We also used invariance of the solar rotation profile with central meridian distance (CMD) to determine the height of CBPs in 19.3 nm channel. Results. Best fit solar rotation profile is given by $\\omega(b)=(14.4060\\pm0.0051 + (-1.662\\pm0.050)\\sin^{2}b + (-2.742\\pm0.081)\\sin^{4}b)${\\degr} day$^{-1}$. Height of CBPs in SDO/AIA 19.3 nm channel was found to be $\\approx$6500 km. Meridional motion is predominantly poleward for all latitudes, while solar velocity residuals show signs of torsional oscill...

  15. Characteristics of winter-time meridional thermospheric winds over Tromsø during solar minimum

    Science.gov (United States)

    Cai, Hongtao; Zhan, Weijia; Huang, Dingjuan; Li, Fei; Zhou, Kangjun; Shen, Ge; Willian McCrea, Ian; Ma, Shuying

    2015-04-01

    The background of the winter-time thermospheric wind over Tromsø (69 °N, 19 °E) were focused on in this paper. The meridional component of the neutral wind in F-region were derived from the field-aligned ion velocity detected by the European incoherent scattering (EISCAT) radar. In order to eliminate possible influences from solar activity variances and geomagnetic disturbance, only measurements accomplished under geomagnetically quiet conditions (with maximum Kp ≤ 3) around the winter solstice during solar minimum (2008-2009) were chosen in present work. Two major characteristics of the radar derived winds are revealed. The first feature is the vertical variations of the meridional winds. Magnitudes of the equatorward winds observed show a hint of increasing with altitudes during nighttime. The second one is the persistent equatorward winds at altitudes higher than 280 km height during daytime, especially around local noon, whilst the prevailing poleward winds appear at lower altitudes. Thus, significant shears of horizontal winds are expected in the vertical direction. Detail comparisons with models and discussions of the possible driving forces for the day-time equatorward winds will be presented in the report.

  16. On the role of meridional flows in flux transport dynamo models

    CERN Document Server

    Jouve, L

    2007-01-01

    The Sun is a magnetic star whose magnetism and cyclic activity is linked to the existence of an internal dynamo. We aim to understand the establishment of the solar magnetic 22-yr cycle, its associated butterfly diagram and field parity selection through numerical simulations of the solar global dynamo. Inspired by recent observations and 3D simulations that both exhibit multicellular flows in the solar convection zone, we seek to characterise the influence of various profiles of circulation on the behaviour of solar mean-field dynamo models. We are using 2-D mean field flux transport Babcock-Leighton numerical models in which we test several types of meridional flows: 1 large single cell, 2 cells in radius and 4 cells per hemisphere. We confirm that adding cells in latitude tends to speed up the dynamo cycle whereas adding cells in radius more than triples the period. We find that the cycle period in the four cells model is less sensitive to the flow speed than in the other simpler meridional circulation pro...

  17. Meridional lenticular astigmatism associated with bilateral concurrent uveal metastases in renal cell carcinoma

    Directory of Open Access Journals (Sweden)

    Priluck JC

    2012-11-01

    Full Text Available Joshua C Priluck, Sandeep Grover, KV ChalamDepartment of Ophthalmology, University of Florida College of Medicine, Jacksonville, FL, USAPurpose: To demonstrate a case illustrating meridional lenticular astigmatism as a result of renal cell carcinoma uveal metastases.Methods: Case report with images.Results: Clinical findings and diagnostic testing of a patient with acquired meridional lenticular astigmatism are described. The refraction revealed best-corrected visual acuity of 20/20–1 OD (−2.50 + 0.25 × 090 and 20/50 OS (−8.25 + 3.25 × 075. Bilateral concurrent renal cell carcinoma metastases to the choroid and ciliary body are demonstrated by utilizing ultrasonography, ultrawidefield fluorescein angiography, and unique spectral-domain optical coherence tomography.Conclusions: Metastatic disease should be included in the differential of acquired astigmatism. Spectral-domain optical coherence tomography, ultrawidefield fluorescein angiography, and ultrasonography have roles in delineating choroidal metastases.Keywords: astigmatism, metastasis, optical coherence tomography, renal cell carcinoma

  18. Automated Quantitative Spectral Classification of Stars in Areas of the main Meridional Section of the Galaxy

    Science.gov (United States)

    Shvelidze, Teimuraz; Malyuto, Valeri

    2015-08-01

    Quantitative spectral classification of F, G and K stars with the 70-cm telescope of the Ambastumani Astrophysical Observatory in areas of the main meridional section of the Galaxy, and for which proper motion data are available, has been performed. Fundamental parameters have been obtained for several hundred stars. Space densities of stars of different spectral types, the stellar luminosity function and the relationships between the kinematics and metallicity of stars have been studied. The results have confirmed and completed the conclusions made on the basis of some previous spectroscopic and photometric surveys. Many plates have been obtained for other important directions in the sky: the Kapteyn areas, the Galactic anticentre, the main meridional section of the Galaxy and etc. Very rich collection of photographic objective spectral plates (30,000 were accumulated during last 60 years) is available at Abastumani Observatory-wavelength range 3900-4900 A, about 2A resolution. Availability of new devices for automatic registration of spectra from photographic plates as well as some recently developed classification techniques may allow now to create a modern system of automatic spectral classification and with expension of classification techniques to additional types (B-A, M spectral classes). The data can be treated with the same quantitative method applied here. This method may also be applied to other available and future spectroscopic data of similar resolution, notably that obtained with large format CCD detectors on Schmidt-type telescopes.

  19. Verification of the helioseismic Fourier-Legendre analysis for meridional flow measurements

    CERN Document Server

    Roth, Markus; Hartlep, Thomas

    2016-01-01

    Measuring the Sun's internal meridional flow is one of the key issues of helioseismology. Using the Fourier-Legendre analysis is a technique for addressing this problem. We validate this technique with the help of artificial helioseismic data. The analysed data set was obtained by numerically simulating the effect of the meridional flow on the seismic wave field in the full volume of the Sun. In this way, a 51.2-hour long time series was generated. The resulting surface velocity field is then analyzed in various settings: Two $360^\\circ \\times 90^\\circ$ halfspheres, two $120^\\circ \\times 60^\\circ$ patches on the front and farside of the Sun (North and South, respectively) and two $120^\\circ \\times 60^\\circ$ patches on the northern and southern frontside only. We compare two possible measurement setups: observations from Earth and from an additional spacecraft on the solar farside, and observations from Earth only, in which case the full information of the global solar oscillation wave field was available. We ...

  20. Variability and trends of the meridional energy transports and implications for the Hadley circulation

    Science.gov (United States)

    Boschat, Ghyslaine; Simmonds, Ian

    2016-04-01

    The atmosphere and the ocean play a critical role in the Earth energy balance by transporting heat from the equator to the poles. In the atmosphere, this net meridional energy transport is the sum of many atmospheric processes on very different scales in space and time: in the tropics most of the energy is transported poleward by the Hadley circulation, whereas eddies become the principal agency of heat transport in higher latitudes. However these synoptic systems are also believed to interact in a quite complex manner with the Hadley circulation. The aim of this study is to perform a detailed and updated analysis of the meridional heat transports by the atmosphere and determine the relative role of the Hadley circulation and eddy activity in this energy redistribution. Using 6 hourly ERA-Interim data from 1979 to 2014, we examine the spatial contrasts in the transport of sensible heat, latent heat and potential energy components, and diagnose how these may have been changing on seasonal to inter-annual timescales. These contributions are further partitioned into mean circulations and (stationary and transient) eddies' activities, to explore the complementary variations occurring between baroclinic synoptic systems and mean tropical cells. Finally, this "unifying conceptual framework" provides new insights into the variability and trends of the Hadley circulation, which help us better understand the factors controlling the behavior of the cell both in the present climate and under a global warming scenario.

  1. Meridional-Flow Measurements from 15 Years of GONG Spherical-Harmonic Time Series

    International Nuclear Information System (INIS)

    We present results of meridional-flow measurements for 1995-2009, using travel-time differences from velocity images reconstructed using GONG spherical harmonic (SH) coefficients after applying phase-velocity and low-m filters. This filtering technique increases the signal-to-noise ratio and thus extends travel-time measurements to relatively high latitudes and deep into the convection zone. Preliminary analyses shows a strong one-year periodicity presumably due to solar pole misalignment and B0-angle artifacts, which makes it difficult to see underlying temporal variations. Removing a simple one-year-period sine wave fit reveals long-term temporal variations of the flow on top of this yearly periodicity. High-latitude measurements are affected more stronger by foreshortening and B0 -angle artifacts. We analyze different B0-angle intervals separately, so in each hemisphere better high-latitude visibility comes six months apart. This approach suggests why at high latitudes travel-time measurements of meridional flow shows a tendency to change sign instead of continuing towards the poles.

  2. Atlantic menhaden adult tagging study

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Atlantic menhaden are a schooling forage fish species, which are subject to a large commercial purse seine fishery. Atlantic menhaden are harvested for reduction...

  3. Study on mechanism of interdecadal Atlantic thermohaline circulation variability Ⅲ.Influences of inter-decadal variations by ocean-atmosphere elements%大西洋热盐环流年代际变化机制研究Ⅲ.北大西洋海气要素对热盐环流年代际振荡的影响

    Institute of Scientific and Technical Information of China (English)

    牟林; 陈学恩; 宋军; 李欢; 李琰; 姜晓轶; 李海; 陈幸荣

    2011-01-01

    Using the advanced climate ocean-atmosphere coupled model described in the first paper of this series of studies, response analyses of inter-decadal variations of the Atlantic thermohaline circulation by ocean-atmosphere elements were deliberated. For studying the relationship between the ocean elements of the North Atlantic and inter-decadal variations of Atlantic thermohaline circulation, subpolar sea-surface-density index (SSI) and North-Atlantic-Current Strength Index (NSI) were defined and analyzed. The results of analyses indicate that SSI changes 7 years earlier than Atlantic meridional overturning circulation (MOO while NSI changing 4 years earlier than MOC. The strength of water overflows from Greenland-Scotland sea ridge (including Denmark Strait and Faro Strait), which is an important water resource ofNorth Atlantic deep water, changes 3 years ahead MOC. The inter-decadal variations of Atlantic thermohaline circulation THC are influenced by North Atlantic atmosphere elements significantly. 2 years before subpolar current and North Atlantic Current (NAC) reaching their full strength, High-latitude atmosphere is abnormal in the pattern of cyclonic circulation and middle-latitude atmosphere is abnormal in the pattern of anticyclonic circulation. Meanwhile, the sea surface heat flux in Atlantic subpolar sea area is negative anomaly. All of those abnormal conditions enhance the strength of subpolar current and NAC. More water with higher salinity intruding into Greenland-Icelandic-Norwegian Sea (GIN) brings higher sea surface density of GIN. This weakens the stability of water stratification and increases the probability of occurrence of deep convection. Meanwhile, the variation of atmosphere influences the deep water generating process in GIN by the curl of wind stress and sea surface heat flux. Then the strength of water overflows from Greenland-Scotland sea ridge is strengthened.%基于该系列文章前文研究中构建的海气耦合气候模式和所

  4. Importance of Meridional Circulation in Flux Transport Dynamo: The Possibility of a Maunder-like Grand Minimum

    OpenAIRE

    Karak, Bidya Binay

    2010-01-01

    Meridional circulation is an important ingredient in flux transport dynamo models. We have studied its importance on the period, the amplitude of the solar cycle, and also in producing Maunder-like grand minima in these models. First, we model the periods of the last 23 sunspot cycles by varying the meridional circulation speed. If the dynamo is in a diffusion-dominated regime, then we find that most of the cycle amplitudes also get modeled up to some extent when we model the periods. Next, w...

  5. The Aqua-planet Experiment (APE): Response to Changed Meridional SST Profile

    Science.gov (United States)

    Williamson, David L.; Blackburn, Michael; Nakajima, Kensuke; Ohfuchi, Wataru; Takahashi, Yoshiyuki O.; Hayashi, Yoshi-Yuki; Nakamura, Hisashi; Ishiwatari, Masaki; Mcgregor, John L.; Borth, Hartmut; Wirth, Volkmar; Frank, Helmut; Bechtold, Peter; Wedi, Nils P.; Tomita, Hirofumi; Satoh, Masaki; Zhao, Ming; Held, Isaac M.; Suarez, Max J.; Lee, Myong-In; Watanabe, Masahiro; Kimoto, Masahide; Liu, Yimin; Wang, Zaizhi; Molod, Andrew; RajenDran, Kavirajan; Kitoh, Akio; Stratton, Rachel

    2013-01-01

    This paper explores the sensitivity of Atmospheric General Circulation Model (AGCM) simulations to changes in the meridional distribution of sea surface temperature (SST). The simulations are for an aqua-planet, a water covered Earth with no land, orography or sea- ice and with specified zonally symmetric SST. Simulations from 14 AGCMs developed for Numerical Weather Prediction and climate applications are compared. Four experiments are performed to study the sensitivity to the meridional SST profile. These profiles range from one in which the SST gradient continues to the equator to one which is flat approaching the equator, all with the same maximum SST at the equator. The zonal mean circulation of all models shows strong sensitivity to latitudinal distribution of SST. The Hadley circulation weakens and shifts poleward as the SST profile flattens in the tropics. One question of interest is the formation of a double versus a single ITCZ. There is a large variation between models of the strength of the ITCZ and where in the SST experiment sequence they transition from a single to double ITCZ. The SST profiles are defined such that as the equatorial SST gradient flattens, the maximum gradient increases and moves poleward. This leads to a weakening of the mid-latitude jet accompanied by a poleward shift of the jet core. Also considered are tropical wave activity and tropical precipitation frequency distributions. The details of each vary greatly between models, both with a given SST and in the response to the change in SST. One additional experiment is included to examine the sensitivity to an off-equatorial SST maximum. The upward branch of the Hadley circulation follows the SST maximum off the equator. The models that form a single precipitation maximum when the maximum SST is on the equator shift the precipitation maximum off equator and keep it centered over the SST maximum. Those that form a double with minimum on the equatorial maximum SST shift the double

  6. Relation between sea surface temperature anomaly in the Atlantic and summer precipitation over the Northeast China

    Institute of Scientific and Technical Information of China (English)

    白人海

    2001-01-01

    Based on global monthly average data set of sea surface temperature (SST) during 1950 -1992 and global monthly average 500 hPa height during 1950 - 1997 offered by NCAR/NCEP, the feature of SST anomaly in the Atlantic and its relation with summer precipitation over the Northeast China are analyzed. The results show that, the second eigenvector of the SST′s empirical orthogonal expanssion in winter season over the North Atlantic suggests that distribution of SST anomaly has unusual meridional difference; The location of its center is basically identical to center of significant correlation region between summer precipitation over the Northeast China and winter SST in the Atlantic. When winter SST in the North Atlantic is hot in south and cold in north, the blocking situation is stronger in the middle- high latitude. Correspondingly, the blocking high pressure in the northern North Pacific is also getting stronger,the westerlies circulation index in East Asia in next summer would be lower, asa result, more precipitation in the summer would be experienced over Northeast China and vice versa.

  7. Calculation of a residual mean meridional circulation for a zonal-mean tracer transport model

    Energy Technology Data Exchange (ETDEWEB)

    Choi, W.K.; Rotman, D.A.; Wuebbles, D.J. [Lawrence Livermore National Lab., CA (United States). Global Climate Research Div.

    1995-04-01

    Because of their computational advantages, zonally-averaged chemical-radiative-transport models are widely used to investigate the distribution of chemical species and their change due to the anthropogenic chemicals in the lower and middle atmosphere. In general, the Lagrangian-mean formulation would be ideal to treat transport due to the zonal mean circulation and eddies. However, the Lagrangian formulation is difficult to use in practical applications. The most widely-used formulation for treating global atmospheric dynamics in two-dimensional models is the transformed Eulerian mean (TEM) equations. The residual mean meridional circulation (RMMC) in the TEM system is used to advect tracers. In this study, the authors describe possible solution techniques for obtaining the RMMC in the LLNL two-dimensional chemical-radiative-transport model. In the first section, the formulation will be described. In sections 3 and 4, possible solution procedures will be described for a diagnostic and prognostic case, respectively.

  8. Tierra y familia en la España meridional, siglos XIII-XIX.

    Directory of Open Access Journals (Sweden)

    Igor Goicovic Donoso

    2011-10-01

    Full Text Available Las siete contribuciones recopiladas por Francisco García Gon-zález en el texto Tierra y familia en la España meridional, siglos XIII-XIX, nos sitúan frente a la historia social a partir de dos inflexiones epistemológicas íntimamente relacionadas en la historia: tierra y familia. Efectivamente, la diada tierra-familia, durante el Antiguo Régimen europeo, se convirtió en un factor explicativo de buena parte de los procesos de articulación de la sociedad. Así, la relación de los sujetos con la propiedad y usufructo de la tierra, y las formas de articulación familiar desplegadas por los mismos, tienden a imbricarse recurrentemente en complejos procesos de reproducción social.

  9. Zonal superrotation above Venus' cloud base induced by the semidiurnal tide and the mean meridional circulation

    Science.gov (United States)

    Hou, Arthur Y.; Goody, Richard M.; Fels, Stephen B.

    1990-01-01

    The equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the Venus cloud base were calculated. The results show that the tidal mechanism proposed by Fels and Lindzen (1974) can account for a substantial fraction (and possibly all) of the increase of the equatorial wind speed above the cloud base. Above the cloud tops, tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data. Tidal forcing does not explain the superrotation below the clouds, and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes.

  10. Atlantic City memories.

    Science.gov (United States)

    Epstein, Franklin H

    2008-04-01

    Fifty years ago, the Atlantic City meetings, held the first week in May of every year, were attended by all the elite of American academic medicine and all who wanted to join that group. Part of the magic of those meetings was that professors and neophytes took each other seriously and talked to each other. PMID:18382726

  11. Meridional Flow in the Solar Convection Zone. II. Helioseismic Inversions of GONG Data

    Science.gov (United States)

    Jackiewicz, J.; Serebryanskiy, A.; Kholikov, S.

    2015-06-01

    Meridional flow is thought to play a very important role in the dynamics of the solar convection zone; however, because of its relatively small amplitude, precisely measuring it poses a significant challenge. Here we present a complete time-distance helioseismic analysis of about 2 years of ground-based Global Oscillation Network Group (GONG) Doppler data to retrieve the meridional circulation profile for modest latitudes in an attempt to corroborate results from other studies. We use an empirical correction to the travel times due to an unknown center-to-limb systematic effect. The helioseismic inversion procedure is first tested and reasonably validated on artificial data from a large-scale numerical simulation followed by a test to broadly recover the solar differential rotation found from global seismology. From GONG data, we measure poleward photospheric flows at all latitudes with properties that are comparable with earlier studies and a shallow equatorward flow about 65 Mm beneath the surface, in agreement with recent findings from Helioseismic and Magnetic Imager (HMI) data. No strong evidence of multiple circulation cells in depth or latitude is found, yet the whole phase space has not yet been explored. Tests of mass flux conservation are then carried out on the inferred GONG and HMI flows and compared to a fiducial numerical baseline from models, and we find that the continuity equation is poorly satisfied. While the two disparate data sets do give similar results for about the outer 15% of the interior radius, the total inverted circulation pattern appears to be unphysical in terms of mass conservation when interpreted over modest time scales. We can likely attribute this to both the influence of realization noise and subtle effects in the data and measurement procedure.

  12. Control of Meridional Flow by a Non-Uniform Rotational Magnetic Field

    Science.gov (United States)

    Mazuruk, Konstantin; Ramachandran, Narayanan

    1999-01-01

    The diffusive mass transfer of species during crystal growth in vertical ampoules is significantly affected by fluid flow in the liquid mother phase (melt). For electrically conductive melts, an elegant way of remotely inducing and controlling this flow is by utilizing a uniform rotational magnetic field (RMF) in the transverse direction. It induces an azimuthal flow which tends to homogenize the thermal and solutal fields. The rotating field also reduces the diffusion boundary layer, stabilizes temperature fluctuations, and promotes better overall crystal growth. For moderate strengths of the applied magnetic field (2-20 m Tesla) with frequencies of up to 400 Hz, the induced secondary meridional flow becomes significant. It typically consists of one roll at the bottom of the liquid column and a second roll (vortex) at the top. The flow along the centerline (ampoule axis) is directed from the growing solid (interface) towards the liquid (melt). In case of convex interfaces (e.g. in floating zone crystal growth) such flow behavior is beneficial since it suppresses diffusion at the center. However, for concave interfaces (e.g. vertical Bridgman crystal growth) such a flow tends to exacerbate the situation in making the interface shape more concave. It would be beneficial to have some control of this meridional flow- for example, a single recirculating cell with controllable direction and flow magnitude will make this technique even more attractive for crystal growth. Such flow control is a possibility if a non-uniform PNE field is utilized for this purpose. Although this idea has been proposed earlier, it has not been conclusively demonstrated so far. In this work, we derive the governing equations for the fluid dynamics for such a system and obtain solutions for a few important cases. Results from parallel experimental measurements of fluid flow in a mercury column subjected to non-uniform RMF will also be presented.

  13. Atlantic tropical cyclones revisited

    Science.gov (United States)

    Mann, Michael E.; Emanuel, Kerry A.; Holland, Greg J.; Webster, Peter J.

    Vigorous discussions have taken place recently in Eos [e.g., Mann and Emanuel, 2006; Landsea, 2007] and elsewhere [Emanuel, 2005; Webster et al., 2005; Hoyos et al., 2006; Trenberth and Shea, 2006; Kossin et al., 2007] regarding trends in North Atlantic tropical cyclone (TC) activity and their potential connection with anthropogenic climate change. In one study, for example [Landsea, 2007], it is argued that a substantial underestimate of Atlantic tropical cyclone counts in earlier decades arising from insufficient observing systems invalidates the conclusion that trends in TC behavior may be connected to climate change. Here we argue that such connections are in fact robust with respect to uncertainties in earlier observations.Several recent studies have investigated trends in various measures of TC activity. Emanuel [2005] showed that a measure of total power dissipation by TCs (the power dissipation index, or PDI) is highly correlated with August-October sea surface temperatures (SST) over the main development region (MDR) for Atlantic TCs over at least the past half century. Some support for this conclusion was provided by Sriver and Ruber [2006]. Webster et al. [2005] demonstrated a statistically significant increase in recent decades in both the total number of the strongest category cyclones (categories 4 and 5) and the proportion of storms reaching hurricane intensity. Hoyos et al. [2006] showed that these increases were closely tied to warming trends in tropical Atlantic SST, while, for example, the modest decrease in vertical wind shear played a more secondary role. Kossin et al. [2007] called into question some trends in other basins, based on a reanalysis of past TC data, but they found the North Atlantic trends to be robust.

  14. A GCM Study of Responses of the Atmospheric Water Cycle of West Africa and the Atlantic to Saharan Dust Radiative Forcing

    Science.gov (United States)

    Lau, K. M.; Kim, K. M.; Sud, Y. C.; Walker, G. K.

    2009-01-01

    The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summerr, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are ehanIed over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a large-scale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer overr the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at0

  15. Cloud Effects on Meridional Atmospheric Energy Budget Estimated from Clouds and the Earth's Radiant Energy System (CERES) Data

    Science.gov (United States)

    Kato, Seiji; Rose, Fred G.; Rutan, David A.; Charlock, Thomas P.

    2008-01-01

    The zonal mean atmospheric cloud radiative effect, defined as the difference of the top-of-atmosphere (TOA) and surface cloud radiative effects, is estimated from three years of Clouds and the Earth's Radiant Energy System (CERES) data. The zonal mean shortwave effect is small, though it tends to be positive (warming). This indicates that clouds increase shortwave absorption in the atmosphere, especially in midlatitudes. The zonal mean atmospheric cloud radiative effect is, however, dominated by the longwave effect. The zonal mean longwave effect is positive in the tropics and decreases with latitude to negative values (cooling) in polar regions. The meridional gradient of cloud effect between midlatitude and polar regions exists even when uncertainties in the cloud effect on the surface enthalpy flux and in the modeled irradiances are taken into account. This indicates that clouds increase the rate of generation of mean zonal available potential energy. Because the atmospheric cooling effect in polar regions is predominately caused by low level clouds, which tend to be stationary, we postulate that the meridional and vertical gradients of cloud effect increase the rate of meridional energy transport by dynamics in the atmosphere from midlatitude to polar region, especially in fall and winter. Clouds then warm the surface in polar regions except in the Arctic in summer. Clouds, therefore, contribute in increasing the rate of meridional energy transport from midlatitude to polar regions through the atmosphere.

