An Extreme Predecessor Rain Event in Central China Amplified by Upper-Level Jet Streak

Abstract A comprehensive study is conducted on a predecessor rain event (PRE) closely associated with the upper-level jet (ULJ) in central China during July 2021, utilizing the Weather Research and Forecasting (WRF) Model. The ULJ and precipitation patterns are reasonably reproduced in the control experiment. In the sensitivity experiment (NOULJ), the ULJ is largely suppressed by the piecewise potential vorticity inversion method. The comparison of the two simulations indicates that the ULJ promotes the development of secondary circulation, lower-level jet (LLJ), moisture transport, and atmospheric instability. Synergistic effects among these processes amplify this PRE. The strong updrafts in the precipitation region are closely associated with the inverse secondary circulation that develops on the south side of ULJ entrance. The upper-level mass divergence associated with the ULJ enhances the lower-level convergence, promoting the development of lower-level vorticity and LLJ. The LLJ facilitates moisture transport into the precipitation region and increasing atmospheric instability. In contrast, the precipitation in NOULJ is decreased by 34% due to the weakening of favorable conditions.