Constraining MODIS snow albedo at large solar zenith angles: Implications for the surface energy budget in Greenland
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 non-s...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.227.4201 http://dust.ess.uci.edu/xianweiw/publications/WangX_Zender_2010_JGR_Constraining_MODIS_snow_albedo_at_large_SZA.pdf |
| Summary: | 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 non-summer months. In contrast, poor quality MODIS retrievals provide adequate spatio-temporal coverage, but are not recommended for use at large solar zenith angles (SZAs) where they have a systematic low bias. We introduce an empirical adjustment to the poor quality data based on high quality reference albedos and constrained by GC-Net data and theory, and use the adjusted data to improve estimates and fill-in gaps of the yearround, Greenland-wide, albedo and surface energy budget. For observations made with SZAs between 55 ° and 75°, the mean differences (MODIS minus GC-Net) between our adjusted MODIS albedo and GC-Net measurements are-0.02 and-0.03 at Saddle and Summit, respectively, compared to-0.05 and-0.08 between the unadjusted MODIS albedo and GC-Net measurements. The adjusted MODIS snow albedos are usually between 0.75 and 0.87 over dry snow when SZA is larger than 55°, and they reduce unrealistic seasonal and meridional trends associated with MODIS retrievals at large SZA, defined as SZA> 55 ° and 70°, respectively, for low- and high-quality retrievals. The impact of the adjusted albedo on the surface energy budget, relative to the unadjusted albedo from all MODIS data, is smallest (-0.7±0.1W/m 2) in June, and largest (-6.2±0.9 W/m 2) in September for the black-sky albedo (BSA). The mean annual absorbed solar radiation (ASR) |
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