Late Miocene upward and outward growth of eastern Tibet and decreasing monsoon rainfall over the northwestern Indian subcontinent since ∼10 Ma

Authors

  • Peter Molnar,

    Corresponding author
    1. Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA
    2. Cooperative Institute for Research in Environmental Sciences, Boulder, Colorado, USA
    • Corresponding Author: P. Molnar, Department of Geological Sciences, University of Colorado at Boulder, Boulder, CO 80309, USA. (molnar@colorado.edu)

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  • Balaji Rajagopalan

    1. Cooperative Institute for Research in Environmental Sciences, Boulder, Colorado, USA
    2. Department of Civil, Environmental, and Architectural Engineering, University of Colorado at Boulder, Boulder, Colorado, USA
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Abstract

[1] Many geologic observations suggest that the eastern portion of the Tibetan Plateau has expanded eastward and grown in height over the past 15-10 Ma, and other observations suggest that climate over the northwestern Indian subcontinent (“NW India”) became more arid between ∼11 and 7 Ma. We suggest that they are linked: higher terrain increased orographic precipitation over eastern Tibet, which diabatically heated the atmosphere there; that heating then forced subsidence to the west via the mechanism proposed by Rodwell and Hoskins; and subsidence suppressed rainfall. Simple Gill-model calculations for a heat source displaced from the equator show such subsidence, and a regression of July-August outgoing long-wave radiation (OLR) over southeastern Tibet with rainfall shows a negative relationship between eastern Tibet and NW India, consistent with the proposed link between growth of eastern Tibet and diminished South Asian monsoon rainfall over the northwestern Indian subcontinent.

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