Diurnal Pulses in Tropical Cyclones as Convectively Coupled Gravity Waves

This study uses convection‐permitting simulations to examine the vertical extent, propagation,
and nighttime preference of diurnal pulses (DPs) in tropical cyclones (TCs). DPs are outward‐moving rings of
cooler brightness temperatures near the storm center and may indicate TC intensification. Their initiation and
propagation are poorly understood due to limited high‐resolution observations. Here we leverage ensemble case
study simulations of Typhoon Haiyan (2013) and Hurricane Maria (2017) to analyze DP events and quantify
their structure and propagation characteristics. Results show that DPs are deep, column‐spanning features
visible in multiple atmospheric variables, including precipitation, temperature, vertical velocity, and radial
wind. Interpreted through gravity‐wave theory, their speeds and vertical structure largely match theoretical
expectations, with deviations that are consistent with convectively coupled gravity waves. DPs are more
frequent at night, likely due to constructive interference with the TC's diurnal circulation. These insights into
DPs help clarify their initiation and propagation mechanisms.