The Importance of Radiative Feedbacks in Tropical Cyclogenesis

Interactions between clouds, radiation, and circulations are fundamental to tropical climate, but until recently, the impact of these interactions on tropical cyclones (TCs) has been relatively unexplored. Here, we investigate the importance of radiative feedbacks in TC genesis and the mechanisms underlying their influence. TC genesis is considered here in a hierarchy of simulations: (1) a set of idealized cloud-resolving simulations in which a TC is allowed to develop after initialization from a mesoscale warm, saturated bubble on an f-plane, in an otherwise quiescent and moist neutral environment; and (2) realistic simulations initialized from the GFS analysis on a large cloud-resolving grid of the case study of Hurricane Maria (2017).

In the idealized simulations, TC genesis is delayed by a factor of two or three when radiative feedbacks are removed by prescribing a fixed cooling profile or spatially homogenizing the model-calculated cooling profiles. Further analysis and additional mechanism denial experiments pinpoint the cloud-longwave radiative feedback as the strongest influence. Simulations of Hurricane Maria (2017) in which clouds are made transparent to longwave radiation demonstrate that this feedback also favors the formation and accelerates the intensification of TCs in realistic scenarios. We find that the radiative effect of deep convective clouds in a developing TC acts to accelerate TC genesis and intensification through anomalous warming of the lower-mid-troposphere that invigorates deep convection and enhances the transverse overturning circulation. These findings imply that improving the representation of cloud-radiative feedbacks in forecast models has the potential to yield critical advancements in TC prediction.