Could Developing Frontal Rainfall Influence Warm‐Sector Rainfall?

Abstract

Abstract Forecasting warm‐sector rainfall (WR) remains a major challenge, primarily due to weak synoptic forcing. Through cloud‐permitting numerical simulations, in addition to direct triggering mechanism from low‐level jets, we identify the important role of gravity waves in a heavy WR event in South China via convective preconditioning. The preconditioning manifests as mid‐level moistening and destabilization with wave‐like variations. This process is driven by fast‐propagating (∼24 m s−1) n = 2 waves, associated with lower‐tropospheric ascents and upper‐tropospheric descents. Waves are generated during the evolution of northern frontal rainfall (FR). As FR intensifies, surges in low‐level diabatic cooling mainly resulting from microphysical processes, trigger n = 2 waves, which further precondition the environment along their path. In contrast, a sensitivity experiment involving stably developing FR fails to reproduce the preconditioning process by waves and the subsequent occurrence of WR. Overall, our study illuminates a new pathway through which FR significantly influences WR via gravity waves.

Keywords

• warm‐sector rainfall
• gravity waves
• frontal rainfall
• convection initiation
• microphysical process