The Dynamic Plateau Monsoon Index and Its Association with General Circulation Anomalies

Based on monthly ECMWF reanalysis-Interim （ERA-Interim） reanalysis data, along with monthly precipitation and temperature data, the Dynamic Plateau Monsoon Index （DPMI） is defined. The results of a contrast analysis of the DPMI versus the Traditional Plateau Monsoon Index （TPMI） are described. The response of general circulation to northern Qinghai-Xizang Plateau summer monsoon anomalies and the correlation of the DPMI with general circulation anomalies are investigated. The results show that, the DPMI reflected meteorological elements better and depicted climate variation more accurately than the TPMI. In years when the plateau summer monsoon is strong, the low over the plateau and the trough near the eastern coast of Asia are deeper and higher than normal over South China. This correlation corresponds to two anomalous cyclones over the plateau and the eastern coast of Asia and an anomalous anticyclone in South China. The plateau and its adjacent regions are affected by anomalous southwesterly winds that transport more moisture to South China and cause more precipitation. The lower reaches of the Yangtze River appear to receive more precipitation by means of the strong westerly water vapor flow transported from the ＂large triangle affecting the region＂. In years when the plateau summer monsoon is weak, these are opposite. The plateau monsoon is closely related to the intensity and position of the South Asian high, and the existence of a teleconnection pattern in the mid-upper levels suggests a possible linkage of the East Asian monsoon and the Indian monsoon to the plateau summer monsoon.

SENSITIVITY EXPERIMENTS ON INFLUENCES OF UPLIFT OF QINGHAI-XIZANG PLATEAU ON CIRCULATION IN SUMMER

A coupled general circulation model in a zonal belt is used to simulate the variation of circulation features in the process of uplift of the Qinghai-Xizang Plateau.The results reveal that the heating rates of the Plateau increase with the rising of the Plateau topography,and the latent heating compo- nent in the heating field tends to be the most important heating factor.The uplift of the Plateau en- hances the upward motion,intensifies the pressure systems in the high and low level atmosphere,re- inforces Southeast Asia monsoon strength,increases precipitation and severely decreases the surface temperature over the Qinghai-Xizang Plateau. However.the basic structures of the general circulation do not vary much due to the uplift of the Qinghai-Xizang Plateau.and it is the land-sea distribution that is the decisive factor to form the pre- sent circulation pattern and monsoon.Therefore,to simulate the paleoclimate during the geological period people should consider more factors,especially the land-sea distribution.