Combined Effects of Midlevel Dry Air and Vertical Wind Shear on Tropical Cyclone Development. Part II: Radial Ventilation

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  • 1 National Center for Atmospheric Research, Boulder, Colorado
  • 2 Department of Atmospheric and Environmental Sciences, University at Albany - State University of New York, Albany, New York
  • 3 National Center for Atmospheric Research, Boulder, Colorado
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Abstract

This study demonstrates how midlevel dry air and vertical wind shear (VWS) can modulate tropical cyclone (TC) development via radial ventilation. A suite of experiments was conducted with different combinations of initial midlevel moisture and VWS environments. Two radial ventilation structures are documented. The first structure is positioned in a similar region as rainband activity and downdraft ventilation (documented in Part I) between heights of 0 and 3 km. Parcels associated with this first structure transport low-equivalent potential temperature air inward and downward left-of-shear and upshear to suppress convection. The second structure is associated with the vertical tilt of the vortex and storm-relative flow between heights of 5 and 9 km. Parcels associated with this second structure transport low-relative humidity air inward upshear and right-of-shear to suppress convection. Altogether, the modulating effects of radial ventilation on TC development are the inward transport of low-equivalent potential temperature air, as well as low-level radial outflow upshear, which aid in reducing the areal extent of strong upward motions, thereby reducing the vertical mass flux in the inner core, and stunting TC development.

Corresponding author address: National Center for Atmospheric Research, P.O. Box 3000, Boulder CO 80307, USA. E-mail: jalland@ucar.edu

This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977.

Abstract

This study demonstrates how midlevel dry air and vertical wind shear (VWS) can modulate tropical cyclone (TC) development via radial ventilation. A suite of experiments was conducted with different combinations of initial midlevel moisture and VWS environments. Two radial ventilation structures are documented. The first structure is positioned in a similar region as rainband activity and downdraft ventilation (documented in Part I) between heights of 0 and 3 km. Parcels associated with this first structure transport low-equivalent potential temperature air inward and downward left-of-shear and upshear to suppress convection. The second structure is associated with the vertical tilt of the vortex and storm-relative flow between heights of 5 and 9 km. Parcels associated with this second structure transport low-relative humidity air inward upshear and right-of-shear to suppress convection. Altogether, the modulating effects of radial ventilation on TC development are the inward transport of low-equivalent potential temperature air, as well as low-level radial outflow upshear, which aid in reducing the areal extent of strong upward motions, thereby reducing the vertical mass flux in the inner core, and stunting TC development.

Corresponding author address: National Center for Atmospheric Research, P.O. Box 3000, Boulder CO 80307, USA. E-mail: jalland@ucar.edu

This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977.

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