[Eoas-seminar] Meteorology PhD Defense for Allison Brannan, Thursday, December 10, 2020, 2:00 PM on zoom https://fsu.zoom.us/j/96174470780

[eoas-seminar at lists.fsu.edu]

Meteorology Seminar

Allie Brannan

PhD Meteorology Candidate



Title: An Analysis of the Extratropical Flow Response to Recurving Atlantic Tropical Cyclones

Co-Major Professors:  Dr. Jeffrey Chagnon & Dr. Robert Hart

Date: December 10th, 2020                              Time: 2:00 PM


Location: Zoom Meeting: https://fsu.zoom.us/j/96174470780

ABSTRACT

Previous case studies have noted a significant extratropical flow response to recurving Atlantic tropical cyclones (TCs), which is often linked to extreme weather events downstream. This study examines the modification of Rossby waves on the extratropical jet in response to recurving Atlantic TCs from both climatological and predictability perspectives. Changes in amplitude and location of Rossby waves are identified using a wavelet decomposition technique on isentropic potential vorticity. The climatology demonstrates that recurving Atlantic TC events are capable of modifying the amplitude of the extratropical flow. The nature of the extratropical flow response is most strongly tied to the average translation speed of the TC relative to the Rossby wave over the 72 hours following recurvature. The ability of Atlantic recurving TCs to significantly modify the amplitude of downstream Rossby waves motivates the investigation into whether the predictability of the extratropical flow is also affected by the TC and its Rossby wave relative speed.

Predictability is evaluated as the standard deviation of isentropic potential vorticity among a 50-member ensemble and is compared to climatology. This study found subsets of recurvature cases that contain areas of significantly modified ensemble spread which were anchored in time and space to the recurvature of the TC. It is shown that forecast uncertainty is dependent upon the location of the nearest trough at the time of recurvature and the relative speed between the TC and the Rossby wave train after recurvature. Predictability is significantly degraded when recurvature occurs downstream of a trough; the elevated uncertainty subsequently propagates downstream along with the trough axis. An analysis in spectral space demonstrates that the increase in uncertainty is not solely attributed to the trough location, as there is also significantly elevated uncertainty in the Rossby wave amplitude across downstream troughs and ridges. Uncertainty is enhanced in locations where baroclinic growth processes are most pronounced, specifically where the TC and upper-level trough are optimally phased.



Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1011 Academic Way, 2019 EOA Building
Tallahassee, FL 32306
850-644-8582
To make an appointment please login to my.fsu.edu and choose the Campus Connect (CC) icon

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