Response of extreme precipitation to increasing extratropical cyclonic vortex frequency

自21世纪以来,热带外极端降水频次增加.随着中高纬度的显著增温,经向温度梯度减弱导致低层大气斜压性减小,由此产生的气旋型瞬变涡天气系统等活动减弱.然而,热力分布导致西风急流带变宽,经向环流加大,有助于行星尺度波动相关的涡旋异常增加,如东北冷涡,中亚涡,东欧-地中海涡,北美涡等,进而增加了气旋涡影响范围的极端降水频次.在未来变暖背景和1.5℃增温的目标内,热带外气旋涡增强会进一步促进极端降水发生.

Since the 2000 s,extratropical extremes have been more frequent,which are closely related to anomalies of planetary-scale and synoptic-scale systems.This study focuses on a key synoptic system,the extratropical cyclonic vortex(ECV)over land,to investigate its relations with extreme precipitation.It was found that ECVs have been more active post-2000,which has induced more extreme precipitation,and such variation is projected to persist along with increasing temperature within 1.5℃of global warming.An enhanced quasi-stationary vortex(QSV)primarily contributes to the ECV,rather than inactive synoptic-scale transient eddies(STEs).Inactive STEs respond to a decline in baroclinicity due to the tendency of the homogeneous temperature gradient.However,such conditions are helpful to widening the westerly jet belt,favoring strong dynamic processes of quasi-resonant amplification and interaction of STEs with the quasi-stationary wave,and the result favors an increasing frequency and persistence of QSVs,contributing to extreme precipitation.