MODELING STUDIES ON THE IMPACTS OF THE HINDU KUSH MOUNTAINS AND IRANIAN PLATEAU ON THE CLIMATE EVOLUTION IN MONSOONAL SOUTH ASIA AND ARID CENTRAL ASIA

The uplifts of the Tibetan Plateau and the adjacent mountain ranges have distinct and complex influences on the evolution of Asian climate. According to accumulated paleoclimate proxies, the onset of the South Asian summer monsoon (SASM) could be traced back to the Eocene. Geological records also reveal stages of remarkable intensification of the SASM in the early and late Miocene. Meanwhile, tectonic evidence shows that the Hindu Kush Mountains (HKM) and the Iranian Plateau (IP) had experienced dramatic uplift since 10~ 12 Ma. However, whether and how the HKM and the IP, as two topographies naturally separating the moist South Asia and arid Central Asia (ACA), influence the evolution and differentiation of the climate over the South Asia and the Central Asia are still unknown. In this study, we conducted a series of sensitivity experiments to systematically evaluate the impacts of the HKM and the IP on the climate over the South Asia and Central Asia, by utilizing a general circulation model with high resolution. The result shows that both of the uplift of the HKM and the IP contributed largely to the strengthening of the SASM and the aridity over the ACA. Comparatively, the intensification and northward expansion of the SASM are dominated by the inclusion of the HKM. The HKM-induced increase in precipitation over the South Asia in summer accounts for 65. 6% of the increase induced by the combined HKM-IP. With the addition of the HKM, the precipitation is significantly intensified over the whole South Asian regions north of 15° N, especially the central and northwestern Indian subcontinent. In addition, the southwesterly winds over the Arabian Sea and southerlies over the northwestern Indian subcontinent are significantly intensified. Compared with the effects of the HKM, the inclusion of the IP results in more intense decrease in precipitation over the ACA and the decrease is predominant in winter. The IP-induced decrease in precipitation over the ACA in winter accounts for 71.4% of the total decrease induced by the combined HKM-IP. With the inclusion of the IP, the prevailing westerlies over the ACA in winter is significantly weakened and the precipitation is thus suppressed. Our result implies that the strengthening of the SASM in the late Miocene documented by paleoclimate proxies might closely related to the tectonic uplift of the HKM and the IP.