Orographic effects on precipitation microphysics and vertical structure over the Sichuan Basin and its sur-rounding regions using GPM-DPR data (2015–2022)

Using GPM-DPR observations from 2015 to 2022, this study investigates how two key topographic factors—elevation and slope—shape the vertical structures and microphysical characteristics of stratiform precipitation (SP) and convective precipitation (CP) over the Sichuan Basin and its surrounding regions. The main findings are as follows. (1) The freezing height (F z H) and the storm top height (STH) exhibit pronounced seasonal variability, and the influence of terrain shows clear seasonal dependence, with shallow convection occurring primarily over low elevations and gentle slopes. (2) SP shows a pronounced bright band near the F z H, whereas CP exhibits stronger Z e throughout the precipitation column; under rainfall rates ≥ 8 mm h⁻ 1 , near-surface Z e commonly reaches ≥ 40 dBZ over low and mid-elevation areas. The volume-weighted mean diameter (D m ) increases with rainfall rate (CP > SP) and shows a non-monotonic vertical pattern at mid-elevations. The normalized intercept parameter (N w ) increases with rainfall rate (SP > CP), is higher at low and mid-elevations than at high elevations, and tends to be higher on steeper slopes where D m is correspondingly smaller. (3) When rainfall rate RR ≥ 4 mm h⁻ 1 , particle growth in low elevation regions is dominated by collision–coalescence, but transitions toward a coalescence–breakup equilibrium with increasing elevation. Steeper slopes further suppress coalescence. These findings advance the understanding of how complex topography modulates precipitation structures and microphysical processes over mountainous regions.