Date of Award

Summer 2024

Language

English

Embargo Period

7-12-2024

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Atmospheric and Environmental Sciences

Program

Atmospheric Science

First Advisor

Kristen Corbosiero

Second Advisor

Brian Tang

Keywords

tropical cyclones, vertical wind shear

Subject Categories

Earth Sciences | Other Earth Sciences

Abstract

The development of a new low-level circulation center in tropical cyclones, known as downshear reformation, can lead to sudden changes in storm structure and intensity, representing a challenge in forecasting tropical cyclones. This phenomenon is commonly observed in weak tropical cyclones (e.g., tropical depressions, tropical storms) experiencing moderate to strong vertical wind shear (> 5 m s-1), when the vertical wind shear organizes convection in the downshear region of the tropical cyclone, and lower-tropospheric vorticity is generated within the intense convection. Downshear reformation has been proposed as a mechanism for intensification, sometimes rapidly, in tropical cyclones under unfavorable environmental wind shear. Some of the processes involved in the reformation that aid the intensification of the storm include the increase of diabatic heating near the center, vortex tilt and misalignment reduction, and the repositioning of the center in a more favorable environment. However, not all sheared tropical cyclones undergo downshear reformation, and the factors associated with this process still need to be clarified. This research aims to identify the factors and mechanisms that favor downshear reformation in tropical cyclones, using an analog approach.

Tropical cyclones that reformed in the North Atlantic Basin from 1998-2020 were compared to analog tropical cyclones with similar intensity, vertical wind shear, and maximum potential intensity but did not undergo downshear reformation using ERA5 reanalysis and GridSat-B1 data. The comparison between composites showed that reformed storms have greater low-level and mid-tropospheric relative humidity downshear, more significant surface latent heat fluxes downshear, and larger low-level equivalent potential temperatures. These factors increase thermodynamic favorability and sustained convection downshear, favoring a new center's development.

License

This work is licensed under the University at Albany Standard Author Agreement.

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