Relationship between the Asian Westerly Jet Stream and Summer Rainfall over Central Asia and North China: Roles of the Indian Monsoon and the South Asian High

Abstract

Diagnostic analyses are performed to investigate the relationship between the upper-level Asian westerly jet stream (AWJS) and the associated rainfall pattern over the AWJS region in boreal summer on interannual time scales. Results show an out-of-phase rainfall variation over central Asia (CA) and north China (NC), which is closely related to the southeast–northwest (SE–NW) shift of the AWJS. The physical mechanisms on the relationship between the AWJS and the rainfall pattern are revealed by exploring the effects of the Indian summer monsoon (ISM) and the South Asian high (SAH). It is found that the SE–NW shifts of the AWJS and SAH associated with the ISM lead to the anomalous circulations over the midlatitudes in the AWJS region and cause rainfall anomalies over CA and NC. A weak ISM results in a southeastward shift of SAH, which is responsible for a southeastward shift of the AWJS. The anomalous atmospheric circulation associated with the southeastward located SAH produces anomalous updrafts (downdrafts) over the western (eastern) AWJS region, resulting in increased rainfall over CA and decreased rainfall over NC. It is proposed that the upper-level system SAH plays a crucial role in the teleconnection among the summer rainfall over the midlatitude AWJS region and ISM region.