The influence of the tibetan plateau elevation on the global and asian monsoons
Abstract
It has been long hypothesized that large-scale topographic changes, such as the surface uplift of the Tibetan Plateau, impacts the development of the South Asian and East Asian monsoons and influences other monsoon regions. However, recent modeling has shown that spatial distribution of the global monsoon, which includes the South Asian and East Asian monsoons is largely unaffected by the elevation of the plateau. In this study, we present results from a series of modern day simulations using CESM1.0 in a mixed-layer (slab ocean) configuration. The Tibetan Plateau height is varied from double that of the modern maximum plateau elevation (~9000 m), down to near sea level elevation (~10 m). Overall we find that the Asian monsoon system exists regardless of the plateau's elevation but its impact on Asia's hydrological system is undeniable. Specifically, reducing plateau elevation increases precipitation rates over Southern Asia and behind the plateau, but decreases orographic precipitation. In addition, when we remove the Tibetan Plateau, diabatic heating produced over the Himalayan Mountains and Tibetan Plateau disappears, and as a result, the integrated mean eddy moisture flux over Southern Asia is reduced. In contrast, our double topography simulation shows a decrease in precipitation over Southern and Eastern Asia, but an increase in orographic precipitation. Furthermore, we see an increase in diabatic heating in our double plateau simulation, which contributes to an increase in mean integrated eddy moisture flux over Southern Asia. Our study suggests that diabatic heating produced by the plateau is an important mechanism that draws moisture over Asia, while removing the plateau reduces orographic precipitation and redistributes moisture over Southern Asia and further inland. In general, global surface temperature decreases linearly as we increase the Tibetan Plateau's elevation. However, using a monsoon index based on the ratio of summer precipitation to annual precipitation, we show that the distribution of the global monsoon does not change substantially and the plateau's impact on the global circulation is relatively weak.
Degree
M.S.
Advisors
Agee, Purdue University.
Subject Area
Climate Change|Environmental Geology|Meteorology
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