Relationships between the West Asian subtropical westerly jet and summer precipitation in northern Xinjiang

Yong Zhao,Wen Huo,HongJun Li,Qing Yang,MinZhong Wang,AnNing Huang

doi:10.1007/s00704-013-0948-3

Yong Zhao, Wen Huo + Show 4 more

Open Access

https://doi.org/10.1007/s00704-013-0948-3

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Abstract

The relation between the spatial and temporal variations of the West Asian subtropical westerly jet (WASWJ) and the summer precipitation in northern Xinjiang has been explored using the NCEP/NCAR reanalysis data and the summer precipitation data at 43 stations in northern Xinjiang during 1961 to 2007. Results show that the position of the WASWJ is more important than its strength in influencing the summer precipitation in northern Xinjiang. When the jet position is further south, the anomalous southwesterly flow crossing the Indian subcontinent along the southern foothill of the Tibetan Plateau is favorable for the southwestward warm and wet air penetrating from low latitudes into Central Asia and northern Xinjiang and more rainfall formation. Further analysis shows that the interannual variations of the jet position are well correlated with the Arctic Oscillation (AO). In the weak AO years, the middle to upper troposphere becomes colder than normal and results in an anomalous cyclonic circulation at 200 hPa over Western and Central Asia, which enhances the westerly wind over middle and low latitudes and leads to the WASWJ located further south.

Highlights

In recent decades, changes in mean precipitation across many regions have been documented (IPCC 2007)
Different from the East Asian subtropical westerly jet which has its maximum between 80 and 130° E, this westerly jet is defined as the West Asian subtropical westerly jet (WASWJ)
4 Conclusions and discussions Previous studies have identified an increase of summer rainfall over Xinjiang in recent decades (Mao et al 2006; Zhao et al 2010), but there is not enough understanding on the processes responding to such an increase

Summary

Introduction

Changes in mean precipitation across many regions have been documented (IPCC 2007). The subtropical westerly jet over the northern hemisphere is an important planetary scale atmospheric circulation pattern in the upper troposphere. It is one of the critical systems influencing the weather and climate in China and the Asian-Pacific regions, with three active centers over Asia (the Caspian Sea, Tibetan Plateau (80–100° E) and the Asian-Pacific regions) in summer (Yang et al 2008a; Schiemann et al 2009). Previous studies were more focused on eastern China and Asian-Pacific regions, less attention has been paid to the connection between the subtropical westerly jet and summer precipitation in the arid region.

Position and strength of the West Asian subtropical westerly jet

Relationship between the WASWJ and summer precipitation in northern Xinjiang

Relationship between the Arctic Oscillation and the WASWJ position

Conclusions and discussions