  16. Evaluation of overturning capacity of low level radioactive waste drum during earthquake. Part 2. Investigation of drum weight distribution effect and drum columns interaction by numerical analysis

    International Nuclear Information System (INIS)

    Numerical analysis case study is carried out for three layered and four layered low level radioactive waste drums by numerical models based on the results of shaking table test. First of all, numerical analysis results about drums displacement due to uplift and sliding on pallets during earthquake are compared with the experimental results and it is shown good agreement in both results. By this analytical model effects of drum weight distribution along height direction and drum columns interaction followed by each other drum's collisions on overturning capacity during earthquake are researched. From numerical analysis results the limit acceleration which is minimum value of input acceleration at storage building floor when three layered or four layered waste drums overturn is researched. It is shown that overturning capacity during earthquake decline when height of gravity center of three layered and four layered drums get large. So it is available to get down height of gravity center by controlling drum weight distribution along height direction. And as effect of drum columns interaction it is indicated that overturning capacity of single column arrangement drums is larger than that of many columns arrangement drums because phase deference between drum columns occur and decrease vibration amplitude by each other collisions. (author)

  17. Reliability Evaluation of a Concrete Crown Wall on a Rubble Mound Breakwater considering Sliding Failure, Overturning and Rupture Failure of the Foundation

    DEFF Research Database (Denmark)

    Christiani, E.; Sørensen, Jørgen S.; Burcharth, Hans F.

    1994-01-01

    Wave breaking forces on a crown wall will be determined from Burcharth 's wave force formula. Based on these formulae a deterministic design is found. A reliability evaluation of the same structure is then performed using a level II FORM analysis. In this only the failure modes sliding1 overturning...

  18. Moisture transport between the South Atlantic Ocean and southern Africa: relationships with summer rainfall and associated dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Vigaud, N.; Rouault, M. [University of Cape Town, Oceanography Department, Rondebosch (South Africa); Richard, Y.; Fauchereau, N. [UMR 5210 CNRS/ Universite de Bourgogne, Centre de Recherches de Climatologie, Dijon (France)

    2009-01-15

    Moisture exchange between the South Atlantic and southern Africa is examined in this study through zonal moisture transport. Along the west coast of southern Africa, a multivariate analysis of the zonal flow of moisture computed from NCEP-DOE AMIP II Re-analyses reveals a primary mode of variability typical of variations in intensity and of the latitudinal migration of the circulation associated with the midlatitude westerlies and the South Atlantic anticyclone. In austral summer (January-February), this mode, referred to as the South Atlantic midlatitude mode, is found to be well correlated with rainfall over southern Africa (i.e. to the south of the upper lands surrounding the Congo basin). Its positive/negative phases are found to correspond with surface pressures changes over the South Atlantic region in austral summer when the South Atlantic anticyclone is shifted northward/southward respectively. Such changes are accompanied by dipole-like SST anomalies in the midlatitude South Atlantic Ocean, while simultaneous SST anomalies with a similar structure are also found over South Indian Ocean regions. In January-February, positive/negative events linked to the South Atlantic midlatitude mode are marked by meridional shifts (northward/southward) and weakening/strengthening of the ITCZ over the southern tropics, together with modulations in intensity (weakened/sustained) of the Angola low, which could act as a tropical source of moisture for Tropical Temperate Troughs (TTTs). In association with a strengthened/weakened zonal component of the southern extension of the African Easterly Jet (AEJ), this could modulate the meridional transfer of moisture south of 15 S to the advantage/detriment of Angolan coastal regions, where above/below rainfall are expected. Variations in the latitudinal position (northward/southward) of the South Atlantic anticyclone, and thus of the midlatitude westerlies, are also found to reduce/favour moisture advection towards southern Africa

  19. Application of Overturning Technology in Invert Block Prefabrication%空中翻转技术在仰拱预制块生产中的应用

    Institute of Scientific and Technical Information of China (English)

    刘清泉

    2011-01-01

    Vacuum suction type overturning machine is ing method of invert block overturning on the ground is not applicable to the overturning of invert blocks, and the exist- laggard and has many disadvantages. New hydraulic type overturning machine is used in the construction of West Qinling tunnel, which is the first time in China. A set of proved overturning technology is summarized on basis of practice and improvement in the site. Some key points of the new technology are presented. The comparison and contrast between the new method and the existing method show that the new method is superior to the existing one.%为解决长期以来真空吸吊翻转机不适用于仰拱预制块翻转、地面翻滚仰拱预制块技术落后且弊端明显的问题,以适应TBM快速高效的施工节奏,西秦岭隧道全国首次引入仰拱预制块液压起吊翻转机。通过现场实践和改进,总结出一套比较成熟的空中翻转技术,并介绍新技术引入后的一些注意事项。通过方法对比,人员配置及作业时间等均优于地面翻滚法4倍左右,并可有效消除掉块和开裂损伤,对于确保预制块生产进度和生产质量意义重大。

  20. Impacts of Indian and Atlantic oceans on ENSO in a comprehensive modeling framework

    Science.gov (United States)

    Terray, Pascal; Masson, Sébastien; Prodhomme, Chloé; Roxy, Mathew Koll; Sooraj, K. P.

    2016-04-01

    run. These results may be explained by modulations of the Walker circulation induced directly or indirectly by the Indian and Atlantic SSTs. Another interesting result is that decoupling the Atlantic or Indian oceans change the timing of ENSO onset and the relative role of other ENSO atmospheric precursors such as the extra-tropical Pacific Meridional Modes or the Western North Pacific SSTs.

  1. Atlantic Basin refining profitability

    International Nuclear Information System (INIS)

    A review of the profitability margins of oil refining in the Atlantic Basin was presented. Petroleum refiners face the continuous challenge of balancing supply with demand. It would appear that the profitability margins in the Atlantic Basin will increase significantly in the near future because of shrinking supply surpluses. Refinery capacity utilization has reached higher levels than ever before. The American Petroleum Institute reported that in August 1997, U.S. refineries used 99 per cent of their capacity for several weeks in a row. U.S. gasoline inventories have also declined as the industry has focused on reducing capital costs. This is further evidence that supply and demand are tightly balanced. Some of the reasons for tightening supplies were reviewed. It was predicted that U.S. gasoline demand will continue to grow in the near future. Gasoline demand has not declined as expected because new vehicles are not any more fuel efficient today than they were a decade ago. Although federally-mandated fuel efficiency standards were designed to lower gasoline consumption, they may actually have prevented consumption from falling. Atlantic margins were predicted to continue moving up because of the supply and demand evidence: high capacity utilization rates, low operating inventories, limited capacity addition resulting from lower capital spending, continued U.S. gasoline demand growth, and steady total oil demand growth. 11 figs

  2. Atlantic Oceanographic and Meteorological Laboratory

    Data.gov (United States)

    Federal Laboratory Consortium — The Atlantic Oceanographic and Meteorological Laboratory conducts research to understand the physical, chemical, and biological characteristics and processes of the...

  3. Two Distinct Roles of Atlantic SSTs in ENSO Variability: North Tropical Atlantic SST and Atlantic Nino

    Science.gov (United States)

    Ham, Yoo-Geun; Kug, Jong-Seong; Park, Jong-Yeon

    2013-01-01

    Two distinct roles of the Atlantic sea surface temperatures (SSTs), namely, the North Tropical Atlantic (NTA) SST and the Atlantic Nino, on the El Nino-Southern Oscillation (ENSO) variability are investigated using the observational data from 1980 to 2010 and coupled model experiments. It appears that the NTA SST and the Atlantic Nino can be used as two independent predictors for predicting the development of ENSO events in the following season. Furthermore, they are likely to be linked to different types of El Nino events. Specifically, the NTA SST cooling during February, March, and April contributes to the central Pacific warming at the subsequent winter season, while the negative Atlantic Nino event during June, July, and August contributes to enhancing the eastern Pacific warming. The coupled model experiments support these results. With the aid of a lagged inverse relationship, the statistical forecast using two Atlantic indices can successfully predict various ENSO indices.

  4. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution parallel ocean model

    Science.gov (United States)

    Topper, R. P. M.; Meijer, P. Th.

    2014-07-01

    A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations on the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic-Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is less and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic-Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which

  5. Solar activity variations of nocturnal thermospheric meridional winds over Indian longitude sector

    Science.gov (United States)

    Madhav Haridas, M. K.; Manju, G.; Arunamani, T.

    2016-09-01

    The night time F-layer base height information from ionosondes located at two equatorial stations Trivandrum (TRV 8.5°N, 77°E) and Sriharikota (SHAR 13.7°N, 80.2°E) spanning over two decades are used to derive the climatology of equatorial nocturnal Thermospheric Meridional Winds (TMWs) prevailing during High Solar Activity (HSA) and Low Solar Activity (LSA) epochs. The important inferences from the analysis are 1) Increase in mean equatorward winds observed during LSA compared to HSA during pre midnight hours; 25 m/s for VE (Vernal Equinox) and 20 m/s for SS (Summer Solstice), AE (autumnal Equinox) and WS (Winter Solstice). 2) Mean wind response to Solar Flux Unit (SFU) is established quantitatively for all seasons for pre-midnight hours; rate of increase is 0.25 m/s/SFU for VE, 0.2 m/s/SFU for SS and WS and 0.08 m/s/SFU for AE. 3) Theoretical estimates of winds for the two epochs are performed and indicate the role of ion drag forcing as a major factor influencing TMWs. 4) Observed magnitude of winds and rate of flux dependencies are compared to thermospheric wind models. 5) Equinoctial asymmetry in TMWs is observed for HSA at certain times, with more equatorward winds during AE. These observations lend a potential to parameterize the wind components and effectively model the winds, catering to solar activity variations.

  6. Sub-Surface Meridional flow, Vorticity and the life time if Solar Active Regions

    CERN Document Server

    Maurya, R A

    2010-01-01

    Solar sub-surface fluid topology provides an indirect approach to examine the internal characteristics of active regions (ARs). Earlier studies have revealed the prevalence of strong flows in the interior of ARs having complex magnetic fields. Using the Doppler data obtained by the Global Oscillation Network Group (GONG) project for a sample of 74 ARs, we have discovered the presence of steep gradients in meridional velocity at depths ranging from 1.5 to 5 Mm in flare productive ARs. The sample of these ARs is taken from the Carrington rotations 1980--2052 covering the period August 2001-January 2007. The gradients showed an interesting hemispheric trend of negative (positive) signs in the northern (southern) hemisphere, i.e., directed toward the equator. We have discovered three sheared layers in the depth range of 0 - 10 Mm, providing an evidence of complex flow structures in several ARs. An important inference derived from our analysis is that the location of the deepest zero vertical vorticity is correlat...

  7. ENSO and meridional modes: A null hypothesis for Pacific climate variability

    Science.gov (United States)

    Di Lorenzo, E.; Liguori, G.; Schneider, N.; Furtado, J. C.; Anderson, B. T.; Alexander, M. A.

    2015-11-01

    Pacific low-frequency variability (timescale > 8 years) exhibits a well-known El Niño-like pattern of basin-scale sea surface temperature, which is found in all the major modes of Pacific decadal climate. Using a set of climate model experiments and observations, we decompose the mechanisms contributing to the growth, peak, and decay of the Pacific low-frequency spatial variance. We find that the El Niño-like interdecadal pattern is established through the combined actions of Pacific meridional modes (MM) and the El Niño-Southern Oscillation (ENSO). Specifically, in the growth phase of the pattern, subtropical stochastic excitation of the MM energizes the tropical low-frequency variance acting as a red noise process. Once in the tropics, this low-frequency variance is amplified by ocean-atmospheric feedbacks as the pattern reaches its peak phase. At the same time, atmospheric teleconnections distribute the variance from the tropics to the extratropics, where the pattern ultimately decays. In this stochastic red noise model of Pacific climate, the timescale of the extra-tropical/tropical interactions (1-2 years) permits the stochastic excitation of the ENSO-like pattern of decadal and interdecadal variance.

  8. MAPEAMENTO DE UNIDADES DE RELEVO NA MÉDIA SERRA DO ESPINHAÇO MERIDIONAL - MG

    Directory of Open Access Journals (Sweden)

    Éric Andrade Rezende

    2011-04-01

    Full Text Available This paper proposes a mapping of landforms units for the southern portion of the middle third of the Serra do Espinhaço Meridional. The landforms units were delineated from the integrated analysis of thematic maps and satellite images that allowed the observation of changes in morphology, altimetry, slope, lithostructure and organization of the drainage network. The step of digital mapping, processed in the software ArcGIS 9.2, was based in the use of SRTM products (Shuttle Radar Topography Mission. The methodological procedures also included field work and literature research. The taxonomy of geomorphological mapping proposed by IBGE (2009 was applied , through which fourteen Geomorphologycal Units were individualized. The units are distributed amongst five different compartments as follows: two plateaux, two escarpments, six depressions, three sets of ridges and one set of intermediate levels. It was observed that the general layout of the units reflects the strong lithostructural control forced to regional relief. The differentiated resistance of the various lithologies in relation to denudational processes and the influence of neotectonic on landscape evolution are noteworthy.

  9. The implication of radiative forcing and feedback for meridional energy transport

    Science.gov (United States)

    Huang, Yi; Zhang, Minghong

    2014-03-01

    The distributions of radiative forcing and feedback in the Coupled Model Intercomparison Project phase 5 abrupt4xCO2 and Historical experiments are diagnosed, with a focus on their effects on the zonal mean structure of the top-of-the-atmosphere radiation anomalies and implications for the meridional energy transport. It is found that because the greenhouse gas longwave forcing peaks in the low latitudes, it reinforces the equator-to-pole net radiation gradient and accounts for the increase in the poleward energy transport in both hemispheres under global warming. The shortwave forcing by aerosol, ozone, etc. peaks in the Northern Hemisphere and instead implies an interhemispheric energy transport. Although the water vapor feedback also reinforces the equator-to-pole gradient of the net radiation, the temperature and albedo feedback act against it. The feedback tend to offset the zonal mean radiation anomaly caused by the forcing, although the overall feedback effect on the energy transport is rather uncertain, mainly due to the uncertainty in the cloud feedback.

  10. Meridional thermal field of a coupled ocean-atmosphere system: a conceptual model

    Science.gov (United States)

    Ou, Hsien-Wang

    2006-05-01

    This paper constitutes the author's continuing effort in the construction of a minimal theory of the earth's climate. In an earlier paper published in the Journal of Climate in 2001, this author has derived the global-mean fields of an aquatic planet forced by the solar insolation, which provide the necessary constraints for the present derivation of the meridional thermal field. The model closure invokes maximized entropy production (MEP), a thermodynamic principle widely used in turbulence and climate studies. Based on differing convective regimes of the ocean and atmosphere, both fluids are first reduced two thermal masses with aligned fronts, consistent with a minimal description of the observed field. Subjected to natural bounds, a robust solution is then found, characterized by an ice-free ocean, near-freezing cold fluid masses, mid-latitude fronts, and comparable ocean and atmosphere heat transports. The presence of polar continents, however, sharply reduces the ocean heat transport outside the tropics, but leaves the thermal field largely unchanged. Given the limitation of an extremely crude model, the deduced thermal field nonetheless seems sensible, suggesting that the model has captured the physics for a minimal account of the observed field. Together with the above-mentioned paper, the model reinforces the pre-eminent role of the triple point of water in stabilizing the surface temperature - against changing external condition. Such internal control is made possible by the turbulent nature of the climate fluids, which necessitates a selection rule based on extremization.

  11. A meridional dipole in pre-monsoon Bay of Bengal tropical cyclone activity induced by ENSO

    Energy Technology Data Exchange (ETDEWEB)

    Balaguru, Karthik; Leung, Ruby L.; Lu, Jian; Foltz, Gregory R.

    2016-06-30

    Analysis of Bay of Bengal tropical cyclone (TC) track data for the month of May during 1980-2013 reveals a meridional dipole in TC intensification: TC intensification rates increased in the northern Bay and decreased in the southern Bay. The dipole was driven by an increase in low-level vorticity and atmospheric humidity in the northern Bay, making the environment more favorable for TC intensification, and enhanced vertical wind shear in the southern Bay, tending to reduce TC development. These environmental changes were associated with a strengthening of the monsoon circulation for the month of May, driven by a La Nin˜a-like shift in tropical Pacific SSTs andassociated tropical wave dynamics. Analysis of a suite of climate models fromthe CMIP5 archive for the 150-year historical period shows that most models correctly reproduce the link between ENSO and Bay of Bengal TC activity through the monsoon at interannual timescales. Under the RCP 8.5 scenario the same CMIP5 models produce an El Nin˜o like warming trend in the equatorial Pacific, tending to weaken the monsoon circulation. These results suggest

  12. Energetics of IPCC4AR Climate Models: Energy Balance and Meridional Enthalpy Transports

    CERN Document Server

    Lucarini, Valerio

    2009-01-01

    We consider the climate simulations performed using pre-industrial and SRESA1B scenarios and analyse the outputs of the state-of-the-art models included in IPCC4AR. For control simulations, large energy biases are present for several models both when global climate budgets and when energy budgets of the atmospheric, oceanic, and land subdomains are considered. The energy biases depend on the imperfect closure of the energy cycle in the fluid components of the climate system and on issues in the treatment of phase transitions and heat fluxes over land. Additionally, the consequence of a positive global energy bias, which is what most models feature, is the underestimation of the thermodynamic emission temperature of the planet and of the globally averaged surface temperature. This may help explaining the cold bias of climate models. Models agree on the representation of meridional enthalpy transports in terms of location of the peaks of the total and atmospheric transports, whereas quantitative disagreements o...

  13. The role of the PMOC in modulating the deglacial shift of the ITCZ

    Science.gov (United States)

    Liu, Wei; Hu, Aixue

    2015-12-01

    Based on an energy-constraint framework, the effect of the Pacific meridional overturning circulation (PMOC) has been investigated on the meridional shift of the intertropical convergence zone (ITCZ). During Heinrich Event 1, the global ITCZ displaces southward in response to a shutdown of the Atlantic meridional overturning circulation (AMOC). However, the PMOC resumes and induces an enhanced northward meridional heat transport (MHT). Further analyses show that the resumption of the PMOC and its associated MHT can relieve the decrease of oceanic cross-equatorial heat transport by the collapsed AMOC and lower the compensating decline of atmospheric cross-equatorial meridional heat transport by 0.09PW, leading to an offset of the southward shift of the global ITCZ by 0.5°. Regionally the developed PMOC does not affect the southward movement of the Atlantic ITCZ much since the latter is dominated by the collapsed AMOC that induces the change of Atlantic MHT. In contrast, the PMOC-induced northward heat transport largely abates the hemispheric temperature contrast in the tropical Pacific and reduces the southward ITCZ shift by as much as 5° in the eastern Pacific.

  14. Impact of the North Atlantic Sea Surface Temperature Tripole on the East Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    ZUO Jinqing; LI Weijing; SUN Chenghu; XU Li; REN Hong-Li

    2013-01-01

    A strong (weak) East Asian summer monsoon (EASM) is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer,which has positive (negative)SST anomalies in the northwestern North Atlantic and negative (positive) SST anomalies in the subpolar and tropical ocean.The mechanisms responsible for this linkage are diagnosed in the present study.It is shown that a barotropic wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer.This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains,which has a substantial effect on the EASM.Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing.Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation (NAO),the relationships between these two factors and the EASM are also examined.It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole,which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO.The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.

  15. Variability of the North Atlantic summer storm track: mechanisms and impacts on European climate

    International Nuclear Information System (INIS)

    The summertime variability of the extratropical storm track over the Atlantic sector and its links to European climate have been analysed for the period 1948–2011 using observations and reanalyses. The main results are as follows. (1) The dominant mode of the summer storm track density variability is characterized by a meridional shift of the storm track between two distinct paths and is related to a bimodal distribution in the climatology for this region. It is also closely related to the Summer North Atlantic Oscillation (SNAO). (2) A southward shift is associated with a downstream extension of the storm track and a decrease in blocking frequency over the UK and northwestern Europe. (3) The southward shift is associated with enhanced precipitation over the UK and northwestern Europe and decreased precipitation over southern Europe (contrary to the behaviour in winter). (4) There are strong ocean–atmosphere interactions related to the dominant mode of storm track variability. The atmosphere forces the ocean through anomalous surface fluxes and Ekman currents, but there is also some evidence consistent with an ocean influence on the atmosphere, and that coupled ocean–atmosphere feedbacks might play a role. The ocean influence on the atmosphere may be particularly important on decadal timescales, related to the Atlantic Multidecadal Oscillation (AMO). (letter)

  16. Two-core structure in northern winter mid-stratosphere meridional winds and its long-term evolution

    Czech Academy of Sciences Publication Activity Database

    Laštovička, Jan; Kozubek, Michal; Križan, Peter

    Kiel: GEOMAR Helmholtz Centre for Ocean Research, 2015. [Conference on Sun-Climate Connections (SCC). 16.03.2015–19.03.2015, Kiel] Institutional support: RVO:68378289 Keywords : stratospheric dynamics * meridional wind * long-term trend Subject RIV: DG - Athmosphere Sciences, Meteorology file:///C:/Users/K%C3%A1%C4%8Da/Downloads/a_873_1417008849%20(1).pdf

  17. A study of the sensitivity of the winter mean meridional circulation to sources of heat and momentum

    OpenAIRE

    Crawford, S. L.; SASAMORI, T.

    2011-01-01

    The time and zonally averaged momentum and thermodynamic equations on a spherical earth are combined to formulate an equation for the mean meridional circulation based on the quasi-static assumption discussed in Eliassen (Astrophys. Nor. 1951, 19–60). The forcing terms and coefficients in the equation are taken from previously published zonally and seasonally averaged data, which include the net radiative heating, condensation heating, boundary layer friction and sensible heating, tropical cu...

  18. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution ocean model

    Directory of Open Access Journals (Sweden)

    R. P. M. Topper

    2015-02-01

    Full Text Available A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations of the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation. A series of experiments with different sill depths in the Atlantic–Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is shallower and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin, a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic–Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian

  19. A Babcock-Leighton solar dynamo model with multi-cellular meridional circulation in advection- and diffusion-dominated regimes

    CERN Document Server

    Belucz, Bernadett; Forgacs-Dajka, Emese

    2015-01-01

    Babcock-Leighton type solar dynamo models with single-celled meridional circulation are successful in reproducing many solar cycle features. Recent observations and theoretical models of meridional circulation do not indicate a single-celled flow pattern. We examine the role of complex multi-cellular circulation patterns in a Babcock-Leighton solar dynamo in advection- and diffusion-dominated regimes. We show from simulations that presence of a weak, second, high-latitude reverse cell speeds up the cycle and slightly enhances the poleward branch in butterfly diagram, whereas the presence of a second cell in depth reverses the tilt of butterfly wing to an anti-solar type. A butterfly diagram constructed from middle of convection zone yields a solar-like pattern, but this may be difficult to realize in the Sun because of magnetic buoyancy effects. Each of the above cases behaves similarly in higher and lower magnetic diffusivity regimes. However, our dynamo with a meridional circulation containing four cells in...

  20. Meridional circulation in the solar convection zone: time-distance helioseismic inferences from four years of HMI/SDO observations

    CERN Document Server

    Rajaguru, S P

    2015-01-01

    We present and discuss results from time-distance helioseismic measurements of meridional circulation in the solar convection zone using 4 years of Doppler velocity observations by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Using an in-built mass conservation constraint in terms of the stream function we invert helioseismic travel times to infer meridional circulation in the solar convection zone. We find that the return flow that closes the meridional circulation is possibly beneath the depth of $0.77 R_{\\odot}$. We discuss the significance of this result in relation to other helioseismic inferences published recently and possible reasons for the differences in the results. Our results show clearly the pitfalls involved in the measurements of material flows in the deep solar interior given the current limits on signal-to-noise and our limited understanding of systematics in the data. We also discuss the implications of our results for the dynamics of solar interi...

  1. Variations of the tropical Atlantic and Pacific SSS minimum zones and their relations to the ITCZ and SPCZ rain bands (1979-2009)

    Science.gov (United States)

    Tchilibou, M.; Delcroix, T.; Alory, G.; Arnault, S.; Reverdin, G.

    2015-07-01

    This study focuses on the time-space variability of the low Sea Surface Salinity (SSS) waters extending zonally within 2°N-12°N in the Atlantic and Pacific and within 6°S-16°S in the western third of the Pacific. The analysis is based on a combination of in situ SSS observations collected in the last three decades from voluntary observing ships, TAO/TRITON and PIRATA moorings, Argo floats, and (few) CTD profiles. The mean latitudes of the Atlantic and Pacific low SSS waters appear 1°-3° further poleward than the Evaporation minus Precipitation (E-P) minima linked to the Inter Tropical Convergence Zones (ITCZ) and South Pacific Convergence Zone (SPCZ). At the seasonal time scale, the E-P minima migrate poleward in summer hemispheres, leading the migration of the SSS minima by 2-3 months in the Atlantic ITCZ, Pacific SPCZ, and in the eastern part of the Pacific ITCZ. On the other hand, the seasonal displacements of E-P and SSS minima are in antiphase in the central and western parts of the Pacific ITCZ. At the interannual time scale, the E-P and SSS minima migrate poleward during La Nina events in the Pacific and during the positive phase of the Atlantic Meridional Dipole (AMD) in the Atlantic (and vice versa during El Nino and the negative phase of the AMD). We further document long-term (1979-2009) meridional migrations of the E-P and SSS minima, especially in the SPCZ region, and discuss whether or not they are consistent with documented SST and wind stress trends.

