Anisotropy parameterization development and evaluation for glacier surface albedo retrieval from satellite observations.

Glacier albedo determines the net shortwave radiation absorbed at the glacier surface and plays a crucial role in glacier energy and mass balance. Remote sensing techniques are efficient means to retrieve glacier surface albedo over large and inaccessible areas and to study its variability. However, corrections of anisotropic reflectance of glacier surface have been established for specific shortwave bands only, such as Landsat 5 Thematic Mapper (L5/TM) band 2 and band 4, which is a major limitation of current retrievals of glacier broadband albedo. In this study, we calibrated and evaluated four anisotropy correction models for glacier snow and ice, applicable to visible, near-infrared and shortwave-infrared wavelengths using airborne datasets of Bidirectional Reflectance Distribution Function (BRDF). We then tested the ability of the best-performing anisotropy correction model, referred to from here on as the ‘updated model’, to retrieve albedo from L5/TM, Landsat 8 Operational Land Imager (L8/OLI) and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, and evaluated these results with field measurements collected on eight glaciers around the world. Our results show that the updated model: (1) can accurately estimate anisotropic factors of reflectance for snow and ice surfaces; (2) generally performs better than prior approaches for L8/OLI albedo retrieval but is not appropriate for L5/TM; (3) generally retrieves MODIS albedo better than the MODIS standard albedo product (MCD43A3) in both absolute values and glacier albedo temporal evolution, i.e., exhibiting both fewer gaps and better agreement with field observations. As the updated model enables anisotropy correction of a maximum of 10 multispectral bands and is implemented in Google Earth Engine (GEE), it is promising for observing and analyzing glacier albedo at large spatial scales

Blue-Sky Albedo Reduction and Associated Influencing Factors of Stable Land Cover Types in the Middle-High Latitudes of the Northern Hemisphere during 1982–2015

Land surface albedo (LSA) directly affects the radiation balance and the surface heat budget. LSA is a key variable for local and global climate research. The complexity of LSA variations and the driving factors highlight the importance of continuous spatial and temporal monitoring. Snow, vegetation and soil are the main underlying surface factors affecting LSA dynamics. In this study, we combined Global Land Surface Satellite (GLASS) products and ERA5 reanalysis products to analyze the spatiotemporal variation and drivers of annual mean blue-sky albedo for stable land cover types in the middle-high latitudes of the Northern Hemisphere (30~90°N) from 1982 to 2015. Snow cover (SC) exhibited a decreasing trend in 99.59% of all pixels (23.73% significant), with a rate of −0.0813. Soil moisture (SM) exhibited a decreasing trend in 85.66% of all pixels (22.27% significant), with a rate of −0.0002. The leaf area index (LAI) exhibited a greening trend in 74.38% of all pixels (25.23% significant), with a rate of 0.0014. Blue-sky albedo exhibited a decreasing trend in 98.97% of all pixels (65.12% significant), with a rate of −0.0008 (OLS slope). Approximately 98.16% of all pixels (57.01% significant) exhibited a positive correlation between blue-sky albedo and SC. Approximately 47.78% and 67.38% of all pixels (17.13% and 25.3% significant, respectively) exhibited a negative correlation between blue-sky albedo and SM and LAI, respectively. Approximately 10.31%, 20.81% and 68.88% of the pixel blue-sky albedo reduction was mainly controlled by SC, SM and LAI, respectively. The decrease in blue-sky albedo north of 40°N was mainly caused by the decrease in SC. The decrease in blue-sky albedo south of 40°N was mainly caused by SM reduction and vegetation greening. The decrease in blue-sky albedo in the western Tibetan Plateau was caused by vegetation greening, SM increase and SC reduction. The results have important scientific significance for the study of surface processes and global climate change

Estimation of surface energy fluxes under complex terrain of Mt. Qomolangma over the Tibetan Plateau

Surface solar radiation is an important parameter in surface energy balance models and in estimation of evapotranspiration. This study developed a DEM based radiation model to estimate instantaneous clear sky solar radiation for surface energy balance system to obtain accurate energy absorbed by the mountain surface. Efforts to improve spatial accuracy of satellite based surface energy budget in mountainous regions were made in this work. Based on eight scenes of Landsat TM/ETM+ (Thematic Mapper/Enhanced Thematic Mapper+) data and observations around the Qomolangma region of the Tibetan Plateau, the topographical enhanced surface energy balance system (TESEBS) was tested for deriving net radiation, ground heat flux, sensible heat flux and latent heat flux distributions over the heterogeneous land surface. The land surface energy fluxes over the study area showed a wide range in accordance with the surface features and their thermodynamic states. The model was validated by observations at QOMS/CAS site in the research area with a reasonable accuracy. The mean bias of net radiation, sensible heat flux, ground heat flux and latent heat flux is lower than 23.6 W m−2. The surface solar radiation estimated by the DEM based radiation model developed by this study has a mean bias as low as −9.6 W m−2. TESEBS has a decreased mean bias of about 5.9 W m−2 and 3.4 W m−2 for sensible heat and latent heat flux, respectively, compared to the Surface Energy Balance System (SEBS)

