Mesoscale Moisture Transport in Determining the Location of Daytime Convection Initiations Clustered in Time and Space Over Southern China

Abstract

AbstractConvective initiation (CI) episodes are defined as a series of CIs that occur in clusters in time and space, and their prediction remains a challenge due to their complex mechanisms. In the present study, high‐resolution convection‐permitting simulations and observations were conducted to investigate the source of inhomogeneous instability for a cluster of daytime CIs gathering in a northeast‐southwest oriented region in South China where the convergence boundary for lifting was not evident. In the region of the CI episode, low‐level water vapor was enhanced significantly, which thus induced the heterogeneity of convective available potential energy. The enhanced moisture and instability in the CI episode region were caused by a mesoscale anticyclonic moisture channel. Mesoscale moisture transport formed under both the inertial oscillation of ageostrophic winds and the mesoscale high‐pressure disturbances in the daytime. The revealed mechanism is further confirmed by sensitivity experiments, where mesoscale anticyclonic transport is highly sensitive. Water vapor transport was affected by the evolution of mesoscale pressure disturbances and dominated the location and shape of the CI episode. Stronger mesoscale pressure disturbances resulted in the subsequent mesoscale anticyclonic airflow coming from various high‐pressure systems and conveying moisture farther east, and therefore, a CI episode occurred farther east by dozens to hundreds of kilometers. The climatology of the daytime CI episode also showed that the various mesoscale moisture transports confined moisture within the CI episode regions under weak convergence.