Insights into the convective and microphysical properties of heavy precipitation over the northwestern and northeastern margins of the <scp>Sichuan Basin</scp>

Abstract The Sichuan Basin (SCB) is located to the east of the Tibetan Plateau (TP), with the Daba Mountains (DM) to its northeast. Both the northwestern (eastern slope of the TP) and the northeastern (windward slope of the DM) margins of the SCB are prone to heavy precipitation. The microphysical properties and underlying mechanisms of heavy precipitation in these two distinct topographic regions remain poorly understood, largely due to limited microphysical observations and the complex cloud precipitation processes over and around the eastern TP. In this study, the convective and microphysical properties of heavy precipitation between these two regions are compared using two‐year merged dual‐polarization radar observations covering the SCB during the warm season. The results reveal pronounced regional disparities in microphysical properties across the SCB. Convective echoes (CEs) associated with heavy precipitation occur more frequently over the northwestern SCB (NWS) than over the northeastern SCB (NES), predominantly occurring in July with a diurnal peak around midnight. Significantly deeper convection is observed over the NWS, with a relatively higher echo top (defined by a maximum height of 18 dBZ radar reflectivity) reaching about 11 km. Polarimetric signatures demonstrate that the CEs over the NWS have larger polarization reflectivity ( Z H ), differential reflectivity ( Z DR ), and specific differential phase ( K DP ), implying more intense convective activity, larger raindrop sizes, and higher liquid water content compared to those over the NES. This is consistent with more rimed graupel particles above the melting layer over the NWS. Orographically induced convergence of low‐level winds around the periphery of the TP significantly intensifies moisture transport, thereby contributing to the occurrence of heavy precipitation over windward slopes. Compared with the NES, the stronger convective updrafts and larger convective available potential energy (CAPE) lead to more intense convection, characterized by active riming aggregation processes and increased raindrop sizes through higher collision–coalescence efficiency over the NWS.