Diurnal Cloud and Circulation Changes in Simulated Tropical Cyclones

Observations of the diurnal cycle in tropical cyclones (TCs) systematically indicate a ∼12-hr offset between peak rainfall rate and the maximum height of anvil clouds in the TC cloud canopy. This phasing conflicts with archetypal models of organized deep convection, which suggest a tight coupling between rainfall, vertical cloud growth, and anvil clouds. We show that this phasing owes to the bimodal diurnal evolution of the transverse circulation, which peaks nocturnally from low–midlevels, and during daytime in the upper troposphere. The bottom-heavy nocturnal circulation state is driven by latent heating from nocturnally invigorated deep convection, while the top-heavy daytime state is the thermally direct circulation response to strong shortwave-cloud warming in the optically thick TC cloud canopy. This daytime upper-level circulation response manifests in a lifting of the maximum height of the TC outflow and, in turn, a lifting and invigoration of the upper-level anvil clouds of the TC cloud canopy.