A positive climatic feedback mechanism for Himalayan glaciation

Glaciation at elevated sites in low latitudes has the potential to play an important role in the global radiation budget because the magnitudes of incoming and reflected shortwave radiation are so large. A climatic mechanism is presented which provides a positive feedback for glaciation in the Himalayan mountains. A higher bare surface albedo in the Himalayas induces an atmospheric circulation response that consists of cooling and descent over the Himalayas and warming and a contrasting air mass uplift to the west over the Persian Gulf and the Arabian peninsula. Although annual mean rainfall over the subcontinent south of the Himalayas decreases, the summer southwesterly monsoon winds are stronger over the mountains in northwestern India and carry more moisture to higher elevations where it is precipitated as snow. Conversely in wintertime, the northeasterly monsoon winds are weakened over the Himalayas and surface wind convergence and snowfall are increased there. Increased snowfall in the mountains expands the surface area of the high albedo region in both seasons, leading to a positive feedback. The peak amplitude of this feedback is ultimately regulated by springtime melting rates. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.