Effects of Convective Heating on Movement and Vertical Coupling of Tropical Cyclones: A Numerical Study*

Abstract

The influence of convective heating on movement and vertical coupling of tropical cyclones (TCs) is investigated using a hurricane model with different environmental flows. The authors identify two processes by which convective heating may affect TC motion. One is the advection of symmetric potential vorticity (PV) by heatinginduced asymmetric flow. The other is the direct generation of a positive PV tendency by asymmetric heating, which acts to shift a TC to the region of maximum downward gradient of asymmetric heating. A steering level exists that is located at the level where the direct influence of asymmetric heating vanishes, normally in the lower troposphere. At that level, a TC moves with the asymmetric flow averaged within a radius of 200 km, because the influence of asymmetric flows on TC motion is weighted by the horizontal PV gradient that is primarily confined within the TC core. Although the vertical shear in the asymmetric flow (including environmental and heating-induced flows) could tilt the vortex, the influence of asymmetric heating tends to offset the vertical tilt caused by the vertical shear through a fast adjustment between the asymmetric wind and diabatic heating. Therefore, diabatic heating enhances the vertical coupling.

Revisiting the steering principal of tropical cyclone motion in a numerical experiment

“…As discussed in Wu and Wang (2001b), the HA term in the PVT equation can be approximately written as V 1 × ∇P s − V s × ∇P 1 , where V s is the symmetric component of the tangential wind and V 1 is the wave-number-one component of the asymmetric wind. The first term (HA1) represents the advection of the symmetric potential vorticity component by the asymmetric flow.…”

“…Wang (2000, 2001a) evaluated the PVT approach using the output of idealized numerical experiments with a coarse spacing of 25 km and understood the vertical coupling of tropical cyclone circulation under the influence of vertical wind shear. Wu and Wang (2001b) found that convective heating can affect tropical cyclone motion by the heating-induced flow and the positive PVT that is directly generated by convective heating.…”

Impact of cloud parameterization on the numerical simulation of a super cyclone

“…During the cyclone evolution, the intensity and track forecast depends largely on the evolution and distribution of the heating rates (Wu and Wang, 2001;Wang, 2009), which is mostly decided by the release of latent heat by the condensate within the system. To examine the associated vertical heating profiles that play an important role in determining intensification, diabatic heating rate (dθ/dt) is calculated.…”

Increasing duration of tropical cyclones over China

“…TC movement is primarily determined by large-scale steering plus a minor propagation component [Holland, 1983;Carr and Elsberry, 1990;Wang and Li, 1992]. The propagation component arises from nonlinear interactions among the environmental flow, planetary vorticity gradient, and TC circulation [Holland, 1983;Carr and Elsberry, 1990;Wang and Li, 1992] and from diabatic heating [Wu and Wang, 2001]. Figure 2a shows changes in large-scale steering flows over the period , which are obtained by calculating the linear trends of the zonal and meridional components of the steering flows.…”