Satellite data and high-resolution regional simulations show that transported aerosol layers deposit dust at high elevations of high-mountain Asia (HMA), reducing snow’s light-reflecting property1.
This causes snow to absorb more sunlight, leading to snowmelt in HMA, an international team of researchers has found. The HMA is the largest repository of snow on Earth outside the poles, and caters to the annual freshwater needs of millions of people in South Asia.
This finding, the researchers say, is important for assessing snow mass trends and making predictions of freshwater resources in this region.
Scientists, including a researcher from the Indian Institute of Technology in Chennai, India, analysed the vertical distribution of dust-containing aerosol layers in HMA.
On a typical summer day, they found two distinct aerosol layers: a surface layer below 1,500 metres and an elevated aerosol layer (EAL) between 1,500 and 6,000 metres. After mid-March, dusty EALs arrive from arid regions located upwind of HMA, including Saudi Arabia, Pakistan, the Thar Desert and the Sahara.
The frequency of EALs reaching western HMA increases with altitude from two to five kilometres but decreases at higher altitudes. In contrast, the number of EALs reaching eastern HMA, including the central and eastern Himalayas, is much smaller, they report.
Analysis revealed the dominance of non-spherical dust particles in EALs over the Indus River basin, with higher proportions of coarse dust particles than black carbon. By late June, snow grains at higher elevations coarsen and increase absorption of sunlight, contributing to snowmelt, the researchers say.
References
1. Sarangi, C. et al. Dust dominates high-altitude snow darkening and melt over high-mountain Asia. Nat. Clim. Change. 10, 1045-1051 (2020) doi: 10.1038/s41558-020-00909-3
