The Tropical Cyclone Model 3 (TCM3) is utilized to conduct four numerical experiments investigating the effects of vertically sheared environmental flows on the inner core asymmetric structure of tropical cyclones (TC) and its relationship to TC intensification. The particular focus of this study is the modes of response of TCs to varying magnitudes of shear at different stages of development. The TCM3, with a high resolution inner nest and explicit cloud microphysics, is ideal for such studies.

The presence of vertical shear results in the development of an azimuthal wavenumber one pattern of convection, with preferential enhancement of convection on the downshear side. This change in structure is brought about in response to not only induced relative flow through the vortex core and vertical tilt as identified in previous studies, but also the downshear displacement of upper-level stratiform clouds. This displacement results in an increased production of cool, dry mesoscale downdrafts on the downshear side of the simulated TC that triggers outer rainband development. The net effect of these processes is an enhancement of convection and asymmetric rainbands on the downshear side of the TC at radii that increase with increasing shear.

We hypothesize that these structure changes have a twofold effect in limiting the rate of intensification of the simulated TCs. First, enhanced mesoscale downdrafts and asymmetric convection on the downshear side hinder the critical warm, moist inflow to the eyewall through (a) mixing of cool, dry downdraft air into the inflow layer and (b) depletion in rainbands (the so-called "barrier effect"). Second, persistent forcing of wavenumber one asymmetric rainbands systematically hinders the axisymmetrization process, delaying the critical development of an eye early on and inducing breakdown of the eyewall after the mature stage. These processes ultimately decrease symmetric upward vertical velocity and associated heating near the TC center and limit the transport of cyclonic angular momentum to the inner core, further limiting the simulated TC development.

In this study, a magnitude of shear of about 10 m s^-1 between 200 hPa and 850 hPa dissipates the developing disturbance, in agreement with previous observational and modeling studies. On the other hand, the initially mature TC intensifies despite the presence of shear of the same magnitude. These results suggest that a mature TC of sufficient intensity may resist the detrimental effects of vertical shear and intensify toward its thermodynamic limit, albeit at a slower rate than if vertical shear were not present.