Dominant control of the South Asian monsoon by orographic insulation versus plateau heating

Abstract

The Tibetan plateau, like any landmass, emits energy into the atmosphere in the form of dry heat and water vapour, but its mean surface elevation is more than 5 km above sea level. This elevation is widely held to cause the plateau to serve as a heat source that drives the South Asian summer monsoon, potentially coupling uplift of the plateau to climate changes on geologic timescales. Observations of the present climate, however, do not clearly establish the Tibetan plateau as the dominant thermal forcing in the region: peak upper-tropospheric temperatures during boreal summer are located over continental India, south of the plateau. Here we show that, although Tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model, the large-scale South Asian summer monsoon circulation is otherwise unaffected by removal of the plateau, provided that the narrow orography of the Himalayas and adjacent mountain ranges is preserved. Additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm, moist air over continental India from the cold and dry extratropics. These results call for both a reinterpretation of how South Asian climate may have responded to orographic uplift, and a re-evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades.

Influence of the Tibetan Plateau uplift on the Asian monsoon-arid environment evolution

“…Boos and Kuang [11], by removing the main body of the TP and retaining only the narrow terrain of the Himalayas in their numerical experiments, found that the simulated South Asian summer monsoon, precipitation and large-scale atmospheric circulation structures were similar to the simulated results with all topography retained. Thus they concluded that the dynamic barrier effect caused by the uplift of the Himalayas was much more important than the thermal effect of the TP for the formation and development of the South Asian summer monsoon.…”

“…This has led some scholars to speculate that to what extent the East Asian Monsoon should be regarded as monsoon [69]. Subsequently, the work by Boos and Kuang [11] was challenged. Wu et al [77] pointed out that though their numerical experiments removed the main body of the TP and retained only the Himalayas and adjacent narrow terrain, the surface sensible heat flux of the Himalayas was retained as well, To examine the effect of the uplift of southern TP…”

“…It is not difficult to understand the existence of regional differences in the plateau uplift. Many recent studies with numerical simulations were exactly aimed at revealing the climatic and environmental effects of different sub-regional uplift of the TP [11,12,[75][76][77]. With the topography of southern or northern TP, western or eastern Asia, and even Africa being taken into consideration, these studies examined the role of sub-regional uplift in the formation and evolution of the Asian monsoon climate.…”

“…With respect to modeling study, increasinglysophisticated numerical experiments, from the bulk-plateau uplift experiment in the past to recent phased uplift and sub-regional uplift experiments (e.g. [9][10][11][12]), have greatly deepened our understanding of the influence of plateau uplift forms on the climate change in different Asian regions and underlying mechanisms. However, due to a number of uncertainties in recognizing various feedback effects, the nonlinear response of climatic and environmental changes to the uplift, and scale superimposition and multi-factor comprehensive effects and so on during the uplift process, there are a number of problems worthy of further study and discussion, and new problems are emerging constantly.…”

A late Eocene palynological record of climate change and Tibetan Plateau uplift (Xining Basin, China)

“…Climate models show that uplift of the Tibetan Plateau and the redistribution of land and sea, associated with the continentcontinent collision of India and Asia, caused continental aridification and intensification of the monsoons (Ramstein et al, 1997;Boos and Kuang, 2010). As a result, paleoenvironmental records have invariably associated Tibetan and Himalayan uplift with evidence for aridification north of the Tibetan Plateau and monsoon intensification to the south (e.g.…”