  2. Decontamination by high-pressure washing, hydrochloric acid treatment, shading by materials and overturning radioactively contaminated concrete and stones surfaces in Northern Fukushima Prefecture

    International Nuclear Information System (INIS)

    Techniques to decontaminate stone and concrete surfaces by an easy and practical method were studied in Northern Fukushima Prefecture, which experienced radioactive contamination due to the accident at the TEPCO's Fukushima Daiichi Nuclear Power Plant. Radioactivity counting rate could be decreased to 1/5.5 by high-pressure washing with hydrochloric acid treatment with clothes after treating concrete surfaces twice with high-pressure washing. Radioactive contaminants could be disposed using high-pressure washing by collecting soil saturated with polluted water from crevices in concrete pavements. In addition, radioactivity counting rate decreased by overturning surfaces of small stones and concrete. In conclusion, hydrochloric acid treatment and covering could be used if the decontamination of concrete and stone surfaces by high-pressure washing and overturning was insufficient; however, the cost and dangers of using hydrochloric acid must be considered. (author)

  3. Predicting Atlantic seasonal hurricane activity using outgoing longwave radiation over Africa

    Science.gov (United States)

    Karnauskas, Kristopher B.; Li, Laifang

    2016-07-01

    Seasonal hurricane activity is a function of the amount of initial disturbances (e.g., easterly waves) and the background environment in which they develop into tropical storms (i.e., the main development region). Focusing on the former, a set of indices based solely upon the meridional structure of satellite-derived outgoing longwave radiation (OLR) over the African continent are shown to be capable of predicting Atlantic seasonal hurricane activity with very high rates of success. Predictions of named storms based on the July OLR field and trained only on the time period prior to the year being predicted yield a success rate of 87%, compared to the success rate of NOAA's August outlooks of 53% over the same period and with the same average uncertainty range (±2). The resulting OLR indices are statistically robust, highly detectable, physically linked to the predictand, and may account for longer-term observed trends.

  4. Estado actual de las investigaciones bioarqueológicas en Patagonia centro-meridional

    Directory of Open Access Journals (Sweden)

    Barrientos, Gustavo

    2001-01-01

    Full Text Available Desde el año 1996 se encuentran en desarrollo investigaciones en diversos sectores de Patagonia Centro-Meridional orientadas a la obtención de información bioarqueológica para discutir distintos problemas arqueológicos de alcance regional. Las mismas se hallan centradas en el estudio de la cuenca del lago Salitroso (N.O. de la provincia de Santa Cruz, aunque también se han realizado prospecciones en el lago Cardiel y pampas intermedias (del Asador y de la Chispa, que condujeron al registro y excavación de distintos tipos de estructuras funerarias (v.g. chenques y entierros en hoquedades naturales sobre rocas. Hasta el presente, las muestras recuperadas corresponden en su totalidad al lapso comprendido entre ca. 2500 a 300 años AP. Uno de los objetivos centrales de esta investigación es obtener información que permita analizar el grado y la forma de las adaptaciones (a nivel morfológico, fisiológico y organizacional alcanzadas por las poblaciones cazadoras-recolectoras del área durante el Holoceno tardío, y evaluar las condiciones previas a la extinción de las mismas en momentos históricos. El objetivo de esta presentación es exponer el conjunto de los resultados parciales obtenidos hasta el presente, a partir de la realización de análisis distribucionales, tafonómicos, paleodemográficos, isotópicos y morfológicos.

  5. Inter-comparison of stratospheric mean-meridional circulation and eddy mixing among six reanalysis datasets

    Directory of Open Access Journals (Sweden)

    K. Miyazaki

    2015-10-01

    Full Text Available The stratospheric mean-meridional circulation (MMC and eddy mixing are compared among six meteorological reanalysis datasets: NCEP-NCAR, NCEP-CFSR, ERA-40, ERA-Interim, JRA-25, and JRA-55 for the period 1979–2012. The reanalysis datasets produced using advanced systems (i.e., NCEP-CFSR, ERA-Interim, and JRA-55 generally reveal a weaker MMC and stronger eddy mixing in the Northern Hemisphere (NH compared with those produced using older systems (i.e., NCEP/NCAR, ERA-40, and JRA-25. In the NH lower stratosphere, the stronger eddy mixing is attributed to stronger planetary-scale mixing in the new datasets, whereas small-scale mixing is weaker in the new datasets. Conventional data assimilation techniques introduce analysis increments without maintaining physical balance, which may have caused an overly strong MMC and spurious small-scale eddies in the old datasets. At the NH mid-latitudes, only ERA-Interim reveals a weakening MMC trend in the deep branch of the Brewer–Dobson Circulation (BDC. The relative importance of the eddy mixing compared with the mean transport in the subtropical lower stratosphere is considered to be important in controlling mean Age-of-Air (AoA variations above, which showed increasing trends in ERA-Interim and JRA-55; this together with the weakened MMC in the deep branch may imply an increasing AoA trend in the NH middle stratosphere in ERA-Interim. Overall, discrepancies between the different variables and trends therein as derived from the different reanalyses are still relatively large, suggesting that more investments into these products are needed in order to obtain a consolidated picture of observed changes in the BDC and the mechanisms that drive them.

  6. El registro biológico humano de la costa meridional de Santa Cruz

    Directory of Open Access Journals (Sweden)

    Suby, Jorge A.

    2009-01-01

    Full Text Available La costa patagónica constituye un sector de riesgo para el registro arqueológico, asociado a factores naturales y antrópicos. Al mismo tiempo, la conservación de las colecciones bioarqueológicas, destacándose la pérdida de restos óseos e información asociada por escasez de recursos, desconocimiento o falta de atención especializada, representa escenarios de riesgo para el registro. Una de las áreas para las cuales no se dispone hasta el momento de información bioarqueológica es la región que comprende la costa meridional de la provincia de Santa Cruz. Considerando esta ausencia de información, el objetivo de este trabajo es presentar y discutir los primeros resultados sobre restos óseos humanos hallados en la región costera próxima a la desembocadura del Río Santa Cruz (Santa Cruz, Argentina. Los estudios incluyen el análisis de las situaciones de hallazgo y riesgo de los restos recuperados en acciones de rescate, el reconocimiento y puesta en valor de materiales depositados en el Museo Regional "Carlos Borgialli" (Puerto Santa Cruz, Santa Cruz, Argentina y estudios paleopatológicos. Al mismo tiempo se informan y analizan resultados cronológicos e isotópicos. Los resultados brindan evidencias claras de la ocupación de la región costera al menos durante los últimos 2000 años, consumo de recursos predominantemente terrestres y un estilo de vida que favorece el desarrollo de lesiones articulares, con escasos indicios de estrés sistémico que coinciden con los resultados reportados para la región continental del estrecho de Magallanes.

  7. Estudios sobre la vegetación del estado de Paraná (Brasil meridional

    Directory of Open Access Journals (Sweden)

    de Bolòs, Oriol

    1991-12-01

    Full Text Available Contribution to knowledge about the vegetation of the state of Paraná in southern Brazil (Serra do Mar, Planaltos, Iguaçu Valley. Numerous plant associations are described and grouped together in the following classes: Pistio-Eichhornietea (communities of floating cormophytes Xyrido-Typhetea (helophytic herbaceous vegetation Polypodio-Tillandsietea (epiphytic and comophytic vegetation Ruderali-Manihotetea (ruderal and segetal vegetation Andropogono-Baccharidetea (savanoid vegetation Rhizophoretea (mangroves Lantano-Chusqueetea (woody marginal communities of the forest Cedrelo-Ocoteetea (rain and mesophilous forest. Special attention is paid to the study of the physiognomy, structure and dynamism of the vegetation and its biogeographical significance.

    Aportación al conocimiento de la vegetación del estado de Paraná en el Brasil meridional (Serra do Mar, Planaltos, valle del Iguaçu. Se describen numerosas asociaciones vegetales agrupadas en las clases siguientes: Pistio-Eichhornietea (comunidades de cormófitos flotantes. Xyrido-Typhetea (vegetación herbácea helofítica. Polypodio-Tillandsietea (vegetación epifítica y comofítica. Ruderali-Manihotetea (vegetación ruderal, viaria y arvense. Andropogono-Baccharidetea (vegetación sabanoide. Rhizophoretea (manglar. Lantano-Chusqueetea (manto marginal leñoso de la selva. Cedrelo-Ocoteetea (selva pluvial y mesófila. Se dedica atención especial al estudio de la fisionomía, estructura y dinamismo de la vegetación y a su significación biogeográfica.

  8. Interannual variability of the January meridional heat transport by planetary waves in the northern latitudes

    International Nuclear Information System (INIS)

    Evidence of large temporal and spatial variability in the eddy fluxes of sensible heat in the lower troposphere (100-50 kPa thickness layer) in January, from 1946 to 1988, is presented. The spatial distribution of the standing eddy heat flux is dominated by three main features, or centers of action: (1) a region north of Korea (extreme eastern Siberia), (2) northeastern Atlantic Ocean, and (3) the Gulf of Alaska. Even though the center just north of Korea is the most active heat transport area, most of the interannual variability of the January standing eddy heat flux is associated with the heat transport centers over the northeastern Atlantic and the Gulf of Alaska, correlated with the positions of the Icelandic Low and the Aleutian Low, respectively. This year-to-year variability in these two geographical locations is due to interannual variability in the planetary waves, and a significant role of the air-sea interaction in this respect cannot be ruled out

  9. The global ocean circulation on a retrograde rotating earth

    OpenAIRE

    Kamphuis, V.; Huisman, S.E.; Dijkstra, H. A.

    2011-01-01

    To understand the three-dimensional ocean circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global ocean circulation. This circulation, often referred to as the Conveyor state, is characterised by an Atlantic Meridional Overturning Circulation (MOC) with a deep water formation at northern latitudes and the absence of ...

  10. The response of Southern Ocean eddies to increased midlatitude westerlies: a non-eddy resolving model study

    OpenAIRE

    Hofmann, M.; M. A. Morales Maqueda

    2011-01-01

    The midlatitude westerlies of the southern hemisphere have intensified since the 1970s. Non-eddy resolving general circulation models respond to such wind intensification with steeper isopycnals, a faster Antarctic Circumpolar Current (ACC), and a stronger Atlantic Meridional Overturning Circulation (AMOC). However, hydrographic observations show little change in the slope of the Southern Ocean isopycnals over the past 40 years. This insensitivity seems to result from a compensating mechanism...

  11. Competition between global warming and an abrupt collapse of the AMOC in Earth’s energy imbalance

    OpenAIRE

    Sybren Drijfhout

    2015-01-01

    A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to global cooling through fast feedbacks that selectively amplify the response in the Northern Hemisphere (NH). How such cooling competes with global warming has long been a topic for speculation, but was never addressed using a climate model. Here it is shown that global cooling due to a collapsing AMOC obliterates global warming for a period of 15–20 years. Thereafter, the global mean temperature trend is reversed an...

  12. Response of the AMOC to reduced solar radiation – the modulating role of atmospheric-chemistry

    OpenAIRE

    Muthers, Stefan; Raible, Christoph C.; Thomas F Stocker

    2016-01-01

    The influence of reduced solar forcing (grand solar minimum or geoengineering scenarios like solar radiation management) on the Atlantic meridional overturning circulation (AMOC) is assessed in an ensemble of atmosphere-ocean-chemistry-climate model simulations. Ensemble sensitivity simulations are performed with and without interactive chemistry. Without chemistry-climate interaction the AMOC is intensified in the course of the solar radiation reduction (SRR), which is ...

  13. Influence of assimilating transports and in situ data from the Rapid-MOCHA array into the GECCO2 ocean synthesis

    OpenAIRE

    Köhl, A.

    2015-01-01

    By assimilating information required for the estimation of the Atlantic meridional overturning circulation (AMOC) by the Rapid-MOCHA array, we investigate how transports should be constrained. For the period 2004–2011, we find that even the large adjustments in Florida Strait transport (FST) imposed by assimilating FST data do not impact the AMOC strength at 26.5° N while the AMOC away from this section changes due to the baroclinic response. Moreover, the high correlation betw...

  14. Oceanic heat advection to the Arctic in the last Millennium

    OpenAIRE

    Spielhagen, Robert F.; Werner, Kirstin; Aagaard-Sørensen, Steffen; Zamelczyk, Katarzyna; Kandiano, Evguenia; Budeus, Gereon; Husum, Katrine; Marchitto, Thomas M.; Hald, Morten

    2011-01-01

    EGU2011-8738 At present, the Arctic is responding faster to global warming than most other areas on earth, as indicated by rising air temperatures, melting glaciers and ice sheets and a decline of the sea ice cover. As part of the meridional overturning circulation which connects all ocean basins and influences global climate, northward flowing Atlantic Water is the major means of heat and salt advection towards the Arctic where it strongly affects the sea ice distribution. Records of its ...

  15. Air-sea interactions during glacial Heinrich events

    OpenAIRE

    Krebs, Uta

    2006-01-01

    'Heinrich events' - massive iceberg discharges from Northern Hemisphere ice sheets during the last ice age - coincided with cold periods and subsequent abrupt warmings on the Northern Hemisphere. Climate reconstructions suggest that the associated freshwater pulses caused a temporary collapse of the Atlantic Meridional Overturning Circulation (AMOC) by stabilizing stratification in the regions of deep water formation. In the present work a coupled atmosphere-ocean-sea ice model is employed u...

  16. Volcanic forcing of the North Atlantic Oscillation over the last 2,000 years

    Science.gov (United States)

    Breitenbach, Sebastian F. M.; Ridley, Harriet E.; Lechleitner, Franziska A.; Asmerom, Yemane; Rehfeld, Kira; Prufer, Keith M.; Kennett, Douglas J.; Aquino, Valorie V.; Polyak, Victor; Goswami, Bedartha; Marwan, Norbert; Haug, Gerald H.; Baldini, James U. L.

    2015-04-01

    The North Atlantic Oscillation (NAO) is a principal mode of atmospheric circulation in the North Atlantic realm (Hurrell et al. 2003) and influences rainfall distribution over Europe, North Africa and North America. Although observational data inform us on multi-annual variability of the NAO, long and detailed paleoclimate datasets are required to understand the mechanisms and full range of its variability and the spatial extent of its influence. Chronologies of available proxy-based NAO reconstructions are often interdependent and cover only the last ~1,100 years, while longer records are characterized by low sampling resolution and chronological constraints. This complicates the reconstruction of regional responses to NAO changes. We present data from a 2,000 year long sub-annual carbon isotope record from speleothem YOK-I from Yok Balum Cave, Belize, Central America. YOK-I has been extensively dated using U-series (Kennett et al. 2012). Monitoring shows that stalagmite δ13C in Yok Balum cave is governed by infiltration changes associated with tropical wet season rainfall. Higher (lower) δ13C values reflect drier (wetter) conditions related to Intertropical Convergence Zone position and trade winds intensity. Comparison with NAO reconstructions (Proctor et al. 2000, Trouet et al. 2009, Wassenburg et al. 2013) reveals that YOK-I δ13C sensitively records NAO-related rainfall dynamics over Belize. The Median Absolute Deviation (MAD) of δ13C extends NAO reconstructions to the last 2,000 years and indicates that high latitude volcanic aerosols force negative NAO phases. We infer that volcanic aerosols modify inter-hemispheric temperature contrasts at multi-annual scale, resulting in meridional relocation of the ITCZ and the Bermuda-Azores High, altering NAO and tropical rainfall patterns. Decade-long dry periods in the 11th and the late 18th century relate to major high northern latitude eruptions and exemplify the climatic response to volcanic forcing by

  17. VA Atlantic Coast Recreational Use

    Data.gov (United States)

    Virginia Department of Environmental Quality — As a member of the Mid-Atlantic Regional Council on the Ocean (MARCO), Virginia, through its Coastal Zone Management (CZM) Program, collected information on how the...

  18. Atlantic Offshore Seabird Dataset Catalog

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Several bureaus within the Department of Interior compiled available information from seabird observation datasets from the Atlantic Outer Continental Shelf into a...

  19. Virginia Atlantic Coast Recreational Use

    Data.gov (United States)

    Virginia Department of Environmental Quality — As a member of the Mid-Atlantic Regional Council on the Ocean (MARCO), Virginia, through its Coastal Zone Management (CZM) Program, collected information on how the...

  20. Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal

    Indian Academy of Sciences (India)

    D Shankar; S R Shetye; P V Joseph

    2007-10-01

    We use daily satellite estimates of sea surface temperature (SST)and rainfall during 1998 –2005 to show that onset of convection over the central Bay of Bengal (88-92°E, 14-18°N)during the core summer monsoon (mid-May to September)is linked to the meridional gradient of SST in the bay.The SST gradient was computed between two boxes in the northern (88-92°E, 18-22°N) and southern (82-88°E, 4-8°N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current.Convection over central bay followed the SST difference between the northern and southern bay ( ) exceeding 0.75°C in 28 cases.There was no instance of exceeding this threshold without a burst in convection.There were,however,five instances of convection occurring without this SST gradient.Long rainfall events (events lasting more than a week)were associated with an SST event ( ≥ 0.75°C);rainfall events tended to be short when not associated with an SST event.The SST gradient was important for the onset of convection, but not for its persistence:convection often persisted for several days even after the SST gradient weakened.The lag between exceeding 0.75°C and the onset of convection was 0-18 days,but the lag histogram peaked at one week.In 75% of the 28 cases,convection occurred within a week of exceeding the threshold of 0.75°C. The northern bay SST, contributed more to but it was a weaker criterion for convection than the SST gradient.A sensitivity analysis showed that the corresponding threshold for was 29°C. We hypothesise that the excess heating (∼1° C above the threshold for deep convection)required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.

  1. Inter-comparison of stratospheric mean-meridional circulation and eddy mixing among six reanalysis data sets

    OpenAIRE

    Miyazaki, Kazuyuki; Iwasaki, Toshiki; Kawatani, Yoshio; Kobayashi, Chiaki; Sugawara, Satoshi; Hegglin, Michaela I.

    2016-01-01

    The stratospheric mean-meridional circulation (MMC) and eddy mixing are compared among six meteorological reanalysis data sets: NCEP-NCAR, NCEP-CFSR, ERA-40, ERA-Interim, JRA-25, and JRA-55 for the period 1979–2012. The reanalysis data sets produced using advanced systems (i.e., NCEP-CFSR, ERA-Interim, and JRA-55) generally reveal a weaker MMC in the Northern Hemisphere (NH) compared with those produced using older systems (i.e., NCEP/NCAR, ERA-40, and JRA-25). The mean mixi...

  2. Centennial-scale teleconnection between North Atlantic sea surface temperatures and the Indian summer monsoon during the Holocene

    Science.gov (United States)

    Zhang, Xiaojian; Jin, Liya; Jia, Wanna

    2016-05-01

    Proxy records have shown that abrupt changes in the Indian summer monsoon (ISM) are closely linked to cold events in the North Atlantic at centennial timescales during the Holocene. However, mechanisms for these co-occurring phenomena are not fully understood. This study uses simulation results from a coupled atmosphere-ocean-sea-ice general circulation model forced by astronomical variations to investigate how summer (June, July, August and September) North Atlantic sea surface temperatures (SSTs) may have influenced the ISM at centennial timescales during the Holocene (9.5-0 ka BP). Our analyses identified an intimate relationship between the North Atlantic tripole SST (NATS) mode and the ISM. The NATS mode can affect the ISM in several ways. First, air-sea interactions over the tropical Atlantic can induce negative tropospheric temperature (TT) anomalies over the Indian Ocean, resulting in a strengthened meridional TT gradient favorable to a prolonged monsoonal rainy season. Second, a positive NATS mode tends to induce closed zonal vertical circulation over the tropical Atlantic, North Africa and the tropical Indian Ocean, creating anomalous convergence over India, and hence an enhanced ISM. Third, westerly surface wind anomalies, related to the NATS mode and coursing over the Arabian Sea, can increase moisture delivery to the monsoon region, causing enhanced rainfall in India. This mechanism resembles a decadal-scale mechanism that operates in the present-day climate. We also compared the Atlantic multidecadal oscillation (AMO), an alternative North Atlantic SST mode, with the NATS mode to determine their relationships to the ISM. A Holocene transient simulation indicates that the AMO's trend has diverged from that of the ISM since 5.5 ka BP, due to inverse SST trends over the tropical and extratropical North Atlantic. This latter trend leads to a much weaker relationship between the AMO and the ISM, relative to that observed between the NATS mode and the ISM

  3. Measurement and Interpretation of Travel-Time Shifts in the context of Time-Distance Helioseismic Detection of Meridional Flows in the Solar Convection Zone

    Science.gov (United States)

    Chakraborty, S.; Duvall, T. L., Jr.; Hanasoge, S.; Hartlep, T.; Larson, T. P.; Kholikov, S.

    2014-12-01

    The role of meridional flow in maintaining the solar dynamo and differential rotation in the solar convection zone is not well understood and is currently under scrutiny. The traditional flux-transport dynamo models have posited the well known single-cell meridional flow with poleward flow at the photosphere and equatorward flow near the base of the convection zone. However, recent investigations seem to be revealing a different picture of meridional flow which is double celled in the radial direction with poleward flow at the photosphere and equatorward flow at a much shallower level in the convection zone. In this work time-distance helioseismology is used to probe the solar convection zone to accurately determine the structure of meridional circulation. Helioseismology uses the photospherically visible aspect of (acoustic, surface-gravity) waves, that propagate and interfere throughout the Sun to form standing oscillation modes, as probes to make inferences about the structure and flows on the solar surface and interior. Time-distance helioseismology is based on measuring the travel-times of wave-packets moving between distinct points on the solar surface. Travel-time shifts obtained by calculating the difference in the travel-times of counter-propagating waves between the same points on the solar surface yield information about flows throughout the solar convection zone. In this work time-distance techniques are applied on artificial and solar Doppler velocity images to detect travel-time shifts due to meridional flow. Modifications are suggested to enhance the signal-to-noise ratio of travel-time shift measurements. The artificial data is constructed by embedding various meridional flow models in 3D acoustic simulators, which is then used to discuss the interpretation of travel-time shifts, so that in the future an inversion procedure may be designed to calculate meridional flow velocities with greater accuracy. The solar data is obtained from the Helioseismic

  4. Atlantic NAD 83 OCS Planning Areas

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains BOEM Planning Area outlines in ESRI shapefile format for the BOEM Atlantic Region. The old Atlantic Planning Area outlines were changed as of...

  5. Physical and remineralization processes govern the cobalt distribution in the deep western Atlantic ocean

    Directory of Open Access Journals (Sweden)

    G. Dulaquais

    2013-10-01

    Full Text Available The distributions of the bio-essential trace element dissolved Co (DCo and the apparent particulate Co (PCo are presented along the GEOTRACES-A02 deep section from 64° N to 50° S in the West Atlantic Ocean. PCo was determined as the difference between total cobalt (TCo, unfiltered samples and DCo. DCo concentrations ranged from 14.7 pM to 94.3 pM, and PCo concentrations from undetectable values to 18.8 pM. The lowest DCo concentrations were observed in the subtropical domains, and the highest in the low-oxygenated Atlantic Central Waters (ACW that appeared to be the major reservoir of DCo in the West Atlantic. In the Antarctic Bottom Waters, the enrichment in DCo with ageing of the water-mass can be related to suspension and redissolution of bottom sediments a well as diffusion of DCo from abyssal sediments. Mixing and dilution of deep water-masses, rather than scavenging of DCo onto settling particles, generated the meridional decrease of DCo along the southward large-scale circulation in the deep West Atlantic. Furthermore the apparent scavenged profile of DCo observed in the deep waters likely resulted from the persistence of relatively high concentrations in intermediate waters and low DCo concentrations in underlaying bottom waters. We suggested that the 2010 Icelandic volcanic eruption can be a source of DCo that could have been transported in the core of the North-East Atlantic Deep Waters. At intermediate depths, the high concentrations of DCo recorded in the ACW linearly correlated with the apparent utilization of oxygen (AOU, indicating that remineralization of DCo can be significant (representing up to 29% of the DCo present. Furthermore the preferential remineralization of phosphate (P compared to Co in these low-oxygenated waters suggested a decoupling between the deep cycles of P and Co. The vertical diffusion of DCo from the ACW appeared to be a significant source of DCo into the surface waters of the equatorial domain

  6. The joint influence of topography and atmosphere on the meridional transport fluctuations in the Southern Ocean and its link with the ENSO events

    CERN Document Server

    Stepanov, V N

    2007-01-01

    This article deals with the investigation of the influence of topography and coastlines on the dynamics of the depth averaged Antarctic Circumpolar Current (ACC), driven by wind and atmospheric pressure. This is achieved with the help of a global barotropic circulation model, under idealized and real atmospheric conditions. It is shown that the variability of meridional mass fluxes due to the atmospheric conditions over the ACC can induce short-period density anomalies in the Southern Ocean to the north in the vicinity of 47S, which can be transferred to low latitudes by the wave mechanism described by Ivchenko et al. 2004, that could have significance with respect to rapid extra-tropical oceanic links. The results of the barotropic modeling demonstrate that changes in wind strength over the ACC, together with the effect of bottom topography and coastlines, induce some meridional flow variability in the Southern Ocean, and this meridional flux variability in the Pacific Ocean is anticorrelated with the streng...

