Satellite observations of darkening of Himalayan snowpack by desert dust deposition
The Himalayas are among the largest ice-covered regions of the Earth's surface, outside the poles, and their glaciers form a source of major rivers in Asia, that serve a large population base downstream. Recent studies have shown climate warming, accelerated snowmelt over the elevated Himalayas as well as perturbations to the Asian summer monsoon rainfall, partly due to enhanced absorption of solar radiation by natural and anthropogenic aerosols.
Figure 1: (a) Satellite image of a major dust outbreak over South Asia, on 9 June 2003, leading to dust-capped snow surface in the western Himalayas (highlighted in red); (b) Top of Atmosphere spectral reflectivity over dust-capped western Himalayas (red) and relatively clean Karakoram snow surface; (c) Intra-seasonal variations of spectral reflectivity over western Himalayas snow surface; (d) theoretical calculations of reflectivity of pure snow mixed with different levels of dust impurity.
Prior to the onset of the summer monsoon, mineral dust lifted from Southwest Asian deserts and from as far as the Arabian Peninsula, is transported over South Asia on a seasonal basis. Mixed with anthropogenic pollution, mineral dust forms a widespread vertically extended brown haze lapping against the southern slopes of the Himalayas. Episodic dust plumes are also advected over the Himalayas, leading to dust-capped snow surfaces. Fundamentally, aerosol deposition over snow surface can lead to accelerated snowmelt due to darkening of snow surface i.e., reduction of snow albedo and enhanced absorption of solar radiation. From an observational viewpoint, this study utilizes spaceborne measurements of reflectivity over the Himalayan snow cover to estimate the reduction of snow albedo induced by dust deposition.
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