ORCID

https://orcid.org/0000-0002-1381-026X

Date of Award

Fall 2024

Language

English

Embargo Period

12-17-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Program

Atmospheric Science

First Advisor

Robert Fovell

Committee Members

Kristen Corbosiero, Brian Tang, Ryan Torn

Keywords

tropical cyclone, numerical weather prediction, WRF, outflow, symmetric instability, TC–trough interaction

Subject Categories

Atmospheric Sciences | Meteorology

Abstract

The tropical cyclone (TC) outflow layer is an integral part of the TC transverse circulation: warm and moist air converges in the boundary layer of the TC; rising motion and condensational heating occur in the TC eyewall and rainbands; the TC warm core and divergent anticyclone establish in the mid-upper troposphere, with the mass imported into the TC center exported away through outflow near the tropopause.

A series of state-of-the-art numerical simulations were utilized to investigate different scenarios of TC outflow evolution, from an idealized axisymmetric setup to a semi-idealized asymmetric setup, to a real-case setup of TC–trough interaction. Large areas satisfying the criteria for symmetric instability were identified in the upper troposphere of simulated TCs, primarily due to the presence of negative isentropic vorticity. This reservoir of symmetric instability is thought to be an intrinsic characteristic for any TC-like, convectively driven system. The assumption of gradient wind balance breaks down in the TC outflow layer, rendering it susceptible to mass-wind field adjustments.

When imposed external perturbations, the modeled TC outflow expanded in a preferential direction. Budget analysis attributed the wind speed increase in asymmetric outflow jets to the result of unbalanced pressure gradient force acting upon the flow in areas of symmetric instability, converting potential energy to kinetic energy via cross-isobaric flow. In the case of TC–trough interaction, we observed the rapid development of a poleward outflow channel in between the TC and the trough in hours leading to and during rapid intensification. The excess pressure gradient force brought upon the TC by the trough acted as the agent for net wind speed acceleration into the outflow channel. Trajectory analysis of air parcels ending within the core of the outflow channel demonstrated wind speed increase at the expense of negative isentropic vorticity. Our analyses revealed the physical picture of divergent anticyclones as an important source of kinetic energy in the atmosphere through the creation and release of symmetric instability.

License

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

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