Abstract
The impact of snow darkening by deposition of light absorbing aerosols (LAAs) on snow cover over the Himalaya-Tibetan-Plateau (HTP) and influence on the Asian summer monsoon are investigated using the NASA Goddard Earth Observing System Model Version 5 (GEOS-5). We find that during April-May-June, deposition of LAAs on snow leads to a reduction in surface albedo, initiating a sequence of feedback processes, starting with increased net surface solar radiation, rapid snowmelt in 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 is amplified by increased dust aerosol heating, and subsequently amplified by latent heating from enhanced precipitation over the Himalaya foothills and northern India, via the Elevated Heat Pump (EHP) effect during June-July-August. The reduced snow cover in the HTP anchors 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 wavetrain over East Asia, leading to weakening of the subtropical westerly jet, and northward displacement and intensification of the Mei-Yu rainbelt. Our results suggest that atmosphere-land heating induced by LAAs, particularly desert dust play a fundamental role in physical processes underpinning the snow-monsoon relationship proposed by Blanford more than a century ago.
Highlights
Since Blanford [1] first reported a possible inverse relationship, that is, an increased Himalayan snow cover linked to a weakened South Asian summer monsoon (SASM), nearly a century had elapsed before researchers began the rigorous pursuit to better understand the relationship using modern satellite observations and global climate models
Included in this strand were studies showing that the different patterns of Eurasian snow cover were controlled by various modes of natural climate variability, and that during certain periods, increased SASM precipitation was found to be preceded by above-normal winter and spring snow cover over the Tibetan Plateau, contrary to the Blanford hypothesis [18,19]
Based on numerical simulations using the NASA Goddard Earth Observing System Model Version 5 (GEOS-5) climate model, the authors examined the possible impact of snow-darkening effects (SDE) by deposition of light-absorbing aerosols (LAAs) on snow cover over the Himalayas–Tibetan Plateau (HTP), and the subsequent influence on the Asian summer monsoon
Summary
Since Blanford [1] first reported a possible inverse relationship, that is, an increased Himalayan snow cover linked to a weakened South Asian summer monsoon (SASM), nearly a century had elapsed before researchers began the rigorous pursuit to better understand the relationship using modern satellite observations and global climate models. Niño Southern Oscillation (ENSO) on both snow cover and monsoon, and that the relationship was strongly masked by the influence of ENSO [11,12,13,14,15,16,17] Included in this strand were studies showing that the different patterns of Eurasian snow cover were controlled by various modes of natural climate variability, and that during certain periods, increased SASM precipitation was found to be preceded by above-normal winter and spring snow cover over the Tibetan Plateau, contrary to the Blanford hypothesis [18,19]. Others have surmised that a weakening of the snow–monsoon relationship in recent decades may be related to a weakened ENSO–monsoon relationship, possibly due to climate change [20,21]
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