On the Dynamics of Complexly Sheared Tropical Cyclone Convection

Monday, 18 April 2016: 1:30 PM
Ponce de Leon A (The Condado Hilton Plaza)
Christopher M. Rozoff, CIMSS/Univ. of Wisconsin, Madison, WI; and W. D. Terwey

The kinematic and thermodynamic controls on convective morphology often vary considerably in a tropical cyclone (TC), but the impact of these variations on convective dynamics is complex and has not heretofore been fully examined. In the TC inner-core, low-level vertical wind shear (VWS) and horizontal wind shear (HWS) can be intense, but it is unknown whether the VWS more often drives vigorous, rotating updrafts or whether strong HWS suppresses convection. Elsewhere in a TC, VWS and HWS are weaker but may interact in complex ways to impact convective behaviors.

We will show results from an idealized, high-resolution cloud model to clarify the impacts of complex 3D wind shear on the behavior of convective clouds. It will be shown how strong VWS favors longer-lived, vigorous convection due through dynamic pressure perturbations. HWS can transiently intensify convection, but convective updrafts are primarily driven by buoyant forces in HWS. On the other hand, the combination of sufficiently intense HWS and VWS can be detrimental to convective updrafts. In 3D shear, HWS filaments convection and, furthermore, reduces the preference for a right-turning, cyclonically rotating updraft split that emerges in the VWS-only experiments. However, the vorticity dynamics and the vertical updraft accelerations are quite similar to VWS-only experiments. The idealized convection simulations also show that intense 3D shear in TC inner cores can help suppress convection, but this suppression is a result of interactions between HWS and VWS. Furthermore, the results are sensitive to the background convective instability, suggesting a nuanced relationship between intense 3D shear and convection. We will also discuss how these results impact tropical cyclone dynamics, including rainband behavior and TC structure change.

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