Changes in the Deep Convective Structures of Tropical Cyclones Associated With the Diurnal Pulse

Abstract

This study uses satellite passive microwave (PMW) and spaceborne precipitation radar (PR) observations to investigate changes in the cloud and precipitation structures of tropical cyclones (TCs) experiencing diurnal pulses (DPs). A total of 4677 PMW and 3074 PR snapshots are matched with DP and non-DP events of TCs objectively identified from infrared satellite images. The PMW observations suggest that compared to non-DP events, the inner-core (0–100 km) cold clouds containing both ice and liquid particles become more frequent and widespread when DP occurs. The greatest DP-associated enhancement of cold clouds occurs in the downshear left quadrant of weak TCs (tropical storms) and in the upshear region of moderate-to-strong (≥ CAT 1) hurricanes, respectively. Also, the inner-core cold clouds of DP events still maintain a relatively symmetric distribution under high-shear (>10 ms⁻¹) environments compared to non-DP counterparts. The inner-core warm cloud, dominated by liquid hydrometeors, increases in regions right of the shear but decreases left of the shear during DP events. Similarly, PR echo-top height statistics show significant increases of moderate-to-deep convection in the TC inner region (0–300 km) on DP events especially for weak TCs. Particularly, the upshear-right quadrant has the greatest increase in moderate-to-deep convection during DP events. These changes lead to a deeper and more symmetric convective structure of TCs' inner region with the occurrence of DPs.