Impact of Snow Darkening by Deposition of Light-Absorbing Aerosols on Snow Cover in the Himalayas-Tibetan Plateau and Influence on the Asian Summer Monsoon: A Possible Mechanism for the Blanford Hypothesis

The impact of snow darkening by deposition of light-absorbing aerosols (LAAs) on snow cover over the Himalayas-Tibetan Plateau (HTP) and the influence on the Asian summer monsoon were investigated using the NASA Goddard Earth Observing System Model Version 5 (GEOS-5). The authors found that during April-May-June, the deposition of LAAs on snow led to a reduction in surface albedo, initiating a sequence of feedback processes, starting with increased net surface solar radiation, rapid snowmelt in the HTP and warming of the surface and upper troposphere, followed by enhanced low-level southwesterlies and increased dust loading over the Himalayas-Indo-Gangetic Plain. The warming was amplified by increased dust aerosol heating, and subsequently amplified by latent heating from enhanced precipitation over the Himalayan foothills and northern India, via the elevated heat pump (EHP) effect during June-July-August. The reduced snow cover in the HTP anchored the enhanced heating over the Tibetan Plateau and its southern slopes, in conjunction with an enhancement of the Tibetan Anticyclone, and the development of an anomalous Rossby wave train over East Asia, leading to a weakening of the subtropical westerly jet, and northward displacement and intensification of the Mei-Yu rain belt. The authors' results suggest that the atmosphere-land heating induced by LAAs, particularly desert dust, plays a fundamental role in physical processes underpinning the snow-monsoon relationship proposed by Blanford more than a century ago.