Diabatic Rossby Vortex World: Finite-Amplitude Effects in Moist Cyclogenesis

Abstract Diabatic Rossby vortices (DRVs) are a special class of heavily precipitating extratropical cyclone in which latent heating effects play a key role. As such, their dynamics defies the classic mechanism of midlatitude storm formation and poses challenges to modeling and theoretical understanding. Here, we build on recent theoretical advances on the growth of DRV modes in small-amplitude moist instability calculations by exploring the structure of finite-amplitude DRV storms in a hierarchy of models of moist macroturbulence. Simulations of moist quasigeostrophic turbulence show a transition to a DRV-dominated flow (DRV world) when the latent heating is strong. The potential vorticity (PV) structure of the DRVs is similar to the PV structure from small-amplitude DRV modal theory. Simulations of the moist primitive equations also transition to DRV world when both the latent heating is strong and the Rossby number is sufficiently low. At high Rossby numbers, however, the PV structure of storms with strong latent heating is bottom intensified compared to DRV modal theory due to higher-order effects beyond quasigeostrophy, and the macroturbulent flow has both DRV-like storms and frontal structures. A 1D model of the vertical structure of PV is solved for different Rossby numbers and stratification profiles to reconcile the PV structures of DRVs in the simulations, small-amplitude modal theory, and observations. Significance Statement Diabatic Rossby vortices (DRVs) are a special class of heavily precipitating extratropical cyclones which grow from the effects of latent heating and as such go beyond the classic growth mechanism of midlatitude storm formation. DRVs have been implicated in extreme and poorly predicted forms of cyclogenesis and pose challenges to both modeling and theoretical understanding. Here, we extend our previous study on the structure and emergence of DRVs in small-amplitude instability calculations by exploring the structure of DRV storms and the conditions for the emergence of DRV-dominated atmospheres (“DRV world”) in a range of different finite-amplitude simulations.