Abstract
It has been demonstrated in climate models that both the Indian and East Asian summer monsoons (ISM and EASM) are strengthened by the uplift of the entire Asian orography or Tibetan Plateau (TP) (i.e. bulk mountain uplift). Such an effect is widely perceived as the major mechanism contributing to the evolution of Asian summer monsoons in the Neogene. However, geological evidence suggests more diachronous growth of the Asian orography (i.e. regional mountain uplift) than bulk mountain uplift. This demands a re-evaluation of the relation between mountain uplift and the Asian monsoon in the geological periods. In this study, sensitivity experiments considering the diachronous growth of different parts of the Asian orography are performed using the regional climate model COSMO-CLM to investigate their effects on the Asian summer monsoons. The results show that, different from the bulk mountain uplift, the regional mountain uplift can lead to an asynchronous development of the ISM and EASM. While the ISM is primarily intensified by the thermal insulation (mechanical blocking) effect of the southern TP (Zagros Mountains), the EASM is mainly enhanced by the surface sensible heating of the central, northern and eastern TP. Such elevated surface heating can induce a low-level cyclonic anomaly around the TP that reduces the ISM by suppressing the lower tropospheric monsoon vorticity, but promotes the EASM by strengthening the warm advection from the south of the TP that sustains the monsoon convection. Our findings provide new insights to the evolution of the Asian summer monsoons and their interaction with the tectonic changes in the Neogene.
Highlights
The Tibetan Plateau (TP) and the surrounding orography, which peak above 8,000 m, cover more than 70 % of the land surface in Asia
This article is published with open access at Springerlink.com. It has been demonstrated in climate models that both the Indian and East Asian summer monsoons (ISM and EASM) are strengthened by the uplift of the entire Asian orography or Tibetan Plateau (TP)
No mountains (B250 m above sea level) The southern TP is added compared to M00 The central TP is added compared to MsTibet The northern and southeastern TP are added compared to McTibet The Zagros and Hindu Kush Mountains are added compared to MnTibet The Tianshan and Gobi Altai Mountains are added compared to MZagros 50 % of the present-day height of all the orography The present-day height of all the orography
Summary
The Tibetan Plateau (TP) and the surrounding orography, which peak above 8,000 m, cover more than 70 % of the land surface in Asia. In East Asia, it is characterized by the intensification and northward penetration of the low-level southerly flow, the inland-ward expansion of the Western North Pacific (WNP) Subtropical High and the rain front along its northern periphery (e.g. An et al 2001; Jiang et al 2008; Kitoh 2004; Liu and Yin 2002) Such effects on the ISM and EASM have been largely attributed to the diabatic heating of the uplifted plateau which maintains an upper tropospheric thermal high pressure over the TP. The model domain covers the Asian monsoon area (0–60°N and 50–140°E) with a spatial resolution of 1° 9 1° on the rotated model grid (the north pole is at 60°N, 80°W) and 20 vertical levels
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