Low level jet controlled dynamical and thermodynamical regimes of the diurnal cycle of rainfall over the western ghats

Abstract Summer monsoon rainfall over the Western Ghats (WG) of India exhibits pronounced variability across multiple timescales, including the diurnal scale, which plays a key role in shaping regional precipitation. Although recent observational studies have improved understanding of the WG diurnal cycle, the physical mechanisms governing variability in storm structures and convective processes remain unclear. Using high-resolution satellite and reanalysis data, this study shows that diurnal rainfall variability over the WG is primarily governed by two physical regimes: a dynamical regime (DR) and a thermodynamical regime (TR). We demonstrate that contrasts in low-level jet strength and land–sea breeze intensity regulate the diurnal amplitude, phase, and storm depth. The DR (TR) is associated with a strong (weak) Somali jet and weak (strong) land–sea breeze within the boundary layer, with land–sea breeze intensity nearly four times stronger during TR. Consequently, diurnal rainfall is more vigorous and spatially extensive during TR. Shallow storms dominate during DR, indicating warm-rain processes, whereas TR features deeper convection involving both warm and cold microphysics, with storm-top heights reaching 5 km in DR and 8 km in TR. Favourable vertical profiles of equivalent potential temperature, geopotential height, and vertical velocity during TR, together with stronger afternoon CAPE, lower midday CINE, and increasing total column water vapour, support deep convection. In contrast, DR exhibits localized intense rainfall mainly over the northern WG with a latitudinal shift in diurnal peak timing. Although daily mean rainfall is higher during DR, the diurnal component contributes about 10% and 50% of the daily mean rainfall during DR and TR, respectively. These results provide a framework for regime-dependent diurnal rainfall variability over the WG and have implications for improving weather and climate models.