Mixed-layer current and cyclonic eddy induced by global tropical cyclones

Speaker:

Prof. Ruo-Shan TSENG, Department of Oceanography, National Sun Yat-sen University

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 (U_h) 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 U_h 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 (U_h ~ 1 m s^-1) and intense (category 3, 4, and 5 of the Saffir-Simpson Scale) TCs, either 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.