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General Session 1: Physical oceanic processes: Dynamics and physical-biological-biogeochemical interactions |
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Mixed-layer current and cyclonic eddies induced by tropical cyclones
GS1-04-S
Yi-Ting Cheng* , National Sun Yat-sen University
Presenter Email: z123456776@yahoo.com.tw
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| Oceanic response to tropical cyclones (TCs) have attracted the attention of numerous researchers for decades due to its profound influence on our environment. Many studies show that strong winds associated with TCs induce upper-ocean cooling and mixed-layer deepening on the wake of TCs and generate upwelling and near-inertial currents beneath storms. In this study, a new and rare phenomenon, i.e., mesoscale cyclonic eddies, is shown to occur under super typhoons (TCs of category 3 and up) moving with a relatively slow translational speed. ˇˇˇˇGlobal velocity data from SVP drifters of the Surface Velocity Program and the sea surface height and geostrophic velocity data from satellite altimetry observations under tropical cyclones (TCs) are 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. 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 are 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, in both NH and SH. This study provides the first discovery of TC-induced cyclonic eddies and the characterization of the near-surface OML velocity response to all recorded TCs in the global oceans from direct velocity measurements. |
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