2B.1
Impacts of dust and black carbon on accelerated melting of seasonal snowpack over the HimalayasóCauses and Consequences (Invited Presentation)

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Monday, 3 February 2014: 1:30 PM
Room C207 (The Georgia World Congress Center )
William K. M. Lau, NASA/GSFC, Greenbelt, MD

In this talk, I will review past and ongoing work by the interdisciplinary team at GSFC on observations and modeling of possible causes and consequences of accelerated melting of Himalayan seasonal snowpack. Observational and modeling studies by the team have significantly advanced the basic premises that absorbing aerosols (dust and black carbon) can cause accelerated melting of Himalayan snowpack via a) atmospheric heating and induced feedback via the Elevated Heat Pump (EHP) effect, b) snow - darkening (SND) through surface albedo reduction by impurities in snow, and that c) snow cover and altered surface reflectance through EHP and SND are strong driver of climate variability and water resources of the Asian monsoon. Trend analysis of atmospheric temperature data from the Microwave Sounding Unit (MSU) have shown a positive multi-decadal trend of tropospheric heating over the western Himalayas in boreal spring, most pronounced in May, which can be attributed to aerosol atmospheric heating, consistent with the EHP effect. Characteristic spectral signature of dust impurities in Himalayan snowpack have been detected from MODIS surface reflectance data, with the most pronounced signal found over the southern slopes of the Himalayas, confirming earlier results from in-situ observations. A more recent study has found that Himalayan/Tibetan snow cover is an integral component of the South Asian monsoon in that EHP and SND may have contributed not only to long-term climate change, but also to strong interannual variability of monsoon rainfall. Composite analyses show that years with high (low) atmospheric loading of aerosol over the Indo-Gangetic Plain are associated with decreased (increased) spring snow water equivalent, with EHP and SND contributing to amplification of La Nina (El Nino) influence on the South Asian monsoon rainfall. Preliminary results from another ongoing study on SND impacts on Himalayan and Eurasian snow cover on warm season climate through atmosphere-land hydrology feedback will also be discussed.