WorldWideScience

Sample records for surface albedo feedbacks

  1. Sand Dune Albedo Feedback

    Directory of Open Access Journals (Sweden)

    Yosef Ashkenazy

    2018-02-01

    Full Text Available Sand dunes cover substantial parts of desert areas. Fully active dunes are bare, while fixed dunes are stabilized by vegetation and biogenic crust, and the dune activity is affected by the wind. Here we suggest the following atmosphere-sand dune feedback: spatial differences in the dunes’ vegetation and biogenic crust cover lead to differences in albedo as the albedo of bare sand is larger than that of vegetation and biogenic crust. This leads to a higher temperature over the vegetated area, resulting in air flow from the bare dune area to the vegetated dune area, thus increasing the wind activity over the vegetated dune area. In turn, this leads to enhanced stress on the vegetation and enhanced dune activity and thus to a decrease in vegetation. These changes in vegetation cover affect the surface albedo, leading to a change in wind activity. We examined this feedback using an atmospheric general circulation model, Weather Research and Forecasting (WRF, in selected regions of the northwestern Negev Desert and the Sahara/Sahel region, and we show that changes in surface albedo do indeed lead to significantly enhanced wind activity over the lower albedo region. We then incorporated this feedback into a simple vegetated dune model, showing that the multiple states associated with active and fixed dunes can be obtained for a larger range of parameters and that the stables states become more extreme (i.e., the fixed dune state becomes more vegetated and the active dune state becomes less vegetated.

  2. Land surface albedo and vegetation feedbacks enhanced the millennium drought in south-east Australia

    Science.gov (United States)

    Evans, Jason P.; Meng, Xianhong; McCabe, Matthew F.

    2017-01-01

    In this study, we have examined the ability of a regional climate model (RCM) to simulate the extended drought that occurred throughout the period of 2002 through 2007 in south-east Australia. In particular, the ability to reproduce the two drought peaks in 2002 and 2006 was investigated. Overall, the RCM was found to reproduce both the temporal and the spatial structure of the drought-related precipitation anomalies quite well, despite using climatological seasonal surface characteristics such as vegetation fraction and albedo. This result concurs with previous studies that found that about two-thirds of the precipitation decline can be attributed to the El Niño-Southern Oscillation (ENSO). Simulation experiments that allowed the vegetation fraction and albedo to vary as observed illustrated that the intensity of the drought was underestimated by about 10 % when using climatological surface characteristics. These results suggest that in terms of drought development, capturing the feedbacks related to vegetation and albedo changes may be as important as capturing the soil moisture-precipitation feedback. In order to improve our modelling of multi-year droughts, the challenge is to capture all these related surface changes simultaneously, and provide a comprehensive description of land surface-precipitation feedback during the droughts development.

  3. Land surface albedo and vegetation feedbacks enhanced the millennium drought in south-east Australia

    KAUST Repository

    Evans, Jason P.

    2017-01-24

    In this study, we have examined the ability of a regional climate model (RCM) to simulate the extended drought that occurred throughout the period of 2002 through 2007 in south-east Australia. In particular, the ability to reproduce the two drought peaks in 2002 and 2006 was investigated. Overall, the RCM was found to reproduce both the temporal and the spatial structure of the drought-related precipitation anomalies quite well, despite using climatological seasonal surface characteristics such as vegetation fraction and albedo. This result concurs with previous studies that found that about two-thirds of the precipitation decline can be attributed to the El Ninõ–Southern Oscillation (ENSO). Simulation experiments that allowed the vegetation fraction and albedo to vary as observed illustrated that the intensity of the drought was underestimated by about 10ĝ% when using climatological surface characteristics. These results suggest that in terms of drought development, capturing the feedbacks related to vegetation and albedo changes may be as important as capturing the soil moisture–precipitation feedback. In order to improve our modelling of multi-year droughts, the challenge is to capture all these related surface changes simultaneously, and provide a comprehensive description of land surface–precipitation feedback during the droughts development.

  4. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers

    Directory of Open Access Journals (Sweden)

    J. E. Box

    2012-08-01

    Full Text Available Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite-derived surface albedo with calibrated regional climate modeled surface air temperature and surface downward solar irradiance, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback over 12 summer periods beginning in 2000. We find that, while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97% of the ice sheet, when defined using paired annual anomalies, a second-order negative feedback is evident over 63% of the accumulation area. This negative feedback damps the accumulation area response to warming due to a positive correlation between snowfall and surface air temperature anomalies. Positive anomaly-gauged feedback concentrated in the ablation area accounts for more than half of the overall increase in melting when satellite-derived melt duration is used to define the timing when net shortwave flux is sunk into melting. Abnormally strong anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007, enabled three amplifying mechanisms to maximize the albedo feedback: (1 increased warm (south air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2 increased surface downward shortwave flux, leading to more surface heating and further albedo reduction; and (3 reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net infrared and solar radiation for the high elevation accumulation area approached

  5. Quantifying the ice-albedo feedback through decoupling

    Science.gov (United States)

    Kravitz, B.; Rasch, P. J.

    2017-12-01

    The ice-albedo feedback involves numerous individual components, whereby warming induces sea ice melt, inducing reduced surface albedo, inducing increased surface shortwave absorption, causing further warming. Here we attempt to quantify the sea ice albedo feedback using an analogue of the "partial radiative perturbation" method, but where the governing mechanisms are directly decoupled in a climate model. As an example, we can isolate the insulating effects of sea ice on surface energy and moisture fluxes by allowing sea ice thickness to change but fixing Arctic surface albedo, or vice versa. Here we present results from such idealized simulations using the Community Earth System Model in which individual components are successively fixed, effectively decoupling the ice-albedo feedback loop. We isolate the different components of this feedback, including temperature change, sea ice extent/thickness, and air-sea exchange of heat and moisture. We explore the interactions between these different components, as well as the strengths of the total feedback in the decoupled feedback loop, to quantify contributions from individual pieces. We also quantify the non-additivity of the effects of the components as a means of investigating the dominant sources of nonlinearity in the ice-albedo feedback.

  6. Greenland ice sheet albedo variability and feedback: 2000-2015

    Science.gov (United States)

    Box, J. E.; van As, D.; Fausto, R. S.; Mottram, R.; Langen, P. P.; Steffen, K.

    2015-12-01

    Absorbed solar irradiance represents the dominant source of surface melt energy for Greenland ice. Surface melting has increased as part of a positive feedback amplifier due to surface darkening. The 16 most recent summers of observations from the NASA MODIS sensor indicate a darkening exceeding 6% in July when most melting occurs. Without the darkening, the increase in surface melting would be roughly half as large. A minority of the albedo decline signal may be from sensor degradation. So, in this study, MOD10A1 and MCD43 albedo products from MODIS are evaluated for sensor degradation and anisotropic reflectance errors. Errors are minimized through calibration to GC-Net and PROMICE Greenland snow and ice ground control data. The seasonal and spatial variability in Greenland snow and ice albedo over a 16 year period is presented, including quantifying changing absorbed solar irradiance and melt enhancement due to albedo feedback using the DMI HIRHAM5 5 km model.

  7. Mimicking biochar-albedo feedback in complex Mediterranean agricultural landscapes

    International Nuclear Information System (INIS)

    Bozzi, E; Genesio, L; Miglietta, F; Toscano, P; Pieri, M

    2015-01-01

    Incorporation of charcoal produced by biomass pyrolysis (biochar) in agricultural soils is a potentially sustainable strategy for climate change mitigation. However, some side effects of large-scale biochar application need to be investigated. In particular a massive use of a low-reflecting material on large cropland areas may impact the climate via changes in surface albedo. Twelve years of MODIS-derived albedo data were analysed for three pairs of selected agricultural sites in central Italy. In each pair bright and dark coloured soil were identified, mimicking the effect of biochar application on the land surface albedo of complex agricultural landscapes. Over this period vegetation canopies never completely masked differences in background soil colour. This soil signal, expressed as an albedo difference, induced a local instantaneous radiative forcing of up to 4.7 W m −2 during periods of high solar irradiance. Biochar mitigation potential might therefore be reduced up to ∼30%. This study proves the importance of accounting for crop phenology and crop management when assessing biochar mitigation potential and provides more insights into the analysis of its environmental feedback. (letter)

  8. Time-Dependent Variations in the Arctic’s Surface Albedo Feedback and the Link to Seasonality in Sea Ice

    NARCIS (Netherlands)

    Andry, Olivier; Bintanja, Richard; Hazeleger, Wilco

    2017-01-01

    The Arctic is warming 2 to 3 times faster than the global average. Arctic sea ice cover is very sensitive to this warming and has reached historic minima in late summer in recent years (e.g., 2007 and 2012). Considering that the Arctic Ocean is mainly ice covered and that the albedo of sea ice is

  9. The dependence of the ice-albedo feedback on atmospheric properties.

    Science.gov (United States)

    von Paris, P; Selsis, F; Kitzmann, D; Rauer, H

    2013-10-01

    Ice-albedo feedback is a potentially important destabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover, and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced due to the strong spectral dependence of stellar radiation and snow/ice albedos; that is, M stars primarily emit in the near IR, where the snow and ice albedo is low, and less in the visible, where the snow/ice albedo is high. This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) on this feedback, since an atmosphere was neglected in previous studies. A plane-parallel radiative transfer model was used for the calculation of planetary albedos. We varied CO₂ partial pressures as well as the H₂O, CH₄, and O₃ content in the atmosphere for planets orbiting Sun-like and M type stars. Results suggest that, for planets around M stars, the ice-albedo effect is significantly reduced, compared to planets around Sun-like stars. Including the effects of an atmosphere further suppresses the sensitivity to the ice-albedo effect. Atmospheric key properties such as surface pressure, but also the abundance of radiative trace gases, can considerably change the strength of the ice-albedo feedback. For dense CO₂ atmospheres of the order of a few to tens of bar, atmospheric rather than surface properties begin to dominate the planetary radiation budget. At high CO₂ pressures, the ice-albedo feedback is strongly reduced for planets around M stars. The presence of trace amounts of H₂O and CH₄ in the atmosphere also weakens the ice-albedo effect for both stellar types considered. For planets around Sun-like stars, O₃ could also lead to a very strong decrease of the ice-albedo feedback at high CO₂ pressures.

  10. Assessing the possibility of a runaway ice-albedo feedback

    Science.gov (United States)

    Eisenman, I.

    2012-12-01

    If the ice-albedo feedback becomes dominant in high latitudes at some point as the climate warms, a runaway feedback will ensue in which the climate transitions to a new state. Such a transition occurs at a bifurcation point and is characterized by a discontinuity in the stable states available to the climate system. The possibility of such a runaway feedback in the Arctic has been investigated previously in a number of studies using both single-column models and comprehensive global models, and they have produced widely differing results. Here, I will use a toy model to evaluate the varied previously published results. The toy model represents the physics of sea ice growth and melt below a single column of the atmosphere, and the strength of interacting climate feedbacks such as albedo, clouds, and water vapor are controlled by scalable parameters. The toy model results suggest a novel measure, which can be assessed based on the current climate state, of how prone to instability the sea ice cover will be under global warming. I will demonstrate this measure in simulations from two state-of-the-art climate models, one of which has been shown to simulate a runaway ice-albedo feedback in the Arctic climate response to substantial greenhouse forcing and the other of which has been shown not to. This measure, which is based only on the simulated 20th century climate in each model, correctly identifies the model more prone to Arctic sea ice instability under substantial global warming.

  11. Enhanced albedo feedback in North Africa from possible combined vegetation and soil-formation processes

    Energy Technology Data Exchange (ETDEWEB)

    Knorr, Wolfgang [University of Bristol, Department of Earth Sciences, Bristol (United Kingdom); Schnitzler, Karl-Georg [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany)

    2006-01-01

    It has long been recognized that albedo related vegetation feedbacks amplify climate variability in North Africa. Recent studies have revealed that areas of very high albedo associated with certain desert soil types contribute to the current dry climate of the region. We construct three scenarios of North African albedo, one based on satellite measurements, one where the highest albedo resembles that of soils in the desert transition zones, and one based on a vegetation map for the ''green Sahara'' state of the middle Holocene, ca. 6,000 years ago. Using a series of climate model simulations, we find that the additional amplitude of albedo change from the middle Holocene to the present caused by the very bright desert soils enhances the magnitude of the June-to-August precipitation change in the region of the present Sahara from 0.6 to 1.0 mm/day on average. We also find that albedo change has a larger effect on regional precipitation than changes in either the Earth's orbit or sea surface temperatures between 6,000 years ago and today. Simulated precipitation agrees rather well with present observations and mid Holocene reconstructions. Our results suggest that there may exist an important climate feedback from soil formation processes that has so far not been recognized. (orig.)

  12. The seasonal cycle of snow cover, sea ice and surface albedo

    Science.gov (United States)

    Robock, A.

    1980-01-01

    The paper examines satellite data used to construct mean snow cover caps for the Northern Hemisphere. The zonally averaged snow cover from these maps is used to calculate the seasonal cycle of zonally averaged surface albedo. The effects of meltwater on the surface, solar zenith angle, and cloudiness are parameterized and included in the calculations of snow and ice albedo. The data allows a calculation of surface albedo for any land or ocean 10 deg latitude band as a function of surface temperature ice and snow cover; the correct determination of the ice boundary is more important than the snow boundary for accurately simulating the ice and snow albedo feedback.

  13. SURFACE ALBEDO AND SPECTRAL VARIABILITY OF CERES

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jian-Yang; Reddy, Vishnu; Corre, Lucille Le; Sykes, Mark V.; Prettyman, Thomas H. [Planetary Science Institute, 1700 E. Ft. Lowell Road, Suite 106, Tucson, AZ 85719 (United States); Nathues, Andreas; Hoffmann, Martin; Schaefer, Michael [Max Planck Institute for Solar System Research, Göttingen (Germany); Izawa, Matthew R. M.; Cloutis, Edward A. [University of Winnipeg, Winnipeg, Manitoba (Canada); Carsenty, Uri; Jaumann, Ralf; Krohn, Katrin; Mottola, Stefano; Schröder, Stefan E. [German Aerospace Center (DLR), Institute of Planetary Research, Berlin (Germany); Castillo-Rogez, Julie C. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Schenk, Paul [Lunar and Planetary Institute, Houston, TX 77058 (United States); Williams, David A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Smith, David E. [Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Zuber, Maria T. [Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); and others

    2016-02-01

    Previous observations suggested that Ceres has active, but possibly sporadic, water outgassing as well as possibly varying spectral characteristics over a timescale of months. We used all available data of Ceres collected in the past three decades from the ground and the Hubble Space Telescope, as well as the newly acquired images by the Dawn  Framing Camera, to search for spectral and albedo variability on Ceres, on both a global scale and in local regions, particularly the bright spots inside the Occator crater, over timescales of a few months to decades. Our analysis has placed an upper limit on the possible temporal albedo variation on Ceres. Sporadic water vapor venting, or any possibly ongoing activity on Ceres, is not significant enough to change the albedo or the area of the bright features in the Occator crater by >15%, or the global albedo by >3% over the various timescales that we searched. Recently reported spectral slope variations can be explained by changing Sun–Ceres–Earth geometry. The active area on Ceres is less than 1 km{sup 2}, too small to cause global albedo and spectral variations detectable in our data. Impact ejecta due to impacting projectiles of tens of meters in size like those known to cause observable changes to the surface albedo on Asteroid Scheila cannot cause detectable albedo change on Ceres due to its relatively large size and strong gravity. The water vapor activity on Ceres is independent of Ceres’ heliocentric distance, ruling out the possibility of the comet-like sublimation process as a possible mechanism driving the activity.

  14. Surface albedo following biochar application in durum wheat

    International Nuclear Information System (INIS)

    Genesio, L; Miglietta, F; Lugato, E; Baronti, S; Pieri, M; Vaccari, F P

    2012-01-01

    The agronomic use of charcoal from biomass pyrolysis (biochar) represents an interesting option for increasing soil fertility and sequestering atmospheric CO 2 . However, before moving toward large-scale biochar applications, additional research must evaluate all possible land–atmosphere feedbacks. Despite the increasing number of studies investigating the effect of biochar on soil physical, chemical and biological properties, only a few have been done on surface albedo variations on agricultural lands. The present work had the aim of characterizing the annual albedo cycle for a durum wheat crop in Central Italy, by means of a spectroradiometer measurement campaign. Plots treated with biochar, at a rate of 30–60 t ha −1 , showed a surface albedo decrease of up to 80% (after the application) with respect to the control in bare soil conditions, while this difference tended to decrease during the crop growing season, because of the prevailing effect of canopy development on the radiometer response. After the post-harvesting tillage, the soil treated with biochar again showed a lower surface albedo value (<20–26% than the control), while the measurements taken in the second year after application suggested a clear decrease of biochar influence on soil color. The modeling of the surface energy balance highlighted changes in the partitioning of heat fluxes and in particular a substantial increase of ground heat fluxes on an annual basis. (letter)

  15. Albedo feedbacks to future climate via climate change impacts on dryland biocrusts

    Science.gov (United States)

    Rutherford, William A.; Painter, Thomas H.; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S.; Flagg, Cody; Reed, Sasha C.

    2017-03-01

    Drylands represent the planet’s largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

  16. Albedo feedbacks to future climate via climate change impacts on dryland biocrusts

    Science.gov (United States)

    Rutherford, William A.; Painter, Thomas H.; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S.; Flagg, Cody B.; Reed, Sasha C.

    2017-01-01

    Drylands represent the planet’s largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

  17. Variability of soil moisture and its relationship with surface albedo ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 119; Issue 4. Variability of soil moisture and its relationship with surface albedo and soil thermal ... The diurnal variation of surface albedo appears as a U-shaped curve on sunny days. Surface albedo decreases with the increase of solar elevation angle, and it tends ...

  18. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Artic Sea Ice Cover

    Science.gov (United States)

    2015-11-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. SUNLIGHT, SEA ICE , AND THE ICE ALBEDO FEEDBACK IN A...iv) onset dates of melt and freeze up. 4. Assess the magnitude of the contribution from ice - albedo feedback to the observed decrease of sea ice in... sea ice prediction and modeling community to improve the treatment of solar radiation and the ice - albedo feedback. This transfer will take the form of

  19. Validation of snow characteristics and snow albedo feedback in the Canadian Regional Climate Model simulations over North America

    Science.gov (United States)

    Fang, B.; Sushama, L.; Diro, G. T.

    2015-12-01

    Snow characteristics and snow albedo feedback (SAF) over North America, as simulated by the fifth-generation Canadian Regional Climate Model (CRCM5), when driven by ERA-40/ERA-Interim, CanESM2 and MPI-ESM-LR at the lateral boundaries, are analyzed in this study. Validation of snow characteristics is performed by comparing simulations against available observations from MODIS, ISCCP and CMC. Results show that the model is able to represent the main spatial distribution of snow characteristics with some overestimation in snow mass and snow depth over the Canadian high Arctic. Some overestimation in surface albedo is also noted for the boreal region which is believed to be related to the snow unloading parameterization, as well as the overestimation of snow albedo. SAF is assessed both in seasonal and climate change contexts when possible. The strength of SAF is quantified as the amount of additional net shortwave radiation at the top of the atmosphere as surface albedo decreases in association with a 1°C increase in surface temperature. Following Qu and Hall (2007), this is expressed as the product of the variation in planetary albedo with surface albedo and the change in surface albedo for 1°C change in surface air temperature during the season, which in turn is determined by the strength of the snow cover and snowpack metamorphosis feedback loops. Analysis of the latter term in the seasonal cycle suggests that for CRCM5 simulations, the snow cover feedback loop is more dominant compared to the snowpack metamorphosis feedback loop, whereas for MODIS, the two feedback loops have more or less similar strength. Moreover, the SAF strength in the climate change context appears to be weaker than in the seasonal cycle and is sensitive to the driving GCM and the RCP scenario.

  20. Impacts of Satellite-Based Snow Albedo Assimilation on Offline and Coupled Land Surface Model Simulations.

    Science.gov (United States)

    Wang, Tao; Peng, Shushi; Krinner, Gerhard; Ryder, James; Li, Yue; Dantec-Nédélec, Sarah; Ottlé, Catherine

    2015-01-01

    Seasonal snow cover in the Northern Hemisphere is the largest component of the terrestrial cryosphere and plays a major role in the climate system through strong positive feedbacks related to albedo. The snow-albedo feedback is invoked as an important cause for the polar amplification of ongoing and projected climate change, and its parameterization across models is an important source of uncertainty in climate simulations. Here, instead of developing a physical snow albedo scheme, we use a direct insertion approach to assimilate satellite-based surface albedo during the snow season (hereafter as snow albedo assimilation) into the land surface model ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) and assess the influences of such assimilation on offline and coupled simulations. Our results have shown that snow albedo assimilation in both ORCHIDEE and ORCHIDEE-LMDZ (a general circulation model of Laboratoire de Météorologie Dynamique) improve the simulation accuracy of mean seasonal (October throughout May) snow water equivalent over the region north of 40 degrees. The sensitivity of snow water equivalent to snow albedo assimilation is more pronounced in the coupled simulation than the offline simulation since the feedback of albedo on air temperature is allowed in ORCHIDEE-LMDZ. We have also shown that simulations of air temperature at 2 meters in ORCHIDEE-LMDZ due to snow albedo assimilation are significantly improved during the spring in particular over the eastern Siberia region. This is a result of the fact that high amounts of shortwave radiation during the spring can maximize its snow albedo feedback, which is also supported by the finding that the spatial sensitivity of temperature change to albedo change is much larger during the spring than during the autumn and winter. In addition, the radiative forcing at the top of the atmosphere induced by snow albedo assimilation during the spring is estimated to be -2.50 W m-2, the magnitude of

  1. Impacts of Satellite-Based Snow Albedo Assimilation on Offline and Coupled Land Surface Model Simulations.

    Directory of Open Access Journals (Sweden)

    Tao Wang

    Full Text Available Seasonal snow cover in the Northern Hemisphere is the largest component of the terrestrial cryosphere and plays a major role in the climate system through strong positive feedbacks related to albedo. The snow-albedo feedback is invoked as an important cause for the polar amplification of ongoing and projected climate change, and its parameterization across models is an important source of uncertainty in climate simulations. Here, instead of developing a physical snow albedo scheme, we use a direct insertion approach to assimilate satellite-based surface albedo during the snow season (hereafter as snow albedo assimilation into the land surface model ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms and assess the influences of such assimilation on offline and coupled simulations. Our results have shown that snow albedo assimilation in both ORCHIDEE and ORCHIDEE-LMDZ (a general circulation model of Laboratoire de Météorologie Dynamique improve the simulation accuracy of mean seasonal (October throughout May snow water equivalent over the region north of 40 degrees. The sensitivity of snow water equivalent to snow albedo assimilation is more pronounced in the coupled simulation than the offline simulation since the feedback of albedo on air temperature is allowed in ORCHIDEE-LMDZ. We have also shown that simulations of air temperature at 2 meters in ORCHIDEE-LMDZ due to snow albedo assimilation are significantly improved during the spring in particular over the eastern Siberia region. This is a result of the fact that high amounts of shortwave radiation during the spring can maximize its snow albedo feedback, which is also supported by the finding that the spatial sensitivity of temperature change to albedo change is much larger during the spring than during the autumn and winter. In addition, the radiative forcing at the top of the atmosphere induced by snow albedo assimilation during the spring is estimated to be -2.50 W m-2, the

  2. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover

    Science.gov (United States)

    2015-09-30

    Figure 1). When the ice is snow covered there is little difference in albedo and partitioning between first year and multiyear ice. Once the snow melts...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Sunlight, Sea Ice, and the Ice Albedo Feedback in a...and iv) onset dates of melt and freeze up. 4. Assess the magnitude of the contribution from ice- albedo feedback to the observed decrease of sea ice

  3. Vegetation controls on northern high latitude snow-albedo feedback: Observations and CMIP5 model simulations

    OpenAIRE

    Loranty, MM; Berner, LT; Goetz, SJ; Jin, Y; Randerson, JT

    2014-01-01

    The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, ...

  4. Climate warming feedback from mountain birch forest expansion: reduced albedo dominates carbon uptake.

    Science.gov (United States)

    de Wit, Heleen A; Bryn, Anders; Hofgaard, Annika; Karstensen, Jonas; Kvalevåg, Maria M; Peters, Glen P

    2014-07-01

    Expanding high-elevation and high-latitude forest has contrasting climate feedbacks through carbon sequestration (cooling) and reduced surface reflectance (warming), which are yet poorly quantified. Here, we present an empirically based projection of mountain birch forest expansion in south-central Norway under climate change and absence of land use. Climate effects of carbon sequestration and albedo change are compared using four emission metrics. Forest expansion was modeled for a projected 2.6 °C increase in summer temperature in 2100, with associated reduced snow cover. We find that the current (year 2000) forest line of the region is circa 100 m lower than its climatic potential due to land-use history. In the future scenarios, forest cover increased from 12% to 27% between 2000 and 2100, resulting in a 59% increase in biomass carbon storage and an albedo change from 0.46 to 0.30. Forest expansion in 2100 was behind its climatic potential, forest migration rates being the primary limiting factor. In 2100, the warming caused by lower albedo from expanding forest was 10 to 17 times stronger than the cooling effect from carbon sequestration for all emission metrics considered. Reduced snow cover further exacerbated the net warming feedback. The warming effect is considerably stronger than previously reported for boreal forest cover, because of the typically low biomass density in mountain forests and the large changes in albedo of snow-covered tundra areas. The positive climate feedback of high-latitude and high-elevation expanding forests with seasonal snow cover exceeds those of afforestation at lower elevation, and calls for further attention of both modelers and empiricists. The inclusion and upscaling of these climate feedbacks from mountain forests into global models is warranted to assess the potential global impacts. © 2013 John Wiley & Sons Ltd.

  5. Mapping Surface Broadband Albedo from Satellite Observations: A Review of Literatures on Algorithms and Products

    Directory of Open Access Journals (Sweden)

    Ying Qu

    2015-01-01

    Full Text Available Surface albedo is one of the key controlling geophysical parameters in the surface energy budget studies, and its temporal and spatial variation is closely related to the global climate change and regional weather system due to the albedo feedback mechanism. As an efficient tool for monitoring the surfaces of the Earth, remote sensing is widely used for deriving long-term surface broadband albedo with various geostationary and polar-orbit satellite platforms in recent decades. Moreover, the algorithms for estimating surface broadband albedo from satellite observations, including narrow-to-broadband conversions, bidirectional reflectance distribution function (BRDF angular modeling, direct-estimation algorithm and the algorithms for estimating albedo from geostationary satellite data, are developed and improved. In this paper, we present a comprehensive literature review on algorithms and products for mapping surface broadband albedo with satellite observations and provide a discussion of different algorithms and products in a historical perspective based on citation analysis of the published literature. This paper shows that the observation technologies and accuracy requirement of applications are important, and long-term, global fully-covered (including land, ocean, and sea-ice surfaces, gap-free, surface broadband albedo products with higher spatial and temporal resolution are required for climate change, surface energy budget, and hydrological studies.

  6. Vegetation controls on northern high latitude snow-albedo feedback: observations and CMIP5 model simulations.

    Science.gov (United States)

    Loranty, Michael M; Berner, Logan T; Goetz, Scott J; Jin, Yufang; Randerson, James T

    2014-02-01

    The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow-covered and snow-free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow-albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions. © 2013 John Wiley & Sons Ltd.

  7. The Alpine snow-albedo feedback in regional climate models

    Science.gov (United States)

    Winter, Kevin J.-P. M.; Kotlarski, Sven; Scherrer, Simon C.; Schär, Christoph

    2017-02-01

    The effect of the snow-albedo feedback (SAF) on 2m temperatures and their future changes in the European Alps is investigated in the ENSEMBLES regional climate models (RCMs) with a focus on the spring season. A total of 14 re-analysis-driven RCM experiments covering the period 1961-2000 and 10 GCM-driven transient climate change projections for 1950-2099 are analysed. A positive springtime SAF is found in all RCMs, but the range of the diagnosed SAF is large. Results are compared against an observation-based SAF estimate. For some RCMs, values very close to this estimate are found; other models show a considerable overestimation of the SAF. Net shortwave radiation has the largest influence of all components of the energy balance on the diagnosed SAF and can partly explain its spatial variability. Model deficiencies in reproducing 2m temperatures above snow and ice and associated cold temperature biases at high elevations seem to contribute to a SAF overestimation in several RCMs. The diagnosed SAF in the observational period strongly influences the estimated SAF contribution to twenty first century temperature changes in the European Alps. This contribution is subject to a clear elevation dependency that is governed by the elevation-dependent change in the number of snow days. Elevations of maximum SAF contribution range from 1500 to 2000 m in spring and are found above 2000 m in summer. Here, a SAF contribution to the total simulated temperature change between 0 and 0.5 °C until 2099 (multi-model mean in spring: 0.26 °C) or 0 and 14 % (multi-model mean in spring: 8 %) is obtained for models showing a realistic SAF. These numbers represent a well-funded but only approximate estimate of the SAF contribution to future warming, and a remaining contribution of model-specific SAF misrepresentations cannot be ruled out.

  8. Variability of soil moisture and its relationship with surface albedo ...

    Indian Academy of Sciences (India)

    30 N latitude) are used to study the diurnal, monthly and seasonal soil moisture variations. The effect of rainfall on diurnal and seasonal soil moisture is discussed. We have investigated relationships of soil moisture with sur- face albedo and soil thermal diffusivity. The diurnal variation of surface albedo appears as a.

  9. Long-Term Variability of Surface Albedo and Its Correlation with Climatic Variables over Antarctica

    Directory of Open Access Journals (Sweden)

    Minji Seo

    2016-11-01

    Full Text Available The cryosphere is an essential part of the earth system for understanding climate change. Components of the cryosphere, such as ice sheets and sea ice, are generally decreasing over time. However, previous studies have indicated differing trends between the Antarctic and the Arctic. The South Pole also shows internal differences in trends. These phenomena indicate the importance of continuous observation of the Polar Regions. Albedo is a main indicator for analyzing Antarctic climate change and is an important variable with regard to the radiation budget because it can provide positive feedback on polar warming and is related to net radiation and atmospheric heating in the mainly snow- and ice-covered Antarctic. Therefore, in this study, we analyzed long-term temporal and spatial variability of albedo and investigated the interrelationships between albedo and climatic variables over Antarctica. We used broadband surface albedo data from the Satellite Application Facility on Climate Monitoring and data for several climatic variables such as temperature and Antarctic oscillation index (AAO during the period of 1983 to 2009. Time series analysis and correlation analysis were performed through linear regression using albedo and climatic variables. The results of this research indicated that albedo shows two trends, west trend and an east trend, over Antarctica. Most of the western side of Antarctica showed a negative trend of albedo (about −0.0007 to −0.0015 year−1, but the other side showed a positive trend (about 0.0006 year−1. In addition, albedo and surface temperature had a negative correlation, but this relationship was weaker in west Antarctica than in east Antarctica. The correlation between albedo and AAO revealed different relationships in the two regions; west Antarctica had a negative correlation and east Antarctica showed a positive correlation. In addition, the correlation between albedo and AAO was weaker in the west. This

  10. Surface albedo measurements in Mexico City metropolitan area

    Energy Technology Data Exchange (ETDEWEB)

    Castro, T; Mar, B; Longoria, R; Ruiz Suarez, L. G [Centro de Ciencias de la Atmosfera, UNAM, Mexico, D.F. (Mexico); Morales, L [Instituto de Geografia, UNAM, Mexico, D.F. (Mexico)

    2001-04-01

    Optical and thermal properties of soils are important input data for the meteorological and photochemical modules of air quality models. As development of these models increase on spatial resolution good albedo data become more important. In this paper measurements of surface albedo of UV (295-385 nm) and visible (450-550 nm) radiation are reported for different urban and rural surfaces in the vicinity of Mexico City. It was found for the downtown zone and average albedo value of 0.05 which is in very good agreement with reported values for urban surfaces. Our albedo values measured in UV region for grey cement and green grass are of 0.10 and 0.009, respectively, and quite similar to those found at the literature of 0.11 and 0.008 for those type of surfaces. [Spanish] Las propiedades opticas y termicas de suelos son datos importantes para los modulos meteorologicos y fotoquimicos de los modelos de calidad del aire. Conforme aumenta la resolucion espacial del modelo se vuelve mas importante contar con buenos datos de albedo. En este articulo se presentan mediciones de albedo superficial de radiacion Ultravioleta (295-385 nm) y visible (450-550 nm) para diferentes superficies urbanas. Los valores medidos de albedo en la region UV para cemento gris y pasto verde son de 0.10 y 0.009, respectivamente, y son muy similares a los reportados en la literatura, 0.11 y 0.008 para este tipo de superficies.

  11. Fire disturbance effects on land surface albedo in Alaskan tundra

    Science.gov (United States)

    French, Nancy H. F.; Whitley, Matthew A.; Jenkins, Liza K.

    2016-03-01

    The study uses satellite Moderate Resolution Imaging Spectroradiometer albedo products (MCD43A3) to assess changes in albedo at two sites in the treeless tundra region of Alaska, both within the foothills region of the Brooks Range, the 2007 Anaktuvuk River Fire (ARF) and 2012 Kucher Creek Fire (KCF). Results are compared to each other and other studies to assess the magnitude of albedo change and the longevity of impact of fire on land surface albedo. In both sites there was a marked decrease of albedo in the year following the fire. In the ARF, albedo slowly increased until 4 years after the fire, when it returned to albedo values prior to the fire. For the year immediately after the fire, a threefold difference in the shortwave albedo decrease was found between the two sites. ARF showed a 45.3% decrease, while the KCF showed a 14.1% decrease in shortwave albedo, and albedo is more variable in the KCF site than ARF site 1 year after the fire. These differences are possibly the result of differences in burn severity of the two fires, wherein the ARF burned more completely with more contiguous patches of complete burn than KCF. The impact of fire on average growing season (April-September) surface shortwave forcing in the year following fire is estimated to be 13.24 ± 6.52 W m-2 at the ARF site, a forcing comparable to studies in other treeless ecosystems. Comparison to boreal studies and the implications to energy flux are discussed in the context of future increases in fire occurrence and severity in a warming climate.

  12. Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

    OpenAIRE

    Y. Liu; W. Wu; M. P. Jensen; T. Toto

    2011-01-01

    This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surfaced-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fractio...

  13. Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

    OpenAIRE

    Y. Liu; W. Wu; M. P. Jensen; T. Toto

    2011-01-01

    This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surface-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fraction...

  14. Inclusion of Solar Elevation Angle in Land Surface Albedo Parameterization Over Bare Soil Surface.

    Science.gov (United States)

    Zheng, Zhiyuan; Wei, Zhigang; Wen, Zhiping; Dong, Wenjie; Li, Zhenchao; Wen, Xiaohang; Zhu, Xian; Ji, Dong; Chen, Chen; Yan, Dongdong

    2017-12-01

    Land surface albedo is a significant parameter for maintaining a balance in surface energy. It is also an important parameter of bare soil surface albedo for developing land surface process models that accurately reflect diurnal variation characteristics and the mechanism behind the solar spectral radiation albedo on bare soil surfaces and for understanding the relationships between climate factors and spectral radiation albedo. Using a data set of field observations, we conducted experiments to analyze the variation characteristics of land surface solar spectral radiation and the corresponding albedo over a typical Gobi bare soil underlying surface and to investigate the relationships between the land surface solar spectral radiation albedo, solar elevation angle, and soil moisture. Based on both solar elevation angle and soil moisture measurements simultaneously, we propose a new two-factor parameterization scheme for spectral radiation albedo over bare soil underlying surfaces. The results of numerical simulation experiments show that the new parameterization scheme can more accurately depict the diurnal variation characteristics of bare soil surface albedo than the previous schemes. Solar elevation angle is one of the most important factors for parameterizing bare soil surface albedo and must be considered in the parameterization scheme, especially in arid and semiarid areas with low soil moisture content. This study reveals the characteristics and mechanism of the diurnal variation of bare soil surface solar spectral radiation albedo and is helpful in developing land surface process models, weather models, and climate models.

  15. Early Student Support to Investigate the Role of Sea Ice-Albedo Feedback in Sea Ice Predictions

    Science.gov (United States)

    2014-09-30

    Ice - Albedo Feedback in Sea Ice Predictions Cecilia M. Bitz Atmospheric Sciences MS351640 University of Washington Seattle, WA 98196-1640 phone...TERM GOALS The overarching goals of this project are to understand the role of sea ice - albedo feedback on sea ice predictability, to improve how...sea- ice albedo is modeled and how sea ice predictions are initialized, and then to evaluate how these improvements influence inherent sea ice

  16. A Synthetical Estimation of Northern Hemisphere Sea-ice Albedo Radiative Forcing and Feedback between 1982 and 2009

    Science.gov (United States)

    Cao, Y.

    2014-12-01

    The decreasing surface albedo caused by continously vanishing sea ice over the Arctic plays a very important role in Arctic warming amplification. However, the quantification of the change of radiative forcing at top of atmosphere (TOA) introduced by the decreasing sea ice albedo and its generated feedback to the climate remain uncertain. Two recent representative studies showed a large difference with each other: Flanner et al. (2011) used a method of synthesis of surface albedo and radiative kernels and found that the change of sea ice radiative forcing (ΔSIRF) in Northern Hemisphere (NH) from 1979 to 2008 was 0.22 (0.15 - 0.32) W m-2, and the corresponding sea ice albedo feedback (SIAF) over NH was 0.28 (0.19 - 0.41) W m-2 K-1; while Pistone et al. (2014) directly used the observed planetary albedo to estimate the NH ΔSIRF and SIAF from 1979 to 2011 and draw a NH ΔSIRF of 0.43 ± 0.07 W m-2, which was nearly twice as larger as Flanner's result, and the estimated global SIAF was 0.31 ± 0.04 W m-2 K-1. Motivated by reconciling the difference between these two studies and obtaining a more accurate qualification of the NH ΔSIRF, we used a newly released satellite-retrieved surface albedo product CLARA-A1 and made an attempt in two steps: Firstly, based on synthesising the surface albedo and raditive kernels, we calcualted the ΔSIRF from 1982 to 2009 was 0.20 ± 0.05 W m-2, and the NH SIAF was 0.25 W m-2 K-1; After comparing with TOA observed radiative flux, we found it's quite likely the kernel methods yield an underestimation for the all-sky ΔSIRF. Then, we tried to use TOA observed broadband radiative flux to adjust the estimation with kernels. After an adjustment, the NH all-sky ΔSIRF was 0.34 ± 0.09 W m-2, and the corresponding SIAF was 0.43 W m-2 K-1 over NH and 0.31 W m-2 K-1 over the entire globe.

  17. 30-m Land Surface Albedo by Integrating Landsat directional reflectance and MODIS anisotropic information

    Science.gov (United States)

    Shuai, Y.; Masek, J. G.; Gao, F.; Schaaf, C.; Williams, C. A.; Wang, Z.

    2012-12-01

    Land surface albedo as a key physical variable determining the solar energy absorbed by the land surface, and can affect climate through ecosystem feedback processes. Some studies have highlighted that positive radiative forcing (warming) induced by increased forest cover and decreased albedo in temperate and boreal forest regions could offset the negative forcing expected from carbon sequestration (Betts 2000). However, these studies have not used data at the spatial resolution of human land dynamics (e.g. 30m Landsat resolution). Therefore, there is a need for improved estimates of land surface albedo at high resolution to fully understand the role of land cover change in climate forcing and carbon cycle. Following our initial "concurrent" approach applied to Landsat data acquired during the post-2000 MODIS era (Shuai et al.2011), we have developed a "pre-MODIS era" approach to generate 30-meter albedos using Landsat surface directional reflectance (1970s-2000) and Look-Up-Tables (LUT) of anisotropy information extracted from MODIS BRDF data. We use a NLCD (National Land Cover Dataset)-class-based LUT for non-disturbed land cover. Disturbed forest patches are identified from the Monitoring Trends in Burn Severity (MTBS) and North American Forest Dynamics (NAFD) datasets. For each category, high quality MODIS BRDF parameters (MCD43A1 product) are retrieved and used to populate the LUT. Each entry in the LUT reflects a unique combination of land cover type, disturbance age and type, season/month, and sensor bands. The initial BRDF LUT generated for the Pacific Northwest of the United States exhibits various BRDF evolution trajectories for disturbed classes, including different recovery trajectories for fire and non-fire disturbance. The albedo-to-nadir-ratio method (Shuai et al., 2011) is applied to the BRDF LUT to calculate spectral albedos, followed by a narrow-to-broadband conversion (Liang 2000) to generate broad-band shortwave albedo. Our preliminary

  18. Strength of forest-albedo feedback in mid-Holocene climate simulations

    Directory of Open Access Journals (Sweden)

    J. Otto

    2011-09-01

    Full Text Available Reconstructions of the mid-Holocene climate, 6000 years before present, suggest that spring temperatures were higher at high northern latitudes compared to the pre-industrial period. A positive feedback between expansion of forest and climate presumably contributed to this warming. In the presence of snow, forests have a lower albedo than grass land. Therefore, the expansion of forest likely favoured a warming in spring, counteracting the lower insolation at the mid-Holocene.

    We investigate the sensitivity of the vegetation-atmosphere interaction under mid-Holocene orbital forcing with respect to the strength of the forest-albedo feedback by using a comprehensive coupled atmosphere-vegetation model (ECHAM5/JSBACH. We perform two sets of model simulations: a first set of simulations with a relatively weak reduction of albedo of snow by forest; and a second set of simulations with a relatively strong reduction of the albedo of snow by forest.

    We show that the parameterisation of the albedo of snow leads to uncertainties in the temperature signal. Compared to the set with weak snow masking, the simulations with strong snow masking reveal a spring warming that is three times higher, by 0.34 °C north of 60° N. This warming is related to a forest expansion of only 13%.

  19. The effect of host star spectral energy distribution and ice-albedo feedback on the climate of extrasolar planets.

    Science.gov (United States)

    Shields, Aomawa L; Meadows, Victoria S; Bitz, Cecilia M; Pierrehumbert, Raymond T; Joshi, Manoj M; Robinson, Tyler D

    2013-08-01

    Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO(2) (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an M-dwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO(2) in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global ice

  20. Monitoring land surface albedo and vegetation dynamics using high spatial and temporal resolution synthetic time series from Landsat and the MODIS BRDF/NBAR/albedo product

    Science.gov (United States)

    Wang, Zhuosen; Schaaf, Crystal B.; Sun, Qingsong; Kim, JiHyun; Erb, Angela M.; Gao, Feng; Román, Miguel O.; Yang, Yun; Petroy, Shelley; Taylor, Jeffrey R.; Masek, Jeffrey G.; Morisette, Jeffrey T.; Zhang, Xiaoyang; Papuga, Shirley A.

    2017-07-01

    Seasonal vegetation phenology can significantly alter surface albedo which in turn affects the global energy balance and the albedo warming/cooling feedbacks that impact climate change. To monitor and quantify the surface dynamics of heterogeneous landscapes, high temporal and spatial resolution synthetic time series of albedo and the enhanced vegetation index (EVI) were generated from the 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) operational Collection V006 daily BRDF/NBAR/albedo products and 30 m Landsat 5 albedo and near-nadir reflectance data through the use of the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM). The traditional Landsat Albedo (Shuai et al., 2011) makes use of the MODIS BRDF/Albedo products (MCD43) by assigning appropriate BRDFs from coincident MODIS products to each Landsat image to generate a 30 m Landsat albedo product for that acquisition date. The available cloud free Landsat 5 albedos (due to clouds, generated every 16 days at best) were used in conjunction with the daily MODIS albedos to determine the appropriate 30 m albedos for the intervening daily time steps in this study. These enhanced daily 30 m spatial resolution synthetic time series were then used to track albedo and vegetation phenology dynamics over three Ameriflux tower sites (Harvard Forest in 2007, Santa Rita in 2011 and Walker Branch in 2005). These Ameriflux sites were chosen as they are all quite nearby new towers coming on line for the National Ecological Observatory Network (NEON), and thus represent locations which will be served by spatially paired albedo measures in the near future. The availability of data from the NEON towers will greatly expand the sources of tower albedometer data available for evaluation of satellite products. At these three Ameriflux tower sites the synthetic time series of broadband shortwave albedos were evaluated using the tower albedo measurements with a Root Mean Square Error (RMSE) less than 0.013 and a

  1. The retrieval of land surface albedo in rugged terrain

    NARCIS (Netherlands)

    Gao, B.; Jia, L.; Menenti, M.

    2012-01-01

    Land surface albedo may be derived from the satellite data through the estimation of a bidirectional reflectance distribution function (BRDF) model and angular integration. However many BRDF models do not consider explicitly the topography. In rugged terrain, the topography influences the observed

  2. The effect of surface albedo and grain size distribution on ...

    African Journals Online (AJOL)

    Sand dams are very useful in arid and semi arid lands (ASALs) as facilities for water storage and conservation. Soils in ASALs are mainly sandy and major water loss is by evaporation and infiltration. This study investigated the effect of sand media characteristics, specifically surface albedo, grain size and stratification on ...

  3. Spring Snow-Albedo Feedback Analysis Over the Third Pole: Results From Satellite Observation and CMIP5 Model Simulations

    Science.gov (United States)

    Guo, Hui; Wang, Xiaoyi; Wang, Tao; Ma, Yaoming; Ryder, James; Zhang, Taotao; Liu, Dan; Ding, Jinzhi; Li, Yue; Piao, Shilong

    2018-01-01

    The snow-albedo feedback is a crucial component in high-altitude cryospheric change but is poorly quantified over the Third Pole, encompassing the Karakoram and Tibetan Plateau. Here we present an analysis of present-day and future spring snow-albedo feedback over the Third Pole, using a 28 year satellite-based albedo and the latest climate model simulations. We show that present-day spring snow-albedo feedback strength is primarily determined by the decrease in albedo due to snow metamorphosis, rather than that due to reduced snow cover in the Karakoram, but not found in Southeastern Tibet. We further demonstrate an emergent relationship between snow-albedo feedback from the seasonal cycle and that from climate change across models. Combined with contemporary satellite-based snow-albedo feedback from seasonal cycle, this relationship enables us to estimate that the feedback strength for the Karakoram with a relatively high glaciated area is -2.42 ± 0.48% K-1 under an unmitigated scenario, which is much stronger than that for Southeastern Tibet (-1.64 ± 0.48% K-1) and for the Third Pole (-0.89 ± 0.44% K-1), respectively. Moreover, it is noteworthy that the magnitude of the constrained strength is only half of the unconstrained model estimate for the Third Pole, suggesting that current climate models generally overestimate the feedback of spring snow change to temperature change based on the unmitigated scenario.

  4. Evaluation of coarse scale land surface remote sensing albedo product over rugged terrain

    Science.gov (United States)

    Wen, J.; Xinwen, L.; You, D.; Dou, B.

    2017-12-01

    Satellite derived Land surface albedo is an essential climate variable which controls the earth energy budget and it can be used in applications such as climate change, hydrology, and numerical weather prediction. The accuracy and uncertainty of surface albedo products should be evaluated with a reliable reference truth data prior to applications. And more literatures investigated the validation methods about the albedo validation in a flat or homogenous surface. However, the albedo performance over rugged terrain is still unknow due to the validation method limited. A multi-validation strategy is implemented to give a comprehensive albedo validation, which will involve the high resolution albedo processing, high resolution albedo validation based on in situ albedo, and the method to upscale the high resolution albedo to a coarse scale albedo. Among them, the high resolution albedo generation and the upscale method is the core step for the coarse scale albedo validation. In this paper, the high resolution albedo is generated by Angular Bin algorithm. And a albedo upscale method over rugged terrain is developed to obtain the coarse scale albedo truth. The in situ albedo located 40 sites in mountain area are selected globally to validate the high resolution albedo, and then upscaled to the coarse scale albedo by the upscale method. This paper takes MODIS and GLASS albedo product as a example, and the prelimarily results show the RMSE of MODIS and GLASS albedo product over rugged terrain are 0.047 and 0.057, respectively under the RMSE with 0.036 of high resolution albedo.

  5. Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone

    OpenAIRE

    Kashiwase, Haruhiko; Ohshima, Kay I.; Nihashi, Sohey; Eicken, Hajo

    2017-01-01

    Ice-albedo feedback due to the albedo contrast between water and ice is a major factor in seasonal sea ice retreat, and has received increasing attention with the Arctic Ocean shifting to a seasonal ice cover. However, quantitative evaluation of such feedbacks is still insufficient. Here we provide quantitative evidence that heat input through the open water fraction is the primary driver of seasonal and interannual variations in Arctic sea ice retreat. Analyses of satellite data (1979?2014) ...

  6. Land surface albedo bias in climate models and its association with tropical rainfall

    Science.gov (United States)

    Levine, Xavier J.; Boos, William R.

    2017-06-01

    The influence of surface albedo on tropical precipitation is widely appreciated, but albedo bias over snow-free areas in climate models has been studied little. Here historical Coupled Model Intercomparison Project Phase 5 simulations are shown to exhibit large multimodel mean bias and intermodel variability in boreal summer mean surface broadband shortwave albedo. Intermodel variability in this albedo is globally coherent over vegetated regions and correlates with intermodel tropical precipitation variability. Evidence supports the hypothesis that these spatially coherent albedo variations cause precipitation variations. Specifically, spatial structures of albedo and precipitation variations are distinct, suggesting the latter do not cause the former by darkening soil. Furthermore, simulated interannual albedo variance is small compared to intermodel albedo variance, while the ratio of interannual to intermodel precipitation variance is much larger. Finally, imposing the dominant pattern of intermodel albedo variability in one climate model causes a precipitation change with structure similar to that of the intermodel variability.

  7. The potential impacts of climate change induced changes to tropical leaf albedo and its feedback on global climate

    Science.gov (United States)

    Doughty, C.; Shenkin, A.; Bentley, L. P.; Malhi, Y.

    2017-12-01

    Tropical forest leaf albedo plays a critical role in global climate by determining how much radiation the planet absorbs near the equator. However, little is known about how tropical leaf albedo could be affected by climate change and how any such changes in albedo could, in turn, impact global climate. Here we measure sunlit leaf albedo along two elevation temperature gradients (a 3000-meter gradient in Peru (10 plots) and a 1500 m gradient in Australia (10 plots) and along two wet to dry transects (a 2000 mm yr-1 gradient in Ghana (10 plots) and a 2000 mm yr-1 gradient in Brazil (10 plots). We found a highly significant increase in visible leaf albedo with wetness at both wet to dry gradients. We also found a marginally significant trend of increased albedo with warmer temperatures along one of the elevation gradients. Leaf albedo can also be impacted by changes in species composition, variations in interspecific variation, and changes in leaf chlorophyll concentrations. We removed the dominant two species from the basal area weighting for each plots but found no significant change, a directional change of interspecific variation could change albedo by 0.01 in the NIR, and changes in chlorophyll could decrease visible albedo by 0.005. We then simulated changes in tropical leaf albedo with a climate model and show that such changes could act as a small negative feedback on climate, but most likely will not have a large impact on future climate.

  8. Role of snow-albedo feedback in higher elevation warming over the Himalayas, Tibetan Plateau and Central Asia

    International Nuclear Information System (INIS)

    Ghatak, Debjani; Sinsky, Eric; Miller, James

    2014-01-01

    Recent literature has shown that surface air temperature (SAT) in many high elevation regions, including the Tibetan Plateau (TP) has been increasing at a faster rate than at their lower elevation counterparts. We investigate projected future changes in SAT in the TP and the surrounding high elevation regions (between 25°–45°N and 50°–120°E) and the potential role snow-albedo feedback may have on amplified warming there. We use the Community Climate System Model version 4 (CCSM4) and Geophysical Fluid Dynamics Laboratory (GFDL) model which have different spatial resolutions as well as different climate sensitivities. We find that surface albedo (SA) decreases more at higher elevations than at lower elevations owing to the retreat of the 0 °C isotherm and the associated retreat of the snow line. Both models clearly show amplified warming over Central Asian mountains, the Himalayas, the Karakoram and Pamir during spring. Our results suggest that the decrease of SA and the associated increase in absorbed solar radiation (ASR) owing to the loss of snowpack play a significant role in triggering the warming over the same regions. Decreasing cloud cover in spring also contributes to an increase in ASR over some of these regions in CCSM4. Although the increase in SAT and the decrease in SA are greater in GFDL than CCSM4, the sensitivity of SAT to changes in SA is the same at the highest elevations for both models during spring; this suggests that the climate sensitivity between models may differ, in part, owing to their corresponding treatments of snow cover, snow melt and the associated snow/albedo feedback. (letter)

  9. Effect of ice-albedo feedback on global sensitivity in a one-dimensional radiative-convective climate model

    Science.gov (United States)

    Wang, W.-C.; Stone, P. H.

    1980-01-01

    The feedback between the ice albedo and temperature is included in a one-dimensional radiative-convective climate model. The effect of this feedback on global sensitivity to changes in solar constant is studied for the current climate conditions. This ice-albedo feedback amplifies global sensitivity by 26 and 39%, respectively, for assumptions of fixed cloud altitude and fixed cloud temperature. The global sensitivity is not affected significantly if the latitudinal variations of mean solar zenith angle and cloud cover are included in the global model. The differences in global sensitivity between one-dimensional radiative-convective models and energy balance models are examined. It is shown that the models are in close agreement when the same feedback mechanisms are included. The one-dimensional radiative-convective model with ice-albedo feedback included is used to compute the equilibrium ice line as a function of solar constant.

  10. Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone.

    Science.gov (United States)

    Joshi, Manoj M; Haberle, Robert M

    2012-01-01

    M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 μm, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought.

  11. Competing effects of surface albedo and orographic elevated heating on regional climate

    Science.gov (United States)

    Hu, Shineng; Boos, William R.

    2017-07-01

    All else being equal, a given atmospheric pressure level is thought to be warmer over a plateau than over surrounding nonelevated terrain because of orographic "elevated heating." However, elevated surfaces are also typically brighter due to reduced vegetation and increased ice cover. Here we assess the degree to which surface albedo compensates for orographic elevated heating. We confirm that land surface albedo generally increases with surface elevation in observations. Using a cloud system-resolving model, we show that increased surface albedo strongly compensates for orographic elevated heating in radiative-convective equilibrium. A nonelevated surface with the albedo of modern India would enter a runaway greenhouse regime without ventilation by monsoonal winds, while a surface with the albedo and elevation of Tibet would achieve a cooler radiative-convective equilibrium. Surface albedo changes may thus be just as important as surface elevation changes for the evolution of low-latitude regional climate throughout Earth's history.

  12. Modulation of ice ages via precession and dust-albedo feedbacks

    Directory of Open Access Journals (Sweden)

    Ralph Ellis

    2016-11-01

    Full Text Available We present here a simple and novel proposal for the modulation and rhythm of ice-ages and interglacials during the late Pleistocene. While the standard Milankovitch-precession theory fails to explain the long intervals between interglacials, these can be accounted for by a novel forcing and feedback system involving CO2, dust and albedo. During the glacial period, the high albedo of the northern ice sheets drives down global temperatures and CO2 concentrations, despite subsequent precessional forcing maxima. Over the following millennia more CO2 is sequestered in the oceans and atmospheric concentrations eventually reach a critical minima of about 200 ppm, which combined with arid conditions, causes a die-back of temperate and boreal forests and grasslands, especially at high altitude. The ensuing soil erosion generates dust storms, resulting in increased dust deposition and lower albedo on the northern ice sheets. As northern hemisphere insolation increases during the next Milankovitch cycle, the dust-laden ice-sheets absorb considerably more insolation and undergo rapid melting, which forces the climate into an interglacial period. The proposed mechanism is simple, robust, and comprehensive in its scope, and its key elements are well supported by empirical evidence.

  13. The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

    Science.gov (United States)

    Meadows, Victoria S.; Bitz, Cecilia M.; Pierrehumbert, Raymond T.; Joshi, Manoj M.; Robinson, Tyler D.

    2013-01-01

    Abstract Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO2 (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an M-dwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO2 in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global

  14. Spatiotemporal variability of Canadian High Arctic glacier surface albedo from MODIS data, 2001–2016

    Directory of Open Access Journals (Sweden)

    C. A. Mortimer

    2018-02-01

    Full Text Available Inter-annual variations and longer-term trends in the annual mass balance of glaciers in Canada's Queen Elizabeth Islands (QEI are largely attributable to changes in summer melt. The largest source of melt energy in the QEI in summer is net shortwave radiation, which is modulated by changes in glacier surface albedo. We used measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS sensors to investigate large-scale spatial patterns, temporal trends, and variability in the summer surface albedo of QEI glaciers from 2001 to 2016. Mean summer black-sky shortwave broadband albedo (BSA decreased at a rate of 0.029±0.025 decade−1 over that period. Larger reductions in BSA occurred in July (−0.050±0.031 decade−1. No change in BSA was observed in either June or August. Most of the decrease in BSA, which was greatest at lower elevations around the margins of the ice masses, occurred between 2007 and 2012, when mean summer BSA was anomalously low. The first principal component of the 16-year record of mean summer BSA was well correlated with the mean summer North Atlantic Oscillation index, except in 2006, 2010, and 2016, when the mean summer BSA appears to have been dominated by the August BSA. During the period 2001–2016, the mean summer land surface temperature (LST over the QEI glaciers and ice caps increased by 0.049±0.038 °C yr−1, and the BSA record was negatively correlated (r: −0.86 with the LST record, indicative of a positive ice-albedo feedback that would increase rates of mass loss from the QEI glaciers.

  15. Spatiotemporal variability of Canadian High Arctic glacier surface albedo from MODIS data, 2001-2016

    Science.gov (United States)

    Mortimer, Colleen A.; Sharp, Martin

    2018-02-01

    Inter-annual variations and longer-term trends in the annual mass balance of glaciers in Canada's Queen Elizabeth Islands (QEI) are largely attributable to changes in summer melt. The largest source of melt energy in the QEI in summer is net shortwave radiation, which is modulated by changes in glacier surface albedo. We used measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors to investigate large-scale spatial patterns, temporal trends, and variability in the summer surface albedo of QEI glaciers from 2001 to 2016. Mean summer black-sky shortwave broadband albedo (BSA) decreased at a rate of 0.029±0.025 decade-1 over that period. Larger reductions in BSA occurred in July (-0.050±0.031 decade-1). No change in BSA was observed in either June or August. Most of the decrease in BSA, which was greatest at lower elevations around the margins of the ice masses, occurred between 2007 and 2012, when mean summer BSA was anomalously low. The first principal component of the 16-year record of mean summer BSA was well correlated with the mean summer North Atlantic Oscillation index, except in 2006, 2010, and 2016, when the mean summer BSA appears to have been dominated by the August BSA. During the period 2001-2016, the mean summer land surface temperature (LST) over the QEI glaciers and ice caps increased by 0.049±0.038 °C yr-1, and the BSA record was negatively correlated (r: -0.86) with the LST record, indicative of a positive ice-albedo feedback that would increase rates of mass loss from the QEI glaciers.

  16. Upwelling UV spectral irradiances and surface albedo measurements at Lauder, New Zealand

    Science.gov (United States)

    McKenzie, R. L.; Kotkamp, M.; Ireland, W.

    Simultaneous measurements of upwelling and downwelling ultraviolet (UV) spectral irradiance were used to deduce the wavelength dependence and the solar zenith angle dependence of the albedo of the ground surface (long grass) at Lauder, New Zealand (45.05°S, 169.68°E). In the UVB region the deduced albedos are approximately 1%. At longer wavelengths the albedo increases to approximately 2% at 400 nm, and 4.5% at 450 nm. These albedos are significantly smaller than those generally quoted for the visible region. The deduced albedos tend to increase at larger solar zenith angles, demonstrating that the surface is not strictly Lambertian.

  17. Ice Caps and Ice Belts: The Effects of Obliquity on Ice−Albedo Feedback

    Energy Technology Data Exchange (ETDEWEB)

    Rose, Brian E. J. [Department of Atmospheric and Environmental Sciences, University at Albany (State University of New York), 1400 Washington Avenue, Albany, NY 12222 (United States); Cronin, Timothy W. [Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Bitz, Cecilia M., E-mail: brose@albany.edu [Department of Atmospheric Sciences, MS 351640, University of Washington, Seattle, WA 98195-1640 (United States)

    2017-09-01

    Planetary obliquity determines the meridional distribution of the annual mean insolation. For obliquity exceeding 55°, the weakest insolation occurs at the equator. Stable partial snow and ice cover on such a planet would be in the form of a belt about the equator rather than polar caps. An analytical model of planetary climate is used to investigate the stability of ice caps and ice belts over the widest possible range of parameters. The model is a non-dimensional diffusive Energy Balance Model, representing insolation, heat transport, and ice−albedo feedback on a spherical planet. A complete analytical solution for any obliquity is given and validated against numerical solutions of a seasonal model in the “deep-water” regime of weak seasonal ice line migration. Multiple equilibria and unstable transitions between climate states (ice-free, Snowball, or ice cap/belt) are found over wide swaths of parameter space, including a “Large Ice-Belt Instability” and “Small Ice-Belt Instability” at high obliquity. The Snowball catastrophe is avoided at weak radiative forcing in two different scenarios: weak albedo feedback and inefficient heat transport (favoring stable partial ice cover), or efficient transport at high obliquity (favoring ice-free conditions). From speculative assumptions about distributions of planetary parameters, three-fourths to four-fifths of all planets with stable partial ice cover should be in the form of Earth-like polar caps.

  18. Ice Caps and Ice Belts: The Effects of Obliquity on Ice-Albedo Feedback

    Science.gov (United States)

    Rose, Brian E. J.; Cronin, Timothy W.; Bitz, Cecilia M.

    2017-09-01

    Planetary obliquity determines the meridional distribution of the annual mean insolation. For obliquity exceeding 55°, the weakest insolation occurs at the equator. Stable partial snow and ice cover on such a planet would be in the form of a belt about the equator rather than polar caps. An analytical model of planetary climate is used to investigate the stability of ice caps and ice belts over the widest possible range of parameters. The model is a non-dimensional diffusive Energy Balance Model, representing insolation, heat transport, and ice-albedo feedback on a spherical planet. A complete analytical solution for any obliquity is given and validated against numerical solutions of a seasonal model in the “deep-water” regime of weak seasonal ice line migration. Multiple equilibria and unstable transitions between climate states (ice-free, Snowball, or ice cap/belt) are found over wide swaths of parameter space, including a “Large Ice-Belt Instability” and “Small Ice-Belt Instability” at high obliquity. The Snowball catastrophe is avoided at weak radiative forcing in two different scenarios: weak albedo feedback and inefficient heat transport (favoring stable partial ice cover), or efficient transport at high obliquity (favoring ice-free conditions). From speculative assumptions about distributions of planetary parameters, three-fourths to four-fifths of all planets with stable partial ice cover should be in the form of Earth-like polar caps.

  19. On the nature of the sea ice albedo feedback in simple models.

    Science.gov (United States)

    Moon, W; Wettlaufer, J S

    2014-08-01

    We examine the nature of the ice-albedo feedback in a long-standing approach used in the dynamic-thermodynamic modeling of sea ice. The central issue examined is how the evolution of the ice area is treated when modeling a partial ice cover using a two-category-thickness scheme; thin sea ice and open water in one category and "thick" sea ice in the second. The problem with the scheme is that the area evolution is handled in a manner that violates the basic rules of calculus, which leads to a neglected area evolution term that is equivalent to neglecting a leading-order latent heat flux. We demonstrate the consequences by constructing energy balance models with a fractional ice cover and studying them under the influence of increased radiative forcing. It is shown that the neglected flux is particularly important in a decaying ice cover approaching the transitions to seasonal or ice-free conditions. Clearly, a mishandling of the evolution of the ice area has leading-order effects on the ice-albedo feedback. Accordingly, it may be of considerable importance to reexamine the relevant climate model schemes and to begin the process of converting them to fully resolve the sea ice thickness distribution in a manner such as remapping, which does not in principle suffer from the pathology we describe.

  20. Assessment of the Suomi NPP VIIRS Land Surface Albedo Data Using Station Measurements and High-Resolution Albedo Maps

    Directory of Open Access Journals (Sweden)

    Yuan Zhou

    2016-02-01

    Full Text Available Land surface albedo (LSA, one of the Visible Infrared Imaging Radiometer Suite (VIIRS environmental data records (EDRs, is a fundamental component for linking the land surface and the climate system by regulating shortwave energy exchange between the land and the atmosphere. Currently, the improved bright pixel sub-algorithm (BPSA is a unique algorithm employed by VIIRS to routinely generate LSA EDR from VIIRS top-of-atmosphere (TOA observations. As a product validation procedure, LSA EDR reached validated (V1 stage maturity in December 2014. This study summarizes recent progress in algorithm refinement, and presents comprehensive validation and evaluation results of VIIRS LSA by using extensive field measurements, Moderate Resolution Imaging Spectroradiometer (MODIS albedo product, and Landsat-retrieved albedo maps. Results indicate that: (1 by testing the updated desert-specific look-up-table (LUT that uses a stricter standard to select the training data specific for desert aerosol type in our local environment, it is found that the VIIRS LSA retrieval accuracy is improved over a desert surface and the absolute root mean square error (RMSE is reduced from 0.036 to 0.023, suggesting the potential of the updated desert LUT to the improve the VIIRS LSA product accuracy; (2 LSA retrieval on snow-covered surfaces is more accurate if the newly developed snow-specific LUT (RMSE = 0.082 replaces the generic LUT (RMSE = 0.093 that is employed in the current operational LSA EDR production; (3 VIIRS LSA is also comparable to high-resolution Landsat albedo retrieval (RMSE < 0.04, although Landsat albedo has a slightly higher accuracy, probably owing to higher spatial resolution with less impacts of mixed pixel; (4 VIIRS LSA retrievals agree well with the MODIS albedo product over various land surface types, with overall RMSE of lower than 0.05 and the overall bias as low as 0.025, demonstrating the comparable data quality between VIIRS and the MODIS LSA

  1. Land Surface Albedo Estimation from Chinese HJ Satellite Data Based on the Direct Estimation Approach

    Directory of Open Access Journals (Sweden)

    Tao He

    2015-05-01

    Full Text Available Monitoring surface albedo at medium-to-fine resolution (<100 m has become increasingly important for medium-to-fine scale applications and coarse-resolution data evaluation. This paper presents a method for estimating surface albedo directly using top-of-atmosphere reflectance. This is the first attempt to derive surface albedo for both snow-free and snow-covered conditions from medium-resolution data with a single approach. We applied this method to the multispectral data from the wide-swath Chinese HuanJing (HJ satellites at a spatial resolution of 30 m to demonstrate the feasibility of this data for surface albedo monitoring over rapidly changing surfaces. Validation against ground measurements shows that the method is capable of accurately estimating surface albedo over both snow-free and snow-covered surfaces with an overall root mean square error (RMSE of 0.030 and r-square (R2 of 0.947. The comparison between HJ albedo estimates and the Moderate Resolution Imaging Spectral Radiometer (MODIS albedo product suggests that the HJ data and proposed algorithm can generate robust albedo estimates over various land cover types with an RMSE of 0.011–0.014. The accuracy of HJ albedo estimation improves with the increase in view zenith angles, which further demonstrates the unique advantage of wide-swath satellite data in albedo estimation.

  2. Land Surface Albedo Estimation from Chinese HJ Satellite Data Based on the Direct Estimation Approach

    OpenAIRE

    He, Tao; Liang, Shunlin; Wang, Dongdong; Chen, Xiaona; Song, Dan-Xia; Jiang, Bo

    2015-01-01

    Monitoring surface albedo at medium-to-fine resolution (<100 m) has become increasingly important for medium-to-fine scale applications and coarse-resolution data evaluation. This paper presents a method for estimating surface albedo directly using top-of-atmosphere reflectance. This is the first attempt to derive surface albedo for both snow-free and snow-covered conditions from medium-resolution data with a single approach. We applied this method to the multispectral data from the wide-...

