15D.9A Barrier Layer Development within Tropical Cyclones Based on Argo Float Network Observations

Friday, 20 April 2018: 10:00 AM
Heritage Ballroom (Sawgrass Marriott)
John Daniel Steffen, Florida State Univ./Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL; and M. Bourassa

A climatology of Argo float measurements is developed from 2000-2014 for the Atlantic (na = 497), Eastern Pacific (ne = 675), and Central Pacific (nc = 249) basins to study the upper-ocean salinity (S) and temperature (T) responses to translating tropical cyclones (TCs). The Argo float dataset consists of both a pre-storm and post-storm T,S profile pair to determine changes in oceanic barrier layer characteristics. Also, a non-TC forced Argo pair dataset is derived for comparison to account for natural ocean state variability and instrument sensitivity over a ~10 day period.

The Atlantic basin shows a statistically significant increase in barrier layer thickness (BLT) and potential energy (BLPE) that is largely attributable to an average increase of 3 m in the post-TC isothermal layer depth (ITLD). The Eastern Pacific basin has no significant changes to any barrier layer characteristics, likely due to a shallow and highly stratified pycnocline. Finally, the Central Pacific has a statistically significant freshening in the upper 20-30 m that increases upper-ocean stratification. In addition, the Argo data is subdivided to investigate relationships with TC intensity, radial distance from center, translation speed, and time after TC passage.

Finally, a case study of Hurricane Gonzalo (2014) is presented. Observations from a Bermuda Institute of Ocean Sciences glider provides high frequency sampling of the upper-ocean in Gonzalo’s right quadrant. During the TC forced stage, surface salinity decreases by 0.1-0.2 psu. The near-surface stratification increases and is the same order of magnitude as the top of the pycnocline. BLT and BLPE increase as Hurricane Gonzalo approaches and peak several hours after passage. Barrier layer formation is likely a result of both ITLD deepening and near-surface freshening from precipitation.

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