Evaluation and Improvements of the Offline CLM4 Using ARM Data

Hourly ground observations for year 2004 from the Atmospheric Radiation Measurement (ARM) program of the Department of Energy were used to examine the surface and subsurface energy simulations of the Community Land Model version 4 (CLM4). The 2 m air temperature, wind speed, solar radiation, downward longwave radiation, and precipitation observed by the ARM project were used to force the offline CLM4, and the ARM land surface and soil observations including skin temperature (Tskin), soil temperature and moisture, and sensible, latent, and ground heat fluxes were used to evaluate the model outputs. The default and ARM-forced CLM4 runs for 2004 were compared to assess the improvements to the model for hourly, daily, and seasonal timescales. The root mean square error and the Pearson correlation coefficient show that the ARM-forced offline CLM4 leads to improved accuracy in surface and soil energy fluxes in comparison with the default offline CLM4. Nevertheless, a warm bias of 2°C to 3°C was assessed on Tskin in summer due to warm maximum temperatures and in winter due to warm minimum temperatures. To improve CLM4 Tskin simulations, a proposed vegetation emissivity parameterization was evaluated locally and globally using both ARM and Moderate Resolution Imaging Spectroradiometer remote-sensing observations. This new algorithm results in cooling and an improvement of 0.17 K for the ARM site. Global evaluation revealed improvement in areas of intermediate canopy density

Diagnosis and Improvement of Cryosphere Shortwave Radiation Biases in Global Climate Models.

Faithful representation of cryospheric change is critical for accurate climate modeling, but there are complicating issues in representing snow extent and reflectance in physically realistic ways. This thesis is a collection of diagnostics and improvements of cryospheric shortwave radiation in climate models. Firstly, we incorporate a diagnostic called the cryosphere radiative effect (CrRE), the instantaneous influence of surface snow and sea ice on the top-of-model solar energy budget, into two released versions of the Community Earth System Model. CrRE offers a more climatically relevant metric of the cryospheric state than snow and sea ice extent and is influenced by factors such as the seasonal cycle of insolation, cloud masking, and vegetation cover. We evaluate CrRE during the late 20th century and over the 21st century, specifically diagnosing the CrRE contributions from terrestrial and marine sources. Present-day boreal CrRE compares well with observationally derived estimates. Similar present-day CrRE in the two model versions results from compensating differences in cloud masking and sea ice extent. Radiative forcing in future warming scenarios reduces boreal and austral sea ice cover, and boreal snow cover, which each contribute roughly 1 W/m-2 to enhancing global absorbed shortwave radiation. Similar global cryospheric albedo feedbacks between 0.41-0.45 W/m2/K indicate the models exhibit similar temperature-normalized CrRE change. Secondly, we incorporated a modified canopy scheme into the Community Land Model with snow interception as a prognostic variable and snow unloading tuned to in-situ measurements. The canopy radiation scheme has been updated from a direct temperature dependence of optical parameters to a dependence on the prognostic snow storage. With these improvements, boreal forest zones show large, significant albedo error reductions relative to MODIS observations. 13% gridcell RMSE reduction during spring results from a more gradual seasonal transition in albedo, while 27% reduction in winter is from a lower albedo. Over all North Hemisphere land area, error was also reduced. Thirdly, we assess the impacts of the snow canopy vegetation treatment in coupled model warming scenarios. Little change in global albedo feedback or climate sensitivity were shown, but significant alterations resulted that varied both regionally and temporally.PhDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113453/1/perketj_1.pd

Snow cover and snow albedo changes in the central Andes of Chile and Argentina from daily MODIS observations (2000-2016)

The variables of snow cover extent (SCE), snow cover duration (SCD), and snow albedo (SAL) are primary factors determining the surface energy balance and hydrological response of the cryosphere, influencing snow pack and glacier mass-balance, melt, and runoff conditions. This study examines spatiotemporal patterns and trends in SCE, SCD, and SAL (2000–2016; 16 years) for central Chilean and Argentinean Andes using the MODIS MOD10A1 C6 daily snow product. Observed changes in these variables are analyzed in relation to climatic variability by using ground truth observations (meteorological data from the El Yeso Embalse and Valle Nevado weather stations) and the Multivariate El Niño index (MEI) data. We identified significant downward trends in both SCE and SAL, especially during the onset and offset of snow seasons. SCE and SAL showed high inter-annual variability which correlate significantly with MEI applied with a one-month time-lag. SCE and SCD decreased by an average of ~13 ± 2% and 43 ± 20 days respectively, over the study period. Analysis of spatial pattern of SCE indicates a slightly greater reduction on the eastern side (~14 ± 2%) of the Andes Cordillera compared to the western side (~12 ± 3%). The downward SCE, SAL, and SCD trends identified in this study are likely to have adverse impacts on downstream water resource availability to agricultural and densely populated regions in central Chile and Argentina