  3. Radiative forcing by changes in surface albedo caused by changes in vegetation

    OpenAIRE

    Kvalevåg, Maria Malene

    2005-01-01

    The human influence on vegetation causes changes in the surface reflective properties. By using MODIS land cover and MODIS surface albedo products, an estimation of radiative forcing due to surface albedo changes caused by vegetation changes is performed. A potential natural vegetation data set is used to compute radiative forcing estimates from pre agricultural times to present. A combination between MODIS blacksky and whitesky albedo and diffuse and direct radiation at gr...

  4. An Evaluation of High-Resolution Regional Climate Model Simulated Snow Cover Using Satellite Data (With Implications for the Simulated Snow-Albedo Feedback)

    Science.gov (United States)

    Minder, J. R.; Letcher, T.

    2015-12-01

    Snow cover often exhibits large spatial variability over mountainous regions where variations in elevation, aspect, vegetation, winds, and orographic precipitation all modulate snow cover. Under climate change, reductions in mountain snow cover are likely to substantially amplify regional warming via the snow-albedo feedback. To capture this important feedback it is crucial that regional climate models (RCMs) adequately simulate spatial and temporal variations in snow cover. Snow cover simulated by high-resolution RCMs over the central Rocky Mountains of the United States is evaluated. RCM simulations were conducted using the Weather Research and Forecasting (WRF) model on a 4 km horizontal grid forced by reanalysis boundary conditions over a seven-year time period. A pair of simulations is considered that differ in the domain size (regional vs. continental) and the land surface model (Noah vs. Noah-MP) employed. RCM output is compared with high-resolution gridded satellite analyses of surface albedo and fractional snow cover derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). Results reveal that both RCMs are generally successful at reproducing the observed seasonal cycle and interannual variability of snow extent over the high terrain of the Rockies. However, in simulations using the Noah land surface model (LSM), sub-grid scale fractional snow covered area of grid cells containing snow is systematically too high compared to observations, often exceeding observations by more than 0.2. This bias in fractional snow cover leads to a substantial positive bias in regional surface albedo. Simulations using the Noah-MP LSM produce more realistic variations in fractional snow cover and surface albedo, likely due to its more-realistic treatment of canopy effects. We quantify how differences in simulated snow cover affect the strength of the snow-albedo feedback under climate change. Both RCMs were used to conduct representative 7-year simulations of a

  5. Land Surface Albedos Computed from BRF Measurements with a Study of Conversion Formulae

    Directory of Open Access Journals (Sweden)

    Aku Riihelä

    2010-08-01

    Full Text Available Land surface hemispherical albedos of several targets have been resolved using the bidirectional reflectance factor (BRF library of the Finnish Geodetic Institute (FGI. The library contains BRF data measured by FGI during the years 2003–2009. Surface albedos are calculated using selected BRF datasets from the library. Polynomial interpolation and extrapolation have been used in computations. Several broadband conversion formulae generally used for satellite based surface albedo retrieval have been tested. The albedos were typically found to monotonically increase with increasing zenith angle of the Sun. The surface albedo variance was significant even within each target category / surface type. In general, the albedo estimates derived using diverse broadband conversion formulas and estimates obtained by direct integration of the measured spectra were in line.

  6. Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8 Optical Data

    Directory of Open Access Journals (Sweden)

    Kathrin Naegeli

    2017-01-01

    Full Text Available Surface albedo partitions the amount of energy received by glacier surfaces from shortwave fluxes and modulates the energy available for melt processes. The ice-albedo feedback, influenced by the contamination of bare-ice surfaces with light-absorbing impurities, plays a major role in the melting of mountain glaciers in a warming climate. However, little is known about the spatial and temporal distribution and variability of bare-ice glacier surface albedo under changing conditions. In this study, we focus on two mountain glaciers located in the western Swiss Alps and perform a cross-comparison of different albedo products. We take advantage of high spectral and spatial resolution (284 bands, 2 m imaging spectrometer data from the Airborne Prism Experiment (APEX and investigate the applicability and potential of Sentinel-2 and Landsat 8 data to derive broadband albedo products. The performance of shortwave broadband albedo retrievals is tested and we assess the reliability of published narrow-to-broadband conversion algorithms. The resulting albedo products from the three sensors and different algorithms are further cross-compared. Moreover, the impact of the anisotropy correction is analysed depending on different surface types. While degradation of the spectral resolution impacted glacier-wide mean albedo by about 5%, reducing the spatial resolution resulted in changes of less than 1%. However, in any case, coarser spatial resolution was no longer able to represent small-scale variability of albedo on glacier surfaces. We discuss the implications when using Sentinel-2 and Landsat 8 to map dynamic glaciological processes and to monitor glacier surface albedo on larger spatial and more frequent temporal scales.

  7. An energy balance model exploration of the impacts of interactions between surface albedo, cloud cover and water vapor on polar amplification

    Science.gov (United States)

    Södergren, A. Helena; McDonald, Adrian J.; Bodeker, Gregory E.

    2017-11-01

    We examine the effects of non-linear interactions between surface albedo, water vapor and cloud cover (referred to as climate variables) on amplified warming of the polar regions, using a new energy balance model. Our simulations show that the sum of the contributions to surface temperature changes due to any variable considered in isolation is smaller than the temperature changes from coupled feedback simulations. This non-linearity is strongest when all three climate variables are allowed to interact. Surface albedo appears to be the strongest driver of this non-linear behavior, followed by water vapor and clouds. This is because increases in longwave radiation absorbed by the surface, related to increases in water vapor and clouds, and increases in surface absorbed shortwave radiation caused by a decrease in surface albedo, amplify each other. Furthermore, our results corroborate previous findings that while increases in cloud cover and water vapor, along with the greenhouse effect itself, warm the polar regions, water vapor also significantly warms equatorial regions, which reduces polar amplification. Changes in surface albedo drive large changes in absorption of incoming shortwave radiation, thereby enhancing surface warming. Unlike high latitudes, surface albedo change at low latitudes are more constrained. Interactions between surface albedo, water vapor and clouds drive larger increases in temperatures in the polar regions compared to low latitudes. This is in spite of the fact that, due to a forcing, cloud cover increases at high latitudes and decreases in low latitudes, and that water vapor significantly enhances warming at low latitudes.

  8. Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone.

    Science.gov (United States)

    Kashiwase, Haruhiko; Ohshima, Kay I; Nihashi, Sohey; Eicken, Hajo

    2017-08-15

    Ice-albedo feedback due to the albedo contrast between water and ice is a major factor in seasonal sea ice retreat, and has received increasing attention with the Arctic Ocean shifting to a seasonal ice cover. However, quantitative evaluation of such feedbacks is still insufficient. Here we provide quantitative evidence that heat input through the open water fraction is the primary driver of seasonal and interannual variations in Arctic sea ice retreat. Analyses of satellite data (1979-2014) and a simplified ice-upper ocean coupled model reveal that divergent ice motion in the early melt season triggers large-scale feedback which subsequently amplifies summer sea ice anomalies. The magnitude of divergence controlling the feedback has doubled since 2000 due to a more mobile ice cover, which can partly explain the recent drastic ice reduction in the Arctic Ocean.

  9. Albedo, Land Cover, and Daytime Surface Temperature Variation Across an Urbanized Landscape

    Science.gov (United States)

    Trlica, A.; Hutyra, L. R.; Schaaf, C. L.; Erb, A.; Wang, J. A.

    2017-11-01

    Land surface albedo is a key parameter controlling the local energy budget, and altering the albedo of built surfaces has been proposed as a tool to mitigate high near-surface temperatures in the urban heat island. However, most research on albedo in urban landscapes has used coarse-resolution data, and few studies have attempted to relate albedo to other urban land cover characteristics. This study provides an empirical description of urban summertime albedo using 30 m remote sensing measurements in the metropolitan area around Boston, Massachusetts, relating albedo to metrics of impervious cover fraction, tree canopy coverage, population density, and land surface temperature (LST). At 30 m spatial resolution, median albedo over the study area (excluding open water) was 0.152 (0.112-0.187). Trends of lower albedo with increasing urbanization metrics and temperature emerged only after aggregating data to 500 m or the boundaries of individual towns, at which scale a -0.01 change in albedo was associated with a 29 (25-35)% decrease in canopy cover, a 27 (24-30)% increase in impervious cover, and an increase in population from 11 to 386 km-2. The most intensively urbanized towns in the region showed albedo up to 0.035 lower than the least urbanized towns, and mean mid-morning LST 12.6°C higher. Trends in albedo derived from 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) measurements were comparable, but indicated a strong contribution of open water at this coarser resolution. These results reveal linkages between albedo and urban land cover character, and offer empirical context for climate resilient planning and future landscape functional changes with urbanization.

  10. Simulation and Analysis of Topographic Effect on Land Surface Albedo over Mountainous Areas

    Science.gov (United States)

    Hao, D.; Wen, J.; Xiao, Q.

    2017-12-01

    Land surface albedo is one of the significant geophysical variables affecting the Earth's climate and controlling the surface radiation budget. Topography leads to the formation of shadows and the redistribution of incident radiation, which complicates the modeling and estimation of the land surface albedo. Some studies show that neglecting the topography effect may lead to significant bias in estimating the land surface albedo for the sloping terrain. However, for the composite sloping terrain, the topographic effects on the albedo remain unclear. Accurately estimating the sub-topographic effect on the land surface albedo over the composite sloping terrain presents a challenge for remote sensing modeling and applications. In our study, we focus on the development of a simplified estimation method for land surface albedo including black-sky albedo (BSA) and white-sky albedo (WSA) of the composite sloping terrain at a kilometer scale based on the fine scale DEM (30m) and quantitatively investigate and understand the topographic effects on the albedo. The albedo is affected by various factors such as solar zenith angle (SZA), solar azimuth angle (SAA), shadows, terrain occlusion, and slope and aspect distribution of the micro-slopes. When SZA is 30°, the absolute and relative deviations between the BSA of flat terrain and that of rugged terrain reaches 0.12 and 50%, respectively. When the mean slope of the terrain is 30.63° and SZA=30°, the absolute deviation of BSA caused by SAA can reach 0.04. The maximal relative and relative deviation between the WSA of flat terrain and that of rugged terrain reaches 0.08 and 50%. These results demonstrate that the topographic effect has to be taken into account in the albedo estimation.

  11. PROVE Surface albedo of Jornada Experimental Range, New Mexico, 1997

    Data.gov (United States)

    National Aeronautics and Space Administration — The objective of this study was to determine the spatial variations in field measurements of broadband albedo as related to the ground cover and under a range of...

  12. PROVE Surface albedo of Jornada Experimental Range, New Mexico, 1997

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: The objective of this study was to determine the spatial variations in field measurements of broadband albedo as related to the ground cover and under a...

  13. ARM Climate Research Facility Spectral Surface Albedo Value-Added Product (VAP) Report

    Energy Technology Data Exchange (ETDEWEB)

    McFarlane, S; Gaustad, K; Long, C; Mlawer, E

    2011-07-15

    This document describes the input requirements, output data products, and methodology for the Spectral Surface Albedo (SURFSPECALB) value-added product (VAP). The SURFSPECALB VAP produces a best-estimate near-continuous high spectral resolution albedo data product using measurements from multifilter radiometers (MFRs). The VAP first identifies best estimates for the MFR downwelling and upwelling shortwave irradiance values, and then calculates narrowband spectral albedo from these best-estimate irradiance values. The methodology for finding the best-estimate values is based on a simple process of screening suspect data and backfilling screened and missing data with estimated values when possible. The resulting best-estimate MFR narrowband spectral albedos are used to determine a daily surface type (snow, 100% vegetation, partial vegetation, or 0% vegetation). For non-snow surfaces, a piecewise continuous function is used to estimate a high spectral resolution albedo at 1 min temporal and 10 cm-1 spectral resolution.

  14. Assimilation of satellite observed snow albedo in a land surface model

    NARCIS (Netherlands)

    Malik, M.J.; van der Velde, R.; Vekerdy, Z.; Su, Zhongbo

    2012-01-01

    This study assesses the impact of assimilating satellite-observed snow albedo on the Noah land surface model (LSM)-simulated fluxes and snow properties. A direct insertion technique is developed to assimilate snow albedo into Noah and is applied to three intensive study areas in North Park

  15. Revisiting surface albedo changes over Greenland since 1980s using satellite data from GLASS, CLARA, MODIS, and Landsat

    Science.gov (United States)

    He, T.; Liang, S.; Zhang, Y.

    2017-12-01

    Massive melting events over Greenland have been observed over the past few decades. Accompanying the melting events are the surface albedo changes, which had temporal and spatial variations. Albedo changes over Greenland during the past few decades have been reported in previous studies with the help of satellite observations; however, magnitudes and timing in albedo trends differ greatly in those studies. This has limited our understanding of albedo change mechanisms over Greenland. In this study, we present an analysis of surface albedo change over Greenland since 1980s combining four satellite albedo datasets, namely MODIS, GLASS, CLARA, and Landsat. MODIS, GLASS, and CLARA albedo data are publicly available and Landsat albedos were derived in our earlier study trying to bridge the scale difference between coarse resolution data and ground measurements available from early 1980s. Inter-comparisons were made among the satellite albedos and against ground measurements. We have several new findings. First, trends in surface albedo change among the satellite albedo datasets generally agree with each other and with ground measurements. Second, all datasets showed negative albedo trends after 2000, but magnitudes differ greatly. Third, trends before 2000 from coarse resolution data are not significant but Landsat data observed positive albedo changes. Fourth, the turning point of albedo trend was found to be earlier than 2000. Those findings may bring new research topics on timing and magnitude, and an improved understanding mechanisms of the albedo changes over Greenland during the past few decades.

  16. Improvement of Mars surface snow albedo modeling in LMD Mars GCM with SNICAR

    Science.gov (United States)

    Singh, D.; Flanner, M.; Millour, E.

    2017-12-01

    The current version of Laboratoire de Météorologie Dynamique (LMD) Mars GCM (original-MGCM) uses annually repeating (prescribed) albedo values from the Thermal Emission Spectrometer observations. We integrate the Snow, Ice, and Aerosol Radiation (SNICAR) model with MGCM (SNICAR-MGCM) to prognostically determine H2O and CO2 ice cap albedos interactively in the model. Over snow-covered regions mean SNICAR-MGCM albedo is higher by about 0.034 than original-MGCM. Changes in albedo and surface dust content also impact the shortwave energy flux at the surface. SNICAR-MGCM model simulates a change of -1.26 W/m2 shortwave flux on a global scale. Globally, net CO2 ice deposition increases by about 4% over one Martian annual cycle as compared to original-MGCM simulations. SNICAR integration reduces the net mean global surface temperature, and the global surface pressure of Mars by about 0.87% and 2.5% respectively. Changes in albedo also show a similar distribution as dust deposition over the globe. The SNICAR-MGCM model generates albedos with higher sensitivity to surface dust content as compared to original-MGCM. For snow-covered regions, we improve the correlation between albedo and optical depth of dust from -0.91 to -0.97 with SNICAR-MGCM as compared to original-MGCM. Using new diagnostic capabilities with this model, we find that cryospheric surfaces (with dust) increase the global surface albedo of Mars by 0.022. The cryospheric effect is severely muted by dust in snow, however, which acts to decrease the planet-mean surface albedo by 0.06.

  17. An Investigation of Ice Surface Albedo and Its Influence on the High-Altitude Lakes of the Tibetan Plateau

    Directory of Open Access Journals (Sweden)

    Jiahe Lang

    2018-02-01

    Full Text Available Most high-altitude lakes are more sensitive to global warming than the regional atmosphere. However, most existing climate models produce unrealistic surface temperatures on the Tibetan Plateau (TP lakes, and few studies have focused on the influence of ice surface albedo on high-altitude lakes. Based on field albedo measurements, moderate resolution imaging spectrometer (MODIS albedo products and numerical simulation, this study evaluates the ice albedo parameterization schemes in existing lake models and investigates the characteristics of the ice surface albedo in six typical TP lakes, as well as the influence of ice albedo error in the FLake model. Compared with observations, several ice albedo schemes all clearly overestimate the lake ice albedo by 0.26 to 0.66, while the average bias of MODIS albedo products is only 0.07. The MODIS-observed albedo of a snow-covered lake varies with the snow proportion, and the lake surface albedo in a snow-free state is approximately 0.15 during the frozen period. The MODIS-observed ice surface (snow-free albedos are concentrated within the ranges of 0.14–0.16, 0.08–0.10 and 0.10–0.12 in Aksai Chin Lake, Nam Co Lake and Ngoring Lake, respectively. The simulated lake surface temperature is sensitive to variations in lake ice albedo especially in the spring and winter.

  18. Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains Central Facility

    Energy Technology Data Exchange (ETDEWEB)

    McFarlane, Sally A.; Gaustad, Krista L.; Mlawer, Eli J.; Long, Charles N.; Delamere, Jennifer

    2011-09-01

    We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

  19. Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

    Science.gov (United States)

    McFarlane, S. A.; Gaustad, K. L.; Mlawer, E. J.; Long, C. N.; Delamere, J.

    2011-09-01

    We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

  20. Near-ground cooling efficacies of trees and high-albedo surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Levinson, Ronnen M. [Univ. of California, Berkeley, CA (United States). Dept. of Mechanical Engineering

    1997-05-01

    Daytime summer urban heat islands arise when the prevalence of dark-colored surfaces and lack of vegetation make a city warmer than neighboring countryside. Two frequently-proposed summer heat island mitigation measures are to plant trees and to increase the albedo (solar reflectivity) of ground surfaces. This dissertation examines the effects of these measures on the surface temperature of an object near the ground, and on solar heating of air near the ground. Near-ground objects include people, vehicles, and buildings. The variation of the surface temperature of a near-ground object with ground albedo indicates that a rise in ground albedo will cool a near-ground object only if the object`s albedo exceeds a critical value. This critical value of object albedo depends on wind speed, object geometry, and the height of the atmospheric thermal boundary layer. It ranges from 0.15 to 0.37 for a person. If an object has typical albedo of 0.3, increasing the ground albedo by.

  1. Regular network model for the sea ice-albedo feedback in the Arctic.

    Science.gov (United States)

    Müller-Stoffels, Marc; Wackerbauer, Renate

    2011-03-01

    The Arctic Ocean and sea ice form a feedback system that plays an important role in the global climate. The complexity of highly parameterized global circulation (climate) models makes it very difficult to assess feedback processes in climate without the concurrent use of simple models where the physics is understood. We introduce a two-dimensional energy-based regular network model to investigate feedback processes in an Arctic ice-ocean layer. The model includes the nonlinear aspect of the ice-water phase transition, a nonlinear diffusive energy transport within a heterogeneous ice-ocean lattice, and spatiotemporal atmospheric and oceanic forcing at the surfaces. First results for a horizontally homogeneous ice-ocean layer show bistability and related hysteresis between perennial ice and perennial open water for varying atmospheric heat influx. Seasonal ice cover exists as a transient phenomenon. We also find that ocean heat fluxes are more efficient than atmospheric heat fluxes to melt Arctic sea ice.

  2. CLARA-SAL: a global 28 yr timeseries of Earth's black-sky surface albedo

    Directory of Open Access Journals (Sweden)

    A. Riihelä

    2013-04-01

    Full Text Available We present a novel 28 yr dataset of Earth's black-sky surface albedo, derived from AVHRR instruments. The dataset is created using algorithms to separately derive the surface albedo for different land use areas globally. Snow, sea ice, open water and vegetation are all treated independently. The product features corrections for the atmospheric effect in satellite-observed surface radiances, a BRDF correction for the anisotropic reflectance properties of natural surfaces, and a novel topography correction of geolocation and radiometric accuracy of surface reflectance observations over mountainous areas. The dataset is based on a homogenized AVHRR radiance timeseries. The product is validated against quality-controlled in situ observations of clear-sky surface albedo at various BSRN sites around the world. Snow and ice albedo retrieval validation is given particular attention using BSRN sites over Antarctica, Greenland Climate Network stations on the Greenland Ice Sheet (GrIS, as well as sea ice albedo data from the SHEBA and Tara expeditions. The product quality is found to be comparable to other previous long-term surface albedo datasets from AVHRR.

  3. An Investigation of Ice Surface Albedo and Its Influence on the High-Altitude Lakes of the Tibetan Plateau

    OpenAIRE

    Jiahe Lang; Shihua Lyu; Zhaoguo Li; Yaoming Ma; Dongsheng Su

    2018-01-01

    Most high-altitude lakes are more sensitive to global warming than the regional atmosphere. However, most existing climate models produce unrealistic surface temperatures on the Tibetan Plateau (TP) lakes, and few studies have focused on the influence of ice surface albedo on high-altitude lakes. Based on field albedo measurements, moderate resolution imaging spectrometer (MODIS) albedo products and numerical simulation, this study evaluates the ice albedo parameterization schemes in existing...

  4. Arctic and Antarctic diurnal and seasonal variations of snow albedo from multiyear Baseline Surface Radiation Network measurements

    OpenAIRE

    Wang, Xianwei; Zender, Charles S

    2011-01-01

    This study analyzes diurnal and seasonal variations of snow albedo at four Baseline Surface Radiation Network stations in the Arctic and Antarctica from 2003 to 2008 to elucidate similarities and differences in snow albedo diurnal cycles across geographic zones and to assess how diurnal changes in snow albedo affect the surface energy budget. At the seasonal scale, the daily albedo for the perennial snow at stations South Pole and Georg von Neumayer in Antarctica has a similar symmetric varia...

  5. Effect of urban albedo surfaces on thermal comfort | Mansouri ...

    African Journals Online (AJOL)

    It turns out that the reflectivity of materials known as the albedo, plays a leading role in this degradation. A numerical study was carried out to assess the thermal comfort of citizens by applying reflective materials for roofs, facades and floor. The results show that the reflective light paints help in moderating the microclimate, ...

  6. Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

    NARCIS (Netherlands)

    van Angelen, J.H.|info:eu-repo/dai/nl/325922470; Lenaerts, J.T.M.|info:eu-repo/dai/nl/314850163; Lhermitte, S.; Fettweis, X.; Kuipers Munneke, P.|info:eu-repo/dai/nl/304831891; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; van Meijgaard, E.; Smeets, C.J.P.P.|info:eu-repo/dai/nl/191522236

    2012-01-01

    We present a sensitivity study of the surface mass balance (SMB) of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme. The snow albedo scheme uses grain size as a prognostic variable and further depends on cloud cover,

  7. Spatially Complete Surface Albedo Data Sets: Value-Added Products Derived from Terra MODIS Land Products

    Science.gov (United States)

    Moody, Eric G.; King, Michael D.; Platnick, Steven; Schaaf, Crystal B.; Gao, Feng

    2004-01-01

    Spectral land surface albedo is an important parameter for describing the radiative properties of the Earth. Accordingly it reflects the consequences of natural and human interactions, such as anthropogenic, meteorological, and phenological effects, on global and local climatological trends. Consequently, albedos are integral parts in a variety of research areas, such as general circulation models (GCMs), energy balance studies, modeling of land use and land use change, and biophysical, oceanographic, and meteorological studies. Recent observations of diffuse bihemispherical (white-sky) and direct beam directional hemispherical (black-sky ) land surface albedo included in the MOD43B3 product from MODIS instruments aboard NASA's Terra and Aqua satellite platforms have provided researchers with unprecedented spatial, spectral, and temporal characteristics. Cloud and seasonal snow cover, however, curtail retrievals to approximately half the global land surfaces on an annual equal-angle basis, precluding MOD43B3 albedo products from direct inclusion in some research projects and production environments.

  8. The surface abundance and stratigraphy of lunar rocks from data about their albedo

    Science.gov (United States)

    Shevchenko, V. V.

    1977-01-01

    The data pf ground-based studies and surveys of the lunar surface by the Zond and Apollo spacecraft have been used to construct an albedo map covering 80 percent of the lunar sphere. Statistical analysis of the distribution of areas with various albedos shows several types of lunar surface. Comparison of albedo data for maria and continental areas with the results of geochemical orbital surveys allows the identification of the types of surface with known types of lunar rock. The aluminum/silcon and magnesium/silicon ratios as measured by the geochemical experiments on the Apollo 15 and Apollo 16 spacecraft were used as an indication of the chemical composition of the rock. The relationship of the relative aluminum content to the age of crystalline rocks allows a direct dependence to be constructed between the mean albedo of areas and the age of the rocks of which they are composed.

  9. Estimation of surface albedo from NOAA AVHRR data in high latitudes

    Science.gov (United States)

    Laine, Vesa; Heikinheimo, Martti

    1996-05-01

    A method for determining the surface albedo from routine daily NOAA AVHRR data is described and tested for applicability under high latitude conditions in a boreal-sub-arctic region. The test period included all received satellite data from April to October 1994, giving a good coverage of various and changing surface conditions. Albedo values obtained initially for each cloud-free pixel and satellite over-pass were averaged over nine-day periods to include a full cycle of measuring geometries and to obtain an adequate number of cloud-free pixels in the final average images. With the automated image navigation provided by the present receiving system, spatial averaging over a minimum of 24×24 pixel squares was needed to obtain acceptable repeatability of local albedo values. The atmospheric correction was made using a bi-directional atmospheric correction method. In early April, the albedo over the sea in the ice-covered northern Gulf of Bothnia and in the open mountain regions was typically above 60%. Over snow-covered forested areas, the albedo was near 50% in the sub-arctic zone, and near 30% for the central boreal forest-covered surface. The difference in albedo between the northern and southern forested locations in the presence of snow was attributed to the higher biomass density of forests in the south and possibly more snow remaining on trees in the north. For snow-free conditions, forested areas typically showed an albedo in the range 11 13%. Agricultural regions, mixed with minor patches of forest, generally showed an albedo below 15% for conditions of low crop leaf area coverage, but reached as high as 18% under conditions of maximum leaf area coverage in mid-summer. Retrieval of the edge of snow cover in spring and the appearance of newly fallen snow in autumn could readily be carried out using a threshold albedo of 20%.

  10. Increasing surface albedo in the dry subtropical forests of South America: the role of agriculture expansion and management

    Science.gov (United States)

    Houspanossian, J.; Kuppel, S.; Gimenez, R.; Jobbagy, E. G.; Nosetto, M. D.

    2014-12-01

    The increase in surface albedo inherent to land clearing and cultivation (land-cover change, LCC) in the subtropical dry forests of the South American Chaco offsets part of the radiative forcing (RF) of the related carbon emissions. The magnitude of these albedo changes, however, is also dependent on shifts in agricultural practices (land-management change, LMC) and will influence the net effect on Earth's radiation balance as well as other potential feedbacks on climate. We quantified the surface albedo changes between 2001 and 2013 and the consequent shifts in the radiation balance resulting from LCC and LMC, using MODIS imagery a columnar radiation model parameterized with satellite data. Agricultural systems replacing dry forests presented a large variety of managements, ranging from pasture systems with remnant trees to different grain crops, displaying a wide range of phenologies. Cultivated lands showed higher and more variable albedo values (mean = 0.162, Standard Deviation = 0.013, n = 10,000 pixels) than the dry forests they replace (mean = 0.113, SD = 0.010, n = 10,000). These albedo contrasts resulted in a cooling RF of deforestation of -10.1 W m-2 on average, but both livestock and grain crop production systems showed large differences among the different land management options. For instance, livestock systems based on open pasture lands showed higher albedo change and RF (0.06 and -16.3 W m-2, respectively) than silvopastoral systems (0.02 and -4.4 W m-2). Similarly in cropping systems, the replacement of double-cropping by single summer crops, a widespread process in the region lately, resulted in higher albedo change (0.06 vs. 0.08) and RF (-16.3 vs. -22.3 W m-2). Although the effects of LCC on climate are widely acknowledged, those of LMC are still scarcely understood. In the Chaco region, the latter could play an important role and offer a yet-overlooked pathway to influence the radiative balance of our planet.

  11. Surface melt on Antarctic ice shelves driven by wind-albedo interactions

    Science.gov (United States)

    Lhermitte, Stef; Lenaerts, Jan

    2017-04-01

    Surface melt and subsequent firn air depletion is considered an important precursor for disintegration of Antarctic ice shelves, causing grounded glaciers to accelerate and sea level to rise. Recent studies have highlighted the impact of surface winds on Antarctic ice shelf melt, both on the Antarctic Peninsula and in East Antarctica. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. On the East Antarctic ice shelves, on the other hand, meltwater-induced firn air depletion is found in the grounding zone as result of persistent katabatic winds, regionally warming the atmosphere and inducing a melt-albedo feedback. Here, we use a combination multi-source satellite imagery, snow modelling, climate model output and in-situ observations to highlight the importance of this wind-induced melt and to show its widespread occurrence across Antarctica. The satellite imagery gives insight in the meltwater drainage systems, showing spatio-temporal changes in both supraglacial and englacial water throughout the melt season and during the subsequent winter. Although the wind-induced melt is a regional phenomenon with strong inter-annual variability, it is strongly correlated to larger scale climate parameters, such as summer surface temperature. Based on these correlations and snow model output driven by future climate scenarios, we can constrain the future changes to this local melt near the grounding line.

  12. Empirical models of monthly and annual surface albedo in managed boreal forests of Norway

    Science.gov (United States)

    Bright, Ryan M.; Astrup, Rasmus; Strømman, Anders H.

    2013-04-01

    As forest management activities play an increasingly important role in climate change mitigation strategies of Nordic regions such as Norway, Sweden, and Finland -- the need for a more comprehensive understanding of the types and magnitude of biogeophysical climate effects and their various tradeoffs with the global carbon cycle becomes essential to avoid implementation of sub-optimal policy. Forest harvest in these regions reduces the albedo "masking effect" and impacts Earth's radiation budget in opposing ways to that of concomitant carbon cycle perturbations; thus, policies based solely on biogeochemical considerations in these regions risk being counterproductive. There is therefore a need to better understand how human disturbances (i.e., forest management activities) affect important biophysical factors like surface albedo. An 11-year remotely sensed surface albedo dataset coupled with stand-level forest management data for a variety of stands in Norway's most productive logging region are used to develop regression models describing temporal changes in monthly and annual forest albedo following clear-cut harvest disturbance events. Datasets are grouped by dominant tree species and site indices (productivity), and two alternate multiple regression models are developed and tested following a potential plus modifier approach. This resulted in an annual albedo model with statistically significant parameters that explains a large proportion of the observed variation, requiring as few as two predictor variables: i) average stand age - a canopy modifier predictor of albedo, and ii) stand elevation - a local climate predictor of a forest's potential albedo. The same model structure is used to derive monthly albedo models, with models for winter months generally found superior to summer models, and conifer models generally outperforming deciduous. We demonstrate how these statistical models can be applied to routine forest inventory data to predict the albedo

  13. Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

    Science.gov (United States)

    Nihashi, Sohey; Cavalieri, Donald J.

    2007-01-01

    The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

  14. A Multilayer Surface Temperature, Surface Albedo, and Water Vapor Product of Greenland from MODIS

    Directory of Open Access Journals (Sweden)

    Dorothy K. Hall

    2018-04-01

    Full Text Available A multilayer, daily ice surface temperature (IST–albedo–water vapor product of Greenland, extending from March 2000 through December 2016, has been developed using standard MODerate-resolution Imaging Spectroradiometer (MODIS data products from the Terra satellite. To meet the needs of the ice sheet modeling community, this new Earth Science Data Record (ESDR is provided in a polar stereographic projection in NetCDF format, and includes the existing standard MODIS Collection 6.1 IST and derived melt maps, and Collection 6 snow albedo and water vapor maps, along with ancillary data, and is provided at a spatial resolution of ~0.78 km. This ESDR enables relationships between IST, surface melt, albedo, and water vapor to be evaluated easily. We show examples of the components of the ESDR and describe some uses of the ESDR such as for comparison with skin temperature, albedo, and water vapor output from Modern Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2. Additionally, we show validation of the MODIS IST using in situ and aircraft data, and validation of MERRA-2 skin temperature maps using MODIS IST and in situ data. The ESDR has been assigned a DOI and will be available through the National Snow and Ice Data Center by the summer of 2018.

  15. Representation of vegetation effects on the snow-covered albedo in the Noah land surface model with multiple physics options

    OpenAIRE

    S. Park; S. K. Park

    2015-01-01

    Snow albedo plays a critical role in calculating the energy budget, but parameterization of the snow surface albedo is still under great uncertainty. It varies with snow grain size, snow cover thickness, snow age, forest shading factor and other variables. Snow albedo of forest is typically lower than that of short vegetation; thus snow albedo is dependent on the spatial distributions of characteristic land cover and on the canopy density and structure. In the No...

  16. Surface Albedo Darkening from wildfires in Northern Sub-Saharan Africa

    Science.gov (United States)

    Gatebe, C. K.; Ichoku, C. M.; Poudal, R.; Roman, M. O.; Wilcox, E.

    2014-01-01

    Wildfires are recognized as a key physical disturbance of terrestrial ecosystems and a major source of atmospheric trace gases and aerosols. They are known to produce changes in landscape patterns and lead to changes in surface albedo that can persist for long periods. Here, we estimate the darkening of surface albedo due to wildfires in different land cover ecosystems in the Northern Sub-Saharan Africa using data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We determined a decrease in albedo after fires over most land cover types (e.g. woody savannas: (-0.00352 0.00003) and savannas: (- 0.003910.00003), which together accounted for >86% of the total MODIS fire count between 2003 and 2011). Grasslands had a higher value (-0.00454 0.00003) than the savannas, but accounted for only about 5% of the total fire count. A few other land cover types (e.g. Deciduous broad leaf: (0.00062 0.00015), and barren: 0.00027 0.00019), showed an increase in albedo after fires, but accounted for less than 1% of the total fires. Albedo change due to wildfires is more important during the fire season (October-February). The albedo recovery progresses rapidly during the first year after fires, where savannas show the greatest recovery (>77%) within one year, while deciduous broadleaf, permanent wetlands and barren lands show the least one-year recovery (56%). The persistence of surface albedo darkening in most land cover types is limited to about six to seven years, after which at least 98% of the burnt pixels recover to their pre-fire albedo.

  17. Quality assurance of in-situ measurements of land surface albedo: A model-based approach

    Science.gov (United States)

    Adams, Jennifer; Gobron, Nadine; Widlowski, Jean-Luc; Mio, Corrado

    2016-04-01

    This paper presents the development of a model-based framework for assessing the quality of in-situ measurements of albedo used to validate land surface albedo products. Using a 3D Monte Carlo Ray Tracing (MCRT) radiative transfer model, a quality assurance framework is built based on simulated field measurements of albedo within complex 3D canopies and under various illumination scenarios. This method provides an unbiased approach in assessing the quality of field measurements, and is also able to trace the contributions of two main sources of uncertainty in field-measurements of albedo; those resulting from 1) the field measurement protocol, such as height or placement of field measurement within the canopy, and 2) intrinsic factors of the 3D canopy under specific illumination characteristics considered, such as the canopy structure and landscape heterogeneity, tree heights, ecosystem type and season.

  18. Evaluation of MuSyQ land surface albedo based on LAnd surface Parameters VAlidation System (LAPVAS)

    Science.gov (United States)

    Dou, B.; Wen, J.; Xinwen, L.; Zhiming, F.; Wu, S.; Zhang, Y.

    2016-12-01

    satellite derived Land surface albedo is an essential climate variable which controls the earth energy budget and it can be used in applications such as climate change, hydrology, and numerical weather prediction. However, the accuracy and uncertainty of surface albedo products should be evaluated with a reliable reference truth data prior to applications. A new comprehensive and systemic project of china, called the Remote Sensing Application Network (CRSAN), has been launched recent years. Two subjects of this project is developing a Multi-source data Synergized Quantitative Remote Sensin g Production System ( MuSyQ ) and a Web-based validation system named LAnd surface remote sensing Product VAlidation System (LAPVAS) , which aims to generate a quantitative remote sensing product for ecosystem and environmental monitoring and validate them with a reference validation data and a standard validation system, respectively. Land surface BRDF/albedo is one of product datasets of MuSyQ which has a pentad period with 1km spatial resolution and is derived by Multi-sensor Combined BRDF Inversion ( MCBI ) Model. In this MuSyQ albedo evaluation, a multi-validation strategy is implemented by LAPVAS, including directly and multi-scale validation with field measured albedo and cross validation with MODIS albedo product with different land cover. The results reveal that MuSyQ albedo data with a 5-day temporal resolution is in higher sensibility and accuracy during land cover change period, e.g. snowing. But results without regard to snow or changed land cover, MuSyQ albedo generally is in similar accuracy with MODIS albedo and meet the climate modeling requirement of an absolute accuracy of 0.05.

  19. The Effect of Bond Albedo on Venus' Atmospheric and Surface Temperatures

    Science.gov (United States)

    Bullock, M. A.; Limaye, S. S.; Grinspoon, D. H.; Way, M.

    2017-12-01

    In spite of Venus' high planetary albedo, sufficient solar energy reaches the surface to drive a powerful greenhouse effect. The surface temperature is three times higher than it would be without an atmosphere. However, the details of the energy balance within Venus' atmosphere are poorly understood. Half of the solar energy absorbed within the clouds, where most of the solar energy is absorbed, is due to an unknown agent. One of the challenges of modeling Venus' atmosphere has been to account for all the sources of opacity sufficient to generate a globally averaged surface temperature of 735 K, when only 2% of the incoming solar energy is deposited at the surface. The wavelength and spherically integrated albedo, or Bond albedo, has typically been cited as between 0.7 and 0.82 (Colin 1983). Yet, recent photometry of Venus at extended phase angles between 2 and 179° indicate a Bond albedo of 0.90 (Mallama et al., 2006). The authors note an increase in cloud top brightness at phase angles right). Venus surface temperature as Bond Albedo changes. Radiative-convective equilibrium models predict the correct globally averaged surface temperature at a=0.81. Calculations here show that a Bond albedo of a=0.9 would yield a surface temperature of 666.4 K, about 70 K too low, unless there is additional thermal absorption within the atmosphere that is not understood. Colin, L.,, Venus, University of Arizona Press, Tucson, 1983, pp 10-26. Mallama, A., et al., 2006. Icarus. 182, 10-22.

  20. Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

    Directory of Open Access Journals (Sweden)

    J. Delamere

    2011-09-01

    Full Text Available We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM facility at the Southern Great Plains (SGP site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs, four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated can be identified. A normalized difference vegetation index (NDVI is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

  1. Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

    Science.gov (United States)

    Huang, Shengli; Dahal, Devendra; Liu, Heping; Jin, Suming; Young, Claudia J.; Liu, Shuang; Liu, Shu-Guang

    2015-01-01

    The albedo change caused by both fires and subsequent succession is spatially heterogeneous, leading to the need to assess the spatiotemporal variation of surface shortwave forcing (SSF) as a component to quantify the climate impacts of high-latitude fires. We used an image reconstruction approach to compare postfire albedo with the albedo assuming fires had not occurred. Combining the fire-caused albedo change from the 2001-2010 fires in interior Alaska and the monthly surface incoming solar radiation, we examined the spatiotemporal variation of SSF in the early successional stage of around 10 years. Our results showed that while postfire albedo generally increased in fall, winter, and spring, some burned areas could show an albedo decrease during these seasons. In summer, the albedo increased for several years and then declined again. The spring SSF distribution did not show a latitudinal decrease from south to north as previously reported. The results also indicated that although the SSF is usually largely negative in the early successional years, it may not be significant during the first postfire year. The annual 2005-2010 SSF for the 2004 fire scars was -1.30, -4.40, -3.31, -4.00, -3.42, and -2.47 Wm-2. The integrated annual SSF map showed significant spatial variation with a mean of -3.15 Wm-2 and a standard deviation of 3.26 Wm-2, 16% of burned areas having positive SSF. Our results suggest that boreal deciduous fires would be less positive for climate change than boreal evergreen fires. Future research is needed to comprehensively investigate the spatiotemporal radiative and non-radiative forcings to determine the effect of boreal fires on climate.

  2. Vegetation masking effect on future warming and snow albedo feedback in a boreal forest region of northern Eurasia according to MIROC-ESM

    Science.gov (United States)

    Abe, Manabu; Takata, Kumiko; Kawamiya, Michio; Watanabe, Shingo

    2017-09-01

    The Earth system model, Model for Interdisciplinary Research on Climate-Earth system model (MIROC-ESM), in which the leaf area index (LAI) is calculated interactively with an ecological land model, simulated future changes in the snow water equivalent under the scenario of global warming. Using MIROC-ESM, the effects of the snow albedo feedback (SAF) in a boreal forest region of northern Eurasia were examined under the possible climate future scenario RCP8.5. The simulated surface air temperature (SAT) in spring greatly increases across Siberia and the boreal forest region, whereas the snow cover decreases remarkably only in western Eurasia. The large increase in SAT across Siberia is attributed to strong SAF, which is caused by both the reduced snow-covered fraction and the reduced surface albedo of the snow-covered portion due to the vegetation masking effect in those grid cells. A comparison of the future changes with and without interactive LAI changes shows that in Siberia, the vegetation masking effect increases the spring SAF by about two or three times and enhances the spring warming by approximately 1.5 times. This implies that increases in vegetation biomass in the future are a potential contributing factor to warming trends and that further research on the vegetation masking effect is needed for reliable future projection.

  3. A minimal, statistical model for the surface albedo of Vestfonna ice cap, Svalbard

    Directory of Open Access Journals (Sweden)

    M. Möller

    2012-09-01

    Full Text Available The ice cap Vestfonna is located in northeastern Svalbard and forms one of the largest ice bodies of the Eurasian Arctic. Its surface albedo plays a key role in the understanding and modelling of its energy and mass balance. The principle governing factors for albedo evolution, i.e. precipitation and air temperature and therewith snow depth and melt duration, were found to vary almost exclusively with terrain elevation throughout the ice cap. Hence, surface albedo can be expected to develop a comparable pattern. A new statistical model is presented that estimates this mean altitudinal albedo profile of the ice cap on the basis of a minimal set of meteorological variables on a monthly resolution. Model calculations are based on a sigmoid function of the artificial quantity rain-snow ratio and a linear function of cumulative snowfall and cumulative positive degree days. Surface albedo fields of the MODIS snow product MOD10A1 from the period March to October in the years 2001–2008 serve as a basis for both calibration and cross-validation of the model. The meteorological model input covers the period September 2000 until October 2008 and is based on ERA-Interim data of a grid point located close to the ice cap. The albedo model shows a good performance. The root mean square error between observed and modelled albedo values along the altitudinal profile is 0.057±0.028 (mean ± one standard deviation. The area weighted mean even reduces to a value of 0.054. Distinctly higher deviations (0.07–0.09 are only present throughout the very lowest and uppermost parts of the ice cap that are either small in area or hardly affected by surface melt. Thus, the new, minimal, statistical albedo model presented in this study is found to reproduce the albedo evolution on Vestfonna ice cap on a high level of accuracy and is thus suggested to be fully suitable for further application in broader energy or mass-balance studies of the ice cap.

  4. Spatially Complete Global Surface Albedos Derived from Terra/MODIS Data

    Science.gov (United States)

    King, Michael D.; Moody, Eric G.; Schaaf, Crystal B.; Platnick, Steven

    2006-01-01

    Spectral land surface albedo is an important parameter for describing the radiative properties of the Earth. Accordingly it reflects the consequences of natural and human interactions, such as anthropogenic, meteorological, and phenological effects, on global and local climatological trends. Consequently, albedos are integral parts in a variety of research areas, such as general circulation models (GCMs), energy balance studies, modeling of land use and land use change, and biophysical, oceanographic, and meteorological studies. , Over five years of land surface anisotropy, diffuse bihemispherical (white-sky) albedo and direct beam directional hemispherical (black-sky) albedo from observations acquired by the MODIS instruments aboard NASA s Terra and Aqua satellite platforms have provided researchers with unprecedented spatial, spectral, and temporal information on the land surface s radiative characteristics. However, roughly 30% of the global land surface, on an annual equal-angle basis, is obscured due to persistent and transient cloud cover, while another 207% is obscured due to ephemeral and seasonal snow effects. This precludes the MOD43B3 albedo products from being directly used in some remote sensing and ground-based applications, climate models, and global change research projects. To provide researchers with the requisite spatially complete global snow-free land surface albedo dataset, an ecosystem-dependent temporal interpolation technique was developed to fill missing or lower quality data and snow covered values from the official MOD43B3 dataset with geophysically realistic values. The method imposes pixel-level and local regional ecosystem-dependent phenological behavior onto retrieved pixel temporal data in such a way as to maintain pixel-level spatial and spectral detail and integrity. The phenological curves are derived from statistics based on the MODIS MOD12Q1 IGBP land cover classification product geolocated with the MOD43B3 data.

  5. Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

    Directory of Open Access Journals (Sweden)

    J. H. van Angelen

    2012-10-01

    Full Text Available We present a sensitivity study of the surface mass balance (SMB of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme. The snow albedo scheme uses grain size as a prognostic variable and further depends on cloud cover, solar zenith angle and black carbon concentration. For the control experiment the overestimation of absorbed shortwave radiation (+6% at the K-transect (west Greenland for the period 2004–2009 is considerably reduced compared to the previous density-dependent albedo scheme (+22%. To simulate realistic snow albedo values, a small concentration of black carbon is needed, which has strongest impact on melt in the accumulation area. A background ice albedo field derived from MODIS imagery improves the agreement between the modeled and observed SMB gradient along the K-transect. The effect of enhanced meltwater retention and refreezing is a decrease of the albedo due to an increase in snow grain size. As a secondary effect of refreezing the snowpack is heated, enhancing melt and further lowering the albedo. Especially in a warmer climate this process is important, since it reduces the refreezing potential of the firn layer that covers the Greenland Ice Sheet.

  6. Quality assessment and improvement of the EUMETSAT Meteosat Surface Albedo Climate Data Record

    Directory of Open Access Journals (Sweden)

    A. Lattanzio

    2015-10-01

    Full Text Available Surface albedo has been identified as an important parameter for understanding and quantifying the Earth's radiation budget. EUMETSAT generated the Meteosat Surface Albedo (MSA Climate Data Record (CDR currently comprising up to 24 years (1982–2006 of continuous surface albedo coverage for large areas of the Earth. This CDR has been created within the Sustained, Coordinated Processing of Environmental Satellite Data for Climate Monitoring (SCOPE-CM framework. The long-term consistency of the MSA CDR is high and meets the Global Climate Observing System (GCOS stability requirements for desert reference sites. The limitation in quality due to non-removed clouds by the embedded cloud screening procedure is the most relevant weakness in the retrieval process. A twofold strategy is applied to efficiently improve the cloud detection and removal. The first step consists of the application of a robust and reliable cloud mask, taking advantage of the information contained in the measurements of the infrared and visible bands. Due to the limited information available from old radiometers, some clouds can still remain undetected. A second step relies on a post-processing analysis of the albedo seasonal variation together with the usage of a background albedo map in order to detect and screen out such outliers. The usage of a reliable cloud mask has a double effect. It enhances the number of high-quality retrievals for tropical forest areas sensed under low view angles and removes the most frequently unrealistic retrievals on similar surfaces sensed under high view angles. As expected, the usage of a cloud mask has a negligible impact on desert areas where clear conditions dominate. The exploitation of the albedo seasonal variation for cloud removal has good potentialities but it needs to be carefully addressed. Nevertheless it is shown that the inclusion of cloud masking and removal strategy is a key point for the generation of the next MSA CDR release.

  7. Influence of soil moisture content on surface albedo and soil thermal ...

    Indian Academy of Sciences (India)

    The large variability in the soil moisture content is attributed to the rainfall during all the seasons and also to the evaporation/movement of water to deeper layers. The relationship of surface albedo on soil moisture content on different time scales are studied and the influence of solar elevation angle and cloud cover are also ...

  8. Influence of soil moisture content on surface albedo and soil thermal ...

    Indian Academy of Sciences (India)

    atively longer memory of soil moisture in com- parison with the variation of controlling parame- ters often leads to climatic ... and vegetation cover changes the soil colour and thus varies the surface albedo (Todd and Hoffer. 1998). .... The colour of the soil at the experimental site varied from dark brown to dark reddish brown.

  9. Validation of AVHRR- and MODIS-derived albedos of snow and ice surfaces by means of helicopter measurements

    NARCIS (Netherlands)

    Greuell, W.; Oerlemans, J.

    2005-01-01

    We describe the validation of surface albedos of snow and glacier ice as derived from Advanced Very High Resolution Radiometer (AVHRR) and MOderate Resolution Imaging Spectrometer (MODIS) satellite data. For this purpose we measured surface albedos from a helicopter over Vatnajökull, Iceland, and

  10. Assessment of the surface mass balance along the K-transect (Greenland ice sheet) from satellite-derived albedos

    NARCIS (Netherlands)

    Oerlemans, J.; Greuell, W.

    This paper explores the potential of using satellite-derived albedos to estimate the surface mass balance of the Kangerlussuaq transect (K-transect; Greenland ice sheet). We first retrieved surface albedos from Advanced Very High Resolution Radar data by using, among other techniques, a new

  11. Constraining MODIS snow albedo at large solar zenith angles: Implications for the surface energy budget in Greenland

    OpenAIRE

    Wang, Xianwei; Zender, Charles S

    2010-01-01

    An understanding of the surface albedo of high latitudes is crucial for climate change studies. MODIS albedo retrievals flagged as high-quality compare well with in situ Greenland Climate Network (GC-Net) measurements but cover too small an area to fully characterize Greenland's albedo in nonsummer months. In contrast, poor quality MODIS retrievals provide adequate spatiotemporal coverage, but are not recommended for use at large solar zenith angles (SZAs) where they have a systematic low bia...

  12. Impact of MODIS Sensor Calibration Updates on Greenland Ice Sheet Surface Reflectance and Albedo Trends

    Science.gov (United States)

    Casey, Kimberly A.; Polashenski, Chris M.; Chen, Justin; Tedesco, Marco

    2017-01-01

    We evaluate Greenland Ice Sheet (GrIS) surface reflectance and albedo trends using the newly released Collection 6 (C6) MODIS (Moderate Resolution Imaging Spectroradiometer) products over the period 2001-2016. We find that the correction of MODIS sensor degradation provided in the new C6 data products reduces the magnitude of the surface reflectance and albedo decline trends obtained from previous MODIS data (i.e., Collection 5, C5). Collection 5 and 6 data product analysis over GrIS is characterized by surface (i.e., wet vs. dry) and elevation (i.e., 500-2000 m, 2000 m and greater) conditions over the summer season from 1 June to 31 August. Notably, the visible-wavelength declining reflectance trends identified in several bands of MODIS C5 data from previous studies are only slightly detected at reduced magnitude in the C6 versions over the dry snow area. Declining albedo in the wet snow and ice area remains over the MODIS record in the C6 product, albeit at a lower magnitude than obtained using C5 data. Further analyses of C6 spectral reflectance trends show both reflectance increases and decreases in select bands and regions, suggesting that several competing processes are contributing to Greenland Ice Sheet albedo change. Investigators using MODIS data for other ocean, atmosphere and/or land analyses are urged to consider similar re-examinations of trends previously established using C5 data.

  13. Impact of MODIS sensor calibration updates on Greenland Ice Sheet surface reflectance and albedo trends

    Science.gov (United States)

    Casey, Kimberly A.; Polashenski, Chris M.; Chen, Justin; Tedesco, Marco

    2017-08-01

    We evaluate Greenland Ice Sheet (GrIS) surface reflectance and albedo trends using the newly released Collection 6 (C6) MODIS (Moderate Resolution Imaging Spectroradiometer) products over the period 2001-2016. We find that the correction of MODIS sensor degradation provided in the new C6 data products reduces the magnitude of the surface reflectance and albedo decline trends obtained from previous MODIS data (i.e., Collection 5, C5). Collection 5 and 6 data product analysis over GrIS is characterized by surface (i.e., wet vs. dry) and elevation (i.e., 500-2000 m, 2000 m and greater) conditions over the summer season from 1 June to 31 August. Notably, the visible-wavelength declining reflectance trends identified in several bands of MODIS C5 data from previous studies are only slightly detected at reduced magnitude in the C6 versions over the dry snow area. Declining albedo in the wet snow and ice area remains over the MODIS record in the C6 product, albeit at a lower magnitude than obtained using C5 data. Further analyses of C6 spectral reflectance trends show both reflectance increases and decreases in select bands and regions, suggesting that several competing processes are contributing to Greenland Ice Sheet albedo change. Investigators using MODIS data for other ocean, atmosphere and/or land analyses are urged to consider similar re-examinations of trends previously established using C5 data.

  14. Impact of MODIS sensor calibration updates on Greenland Ice Sheet surface reflectance and albedo trends

    Directory of Open Access Journals (Sweden)

    K. A. Casey

    2017-08-01

    Full Text Available We evaluate Greenland Ice Sheet (GrIS surface reflectance and albedo trends using the newly released Collection 6 (C6 MODIS (Moderate Resolution Imaging Spectroradiometer products over the period 2001–2016. We find that the correction of MODIS sensor degradation provided in the new C6 data products reduces the magnitude of the surface reflectance and albedo decline trends obtained from previous MODIS data (i.e., Collection 5, C5. Collection 5 and 6 data product analysis over GrIS is characterized by surface (i.e., wet vs. dry and elevation (i.e., 500–2000 m, 2000 m and greater conditions over the summer season from 1 June to 31 August. Notably, the visible-wavelength declining reflectance trends identified in several bands of MODIS C5 data from previous studies are only slightly detected at reduced magnitude in the C6 versions over the dry snow area. Declining albedo in the wet snow and ice area remains over the MODIS record in the C6 product, albeit at a lower magnitude than obtained using C5 data. Further analyses of C6 spectral reflectance trends show both reflectance increases and decreases in select bands and regions, suggesting that several competing processes are contributing to Greenland Ice Sheet albedo change. Investigators using MODIS data for other ocean, atmosphere and/or land analyses are urged to consider similar re-examinations of trends previously established using C5 data.

  15. Factors affecting projected Arctic surface shortwave heating and albedo change in coupled climate models.

    Science.gov (United States)

    Holland, Marika M; Landrum, Laura

    2015-07-13

    We use a large ensemble of simulations from the Community Earth System Model to quantify simulated changes in the twentieth and twenty-first century Arctic surface shortwave heating associated with changing incoming solar radiation and changing ice conditions. For increases in shortwave absorption associated with albedo reductions, the relative influence of changing sea ice surface properties and changing sea ice areal coverage is assessed. Changes in the surface sea ice properties are associated with an earlier melt season onset, a longer snow-free season and enhanced surface ponding. Because many of these changes occur during peak solar insolation, they have a considerable influence on Arctic surface shortwave heating that is comparable to the influence of ice area loss in the early twenty-first century. As ice area loss continues through the twenty-first century, it overwhelms the influence of changes in the sea ice surface state, and is responsible for a majority of the net shortwave increases by the mid-twenty-first century. A comparison with the Arctic surface albedo and shortwave heating in CMIP5 models indicates a large spread in projected twenty-first century change. This is in part related to different ice loss rates among the models and different representations of the late twentieth century ice albedo and associated sea ice surface state. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  16. Near-ground cooling efficacies of trees and high-albedo surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Levinson, Ronnen Michael [Univ. of California, Berkeley, CA (United States)

    1997-05-01

    Daytime summer urban heat islands arise when the prevalence of dark-colored surfaces and lack of vegetation make a city warmer than neighboring countryside. Two frequentlyproposed summer heat island mitigation measures are to plant trees and to increase the albedo (solar reflectivity) of ground surfaces. This dissertation examines the effects of these measures on the surface temperature of an object near the ground, and on solar heating of air near the ground. Near-ground objects include people, vehicles, and buildings. The variation of the surface temperature of a near-ground object with ground albedo indicates that a rise in ground albedo will cool a near-ground object only if the object’s albedo exceeds a critical value. This critical value of object albedo depends on wind speed, object geometry, and the height of the atmospheric thermal boundary layer. It ranges from 0.15 to 0.37 for a person. If an object has typical albedo of 0.3, increasing the ground albedo by 0.25 perturbs the object’s surface temperature by -1 to +2 K. Comparing a tree’s canopy-to-air convection to the reduction in ground-to-air convection induced by tree shading of the ground indicates that the presence of a tree can either increase or decrease solar heating of ground-level air. The tree’s net effect depends on the extent to which solar heating of the canopy is dissipated by evaporation, and on the fraction of air heated by the canopy that flows downward and mixes with the ground-level air. A two-month lysimeter (plant-weighing) experiment was conducted to measure instantaneous rates of water loss from a tree under various conditions of weather and soil-moisture. Calculations of canopy-to-air convection and the reduction of ground-to-air convection based on this data indicate that canopy-induced heating would negate shadowinduced cooling if approximately 45% of the canopy-heated air mixed with ground level air. This critical fraction is comparable to typical downward mixing

  17. Parameterization of albedo, thermal inertia, and surface roughness of desert scrub/sandy soil surface

    Science.gov (United States)

    Otterman, J.; Mccumber, M.

    1986-01-01

    Spectral albedo, A sub n, for the direct solar beam is defined as A sub n (r sub i,s, theta sub 0) = r sub i exp(-s tan theta sub 0)1-I(s) where I(s) is the integral over all reflection angles describing the interception by the absorbing plants of the flux reflected from the soil, r sub i soil reflectance, assumed Lambertian, S the projection on a vertical plane of plants per unit surface area, and theta sub 0 is the solar zenith angle. Hemispheric reflectance for the direct solar beam equals 1-I(s) times the reflectance to the zenith. The values of s of 0.1, 0.2, and 0.3 respectively quantify sparse, moderately dense, and very dense desert scrub. Thin plants are assumed to be of negligible thermal inertia, and thus directly yield the absorbed insolation to the atmosphere. Surface thermal inertia is therefore effectively reduced. The ratio of surface roughness height to plant height is parameterized for sparse, moderately dense, and very dense desert-scrub as a function of s based on data expressing the dependence of this ratio on plant silhouette.

  18. Land Surface Albedo From EPS/AVHRR : Method For Retrieval and Validation

    Science.gov (United States)

    Jacob, G.

    2015-12-01

    The scope of Land Surface Analysis Satellite Applications Facility (LSA-SAF) is to increase benefit from EUMETSAT Satellites (MSG and EPS) data by providing added value products for the meteorological and environmental science communities with main applications in the fields of climate modelling, environmental management, natural hazards management, and climate change detection. The MSG/SEVIRI daily albedo product is disseminated operationally by the LSA-SAF processing centre based in Portugal since 2009. This product so-called MDAL covers Europe and Africa includes in the visible, near infrared and shortwave bands at a resolution of 3km at the equator. Recently, an albedo product at 1km so-called ETAL has been built from EPS/AVHRR observations in order to primarily MDAL product outside the MSG disk, while ensuring a global coverage. The methodology is common to MSG and EPS data and relies on the inversion of the BRDF (Bidirectional Reflectance Distribution Function) model of Roujean et al. On a given target, ETAL products exploits the variability of viewing angles whereas MDAL looks at the variations of solar illumination. The comparison of ETAL albedo product against MODIS and MSG/SEVIRI products over the year 2015 is instructive in many ways and shows in general a good agreement between them. The dispersion may be accounted by different factors that will be explained The additional information provided by EPS appears to be particularly beneficial for high latitudes during winter and for snow albedo.

  19. Large-scale simulations of snow albedo masking by forests

    OpenAIRE

    Essery, Richard

    2013-01-01

    Comparisons between climate models have found large differences in predictions for the albedo of forested regions with snow cover, leading to uncertainty in the strength of snow albedo feedbacks on climate change predicted by these models. To explore this uncertainty, three commonly used methods for calculating the albedo of vegetated surfaces are compared, taking observed snow and vegetation distributions as inputs. Surprisingly, all three methods produce similar results and compare reasonab...

  20. Surface albedo in relation to disturbance and early stand dynamics in the boreal forest: Implications for climate models

    Science.gov (United States)

    Halim, M. A.; Thomas, S. C.

    2017-12-01

    Surface albedo is the most important biophysical radiative forcing in the boreal forest. General Circulation Model studies have suggested that harvesting of boreal forest has a net cooling effect, in contrast to other terrestrial biomes, by increasing surface albedo. However, albedo estimation in these models has been achieved by simplifying processes governing albedo at a coarse scale (both spatial and temporal). Biophysical processes that determine albedo likely operate on small spatial and temporal scales, requiring more direct estimates of effects of landcover change on net radiation. We established a chronosequence study in post-fire and post-clearcut sites (2013, 2006, 1998), logging data from July 2013 to July 2017 in boreal forest sites in northwestern Ontario, Canada. Each age-class X disturbance had 3 three replicates, matched to 18 permanent circular plots (10-m radius) each with an instrumented tower measuring surface albedo, air and soil temperature, and soil moisture. We also measured leaf area index, species composition and soil organic matter content at each site. BRDF-corrected surface albedo was calculated from daily 30m x 30m reflectance data fused from the MODIS MOD09GA product and Landsat 7 reflectance data. Calculated albedo was verified using ground-based measurements. Results show that fire sites generally had lower (15-25%) albedo than clearcut sites in all seasons. Because of rapid forest regrowth, large perturbations of clearcut harvests on forest albedo started to fade out within a year. Albedo differences between fire and clearcut sites also declined sharply with stand age. Younger stands generally had higher albedo than older stands mainly due to the presence of broadleaf species (for example, Populus tremuloides). In spring, snow melted 10-12 days earlier in recent (2013) clearcut sites compared to closed-canopy sites, causing a sharp reduction in surface albedo in comparison to old clearcut/fire sites (2006 and 1998). Snow melted

  1. Monitoring glacier albedo as a proxy to derive summer and annual surface mass balances from optical remote-sensing data

    Science.gov (United States)

    Davaze, Lucas; Rabatel, Antoine; Arnaud, Yves; Sirguey, Pascal; Six, Delphine; Letreguilly, Anne; Dumont, Marie

    2018-01-01

    Less than 0.25 % of the 250 000 glaciers inventoried in the Randolph Glacier Inventory (RGI V.5) are currently monitored with in situ measurements of surface mass balance. Increasing this archive is very challenging, especially using time-consuming methods based on in situ measurements, and complementary methods are required to quantify the surface mass balance of unmonitored glaciers. The current study relies on the so-called albedo method, based on the analysis of albedo maps retrieved from optical satellite imagery acquired since 2000 by the MODIS sensor, on board the TERRA satellite. Recent studies revealed substantial relationships between summer minimum glacier-wide surface albedo and annual surface mass balance, because this minimum surface albedo is directly related to the accumulation-area ratio and the equilibrium-line altitude. On the basis of 30 glaciers located in the French Alps where annual surface mass balance data are available, our study conducted on the period 2000-2015 confirms the robustness and reliability of the relationship between the summer minimum surface albedo and the annual surface mass balance. For the ablation season, the integrated summer surface albedo is significantly correlated with the summer surface mass balance of the six glaciers seasonally monitored. These results are promising to monitor both annual and summer glacier-wide surface mass balances of individual glaciers at a regional scale using optical satellite images. A sensitivity study on the computed cloud masks revealed a high confidence in the retrieved albedo maps, restricting the number of omission errors. Albedo retrieval artifacts have been detected for topographically incised glaciers, highlighting limitations in the shadow correction algorithm, although inter-annual comparisons are not affected by systematic errors.

  2. Assessment of the accuracy of snow surface direct beam spectral albedo under a variety of overcast skies derived by a reciprocal approach through radiative transfer simulation.

    Science.gov (United States)

    Li, Shusun; Zhou, Xiaobing

    2003-09-20

    With radiative transfer simulations it is suggested that stable estimates of the highly anisotropic direct beam spectral albedo of snow surface can be derived reciprocally under a variety of overcast skies. An accuracy of +/- 0.008 is achieved over a solar zenith angle range of theta0 snow surface albedo for the polar regions where direct measurement of clear-sky surface albedo is limited to large theta0's only. The enhancement will assist in the validation of snow surface albedo models and improve the representation of polar surface albedo in global circulation models.

  3. Landcover Change, Land Surface Temperature, Surface Albedo and Topography in the Plateau Region of North-Central Nigeria

    Directory of Open Access Journals (Sweden)

    Shakirudeen Odunuga

    2015-04-01

    Full Text Available This study assessed the change in some environmental parameters in the Plateau region of North-Central Nigeria (Barakinladi, Jos, and Kafachan environs using the nexus of landcover change, land surface temperature, surface albedo, and topography. The study employed both remote sensing and statistical techniques for the period between 1986 and 2014 to analyze the dynamics between and within these environmental variables. In Barakinladi, the built up landcover change is highest (increasing from 39.53% to 47.59% between 1986 and 2014; LST ranges from 19.09 °C to 38.59 °C in 1986 and from 22.68 °C and 41.68 °C in 2014; and the albedo ranges between 0.014 and 0.154 in 1986 and 0.017 and 0.248 in 2014. In Jos, the built-up landcover occupied 34.26% in 1986 and 36.67% in 2014; LST values range between 20.83 °C and 41.33 °C in 1986 and between 21.61 °C and 42.64 °C in 2014; and the albedo ranges between 0.003 and 0.211 in 1986 and 0.15 and 0.237 in 2014. In Kafachan area, the built up landcover occupied 32.95% in 1986 and 39.01% in 2014. Urbanization and agricultural activities, including animal grazing, were responsible for the gradual loss in vegetation and increasing average LST and albedo. The results also revealed that changing landcover and topography have a relationship with surface albedo and land surface temperature, thereby impacting significantly on ecosystem services delivered by the natural system.

  4. Quality assessment and improvement of the EUMETSAT Meteosat Surface Albedo dataset

    Science.gov (United States)

    Lattanzio, Alessio; Fell, Frank; Bennartz, Ralf; Muller, Jan-Peter; Trigo, Isabel; Löw, Alexander; Schulz, Jörg

    2015-04-01

    Surface albedo is an important parameter for quantifying and understanding the nature of the Earth's radiation budget. This study describes a comprehensive validation of the EUMETSAT Meteosat Surface Albedo (MSA) Climate Data Record (CDR) currently comprising up to 24 years (1982-2006) of continuous surface albedo coverage for large areas covering Africa, Europe and western parts of Asia. In addition it is discussing retrieval improvements as a consequence of the validation results. The MSA CDR has been generated within a project of the WMO entitled Sustained and Coordinated Processing of Environmental Satellite Data for Climate Monitoring (SCOPE-CM) initiative. The MSA CDR went into a two step validation process. Firstly, the satellite product has been compared to available in situ and satellite data assessing systematic and random deviations among the products. This also included an assessment of the temporal stability over desert sites that are assumed to remain stable over time. Furthermore impact on product quality due to anisotropic effects or snow covered surfaces has been analysed. The evaluation has revealed a number of specific strengths and weaknesses. The long-term consistency is very high and meets the Global Climate Observing System (GCOS) stability requirements for desert reference sites. The limitation in quality appears to be due primarily to clouds not removed by the embedded cloud screening procedure as the most significant weakness of the retrieval process. Two alternative strategies are followed to efficiently improve the cloud detection and removal. The first is based on the application of a robust and reliable cloud mask during the retrieval taking advantage of the information contained in the measurements of the infrared and visible bands. The second, in order to screen out outlier values, relies on a post processing analysis of the albedo seasonal variation together with the usage of "a priori" information contained in a background albedo

  5. A model-based framework for the quality assessment of surface albedo in situ measurement protocols

    Science.gov (United States)

    Adams, Jennifer; Gobron, Nadine; Widlowski, Jean-Luc; Mio, Corrado

    2016-09-01

    Satellite-based retrievals of land surface albedo are essential for climate and environmental modelling communities. To be of use, satellite-retrievals are required to comply to given accuracy requirements, mainly achieved through comparison with in situ measurements. Differences between in situ and satellite-based retrievals depend on their actual difference and their associated uncertainties. It is essential that these uncertainties can be computed to properly understand the differences between satellite-based and in situ measurements of albedo, however quantifying the individual contributions of uncertainty is difficult. This study introduces a model-based framework for assessing the quality of in situ albedo measurements. A 3D Monte Carlo Ray Tracing (MCRT) radiative transfer model is used to simulate field measurements of surface albedo, and is able to identify and quantify potential sources of error in the field measurement. Compliance with the World Meteorological Organisation (WMO) requirement for 3% accuracy is tested. 8 scenarios were investigated, covering a range of ecosystem types and canopy structures, seasons, illumination angles and tree heights. Results indicate that height of measurement above the canopy is the controlling factor in accuracy, with each canopy scenario reaching the WMO requirement at different heights. Increasing canopy heterogeneity and tree height noticeably reduces the accuracy, whereas changing seasonality from summer to winter in a deciduous forest increases accuracy. For canopies with a row structure, illumination angle can significantly impact accuracy as a result of shadowing effects. Tests were made on the potential use of multiple in situ measurements, indicating considerably increased accuracy if two or more in situ measurements can be made.

