ORCID

https://orcid.org/0009-0002-7990-3562

Date of Award

Summer 2026

Language

English

Embargo Period

7-31-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Program

Atmospheric Science

First Advisor

Brian Tang

Second Advisor

Kristen Corbosiero

Committee Members

Ryan Torn, Robert Fovell, Jonathan Moskaitis

Keywords

Tropical Cyclones, Aircraft Observations, Dropsondes, Vertical Wind, Ventilation, Moderate Shear

Subject Categories

Atmospheric Sciences | Meteorology

Abstract

Tropical cyclone (TC) intensity can be challenging to predict since it is modulated by many physical processes. One of these processes is ventilation: the injection of relatively cool, dry environmental air into the warm core of a TC that acts as “anti-fuel”, inhibiting intensification and increasing uncertainty with intensity forecasts. While ventilation has been examined in numerical modeling studies, there have been a limited number of observational studies investigating ventilation. The two primary objectives of this dissertation are to develop methods for measuring downdraft ventilation from aerial reconnaissance observations and to use those observations to better understand how ventilation affects TC intensity and structure. Downdraft ventilation can be measured from dropsondes, which provide the necessary observations of both wind and thermodynamics. Observations of downdraft ventilation were compared with the TC convective structure sampled by aircraft Doppler radar.

An initial examination of downdraft ventilation was performed using observations in a case study of Hurricane Delta (2020). Delta experienced rapid intensification (RI) before abruptly weakening before making landfall. During RI and weakening, the vertical wind shear increased, causing the vortex to tilt and exposing Delta's inner core to the surrounding environment. The increased shear provided a pathway for downdraft ventilation to transport low-entropy air aloft into the boundary layer via downdrafts. Toward the end of RI, there were intense, deep downdrafts near the TC center; however, minimal downdraft ventilation was observed. During the weakening period, downdraft ventilation was more prevalent with moderate to intense downdrafts and low-entropy air concentrated on the left-of-tilt side of the storm. The observations show that as Delta weakened, the inner core became diluted with low-entropy air from downdraft ventilation and the convection was limited to the downtilt and left-of-tilt regions of the storm.

When calculating downdraft ventilation from dropsondes, the vertical wind is estimated by finding the difference between the dropsonde's measured fall rate and terminal velocity. Determining an accurate dropsonde terminal velocity is challenging since it requires either laboratory experimentation or analyses of dropsonde observations within potentially strong convective motions. Two methods for finding the dropsonde terminal velocity and resulting vertical wind were examined. The first method determines a theoretical terminal velocity based on the dropsonde design, parachute size, and a drag coefficient. The second method estimates the terminal velocity by finding the median fall rate of a large sample of dropsondes with similar designs. The fall rates and vertical winds were calculated from four different dropsonde models released over a 14-year period. For three of the dropsonde models, the median fall rates were faster than the corresponding theoretical terminal velocity, resulting in an unrealistically large percentage of downward motion. Unlike the theoretical method, the median-fall-rate method accounts for the differences among dropsonde models and does not rely on limiting assumptions about the dropsonde design. For these reasons, estimating vertical wind from dropsondes using the median fall rate for the corresponding dropsonde model is recommended versus using the theoretical terminal velocity.

The final component of this dissertation builds on the case study of Hurricane Delta through an analysis of downdraft ventilation using observations from multiple TCs over the past 14 years. The results show that the strongest and most frequent downdraft ventilation occurs in the downtilt-left quadrant of the inner-core region of moderately-sheared TCs. This preferred azimuthal location appears to result from the asymmetric convective structure of moderately-sheared TCs, in which precipitation from downtilt convection is advected left-of-tilt where it falls into unsaturated air below and produces evaporatively cooled downdrafts of low-entropy air. The observed asymmetries of both downdraft ventilation and the TC convective structure are consistent with previous studies as well as the case study of Hurricane Delta.

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

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