Global and Regional Characteristics of Radially Outward Propagating Tropical Cyclone Diurnal Pulses

Abstract

AbstractThe radially outward propagating, cloud top cooling, diurnal pulse (DP) is a prominent feature in tropical cyclones (TCs) that has important implications for changes in TC structure and intensity. By using an objective identification algorithm, this study characterizes DPs over various ocean basins and examines their environmental conditions and convective structures. DPs occur on 52% of TC days globally and the occurrence frequency exhibits significant regional variability. The Northwest Pacific (NWP) has the highest DP frequency (60%) and shares the largest fraction of DPs worldwide (34%). The median duration and propagation distance of DPs are 12–15 hr and 500–600 km, respectively. Although the mean propagation speed of DPs is 11–13 m s−1, persistent DPs (lasting >15 hr) mostly propagate at speeds similar to internal inertial gravity waves (5–10 m s−1). Additionally, the longer the pulse duration, the stronger the pulse amplitude. Further, most DPs initiate in the inner core overnight, in phase with inner‐core deep convection. Inner‐core cold clouds, precipitation, and lightning are all markedly enhanced on DP days compared to non‐DP days. Interestingly, the DP signal significantly weakens and becomes slower while propagating through the 200–400‐km annulus during 09–12 local time (LT). Finally, DPs are more likely to occur over warm sea surface temperatures (SSTs), in low shear, and with a moist mid‐to‐upper troposphere. SST plays an important role in DP development over all basins, while shear and humidity are less important in the Northeast Pacific (NEP) and North Atlantic (NA) basins.