  6. Observational estimation of radiative feedback to surface air temperature over Northern High Latitudes

    Science.gov (United States)

    Hwang, Jiwon; Choi, Yong-Sang; Kim, WonMoo; Su, Hui; Jiang, Jonathan H.

    2018-01-01

    The high-latitude climate system contains complicated, but largely veiled physical feedback processes. Climate predictions remain uncertain, especially for the Northern High Latitudes (NHL; north of 60°N), and observational constraint on climate modeling is vital. This study estimates local radiative feedbacks for NHL based on the CERES/Terra satellite observations during March 2000-November 2014. The local shortwave (SW) and longwave (LW) radiative feedback parameters are calculated from linear regression of radiative fluxes at the top of the atmosphere on surface air temperatures. These parameters are estimated by the de-seasonalization and 12-month moving average of the radiative fluxes over NHL. The estimated magnitudes of the SW and the LW radiative feedbacks in NHL are 1.88 ± 0.73 and 2.38 ± 0.59 W m-2 K-1, respectively. The parameters are further decomposed into individual feedback components associated with surface albedo, water vapor, lapse rate, and clouds, as a product of the change in climate variables from ERA-Interim reanalysis estimates and their pre-calculated radiative kernels. The results reveal the significant role of clouds in reducing the surface albedo feedback (1.13 ± 0.44 W m-2 K-1 in the cloud-free condition, and 0.49 ± 0.30 W m-2 K-1 in the all-sky condition), while the lapse rate feedback is predominant in LW radiation (1.33 ± 0.18 W m-2 K-1). However, a large portion of the local SW and LW radiative feedbacks were not simply explained by the sum of these individual feedbacks.

  7. Assessing modeled Greenland surface mass balance in the GISS Model E2 and its sensitivity to surface albedo

    Science.gov (United States)

    Alexander, Patrick; LeGrande, Allegra N.; Koenig, Lora S.; Tedesco, Marco; Moustafa, Samiah E.; Ivanoff, Alvaro; Fischer, Robert P.; Fettweis, Xavier

    2016-04-01

    The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) plays an important role in global sea level change. Regional Climate Models (RCMs) such as the Modèle Atmosphérique Régionale (MAR) have been employed at high spatial resolution with relatively complex physics to simulate ice sheet SMB. Global climate models (GCMs) incorporate less sophisticated physical schemes and provide outputs at a lower spatial resolution, but have the advantage of modeling the interaction between different components of the earth's oceans, climate, and land surface at a global scale. Improving the ability of GCMs to represent ice sheet SMB is important for making predictions of future changes in global sea level. With the ultimate goal of improving SMB simulated by the Goddard Institute for Space Studies (GISS) Model E2 GCM, we compare simulated GrIS SMB against the outputs of the MAR model and radar-derived estimates of snow accumulation. In order to reproduce present-day climate variability in the Model E2 simulation, winds are constrained to match the reanalysis datasets used to force MAR at the lateral boundaries. We conduct a preliminary assessment of the sensitivity of the simulated Model E2 SMB to surface albedo, a parameter that is known to strongly influence SMB. Model E2 albedo is set to a fixed value of 0.8 over the entire ice sheet in the initial configuration of the model (control case). We adjust this fixed value in an ensemble of simulations over a range of 0.4 to 0.8 (roughly the range of observed summer GrIS albedo values) to examine the sensitivity of ice-sheet-wide SMB to albedo. We prescribe albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) MCD43A3 v6 to examine the impact of a more realistic spatial and temporal variations in albedo. An age-dependent snow albedo parameterization is applied, and its impact on SMB relative to observations and the RCM is assessed.

  8. A framework for consistent estimation of leaf area index, fraction of absorbed photosynthetically active radiation, and surface albedo from MODIS time-series data

    DEFF Research Database (Denmark)

    Xiao, Zhiqiang; Liang, Shunlin; Wang, Jindi

    2015-01-01

    model and the MODIS surface reflectance data. The estimated LAI values were then input into the ACRM to calculate the surface albedo and the fraction of absorbed photosynthetically active radiation (FAPAR). For snow-covered areas, the surface albedo was calculated as the underlying vegetation canopy...... albedo plus the weighted distance between the underlying vegetation canopy albedo and the albedo over deep snow. The LAI/FAPAR and surface albedo values estimated using this framework were compared with MODIS collection 5 eight-day 1-km LAI/FAPAR products (MOD15A2) and 500-m surface albedo product (MCD43......-series MODerate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data. If the reflectance data showed snow-free areas, an ensemble Kalman filter (EnKF) technique was used to estimate leaf area index (LAI) for a two-layer canopy reflectance model (ACRM) by combining predictions from a phenology...

  9. PHOTOMETRIC STEREO SHAPE-AND-ALBEDO-FROM-SHADING FOR PIXEL-LEVEL RESOLUTION LUNAR SURFACE RECONSTRUCTION

    Directory of Open Access Journals (Sweden)

    W. C. Liu

    2017-07-01

    Full Text Available Shape and Albedo from Shading (SAfS techniques recover pixel-wise surface details based on the relationship between terrain slopes, illumination and imaging geometry, and the energy response (i.e., image intensity captured by the sensing system. Multiple images with different illumination geometries (i.e., photometric stereo can provide better SAfS surface reconstruction due to the increase in observations. Photometric stereo SAfS is suitable for detailed surface reconstruction of the Moon and other extra-terrestrial bodies due to the availability of photometric stereo and the less complex surface reflecting properties (i.e., albedo of the target bodies as compared to the Earth. Considering only one photometric stereo pair (i.e., two images, pixel-variant albedo is still a major obstacle to satisfactory reconstruction and it needs to be regulated by the SAfS algorithm. The illumination directional difference between the two images also becomes an important factor affecting the reconstruction quality. This paper presents a photometric stereo SAfS algorithm for pixel-level resolution lunar surface reconstruction. The algorithm includes a hierarchical optimization architecture for handling pixel-variant albedo and improving performance. With the use of Lunar Reconnaissance Orbiter Camera - Narrow Angle Camera (LROC NAC photometric stereo images, the reconstructed topography (i.e., the DEM is compared with the DEM produced independently by photogrammetric methods. This paper also addresses the effect of illumination directional difference in between one photometric stereo pair on the reconstruction quality of the proposed algorithm by both mathematical and experimental analysis. In this case, LROC NAC images under multiple illumination directions are utilized by the proposed algorithm for experimental comparison. The mathematical derivation suggests an illumination azimuthal difference of 90 degrees between two images is recommended to achieve

  10. The effects of additional black carbon on Arctic sea ice surface albedo: variation with sea ice type and snow cover

    OpenAIRE

    A. A. Marks; M. D. King

    2013-01-01

    Black carbon in sea ice will decrease sea ice surface albedo through increased absorption of incident solar radiation, exacerbating sea ice melting. Previous literature has reported different albedo responses to additions of black carbon in sea ice and has not considered how a snow cover may mitigate the effect of black carbon in sea ice. Sea ice is predominately snow covered. Visible light absorption and light scattering coefficients are calculated for a typical first year and multi-y...

  11. An Algorithm for the Retrieval of 30-m Snow-Free Albedo from Landsat Surface Reflectance and MODIS BRDF

    Science.gov (United States)

    Shuai, Yanmin; Masek, Jeffrey G.; Gao, Feng; Schaaf, Crystal B.

    2011-01-01

    We present a new methodology to generate 30-m resolution land surface albedo using Landsat surface reflectance and anisotropy information from concurrent MODIS 500-m observations. Albedo information at fine spatial resolution is particularly useful for quantifying climate impacts associated with land use change and ecosystem disturbance. The derived white-sky and black-sky spectral albedos maybe used to estimate actual spectral albedos by taking into account the proportion of direct and diffuse solar radiation arriving at the ground. A further spectral-to-broadband conversion based on extensive radiative transfer simulations is applied to produce the broadband albedos at visible, near infrared, and shortwave regimes. The accuracy of this approach has been evaluated using 270 Landsat scenes covering six field stations supported by the SURFace RADiation Budget Network (SURFRAD) and Atmospheric Radiation Measurement Southern Great Plains (ARM/SGP) network. Comparison with field measurements shows that Landsat 30-m snow-free shortwave albedos from all seasons generally achieve an absolute accuracy of +/-0.02 - 0.05 for these validation sites during available clear days in 2003-2005,with a root mean square error less than 0.03 and a bias less than 0.02. This level of accuracy has been regarded as sufficient for driving global and regional climate models. The Landsat-based retrievals have also been compared to the operational 16-day MODIS albedo produced every 8-days from MODIS on Terra and Aqua (MCD43A). The Landsat albedo provides more detailed landscape texture, and achieves better agreement (correlation and dynamic range) with in-situ data at the validation stations, particularly when the stations include a heterogeneous mix of surface covers.

  12. Inferring past land use-induced changes in surface albedo from satellite observations: a useful tool to evaluate model simulations

    Directory of Open Access Journals (Sweden)

    J. P. Boisier

    2013-03-01

    Full Text Available Regional cooling resulting from increases in surface albedo has been identified in several studies as the main biogeophysical effect of past land use-induced land cover changes (LCC on climate. However, the amplitude of this effect remains quite uncertain due to, among other factors, (a uncertainties in the extent of historical LCC and, (b differences in the way various models simulate surface albedo and more specifically its dependency on vegetation type and snow cover. We derived monthly albedo climatologies for croplands and four other land cover types from the Moderate Resolution Imaging Spectroradiometer (MODIS satellite observations. We then reconstructed the changes in surface albedo between preindustrial times and present-day by combining these climatologies with the land cover maps of 1870 and 1992 used by seven land surface models (LSMs in the context of the LUCID ("Land Use and Climate: identification of robust Impacts" intercomparison project. These reconstructions show surface albedo increases larger than 10% (absolute in winter, and larger than 2% in summer between 1870 and 1992 over areas that experienced intense deforestation in the northern temperate regions. The historical surface albedo changes estimated with MODIS data were then compared to those simulated by the various climate models participating in LUCID. The inter-model mean albedo response to LCC shows a similar spatial and seasonal pattern to the one resulting from the MODIS-based reconstructions, that is, larger albedo increases in winter than in summer, driven by the presence of snow. However, individual models show significant differences between the simulated albedo changes and the corresponding reconstructions, despite the fact that land cover change maps are the same. Our analyses suggest that the primary reason for those discrepancies is how LSMs parameterize albedo. Another reason, of secondary importance, results from differences in their simulated snow extent

  13. Effect of land cover change on snow free surface albedo across the continental United States

    Science.gov (United States)

    Land cover changes (e.g., forest to grassland) affect albedo, and changes in albedo can influence radiative forcing (warming, cooling). We empirically tested albedo response to land cover change for 130 locations across the continental United States using high resolution (30 m-&t...

  14. The Impact Snow Albedo Feedback over Mountain Regions as Examined through High-Resolution Regional Climate Change Experiments over the Rocky Mountains

    Science.gov (United States)

    Letcher, Theodore

    As the climate warms, the snow albedo feedback (SAF) will play a substantial role in shaping the climate response of mid-latitude mountain regions with transient snow cover. One such region is the Rocky Mountains of the western United States where large snow packs accumulate during the winter and persist throughout the spring. In this dissertation, the Weather Research and Forecast model (WRF) configured as a regional climate model is used to investigate the role of the SAF in determining the regional climate response to forced anthropogenic climate change. The regional effects of climate change are investigated by using the pseudo global warming (PGW) framework, which is an experimental configuration in a which a mean climate perturbation is added to the boundary forcing of a regional model, thus preserving the large-scale circulation entering the region through the model boundaries and isolating the mesoscale climate response. Using this framework, the impact of the SAF on the regional energetics and atmospheric dynamics is examined and quantified. Linear feedback analysis is used to quantify the strength of the SAF over the Headwaters region of the Colorado Rockies for a series of high-resolution PGW experiments. This technique is used to test sensitivity of the feedback strength to model resolution and land surface model. Over the Colorado Rockies, and integrated over the entire spring season, the SAF strength is largely insensitive to model resolution, however there are more substantial differences on the sub-seasonal (monthly) timescale. In contrast, the SAF strength over this region is very sensitive to choice of land surface model. These simulations are also used to investigate how spatial and diurnal variability in warming caused by the SAF influences the dynamics of thermally driven mountain-breeze circulations. It is shown that, the SAF causes stronger daytime mountain-breeze circulations by increasing the warming on the mountains slopes thus enhancing

  15. Impact of soil moisture and winter wheat height from the Loess Plateau in Northwest China on surface spectral albedo

    Science.gov (United States)

    Li, Zhenchao; Yang, Jiaxi; Gao, Xiaoqing; Zheng, Zhiyuan; Yu, Ye; Hou, Xuhong; Wei, Zhigang

    2018-02-01

    The understanding of surface spectral radiation and reflected radiation characteristics of different surfaces in different climate zones aids in the interpretation of regional surface energy transfers and the development of land surface models. This study analysed surface spectral radiation variations and corresponding surface albedo characteristics at different wavelengths as well as the relationship between 5-cm soil moisture and surface albedo on typical sunny days during the winter wheat growth period. The analysis was conducted using observational Loess Plateau winter wheat data from 2015. The results show that the ratio of atmospheric downward radiation to global radiation on typical sunny days is highest for near-infrared wavelengths, followed by visible wavelengths and ultraviolet wavelengths, with values of 57.3, 38.7 and 4.0%, respectively. The ratio of reflected spectral radiation to global radiation varies based on land surface type. The visible radiation reflected by vegetated surfaces is far less than that reflected by bare ground, with surface albedos of 0.045 and 0.27, respectively. Thus, vegetated surfaces absorb more visible radiation than bare ground. The atmospheric downward spectral radiation to global radiation diurnal variation ratios vary for near-infrared wavelengths versus visible and ultraviolet wavelengths on typical sunny days. The near-infrared wavelengths ratio is higher in the morning and evening and lower at noon. The visible and ultraviolet wavelengths ratios are lower in the morning and evening and higher at noon. Visible and ultraviolet wavelength surface albedo is affected by 5-cm soil moisture, demonstrating a significant negative correlation. Excluding near-infrared wavelengths, correlations between surface albedo and 5-cm soil moisture pass the 99% confidence test at each wavelength. The correlation with 5-cm soil moisture is more significant at shorter wavelengths. However, this study obtained surface spectral radiation

  16. Close packing effects on clean and dirty snow albedo and associated climatic implications

    Science.gov (United States)

    He, Cenlin; Takano, Yoshi; Liou, Kuo-Nan

    2017-04-01

    Previous modeling of snow albedo, a key climate feedback parameter, follows the independent scattering approximation (ISA) such that snow grains are considered as a number of separate units with distances longer than wavelengths. Here we develop a new snow albedo model for widely observed close-packed snow grains internally mixed with black carbon (BC) and demonstrate that albedo simulations match closer to observations. Close packing results in a stronger light absorption for clean and BC-contaminated snow. Compared with ISA, close packing reduces pure snow albedos by up to 0.05, whereas it enhances BC-induced snow albedo reduction and associated surface radiative forcing by up to 15% (20%) for fresh (old) snow, with larger enhancements for stronger structure packing. Finally, our results suggest that BC-snow albedo forcing and snow albedo feedback (climate sensitivity) are underestimated in previous modeling studies, making snow close packing consideration a necessity in climate modeling and analysis.

  17. Albedo and land surface temperature shift in hydrocarbon seepage potential area, case study in Miri Sarawak Malaysia

    International Nuclear Information System (INIS)

    Suherman, A; Rahman, M Z A; Busu, I

    2014-01-01

    The presence of hydrocarbon seepage is generally associated with rock or mineral alteration product exposures, and changes of soil properties which manifest with bare development and stress vegetation. This alters the surface thermodynamic properties, changes the energy balance related to the surface reflection, absorption and emission, and leads to shift in albedo and LST. Those phenomena may provide a guide for seepage detection which can be recognized inexpensively by remote sensing method. District of Miri is used for study area. Available topographic maps of Miri and LANDSAT ETM+ were used for boundary construction and determination albedo and LST. Three land use classification methods, namely fixed, supervised and NDVI base classifications were employed for this study. By the intensive land use classification and corresponding statistical comparison was found a clearly shift on albedo and land surface temperature between internal and external seepage potential area. The shift shows a regular pattern related to vegetation density or NDVI value. In the low vegetation density or low NDVI value, albedo of internal area turned to lower value than external area. Conversely in the high vegetation density or high NDVI value, albedo of internal area turned to higher value than external area. Land surface temperature of internal seepage potential was generally shifted to higher value than external area in all of land use classes. In dense vegetation area tend to shift the temperature more than poor vegetation area

  18. Assessing surface albedo change and its induced radiation budget under rapid urbanization with Landsat and GLASS data

    Science.gov (United States)

    Hu, Yonghong; Jia, Gensuo; Pohl, Christine; Zhang, Xiaoxuan; van Genderen, John

    2016-02-01

    Radiative forcing (RF) induced by land use (mainly surface albedo) change is still not well understood in climate change science, especially the effects of changes in urban albedo due to rapid urbanization on the urban radiation budget. In this study, a modified RF derivation approach based on Landsat images was used to quantify changes in the solar radiation budget induced by variations in surface albedo in Beijing from 2001 to 2009. Field radiation records from a Beijing meteorological station were used to identify changes in RF at the local level. There has been rapid urban expansion over the last decade, with the urban land area increasing at about 3.3 % annually from 2001 to 2009. This has modified three-dimensional urban surface properties, resulting in lower albedo due to complex building configurations of urban centers and higher albedo on flat surfaces of suburban areas and cropland. There was greater solar radiation (6.93 × 108 W) in the urban center in 2009 than in 2001. However, large cropland and urban fringe areas caused less solar radiation absorption. RF increased with distance from the urban center (less than 14 km) and with greater urbanization, with the greatest value being 0.41 W/m2. The solar radiation budget in urban areas was believed to be mainly influenced by urban structural changes in the horizontal and vertical directions. Overall, the results presented herein indicate that cumulative urbanization impacts on the natural radiation budget could evolve into an important driver of local climate change.

  19. Effect of land cover change on snow free surface albedo across the continental United States

    Science.gov (United States)

    Wickham, J.; Nash, M.S.; Barnes, Christopher A.

    2016-01-01

    Land cover changes (e.g., forest to grassland) affect albedo, and changes in albedo can influence radiative forcing (warming, cooling). We empirically tested albedo response to land cover change for 130 locations across the continental United States using high resolution (30 m-×-30 m) land cover change data and moderate resolution (~ 500 m-×-500 m) albedo data. The land cover change data spanned 10 years (2001 − 2011) and the albedo data included observations every eight days for 13 years (2001 − 2013). Empirical testing was based on autoregressive time series analysis of snow free albedo for verified locations of land cover change. Approximately one-third of the autoregressive analyses for woody to herbaceous or forest to shrub change classes were not significant, indicating that albedo did not change significantly as a result of land cover change at these locations. In addition, ~ 80% of mean differences in albedo arising from land cover change were less than ± 0.02, a nominal benchmark for precision of albedo measurements that is related to significant changes in radiative forcing. Under snow free conditions, we found that land cover change does not guarantee a significant albedo response, and that the differences in mean albedo response for the majority of land cover change locations were small.

  20. Sensitivity of mountain glacier mass balance to changes in bare-ice albedo

    OpenAIRE

    Naegeli, Kathrin; Huss, Matthias

    2017-01-01

    Albedo is an important parameter in the energy balance of bare-ice surfaces and modulates glacier melt rates. The prolongation of the ablation period enforces the albedo feedback and highlights the need for profound knowledge on impacts of bare-ice albedo on glacier mass balance. In this study, we assess the mass balance sensitivity of 12 Swiss glaciers with abundant long-term in-situ data on changes in bare-ice albedo. We use pixel-based bare-ice albedo derived from Landsat 8. A distributed ...

  1. VIS and NIR land surface albedo sensitivity of the Ent Terrestrial Biosphere Model to forcing leaf area index

    Science.gov (United States)

    Montes, C.; Kiang, N. Y.; Ni-Meister, W.; Yang, W.; Schaaf, C.; Aleinov, I. D.; Jonas, J.; Zhao, F. A.; Yao, T.; Wang, Z.; Sun, Q.; Carrer, D.

    2016-12-01

    Land surface albedo is a major controlling factor in vegetation-atmosphere transfers, modifying the components of the energy budget, the ecosystem productivity and patterns of regional and global climate. General Circulation Models (GCMs) are coupled to Dynamic Global Vegetation Models (DGVMs) to solve vegetation albedo by using simple schemes prescribing albedo based on vegetation classification, and approximations of canopy radiation transport for multiple plant functional types (PFTs). In this work, we aim at evaluating the sensitivity of the NASA Ent Terrestrial Biosphere Model (TBM), a demographic DGVM coupled to the NASA Goddard Institute for Space Studies (GISS) GCM, in estimating VIS and NIR surface albedo by using variable forcing leaf area index (LAI). The Ent TBM utilizes a new Global Vegetation Structure Dataset (GVSD) to account for geographically varying vegetation tree heights and densities, as boundary conditions to the gap-probability based Analytical Clumped Two-Stream (ACTS) canopy radiative transfer scheme (Ni-Meister et al., 2010). Land surface and vegetation characteristics for the Ent GVSD are obtained from a number of earth observation platforms and algorithms, including the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover and plant functional types (PFTs) (Friedl et al., 2010), soil albedo derived from MODIS (Carrer et al., 2014), and vegetation height from the Geoscience Laser Altimeter System (GLAS) on board ICESat (Ice, Cloud, and land Elevation Satellite) (Simard et al., 2011; Tang et al., 2014). Three LAI products are used as input to ACTS/Ent TBM: MODIS MOD15A2H product (Yang et al., 2006), Beijing Normal University LAI (Yuan et al., 2011), and Global Data Sets of Vegetation (LAI3g) (Zhu et al. 2013). The sensitivity of the Ent TBM VIS and NIR albedo to the three LAI products is assessed, compared against the previous GISS GCM vegetation classification and prescribed Lambertian albedoes (Matthews, 1984), and against

  2. Surface and top-of-atmosphere radiative feedback kernels for CESM-CAM5

    Science.gov (United States)

    Pendergrass, Angeline G.; Conley, Andrew; Vitt, Francis M.

    2018-02-01

    Radiative kernels at the top of the atmosphere are useful for decomposing changes in atmospheric radiative fluxes due to feedbacks from atmosphere and surface temperature, water vapor, and surface albedo. Here we describe and validate radiative kernels calculated with the large-ensemble version of CAM5, CESM1.1.2, at the top of the atmosphere and the surface. Estimates of the radiative forcing from greenhouse gases and aerosols in RCP8.5 in the CESM large-ensemble simulations are also diagnosed. As an application, feedbacks are calculated for the CESM large ensemble. The kernels are freely available at https://doi.org/10.5065/D6F47MT6" target="_blank">https://doi.org/10.5065/D6F47MT6, and accompanying software can be downloaded from https://github.com/apendergrass/cam5-kernels" target="_blank">https://github.com/apendergrass/cam5-kernels.

  3. A Remote Sensing Analysis on the Spatiotemporal Variation of Land Surface Albedo and Emissivity in South Florida: An Implication for Surface-Atmosphere Energy and Water Exchange

    Science.gov (United States)

    Kandel, H. P.; Melesse, A. M.

    2016-12-01

    Land use /land cover has wide range of impacts from surface energy budget to radiative forcing of climate change. This study aims to analyze the variation in two radiative properties, albedo and emissivity in South Florida landscape to investigate how radially distinct surfaces lead to a energy and moisture contrast on the near-surface atmosphere and eventually to surface-induced climate. Maps of land surface albedo and emissivity were prepared using algorithms that convert narrow-band spectral reflectance to total short-wave albedo, and vegetation index to emissivity from Landsat -5 TM images of several different summer dates. A comparative analysis was made using the zonal statistics in ArcGIS. Relatively higher albedos were found over cultivated and developed lands (0.17 - 0.21) than in forests and herbaceous wetland (0.09 - 0.16). The emissivities, on the other hand, are lower for developed and drained lands. Average albedo exhibits a slight increase whereas emissivity is found to be decreasing through time. Urban areas showing higher albedos, a unique occurrence in this landscape, store less short-wave radiation, however, their lower emissivities points to increased storage of long-wave radiation. The results imply that the emissivity perhaps play a dominant role in heat island development and initiation of local circulation in urbanized South Florida.

  4. Development of a MODIS-Derived Surface Albedo Data Set: An Improved Model Input for Processing the NSRDB

    Energy Technology Data Exchange (ETDEWEB)

    Maclaurin, Galen [National Renewable Energy Lab. (NREL), Golden, CO (United States); Sengupta, Manajit [National Renewable Energy Lab. (NREL), Golden, CO (United States); Xie, Yu [National Renewable Energy Lab. (NREL), Golden, CO (United States); Gilroy, Nicholas [National Renewable Energy Lab. (NREL), Golden, CO (United States)

    2016-12-01

    A significant source of bias in the transposition of global horizontal irradiance to plane-of-array (POA) irradiance arises from inaccurate estimations of surface albedo. The current physics-based model used to produce the National Solar Radiation Database (NSRDB) relies on model estimations of surface albedo from a reanalysis climatalogy produced at relatively coarse spatial resolution compared to that of the NSRDB. As an input to spectral decomposition and transposition models, more accurate surface albedo data from remotely sensed imagery at finer spatial resolutions would improve accuracy in the final product. The National Renewable Energy Laboratory (NREL) developed an improved white-sky (bi-hemispherical reflectance) broadband (0.3-5.0 ..mu..m) surface albedo data set for processing the NSRDB from two existing data sets: a gap-filled albedo product and a daily snow cover product. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard the Terra and Aqua satellites have provided high-quality measurements of surface albedo at 30 arc-second spatial resolution and 8-day temporal resolution since 2001. The high spatial and temporal resolutions and the temporal coverage of the MODIS sensor will allow for improved modeling of POA irradiance in the NSRDB. However, cloud and snow cover interfere with MODIS observations of ground surface albedo, and thus they require post-processing. The MODIS production team applied a gap-filling methodology to interpolate observations obscured by clouds or ephemeral snow. This approach filled pixels with ephemeral snow cover because the 8-day temporal resolution is too coarse to accurately capture the variability of snow cover and its impact on albedo estimates. However, for this project, accurate representation of daily snow cover change is important in producing the NSRDB. Therefore, NREL also used the Integrated Multisensor Snow and Ice Mapping System data set, which provides daily snow cover observations of the

  5. A Tailorable Structural Composite for GCR and Albedo Neutron Protection on the Lunar Surface, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — A tailorable structural composite that will provide protection from the lunar radiation environment, including GCR and albedo neutrons will be developed. This...

  6. Aerosol Direct, Indirect, Semidirect, and Surface Albedo Effects from Sector Contributions Based on the IPCC AR5 Emissions for Preindustrial and Present-day Conditions

    Science.gov (United States)

    Bauer, Susanne E.; Menon, Surabi

    2012-01-01

    The anthropogenic increase in aerosol concentrations since preindustrial times and its net cooling effect on the atmosphere is thought to mask some of the greenhouse gas-induced warming. Although the overall effect of aerosols on solar radiation and clouds is most certainly negative, some individual forcing agents and feedbacks have positive forcing effects. Recent studies have tried to identify some of those positive forcing agents and their individual emission sectors, with the hope that mitigation policies could be developed to target those emitters. Understanding the net effect of multisource emitting sectors and the involved cloud feedbacks is very challenging, and this paper will clarify forcing and feedback effects by separating direct, indirect, semidirect and surface albedo effects due to aerosols. To this end, we apply the Goddard Institute for Space Studies climate model including detailed aerosol microphysics to examine aerosol impacts on climate by isolating single emission sector contributions as given by the Coupled Model Intercomparison Project Phase 5 (CMIP5) emission data sets developed for Intergovernmental Panel on Climate Change (IPCC) AR5. For the modeled past 150 years, using the climate model and emissions from preindustrial times to present-day, the total global annual mean aerosol radiative forcing is -0.6 W/m(exp 2), with the largest contribution from the direct effect (-0.5 W/m(exp 2)). Aerosol-induced changes on cloud cover often depends on cloud type and geographical region. The indirect (includes only the cloud albedo effect with -0.17 W/m(exp 2)) and semidirect effects (-0.10 W/m(exp 2)) can be isolated on a regional scale, and they often have opposing forcing effects, leading to overall small forcing effects on a global scale. Although the surface albedo effects from aerosols are small (0.016 W/m(exp 2)), triggered feedbacks on top of the atmosphere (TOA) radiative forcing can be 10 times larger. Our results point out that each

  7. Reductions in soil surface albedo as a function of biochar application rate: implications for global radiative forcing

    International Nuclear Information System (INIS)

    Verheijen, Frank G A; Bastos, Ana Catarina; Keizer, Jan Jacob; Jeffery, Simon; Van der Velde, Marijn; Penížek, Vít; Beland, Martin

    2013-01-01

    Biochar can be defined as pyrolysed (charred) biomass produced for application to soils with the aim of mitigating global climate change while improving soil functions. Sustainable biochar application to soils has been estimated to reduce global greenhouse gas emissions by 71–130 Pg CO 2 -C e over 100 years, indicating an important potential to mitigate climate change. However, these estimates ignored changes in soil surface reflection by the application of dark-coloured biochar. Through a laboratory experiment we show a strong tendency for soil surface albedo to decrease as a power decay function with increasing biochar application rate, depending on soil moisture content, biochar application method and land use. Surface application of biochar resulted in strong reductions in soil surface albedo even at relatively low application rates. As a first assessment of the implications for climate change mitigation of these biochar–albedo relationships, we applied a first order global energy balance model to compare negative radiative forcings (from avoided CO 2 emissions) with positive radiative forcings (from reduced soil surface albedos). For a global-scale biochar application equivalent to 120 t ha −1 , we obtained reductions in negative radiative forcings of 5 and 11% for croplands and 11 and 23% for grasslands, when incorporating biochar into the topsoil or applying it to the soil surface, respectively. For a lower global biochar application rate (equivalent to 10 t ha −1 ), these reductions amounted to 13 and 44% for croplands and 28 and 94% for grasslands. Thus, our findings revealed the importance of including changes in soil surface albedo in studies assessing the net climate change mitigation potential of biochar, and we discuss the urgent need for field studies and more detailed spatiotemporal modelling. (letter)

  8. The surface albedo of the Vatnajökull ice cap, Iceland: comparison between satellite-derived and ground-based measurements

    NARCIS (Netherlands)

    Reijmer, C.; Knap, W.H.; Oerlemans, J.

    1999-01-01

    The temporal and spatial variations in the surface albedo of the Vatnajökull ice cap, Iceland, are investigated. A time series of the surface albedo is composed for the summer of 1996 using satellite radiance measurements from the Advanced Very High Resolution Radiometer (AVHRR). This time series is

  9. Use of In Situ and Airborne Multiangle Data to Assess MODIS- and Landsat-based Estimates of Surface Albedo

    Science.gov (United States)

    Roman, Miguel O.; Gatebe, Charles K.; Shuai, Yanmin; Wang, Zhuosen; Gao, Feng; Masek, Jeff; Schaaf, Crystal B.

    2012-01-01

    The quantification of uncertainty of global surface albedo data and products is a critical part of producing complete, physically consistent, and decadal land property data records for studying ecosystem change. A current challenge in validating satellite retrievals of surface albedo is the ability to overcome the spatial scaling errors that can contribute on the order of 20% disagreement between satellite and field-measured values. Here, we present the results from an uncertain ty analysis of MODerate Resolution Imaging Spectroradiometer (MODIS) and Landsat albedo retrievals, based on collocated comparisons with tower and airborne multi-angular measurements collected at the Atmospheric Radiation Measurement Program s (ARM) Cloud and Radiation Testbed (CART) site during the 2007 Cloud and Land Surface Interaction Campaign (CLAS33 IC 07). Using standard error propagation techniques, airborne measurements obtained by NASA s Cloud Absorption Radiometer (CAR) were used to quantify the uncertainties associated with MODIS and Landsat albedos across a broad range of mixed vegetation and structural types. Initial focus was on evaluating inter-sensor consistency through assessments of temporal stability, as well as examining the overall performance of satellite-derived albedos obtained at all diurnal solar zenith angles. In general, the accuracy of the MODIS and Landsat albedos remained under a 10% margin of error in the SW(0.3 - 5.0 m) domain. However, results reveal a high degree of variability in the RMSE (root mean square error) and bias of albedos in both the visible (0.3 - 0.7 m) and near-infrared (0.3 - 5.0 m) broadband channels; where, in some cases, retrieval uncertainties were found to be in excess of 20%. For the period of CLASIC 07, the primary factors that contributed to uncertainties in the satellite-derived albedo values include: (1) the assumption of temporal stability in the retrieval of 500 m MODIS BRDF values over extended periods of cloud

  10. Monitoring spatial and temporal variations of surface albedo on Saint Sorlin Glacier (French Alps using terrestrial photography

    Directory of Open Access Journals (Sweden)

    M. Dumont

    2011-09-01

    Full Text Available Accurate knowledge of temperate glacier mass balance is essential to understand the relationship between glacier and climate. Defined as the reflected fraction of incident radiation over the whole solar spectrum, the surface broadband albedo is one of the most important variable in a glacier's mass balance. This study presents a new method to retrieve the albedo of frozen surfaces from terrestrial photography at visible and near infrared wavelengths. This method accounts for the anisotropic reflectance of snow and ice surfaces and uses a radiative transfer model for narrow-to-broadband conversion. The accuracy of the method was assessed using concomitant measurements of albedo during the summers 2008 and 2009 on Saint Sorlin Glacier (Grandes Rousses, France. These albedo measurements are performed at two locations on the glacier, one in the ablation area and the other in the accumulation zone, with a net radiometer Kipp and Zonen CNR1. The main sources of uncertainty are associated with the presence of high clouds and the georeferencing of the photographs.

  11. Black carbon aerosols over the Himalayas: direct and surface albedo forcing

    Directory of Open Access Journals (Sweden)

    Vijayakumar S. Nair

    2013-09-01

    Full Text Available Absorbing aerosols such as black carbon (BC or dust over high-altitude Himalayan regions have potential implications on the regional climate and hydrological cycle over South Asia. Making use of extensive measurements of atmospheric BC from several Himalayan stations, an assessment of radiative forcing due to direct and snow-albedo darkening is examined. Generally, BC concentration in the atmosphere peaks during pre-monsoon season over the Himalayas and the climatological mean of atmospheric BC over Hanle (western Himalayas, 4.5 km msl and Nepal Climate Observatory-Pyramid (central Himalayas, 5 km msl are 106±27 ng m−3 and 190±95 ng m−3, respectively. Based on the optical and physical properties of composite aerosols measured at Hanle, clear sky direct radiative forcing (DRF at the top of the atmosphere is estimated as 1.69 W m−2 over snow surface and −1.54 W m−2 over sandy surface during pre-monsoon season. The estimated amount of BC in the snow varied from 117 to 1.7 µg kg−1 for wide range of dry deposition velocities (0.01–0.054 cm s−1 of BC, snow depth (2–10 cm and snow densities (195–512 kg m−3. Using a size-resolved wet scavenging parametrisation, the amount of BC on snow due to wet scavenging is estimated as 29 µg kg−1 for an accumulated snow depth of 27 cm. For the range of 10–200 µg kg−1 of BC in snow, the diurnally averaged forcing due to snow darkening has been found to vary from 0.87 to 10.2 W m−2 for fresh snow and from 2.6 to 28.1 W m−2 for the aged snow, which is significantly higher than the DRF. The direct and surface albedo radiative forcing could lead to significant warming over the Himalayas during pre-monsoon.

  12. ISLSCP II MODIS (Collection 4) Albedo, 2002

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: The MODIS BRDF/Albedo Product (MOD43B) provides measures of clear sky surface albedo every 16 days. Both white-sky albedo (bihemispherical reflectance) and...

  13. Decreased surface albedo driven by denser vegetation on the Tibetan Plateau

    International Nuclear Information System (INIS)

    Tian, Li; Zhang, Yangjian; Zhu, Juntao

    2014-01-01

    The Tibetan Plateau (TP) has fundamental ecological and environmental significance to China and Asia through its influence on regional and continental climates. In recent years, climate warming has caused unprecedented changes to land surface processes on the TP, which would unavoidably undermine the ecological and environmental functions of the TP. Among the numerous land surface processes potentially impacted by climate warming, the effect of vegetation greenness on surface energy balance is one of the most critical, but has been long ignored. In this study, we investigated the spatial and temporal patterns of land surface albedo (LSA) on the TP and evaluated the vegetation greenness in relation to patterns of LSA. We found that LSA has been decreasing in most of the vegetated grasslands on the TP from 2000 to 2013, as compared to a flat trend for desert area. The regions where LSA has been decreasing were spatially correlated to areas of increased vegetation greenness. Along rising altitude, LSA decreasing rate exhibited an overall decreasing trend. Across the TP, elevated vegetation greenness in grasslands acted as a primary factor pulling down LSA. The driving effects of vegetation greenness on LSA vary with grassland types, as revealed by a more significant relationship between vegetation greenness and LSA for the sparsely vegetated zone (i.e. steppe) than the more densely vegetated zone (i.e. meadow). Furthermore, the driving effect of vegetation greenness on LSA exhibited an obvious dependence on altitude as effects with rising altitude were relatively strong up to 3000 m, then weakened from 3500 m to 5000 m, and then the effects again increased from 5000 to 6000 m. The growing season LSA trend revealed in this study emphasizes the need to give greater attention to the growing season LSA flux in future surface energy balance studies. (letter)

  14. Time-Dependent Cryospheric Longwave Surface Emissivity Feedback in the Community Earth System Model

    Science.gov (United States)

    Kuo, Chaincy; Feldman, Daniel R.; Huang, Xianglei; Flanner, Mark; Yang, Ping; Chen, Xiuhong

    2018-01-01

    Frozen and unfrozen surfaces exhibit different longwave surface emissivities with different spectral characteristics, and outgoing longwave radiation and cooling rates are reduced for unfrozen scenes relative to frozen ones. Here physically realistic modeling of spectrally resolved surface emissivity throughout the coupled model components of the Community Earth System Model (CESM) is advanced, and implications for model high-latitude biases and feedbacks are evaluated. It is shown that despite a surface emissivity feedback amplitude that is, at most, a few percent of the surface albedo feedback amplitude, the inclusion of realistic, harmonized longwave, spectrally resolved emissivity information in CESM1.2.2 reduces wintertime Arctic surface temperature biases from -7.2 ± 0.9 K to -1.1 ± 1.2 K, relative to observations. The bias reduction is most pronounced in the Arctic Ocean, a region for which Coupled Model Intercomparison Project version 5 (CMIP5) models exhibit the largest mean wintertime cold bias, suggesting that persistent polar temperature biases can be lessened by including this physically based process across model components. The ice emissivity feedback of CESM1.2.2 is evaluated under a warming scenario with a kernel-based approach, and it is found that emissivity radiative kernels exhibit water vapor and cloud cover dependence, thereby varying spatially and decreasing in magnitude over the course of the scenario from secular changes in atmospheric thermodynamics and cloud patterns. Accounting for the temporally varying radiative responses can yield diagnosed feedbacks that differ in sign from those obtained from conventional climatological feedback analysis methods.

  15. Derivation of Land Surface Albedo at High Resolution by Combining HJ-1A/B Reflectance Observations with MODIS BRDF Products

    Directory of Open Access Journals (Sweden)

    Bo Gao

    2014-09-01

    Full Text Available Land surface albedo is an essential parameter for monitoring global/regional climate and land surface energy balance. Although many studies have been conducted on global or regional land surface albedo using various remote sensing data over the past few decades, land surface albedo product with a high spatio–temporal resolution is currently very scarce. This paper proposes a method for deriving land surface albedo with a high spatio–temporal resolution (space: 30 m and time: 2–4 days. The proposed method works by combining the land surface reflectance data at 30 m spatial resolution obtained from the charge-coupled devices in the Huanjing-1A and -1B (HJ-1A/B satellites with the Moderate Resolution Imaging Spectroradiometer (MODIS land surface bidirectional reflectance distribution function (BRDF parameters product (MCD43A1, which is at a spatial resolution of 500 m. First, the land surface BRDF parameters for HJ-1A/B land surface reflectance with a spatial–temporal resolutions of 30 m and 2–4 day are calculated on the basis of the prior knowledge from the MODIS BRDF product; then, the calculated high resolution BRDF parameters are integrated over the illuminating/viewing hemisphere to produce the white- and black-sky albedos at 30 m resolution. These results form the basis for the final land surface albedo derivation by accounting for the proportion of direct and diffuse solar radiation arriving at the ground. The albedo retrieved by this novel method is compared with MODIS land surface albedo products, as well as with ground measurements. The results show that the derived land surface albedo during the growing season of 2012 generally achieved a mean absolute accuracy of ±0.044, and a root mean square error of 0.039, confirming the effectiveness of the newly proposed method.

  16. SAFARI 2000 Surface Albedo and Radiation Fluxes at Mongu and Skukuza, 2000-2002

    Data.gov (United States)

    National Aeronautics and Space Administration — Top-of-the-canopy broadband albedo and radiation fluxes are calculated from measurements at the Mongu and Skukuza flux tower sites in southern Africa from March 2000...

  17. High-resolution mapping and modelling of surface albedo in Norwegian boreal forests: from remotely sensed data to predictions

    Science.gov (United States)

    Cherubini, Francesco; Hu, Xiangping; Vezhapparambu, Sajith; Stromman, Anders

    2017-04-01

    Surface albedo, a key parameter of the Earth's climate system, has high variability in space, time, and land cover and its parameterization is among the most important variables in climate models. The lack of extensive estimates for model improvement is one of the main limitations for accurately quantifying the influence of surface albedo changes on the planetary radiation balance. We use multi-year satellite retrievals of MODIS surface albedo (MCD43A3), high resolution land cover maps, and meteorological records to characterize albedo variations in Norway across latitude, seasons, land cover type, and topography. We then use this dataset to elaborate semi-empirical models to predict albedo values as a function of tree species, age, volume and climate variables like temperature and snow water equivalents (SWE). Given the complexity of the dataset and model formulation, we apply an innovative non-linear programming approach simultaneously coupled with linear un-mixing. The MODIS albedo products are at a resolution of about 500 m and 8 days. The land cover maps provide vegetation structure information on relative abundance of tree species, age, and biomass volumes at 16 m resolution (for both deciduous and coniferous species). Daily observations of meteorological information on air temperature and SWE are produced at 1 km resolution from interpolation of meteorological weather stations in Norway. These datasets have different resolution and projection, and are harmonized by identifying, for each MODIS pixel, the intersecting land cover polygons and the percentage area of the MODIS pixel represented by each land cover type. We then filter the subplots according to the following criteria: i) at least 96% of the total pixel area is covered by a single land cover class (either forest or cropland); ii) if forest area, at least 98% of the forest area is covered by spruce, deciduous or pine. Forested pixels are then categorized as spruce, deciduous, or pine dominant if the

  18. Modeling glacier-surface albedo across Svalbard for the 1979-2015 period: The HiRSvaC500-α data set

    Science.gov (United States)

    Möller, Marco; Möller, Rebecca

    2017-03-01

    Albedo is an important quantity for determining the energy balance of snow and ice surfaces and thus also for the mass balance of glaciers. It is especially important in polar regions where shortwave radiation fluxes typically provide most of the energy input to a glacier. In order to use albedo data in any spatially distributed glaciological modeling, it is vital that the albedo fields are not only of high accuracy but also available on sufficiently high spatial resolution and in a manner that is consistent over time. This article presents the newly developed data set HiRSvaC500-α, which provides daily updated, gapless albedo fields for all glacierized areas of the Arctic archipelago Svalbard on a 500 m resolution over the period 1979-2015. Albedo modeling for creation of the data set is done using a multistep geostatistical approach on the basis of remotely sensed Moderate Resolution Imaging Spectroradiometer (MODIS) albedo data and gridded ERA-Interim climate data. Validation of the modeled HiRSvaC500-α albedo fields against in situ albedo measurements at automatic weather stations operated on two different glaciers suggests that the accuracy of the newly developed data set lies close to that of remotely sensed MODIS albedo data. An analysis of the HiRSvaC500-α albedo data set yields a mean annual-average albedo of 0.754 across all glaciers of Svalbard over 1979-2015. A decrease of albedo with time is found, following a highly significant (95% level) trend of -0.010 per decade. For certain subregions, this trend even reaches up to -0.014 per decade.

  19. Evaluation of the global MODIS 30 arc-second spatially and temporally complete snow-free land surface albedo and reflectance anisotropy dataset

    Science.gov (United States)

    Sun, Qingsong; Wang, Zhuosen; Li, Zhan; Erb, Angela; Schaaf, Crystal B.

    2017-06-01

    Land surface albedo is an essential variable for surface energy and climate modeling as it describes the proportion of incident solar radiant flux that is reflected from the Earth's surface. To capture the temporal variability and spatial heterogeneity of the land surface, satellite remote sensing must be used to monitor albedo accurately at a global scale. However, large data gaps caused by cloud or ephemeral snow have slowed the adoption of satellite albedo products by the climate modeling community. To address the needs of this community, we used a number of temporal and spatial gap-filling strategies to improve the spatial and temporal coverage of the global land surface MODIS BRDF, albedo and NBAR products. A rigorous evaluation of the gap-filled values shows good agreement with original high quality data (RMSE = 0.027 for the NIR band albedo, 0.020 for the red band albedo). This global snow-free and cloud-free MODIS BRDF and albedo dataset (established from 2001 to 2015) offers unique opportunities to monitor and assess the impact of the changes on the Earth's land surface.

  20. Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet.

    Science.gov (United States)

    Yallop, Marian L; Anesio, Alexandre M; Perkins, Rupert G; Cook, Joseph; Telling, Jon; Fagan, Daniel; MacFarlane, James; Stibal, Marek; Barker, Gary; Bellas, Chris; Hodson, Andy; Tranter, Martyn; Wadham, Jemma; Roberts, Nicholas W

    2012-12-01

    Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet.

  1. Enhancement of the MODIS Daily Snow Albedo Product

    Science.gov (United States)

    Hall, Dorothy K.; Schaaf, Crystal B.; Wang, Zhuosen; Riggs, George A.

    2009-01-01

    The MODIS daily snow albedo product is a data layer in the MOD10A1 snow-cover product that includes snow-covered area and fractional snow cover as well as quality information and other metadata. It was developed to augment the MODIS BRDF/Albedo algorithm (MCD43) that provides 16-day maps of albedo globally at 500-m resolution. But many modelers require daily snow albedo, especially during the snowmelt season when the snow albedo is changing rapidly. Many models have an unrealistic snow albedo feedback in both estimated albedo and change in albedo over the seasonal cycle context, Rapid changes in snow cover extent or brightness challenge the MCD43 algorithm; over a 16-day period, MCD43 determines whether the majority of clear observations was snow-covered or snow-free then only calculates albedo for the majority condition. Thus changes in snow albedo and snow cover are not portrayed accurately during times of rapid change, therefore the current MCD43 product is not ideal for snow work. The MODIS daily snow albedo from the MOD10 product provides more frequent, though less robust maps for pixels defined as "snow" by the MODIS snow-cover algorithm. Though useful, the daily snow albedo product can be improved using a daily version of the MCD43 product as described in this paper. There are important limitations to the MOD10A1 daily snow albedo product, some of which can be mitigated. Utilizing the appropriate per-pixel Bidirectional Reflectance Distribution Functions (BRDFs) can be problematic, and correction for anisotropic scattering must be included. The BRDF describes how the reflectance varies with view and illumination geometry. Also, narrow-to-broadband conversion specific for snow on different surfaces must be calculated and this can be difficult. In consideration of these limitations of MOD10A1, we are planning to improve the daily snow albedo algorithm by coupling the periodic per-pixel snow albedo from MCD43, with daily surface ref|outanoom, In this paper, we

  2. AVHRR Surface Temperature and Narrow-Band Albedo Comparison with Ground Measurements for the Greenland Ice Sheet

    Science.gov (United States)

    Haefliger, M.; Steffen, K.; Fowler, C.

    1993-01-01

    An ice-surface temperature retrieval algorithm for the Greenland ice sheet was developed using NOAA 11 thermal radiances from channels 4 and 5. Temperature, pressure and humidity profiles, cloud observations and skin temperatures from the Swiss Federal Institute of Technology (ETH) camp, located at the equilibrium line altitude at 49 deg17 min W, 69 deg 34 min N, were used in the LOWTRAN 7 model. Through a statistical analysis of daily clear sky profiles, the coefficients that correct for the atmospheric effects were determined for the ETH-Camp field season (May to August). Surface temperatures retrieved by this method were then compared against the in situ observations with a maximum difference of 0.6 K. The NOAA 11 narrow-band planetary albedo values for channels 1 and 2 were calculated using pre-launch calibration coefficients. Scattering and absorption by the atmosphere were modelled with LOWTRAN 7. Then, narrow-band albedo values for the AVHRR visible and near infrared channels were compared with in situ high resolution spectral reflectance measurements. In the visible band (580-680 nm), AVHRR-derived narrow-band albedo and the in situ measurements corrected with radiative transfer model LOWTRAN 7 showed a difference of less than 2%. For the near infrared channel (725-1100 nm) the difference between the measured and modelled narrow-band albedo was 14%. These discrepancies could be either the result of inaccurate aerosol scattering modelling (lack of the in situ observation), or the result of sensor drift due to degradation.

  3. The influence of rolled erosion control systems on soil temperature and surface albedo: part I. A greenhouse experiment

    International Nuclear Information System (INIS)

    Sutherland, R.A.; Menard, T.; Perry, J.L.; Penn, D.C.

    1998-01-01

    A greenhouse study examined the influences of various surface covers (a bare control soil and seven rolled erosion control systems—RECS) on surface radiative properties, and soil temperature. In our companion paper we examine relationships with soil moisture, biomass production, and nutrient assimilation. Randomization and replication were key components to our study of microclimate under tropical radiation conditions. The bare Oxisol control soil exhibited the most extreme microclimatic conditions with the lowest albedo (not significantly different from that of P300© North American Green, a dark green polypropylene system), and the highest mean and maximum hourly temperatures recorded at depths of 5 and 8 cm. This hostile climatic environment was not conducive to biomass production or moisture storage and it is likely that the observed soil surface crusts impeded plant emergence. Rolled erosion control systems, on the other hand, generally moderated soil temperatures by reflecting more shortwave radiation, implying less heat energy at the surface for conduction to the soil. The result was that RECS exhibited lower mean soil temperatures, higher minimum temperatures and lower maximum soil temperatures. An aspen excelsior system (Curlex I© Excelsior) had the highest albedo and the soil beneath this system exhibited the greatest temperature modulation. Open-weave systems composed of jute (Geojute© Price & Pictures) and coconut fibers (BioD-Mat 70© RoLanka) were the RECS most similar in temperature response to the bare control soil. Other systems examined were intermediate in their temperature response and surface albedo (i.e., SC150BN© North American Green, C125© North American Green and Futerra© Conwed Fibers). (author)

  4. Sea Ice, Clouds, Sunlight, and Albedo: The Umbrella Versus the Blanket

    Science.gov (United States)

    Perovich, D. K.

    2017-12-01

    The Arctic sea ice cover has undergone a major decline in recent years, with reductions in ice extent, ice thickness, and ice age. Understanding the feedbacks and forcing driving these changes is critical in improving predictions. The surface radiation budget plays a central role in summer ice melt and is governed by clouds and surface albedo. Clouds act as an umbrella reducing the downwelling shortwave, but also serve as a blanket increasing the downwelling longwave, with the surface albedo also determining the net balance. Using field observations from the SHEBA program, pairs of clear and cloudy days were selected for each month from May through September and the net radiation flux was calculated for different surface conditions and albedos. To explore the impact of albedo we calculated a break even albedo, where the net radiation for cloudy skies is the same as clear skies. For albedos larger than the break-even value the net radiation flux is smaller under clear skies compared to cloudy skies. Break-even albedos ranged from 0.30 in September to 0.58 in July. For snow covered or bare ice, clear skies always resulted in less radiative heat input. In contrast, leads always had, and ponds usually had, more radiative heat input under clear skies than cloudy skies. Snow covered ice had a net radiation flux that was negative or near zero under clear skies resulting in radiative cooling. We combined the albedo of individual ice types with the area of those ice types to calculate albedos averaged over a 50 km x 50 km area. The July case had the smallest areally averaged albedo of 0.50. This was less than the breakeven albedo, so cloudy skies had a smaller net radiation flux than clear skies. For the cases from the other four months, the areally averaged albedo was greater than the break-even albedo. The areally averaged net radiation flux was negative under clear skies for the May and September cases.

  5. Fire-induced albedo change and surface radiative forcing in sub-Saharan Africa savanna ecosystems: Implications for the energy balance

    Science.gov (United States)

    Dintwe, Kebonye; Okin, Gregory S.; Xue, Yongkang

    2017-06-01

    Surface albedo is a critical parameter that controls surface energy balance. In dryland ecosystems, fires play a significant role in decreasing surface albedo, resulting in positive radiative forcing. Here we investigate the long-term effect of fire on surface albedo. We devised a method to calculate short-, medium-, and long-term effect of fire-induced radiative forcing and their relative effects on energy balance. We used Moderate Resolution Imaging Spectroradiometer (MODIS) data in our analysis, covering different vegetation classes in sub-Saharan Africa (SSA). Our analysis indicated that mean short-term fire-induced albedo change in SSA was -0.022, -0.035, and -0.041 for savannas, shrubland, and grasslands, respectively. At regional scale, mean fire-induced albedo change in savannas was -0.018 and -0.024 for northern sub-Saharan of Africa and the southern hemisphere Africa, respectively. The short-term mean fire-induced radiative forcing in burned areas in sub-Saharan Africa (SSA) was 5.41 W m-2, which contributed continental and global radiative forcings of 0.25 and 0.058 W m-2, respectively. The impact of fire in surface albedo has long-lasting effects that varies with vegetation type. The long-term energetic effects of fire-induced albedo change and associated radiative forcing were, on average, more than 19 times greater across SSA than the short-term effects, suggesting that fires exerted far more radiative forcing than previously thought. Taking into account the actual duration of fire's effect on surface albedo, we conclude that the contribution of SSA fires, globally and throughout the year, is 0.12 W m-2. These findings provide crucial information on possible impact of fire on regional climate variability.

  6. Temporal Arctic longwave surface emissivity feedbacks in the Community Earth System Model

    Science.gov (United States)

    Kuo, C.; Feldman, D.; Huang, X.; Flanner, M.; Yang, P.; Chen, X.

    2017-12-01

    We have investigated how the inclusion of realistic and consistent surface emissivity in both land-surface and atmospheric components of the CESM coupled-climate model affects a wide range of climate variables. We did this by replacing the unit emissivity values in RRTMG_LW for water, fine-grained snow, and desert scenes with spectral emissivity values, and by replacing broadband emissivity values in surface components with the Planck-curve weighted counterparts. We find that this harmonized treatment of surface emissivity within CESM can be important for reducing high-latitude temperature biases. We also find that short-term effects of atmospheric dynamics and spectral information need to be considered to understand radiative effects in higher detail, and are possible with radiative kernels computed for every grid and time point for the entire model integration period. We find that conventional climatological feedback calculations indicate that sea-ice emissivity feedback is positive in sign, but that the radiative effects of the difference in emissivity between frozen and unfrozen surfaces exhibit seasonal dependence. Furthermore, this seasonality itself exhibits meridional asymmetry due to differences in sea-ice response to climate forcing between the Arctic and the Antarctic. In the Arctic, this seasonal, temporally higher order analysis exhibits increasing outgoing surface emissivity radiative response in a warming climate. While the sea-ice emissivity feedback and seasonal sea-ice emissivity radiative response amplitudes are a few percent of surface albedo feedbacks, the feedback analysis methods outlined in this work demonstrate that spatially and temporally localized feedback analysis can give insight into the mechanisms at work on those scales which differ in amplitude and sign from conventional climatological analyses. We note that the inclusion of this realistic physics leads to improved agreement between CESM model results and Arctic surface

  7. Correction of sub-pixel topographical effects on land surface albedo retrieved from geostationary satellite (FengYun-2D) observations

    International Nuclear Information System (INIS)

    Roupioz, L; Nerry, F; Jia, L; Menenti, M

    2014-01-01

    The Qinghai-Tibetan Plateau is characterised by a very strong relief which affects albedo retrieval from satellite data. The objective of this study is to highlight the effects of sub-pixel topography and to account for those effects when retrieving land surface albedo from geostationary satellite FengYun-2D (FY-2D) data with 1.25km spatial resolution using the high spatial resolution (30 m) data of the Digital Elevation Model (DEM) from ASTER. The methodology integrates the effects of sub-pixel topography on the estimation of the total irradiance received at the surface, allowing the computation of the topographically corrected surface reflectance. Furthermore, surface albedo is estimated by applying the parametric BRDF (Bidirectional Reflectance Distribution Function) model called RPV (Rahman-Pinty-Verstraete) to the terrain corrected surface reflectance. The results, evaluated against ground measurements collected over several experimental sites on the Qinghai-Tibetan Plateau, document the advantage of integrating the sub-pixel topography effects in the land surface reflectance at 1km resolution to estimate the land surface albedo. The results obtained after using sub-pixel topographic correction are compared with the ones obtained after using pixel level topographic correction. The preliminary results imply that, in highly rugged terrain, the sub-pixel topography correction method gives more accurate results. The pixel level correction tends to overestimate surface albedo

  8. Seasonal changes in surface albedo of Himalayan glaciers from MODIS data and links with the annual mass balance

    Directory of Open Access Journals (Sweden)

    F. Brun

    2015-02-01

    Full Text Available Few glaciological field data are available on glaciers in the Hindu Kush–Karakoram–Himalayan (HKH region, and remote sensing data are thus critical for glacier studies in this region. The main objectives of this study are to document, using satellite images, the seasonal changes of surface albedo for two Himalayan glaciers, Chhota Shigri Glacier (Himachal Pradesh, India and Mera Glacier (Everest region, Nepal, and to reconstruct the annual mass balance of these glaciers based on the albedo data. Albedo is retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS images, and evaluated using ground based measurements. At both sites, we find high coefficients of determination between annual minimum albedo averaged over the glacier (AMAAG and glacier-wide annual mass balance (Ba measured with the glaciological method (R2 = 0.75. At Chhota Shigri Glacier, the relation between AMAAG found at the end of the ablation season and Ba suggests that AMAAG can be used as a proxy for the maximum snow line altitude or equilibrium line altitude (ELA on winter-accumulation-type glaciers in the Himalayas. However, for the summer-accumulation-type Mera Glacier, our approach relied on the hypothesis that ELA information is preserved during the monsoon. At Mera Glacier, cloud obscuration and snow accumulation limits the detection of albedo during the monsoon, but snow redistribution and sublimation in the post-monsoon period allows for the calculation of AMAAG. Reconstructed Ba at Chhota Shigri Glacier agrees with mass balances previously reconstructed using a positive degree-day method. Reconstructed Ba at Mera Glacier is affected by heavy cloud cover during the monsoon, which systematically limited our ability to observe AMAAG at the end of the melting period. In addition, the relation between AMAAG and Ba is constrained over a shorter time period for Mera Glacier (6 years than for Chhota Shigri Glacier (11 years. Thus the mass balance reconstruction

  9. Operational Estimates of Surface Albedo, Vegetation Photosynthetic Activity and Surface Structure: An Overview of the GVM/SAI Activities

    Science.gov (United States)

    Verstraete, M. M.; Pinty, B.; Gobron, N.; Widlowski, J.

    2001-05-01

    The GVM Unit of the SAI derives reliable, accurate, quantitative information on the state and evolution of the biosphere from remote sensing data, using state of the art techniques. This information is provided to various services of the European Commission in support of the verification of compliance with national and international treaties, protocols and conventions, and to the scientific community in the framework of defined collaborations. Estimates of land surface albedo have been obtained from an analysis of monospectral but multiangular observations from the geostationary Meteosat platform. An analysis of these results has shown the continental scale impact of human activities (in particular biomass burning over large areas). An extension of this approach to the more advanced Meteosat Second Generation platform, to be launched in 2002, will yield more and better products. High performance yet very fast algorithms have been derived to optimally assess the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) of live green vegetation, which largely controls the productivity of plants and therefore their ability to sequester atmospheric carbon dioxide. These algorithms, typically used with multispectral but monoangular sensors such as AVHRR, SeaWiFS, or VEGETATION, have now been further developed to take advantage of the high spatial resolution or multiangular views offered by modern sensors such as the MISR on NASA's Terra platform. Recent advances in radiation transfer modeling and scientific collaborations with the cloud community have opened new vistas on the possibility of characterizing the structure of ecosystems a the sub-pixel scale on the basis of multiangular data, and may lead to improved land cover classifications and new applications.

  10. Comparing MODIS-Terra and GOES surface albedo for New York City NY, Baltimore MD and Washington DC for 2005

    Science.gov (United States)

    Mubenga, K.; Hoff, R.; McCann, K.; Chu, A.; Prados, A.

    2006-05-01

    The NOAA GOES Aerosol and Smoke Product (GASP) is a product displaying the Aerosol Optical Depth (AOD) over the United States. The GASP retrieval involves discriminating the upwelling radiance from the atmosphere from that of the variable underlying surface. Unlike other sensors with more visible and near- infrared spectral channels such as MODIS, the sensors on GOES 8 through 12 only have one visible and a several far infrared channels. The GASP algorithm uses the detection of the second-darkest pixel from the visible channel over a 28-day period as the reference from which a radiance look-up table gives the corresponding AOD. GASP is reliable in capturing the AOD during large events. As an example, GASP was able to precisely show the Alaska and British Columbia smoke plume advecting from Alaska to the northeastern U.S. during the summer of 2004. Knapp et al. (2005) has shown that the AOD retrieval for GOES- 8 is within +/-0.13 of AERONET ground data with a coefficient of correlation of 0.72. Prados (this meeting) will update that study. However, GASP may not be as reliable when it comes to observing smaller AOD events in the northeast where the surface brightness is relatively high. The presence of large cities, such as New York, increases the surface albedo and produces a bright background against which it may be difficult to deduce the AOD. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the Earth Observing System Terra and Aqua platforms provides an independent measurement of the surface albedo at a resolution greater than available on GOES. In this research, the MODIS and GOES surface albedo product for New York, Washington and Baltimore are compared in order to see how we can improve the AOD retrieval in urban areas for air quality applications. Ref: K. Knapp et al. 2005. Toward aerosol optical depth retrievals over land from GOES visible radiances: determining surface reflectance. Int.Journal of Remote Sensing 26, 4097-4116

  11. Influence of Dust and Black Carbon on the Snow Albedo in the NASA Goddard Earth Observing System Version 5 Land Surface Model

    Science.gov (United States)

    Yasunari, Teppei J.; Koster, Randal D.; Lau, K. M.; Aoki, Teruo; Sud, Yogesh C.; Yamazaki, Takeshi; Motoyoshi, Hiroki; Kodama, Yuji

    2011-01-01

    Present-day land surface models rarely account for the influence of both black carbon and dust in the snow on the snow albedo. Snow impurities increase the absorption of incoming shortwave radiation (particularly in the visible bands), whereby they have major consequences for the evolution of snowmelt and life cycles of snowpack. A new parameterization of these snow impurities was included in the catchment-based land surface model used in the National Aeronautics and Space Administration Goddard Earth Observing System version 5. Validation tests against in situ observed data were performed for the winter of 2003.2004 in Sapporo, Japan, for both the new snow albedo parameterization (which explicitly accounts for snow impurities) and the preexisting baseline albedo parameterization (which does not). Validation tests reveal that daily variations of snow depth and snow surface albedo are more realistically simulated with the new parameterization. Reasonable perturbations in the assigned snow impurity concentrations, as inferred from the observational data, produce significant changes in snowpack depth and radiative flux interactions. These findings illustrate the importance of parameterizing the influence of snow impurities on the snow surface albedo for proper simulation of the life cycle of snow cover.

  12. Remote sensing of surface hemispherical reflectance (albedo) using pointable multispectral imaging spectroradiometers

    Science.gov (United States)

    Kimes, D. S.; Deering, D. W.

    1992-01-01

    Remote techniques for determining albedo are examined in terms of the range of view angles required in the use of string techniques with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the High Resolution Imaging Spectroradiometer (HIRIS). Ground data are used to compute full and half strings out to 15, 30, 45, and 60 degrees for various sun angles and ground cover types. A knowledge-based system is employed to evaluate both the visible and near-IR bands, and the results indicate errors of up to 7 percent for the MODIS data, HIRIS data, and the full-string +/- 60 degrees. In the cases of large extrapolations greater ranges of error are noted indicating that 60-deg systems are most effective. The error is increased in the case of sensor systems that only view in the fore or aft direction, and the MODIS full string for +/- 45 deg is also considered a good system.

  13. Quantifying the effect of crops surface albedo variability on GHG budgets in a life cycle assessment approach : methodology and results.

    Science.gov (United States)

    Ferlicoq, Morgan; Ceschia, Eric; Brut, Aurore; Tallec, Tiphaine

    2013-04-01

    We tested a new method to estimate the radiative forcing of several crops at the annual and rotation scales, using local measurements data from two ICOS experimental sites. We used jointly 1) the radiative forcing caused by greenhouse gas (GHG) net emissions, calculated by using a Life Cycle Analysis (LCA) approach and in situ measurements (Ceschia et al. 2010), and 2) the radiative forcing caused by rapid changes in surface albedo typical from those ecosystems and resulting from management and crop phenology. The carbon and GHG budgets (GHGB) of 2 crop sites with contrasted management located in South West France (Auradé and Lamasquère sites) was estimated over a complete rotation by combining a classical LCA approach with on site flux measurements. At both sites, carbon inputs (organic fertilisation and seeds), carbon exports (harvest) and net ecosystem production (NEP), measured with the eddy covariance technique, were calculated. The variability of the different terms and their relative contributions to the net ecosystem carbon budget (NECB) were analysed for all site-years, and the effect of management on NECB was assessed. To account for GHG fluxes that were not directly measured on site, we estimated the emissions caused by field operations (EFO) for each site using emission factors from the literature. The EFO were added to the NECB to calculate the total GHGB for a range of cropping systems and management regimes. N2O emissions were or calculated following the IPCC (2007) guidelines, and CH4 emissions were assumed to be negligible compared to other contributions to the net GHGB. Additionally, albedo was calculated continuously using the short wave incident and reflected radiation measurements in the field (0.3-3µm) from CNR1 sensors. Mean annual differences in albedo and deduced radiative forcing from a reference value were then compared for all site-years. Mean annual differences in radiative forcing were then converted in g C equivalent m-2 in order

  14. Evaluation of MODIS Albedo Product (MCD43A) over Grassland, Agriculture and Forest Surface Types During Dormant and Snow-Covered Periods

    Science.gov (United States)

    Wang, Zhousen; Schaaf, Crystal B.; Strahler, Alan H.; Chopping, Mark J.; Roman, Miguel O.; Shuai, Yanmin; Woodcock, Curtis E.; Hollinger, David Y.; Fitzjarrald, David R.

