Examining the contribution of surface sensible heat flux induced sensible heating to tropical cyclone intensification from the balance dynamics theory

Abstract

Observations and numerical simulations demonstrate that surface sensible heat fluxes (SHX) can account for 20%–30% of surface enthalpy fluxes in the inner core of tropical cyclones (TCs). The SHX have effects of warming the near surface air directly. However, the SHX are found to have no distinct contribution to the TC intensification. The possible reason for the minor role of SHX is investigated in this study by resolving the Sawyer-Eliassen equation and computing the tangential wind tendency equation with the SHX-induced sensible heating as the forcing source. Results reveal that the SHX-induced sensible heating merely forces very weak radial inflow near the surface and downward motion in the eyewall region, even by elevating it to larger magnitudes than eyewall heating. A decomposition of diabatic heating into horizontal and vertical gradient parts in the Sawyer-Eliassen equation suggests that the horizontal gradient of diabatic heating is essential for driving the TC response, while the influence of vertical gradient of diabatic heating is almost negligible. It implies that the processes that can alter radial distributions of diabatic heating in TC systems should be paid more attention. Although the SHX-induced sensible heating possesses relatively large vertical gradient, it changes smoothly in the radial direction and produces quite small horizontal gradient. Hence the SHX-induced sensible heating cannot contribute to the intensification of the TC remarkably even by enhancing it to very large values. It is therefore proposed that the insignificant contribution of SHX is not simply attributed to its small fraction to total surface enthalpy fluxes, but is because the SHX are inefficient in driving the spin up of the TC. It should be noted that the conclusions based on balanced dynamics can only reveal the direct contribution of SHX-induced heating to the intensification.