  7. Meridional Variation of the 1955-2003 Sea Level Anomalies in the Tropical Pacific Ocean Associated with El Ni(n)o Events

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Sea Level Anomaly-Torque (SLAT, relative to a reference location in the Pacific Ocean), which means the total torque of the gravity forces of sea waters with depths equal to the Sea Level Anomaly (SLA) in the tropical Pacific Ocean, is defined in this study. The time series of the SLAT from merged altimeter data (1993-2003) had a great meridional variation during the 1997-1998 El Ni(n)o event. By using historical upper layer temperature data (1955-2003) for the tropical Pacific Ocean, the temperature-based SLAT is also calculated and the meridional variation can be found in the historical El Ni(n)o events (1955-2003), which suggests that the meridional shifts of the sea level anomaly are also intrinsic oscillating modes of the El Ni(n)o cycles like the zonal shifts.

  8. The North Atlantic Oscillation in the Atlantic-European SLP*

    OpenAIRE

    GLOWIENKA-HENSE, RITA

    2011-01-01

    An analysis of the signature of the North Atlantic Oscillation (NAO) in the Atlantic-European sea level pressure (SLP) is presented for observed (German Weather Service) and ECMWF T21 model data. The former time series consists of 1881–1984 January to December fields and the latter of 42 monthly fields from 3 permanent January simulations. The NAO is shown to be one of the dominant eigenmodes of SLP for all calendar months. A very similar NAO anomaly pattern is filtered from the T21 model dat...

  9. Propagation of Convective Complexes Observed by TRMM in the Eastern Tropical Atlantic

    Science.gov (United States)

    Druyan, Leonard M.; Fulazeka, Matthew

    2012-01-01

    Precipitation maxima during the West African summer monsoon propagate generally westward in tandem with African easterly waves. A heretofore unreported, repeating pattern of northward drift of precipitation maxima is detected on Tropical Rainfall Measurement Mission (TRMM satellite) time-latitude distributions of daily accumulations over the eastern tropical Atlantic. Corresponding 3-hourly TRMM accumulations show that the northward drifting envelopes of precipitation during August 2006 are often comprised of individual swaths propagating towards the southwest, presumably as mesoscale squall lines. The implied northward drift on the time-latitude distribution is a component of a resultant northwestward movement. The study examines the entire available record of TRMM precipitation observations, 1998-2010, to summarize TRMM maxima propagation over the eastern tropical Atlantic. Meridional displacements of precipitation maxima are most prevalent in June-September 2006, occurring less frequently during other summers. An investigation of geopotential and circulation fields, limited to two case studies, suggests mechanisms to explain some of the observed propagation of TRMM maxima. In one event, northward drift of the precipitation envelope is consistent with the corresponding displacement of the intertropical convergence zone trough, although the southwest propagation of individual mesoscale convection maxima does not correspond to any synoptic feature on reanalysis circulation or reanalysis downscaled by a regional model. One speculation is that southwestward propagation of precipitation maxima could be caused by regeneration of convection at outflow boundaries of mature thunderstorms.

  10. Anomalous mid-twentieth century atmospheric circulation change over the South Atlantic compared to the last 6000 years

    Science.gov (United States)

    Turney, Chris S. M.; Jones, Richard T.; Lister, David; Jones, Phil; Williams, Alan N.; Hogg, Alan; Thomas, Zoë A.; Compo, Gilbert P.; Yin, Xungang; Fogwill, Christopher J.; Palmer, Jonathan; Colwell, Steve; Allan, Rob; Visbeck, Martin

    2016-06-01

    Determining the timing and impact of anthropogenic climate change in data-sparse regions is a considerable challenge. Arguably, nowhere is this more difficult than the Antarctic Peninsula and the subantarctic South Atlantic where observational records are relatively short but where high rates of warming have been experienced since records began. Here we interrogate recently developed monthly-resolved observational datasets from the Falkland Islands and South Georgia, and extend the records back using climate-sensitive peat growth over the past 6000 years. Investigating the subantarctic climate data with ERA-Interim and Twentieth Century Reanalysis, we find that a stepped increase in precipitation across the 1940s is related to a change in synoptic atmospheric circulation: a westward migration of quasi-permanent positive pressure anomalies in the South Atlantic has brought the subantarctic islands under the increased influence of meridional airflow associated with the Amundsen Sea Low. Analysis of three comprehensively multi-dated (using 14C and 137Cs) peat sequences across the two islands demonstrates unprecedented growth rates since the mid-twentieth century relative to the last 6000 years. Comparison to observational and reconstructed sea surface temperatures suggests this change is linked to a warming tropical Pacific Ocean. Our results imply ‘modern’ South Atlantic atmospheric circulation has not been under this configuration for millennia.

  11. Oceanic source strength of carbon monoxide on the basis of basin-wide observations in the Atlantic.

    Science.gov (United States)

    Park, Keyhong; Rhee, Tae Siek

    2016-01-01

    We measured the carbon monoxide (CO) concentrations in the marine boundary layer and the surface waters of the Atlantic Ocean from 50°N to 50°S during the UK Atlantic Meridional Transect expedition (AMT-7) in October 1998, covering the open ocean and coastal regions. Throughout the cruise track, atmospheric CO concentrations continually decreased southwards in the northern hemisphere with sporadic low and high concentrations encountered. South of the intertropical convergence zone (ITCZ) atmospheric CO was enhanced by ∼10 ppb compared to north of the ITCZ due likely to biomass burning emissions prevailing in the tropical continents. The remainder of the southern hemisphere remains nearly invariable except for the vicinity of Rio de la Plata. The surface seawater was supersaturated everywhere along the track and its saturation anomaly oscillated up to 90, exhibiting a typical diurnal cycle. The maximal dissolved CO concentration in the diurnal cycle appeared 2-5 hours behind the local maximum of solar insolation in the open ocean and the time lag further increased in the coastal region. The global ocean flux of CO to the atmosphere was estimated to be 14 Tg(CO) a(-1) within the range of 4-24 Tg(CO) a(-1). This is within uncertainty almost identical to what was estimated on the basis of the basin-wide observations in the Pacific and the Atlantic, but more than ∼4 times lower than the values appeared in the Intergovernmental Panel on Climate Change (IPCC) reports. PMID:26648555

  12. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution parallel ocean model

    Directory of Open Access Journals (Sweden)

    R. P. M. Topper

    2014-07-01

    Full Text Available A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations on the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation. A series of experiments with different sill depths in the Atlantic–Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is less and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic–Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity

  13. Atlantic CFC data in CARINA

    Directory of Open Access Journals (Sweden)

    R. Steinfeldt

    2010-01-01

    Full Text Available Water column data of carbon and carbon-relevant parameters have been collected and merged into a new database called CARINA (CARbon IN the Atlantic. In order to provide a consistent data set, all data have been examined for systematic biases and adjusted if necessary (secondary quality control (QC. The CARINA data set is divided into three regions: the Arctic/Nordic Seas, the Atlantic region and the Southern Ocean. Here we present the CFC data for the Atlantic region, including the chlorofluorocarbons CFC-11, CFC-12 and CFC-113 as well as carbon tetrachloride (CCl4. The methods applied for the secondary quality control, a crossover analyses, the investigation of CFC ratios in the ocean and the CFC surface saturation are presented. Based on the results, the CFC data of some cruises are adjusted by a certain factor or given a "poor'' quality flag.

  14. Atlantic versus Indo-Pacific influence on Atlantic-European climate

    OpenAIRE

    Pohlmann, Holger; Latif, Mojib

    2005-01-01

    The influence of the Atlantic and Indo-Pacific oceans on Atlantic-European climate is investigated by analyzing ensemble integrations with the atmospheric general circulation model ECHAM4 forced by anomalous sea surface temperature and sea ice conditions restricted to the Atlantic (AOGA) and Indo-Pacific (I+POGA) oceans. The forcing from both the Indo-Pacific and Atlantic oceans are important for the generation of the sea level pressure (SLP) variability in the Atlantic region in the boreal w...

  15. Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics.

    Science.gov (United States)

    Partin, J W; Quinn, T M; Shen, C-C; Okumura, Y; Cardenas, M B; Siringan, F P; Banner, J L; Lin, K; Hu, H-M; Taylor, F W

    2015-01-01

    Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10-100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland. PMID:26329911

  16. Modeling spatial and temporal variations in temperature and salinity during stratification and overturn in Dexter Pit Lake, Tuscarora, Nevada, USA

    Energy Technology Data Exchange (ETDEWEB)

    Balistrieri, Laurie S. [U.S. Geological Survey, University of WA, School of Oceanography, Seattle, WA 98195 (United States)]. E-mail: balistri@usgs.gov; Tempel, Regina N. [Department of Geological Sciences, University of NV- Reno, Reno, NV 89557 (United States); Stillings, Lisa L. [U.S. Geological Survey, Mackay School of Mines, University of NV-Reno, Reno, NV 89557 (United States); Shevenell, Lisa A. [Nevada Bureau of Mines and Geology, University of NV-Reno, Reno, NV 89557 (United States)

    2006-07-15

    (wind stirring, convective overturn, shear, and eddy diffusion). Inputs to the model include the size and shape of the lake, daily meteorological data (short wave radiation, long wave radiation or cloud cover, air temperature, vapor pressure, wind speed, and rainfall), rates for water inputs and outputs, the composition of inflowing water, and initial profiles of temperature and salinity. Predicted temperature profiles, which are influenced by seasonal changes in the magnitude of solar radiation, are in good agreement with observations and show the development of a strong thermocline in the summer, erosion of the thermocline during early fall, and turnover in late fall. Predicted salinity profiles are in reasonable agreement with observations and are affected by the hydrologic balance, particularly inflow of surface and groundwater and, to a lesser degree, evaporation. Defining the hydrodynamics model for Dexter pit lake is the first step in using a coupled physical - biogeochemical model (Dynamic Reservoir Simulation Model-Computational Aquatic Ecosystem Dynamics Model or DYRESM-CAEDYM) to predict the behavior of non-conservative elements (e.g., dissolved O{sub 2}, Mn, and Fe) and their effect on water quality in this system.

  17. Modeling spatial and temporal variations in temperature and salinity during stratification and overturn in Dexter Pit Lake, Tuscarora, Nevada, USA

    International Nuclear Information System (INIS)

    , convective overturn, shear, and eddy diffusion). Inputs to the model include the size and shape of the lake, daily meteorological data (short wave radiation, long wave radiation or cloud cover, air temperature, vapor pressure, wind speed, and rainfall), rates for water inputs and outputs, the composition of inflowing water, and initial profiles of temperature and salinity. Predicted temperature profiles, which are influenced by seasonal changes in the magnitude of solar radiation, are in good agreement with observations and show the development of a strong thermocline in the summer, erosion of the thermocline during early fall, and turnover in late fall. Predicted salinity profiles are in reasonable agreement with observations and are affected by the hydrologic balance, particularly inflow of surface and groundwater and, to a lesser degree, evaporation. Defining the hydrodynamics model for Dexter pit lake is the first step in using a coupled physical - biogeochemical model (Dynamic Reservoir Simulation Model-Computational Aquatic Ecosystem Dynamics Model or DYRESM-CAEDYM) to predict the behavior of non-conservative elements (e.g., dissolved O2, Mn, and Fe) and their effect on water quality in this system

  18. Mean zonal and meridional accelerations and mean heating induced by solar tides for equinox and solstice conditions

    International Nuclear Information System (INIS)

    Evaluations are presented of the momentum and energy flux divergences of the diurnal and semidiurnal tidal fields calculated by Forbes from 0 to 400 km altitude. Results are presented in the form of meridional cross-sections from 0 to 780N or S latitude with a 60 latitude interval. Comparisons are made with evaluations of the momentum flux divergences of the diurnal tide by Miyahara and good agreement is obtained in the lower thermosphere (below about 130 km) but a large disparity arises in the upper thermosphere. In the lower thermosphere momentum flux divergences of the semidiurnal tide are comparable with those of the diurnal tide and should be included in general circulation calculations of the 90-120 km region. (author)

  19. North and South Atlantic Bidecadal SL variability: Rossby Waves, AMOC fingerprints and Regime Shifts

    Science.gov (United States)

    Vianna, M. L.; Menezes, V. V.

    2014-12-01

    The relationship between the North and South Atlantic bidecadal sea level (SL) oscillations in the twentieth century (1908-2008) is investigated using SODA 2.2.4 reanalysis and 102 monthly mean SL time series from TG stations provided by PSMSL. Bidecadal SL signal extraction was done using our method of subjectively choosing groupings of space-time data into non-overlapping period bands by use of Singular Spectrum Analysis (SSA)/ Maximum Entropy Method (MEM) analysis. A CEOF analysis of the SODA bidecadal band shows dominance of 22-24 year periods. Propagating bidecadal mode expansions were then determined through this analysis, which gives two principal modes. The first mode is dominant from 1915 to 1965 and the second from 1970 onward. The amplitude variabilities obtained suggests the presence of regime shifts, which coincide in time with shifts actually observed in European climate and South African lobster fisheries. The first mode is characterized by states with North and South Atlantic subtropical gyres in phase, while tropical and subpolar regions are in opposite phase relative to them. The second mode is characterized by the subpolar gyre and North subtropical gyre almost in quadrature, with North and South subtropical gyres out of phase. The evolution mechanism of this latter mode is related to east-west density contrasts and westward propagating Rossby waves. These waves show phase speeds dominated by geostrophic self-advection of density anomalies relative to the mean meridional density gradient as known from previous studies, but are shown to be additionally influenced by bottom topography. The oscillations caused by these waves are shown to have phase differences (quadrature in the North Atlantic) with regional indices of bidecadal AMOC oscillations. A number of SL-AMOC fingerprints are also reviewed, and a new eastern equatorial fingerprint is proposed.

  20. Inter-comparison of stratospheric mean-meridional circulation and eddy mixing among six reanalysis data sets

    Science.gov (United States)

    Miyazaki, Kazuyuki; Iwasaki, Toshiki; Kawatani, Yoshio; Kobayashi, Chiaki; Sugawara, Satoshi; Hegglin, Michaela I.

    2016-05-01

    The stratospheric mean-meridional circulation (MMC) and eddy mixing are compared among six meteorological reanalysis data sets: NCEP-NCAR, NCEP-CFSR, ERA-40, ERA-Interim, JRA-25, and JRA-55 for the period 1979-2012. The reanalysis data sets produced using advanced systems (i.e., NCEP-CFSR, ERA-Interim, and JRA-55) generally reveal a weaker MMC in the Northern Hemisphere (NH) compared with those produced using older systems (i.e., NCEP/NCAR, ERA-40, and JRA-25). The mean mixing strength differs largely among the data products. In the NH lower stratosphere, the contribution of planetary-scale mixing is larger in the new data sets than in the old data sets, whereas that of small-scale mixing is weaker in the new data sets. Conventional data assimilation techniques introduce analysis increments without maintaining physical balance, which may have caused an overly strong MMC and spurious small-scale eddies in the old data sets. At the NH mid-latitudes, only ERA-Interim reveals a weakening MMC trend in the deep branch of the Brewer-Dobson circulation (BDC). The relative importance of the eddy mixing compared with the mean-meridional transport in the subtropical lower stratosphere shows increasing trends in ERA-Interim and JRA-55; this together with the weakened MMC in the deep branch may imply an increasing age-of-air (AoA) in the NH middle stratosphere in ERA-Interim. Overall, discrepancies between the different variables and trends therein as derived from the different reanalyses are still relatively large, suggesting that more investments in these products are needed in order to obtain a consolidated picture of observed changes in the BDC and the mechanisms that drive them.

  1. A study of the equatorial ionization anomaly and thermospheric meridional winds during quiet and disturbed periods over Brazilian low latitudes

    International Nuclear Information System (INIS)

    Complete text of publication follows. The aim of this work is the study of meridional thermospheric winds, during geomagnetically quiet and disturbed periods and their effects on the development of equatorial ionization anomaly. This research theme depends on the theoretical and experimental knowledge of the coupled ionosphere/thermosphere/magnetosphere system. This study is based on ionospheric data collected by digital ionosondes operating in Sao Luis, Fortaleza and Cachoeira Paulista and by Global Positioning System (GPS) receivers installed in Sao Jose dos Campos and Sao Luis. Here, the nighttime thermospheric neutral winds aligned to the magnetic meridian are derived from F-region height variations between two equatorial stations, Sao Luis and Fortaleza. In order to evaluate the strength and development of the equatorial anomaly, two parameters were determined: ΔfoF2 and ΔVTEC. During the magnetic storm, the ionosphere goes through disturbances on a global level. The main ionospheric effects produced by storms which studied here, are: the response of the F-layer to prompt penetration of zonal electric field from the auroral to the equatorial region, and the effects of disturbance dynamo electric fields and the meridional winds. The methodology employed to study the magnetic storm effects in the equatorial ionosphere consists on the comparison of the ionospheric parameters on disturbed and quiet days. The magnetic parameters such as the auroral index AE, components of the interplanetary magnetic field Bz and the Dst index, were used to analyze the storm. The results show significant variation in the plasma vertical drift, in the thermospheric winds and in the equatorial anomaly developments during different phases of the storms.

  2. The stability of the thermohaline circulation in a coupled ocean-atmosphere general circulation model

    Energy Technology Data Exchange (ETDEWEB)

    Schiller, A. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Mikolajewicz, U. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Voss, R. [Deutsches Klimarechenzentrum (DKRZ), Hamburg (Germany)

    1996-02-01

    The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere general circulation model. The meltwater input to the Labrador Sea is increased linearly for 250 years to a maximum input of 0.625 Sv and then reduced again to 0 (both instantaneously and slowly decreasing over 250 years). The resulting freshening forces a shutdown of the formation of North Atlantic deepwater and a subsequent reversal of the thermohaline circulation of the Atlantic, filling the deep Atlantic with Antarctic bottom water. The change in the overturning pattern causes a drastic reduction of the Atlantic northward heat transport, resulting in a strong cooling with maximum amplitude over the northern North Atlantic and a southward shift of the sea-ice margin in the Atlantic. Due to the increased meridional temperature gradient, the Atlantic intertropical convergence zone is displaced southward and the westerlies in the northern hemisphere gain strength. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in the overturning circulation of the Atlantic leads to longer residence times of the surface waters in high northern latitudes, which allows them to accumulate more precipitation and runoff from the continents, which results in an increased stability in the North Atlantic.

  3. La heterogeneidad interna del español meridional o atlántico: variación diasistemática vs. pluricentrismo

    Directory of Open Access Journals (Sweden)

    Araceli López Serena

    2013-07-01

    Full Text Available ResumenEste trabajo se propone mostrar la idoneidad del marco teórico de la Lingüística de las variedades desarrollado por la Escuela de Friburgo para abordar el problema de la heterogeneidad interna del llamado español meridional o atlántico. Dicha heterogeneidad concierne a las diferencias de estatus que unos mismos rasgos lingüísticos manifiestan en las variedades andaluzas y americanas de la lengua; de ahí que su abordaje precise un marco de análisis que permita describir el funcionamiento discursivo de los distintos fenómenos de variación que afloran en el español hablado en Andalucía y en América desde una perspectiva dinámica, respetuosa con la extraordinaria complejidad de la interacción que, en el discurso, tiene lugar entre hechos de variación de distinta naturaleza (diatópica, diastrática o diafásica. Gracias a la modelización del comportamiento lingüístico diferenciado de los hablantes en situaciones de comunicación diversas que permite llevar a cabo el aparato conceptual de la Lingüística de las variedades, podremos dirimir cómo, por encima de la posible identidad material de algunos hechos lingüísticos compartidos por andaluz, canario y español de América, es necesario atribuir a fenómenos, en principio equivalentes, un estatus, sin embargo, muy desigual: diasistemáticamente marcado en unas comunidades, pero no marcado o estándar en otras, en las que el rasgo lingüístico en cuestión tenga, por tanto, el rango de norma diferenciada en el seno de una lengua policéntrica como es la española. AbstractThis paper claims that the inner heterogeneity of the so-called Southern or Atlantic Spanish can be best analyzed under the theoretical framework commonly known as German Varieties Linguistics developed by the Fribourg School. This heterogeneity is shown in the diverse status of materially identical linguistic facts in the Andalusian and American varieties of the Spanish language. The paper argues

  4. Easterly wave regimes and associated convection over West Africa and tropical Atlantic: results from the NCEP/NCAR and ECMWF reanalyses

    Energy Technology Data Exchange (ETDEWEB)

    Diedhiou, A. [Ecole Polytechnique, 91 - Palaiseau (France). Lab. de Meteorologie Dynamique; Janicot, S. [METEO-FRANCE, Laboratoire de Meteorologie Dynamique du CNRS, Ecole Polytechnique, Palaiseau (France); Viltard, A.; de Felice, P. [Universite Paris XII, Laboratoire de Meteorologie Dynamique du CNRS, Ecole Polytechnique, Palaiseau (France); Laurent, H. [Institut de Recherche pour le Developpement, Montpellier (France)

    1999-11-04

    NCEP/NCAR and ECMWF daily reanalyses are used to investigate the synoptic variability of easterly waves over West Africa and tropical Atlantic at 700 hPa in northern summer between 1979-1995 (1979-1993 for ECMWF). Spectral analysis of the meridional wind component at 700 hPa highlighted two main periodicity bands, between 3 and 5 days, and 6 and 9 days. The 3-5-day easterly wave regime has already been widely investigated, but only on shorter datasets. These waves grow both north and south of the African easterly jet (AEJ). The two main tracks, noted over West Africa at 5 N and 15 N, converge over the Atlantic on latitude 17.5 N. These waves are more active in August-September than in June-July. Their average wavelength/phase speed varies from about 3000 km/8 ms{sup -1} north of the jet to 5000 km/12 ms{sup -1} south of the jet. Rainfall, convection and monsoon flux are significantly modulated by these waves, convection in the intertropical convergence zone (ITCZ) being enhanced in the trough and ahead of it, with a wide meridional extension. Compared to the 3-5-day waves, the 6-9-day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics. The only main track is located north of the AEJ along 17.5 N both over West Africa and the Atlantic. The mean wavelength is higher, about 5000 km long, and the average phase speed is about 7 m s{sup -1}. Then the wind field perturbation is mostly evident at the AEJ latitude and north of it. The perturbation structure is similar to that of 3-5-days in the north except that the more developed circulation centers, moving more to the north, lead to a large modulation of the jet zonal wind component. (orig.)

  5. Hydrography and through-flow in the north-eastern North Atlantic Ocean: the NANSEN project

    Science.gov (United States)

    van Aken, H. M.; Becker, G.

    The circulation and hydrography of the north-eastern North Atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the Oceanic Conveyor Belt. Over 900 hydrographic stations were used for this study, mainly from the 1987-1991 period. The hydrographic properties of Subpolar Mode Water in the upper layer, which is transported towards the Norwegian Sea, showed large regional variation. The deep water mass was dominated by the cold inflow of deep water from the Norwegian Sea and by a cyclonic recirculation of Lower Deep Water with a high Antarctic Bottom Water content. At intermediate levels the dominating water type was Labrador Sea Water with only minor influence of Mediterranean Sea Water. In the permanent pycnocline traces of Antarctic Intermediate Water were found. Geostrophic transports have been estimated, and these agreed in order of magnitude with the local heat budget, with current measurements, with data from surface drifters, and with the observed water mass modification. A total of 23 Sv of surface water entered the region, of which 20 Sv originated from the North Atlantic Current, while 3 Sv entered via an eastern boundary current. Of this total, 13 Sv of surface water left the area across the Reykjanes Ridge, and 7 Sv entered the Norwegian Sea, while 3 Sv was entrained by the cold overflow across the Iceland-Scotland Ridge. Approximately 1.4 Sv of Norwegian Sea Deep Water was involved in the overflow into the Iceland Basin, which, with about 1.1 Sv of entrained water and 1.1 Sv recirculating Lower Deep Water, formed a deep northern boundary current in the Iceland Basin. At intermediate depths, where Labrador Sea Water formed the dominant water type, about 2 Sv of entrained surface water contributed to a saline water mass which was transported westwards along the south Icelandic slope.

  6. CARINA oxygen data in the Atlantic Ocean

    OpenAIRE

    Stendardo, I.; Gruber, N.; A. Körtzinger

    2009-01-01

    In the CARINA (Carbon dioxide in the Atlantic Ocean) project, a new dataset with many previously unpublished hydrographic data from the Atlantic, Arctic and Southern Ocean was assembled and subjected to careful quality control (QC) procedures. Here, we present the dissolved oxygen measurements in the Atlantic region of the dataset and describe in detail the secondary QC procedures that aim to ensure that the data are internally consistent. This is achieved by a cross-over analysis, i.e. the c...

  7. 77 FR 69596 - Atlantic Highly Migratory Species; Advisory Panel for Atlantic Highly Migratory Species Southeast...

    Science.gov (United States)

    2012-11-20

    ... but not limited to data and models, used in stock assessments for oceanic sharks in the Atlantic Ocean... assessments for oceanic sharks in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. While the SEDAR Pool was created specifically for Atlantic oceanic sharks, it may be expanded to include other HMS,...

  8. 76 FR 65700 - Atlantic Highly Migratory Species; Advisory Panel for Atlantic Highly Migratory Species Southeast...

    Science.gov (United States)

    2011-10-24

    ..., used in stock assessments for oceanic sharks in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea... sharks in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. While the SEDAR Pool was created specifically for Atlantic oceanic sharks, it may be expanded to include other HMS, as needed. The...