    2013-01-01

    This study assesses the Moderate-resolution Imaging Spectroradiometer (MODIS) BRDF/albedo 8 day standard product and products from the daily Direct Broadcast BRDF/albedo algorithm, and shows that these products agree well with ground-based albedo measurements during the more difficult periods of vegetation dormancy and snow cover. Cropland, grassland, deciduous and coniferous forests are considered. Using an integrated validation strategy, analyses of the representativeness of the surface heterogeneity under both dormant and snow-covered situations are performed to decide whether direct comparisons between ground measurements and 500-m satellite observations can be made or whether finer spatial resolution airborne or spaceborne data are required to scale the results at each location. Landsat Enhanced Thematic Mapper Plus (ETM +) data are used to generate finer scale representations of albedo at each location to fully link ground data with satellite data. In general, results indicate the root mean square errors (RMSEs) are less than 0.030 over spatially representative sites of agriculture/grassland during the dormant periods and less than 0.050 during the snow-covered periods for MCD43A albedo products. For forest, the RMSEs are less than 0.020 during the dormant period and 0.025 during the snow-covered periods. However, a daily retrieval strategy is necessary to capture ephemeral snow events or rapidly changing situations such as the spring snow melt.

  15. Multi-Staged NDVI Dependent Snow-Free Land-Surface Shortwave Albedo Narrowband-to-Broadband (NTB Coefficients and Their Sensitivity Analysis

    Directory of Open Access Journals (Sweden)

    Shi Peng

    2017-01-01

    Full Text Available Narrowband-to-broadband conversion is a critical procedure for mapping land-surface broadband albedo using multi-spectral narrowband remote-sensing observations. Due to the significant difference in optical characteristics between soil and vegetation, NTB conversion is influenced by the variation in vegetation coverage on different surface types. To reduce this influence, this paper applies an approach that couples NTB coefficient with the NDVI. Multi-staged NDVI dependent NTB coefficient look-up tables (LUT for Moderate Resolution Imaging Spectroradiometer (MODIS, Polarization and Directionality of Earth’s Reflectance (POLDER and Advanced Very High Resolution Radiometer (AVHRR were calculated using 6000 spectra samples collected from two typical spectral databases. Sensitivity analysis shows that NTB conversion is affected more by the NDVI for sensors with fewer band numbers, such as POLDER and AVHRR. Analysis of the validation results based on simulations, in situ measurements and global albedo products indicates that by using the multi-staged NDVI dependent NTB method, the conversion accuracies of these two sensors could be improved by 2%–13% on different NDVI classes compared with the general method. This improvement could be as high as 15%, on average, and 35% on dense vegetative surface compared with the global broadband albedo product of POLDER. This paper shows that it is necessary to consider surface reflectance characteristics associated with the NDVI on albedo-NTB conversion for remote sensors with fewer than five bands.

  16. An Approach for the Long-Term 30-m Land Surface Snow-Free Albedo Retrieval from Historic Landsat Surface Reflectance and MODIS-based A Priori Anisotropy Knowledge

    Science.gov (United States)

    Shuai, Yanmin; Masek, Jeffrey G.; Gao, Feng; Schaaf, Crystal B.; He, Tao

    2014-01-01

    Land surface albedo has been recognized by the Global Terrestrial Observing System (GTOS) as an essential climate variable crucial for accurate modeling and monitoring of the Earth's radiative budget. While global climate studies can leverage albedo datasets from MODIS, VIIRS, and other coarse-resolution sensors, many applications in heterogeneous environments can benefit from higher-resolution albedo products derived from Landsat. We previously developed a "MODIS-concurrent" approach for the 30-meter albedo estimation which relied on combining post-2000 Landsat data with MODIS Bidirectional Reflectance Distribution Function (BRDF) information. Here we present a "pre-MODIS era" approach to extend 30-m surface albedo generation in time back to the 1980s, through an a priori anisotropy Look-Up Table (LUT) built up from the high quality MCD43A BRDF estimates over representative homogenous regions. Each entry in the LUT reflects a unique combination of land cover, seasonality, terrain information, disturbance age and type, and Landsat optical spectral bands. An initial conceptual LUT was created for the Pacific Northwest (PNW) of the United States and provides BRDF shapes estimated from MODIS observations for undisturbed and disturbed surface types (including recovery trajectories of burned areas and non-fire disturbances). By accepting the assumption of a generally invariant BRDF shape for similar land surface structures as a priori information, spectral white-sky and black-sky albedos are derived through albedo-to-nadir reflectance ratios as a bridge between the Landsat and MODIS scale. A further narrow-to-broadband conversion based on radiative transfer simulations is adopted to produce broadband albedos at visible, near infrared, and shortwave regimes.We evaluate the accuracy of resultant Landsat albedo using available field measurements at forested AmeriFlux stations in the PNW region, and examine the consistency of the surface albedo generated by this approach

  17. Effect of surface albedo, water vapour, and atmospheric aerosols on the cloud-free shortwave radiative budget in the Arctic

    Energy Technology Data Exchange (ETDEWEB)

    Di Biagio, C. [ENEA, Laboratory for Earth Observations and Analyses, Rome (Italy); University of Siena, Department of Earth Science, Siena (Italy); Di Sarra, A. [ENEA, Laboratory for Earth Observations and Analyses, Rome (Italy); Eriksen, P. [Danish Climate Centre, DMI, Danish Meteorological Institute, Copenhagen (Denmark); Ascanius, S.E. [DMI, Danish Meteorological Institute, Qaanaaq (Greenland); Muscari, G. [INGV, Istituto Nazionale di Geofisica e Vulcanologia, Rome (Italy); Holben, B. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

    2012-08-15

    This study is based on ground-based measurements of downward surface shortwave irradiance (SW), columnar water vapour (wv), and aerosol optical depth ({tau}) obtained at Thule Air Base (Greenland) in 2007-2010, together with MODIS observations of the surface shortwave albedo (A). Radiative transfer model calculations are used in combination with measurements to separate the radiative effect of A ({Delta}SW{sub A}), wv ({Delta}SW{sub wv}), and aerosols ({Delta}SW{sub {tau}}) in modulating SW in cloud-free conditions. The shortwave radiation at the surface is mainly affected by water vapour absorption, which produces a reduction of SW as low as -100 Wm{sup -2} (-18%). The seasonal change of A produces an increase of SW by up to +25 Wm{sup -2} (+4.5%). The annual mean radiative effect is estimated to be -(21-22) Wm{sup -2} for wv, and +(2-3) Wm{sup -2} for A. An increase by +0.065 cm in the annual mean wv, to which corresponds an absolute increase in {Delta}SW{sub wv} by 0.93 Wm{sup -2} (4.3%), has been observed to occur between 2007 and 2010. In the same period, the annual mean A has decreased by -0.027, with a corresponding decrease in {Delta}SW{sub A} by 0.41 Wm{sup -2} (-14.9%). Atmospheric aerosols produce a reduction of SW as low as -32 Wm{sup -2} (-6.7%). The instantaneous aerosol radiative forcing (RF{sub {tau}}) reaches values of -28 Wm{sup -2} and shows a strong dependency on surface albedo. The derived radiative forcing efficiency (FE{sub {tau}}) for solar zenith angles between 55 and 70 is estimated to be (-120.6 {+-} 4.3) for 0.1 < A < 0.2, and (-41.2 {+-} 1.6) Wm{sup -2} for 0.5 < A < 0.6. (orig.)

  18. Development of a Novel Multispectral Instrument for Handheld and UAS Measurements of Surface Albedo; First Applications for Glaciers in the Peruvian Andes and for Nevada's Black Rock Desert

    Science.gov (United States)

    Boehmler, J. M.; Stevens, C.; Arnott, W. P.; Watts, A.; All, J.; Schmitt, C. G.

    2017-12-01

    Accurate atmospheric aerosol characteristics derived from satellite measurements are needed over a variety of land surfaces. Nonhomogeneous and bright surface reflectance across California and Nevada may be a contributing factor in the discrepancies observed between ground based and satellite-retrieved atmospheric aerosol optical depth (AOD). We developed and deployed a compact and portable instrument to measure albedo to evaluate a major factor that influences the accuracy of AOD retrievals. The instrument will be operated on an unmanned aircraft system (UAS) to control areal averaging for comparison with satellite derived albedo from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS). A handheld version of the instrument was mounted on a trekking pole and used for obtaining in situ glacier albedo measurements in the Cordillera Blanca of Peru during the summer of 2017. The instrument weighs approximately 433 g and consists of two parts, a mountable, payload portion (300 g) which houses the sensors, and a handheld screen (133 g) to display real-time data from the payload portion. Both parts are powered by a 9V battery and run on a Teensy 3.6/3.2 microcontroller. To retrieve albedo, two micro-spectrometers manufactured by Hamamatsu Photonics, each with a spectral range of 340 -780 nm, are utilized; one for obtaining the downwelling solar radiation and the other for measuring the solar radiation reflected from the surface. Additional components on the instrument include temperature, pressure and humidity sensors with a one second time response; a GPS for position and altitude; an infrared sensor to measure ground temperature; a digital level and compass for orienting the instrument; a camera for taking photos of the sky and surface; a radio for two-way communication between the screen display and sensor payload; and a micro SD card for recording data. We will present the instrument design along with surface albedo measurements for glaciers of the Peruvian

  19. Effect of Spectrally Varying Albedo of Vegetation Surfaces on Shortwave Radiation Fluxes and Aerosol Direct Radiative Forcing

    Science.gov (United States)

    Zhu, L.; Martins, J. V.; Yu, H.

    2012-01-01

    This study develops an algorithm for representing detailed spectral features of vegetation albedo based on Moderate Resolution Imaging Spectrometer (MODIS) observations at 7 discrete channels, referred to as the MODIS Enhanced Vegetation Albedo (MEVA) algorithm. The MEVA algorithm empirically fills spectral gaps around the vegetation red edge near 0.7 micrometers and vegetation water absorption features at 1.48 and 1.92 micrometers which cannot be adequately captured by the MODIS 7 channels. We then assess the effects of applying MEVA in comparison to four other traditional approaches to calculate solar fluxes and aerosol direct radiative forcing (DRF) at the top of atmosphere (TOA) based on the MODIS discrete reflectance bands. By comparing the DRF results obtained through the MEVA method with the results obtained through the other four traditional approaches, we show that filling the spectral gap of the MODIS measurements around 0.7 micrometers based on the general spectral behavior of healthy green vegetation leads to significant improvement in the instantaneous aerosol DRF at TOA (up to 3.02Wm(exp -2) difference or 48% fraction of the aerosol DRF, .6.28Wm(exp -2), calculated for high spectral resolution surface reflectance from 0.3 to 2.5 micrometers for deciduous vegetation surface). The corrections of the spectral gaps in the vegetation spectrum in the near infrared, again missed by the MODIS reflectances, also contributes to improving TOA DRF calculations but to a much lower extent (less than 0.27Wm(exp -2), or about 4% of the instantaneous DRF). Compared to traditional approaches, MEVA also improves the accuracy of the outgoing solar flux between 0.3 to 2.5 micrometers at TOA by over 60Wm(exp -2) (for aspen 3 surface) and aerosol DRF by over 10Wm(exp -2) (for dry grass). Specifically, for Amazon vegetation types, MEVA can improve the accuracy of daily averaged aerosol radiative forcing in the spectral range of 0.3 to 2.5 micrometers at equator at the

  20. The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature

    Energy Technology Data Exchange (ETDEWEB)

    Blok, Daan; Heijmans, Monique M P D; Berendse, Frank [Nature Conservation and Plant Ecology Group, Wageningen University, PO Box 47, 6700 AA, Wageningen (Netherlands); Schaepman-Strub, Gabriela [Institute of Evolutionary Biology and Environmental Studies, University of Zuerich, Winterthurerstrasse 190, 8057 Zuerich (Switzerland); Bartholomeus, Harm [Centre for Geo-Information, Wageningen University, PO Box 47, 6700 AA, Wageningen (Netherlands); Maximov, Trofim C, E-mail: daan.blok@wur.nl [Biological Problems of the Cryolithozone, Russian Academy of Sciences, Siberian Division, 41, Lenin Prospekt, Yakutsk, The Republic of Sakha, Yakutia 677980 (Russian Federation)

    2011-07-15

    Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000-10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.

  1. The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature

    International Nuclear Information System (INIS)

    Blok, Daan; Heijmans, Monique M P D; Berendse, Frank; Schaepman-Strub, Gabriela; Bartholomeus, Harm; Maximov, Trofim C

    2011-01-01

    Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000-10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.

  2. Using the Surface Temperature-Albedo Space to Separate Regional Soil and Vegetation Temperatures from ASTER Data

    Directory of Open Access Journals (Sweden)

    Lisheng Song

    2015-05-01

    Full Text Available Soil and vegetation component temperatures in non-isothermal pixels encapsulate more physical meaning and are more applicable than composite temperatures. The component temperatures however are difficult to be obtained from thermal infrared (TIR remote sensing data provided by single view angle observations. Here, we present a land surface temperature and albedo (T-α space approach combined with the mono-surface energy balance (SEB-1S model to derive soil and vegetation component temperatures. The T-α space can be established from visible and near infrared (VNIR and TIR data provided by single view angle observations. This approach separates the soil and vegetation component temperatures from the remotely sensed composite temperatures by incorporating soil wetness iso-lines for defining equivalent soil temperatures; this allows vegetation temperatures to be extracted from the T-α space. This temperature separation methodology was applied to advanced scanning thermal emission and reflection radiometer (ASTER VNIR and high spatial resolution TIR image data in an artificial oasis area during the entire growing season. Comparisons with ground measurements showed that the T-α space approach produced reliable soil and vegetation component temperatures in the study area. Low root mean square error (RMSE values of 0.83 K for soil temperatures and 1.64 K for vegetation temperatures, respectively, were obtained, compared to component temperatures measurements from a ground-based thermal camera. These results support the use of soil wetness iso-lines to derive soil surface temperatures. It was also found that the estimated vegetation temperatures were extremely close to the near surface air temperature observations when the landscape is well watered under full vegetation cover. More robust soil and vegetation temperature estimates will improve estimates of soil evaporation and vegetation transpiration, leading to more reliable the monitoring of crop

  3. Phenology and species determine growing-season albedo increase at the altitudinal limit of shrub growth in the sub-Arctic.

    Science.gov (United States)

    Williamson, Scott N; Barrio, Isabel C; Hik, David S; Gamon, John A

    2016-11-01

    Arctic warming is resulting in reduced snow cover and increased shrub growth, both of which have been associated with altered land surface-atmospheric feedback processes involving sensible heat flux, ground heat flux and biogeochemical cycling. Using field measurements, we show that two common Arctic shrub species (Betula glandulosa and Salix pulchra), which are largely responsible for shrub encroachment in tundra, differed markedly in albedo and that albedo of both species increased as growing season progressed when measured at their altitudinal limit. A moveable apparatus was used to repeatedly measure albedo at six precise spots during the summer of 2012, and resampled in 2013. Contrary to the generally accepted view of shrub-covered areas having low albedo in tundra, full-canopy prostrate B. glandulosa had almost the highest albedo of all surfaces measured during the peak of the growing season. The higher midsummer albedo is also evident in localized MODIS albedo aggregated from 2000 to 2013, which displays a similar increase in growing-season albedo. Using our field measurements, we show the ensemble summer increase in tundra albedo counteracts the generalized effect of earlier spring snow melt on surface energy balance by approximately 40%. This summer increase in albedo, when viewed in absolute values, is as large as the difference between the forest and tundra transition. These results indicate that near future (albedo related to Arctic vegetation change are unlikely to be particularly large and might constitute a negative feedback to climate warming in certain circumstances. Future efforts to calculate energy budgets and a sensible heating feedback in the Arctic will require more detailed information about the relative abundance of different ground cover types, particularly shrub species and their respective growth forms and phenology. © 2016 John Wiley & Sons Ltd.

  4. Measurements of light-absorbing particles in snow across the Arctic, North America, and China: Effects on surface albedo

    Science.gov (United States)

    Dang, Cheng; Warren, Stephen G.; Fu, Qiang; Doherty, Sarah J.; Sturm, Matthew; Su, Jing

    2017-10-01

    Using field observations, we perform radiative transfer calculations on snowpacks in the Arctic, China, and North America to quantify the impact of light-absorbing particles (LAPs) on snow albedo and its sensitivity to different factors. For new snow, the regional-averaged albedo reductions caused by all LAPs in the Arctic, North America, and China are 0.009, 0.012, and 0.077, respectively, of which the albedo reductions caused by black carbon (BC) alone are 0.005, 0.005, and 0.031, corresponding to a positive radiative forcing of 0.06, 0.3, and 3 W m-2. For the same particulate concentrations, the albedo reduction for old melting snow is larger than that of new snow by a factor of 2; this leads to 3-8 times larger radiative forcing, in part due to higher solar irradiance in the melting season. These calculations used ambient snowpack properties; if all snowpacks were instead assumed to be optically thick, the albedo reduction would be 20-50% larger for new snow in the Arctic and North America and 120-300% larger for old snow. Accounting for non-BC LAPs reduces the albedo reduction by BC in the Arctic, North America, and China by 32%, 29%, and 70%, respectively, for new snow and 11%, 7%, and 51% for old snow. BC-in-snow albedo reduction computed using a two-layer model agrees reasonably with that computed using a multilayer model. Biases in BC concentration or snow depth often lead to nonlinear biases in BC-induced albedo reduction.

  5. Assimilation of MODIS Ice Surface Temperature and Albedo into the Snow and Ice Model CROCUS Over the Greenland Ice Sheet Along the K-transect Stations

    Science.gov (United States)

    Navari, M.; Margulis, S. A.; Bateni, S. M.; Alexander, P. M.; Tedesco, M.

    2016-12-01

    Estimating the Greenland Ice Sheet (GrIS) surface mass balance (SMB) is an important component of current and future projections of sea level rise. In situ measurement provides direct estimates of the SMB, but are inherently limited by their spatial extent and representativeness. Given this limitation, physically based regional climate models (RCMs) are critical for understanding GrIS physical processes and estimating of the GrIS SMB. However, the uncertainty in estimates of SMB from RCMs is still high. Surface remote sensing (RS) has been used as a complimentary tool to characterize various aspects related to the SMB. The difficulty of using these data streams is that the links between them and the SMB terms are most often indirect and implicit. Given the lack of in situ information, imperfect models, and under-utilized RS data it is critical to merge the available data in a systematic way to better characterize the spatial and temporal variation of the GrIS SMB. This work proposes a data assimilation (DA) framework that yields temporally-continuous and physically consistent SMB estimates that benefit from state-of-the-art models and relevant remote sensing data streams. Ice surface temperature (IST) is the most important factor that regulates partitioning of the net radiation into the subsurface snow/ice, sensible and latent heat fluxes and plays a key role in runoff generation. Therefore it can be expected that a better estimate of surface temperature from a data assimilation system would contribute to a better estimate of surface mass fluxes. Albedo plays an important role in the surface energy balance of the GrIS. However, even advanced albedo modules are not adequate to simulate albedo over the GrIS. Therefore, merging remotely sensed albedo product into a physically based model has a potential to improve the estimates of the GrIS SMB. In this work a MODIS-derived IST and a 16-day albedo product are independently assimilated into the snow and ice model CROCUS

  6. Low Albedo Surfaces and Eolian Sediment: Mars Orbiter Camera Views of Western Arabia Terra Craters and Wind Streaks

    Science.gov (United States)

    Edgett, Kenneth S.

    2001-01-01

    High spatial resolution (1.5 to 12 m/pixel) Mars Global Surveyor Mars Orbiter Camera images obtained September 1997 through June 2001 indicate that the large, dark wind streaks of western Arabia Terra each originate at a barchan dune field on a crater floor. The streaks consist of a relatively thin coating of sediment deflated from the dune fields and their vicinity. This sediment drapes a previous mantle that more thickly covers nearly all of western Arabia Terra. No dunes or eolian bedforms are found within the dark wind streaks, nor do any of the intracrater dunes climb up crater walls to provide sand to the wind streaks. The relations between dunes, wind streak, and subjacent terrain imply that dark-toned grains finer than those which comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain. Such grains are most likely in the silt size range (3.9-62.5 micrometers). The streaks change in terms of extent, relative albedo, and surface pattern over periods measured in years, but very little evidence for recent eolian activity (dust plumes, storms, dune movement) has been observed.

  7. Effects of illumination differences on photometric stereo shape-and-albedo-from-shading for precision lunar surface reconstruction

    Science.gov (United States)

    Chung Liu, Wai; Wu, Bo; Wöhler, Christian

    2018-02-01

    Photoclinometric surface reconstruction techniques such as Shape-from-Shading (SfS) and Shape-and-Albedo-from-Shading (SAfS) retrieve topographic information of a surface on the basis of the reflectance information embedded in the image intensity of each pixel. SfS or SAfS techniques have been utilized to generate pixel-resolution digital elevation models (DEMs) of the Moon and other planetary bodies. Photometric stereo SAfS analyzes images under multiple illumination conditions to improve the robustness of reconstruction. In this case, the directional difference in illumination between the images is likely to affect the quality of the reconstruction result. In this study, we quantitatively investigate the effects of illumination differences on photometric stereo SAfS. Firstly, an algorithm for photometric stereo SAfS is developed, and then, an error model is derived to analyze the relationships between the azimuthal and zenith angles of illumination of the images and the reconstruction qualities. The developed algorithm and error model were verified with high-resolution images collected by the Narrow Angle Camera (NAC) of the Lunar Reconnaissance Orbiter Camera (LROC). Experimental analyses reveal that (1) the resulting error in photometric stereo SAfS depends on both the azimuthal and the zenith angles of illumination as well as the general intensity of the images and (2) the predictions from the proposed error model are consistent with the actual slope errors obtained by photometric stereo SAfS using the LROC NAC images. The proposed error model enriches the theory of photometric stereo SAfS and is of significance for optimized lunar surface reconstruction based on SAfS techniques.

  8. Reflectance model for densely packed media: Estimates of the surface properties of the high-albedo satellites of Saturn

    Science.gov (United States)

    Tishkovets, V. P.; Petrova, E. V.

    2017-07-01

    Interpretation of photometric and polarimetric observations of atmosphereless celestial bodies faces the problems connected with both the insufficient accuracy and level of details in groundbased observations and the current state of the theory of the multiple scattering of light. In application to sparse media, where the electromagnetic waves, propagating between the scatterers, can be considered as spherical (the socalled far-field approximation), this theory is rather well developed for both the diffuse and coherent components of the scattered radiation. In this paper, we show that this theory can be also successfully applied to the measurements of polarization of light scattered by densely packed, though nonabsorbing or weakly absorbing, media. For this purpose, we calculated the models for a semi-infinite layer of the medium composed of randomly oriented clusters of spherical particles and compared them with the data of laboratory and astronomical measurements. The potential of the present approach is illustrated by an example of the interpretation of the polarization measurements of the ice satellites of Saturn—Rhea and Enceladus—which allowed some properties of the surface of these celestial bodies to be estimated. In particular, the ratio of the surface area that makes no contribution to the negative polarization of light reflected at small phase angles to the area producing the negative polarization branch was found. Under the assumption of the same albedo of these areas, this ratio turned out to be 3.31-3.66 and 1.7-3.8 for Rhea and Enceladus, respectively. For Enceladus, it is difficult to obtain a sufficiently narrow range of the estimated parameters, since the number of measurement points in the phase dependence of polarization of this satellite is small. For the surface of Rhea, the estimated packing density of particles, participating in the opposition effects, is approximately 15%, while their smallest size is of the order of the wavelength of

  9. Tundra vegetation effects on pan-Arctic albedo

    International Nuclear Information System (INIS)

    Loranty, Michael M; Goetz, Scott J; Beck, Pieter S A

    2011-01-01

    Recent field experiments in tundra ecosystems describe how increased shrub cover reduces winter albedo, and how subsequent changes in surface net radiation lead to altered rates of snowmelt. These findings imply that tundra vegetation change will alter regional energy budgets, but to date the effects have not been documented at regional or greater scales. Using satellite observations and a pan-Arctic vegetation map, we examined the effects of shrub vegetation on albedo across the terrestrial Arctic. We included vegetation classes dominated by low shrubs, dwarf shrubs, tussock-dominated graminoid tundra, and non-tussock graminoid tundra. Each class was further stratified by bioclimate subzones. Low-shrub tundra had higher normalized difference vegetation index values and earlier albedo decline in spring than dwarf-shrub tundra, but for tussock tundra, spring albedo declined earlier than for low-shrub tundra. Our results illustrate how relatively small changes in vegetation properties result in differences in albedo dynamics, regardless of shrub growth, that may lead to differences in net radiation upwards of 50 W m -2 at weekly time scales. Further, our findings imply that changes to the terrestrial Arctic energy budget during this important seasonal transition are under way regardless of whether recent satellite observed productivity trends are the result of shrub expansion. We conclude that a better understanding of changes in vegetation productivity and distribution in Arctic tundra is essential for accurately quantifying and predicting carbon and energy fluxes and associated climate feedbacks.

  10. Model test of CCN-cloud albedo climate forcing

    Science.gov (United States)

    Ghan, S. J.; Taylor, K. E.; Penner, J. E.; Erickson, D. J., III

    1990-01-01

    Cloud condensation nuclei (CCN) influence cloud albedo through their effect on the cloud droplet size distribution. A number of studies have evaluated the climatic impact of the CCN-cloud albedo feedback, but all have assumed that cloud distributions, cloud thicknesses, and cloud liquid water contents would remain constant as the climate adjusted. This assumption has been tested using the Livermore version of the National Center for Atmospheric Research Community Climate Model. The results indicate that there are no significant compensating changes in cloud properties that would counteract the 1.7 percent global albedo increase resulting from a fourfold increase in marine CCN concentration. Furthermore, when ocean surface temperatures are decreased 4 C in a manner broadly consistent with the enhanced cloud albedos, an increase in cloud fraction of 3.5 percent and a reduction in cloud altitude are predicted, leading to a positive feedback from clouds that would imply a climate impact roughly double that calculated from cloud droplet size distribution change alone.

  11. Constraining Agricultural Irrigation Surface Energy Budget Feedbacks in Atmospheric Models

    Science.gov (United States)

    Aufforth, M. E.; Desai, A. R.; Suyker, A.

    2017-12-01

    The expansion and modernization of irrigation increased the relevance of knowing the effects it has on regional weather and climate feedbacks. We conducted a set of observationally-constrained simulations determining the result irrigation exhibits on the surface energy budget, the atmospheric boundary layer, and regional precipitation feedbacks. Eddy covariance flux tower observations were analyzed from two irrigated and one rain-fed corn/soybean rotation sites located near Mead, Nebraska. The evaluated time period covered the summer growing months of June, July, and August (JJA) during the years when corn grew at all three sites. As a product of higher continuous surface moisture availability, the irrigated crops had significantly higher amounts of energy partitioned towards latent heating than the non-irrigated site. The daily average peak of latent heating at the rain-fed site occurred before the irrigated sites and was approximately 45 W/m2 lower. Land surface models were evaluated on their ability to reproduce these effects, including those used in numerical weather prediction and those used in agricultural carbon cycle projection. Model structure, mechanisms, and parameters that best represent irrigation-surface energy impacts will be compared and discussed.

  12. Quantifying surface albedo and other direct biogeophysical climate forcings of forestry activities.

    Science.gov (United States)

    Bright, Ryan M; Zhao, Kaiguang; Jackson, Robert B; Cherubini, Francesco

    2015-09-01

    By altering fluxes of heat, momentum, and moisture exchanges between the land surface and atmosphere, forestry and other land-use activities affect climate. Although long recognized scientifically as being important, these so-called biogeophysical forcings are rarely included in climate policies for forestry and other land management projects due to the many challenges associated with their quantification. Here, we review the scientific literature in the fields of atmospheric science and terrestrial ecology in light of three main objectives: (i) to elucidate the challenges associated with quantifying biogeophysical climate forcings connected to land use and land management, with a focus on the forestry sector; (ii) to identify and describe scientific approaches and/or metrics facilitating the quantification and interpretation of direct biogeophysical climate forcings; and (iii) to identify and recommend research priorities that can help overcome the challenges of their attribution to specific land-use activities, bridging the knowledge gap between the climate modeling, forest ecology, and resource management communities. We find that ignoring surface biogeophysics may mislead climate mitigation policies, yet existing metrics are unlikely to be sufficient. Successful metrics ought to (i) include both radiative and nonradiative climate forcings; (ii) reconcile disparities between biogeophysical and biogeochemical forcings, and (iii) acknowledge trade-offs between global and local climate benefits. We call for more coordinated research among terrestrial ecologists, resource managers, and coupled climate modelers to harmonize datasets, refine analytical techniques, and corroborate and validate metrics that are more amenable to analyses at the scale of an individual site or region. © 2015 John Wiley & Sons Ltd.

  13. Early Spring Post-Fire Snow Albedo Dynamics in High Latitude Boreal Forests Using Landsat-8 OLI Data

    Science.gov (United States)

    Wang, Zhuosen; Erb, Angela M.; Schaaf, Crystal B.; Sun, Qingsong; Liu, Yan; Yang, Yun; Shuai, Yanmin; Casey, Kimberly A.; Roman, Miguel O.

    2016-01-01

    Taking advantage of the improved radiometric resolution of Landsat-8 OLI which, unlike previous Landsat sensors, does not saturate over snow, the progress of fire recovery progress at the landscape scale (less than 100 m) is examined. High quality Landsat-8 albedo retrievals can now capture the true reflective and layered character of snow cover over a full range of land surface conditions and vegetation densities. This new capability particularly improves the assessment of post-fire vegetation dynamics across low- to high-burn severity gradients in Arctic and boreal regions in the early spring, when the albedos during recovery show the greatest variation. We use 30 m resolution Landsat-8 surface reflectances with concurrent coarser resolution (500 m) MODIS high quality full inversion surface Bidirectional Reflectance Distribution Functions (BRDF) products to produce higher resolution values of surface albedo. The high resolution full expression shortwave blue sky albedo product performs well with an overall RMSE of 0.0267 between tower and satellite measures under both snow-free and snow-covered conditions. While the importance of post-fire albedo recovery can be discerned from the MODIS albedo product at regional and global scales, our study addresses the particular importance of early spring post-fire albedo recovery at the landscape scale by considering the significant spatial heterogeneity of burn severity, and the impact of snow on the early spring albedo of various vegetation recovery types. We found that variations in early spring albedo within a single MODIS gridded pixel can be larger than 0.6. Since the frequency and severity of wildfires in Arctic and boreal systems is expected to increase in the coming decades, the dynamics of albedo in response to these rapid surface changes will increasingly impact the energy balance and contribute to other climate processes and physical feedback mechanisms. Surface radiation products derived from Landsat-8 data will

  14. Impacts of global open-fire aerosols on direct radiative, cloud and surface-albedo effects simulated with CAM5

    Directory of Open Access Journals (Sweden)

    Y. Jiang

    2016-11-01

    Full Text Available Aerosols from open-land fires could significantly perturb the global radiation balance and induce climate change. In this study, Community Atmosphere Model version 5 (CAM5 with prescribed daily fire aerosol emissions is used to investigate the spatial and seasonal characteristics of radiative effects (REs, relative to the case of no fires of open-fire aerosols including black carbon (BC and particulate organic matter (POM from 2003 to 2011. The global annual mean RE from aerosol–radiation interactions (REari of all fire aerosols is 0.16 ± 0.01 W m−2 (1σ uncertainty, mainly due to the absorption of fire BC (0.25 ± 0.01 W m−2, while fire POM induces a small effect (−0.05 and 0.04 ± 0.01 W m−2 based on two different methods. Strong positive REari is found in the Arctic and in the oceanic regions west of southern Africa and South America as a result of amplified absorption of fire BC above low-level clouds, in general agreement with satellite observations. The global annual mean RE due to aerosol–cloud interactions (REaci of all fire aerosols is −0.70 ± 0.05 W m−2, resulting mainly from the fire POM effect (−0.59 ± 0.03 W m−2. REari (0.43 ± 0.03 W m−2 and REaci (−1.38 ± 0.23 W m−2 in the Arctic are stronger than in the tropics (0.17 ± 0.02 and −0.82 ± 0.09 W m−2 for REari and REaci, although the fire aerosol burden is higher in the tropics. The large cloud liquid water path over land areas and low solar zenith angle of the Arctic favor the strong fire aerosol REaci (up to −15 W m−2 during the Arctic summer. Significant surface cooling, precipitation reduction and increasing amounts of low-level cloud are also found in the Arctic summer as a result of the fire aerosol REaci based on the atmosphere-only simulations. The global annual mean RE due to surface-albedo changes (REsac over land areas (0.03 ± 0.10 W m−2 is small and

  15. Narrowband-to-broadband albedo conversion for glacier ice and snowbased on aircraft and near-surface measurements

    NARCIS (Netherlands)

    Greuell, W.; Reijmer, C.; Oerlemans, J.

    2002-01-01

    This article presents albedo measurements of snow and glacier ice at Vatnajökull (Iceland) and the Kangerlussuaq transect (Greenland). Radiative fluxes were measured in the broadband and in four narrowbands, namely, Thematic Mapper (TM) Bands 2 and 4, and Advanced Very High Resolution Radiometer

  16. The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature

    NARCIS (Netherlands)

    Blok, D.; Schaepman-Strub, G.; Bartholomeus, H.; Heijmans, M.M.P.D.; Maximov, T.C.; Berendse, F.

    2011-01-01

    Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming.

  17. Improving snow albedo processes in WRF/SSiB regional climate model to assess impact of dust and black carbon in snow on surface energy balance and hydrology over western U.S.

    OpenAIRE

    Oaida, CM; Xue, Y; Flanner, MG; Skiles, SMK; De Sales, F; Painter, TH

    2015-01-01

    © 2015. American Geophysical Union. All Rights Reserved. Two important factors that control snow albedo are snow grain growth and presence of light-absorbing impurities (aerosols) in snow. However, current regional climate models do not include such processes in a physically based manner in their land surface models. We improve snow albedo calculations in the Simplified Simple Biosphere (SSiB) land surface model coupled with the Weather Research and Forecasting (WRF) regional climate model (R...

  18. Quantifying the effects of spring freeze-thaw transitions and snowpack dynamics on surface albedo change using satellite optical and microwave remote sensing

    Science.gov (United States)

    Kim, Y.; Kimball, J. S.; Du, J.; Glassy, J.; Schaaf, C.

    2016-12-01

    The freeze-thaw (FT) state parameter from satellite microwave remote sensing is closely linked to changes in surface energy exchange, evapotranspiration, snowmelt dynamics, and vegetation phenology over high northern lands affected by seasonally frozen temperatures. Direct impacts of snowpack melt and FT transitions on spring surface energy exchange and vegetation activity are largely unknown. In this study, we use a finer scale satellite microwave Earth System Data Record of daily landscape freeze-thaw status (FT-ESDR) developed from 6-km 36.5 GHz, vertically polarized brightness temperature (Tb) retrievals from NASA AMSR-E and JAXA AMSR2 sensors over a polar grid. The FT retrieval uses a modified seasonal threshold algorithm that classifies daily Tb variations in relation to grid cell-wise FT thresholds calibrated using surface air temperatures (SAT) downscaled from coarser ERA-Interim reanalysis data and ancillary elevations, and environmental lapse rates. The 6 km FT record shows improved accuracy against in-situ SAT measurements from regional weather stations and enhanced delineation of FT heterogeneity relative to a coarser 25-km global FT-ESDR. The polar FT-ESDR is compared against satellite optical-IR sensor based vegetation phenology and shortwave broadband albedo records. These results show that the spring FT transition coincides with a large albedo decrease, rapid SAT warming and vegetation growing season onset over Alaska. Snowpack melt seasons identified by integrating satellite FT and snow cover extent records reveal the timing, extent and duration of wet snow conditions and associated shifts in surface albedo and NDVI. These results also reveal linkages between FT related snowpack melt onset and associated changes in surface energy partitioning and vegetation activity.

  19. The Effects of Surface Properties and Albedo on Methane Retrievals with the Airborne Visible/Infrared Imaging Spectrometer Next Generation (AVIRIS-NG)

    Science.gov (United States)

    Ayasse, A.; Thorpe, A. K.; Roberts, D. A.

    2017-12-01

    Atmospheric methane has increased by a factor of 2.5 since the beginning of the industrial era in response to anthropogenic emissions (Ciais et al., 2013). Although it is less abundant than carbon dioxide it is 86 time more potent on a 20 year time scale (Myhre et al., 2013) and is therefore responsible for about 20% of the total global warming induced by anthropogenic greenhouse gasses (Kirschke et al., 2013). Given the importance of methane to global climate change, monitoring and measuring methane emissions using techniques such as remote sensing is of increasing interest. Recently the Airborne Visible-Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) has proven to be a valuable instrument for quantitative mapping of methane plumes (Frankenberg et al., 2016; Thorpe et al., 2016; Thompson et al., 2015). In this study, we applied the Iterative Maximum a Posterior Differential Optical Spectroscopy (IMAP-DOAS) methane retrieval algorithm to a synthetic image with variable methane concentrations, albedo, and land cover. This allowed for characterizing retrieval performance, including potential sensitivity to variable land cover, low albedo surfaces, and surfaces known to cause spurious signals. We conclude that albedo had little influence on the IMAP-DOAS results except at very low radiance levels. Water (without sun glint) was found to be the most challenging surface for methane retrievals while hydrocarbons and some green vegetation also caused error. Understanding the effect of surface properties on methane retrievals is important given the increased use of AVIRIS-NG to map gas plumes over diverse locations and methane sources. This analysis could be expanded to include additional gas species like carbon dioxide and to further investigate gas sensitivity of proposed instruments for dedicated gas mapping from airborne and spaceborne platforms.

  20. Shortwave radiative forcing, rapid adjustment, and feedback to the surface by sulfate geoengineering: analysis of the Geoengineering Model Intercomparison Project G4 scenario

    Science.gov (United States)

    Kashimura, Hiroki; Abe, Manabu; Watanabe, Shingo; Sekiya, Takashi; Ji, Duoying; Moore, John C.; Cole, Jason N. S.; Kravitz, Ben

    2017-03-01

    This study evaluates the forcing, rapid adjustment, and feedback of net shortwave radiation at the surface in the G4 experiment of the Geoengineering Model Intercomparison Project by analysing outputs from six participating models. G4 involves injection of 5 Tg yr-1 of SO2, a sulfate aerosol precursor, into the lower stratosphere from year 2020 to 2069 against a background scenario of RCP4.5. A single-layer atmospheric model for shortwave radiative transfer is used to estimate the direct forcing of solar radiation management (SRM), and rapid adjustment and feedbacks from changes in the water vapour amount, cloud amount, and surface albedo (compared with RCP4.5). The analysis shows that the globally and temporally averaged SRM forcing ranges from -3.6 to -1.6 W m-2, depending on the model. The sum of the rapid adjustments and feedback effects due to changes in the water vapour and cloud amounts increase the downwelling shortwave radiation at the surface by approximately 0.4 to 1.5 W m-2 and hence weaken the effect of SRM by around 50 %. The surface albedo changes decrease the net shortwave radiation at the surface; it is locally strong (˜ -4 W m-2) in snow and sea ice melting regions, but minor for the global average. The analyses show that the results of the G4 experiment, which simulates sulfate geoengineering, include large inter-model variability both in the direct SRM forcing and the shortwave rapid adjustment from change in the cloud amount, and imply a high uncertainty in modelled processes of sulfate aerosols and clouds.

  1. Changes in summer sea ice, albedo, and portioning of surface solar radiation in the Pacific sector of Arctic Ocean during 1982-2009

    OpenAIRE

    Lei, Ruibo; Tian-Kunze, Xiangshan; Leppäranta, Matti; Wang, Jia; Kaleschke, Lars; Zhang, Zhanhai

    2016-01-01

    SSM/I sea ice concentration and CLARA black-sky composite albedo were used to estimate sea ice albedo in the region 70 degrees N-82 degrees N, 130 degrees W-180 degrees W. The long-term trends and seasonal evolutions of ice concentration, composite albedo, and ice albedo were then obtained. In July-August 1982-2009, the linear trend of the composite albedo and the ice albedo was -0.069 and -0.046 units per decade, respectively. During 1 June to 19 August, melting of sea ice resulted in an inc...

  2. The importance of accurate glacier albedo for estimates of surface mass balance on Vatnajökull: evaluating the surface energy budget in a regional climate model with automatic weather station observations

    Science.gov (United States)

    Steffensen Schmidt, Louise; Aðalgeirsdóttir, Guðfinna; Guðmundsson, Sverrir; Langen, Peter L.; Pálsson, Finnur; Mottram, Ruth; Gascoin, Simon; Björnsson, Helgi

    2017-07-01

    A simulation of the surface climate of Vatnajökull ice cap, Iceland, carried out with the regional climate model HIRHAM5 for the period 1980-2014, is used to estimate the evolution of the glacier surface mass balance (SMB). This simulation uses a new snow albedo parameterization that allows albedo to exponentially decay with time and is surface temperature dependent. The albedo scheme utilizes a new background map of the ice albedo created from observed MODIS data. The simulation is evaluated against observed daily values of weather parameters from five automatic weather stations (AWSs) from the period 2001-2014, as well as in situ SMB measurements from the period 1995-2014. The model agrees well with observations at the AWS sites, albeit with a general underestimation of the net radiation. This is due to an underestimation of the incoming radiation and a general overestimation of the albedo. The average modelled albedo is overestimated in the ablation zone, which we attribute to an overestimation of the thickness of the snow layer and not taking the surface darkening from dirt and volcanic ash deposition during dust storms and volcanic eruptions into account. A comparison with the specific summer, winter, and net mass balance for the whole of Vatnajökull (1995-2014) shows a good overall fit during the summer, with a small mass balance underestimation of 0.04 m w.e. on average, whereas the winter mass balance is overestimated by on average 0.5 m w.e. due to too large precipitation at the highest areas of the ice cap. A simple correction of the accumulation at the highest points of the glacier reduces this to 0.15 m w.e. Here, we use HIRHAM5 to simulate the evolution of the SMB of Vatnajökull for the period 1981-2014 and show that the model provides a reasonable representation of the SMB for this period. However, a major source of uncertainty in the representation of the SMB is the representation of the albedo, and processes currently not accounted for in RCMs

  3. The importance of accurate glacier albedo for estimates of surface mass balance on Vatnajökull: evaluating the surface energy budget in a regional climate model with automatic weather station observations

    Directory of Open Access Journals (Sweden)

    L. S. Schmidt

    2017-07-01

    Full Text Available A simulation of the surface climate of Vatnajökull ice cap, Iceland, carried out with the regional climate model HIRHAM5 for the period 1980–2014, is used to estimate the evolution of the glacier surface mass balance (SMB. This simulation uses a new snow albedo parameterization that allows albedo to exponentially decay with time and is surface temperature dependent. The albedo scheme utilizes a new background map of the ice albedo created from observed MODIS data. The simulation is evaluated against observed daily values of weather parameters from five automatic weather stations (AWSs from the period 2001–2014, as well as in situ SMB measurements from the period 1995–2014. The model agrees well with observations at the AWS sites, albeit with a general underestimation of the net radiation. This is due to an underestimation of the incoming radiation and a general overestimation of the albedo. The average modelled albedo is overestimated in the ablation zone, which we attribute to an overestimation of the thickness of the snow layer and not taking the surface darkening from dirt and volcanic ash deposition during dust storms and volcanic eruptions into account. A comparison with the specific summer, winter, and net mass balance for the whole of Vatnajökull (1995–2014 shows a good overall fit during the summer, with a small mass balance underestimation of 0.04 m w.e. on average, whereas the winter mass balance is overestimated by on average 0.5 m w.e. due to too large precipitation at the highest areas of the ice cap. A simple correction of the accumulation at the highest points of the glacier reduces this to 0.15 m w.e. Here, we use HIRHAM5 to simulate the evolution of the SMB of Vatnajökull for the period 1981–2014 and show that the model provides a reasonable representation of the SMB for this period. However, a major source of uncertainty in the representation of the SMB is the representation of the albedo, and processes

  4. Potential feedbacks between snow cover, soil moisture and surface energy fluxes in Southern Norway

    Science.gov (United States)

    Brox Nilsen, Irene; Tallaksen, Lena M.; Stordal, Frode

    2017-04-01

    At high latitudes, the snow season has become shorter during the past decades because snowmelt is highly sensitive to a warmer climate. Snowmelt influences the energy balance by changing the albedo and the partitioning between latent and sensible heat fluxes. It further influences the water balance by changing the runoff and soil moisture. In a previous study, we identified southern Norway as a region where significant temperature changes in summer could potentially be explained by land-atmosphere interactions. In this study we hypothesise that changes in snow cover would influence the summer surface fluxes in the succeeding weeks or months. The exceptionally warm summer of 2014 was chosen as a test bed. In Norway, evapotranspiration is not soil moisture limited, but energy limited, under normal conditions. During warm summers, however, such as in 2014, evapotranspiration can be restricted by the available soil moisture. Using the Weather Research and Forecasting (WRF) model we replace the initial ground conditions for 2014 with conditions representative of a snow-poor spring and a snow-rich spring. WRF was coupled to Noah-MP at 3 km horizontal resolution in the inner domain, and the simulations covered mid-May through September 2014. Boundary conditions used to force WRF were taken from the Era-Interim reanalysis. Snow, runoff, soil moisture and soil temperature observational data were provided by the Norwegian Water Resources and Energy Directorate for validation. The validation shows generally good agreement with observations. Preliminary results show that the reduced snowpack, hereafter "sim1" increased the air temperature by up to 5 K and the surface temperature by up to 10 K in areas affected by snow changes. The increased snowpack, hereafter "sim2", decreased the air and surface temperature by the same amount. These are weekly mean values for the first eight simulation weeks from mid May. Because of the higher net energy available ( 100 Wm-2) in sim 1, both

  5. Evaluation of MODIS albedo product (MCD43A) over grassland, agriculture and forest surface types during dormant and snow-covered periods

    Science.gov (United States)

    Zhuosen Wang; Crystal B. Schaaf; Alan H. Strahler; Mark J. Chopping; Miguel O. Román; Yanmin Shuai; Curtis E. Woodcock; David Y. Hollinger; David R. Fitzjarrald

    2014-01-01

    This study assesses the Moderate-resolution Imaging Spectroradiometer (MODIS) BRDF/albedo 8 day standard product and products from the daily Direct Broadcast BRDF/albedo algorithm, and shows that these products agree well with ground-based albedo measurements during the more difficult periods of vegetation dormancy and snow cover. Cropland, grassland, deciduous and...

  6. Sea ice roughness: the key for predicting Arctic summer ice albedo

    Science.gov (United States)

    Landy, J.; Ehn, J. K.; Tsamados, M.; Stroeve, J.; Barber, D. G.

    2017-12-01

    Although melt ponds on Arctic sea ice evolve in stages, ice with smoother surface topography typically allows the pond water to spread over a wider area, reducing the ice-albedo and accelerating further melt. Building on this theory, we simulated the distribution of meltwater on a range of statistically-derived topographies to develop a quantitative relationship between premelt sea ice surface roughness and summer ice albedo. Our method, previously applied to ICESat observations of the end-of-winter sea ice roughness, could account for 85% of the variance in AVHRR observations of the summer ice-albedo [Landy et al., 2015]. Consequently, an Arctic-wide reduction in sea ice roughness over the ICESat operational period (from 2003 to 2008) explained a drop in ice-albedo that resulted in a 16% increase in solar heat input to the sea ice cover. Here we will review this work and present new research linking pre-melt sea ice surface roughness observations from Cryosat-2 to summer sea ice albedo over the past six years, examining the potential of winter roughness as a significant new source of sea ice predictability. We will further evaluate the possibility for high-resolution (kilometre-scale) forecasts of summer sea ice albedo from waveform-level Cryosat-2 roughness data in the landfast sea ice zone of the Canadian Arctic. Landy, J. C., J. K. Ehn, and D. G. Barber (2015), Albedo feedback enhanced by smoother Arctic sea ice, Geophys. Res. Lett., 42, 10,714-10,720, doi:10.1002/2015GL066712.

  7. Albedo recovery for hyperspectral image classification

    Science.gov (United States)

    Zhan, Kun; Wang, Haibo; Xie, Yuange; Zhang, Chutong; Min, Yufang

    2017-07-01

    Image intensity value is determined by both the albedo component and the shading component. The albedo component describes the physical nature of different objects at the surface of the earth, and land-cover classes are different from each other because of their intrinsic physical materials. We, therefore, recover the intrinsic albedo feature of the hyperspectral image to exploit the spatial semantic information. Then, we use the support vector machine (SVM) to classify the recovered intrinsic albedo hyperspectral image. The SVM tries to maximize the minimum margin to achieve good generalization performance. Experimental results show that the SVM with the intrinsic albedo feature method achieves a better classification performance than the state-of-the-art methods in terms of visual quality and three quantitative metrics.

  8. Observed radiative cooling over the Tibetan Plateau for the past three decades driven by snow cover-induced surface albedo anomaly

    Science.gov (United States)

    Chen, Xiaona; Long, Di; Hong, Yang; Liang, Shunlin; Hou, Aizhong

    2017-06-01

    Seasonal snow cover on the Tibetan Plateau (TP) is a sensitive indicator of climate change. Unlike the decreasing snow cover extent and associated weakening of radiative cooling effects for the Northern Hemisphere during recent decades reported by previous studies, snow cover variability over the TP and its impact on the energy budget remain largely unknown. We defined the snow cover-induced radiative forcing (SnRF) as the instantaneous perturbation to Earth's shortwave radiation at the top of the atmosphere (TOA) induced by the presence of snow cover. Here using satellite observations and a radiative kernel approach, we found slightly enhanced SnRF, i.e., a radiative cooling effect on the TP during the past three decades (1982-2014). However, this cooling effect weakened during 2001-2014 because of reduced snow cover at a rate of -0.61% decade-1 and land surface albedo at a rate of -0.72% decade-1. Changes in snow cover fraction are highly correlated with anomalies in land surface albedo (as) over the TP both spatially and temporally. Moreover, the SnRF is closely related to the direct observation of TOA shortwave flux anomalies (R2 = 0.54, p = 0.004) over the TP during 2001-2014. Despite the insignificant interannual variability in SnRF, its intra-annual variability has intensified driven mostly by enhanced SnRF during the snow accumulation season but weakened SnRF during the melt season, indicating greater energy release during the transition between accumulation and melt seasons. This may pose a great challenge to snow meltwater use and flood prediction for transboundary rivers originating from the TP, such as the Brahmaputra River basin.

  9. The magnitudes and timescales of global mean surface temperature feedbacks in climate models

    Directory of Open Access Journals (Sweden)

    A. Jarvis

    2011-12-01

    Full Text Available Because of the fundamental role feedbacks play in determining the response of surface temperature to perturbations in radiative forcing, it is important we understand the dynamic characteristics of these feedbacks. Rather than attribute the aggregate surface temperature feedback to particular physical processes, this paper adopts a linear systems approach to investigate the partitioning with respect to the timescale of the feedbacks regulating global mean surface temperature in climate models. The analysis reveals that there is a dominant net negative feedback realised on an annual timescale and that this is partially attenuated by a spectrum of positive feedbacks with characteristic timescales in the range 10 to 1000 yr. This attenuation was composed of two discrete phases which are attributed to the equilibration of "diffusive – mixed layer" and "circulatory – deep ocean" ocean heat uptake. The diffusive equilibration was associated with time constants on the decadal timescale and accounted for approximately 75 to 80 percent of the overall ocean heat feedback, whilst the circulatory equilibration operated on a centennial timescale and accounted for the remaining 20 to 25 percent of the response. This suggests that the dynamics of the transient ocean heat uptake feedback first discussed by Baker and Roe (2009 tends to be dominated by loss of diffusive heat uptake in climate models, rather than circulatory deep ocean heat equilibration.

  10. A Stabilizing Feedback Between Cloud Radiative Effects and Greenland Surface Melt: Verification From Multi-year Automatic Weather Station Measurements

    Science.gov (United States)

    Zender, C. S.; Wang, W.; van As, D.

    2017-12-01

    Clouds have strong impacts on Greenland's surface melt through the interaction with the dry atmosphere and reflective surfaces. However, their effects are uncertain due to the lack of in situ observations. To better quantify cloud radiative effects (CRE) in Greenland, we analyze and interpret multi-year radiation measurements from 30 automatic weather stations encompassing a broad range of climatological and topographical conditions. During melt season, clouds warm surface over most of Greenland, meaning the longwave greenhouse effect outweighs the shortwave shading effect; on the other hand, the spatial variability of net (longwave and shortwave) CRE is dominated by shortwave CRE and in turn by surface albedo, which controls the potential absorption of solar radiation when clouds are absent. The net warming effect decreases with shortwave CRE from high to low altitudes and from north to south (Fig. 1). The spatial correlation between albedo and net CRE is strong (r=0.93, pCRE seasonal trend is controlled by longwave CRE associated with cloud fraction and liquid water content. It becomes stronger from May to July and stays constant in August. In the ablation zone, albedo determines the net CRE seasonal trend, which decreases from May to July and increases afterwards. On an hourly timescale, we find two distinct radiative states in Greenland (Fig. 2). The clear state is characterized by clear-sky conditions or thin clouds, when albedo and solar zenith angle (SZA) weakly correlates with CRE. The cloudy state is characterized by opaque clouds, when the combination of albedo and SZA strongly correlates with CRE (r=0.85, pCRE, the large melt-season variability of these two non-cloud factors, albedo and solar zenith angle, explains the majority of the CRE variation in spatial distribution, seasonal trend in the ablation zone, and in hourly variability in the cloudy radiative state. Clouds warm the brighter and colder surfaces of Greenland, enhance snow melt, and tend to

  11. The West African monsoon onset in 2006: sensitivity to surface albedo, orography, SST and synoptic scale dry-air intrusions using WRF

    Energy Technology Data Exchange (ETDEWEB)

    Flaounas, Emmanouil [Universite Pierre et Marie Curie (UPMC), LATMOS/IPSL, Paris cedex 05 (France); Janicot, Serge [UPMC, LOCEAN/IPSL, IRD, Paris (France); Bastin, Sophie [UPMC, LATMOS/IPSL, CNRS, Paris (France); Roca, Remy [UPMC, LMD/IPSL, CNRS, Paris (France)

    2012-02-15

    In order to test the sensitivity of the transitional phase of the 2006 West African monsoon (WAM) onset to different mechanisms, weather research and forecasting (WRF) model simulations have been carried out addressing the role of the Saharan heat low (SHL) and its sensitivity to the albedo field and to the northern Africa orography, and the role of the sea surface temperature (SST) in the eastern tropical Atlantic and Mediterranean. Lowering albedo over the desert region induces a northward location of the inter-tropical convergence zone (ITCZ), while removing mountains in North Africa reduces rainfall over West Africa. Shifting SST forward by 15 days leads to a northward location of the ITCZ before the WAM onset. However none of these factors modifies the timing of the WAM onset in 2006. The transitional phase of the 2006 WAM onset has been examined in more detail. The enhancement of SHL intensity, combined with the development of the oceanic cold tongue in the Guinea gulf, leads to low-level moisture flux divergence in the ITCZ reducing rainfall and increasing low-level humidity over the Sahel. However, weakening of convection can be clearly attributed to dry-air intrusions in mid-levels, originating from the subtropical westerly jet and associated with Rossby wave pattern over North Africa. Sensitivity tests on the synoptic scale forcing outside of the WRF model domain confirm the dominating role of large-scale dynamics to control the transitional phase of the WAM onset and its timing. However it is shown that the regional factors can modulate this larger scale forcing. (orig.)

  12. Climate stability and cloud optical thickness feedbacks

    Science.gov (United States)

    Somerville, Richard C. J.; Iacobellis, Sam

    1989-01-01

    An improved radiative-convective model (RCM) has been developed and used to examine the role of cirrus clouds in the optical thickness feedback mechanism. Low and middle clouds are approximately black bodies for infrared radiative transfer, and so any increase in their optical thickness primarily increases the cloud albedo. Thus, if a climate warming is accompanied by an increase in average atmospheric absolute humidity and hence in average cloud liquid water content, low and middle cloud optical thickness and albedo may increase. The result is a negative feedback on the climate change, tending to reduce the surface temperature increase. Recent research suggests that the optical thickness feedback can depend sensitively on aspects of cirrus which are not well observed or adequately incorporated in typical present-day climate models.

  13. Albedo of the ice covered Weddell and Bellingshausen Seas

    OpenAIRE

    Weiss, A. I.; King, J. C.; Lachlan-Cope, T. A.; Ladkin, R. S.

    2012-01-01

    This study investigates the surface albedo of the sea ice areas adjacent to the Antarctic Peninsula during the austral summer. Aircraft measurements of the surface albedo, which were conducted in the sea ice areas of the Weddell and Bellingshausen Seas show significant differences between these two regions. The averaged surface albedo varied between 0.13 and 0.81. The ice cover of the Bellingshausen Sea consisted mainly of first year ice and the sea surface showed an averaged sea ice albedo o...

  14. A Continental United States High Resolution NLCD Land Cover – MODIS Albedo Database to Examine Albedo and Land Cover Change Relationships

    Science.gov (United States)

    Surface albedo influences climate by affecting the amount of solar radiation that is reflected at the Earth’s surface, and surface albedo is, in turn, affected by land cover. General Circulation Models typically use modeled or prescribed albedo to assess the influence of land co...

  15. An interactive ocean surface albedo scheme (OSAv1.0): formulation and evaluation in ARPEGE-Climat (V6.1) and LMDZ (V5A)

    Science.gov (United States)

    Séférian, Roland; Baek, Sunghye; Boucher, Olivier; Dufresne, Jean-Louis; Decharme, Bertrand; Saint-Martin, David; Roehrig, Romain

    2018-01-01

    Ocean surface represents roughly 70 % of the Earth's surface, playing a large role in the partitioning of the energy flow within the climate system. The ocean surface albedo (OSA) is an important parameter in this partitioning because it governs the amount of energy penetrating into the ocean or reflected towards space. The old OSA schemes in the ARPEGE-Climat and LMDZ models only resolve the latitudinal dependence in an ad hoc way without an accurate representation of the solar zenith angle dependence. Here, we propose a new interactive OSA scheme suited for Earth system models, which enables coupling between Earth system model components like surface ocean waves and marine biogeochemistry. This scheme resolves spectrally the various contributions of the surface for direct and diffuse solar radiation. The implementation of this scheme in two Earth system models leads to substantial improvements in simulated OSA. At the local scale, models using the interactive OSA scheme better replicate the day-to-day distribution of OSA derived from ground-based observations in contrast to old schemes. At global scale, the improved representation of OSA for diffuse radiation reduces model biases by up to 80 % over the tropical oceans, reducing annual-mean model-data error in surface upwelling shortwave radiation by up to 7 W m-2 over this domain. The spatial correlation coefficient between modeled and observed OSA at monthly resolution has been increased from 0.1 to 0.8. Despite its complexity, this interactive OSA scheme is computationally efficient for enabling precise OSA calculation without penalizing the elapsed model time.

  16. SAFARI 2000 MODIS L3 Albedo and Land Cover Data, Southern Africa, Dry Season 2000

    Data.gov (United States)

    National Aeronautics and Space Administration — The Filled Land Surface Albedo Product for Southern Africa, which is generated from MOD43B3 Product (the official Terra/MODIS-derived Land Surface Albedo -...

  17. SAFARI 2000 MODIS L3 Albedo and Land Cover Data, Southern Africa, Dry Season 2000

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: The Filled Land Surface Albedo Product for Southern Africa, which is generated from MOD43B3 Product (the official Terra/MODIS-derived Land Surface Albedo -...

  18. Cirrus feedback on interannual climate fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, C; Dessler, A E; Zelinka, M D; Yang, P; Wang, T

    2014-12-28

    Cirrus clouds are not only important in determining the current climate, but also play an important role in climate change and variability. Analysis of satellite observations shows that the amount and altitude of cirrus clouds (optical depth <3.6, cloud top pressure <440 hPa) increase in response to inter-annual surface warming. Thus, cirrus clouds are likely to act as a positive feedback on short-term climate fluctuations, by reducing the planet’s ability to radiate longwave radiation to space in response to planetary surface warming. Using cirrus cloud radiative kernels, the magnitude of cirrus feedback is estimated to be 0.20±0.21W/m2/°C, which is comparable to the surface albedo feedback. Most of the cirrus feedback comes from increasing cloud amount in the tropical tropopause layer (TTL) and subtropical upper troposphere.

  19. Satellite-based albedo, sea surface temperature and effective land roughness maps used in the HIRLAM model for weather and climate scenarios

    Science.gov (United States)

    Hasager, C. B.; Nielsen, N. W.; Christensen, J. H.; Soegaard, H.; Boegh, E.; Rasmussen, M. S.; Jensen, N. O.

    2001-12-01

    A study is conducted on the effect of introducing maps of geophysical parameters retrieved from satellite Earth Observation data into the atmospheric model HIRLAM (HIgh Resolution Limited Area Model). . The HIRLAM system was developed by the HIRLAM project group, a cooperative project of the national weather services in Denmark, Finland, Iceland, Ireland, the Netherlands, Norway and Sweden. It is currently used by weather services in several European countries. The exchanges of sensible heat, water vapour and momentum between the land- and ocean surface and the atmosphere are very important dynamical processes in this type of model. The results from the HIRLAM model when using the improved surface boundary conditions is validated from wind and temperature data at synoptic weather stations and surface flux data from land- and ocean meteorological masts in Denmark. The results from a set of scenarios covering the hurricane in Denmark in December 1999 and several springtime cases in 2000 show improved weather forecasts. The methodology on retrieving improved boundary conditions is based on satellite image data. Maps on the geophysical parameters albedo and sea surface temperature are retrieved at a 1 km spatial resolution from NOAA AVHRR. Furthermore, land cover maps based on Landsat TM satellite data are used to assess the regional roughness. The high-resolution land roughness map (Areal Systems Information in a 25 m pixel resolution) is area-averaged into effective roughness values (15 km grid) by using a non-linear aggregation technique (QJRMS 1999, vol 125, 2075-2102). The area-averaging is highly non-linear due to the turbulent physical processes involved. Thus the effective surface conditions cannot be obtained by simple averaging but only by a flow model taking horizontal advection into consideration. The effect of hedges in the landscape is included as a correction index based on a vector-based map. The land surface fluxes of heat and water vapour is also

  20. Influence of surface nudging on climatological mean and ENSO feedbacks in a coupled model

    Science.gov (United States)

    Zhu, Jieshun; Kumar, Arun

    2018-01-01

    Studies have suggested that surface nudging could be an efficient way to reconstruct the subsurface ocean variability, and thus a useful method for initializing climate predictions (e.g., seasonal and decadal predictions). Surface nudging is also the basis for climate models with flux adjustments. In this study, however, some negative aspects of surface nudging on climate simulations in a coupled model are identified. Specifically, a low-resolution version of the NCEP Climate Forecast System, version 2 (CFSv2L) is used to examine the influence of nudging on simulations of climatological mean and on the coupled feedbacks during ENSO. The effect on ENSO feedbacks is diagnosed following a heat budget analysis of mixed layer temperature anomalies. Diagnostics of the climatological mean state indicates that, even though SST biases in all ocean basins, as expected, are eliminated, the fidelity of climatological precipitation, surface winds and subsurface temperature (or the thermocline depth) could be highly ocean basin dependent. This is exemplified by improvements in the climatology of these variables in the tropical Atlantic, but degradations in the tropical Pacific. Furthermore, surface nudging also distorts the dynamical feedbacks during ENSO. For example, while the thermocline feedback played a critical role during the evolution of ENSO in a free simulation, it only played a minor role in the nudged simulation. These results imply that, even though the simulation of surface temperature could be improved in a climate model with surface nudging, the physics behind might be unrealistic.

  1. Understanding the drivers of post-fire albedo and radiative forcing across Alaska and Canada: implications for management.

    Science.gov (United States)

    Potter, S.; Solvik, K.; Erb, A.; Goetz, S. J.; Johnstone, J. F.; Mack, M. C.; Randerson, J. T.; Roman, M. O.; Schaaf, C. L.; Turetsky, M. R.; Veraverbeke, S.; Wang, Z.; Rogers, B. M.

    2017-12-01

    Boreal forest dynamics including succession, composition, carbon cycling, and surface-atmosphere energy exchanges are largely driven by fire. In Alaska and Canada, burned area and fire frequency have increased since the 1970s, and are projected to continue increasing into the 21st century. In contrast to other biomes, alterations to surface albedo from fires in North American boreal forests are one of the primary feedbacks to climate. Understanding how altered fire regimes impact vegetation composition and energy budgets is therefore critical to forecasting regional and global climate change. High-severity fires cause winter and spring albedo to increase due to increased snow exposure and replacement of evergreen conifers by deciduous broadleaf trees. Although summer albedo decreases initially due to the deposition of black carbon and charred surfaces, it typically increases for several decades thereafter when younger and brighter deciduous trees dominate. The net effect of these albedo changes is expected to result in substantive radiative cooling, but there has been little research to examine how albedo trajectories differ spatially and temporally as a result of differences in burn severity, species composition, topography, climate and soil properties, and what the associated implications for future energy balances are. Here we investigate drivers of post-fire monthly albedo trajectories across Canada and Alaska using a new Collection V006 500 m MODIS daily blue-sky albedo product and historical fires from the Canadian and Alaskan National Fire Databases. The impacts of varying fuel type, landscape position, soils, climate, and burn severity on monthly albedo trajectories are explored using a Random Forest model. This information is then used to predict long-term monthly albedo and radiative forcing for fires that occurred during the MODIS era (2001-2012). We find that higher severity burns in denser forests and environmental conditions that promote either

  2. Arctic sea ice albedo from AVHRR

    Science.gov (United States)

    Lindsay, R. W.; Rothrock, D. A.

    1994-01-01

    The seasonal cycle of surface albedo of sea ice in the Arctic is estimated from measurements made with the Advanced Very High Resolution Radiometer (AVHRR) on the polar-orbiting satellites NOAA-10 and NOAA-11. The albedos of 145 200-km-square cells are analyzed. The cells are from March through September 1989 and include only those for which the sun is more than 10 deg above the horizon. Cloud masking is performed manually. Corrections are applied for instrument calibration, nonisotropic reflection, atmospheric interference, narrowband to broadband conversion, and normalization to a common solar zenith angle. The estimated albedos are relative, with the instrument gain set to give an albedo of 0.80 for ice floes in March and April. The mean values for the cloud-free portions of individual cells range from 0.18 to 0.91. Monthly averages of cells in the central Arctic range from 0.76 in April to 0.47 in August. The monthly averages of the within-cell standard deviations in the central Arctic are 0.04 in April and 0.06 in September. The surface albedo and surface temperature are correlated most strongly in March (R = -0.77) with little correlation in the summer. The monthly average lead fraction is determined from the mean potential open water, a scaled representation of the temperature or albedo between 0.0 (for ice) and 1.0 (for water); in the central Arctic it rises from an average 0.025 in the spring to 0.06 in September. Sparse data on aerosols, ozone, and water vapor in the atmospheric column contribute uncertainties to instantaneous, area-average albedos of 0.13, 0.04, and 0.08. Uncertainties in monthly average albedos are not this large. Contemporaneous estimation of these variables could reduce the uncertainty in the estimated albedo considerably. The poor calibration of AVHRR channels 1 and 2 is another large impediment to making accurate albedo estimates.

