Synergistic Effects of Midlevel Dry Air and Vertical Wind Shear on Tropical Cyclone Development via Ventilation

To better understand how midlevel moisture and vertical wind shear (VWS) synergistically modulate tropical cyclone (TC) development via ventilation, a three-dimensional modeling framework is utilized to conduct a suite of experiments. Each experiment has a different combination of initial midlevel moisture and VWS environments.

The three-dimensional structure of downdraft ventilation has different orientations and strengths, which are controlled by the vertical tilt of the vortex. The modulating effect of downdraft ventilation on TC development is the transport of low-equivalent potential temperature air left-of-shear and into the upshear semicircle from downdraft ventilation regions, which aids in reducing the area of strong upward motions, reducing the vertical mass flux in the inner core, and stunting TC development.

The three-dimensional structure of radial ventilation shows two pathways: the first pathway is associated with rainband activity at low- and mid-levels and is co-located with downdraft ventilation; while the second pathway at mid- and upper-levels is associated with the vertical tilt of the vortex and, in stronger-sheared environments, storm-relative flow induced by VWS. The modulating effect of radial ventilation on TC development is the inward transport of low-equivalent potential temperature air left-of-shear and in the upshear semicircle at low- and mid-levels, and low-RH air upshear and right-of-shear at mid- and upper-levels, which aids in reducing the area of strong upward motions, reducing the vertical mass flux in the inner core, and stunting TC development.

The effects of ventilation on TC development documented in this study are compared to previous ventilation-related studies, and suggestions for future research foci are discussed.