Structure and Propagation of a Large Cyclonic Eddy in the Western North Pacific from Analysis of XBT and Altimetry Data and Numerical Simulation

Abstract

The Kuroshio transport east of Taiwan dropped precititously at the beginning of 1995. At the same time a large cyclonic eddy was spotted in the general vicinity. The time history and vertical structure of this eddy, which originated from the subtropical North Pacific, are reconstructed using XBT and T/P altimetry data. Our results show that dynamic heights calculated from the XBT with reference level to 500m agree well with satellite-derived sea surface height anomalies (SSHA). Application of the Empirical Orthogonal Function (EOF) analysis to XBT data shows that the first mode alone, which explains 75% of the total temperature variance, captures most of the eddy structure. The second mode, which explains most of the remaining variance, reflects the redistribution of vertical temperature structure at the trail of the eddy. The cyclonic eddy propagated in the northwest direction with an averaged speed of about 10 km/day. A quasi-geostrophic model is applied to examine the eddy propagation. The model result suggests that a northward background baroclinic flow of 6 km/day can account for the observed northward propagation. The model also predicts the formation of a strong anticyclonic eddy at the wake of the cyclonic eddy.

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