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Eddy properties in the Pacific sector of the Southern Ocean from satellite altimetry data
Yongliang DUAN, Hongwei LIU, Weidong YU, Yijun HOU
doi: 10.1007/s13131-016-0946-2
Mesoscale eddies play a key role in the ocean dynamics of the Southern Ocean, and eddy response to the climate changes has also been widely noted. Both eddy kinetic energy (EKE) and eddy detection algorithm are used to study the eddy properties in the Pacific sector of the Southern Ocean. Consistent with previous works, the maps of the EKE illustrate that higher energy confines to the Antarctic Polar Frontal Zone (APFZ) and decreases progressively from west to east. It also shows that the most significant increase in the EKE occurs in the western and central parts of the Pacific sector, where the baroclinicity of the Antarctic Circumpolar Current (ACC) is much stronger. Statistical eddy properties reveal that both of the spatial pattern and interannual variation of the EKE are primarily due to the eddy amplitude and the eddy rotational speed, rather than the eddy number or the eddy radius. In general, these results furtherly confirm that anomalous westerly wind forcing associated with the positive Southern Annular Mode (SAM) index enhances the Southern Ocean eddy activity by strengthening the eddy properties.
key words: eddy property, eddy kinetic energy, Southern Ocean, satellite altimeter
Bimodality and growth of the spectra of typhoon-generated waves in northern South China Sea
Dongxue MO, Yahao LIU, Yijun HOU, Ze LIU
Buoy-based observations of wave spectra during the passage of three typhoons in the northern South China Sea are examined. Though most spectra of mature typhoon-generated waves are unimodal, double-peaked spectra account for a significant proportion during the growing and decaying stages. This is due either to the superposition of swells on local wind waves or to the mechanism of nonlinear interaction between different wave components. The growth rate of energy density is an effective way to predict spectrum variation. The dominant wave direction depends on the location of the typhoon center to the site, but the direction spread shows no regularity in distant regions. In this study, a new six-parameter spectral formula is proposed to represent double-peaked spectra and is shown to provide a better fit than previous models. The theoretical relationship between shape parameter and spectral width is still applicable to each peak. The characteristics of the variations of spectral parameters are analyzed. It is demonstrated that the spectral parameters are not only related to the typhoon intensity and typhoon track, but also have strong intercorrelations. Moreover, the growth relation between significant wave height and significant wave period is obtained to fit the typhoon-generated waves.
key words: double peak, South China Sea, spectral parameters, typhoon, wave spectrum

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