  9. Surface mapping, organic matter and water stocks in peatlands of the Serra do Espinhaço meridional - Brazil

    Directory of Open Access Journals (Sweden)

    Márcio Luiz da Silva

    2013-10-01

    Full Text Available Peatlands are soil environments that store carbon and large amounts of water, due to their composition (90 % water, low hydraulic conductivity and a sponge-like behavior. It is estimated that peat bogs cover approximately 4.2 % of the Earth's surface and stock 28.4 % of the soil carbon of the planet. Approximately 612 000 ha of peatlands have been mapped in Brazil, but the peat bogs in the Serra do Espinhaço Meridional (SdEM were not included. The objective of this study was to map the peat bogs of the northern part of the SdEM and estimate the organic matter pools and water volume they stock. The peat bogs were pre-identified and mapped by GIS and remote sensing techniques, using ArcGIS 9.3, ENVI 4.5 and GPS Track Maker Pro software and the maps validated in the field. Six peat bogs were mapped in detail (1:20,000 and 1:5,000 by transects spaced 100 m and each transect were determined every 20 m, the UTM (Universal Transverse Mercator coordinates, depth and samples collected for characterization and determination of organic matter, according to the Brazilian System of Soil Classification. In the northern part of SdEM, 14,287.55 ha of peatlands were mapped, distributed over 1,180,109 ha, representing 1.2 % of the total area. These peatlands have an average volume of 170,021,845.00 m³ and stock 6,120,167 t (428.36 t ha-1 of organic matter and 142,138,262 m³ (9,948 m³ ha-1 of water. In the peat bogs of the Serra do Espinhaço Meridional, advanced stages of decomposing (sapric organic matter predominate, followed by the intermediate stage (hemic. The vertical growth rate of the peatlands ranged between 0.04 and 0.43 mm year-1, while the carbon accumulation rate varied between 6.59 and 37.66 g m-2 year-1. The peat bogs of the SdEM contain the headwaters of important water bodies in the basins of the Jequitinhonha and San Francisco Rivers and store large amounts of organic carbon and water, which is the reason why the protection and preservation

  10. 22 CFR 120.31 - North Atlantic Treaty Organization.

    Science.gov (United States)

    2010-04-01

    ... DEFINITIONS § 120.31 North Atlantic Treaty Organization. North Atlantic Treaty Organization (NATO) is..., France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, The Netherlands,...

  11. Análisis de restos bioarqueológicos de la costa meridional de Santa Cruz

    Directory of Open Access Journals (Sweden)

    Suby, Jorge A.

    2007-01-01

    Full Text Available En este trabajo se presentan análisis bioarqueológicos y paleopatológicos de los restos óseos humanos hallados en el marco del proyecto “Variabilidad del registro arqueológico y bioantropológico de la costa atlántica meridional patagónica” (PIP 5576. Fueron estudiados dos esqueletos humanos hallado en la región costera de amortiguación del Parque Nacional Monte León. Los materiales corresponden a un adulto y un niño, sobre los que se analizaron aspectos paleopatológicos a través de estudios macroscópicos y radiológicos. A su vez se estudiaron variables tafonómicas y de conservación. Los restos óseos mostraron, en el caso del individuo adulto, importantes marcadores de stress ocupacional en su columna vertebral, así como signos de traumatismos costales. En los restos pertenecientes al niño no pudieron identificarse alteraciones patológicas significativas. Se discuten los resultados hallados en relación a los antecedentes correspondientes al registro bioarqueológico de la región. Al mismo tiempo, en el marco del proyecto mencionado, se analizan las condiciones de conservación de los restos óseos tratados.

  12. Meridional transport of magnetic flux in the solar wind between 1 and 10 AU: a theoretical analysis

    International Nuclear Information System (INIS)

    Pioneer 10 observations suggest that the mean (longitudinally averaged) solar wind azimuthal field strength, B/sub phi/, near the ecliptic plane falls off more rapidly with heliocentric distance than would be expected in a classic Parker expansion, showing a deficit of 10--20% (as compared to the projected 1-AU value) by 10 AU. Though this observational interpretation has been challenged by subsequent analyses of Voyager data, it has nevertheless stimulated efforts to explain the inferred deficit on the basis of systematic north-south magnetic pressure gradients generated by the differential spiral wrapping of magnetic field lines in interplanetary space. We reexamine this issue from the theoretical perspective using a three-dimensional MHD nonlinear numerical model for steady, corotating flow. For realistic solar wind parameters we find that a purely axisymmetric expansion is capable of producing sizable magnetic flux deficits only when there are substantial meridional gradients in mean flow conditions localized about the ecliptic plane near the sun. Even then the match between plausible flow states and significant mean B/sub phi/ deficit is achieved over such a limited parameter range that it is unlikely this mechanism alone can produce deficits of the magnitude inferred from the Pioneer data

  13. 2D photochemical modeling of Saturn's stratosphere. Part I: Seasonal variation of atmospheric composition without meridional transport

    CERN Document Server

    Hue, Vincent; Dobrijevic, Michel; Hersant, Franck; Greathouse, Thomas K

    2015-01-01

    Saturn's axial tilt of 26.7{\\deg} produces seasons in a similar way as on Earth. Both the stratospheric temperature and composition are affected by this latitudinally varying insolation along Saturn's orbital path. A new time dependent 2D photochemical model is presented to study the seasonal evolution of Saturn's stratospheric composition. This study focuses on the impact of the seasonally variable thermal field on the main stratospheric C2 hydrocarbon chemistry (C2H2 and C2H6) using a realistic radiative climate model. Meridional mixing and advective processes are implemented in the model but turned off in the present study for the sake of simplicity. The results are compared to a simple study case where a latitudinally and temporally steady thermal field is assumed. Our simulations suggest that, when the seasonally variable thermal field is accounted for, the downward diffusion of the seasonally produced hydrocarbons is faster due to the seasonal compression of the atmospheric column during winter. This ef...

  14. Sistema de asentamiento prehispánico en la sierra meridional de Chañi (Salta, Argentina

    Directory of Open Access Journals (Sweden)

    Christian Vitry

    2007-01-01

    Full Text Available El área de investigación se ubica en el sector meridional de la Sierra de Chañi, Provincia de Salta, República Argentina. La estructura espacial y distribucional de los sitios arqueológicos en el área de estudio y sistemas montañosos aledaños posee un gran potencial informativo. Estos atributos cualicuantitativos nos permiten estudiar la variabilidad y complejidad del sistema de asentamiento en la región. Nuestro abordaje parte desde las perspectivas de la evolución del paisaje cultural y el proceso de cambio geopolítico. El registro arqueológico presente en el área de estudio manifiesta una recurrencia con relación al sistema de asentamiento, para el cual proponemos un modelo hipotético de ocupación del espacio durante los períodos de Desarrollos Regionales e Inka. Durante estos períodos analizamos la interacción de las diferentes formas de poder y posibles situaciones emergentes de desigualdad social

  15. Tropical Cyclone Activity in the North Atlantic Basin During the Weather Satellite Era, 1960-2014

    Science.gov (United States)

    Wilson, Robert M.

    2016-01-01

    ) oceanic Nino index (); (2) Atlantic multi-decadal oscillation () index; (3) Atlantic meridional mode () index; (4) global land-ocean temperature index (); and (5) quasi-biennial oscillation () index. Lastly, the associational aspects (using both linear and nonparametric statistical tests) between selected tropical cyclone parameters and the climatic factors are examined based on their 10-year moving average trend values.

  16. The North Atlantic circulation in the early 1980s - An estimate from inversion of a finite-difference model

    Science.gov (United States)

    Martel, Francoise; Wunsch, Carl

    1993-01-01

    A finite-difference model of the North Atlantic is constructed for the purpose of making an estimate of the circulation through an inverse calculation. The data base is eclectic, and includes hydrography, oxygen, nutrients, current meter and float records, atmospheric momentum, heat and water vapor transfers, as well as estimates of certain integral fluxes. Owing to the available hydrographic database, the model resolution is restricted to 1 deg at best, and is much coarser in many aspects. This limited resolution is a major obstacle to accurate estimates of climatological fluxes. In its final form, there are about 9000 constraints in 29,000 formal unknowns plus 9000 noise unknowns. The system is solved as a tapered least-squares system by a sparse conjugate gradient algorithm. With the exception of a few float velocities, all constraints are found to be consistent within error estimates. The model produces estimates of large-scale fluxes and flux divergences for all conventional properties including heat and nutrients as well as carbon dioxide and alkalinity. Meridional fluxes of carbon are found to be indistinguishable from zero, whereas the North Atlantic tends to export nutrients to the south, but carry heat to the north. Traditional oceanographic depictions of the circulation through combination of nonsynoptic data into steady models may have reached their useful limit in the present calculation, as the conflicts between the data and physical requirements become quantitatively apparent.

  17. Electrically-Active Convection in Tropical Easterly Waves and Implications for Tropical Cyclogenesis in the Atlantic and East Pacific

    Science.gov (United States)

    Leppert, Kenneth D., II; Petersen, Walter A.; Cecil, Daniel J.

    2012-01-01

    In this study, we investigate the characteristics of tropical easterly wave convection and the possible implications of convective structure on tropical cyclogenesis and intensification over the Atlantic Ocean and East Pacific using data from the Tropical Rainfall Measurement Mission Microwave Imager, Precipitation Radar (PR), and Lightning Imaging Sensor as well as infrared (IR) brightness temperature data from the NASA global-merged IR brightness temperature dataset. Easterly waves were partitioned into northerly, southerly, trough, and ridge phases based on the 700-hPa meridional wind from the NCEP-NCAR reanalysis dataset. Waves were subsequently divided according to whether they did or did not develop tropical cyclones (i.e., developing and nondeveloping, respectively), and developing waves were further subdivided according to development location. Finally, composites as a function of wave phase and category were created using the various datasets. Results suggest that the convective characteristics that best distinguish developing from nondeveloping waves vary according to where developing waves spawn tropical cyclones. For waves that developed a cyclone in the Atlantic basin, coverage by IR brightness temperatures .240 K and .210 K provide the best distinction between developing and nondeveloping waves. In contrast, several variables provide a significant distinction between nondeveloping waves and waves that develop cyclones over the East Pacific as these waves near their genesis location including IR threshold coverage, lightning flash rates, and low-level (tropical cyclogenesis forecasting.

  18. Systematic Center-To-Limb Variation in Measured Helioseismic Travel Times and Its Effect on Inferences of Solar Interior Meridional Flows

    Science.gov (United States)

    Zhao, Junwei; Nagashima, Kaori; Bogart, R. S.; Kosovichev, Alexander; Duvall, T. L., Jr.

    2012-01-01

    We report on a systematic center-to-limb variation in measured helioseismic travel times, which must be taken into account for an accurate determination of solar interior meridional flows. The systematic variation, found in time-distance helioseismology analysis using SDO/HMI and SDO/AIA observations, is different in both travel-time magnitude and variation trend for different observables. It is not clear what causes this systematic effect. Subtracting the longitude-dependent east-west travel times, obtained along the equatorial area, from the latitude-dependent north-south travel times, obtained along the central meridian area, gives remarkably similar results for different observables. We suggest this as an effective procedure for removing the systematic center-to-limb variation. The subsurface meridional flows obtained from inversion of the corrected travel times are approximately 10 m s-1 slower than those obtained without removing the systematic effect. The detected center-to-limb variation may have important implications in the derivation of meridional flows in the deep interior and needs to be better understood.

  19. SYSTEMATIC CENTER-TO-LIMB VARIATION IN MEASURED HELIOSEISMIC TRAVEL TIMES AND ITS EFFECT ON INFERENCES OF SOLAR INTERIOR MERIDIONAL FLOWS

    International Nuclear Information System (INIS)

    We report on a systematic center-to-limb variation in measured helioseismic travel times, which must be taken into account for an accurate determination of solar interior meridional flows. The systematic variation, found in time-distance helioseismology analysis using SDO/HMI and SDO/AIA observations, is different in both travel-time magnitude and variation trend for different observables. It is not clear what causes this systematic effect. Subtracting the longitude-dependent east-west travel times, obtained along the equatorial area, from the latitude-dependent north-south travel times, obtained along the central meridian area, gives remarkably similar results for different observables. We suggest this as an effective procedure for removing the systematic center-to-limb variation. The subsurface meridional flows obtained from inversion of the corrected travel times are approximately 10 m s–1 slower than those obtained without removing the systematic effect. The detected center-to-limb variation may have important implications in the derivation of meridional flows in the deep interior and needs to be better understood.

  20. Effects of Drake Passage on a strongly eddying global ocean

    CERN Document Server

    Viebahn, Jan P; Bars, Dewi Le; Dijkstra, Henk A

    2015-01-01

    The climate impact of ocean gateway openings during the Eocene-Oligocene transition is still under debate. Previous model studies employed grid resolutions at which the impact of mesoscale eddies has to be parameterized. We present results of a state-of-the-art eddy-resolving global ocean model with a closed Drake Passage, and compare with results of the same model at non-eddying resolution. An analysis of the pathways of heat by decomposing the meridional heat transport into eddy, horizontal, and overturning circulation components indicates that the model behavior on the large scale is qualitatively similar at both resolutions. Closing Drake Passage induces (i) sea surface warming around Antarctica due to changes in the horizontal circulation of the Southern Ocean, (ii) the collapse of the overturning circulation related to North Atlantic Deep Water formation leading to surface cooling in the North Atlantic, (iii) significant equatorward eddy heat transport near Antarctica. However, quantitative details sign...

  1. Experimental Study of Transient Thermal Convection Following a Catastrophic Lithospheric Overturn: Applications to the Tectonic Style, Thermal Evolution and Topography of Venus

    Science.gov (United States)

    Robin, C. M.; Thayalan, V.; Jellinek, A. M.

    2004-05-01

    The coexistence of dynamically supported highlands and coronae is difficult to reconcile with models of Venusian mantle convection. Coronae are well explained by transient discrete mantle upwellings (thermals), which are characteristic of weak cooling due to the stagnant lid style of convection expected in one-plate planets. In contrast, topographic highlands such as Atla, Beta and Themis Regio are better explained by persistent axisymmetric plumes more typical of the Earth's mantle, which is cooled strongly by subduction and plate tectonics (i.e. mobile lid convection). From the observed crater distribution, it is also inferred that the surface of Venus has a mean age of ~700 Ma. One explanation for this young surface age is that it is a result of a recent and catastrophic resurfacing event. We test a hypothesis that the occurrence of highlands and coronae are a consequence of the style of transient mantle convection driven by sudden overturn of the lithosphere. A series of stagnant lid and mobile lid convection control experiments at thermal equilibrium under conditions appropriate for Venus' mantle are first performed. The mobile lid regime is achieved using a conveyor belt at the cold boundary. Next, we investigate the thermal and temporal characteristics of transitions from steady-state stagnant lid to mobile lid, and from mobile lid to stagnant lid regimes. Using a combination of time-lapse video, shadowgraphs and analyses of time-series of temperature and heat flux data, we identify the qualitative changes in convective regime, the quantitative changes in the heat transfer characteristics of the flows, and the characteristic time scales over which transitions occur. Three regimes are observed: (i) steady-state stagnant lid mode characterized by time-dependent hot (rising) and cold (sinking) thermals; (ii) steady-state mobile-lid mode characterized by active stirring and long-lived plumes; and (iii) a transient mixed mode characterized by the coexistence of

  2. Occurrence and characteristics of mesoscale eddies in the tropical northeast Atlantic Ocean

    Science.gov (United States)

    Schütte, F.; Brandt, P.; Karstensen, J.

    2015-12-01

    Coherent mesoscale features (referred to here as eddies) in the tropical northeast Atlantic (between 12-22° N and 15-26° W) are examined and characterised. The eddies' surface signatures are investigated using 19 years of satellite derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo-Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and salinity (SSS) are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are associated with elevation/depression of SLA and enhanced/reduced SST and SSS patterns. However, about 20 % of all detected anticyclones show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year are identified (52 % cyclones, 39 % anticylones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in-situ temperature and salinity profile data (from Argo float, shipboard and mooring data) inside of the three eddy types, their distinct differences in vertical structure is determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland region and carry South Atlantic Central Water that originates from the northward transport within the Mauretania coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d-1) is confined to distinct corridors with a small meridional deflection dependent on the eddy type (anticyclones - equatorward, cyclones - poleward, ACMEs - no deflection). Heat and salt flux out of the coastal region and across the Cap Verde Frontal Zone, which separates the shadow zone from the ventilated gyre, are calculated.

  3. Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean

    Science.gov (United States)

    Schütte, Florian; Brandt, Peter; Karstensen, Johannes

    2016-05-01

    Coherent mesoscale features (referred to here as eddies) in the tropical northeastern Atlantic Ocean (between 12-22° N and 15-26° W) are examined and characterized. The eddies' surface signatures are investigated using 19 years of satellite-derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo-Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and sea surface salinity (SSS) anomalies are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are identified by an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, about 20 % of all anticyclonically rotating eddies show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year with a minimum lifetime of 7 days are identified (52 % cyclones, 39 % anticyclones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in situ temperature and salinity profiles (from Argo float, shipboard, and mooring data) taken inside of eddies, distinct mean vertical structures of the three eddy types are determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland regions and carry South Atlantic Central Water supplied by the northward flow within the Mauretanian coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d-1) is confined to distinct zonal corridors with a small meridional deflection dependent on the eddy type (anticyclones - equatorward, cyclones - poleward, ACMEs - no deflection). Heat and salt fluxes out of the coastal region and across the Cape Verde Frontal Zone, which separates the shadow zone from

  4. Air-sea CO2 fluxes in the Atlantic as measured during the FICARAM cruises

    Directory of Open Access Journals (Sweden)

    A. F. Ríos

    2009-06-01

    Full Text Available A total of fourteen hydrographic cruises spanning from 2000 to 2008 were conducted during the spring and autumn seasons between Spain and the Southern Ocean, under the framework of the Spanish research project FICARAM. The performed underway measurements are processed and analysed to describe the meridional air-sea CO2 fluxes (FCO2 along the Atlantic Ocean. The data was organised into different biogeochemical oceanographic provinces, according mainly to the thermohaline characteristics. The obtained spatial and temporal distributions of FCO2 follow the generally expected patterns and annual trends. The Subtropical regions in both hemispheres alternated the CO2 source and sink nature from autumn to spring, respectively. On the other hand, Tropical waters and the Patagonian Sea clearly behaved as sinks of atmospheric CO2 like the waters of the Drake Passage during autumn. The obtained results during the cruises also revealed significant long-term trends, such as the warming of equatorial waters (0.11±0.03°C yr−1 and the decrease of surface salinity (−0.16±0.01 yr−1 in tropical waters caused by the influence of the Amazon River plume. This reduction in surface salinity appears to have a direct influence over the CO2 storage rates, fostering the uptake capacity of atmospheric CO2 (−0.09±0.03 mol m−2 yr−1. An analysis of the biogeochemical forcing on the CO2 fugacity (fCO2 variability performed from an empirical algorithm highlighted the major role of the Amazon River input in the tropical North Atlantic fluxes. In addition, it has provided a quantitative measure of the importance of the thermodynamic control of FCO2 at temperate latitudes.

  5. Pedological and isotopic relations of a highland tropical peatland, Mountain Range of the Espinhaço Meridional (Brazil

    Directory of Open Access Journals (Sweden)

    Ingrid Horák

    2011-02-01

    Full Text Available The evolution of organic matter sources in soil is related to climate and vegetation dynamics in the past recorded in paleoenvironmental Quaternary deposits such as peatlands. For this reason, a Histosol of the mineralotrophic peatland from the Pau-de-Fruta Special Protection Area - SPA, Espinhaço Meridional, State of Minas Gerais, was described and characterized to evidence the soil constituent materials and properties as related to changes in environmental conditions, supported by the isotopic and elementary characterization of soil C and N and 14C ages. Samples were collected in a depression at 1,350 m asl, where Histosols are possibly more developed due to the great thickness (505 cm. Nowadays, the area is colonized by vegetation physiognomies of the Cerrado Biome, mainly rocky and wet fields (Campo Rupestre and Campo Úmido, aside from fragments of Semidecidual Seasonal Forest, called Capões forests. The results this study showed that early the genesis of the analyzed soil profile showed a high initial contribution of mostly herbaceous organic matter before 8,090 ± 30 years BP (14C age. In the lower-mid Holocene, between 8,090 ± 30 years AP (14C age to ± 4,100 years BP (interpolated age, the vegetation gradually became more woody, with forest expansion, possibly due to increased humidity, suggesting the existence of a more woody Cerrado in the past than at present. Drier climate conditions than the current were concluded ± 2,500 years BP (interpolated age and that after 430 years BP (14C age the forest gave way to grassland, predominantly. After the dry season, humidity increased to the current conditions. Due to these climate fluctuations during the Holocene, three decomposition stages of organic matter were observed in the Histosols of this study, with prevalence of the most advanced (sapric, typical of a deposit in a highly advanced stage of pedogenetic evolution.

  6. 'Electrically-Hot' Convection and Tropical Cyclone Development in the Eastern Atlantic

    Science.gov (United States)

    Leppert, Kenneth, II; Petersen, Walter A.; Williams, Earle

    2008-01-01

    The depth and intensity of convective-scale "hot" towers in intensifying tropical disturbances has been hypothesized to play a role in tropical cyclogenesis via dynamic and thermodynamic feedbacks on the larger meso-to-synoptic scale circulation. In this investigation we investigate the role that widespread and/or intense lightning-producing convection (i.e., "electrically-hot towers") resident in African Easterly Waves (AEW) may play in tropical cyclogenesis over the eastern Atlantic Ocean. NCEP reanalysis data for the months of July to November for the years 2004, 2006, and 2007 are analyzed for the domain of 5 N - 15 N and 500W - 300 E. Specifically, NCEP data for individual AEWs are partitioned into northerly, southerly, trough, and ridge phases using the 700 hPa meridional winds. Subsequently, information from National Hurricane Center storm reports were divided up into developing and non-developing waves (i.e. tropical cyclogenesis). Finally, composites were created of developing and non-developing waves using the NCEP variables, but with the inclusion of lightning flash count and infrared brightness temperature information. The Zeus and World Wide Lightning Location Network lightning data were used for the lightning information, and the IR brightness temperature data was extracted from the NASA global-merged infrared brightness temperature dataset.

  7. A multidecadal simulation of Atlantic tropical cyclones using a variable-resolution global atmospheric general circulation model

    Science.gov (United States)

    Zarzycki, Colin M.; Jablonowski, Christiane

    2014-09-01

    Using a variable-resolution option within the National Center for Atmospheric Research/Department of Energy Community Atmosphere Model (CAM) Spectral Element (SE) global model, a refined nest at 0.25° (˜28 km) horizontal resolution located over the North Atlantic is embedded within a global 1° (˜111 km) grid. The grid is designed such that fine grid cells are located where tropical cyclones (TCs) are observed to occur during the Atlantic TC season (June-November). Two simulations are compared, one with refinement and one control case with no refinement (globally uniform 1° grid). Both simulations are integrated for 23 years using Atmospheric Model Intercomparison Protocols. TCs are tracked using an objective detection algorithm. The variable-resolution simulation produces significantly more TCs than the unrefined simulation. Storms that do form in the refined nest are much more intense, with multiple storms strengthening to Saffir-Simpson category 3 intensity or higher. Both count and spatial distribution of TC genesis and tracks in the variable-resolution simulation are well matched to observations and represent significant improvements over the unrefined simulation. Some degree of interannual skill is noted, with the variable-resolution grid able to reproduce the observed connection between Atlantic TCs and the El Niño-Southern Oscillation (ENSO). It is shown that Genesis Potential Index (GPI) is well matched between the refined and unrefined simulations, implying that the introduction of variable-resolution does not affect the synoptic environment. Potential "upscale" effects are noted in the variable-resolution simulation, suggesting stronger TCs in refined nests may play a role in meridional transport of momentum, heat, and moisture.