  3. Atmospheric statistical dynamic models. Climate experiments: albedo experiments with a zonal atmospheric model

    International Nuclear Information System (INIS)

    Potter, G.L.; Ellsaesser, H.W.; MacCracken, M.C.; Luther, F.M.

    1978-06-01

    The zonal model experiments with modified surface boundary conditions suggest an initial chain of feedback processes that is largest at the site of the perturbation: deforestation and/or desertification → increased surface albedo → reduced surface absorption of solar radiation → surface cooling and reduced evaporation → reduced convective activity → reduced precipitation and latent heat release → cooling of upper troposphere and increased tropospheric lapse rates → general global cooling and reduced precipitation. As indicated above, although the two experiments give similar overall global results, the location of the perturbation plays an important role in determining the response of the global circulation. These two-dimensional model results are also consistent with three-dimensional model experiments. These results have tempted us to consider the possibility that self-induced growth of the subtropical deserts could serve as a possible mechanism to cause the initial global cooling that then initiates a glacial advance thus activating the positive feedback loop involving ice-albedo feedback (also self-perpetuating). Reversal of the cycle sets in when the advancing ice cover forces the wave-cyclone tracks far enough equatorward to quench (revegetate) the subtropical deserts

  4. Augmented visual feedback counteracts the effects of surface muscular functional electrical stimulation on physiological tremor

    Science.gov (United States)

    2013-01-01

    Background Recent studies suggest that surface muscular functional electrical stimulation (FES) might suppress neurological upper limb tremor. We assessed its effects on upper limb physiological tremor, which is mainly driven by mechanical-reflex oscillations. We investigated the interaction between FES and augmented visual feedback, since (a) most daily activities are performed using visual cues, and (b) augmented visual feedback exacerbates upper limb tremor. Methods 10 healthy subjects (23.4 ± 7.7 years) performed 2 postural tasks with combinations of FES (4 sites; frequency of stimulation: 30 Hz; pulse width: 300 microsec; range of current delivered 10–34 mAmp) and augmented visual feedback. Results Spectral analysis of tremor showed a decrease of power spectral density to 62.18% (p = 0.01), of the integral in the 8-12 Hz frequency band to 57.67% (p = 0.003), and of tremor root mean square (RMS) to 57.16% (p = 0.002) during FES, without any changes in tremor frequency. Augmented visual feedback blocked the beneficial effect of FES, as confirmed by power spectral analysis (p = 0.01). We found a statistically significant interaction between augmented visual feedback and electrical stimulation (p = 0.039). Conclusions Augmented visual feedback antagonizes the effects of FES on physiological tremor. The absence of changes of peak frequency argues against an effect of FES on mechanical properties of the upper limb. PMID:24063436

  5. Feedback Regulation of Intracellular Hydrostatic Pressure in Surface Cells of the Lens.

    Science.gov (United States)

    Gao, Junyuan; Sun, Xiurong; White, Thomas W; Delamere, Nicholas A; Mathias, Richard T

    2015-11-03

    In wild-type lenses from various species, an intracellular hydrostatic pressure gradient goes from ∼340 mmHg in central fiber cells to 0 mmHg in surface cells. This gradient drives a center-to-surface flow of intracellular fluid. In lenses in which gap-junction coupling is increased, the central pressure is lower, whereas if gap-junction coupling is reduced, the central pressure is higher but surface pressure is always zero. Recently, we found that surface cell pressure was elevated in PTEN null lenses. This suggested disruption of a feedback control system that normally maintained zero surface cell pressure. Our purpose in this study was to investigate and characterize this feedback control system. We measured intracellular hydrostatic pressures in mouse lenses using a microelectrode/manometer-based system. We found that all feedback went through transport by the Na/K ATPase, which adjusted surface cell osmolarity such that pressure was maintained at zero. We traced the regulation of Na/K ATPase activity back to either TRPV4, which sensed positive pressure and stimulated activity, or TRPV1, which sensed negative pressure and inhibited activity. The inhibitory effect of TRPV1 on Na/K pumps was shown to signal through activation of the PI3K/AKT axis. The stimulatory effect of TRPV4 was shown in previous studies to go through a different signal transduction path. Thus, there is a local two-legged feedback control system for pressure in lens surface cells. The surface pressure provides a pedestal on which the pressure gradient sits, so surface pressure determines the absolute value of pressure at each radial location. We speculate that the absolute value of intracellular pressure may set the radial gradient in the refractive index, which is essential for visual acuity. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  6. Links between extreme UV-radiation, total ozone, surface albedo and cloudiness: An analysis of 30 years of data from Switzerland and Austria

    Science.gov (United States)

    Rieder, H. E.; Staehelin, J.; Weihs, P.; Vuilleumier, L.; Blumthaler, M.; Holawe, F.; Lindfors, A.; Maeder, J. A.; Simic, S.; Wagner, J. E.; Walker, D.; Ribatet, M.

    2009-04-01

    Since the discovery of anthropogenic ozone depletion in the early 1970s (e.g. Molina and Rowland, 1974; Farman et al., 1985) the interest in stratospheric ozone trends and solar UV-B increased within the scientific community and the general public because of the link between reduced total column ozone and increased UV-radiation doses. Stratospheric ozone (e.g. Koch et al., 2005) and erythemal UV-radiation (e.g. Rieder et al., 2008) in the northern mid-latitudes are characterized by strong temporal variability. Long-term measurements of UV-B radiation are rare and datasets are only available for few locations and most of these measurements do not provide spectral information on the UV part of the spectra. During strong efforts in the reconstruction of erythemal UV, datasets of past UV-radiation doses became available for several measurement sites all over the globe. For Switzerland and Austria reconstructed UV datasets are available for 3 measurement sites (Davos, Sonnblick and Vienna) (Lindfors and Vuilleumier, 2005; Rieder et al., 2008). The world's longest ozone time series dating back to 1926 is available from Arosa, Switzerland, and is discussed in detail by Staehelin et al. (1998a,b). Recently new tools from extreme value theory have been applied to the Arosa time series to describe extreme events in low and high total ozone (Rieder et al., 2009). In our study we address the question of how much of the extremes in UV-radiation can be attributed to extremes in total ozone, high surface albedo and cloudiness. An analysis of the frequency distributions of such extreme events for the last decades is presented to gain a better understanding of the links between extreme erythemal UV-radiation, total ozone, surface albedo and clouds. References: Farman, J. C., Gardiner, B. G., and Shanklin, J. D.: Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction, Nature, 315, 207-210, 1985. Koch, G., Wernli, H., Schwierz, C., Staehelin, J., and Peter, T

  7. Spacecraft Attitude Determination with Earth Albedo Corrected Sun Sensor Measurements

    DEFF Research Database (Denmark)

    Bhanderi, Dan

    This thesis focuses on advanced modeling of the Earth albedo experienced by satellites in Earth orbit. The model of the Earth albedo maintains directional information of the Earth albedo irradiance from each partition on the Earth surface. This allows enhanced modeling of Sun sensor current outputs......-Method, Extended Kalman Filter, and Unscented Kalman Filter algorithms are presented and the results are compared. Combining the Unscented Kalman Filter with Earth albedo and enhanced Sun sensor modeling allows for three-axis attitude determination from Sun sensor only, which previously has been perceived...

  8. Snow cover and vegetation-induced decrease in global albedo from 2002 to 2016

    OpenAIRE

    Li, Qiuping; Ma, Mingguo; Wu, Xiaodan; Yang, Hong

    2018-01-01

    Land surface albedo is an essential parameter in regional and global climate models, and it is markedly influenced by land cover change. Variations in the albedo can affect the surface radiation budget and further impact the global climate. In this study, the interannual variation of albedo from 2002 to 2016 was estimated on the global scale using Moderate Resolution Imaging Spectroradiometer (MODIS) datasets. The presence and causes of the albedo changes for each specific region were also ex...

  9. Roles of energy conservation and climate feedback in Bjerknes compensation: a coupled modeling study

    Science.gov (United States)

    Dai, Haijin; Yang, Haijun; Yin, Jie

    2017-09-01

    The roles of energy balance and climate feedback in Bjerknes compensation (BJC) are studied through wind-perturbation experiments in a coupled climate model. Shutting down surface winds over the ocean causes significant reductions in both wind-driven and thermohaline overturning circulations, leading to a remarkable decrease in poleward ocean heat transport (OHT). The sea surface temperature (SST) responds with an increasing meridional gradient, resulting in a stronger Hadley Cell, and thus an enhanced atmosphere heat transport (AHT), compensating the OHT decrease. This is the so-called BJC. Coupled model experiments confirm that the occurrence of BJC is an intrinsic requirement of local energy conservation, and local climate feedback determines the degree of BJC, consistent with our previous theoretical results. Negative (positive or zero) local feedback results in AHT change undercompensating (overcompensating or perfectly compensating) OHT change. Using the radiative kernel technique, the general local feedback between the radiative balance at the top of the atmosphere and surface temperature can be partitioned into individual feedbacks that are related to perturbations in temperature, water vapor, surface albedo, and clouds. We find that the overcompensation in the tropics (extratropics) is mainly caused by positive feedbacks related to water vapor and clouds (surface albedo). The longwave feedbacks related to SST and atmospheric temperature are always negative and strong outside the tropics, well offsetting positive feedbacks in most regions and resulting in undercompensation. Different dominant feedbacks give different BJC scenarios at different regions, acting together to maintain the local energy balance.

  10. Estimating radiative feedbacks from stochastic fluctuations in surface temperature and energy imbalance

    Science.gov (United States)

    Proistosescu, C.; Donohoe, A.; Armour, K.; Roe, G.; Stuecker, M. F.; Bitz, C. M.

    2017-12-01

    Joint observations of global surface temperature and energy imbalance provide for a unique opportunity to empirically constrain radiative feedbacks. However, the satellite record of Earth's radiative imbalance is relatively short and dominated by stochastic fluctuations. Estimates of radiative feedbacks obtained by regressing energy imbalance against surface temperature depend strongly on sampling choices and on assumptions about whether the stochastic fluctuations are primarily forced by atmospheric or oceanic variability (e.g. Murphy and Forster 2010, Dessler 2011, Spencer and Braswell 2011, Forster 2016). We develop a framework around a stochastic energy balance model that allows us to parse the different contributions of atmospheric and oceanic forcing based on their differing impacts on the covariance structure - or lagged regression - of temperature and radiative imbalance. We validate the framework in a hierarchy of general circulation models: the impact of atmospheric forcing is examined in unforced control simulations of fixed sea-surface temperature and slab ocean model versions; the impact of oceanic forcing is examined in coupled simulations with prescribed ENSO variability. With the impact of atmospheric and oceanic forcing constrained, we are able to predict the relationship between temperature and radiative imbalance in a fully coupled control simulation, finding that both forcing sources are needed to explain the structure of the lagged-regression. We further model the dependence of feedback estimates on sampling interval by considering the effects of a finite equilibration time for the atmosphere, and issues of smoothing and aliasing. Finally, we develop a method to fit the stochastic model to the short timeseries of temperature and radiative imbalance by performing a Bayesian inference based on a modified version of the spectral Whittle likelihood. We are thus able to place realistic joint uncertainty estimates on both stochastic forcing and

  11. The Albedo of Kepler's Small Worlds

    Science.gov (United States)

    Jansen, Tiffany; Kipping, David

    2018-01-01

    The study of exoplanet phase curves has been established as a powerful tool for measuring the atmospheric properties of other worlds. To first order, phase curves have the same amplitude as occultations, yet far greater temporal baselines enabling substantial improvements in sensitivity. Even so, only a relatively small fraction of Kepler planets have detectable phase curves, leading to a population dominated by hot-Jupiters. One way to boost sensitivity further is to stack different planets of similar types together, giving rise to an average phase curve for a specific ensemble. In this work, we measure the average albedo, thermal redistribution efficiency, and greenhouse boosting factor from the average phase curves of 115 Neptunian and 50 Terran (solid) worlds. We construct ensemble phase curve models for both samples accounting for the reflection and thermal components and regress our models assuming a global albedo, redistribution factor and greenhouse factor in a Bayesian framework. We find modest evidence for a detected phase curve in the Neptunian sample, although the albedo and thermal properties are somewhat degenerate meaning we can only place an upper limit on the albedo of Ag < 0.23 and greenhouse factor of f < 1.40 to 95% confidence. As predicted theoretically, this confirms hot-Neptunes are darker than Neptune and Uranus. Additionally, we place a constraint on the albedo of solid, Terran worlds of Ag < 0.42 and f < 1.60 to 95% confidence, compatible with a dark Lunar-like surface.

  12. Analysis of snow feedbacks in 14 general circulation models

    Science.gov (United States)

    Randall, D. A.; Cess, R. D.; Blanchet, J. P.; Chalita, S.; Colman, R.; Dazlich, D. A.; Del Genio, A. D.; Keup, E.; Lacis, A.; Le Treut, H.; Liang, X.-Z.; McAvaney, B. J.; Mahfouf, J. F.; Meleshko, V. P.; Morcrette, J.-J.; Norris, P. M.; Potter, G. L.; Rikus, L.; Roeckner, E.; Royer, J. F.; Schlese, U.; Sheinin, D. A.; Sokolov, A. P.; Taylor, K. E.; Wetherald, R. T.; Yagai, I.; Zhang, M.-H.

    1994-10-01

    Snow feedbacks produced by 14 atmospheric general circulation models have been analyzed through idealized numerical experiments. Included in the analysis is an investigation of the surface energy budgets of the models. Negative or weak positive snow feedbacks occurred in some of the models, while others produced strong positive snow feedbacks. These feedbacks are due not only to melting snow, but also to increases in boundary temperature, changes in air temperature, changes in water vapor, and changes in cloudiness. As a result, the net response of each model is quite complex. We analyze in detail the responses of one model with a strong positive snow feedback and another with a weak negative snow feedback. Some of the models include a temperature dependence of the snow albedo, and this has significantly affected the results.

  13. A statistics-based temporal filter algorithm to map spatiotemporally continuous shortwave albedo from MODIS data

    Directory of Open Access Journals (Sweden)

    N. F. Liu

    2013-06-01

    Full Text Available Land-surface albedo plays a critical role in the earth's radiant energy budget studies. Satellite remote sensing provides an effective approach to acquire regional and global albedo observations. Owing to cloud coverage, seasonal snow and sensor malfunctions, spatiotemporally continuous albedo datasets are often inaccessible. The Global LAnd Surface Satellite (GLASS project aims at providing a suite of key land surface parameter datasets with high temporal resolution and high accuracy for a global change study. The GLASS preliminary albedo datasets are global daily land-surface albedo generated by an angular bin algorithm (Qu et al., 2013. Like other products, the GLASS preliminary albedo datasets are affected by large areas of missing data; beside, sharp fluctuations exist in the time series of the GLASS preliminary albedo due to data noise and algorithm uncertainties. Based on the Bayesian theory, a statistics-based temporal filter (STF algorithm is proposed in this paper to fill data gaps, smooth albedo time series, and generate the GLASS final albedo product. The results of the STF algorithm are smooth and gapless albedo time series, with uncertainty estimations. The performance of the STF method was tested on one tile (H25V05 and three ground stations. Results show that the STF method has greatly improved the integrity and smoothness of the GLASS final albedo product. Seasonal trends in albedo are well depicted by the GLASS final albedo product. Compared with MODerate resolution Imaging Spectroradiometer (MODIS product, the GLASS final albedo product has a higher temporal resolution and more competence in capturing the surface albedo variations. It is recommended that the quality flag should be always checked before using the GLASS final albedo product.

  14. Ocean Heat Uptake Slows 21st Century Surface Warming Driven by Extratropical Cloud Feedbacks

    Science.gov (United States)

    Frey, W.; Maroon, E.; Pendergrass, A. G.; Kay, J. E.

    2017-12-01

    Equilibrium climate sensitivity (ECS), the warming in response to instantaneously doubled CO2, has long been used to compare climate models. In many models, ECS is well correlated with warming produced by transient forcing experiments. Modifications to cloud phase at high latitudes in a state-of-the-art climate model, the Community Earth System Model (CESM), produce a large increase in ECS (1.5 K) via extratropical cloud feedbacks. However, only a small surface warming increase occurs in a realistic 21st century simulation including a full-depth dynamic ocean and the "business as usual" RCP8.5 emissions scenario. In fact, the increase in surface warming is only barely above the internal variability-generated range in the CESM Large Ensemble. The small change in 21st century warming is attributed to subpolar ocean heat uptake in both hemispheres. In the Southern Ocean, the mean-state circulation takes up heat while in the North Atlantic a slowdown in circulation acts as a feedback to slow surface warming. These results show the importance of subpolar ocean heat uptake in controlling the pace of warming and demonstrate that ECS cannot be used to reliably infer transient warming when it is driven by extratropical feedbacks.

  15. Simulations of tropical rainforest albedo: is canopy wetness important?

    Directory of Open Access Journals (Sweden)

    Silvia N.M. Yanagi

    Full Text Available Accurate information on surface albedo is essential for climate modelling, especially for regions such as Amazonia, where the response of the regional atmospheric circulation to the changes on surface albedo is strong. Previous studies have indicated that models are still unable to correctly reproduce details of the seasonal variation of surface albedo. Therefore, it was investigated the role of canopy wetness on the simulated albedo of a tropical rainforest by modifying the IBIS canopy radiation transfer code to incorporate the effects of canopy wetness on the vegetation reflectance. In this study, simulations were run using three versions of the land surface/ecosystem model IBIS: the standard version, the same version recalibrated to fit the data of albedo on tropical rainforests and a modified version that incorporates the effects of canopy wetness on surface albedo, for three sites in the Amazon forest at hourly and monthly scales. The results demonstrated that, at the hourly time scale, the incorporation of canopy wetness on the calculations of radiative transfer substantially improves the simulations results, whereas at the monthly scale these changes do not substantially modify the simulated albedo.

  16. Albedo as a modulator of climate response to tropical deforestation

    Science.gov (United States)

    Dirmeyer, Paul A.; Shukla, J.

    1994-01-01

    An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years' duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, is strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.

  17. Vertical profile of the specific surface area and density of the snow at Dome C and on a transect to Dumont D'Urville, Antarctica – albedo calculations and comparison to remote sensing products

    Directory of Open Access Journals (Sweden)

    J.-C. Gallet

    2011-08-01

    Full Text Available The specific surface area (SSA of snow determines in part the albedo of snow surfaces and the capacity of the snow to adsorb chemical species and catalyze reactions. Despite these crucial roles, almost no value of snow SSA are available for the largest permanent snow expanse on Earth, the Antarctic. We report the first extensive study of vertical profiles of snow SSA near Dome C (DC: 75°06' S, 123°20' E, 3233 m a.s.l. on the Antarctic plateau, and at seven sites during the logistical traverse between Dome C and the French coastal base Dumont D'Urville (DDU: 66°40' S, 140°01' E during the Austral summer 2008–2009. We used the DUFISSS system, which measures the IR reflectance of snow at 1310 nm with an integrating sphere. At DC, the mean SSA of the snow in the top 1 cm is 38 m2 kg−1, decreasing monotonically to 14 m2 kg−1 at a depth of 50 cm. Along the traverse, the snow SSA profile is similar to that at DC in the first 600 km from DC. Closer to DDU, the SSA of the top 5 cm is 23 m2 kg−1, decreasing to 19 m2 kg−1 at 50 cm depth. This difference is attributed to wind, which causes a rapid decrease of surface snow SSA, but forms hard windpacks whose SSA decrease more slowly with time. Since light-absorbing impurities are not concentrated enough to affect albedo, the vertical profiles of SSA and density were used to calculate the spectral albedo of the snow for several realistic illumination conditions, using the DISORT radiative transfer model. A preliminary comparison with MODIS data is presented and our calculations and MODIS data show similar trends.

  18. Observed positive vegetation-rainfall feedbacks in the Sahel dominated by a moisture recycling mechanism.

    Science.gov (United States)

    Yu, Yan; Notaro, Michael; Wang, Fuyao; Mao, Jiafu; Shi, Xiaoying; Wei, Yaxing

    2017-11-30

    Classic, model-based theory of land-atmosphere interactions across the Sahel promote positive vegetation-rainfall feedbacks dominated by surface albedo mechanism. However, neither the proposed positive vegetation-rainfall feedback nor its underlying albedo mechanism has been convincingly demonstrated using observational data. Here, we present observational evidence for the region's proposed positive vegetation-rainfall feedback on the seasonal to interannual time scale, and find that it is associated with a moisture recycling mechanism, rather than the classic albedo-based mechanism. Positive anomalies of remotely sensed vegetation greenness across the Sahel during the late and post-monsoon periods favor enhanced evapotranspiration, precipitable water, convective activity and rainfall, indicative of amplified moisture recycling. The identified modest low-level cooling and anomalous atmospheric subsidence in response to positive vegetation greenness anomalies are counter to the responses expected through the classic vegetation-albedo feedback mechanism. The observational analysis further reveals enhanced dust emissions in response to diminished Sahel vegetation growth, potentially contributing to the positive vegetation-rainfall feedback.

  19. NASA/GEWEX Surface Radiation Budget: Integrated Data Product With Reprocessed Radiance, Cloud, and Meteorology Inputs, and New Surface Albedo Treatment

    Science.gov (United States)

    Cox, Stephen J.; Stackhouse, Paul W., Jr.; Gupta, Shashi K.; Mikovitz, J. Colleen; Zhang, Taiping

    2016-01-01

    The NASA/GEWEX Surface Radiation Budget (SRB) project produces shortwave and longwave surface and top of atmosphere radiative fluxes for the 1983-near present time period. Spatial resolution is 1 degree. The current release 3.0 (available at gewex-srb.larc.nasa.gov) uses the International Satellite Cloud Climatology Project (ISCCP) DX product for pixel level radiance and cloud information. This product is subsampled to 30 km. ISCCP is currently recalibrating and recomputing their entire data series, to be released as the H product, at 10km resolution. The ninefold increase in pixel number will allow SRB a higher resolution gridded product (e.g. 0.5 degree), as well as the production of pixel-level fluxes. In addition to the input data improvements, several important algorithm improvements have been made. Most notable has been the adaptation of Angular Distribution Models (ADMs) from CERES to improve the initial calculation of shortwave TOA fluxes, from which the surface flux calculations follow. Other key input improvements include a detailed aerosol history using the Max Planck Institut Aerosol Climatology (MAC), temperature and moisture profiles from HIRS, and new topography, surface type, and snow/ice. Here we present results for the improved GEWEX Shortwave and Longwave algorithm (GSW and GLW) with new ISCCP data, the various other improved input data sets and the incorporation of many additional internal SRB model improvements. As of the time of abstract submission, results from 2007 have been produced with ISCCP H availability the limiting factor. More SRB data will be produced as ISCCP reprocessing continues. The SRB data produced will be released as part of the Release 4.0 Integrated Product, recognizing the interdependence of the radiative fluxes with other GEWEX products providing estimates of the Earth's global water and energy cycle (I.e., ISCCP, SeaFlux, LandFlux, NVAP, etc.).

  20. Inter-annual variabilities in biogeophysical feedback of terrestrial ecosystem to atmosphere using a land surface model

    Science.gov (United States)

    Seo, C.; Hong, S.; Jeong, H. M.; Jeon, J.

    2017-12-01

    Biogeophysical processes of terrestrial ecosystem such as water vapor and energy flux are the key features to understand ecological feedback to atmospheric processes and thus role of terrestrial ecosystem in climate system. For example, it has been recently known that the ecological feedback through water vapor and energy flux results in regulating regional weathers and climates which is one of the fundamental functions of terrestrial ecosystem. In regional scale, water vapor flux has been known to give negative feedback to atmospheric warming, while energy flux from the surface has been known to positive feedback. In this study, we explored the inter-annual variabilities in these two biogeophysical features to see how the climate regulating functions of terrestrial ecosystem have been changed with climate change. We selected a land surface model involving vegetation dynamics that is forced by atmospheric data from NASA including precipitation, temperature, wind, surface pressure, humidity, and incoming radiations. From the land surface model, we simulated 60-year water vapor and energy fluxes from 1961 to 2010, and calculates feedbacks of terrestrial ecosystem as in radiation amount into atmosphere. Then, we analyzed the inter-annual variabilities in the feedbacks. The results showed that some mid-latitude areas showing very high variabilities in precipitation showed higher positive feedback and/or lower negative feedback. These results suggest deterioration of the biogeophyisical factor of climate regulating function over those regions.

  1. Feedbacks Between Shallow Groundwater Dynamics and Surface Topography on Runoff Generation in Flat Fields

    Science.gov (United States)

    Appels, Willemijn M.; Bogaart, Patrick W.; van der Zee, Sjoerd E. A. T. M.

    2017-12-01

    In winter, saturation excess (SE) ponding is observed regularly in temperate lowland regions. Surface runoff dynamics are controlled by small topographical features that are unaccounted for in hydrological models. To better understand storage and routing effects of small-scale topography and their interaction with shallow groundwater under SE conditions, we developed a model of reduced complexity to investigate SE runoff generation, emphasizing feedbacks between shallow groundwater dynamics and mesotopography. The dynamic specific yield affected unsaturated zone water storage, causing rapid switches between negative and positive head and a flatter groundwater mound than predicted by analytical agrohydrological models. Accordingly, saturated areas were larger and local groundwater fluxes smaller than predicted, leading to surface runoff generation. Mesotopographic features routed water over larger distances, providing a feedback mechanism that amplified changes to the shape of the groundwater mound. This in turn enhanced runoff generation, but whether it also resulted in runoff events depended on the geometry and location of the depressions. Whereas conditions favorable to runoff generation may abound during winter, these feedbacks profoundly reduce the predictability of SE runoff: statistically identical rainfall series may result in completely different runoff generation. The model results indicate that waterlogged areas in any given rainfall event are larger than those predicted by current analytical groundwater models used for drainage design. This change in the groundwater mound extent has implications for crop growth and damage assessments.

  2. Effects of ozone-vegetation coupling on surface ozone air quality via biogeochemical and meteorological feedbacks

    Science.gov (United States)

    Sadiq, Mehliyar; Tai, Amos P. K.; Lombardozzi, Danica; Martin, Maria Val

    2017-02-01

    Tropospheric ozone is one of the most hazardous air pollutants as it harms both human health and plant productivity. Foliage uptake of ozone via dry deposition damages photosynthesis and causes stomatal closure. These foliage changes could lead to a cascade of biogeochemical and biogeophysical effects that not only modulate the carbon cycle, regional hydrometeorology and climate, but also cause feedbacks onto surface ozone concentration itself. In this study, we implement a semi-empirical parameterization of ozone damage on vegetation in the Community Earth System Model to enable online ozone-vegetation coupling, so that for the first time ecosystem structure and ozone concentration can coevolve in fully coupled land-atmosphere simulations. With ozone-vegetation coupling, present-day surface ozone is simulated to be higher by up to 4-6 ppbv over Europe, North America and China. Reduced dry deposition velocity following ozone damage contributes to ˜ 40-100 % of those increases, constituting a significant positive biogeochemical feedback on ozone air quality. Enhanced biogenic isoprene emission is found to contribute to most of the remaining increases, and is driven mainly by higher vegetation temperature that results from lower transpiration rate. This isoprene-driven pathway represents an indirect, positive meteorological feedback. The reduction in both dry deposition and transpiration is mostly associated with reduced stomatal conductance following ozone damage, whereas the modification of photosynthesis and further changes in ecosystem productivity are found to play a smaller role in contributing to the ozone-vegetation feedbacks. Our results highlight the need to consider two-way ozone-vegetation coupling in Earth system models to derive a more complete understanding and yield more reliable future predictions of ozone air quality.

  3. Measurements of spectral snow albedo at Neumayer, Antarctica

    Directory of Open Access Journals (Sweden)

    S. Wuttke

    2006-03-01

    Full Text Available Spectral albedo in high resolution, from 290 to 1050 nm, has been measured at Neumayer, Antarctica, (70°39' S, 8°15' W during the austral summer 2003/2004. At 500 nm, the spectral albedo nearly reaches unity, with slightly lower values below and above 500 nm. Above 600 nm, the spectral albedo decreases to values between 0.45 and 0.75 at 1000 nm. For one cloudless case an albedo up to 1.01 at 500 nm could be determined. This can be explained by the larger directional component of the snow reflectivity for direct incidence, combined with a slightly mislevelled sensor and the snow surface not being perfectly horizontal. A possible explanation for an observed decline in albedo is an increase in snow grain size. The theoretically predicted increase in albedo with increasing solar zenith angle (SZA could not be observed. This is explained by the small range of SZA during albedo measurements, combined with the effect of changing snow conditions outweighing the effect of changing SZA. The measured spectral albedo serves as input for radiative transfer models, describing radiation conditions in Antarctica.

  4. The albedo of snow for partially cloudy skies

    Science.gov (United States)

    Choudhury, B. J.; Chang, A. T. C.

    1980-01-01

    The input parameters of the model are atmospheric precipitable water, ozone content, turbidity, cloud optical thickness, size and shape of ice crystal of snow and surface pressure. The model outputs spectral and integrated solar flux snow reflectance as a function of solar elevation and fractional cloudcover. The model is illustrated using representative parameters for the Antarctic coastal regions. The albedo for a clear sky depends inversely on the solar elevation. At high elevation the albedo depends primarily upon the grain size; at low elevation this dependence is on grain size and shape. The gradient of the albedo-elevation curve increases as the grains get larger and faceted. The albedo for a dense overcast is a few percent higher than the clear sky albedo at high elevations. A simple relation between the grain size and the overcast albedo is obtained. For a set of grain size and shape, the albedo matrices (the albedo as a function of solar elevation and fractional cloudcover) are tabulated.

  5. Combining the effect of crops surface albedo variability on the radiative forcing together with crop GHG budgets calculated from in situ flux measurements in a life cycle assessment approach: methodology and results

    Science.gov (United States)

    Ceschia, E.; Ferlicoq, M.; Brut, A.; Tallec, T.

    2013-12-01

    The carbon and GHG budgets (GHGB) of the 2 crop sites with contrasted management located in South West France was estimated over a complete rotation by combining a classical LCA approach with on site CO2 flux measurements. At both sites, carbon inputs (organic fertilization, seeds), carbon exports (harvest) and net ecosystem production (NEP), measured with the eddy covariance technique, were estimated. The variability of the different terms and their relative contributions to the net ecosystem carbon budget (NECB) were analyzed for all site-years, and the effect of management on NECB was assessed. To account for GHG fluxes that were not directly measured on site, we estimated the emissions caused by field operations (EFO) for each site using emission factors from the literature. The EFO were added to the NECB to calculate the total GHGB for a range of cropping systems and management regimes. N2O emissions were calculated following the IPCC (2007) guidelines or and CH4 emissions were assumed to be negligible. Albedo was calculated continuously using the short wave incident and reflected radiation measurements in the field from CNR1 sensors. Rapid changes in surface albedo typical from those ecosystems and resulting from management and crop phenology were analysed. The annual radiative forcing for each plot was estimated by calculating the difference between a mean annual albedo for each crop and a reference bare soil albedo value calculated over 5 years for each plot. To finalize the radiative forcing calculation, the method developed by Muñoz et al (2010) using up and down atmospheric transmittance had to be corrected so it would only account for up-going atmospheric transmittance. Annual differences in radiative forcing between crops were then converted in g C equivalent m-2 in order to add this effect to the GHG budget of each crop within a rotation. This methodology could be applied to all ICOS/NEON cropland sites. We found that the differences in radiative

  6. The Surface Warfare Community's 360-Degree Feedback Pilot Program: A Preliminary Analysis and Evaluation Plan

    National Research Council Canada - National Science Library

    Williams, James M

    2005-01-01

    The system known as 360-degree feedback, also called multi-source or multi-rater feedback, is a development program that provides a recipient with feedback from supervisors, peers, and subordinates...

  7. Modified neural dynamic surface approach to output feedback of MIMO nonlinear systems.

    Science.gov (United States)

    Sun, Guofa; Li, Dongwu; Ren, Xuemei

    2015-02-01

    We report an adaptive output feedback dynamic surface control (DSC), maintaining the prescribed performance, for a class of uncertain nonlinear systems with multiinput and multioutput. Designing neural network observers and modifying the DSC method achieves several control objectives. First, to achieve output feedback control, the finite-time echo state networks (ESN) observer with fast convergence is designed to obtain the online system states. Thus, the immeasurable states in traditional state feedback control are estimated and the unknown functions are approximated by ESN. Then, a modified DSC approach is developed by introducing a high-order sliding mode differentiator to replace the first-order filter in each step. Thus, the effect of filter performance on closed-loop stability is reduced. Furthermore, the input to state stability guarantees that all signals of the whole closed-loop system are semiglobally uniformly ultimately bounded. Specifically, the performance functions make the tracking errors converge to a compact set around equilibrium. Two numerical examples illustrated the proposed control scheme with satisfactory results.

  8. Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates

    Directory of Open Access Journals (Sweden)

    V. Romanova

    2006-01-01

    Full Text Available Using an atmospheric general circulation model of intermediate complexity coupled to a sea ice – slab ocean model, we perform a number of sensitivity experiments under present-day orbital conditions and geographical distribution to assess the possibility that land albedo, atmospheric CO2, orography and oceanic heat transport may cause an ice-covered Earth. Changing only one boundary or initial condition, the model produces solutions with at least some ice-free oceans in the low latitudes. Using some combination of these forcing parameters, a full Earth's glaciation is obtained. We find that the most significant factor leading to an ice-covered Earth is the high land albedo in combination with initial temperatures set equal to the freezing point. Oceanic heat transport and orography play only a minor role for the climate state. Extremely low concentrations of CO2 also appear to be insufficient to provoke a runaway ice-albedo feedback, but the strong deviations in surface air temperatures in the Northern Hemisphere point to the existence of a strong nonlinearity in the system. Finally, we argue that the initial condition determines whether the system can go into a completely ice covered state, indicating multiple equilibria, a feature known from simple energy balance models.

  9. Assessing spatio-temporal variability and trends in modelled and measured Greenland Ice Sheet albedo (2000-2013)

    NARCIS (Netherlands)

    Alexander, P. M.; Tedesco, M.; Fettweis, X.; Van De Wal, R. S W|info:eu-repo/dai/nl/101899556; Smeets, C. J P P|info:eu-repo/dai/nl/191522236; Van Den Broeke, M. R.|info:eu-repo/dai/nl/073765643

    2014-01-01

    Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater production. In this study, we assess the spatio-temporal variability of GrIS albedo during June, July,

  10. The opposition effect in Saturn's main rings as seen by Cassini ISS: 4. Correlations of the surge morphology with surface albedos and VIMS spectral properties

    Science.gov (United States)

    Déau, Estelle; Dones, Luke; Mishchenko, Michael I.; West, Robert A.; Helfenstein, Paul; Hedman, Matt M.; Porco, Carolyn C.

    2018-05-01

    In this paper, we continue our analysis of the saturnian ring opposition effect seen by Cassini ISS. The ring opposition effect is a peak in the rings' reflectivity caused as the directions from a spot on the rings to the observer and to the light source, respectively, converge toward zero degrees. So far, the exact origin of the ring's opposition effect is still a matter of debate. In our previous work (Déau, et al., 2013, Icarus, 226, 591-603), we compared the opposition effect morphology with the rings' optical depth and found that only the slope of the linear part of the rings' phase curves was strongly correlated with the optical depth. We interpreted this as an indication of the predominant role of interparticle shadowing at moderate phase angles (α ∼ 10-40o). More recently (Déau, 2015, Icarus, 253, 311-345), we showed that interparticle shadowing cannot explain the behavior at low phase angles (α microscopic scale of the regolith, and there is a growing body of evidence that regolith grain size, porosity, roughness, and composition control the opposition surge behavior for α < 1o. To test this hypothesis, we compare the opposition surge morphology to the regolith albedo and other spectral properties related to the regolith, such as water ice band depths and spectral slopes derived from Cassini VIMS data (Hedman et al., 2013, Icarus, 223, 105-130). Indeed, it has been recently proven that coherent backscattering affects the water ice band depth variations with phase angle for icy saturnian regoliths (Kolokolova et al., 2010, The Astrophysical Journal Letters, 711, L71-L74). We find that the opposition surge morphology is strongly correlated with the water ice band depth and the regolith albedo. We interpret this finding as an indication that coherent backscattering plays a role in affecting both the water ice band depths and the opposition surge at low phase angles (α < 1o). As the regolith albedo and spectral properties are related to the grain size

  11. On the role of temperature feedbacks for Arctic amplification

    Science.gov (United States)

    Pithan, Felix; Mauritsen, Thorsten

    2013-04-01

    The amplification of global climate changes at the poles is a well-known feature of the climate system mentioned already by Arrhenius (1896). It has been linked to the surface-albedo feedback, changes in atmospheric and oceanic heat convergence, water vapour and cloud feedbacks and the albedo effect of black carbon on snow (Serreze and Barry, 2011). We here focus on the role of temperature feedbacks, which have received rather little attention in recent debates. The basic temperature feedback is the Planck feedback or the increase in the Earth's blackbody radiation due to a uniform temperature increase. Since the blackbody radiation scales with the fourth power of temperature, stronger warming is necessary in cold regions to balance a globally uniform radiative forcing. The second temperature feedback is caused by changes in the vertical atmospheric temperature structure: In the Tropics, deep convection leads to warming aloft being larger than at the surface, which causes a greater increase in outgoing longwave radiation compared a vertically uniform forcing and thus constitutes a negative feedback mechanism. In the Arctic, where warming is amplified at the surface, the lapse-rate feedback is positive (Wetherald and Manabe, 1975). We use CMIP5 model output and radiative Kernels to investigate the zonal distribution of temperature feedbacks. Arrhenius, S. (1896). On the influence of carbonic acid in the air upon the temperature of the ground Philos. Mag. J. Sci., 5, pp. 237-276 Serreze, M.C. and Barry, R.G. (2011) . Processes and impacts of Arctic amplification: A research synthesis, Global and Planetary Change, 77(1-2), pp. 85-96 Wetherald, R. and Manabe, S. (1975). The effects of changing the solar constant on the climate of a general circulation model. J. Atmos. Sci., 23 pp 2044-2059

  12. High-albedo materials for reducing building cooling energy use

    Energy Technology Data Exchange (ETDEWEB)

    Taha, H.; Sailor, D.; Akbari, H.

    1992-01-01

    One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building`s envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).

  13. High-albedo materials for reducing building cooling energy use

    Energy Technology Data Exchange (ETDEWEB)

    Taha, H.; Sailor, D.; Akbari, H.

    1992-01-01

    One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building's envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).

  14. Effects of support surface stability on feedback control of trunk posture.

    Science.gov (United States)

    Andreopoulou, Georgia; Maaswinkel, Erwin; Cofré Lizama, L Eduardo; van Dieën, Jaap H

    2015-04-01

    This study aimed to examine the interactions of visual, vestibular, proprioceptive, and tactile sensory manipulations and sitting on either a stable or an unstable surface on mediolateral (ML) trunk sway. Fifteen individuals were measured. In each trial, subjects sat as quiet as possible, on a stable or unstable surface, with or without each of four sensory manipulations: visual (eyes open/closed), vestibular (left and right galvanic vestibular stimulation alternating at 0.25 Hz), proprioceptive (left and right paraspinal muscle vibration alternating at 0.25 Hz), and tactile (minimal finger contact with object moving in the frontal plane at 0.25 Hz). The root mean square (RMS) and the power at 0.25 Hz (P25) of the ML trunk acceleration were the dependent variables. The latter was analyzed only for the rhythmic sensory manipulations and the reference condition. RMS was always significantly larger on the unstable than the stable surface. Closing the eyes caused a significant increase in RMS, more so on the unstable surface. Vestibular stimulation significantly increased RMS and P25 and more so on the unstable surface. Main effects of the proprioceptive manipulation were significant, but the interactions with surface condition were not. Finally, also tactile manipulation increased RMS and P25, but did not interact with surface condition. Sensory information in feedback control of trunk posture appears to be reweighted depending on stability of the environment. The absolute effects of visual and vestibular manipulations increase on an unstable surface, suggesting a relative decrease in the weights of proprioceptive and tactile information.

  15. Interacting with the biomolecular solvent accessible surface via a haptic feedback device

    Directory of Open Access Journals (Sweden)

    Hayward Steven

    2009-10-01

    Full Text Available Abstract Background From the 1950s computer based renderings of molecules have been produced to aid researchers in their understanding of biomolecular structure and function. A major consideration for any molecular graphics software is the ability to visualise the three dimensional structure of the molecule. Traditionally, this was accomplished via stereoscopic pairs of images and later realised with three dimensional display technologies. Using a haptic feedback device in combination with molecular graphics has the potential to enhance three dimensional visualisation. Although haptic feedback devices have been used to feel the interaction forces during molecular docking they have not been used explicitly as an aid to visualisation. Results A haptic rendering application for biomolecular visualisation has been developed that allows the user to gain three-dimensional awareness of the shape of a biomolecule. By using a water molecule as the probe, modelled as an oxygen atom having hard-sphere interactions with the biomolecule, the process of exploration has the further benefit of being able to determine regions on the molecular surface that are accessible to the solvent. This gives insight into how awkward it is for a water molecule to gain access to or escape from channels and cavities, indicating possible entropic bottlenecks. In the case of liver alcohol dehydrogenase bound to the inhibitor SAD, it was found that there is a channel just wide enough for a single water molecule to pass through. Placing the probe coincident with crystallographic water molecules suggests that they are sometimes located within small pockets that provide a sterically stable environment irrespective of hydrogen bonding considerations. Conclusion By using the software, named HaptiMol ISAS (available from http://www.haptimol.co.uk, one can explore the accessible surface of biomolecules using a three-dimensional input device to gain insights into the shape and water

  16. Design of a Novel Spectral Albedometer for Validating the MODerate Resolution Imaging Spectroradiometer Spectral Albedo Product

    Directory of Open Access Journals (Sweden)

    Hongmin Zhou

    2018-01-01

    Full Text Available Land surface shortwave broadband albedo is a key parameter in general circulation models and surface energy budget models. Multispectral satellite data are typically used to generate broadband albedo products in a three-step process: atmospheric correction, for converting the top-of-atmosphere observations to surface directional reflectance; angular modeling, for converting the surface directional reflectance to spectral albedo of each individual band; and finally, narrowband-to-broadband conversion, for transforming the spectral albedos to broadband albedos. Spectroradiometers can be used for validating surface directional reflectance products and pyranometers or broadband albedometers, for validating broadband albedo products, but spectral albedo products are rarely validated using ground measurements. In this study, we designed a new type of albedometer that can measure spectral albedos. It consists of multiple interference filters and a silicon detector, for measuring irradiance from 400–1100 nm. The linearity of the sensors is 99%, and the designed albedometer exhibits consistency up to 0.993, with a widely-used commercial instrument. A field experiment for measuring spectral albedo of grassland using this new albedometer was conducted in Yudaokou, China and the measurements are used for validating the MODerate Resolution Imaging Spectroradiometer (MODIS spectral albedos. The results show that the biases of the MODIS spectral albedos of the first four bands are −0.0094, 0.0065, 0.0159, and −0.0001, respectively. This new instrument provides an effective technique for validating spectral albedos of any satellite sensor in this spectral range, which is critical for improving satellite broadband albedo products.

  17. Feedback System Control Optimized Electrospinning for Fabrication of an Excellent Superhydrophobic Surface.

    Science.gov (United States)

    Yang, Jian; Liu, Chuangui; Wang, Boqian; Ding, Xianting

    2017-10-13

    Superhydrophobic surface, as a promising micro/nano material, has tremendous applications in biological and artificial investigations. The electrohydrodynamics (EHD) technique is a versatile and effective method for fabricating micro- to nanoscale fibers and particles from a variety of materials. A combination of critical parameters, such as mass fraction, ratio of N, N-Dimethylformamide (DMF) to Tetrahydrofuran (THF), inner diameter of needle, feed rate, receiving distance, applied voltage as well as temperature, during electrospinning process, to determine the morphology of the electrospun membranes, which in turn determines the superhydrophobic property of the membrane. In this study, we applied a recently developed feedback system control (FSC) scheme for rapid identification of the optimal combination of these controllable parameters to fabricate superhydrophobic surface by one-step electrospinning method without any further modification. Within five rounds of experiments by testing totally forty-six data points, FSC scheme successfully identified an optimal parameter combination that generated electrospun membranes with a static water contact angle of 160 degrees or larger. Scanning electron microscope (SEM) imaging indicates that the FSC optimized surface attains unique morphology. The optimized setup introduced here therefore serves as a one-step, straightforward, and economic approach to fabricate superhydrophobic surface with electrospinning approach.

  18. Glacial changes in warm pool climate dominated by shelf exposure and ice sheet albedo

    Science.gov (United States)

    Di Nezio, P. N.; Tierney, J. E.; Otto-Bliesner, B. L.; Timmermann, A.; Bhattacharya, T.; Brady, E. C.; Rosenbloom, N. A.

    2017-12-01

    The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool (IPWP) are unclear. We addressed this issue combining model simulations and paleoclimate reconstructions of the Last Glacial Maximum (LGM). Two drivers - the exposure of tropical shelves due to lower sea level and a monsoonal response to ice sheet albedo - explain the proxy-inferred patterns of hydroclimate change. Shelf exposure influences IPWP climate by weakening the ascending branch of the Walker circulation. This response is amplified by coupled interactions akin to the Bjerknes feedback involving a stronger sea-surface temperature (SST) gradient along the equatorial Indian Ocean (IO). Ice sheet albedo enhances the import of cold, dry air into the tropics, weakening the Afro-Asian monsoon system. This "ventilation" mechanism alters temperature contrasts between the Arabian Sea and surrounding land leading to further monsoon weakening. Additional simulations show that the altered SST patterns associated with these responses are essential for explaining the proxy-inferred changes. Together our results show that ice sheets are a first order driver of tropical climate on glacial-interglacial timescales. While glacial climates are not a straightforward analogue for the future, our finding of an active Bjerknes feedback deserves further attention in the context of future climate projections.

  19. Drought and Heat Waves: The Role of SST and Land Surface Feedbacks

    Science.gov (United States)

    Schubert, Siegfried

    2011-01-01

    Drought occurs on a wide range of time scales, and within a variety of different types of regional climates. At the shortest time scales it is often associated with heat waves that last only several weeks to a few months but nevertheless can have profound detrimental impacts on society (e.g., heat-related impacts on human health, desiccation of croplands, increased fire hazard), while at the longest time scales it can extend over decades and can lead to long term structural changes in many aspects of society (e.g., agriculture, water resources, wetlands, tourism, population shifts). There is now considerable evidence that sea surface temperatures (SSTs) play a leading role in the development of drought world-wide, especially at seasonal and longer time scales, though land-atmosphere feedbacks can also play an important role. At shorter (subseasonal) time scales, SSTs are less important, but land feedbacks can play a critical role in maintaining and amplifying the atmospheric conditions associated with heat waves and short-term droughts. This talk reviews our current understanding of the physical mechanisms that drive precipitation and temperature variations on subseasonal to centennial time scales. This includes an assessment of predictability, prediction skill, and user needs at all time scales.

  20. Climate feedback analysis of the GFDL IPCC AR4 global warming simulation

    Science.gov (United States)

    Castet, Christelle

    Both observed and modeled global warming pattern shows a large surface polar warming and a large upper atmospheric warming in the tropics. This pattern leads to an amplification (reduction) of the temperature gradient at upper levels (surface). Physical processes behind this temperature change are the external radiative forcing, and subsequent feedback processes that may amplify or dampen the climate response. This unique warming pattern suggests that high latitudes are very sensitive to climate change and also the area where the largest warming projection uncertainties occur. The objective of this study is to apply a new coupled atmosphere-surface climate feedback-response analysis method to quantify the contributions of the external forcing alone (doubling of carbon dioxide), and subsequent feedback processes to the 3-D global warming pattern in the GFDL_CM2.0 model. The feedbacks under consideration include the water vapor feedback, surface albedo feedback, surface turbulent heat flux feedback, and the sum of the change in cloud radiative forcing (CRF), vertical convective, and large-scale scale dynamical feedback. The partial temperature changes due to the external forcing and due to individual feedbacks are additive and their sum converges toward the temperature change produced by the original GFDL_CM2.0 global warming simulations. Therefore, our attributions of the global warming patter to individual thermodynamic and dynamical processes are mathematically robust and physically meaningful. The partial temperature change due to the water vapor feedback is found to be the largest contributor to the globally averaged surface warming. It is twice as large as the warming due to the external radiative forcing alone. The surface albedo feedback and change in surface cloud radiative forcing increase the surface temperature by a smaller amount. In addition, the changes in atmospheric cloud forcing and large-scale dynamics, as well as the surface turbulent heat flux

  1. Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

    Science.gov (United States)

    Cook, Joseph M.; Hodson, Andrew J.; Gardner, Alex S.; Flanner, Mark; Tedstone, Andrew J.; Williamson, Christopher; Irvine-Fynn, Tristram D. L.; Nilsson, Johan; Bryant, Robert; Tranter, Martyn

    2017-11-01

    The darkening effects of biological impurities on ice and snow have been recognised as a control on the surface energy balance of terrestrial snow, sea ice, glaciers and ice sheets. With a heightened interest in understanding the impacts of a changing climate on snow and ice processes, quantifying the impact of biological impurities on ice and snow albedo (bioalbedo) and its evolution through time is a rapidly growing field of research. However, rigorous quantification of bioalbedo has remained elusive because of difficulties in isolating the biological contribution to ice albedo from that of inorganic impurities and the variable optical properties of the ice itself. For this reason, isolation of the biological signature in reflectance data obtained from aerial/orbital platforms has not been achieved, even when ground-based biological measurements have been available. This paper provides the cell-specific optical properties that are required to model the spectral signatures and broadband darkening of ice. Applying radiative transfer theory, these properties provide the physical basis needed to link biological and glaciological ground measurements with remotely sensed reflectance data. Using these new capabilities we confirm that biological impurities can influence ice albedo, then we identify 10 challenges to the measurement of bioalbedo in the field with the aim of improving future experimental designs to better quantify bioalbedo feedbacks. These challenges are (1) ambiguity in terminology, (2) characterising snow or ice optical properties, (3) characterising solar irradiance, (4) determining optical properties of cells, (5) measuring biomass, (6) characterising vertical distribution of cells, (7) characterising abiotic impurities, (8) surface anisotropy, (9) measuring indirect albedo feedbacks, and (10) measurement and instrument configurations. This paper aims to provide a broad audience of glaciologists and biologists with an overview of radiative transfer and

  2. Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

    Directory of Open Access Journals (Sweden)

    J. M. Cook

    2017-11-01

    Full Text Available The darkening effects of biological impurities on ice and snow have been recognised as a control on the surface energy balance of terrestrial snow, sea ice, glaciers and ice sheets. With a heightened interest in understanding the impacts of a changing climate on snow and ice processes, quantifying the impact of biological impurities on ice and snow albedo (bioalbedo and its evolution through time is a rapidly growing field of research. However, rigorous quantification of bioalbedo has remained elusive because of difficulties in isolating the biological contribution to ice albedo from that of inorganic impurities and the variable optical properties of the ice itself. For this reason, isolation of the biological signature in reflectance data obtained from aerial/orbital platforms has not been achieved, even when ground-based biological measurements have been available. This paper provides the cell-specific optical properties that are required to model the spectral signatures and broadband darkening of ice. Applying radiative transfer theory, these properties provide the physical basis needed to link biological and glaciological ground measurements with remotely sensed reflectance data. Using these new capabilities we confirm that biological impurities can influence ice albedo, then we identify 10 challenges to the measurement of bioalbedo in the field with the aim of improving future experimental designs to better quantify bioalbedo feedbacks. These challenges are (1 ambiguity in terminology, (2 characterising snow or ice optical properties, (3 characterising solar irradiance, (4 determining optical properties of cells, (5 measuring biomass, (6 characterising vertical distribution of cells, (7 characterising abiotic impurities, (8 surface anisotropy, (9 measuring indirect albedo feedbacks, and (10 measurement and instrument configurations. This paper aims to provide a broad audience of glaciologists and biologists with an overview of

  3. Ceres Photometry and Albedo from Dawn Framing Camera Images

    Science.gov (United States)

    Schröder, S. E.; Mottola, S.; Keller, H. U.; Li, J.-Y.; Matz, K.-D.; Otto, K.; Roatsch, T.; Stephan, K.; Raymond, C. A.; Russell, C. T.

    2015-10-01

    The Dawn spacecraft is in orbit around dwarf planet Ceres. The onboard Framing Camera (FC) [1] is mapping the surface through a clear filter and 7 narrow-band filters at various observational geometries. Generally, Ceres' appearance in these images is affected by shadows and shading, effects which become stronger for larger solar phase angles, obscuring the intrinsic reflective properties of the surface. By means of photometric modeling we attempt to remove these effects and reconstruct the surface albedo over the full visible wavelength range. Knowledge of the albedo distribution will contribute to our understanding of the physical nature and composition of the surface.

  4. Assessment of NPP VIIRS Albedo Over Heterogeneous Crop Land in Northern China

    Science.gov (United States)

    Wu, Xiaodan; Wen, Jianguang; Xiao, Qing; Yu, Yunyue; You, Dongqin; Hueni, Andreas

    2017-12-01

    In this paper, the accuracy of Suomi National Polar-orbiting Partnership Visible Infrared Imaging Radiometer Suite (VIIRS) land surface albedo, which is derived from the direct estimation algorithm, was assessed using ground-based albedo observations from a wireless sensor network over a heterogeneous cropland in the Huailai station, northern China. Data from six nodes spanning 2013-2014 over vegetation, bare soil, and mixed terrain surfaces were utilized to provide ground reference at VIIRS pixel scale. The performance of VIIRS albedo was also compared with Global LAnd Surface Satellite (GLASS) and Moderate Resolution Imaging Spectroradiometer (MODIS) albedos (Collection 5 and 6). The results indicate that the current granular VIIRS albedo has a high accuracy with a root-mean-square error of 0.02 for typical land covers. They are significantly correlated with ground references indicated by a correlation coefficient (R) of 0.73. The VIIRS albedo shows distinct advantages to GLASS and MODIS albedos over bare soil and mixed-cover surfaces, while it is inferior to the other two products over vegetated surfaces. Furthermore, its time continuity and the ability to capture the abrupt change of surface albedo are better than that of GLASS and MODIS albedo.

  5. A Multi-Scale Validation Strategy for Albedo Products over Rugged Terrain and Preliminary Application in Heihe River Basin, China

    Directory of Open Access Journals (Sweden)

    Xingwen Lin

    2018-01-01

    Full Text Available The issue for the validation of land surface remote sensing albedo products over rugged terrain is the scale effects between the reference albedo measurements and coarse scale albedo products, which is caused by the complex topography. This paper illustrates a multi-scale validation strategy specified for coarse scale albedo validation over rugged terrain. A Mountain-Radiation-Transfer-based (MRT-based albedo upscaling model was proposed in the process of multi-scale validation strategy for aggregating fine scale albedo to coarse scale. The simulated data of both the reference coarse scale albedo and fine scale albedo were used to assess the performance and uncertainties of the MRT-based albedo upscaling model. The results showed that the MRT-based model could reflect the albedo scale effects over rugged terrain and provided a robust solution for albedo upscaling from fine scale to coarse scale with different mean slopes and different solar zenith angles. The upscaled coarse scale albedos had the great agreements with the simulated coarse scale albedo with a Root-Mean-Square-Error (RMSE of 0.0029 and 0.0017 for black sky albedo (BSA and white sky albedo (WSA, respectively. Then the MRT-based model was preliminarily applied for the assessment of daily MODerate Resolution Imaging Spectroradiometer (MODIS Albedo Collection V006 products (MCD43A3 C6 over rugged terrain. Results showed that the MRT-based model was effective and suitable for conducting the validation of MODIS albedo products over rugged terrain. In this research area, it was shown that the MCD43A3 C6 products with full inversion algorithm, were generally in agreement with the aggregated coarse scale reference albedos over rugged terrain in the Heihe River Basin, with the BSA RMSE of 0.0305 and WSA RMSE of 0.0321, respectively, which were slightly higher than those over flat terrain.

  6. Snow Cover and Vegetation-Induced Decrease in Global Albedo From 2002 to 2016

    Science.gov (United States)

    Li, Qiuping; Ma, Mingguo; Wu, Xiaodan; Yang, Hong

    2018-01-01

    Land surface albedo is an essential parameter in regional and global climate models, and it is markedly influenced by land cover change. Variations in the albedo can affect the surface radiation budget and further impact the global climate. In this study, the interannual variation of albedo from 2002 to 2016 was estimated on the global scale using Moderate Resolution Imaging Spectroradiometer (MODIS) datasets. The presence and causes of the albedo changes for each specific region were also explored. From 2002 to 2016, the MODIS-based albedo decreased globally, snow cover declined by 0.970 (percent per pixel), while the seasonally integrated normalized difference vegetation index increased by 0.175. Some obvious increases in the albedo were detected in Central Asia, northeastern China, parts of the boreal forest in Canada, and the temperate steppe in North America. In contrast, noticeable decreases in the albedo were found in the Siberian tundra, Europe, southeastern Australia, and northeastern regions of North America. In the Northern Hemisphere, the greening trend at high latitudes made more contribution to the decline in the albedo. However, the dramatic fluctuation of snow-cover at midlatitudes predominated in the change of albedo. Our analysis can help to understand the roles that vegetation and snow cover play in the variation of albedo on global and regional scales.

  7. Global analysis of radiative forcing from fire-induced shortwave albedo change

    NARCIS (Netherlands)

    López-Saldaña, G.; Bistinas, I.; Pereira, J. M.C.

    2015-01-01

    Land surface albedo, a key parameter to derive Earth's surface energy balance, is used in the parameterization of numerical weather prediction, climate monitoring and climate change impact assessments. Changes in albedo due to fire have not been fully investigated on a continental and global scale.

  8. Diurnal variations in the UV albedo of arctic snow

    Directory of Open Access Journals (Sweden)

    O. Meinander

    2008-11-01

    Full Text Available The relevance of snow for climate studies is based on its physical properties, such as high surface reflectivity. Surface ultraviolet (UV albedo is an essential parameter for various applications based on radiative transfer modeling. Here, new continuous measurements of the local UV albedo of natural Arctic snow were made at Sodankylä (67°22'N, 26°39'E, 179 m a.s.l. during the spring of 2007. The data were logged at 1-min intervals. The accumulation of snow was up to 68 cm. The surface layer thickness varied from 0.5 to 35 cm with the snow grain size between 0.2 and 2.5 mm. The midday erythemally weighted UV albedo ranged from 0.6 to 0.8 in the accumulation period, and from 0.5 to 0.7 during melting. During the snow melt period, under cases of an almost clear sky and variable cloudiness, an unexpected diurnal decrease of 0.05 in albedo soon after midday, and recovery thereafter, was detected. This diurnal decrease in albedo was found to be asymmetric with respect to solar midday, thus indicating a change in the properties of the snow. Independent UV albedo results with two different types of instruments confirm these findings. The measured temperature of the snow surface was below 0°C on the following mornings. Hence, the reversible diurnal change, evident for ~1–2 h, could be explained by the daily metamorphosis of the surface of the snowpack, in which the temperature of the surface increases, melting some of the snow to liquid water, after which the surface freezes again.

  9. Cloud optical thickness feedbacks in the CO2 climate problem

    Science.gov (United States)

    Somerville, R. C. J.

    1985-01-01

    A radiative-convective equilibrium model is developed and applied to study cloud optical thickness feedbacks in the CO2 climate problem. The basic hypothesis is that in the warmer and moister CO2-rich atmosphere, cloud liquid water content will generally be larger than at present, so that cloud optical thickness will be larger too. For clouds other than thin cirrus, the result is to increase the albedo more than to increase the greenhouse effect. Thus the sign of the feedback is negative: cloud optical properties alter in such a way as to reduce the surface and tropospheric warming caused by the addition of CO2. This negative feedback can be substantial. When observational estimates of the temperature dependence of cloud liquid water content are employed in the model, the surface temperature change due to doubling CO2 is reduced by about one half.

  10. Comparison of surface energy budgets and feedbacks to microclimate among different land use types in an agro-pastoral ecotone of northern China.

    Science.gov (United States)

    Zhao, Wei; Hu, Zhongmin; Li, Shenggong; Guo, Qun; Liu, Zhengjia; Zhang, Leiming

    2017-12-01

    The biophysical effect of land use conversion plays a significant role in regulating climate change. Owing to albedo and evapotranspiration (ET) change, the effect of energy budget difference on land surface temperature (LST) is important but unclear among contrasting land use types, especially in temperate semi-arid regions. Based on moderate-resolution imaging spectroradiometer (MODIS) data, we compared the differences in albedo, ET, and LST between cropland and grassland (CR-GR), and between planted forest and grassland (PF-GR) in the Horqin Sandy Land of Inner Mongolia, an agro-pastoral ecotone of northern China. Our main objective was to explore the magnitude and direction of albedo and ET change during the growing season and, subsequently, to estimate the biophysical effects on LST as a result of land use and land cover change. Our results indicate no significant difference in mean monthly albedo for CR-GR and PF-GR. Cropland lost more water through ET and significantly decreased daytime LST compared with grassland from July to September, but no significant differences in ET and LST were observed for PF-GR in any month. The biophysical climate effects were more pronounced for CR-GR compared with PF-GR. The response of LST to the changes in energy budget confirmed that ET was the critical driving factor relative to albedo. Compared with grassland, cropland and planted forest tended to cool the land surface by 5.15°C and 1.51°C during the growing season, respectively, because of the biophysical effects. Our findings suggest the significance of local-scale biophysical effect on climate variation after land use conversion in semi-arid regions. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. ALBEDO PATTERN RECOGNITION AND TIME-SERIES ANALYSES IN MALAYSIA

    Directory of Open Access Journals (Sweden)

    S. A. Salleh

    2012-07-01

    Full Text Available Pattern recognition and time-series analyses will enable one to evaluate and generate predictions of specific phenomena. The albedo pattern and time-series analyses are very much useful especially in relation to climate condition monitoring. This study is conducted to seek for Malaysia albedo pattern changes. The pattern recognition and changes will be useful for variety of environmental and climate monitoring researches such as carbon budgeting and aerosol mapping. The 10 years (2000–2009 MODIS satellite images were used for the analyses and interpretation. These images were being processed using ERDAS Imagine remote sensing software, ArcGIS 9.3, the 6S code for atmospherical calibration and several MODIS tools (MRT, HDF2GIS, Albedo tools. There are several methods for time-series analyses were explored, this paper demonstrates trends and seasonal time-series analyses using converted HDF format MODIS MCD43A3 albedo land product. The results revealed significance changes of albedo percentages over the past 10 years and the pattern with regards to Malaysia's nebulosity index (NI and aerosol optical depth (AOD. There is noticeable trend can be identified with regards to its maximum and minimum value of the albedo. The rise and fall of the line graph show a similar trend with regards to its daily observation. The different can be identified in term of the value or percentage of rises and falls of albedo. Thus, it can be concludes that the temporal behavior of land surface albedo in Malaysia have a uniform behaviours and effects with regards to the local monsoons. However, although the average albedo shows linear trend with nebulosity index, the pattern changes of albedo with respects to the nebulosity index indicates that there are external factors that implicates the albedo values, as the sky conditions and its diffusion plotted does not have uniform trend over the years, especially when the trend of 5 years interval is examined, 2000 shows high

  12. Updating representation of land surface-atmosphere feedbacks in airborne campaign modeling analysis

    Science.gov (United States)

    Huang, M.; Carmichael, G. R.; Crawford, J. H.; Chan, S.; Xu, X.; Fisher, J. A.

    2017-12-01

    An updated modeling system to support airborne field campaigns is being built at NASA Ames Pleiades, with focus on adjusting the representation of land surface-atmosphere feedbacks. The main updates, referring to previous experiences with ARCTAS-CARB and CalNex in the western US to study air pollution inflows, include: 1) migrating the WRF (Weather Research and Forecasting) coupled land surface model from Noah to improved/more complex models especially Noah-MP and Rapid Update Cycle; 2) enabling the WRF land initialization with suitably spun-up land model output; 3) incorporating satellite land cover, vegetation dynamics, and soil moisture data (i.e., assimilating Soil Moisture Active Passive data using the ensemble Kalman filter approach) into WRF. Examples are given of comparing the model fields with available aircraft observations during spring-summer 2016 field campaigns taken place at the eastern side of continents (KORUS-AQ in South Korea and ACT-America in the eastern US), the air pollution export regions. Under fair weather and stormy conditions, air pollution vertical distributions and column amounts, as well as the impact from land surface, are compared. These help identify challenges and opportunities for LEO/GEO satellite remote sensing and modeling of air quality in the northern hemisphere. Finally, we briefly show applications of this system on simulating Australian conditions, which would explore the needs for further development of the observing system in the southern hemisphere and inform the Clean Air and Urban Landscapes (https://www.nespurban.edu.au) modelers.

  13. Generation of synthetic surface electromyography signals under fatigue conditions for varying force inputs using feedback control algorithm.

    Science.gov (United States)

    Venugopal, G; Deepak, P; Ghosh, Diptasree M; Ramakrishnan, S

    2017-11-01

    Surface electromyography is a non-invasive technique used for recording the electrical activity of neuromuscular systems. These signals are random, complex and multi-component. There are several techniques to extract information about the force exerted by muscles during any activity. This work attempts to generate surface electromyography signals for various magnitudes of force under isometric non-fatigue and fatigue conditions using a feedback model. The model is based on existing current distribution, volume conductor relations, the feedback control algorithm for rate coding and generation of firing pattern. The result shows that synthetic surface electromyography signals are highly complex in both non-fatigue and fatigue conditions. Furthermore, surface electromyography signals have higher amplitude and lower frequency under fatigue condition. This model can be used to study the influence of various signal parameters under fatigue and non-fatigue conditions.

  14. The Importance of Snow Albedo for Ice Sheet Evolution over the Last Glacial Cycle

    Science.gov (United States)

    Ganopolski, A.; Willeit, M.

    2017-12-01

    The surface energy and mass balance of ice sheets strongly depends on the amount of solar radiation absorbed at the surface, which is mainly controlled by the albedo of snow and ice. Here, using an Earth system model of intermediate complexity, we explore the role played by surface albedo for the simulation of glacial cycles. We show that the evolution of the Northern Hemisphere ice sheets over the last glacial cycle is very sensitive to the representation of snow albedo in the model. It is well known that the albedo of snow depends strongly on the snow grain size and the content of light absorbing impurities. Excluding either the snow aging effect or the dust darkening effect on snow albedo leads to an excessive ice build-up during glacial times and consequently to a failure in simulating deglaciation. While the effect of snow grain growth on snow albedo is well constrained, the albedo reduction due to the presence of dust in snow is much more uncertain, because the light absorbing properties of dust vary widely as a function of dust composition. We also show that assuming slightly different optical properties of dust leads to very different ice sheet and climate evolutions in the model. Conversely, ice sheet evolution is less sensitive to the choice of ice albedo in the model. We conclude that a proper representation of snow albedo is a fundamental prerequisite for a successful simulation of glacial cycles.

  15. Comparative global albedo and color maps of the Uranian satellites

    International Nuclear Information System (INIS)

    Buratti, B.J.; Mosher, J.A.

