Light absorbing impurity deposition over the Himalayan-Karakoram-Hindu Kush-Tibetan cryosphere: A review and satellite-based characterization

摘要

Light absorbing impurities such as black carbon and dust reduce the reflectance of snow/ice surface. The impurities absorb the incoming solar radiation thereby accelerating snow aging and melting. This further accelerates the processes of snow albedo reduction and melting. A recently-conducted ice core study in Mera Peak shows that annual dust mass fluxes (10.4+/-2.8 g m~(-2) yr~(-1)) are a few orders of magnitude higher than black carbon (7.9+/-2.8 g m~(-2) yr~(-1)). A similar study conducted in the Tibetan Plateau showed a decrease in the amount of mineral dust deposition since 1940s indicating that the increased glacier melt can be attributed to increased black carbon emission than dust. The concentrations of black carbon and dust peak during the pre-monsoon season. Spectral reflectance curves derived from satellite imagery for the Himalayan Tibetan Plateau showed domination of dust-induced solar absorption during the pre-monsoon season. Spatial distribution of reflectance also depends on the transport pathway of impurities, with the south western Hindu Kush and Himalaya experiencing greater dust influx, deposition and snow albedo reduction than northern regions of Karakoram. In this study, we characterize the light absorbing impurities deposited in Himalayan regions using multi spectral data from MODIS and LANDSAT. On comparing the spectral reflectance curves derived from MODIS and LANDSAT for the overlapping periods and areas and by observing the VIS-NIR gradient of spectral reflectance, determination of the type of light absorbing impurity, mainly mineral dust, and its relation to snow properties are derived.