Tropical Cyclone Asymmetry and Wind Shear Interactions Under Global Warming in a Variable-Resolution Climate Model

Tropical cyclone (TC) mean intensity is projected to increase in a warming climate, along with the proportion of TCs that become particularly intense. These projections are rooted in potential intensity (PI) theory, due largely to increasing sea surface temperatures. However, TCs often fail to reach their PI, in many cases resulting from environmental vertical wind shear (VWS). VWS often negatively influences intensity by tilting the vortex, ventilating low-θ_e environmental air into the inner core, and inducing asymmetric convection. Though challenges related to underresolved, parameterized processes remain, global climate models (GCMs) are more realistically representing TC structure, intensity, and climatology. Moreover, recent research suggests that asymmetries associated with VWS can be reasonably captured, particularly in high-resolution GCMs.

Leveraging these recent findings, we present a process-level analysis of TC-VWS interaction under global warming in a variable-resolution GCM, the Community Atmosphere Model version 5 (CAM5). CAM5 is configured with roughly 1˚ grid spacing globally, with a 0.25˚ inner nest over the North Atlantic basin. We examine TCs in a historical climate simulation, and under moderate and high-end warming. Individual TC snapshots are extracted from geopotential thickness and surface pressure fields using the TempestExtremes objective tracking algorithm. Composites of TC structure are then developed for the North Atlantic (0.25˚) and Northwest Pacific (1˚), according to TC intensity, deep-layer VWS, intensity change, and time relative to lifetime maximum intensity. In this framework, we investigate three-dimensional kinematic and thermodynamic fields, and employ quantitative diagnostic tools to examine processes such as ventilation and rainband convection. In doing so, we assess asymmetric structure throughout the TC life cycle, the relationship between VWS and intensity change, and the impact of warming on each at different resolutions.