Postfrontal Deep Convection Over the Southern Ocean and Orographic Precipitation Enhancement Over Tasmania

Abstract The orographic precipitation enhancement (OPE) generated within wintertime post‐frontal air masses is a prominent climate feature of Tasmania. This study investigates a passage of a cold sector of a mid‐latitude cyclone over the Southern Ocean (SO) and Western Tasmania (WTAS) observed from 2100 UTC 11 July to 0300 UTC 13 July. The in situ and remote sensing observations have been used to study clouds and precipitation over the SO and WTAS. Those observations include Optical Particle Size Velocity disdrometers and Micro Rain Radars implemented during a winter field campaign implemented in 2019, 27 rain gauges operated by Hydro Tasmania, C‐band weather radar and satellite‐based observations. ERA5 reanalysis was used to analyze the synoptic meteorology and thermodynamic conditions. Deep convection reaching heights of 8 km was observed over the SO and Tasmania and was triggered by a post‐frontal trough. The microphysical properties of these deep convective clouds were substantially different from those for the shallow open mesoscale cellular convection, which is commonly observed over the SO. The deep convective clouds and OPE produced heavy precipitation exceeding 55 mm over WTAS according to in situ observations during the post‐frontal period (over 30 hr). The GPM‐IMERG satellite‐based precipitation product captured the spatial pattern of the OPE over WTAS though rain gauge calibration induced overestimation of heavy precipitation at some sites. The analysis of C‐band radar observations suggests that orographic convection invigoration and convective‐to‐stratiform transition mechanisms produced OPE over WTAS.