[Eoas-seminar] Meteorology PhD Defense: John Steffen, Wednesday, December 5, 2018, 1:30 PM, LOV353

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Tue Nov 27 08:24:50 EST 2018


Meteorology Seminar



John Steffen

PhD Meteorology Candidate



Title:  BARRIER LAYER DEVELOPMENT LOCAL TO TROPICAL CYCLONES

Major Professor:  Dr. Mark Bourassa

Date: Wednesday, December 5th                  Time: 1:30 PM



Location: Werner A. Baum Seminar Room (353 Love Building)
(Please join us for refreshments served outside room 353 Love @ 1:00 PM)



ABSTRACT

     The objective of this study is to quantify barrier layer development due to tropical cyclone (TC) passage using Argo float observations of temperature and salinity. To accomplish this objective, a climatology of Argo float measurements is developed from 2001-2014 for the Atlantic, eastern Pacific, and central Pacific basins. Each Argo float sample consists of a pre-storm and post-storm temperature and salinity profile pair. In addition, a no-TC Argo pair dataset is derived for comparison to account for natural ocean state variability and instrument sensitivity.
     The Atlantic basin shows a statistically significant increase in post-TC barrier layer thickness (BLT) and barrier layer potential energy (BLPE) that is largely attributable to an increase of 2.6 m in the post-TC isothermal layer depth (ITLD). The eastern Pacific basin shows no significant changes to any barrier layer characteristic, likely due to a shallow and highly stratified pycnocline. However, the near-surface layer freshens in the upper 30 m after TC passage, which increases static stability. Finally, the central Pacific has a statistically significant freshening in the upper 20-30 m that increases upper-ocean stratification by ~35%. The mechanisms responsible for increases in BLPE vary between the Atlantic and both Pacific basins; the Atlantic is sensitive to ITLD deepening, while the Pacific basins show near-surface freshening to be more important in barrier layer development. In addition, Argo data subsets are used to investigate the physical relationships between the barrier layer and TC intensity, TC translation speed, radial distance from TC center, and time after TC passage.
     ROMS model runs of Hurricane Gonzalo (2014) characterize the upper-ocean response to TC precipitation forcing. Several different vertical mixing parameterizations are tested to determine their sensitivity to precipitation. For all mixing schemes, TC precipitation accounts for ocean surface freshening of about 0.3 PSU. The dominant terms in the near-surface salinity budget are the total advection and vertical diffusivity. The influence of precipitation-induced changes to the SST response is more complicated. In some areas, increased upper-ocean stratification mutes the SST cooling response. However, in other areas, cooling can be stronger when precipitation is prescribed. Dynamical changes in upper-ocean currents and the curl of the surface stress can induce a stronger cooling response in these regions.



Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1017 Academic Way, 410 Love Building (Meteorology)
Tallahassee, FL 32306
850-644-8582

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