    1991-01-01

    The surfaces of the Uranian satellites Ariel, Miranda, Oberon, Titania, and Umbriel are characterized on the basis of Voyager observations. Tables of spectrophotometric data and maps of normal reflectances, green/violet ratios, and possible geological formations are presented and discussed in detail. Variations in albedo are found to be associated with impact features, and it is inferred from color differences that the upper surface of Ariel contains a higher proportion of redder material (tentatively identified as accreted low-albedo meteoritic dust) than those of the other moons. 42 refs

  16. The influence of inter-annually varying albedo on regional climate and drought

    KAUST Repository

    Meng, Xianhong

    2013-05-05

    Albedo plays an important role in land-atmosphere interactions and local climate. This study presents the impact on simulating regional climate, and the evolution of a drought, when using the default climatological albedo as is usually done in regional climate modelling, or using the actual observed albedo which is rarely done. Here, time-varying satellite derived albedo data is used to update the lower boundary condition of the Weather Research and Forecasting regional climate model in order to investigate the influence of observed albedo on regional climate simulations and also potential changes to land-atmosphere feedback over south-east Australia. During the study period from 2000 to 2008, observations show that albedo increased with an increasingly negative precipitation anomaly, though it lagged precipitation by several months. Compared to in-situ observations, using satellite observed albedo instead of the default climatological albedo provided an improvement in the simulated seasonal mean air temperature. In terms of precipitation, both simulations reproduced the drought that occurred from 2002 through 2006. Using the observed albedo produced a drier simulation overall. During the onset of the 2002 drought, albedo changes enhanced the precipitation reduction by 20 % on average, over locations where it was active. The area experiencing drought increased 6.3 % due to the albedo changes. Two mechanisms for albedo changes to impact land-atmosphere drought feedback are investigated. One accounts for the increased albedo, leading to reduced turbulent heat flux and an associated decrease of moist static energy density in the planetary boundary layer; the other considers that enhanced local radiative heating, due to the drought, favours a deeper planetary boundary layer, subsequently decreasing the moist static energy density through entrainment of the free atmosphere. Analysis shows that drought related large-scale changes in the regional climate favour a

  17. Global Cooling: Effect of Urban Albedo on Global Temperature

    Energy Technology Data Exchange (ETDEWEB)

    Akbari, Hashem; Menon, Surabi; Rosenfeld, Arthur

    2007-05-22

    In many urban areas, pavements and roofs constitute over 60% of urban surfaces (roof 20-25%, pavements about 40%). The roof and the pavement albedo can be increased by about 0.25 and 0.10, respectively, resulting in a net albedo increase for urban areas of about 0.1. Many studies have demonstrated building cooling-energy savings in excess of 20% upon raising roof reflectivity from an existing 10-20% to about 60%. We estimate U.S. potential savings in excess of $1 billion (B) per year in net annual energy bills. Increasing albedo of urban surfaces can reduce the summertime urban temperature and improve the urban air quality. Increasing the urban albedo has the added benefit of reflecting more of the incoming global solar radiation and countering the effect of global warming. We estimate that increasing albedo of urban areas by 0.1 results in an increase of 3 x 10{sup -4} in Earth albedo. Using a simple global model, the change in air temperature in lowest 1.8 km of the atmosphere is estimated at 0.01K. Modelers predict a warming of about 3K in the next 60 years (0.05K/year). Change of 0.1 in urban albedo will result in 0.01K global cooling, a delay of {approx}0.2 years in global warming. This 0.2 years delay in global warming is equivalent to 10 Gt reduction in CO2 emissions.

  18. Can feedback analysis be used to uncover the physical origin of climate sensitivity and efficacy differences?

    Science.gov (United States)

    Rieger, Vanessa S.; Dietmüller, Simone; Ponater, Michael

    2017-10-01

    Different strengths and types of radiative forcings cause variations in the climate sensitivities and efficacies. To relate these changes to their physical origin, this study tests whether a feedback analysis is a suitable approach. For this end, we apply the partial radiative perturbation method. Combining the forward and backward calculation turns out to be indispensable to ensure the additivity of feedbacks and to yield a closed forcing-feedback-balance at top of the atmosphere. For a set of CO2-forced simulations, the climate sensitivity changes with increasing forcing. The albedo, cloud and combined water vapour and lapse rate feedback are found to be responsible for the variations in the climate sensitivity. An O3-forced simulation (induced by enhanced NOx and CO surface emissions) causes a smaller efficacy than a CO2-forced simulation with a similar magnitude of forcing. We find that the Planck, albedo and most likely the cloud feedback are responsible for this effect. Reducing the radiative forcing impedes the statistical separability of feedbacks. We additionally discuss formal inconsistencies between the common ways of comparing climate sensitivities and feedbacks. Moreover, methodical recommendations for future work are given.

  19. MODIS-Derived 1.64 micron white-sky albedo on a global, 1-minute equal angle grid (Collection 004 and 005)

    Data.gov (United States)

    National Aeronautics and Space Administration — The Filled Land Surface Albedo Product is a global data set of spatially complete albedo maps. It was derived from the MODIS MOD43B3 Land product and includes both...

  20. MODIS Derived 1.24 micron white-sky albedo on a global, 1-minute equal angle grid (Collection 004 and 005)

    Data.gov (United States)

    National Aeronautics and Space Administration — The Filled Land Surface Albedo Product is a global data set of spatially complete albedo maps. It was derived from the MODIS MOD43B3 Land product and includes both s...

  1. MODIS-Derived 0.66 micron white-sky albedo on a global, 1-minute equal angle grid (Collection 004 and 005)

    Data.gov (United States)

    National Aeronautics and Space Administration — Product Description ------------------- The Filled Land Surface Albedo Product is a global data set of spatially complete albedo maps. It was derived from the MODIS...

  2. MODIS Derived 2.13 micron white-sky albedo on a global, 1-minute equal angle grid (Collection 004 and 005)

    Data.gov (United States)

    National Aeronautics and Space Administration — The Filled Land Surface Albedo Product is a global data set of spatially complete albedo maps. It was derived from the MODIS MOD43B3 Land product and includes both...

  3. MODIS Derived 0.86 micron white-sky albedo on a global, 1-minute equal angle grid (Collection 004 and 005)

    Data.gov (United States)

    National Aeronautics and Space Administration — The Filled Land Surface Albedo Product is a global data set of spatially complete albedo maps. It was derived from the MODIS MOD43B3 Land product and includes both...

  4. Variability in modeled cloud feedback tied to differences in the climatological spatial pattern of clouds

    Science.gov (United States)

    Siler, Nicholas; Po-Chedley, Stephen; Bretherton, Christopher S.

    2018-02-01

    Despite the increasing sophistication of climate models, the amount of surface warming expected from a doubling of atmospheric CO_2 (equilibrium climate sensitivity) remains stubbornly uncertain, in part because of differences in how models simulate the change in global albedo due to clouds (the shortwave cloud feedback). Here, model differences in the shortwave cloud feedback are found to be closely related to the spatial pattern of the cloud contribution to albedo (α) in simulations of the current climate: high-feedback models exhibit lower (higher) α in regions of warm (cool) sea-surface temperatures, and therefore predict a larger reduction in global-mean α as temperatures rise and warm regions expand. The spatial pattern of α is found to be strongly predictive (r=0.84) of a model's global cloud feedback, with satellite observations indicating a most-likely value of 0.58± 0.31 Wm^{-2} K^{-1} (90% confidence). This estimate is higher than the model-average cloud feedback of 0.43 Wm^{-2} K^{-1}, with half the range of uncertainty. The observational constraint on climate sensitivity is weaker but still significant, suggesting a likely value of 3.68 ± 1.30 K (90% confidence), which also favors the upper range of model estimates. These results suggest that uncertainty in model estimates of the global cloud feedback may be substantially reduced by ensuring a realistic distribution of clouds between regions of warm and cool SSTs in simulations of the current climate.

  5. The albedo of martian dunes: Insights into aeolian activity and dust devil formation

    Science.gov (United States)

    Bennett, K. A.; Fenton, L.; Bell, J. F.

    2017-06-01

    Wind is the primary geologic process currently active on the surface of Mars. Albedo variations at eight dune fields were tested based on the hypothesis that a dune's ripple migration rate is correlated to its albedo. On Mars, where the atmospheric pressure is low, dust is removed from the surface of a dune by saltating sand. Therefore, more active dunes should remove dust more efficiently than less active dunes. A dune's albedo was found to be low in the first half of the Mars year (Ls = 0-180°) and high in the second half (Ls = 180-360°) during the dusty season. Both dunes with fast- and slow-moving ripples exhibit low albedos, whereas dunes with ripples that migrate at intermediate speeds exhibit high albedos. A dune's minimum albedo does not have a simple correlation with its ripple migration rate. Instead, we propose that dust devils remove dust on slow-moving and immobile dunes, whereas saltating sand caused by strong winds removes dust on faster dunes. Albedo should not be used as a proxy for migration rate of ripples or dune activity, as it may be difficult to distinguish between fast- and slow-moving ripples on dunes that have the same albedo. The presence of dust devil tracks on a dune could indicate the dune and/or its ripples are either immobile or migrating slowly. We also propose that albedo variations on individual dune fields can reveal insight into the local wind regime.

  6. Do state-of-the-art CMIP5 ESMs accurately represent observed vegetation-rainfall feedbacks? Focus on the Sahel

    Science.gov (United States)

    Notaro, M.; Wang, F.; Yu, Y.; Mao, J.; Shi, X.; Wei, Y.

    2017-12-01

    The semi-arid Sahel ecoregion is an established hotspot of land-atmosphere coupling. Ocean-land-atmosphere interactions received considerable attention by modeling studies in response to the devastating 1970s-90s Sahel drought, which models suggest was driven by sea-surface temperature (SST) anomalies and amplified by local vegetation-atmosphere feedbacks. Vegetation affects the atmosphere through biophysical feedbacks by altering the albedo, roughness, and transpiration and thereby modifying exchanges of energy, momentum, and moisture with the atmosphere. The current understanding of these potentially competing processes is primarily based on modeling studies, with biophysical feedbacks serving as a key uncertainty source in regional climate change projections among Earth System Models (ESMs). In order to reduce this uncertainty, it is critical to rigorously evaluate the representation of vegetation feedbacks in ESMs against an observational benchmark in order to diagnose systematic biases and their sources. However, it is challenging to successfully isolate vegetation's feedbacks on the atmosphere, since the atmospheric control on vegetation growth dominates the atmospheric feedback response to vegetation anomalies and the atmosphere is simultaneously influenced by oceanic and terrestrial anomalies. In response to this challenge, a model-validated multivariate statistical method, Stepwise Generalized Equilibrium Feedback Assessment (SGEFA), is developed, which extracts the forcing of a slowly-evolving environmental variable [e.g. SST or leaf area index (LAI)] on the rapidly-evolving atmosphere. By applying SGEFA to observational and remotely-sensed data, an observational benchmark is established for Sahel vegetation feedbacks. In this work, the simulated responses in key atmospheric variables, including evapotranspiration, albedo, wind speed, vertical motion, temperature, stability, and rainfall, to Sahel LAI anomalies are statistically assessed in Coupled Model

  7. Can uncertainties in sea ice albedo reconcile patterns of data-model discord for the Pliocene and 20th/21st centuries?

    Science.gov (United States)

    Howell, Fergus W.; Haywood, Alan M.; Dolan, Aisling M.; Dowsett, Harry J.; Francis, Jane E; Hill, Daniel J.; Pickering, Steven J.; Pope, James O.; Salzmann, Ulrich; Wade, Bidget S

    2014-01-01

    General Circulation Model simulations of the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Myr ago) currently underestimate the level of warming that proxy data suggest existed at high latitudes, with discrepancies of up to 11°C for sea surface temperature estimates and 17°C for surface air temperature estimates. Sea ice has a strong influence on high-latitude climates, partly due to the albedo feedback. We present results demonstrating the effects of reductions in minimum sea ice albedo limits in general circulation model simulations of the mPWP. While mean annual surface air temperature increases of up to 6°C are observed in the Arctic, the maximum decrease in model-data discrepancies is just 0.81°C. Mean annual sea surface temperatures increase by up to 2°C, with a maximum model-data discrepancy improvement of 1.31°C. It is also suggested that the simulation of observed 21st century sea ice decline could be influenced by the adjustment of the sea ice albedo parameterization.

  8. ISLSCP II AVHRR Albedo and BRDF, 1995

    Data.gov (United States)

    National Aeronautics and Space Administration — This Albedo and BRDF (Bidirectional Reflectance Distribution Function) data set contains three files containing BRDF parameters, white- sky albedo and black-sky...

  9. Linking glacier annual mass balance and glacier albedo retrieved from MODIS data

    Directory of Open Access Journals (Sweden)

    M. Dumont

    2012-12-01

    Full Text Available Albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODerate Imaging Spectroradiometer (MODIS on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps. The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the root mean square deviation (RMSD between field measurements and the broadband albedo retrieved from MODIS data at 250 m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000–2009 of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin Glacier during the ablation season. The annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (average over the whole glacier surface observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snow line is located at its highest elevation, thus when the snow line is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally

  10. A new albedo parameterization for use in climate models over the Antarctic ice sheet

    NARCIS (Netherlands)

    Kuipers Munneke, P.|info:eu-repo/dai/nl/304831891; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; Lenaerts, J.T.M.|info:eu-repo/dai/nl/314850163; Flanner, M.G.; Gardner, A.S.; van de Berg, W.J.|info:eu-repo/dai/nl/304831611

    2011-01-01

    A parameterization for broadband snow surface albedo, based on snow grain size evolution, cloud optical thickness, and solar zenith angle, is implemented into a regional climate model for Antarctica and validated against field observations of albedo for the period 1995–2004. Over the Antarctic

  11. Detailed spatiotemporal albedo observations at Greenland's Mittivakkat Gletscher

    Science.gov (United States)

    Mernild, Sebastian H.; Knudsen, Niels T.; Yde, Jacob C.; Malmros, Jeppe K.

    2015-04-01

    Surface albedo is defined as the reflected fraction of incoming solar shortwave radiation at the surface. On Greenland's Mittivakkat Gletscher the mean glacier-wide MODIS-estimated albedo dropped by 0.10 (2000-2013) from 0.43 to 0.33 by the end of the mass balance year (EBY). Hand-held albedo measurements as low as 0.10 were observed over debris-covered ice at the glacier margin at the EBY: these values were slightly below observed values for proglacial bedrock (~0.2). The albedo is highly variable in space - a significant variability occurred within few meters at the glacier margin area ranging from 0.10 to 0.39 due to variability in debris-cover thickness and composition, microbial activity (including algae and cyanobacteria), snow grain crystal metamorphism, bare ice exposure, and meltwater ponding. Huge dark-red-brown-colored ice algae colonies were observed. Albedo measurements on snow patches and bare glacier ice changed significant with increasing elevations (180-600 m a.s.l.) by lapse rates of 0.04 and 0.03 per 100 m, respectively, indicating values as high as 0.82 and 0.40 on the upper part of the glacier. Over a period of two weeks from early August to late August 2014 the hand-held observed mean glacier-wide albedo changed from 0.40 to 0.30 indicating that on average 10% more incoming solar shortwave radiation became available for surface ablation at the end of the melt season.

  12. Study of gain-coupled distributed feedback laser based on high order surface gain-coupled gratings

    Science.gov (United States)

    Gao, Feng; Qin, Li; Chen, Yongyi; Jia, Peng; Chen, Chao; Cheng, LiWen; Chen, Hong; Liang, Lei; Zeng, Yugang; Zhang, Xing; Wu, Hao; Ning, Yongqiang; Wang, Lijun

    2018-03-01

    Single-longitudinal-mode, gain-coupled distributed feedback (DFB) lasers based on high order surface gain-coupled gratings are achieved. Periodic surface metal p-contacts with insulated grooves realize gain-coupled mechanism. To enhance gain contrast in the quantum wells without the introduction of effective index-coupled effect, groove length and depth were well designed. Our devices provided a single longitudinal mode with the maximum CW output power up to 48.8 mW/facet at 971.31 nm at 250 mA without facet coating, 3dB linewidth (39 dB). Optical bistable characteristic was observed with a threshold current difference. Experimentally, devices with different cavity lengths were contrasted on power-current and spectrum characteristics. Due to easy fabrication technique and stable performance, it provides a method of fabricating practical gain-coupled distributed feedback lasers for commercial applications.

  13. Forests, nitrogen and albedo, a very interesting trio indeed

    Directory of Open Access Journals (Sweden)

    Borghetti M

    2009-01-01

    Full Text Available A short comment is made on a recent paper (Ollinger et al. 2008 which shows that forest ecosystem carbon uptake in temperate and boreal forests is directly related to canopy nitrogen concentration and that both carbon uptake capacity and canopy nitrogen concentration are positively correlated with shortwave surface albedo measured with broad-band satellite sensors.

  14. Albedo and color maps of the Saturnian satellites

    International Nuclear Information System (INIS)

    Buratti, B.J.; Mosher, J.A.; Johnson, T.V.

    1990-01-01

    The paper discusses the production of maps of the albedos and colors of Mimas, Enceladus, Tethys, Dione, and Rhea over the full range of their imaged surfaces. Voyager images were used to prepare maps of the normal reflectances and color ratios (0.58/0.41 micron) of these satelites. 67 refs

  15. Albedo matters: Understanding runaway albedo variations on Pluto

    Science.gov (United States)

    Earle, Alissa M.; Binzel, Richard P.; Young, Leslie A.; Stern, S. A.; Ennico, K.; Grundy, W.; Olkin, C. B.; Weaver, H. A.; New Horizons Surface Composition Theme

    2018-03-01

    The data returned from NASA's New Horizons reconnaissance of the Pluto system show striking albedo variations from polar to equatorial latitudes as well as sharp longitudinal boundaries. Pluto has a high obliquity (currently 119°) that varies by 23° over a period of less than 3 million years. This variation, combined with its regressing longitude of perihelion (360° over 3.7 million years), creates epochs of "Super Seasons" where one pole is pointed at the Sun at perihelion, thereby experiencing a short, relatively warm summer followed by its longest possible period of winter darkness. In contrast, the other pole experiences a much longer, less intense summer and a short winter season. We use a simple volatile sublimation and deposition model to explore the relationship between albedo variations, latitude, and volatile sublimation and deposition for the current epoch as well as historical epochs during which Pluto experienced these "Super Seasons." Our investigation quantitatively shows that Pluto's geometry creates the potential for runaway albedo and volatile variations, particularly in the equatorial region, which can sustain stark longitudinal contrasts like the ones we see between Tombaugh Regio and the informally named Cthulhu Regio.

  16. A note on solar elevation dependence of clear sky snow albedo

    Science.gov (United States)

    Choudhury, B. J.

    1981-01-01

    Recent attempts to match shortwave albedo of snow for clear skies using approximate spectral solar fluxes and solutions of the radiative transfer equation for snow were unsuccessful until a separate surface reflection term was introduced. A separate consideration of specular reflection from surface snow grains has been objected to as being ad hoc. Results based on a new parameterization of shortwave radiation are discussed. Compared to the previous radiation models, new model gives higher diffuse insolation and predicts higher albedos. The difference between observed and predicted albedos is substantially reduced without invoking surface reflection.

  17. Advancing Glaciological Applications of Remote Sensing with EO-1: (1) Mapping Snow Grain Size and Albedo on the Greenland Ice Sheet Using an Imaging Spectrometer, and (2) ALI Evaluation for Subtle Surface Topographic Mapping via Shape-from Shading

    Science.gov (United States)

    2003-01-01

    The Hyperion sensor, onboard NASA's Earth Observing-1 (EO-1) satellite,is an imaging spectroradiometer with 220 spectral bands over the spectral range from 0.4 - 2.5 microns. Over the course of summer 2001, the instrument acquired numerous images over the Greenland ice sheet. Our main motivation is to develop an accurate and robust approach for measuring the broadband albedo of snow from satellites. Satellite-derived estimates of broadband have typically been plagued with three problems: errors resulting from inaccurate atmospheric correction, particularly in the visible wavelengths from the conversion of reflectance to albedo (accounting for snow BRDE); and errors resulting from regression-based approaches used to convert narrowband albedo to broadband albedo. A typerspectral method has been developed that substantially reduces these three main sources of error and produces highly accurate estimates of snow albedo. This technique uses hyperspectral data from 0.98 - 1.06 microns, spanning a spectral absorption feature centered at 1.03 microns. A key aspect of this work is that this spectral range is within an atmospheric transmission window and reflectances are largely unaffected by atmospheric aerosols, water vapor, or ozone. In this investigation, we make broadband albedo measurements at four sites on the Greenland ice sheet: Summit, a high altitude station in central Greenland; the ETH/CU camp, a camp on the equilibrium line in western Greenland; Crawford Point, a site located between Summit and the ETH/CU camp; and Tunu, a site located in northeastern Greenland at 2000 m. altitude. Each of these sites has an automated weather station (AWS) that continually measures broadband albedo thereby providing validation data.

  18. Search for the cause of the low albedo of the Moon

    International Nuclear Information System (INIS)

    Gold, T.; Bilson, E.; Baron, R.L.

    1975-01-01

    Experimentation concerning lunar weathering and its effect on the albedo of the surface cover consisted of determination of the surface chemical composition of lunar soil and ground-up rock samples by Auger electron spectroscopy, measurement of the optical albedo of these samples, and proton or alpha-particle irradiation of terrestrial rock chips and rock powders and of ground-up lunar rock samples in order to determine the optical and surface chemical effect of simulated solar wind

  19. Albedo and heat transport in 3-D model simulations of the early Archean climate

    Directory of Open Access Journals (Sweden)

    H. Kienert

    2013-08-01

    Full Text Available At the beginning of the Archean eon (ca. 3.8 billion years ago, the Earth's climate state was significantly different from today due to the lower solar luminosity, smaller continental fraction, higher rotation rate and, presumably, significantly larger greenhouse gas concentrations. All these aspects play a role in solutions to the "faint young Sun paradox" which must explain why the ocean surface was not fully frozen at that time. Here, we present 3-D model simulations of climate states that are consistent with early Archean boundary conditions and have different CO2 concentrations, aiming at an understanding of the fundamental characteristics of the early Archean climate system. In order to do so, we have appropriately modified an intermediate complexity climate model that couples a statistical-dynamical atmosphere model (involving parameterizations of the dynamics to an ocean general circulation model and a thermodynamic-dynamic sea-ice model. We focus on three states: one of them is ice-free, one has the same mean surface air temperature of 288 K as today's Earth and the third one is the coldest stable state in which there is still an area with liquid surface water (i.e. the critical state at the transition to a "snowball Earth". We find a reduction in meridional heat transport compared to today, which leads to a steeper latitudinal temperature profile and has atmospheric as well as oceanic contributions. Ocean surface velocities are largely zonal, and the strength of the atmospheric meridional circulation is significantly reduced in all three states. These aspects contribute to the observed relation between global mean temperature and albedo, which we suggest as a parameterization of the ice-albedo feedback for 1-D model simulations of the early Archean and thus the faint young Sun problem.

  20. Correction to "Influence of Dust and Black Carbon on the Snow Albedo in the NASA Goddard Earth Observing System Version 5 Land Surface Model"

    Science.gov (United States)

    Yasunari, Teppei J.; Koster, Randal D.; Kau, K. M.; Aoki, Teruo; Sud, Yogesh C.; Yamazaki, Takeshi; Motoyoshi, Hiroki; Kokdama, Yuji

    2012-01-01

    The website information describing the forcing meteorological data used for the land surface model (LSM) simulation, which were observed at an Automated Meteorological Station CAWS) at the Sapporo District Meteorological Observatory maintained by the Japan Meteorological Agency (JMA), was missing from the text. The 1-hourly data were obtained from the website of Kisyoutoukeijouhou (Information for available JMA-observed meteorological data in the past) on the website of JMA (in Japanese) (available at: http://www.jma.go.jpijmaimenulreport.html). The measurement height information of 59.5 m for the anemometer at the Sapporo Observatory was also obtained from the website of JMA (in Japanese) (available at: http://www.jma.go.jp/jma/menu/report.html). In addition, the converted 10-m wind speed, based on the AWS/JMA data, was further converted to a 2-m wind speed prior to its use with the land model as a usual treatment of off-line Catchment simulation. Please ignore the ice absorption data on the website mentioned in paragraph [15] which was not used for our calculations (but the data on the website was mostly the same as the estimated ice absorption coefficients by the following method because they partially used the same data by Warren [1984]). We calculated the ice absorption coefficients with the method mentioned in the same paragraph, for which some of the refractive index data by Warren [1984] were used and then interpolated between wavelengths, and also mentioned in paragraph [20] for the visible (VIS) and near-infrared (NIR) ranges. The optical data we used were interpolated between wavelengths as necessary.

  1. Dominance of grain size impacts on seasonal snow albedo at open sites in New Hampshire

    Science.gov (United States)

    Adolph, Alden C.; Albert, Mary R.; Lazarcik, James; Dibb, Jack E.; Amante, Jacqueline M.; Price, Andrea

    2017-01-01

    Snow cover serves as a major control on the surface energy budget in temperate regions due to its high reflectivity compared to underlying surfaces. Winter in the northeastern United States has changed over the last several decades, resulting in shallower snowpacks, fewer days of snow cover, and increasing precipitation falling as rain in the winter. As these climatic changes occur, it is imperative that we understand current controls on the evolution of seasonal snow albedo in the region. Over three winter seasons between 2013 and 2015, snow characterization measurements were made at three open sites across New Hampshire. These near-daily measurements include spectral albedo, snow optical grain size determined through contact spectroscopy, snow depth, snow density, black carbon content, local meteorological parameters, and analysis of storm trajectories using the Hybrid Single-Particle Lagrangian Integrated Trajectory model. Using analysis of variance, we determine that land-based winter storms result in marginally higher albedo than coastal storms or storms from the Atlantic Ocean. Through multiple regression analysis, we determine that snow grain size is significantly more important in albedo reduction than black carbon content or snow density. And finally, we present a parameterization of albedo based on days since snowfall and temperature that accounts for 52% of variance in albedo over all three sites and years. Our improved understanding of current controls on snow albedo in the region will allow for better assessment of potential response of seasonal snow albedo and snow cover to changing climate.

  2. The sensitivity of regional transpiration to land-surface characteristics: significance of feedback.

    NARCIS (Netherlands)

    Jacobs, C.M.J.; Bruin, de H.A.R.

    1992-01-01

    Several authors have determined the sensitivity of transpiration to different environmental parameters using the Penman-Monteith equation. In their studies the interaction between transpiration and, for example, the humidity of the air is ignored: the feedback with the planetary boundary layer (PBL)

  3. Comparing atmosphere-land surface feedbacks from models within the tropics (CALM). Part 1: Evaluation of CMIP5 GCMs to simulate the land surface-atmosphere feedback

    Science.gov (United States)

    Williams, C.; Allan, R.; Kniveton, D.

    2012-04-01

    Man-made transformations to the environment, and in particular the land surface, are having a large impact on the distribution (in both time and space) of rainfall, upon which all life is reliant. From global changes in the composition of the atmosphere, through the emission of greenhouse gases and aerosols, to more localised land use and land cover changes due to an expanding population with an increasing ecological footprint, human activity has a considerable impact on the processes controlling rainfall. This is of particular importance for environmentally vulnerable regions such as many of those in the tropics. Here, widespread poverty, an extensive disease burden and pockets of political instability has resulted in a low resilience and limited adaptative capacity to climate related shocks and stresses. Recently, the 5th Climate Modelling Intercomparison Project (CMIP5) has run a number of state-of-the-art climate models using various present-day and future emission scenarios of greenhouse gases, and therefore provides an unprecedented amount of simulated model data. This paper presents the results of the first stage of a larger project, aiming to further our understanding of how the interactions between tropical rainfall and the land surface are represented in some of the latest climate model simulations. Focusing on precipitation, soil moisture and near-surface temperature, this paper compares the data from all of these models, as well as blended observational-satellite data, to see how the interactions between rainfall and the land surface differs (or agrees) between the models and reality. Firstly, in an analysis of the processes from the "observed" data, the results suggest a strong positive relationship between precipitation and soil moisture at both daily and seasonal timescales. There is a weaker and negative relationship between precipitation and temperature, and likewise between soil moisture and temperature. For all variables, the correlations are

  4. Global color and albedo variations on Io

    Science.gov (United States)

    McEwen, A.S.

    1988-01-01

    Three multispectral mosaics of Io have been produced from Voyager imaging data: a global mosaic from each of the Voyager 1 and Voyager 2 data sets and a high-resolution mosaic of the region surrounding the volcano Ra Patera. The mosaics are maps of normal albedo and color in accurate geometric map formats. Io's photometric behavior, mapped with a two-image technique, is spatially variable, especially in the bright white areas. The disk-integrated color and albedo of the satellite have been remarkably constant over recent decades, despite the volcanic activity and the many differences between Voyager 1 and 2 images (acquired just 4 months apart). This constancy is most likely due to the consistent occurrence of large Pele-type plumes with relatively dark, red deposits in the region from long 240 to 360??. A transient brightening southeast of Pele during the Voyager 1 encounter was probably due to real changes in surface and/or atmospheric materials, rather than to photometric behavior. The intrinsic spectral variability of Io, as seen in a series of two-dimensional histograms of the multispectral mosaics, consists of continuous variation among three major spectral end members. The data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions. Unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur, and it is closely associated with the Peletype plume deposits. Unit 2 is strongly confined to the polar caps above about latitude ??50??, but its composition is unknown. Unit 5 is probably SO2 with relatively minor contamination; it is concentrated in the equatorial region and near the long-lived Prometheus-type plumes. Units 3 and 4 are gradational between units 1 and 5. In addition to SO2 and elemental sulfur, other plausible components of the surface are polysulfur oxides, FeCl2, Na2S, and NaHS. ?? 1988.

  5. Multiplatform observations enabling albedo retrievals with high temporal resolution

    Science.gov (United States)

    Riihelä, Aku; Manninen, Terhikki; Key, Jeffrey; Sun, Qingsong; Sütterlin, Melanie; Lattanzio, Alessio; Schaaf, Crystal

    2017-04-01

    In this paper we show that combining observations from different polar orbiting satellite families (such as AVHRR and MODIS) is physically justifiable and technically feasible. Our proposed approach will lead to surface albedo retrievals at higher temporal resolution than the state of the art, with comparable or better accuracy. This study is carried out in the World Meteorological Organization (WMO) Sustained and coordinated processing of Environmental Satellite data for Climate Monitoring (SCOPE-CM) project SCM-02 (http://www.scope-cm.org/projects/scm-02/). Following a spectral homogenization of the Top-of-Atmosphere reflectances of bands 1 & 2 from AVHRR and MODIS, both observation datasets are atmospherically corrected with a coherent atmospheric profile and algorithm. The resulting surface reflectances are then fed into an inversion of the RossThick-LiSparse-Reciprocal surface bidirectional reflectance distribution function (BRDF) model. The results of the inversion (BRDF kernels) may then be integrated to estimate various surface albedo quantities. A key principle here is that the larger number of valid surface observations with multiple satellites allows us to invert the BRDF coefficients within a shorter time span, enabling the monitoring of relatively rapid surface phenomena such as snowmelt. The proposed multiplatform approach is expected to bring benefits in particular to the observation of the albedo of the polar regions, where persistent cloudiness and long atmospheric path lengths present challenges to satellite-based retrievals. Following a similar logic, the retrievals over tropical regions with high cloudiness should also benefit from the method. We present results from a demonstrator dataset of a global combined AVHRR-GAC and MODIS dataset covering the year 2010. The retrieved surface albedo is compared against quality-monitored in situ albedo observations from the Baseline Surface Radiation Network (BSRN). Additionally, the combined retrieval

  6. Development of feedback-speed-control system of fixed-abrasive tool for mat-surface fabrication

    Science.gov (United States)

    Yanagihara, K.; Kita, R.

    2018-01-01

    This study deals with the new method to fabricate a mat-surface by using fixed-abrasive tool. Mat-surface is a surface with microscopic irregularities whose dimensions are close to the wavelengths of visible light (400-700 nanometers). In order to develop the new method to fabricate mat-surface without pre-masking and large scale back up facility, utilization of fixed-abrasive tool is discussed. The discussion clarifies that abrasives in shot blasting are given kinetic energy along to only plunge-direction while excluding traverse-direction. If the relative motion between tool and work in fixed-abrasive process can be realized as that in blasting, mat-surface will be accomplished with fixed-abrasive process. To realize the proposed idea, new surface-fabrication system to which is adopted feedback-speed-control of abrasive wheel has been designed. The system consists of micro-computer unit (MPU), work-speed sensor, fixed-abrasive wheel, and wheel driving unit. The system can control relative speed between work and wheel in optimum range to produce mat-surface. Finally experiment to verify the developed system is carried out. The results of experiments show that the developed system is effective and it can produce the surface from grinding to mat-surface seamlessly.

  7. Albedo Spatial Variability and Causes on the Western Greenland Ice Sheet Percolation Zone

    Science.gov (United States)

    Lewis, G.; Osterberg, E. C.; Hawley, R. L.; Koffman, B. G.; Marshall, H. P.; Birkel, S. D.; Dibb, J. E.

    2016-12-01

    Many recent studies have concluded that Greenland Ice Sheet (GIS) mass loss has been accelerating over recent decades, but spatial and temporal variations in GIS mass balance remain poorly understood due to a complex relationship among precipitation and temperature changes, increasing melt and runoff, ice discharge, and surface albedo. Satellite measurements from MODerate resolution Imaging Spectroradiometer (MODIS) indicate that albedo has been declining over the past decade, but the cause and extent of GIS albedo change remains poorly constrained by field data. As fresh snow (albedo > 0.85) warms and melts, its albedo decreases due to snow grain growth, promoting solar absorption, higher snowpack temperatures and further melt. However, dark impurities like soot and dust can also significantly reduce snow albedo, even in the dry snow zone. While many regional climate models (e.g. the Regional Atmospheric Climate MOdel - RACMO2) calculate albedo spatial resolutions on the order of 10-30 km, and MODIS averages albedo over 500 m, surface features like sastrugi can affect albedo on much smaller scales. Here we assess the relative importance of grain size and shape vs. impurity concentrations on albedo in the western GIS percolation zone. We collected broadband albedo measurements (300-2500 nm at 3-8 nm resolution) at 35 locations using an ASD FieldSpec4 spectroradiometer to simultaneously quantify radiative fluxes and spectral reflectance. Measurements were collected on 10 x 10 m, 1 x 1 km, 5 x 5 km, and 10 x 10 km grids to determine the spatial variability of albedo as part of the 850-km Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) traverse from Raven/Dye 2 to Summit. Additionally, we collected shallow (0-50 cm) snow pit samples every 5 cm at ASD measurement sites to quantify black carbon and mineral dust concentrations and size distributions using a Single Particle Soot Photometer and Coulter Counter, respectively. Preliminary results

  8. Spatio-temporal Variability of Albedo and its Impact on Glacier Melt Modelling

    Science.gov (United States)

    Kinnard, C.; Mendoza, C.; Abermann, J.; Petlicki, M.; MacDonell, S.; Urrutia, R.

    2017-12-01

    Albedo is an important variable for the surface energy balance of glaciers, yet its representation within distributed glacier mass-balance models is often greatly simplified. Here we study the spatio-temporal evolution of albedo on Glacier Universidad, central Chile (34°S, 70°W), using time-lapse terrestrial photography, and investigate its effect on the shortwave radiation balance and modelled melt rates. A 12 megapixel digital single-lens reflex camera was setup overlooking the glacier and programmed to take three daily images of the glacier during a two-year period (2012-2014). One image was chosen for each day with no cloud shading on the glacier. The RAW images were projected onto a 10m resolution digital elevation model (DEM), using the IMGRAFT software (Messerli and Grinsted, 2015). A six-parameter camera model was calibrated using a single image and a set of 17 ground control points (GCPs), yielding a georeferencing accuracy of accounting for possible camera movement over time. The reflectance values from the projected image were corrected for topographic and atmospheric influences using a parametric solar irradiation model, following a modified algorithm based on Corripio (2004), and then converted to albedo using reference albedo measurements from an on-glacier automatic weather station (AWS). The image-based albedo was found to compare well with independent albedo observations from a second AWS in the glacier accumulation area. Analysis of the albedo maps showed that the albedo is more spatially-variable than the incoming solar radiation, making albedo a more important factor of energy balance spatial variability. The incorporation of albedo maps within an enhanced temperature index melt model revealed that the spatio-temporal variability of albedo is an important factor for the calculation of glacier-wide meltwater fluxes.

  9. Vegetation-cloud feedbacks to future vegetation changes in the Arctic regions

    Science.gov (United States)

    Cho, Mee-Hyun; Yang, Ah-Ryeon; Baek, Eun-Hyuk; Kang, Sarah M.; Jeong, Su-Jong; Kim, Jin Young; Kim, Baek-Min

    2017-07-01

    This study investigates future changes in the Arctic region and vegetation-cloud feedbacks simulated using the National Center for Atmospheric Research Community Atmosphere Model Version 3 coupled with a mixed layer ocean model. Impacts of future greening of the Arctic region are tested using altered surface boundary conditions for hypothetical vegetation distributions: (1) grasslands poleward of 60°N replaced by boreal forests and (2) both grasslands and shrubs replaced by boreal forests. Surface energy budget analysis reveals that future greening induces a considerable surface warming effect locally and warming is largely driven by an increase in short wave radiation. Both upward and downward shortwave radiation contribute to positive surface warming: upward shortwave radiation decreases mainly due to the decreased surface albedo (a darker surface) and downward shortwave radiation increases due to reduced cloud cover. The contribution of downward shortwave radiation at surface due to cloud cover reduction is larger than the contribution from surface albedo alone. The increased roughness length also transported surface fluxes to upper layer more efficiently and induce more heating and dry lower atmosphere. A relatively smaller increase in water vapor compared to the large increase in low-level air temperature in the simulation reduces relative humidity and results in reduced cloud cover. Therefore, vegetation-cloud feedbacks induced from land cover change significantly amplify Arctic warming. In addition to previously suggested feedback mechanisms, we propose that the vegetation-cloud feedback should be considered as one of major components that will give rise to an additional positive feedback to Arctic amplification.

  10. Investigating the Feedback Path in a Jet-Surface Resonant Interaction

    Science.gov (United States)

    Zaman, Khairul; Fagan, Amy; Bridges, James; Brown, Cliff

    2015-01-01

    A resonant interaction between an 8:1 aspect ratio rectangular jet and flat-plates, placed parallel to the jet, is addressed in this study. For certain relative locations of the plates, the resonance takes place with accompanying audible tones. Even when the tone is not audible the sound pressure level spectra is often marked by conspicuous peaks. The frequencies of the spectral peaks, as functions of the streamwise length of the plate and its relative location to the jet as well as the jet Mach number, are explored in an effort of understand the flow mechanism. It is demonstrated that the tones are not due to a simple feedback between the plates trailing edge and the nozzle exit; the leading edge also comes into play in determining the frequency. An acoustic feedback path, involving diffraction from the leading edge, appears to explain the frequencies of some of the spectral peaks.

  11. Late Quaternary vegetation-climate feedbacks

    Directory of Open Access Journals (Sweden)

    M. Claussen*

    2009-06-01

    Full Text Available Feedbacks between vegetation and other components of the climate system are discussed with respect to their influence on climate dynamics during the late Quaternary, i.e., the last glacial-interglacial cycles. When weighting current understanding based on interpretation of palaeobotanic and palaeoclimatic evidence by numerical climate system models, a number of arguments speak in favour of vegetation dynamics being an amplifier of orbital forcing. (a The vegetation-snow albedo feedback in synergy with the sea-ice albedo feedback tends to amplify Northern Hemisphere and global mean temperature changes. (b Variations in the extent of the largest desert on Earth, the Sahara, appear to be amplified by biogeophysical feedback. (c Biogeochemical feedbacks in the climate system in relation to vegetation migration are supposed to be negative on time scales of glacial cycles. However, with respect to changes in global mean temperature, they are presumably weaker than the positive biogeophysical feedbacks.

  12. Albedos

    Science.gov (United States)

    1993-07-01

    Maize 18 Spring wheat 10 - 25 Wheat 18 Swamp rice 11 Tobacco 19 Paddy rice 12 Cassava 19 Kola nuts 13 Potatos 19 Stubble fields 15 - 17 Yams 19 Sugar...441. Perevertun, M. P., 1957, "Spectral Reflectance of Certain Plants in the Range 650-1200 jm," Trans Asrobotan Sect Acad Sci Kazahk SSR, 5. Posey...Barnes) ATTN: AMSMI-RD-DE-SE Fort McClellan, AL 36205-5020 Gordon Lill, Jr. Redstone Arsenal, AL 35898-5245 NASA/Marshall Space Flight Center Deputy

  13. ISLSCP II Monthly Snow-Free Albedo, 1982-1998, and Background Soil Reflectance

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains monthly average snow-free surface shortwave albedo calculated for the period 1982-1998 and estimates of background soil/litter reflectances in...

  14. ISLSCP II NOAA 5-year Average Monthly Snow-free Albedo from AVHRR

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: The objective of this work was to produce a monthly climatology of broadband surface albedos for use in global numerical weather prediction models at the...

  15. ISLSCP II NOAA 5-year Average Monthly Snow-free Albedo from AVHRR

    Data.gov (United States)

    National Aeronautics and Space Administration — The objective of this work was to produce a monthly climatology of broadband surface albedos for use in global numerical weather prediction models at the National...

  16. ISLSCP II Monthly Snow-Free Albedo, 1982-1998, and Background Soil Reflectance

    Data.gov (United States)

    National Aeronautics and Space Administration — ABSTRACT: This data set contains monthly average snow-free surface shortwave albedo calculated for the period 1982-1998 and estimates of background soil/litter...

  17. Neutron albedo effects of underground nuclear explosion

    International Nuclear Information System (INIS)

    Yang Bo; Ying Yangjun; Li Jinhong; Bai Yun

    2013-01-01

    The neutron field distribution is affected by the surrounding medium in the underground nuclear explosion. It will influence the radiation chemical diagnosis. By Monte Carlo simulation, the fuel burnup induced by device and neutron albedo was calculated. The analysis method of albedo effect on radiation chemical diagnosis result under special environment was proposed. Neutron albedo should be considered when capture reaction burnup fraction is used, and then correct analysis can be carried out on the nuclear device.The neutron field distribution is affected by the surrounding medium in the underground nuclear explosion. It will influence the radiation chemical diagnosis. By Monte Carlo simulation, the fuel burnup induced by device and neutron albedo was calculated. The analysis method of albedo effect on radiation chemical diagnosis result under special environment was proposed. Neutron albedo should be considered when capture reaction burnup fraction is used, and then correct analysis can be carried out on the nuclear device. (authors)

  18. Growing season carries stronger contributions to albedo dynamics on the Tibetan plateau.

    Science.gov (United States)

    Tian, Li; Chen, Jiquan; Zhang, Yangjian

    2017-01-01

    The Tibetan Plateau has experienced higher-than-global-average climate warming in recent decades, resulting in many significant changes in ecosystem structure and function. Among them is albedo, which bridges the causes and consequences of land surface processes and climate. The plateau is covered by snow/ice and vegetation in the non-growing season (nGS) and growing season (GS), respectively. Based on the MODIS products, we investigated snow/ice cover and vegetation greenness in relation to the spatiotemporal changes of albedo on the Tibetan Plateau from 2000 through 2013. A synchronous relationship was found between the change in GSNDVI and GSalbedo over time and across the Tibetan landscapes. We found that the annual average albedo had a decreasing trend, but that the albedo had slightly increased during the nGS and decreased during the GS. Across the landscapes, the nGSalbedo fluctuated in a synchronous pattern with snow/ice cover. Temporally, monthly snow/ice coverage also had a high correspondence with albedo, except in April and October. We detected clear dependencies of albedo on elevation. With the rise in altitude, the nGSalbedo decreased below 4000 m, but increased for elevations of 4500-5500 m. Above 5500 m, the nGSalbedo decreased, which was in accordance with the decreased amount of snow/ice coverage and the increased soil moisture on the plateau. More importantly, the decreasing albedo in the most recent decade appeared to be caused primarily by lowered growing season albedo.

  19. The Ultraviolet Albedo of Ganymede

    Science.gov (United States)

    McGrath, Melissa; Hendrix, A.

    2013-10-01

    A large set of ultraviolet images of Ganymede have been acquired with the Hubble Space Telescope over the last 15 years. These images have been used almost exclusively to study Ganymede’s stunning auroral emissions (Feldman et al. 2000; Eviatar et al. 2001; McGrath et al. 2004; Saur et al. 2011; McGrath et al. 2013), and even the most basic information about Ganymede’s UV albedo has yet to be gleaned from these data. We will present a first-cut analysis of both disk-averaged and spatially-resolved UV albedos of Ganymede, with focus on the spatially-resolved Lyman-alpha albedo, which has never been considered previously for this satellite. Ganymede's visibly bright regions are known to be rich in water ice, while the visibly dark regions seem to be more carbonaceous (Carlson et al., 1996). At Lyman-alpha, these two species should also have very different albedo values. References Carlson, R. and 39 co-authors, Near-infrared spectroscopy and spectral mapping of Jupiter and the Galilean satellites: Results from Galileo’s initial orbit, Science, 274, 385-388, 1996. Eviatar, A., D. F. Strobel, B. C. Wolven, P. D. Feldman, M. A. McGrath, and D. J. Williams, Excitation of the Ganymede ultraviolet aurora, Astrophys. J, 555, 1013-1019, 2001. Feldman, P. D., M. A. McGrath, D. F. Strobel, H. W. Moos, K. D. Retherford, and B. C. Wolven, HST/STIS imaging of ultraviolet aurora on Ganymede, Astrophys. J, 535, 1085-1090, 2000. McGrath M. A., Lellouch E., Strobel D. F., Feldman P. D., Johnson R. E., Satellite Atmospheres, Chapter 19 in Jupiter: The Planet, Satellites and Magnetosphere, ed. F. Bagenal, T. Dowling, W. McKinnon, Cambridge University Press, 2004. McGrath M. A., Jia, Xianzhe; Retherford, Kurt; Feldman, Paul D.; Strobel, Darrell F.; Saur, Joachim, Aurora on Ganymede, J. Geophys. Res., doi: 10.1002/jgra.50122, 2013. Saur, J., S. Duling, S., L. Roth, P. D. Feldman, D. F. Strobel, K. D. Retherford, M. A. McGrath, A. Wennmacher, American Geophysical Union, Fall Meeting

  20. MODIS snow albedo bias at high solar zenith angles relative to theory and to in situ observations in Greenland

    OpenAIRE

    Wang, Xianwei; Zender, Charles S

    2010-01-01

    In situ measurements of snow albedo at five stations along a north–south transect in the dry-snow facies of the interior of Greenland follow the theoretically expected dependence of snow albedo with solar zenith angle (SZA). Greenland Climate Network (GC-Net) measurements from 1997 through 2007 exhibit the trend of modest surface brightening with increasing SZA on both diurnal and seasonal timescales. SZA explains up to 50% of seasonal albedo variability. The two other environmental factors c...

  1. CARP: a computer code and albedo data library for use by BREESE, the MORSE albedo package

    International Nuclear Information System (INIS)

    Emmett, M.B.; Rhoades, W.A.

    1978-10-01

    The CARP computer code was written to allow processing of DOT angular flux tapes to produce albedo data for use in the MORSE computer code. An albedo data library was produced containing several materials. 3 tables

  2. Global albedos of Pluto and Charon from LORRI New Horizons observations

    Science.gov (United States)

    Buratti, B. J.; Hofgartner, J. D.; Hicks, M. D.; Weaver, H. A.; Stern, S. A.; Momary, T.; Mosher, J. A.; Beyer, R. A.; Verbiscer, A. J.; Zangari, A. M.; Young, L. A.; Lisse, C. M.; Singer, K.; Cheng, A.; Grundy, W.; Ennico, K.; Olkin, C. B.

    2017-05-01

    The exploration of the Pluto-Charon system by the New Horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's ;Third Zone; of distant ice-rich bodies. Images of the entire illuminated surface of Pluto and Charon obtained by the Long Range Reconnaissance Imager (LORRI) camera provide a global map of Pluto that reveals surface albedo variegations larger than any other Solar System world except for Saturn's moon Iapetus. Normal reflectances on Pluto range from 0.08-1.0, and the low-albedo areas of Pluto are darker than any region of Charon. Charon exhibits a much blander surface with normal reflectances ranging from 0.20-0.73. Pluto's albedo features are well-correlated with geologic features, although some exogenous low-albedo dust may be responsible for features seen to the west of the area informally named Tombaugh Regio. The albedo patterns of both Pluto and Charon are latitudinally organized, with the exception of Tombaugh Regio, with darker regions concentrated at the Pluto's equator and Charon's northern pole. The phase curve of Pluto is similar to that of Triton, the large moon of Neptune believed to be a captured Kuiper Belt Object (KBO), while Charon's is similar to that of the Moon. Preliminary Bond albedos are 0.25 ± 0.03 for Charon and 0.72 ± 0.07 for Pluto. Maps of an approximation to the Bond albedo for both Pluto and Charon are presented for the first time. Our work shows a connection between very high albedo (near unity) and planetary activity, a result that suggests the KBO Eris may be currently active.

  3. Albedo of a hybrid poplar plantation in central Alberta, Canada

    Science.gov (United States)

    Price, D. T.; Bernier, P. Y.; Orchansky, A.; Thomas, B.

    2012-04-01

    Canada's boreal forest resources are coming under increasing pressure from competing land-uses, including establishment of protected areas, and losses of harvestable forest to mining and oil and gas exploration. In the prairie region, concerns about lack of wood supply for pulpmills and potential opportunities for bioenergy production and carbon sequestration for climate change mitigation, have spurred interest in afforestation of marginal agricultural land, notably with fast-growing hybrid poplars (HP). However, global modelling studies suggest that a shift from grassland or crops to forest cover in temperate and boreal regions could result in reduced surface albedo, particularly in winter, causing an increase in radiative forcing and reducing any climate mitigation benefits due to net GHG removal. We report on seven growing seasons of measurements of short-wave canopy albedo using tower-mounted instruments, along with eddy covariance measurements of carbon, water and energy balance, at a site in central Alberta planted with HP cuttings in spring 2005. The data show little systematic change in average albedo as vegetation has changed from bare ground to a plantation of 6 m trees. Reasons for this include very wide (3 m) spacing between the trees, and snow cover which often persists for 4-5 months and is highly visible below the bare canopies during winter. While measurements should continue as the trees grow larger, we postulate that extensive afforestation with HP is unlikely to have major effects on regional-scale surface albedo compared to the agricultural systems they replace. Normal rotation lengths are 15-20 years, hence even if older plantations have significantly lower winter albedo, their contribution to the regional average would be relatively small because they will cover only a small fraction of the landscape (e.g., compared to forests of boreal conifers or temperate broadleaved species).

  4. Evaluation of Moderate-Resolution Imaging Spectroradiometer (MODIS) Snow Albedo Product (MCD43A) over Tundra

    Science.gov (United States)

    Wang, Zhuosen; Schaaf, Crystal B.; Chopping, Mark J.; Strahler, Alan H.; Wang, Jindi; Roman, Miguel O.; Rocha, Adrian V.; Woodcock, Curtis E.; Shuai, Yanmin

    2012-01-01

    This study assesses the MODIS standard Bidirectional Reflectance Distribution Function (BRDF)/Albedo product, and the daily Direct Broadcast BRDF/Albedo algorithm at tundra locations under large solar zenith angles and high anisotropic diffuse illumination and multiple scattering conditions. These products generally agree with ground-based albedo measurements during the snow cover period when the Solar Zenith Angle (SZA) is less than 70deg. An integrated validation strategy, including analysis of the representativeness of the surface heterogeneity, is performed to decide whether direct comparisons between field measurements and 500- m satellite products were appropriate or if the scaling of finer spatial resolution airborne or spaceborne data was necessary. Results indicate that the Root Mean Square Errors (RMSEs) are less than 0.047 during the snow covered periods for all MCD43 albedo products at several Alaskan tundra areas. The MCD43 1- day daily albedo product is particularly well suited to capture the rapidly changing surface conditions during the spring snow melt. Results also show that a full expression of the blue sky albedo is necessary at these large SZA snow covered areas because of the effects of anisotropic diffuse illumination and multiple scattering. In tundra locations with dark residue as a result of fire, the MODIS albedo values are lower than those at the unburned site from the start of snowmelt.

  5. Bacteria increase arid-land soil surface temperature through the production of sunscreens.

    Science.gov (United States)

    Couradeau, Estelle; Karaoz, Ulas; Lim, Hsiao Chien; Nunes da Rocha, Ulisses; Northen, Trent; Brodie, Eoin; Garcia-Pichel, Ferran

    2016-01-20

    Soil surface temperature, an important driver of terrestrial biogeochemical processes, depends strongly on soil albedo, which can be significantly modified by factors such as plant cover. In sparsely vegetated lands, the soil surface can be colonized by photosynthetic microbes that build biocrust communities. Here we use concurrent physical, biochemical and microbiological analyses to show that mature biocrusts can increase surface soil temperature by as much as 10 °C through the accumulation of large quantities of a secondary metabolite, the microbial sunscreen scytonemin, produced by a group of late-successional cyanobacteria. Scytonemin accumulation decreases soil albedo significantly. Such localized warming has apparent and immediate consequences for the soil microbiome, inducing the replacement of thermosensitive bacterial species with more thermotolerant forms. These results reveal that not only vegetation but also microorganisms are a factor in modifying terrestrial albedo, potentially impacting biosphere feedbacks on past and future climate, and call for a direct assessment of such effects at larger scales.

  6. Colour, albedo and nucleus size of Halley's comet

    Science.gov (United States)

    Cruikshank, D. P.; Tholen, D. J.; Hartmann, W. K.

    1985-01-01

    Photometry of Halley's comet in the B, J, V, and K broadband filters during a time when the coma was very weak and presumed to contribute negligibly to the broadband photometry is reported. The V-J and J-K colors suggest that the color of the nucleus of Halley's comet is similar to that of the D-type asteroids, which in turn suggests that the surface of the nucleus has an albedo less than 0.1.

  7. Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets

    Energy Technology Data Exchange (ETDEWEB)

    Menon, Surabi; Akbari, Hashem; Mahanama, Sarith; Sednev, Igor; Levinson, Ronnen

    2010-02-12

    The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present-day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and land surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe by 0.1. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the change in the total outgoing (outgoing shortwave+longwave) radiation and land surface temperature to a 0.1 increase in urban albedos for all global land areas. The global average increase in the total outgoing radiation was 0.5 Wm{sup -2}, and temperature decreased by {approx}0.008 K for an average 0.003 increase in surface albedo. These averages represent all global land areas where data were available from the land surface model used and are for the boreal summer (June-July-August). For the continental U.S. the total outgoing radiation increased by 2.3 Wm{sup -2}, and land surface temperature decreased by {approx}0.03 K for an average 0.01 increase in surface albedo. Based on these forcings, the expected emitted CO{sub 2} offset for a plausible 0.25 and 0.15 increase in albedos of roofs and pavements, respectively, for all global urban areas, was found to be {approx} 57 Gt CO{sub 2}. A more meaningful evaluation of the impacts of urban albedo increases on global climate and the expected CO{sub 2} offsets would require simulations which better characterizes urban surfaces and represents the full annual cycle.

  8. Development of a Multilayer MODIS IST-Albedo Product of Greenland

    Science.gov (United States)

    Hall, D. K.; Comiso, J. C.; Cullather, R. I.; Digirolamo, N. E.; Nowicki, S. M.; Medley, B. C.

    2017-01-01

    A new multilayer IST-albedo Moderate Resolution Imaging Spectroradiometer (MODIS) product of Greenland was developed to meet the needs of the ice sheet modeling community. The multiple layers of the product enable the relationship between IST and albedo to be evaluated easily. Surface temperature is a fundamental input for dynamical ice sheet models because it is a component of the ice sheet radiation budget and mass balance. Albedo influences absorption of incoming solar radiation. The daily product will combine the existing standard MODIS Collection-6 ice-surface temperature, derived melt maps, snow albedo and water vapor products. The new product is available in a polar stereographic projection in NetCDF format. The product will ultimately extend from March 2000 through the end of 2017.

  9. Arctic sea ice albedo - A comparison of two satellite-derived data sets

    Science.gov (United States)

    Schweiger, Axel J.; Serreze, Mark C.; Key, Jeffrey R.

    1993-01-01

    Spatial patterns of mean monthly surface albedo for May, June, and July, derived from DMSP Operational Line Scan (OLS) satellite imagery are compared with surface albedos derived from the International Satellite Cloud Climatology Program (ISCCP) monthly data set. Spatial patterns obtained by the two techniques are in general agreement, especially for June and July. Nevertheless, systematic differences in albedo of 0.05 - 0.10 are noted which are most likely related to uncertainties in the simple parameterizations used in the DMSP analyses, problems in the ISCCP cloud-clearing algorithm and other modeling simplifications. However, with respect to the eventual goal of developing a reliable automated retrieval algorithm for compiling a long-term albedo data base, these initial comparisons are very encouraging.

  10. Biotic and Biogeochemical Feedbacks to Climate Change

    Science.gov (United States)

    Torn, M. S.; Harte, J.

    2002-12-01

    Feedbacks to paleoclimate change are evident in ice core records showing correlations of temperature with carbon dioxide, nitrous oxide, and methane. Such feedbacks may be explained by plant and microbial responses to climate change, and are likely to occur under impending climate warming, as evidenced by results of ecosystem climate manipulation experiments and biometeorological observations along ecological and climate gradients. Ecosystems exert considerable influence on climate, by controlling the energy and water balance of the land surface as well as being sinks and sources of greenhouse gases. This presentation will focus on biotic and biogeochemical climate feedbacks on decadal to century time scales, emphasizing carbon storage and energy exchange. In addition to the direct effects of climate on decomposition rates and of climate and CO2 on plant productivity, climate change can alter species composition; because plant species differ in their surface properties, productivity, phenology, and chemistry, climate-induced changes in plant species composition can exert a large influence on the magnitude and sign of climate feedbacks. We discuss the effects of plant species on ecosystem carbon storage that result from characteristic differences in plant biomass and lifetime, allocation to roots vs. leaves, litter quality, microclimate for decomposition and the ultimate stabilization of soil organic matter. We compare the effect of species transitions on transpiration, albedo, and other surface properties, with the effect of elevated CO2 and warming on single species' surface exchange. Global change models and experiments that investigate the effect of climate only on existing vegetation may miss the biggest impacts of climate change on biogeochemical cycling and feedbacks. Quantification of feedbacks will require understanding how species composition and long-term soil processes will change under global warming. Although no single approach, be it experimental

  11. Analysis of earth albedo effect on sun sensor measurements based on theoretical model and mission experience

    Science.gov (United States)

    Brasoveanu, Dan; Sedlak, Joseph

    1998-01-01

    Analysis of flight data from previous missions indicates that anomalous Sun sensor readings could be caused by Earth albedo interference. A previous Sun sensor study presented a detailed mathematical model of this effect. The model can be used to study the effect of both diffusive and specular reflections and to improve Sun angle determination based on perturbed Sun sensor measurements, satellite position, and an approximate knowledge of attitude. The model predicts that diffuse reflected light can cause errors of up to 10 degrees in Coarse Sun Sensor (CSS) measurements and 5 to 10 arc sec in Fine Sun Sensor (FSS) measurements, depending on spacecraft orbit and attitude. The accuracy of these sensors is affected as long as part of the illuminated Earth surface is present in the sensor field of view. Digital Sun Sensors (DSS) respond in a different manner to the Earth albedo interference. Most of the time DSS measurements are not affected, but for brief periods of time the Earth albedo can cause errors which are a multiple of the sensor least significant bit and may exceed one degree. This paper compares model predictions with Tropical Rainfall Measuring Mission (TRMM) CSS measurements in order to validate and refine the model. Methods of reducing and mitigating the impact of Earth albedo are discussed. ne CSS sensor errors are roughly proportional to the Earth albedo coefficient. Photocells that are sensitive only to ultraviolet emissions would reduce the effective Earth albedo by up to a thousand times, virtually eliminating all errors caused by Earth albedo interference.

  12. Audio Feedback -- Better Feedback?

    Science.gov (United States)

    Voelkel, Susanne; Mello, Luciane V.

    2014-01-01

    National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…

  13. Global neural dynamic surface tracking control of strict-feedback systems with application to hypersonic flight vehicle.

    Science.gov (United States)

    Xu, Bin; Yang, Chenguang; Pan, Yongping

    2015-10-01

    This paper studies both indirect and direct global neural control of strict-feedback systems in the presence of unknown dynamics, using the dynamic surface control (DSC) technique in a novel manner. A new switching mechanism is designed to combine an adaptive neural controller in the neural approximation domain, together with the robust controller that pulls the transient states back into the neural approximation domain from the outside. In comparison with the conventional control techniques, which could only achieve semiglobally uniformly ultimately bounded stability, the proposed control scheme guarantees all the signals in the closed-loop system are globally uniformly ultimately bounded, such that the conventional constraints on initial conditions of the neural control system can be relaxed. The simulation studies of hypersonic flight vehicle (HFV) are performed to demonstrate the effectiveness of the proposed global neural DSC design.

  14. Method to determine snow albedo values in the ultraviolet for radiative transfer modeling.

    Science.gov (United States)

    Schwander, H; Mayer, B; Ruggaber, A; Albold, A; Seckmeyer, G; Koepke, P

    1999-06-20

    For many cases modeled and measured UV global irradiances agree to within +/-5% for cloudless conditions, provided that all relevant parameters for describing the atmosphere and the surface are well known. However, for conditions with snow-covered surfaces this agreement is usually not achievable, because on the one hand the regional albedo, which has to be used in a model, is only rarely available and on the other hand UV irradiance alters with different snow cover of the surface by as much as 50%. Therefore a method is given to determine the regional albedo values for conditions with snow cover by use of a parameterization on the basis of snow depth and snow age, routinely monitored by the weather services. An algorithm is evolved by multiple linear regression between the snow data and snow-albedo values in the UV, which are determined from a best fit of modeled and measured UV irradiances for an alpine site in Europe. The resulting regional albedo values in the case of snow are in the 0.18-0.5 range. Since the constants of the regression depend on the area conditions, they have to be adapted if the method is applied for other sites. Using the algorithm for actual cases with different snow conditions improves the accuracy of modeled UV irradiances considerably. Compared with the use of an average, constant snow albedo, the use of actual albedo values, provided by the algorithm, halves the average deviations between measured and modeled UV global irradiances.

  15. Effects of support surface stability on feedback control of trunk posture

    NARCIS (Netherlands)

    Andreopoulou, G.; Maaswinkel, E.; Cofre Lizama, L.E.; van Dieen, J.H.

    2015-01-01

    This study aimed to examine the interactions of visual, vestibular, proprioceptive, and tactile sensory manipulations and sitting on either a stable or an unstable surface on mediolateral (ML) trunk sway. Fifteen individuals were measured. In each trial, subjects sat as quiet as possible, on a

  16. Albedo enhancement over land to counteract global warming: impacts on hydrological cycle

    Energy Technology Data Exchange (ETDEWEB)

    Bala, Govindasamy; Nag, Bappaditya [Indian Institute of Science, Divecha Center for Climate Change and Center for Atmospheric and Oceanic Sciences, Bangalore (India)

    2012-09-15

    A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO{sub 2} leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (-8.2 W m{sup -2}) to counter global mean radiative forcing from a doubling of CO{sub 2} (3.3 W m{sup -2}) is approximately twice the forcing needed over the oceans (-4.2 W m{sup -2}). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification. (orig.)

  17. Deriving albedo maps for HAPEX-Sahel from ASAS data using kernel-driven BRDF models

    Directory of Open Access Journals (Sweden)

    P. Lewis

    1999-01-01

    Full Text Available This paper describes the application and testing of a method for deriving spatial estimates of albedo from multi-angle remote sensing data. Linear kernel-driven models of surface bi-directional reflectance have been inverted against high spatial resolution multi-angular, multi- spectral airborne data of the principal cover types within the HAPEX-Sahel study site in Niger, West Africa. The airborne data are obtained from the NASA Airborne Solid-state Imaging Spectrometer (ASAS instrument, flown in Niger in September and October 1992. The maps of model parameters produced are used to estimate integrated reflectance properties related to spectral albedo. Broadband albedo has been estimated from this by weighting the spectral albedo for each pixel within the map as a function of the appropriate spectral solar irradiance and proportion of direct and diffuse illumination. Partial validation of the results was performed by comparing ASAS reflectance and derived directional-hemispherical reflectance with simulations of a millet canopy made with a complex geometric canopy reflectance model, the Botanical Plant Modelling System (BPMS. Both were found to agree well in magnitude. Broadband albedo values derived from the ASAS data were compared with ground-based (point sample albedo measurements and found to agree extremely well. These results indicate that the linear kernel-driven modelling approach, which is to be used operationally to produce global 16 day, 1 km albedo maps from forthcoming NASA Earth Observing System spaceborne data, is both sound and practical for the estimation of angle-integrated spectral reflectance quantities related to albedo. Results for broadband albedo are dependent on spectral sampling and on obtaining the correct spectral weigthings.

  18. Modelling Mean Albedo of Individual Roofs in Complex Urban Areas Using Satellite Images and Airborne Laser Scanning Point Clouds

    Science.gov (United States)

    Kalantar, B.; Mansor, S.; Khuzaimah, Z.; Sameen, M. Ibrahim; Pradhan, B.

    2017-09-01

    Knowledge of surface albedo at individual roof scale is important for mitigating urban heat islands and understanding urban climate change. This study presents a method for quantifying surface albedo of individual roofs in a complex urban area using the integration of Landsat 8 and airborne LiDAR data. First, individual roofs were extracted from airborne LiDAR data and orthophotos using optimized segmentation and supervised object based image analysis (OBIA). Support vector machine (SVM) was used as a classifier in OBIA process for extracting individual roofs. The user-defined parameters required in SVM classifier were selected using v-fold cross validation method. After that, surface albedo was calculated for each individual roof from Landsat images. Finally, thematic maps of mean surface albedo of individual roofs were generated in GIS and the results were discussed. Results showed that the study area is covered by 35% of buildings varying in roofing material types and conditions. The calculated surface albedo of buildings ranged from 0.16 to 0.65 in the study area. More importantly, the results indicated that the types and conditions of roofing materials significantly effect on the mean value of surface albedo. Mean albedo of new concrete, old concrete, new steel, and old steel were found to be equal to 0.38, 0.26, 0.51, and 0.44 respectively. Replacing old roofing materials with new ones should highly prioritized.

  19. MODELLING MEAN ALBEDO OF INDIVIDUAL ROOFS IN COMPLEX URBAN AREAS USING SATELLITE IMAGES AND AIRBORNE LASER SCANNING POINT CLOUDS

    Directory of Open Access Journals (Sweden)

    B. Kalantar

    2017-09-01

    Full Text Available Knowledge of surface albedo at individual roof scale is important for mitigating urban heat islands and understanding urban climate change. This study presents a method for quantifying surface albedo of individual roofs in a complex urban area using the integration of Landsat 8 and airborne LiDAR data. First, individual roofs were extracted from airborne LiDAR data and orthophotos using optimized segmentation and supervised object based image analysis (OBIA. Support vector machine (SVM was used as a classifier in OBIA process for extracting individual roofs. The user-defined parameters required in SVM classifier were selected using v-fold cross validation method. After that, surface albedo was calculated for each individual roof from Landsat images. Finally, thematic maps of mean surface albedo of individual roofs were generated in GIS and the results were discussed. Results showed that the study area is covered by 35% of buildings varying in roofing material types and conditions. The calculated surface albedo of buildings ranged from 0.16 to 0.65 in the study area. More importantly, the results indicated that the types and conditions of roofing materials significantly effect on the mean value of surface albedo. Mean albedo of new concrete, old concrete, new steel, and old steel were found to be equal to 0.38, 0.26, 0.51, and 0.44 respectively. Replacing old roofing materials with new ones should highly prioritized.

