Effects of Rotation on Convective Self-Aggregation Onset

Rotation affects the organization of tropical convection. Perhaps most obviously, off-equatorial regions of organized convection under greater planetary vorticity are more likely to undergo tropical cyclogenesis. Rotation has also been shown to affect static stability, meso- and larger-scale circulations, and the relative roles of various radiative-convective feedbacks. The latter is most apparent in simulations of convective self-aggregation, where increasing rotation slows the initial separation of dry and moist regions. Understanding precisely why the onset of self-aggregation is delayed may yield useful physical constraints on the organization of observed tropical convection.

This work leverages 8 convection-permitting f-plane experiments previously performed by the author. These vary only in the Coriolis parameter prescribed throughout the domain, spanning an effective latitude range from 0.1-20˚N. Convection is initialized from radiative-convective equilibrium using identical low-level temperature perturbations in all simulations. Over a 10-day period, the growth rate of column-integrated moist static energy (MSE) variance systematically decreases with increasing f beyond an effective latitude of 2˚N. Noteworthy differences in moist static energy (MSE) variance between simulations emerge at both lower and upper levels within the first 24 hours. This first appears as a difference in the spatial variability of water vapor in the boundary layer and lower free troposphere. Then, shortly after deep convective initiation, spatial variability in temperature near the tropopause tends to decrease with increasing f. A statistical and process-level analysis is performed to examine the different structure and behavior of this early-stage convection under varying rotation, including its interactions with the surrounding environment. This targets dominant mechanisms causing the initial differences in MSE variance to emerge, and explores their connection to rotation theoretically.