The distribution of internal waves in the East China Sea and the Yellow Sea studied by multi-sensor satellite images

Abstract —The distribution of internal waves in the East China Sea and the Yellow Sea has been studied by screening 170 ERS SAR images and 202 SPOT images for sea surface signatures of internal waves. The occurrence of internal wave signatures is correlated with the phase of the spring-neap tidal cycle and with the time of the year which yields information on the stratification of the water column. Internal waves, East China Sea, Yellow Sea, synthetic aperture radar, ERS, SPOT. I. I NTRODUCTION The East China Sea and the Yellow Sea are sea areas where little information exists on the generation, propagation and distribution of internal waves (IWs), see [1], [2], and [ 3 ]. The first systematic study of the distribution of IWs in these sea areas was carried out by Hsu et al. in 2000 [1], who analysed radar images for IW signatures which were acquired by the synthetic aperture radar (SAR) onboard the satellites ERS-1 and ERS-2 between 1993 and 1997. In the present study we have extended his investigation by including ERS SAR images that were acquired after 1997 and by using images that were acquired in the visible bands from the French SPOT satellites. This has increased the data base considerably and made it possible not only to generate much more detailed maps of the distribution of IWs in the East China Sea and the Yellow Sea, but also to study how the occurrence of IWs depends on the phase of spring-neap tidal cycle and on the time of the year. The occurrence of IWs is an indicator for the stratification of the ocean column, i. e., for the existence of a pycnocline. In winter the water columns in the China Sea and the Yellow Sea are usually well mixed due to the prevailing cold winds from the north and thus no internal wave signatures are observed. II.