  8. Palaeomagnetic and 40Ar/39Ar evidence for intrusion of dioritic and peralkaline rocks at Vredefort prior to overturning of the collar

    International Nuclear Information System (INIS)

    Intensive laboratory study has yielded consistent palaeomagnetic results from eight (out of 12) samples collected at two sites in the lamprophyric Lindequesdrift intrusion: n = 8, D = 221+-, I = -37+-, k = 13, α95 = 16+-. This subsidiary stable remanence, with high blocking temperature, is carried by the (titan) hematite coexisting with sphene formed by metasomatic alteration of ilmenite. This alteration is judged to be deuteric, and hence the stable magnetization was acquired penecontemporaneously with original crystallization. 40Ar/39Ar step heating of hornblende and feldspar separated from one of these lamprophyre samples yielded dates of 2163+-31 Ma and 1248+-22 Ma respectively. The hornblende (argon blocking temp. ≅500+-) gives a minimum age for the intrusion, while the feldspar (argon blocking temp. ≤250+-C) date reflects a later thermal disturbance. The orientation of this Lindequesdrift remanent vector, in relation to those previously obtained from the Rietfontein Complex, and the bronzite granophyre ring dyke, is consistent with the hypothesis that the alkalic plutons were intruded prior to overturning of their host collar rocks

  9. An Atlantic influence on Amazon rainfall

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Jin-Ho [University of Maryland, Department of Atmospheric and Oceanic Science, College Park, MD (United States); Zeng, Ning [University of Maryland, Earth System Science Interdisciplinary Center, College Park, MD (United States); University of Maryland, Department of Atmospheric and Oceanic Science, College Park, MD (United States)

    2010-02-15

    Rainfall variability over the Amazon basin has often been linked to variations in Pacific sea surface temperature (SST), and in particular, to the El Nino/Southern Oscillation (ENSO). However, only a fraction of Amazon rainfall variability can be explained by ENSO. Building upon the recent work of Zeng (Environ Res Lett 3:014002, 2008), here we provide further evidence for an influence on Amazon rainfall from the tropical Atlantic Ocean. The strength of the North Atlantic influence is found to be comparable to the better-known Pacific ENSO connection. The tropical South Atlantic Ocean also shows some influence during the wet-to-dry season transition period. The Atlantic influence is through changes in the north-south divergent circulation and the movement of the ITCZ following warm SST. Therefore, it is strongest in the southern part of the Amazon basin during the Amazon's dry season (July-October). In contrast, the ENSO related teleconnection is through anomalous east-west Walker circulation with largely concentrated in the eastern (lower) Amazon. This ENSO connection is seasonally locked to boreal winter. A complication due to the influence of ENSO on Atlantic SST causes an apparent North Atlantic SST lag of Amazon rainfall. Removing ENSO from North Atlantic SST via linear regression resolves this causality problem in that the residual Atlantic variability correlates well and is in phase with the Amazon rainfall. A strong Atlantic influence during boreal summer and autumn is particularly significant in terms of the impact on the hydro-ecosystem which is most vulnerable during the dry season, as highlighted by the severe 2005 Amazon drought. Such findings have implications for both seasonal-interannual climate prediction and understanding the longer-term changes of the Amazon rainforest. (orig.)

  10. 78 FR 3401 - Fisheries of the Northeastern United States; Atlantic Mackerel, Squid, and Butterfish Fisheries...

    Science.gov (United States)

    2013-01-16

    ...; Atlantic Mackerel, Squid, and Butterfish Fisheries; Scoping Process; Mid-Atlantic Fishery Management... support for an amendment (Amendment 16) to the Fishery Management Plan (FMP) for Atlantic Mackerel,...

  11. Meso- to submesocale oxygen variability and lateral oxygen fluxes in the oxygen minimum zone of the eastern tropical North Atlantic

    Science.gov (United States)

    Hahn, Johannes; Brandt, Peter; Krahmann, Gerd

    2015-04-01

    The oxygen minimum zone (OMZ) of the eastern tropical North Atlantic (ETNA) is located between the oxygen-rich equatorial region and the Cape Verde Frontal Zone at 20°N in a depth range between 300m - 700m. Its southern boundary is predominantly set by the equatorial zonal current system, where the northernmost current branch is represented by the eastward flowing North Equatorial Counter Current / North Equatorial Undercurrent (NECC/NEUC) at 5°N. Recent studies have shown enhanced oxygen variability for this location at the OMZ core depth which is generated due to mesoscale stirring induced by tropical instability waves as well as seasonal variability of the NECC/NEUC. An extensive measurement program was carried out in the past decade consisting of repeat ship sections as well as moored and glider observations along the 23°W section in order to study oxygen ventilation and oxygen variability in the ETNA OMZ regime. Moored and shipboard observations of oxygen and velocity reveal an eddy-driven northward oxygen flux towards the OMZ core, which results in an oxygen supply of up to 60% of the observed oxygen consumption. Based on the several year long moored observations at 5°N and 8°N, a seasonal variability of the eddy-driven meridional oxygen flux is found. Corresponding frequency spectra of the mooring time series are used to discuss time scales of enhanced variability of oxygen and meridional velocity. In this study, we explicitly present a measurement program which was conducted at 5°N, 23°W consisting of a triangular mooring array (Nov. 2012 - Apr. 2014) as well as a glider swarm experiment with a fleet of 3 gliders (Nov. - Dec. 2012). Based on this data set, a variogram of oxygen is derived to study spatial scales on the meso- to submesoscale in the NECC/NEUC regime.

  12. Attribution and impacts of warm SST biases over the eastern coastal Pacific and Atlantic in the coupled model SINTEX-F

    Science.gov (United States)

    Doi, T.; Richter, I.; Sasaki, W.; Luo, J.; Behera, S. K.; Masumoto, Y.

    2012-12-01

    Using a fully coupled ocean-atmosphere model of SINTEX-F (a basis of our seasonal prediction system), attribution and impacts of warm SST biases over the eastern coastal Pacific and Atlantic has been investigated. SINTEX-F has warm biases for annual mean SST in the eastern tropical Pacific and Atlantic, which is ubiquitous in other climate models (e.g. IPCC-CMIP3 and CMIP5 models). The warm SST biases could be due to the weak bias of southerly winds along the eastern coastal regions associated with the excessive southward migration bias of the ITCZ. We have to improve these biases, because they could contaminate the seasonal prediction skill over not only local regions, but also global climate. For further understanding and improving the SST biases, we explored impacts of warm SST biases in the eastern coastal Pacific and Atlantic by conducting two sensitivity experiments with SINTEX-F model; "Rest_EP run" and "Rest_EA run". In Rest_EP run, the simulated SST in the eastern coastal Pacific (90-70W, 20S-5N) is strongly restored to the observational monthly climatology, while Rest_EA run is same as Rest_EP run, but for restoring to the eastern coastal Atlantic (0-15E, 20S-5N). By comparison Rest_EP run with Control run, we found that the improvement of warm SST bias in the eastern coastal Pacific can cool global tropical SST, and fix 30% of the warm SST bias in the eastern tropical Atlantic relative to the Control run. On the other hands, the improvement of warm SST bias in the eastern coastal Atlantic warms the northern tropical Atlantic and the eastern equatorial Pacific, and does not much influence on the warm SST bias in the eastern tropical Pacific..Those responses of the improvement of the warm SST biases in the two eastern tropical regions are closely coupled with the ITCZ meridional migration and the zonal Walker circulation, which have strong impacts on the Amazonian rainfall.

  13. Climatic trends in the North Atlantic region during the last 2,000 years in an orbitally forced AOGCM simulation

    Science.gov (United States)

    Wagner, S.; Zorita, E.

    2013-12-01

    The global coverage of temporal highly resolved proxy-based climate reconstructions is extending to cover the last 2,000 years. It is thus important to fully understand the effect of the orbital forcing at these time scales, as the imprint of the orbital forcing becomes clearer when analyzing climate on time scales longer than the last 1,000 years. The slow-varying orbital parameters affect the seasonal distribution of the incoming solar radiation. Although changes are not as pronounced compared to the mid-Holocene, still distinct differences exist, with lower insolation between February and May and higher insolation between July and October over the mid- and high northern latitudes 2,000 years ago compared to present. Here, we analyze a simulation with the coupled climate model ECHO-G forced only with changes in orbital variations for the last 2,000 years. Other factors such as solar activity and greenhouse gas changes are set to constant pre-industrial values. The modeled near-surface temperature trends reflect the expected orbitally induced insolation trends over the northern hemispheric continents and the Arctic, with increased temperatures during May and reduced temperatures during October. Over the North Atlantic Ocean, however SST trends are not directly consistent to changes in orbital forcing throughout the year, mostly showing little or slight uniform cooling trends. The strength of the maximum overturning circulation in the North Atlantic Ocean also shows no clear-cut trends that can be linked to changes in external forcings. Other variables related to oceanic convection and surface heat fluxes indicate, however, spatially heterogeneous trend patterns. For example, regions south of Greenland and off Labrador show increases in convection that compensate the decreases over the Labrador and the Norwegian Sea. This pattern varies in intensity and spatial extent between the different winter half year months. Changes in oceanic convection and surface heat

  14. Atlantic energy and the strategic outlook

    Directory of Open Access Journals (Sweden)

    Paul Isbell

    2013-09-01

    Full Text Available Sweeping changes are beginning to transform energy scenarios around the world. The gas revolution, a renaissance in petroleum technology and exploration, and a chaotic but powerful movement toward the goal of low-carbon economies are three of the principal energy trends currently interacting with structural changes in the geo-economics of the Atlantic world to present new perspectives and opportunitiesfor the diverse actors in the ‘Atlantic Basin’. This article explores how changes in the energy landscape are contributing to a reassessment of the strategic horizon. The potential impacts of the shale revolution, deep-offshore oil, biofuels and other modern renewable energies on the geopolitics of the Atlantic Basin will be assessed, and the hypothesis that an Atlantic Basin energy system is now taking shape will be evaluated, along with an analysis of anticipated impacts.

  15. North Atlantic Coastal Plain aquifer system

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This data set represents the extent of the North Atlantic Coastal Plain aquifer system in North Carolina, Virginia, Maryland, Deleware, and New Jersey.

  16. Atlantic Sharpnose Shark Reproductive Biology Data

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Reproductive data from Atlantic sharpnose sharks were collected from specimens captured throughout the northern Gulf of Mexico on various research vessels. Data...

  17. Atlantic NAD 83 SLA Baseline Tangents

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains baseline tangent lines in ArcGIS shapefile format for the BOEM Atlantic Region. Baseline tangent lines are typically bay or river closing...

  18. Atlantic NAD 83 SLA Baseline Points

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains baseline points in ArcGIS shapefile format for the BOEM Atlantic Region. Baseline points are the discrete coordinate points along the...

  19. Atlantic NAD 83 Continental Shelf Boundary (CSB)

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains Continental Shelf Boundary (CSB) lines in ESRI shapefile format for the BOEM Atlantic Region. The CSB defines the seaward limit of federally...

  20. Atlantic Marine Mammal Assessment Vessel Surveys

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — These data sets are a compilation of large vessel surveys for marine mammal stock assessments in South Atlantic (Florida to Maryland) waters from 1994 to the...

  1. Atlantic Surfclam and Ocean Quahog Survey

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The standardized NEFSC Atlantic Surfclam and Ocean Quahog Survey has covered an area from Cape Hatteras to Georges Bank. The survey was conducted every two or three...

  2. Temperature fluctuations in the Atlantic Ocean

    International Nuclear Information System (INIS)

    The article discusses the temperature fluctuations in connection with drought in Africa, the climate in North America, the European heat waves and the frequent tropical hurricanes in the Atlantic Ocean. Problems with climate modelling and some pollution aspects are mentioned

  3. Divergencia genética en poblaciones prehistóricas del área andina centro meridional

    Directory of Open Access Journals (Sweden)

    Varela, Héctor Hugo

    2007-01-01

    Full Text Available La historia del poblamiento del Área Andina Centro Meridional estuvo determinada por un conjunto de factores culturales, económicos y biológicos que influyeron en la estructura de la población y determinaron una particular dispersión de las frecuencias génicas. En este trabajo se presenta el análisis de una extensa muestra representada por 1586 individuos de ambos sexos del Norte de Chile, N.O. Argentino, y los Valles del este de Bolivia (ca 3000 aC-1500 dC. La variación dentro y entre poblaciones es evaluada dentro del marco de la teoría de la genética de poblaciones mediante caracteres cuantitativos del cráneo y la aplicación de diferentes técnicas estadísticas de análisis multivariado. Los resultados indican que los habitantes de los valles de Cochabamba (Bolivia estuvieron más emparentados con los del Norte de Chile y N.O. Argentino que los de estas subáreas entre sí. Se observa una divergencia genética promedio para el Área Andina Centro Sur de 0.195, presentando el NOA el mayor aislamiento espacial (FST= 0.143 y el Norte de Chile el más bajo (FST= 0.043. Además, se demuestra un mayor aislamiento temporal de los grupos que habitaron los oasis de Atacama (FST= 0.031 y la Costa de Azapa (FST= 0.04 que los del Valle de Azapa (FST= 0.026. Estas evidencias confirman un proceso de poblamiento basado en la dispersión de varias líneas a partir de una misma población ancestral, las cuales se diferenciaron en el espacio y el tiempo dependiendo del tamaño efectivo y de la tasa de flujo génico entre ellas.

  4. El Cretácico del borde meridional del Sistema Central: unidades litoestratigráficas y secuencias deposicionales

    Directory of Open Access Journals (Sweden)

    García, A.

    1996-04-01

    Full Text Available The Central System is an alpine rejuvenation of the hercinian base of the Iberian Plateo The landward ends of the cretaceous carbonate platforms of the Iberian Basin croup out along the southern margino Near to the Iberian Range (NE, the cretaceous sediments are composed of shallow marine and litoral carbonate deposits. They grade towards the basin boundary (Central System into a litoral and continental terrigenous facies. An important reduction southward of the thickness of the sedimentary succession is recognized. The stratigraphic record is organized in sixteen lithostratigraphic units and in nine depositional sequence, that can be correlationed with the chart of cycles global of Haq et al. The age of the studied deposits are Cenomanian to Campanian. The stacking pattern is agradational, with a onlap not very marked in the base, a truncation and an internal uncorformity in the Santonian age. The thickness and facies changing is due to sinsedimentary faults within a distensive context, that have a little vertical displacement. They are younger outward of the sedimentary basin.El Sistema Central es un rejuvenecimiento alpino del zócalo hercínico de la Placa Ibérica. En su borde meridional afloran las terminaciones hacia el continente de las plataformas carbonatadas cretácicas del Surco Ibérico. Los depósitos cretácicos, en las proximidades de la Cordillera Ibérica (NE son carbonatados, de ambientes litorales y marinos someros; mientras que hacia el interior de la Placa Ibérica, pasan a depósitos terrígenos, de medios litorales y continentales. Hay también una importante reducción de los espesores en esa misma dirección. El registro estratigráfico se organiza en dieciséis unidades litoestratigráficas y en ocho secuencias deposicionales, que se correlacionan con la carta de ciclos globales de Haq et al. Los materiales estudiados abarcan desde el Cenomanense al Campaniense. La estructura de apilamiento es agradacional, con un

  5. Air-Sea CO2 fluxes in the Atlantic as measured during boreal spring and autumn

    Directory of Open Access Journals (Sweden)

    A. F. Ríos

    2010-05-01

    Full Text Available A total of fourteen hydrographic cruises from 2000 to 2008 were conducted during the spring and autumn seasons between Spain and the Southern Ocean under the framework of the Spanish research project FICARAM. The underway measurements were processed and analysed to describe the meridional air-sea CO2 fluxes (FCO2 in the covered sector of the Atlantic Ocean. The data has been grouped into different biogeochemical oceanographic provinces based on thermohaline characteristics. The spatial and temporal distributions of FCO2 followed expected distributions and annual trends reproducing the recent climatological ΔfCO2 estimations with a mean difference of −3 ± 18 μatm (Takahashi et al., 2009. The reduction in the CO2 saturation along the meridional FICARAM cruises represented an increase of 0.02 ± 0.14 mol m−2 yr−1 in the ocean uptake of atmospheric CO2. The subtropical waters in both Hemispheres acted as a sink of atmospheric CO2 during the successive spring seasons and as a source in autumn. The coarse reduction of the ocean uptake of atmospheric CO2 observed in the North Atlantic Ocean was linked to conditions of negative phase of the North Atlantic Oscillation that prevailed during the FICARAM period. Surface waters in the North Equatorial Counter Current revealed a significant long-term decrease of sea surface salinity of −0.16 ± 0.01 yr−1 coinciding with a declination of −3.5 ± 0.9 μatm yr−1 in the air–sea disequilibrium of CO2 fugacity and a rise of oceanic CO2 uptake of −0.09 ± 0.03 mol m−2 yr−1. The largest CO2 source was located in the equatorial upwelling system. These tropical waters that reached emissions of 0.7 ± 0.5 and 1.0 ± 0.7 mol m−2 y−1 in spring and autumn, respectively, showed an interannual warming of 0.11 ± 0.03 °C yr−1 and a wind speed decrease of −0.58 ± 0.14 m s−1 yr−1 in spring cruises which suggest the weakening of upwelling events associated with warm El Niño – Southern

  6. Strong winter cooling over the Irminger Sea in winter 2014-2015, exceptional deep convection, and the emergence of anomalously low SST

    Science.gov (United States)

    Jong, Marieke Femke; Steur, Laura

    2016-07-01

    Deep convection is presumed to be vital for the North Atlantic Meridional Overturning Circulation, even though observational evidence for the link remains inconclusive. Modeling studies have suggested that convection will weaken as a result of enhanced freshwater input. The emergence of anomalously low sea surface temperature in the subpolar North Atlantic has led to speculation that this process is already at work. Here we show that strong atmospheric forcing in the winter of 2014-2015, associated with a high North Atlantic Oscillation (NAO) index, produced record mixed layer depths in the Irminger Sea. Local mixing removed the stratification of the upper 1400 m and ventilated the basin to middepths resembling a state similar to the mid-1990s when a positive NAO also prevailed. We show that the strong local atmospheric forcing is predominantly responsible for the negative sea surface temperature anomalies observed in the subpolar North Atlantic in 2015 and that there is no evidence of permanently weakened deep convection.

  7. Spatio-temporal Interplay of RWTs and Cyclones in the North Atlantic

    Science.gov (United States)

    Schuster, M.; Ulbrich, U.

    2014-12-01

    . The Two-Way-Nested region, thus the CCLM domain, covers Central America and the North Atlantic (CANA) and therefore includes the Gulf stream region, whose prevalent strong meridional SST gradients favor the development of perturbations which then propagate downstream, commonly develop into extra-tropical cyclones and strike Europe.

  8. El papel de la molienda en la transición hacia la producción agropastoril: Un análisis desde la Puna Meridional argentina

    OpenAIRE

    María del Pilar Babot

    2006-01-01

    Se efectúa una caracterización de la molienda en Antofagasta de la Sierra, Puna Meridional argentina, desde sus primeras manifestaciones hacia ca. 6500 años AP hasta el momento agropastoril más tardío. Para el análisis del cambio tecnológico se emplean los conceptos de eficiencia e intensidad de uso de los artefactos. Como resultado se establecen tres momentos en la organización de la práctica de la molienda, que marcan situaciones de intensificación creciente de la misma entre ca. 6500-1100 ...

  9. Radiative budget and cloud radiative effect over the Atlantic from ship-based observations

    Directory of Open Access Journals (Sweden)

    J. Kalisch

    2012-10-01

    Full Text Available The aim of this study is to determine cloud-type resolved cloud radiative budgets and cloud radiative effects from surface measurements of broadband radiative fluxes over the Atlantic Ocean. Furthermore, based on simultaneous observations of the state of the cloudy atmosphere, a radiative closure study has been performed by means of the ECHAM5 single column model in order to identify the model's ability to realistically reproduce the effects of clouds on the climate system.

    An extensive database of radiative and atmospheric measurements has been established along five meridional cruises of the German research icebreaker Polarstern. Besides pyranometer and pyrgeometer for downward broadband solar and thermal radiative fluxes, a sky imager and a microwave radiometer have been utilized to determine cloud fraction and cloud type on the one hand and temperature and humidity profiles as well as liquid water path for warm non-precipitating clouds on the other hand.

    Averaged over all cruise tracks, we obtain a total net (solar + thermal radiative flux of 144 W m−2 that is dominated by the solar component. In general, the solar contribution is large for cirrus clouds and small for stratus clouds. No significant meridional dependencies were found for the surface radiation budgets and cloud effects. The strongest surface longwave cloud effects were shown in the presence of low level clouds. Clouds with a high optical density induce strong negative solar radiative effects under high solar altitudes. The mean surface net cloud radiative effect is −33 W m−2.

    For the purpose of quickly estimating the mean surface longwave, shortwave and net cloud effects in moderate, subtropical and tropical climate regimes, a new parameterisation was created, considering the total cloud amount and the solar zenith angle.

    The ECHAM5 single column model provides a surface net cloud effect that is more

  10. 77 FR 61562 - Atlantic Highly Migratory Species; 2013 Atlantic Shark Commercial Fishing Season

    Science.gov (United States)

    2012-10-10

    ... accompanied the 2011 shark quota specifications rule (75 FR 76302; December 8, 2010). Thus, NMFS proposes to... Species; 2013 Atlantic Shark Commercial Fishing Season AGENCY: National Marine Fisheries Service (NMFS... season for the Atlantic commercial shark fisheries. Quotas would be adjusted as allowable based on...

  11. 75 FR 44938 - Atlantic Coastal Fisheries Cooperative Management Act Provisions; Atlantic Coastal Shark Fishery

    Science.gov (United States)

    2010-07-30

    ... on April 27, 2010 (75 FR 22103), and are not repeated here. Activities Pursuant to the Atlantic... Management Act Provisions; Atlantic Coastal Shark Fishery AGENCY: National Marine Fisheries Service (NMFS... coastal sharks in the State waters of New Jersey. NMFS canceled the moratorium, as required by...

  12. 75 FR 22103 - Atlantic Coastal Fisheries Cooperative Management Act Provisions; Atlantic Coastal Shark Fishery

    Science.gov (United States)

    2010-04-27

    ... Register (75 FR 9158, March 1, 2010). NMFS received one comment in response to that notice. The comment... Management Act Provisions; Atlantic Coastal Shark Fishery AGENCY: National Marine Fisheries Service (NMFS... Atlantic Coastal Sharks (Plan) and that the measures New Jersey has failed to implement and enforce...

  13. 77 FR 35357 - Atlantic Highly Migratory Species; Commercial Atlantic Region Non-Sandbar Large Coastal Shark...

    Science.gov (United States)

    2012-06-13

    ...-Stevens Fishery Conservation and Management Act (16 U.S.C. 1801 et seq.). On January 24, 2012 (77 FR 3393... rule implementing the Atlantic HMS electronic dealer ] reporting system (76 FR 37750; June 28, 2011) or...; Commercial Atlantic Region Non-Sandbar Large Coastal Shark Fishery Opening Date AGENCY: National...

  14. 78 FR 65974 - Atlantic Highly Migratory Species; Advisory Panel for Atlantic Highly Migratory Species Southeast...

    Science.gov (United States)

    2013-11-04

    ... not limited to data and models, used in stock assessments for oceanic sharks in the Atlantic Ocean... information, including but not limited to data and models, used in stock assessments for oceanic sharks in the... Atlantic oceanic sharks, it may be expanded to include other HMS, as needed. The primary purpose of...

  15. 75 FR 57698 - Atlantic Highly Migratory Species; Atlantic Billfish Management, White Marlin (Kajikia albidus

    Science.gov (United States)

    2010-09-22

    ... manage: Atlantic tunas, listed by species; oceanic sharks; and, Atlantic swordfish, marlin, and sailfish....), oceanic sharks, sailfishes (Istiophorus spp.), and swordfish (Xiphias gladius).'' Prior to the addition of... Sharks (43 FR 3818), which was supported by an Environmental Impact Statement (42 FR 57716)....

  16. 76 FR 57709 - Atlantic Highly Migratory Species; Atlantic Shark Management Measures

    Science.gov (United States)

    2011-09-16

    .... As outlined in the September 20, 2010, ANPR (75 FR 57235), sharks have been federally managed since... National Oceanic and Atmospheric Administration 50 CFR Part 635 RIN 0648-BA17.e Atlantic Highly Migratory Species; Atlantic Shark Management Measures AGENCY: National Marine Fisheries Service (NMFS),...

  17. 75 FR 11133 - Fisheries of the South Atlantic; South Atlantic Fishery Management Council; Public Meeting

    Science.gov (United States)

    2010-03-10

    ... Wreckfish Shareholders for the South Atlantic region to discuss draft Amendment 20 to the Snapper Grouper... Shareholders for the South Atlantic region. See SUPPLEMENTARY INFORMATION. DATES: The meeting will take place... Wreckfish Shareholders on changes the Council is considering for the current ITQ program in Amendment 20...

  18. The Coupled Mars Dust and Water Cycles: Understanding How Clouds Affect the Vertical Distribution and Meridional Transport of Dust and Water.

    Science.gov (United States)

    Kahre, M. A.

    2015-01-01

    The dust and water cycles are crucial to the current Martian climate, and they are coupled through cloud formation. Dust strongly impacts the thermal structure of the atmosphere and thus greatly affects atmospheric circulation, while clouds provide radiative forcing and control the hemispheric exchange of water through the modification of the vertical distributions of water and dust. Recent improvements in the quality and sophistication of both observations and climate models allow for a more comprehensive understanding of how the interaction between the dust and water cycles (through cloud formation) affects the dust and water cycles individually. We focus here on the effects of clouds on the vertical distribution of dust and water, and how those vertical distributions control the net meridional transport of water. For this study, we utilize observations of temperature, dust and water ice from the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO) combined with the NASA ARC Mars Global Climate Model (MGCM). We demonstrate that the magnitude and nature of the net meridional transport of water between the northern and southern hemispheres during NH summer is sensitive to the vertical structure of the simulated aphelion cloud belt. We further examine how clouds influence the atmospheric thermal structure and thus the vertical structure of the cloud belt. Our goal is to identify and understand the importance of radiative/dynamic feedbacks due to the physical processes involved with cloud formation and evolution on the current climate of Mars.

  19. Preferencia de hábitat del murciélago hortelano meridional Eptesicus isabellinus (Temminck, 1840 en ambientes mediterráneos semiáridos

    Directory of Open Access Journals (Sweden)

    Lisón, F.