  20. Intercomparison of MODIS Albedo Retrievals and In Situ Measurements Across the Global FLUXNET Network

    Science.gov (United States)

    Cescatti, Alessandro; Marcolla, Barbara; Vannan, Suresh K. Santhana; Pan, Jerry Yun; Roman, Miguel O.; Yang, Xiaoyuan; Ciais, Philippe; Cook, Robert B.; Law, Beverly E.; Matteucci, Girogio; hide

    2012-01-01

    Surface albedo is a key parameter in the Earth's energy balance since it affects the amount of solar radiation directly absorbed at the planet surface. Its variability in time and space can be globally retrieved through the use of remote sensing products. To evaluate and improve the quality of satellite retrievals, careful intercomparisons with in situ measurements of surface albedo are crucial. For this purpose we compared MODIS albedo retrievals with surface measurements taken at 53 FLUXNET sites that met strict conditions of land cover homogeneity. A good agreement between mean yearly values of satellite retrievals and in situ measurements was found (R(exp 2)= 0.82). The mismatch is correlated to the spatial heterogeneity of surface albedo, stressing the relevance of land cover homogeneity when comparing point to pixel data. When the seasonal patterns of MODIS albedo is considered for different plant functional types, the match with surface observation is extremely good at all forest sites. On the contrary, in non-forest sites satellite retrievals underestimate in situ measurements across the seasonal cycle. The mismatch observed at grasslands and croplands sites is likely due to the extreme fragmentation of these landscapes, as confirmed by geostatistical attributes derived from high resolution scenes.

  1. The role of albedo and accumulation in the 2010 melting record in Greenland

    NARCIS (Netherlands)

    Tedesco, M.; Fettweis, X.; van den Broeke, M.R.|info:eu-repo/dai/nl/073765643; van de Wal, R.S.W.|info:eu-repo/dai/nl/101899556; Smeets, C.J.P.P.|info:eu-repo/dai/nl/191522236; van de Berg, W.J.|info:eu-repo/dai/nl/304831611; Serreze, M.C.; Box, J.E.

    2011-01-01

    Analyses of remote sensing data, surface observations and output from a regional atmosphere model point to new records in 2010 for surface melt and albedo, runoff, the number of days when bare ice is exposed and surface mass balance of the Greenland ice sheet, especially over its west and southwest

  2. Response to "The Iris Hypothesis: A Negative or Positive Cloud Feedback?"

    Science.gov (United States)

    Chou, Ming-Dah; Lindzen, Richard S.; Hou, Arthur Y.; Lau, William K. M. (Technical Monitor)

    2001-01-01

    Based on radiance measurements of Japan's Geostationary Meteorological Satellite, Lindzen et al. found that the high-level cloud cover averaged over the tropical western Pacific decreases with increasing sea surface temperature. They further found that the response of high-level clouds to the sea surface temperature had an effect of reducing the magnitude of climate change, which is referred as a negative climate feedback. Lin et al. reassessed the results found by Lindzen et al. by analyzing the radiation and clouds derived from the Tropical Rainfall Measuring Mission Clouds and the Earth's Radiant Energy System measurements. They found a weak positive feedback between high-level clouds and the surface temperature. We have found that the approach taken by Lin et al. to estimating the albedo and the outgoing longwave radiation is incorrect and that the inferred climate sensitivity is unreliable.

  3. Atmospheric effects on the mapping of Martian thermal inertia and thermally derived albedo

    Science.gov (United States)

    Hayashi, Joan N.; Jakosky, Bruce M.; Haberle, Robert M.

    1995-01-01

    We examine the effects of a dusty C02 atmosphere on the thermal inertia and thermally derived albedo of Mars and we present a new map of thermal inertias. This new map was produced using a coupled surface atmosphere (CSA) model, dust opacities from Viking infrared thermal mapper (IRTM) data, and C02 columns based on topography. The CSA model thermal inertias are smaller than the 2% model thermal inertias, with the difference largest at large thermal inertia. Although the difference between the thermal inertias obtained with the two models is moderate for much of the region studied, it is largest in regions of either high dust opacity or of topographic lows, including the Viking Lander 1 site and some geologically interesting regions. The CSA model thermally derived albedos do not accurately predict the IRTM measured albedos and are very similar to the thermally derived albedos obtained with models making the 2% assumption.

  4. Seasonal albedo of an urban/rural landscape from satellite observations

    Science.gov (United States)

    Brest, Christopher L.

    1987-01-01

    Using data from 27 calibrated Landsat observations of the Hartford, Connecticut area, the spatial distribution and seasonal variation of surface reflectance and albedo were examined. Mean values of visible reflectance, near-IR reflectance, and albedo are presented (for both snow-free and snow-cover observations) according to 14 land use/land cover categories. A diversity of albedo values was found to exist in this type of environment, associated with land cover. Many land-cover categories display a seasonal dependence, with intracategory seasonal differences being of comparable magnitude to intercategory differences. Key factors in determining albedo (and its seasonal dynamics) are the presence or absence of vegetation and the canopy structure. Snow-cover/snow-free differences range from a few percent (for urban land covers) to over 40 percent (for low-canopy vegetation).

  5. The extreme ultraviolet albedos of the planet Mercury and of the moon

    Science.gov (United States)

    Wu, H. H.; Broadfoot, A. L.

    1977-01-01

    The albedo of the moon in the far UV was measured by Mariner 10 at a solar phase angle of 74 deg, and the geometric albedo of Mercury was measured in same wavelength range (584-1657 A) at solar phase angles ranging from 50 to 120 deg. For both the moon and Mercury there is a general increase in albedo for wavelengths decreasing from 1657 to 584 A. The ratio of the albedos of Mercury and the moon increases from about 0.6 to 0.8 in the range 600-1600 A. This merely points to a difference in the surfaces of the moon and Mercury, there being insufficient data to make any conclusions regarding the nature of the difference.

  6. Feedback control of horizontal position and plasma surface shape in a non-circular tokamak

    International Nuclear Information System (INIS)

    Moriyama, Shin-ichi; Nakamura, Kazuo; Nakamura, Yukio; Itoh, Satoshi

    1986-01-01

    The linear model for the coupled horizontal position and plasma surface shape control in the non-circular tokamak device was described. It enables us to estimate easily the displacement and the distortion due to the changes in plasma pressure and current density distribution. The PI-controller and the optimal regulator were designed with the linear model. Transient-response analysis of the control system in the TRIAM-1M tokamak showed that the optimal regulator is superior to the PI-controller with regard to the mutual-interference between the position control system and the elongation control system. (author)

  7. Number Albedo of Low-Energy Photons

    International Nuclear Information System (INIS)

    Ljubenov, V.; Simovic, R.; Markovic, S.

    2007-01-01

    Number albedo of water, aluminum and iron for incident photons in energy range from 20 keV to 100 keV is presented in this paper. Results are obtained through the Monte Carlo simulations of photon reflection by using the MCNP, FOTELP and PENELOPE computer codes. Calculated values are compared with the classical data published by B. P. Bulatov and his collaborators. Influence of the fluorescence yield to the photon number albedo of iron target is analyzed in detail. (author)

  8. Albedo Corrections for High Albedo Near Earth Objects Observed With Spitzer

    Science.gov (United States)

    Gustafsson, Annika; Trilling, David E.; Mommert, Michael; Hora, Joseph L.

    2017-10-01

    Thermal infrared observations are the most effective way to measure asteroid diameter and albedo. Major surveys like NEOWISE and NEOSurvey return a small fraction of objects with albedo values higher than that believed to exist in the near-Earth object (NEO) population. About 10% of Spitzer-observed NEOs have nominal albedo solutions greater than 0.5. There are many possible causes for these unrealistically high albedos, including thermal lightcurves (leading to a mis-estimate of asteroid diameter) or inaccurate absolute visual magnitudes (either from poor photometry or lightcurve effects). We present here the results of a ground-based optical photometric study of 36 high albedo NEOs from NEOSurvey (Trilling et al. 2016) using measurements from the Discovery Channel Telescope. Our findings indicate that uncertainty in the diameter has the most impact on the derived albedo of our targets, while the uncertainty in the H-magnitude and slope parameter have smaller effects. We supply corrected albedos for our target list, as well as a systematic offset dependent on the solar phase angle of the object (Mommert el al. 2017). These corrected albedo values will help constrain the albedo range in the population to better reflect its physical characteristics. This work is based in part on the observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

  9. Albedo impact on the suitability of biochar systems to mitigate global warming.

    Science.gov (United States)

    Meyer, Sebastian; Bright, Ryan M; Fischer, Daniel; Schulz, Hardy; Glaser, Bruno

    2012-11-20

    Biochar application to agricultural soils can change the surface albedo which could counteract the climate mitigation benefit of biochar systems. However, the size of this impact has not yet been quantified. Based on empirical albedo measurements and literature data of arable soils mixed with biochar, a model for annual vegetation cover development based on satellite data and an assessment of the annual development of surface humidity, an average mean annual albedo reduction of 0.05 has been calculated for applying 30-32 Mg ha(-1) biochar on a test field near Bayreuth, Germany. The impact of biochar production and application on the carbon cycle and on the soil albedo was integrated into the greenhouse gas (GHG) balance of a modeled pyrolysis based biochar system via the computation of global warming potential (GWP) characterization factors. The analysis resulted in a reduction of the overall climate mitigation benefit of biochar systems by 13-22% due to the albedo change as compared to an analysis which disregards the albedo effect. Comparing the use of the same quantity of biomass in a biochar system to a bioenergy district heating system which replaces natural gas combustion, bioenergy heating systems achieve 99-119% of the climate benefit of biochar systems according to the model calculation.

  10. Observational determination of albedo decrease caused by vanishing Arctic sea ice.

    Science.gov (United States)

    Pistone, Kristina; Eisenman, Ian; Ramanathan, V

    2014-03-04

    The decline of Arctic sea ice has been documented in over 30 y of satellite passive microwave observations. The resulting darkening of the Arctic and its amplification of global warming was hypothesized almost 50 y ago but has yet to be verified with direct observations. This study uses satellite radiation budget measurements along with satellite microwave sea ice data to document the Arctic-wide decrease in planetary albedo and its amplifying effect on the warming. The analysis reveals a striking relationship between planetary albedo and sea ice cover, quantities inferred from two independent satellite instruments. We find that the Arctic planetary albedo has decreased from 0.52 to 0.48 between 1979 and 2011, corresponding to an additional 6.4 ± 0.9 W/m(2) of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25% as large as that due to the change in CO2 during this period, considerably larger than expectations from models and other less direct recent estimates. Changes in cloudiness appear to play a negligible role in observed Arctic darkening, thus reducing the possibility of Arctic cloud albedo feedbacks mitigating future Arctic warming.

  11. Modeling the Space-Time Destiny of Pan-Arctic Permafrost DOC in a Global Land Surface Model: Feedback Implications

    Science.gov (United States)

    Bowring, S.; Lauerwald, R.; Guenet, B.; Zhu, D.; Ciais, P.

    2017-12-01

    Most global climate models do not represent the unique permafrost soil environment and its respective processes. This significantly contributes to uncertainty in estimating their responses, and that of the planet at large, to warming. Here, the production, transport and atmospheric release of dissolved organic carbon (DOC) from high-latitude permafrost soils into inland waters and the ocean is explicitly represented for the first time in the land surface component (ORCHIDEE-MICT) of a CMIP6 global climate model (IPSL). This work merges two models that are able to mechanistically simulate complex processes for 1) snow, ice and soil phenomena in high latitude environments, and 2) DOC production and lateral transport through soils and the river network, respectively, at 0.5° to 2° resolution. The resulting model is subjected to a wide range of input forcing data, parameter testing and contentious feedback phenomena, including microbial heat generation as the active layer deepens. We present results for the present and future Pan-Arctic and Eurasia, with a focus on the Lena and Mackenzie River basins, and show that soil DOC concentrations, their riverine transport and atmospheric evasion are reasonably well represented as compared to observed stocks, fluxes and seasonality. We show that most basins exhibit large increases in DOC transport and riverine CO2 evasion across the suite of RCP scenarios to 2100. We also show that model output is strongly influenced by choice of input forcing data. The riverine component of what is known as the `boundless carbon cycle' is little-recognized in global climate modeling. Hydrological mobilization to the river network results either in sedimentary settling or atmospheric `evasion', presently amounting to 0.5-1.8 PgC yr-1. Our work aims at filling in these knowledge gaps, and the response of these DOC-related processes to thermal forcing. Potential feedbacks owing to such a response are of particular relevance, given the magnitude

  12. Theoretical and Observational Determination of Global and Regional Radiation Budget, Forcing and Feedbacks at the Top-of-Atmosphere and Surface

    Science.gov (United States)

    Loeb, Norman G.

    2004-01-01

    Report consists of: 1. List of accomplishments 2. List of publications 3. Abstracts of published or submitted papers and 4. Subject invention disclosure. The accomplishments of the grant listed are: 1. Improved the third-order turbulence closure in cloud resolving models to remove the liquid water oscillation. 2. Used the University of California-Los Angeles (UCLA) large-eddy simulation (LES) model to provide data for radiation transfer testing. 3. Revised shortwave k-distribution models based on HITRAN 2000. 4. Developed a gamma-weighted two-stream radiative transfer model for radiation budget estimate applications. 5. Estimated the effect of spherical geometry to the earth radiation budget. 6. Estimated top-of-atmosphere irradiance over snow and sea ice surfaces. 7. Estimated the aerosol direct radiative effect at the top of the atmosphere. 8. Estimated the top-of-atmosphere reflectance of the clear-sky molecular atmosphere over ocean. 9. Developed and validated new set of Angular Distribution Models for the CERES TRMM satellite instrument (tropical) 10. Developed and validated new set of Angular Distribution Models for the CERES Terra satellite instrument (global) 11. Quantified the top-of-atmosphere direct radiative effect of aerosols over global oceans from merged CERES and MODIS observations 12 Clarified the definition of TOA flux reference level for radiation budget studies 13. Developed new algorithm for unfaltering CERES measured radiances 14. Used multiangle POLDER measurements to produce narrowband angular distribution models and examine the effect of scene identification errors on TOA albedo estimates 15. Developed and validated a novel algorithm called the Multidirectional Reflectance Matching (MRM) model for inferring TOA albedos from ice clouds using multi-angle satellite measurements. 16. Developed and validated a novel algorithm called the Multidirectional Polarized Reflectance Matching (MPRM) model for inferring particle shapes from ice clouds

  13. Diagnostics comparing sea surface temperature feedbacks from operational hurricane forecasts to observations

    Directory of Open Access Journals (Sweden)

    Ian D. Lloyd

    2011-11-01

    Full Text Available This paper examines the ability of recent versions of the Geophysical Fluid Dynamics Laboratory Operational Hurricane Forecast Model (GHM to reproduce the observed relationship between hurricane intensity and hurricane-induced Sea Surface Temperature (SST cooling. The analysis was performed by taking a Lagrangian composite of all hurricanes in the North Atlantic from 1998–2009 in observations and 2005–2009 for the GHM. A marked improvement in the intensity-SST relationship for the GHM compared to observations was found between the years 2005 and 2006–2009 due to the introduction of warm-core eddies, a representation of the loop current, and changes to the drag coefficient parameterization for bulk turbulent flux computation. A Conceptual Hurricane Intensity Model illustrates the essential steady-state characteristics of the intensity-SST relationship and is explained by two coupled equations for the atmosphere and ocean. The conceptual model qualitatively matches observations and the 2006–2009 period in the GHM, and presents supporting evidence for the conclusion that weaker upper oceanic thermal stratification in the Gulf of Mexico, caused by the introduction of the loop current and warm core eddies, is crucial to explaining the observed SST-intensity pattern. The diagnostics proposed by the conceptual model offer an independent set of metrics for comparing operational hurricane forecast models to observations.

  14. Growing season carries stronger contributions to albedo dynamics on the Tibetan plateau.

    Directory of Open Access Journals (Sweden)

    Li Tian

    Full Text Available The Tibetan Plateau has experienced higher-than-global-average climate warming in recent decades, resulting in many significant changes in ecosystem structure and function. Among them is albedo, which bridges the causes and consequences of land surface processes and climate. The plateau is covered by snow/ice and vegetation in the non-growing season (nGS and growing season (GS, respectively. Based on the MODIS products, we investigated snow/ice cover and vegetation greenness in relation to the spatiotemporal changes of albedo on the Tibetan Plateau from 2000 through 2013. A synchronous relationship was found between the change in GSNDVI and GSalbedo over time and across the Tibetan landscapes. We found that the annual average albedo had a decreasing trend, but that the albedo had slightly increased during the nGS and decreased during the GS. Across the landscapes, the nGSalbedo fluctuated in a synchronous pattern with snow/ice cover. Temporally, monthly snow/ice coverage also had a high correspondence with albedo, except in April and October. We detected clear dependencies of albedo on elevation. With the rise in altitude, the nGSalbedo decreased below 4000 m, but increased for elevations of 4500-5500 m. Above 5500 m, the nGSalbedo decreased, which was in accordance with the decreased amount of snow/ice coverage and the increased soil moisture on the plateau. More importantly, the decreasing albedo in the most recent decade appeared to be caused primarily by lowered growing season albedo.

  15. Optimal Nodes Selectiveness from WSN to Fit Field Scale Albedo Observation and Validation in Long Time Series in the Foci Experiment Areas, Heihe

    Directory of Open Access Journals (Sweden)

    Xiaodan Wu

    2015-11-01

    Full Text Available To evaluate and improve the quality of land surface albedo products, validation with ground measurements of albedo is crucial over the spatially and temporally heterogeneous land surface. One of the essential steps for satellite albedo product validation is coarse scale observation technique development with long time ground-based measurements. In this paper, the optimal nodes were selected from the wireless sensor network (WSN to perform observation at large scale and in longer time series for validation of albedo products. The relative difference is used to analyze the spatiotemporal representativeness of each node. The random combination method is used to assess the number of required sites (NRS and then to identify the most representative combination (MRC. On this basis, an upscaling transform function with different weights for each node in the MRC, which are calculated with the ordinary least squares (OLS linear regression method, is used to upscale WSN node albedo from point scale to the field scale. This method is illustrated by selecting the optimal nodes and upscaling surface albedo from point observation to the field scale in the Heihe River basin, China. Primary findings are: (a The method of reducing the number of observations without significant loss of information about surface albedo at field scale is feasible and effective; (b When only few sensors are available, the most representative locations in time and space should be the first priority; when a number of sensors are available in the heterogeneous land surface, it is preferable to install them in different land surface, rather than the most representative locations; (c The most representative combination (MRC combined with the upscaling weight coefficients can give a robust estimate of the field mean surface albedo. These efforts based on ground albedo observations promote the chance to use point information for validation of coarse scale albedo products. Moreover, a

  16. Implications of albedo changes following afforestation on the benefits of forests as carbon sinks

    Directory of Open Access Journals (Sweden)

    M. U. F. Kirschbaum

    2011-12-01

    Full Text Available Increased carbon storage with afforestation leads to a decrease in atmospheric carbon dioxide concentration and thus decreases radiative forcing and cools the Earth. However, afforestation also changes the reflective properties of the surface vegetation from more reflective pasture to relatively less reflective forest cover. This increase in radiation absorption by the forest constitutes an increase in radiative forcing, with a warming effect. The net effect of decreased albedo and carbon storage on radiative forcing depends on the relative magnitude of these two opposing processes.

    We used data from an intensively studied site in New Zealand's Central North Island that has long-term, ground-based measurements of albedo over the full short-wave spectrum from a developing Pinus radiata forest. Data from this site were supplemented with satellite-derived albedo estimates from New Zealand pastures. The albedo of a well-established forest was measured as 13 % and pasture albedo as 20 %. We used these data to calculate the direct radiative forcing effect of changing albedo as the forest grew.

    We calculated the radiative forcing resulting from the removal of carbon from the atmosphere as a decrease in radiative forcing of −104 GJ tC−1 yr−1. We also showed that the observed change in albedo constituted a direct radiative forcing of 2759 GJ ha−1 yr−1. Thus, following afforestation, 26.5 tC ha−1 needs to be stored in a growing forest to balance the increase in radiative forcing resulting from the observed albedo change. Measurements of tree biomass and albedo were used to estimate the net change in radiative forcing as the newly planted forest grew. Albedo and carbon-storage effects were of similar magnitude for the first four to five years after tree planting, but as the stand grew older, the carbon storage effect increasingly dominated. Averaged over the whole

  17. What can decadal variability tell us about climate feedbacks and sensitivity?

    Science.gov (United States)

    Colman, Robert; Power, Scott B.

    2018-02-01

    Radiative feedbacks are known to determine climate sensitivity. Global top-of-atmosphere radiation correlations with surface temperature performed here show that decadal variability in surface temperature is also reinforced by strong positive feedbacks in models, both in the long wave (LW) and short wave (SW), offsetting much of the Planck radiative damping. Net top-of-atmosphere feedback is correlated with the magnitude of decadal temperature variability, particularly in the tropics. This indicates decadal-timescale radiative reinforcement of surface temperature variability. Assuming a simple global ocean mixed layer response, the reinforcement is found to be of a magnitude comparable to that required for typical decadal global scale anomalies. The magnitude of decadal variability in the tropics is uncorrelated with LW feedbacks, but it is correlated with total SW feedbacks, which are, in turn, correlated with tropical SW cloud feedback. Globally, water vapour/lapse rate, surface albedo and cloud feedbacks on decadal timescales are, on average, as strong as those operating under climate change. Together these results suggest that some of the physical processes responsible for setting the magnitude of global temperature change in the twenty-first century and climate sensitivity also help set the magnitude of the natural decadal variability. Furthermore, a statistically significant correlation exists between climate sensitivity and decadal variability in the tropics across CMIP5 models, although this is not apparent in the earlier generation of CMIP3 models. Thus although the link to sensitivity is not conclusive, this opens up potential paths to improve our understanding of climate feedbacks, climate sensitivity and decadal climate variability, and has the potential to reduce the associated uncertainty.

  18. Cloud-Induced Stabilization of Greenland Surface Melt

    Science.gov (United States)

    Wang, W.; Zender, C. S.; van As, D.; Smeets, P.; van den Broeke, M. R.

    2016-12-01

    Surface melt and mass loss of the Greenland ice sheet (GrIS) may play crucial roles in global climate change due to its large fresh water storage and positive feedbacks. Complemented by clear-sky simulations from a radiative transfer model, we use measurements from 30+ automatic weather stations (AWSs) to estimate the strong and most variable contribution to Greenland's surface energy budget: the cloud radiative effects (CREs). AWSs are the only in-situ data source for long term surface energy budget studies across the GrIS. The primary bias in its radiation measurements stem from station tilt caused by spatially heterogeneous snow melt, snow compaction, and glacier dynamics. Over all AWSs on GrIS, hourly absolute biases in insolation can reach up to 200 W/m2, and insolation on fewer than 40% of clear days peaks within ±0.5 hr of the true solar noon time. We developed and used the Retrospective, Iterative, Geometry-Based (RIGB) tilt-correction method to identify and remove per-station mean-absolute biases that average 18 W/m2 over GrIS during melt seasons. We demonstrate using the tilt-adjusted radiation that surface albedo, among other environmental factors and cloud properties, determines the net CRE, a competition between shortwave shading and longwave heating. At stations where surface albedo is high and close to cloud albedo, shortwave shading is suppressed and longwave heating dominates. At stations where albedo is low (e.g., due to temperature-induced snow metamorphism and/or melt), shading effect increases faster than greenhouse effect, driving net CRE toward cooling. We found that a 0.57 albedo threshold distinguishes areas of positive from negative CREs with 99% accuracy. The cooling effect intensifies at lower albedo. During the extensive surface melt across GrIS in 2012, clouds exerted anomalously strong cooling in the southern ablation zone, and only climatological-mean warming in the accumulation zone. Clouds reduced more than promoted surface melt

  19. Gemini NIFS survey of feeding and feedback processes in nearby active galaxies - II. The sample and surface mass density profiles

    Science.gov (United States)

    Riffel, R. A.; Storchi-Bergmann, T.; Riffel, R.; Davies, R.; Bianchin, M.; Diniz, M. R.; Schönell, A. J.; Burtscher, L.; Crenshaw, M.; Fischer, T. C.; Dahmer-Hahn, L. G.; Dametto, N. Z.; Rosario, D.

    2018-02-01

    We present and characterize a sample of 20 nearby Seyfert galaxies selected for having BAT 14-195 keV luminosities LX ≥ 1041.5 erg s-1, redshift z ≤ 0.015, being accessible for observations with the Gemini Near-Infrared Field Spectrograph (NIFS) and showing extended [O III]λ5007 emission. Our goal is to study Active Galactic Nucleus (AGN) feeding and feedback processes from near-infrared integral-field spectra, which include both ionized (H II) and hot molecular (H2) emission. This sample is complemented by other nine Seyfert galaxies previously observed with NIFS. We show that the host galaxy properties (absolute magnitudes MB, MH, central stellar velocity dispersion and axial ratio) show a similar distribution to those of the 69 BAT AGN. For the 20 galaxies already observed, we present surface mass density (Σ) profiles for H II and H2 in their inner ˜500 pc, showing that H II emission presents a steeper radial gradient than H2. This can be attributed to the different excitation mechanisms: ionization by AGN radiation for H II and heating by X-rays for H2. The mean surface mass densities are in the range (0.2 ≤ ΣH II ≤ 35.9) M⊙ pc-2, and (0.2 ≤ ΣH2 ≤ 13.9)× 10-3 M⊙ pc-2, while the ratios between the H II and H2 masses range between ˜200 and 8000. The sample presented here will be used in future papers to map AGN gas excitation and kinematics, providing a census of the mass inflow and outflow rates and power as well as their relation with the AGN luminosity.

  20. A COMPARISON OF OBSERVATION WITH MODELING FOR ALBEDO AND TRANSMITTANCE OF SNOW

    OpenAIRE

    アオキ, テルオ; セコ, カツモト; アオキ, タダオ; フカボリ, マサシ; Teruo, AOKI; Katsumoto, SEKO; Tadao, AOKI; Masashi, FUKABORI

    1994-01-01

    Snow surface albedo and transmittance inside the snow have been investigated by observation and modeling. Observations were taken by a grating type spectrometer at Tokamachi in March 1993. The observed snow was old and very wet. Microscope photo-graphs of snow grains taken at this time indicate that snow grain is spherical particles with size of about 1.0μm. Surface albedo and transmittance of snow by a multiple scattering model for the atmosphere-snow system with pure snow grain size of 1.0μ...

  1. Microgeometry capture and RGB albedo estimation by photometric stereo without demosaicing

    Science.gov (United States)

    Quéau, Yvain; Pizenberg, Mathieu; Durou, Jean-Denis; Cremers, Daniel

    2017-03-01

    We present a photometric stereo-based system for retrieving the RGB albedo and the fine-scale details of an opaque surface. In order to limit specularities, the system uses a controllable diffuse illumination, which is calibrated using a dedicated procedure. In addition, we rather handle RAW, non-demosaiced RGB images, which both avoids uncontrolled operations on the sensor data and simplifies the estimation of the albedo in each color channel and of the normals. We finally show on real-world examples the potential of photometric stereo for the 3D-reconstruction of very thin structures from a wide variety of surfaces.

  2. UV irradiance and albedo at Union Glacier Camp (Antarctica: a case study.

    Directory of Open Access Journals (Sweden)

    Raul R Cordero

    Full Text Available We report on the first spectral measurements of ultraviolet (UV irradiance and the albedo at a Camp located in the southern Ellsworth Mountains on the broad expanse of Union Glacier (700 m altitude, 79° 46' S; 82° 52'W; about 1,000 km from the South Pole. The measurements were carried out by using a double monochromator-based spectroradiometer during a campaign (in December 2012 meant to weight up the effect of the local albedo on the UV irradiance. We found that the albedo measured at noon was about 0.95 in the UV and the visible part of the spectrum. This high surface reflectivity led to enhancements in the UV index under cloudless conditions of about 50% in comparison with snow free surfaces. Spectral measurements carried out elsewhere as well as estimates retrieved from the Ozone Monitoring Instrument (OMI were used for further comparisons.

  3. Preliminary Estimation of Black Carbon Deposition from Nepal Climate Observatory-Pyramid Data and Its Possible Impact on Snow Albedo Changes Over Himalayan Glaciers During the Pre-Monsoon Season

    Science.gov (United States)

    Yasunari, T. J.; Bonasoni, P.; Laj, P.; Fujita, K.; Vuillermoz, E.; Marinoni, A.; Cristofanelli, P.; Duchi, R.; Tartari, G.; Lau, K.-M.

    2010-01-01

    The possible minimal range of reduction in snow surface albedo due to dry deposition of black carbon (BC) in the pre-monsoon period (March-May) was estimated as a lower bound together with the estimation of its accuracy, based on atmospheric observations at the Nepal Climate Observatory-Pyramid (NCO-P) sited at 5079 m a.s.l. in the Himalayan region. We estimated a total BC deposition rate of 2.89 g m-2 day-1 providing a total deposition of 266 micrograms/ square m for March-May at the site, based on a calculation with a minimal deposition velocity of 1.0 10(exp -4) m/s with atmospheric data of equivalent BC concentration. Main BC size at NCO-P site was determined as 103.1-669.8 nm by correlation analysis between equivalent BC concentration and particulate size distribution in the atmosphere. We also estimated BC deposition from the size distribution data and found that 8.7% of the estimated dry deposition corresponds to the estimated BC deposition from equivalent BC concentration data. If all the BC is deposited uniformly on the top 2-cm pure snow, the corresponding BC concentration is 26.0-68.2 microgram/kg assuming snow density variations of 195-512 kg/ cubic m of Yala Glacier close to NCO-P site. Such a concentration of BC in snow could result in 2.0-5.2% albedo reductions. From a simple numerical calculations and if assuming these albedo reductions continue throughout the year, this would lead to a runoff increases of 70-204 mm of water drainage equivalent of 11.6-33.9% of the annual discharge of a typical Tibetan glacier. Our estimates of BC concentration in snow surface for pre-monsoon season can be considered comparable to those at similar altitude in the Himalayan region, where glaciers and perpetual snow region starts in the vicinity of NCO-P. Our estimates from only BC are likely to represent a lower bound for snow albedo reductions, since a fixed slower deposition velocity was used and atmospheric wind and turbulence effects, snow aging, dust deposition

  4. Using albedo to reform wind erosion modelling, mapping and monitoring

    Science.gov (United States)

    Chappell, Adrian; Webb, Nicholas P.

    2016-12-01

    Wind erosion and dust emission models are used to assess the impacts of dust on radiative forcing in the atmosphere, cloud formation, nutrient fertilisation and human health. The models are underpinned by a two-dimensional geometric property (lateral cover; L) used to characterise the three-dimensional aerodynamic roughness (sheltered area or wakes) of the Earth's surface and calibrate the momentum it extracts from the wind. We reveal a fundamental weakness in L and demonstrate that values are an order of magnitude too small and significant aerodynamic interactions between roughness elements and their sheltered areas have been omitted, particularly under sparse surface roughness. We describe a solution which develops published work to establish a relation between sheltered area and the proportion of shadow over a given area; the inverse of direct beam directional hemispherical reflectance (black sky albedo; BSA). We show direct relations between shadow and wind tunnel measurements and thereby provide direct calibrations of key aerodynamic properties. Estimation of the aerodynamic parameters from albedo enables wind erosion assessments over areas, across platforms from the field to airborne and readily available satellite data. Our new approach demonstrated redundancy in existing wind erosion models and thereby reduced model complexity and improved fidelity. We found that the use of albedo enabled an adequate description of aerodynamic sheltering to characterise fluid dynamics and predict sediment transport without the use of a drag partition scheme (Rt) or threshold friction velocity (u∗t). We applied the calibrations to produce global maps of aerodynamic properties which showed very similar spatial patterns to each other and confirmed the redundancy in the traditional parameters of wind erosion modelling. We evaluated temporal patterns of predicted horizontal mass flux at locations across Australia which revealed variation between land cover types that would not

  5. Giving feedback.

    Science.gov (United States)

    Thomas, Jane DeLima; Arnold, Robert M

    2011-02-01

    Giving feedback is a core element of medical education, one that is gaining attention but with a thin evidence base to guide medical educators. This review provides a definition of feedback and its purpose, selectively reviews the literature regarding educators' and learners' attitudes toward feedback, and provides an algorithm for giving feedback. The authors discuss the parallels between giving feedback and breaking bad news, emphasizing the importance of titrating the amount of information given, attending to affect, and making a plan for next steps. Special considerations for giving feedback in palliative care are highlighted, including the effect of heightened emotion in the clinical encounter and the difficulties of giving feedback about communication skills.

  6. Radiative forcing over the conterminous United States due to contemporary land cover land use albedo change

    Science.gov (United States)

    Barnes, Christopher; Roy, David P.

    2008-01-01

    Recently available satellite land cover land use (LCLU) and albedo data are used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 36 ecoregions covering 43% of the conterminous United States (CONUS). Moderate Resolution Imaging Spectroradiometer (MODIS) snow-free broadband albedo values are derived from Landsat LCLU classification maps located using a stratified random sampling methodology to estimate ecoregion estimates of LCLU induced albedo change and surface radiative forcing. The results illustrate that radiative forcing due to LCLU change may be disguised when spatially and temporally explicit data sets are not used. The radiative forcing due to contemporary LCLU albedo change varies geographically in sign and magnitude, with the most positive forcings (up to 0.284 Wm−2) due to conversion of agriculture to other LCLU types, and the most negative forcings (as low as −0.247 Wm−2) due to forest loss. For the 36 ecoregions considered a small net positive forcing (i.e., warming) of 0.012 Wm−2 is estimated.

  7. Retrieval of the ultraviolet effective snow albedo during 1998 winter campaign in the French Alps.

    Science.gov (United States)

    Smolskaia, Irina; Masserot, Dominique; Lenoble, Jacqueline; Brogniez, Colette; de la Casinière, Alain

    2003-03-20

    A measurement campaign was carried out in February 1998 at Briançon Station, French Alps (44.9 degrees N, 6.65 degrees E, 1,310 m above sea level) in order to determine the UV effective snow albedo that was retrieved for both erythemal and UV-A irradiances from measurements and modeling enhancement factors. The results are presented for 15 cloudless days with very variable snow cover and a small snowfall in the middle of the campaign. Erythemal irradiance enhancement due to the surface albedo was found to decrease from approximately +15% to +5% with a jump to +22% after the snowfall, whereas UV-A irradiance enhancement decreased from 7% to 5% and increased to 15% after the snowfall. Thesevalues fit to effective surface albedos of 0.4, 0.1, and 0.5 for erythemal, and to effective albedos of 0.25, 0.1, and 0.4 for UV-A irradiances, respectively. An unexpected difference between the effective albedos retrieved in the two wavelength regions can be explained by the difference of the environment contribution.

  8. Change in Urban Albedo in London: A Multi-scale Perspective

    Science.gov (United States)

    Susca, T.; Kotthaus, S.; Grimmond, S.

    2013-12-01

    Urbanization-induced change in land use has considerable implications for climate, air quality, resources and ecosystems. Urban-induced warming is one of the most well-known impacts. This directly and indirectly can extend beyond the city. One way to reduce the size of this is to modify the surface atmosphere exchanges through changing the urban albedo. As increased rugosity caused by the morphology of a city results in lower albedo with constant material characteristics, the impacts of changing the albedo has impacts across a range of scales. Here a multi-scale assessment of the potential effects of the increase in albedo in London is presented. This includes modeling at the global and meso-scale informed by local and micro-scale measurements. In this study the first order calculations are conducted for the impact of changing the albedo (e.g. a 0.01 increase) on the radiative exchange. For example, when incoming solar radiation and cloud cover are considered, based on data retrieved from NASA (http://power.larc.nasa.gov/) for ~1600 km2 area of London, would produce a mean decrease in the instantaneous solar radiative forcing on the same surface of 0.40 W m-2. The nature of the surface is critical in terms of considering the impact of changes in albedo. For example, in the Central Activity Zone in London pavement and building can vary from 10 to 100% of the plan area. From observations the albedo is seen to change dramatically with changes in building materials. For example, glass surfaces which are being used increasingly in the central business district results in dramatic changes in albedo. Using the documented albedo variations determined across different scales the impacts are considered. For example, the effect of the increase in urban albedo is translated into the corresponding amount of avoided emission of carbon dioxide that produces the same effect on climate. At local scale, the effect that the increase in urban albedo can potentially have on local

  9. NEOWISE DIAMETERS AND ALBEDOS V1.0

    Data.gov (United States)

    National Aeronautics and Space Administration — This PDS data set represents a compilation of published diameters, optical albedos, near-infrared albedos, and beaming parameters for minor planets detected by...

  10. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    Directory of Open Access Journals (Sweden)

    M. M. Helsen

    2017-08-01

    Full Text Available The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB of the Greenland ice sheet (GrIS is poorly resolved in the model. The purpose of this study is to improve the SMB forcing of the GrIS by evaluating different parameter settings within a snow albedo scheme. By allowing ice-sheet albedo to vary as a function of wet and dry conditions, the spatial distribution of albedo and melt rate improves. Nevertheless, the spatial distribution of SMB in EC-Earth is not significantly improved. As a reason for this, we identify omissions in the current snow albedo scheme, such as separate treatment of snow and ice and the effect of refreezing. The resulting SMB is downscaled from the lower-resolution global climate model topography to the higher-resolution ice-sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice-sheet model simulations. From these ice-sheet simulations we conclude that an albedo scheme with a short response time of decaying albedo during wet conditions performs best with respect to long-term simulated ice-sheet volume. This results in an optimized albedo parameterization that can be used in future EC-Earth simulations with an interactive ice-sheet component.

  11. On the importance of the albedo parameterization for the mass balance of the Greenland ice sheet in EC-Earth

    Science.gov (United States)

    Helsen, Michiel M.; van de Wal, Roderik S. W.; Reerink, Thomas J.; Bintanja, Richard; Madsen, Marianne S.; Yang, Shuting; Li, Qiang; Zhang, Qiong

    2017-08-01

    The albedo of the surface of ice sheets changes as a function of time due to the effects of deposition of new snow, ageing of dry snow, bare ice exposure, melting and run-off. Currently, the calculation of the albedo of ice sheets is highly parameterized within the earth system model EC-Earth by taking a constant value for areas with thick perennial snow cover. This is an important reason why the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved in the model. The purpose of this study is to improve the SMB forcing of the GrIS by evaluating different parameter settings within a snow albedo scheme. By allowing ice-sheet albedo to vary as a function of wet and dry conditions, the spatial distribution of albedo and melt rate improves. Nevertheless, the spatial distribution of SMB in EC-Earth is not significantly improved. As a reason for this, we identify omissions in the current snow albedo scheme, such as separate treatment of snow and ice and the effect of refreezing. The resulting SMB is downscaled from the lower-resolution global climate model topography to the higher-resolution ice-sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice-sheet model simulations. From these ice-sheet simulations we conclude that an albedo scheme with a short response time of decaying albedo during wet conditions performs best with respect to long-term simulated ice-sheet volume. This results in an optimized albedo parameterization that can be used in future EC-Earth simulations with an interactive ice-sheet component.

  12. Measuring Longitudinal Albedo Variations of Asteroids with Ground-Based, Part-Per-Million Polarimetry

    Science.gov (United States)

    Wiktorowicz, Sloane; Masiero, Joseph R.

    2017-10-01

    The polarization state of asteroids encodes a wealth of information about their surfaces. Linear polarization and albedo of rocky Solar System bodies has long been known to be anticorrelated (the Umov effect): dark surfaces, dominated by single scattering, are strongly polarized, but multiple scattering in bright surfaces randomizes the electric field orientation and reduces polarization. As an asteroid rotates, both shape changes and surface albedo variations affect reflected light flux, causing difficulty in the identification of albedo variations. As a differential technique, however, polarimetry is insensitive to shape changes: as total flux varies with instantaneous cross-sectional area, fractional polarization does not. Thus, rotational variability in linear polarization is a hallmark of albedo inhomogeneity, and it cannot be identified with photometry alone.Until now, polarimeters have only discovered high significance rotational variation of linear polarization for one asteroid, (4) Vesta. We report on Lick 3-m observations of Main Belt asteroids with the POLISH2 polarimeter, which utilizes photoelastic modulators instead of a waveplate. We have not only confirmed rotational variations in (4) Vesta with 12 sigma significance in a single, 4-hour observation, but we have also discovered variations in (1) Ceres (5 sigma detection) and (7) Iris (7 sigma detection). We observe that both (4) Vesta and (7) Iris harbor strong linear polarization variations, due to the presence of significant albedo heterogeneity on their surfaces, while those of (1) Ceres are markedly weaker due to its relatively homogenous surface.Circular polarization, which may originate from multiple scattering or from the phase retardance introduced by a metalliferous surface, has been observed in nearly all Solar System bodies except for asteroids. POLISH2 simultaneously measures linear and circular polarization, and we report the discovery of non-zero circular polarization from (7) Iris with

  13. Effects of multi-directional vibrotactile feedback on vestibular-deficient postural performance during continuous multi-directional support surface perturbations.

    Science.gov (United States)

    Sienko, K H; Balkwill, M D; Oddsson, L I E; Wall, C

    2008-01-01

    Single-axis vibrotactile feedback of trunk tilt provided in real-time has previously been shown to significantly reduce the root-mean-square (RMS) trunk sway in subjects with vestibular loss during single-axis perturbation. This research examines the effect of multi-directional vibrotactile feedback on postural sway during continuous multi-directional surface perturbations when the subjects' eyes are closed. Eight subjects with vestibular loss donned a multi-axis feedback device that mapped body tilt estimates onto their torsos with a 3-row by 16-column array of tactile actuators (tactors). Tactor row indicated tilt magnitude and tactor column indicated tilt direction. Root-mean-square trunk tilt, elliptical fits to trunk sway trajectory areas, percentage of time spent outside a no vibrotactile feedback zone, RMS center of pressure, and anchoring index parameters indicating intersegmental coordination were used to assess the efficacy of the multi-directional vibrotactile balance aid. Four tactor display configurations in addition to the tactors off configuration were evaluated. Subjects had significantly reduced RMS trunk sway, significantly smaller elliptical fits of the trajectory area, and spent significantly less time outside of the no feedback zone in the tactors on versus the tactors off configuration. Among the displays evaluated in this study, there was not an optimal tactor column configuration for standing tasks involving continuous surface perturbations. Furthermore, subjects performed worse when erroneous information was displayed. Therefore, a spatial resolution of 90 degrees (4 columns) seems to be as effective as a spatial resolution of 22.5 degrees (16 columns) for control of standing.

  14. Dynamical Polar Warming Amplification and a New Climate Feedback Analysis Framework

    Science.gov (United States)

    Cai, M.; Lu, J.

    2008-12-01

    An idealized coupled general circulation model is used to demonstrate that the surface warming due the doubling of CO2 can still be stronger in high latitudes than in low latitudes even without the negative evaporation feedback in low latitudes and positive ice-albedo feedback in high latitudes, as well as without the poleward latent heat transport. The new climate feedback analysis method formulated in Lu and Cai (2008) is used to isolate contributions to the total temperature change obtained with the full GCM model from both radiative and non-radiative feedback processes. The new feedback analysis method considers not only feedbacks that directly affect the TOA radiative fluxes but also those feedbacks that do not directly affect the TOA radiation (such as vertical convections and poleward energy transport). The feedback analysis reveals that the net effect of the external and water-vapor induced radiative energy flux perturbations gives rise a temperature change pattern showing a stronger warming in low latitudes than in high latitudes at the surface and throughout the troposphere and a cooling in the polar upper troposphere and in the stratosphere. The low latitude warming reduction and high-latitude amplification due to non-radiative energy flux perturbations, or dynamical feedbacks, revert the meridionally decreasing warming pattern due to radiative energy flux perturbations at the surface and in the lower troposphere, but not be able to do so in the upper troposphere. As a result, the final warming pattern shows the co-existence of a reduction of the meridional temperature gradient in the lower troposphere and at the surface with an increase of the meridional temperature gradient in the upper troposphere. In terms of the global mean, the external and water-vapor induced radiative energy flux perturbations cause the strongest warming at the surface and strongest cooling in the stratosphere sandwiched with a vertically decreasing warming profile from the

  15. Kinetic and isotherm studies of bisphenol A adsorption onto orange albedo(Citrus sinensis): Sorption mechanisms based on the main albedo components vitamin C, flavones glycosides and carotenoids.

    Science.gov (United States)

    Kamgaing, Theophile; Doungmo, Giscard; Melataguia Tchieno, Francis Merlin; Gouoko Kouonang, Jimmy Julio; Mbadcam, Ketcha Joseph

    2017-07-03

    Orange albedo and its adsorption capacity towards bisphenol A (BPA) were studied. Adsorption experiments were conducted in batch mode at 25-55°C. Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and Fourier transform infrared (FTIR) spectroscopy were used to characterise the biosorbent. The effects of various parameters including adsorption time, equilibrium pH, adsorbent dosage and initial adsorbate concentration were investigated. The optimum contact time and pH for the removal of BPA were 60 min and 2, respectively. It was found that the adsorption isotherms best matched the Freundlich model, the adsorption of BPA being multilayer and that of the albedo surface heterogeneous. From the kinetic studies, it was found that the removal of BPA best matched the pseudo-second order kinetic model. An adsorption mechanism based on the albedo surface molecules is proposed and gives a good account of π-π interactions and hydrogen bonding. Orange albedo, with a maximum BPA loading capacity of 82.36 mg g -1 (significantly higher than that of most agricultural residues), is a good candidate for BPA adsorption in aqueous media.

  16. Bipolar high temporal resolution measurements of snow UV albedo in Sodankylä and Marambio

    Science.gov (United States)

    Meinander, Outi; Kontu, Anna; Asmi, Eija; Sanchez, Ricardo; Mei, Miguel; de Leeuw, Gerrit

    2015-04-01

    In this presentation we will give an overview of our high temporal resolution polar snow UV albedo data from Arctic Sodankylä, and from Marambio, Antarctica. These both are WMO GAW stations with many measurement parameters relevant to the albedo data usage. We will also describe our campaign based polar albedo data (SNORTEX and SOS campaigns), and an important data set of light absorbing impurities (BC) in the Arctic snow. The black carbon (BC) has been estimated to be the second most important human emission after carbon dioxide, in terms of its climate forcing in the present-day atmosphere. The reflectance effect of BC deposited on snow surface is the bigger the smaller the wavelength, i.e. the albedo effect of BC is the biggest at UV. This is also shown in SNICAR-model simulated albedo values. In Sodankylä, our bipolar snow ultraviolet (UV) albedo research started within the International Polar Year (IPY) 2007-2008. In 2007, the continuous Sodankylä snow UV albedo measurements were installed in Sodankylä, in the operational albedo field of the Finnish Meteorological Institute Arctic Research Center (FMI-ARC). These Sodankylä 1-min data during snow time were soon compared with the German Antarctic Neumayer Station UV albedo data, also with the same sensor type. In both data we found an up to 10 % decrease in albedo as a function of time within a day, ranging from 0.77 to 0.67 in Sodankylä and from 0.96 to 0.86 in Neumeyer. Physical explanations to asymmetry were found for cases with high relative humidity and low surface temperature during the previous night, favorable to frost and higher albedo on the next morning; new snow on the previous night; snow melting during day time and refreezing during night. In Marambio, in the beginning of 2013, our new continuous Finnish-Argentinian co-operation snow UV albedo measurements were installed and started as part of a larger continuous meteorological and environmental instrumentation. These new UV radiation data

  17. Albedo decline on Greenland's Mittivakkat Gletscher in a warming climate

    DEFF Research Database (Denmark)

    Mernild, Sebastian H; Malmros, Jeppe K.; Yde, Jacob Clement

    2015-01-01

    balance year (EBY), MG's AWS observed bare ice albedo reached ∼0.3 only just exceeding values observed for proglacial bedrock (∼0.2). The analysis reveals negative mean trends in the MODIS-derived MG EBY albedo for the period 2000–2013 with a significant decline in mean glacier-wide albedo of 0...

  18. Albedo observation of near Earth C-type asteroid by Hayabusa2 LIDAR

    Science.gov (United States)

    Yamada, R.; Senshu, H.; Namiki, N.; Mizuno, T.; Noda, H.; Asari, K.; Yoshida, F.; Abe, S.; Oshigami, S.; Hirata, N.; Ishihara, Y.; Matsumoto, K.

    2016-12-01

    The Japanese asteroid explorer Hayabusa2 was launched at the end of 2014. Hayabusa2 is supposed to observe the near-Earth C-type asteroid 162173 Ryugu and bring surface material samples back to Earth in 2020. Hayabusa2 has the laser altimeter (LIDAR) for laser ranging. The LIDAR also has the function of measuring the intensities of a transmitted laser pulse and received pulse. We will apply these data to estimate the distribution of the normal albedo of Ryugu at a laser wavelength of 1.064 μm. The albedo variations on C-type asteroid was not found from previous exploration; NEAR Shoemaker due to observation at far distance (1200 km) during short term (40 min). Hayabusa2 will continue the observation at an altitude of 20km over a year and a half, and the albedo observation using the LIDAR will give first detailed information about normal albedo variation at 1.064 μm on C-type asteroid. In this presentation, we firstly describe a method used to estimate the normal albedo from the LIDAR data and the error. The intensities of the transmitted and received laser pulses are recorded by the LIDAR as digital power values. Therefore, we have determined the transfer functions of the laser module and receiver to convert these digital values into the pulse energies. The ratio of energy transmitted into the field of view of the LIDAR telescope to the total energy (the utilization ratio) has been also investigated to estimate received pulse energies. Then, we have evaluated the contribution of the errors of transfer functions and the utilization ratio to the normal albedo uncertainty. It has been found that the error of normal albedo will be 18.0 % at a nominal altitude of 20 km if the effects of the asteroid surface slope and roughness on the received pulse are accurately corrected. On the other hand, we don't have knowledges about how the albedo on C-type asteroid vary due to space weathering and aqueous alternation at observation condition of the LIDAR (1.064 μm and 0

  19. Snow driven Radiative Forcing in High Latitude Areas of Disturbance Using Higher Resolution Albedo Products from Landsat and Sentinel-2

    Science.gov (United States)

    Erb, A.; Li, Z.; Schaaf, C.; Wang, Z.; Rogers, B. M.

    2017-12-01

    Land surface albedo plays an important role in the surface energy budget and radiative forcing by determining the proportion of absorbed incoming solar radiation available to drive photosynthesis and surface heating. In Arctic regions, albedo is particularly sensitive to land cover and land use change (LCLUC) and modeling efforts have shown it to be the primary driver of effective radiative forcing from the biogeophysical effects of LCLUC. In boreal forests, the effects of these changes are complicated during snow covered periods when newly exposed, highly reflective snow can serve as the primary driver of radiative forcing. In Arctic biomes disturbance scars from fire, pest and harvest can remain in the landscape for long periods of time. As such, understanding the magnitude and persistence of these disturbances, especially in the shoulder seasons, is critical. The Landsat and Sentinel-2 Albedo Products couple 30m and 20m surface reflectances with concurrent 500m BRDF Products from the MODerate resolution Imaging Spectroradiometer (MODIS). The 12 bit radiometric fidelity of Sentinel-2 and Landsat-8 allow for the inclusion of high-quality, unsaturated albedo calculations over snow covered surfaces at scales more compatible with fragmented landscapes. Recent work on the early spring albedo of fire scars has illustrated significant post-fire spatial heterogeneity of burn severity at the landscape scale and highlights the need for a finer spatial resolution albedo record. The increased temporal resolution provided by multiple satellite instruments also allows for a better understanding of albedo dynamics during the dynamic shoulder seasons and in historically difficult high latitude locations where persistent cloud cover limits high quality retrievals. Here we present how changes in the early spring albedo of recent boreal forest disturbance in Alaska and central Canada affects landscape-scale radiative forcing. We take advantage of the long historical Landsat record

  20. Widespread albedo decreasing and induced melting of Himalayan snow and ice in the early 21st century.

    Directory of Open Access Journals (Sweden)

    Jing Ming

    Full Text Available The widely distributed glaciers in the greater Himalayan region have generally experienced rapid shrinkage since the 1850s. As invaluable sources of water and because of their scarcity, these glaciers are extremely important. Beginning in the twenty-first century, new methods have been applied to measure the mass budget of these glaciers. Investigations have shown that the albedo is an important parameter that affects the melting of Himalayan glaciers.The surface albedo based on the Moderate Resolution Imaging Spectroradiometer (MODIS data over the Hindu Kush, Karakoram and Himalaya (HKH glaciers is surveyed in this study for the period 2000-2011. The general albedo trend shows that the glaciers have been darkening since 2000. The most rapid decrease in the surface albedo has occurred in the glacial area above 6000 m, which implies that melting will likely extend to snow accumulation areas. The mass-loss equivalent (MLE of the HKH glacial area caused by surface shortwave radiation absorption is estimated to be 10.4 Gt yr-1, which may contribute to 1.2% of the global sea level rise on annual average (2003-2009.This work probably presents a first scene depicting the albedo variations over the whole HKH glacial area during the period 2000-2011. Most rapidly decreasing in albedo has been detected in the highest area, which deserves to be especially concerned.

  1. Widespread albedo decreasing and induced melting of Himalayan snow and ice in the early 21st century.

    Science.gov (United States)

    Ming, Jing; Wang, Yaqiang; Du, Zhencai; Zhang, Tong; Guo, Wanqin; Xiao, Cunde; Xu, Xiaobin; Ding, Minghu; Zhang, Dongqi; Yang, Wen

    2015-01-01

    The widely distributed glaciers in the greater Himalayan region have generally experienced rapid shrinkage since the 1850s. As invaluable sources of water and because of their scarcity, these glaciers are extremely important. Beginning in the twenty-first century, new methods have been applied to measure the mass budget of these glaciers. Investigations have shown that the albedo is an important parameter that affects the melting of Himalayan glaciers. The surface albedo based on the Moderate Resolution Imaging Spectroradiometer (MODIS) data over the Hindu Kush, Karakoram and Himalaya (HKH) glaciers is surveyed in this study for the period 2000-2011. The general albedo trend shows that the glaciers have been darkening since 2000. The most rapid decrease in the surface albedo has occurred in the glacial area above 6000 m, which implies that melting will likely extend to snow accumulation areas. The mass-loss equivalent (MLE) of the HKH glacial area caused by surface shortwave radiation absorption is estimated to be 10.4 Gt yr-1, which may contribute to 1.2% of the global sea level rise on annual average (2003-2009). This work probably presents a first scene depicting the albedo variations over the whole HKH glacial area during the period 2000-2011. Most rapidly decreasing in albedo has been detected in the highest area, which deserves to be especially concerned.

  2. Assessment of radiative feedback in climate models using satellite observations of annual flux variation.

    Science.gov (United States)

    Tsushima, Yoko; Manabe, Syukuro

    2013-05-07

    In the climate system, two types of radiative feedback are in operation. The feedback of the first kind involves the radiative damping of the vertically uniform temperature perturbation of the troposphere and Earth's surface that approximately follows the Stefan-Boltzmann law of blackbody radiation. The second kind involves the change in the vertical lapse rate of temperature, water vapor, and clouds in the troposphere and albedo of the Earth's surface. Using satellite observations of the annual variation of the outgoing flux of longwave radiation and that of reflected solar radiation at the top of the atmosphere, this study estimates the so-called "gain factor," which characterizes the strength of radiative feedback of the second kind that operates on the annually varying, global-scale perturbation of temperature at the Earth's surface. The gain factor is computed not only for all sky but also for clear sky. The gain factor of so-called "cloud radiative forcing" is then computed as the difference between the two. The gain factors thus obtained are compared with those obtained from 35 models that were used for the fourth and fifth Intergovernmental Panel on Climate Change assessment. Here, we show that the gain factors obtained from satellite observations of cloud radiative forcing are effective for identifying systematic biases of the feedback processes that control the sensitivity of simulated climate, providing useful information for validating and improving a climate model.

  3. Modeling Earth Albedo Currents on Sun Sensors for Improved Vector Observations

    DEFF Research Database (Denmark)

    Bhanderi, Dan

    2006-01-01

    Earth albedo influences vector measurements of the solar line of sight vector, due to the induced current on in the photo voltaics of Sun sensors. Although advanced digital Sun sensors exist, these are typically expensive and may not be suited for satellites in the nano or pico-class. Previously...... for modeling Sun sensor output by incorporating the Earth albedo model is presented. This model utilizes the directional information of in the Earth albedo model, which is achieved by Earth surface partitioning. This allows accurate simulation of the Sun sensor output and the results are consistent with Ørsted...... and useful for space environment simulations, and may be utilized to improve attitude estimation algorithms applying Sun sensor vector observations....

  4. Evaluation of Satellite Remote Sensing Albedo Retrievals over the Ablation Area of the Southwestern Greenland Ice Sheet

    Science.gov (United States)

    Moustafa, Samiah E.; Rennermalm, Asa K.; Roman, Miguel O.; Wang, Zhuosen; Schaaf, Crystal B.; Smith, Laurence C.; Koenig, Lora S.; Erb, Angela

    2017-01-01

    MODerate resolution Imaging Spectroradiometer (MODIS) albedo products have been validated over spatially uniform, snow-covered areas of the Greenland ice sheet (GrIS) using the so-called single 'point-to-pixel' method. This study expands on this methodology by applying a 'multiple-point-to-pixel' method and examination of spatial autocorrelation (here using semivariogram analysis) by using in situ observations, high-resolution World- View-2 (WV-2) surface reflectances, and MODIS Collection V006 daily blue-sky albedo over a spatially heterogeneous surfaces in the lower ablation zone in southwest Greenland. Our results using 232 ground-based samples within two MODIS pixels, one being more spatial heterogeneous than the other, show little difference in accuracy among narrow and broad band albedos (except for Band 2). Within the more homogenous pixel area, in situ and MODIS albedos were very close (error varied from -4% to +7%) and within the range of ASD standard errors. The semivariogram analysis revealed that the minimum observational footprint needed for a spatially representative sample is 30 m. In contrast, over the more spatially heterogeneous surface pixel, a minimum footprint size was not quantifiable due to spatial autocorrelation, and far exceeds the effective resolution of the MODIS retrievals. Over the high spatial heterogeneity surface pixel, MODIS is lower than ground measurements by 4-7%, partly due to a known in situ undersampling of darker surfaces that often are impassable by foot (e.g., meltwater features and shadowing effects over crevasses). Despite the sampling issue, our analysis errors are very close to the stated general accuracy of the MODIS product of 5%. Thus, our study suggests that the MODIS albedo product performs well in a very heterogeneous, low-albedo, area of the ice sheet ablation zone. Furthermore, we demonstrate that single 'point-to-pixel' methods alone are insufficient in characterizing and validating the variation of surface

  5. Modeling Earth Albedo for Satellites in Earth Orbit

    DEFF Research Database (Denmark)

    Bhanderi, Dan; Bak, Thomas

    2005-01-01

    Many satellite are influences by the Earthøs albedo, though very few model schemes exist.in order to predict this phenomenon. Earth albedo is often treated as noise, or ignored completely. When applying solar cells in the attitude hardware, Earth albedo can cause the attitude estimate to deviate...... with as much as 20 deg. Digital Sun sensors with Earth albedo correction in hardware exist, but are expensive. In addition, albedo estimates are necessary in thermal calculations and power budgets. We present a modeling scheme base4d on Eartht reflectance, measured by NASA's Total Ozone Mapping Spectrometer......, in which the Earth Probe Satellite has recorded reflectivity data daily since mid 1996. The mean of these data can be used to calculate the Earth albedo given the positions of the satellite and the Sun. Our results show that the albedo varies highly with the solar angle to the satellite's field of view...

  6. Mars - Experimental study of albedo changes caused by dust fallout

    Science.gov (United States)

    Wells, E. N.; Veverka, J.; Thomas, P.

    1984-01-01

    A laboratory apparatus was used to simulate the uniform fallout and deposition of particles 1 to 5 microns in diameter in an experimental study on how the spectral and photometric properties of representative Martian areas are affected by fallout of atmospheric dust (smaller than or equalling 60 microns) suspended during dust storms. In this study, measurements are made in the changes in reflectance at optical and near-infrared wavelengths (0.4 to 1.2 micron) caused by deposition of varying amounts of a Mars-analog dust on bright and dark substrates before and after deposition of 6 x 10 to the -5th to 1.5 x 10 to the -3rd g/sq cm of simulated fallout. It is believed that only small amounts of dust particles (approximately 3 x 10 to the -4th g/sq cm) are needed to make significant albedo changes in dark areas of Mars, and that this would rule out uniform dust deposition on the surface of the planet. Data also indicate that other high albedo features like bright crater-related wind streaks may not be areas of significant sediment deposits. Laboratory simulations have permitted estimates of how much the reflectance of an area on Mars would change given a certain amount of dust fallout (g/sq cm) or reflectance data. These simulations may also be useful in tracking the transport and deposition of the dust.

  7. Tackling regional climate change by leaf albedo bio-geoengineering.

    Science.gov (United States)

    Ridgwell, Andy; Singarayer, Joy S; Hetherington, Alistair M; Valdes, Paul J

    2009-01-27

    The likelihood that continuing greenhouse-gas emissions will lead to an unmanageable degree of climate change has stimulated the search for planetary-scale technological solutions for reducing global warming ("geoengineering"), typically characterized by the necessity for costly new infrastructures and industries. We suggest that the existing global infrastructure associated with arable agriculture can help, given that crop plants exert an important influence over the climatic energy budget because of differences in their albedo (solar reflectivity) compared to soils and to natural vegetation. Specifically, we propose a "bio-geoengineering" approach to mitigate surface warming, in which crop varieties having specific leaf glossiness and/or canopy morphological traits are specifically chosen to maximize solar reflectivity. We quantify this by modifying the canopy albedo of vegetation in prescribed cropland areas in a global-climate model, and thereby estimate the near-term potential for bio-geoengineering to be a summertime cooling of more than 1 degrees C throughout much of central North America and midlatitude Eurasia, equivalent to seasonally offsetting approximately one-fifth of regional warming due to doubling of atmospheric CO(2). Ultimately, genetic modification of plant leaf waxes or canopy structure could achieve greater temperature reductions, although better characterization of existing intraspecies variability is needed first.

  8. Future projections of the Greenland ice sheet energy balance driving the surface melt

    Directory of Open Access Journals (Sweden)

    B. Franco

    2013-01-01

    Full Text Available In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from three CMIP5 global circulation models (GCMs, in order to investigate the projected changes of the surface energy balance (SEB components driving the surface melt. Analysis of 2000–2100 melt anomalies compared to melt results over 1980–1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface air temperature (TAS anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are preferentially driven by stronger sensible heat fluxes, induced by enhanced warm air advection over the ice sheet. Over the central dry snow zone, the surface albedo positive feedback induced by the increase in summer melt exceeds the negative feedback of heavier snowfall for TAS anomalies higher than 4 °C. In addition to the incoming longwave flux increase associated with the atmosphere warming, GCM-forced MAR simulations project an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-Interim–forced MAR for recent climate conditions, where the observed melt increase since the 1990s seems mainly to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season, which highlights the importance of solar radiation absorbed by the ice sheet surface in the melt SEB.

  9. The effect of a dynamic background albedo scheme on Sahel/Sahara precipitation during the mid-Holocene

    Directory of Open Access Journals (Sweden)

    F. S. E. Vamborg

    2011-02-01

    Full Text Available We have implemented a new albedo scheme that takes the dynamic behaviour of the surface below the canopy into account, into the land-surface scheme of the MPI-ESM. The standard (static scheme calculates the seasonal canopy albedo as a function of leaf area index, whereas the background albedo is a gridbox constant derived from satellite measurements. The new (dynamic scheme additionally models the background albedo as a slowly changing function of organic matter in the ground and of litter and standing dead biomass covering the ground. We use the two schemes to investigate the interactions between vegetation, albedo and precipitation in the Sahel/Sahara for two time-slices: pre-industrial and mid-Holocene. The dynamic scheme represents the seasonal cycle of albedo and the correspondence between annual mean albedo and vegetation cover in a more consistent way than the static scheme. It thus gives a better estimate of albedo change between the two time periods. With the introduction of the dynamic scheme, precipitation is increased by 30 mm yr−1 for the pre-industrial simulation and by about 80 mm yr−1 for the mid-Holocene simulation. The present-day dry bias in the Sahel of standard ECHAM5 is thus reduced and the sensitivity of precipitation to mid-Holocene external forcing is increased by around one third. The locations of mid-Holocene lakes, as estimated from reconstructions, lie south of the modelled desert border in both mid-Holocene simulations. The magnitude of simulated rainfall in this area is too low to fully sustain lakes, however it is captured better with the dynamic scheme. The dynamic scheme leads to increased vegetation variability in the remaining desert region, indicating a higher frequency of green spells, thus reaching a better agreement with the vegetation distribution as derived from pollen records.

  10. Imaging spectroscopy to assess the composition of ice surface materials and their impact on glacier mass balance

    Science.gov (United States)

    Naegeli, Kathrin; Huss, Matthias; Damm, Alexander; de Jong, Rogier; Schaepman, Michael; Hoelzle, Martin

    2014-05-01

    The ice-albedo feedback plays a crucial role in various glaciological processes, but especially influences ice melt. Glacier surface albedo is one of the most important variables in the energy balance of snow and ice, but depends in a complicated way on many factors, such as cryoconite concentration, impurities due to mineral dust, soot or organic matter, grain size or ice surface morphology. Our understanding on how these various factors influence glacier albedo is still limited hindering a spatially and temporally explicit parameterization of energy balance models and requiring strongly simplified assumptions on actual albedo values. Over the last two decades, several studies have focused on glacier surface albedo using automatic in-situ weather stations in combination with radiation measurement setups or satellite images. Due to limitations of both approaches in matching either the spatial or the temporal length scale of glacier albedo, still fairly little is known about the state, changes and impact of glacier surface albedo in the Swiss Alps, although there are obvious changes in surface characteristics on most alpine glaciers over the last years. With use of the APEX (Airborne Prism EXperiment) image spectrometer, measurements of reflected radiation were acquired in high spatial and spectral resolution on Glacier de la Plaine Morte, Switzerland, to explicitly analyse the ice surface. In-situ radiometric measurements were acquired with an ASD field spectrometer in parallel to APEX overflights. These data are intended to be used for validation purposes as well as input data for the linear spectral unmixing analysis of the APEX data. Seasonal glacier mass balance is monitored since five years using the direct glaciological method. This contribution presents a first evaluation of the data collected in summer 2013. The obtained in-situ and airborne reflectance measurements were used in combination with a spectral mixture analysis (SMA) approach to assess the

  11. MODIS/Terra+Aqua BRDF/Albedo Black Sky Albedo Shortwave Daily L3 Global 30ArcSec CMG V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MCD43D51 Version 6 Bidirectional Reflectance Distribution Function and Albedo (BRDF/Albedo) Black Sky Albedo near shortwave broadband data set is a daily 16-day...

  12. MODIS/Terra+Aqua BRDF/Albedo Black Sky Albedo VIS Daily L3 Global 30ArcSec CMG V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MCD43D49 Version 6 Bidirectional Reflectance Distribution Function and Albedo (BRDF/Albedo) Black Sky Albedo visible broadband data set is a daily 16-day...

