Letter

Nature 463, 218-222 (14 January 2010) | doi:10.1038/nature08707; Received 28 April 2009; Accepted 18 November 2009

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

William R. Boos1 & Zhiming Kuang1,2

  1. Department of Earth and Planetary Sciences,
  2. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

Correspondence to: William R. Boos1 Correspondence and requests for materials should be addressed to W.R.B. (Email: billboos@alum.mit.edu).

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 5km 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 timescales1, 2, 3, 4, 5. 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.

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