Seasonal variation of westerly jet over Asia in Last Glacial Maximum: Role of the Tibetan Plateau heating

The westerly jet (WJ) is an important component of atmospheric circulation, which is characterized by prominent seasonal variations in intensity and position. However, the response of WJ over Asia during the Last Glacial Maximum (LGM) is still not clear. Using general circulation model experiments, the seasonal behaviors of WJ over Central Asia and Japan are analyzed in this paper. The results show that, compared to present day (PD), the WJ presents a complicated response during the LGM, both in intensity and position. Over Central Asia, it becomes weaker in both summer and winter. But over Japan, it is enhanced in summer but becomes diminished in winter. In terms of position, the WJ over Central Asia shifts southwards in both summer and winter, while the WJ over Japan moves southwards in summer but does not change obviously relative to PD in winter. Such WJ changes are well explained by meridional temperature gradients in high troposphere, which is closely linked to seasonal thermal anomalies over the Tibetan Plateau (TP). Despite of cooler LGM condition, the anomalous warming center over TP becomes stronger in summer. Derived from the heat budget equation, the stronger heating center is mainly caused by the weaker adiabatic cooling generated from ascending motion over south of TP. In winter, the cooling over TP is also strengthened and mostly owes to the subsidence-induced weaker adiabatic heating. Due to the importance of WJ, the potential role of TP thermal effect should be focused when explaining the East Asian climate change during the LGM.