[Eoas-seminar] MET seminar TODAY - Tuesday Sep 3 - Dr. Jie Sun (FSU)

[eoas-seminar at lists.fsu.edu]

All,

This is a reminder of the Meteorology seminar TODAY at 3pm. Please join us for a talk by our own Dr. Jie Sun (FSU) on the topic of “Understanding of Hurricane Surface Wind Profiles from the Effective Absolute Angular Momentum Perspective.”

DATE: Tuesday Sep 3
TIME: 3 PM
LOCATION: EOAS 1044
SPEAKER: Dr. Jie Sun

TITLE: Understanding of Hurricane Surface Wind Profiles from the Effective Absolute Angular Momentum Perspective

ABSTRACT:
Tropical cyclones (TCs) are among the deadliest and costliest natural hazards. Beside TC track, the intensity and size are the two important metrics for assessing TC severity and potential hazards. Despite considerable progress in predicting TC track, our current understanding and prediction capabilities regarding the TC intensity-size relation and the resultant TC surface wind profile remain limited. Our previous study (Sun et al., 2022) reveals that the radial profile of a TC's surface wind is primarily governed by its effective absolute angular momentum (eAAM). The eAAM combines the TC's absolute angular momentum (AAM) with its inward frictional loss rates, serving as a radial invariant for the TC. The radial profiles of surface winds for individual TCs can be uniquely determined based on the inward frictional loss rates and their eAAM values.
In this talk, I will present results obtained from two series of idealized axis-symmetric TC simulations using Cloud Model 1 (CM1). Each of the two series consists of idealized axis-symmetric TC simulations initialized with different initial vortices. One series uses a lower value for the momentum exchange coefficient (Cd) and the other uses a higher value, representing two different environment conditions for TCs.  Our findings indicate that under the same value of Cd, the radial profiles of TC surface winds simulated by the CM1 model with different initial vortices can be accurately reproduced by the eAAM model under the same parameters for the inward loss rates of AAM. Larger initial vortices have lager radii for inflows towards TC centers under the same conditions of surface roughness, sea surface temperature, and moisture content. Therefore, larger initial vortices result in larger values of eAAM for TCs. The larger their eAAM values, the stronger their surface winds are at the same radii. The effect of differences in Cd can be modeled by different parameter values for the inward loss rates of AAM in the eAAM model. The immediate consequence of the increase in the inward loss rates of AAM is the weakening of surface winds at the same radii. For the same initial vortices, the increase in the inward loss rates of AAM also affects radial profiles of TC surface winds inevitably by decreasing their eAAM values. The decrease in eAAM values is a result of the contraction of the radii for inflows towards TC centers when TCs reach their equilibrium states.  The reduction in eAAM values under stronger surface roughness also contributes to the weakening of surface winds at the same radii.




Christopher D. Holmes, PhD

Associate Professor of Meteorology and Environmental Science
Earth, Ocean and Atmospheric Science

Florida State University



EOAS Room 6091
phone: 850-645-0972

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