Changes in the Structure and Intensity of Tropical Cyclones associated with Diurnal Pulsing

One of the most prominent diurnal cycle features in tropical cyclones (TCs) is the radially outward propagation of a cooling signal in the upper-level clouds, the so-called diurnal pulse (DP). Previous studies suggested that some of the DPs occur in the deeper convective layer and therefore may impact the TC structure and intensity. This study investigates how the internal structures and intensity will change associated with DPs in global TCs using 18 years of multi-source satellite observations. Over 3000 DP events are identified based on objective method using satellite infrared data. Satellite microwave observations and spaceborne radar measurements are used to examine the changes of the TC convective structures related to DP events. Results show that the precipitation, microwave ice scattering, radar-echo top height, and lightning in the TC inner core are all markedly enhanced on DP days compared to non-DP days. Spaceborne radar observations further indicate that convection becomes deeper in the upshear quadrants with the presence of DPs and convective depths remain similar in the downshear quadrants. These changes in the TC internal structures are consistent to changes in rapidly intensifying TCs reported in the literature. In fact, this study shows that rapidly intensifying TCs have a higher frequency of the long-duration DP event and significantly longer DP duration than steady-state and gradually intensifying TCs.