Thermodynamics of Overland Tropical Cyclone Intensity Change in Weakly/Non-Baroclinic Environments

There are two leading theories regarding how tropical cyclones maintain or increase their intensity over land in weakly to non-baroclinic environments. In the first, tropical cyclones are maintained overland by enhanced upward surface enthalpy fluxes facilitated by the tropical cyclone’s rains, whereas in the second, tropical cyclones are maintained by enhanced enthalpy fluxes under inflowing trajectories at larger radii from the cyclone’s center. These theories have yet to be rigorously tested, however. To rigorously test these hypotheses, this study uses a quasi-idealized version of the Advanced Research version of the Weather Research and Forecasting model to test the sensitivity of overland tropical cyclone intensity to the underlying land surface’s characteristics. In simulations without parameterized radiation, simulated tropical cyclone intensity is primarily governed by the low-level stability which, in turn, impacts outer rainband activity that governs the enthalpy of the near-surface air along inflowing trajectories. Low-level instability was found to be influenced primarily by the sensible heat flux resulting from the difference in temperature of the land surface to the near-surface air temperature. Consequently, within these simulations, neither of the two leading hypotheses appear to be the primary process for tropical cyclone maintenance overland. Ongoing research is evaluating the sensitivity of these results to the inclusion of parameterized radiation.