    2014-06-01

    Full Text Available Habitat preference of the meridional serotine bat Eptesicus isabellinus (Temminck, 1840 in semiarid Mediterranean landscapes Several molecular studies have recently reported the presence of a second species of the genus Eptesicus in the Iberian peninsula, the meridional serotine bat, E. isabellinus. This species is present in the south of Iberia and it seems to have an allopatric distribution with its twin species, E. serotinus. Ecological studies are now needed to understand the biology of E. isabellinus in southeast Spain. In this study, we used presence–only data for E. isabellinus to perform an ecological niche factor analysis (ENFA and to create a habitat suitability map (HSM. Our results show that the species has a low marginality index, suggesting it is well adapted to the semiarid conditions of the study area. The main habitats used by E. isabellinus are water courses, scrublands, and zones with high primary productivity. The species avoids non–irrigated cropland and shows no preference for human settlements or irrigated cropland. This study provides information about the ecology of E. isabellinus in southeast Spain and allows us to discuss relevant aspects for its conservation.

  20. RV Knorr Cruise KN200-4, 13 Apr-03 May 2011. RAPID Mooring Cruise

    OpenAIRE

    Johns, W.; Frajka-Williams, E.; et al, .

    2011-01-01

    This report describes the mooring operations conducted during RV Knorr cruise KN200-4 between 13 April and 3 May 2011. These mooring operations were completed as part of the United Kingdom Natural Environment Research Council (NERC) funded RAPID-WATCH Programme to monitor the Atlantic Meridional Overturning Circulation (MOC) at 26.5°N. The primary purpose on this cruise for the UK team was to service the RAPID Western Boundary moorings while the US teams worked on the Western Boundary Tim...

  1. Atlantic reef fish biogeography and evolution

    Science.gov (United States)

    Floeter, S.R.; Rocha, L.A.; Robertson, D.R.; Joyeux, J.C.; Smith-Vaniz, W.F.; Wirtz, P.; Edwards, A.J.; Barreiros, J.P.; Ferreira, C.E.L.; Gasparini, J.L.; Brito, A.; Falcon, J.M.; Bowen, B.W.; Bernardi, G.

    2008-01-01

    Aim: To understand why and when areas of endemism (provinces) of the tropical Atlantic Ocean were formed, how they relate to each other, and what processes have contributed to faunal enrichment. Location: Atlantic Ocean. Methods: The distributions of 2605 species of reef fishes were compiled for 25 areas of the Atlantic and southern Africa. Maximum-parsimony and distance analyses were employed to investigate biogeographical relationships among those areas. A collection of 26 phylogenies of various Atlantic reef fish taxa was used to assess patterns of origin and diversification relative to evolutionary scenarios based on spatio-temporal sequences of species splitting produced by geological and palaeoceanographic events. We present data on faunal (species and genera) richness, endemism patterns, diversity buildup (i.e. speciation processes), and evaluate the operation of the main biogeographical barriers and/or filters. Results: Phylogenetic (proportion of sister species) and distributional (number of shared species) patterns are generally concordant with recognized biogeographical provinces in the Atlantic. The highly uneven distribution of species in certain genera appears to be related to their origin, with highest species richness in areas with the greatest phylogenetic depth. Diversity buildup in Atlantic reef fishes involved (1) diversification within each province, (2) isolation as a result of biogeographical barriers, and (3) stochastic accretion by means of dispersal between provinces. The timing of divergence events is not concordant among taxonomic groups. The three soft (non-terrestrial) inter-regional barriers (mid-Atlantic, Amazon, and Benguela) clearly act as 'filters' by restricting dispersal but at the same time allowing occasional crossings that apparently lead to the establishment of new populations and species. Fluctuations in the effectiveness of the filters, combined with ecological differences among provinces, apparently provide a mechanism

  2. Kinematics of the South Atlantic rift

    Directory of Open Access Journals (Sweden)

    C. Heine

    2013-01-01

    Full Text Available The South Atlantic rift basin evolved as branch of a large Jurassic-Cretaceous intraplate rift zone between the African and South American plates during the final breakup of western Gondwana. While the relative motions between South America and Africa for post-breakup times are well resolved, many issues pertaining to the fit reconstruction and particular the relation between kinematics and lithosphere dynamics during pre-breakup remain unclear in currently published plate models. We have compiled and assimilated data from these intraplated rifts and constructed a revised plate kinematic model for the pre-breakup evolution of the South Atlantic. Based on structural restoration of the conjugate South Atlantic margins and intracontinental rift basins in Africa and South America, we achieve a tight fit reconstruction which eliminates the need for previously inferred large intracontinental shear zones, in particular in Patagonian South America. By quantitatively accounting for crustal deformation in the Central and West African rift zone, we have been able to indirectly construct the kinematic history of the pre-breakup evolution of the conjugate West African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic Pre-salt sag basin and the São Paulo High. We model an initial E–W directed extension between South America and Africa (fixed in present-day position at very low extensional velocities until Upper Hauterivian times (≈126 Ma when rift activity along in the equatorial Atlantic domain started to increase significantly. During this initial ≈17 Myr-long stretching episode the Pre-salt basin width on the conjugate Brazilian and West African margins is generated. An intermediate stage between 126.57 Ma and Base Aptian is characterised by strain localisation, rapid lithospheric weakening in the

  3. Nitrous oxide in the North Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    S. Walter

    2006-01-01

    Full Text Available In order to get a comprehensive picture of the distribution of nitrous oxide (N2O in the North Atlantic Ocean, measurements of dissolved nitrous oxide were made during three cruises in the tropical, subtropical and cold-temperate North Atlantic Ocean in October/November 2002, March/April 2004, and May 2002, respectively. To account for the history of atmospheric N2O, we suggest a new depth-dependent calculation of excess N2O (ΔN2O. N2O depth profiles showed supersaturation throughout the water column with a distinct increasing trend from the cold-temperate to the tropical region. Lowest nitrous oxide concentrations, near equilibrium and with an average of 11.0±1.7 nmol L−1, were found in the cold-temperate North Atlantic where the profiles showed no clear maxima. Highest values up to 37.3 nmol L−1 occurred in the tropical North Atlantic with clear maxima at approximately 400 m. A positive correlation of nitrous oxide with nitrate, as well as excess nitrous oxide with the apparent oxygen utilization (AOU, was only observed in the subtropical and tropical regions. Therefore, we conclude that the formation of nitrous oxide via nitrification occurs in the tropical region rather than in the cold-temperate region of the North Atlantic Ocean

  4. 76 FR 53413 - South Atlantic Fishery Management Council Meeting

    Science.gov (United States)

    2011-08-26

    ... Enforcement Committee; Ecosystem-Based Management Committee; Executive/ Finance Committees; King and Spanish... National Oceanic and Atmospheric Administration RIN 0648-XA660 South Atlantic Fishery Management Council... (NOAA), Commerce. ACTION: Notice of public meeting of the South Atlantic Fishery Management...

  5. Carotenoid dynamics in Atlantic salmon

    Directory of Open Access Journals (Sweden)

    Omholt Stig W

    2006-04-01

    Full Text Available Abstract Background Carotenoids are pigment molecules produced mainly in plants and heavily exploited by a wide range of organisms higher up in the food-chain. The fundamental processes regulating how carotenoids are absorbed and metabolized in vertebrates are still not fully understood. We try to further this understanding here by presenting a dynamic ODE (ordinary differential equation model to describe and analyse the uptake, deposition, and utilization of a carotenoid at the whole-organism level. The model focuses on the pigment astaxanthin in Atlantic salmon because of the commercial importance of understanding carotenoid dynamics in this species, and because deposition of carotenoids in the flesh is likely to play an important life history role in anadromous salmonids. Results The model is capable of mimicking feed experiments analyzing astaxanthin uptake and retention over short and long time periods (hours, days and years under various conditions. A sensitivity analysis of the model provides information on where to look for possible genetic determinants underlying the observed phenotypic variation in muscle carotenoid retention. Finally, the model framework is used to predict that a specific regulatory system controlling the release of astaxanthin from the muscle is not likely to exist, and that the release of the pigment into the blood is instead caused by the androgen-initiated autolytic degradation of the muscle in the sexually mature salmon. Conclusion The results show that a dynamic model describing a complex trait can be instrumental in the early stages of a project trying to uncover underlying determinants. The model provides a heuristic basis for an experimental research programme, as well as defining a scaffold for modelling carotenoid dynamics in mammalian systems.

  6. The Overturning Structure of Sodium Layer in Lower-thermospheric Region and Its Relevance to Ionospheric Field Align Irregularity (FAI) and Gravity Waves

    Science.gov (United States)

    Xue, X.; Dou, X.

    2014-12-01

    We report a surge-like overturning structure of the sodium layer in the lower thermospheric region (~110-120km) observed by a sodium lidar located at Haikou (20.0N, 110.3E), China. During 15:00UT ~ 15:30UT (Local time +8h), the sodium density shows an abrupt vertical increasing from ~100km to ~120km, and then falls down with a speed of ~2.5km/hr. The adjacent radio observations from COSMIC satellites and two ionosondes located at Fuke (19.5N, 109.1E) and Sanya (18.4N, 109.6E) indicate complicated ionospheric E region structures, i.e., multiple sporadic-E (Es) layers, covering the Hainan island region (18N-21N, 108-111E). Further more, a VHF radar located at Sanya (18.4, 109.6E) observed the field align irregularities (FAIs), which appear almost simultaneously with the surge-like structure of the sodium. The radar receiving SNR and the corresponding Doppler speed show a similar vertical increasing structure extending from ~100km to ~130km and the charged particles moving away (i.e., upward) from radar at the beginning of the FAIs and follows by descend-layer-like FAIs with a downward speed of 2.9km/hr. From these observational evidence, the surge-like structure of sodium layer is linked to the ionospheric E-region FAIs. We propose the possible process related to the formation of the surge-like sodium layer: the preexisted Es might provide a suitable gradient, and the gravity wave could trigger the K-H instability and push the upward moving of the charged particles, which are the source of Na+ and can be converted to Na through the chemical reactions. The investigations using the lidar temperature (35-55km), meteor radar wind (85-95km) and sodium column density and centroid height indicate that the gravity wave with period of ~4 hours and vertical wavelength of ~10km might be potential driver.

  7. 78 FR 61844 - North Atlantic Coast Comprehensive Study

    Science.gov (United States)

    2013-10-04

    ... Department of the Army; Corps of Engineers North Atlantic Coast Comprehensive Study AGENCY: Department of the... Atlantic Coast Comprehensive Study (Hurricane Sandy). The USACE is preparing a report that will be submitted to Congress in 2015. The goals of the North Atlantic Coast Comprehensive Study authorized...

  8. CARINA alkalinity data in the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    A. Velo

    2009-08-01

    Full Text Available Data on carbon and carbon-relevant hydrographic and hydrochemical parameters from previously non-publicly available cruise data sets in the Arctic, Atlantic and Southern Ocean have been retrieved and merged to a new database: CARINA (CARbon IN the Atlantic.

    These data have gone through rigorous quality control (QC procedures to assure the highest possible quality and consistency. The data for most of the measured parameters in the CARINA data base were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the data products, i.e. three merged data files with measured, calculated and interpolated data for each of the three CARINA regions; Arctic, Atlantic and Southern Ocean. Out of a total of 188 cruise entries in the CARINA database, 98 were conducted in the Atlantic Ocean and of these, 75 cruises report alkalinity values.

    Here we present details of the secondary QC on alkalinity for the Atlantic Ocean part of CARINA. Procedures of quality control, including crossover analysis between cruises and inversion analysis of all crossover data are briefly described. Adjustments were applied to the alkalinity values for 16 of the cruises in the Atlantic Ocean region. With these adjustments the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s. Based on our analysis we estimate the internal accuracy of the CARINA-ATL alkalinity data to be 3.3 μmol kg−1. The CARINA data are now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation.

  9. CARINA: nutrient data in the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    T. Tanhua

    2009-07-01

    Full Text Available Data on carbon and carbon-relevant hydrographic and hydrochemical parameters from previously non-publicly available cruise data sets in the Arctic, Atlantic and Southern Ocean have been retrieved and merged to a new database: CARINA (CARbon IN the Atlantic. These data have gone through rigorous quality control (QC procedures to assure the highest possible quality and consistency. The data for most of the measured parameters in the CARINA data base were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the data products, i.e. three merged data files with measured, calculated and interpolated data for each of the three CARINA regions; Arctic, Atlantic and Southern Ocean. Out of a total of 188 cruise entries in the CARINA database, 98 were conducted in the Atlantic Ocean and of these 84 cruises report nitrate values, 79 silicate, and 78 phosphate. Here we present details of the secondary QC for nutrients for the Atlantic Ocean part of CARINA. Procedures of quality control, including crossover analysis between cruises and inversion analysis of all crossover data are briefly described. Adjustments were applied to the nutrient values for 43 of the cruises in the Atlantic Ocean region. With these adjustments the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s (Key et al., 2004. Based on our analysis we estimate the internal accuracy of the CARINA-ATL nutrient data to be: nitrate 1.5%; phosphate 2.6%; silicate 3.1%. The CARINA data are now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation.

  10. Millennial changes in North Atlantic oxygen concentrations

    Science.gov (United States)

    Hoogakker, B. A. A.; Thornalley, D. J. R.; Barker, S.

    2016-01-01

    Glacial-interglacial changes in bottom water oxygen concentrations [O2] in the deep northeast Atlantic have been linked to decreased ventilation relating to changes in ocean circulation and the biological pump (Hoogakker et al., 2015). In this paper we discuss seawater [O2] changes in relation to millennial climate oscillations in the North Atlantic over the last glacial cycle, using bottom water [O2] reconstructions from 2 cores: (1) MD95-2042 from the deep northeast Atlantic (Hoogakker et al., 2015) and (2) ODP (Ocean Drilling Program) Site 1055 from the intermediate northwest Atlantic. The deep northeast Atlantic core MD95-2042 shows decreased bottom water [O2] during millennial-scale cool events, with lowest bottom water [O2] of 170, 144, and 166 ± 17 µmol kg-1 during Heinrich ice rafting events H6, H4, and H1. Importantly, at intermediate depth core ODP Site 1055, bottom water [O2] was lower during parts of Marine Isotope Stage 4 and millennial cool events, with the lowest values of 179 and 194 µmol kg-1 recorded during millennial cool event C21 and a cool event following Dansgaard-Oeschger event 19. Our reconstructions agree with previous model simulations suggesting that glacial cold events may be associated with lower seawater [O2] across the North Atlantic below ˜ 1 km (Schmittner et al., 2007), although in our reconstructions the changes are less dramatic. The decreases in bottom water [O2] during North Atlantic Heinrich events and earlier cold events at the two sites can be linked to water mass changes in relation to ocean circulation changes and possibly productivity changes. At the intermediate depth site a possible strong North Atlantic Intermediate Water cell would preclude water mass changes as a cause for decreased bottom water [O2]. Instead, we propose that the lower bottom [O2] there can be linked to productivity changes through increased export of organic material from the surface ocean and its subsequent remineralization in the water column

  11. 75 FR 27219 - Fisheries of the Northeastern United States; Atlantic Deep-Sea Red Crab Fisheries; 2010 Atlantic...

    Science.gov (United States)

    2010-05-14

    ... United States; Atlantic Deep-Sea Red Crab Fisheries; 2010 Atlantic Deep-Sea Red Crab Specifications...), Commerce. ACTION: Final rule. SUMMARY: NMFS issues final specifications for the 2010 Atlantic deep- sea red... document is also accessible via the Internet at http://www.nefmc.org . NMFS prepared a Final...

  12. Transports and budgets of anthropogenic CO2 in the tropical North Atlantic in 1992-1993 and 2010-2011

    Science.gov (United States)

    Zunino, Patricia; Pérez, Fiz F.; Fajar, Noelia M.; Guallart, Elisa F.; Ríos, Aida F.; Pelegrí, Josep L.; Hernández-Guerra, Alonso

    2015-07-01

    The meridional transport of anthropogenic CO2 (Cant) in the tropical North Atlantic (TNA) is investigated using data from transoceanic sections along 7.5°N and 24.5°N, carried out in the early 1990s and 2010s. The net Cant transport across both sections is northward. At 7.5°N, this transport increased from 315 ± 47 kmol s-1 in 1993 to 493 ± 51 kmol s-1 in 2010; similarly, across 24.5°N it grew from 530 ± 46 kmol s-1 in 1992 to 662 ± 49 kmol s-1 in 2011. These changes result from modifications in the intermediate and deep circulation patterns, as well as from Cant increase within the thermocline waters. In deep waters, lateral advection causes a net Cant input of 112 ± 60 kmol s-1 (234 ± 65 kmol s-1) in 1992-1993 (2010-2011); within these deep waters, the storage rate of Cant is not statistically different from the net Cant input, 139 ± 21 kmol s-1 (188 ± 21 kmol s-1) in 1992-1993 (2010-2011). The Cant increase in deep waters is due to the large injection of Cant across the 24.5°N by the Deep Western Boundary Current and the northward recirculation of North Atlantic Deep Water along 7.5°N. In contrast, a large net Cant output in the upper layer is caused by the Florida Current. Despite this net Cant output, the Cant accumulates at a rate of 215 ± 24 kmol s-1 (291 ± 24 kmol s-1) referenced to year 1993 (2010). From the two Cant budgets, we infer a Cant air-sea flux of 0.23 ± 0.02 Pg yr-1in the TNA, much larger than previous estimates.

  13. A simulated lagged response of the North Atlantic Oscillation to the solar cycle over the period 1960–2009

    International Nuclear Information System (INIS)

    Numerous studies have suggested an impact of the 11 year solar cycle on the winter North Atlantic Oscillation (NAO), with an increased tendency for positive (negative) NAO signals to occur at maxima (minima) of the solar cycle. Climate models have successfully reproduced this solar cycle modulation of the NAO, although the magnitude of the effect is often considerably weaker than implied by observations. A leading candidate for the mechanism of solar influence is via the impact of ultraviolet radiation variability on heating rates in the tropical upper stratosphere, and consequently on the meridional temperature gradient and zonal winds. Model simulations show a zonal mean wind anomaly that migrates polewards and downwards through wave–mean flow interaction. On reaching the troposphere this produces a response similar to the winter NAO. Recent analyses of observations have shown that solar cycle–NAO link becomes clearer approximately three years after solar maximum and minimum. Previous modelling studies have been unable to reproduce a lagged response of the observed magnitude. In this study, the impact of solar cycle on the NAO is investigated using an atmosphere–ocean coupled climate model. Simulations that include climate forcings are performed over the period 1960–2009 for two solar forcing scenarios: constant solar irradiance, and time-varying solar irradiance. We show that the model produces significant NAO responses peaking several years after extrema of the solar cycle, persisting even when the solar forcing becomes neutral. This confirms suggestions of a further component to the solar influence on the NAO beyond direct atmospheric heating and its dynamical response. Analysis of simulated upper ocean temperature anomalies confirms that the North Atlantic Ocean provides the memory of the solar forcing required to produce the lagged NAO response. These results have implications for improving skill in decadal predictions of the European and North

  14. A Northward Shift of the North Atlantic Ocean Intertropical Convergence Zone in Response to Summertime Saharan Dust Outbreaks

    Science.gov (United States)

    Wilcox, Eric M.; Lau, K. M.; Kim, Kyu-Myong

    2010-01-01

    The influence on the summertime North Atlantic Ocean inter-tropical convergence zone (ITCZ) of Saharan dust outbreaks is explored using nine years of continuous satellite observations and atmospheric reanalysis products. During dust outbreak events rainfall along the ITCZ shifts northward by 1 to 4 degrees latitude. Dust outbreaks coincide with warmer lower-tropospheric temperatures compared to low dust conditions, which is attributable to advection of the warm Saharan Air Layer, enhanced subtropical subsidence, and radiative heating of dust. The enhanced positive meridional temperature gradient coincident with dust outbreaks is accompanied by an acceleration of the easterly winds on the n011h side of the African Easterly Jet (AEJ). The center of the positive vorticity region south of the AEJ moves north drawing the center of low-level convergence and ITCZ rainfall northward with it. The enhanced precipitation on the north side of the ITCZ occurs in spite of widespread sea surface temperature cooling north of the ITCZ owing to reduced surface solar insolation by dust scattering.

  15. The POMME meso-scale analyses of the circulation in the NE Atlantic

    Science.gov (United States)

    Reverdin, G.; Assenbaum, M.; Caniaux, G.; Gaillard, F.; Giordani, H.; L'Herminier, P.; Memery, L.; Prieur, L.

    2003-04-01

    The Programme "Ocean Multidisciplinaire Meso Echelle" (POMME) seeks to understand the impact of meso-scale dynamics on mode water formation and subduction, and on the seasonal evolution of the water mass characteristics and biological activity in the NE Atlantic ocean (15-20W, 38-45N). The one-year field work, achieved in the autumn 2001, was based on three 6-week cruises with two vessels, nine moorings equipped with current-meters and other instruments, including four with sediment traps, and over 100 drifters and subsurface floats, as well as intensive meteorological measurements. Some of these floats and drifters were deployed during earlier cruises starting in October 1999 which provide a pluri-annual context. A significant meso-scale signal was observed in this low-energy region. A few coherent structures were identified which contribute to the horizontal transport of heat, salinity, stratification and tracers. These meso-scales also contribute to the distorsion of late-winter mixed layer depth that is primarily controlled by the air-sea buoyancy fluxes. Different analyses of the surface flow, temperature and salinity and of their evolution over a year will be presented. The water mass displacements and particle dispersion are also tentatively quantified that are compared to the actual subsurface float displacements and hydrographic parrays. The analyses are also used to illustrate the distorsion caused by advection on passive tracers (stirring of the large-scale horizontal gradient by the meso-scale eddies). How this varies with the vertical and what are the layers which contribute to the meridional heat and freshwater transport by the eddies will be explored. Areas of trapped flow in coherent eddies are tentatively identified, as well as areas favorable for the development of filaments.

  16. Atlantic hurricane activity during the last millennium

    Science.gov (United States)

    Burn, Michael J.; Palmer, Suzanne E.

    2015-08-01

    Hurricanes are a persistent socio-economic hazard for countries situated in and around the Main Development Region (MDR) of Atlantic tropical cyclones. Climate-model simulations have attributed their interdecadal variability to changes in solar and volcanic activity, Saharan dust flux, anthropogenic greenhouse gas and aerosol emissions and heat transport within the global ocean conveyor belt. However, the attribution of hurricane activity to specific forcing factors is hampered by the short observational record of Atlantic storms. Here, we present the Extended Hurricane Activity (EHA) index, the first empirical reconstruction of Atlantic tropical cyclone activity for the last millennium, derived from a high-resolution lake sediment geochemical record from Jamaica. The EHA correlates significantly with decadal changes in tropical Atlantic sea surface temperatures (SSTs; r = 0.68 1854-2008), the Accumulated Cyclone Energy index (ACE; r = 0.90 1851-2010), and two annually-resolved coral-based SST reconstructions (1773-2008) from within the MDR. Our results corroborate evidence for the increasing trend of hurricane activity during the Industrial Era; however, we show that contemporary activity has not exceeded the range of natural climate variability exhibited during the last millennium.

  17. Coccolithophores in the equatorial Atlantic Ocean

    DEFF Research Database (Denmark)

    Kinkel, Hanno; Baumann, K.-H.; Cepek, M.

    2000-01-01

    The present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial Atlantic. Data from a range of different samples, from the plankton, surface sediments as well as sediment cores are shown and compare...

  18. Population structure of Atlantic Mackerel (Scomber scombrus)

    DEFF Research Database (Denmark)

    Jansen, Teunis; Gislason, Henrik

    2013-01-01

    model where the population structure of mackerel is described as a dynamic cline, rather than as connected contingents. Temporal changes in hydrography and mackerel behavior may affect the steepness of the cline at various locations. The new interpretation of the population structure of Atlantic...

  19. MID-ATLANTIC REGIONAL ASSESSMENT: PROJECT DESCRIPTION

    Science.gov (United States)

    As part of the USGCRP's First National Assessment effort, EPA's Global Change Research Program sponsored the first Mid-Atlantic Regional Assessment. A multi-disciplinary team of 14 Pennsylvania State University (Penn State) faculty members led this regional assessment effort.