  13. Raising the Albedo of 2010 GY6: Fitting ATPM to Wise Data

    Science.gov (United States)

    Wooden, D. H.; Rozitis, B. D.; Jefferson, J. D.; Nelson, T. W.; Dotson, J. L.

    2017-01-01

    Near-Earth Asteroid 462775 (2010 GY6) is in the Apollo orbit-family with a 1.46 year orbital period. 2010 GY6 was measured by WISE and fitted with NEATM, yielding NEATM model parameters of D=1.1 km, pv=0.028 and eta=2.3.The NEATM-derived geometric albedo of 2010 GY6 is lower than the surface of comet 67P/C-G. The eta value is considerably higher than typical for its phase angle of 33 deg, indicating a cooler surface due to non-zero thermal inertia and/or surface roughness are important. If the thermal inertia and surface roughness are constrained by fitting the Advanced Thermophysical Model (ATPM) to the WISE data, what would the resulting geometric albedo? We find pv=0.06-0.08, in the same range as B- or C-type NEAs like Bennu or JU3.

  14. Acquisition of Ice Thickness and Ice Surface Characteristics In the Seasonal Ice Zone by CULPIS-X During the US Coast Guards Arctic Domain Awareness Program

    Science.gov (United States)

    2015-09-30

    ponds on thinner ice are often darker, accelerating the ice - albedo feedback over thin ice in summer. During winter, leads and very thin ice are centers...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Acquisition of Ice Thickness and Ice Surface...Characteristics In the Seasonal Ice Zone by CULPIS-X During the US Coast Guard’s Arctic Domain Awareness Program PI: Mark A. Tschudi University of

  15. Calculation of neutron albedo from laminated semiinfinite media

    International Nuclear Information System (INIS)

    Dobrynin, Yu.L.; Mikaehlyan, L.A.; Skorokhvatov, M.D.

    1978-01-01

    A version of a laminated neutron detector with increased efficiency for recording external neutron fluxes by gamma-quanta from neutron capture is considered. The detector comprises two zones. The first zone constitutes an absorbent layer (europium oxide) 0.5 cm thick, and the second one is a moderator (water with gadolinium salt at the concentration of 0.8 g/l). Mono-energetic neutrons fall normally onto the detector surface. Neutron energy varied from 0.1 eV to MeV. The results of calculations of the integral numerical current albedo (INCA) of neutrons by the Monte Carlo method are presented. The INCA dependences on neutron energy are obtained for one moderator with different gadolinium contents; for the absorbent with the moderator containing and lacking the gadolinium. The resultant dependences are indicative of preferential capture of neutrons by the gadolinium in the moderator, this being more desirable for recording neutrons in the (n, γ) reaction

  16. Estimating Crop Albedo in the Application of a Physical Model Based on the Law of Energy Conservation and Spectral Invariants

    Directory of Open Access Journals (Sweden)

    Jingjing Peng

    2015-11-01

    Full Text Available Albedo characterizes the radiometric interface of land surfaces, especially vegetation, and the atmosphere. Albedo is a critical input to many models, such as crop growth models, hydrological models and climate models. For the extensive attention to crop monitoring, a physical albedo model for crops is developed based on the law of energy conservation and spectral invariants, which is derived from a prior forest albedo model. The model inputs have been efficiently and physically parameterized, including the dependency of albedo on the solar zenith/azimuth angle, the fraction of diffuse skylight in the incident radiance, the canopy structure, the leaf reflectance/transmittance and the soil reflectance characteristics. Both the anisotropy of soil reflectance and the clumping effect of crop leaves at the canopy scale are considered, which contribute to the improvement of the model accuracy. The comparison between the model results and Monte Carlo simulation results indicates that the canopy albedo has high accuracy with an RMSE < 0.005. The validation using ground measurements has also demonstrated the reliability of the model and that it can reflect the interaction mechanism between radiation and the canopy-soil system.

  17. Bright is the New Black - Multi-Year Performance of Generic High-Albedo Roofs in an Urban Climate

    Science.gov (United States)

    Gaffin, S. R.; Imhoff, M.; Rosenzweig, C.; Khanbilvardi, R.; Pasqualini, A.; Kong, A. Y. Y.; Grillo, D.; Freed, A.; Hillel, D.; Hartung, E.

    2012-01-01

    High-albedo white and cool roofing membranes are recognized as a fundamental strategy that dense urban areas can deploy on a large scale, at low cost, to mitigate the urban heat island effect. We are monitoring three generic white membranes within New York City that represent a cross-section of the dominant white membrane options for U.S. flat roofs: (1) an ethylene propylene diene monomer (EPDM) rubber membrane; (2) a thermoplastic polyolefin (TPO) membrane and; (3) an asphaltic multi-ply built-up membrane coated with white elastomeric acrylic paint. The paint product is being used by New York City s government for the first major urban albedo enhancement program in its history. We report on the temperature and related albedo performance of these three membranes at three different sites over a multi-year period. The results indicate that the professionally installed white membranes are maintaining their temperature control effectively and are meeting the Energy Star Cool Roofing performance standards requiring a three-year aged albedo above 0.50. The EPDM membrane however shows evidence of low emissivity. The painted asphaltic surface shows high emissivity but lost about half of its initial albedo within two years after installation. Given that the acrylic approach is an important "do-it-yourself," low-cost, retrofit technique, and, as such, offers the most rapid technique for increasing urban albedo, further product performance research is recommended to identify conditions that optimize its long-term albedo control. Even so, its current multi-year performance still represents a significant albedo enhancement for urban heat island mitigation.

  18. Parameterizations for narrowband and broadband albedo of pure snow and snow containing mineral dust and black carbon

    Science.gov (United States)

    Dang, Cheng; Brandt, Richard E.; Warren, Stephen G.

    2015-06-01

    The reduction of snow spectral albedo by black carbon (BC) and mineral dust, both alone and in combination, is computed using radiative transfer modeling. Broadband albedo is shown for mass fractions covering the full range from pure snow to pure BC and pure dust, and for snow grain radii from 5 µm to 2500 µm, to cover the range of possible grain sizes on planetary surfaces. Parameterizations are developed for opaque homogeneous snowpacks for three broad bands used in general circulation models and several narrower bands. They are functions of snow grain radius and the mass fraction of BC and/or dust and are valid up to BC content of 10 ppm, needed for highly polluted snow. A change of solar zenith angle can be mimicked by changing grain radius. A given mass fraction of BC causes greater albedo reduction in coarse-grained snow; BC and grain radius can be combined into a single variable to compute the reduction of albedo relative to pure snow. The albedo reduction by BC is less if the snow contains dust, a common situation on mountain glaciers and in agricultural and grazing lands. Measured absorption spectra of mineral dust are critically reviewed as a basis for specifying dust properties for modeling. The effect of dust on snow albedo at visible wavelengths can be represented by an "equivalent BC" amount, scaled down by a factor of about 200. Dust has little effect on the near-IR albedo because the near-IR albedo of pure dust is similar to that of pure snow.

  19. A New Method for the Estimation of Broadband Apparent Albedo Using Hyperspectral Airborne Hemispherical Directional Reflectance Factor Values

    Directory of Open Access Journals (Sweden)

    Javier F. Calleja

    2016-02-01

    Full Text Available The broadband albedo values retrieved from satellite sensors are usually compared directly to ground measurements. Some authors have noted the necessity of high spatial resolution albedo estimates to fill the gap between ground measurements and satellite retrievals. In this respect, hyperspectral airborne data with high spatial resolution is a powerful tool. Here, a new operational method for the calculation of airborne broadband apparent albedo over the spectral range of 350–2500 nm is presented. This new method uses the Hemispherical Directional Reflectance Factor (HDRF as a proxy for the narrowband albedo, assuming a Lambertian approximation. The broadband apparent albedo obtained is compared to that estimated using theapparent albedo equation devised for the Moderate Resolution Imaging Spectroradiometer (MODIS. Airborne data were collected using the Airborne Hyperspectral Scanner (AHS. Field data were acquired at three sites: a camelina field, a green grass field, and a vineyard.  The HDRF can be used to approximate the narrowband albedo for all View Zenith Angle (VZA values for flights parallel to the solar principal plane (SPP; for flights orthogonal to the SPP, discrepancies are observed when the VZA approaches −45°. Root Mean Square Error (RMSE values in the range 0.009–0.018 were obtained using the new method, improving upon previous results over the same area (RMSEs of 0.01–0.03. The relative error in the albedo estimation using the new method is 12% for −36.2° < VZA < 40.8° in the case of flights parallel to the SPP and less than 15% for −13° < VZA < 45° and 45% for VZA = −45° for flights orthogonal to the SPP. The good performance of the new method lies in the use of the at-surface solar irradiance and the proposed integration method.

  20. Bright is the new black—multi-year performance of high-albedo roofs in an urban climate

    Science.gov (United States)

    Gaffin, S. R.; Imhoff, M.; Rosenzweig, C.; Khanbilvardi, R.; Pasqualini, A.; Kong, A. Y. Y.; Grillo, D.; Freed, A.; Hillel, D.; Hartung, E.

    2012-03-01

    High-albedo white and cool roofing membranes are recognized as a fundamental strategy that dense urban areas can deploy on a large scale, at low cost, to mitigate the urban heat island effect. We are monitoring three generic white membranes within New York City that represent a cross section of the dominant white membrane options for US flat roofs: (1) an ethylene-propylene-diene monomer (EPDM) rubber membrane; (2) a thermoplastic polyolefin (TPO) membrane; and (3) an asphaltic multi-ply built-up membrane coated with white elastomeric acrylic paint. The paint product is being used by New York City’s government for the first major urban albedo enhancement program in its history. We report on the temperature and related albedo performance of these three membranes at three different sites over a multi-year period. The results indicate that the professionally installed white membranes are maintaining their temperature control effectively and are meeting the Energy Star Cool Roofing performance standards requiring a three-year aged albedo above 0.50. The EPDM membrane shows evidence of low emissivity; however this had the interesting effect of avoiding any ‘winter heat penalty’ for this building. The painted asphaltic surface shows high emissivity but lost about half of its initial albedo within two years of installation. Given that the acrylic approach is such an important ‘do-it-yourself’, low-cost, retrofit technique, and, as such, offers the most rapid technique for increasing urban albedo, further product performance research is recommended to identify conditions that optimize its long-term albedo control. Even so, its current multi-year performance still represents a significant albedo enhancement for urban heat island mitigation.

  1. Water Ice Albedo Variations on the Martian Northern Polar Cap

    Science.gov (United States)

    Hale, A. S.; Bass, D. S.; Tamppari, L. K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result which suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (L(sub s)). Reevaluation of this dataset indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue to compare Mariner 9 and Viking Orbiter imaging observations and thermal data of the north residual polar cap to data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) instrument. In the current study, our goal is to examine all released data from MGS MOC in the northern summer season, along with applicable TES data in order to better understand the albedo variations in the northern summer and their implications on water transport. To date, work has focused primarily on the MOC dataset. In 1999, data acquisition of the northern polar regions began at L(sub s) = 107, although there was little north polar data acquired from L(sub s)= 107 to L(sub s) = 109. We examined a total of 409 images from L(sub s) = 107 to L(sub s)=148. We have also examined data from 2000 from L(sub s)= 93 to L(sub s)= 110; additional progress is ongoing. Here we present a progress report of our observations, and continue to determine their implications for the Martian water cycle.

  2. Neither Dust Nor Black Carbon Causing Apparent Albedo Decline in Greenland's Dry Snow Zone; Uncorrected Sensor Degradation Impacting MODIS C5 Results

    Science.gov (United States)

    Polashenski, C.; Dibb, J. E.; Flanner, M.; Chen, J.; Courville, Z.; Lai, A.; Schauer, J. J.; Shafer, M. M.; Bergin, M. H.

    2015-12-01

    Observations suggest the Greenland ice sheet albedo has declined since 2001, even in the dry snow zone (DSZ). We seek to explain the apparent DSZ albedo decline. We analyze samples representing 2012-2014 snowfall across NW Greenland for absorbing impurities (black carbon and dust) and model their impacts on snow albedo. Albedo reductions due to absorbing impurities are small, averaging 0.003, with episodic enhancements resulting in reductions of 0.01-0.02. No significant increase in black carbon or dust concentrations relative to recent decades is indicated. Enhanced deposition of absorbing impurities is not, therefore, causing significant albedo reduction in the DSZ or driving recent melt events. Analysis of MODIS surface reflectance indicates that the decline and spectral shift in DSZ albedo seen in C5 MODIS data contains contributions from uncorrected Terra sensor degradation. The discrepancies between Terra and Aqua are generally below the stated accuracy of MODIS products (0.05), but since discussions of Greenland albedo trends below this level are common in the literature, the identification of these discrepancies likely requires revisiting conclusions about the trends and spectral signature of Greenland DSZ albedo after C6 data is released.

  3. Albedo and transmittance of inhomogeneous stratus clouds

    Energy Technology Data Exchange (ETDEWEB)

    Zuev, V.E.; Kasyanov, E.I.; Titov, G.A. [Institute of Atmospheric Optics, Tomsk (Russian Federation)] [and others

    1996-04-01

    A highly important topic is the study of the relationship between the statistical parameters of optical and radiative charactertistics of inhomogeneous stratus clouds. This is important because the radiation codes of general circulation models need improvement, and it is important for geophysical information. A cascade model has been developed at the Goddard Space Flight Center to treat stratocumulus clouds with the simplest geometry and horizontal fluctuations of the liquid water path (optical thickness). The model evaluates the strength with which the stochastic geometry of clouds influences the statistical characteristics of albedo and the trnasmittance of solar radiation.

  4. Role of the Soil Thermal Inertia in the short term variability of the surface temperature and consequences for the soil-moisture temperature feedback

    Science.gov (United States)

    Cheruy, Frederique; Dufresne, Jean-Louis; Ait Mesbah, Sonia; Grandpeix, Jean-Yves; Wang, Fuxing

    2017-04-01

    ) ''hot spots'', it is generally admitted that the variability of the surface temperature is explained by the soil moisture trough its control on the evaporation. This work suggests that the impact of the soil moisture on the temperature through its impact on the thermal inertia can be as important as its direct impact on the evaporation. Contrarily to the evaporation related soil-moisture temperature negative feedback, the thermal inertia soil-moisture related feedback newly identified by this work is a positive feedback which limits the cooling when the soil moisture increases. These results suggest that uncertainties in the representation of the soil and snow thermal properties can be responsible of significant biases in numerical simulations and emphasize the need to carefully document and evaluate these quantities in the Land Surface Modules implemented in the climate models.

  5. Incorporating Prognostic Marine Nitrogen Fixers and Related Bio-Physical Feedbacks in an Earth System Model

    Science.gov (United States)

    Paulsen, H.; Ilyina, T.; Six, K. D.

    2016-02-01

    Marine nitrogen fixers play a fundamental role in the oceanic nitrogen and carbon cycles by providing a major source of `new' nitrogen to the euphotic zone that supports biological carbon export and sequestration. Furthermore, nitrogen fixers may regionally have a direct impact on ocean physics and hence the climate system as they form extensive surface mats which can increase light absorption and surface albedo and reduce the momentum input by wind. Resulting alterations in temperature and stratification may feed back on nitrogen fixers' growth itself.We incorporate nitrogen fixers as a prognostic 3D tracer in the ocean biogeochemical component (HAMOCC) of the Max Planck Institute Earth system model and assess for the first time the impact of related bio-physical feedbacks on biogeochemistry and the climate system.The model successfully reproduces recent estimates of global nitrogen fixation rates, as well as the observed distribution of nitrogen fixers, covering large parts of the tropical and subtropical oceans. First results indicate that including bio-physical feedbacks has considerable effects on the upper ocean physics in this region. Light absorption by nitrogen fixers leads locally to surface heating, subsurface cooling, and mixed layer depth shoaling in the subtropical gyres. As a result, equatorial upwelling is increased, leading to surface cooling at the equator. This signal is damped by the effect of the reduced wind stress due to the presence of cyanobacteria mats, which causes a reduction in the wind-driven circulation, and hence a reduction in equatorial upwelling. The increase in surface albedo due to nitrogen fixers has only inconsiderable effects. The response of nitrogen fixers' growth to the alterations in temperature and stratification varies regionally. Simulations with the fully coupled Earth system model are in progress to assess the implications of the biologically induced changes in upper ocean physics for the global climate system.

  6. Low Cloud Feedback to Surface Warming in the World's First Global Climate Model with Explicit Embedded Boundary Layer Turbulence

    Science.gov (United States)

    Parishani, H.; Pritchard, M. S.; Bretherton, C. S.; Wyant, M. C.; Khairoutdinov, M.; Singh, B.

    2017-12-01

    Biases and parameterization formulation uncertainties in the representation of boundary layer clouds remain a leading source of possible systematic error in climate projections. Here we show the first results of cloud feedback to +4K SST warming in a new experimental climate model, the ``Ultra-Parameterized (UP)'' Community Atmosphere Model, UPCAM. We have developed UPCAM as an unusually high-resolution implementation of cloud superparameterization (SP) in which a global set of cloud resolving arrays is embedded in a host global climate model. In UP, the cloud-resolving scale includes sufficient internal resolution to explicitly generate the turbulent eddies that form marine stratocumulus and trade cumulus clouds. This is computationally costly but complements other available approaches for studying low clouds and their climate interaction, by avoiding parameterization of the relevant scales. In a recent publication we have shown that UP, while not without its own complexity trade-offs, can produce encouraging improvements in low cloud climatology in multi-month simulations of the present climate and is a promising target for exascale computing (Parishani et al. 2017). Here we show results of its low cloud feedback to warming in multi-year simulations for the first time. References: Parishani, H., M. S. Pritchard, C. S. Bretherton, M. C. Wyant, and M. Khairoutdinov (2017), Toward low-cloud-permitting cloud superparameterization with explicit boundary layer turbulence, J. Adv. Model. Earth Syst., 9, doi:10.1002/2017MS000968.

  7. MODIS/Terra+Aqua BRDF/Albedo Albedo Daily L3 Global - 500m V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MODIS MCD43A3 Version 6 Albedo Model data set is a daily 16-day product. The Julian date in the granule ID of each specific file represents the 9th day of the 16...

  8. Developing a Validated Long-Term Satellite-Based Albedo Record in the Central Alaska Range to Improve Regional Hydroclimate Reconstructions

    Science.gov (United States)

    Kreutz, K. J.; Godaire, T. P.; Burakowski, E. A.; Winski, D.; Campbell, S. W.; Wang, Z.; Sun, Q.; Hamilton, G. S.; Birkel, S. D.; Wake, C. P.; Osterberg, E. C.; Schaaf, C.

    2015-12-01

    Mountain glaciers around the world, particularly in Alaska, are experiencing significant surface mass loss from rapid climatic shifts and constitute a large proportion of the cryosphere's contribution to sea level rise. Surface albedo acts as a primary control on a glacier's mass balance, yet it is difficult to measure and quantify spatially and temporally in steep, mountainous settings. During our 2013 field campaign in Denali National Park to recover two surface to bedrock ice cores, we used an Analytical Spectral Devices (ASD) FieldSpec4 Standard Resolution spectroradiometer to measure incoming solar radiation, outgoing surface reflectance and optical grain size on the Kahiltna Glacier and at the Kahiltna Base Camp. A Campbell Scientific automatic weather station was installed on Mount Hunter (3900m) in June 2013, complementing a longer-term (2008-present) station installed at Kahiltna Base Camp (2100m). Use of our in situ data aids in the validation of surface albedo values derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat satellite imagery. Comparisons are made between ASD FieldSpec4 ground measurements and 500m MODIS imagery to assess the ability of MODIS to capture the variability of surface albedo across the glacier surface. The MODIS MCD43A3 BRDF/Albedo Product performs well at Kahiltna Base Camp (MODIS albedo (10-28% relative to ASD data) appear to occur along the Kahiltna Glacier due to the snow-free valley walls being captured in the 500m MODIS footprint. Incorporating Landsat imagery will strengthen our interpretations and has the potential to produce a long-term (1982-present) validated satellite albedo record for steep and mountainous terrain. Once validation is complete, we will compare the satellite-derived albedo record to the Denali ice core accumulation rate, aerosol records (i.e. volcanics and biomass burning), and glacier mass balance data. This research will ultimately contribute to an improved understanding of

  9. Measurements of spectral snow albedo at Neumayer, Antarctica

    OpenAIRE

    Wuttke Sigrid; Seckmeyer G; König-Langlo Gert

    2006-01-01

    Spectral albedo in high resolution, from 290 to 1050 nm, has been measured at Neumayer, Antarctica, (70°39' S, 8°15' W) during the austral summer 2003/2004. At 500 nm, the spectral albedo nearly reaches unity, with slightly lower values below and above 500 nm. Above 600 nm, the spectral albedo decreases to values between 0.45 and 0.75 at 1000 nm. For one cloudless case an albedo up to 1.01 at 500 nm could be determined. This can be explained by the larger directional...

  10. LUNAR TERRAIN AND ALBEDO RECONSTRUCTION FROM APOLLO IMAGERY

    Data.gov (United States)

    National Aeronautics and Space Administration — LUNAR TERRAIN AND ALBEDO RECONSTRUCTION FROM APOLLO IMAGERY ARA V NEFIAN*, TAEMIN KIM, MICHAEL BROXTON, AND ZACH MORATTO Abstract. Generating accurate three...

  11. Formativ Feedback

    DEFF Research Database (Denmark)

    Hyldahl, Kirsten Kofod

    Denne bog undersøger, hvordan lærere kan anvende feedback til at forbedre undervisningen i klasselokalet. I denne sammenhæng har John Hattie, professor ved Melbourne Universitet, udviklet en model for feedback, hvilken er baseret på synteser af meta-analyser. I 2009 udgav han bogen "Visible...

  12. Feedbacks and Acceleration of Global Change

    Science.gov (United States)

    Hay, William

    2014-05-01

    The burning of fossil fuels since the beginning of the Industrial revolution has increased the level of atmospheric CO2 by about 45 % over that of earlier times. The increasing greenhouse effect is augmented by a series of feedbacks; most have been positive, but a few are negative. The most important are 1) Slowing of the thermohaline circulation system; 2) Decreasing Atlantic to Pacific vapor transport; 3) Increasing Arctic river runoff; 4) Melting of Arctic sea ice; 5) Periodic replacement of the Arctic atmospheric high by a cyclonic low pressure system; 6) Increased exchange of waters between the Arctic and North Atlantic; 7) Lessening of the Northern Hemisphere ice-albedo feedback effect; 8) Addition of methane from melting permafrost; 9) Overall changes in the rate of ocean mixing; 10) Overall changes in vegetation cover of land; 11) Increase in the area covered by C4 vegetation; 12) Addition of nitrous oxide from agricultural practices; 13) Changes in insect populations and their effect on vegetation; 14) Wildfires; 15) Soot accumulation on snow and ice; 16) Accelerated melting of the Greenland Ice Sheet; 17) Changes in the East Antarctic Ice Sheet; 18) Closing of the ozone hole over Antarctica; 19) Decay of the West Antarctic Ice Sheet; 20) Expansion of Southern Ocean sea ice; 21) Slowing of the rate of organic matter sinking into the deep ocean; 22) Decrease in insolation reaching the surface of the Earth as a result of introduction of aerosols into the atmosphere; 23) Depletion of stratospheric ozone by nitrous oxide. The global and regional effects and relative importance of many of these feedbacks are uncertain, and they may change both in magnitude and sign with time. New and unexpected mechanisms are constantly being discovered. The uncertainties and complexity associated with climate system feedbacks are responsible for the acceleration of climate change beyond the rates predicted by numerical modeling. To add to the difficulties inherent in

  13. Adapting observationally based metrics of biogeophysical feedbacks from land cover/land use change to climate modeling

    International Nuclear Information System (INIS)

    Chen, Liang; Dirmeyer, Paul A

    2016-01-01

    To assess the biogeophysical impacts of land cover/land use change (LCLUC) on surface temperature, two observation-based metrics and their applicability in climate modeling were explored in this study. Both metrics were developed based on the surface energy balance, and provided insight into the contribution of different aspects of land surface change (such as albedo, surface roughness, net radiation and surface heat fluxes) to changing climate. A revision of the first metric, the intrinsic biophysical mechanism, can be used to distinguish the direct and indirect effects of LCLUC on surface temperature. The other, a decomposed temperature metric, gives a straightforward depiction of separate contributions of all components of the surface energy balance. These two metrics well capture observed and model simulated surface temperature changes in response to LCLUC. Results from paired FLUXNET sites and land surface model sensitivity experiments indicate that surface roughness effects usually dominate the direct biogeophysical feedback of LCLUC, while other effects play a secondary role. However, coupled climate model experiments show that these direct effects can be attenuated by large scale atmospheric changes (indirect feedbacks). When applied to real-time transient LCLUC experiments, the metrics also demonstrate usefulness for assessing the performance of climate models and quantifying land–atmosphere interactions in response to LCLUC. (letter)

  14. Mars seasonal CO2 ice lifetimes and the angular dependence of albedo

    Science.gov (United States)

    Lindner, Bernhard Lee

    1992-01-01

    The albedo of the polar caps on Mars brightens appreciably at high solar zenith angle (Warren et al., J. Geophys. Res., 95, 14717, 1990), an effect not included in prior polar-cap energy-balance models. This decreases absorption of sunlight by the polar cap, hence decreasing sublimation of CO2 ice. Lindner (J. Geophys. Res., 95, 1367, 1990) has shown that the radiative effects of clouds and airborne dust will increase sublimation of CO2 ice over that predicted by prior polar-cap energy-balance models. Furthermore, observations hint that more clouds may exist in the Northern Hemisphere, which Lindner (1990) has shown would sublime CO2 ice more quickly in the north than in the south. I show here that the effects of the solar zenith angle dependence of albedo and the radiative effects of clouds and dust offset each other, but act to extend the lifetime of CO2 ice on the south pole more than on the north pole, possibly explaining the observed hemispherical asymmetry in the residual polar caps without the need of a hemispherical asymmetry in polar-cap albedo required by prior models. Another positive aspect of this solution is that neither the inclusion of the solar zenith angle dependence of albedo nor the radiative effects of clouds and dust should appreciably change prior model agreement with observations of the annual cycle of surface pressure and the recession of the polar caps equatorward of 75 degrees latitude.

  15. Urban Morphology Influence on Urban Albedo: A Revisit with the S olene Model

    Science.gov (United States)

    Groleau, Dominique; Mestayer, Patrice G.

    2013-05-01

    This heuristic study of the urban morphology influence on urban albedo is based on some 3,500 simulations with the S olene model. The studied configurations include square blocks in regular and staggered rows, rectangular blocks with different street widths, cross-shaped blocks, infinite street canyons and several actual districts in Marseilles, Toulouse and Nantes, France. The scanned variables are plan density, facade density, building height, layout orientation, latitude, date and time of the day. The sky-view factors of the ground and canopy surfaces are also considered. This study demonstrates the significance of the facade density, in addition to the built plan density, as the explanatory geometrical factor to characterize the urban morphology, rather than building height. On the basis of these albedo calculations the puzzling results of Kondo et al. (Boundary-Layer Meteorol 100:225-242, 2001) for the influence of building height are explained, and the plan density influence is quantitatively assessed. It is shown that the albedo relationship with plan and facade densities obtained with the regular square plot configuration may be considered as a reference for all other configurations, with the exception of the infinite street canyon that shows systematic differences for the lower plan densities. The curves representing this empirical relationship may be used as a sort of abacus for all other geometries while an approximate simple mathematical model is proposed, as well as relationships between the albedo and sky-view factors.

  16. Arctic Vegetation Change and Feedbacks under Future Climate (Invited)

    Science.gov (United States)

    Goetz, S. J.; Loranty, M. M.; Beck, P.; Phillips, S.; Damoulas, T.; Pearson, R. G.

    2013-12-01

    Arctic surface air temperatures have risen at approximately twice the global rate, produce multiple climate feedbacks, e.g. via expansion of woody shrubs and trees into the tundra biome increasing surface net shortwave radiation due to reductions in albedo. To explore the feedbacks of future Arctic vegetation change on climate, we modeled vegetation type distribution across the circumpolar domain using machine-learning ecological niche models at moderately fine (4.5 x 4.5 km) spatial resolution. Vegetation was resolved into four classes of graminoids, four classes of shrubs, and two classes of tree cover. Comparison of observed and modeled classes under present climate revealed strong predictive performance. When simulating into the 2050s under scenarios of restricted tree dispersal and climate change, we found vegetation in 48-69% of our study area would shift to a different physiognomic class. Under an equilibrium scenario with unrestricted dispersal 57-84% of the area is predicted to shift to a different class. This latter scenario is supported by evidence of rapid shifts to larger growth-forms due to rapid colonization due to long-distance dispersal, expansion from refugia, and favorable conditions for establishment following disturbance like tundra fires and thermal erosion related to permafrost thaw. Distributions of lower-lying vegetation classes with sparse plant cover are predicted to contract in some places as larger shrubs and trees expand their ranges, but this outcome is mostly restricted to regions that do not have more northerly land masses to which vegetation could shift as trees and larger shrubs migrate from the south. We also estimated future changes in albedo, evapotranspiration and above-ground biomass, each of which would change substantially with our predicted widespread redistribution of Arctic vegetation. In terms of climate feedbacks, the predicted increases in ET were relatively small, and predicted maximum total increases in biomass (1

  17. Estimate of Top-of-Atmosphere Albedo for a Molecular Atmosphere over Ocean using Clouds and the Earth's Radiant Energy System (CERES) Measurements

    Science.gov (United States)

    Kato, S.; Loeb, N. G.; Rutledge, C. K.

    2002-01-01

    The shortwave broadband albedo at the top of a molecular atmosphere over ocean between 40deg N and 40deg S is estimated using radiance measurements from the Clouds and the Earth's Radiant Energy System (CERES) instrument and the Visible Infrared Scanner (VIRS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. The albedo monotonically increases from 0.059 at a solar zenith angle of 10deg to 0.107 at a solar zenith angle of 60deg. The estimated uncertainty in the albedo is 3.5 x 10(exp -3) caused by the uncertainty in CERES-derived irradiances, uncertainty in VIRS-derived aerosol optical thicknesses, variations in ozone and water vapor, and variations in surface wind speed. The estimated uncertainty is similar in magnitude to the standard deviation of 0.003 that is derived from 72 areas divided by 20deg latitude by 20deg longitude grid boxes. The empirically estimated albedo is compared with the modeled albedo using a radiative transfer model combined with an ocean surface bidirectional reflectivity model. The modeled albedo with standard tropical atmosphere is 0.061 and 0.111 at the solar zenith angles of 10deg and 60deg, respectively. This empirically estimated albedo can be used to estimate the direct radiative effect of aerosols at the top of the atmosphere over oceans.

  18. Enhanced chemistry-climate feedbacks in past greenhouse worlds.

    Science.gov (United States)

    Beerling, David J; Fox, Andrew; Stevenson, David S; Valdes, Paul J

    2011-06-14

    Trace greenhouse gases are a fundamentally important component of Earth's global climate system sensitive to global change. However, their concentration in the pre-Pleistocene atmosphere during past warm greenhouse climates is highly uncertain because we lack suitable geochemical or biological proxies. This long-standing issue hinders assessment of their contribution to past global warmth and the equilibrium climate sensitivity of the Earth system (E(ss)) to CO(2). Here we report results from a series of three-dimensional Earth system modeling simulations indicating that the greenhouse worlds of the early Eocene (55 Ma) and late Cretaceous (90 Ma) maintained high concentrations of methane, tropospheric ozone, and nitrous oxide. Modeled methane concentrations were four- to fivefold higher than the preindustrial value typically adopted in modeling investigations of these intervals, even after accounting for the possible high CO(2)-suppression of biogenic isoprene emissions on hydroxyl radical abundance. Higher concentrations of trace greenhouse gases exerted marked planetary heating (> 2 K), amplified in the high latitudes (> 6 K) by lower surface albedo feedbacks, and increased E(ss) in the Eocene by 1 K. Our analyses indicate the requirement for including non-CO(2) greenhouse gases in model-based E(ss) estimates for comparison with empirical paleoclimate assessments, and point to chemistry-climate feedbacks as possible amplifiers of climate sensitivity in the Anthropocene.

  19. The effect of pulverization on the albedo of lunar rocks

    NARCIS (Netherlands)

    Minnaert, Marcel Gilles Jozef

    1969-01-01

    Measures of the albedo under full-moon conditions have been made on two samples of very dark rocks, pulverized and sieved so as to obtain powders of different grain size. Below a size of 0.05 mm the albedo suddenly increases, obviously because the individual grains become transparent. By a rough

  20. Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations

    Science.gov (United States)

    Lee, Wei-Liang; Liou, K. N.; He, Cenlin; Liang, Hsin-Chien; Wang, Tai-Chi; Li, Qinbin; Liu, Zhenxin; Yue, Qing

    2017-08-01

    We investigate the snow albedo variation in spring over the southern Tibetan Plateau induced by the deposition of light-absorbing aerosols using remote sensing data from moderate resolution imaging spectroradiometer (MODIS) aboard Terra satellite during 2001-2012. We have selected pixels with 100 % snow cover for the entire period in March and April to avoid albedo contamination by other types of land surfaces. A model simulation using GEOS-Chem shows that aerosol optical depth (AOD) is a good indicator for black carbon and dust deposition on snow over the southern Tibetan Plateau. The monthly means of satellite-retrieved land surface temperature (LST) and AOD over 100 % snow-covered pixels during the 12 years are used in multiple linear regression analysis to derive the empirical relationship between snow albedo and these variables. Along with the LST effect, AOD is shown to be an important factor contributing to snow albedo reduction. We illustrate through statistical analysis that a 1-K increase in LST and a 0.1 increase in AOD indicate decreases in snow albedo by 0.75 and 2.1 % in the southern Tibetan Plateau, corresponding to local shortwave radiative forcing of 1.5 and 4.2 W m-2, respectively.

  1. Impacts of Aerosol Direct Effects on the South Asian Climate: Assessment of Radiative Feedback Processes Using Model Simulations and Satellite/Surface Measurements

    Science.gov (United States)

    Wang, Sheng-Hsiang; Gautam, Ritesh; Lau, William K. M.; Tsay, Si-Chee; Sun, Wen-Yih; Kim, Kyu-Myong; Chern, Jiun-Dar; Hsu, Christina; Lin, Neng-Huei

    2011-01-01

    Current assessment of aerosol radiative effect is hindered by our incomplete knowledge of aerosol optical properties, especially absorption, and our current inability to quantify physical and microphysical processes. In this research, we investigate direct aerosol radiative effect over heavy aerosol loading areas (e.g., Indo-Gangetic Plains, South/East Asia) and its feedbacks on the South Asian climate during the pre-monsoon season (March-June) using the Purdue Regional Climate Model (PRCM) with prescribed aerosol data derived by the NASA Goddard Earth Observing System Model (GEOS-5). Our modeling domain covers South and East Asia (60-140E and 0-50N) with spatial resolutions of 45 km in horizontal and 28 layers in vertical. The model is integrated from 15 February to 30 June 2008 continuously without nudging (i.e., only forced by initial/boundary conditions). Two numerical experiments are conducted with and without the aerosol-radiation effects. Both simulations are successful in reproducing the synoptic patterns on seasonal-to-interannual time scales and capturing a pre-monsoon feature of the northward rainfall propagation over Indian region in early June which shown in Tropical Rainfall Measuring Mission (TRMM) observation. Preliminary result suggests aerosol-radiation interactions mainly alter surface-atmosphere energetics and further result in an adjustment of the vertical temperature distribution in lower atmosphere (below 700 hPa). The modifications of temperature and associated rainfall and circulation feedbacks on the regional climate will be discussed in the presentation.

  2. NEOWISE REACTIVATION MISSION YEAR TWO: ASTEROID DIAMETERS AND ALBEDOS

    Energy Technology Data Exchange (ETDEWEB)

    Nugent, C. R.; Cutri, R. M. [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Mainzer, A.; Bauer, J.; Kramer, E. A.; Masiero, J.; Sonnett, S. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Grav, T. [Planetary Science Institute, Tucson, AZ (United States); Wright, E. L., E-mail: cnugent@ipac.caltech.edu [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)

    2016-09-01

    The Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) mission continues to detect, track, and characterize minor planets. We present diameters and albedos calculated from observations taken during the second year since the spacecraft was reactivated in late 2013. These include 207 near-Earth asteroids (NEAs) and 8885 other asteroids. Of the NEAs, 84% NEAs did not have previously measured diameters and albedos by the NEOWISE mission. Comparison of sizes and albedos calculated from NEOWISE measurements with those measured by occultations, spacecraft, and radar-derived shapes shows accuracy consistent with previous NEOWISE publications. Diameters and albedos fall within ±∼20% and ±∼40%, 1-sigma, respectively, of those measured by these alternate techniques. NEOWISE continues to preferentially discover near-Earth objects which are large (>100 m), and have low albedos.

  3. Influence of surface roughness of a desert

    Science.gov (United States)

    Sud, Y. C.; Smith, W. E.

    1984-01-01

    A numerical simulation study, using the current GLAS climate GCM, was carried out to examine the influence of low bulk aerodynamic drag parameter in the deserts. The results illustrate the importance of yet another feedback effect of a desert on itself, that is produced by the reduction in surface roughness height of land once the vegetation dies and desert forms. Apart from affecting the moisture convergence, low bulk transport coefficients of a desert lead to enhanced longwave cooling and sinking which together reduce precipitation by Charney's (1975) mechanism. Thus, this effect, together with albedo and soil moisture influence, perpetuate a desert condition through its geophysical feedback effect. The study further suggests that man made deserts is a viable hypothesis.

  4. Use of wrist albedo neutron dosimeters

    International Nuclear Information System (INIS)

    Hankins, D.E.

    1983-01-01

    We are developing a wrist dosimeter that can be used to measure the exposure at the wrist to x-rays, gamma rays, beta-particles, thermal neutrons and fast neutrons. It consists of a modified Hankins Type albedo neutron dosimeter and also contains three pieces of CR-39 plastic. ABS plastic in the form of an elongated hemisphere provides the beta and low energy x-ray shielding necessary to meet the requirement of depth dose measurements at 1 cm. The dosimeter has a beta window located in the side of the hemisphere oriented towards an object being held in the hands. A TLD 600 is positioned under the 1 cm thick ABS plastic and is used to measure the thermal neutron dose. At present we are using Velcro straps to hold the dosimeter on the inside of the wrist. 9 figures

  5. Climate mitigation from vegetation biophysical feedbacks during the past three decades

    Science.gov (United States)

    Zeng, Zhenzhong; Piao, Shilong; Li, Laurent Z. X.; Zhou, Liming; Ciais, Philippe; Wang, Tao; Li, Yue; Lian, Xu; Wood, Eric F.; Friedlingstein, Pierre; Mao, Jiafu; Estes, Lyndon D.; Myneni, Ranga B.; Peng, Shushi; Shi, Xiaoying; Seneviratne, Sonia I.; Wang, Yingping

    2017-06-01

    The surface air temperature response to vegetation changes has been studied for the extreme case of land-cover change; yet, it has never been quantified for the slow but persistent increase in leaf area index (LAI) observed over the past 30 years (Earth greening). Here we isolate the fingerprint of increasing LAI on surface air temperature using a coupled land-atmosphere global climate model prescribed with satellite LAI observations. We find that the global greening has slowed down the rise in global land-surface air temperature by 0.09 +/- 0.02 °C since 1982. This net cooling effect is the sum of cooling from increased evapotranspiration (70%), changed atmospheric circulation (44%), decreased shortwave transmissivity (21%), and warming from increased longwave air emissivity (-29%) and decreased albedo (-6%). The global cooling originated from the regions where LAI has increased, including boreal Eurasia, Europe, India, northwest Amazonia, and the Sahel. Increasing LAI did not, however, significantly change surface air temperature in eastern North America and East Asia, where the effects of large-scale atmospheric circulation changes mask local vegetation feedbacks. Overall, the sum of biophysical feedbacks related to the greening of the Earth mitigated 12% of global land-surface warming for the past 30 years.

  6. Climate mitigation from vegetation biophysical feedbacks during the past three decades

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Zhenzhong [Peking Univ., Beijing (China); Piao, Shilong [Peking Univ., Beijing (China); Chinese Academy of Sciences (CAS), Beijing (China); Li, Laurent Z. X. [Sorbonne Univ. Paris (France); Zhou, Liming [State Univ. of New York (SUNY), Albany, NY (United States); Ciais, Philippe [Alternative Energies and Atomic Energy Commission (CEA), Gif-sur-Yvette (France); Wang, Tao [Chinese Academy of Sciences (CAS), Beijing (China); Li, Yue [Peking Univ., Beijing (China); Lian, Xu [Peking Univ., Beijing (China); Wood, Eric F. [Princeton Univ., NJ (United States); Friedlingstein, Pierre [Univ. of Exeter (United Kingdom); Mao, Jiafu [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Estes, Lyndon D. [Princeton Univ., NJ (United States); Clark Univ., Worcester, MA (United States); Myneni, Ranga B. [Boston Univ., MA (United States); Peng, Shushi [Peking Univ., Beijing (China); Shi, Xiaoying [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Seneviratne, Sonia I. [ETH Zurich (Switzerland); Wang, Yingping [Commonwealth Scientific and Industrial Research Organization (CSIRO), Aspendale, VIC (Australia)

    2017-05-22

    The surface air temperature response to vegetation changes has been studied for the extreme case of land-cover change; yet, it has never been quantified for the slow but persistent increase in leaf area index (LAI) observed over the past 30 years (Earth greening). We isolate the fingerprint of increasing LAI on surface air temperature using a coupled land–atmosphere global climate model prescribed with satellite LAI observations. Furthermore, we found that the global greening has slowed down the rise in global land-surface air temperature by 0.09 ± 0.02 °C since 1982. This net cooling effect is the sum of cooling from increased evapotranspiration (70%), changed atmospheric circulation (44%), decreased shortwave transmissivity (21%), and warming from increased longwave air emissivity (-29%) and decreased albedo (-6%). The global cooling originated from the regions where LAI has increased, including boreal Eurasia, Europe, India, northwest Amazonia, and the Sahel. Increasing LAI did not, but, significantly change surface air temperature in eastern North America and East Asia, where the effects of large-scale atmospheric circulation changes mask local vegetation feedbacks. Overall, the sum of biophysical feedbacks related to the greening of the Earth mitigated 12% of global land-surface warming for the past 30 years.

  7. A novel integrated method to describe dust and fine supraglacial debris and their effects on ice albedo: the case study of Forni Glacier, Italian Alps

    Science.gov (United States)

    Azzoni, R. S.; Senese, A.; Zerboni, A.; Maugeri, M.; Smiraglia, C.; Diolaiuti, G. A.

    2014-06-01

    We investigated the characteristics of sparse and fine debris coverage at the glacier melting surface and its relation to ice albedo. In spite of the abundant literature dealing with dust and black carbon deposition on glacier accumulation areas (i.e.: on snow and firn), few studies that describe the distribution and properties of fine and discontinuous debris and black carbon at the melting surface of glaciers are available. Furthermore, guidelines are needed to standardize field samplings and lab analyses thus permitting comparisons among different glaciers. We developed a protocol to (i) sample fine and sparse supraglacial debris and dust, (ii) quantify their surface coverage and the covering rate, (iii) describe composition and sedimentological properties, (iv) measure ice albedo and (v) identify the relationship between ice albedo and fine debris coverage. The procedure was tested on the Forni Glacier surface (northern Italy), in summer 2011, 2012 and 2013, when the fine debris and dust presence had marked variability in space and time (along the glacier tongue and from the beginning to the end of summer) thus influencing ice albedo: in particular the natural logarithm of albedo was found to depend on the percentage of glacier surface covered by debris. Debris and dust analyses indicate generally a local origin (from nesting rockwalls) and the organic content was locally high. Nevertheless the finding of some cenospheres suggests an anthropic contribution to the superficial dust as well. Moreover, the effect of liquid precipitation on ice albedo was not negligible, but short lasting (from 1 to 4 day long), thus indicating that also other processes affect ice albedo and ice melt rates and then some attention has to be spent analysing frequency and duration of summer rainfalls for better describing albedo and melt variability.

  8. Changes in the Albedo of the Pegasus and Phoenix Runways, 2000-2017

    Science.gov (United States)

    2017-07-18

    albedo, increase solar energy absorption in the ice shelf, and significantly alter the energy balance, resulting in in- creased melting, snow density...which floats on the McMurdo Sound . ERDC/CRREL TR-17-10 4 Because of this limitation, MODIS’s narrowband surface reflectance (which could be...Multispectral satellites generally leverage regions of the electromagnetic spectrum out- side of these absorption bands (atmospheric windows) where

  9. Variation of Arctic's Sea-ice Albedo between 2000 and 2016 by fusion of MISR and MODIS data

    Science.gov (United States)

    Muller, Jan-Peter; Kharbouche, Said

    2017-04-01

    Many research studies have demonstrated that sea-ice plays a key role in climate change and global warming. Most of these studies are based either on ground in-situ data or on remotely sensed data. The latter data are provided mainly by active (SAR and LiDAR) sensors such as Cryosat2, ERS1/2, ENVISAT, Radarsat1/2, ICESat as well as passive sensors such as SSM/I. Nevertheless, the contribution of such active optical sensors data is limited to parameters such as thickness and sea-ice concentration from which albedo may be inferred. The creation of high quality albedo for sea-ice using optical satellites is confronted with two main obstacles: 1) the Arctic is a very cloudy region and, high quality albedo requires multi-angle observations over a relatively short period; 2) cloud masking over sea-ice is a very difficult task, especially for sensor with low spectral resolution. To overcome the above two obstacles, we discuss in a separate report the generation of this fused daily, weekly, fortnightly and monthly product at 1km and 5km resolution on a polar stereographic grid [1]. The limited swath (380km) of MISR means that not all of the Arctic is covered on a daily basis so composites on different time-steps were produced. The results show that sea-ice albedo has been in continuous decline since 2000 with thinner sea-ice and greater leads and open water as well as more ponding at earlier times in the year. The implications of these results are discussed in terms of the sea-ice climate feedback. Animated visualisations of the albedo patterns each year, the decline in average and the increase in standard deviation in albedo for every single day for all 17 years will be shown to demonstrate the effects of climate change over sea-ice albedo. References [1] Kharbouche & Muller, Production of Arctic sea-ice albedo by fusion of MISR and MODIS data. This conference. Acknowledgements This work was supported by www.QA4ECV.eu, a project of European Union's Seventh Framework

  10. The Impact of Albedo Increase to Mitigate the Urban Heat Island in Terni (Italy Using the WRF Model

    Directory of Open Access Journals (Sweden)

    Elena Morini

    2016-10-01

    Full Text Available The impacts of the urban heat island (UHI phenomenon on energy consumption, air quality, and human health have been widely studied and described. Mitigation strategies have been developed to fight the UHI and its detrimental consequences. A potential countermeasure is the increase of urban albedo by using cool materials. Cool materials are highly reflective materials that can maintain lower surface temperatures and thus can present an effective solution to mitigate the UHI. Terni’s proven record of high temperatures along with related environmental and comfort issues in its urban areas have reflected the local consequences of global warming. On the other hand, it promoted integrated actions by the government and research institutes to investigate solutions to mitigate the UHI effects. In this study, the main goal is to investigate the effectiveness of albedo increase as a strategy to tackle the UHI, by using the Weather Research and Forecasting (WRF mesoscale model to simulate the urban climate of Terni (Italy. Three different scenarios through a summer heat wave in the summer of 2015 are analyzed. The Base Scenario, which simulates the actual conditions of the urban area, is the control case. In the Albedo Scenario (ALB Scenario, the albedo of the roof, walls and road of the whole urban area is increased. In the Albedo-Industrial Scenario (ALB-IND Scenario, the albedo of the roof, walls and road of the area occupied by the main industrial site of Terni, located in close proximity to the city center, is increased. The simulation results show that the UHI is decreased up to 2 °C both at daytime and at nighttime in the ALB and in ALB-IND Scenarios. Peak temperatures in the urban area can be decreased by 1 °C at daytime, and by about 2 °C at nighttime. Albedo increase in the area of interest might thus represent an opportunity to decrease the UHI effect and its consequences.

  11. MISR Level 2 Surface parameters V002

    Data.gov (United States)

    National Aeronautics and Space Administration — This Level 2 Land Surface product contains information on land directional reflectance properties,albedos(spectral & PAR integrated),FPAR,asssociated radiation...

  12. The role of sea-ice albedo in the climate of slowly rotating aquaplanets

    Science.gov (United States)

    Salameh, Josiane; Popp, Max; Marotzke, Jochem

    2018-04-01

    We investigate the influence of the rotation period (P_{rot}) on the mean climate of an aquaplanet, with a focus on the role of sea-ice albedo. We perform aquaplanet simulations with the atmospheric general circulation model ECHAM6 for various rotation periods from one Earth-day to 365 Earth-days in which case the planet is synchronously rotating. The global-mean surface temperature decreases with increasing P_{rot} and sea ice expands equatorwards. The cooling of the mean climate with increasing P_{rot} is caused partly by the high surface albedo of sea ice on the dayside and partly by the high albedo of the deep convective clouds over the substellar region. The cooling caused by these deep convective clouds is weak for non-synchronous rotations compared to synchronous rotation. Sensitivity simulations with the sea-ice model switched off show that the global-mean surface temperature is up to 27 K higher than in our main simulations with sea ice and thus highlight the large influence of sea ice on the climate. We present the first estimates of the influence of the rotation period on the transition of an Earth-like climate to global glaciation. Our results suggest that global glaciation of planets with synchronous rotation occurs at substantially lower incoming solar irradiation than for planets with slow but non-synchronous rotation.

  13. Derivation of high spatial resolution albedo from UAV digital imagery: application over the Greenland Ice Sheet

    Science.gov (United States)

    Ryan, Jonathan C.; Hubbard, Alun; Box, Jason E.; Brough, Stephen; Cameron, Karen; Cook, Joseph M.; Cooper, Matthew; Doyle, Samuel H.; Edwards, Arwyn; Holt, Tom; Irvine-Fynn, Tristram; Jones, Christine; Pitcher, Lincoln H.; Rennermalm, Asa K.; Smith, Laurence C.; Stibal, Marek; Snooke, Neal

    2017-05-01

    Measurements of albedo are a prerequisite for modelling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimetre resolution albedo products with accuracies of 5% using consumer-grade digital camera and unmanned aerial vehicle (UAV) technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique will likely become increasingly attractive in field studies and used in a wide range of applications for high temporal and spatial resolution surface mapping of debris, dust, cryoconite and bioalbedo and for directly constraining surface energy balance models.

  14. A fast, magnetics-free flux surface estimation and q-profile reconstruction algorithm for feedback control of plasma profiles

    NARCIS (Netherlands)

    Hommen, G.; de M. Baar,; Citrin, J.; de Blank, H. J.; Voorhoeve, R. J.; de Bock, M. F. M.; Steinbuch, M.

    2013-01-01

    The flux surfaces' layout and the magnetic winding number q are important quantities for the performance and stability of tokamak plasmas. Normally, these quantities are iteratively derived by solving the plasma equilibrium for the poloidal and toroidal flux. In this work, a fast, non-iterative

  15. The Influence of Historical and Potential Future Deforestation on the Stream Flow of the Amazon River -- Land Surface Processes and Atmospheric Feedbacks

    Science.gov (United States)

    Coe, M. T.; Costa, M. H.; Soares-Filho, B.

    2008-12-01

    Global economic and regional population and development pressures have resulted in high rates of deforestation in the Amazon River basin, mostly in the eastern and southern portion of the basin. Recent deforestation rates reflect the global demand for Brazilian free-range beef and soybeans with about 22,000 km2 deforested each year between 2000 and 2004 and 7000 km2 deforested in the final months of 2007. Land cover and land use changes influence the quantity of surface water resources by changing how incoming precipitation and radiation are partitioned among sensible and latent heat fluxes, runoff, and river discharge and altering regional and continental scale precipitation patterns. Results from coupled land surface and global climate model simulations clarify a few important points about the impact of deforestation on the Amazon River: 1) The local evapotranspiration decrease and subsequent discharge increase can be a significant fraction of the water balance when greater than 50% of a watershed is deforested. 2) The atmospheric feedbacks from large-scale deforestation may be of the same order of magnitude as the changes to local land surface processes, but of opposite sign and are not limited to those basins where deforestation has occurred. 3) Changes to discharge and aquatic environments with future deforestation of the Amazon will likely be a complex function of how much vegetation has been removed from a particular watershed and how much has been removed from the entire Amazon Basin.

  16. Documenting feedbacks between surface processes and structural deformation in East Timor using stream profile and drainage network analysis

    Science.gov (United States)

    Tate, G. W.; Willett, S.; McQuarrie, N.; Goren, L.; Fox, M.

    2013-12-01

    While river profile analyses have long been used to evaluate the development of landforms, recent advances in analyzing drainage networks have significantly improved the ability to positively link stream profiles with surface uplift. In one such method, Perron and Royden (2012) define the value chi, an integral quantity based on the steady-state stream power equation which aids in determining the conformity of rivers and drainage basins to steady-state behavior. East Timor is an ideal location to test new methods using chi, as it is an active and unglaciated orogen with independent constraints of the deformational history through thermochronology and structural geology. We utilize the calculation of chi in our analyses of the drainage network to provide new constraints on the most recent uplift history of the island of Timor. Discontinuities in chi across drainage divides imply different steady state baselevel for hillslopes and therefore active migration of the divide. We confirm this by noting visible landslides in satellite images and asymmetries in hillslope steepness. Analyses of chi and elevation reveal in some locations that tributaries within a single basin have experienced distinctly different histories, documenting instances where previous river capture has occurred. In other locations the relationships between chi and elevation along single rivers denote spatial changes in surface uplift rate. Many of these observations from the drainage network correspond well to patterns of recent exhumation identified from thermochronologic analyses as well as structural constraints from field mapping and balanced cross-sections. Much of the fastest exhumation on the island (as indicated by zircon (U-Th)/He ages of 1.5-3.8 Ma and modeled exhumation rates of 1-3 mm/yr) is in the hinterland slate belt, which also contains the most stream profile remnants of paleo-capture events. Many locations of active river capture correspond well to independently constrained

  17. Measurement of spectral sea ice albedo at Qaanaaq fjord in northwest Greenland

    Science.gov (United States)

    Tanikawa, T.

    2017-12-01

    The spectral albedos of sea ice were measured at Qaanaaq fjord in northwest Greenland. Spectral measurements were conducted for sea ice covered with snow and sea ice without snow where snow was artificially removed around measurement point. Thickness of the sea ice was approximately 1.3 m with 5 cm of snow over the sea ice. The measurements show that the spectral albedos of the sea ice with snow were lower than those of natural pure snow especially in the visible regions though the spectral shapes were similar to each other. This is because the spectral albedos in the visible region have information of not only the snow but also the sea ice under the snow. The spectral albedos of the sea ice without the snow were approximately 0.4 - 0.5 in the visible region, 0.05-0.25 in the near-infrared region and almost constant of approximately 0.05 in the region of 1500 - 2500 nm. In the visible region, it would be due to multiple scattering by an air bubble within the sea ice. In contrast, in the near-infrared and shortwave infrared wavelengths, surface reflection at the sea ice surface would be dominant. Since a light absorption by the ice in these regions is relatively strong comparing to the visible region, the light could not be penetrated deeply within the sea ice, resulting that surface reflection based on Fresnel reflection would be dominant. In this presentation we also show the results of comparison between the radiative transfer calculation and spectral measurement data.

  18. Use of in situ and airborne data to assess satellite-based estimates of directional reflectance and albedo

    Science.gov (United States)

    Roman, Miguel O.

    Accurate representation of the regional characteristics of anisotropic light scattering by land surfaces under a wide range of sky conditions is required (1) for modeling atmospheric shortwave radiative fluxes; (2) for modeling the energy exchange between the earth and atmosphere; and (3) determining the lower boundary conditions for atmospheric radiative transfer models. However, uncertainties due to spatial scale arise when models that describe the albedo and reflectance anisotropy of land surfaces are directly compared against in-situ measurements. This research focuses on comparisons between satellite, airborne, and ground measurements, namely, MODerate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) and Albedo products, airborne angular reflectance measurements, and point tower albedo measurements. A new integrated methodology for establishing the spatial representativeness between tower measurements of surface albedo and MODIS retrievals is developed. This method brings together knowledge of the intrinsic biophysical properties of a given spatial domain and its surrounding landscape to produce a number of geostatistical attributes that describe the overall variability, spatial extent, strength, and temporal structure of surface albedo patterns at separated seasonal periods throughout the year. Local upscaling results over a wide range of forested ecosystems demonstrate the ability of this method to identify landscapes that capture the spatial and seasonal features of surface albedo over large enough footprints to be suitable for use in modeling studies. Airborne measurements from NASA's Cloud Absorption Radiometer taken over agricultural and natural landscapes in the Southern Great Plains (SGP) region during the Cloud and Land Surface Interaction Campaign (CLASIC) were utilized to compare the spatial characteristics between finer-scale BRDFs and MODIS retrievals in a well-characterized atmospheric regime

  19. Transverse feedback

    CERN Document Server

    Cornelis, K; Sladen, Jonathan P H; CERN. Geneva. SPS and LEP Division

    1997-01-01

    The aim of these MD's was to set up the transverse feedback for damping in both planes, and to test the charge normalization and gain compensation. The latter is intended to reduce the gain of the feedback for small oscillations in order to improve compatibility with the Q loop. All work was done with 2 x 4 bunches, family A. In the first two MD's the feedback was set up for damping in both planes with charge normalization. In the third, gain compensation was commissioned in the vertical plane with Qv' set to -2. It was found either to increase the level of the m = 0 mode or to leave it unchanged. Under these conditions 6mA total current was accumulated.

  20. Changes in Snow Albedo Resulting from Snow Darkening Caused by Black Carbon

    Science.gov (United States)

    Engels, J.; Kloster, S.; Bourgeois, Q.

    2014-12-01

    We investigate the potential impact of snow darkening caused by pre-industrial and present-day black carbon (BC) emissions on snow albedo and subsequently climate. To assess this impact, we implemented the effect of snow darkening caused by BC emitted from natural as well as anthropogenic sources into the Max Planck Institute for Meteorology Earth System Model (MPI-M ESM). Considerable amounts of BC are emitted e.g. from fires and are transported through the atmosphere for several days before being removed by rain or snow precipitation in snow covered regions. Already very small quantities of BC reduce the snow reflectance significantly, with consequences for snow melting and snow spatial coverage. We implemented the snow albedo reduction caused by BC contamination and snow aging in the one layer land surface component (JSBACH) of the atmospheric general circulation model ECHAM6, developed at MPI-M. For this we used the single-layer simulator of the SNow, Ice, and Aerosol Radiation (SNICAR-Online (Flanner et al., 2007); http://snow.engin.umich.edu) model to derive snow albedo values for BC in snow concentrations ranging between 0 and 1500 ng(BC)/g(snow) for different snow grain sizes for the visible (0.3 - 0.7 μm) and near infrared range (0.7 - 1.5 μm). As snow grains grow over time, we assign different snow ages to different snow grain sizes (50, 150, 500, and 1000 μm). Here, a radius of 50 μm corresponds to new snow, whereas a radius of 1000 μm corresponds to old snow. The deposition rates of BC on snow are prescribed from previous ECHAM6-HAM simulations for two time periods, pre-industrial (1880-1889) and present-day (2000-2009), respectively. We perform a sensitivity study regarding the scavenging of BC by snow melt. To evaluate the newly implemented albedo scheme we will compare the modeled black carbon in snow concentrations to observed ones. Moreover, we will show the impact of the BC contamination and snow aging on the simulated snow albedo. The

  1. Modeling the Diagnostic Effects of Vegetation, Soil Albedo, and Dust on Mid-Holocene Saharan Climate

    Science.gov (United States)

    Thompson, A.; Poulsen, C. J.; Skinner, C. B.

    2017-12-01

    Unlike today, the Mid-Holocene (MH, 6,000 BP) African Sahara comprised of mixed vegetation and permanent lakes that supported human settlements. Climate proxies including leaf wax isotope, pollen, and dust flux records suggest that African monsoonal precipitation reached 31°N, compared to 15°N today. Changes in orbital forcing are partly responsible for the intensification of the African monsoon, but alone cannot explain the more humid MH Sahara. Modeling studies have shown that vegetation and soil albedo feedbacks greatly increase Saharan rainfall but still fall short of levels indicated by proxies. A recent study proposed that reduced Saharan dust concentrations due to greater vegetation coverage further increased MH rainfall. However, this study used idealized dust concentrations to improve proxy agreement and did not include the dust aerosol indirect effects in its model physics. Here we use CESM CAM5-chem to quantify the impact of diagnostic changes in Saharan dust, including indirect effects, on MH Saharan climate and compare it to changes in orbital forcing, soil albedo, and vegetation. Consistent with previous studies, a change in MH orbital forcing alone leads to a 20% increase in summer (June-Sept.) precipitation over Northern Africa (0°-30°N, 20°W-30°E) relative to a pre-industrial control, but still fails to reach the northward extent suggested by proxies. Adding MH soil albedo or vegetation increases summer precipitation by 45% and 52%, and shifts the maximum latitudinal rainfall extent 10° and 12° northward, respectively. These increases are 2.28 and 2.64 times greater than the precipitation increase from MH orbital forcing alone. MH soil albedo results in a dust burden increase of 22%, yet MH vegetation results in a 96% reduction. Both MH soil albedo and vegetation combined increase summer precipitation by 56% and 13° northward, an increase 2.84 times greater than the orbital forcing alone, and reduces dust burden by 97%. An additional

  2. Energy-balance climate models: stability experiments with a refined albedo and updated coefficients for infrared emission

    NARCIS (Netherlands)

    Oerlemans, J.

    1978-01-01

    A zonally averaged' climate model of the energy-balance type is examined. Recently published satellite measurements were used to improve existing parameterizations of planetary albedo and outgoing radiation in terms of surface and sea level temperature. A realistic constant for the diffusion of

  3. Albedo's determination by the method of neutron impulse

    International Nuclear Information System (INIS)

    Flores Calderon, J.E.

    1982-01-01

    Experiments with non-stationary neutron transport in large cavity moderators (l>>Σsub(tr) -1 ) (where l is the characteristic cavity length and Σsub(tr) -1 the macroscopic transport section of the moderator) led to the method reported in this study which, based on neutron impulses for determining albedo of thermal neutrons, gave a precision greater by an order of magnitude over previous methods. A sufficient time interval after introduction of the neutron flux into the moderator chamber decreased exponentially the decay constant L, which was itself related to albedo by a function called f. Numerical calculations of albedo were assisted. (author)

  4. Assessing the influence of groundwater and land surface scheme in the modelling of land surface-atmosphere feedbacks over the FIFE area in Kansas, USA

    DEFF Research Database (Denmark)

    Larsen, Morten Andreas Dahl; Højmark Rasmussen, Søren; Drews, Martin

    2016-01-01

    by HIRHAM simulated precipitation. The last two simulations include iv) a standard HIRHAM simulation, and v) a fully coupled HIRHAM-MIKE SHE simulation locally replacing the land surface scheme by MIKE SHE for the FIFE area, while HIRHAM in standard configuration is used for the remaining model area......The land surface-atmosphere interaction is described differently in large scale surface schemes of regional climate models and small scale spatially distributed hydrological models. In particular, the hydrological models include the influence of shallow groundwater on evapotranspiration during dry...... experiments include five simulations. First MIKE SHE is forced by observed climate data in two versions i) with groundwater at a fixed uniform depth, and ii) with a dynamical groundwater component simulating shallow groundwater conditions in river valleys. iii) In a third simulation MIKE SHE is forced...

  5. Albedo Observation by Hayabusa2 LIDAR: Instrument Performance and Error Evaluation

    Science.gov (United States)

    Yamada, Ryuhei; Senshu, Hiroki; Namiki, Noriyuki; Mizuno, Takahide; Abe, Shinsuke; Yoshida, Fumi; Noda, Hirotomo; Hirata, Naru; Oshigami, Shoko; Araki, Hiroshi; Ishihara, Yoshiaki; Matsumoto, Koji

    2017-07-01

    The Japanese asteroid explorer Hayabusa2 was launched at the end of 2014. Hayabusa2 is supposed to observe the near-Earth C-type asteroid 162173 Ryugu (1999 JU3) and bring surface material samples back to Earth in 2020. It is equipped with Light Detection and Ranging (LIDAR) instrument for laser ranging which can be used to measure the intensities of transmitted and received pulses. The intensity data can be used to estimate the normal albedo of Ryugu at a laser wavelength of 1.064 μm. To perform this estimation, we determined the transfer functions of the laser module and receiver to convert the intensity data into pulse energies, along with the utilization ratio of the returned pulse energy, through verification tests of the LIDAR flight model. Then, we evaluated the error of the normal albedo. This error is affected not only by the performance of the LIDAR but also by the slope and roughness of the asteroid's surface. In this paper, we focus on the error in the normal albedo due only to the instrument error, which will be 18.0 % in an observation at a nominal altitude of 20 km.

  6. Derivation of High Spatial Resolution Albedo from UAV Digital Imagery: Application over the Greenland Ice Sheet

    Directory of Open Access Journals (Sweden)

    Jonathan C. Ryan

    2017-05-01

    Full Text Available Measurements of albedo are a prerequisite for modeling surface melt across the Earth's cryosphere, yet available satellite products are limited in spatial and/or temporal resolution. Here, we present a practical methodology to obtain centimeter resolution albedo products with accuracies of ±5% using consumer-grade digital camera and unmanned aerial vehicle (UAV technologies. Our method comprises a workflow for processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. We demonstrate the method with a set of UAV sorties over the western, K-sector of the Greenland Ice Sheet. The resulting albedo product, UAV10A1, covers 280 km2, at a resolution of 20 cm per pixel and has a root-mean-square difference of 3.7% compared to MOD10A1 and 4.9% compared to ground-based broadband pyranometer measurements. By continuously measuring downward solar irradiance, the technique overcomes previous limitations due to variable illumination conditions during and between surveys over glaciated terrain. The current miniaturization of multispectral sensors and incorporation of upward facing radiation sensors on UAV packages means that this technique could become increasingly common in field studies and used for a wide range of applications. These include the mapping of debris, dust, cryoconite and bioalbedo, and directly constraining surface energy balance models.

  7. Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU2

    Science.gov (United States)

    Kuroda, Daisuke; Ishiguro, Masateru; Watanabe, Makoto; Hasegawa, Sunao; Sekiguchi, Tomohiko; Naito, Hiroyuki; Usui, Fumihiko; Imai, Masataka; Sato, Mitsuteru; Kuramoto, Kiyoshi

    2018-03-01

    We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 ± 0.5% in the RC band and 44.0 ± 0.6% in the V band at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.

  8. The Influence of green areas and roof albedos on air temperatures during Extreme Heat Events in Berlin, Germany

    Directory of Open Access Journals (Sweden)

    Sebastian Schubert

    2013-04-01

    Full Text Available The mesoscale atmospheric model COSMO-CLM (CCLM with the Double Canyon Effect Parametrization Scheme (DCEP is applied to investigate possible adaption measures to extreme heat events (EHEs for the city of Berlin, Germany. The emphasis is on the effects of a modified urban vegetation cover and roof albedo on near-surface air temperatures. Five EHEs with a duration of 5 days or more are identified for the period 2000 to 2009. A reference simulation is carried out for each EHE with current vegetation cover, roof albedo and urban canopy parameters (UCPs, and is evaluated with temperature observations from weather stations in Berlin and its surroundings. The derivation of the UCPs from an impervious surface map and a 3-D building data set is detailed. Characteristics of the simulated urban heat island for each EHE are analysed in terms of these UCPs. I