The Statistical Analysis Of Mesoscale Eddy In The North Pacific Ocean

Using surface geostrophic velocity anomaly which derived from altimetric dataset, the mesoscale eddies were detected and tracked by a geometry-based eddy detection method in the north Pacific Ocean from January 1993 to October 2014.A total of 20373 cyclonic eddies and 18875 anticyclonic eddies were identified, which includes the following characteristic parameters: eddy polarity, eddy lifetime, eddy radius, eddy propagation distance and eddy propagation speed. The mean lifetime was 18.7 weeks for cyclonic eddies and was 19.8 weeks for anticyclonic eddies,respectively, and the mean radius was 45 km and 46 km, respectively, and the mean propagation distance was 559 km and 562 km,respectively, and the mean propagation speed was 5.1cm/s and 5.0cm/s, respectively. The four above parameters’ distribution of cyclonic eddies and anticyclonic eddies are basically the same,furthermore, eddy radius, eddy propagation distance and eddy propagation speed are approximated by logarithm normal distribution.Cyclonic eddies genesis and anticyclonic eddies genesis have apparent seasonal variations,and their trend are almost the same. Analysis further demonstrates that the number of the eddies generated is maximum in the winter but minimum in the summer. The eddies mainly generate in the eastern north Pacific ocean in winter and summer,and the major difference in the distribution of generated eddies in winter and summer is in the region 15°N-35°N.Meanwhile, in 1995,2001,2010, the genesis number are abnormal increase, in contrast, the number are abnormal decrease in 2003.But the abnormal number are not produced mainly in winter,the other three seasons also have certain contribution. In winter, the variation trend of eddies genesis anomaly and SST anomaly have negative correlation, which also exist in the eddies genesis anomaly and wind stress curl anomaly. Correlation analysis implies that eddy activity is sensitive to SST and wind stress curl on interannual timescales, especially in winter. And anomalous SST changes the stratification of the upper layer of the ocean and thus affects the generation of eddies.In addition, the zonal variation of eddy radius and the first baroclinic Rossby deformation radius have large differences, and so do eddy propagation speed and the first baroclinic Rossby phase speed. This shows that mesoscale eddy can’t be explained by the first baroclinic Rossby wave.