  20. Oil's not well on the Atlantic frontier

    International Nuclear Information System (INIS)

    This article focuses on the effects of oil exploration on global warming, and discusses Greenpeace's call for the petroleum industry to halt exploration in the Atlantic Frontier, the United Nations Climate Convention which commits governments to work towards the stabilisation of atmospheric greenhouse gas emissions, and the expansion of BP's Solar subsidiary. (UK)

  1. Atributos Físicos, Macro e Micromorfológicos de Neossolos Regolíticos no Agreste Meridional de Pernambuco

    Directory of Open Access Journals (Sweden)

    Alison Van Der Linden de Almeida

    2015-10-01

    Full Text Available RESUMO Neossolos Regolíticos no Agreste Meridional de Pernambuco são utilizados para diversas atividades agrícolas, com destaque para a produção de feijão. Há uma variação expressiva na produção dessa cultura, possivelmente associada à presença de lamelas, que conferem comportamento hídrico distinto entre esses solos. Objetivou-se analisar as características macromorfológicas, micromorfológicas e físicas de Neossolos Regolíticos localizados no Agreste Meridional de Pernambuco, com a finalidade de se entender o comportamento hídrico desses solos. Foram coletados e analisados dois perfis de solos localizados nos municípios de Paranatama (P1 - sem lamela e de São João (P2 - com lamela. Os resultados mostraram que nos atributos morfológicos (cor, textura, estrutura e consistência não foram observadas diferenças expressivas entre os dois perfis de solos; os atributos físicos (teor de argila, macroporosidade, microporosidade, capacidade de campo e ponto de murcha permanente apresentaram diferença significativa entre os horizontes dos perfis estudados; a micromorfologia indicou que a maior retenção de água no P2 é consequência da presença de zonas com empacotamento mais denso de seus componentes (empacotamento aglomerático e expressividade das pontes de argila; e sugere-se adoção do termo “lamélico” pelo atual Sistema Brasileiro de Classificação de Solos (em 4º nível categórico para diferenciação dos perfis estudados.

  2. Data Assimilation in a Solar Dynamo Model Using Ensemble Kalman Filters: Sensitivity and Robustness in Reconstruction of Meridional Flow Speed

    Science.gov (United States)

    Dikpati, Mausumi; Anderson, Jeffrey L.; Mitra, Dhrubaditya

    2016-09-01

    We implement an Ensemble Kalman Filter procedure using the Data Assimilation Research Testbed for assimilating “synthetic” meridional flow-speed data in a Babcock–Leighton-type flux-transport solar dynamo model. By performing several “observing system simulation experiments,” we reconstruct time variation in meridional flow speed and analyze sensitivity and robustness of reconstruction. Using 192 ensemble members including 10 observations, each with 4% error, we find that flow speed is reconstructed best if observations of near-surface poloidal fields from low latitudes and tachocline toroidal fields from midlatitudes are assimilated. If observations include a mixture of poloidal and toroidal fields from different latitude locations, reconstruction is reasonably good for ≤slant 40 % error in low-latitude data, even if observational error in polar region data becomes 200%, but deteriorates when observational error increases in low- and midlatitude data. Solar polar region observations are known to contain larger errors than those in low latitudes; our forward operator (a flux-transport dynamo model here) can sustain larger errors in polar region data, but is more sensitive to errors in low-latitude data. An optimal reconstruction is obtained if an assimilation interval of 15 days is used; 10- and 20-day assimilation intervals also give reasonably good results. Assimilation intervals \\lt 5 days do not produce faithful reconstructions of flow speed, because the system requires a minimum time to develop dynamics to respond to flow variations. Reconstruction also deteriorates if an assimilation interval \\gt 45 days is used, because the system’s inherent memory interferes with its short-term dynamics during a substantially long run without updating.

  3. The flow field of the upper hypoxic eastern tropical North Atlantic oxygen minimum zone

    Science.gov (United States)

    Stramma, L.; Czeschel, R.; Tanhua, T.; Brandt, P.; Visbeck, M.; Giese, B. S.

    2016-01-01

    A subsurface low oxygen zone is located in the eastern tropical North Atlantic Ocean (ETNA) in the upper ocean with the core of the hypoxic (O2 ≦60 µmol kg-1) oxygen minimum zone (OMZ) at 400 to 500 m depth. The subsurface circulation in the OMZ region is derived from observations and data assimilation results. Measurements in the ETNA of velocity, oxygen and of a tracer (CF3SF5) that was released in April 2008 at ˜ 8° N, 23° W (at ˜ 330 m depth) in November-December 2008, in November-December 2009 and October-November 2010 show the circulation in the upper part of the OMZ with spreading to the east in the North Equatorial Countercurrent (NECC) region and northwestward around the Guinea Dome. Three floats equipped with oxygen sensors deployed at ˜ 8° N, 23° W with parking depths at 330, 350 and 400 m depths were used to estimate velocity along the float trajectory at the surface and at the parking depth. At the 350 m park depth north of 9° N a cyclonic northwestward flow across the OMZ was observed. The northward drift of a float into the upper OMZ and a stronger cyclonic flow around the Guinea Dome seem to be connected to a strong Atlantic Meridional Mode (AMM) event in 2009. A near-surface cyclonic circulation cell east of the Cape Verde Islands reaches down into the OMZ layer. The circulation of the upper OMZ mirrors the near-surface circulation. Oxygen measurements from the cruises used here, as well as from other recent cruises up to the year 2014, confirm the continuous deoxygenation trend in the upper OMZ since the 1960s near the Guinea Dome. The three floats deployed with the tracer show spreading paths consistent with the overall observed tracer spreading. Oxygen sensors on the floats remained well calibrated for more than 20 months, and so the oxygen profiles can be used to investigate mesoscale eddy signatures. Mesoscale eddies may modify the oxygen distribution in OMZs. However, in general eddies are less energetic in the ETNA south of the

  4. Mesoscale eddies in the coastal upwelling region of the tropical northeast Atlantic Ocean

    Science.gov (United States)

    Schütte, Florian; Brandt, Peter; Karstensen, Johannes

    2014-05-01

    The mesoscale variability in the tropical northeast Atlantic (between 12°N - 22°N and 15°W - 26°W) is examined and characterised. We applied two automated methods for eddy identification to 16 years of satellite altimetry measurements: the geometrical method, based on closed streamlines around eddy cores, and the Okubo-Weiß method, based on the relationship between vorticity and the strain tensors. In general, both methods agree well. On average about 125 (±11) eddies per year were identified, separating in 52% cyclones and 48% anticylones. We found an average radius of about 50 (±20) km, a westward propagation speed of about 2.8 (±1.2) km/d and an average lifetime of about 40 days. Several eddies (more anticylones than cyclones) were detectable up to 300 days. Three main eddy formation regions in the coastal upwelling region that can be associated with headlands of the coast are detectable. This suggests that dynamic instability of the along-shore current is an important generation mechanism. We identified that cyclones are produced predominantly during boreal winter, especially in January, whereas anticyclones are generated predominantly during boreal summer. From the three eddy generation areas, almost all eddies propagate westward along distinct corridors with a small polarity depending meridional deflection (anticyclones - equatorward, cyclones - poleward). Considering occupied area and number of eddies, about 17% of the tropical northeast Atlantic region under investigation was occupied by eddies in every moment in time. About 30 (±5) eddies per year originate from the upwelling region off Senegal and Mauretania. Considering in-situ temperature and salinity observations (Argo, ship, mooring data) within and outside of eddies detected by the algorithms the mean vertical structure of the mesoscale eddies were determined. From together 2191 Profiles, 106 (144) profiles were within anticyclonic (cyclonic) mesoscale eddies. On average the maximum

  5. AtlantOS - Optimizing and Enhancing the Integrated Atlantic Ocean Observing System

    Science.gov (United States)

    Reitz, Anja; Visbeck, Martin; AtlantOS consortium, the

    2016-04-01

    Atlantic Ocean observation is currently undertaken through loosely-coordinated, in-situ observing networks, satellite observations and data management arrangements of heterogeneous international, national and regional design to support science and a wide range of information products. Thus there is tremendous opportunity to develop the systems towards a fully integrated Atlantic Ocean Observing System consistent with the recently developed 'Framework of Ocean Observing'. The vision of AtlantOS is to improve and innovate Atlantic observing by using the Framework of Ocean Observing to obtain an international, more sustainable, more efficient, more integrated, and fit-for-purpose system. Hence, the AtlantOS initiative will have a long-lasting and sustainable contribution to the societal, economic and scientific benefit arising from this integrated approach. This will be delivered by improving the value for money, extent, completeness, quality and ease of access to Atlantic Ocean data required by industries, product supplying agencies, scientist and citizens. The overarching target of the AtlantOS initiative is to deliver an advanced framework for the development of an integrated Atlantic Ocean Observing System that goes beyond the state-of -the-art, and leaves a legacy of sustainability after the life of the project. The legacy will derive from the following aims: i) to improve international collaboration in the design, implementation and benefit sharing of ocean observing, ii) to promote engagement and innovation in all aspects of ocean observing, iii) to facilitate free and open access to ocean data and information, iv) to enable and disseminate methods of achieving quality and authority of ocean information, v) to strengthen the Global Ocean Observing System (GOOS) and to sustain observing systems that are critical for the Copernicus Marine Environment Monitoring Service and its applications and vi) to contribute to the aims of the Galway Statement on Atlantic

  6. Linking the 8.2 ka Event and its Freshwater Forcing in the Labrador Sea

    Science.gov (United States)

    Hoffman, Jeremy S.; Carlson, Anders E.; Winsor, Kelsey; Klinkhammer, Gary P.; LeGrande, Allegra N.; Andrews, John T.; Strasser, C.

    2012-01-01

    The 8.2 ka event was the last deglacial abrupt climate event. A reduction in the Atlantic meridional overturning circulation (AMOC) attributed to the drainage of glacial Lake Agassiz may have caused the event, but the freshwater signature of Lake Agassiz discharge has yet to be identified in (delta)18O of foraminiferal calcite records from the Labrador Sea, calling into question the connection between freshwater discharge to the North Atlantic and AMOC strength. Using Mg/Ca-paleothermometry, we demonstrate that approx. 3 C of near-surface ocean cooling masked an 1.0 % decrease in western Labrador Sea (delta)18O of seawater concurrent with Lake Agassiz drainage. Comparison with North Atlantic (delta)18O of seawater records shows that the freshwater discharge was transported to regions of deep-water formation where it could perturb AMOC and force the 8.2 ka event.

  7. 大型升船机塔柱简化结构的抗倾覆稳定性分析%Analysis of anti-overturning stability of simple model of large-scale ship lift tower

    Institute of Scientific and Technical Information of China (English)

    高建勇; 胡晓; 邢义川

    2014-01-01

    鉴于齿轮齿条式升船机过坝速度快、运行安全可靠,已在我国的大型水利水电工程中得到广泛应用。由于升船机支承塔柱高宽比通常大于6,在水平地震荷载作用下,受到很大的倾覆力矩,使得基础的一侧发生破坏,当结构倾覆力矩超过由结构自重产生的恢复力矩时,结构将发生转动,当转角大于临界倾覆角时结构将会发生倾覆。因此需要评价升船机塔柱结构在强震作用下的转动稳定性。本文基于 MATLAB 7.0,编制了摇摆反应控制方程求解程序,利用该程序对大型升船机塔柱简化结构进行了抗倾覆稳定性分析。研究表明:地震波的频谱特性、高宽比、结构尺寸对结构抗倾覆能力有很大影响。应重点关注升船机塔柱结构底部拉应力集中区以防止应力过大引起底部脱开而发生摇摆失稳。%The vertical gear-rack ship-lift has been widely applied to large water and hydropower projects in China, due to its speed, safety and reliability. Since the width-height ratio of tower structure of ship lift is typically greater than 6, under horizontal ground motion, the resulting overturning moment of tower struc-ture is so large that the interface between structure and foundation will be destroyed. When overturning mo-ment exceeds restoring moment capacity,structure will tip about an edge of its base. It is necessary to ana-lyze the anti-overturning stability of tower structure of ship lift under strong ground motion. Based on MAT-LAB 7.0 platform, the solving program of rocking equations of rigid bodies has been developed. After verifi-cation, the overturning stability of simplified tower structure of ship lift has been analyzed in this paper. The results show that the characteristics of earthquake waves, width-height ratio and sizes have important impact on overturning stabilities of tower structures. More attention should be paid to the concentration zones of tensile

  8. Differential response of continental stock complexes of Atlantic salmon (Salmo salar) to the Atlantic Multidecadal Oscillation

    Science.gov (United States)

    Friedland, Kevin D.; Shank, Burton V.; Todd, Christopher D.; McGinnity, Philip; Nye, Janet A.

    2014-05-01

    Atlantic salmon, Salmo salar, in the North Atlantic are managed as a set of population complexes distributed in North America and Europe. In recent years, these complexes have experienced reduced marine survival and many populations within the complexes are at risk, especially those at the southern ends of the species amphi-Atlantic range. Atlantic salmon is an anadromous fish dividing its life history between residence in freshwater and the marine environment. The freshwater portion of the life history includes spawning and the rearing of juveniles where in-river production has tended to be relatively stable, whereas the first year at sea, termed the post-smolt year, is characterized by more variable rates of mortality. Although their habitats are widely separated geographically along the North Atlantic seaboards, strong recruitment coherence exists between North American and European stock complexes. This recruitment coherence is correlated with ocean temperature variation associated with the Atlantic Multidecadal Oscillation (AMO). The North Atlantic Oscillation (NAO) appears to be relatively unimportant as a driver of salmon abundance. The mechanism determining the link between AMO-related thermal variation and abundance appears to differ fundamentally for the two continental stock groupings. Whereas ocean climate variability during the first springtime months of juvenile salmon migration to sea appears to be important to the survival of North American stocks, summer climate variation appears to be central to adult recruitment variation for European stocks. This contrast in seasonal effects appears to be related to the varying roles of predation pressure and size-related mortality on the continental stock complexes. The anticipated warming due to global climate change will impose thermal conditions on salmon populations outside historical context and challenge the ability of many populations to persist.

  9. Hydrothermal Fluxes at the Mid-Atlantic Ridge, 5°S

    Science.gov (United States)

    Mertens, C.; Walter, M.; Koehler, J.; Sueltenfuss, J.; Rhein, M.

    2011-12-01

    The growing number of known hydrothermal vent sites has lead to an increasing recognition of the quantitative importance of hydrothermally derived materials in the large scale ocean circulation due to their possible impact on the ocean carbon cycle. The basin wide spreading of primordial helium measured during the WOCE era revealed intense hydrothermal venting in the South Atlantic, but it was not until 2005 that the first vent fields were located after intense surveys along the Mid-Atlantic Ridge. Before these sur- veys no hydrothermal fields were known in the Atlantic between 12°N and the Southern Ocean, thus leaving a large gap in the biogeography of hydrothermal vent fauna. One of the newly discovered sites is located in a relatively short segment of the rift valley at 5°S. It consists of three known high temperature fields: Turtle Pits, Comfortless Cove, and Red Lion, as well as several areas were diffuse venting was found. Hydrographic measurements were carried out at the Turtle Pits vent site during three cruises: Meteor cruise 68/1 in May 2006, a cruise with the french vessel L'Atalante in January 2008, and Meteor cruise 78/2 in April/May 2009. The data collected during these cruises are vertical profiles and towed sections of temperature, salinity, and turbidity, direct velocity measurements with lowered acoustic Doppler current profilers, as well as water samples for Helium isotope analysis. The hydrography at the vent sites is largely determined by the location of the sites in relation to the surrounding rift valley. The vents are situated in the center of the valley at a topographic sill. The water column plumes of the vent fields are clearly visible by strong signals in turbidity and temperature anomalies, and show a maximum rise height of more than 200 m, which does not exceed the height of the side walls of the graben. The currents in the rift valley are predominantly northward; the difference in stratification between upstream and downstream

  10. Teleconnections of Indian monsoon rainfall with AMO and Atlantic tripole

    Science.gov (United States)

    Krishnamurthy, Lakshmi; Krishnamurthy, V.

    2016-04-01

    The teleconnections between the decadal modes in the Indian monsoon rainfall (IMR) and the North Atlantic sea surface temperature are investigated. The two decadal modes of variability in the North Atlantic, the Atlantic multidecadal oscillation (AMO) and the Atlantic tripole, have opposite relation with the two decadal modes of IMR. The AMO has positive correlation with the monsoon rainfall while the Atlantic tripole has negative correlation. This study has put forward hypotheses for the mechanisms involved in the teleconnections of the AMO and the Atlantic tripole with the IMR. The warm phase of AMO may influence the monsoon through the summer North Atlantic Oscillation (SNAO) and further through the equatorial zonal winds which increase the moisture flow over India by enhancing the southwesterly flow. The warm phase of Atlantic tripole may impact the monsoon through the all-season NAO, leading to decreased moisture flow over India through the equatorial wind pattern. The observed relations between the decadal modes in the North Atlantic and the Indian monsoon are explored in the simulations of National Center for Atmospheric Research Community Climate System Model version 4 (CCSM4) model. Although the model supports the observed decadal teleconnection between the Atlantic Ocean and Indian monsoon, it has limitations in capturing the details of the spatial pattern associated with the teleconnection. The teleconnections of AMO and Atlantic tripole with the Indian monsoon is further demonstrated through an experiment with CCSM4 by decoupling the North Atlantic Ocean. The hypotheses for the mechanisms of the Atlantic teleconnections are also explored in the CCSM4 simulation.

  11. Coherent water transport across the South Atlantic

    CERN Document Server

    Wang, Y; Beron-Vera, F J

    2015-01-01

    The role of mesoscale eddies in transporting Agulhas leakage is investigated using a recent technique from nonlinear dynamical systems theory applied on geostrophic currents inferred from the over two-decade-long satellite altimetry record. Eddies are found to acquire material coherence away from the Agulhas retroflection, near the Walvis Ridge in the South Atlantic. Yearly, 1 to 4 coherent material eddies are detected with diameters ranging from 40 to 280 km. A total of 23 eddy cores of about 50 km in diameter and with at least 30% of their contents traceable into the Indian Ocean were found to travel across the subtropical gyre with minor filamentation. No more than 5\\% of such cores pour their contents on the North Brazil Current. While ability of eddies to carry Agulhas leakage northwestward across the South Atlantic is supported by our analysis, this is more restricted than suggested by earlier ring transport assessments.

  12. Displaced fracture through the anterior atlantal synchondrosis

    Energy Technology Data Exchange (ETDEWEB)

    Thakar, Chrishan; Allibone, James [Royal National Orthopaedic Hospital NHS Trust, Department of Spinal Deformity, Stanmore, Middlesex (United Kingdom); Harish, Srinivasan [Royal National Orthopaedic Hospital NHS Trust, Department of Radiology, Stanmore, Middlesex (United Kingdom); Saifuddin, Asif [Royal National Orthopaedic Hospital NHS Trust, Department of Radiology, Stanmore, Middlesex (United Kingdom); University College, The Institute of Orthopaedics and Musculoskeletal Sciences, London (United Kingdom)

    2005-09-01

    In the acute setting, accurate radiological interpretation of paediatric cervical spine trauma can be difficult due to a combination of normal variants and presence of multiple synchondroses. We present a rare case of a fracture through the anterior atlantal synchondrosis in a paediatric spine. A five-year-old boy, who fell backwards onto the top of his head while swinging across on a monkey bar frame, presented with neck pain, cervical muscle spasm and decreased right lateral rotation and extension of his neck. Computed tomography showed a displaced diastatic fracture through right anterior atlantal synchondrosis. There are only 12 cases of paediatric C1 fractures reported in the world literature. The importance of considering this diagnosis in the appropriate clinical setting, and the normal variants in the paediatric atlas that can cause diagnostic dilemma to the interpreting radiologist, are discussed in this case report. (orig.)

  13. Storms of Mediterranean and Atlantic legends

    Science.gov (United States)

    Schoenenwald, N.; Tabeaud, M.

    2009-09-01

    Weather extremes and notably wind storms are very often the channel ones since they are suspected of being the outward signs of climate change. However, even if audiovisual medias talk about wind storms in a very similar way, tales and legends stories account for the richness of their representations. Coastal and insular regions, whatever Atlantic or Mediterranean, are the ones where wind storms are most mentioned. The comparison between the tales and legends of these two regions, with distinct climatic characteristics, allows to underline the similarities and dissimilarities about the impregnation (or impact) of wind storms on these territories. Winds and storms distinguish spaces through vocabulary which can be peculiar to a region. Nevertheless, they also bring them together because above the local cultures is the human thought upon which wind storms create comparable perceptions, whatever the region. Key words: wind storms, Mediterranean regions, Atlantic regions, perceptions, representations.

  14. Fisheries. Population of origin of Atlantic cod.

    Science.gov (United States)

    Nielsen, E E; Hansen, M M; Schmidt, C; Meldrup, D; Grønkjaer, P

    2001-09-20

    Most of the world's cod (Gadus morhua) fisheries are now tightly regulated or closed altogether. Being able to link individual fish to their population of origin would assist enormously in policing regulations and in identifying poachers. Here we show that microsatellite genetic markers can be used to assign individual cod from three different populations in the northeastern Atlantic Ocean to their population of origin. PMID:11565021

  15. Indian - Atlantic interocean exchange: variability and controls

    OpenAIRE

    Schouten, Mathijs Wilhelmus

    2003-01-01

    South of Africa, warm Indian Ocean water enters the Atlantic Ocean by means of large Agulhas Rings. These rings, with diameters up to 350 km and reaching all the way to the ocean floor at 5 km depth, form an important link in the global thermohaline circulation, which is the driving force behind the moderate temperatures over Northern Europe. For six years, the shedding of Agulhas rings has been monitored from space, using satellite altimeter measurements of the sea surface height. Rings can ...

  16. Atlantic and indian oceans pollution in africa

    Science.gov (United States)

    Abubakar, Babagana

    Africa is the second largest and most populated continent after Asia. Geographically it is located between the Atlantic and Indian Oceans. Most of the Africa's most populated and industrialized cities are located along the coast of the continent facing the Atlantic and Indian Oceans, example of such cities include Casablanca, Dakar, Accra, Lagos, Luanda and Cape town all facing the Atlantic Ocean and cities like East London, Durban, Maputo, Dar-es-salaam and Mogadishu are all facing the Indian Ocean. As a result of the geographical locations of African Coastal Cities plus increase in their population, industries, sea port operations, petroleum exploration activities, trafficking of toxic wastes and improper waste management culture lead to the incessant increase in the pollution of the two oceans. NATURE OF POLLUTION OF THE ATLANTIC OCEAN i. The petroleum exploration activities going on along the coast of "Gulf of Guinea" region and Angola continuously causes oil spillages in the process of drilling, bunkering and discharging of petroleum products in the Atlantic Ocean. ii. The incessant degreasing of the Sea Ports "Quay Aprons" along the Coastal cities of Lagos, Luanda, Cape Town etc are continuously polluting the Atlantic Ocean with chemicals. iii. Local wastes generated from the houses located in the coastal cities are always finding their ways into the Atlantic Ocean. NATURE OF POLLUTION OF THE INDIAN OCEAN i. Unlike the Atlantic ocean where petroleum is the major pollutant, the Indian Ocean is polluted by Toxic / Radioactive waste suspected to have been coming from the developed nations as reported by the United Nations Environmental Programme after the Tsunami disaster in December 2004 especially along the coast of Somalia. ii. The degreasing of the Quay Aprons at Port Elizabeth, Maputo, Dar-es-Salaam and Mongolism Sea Ports are also another major source polluting the Indian Ocean. PROBLEMS GENERATED AS A RESULT OF THE OCEANS POLLUTION i. Recent report

  17. In Brief: Atlantic seasonal hurricane forecast

    Science.gov (United States)

    Showstack, Randy

    2007-12-01

    Two hurricane forecasters are predicting that 2008 will be an above-average Atlantic basin tropical cyclone season with an above-average probability of a major hurricane making landfall in the United States. During 2008, there could be about seven hurricanes (the annual average is 5.9) and 13 named storms (the average is 9.6), according to a 7 December report by Philip Klotzbach, research scientist at Colorado State University in Fort Collins, and William Gray, university professor emeritus of atmospheric sciences. The forecasters indicate that they believe the Atlantic basin is in an active hurricane cycle that is associated with a strong thermohaline circulation and an active phase of the Atlantic Multidecadal Oscillation. The report notes that, ``real-time operational early December forecasts have not shown forecast skill over climatology during this 16-year period [1992-2007]. This has occurred despite the fact that the skill over the hindcast period...showed appreciable skill.'' For more information, visit the Web site: http://hurricane.atmos.colostate.edu/Forecasts/2007/dec2007/dec2007.pdf.

  18. Local and remote impacts of a tropical Atlantic salinity anomaly

    OpenAIRE

    Mignot, Juliette; Frankignoul, Claude

    2009-01-01

    The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean-atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector afte...

  19. Mechanisms and predictability of North Atlantic - European Climate

    OpenAIRE

    Pohlmann, H.

    2005-01-01

    This study investigates the mechanisms of North Atlantic-European climate using atmosphere general circulation models (AGCMs). Experiments with the AGCM ECHAM4, in which the sea surface temperature (SST) forcing is restricted to either the Atlantic or the Indo-Pacific oceans, show that both oceanic regions have an influence on North Atlantic-European climate in winter. In the experiment with SST forcing restricted to the Indo-Pacific oceans the atmospheric response projects on the North Atlan...

  20. Evidence of remote forcing in the Equatorial Atlantic ocean

    OpenAIRE

    Servain, J.; Picaut, Joël; Merle, Jacques

    1982-01-01

    An analysis of sea-surface temperature (STT) and surface winds in selected areas of the Tropical Atlantic indicates that the nonseasonal variability of SST in the Eastern Equatorial Atlantic (Gulf of Guinea) is highly correlated with the nonseasonal variability of the zonal wind stress in the Western Equatorial Atlantic. A negative (positive) anomaly of the zonal wind stress near the North Brazilian coast is followed by a positive (negative) SST anomaly in the Gulf of Guinea about one month l...