"Off-the-Clock" Tropical Cyclone Diurnal Pulses

The radially-outward propagating, cloud-top cooling, diurnal pulse (DP) is a prominent feature in tropical cyclones (TCs) that has significant impacts on structure and intensity. Most DPs initiate in the TC inner core overnight, in phase with deep convection, but non-negligible numbers (~40%) of DPs initiate during the afternoon to evening hours and/or outside the inner core. This timing and initiation location differs from the diurnal pulse clock proposed by Dunion et al. (2014) and most numerical modeling studies of the TC diurnal cycle. This presentation will explore the observational characteristics of these “off-the-clock” DPs including their basin variability, latitudinal distribution, and environmental characteristics. Preliminary results indicate the frequency of off-the-clock DPs increases with latitude, vertical wind shear, and contrastingly, TC intensity, with large interbasin variability. Numerical model simulations will also be employed to examine the genesis mechanisms of off-the-clock pulses, exploring the effects of varying incoming solar radiation and cloud microphysical schemes.