WESTERLY JET AND ITS EFFECTS ON PRECIPITATION IN THE THIRD POLE

Abstract

This study explores the upper troposphere and monsoon-influenced climate dynamics of the Tibetan plateau (TP) and its surrounding regions in East Asia, also known as the Third Pole, for the summer season (JJA) and the period of 1980-2019. The domain is characterized by mountainous and remote environments, where climatological observations are sparse. The complicated topography is dynamically and thermally modifying the atmosphere, especially during the summer months with the onset of the monsoon season, which in turn alters upper troposphere structures such as the East Asian Subtropical Westerly Jet (EASWJ). The study's primary focus was on the key features (position and strength) of EASWJ and its effects on precipitation patterns as seen in high resolution regional climate models (RCM) and modern global reanalyses. More specifically, the study illustrated how each reanalysis performs in locating the upper troposphere westerly jet and in determining its intensity values. 7 global reanalyses were utilized in the current work, specifically, ERA5, ERA-Interim, JRA-55, MERRA-2, NCEP-1, NCEP-2, and CFSR covering the period 1980-2019. 9 km simulations done by WRF during the same period are also analyzed. While there was generally high agreement on its meridional variability and intensity, the greatest uncertainties were shown to be about its longitudinal position and intensity over complex topography. Generally, reanalyses agree with each other quite well regarding the response of precipitation pattern to the changes in EASWJ, both in position and strength. However, one of the higher resolution reanalysis, CSFR, displayed disparities in precipitation patterns, which is due to a different pattern of the response of the water vapor transport to the change in EASWJ.