A Mechanism for the Reversal of Long-term Average Vertical Velocities around East Asia during the Cold Season

Abstract

The formation mechanism of a systematic vertical-velocity reversal over East Asia was studied during the cold season by using MU radar data and global analysis data. Although active gravity waves may modify the vertical wind pattern in the stratosphere, clear reversal patterns are also observed in the periods when gravity waves are quiet. The frontogenesis function is positive in all the reversal periods. These facts suggest that the reversal is a part of the frontogenetically forced secondary circulations associated with an upper tropospheric jet streak. Calculation of the geostrophically forced secondary circulation following frontogenesis theory supports this conclusion.