THE TIBETAN PLATEAU SURFACE ENERGY BUDGET AND ITS TELECONNECTION WITH THE EAST ASIAN SUMMER MONSOON: EVIDENCE FROM GROUND OBSERVATIONS, REMOTE SENSING, AND REANALYSIS DATASETS

Estimations from meteorological stations indicate that the surface sensible heat flux over the Tibetan Plateau has been decreasing continuously since the 1980s. Modeling studies suggest that such change is physically linked to the weakening of the East Asian summer monsoon through Rossby wave trains. However, the relationship between the surface energy budget over the entire Tibetan Plateau and the East Asian summer monsoon rainfall has rarely been examined. The objective of this study is to quantify the relationship between the surface energy budget over the Tibetan Plateau and the East Asian summer monsoon, using ground observations, remote sensing, and reanalysis datasets with three specific questions: What are the spatiotemporal characteristics of the surface radiation and energy budgets over the Tibetan Plateau in recent decades? How does the interannual variation of the surface radiation and energy budgets correlate to, respond to, and impact the observed regional surface and atmospheric anomalies? And can the changes of the surface energy budget component over the Tibetan Plateau explain the weakening of the East Asian summer monsoon and associated precipitation changes in China? To address those questions, I 1) develop a fused monthly surface radiation and energy budgets dataset over the Tibetan Plateau using ground and satellite observations and reanalysis datasets; 2) analyze the spatial distribution of the fused surface radiation and energy budgets, and assess its correlations with the observed surface and atmospheric conditions over the Tibetan Plateau; and 3) test the hypothesis of whether the Asian summer monsoon rainfall is under the impact of the spring sensible heat flux over the Tibetan Plateau through correlation analysis, regression analysis, Granger causality test, and composite analysis. The root mean square errors from cross validation are 18.9 Wm-2, 10.3 Wm-2, 14.3 Wm-2 for the fused monthly surface net radiation, latent heat flux, and sensible heat flux. The fused downward shortwave irradiance, sensible heat flux, and latent heat flux anomalies are consistent with those estimated from meteorological stations. The associations among the fused surface radiation and energy budgets and the related surface anomalies such as mean temperature, temperature range, snow cover, and Normalized Difference Vegetation Index in addition to the atmospheric anomalies such as cloud cover and water vapor show seasonal dependence over the Tibetan Plateau. The decreased late spring sensible heat flux, which is sustained throughout the summer, has been associated with suppressed summer rainfall in the north of China and the north of Indian and enhanced rainfall in the west of India. The mechanism of those associations is found through a lower-level Rossby wave train as a result of anomalous sensible heating over the Tibetan Plateau. The decreased late spring sensible heat flux has also been associated with dry weather in the Yangtze River basin through a descending motion to the east of the Tibetan Plateau. This dissertation is the first synthesized analysis of the surface radiation and energy budgets at a spatial scale covering the entire Tibetan Plateau over a temporal period of two decades. The results of this study could contribute to a better understanding of the land-atmosphere interactions over the Tibetan Plateau, and the role of the Tibetan Plateau sensible heating in regulating the strength of the Asian summer monsoon. This study demonstrates a linkage between the spring sensible heat over the Tibetan Plateau and the Asian summer monsoon rainfall that affect about one fourth of the world's population, which has implications that will benefit local agriculture practices, disaster management, and climate change mitigation

Development of a 10-year (2001-2010) 0.1° data set of land-surface energy balance for mainland China

© Author(s) 2014. In the absence of high-resolution estimates of the components of surface energy balance for China, we developed an algorithm based on the surface energy balance system (SEBS) to generate a data set of land-surface energy and water fluxes on a monthly timescale from 2001 to 2010 at a 0.1 x 0.1° spatial resolution by using multi-satellite and meteorological forcing data. A remote-sensing-based method was developed to estimate canopy height, which was used to calculate roughness length and flux dynamics. The landsurface flux data set was validated against "ground-truth" observations from 11 flux tower stations in China. The estimated fluxes correlate well with the stations' measurements for different vegetation types and climatic conditions (average bias = 11.2 Wm-2, RMSE = 22.7 Wm-2). The quality of the data product was also assessed against the GLDAS data set. The results show that our method is efficient for producing a high-resolution data set of surface energy flux for the Chinese landmass from satellite data. The validation results demonstrate that more accurate downward long-wave radiation data sets are needed to be able to estimate turbulent fluxes and evapotranspiration accurately when using the surface energy balance model. Trend analysis of land-surface radiation and energy exchange fluxes revealed that the Tibetan Plateau has undergone relatively stronger climatic change than other parts of China during the last 10 years. The capability of the data set to provide spatial and temporal information on water-cycle and land-atmosphere interactions for the Chinese landmass is examined. The product is free to download for studies of the water cycle and environmental change in China