MIXED-LAYER CURRENT AND CYCLONIC EDDY INDUCED BY GLOBAL TROPICAL CYCLONES

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Research areas:
Year:
2017
Type of Publication:
Article
Keywords:
tropical cyclone, eddy, mixed-layer current, surface drifter, satellite altimetry
Authors:
Ruo-Shan Tseng, Yi-Ting Cheng
Abstract:
Global velocity data from drifters of the Surface Velocity Program and the sea surface height and geostrophic velocity data from satellite altimetry observations under tropical cyclones (TCs) were analyzed to demonstrate strong ocean currents and their characteristics under various storm intensities in the Northern Hemisphere (NH) and in the Southern Hemisphere (SH). Mean TC's translation speed (Uh) is faster in the NH (~4.7 m s-1) than in the SH (~4.0 m s-1), owing to the fact that TCs are more intense in the NH than in the SH and the steering flow is more favorable in the NH . The rightward (leftward) bias of ocean mixed-layer (OML) velocity occurs in the NH (SH). As a result of this slower Uh and thus a smaller Froude number in the SH, the flow patterns in the SH under the same intensity levels of TCs are more symmetric relative to the TC center and the OML velocities are stronger than those in the NH. Several special cases were reported in this study showing the occurrence of prominent cyclonic eddies with a life span of several months which were induced by slow-moving (Uh ~ 1 m s-1) and intense (category 3, 4, and 5 of the Saffir-Simpson Scale) TCs, both in the NH and SH. This study provides the first characterization of the near-surface OML velocity response to all recorded TCs in the SH from direct velocity measurements. Our findings provide observational evidence of generation of extremely strong cyclonic oceanic eddy or enhancement of weak existing cyclonic oceanic eddy under slow-moving category-5 TCs, which will support further improvements of their representation in ocean dynamics and numerical air-ocean prediction.
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