THE VERTICAL CHARACTERISTICS OF INTERNAL WAVES IN SHALLOW REGION OF THE EAST CHINA SEA ANALYSED FROM CTD DATA

The vertical characters of temperature, salinity and density fluctuations in shallow region of the East China Sea are analysed by using 12 CTD short records with 1-hour intervals. The average S,t and p profiles can be divided into three distinctive layers: the thermocline, and the layers above and below it. The fluctuations of t, S and p are basically caused by internal waves, but there are somewhat intrusions or entrainments at the thermocline boundaries. The vertical displacement of the thermocline centre is up to more than 6.35m and the thermocline thickness changes from 3.5 to 8.0 m. Their varature with time are intermittent and rather irregular. The vertical wavenumber spectra of temperature fluctuations have been estimated by using the maximum entropy method, indicating that energy is mainly contained in the low-wavenumber range (0.13cpm) with two sharp peaks probably corresponding to the first and second modes of internal waves, whose dependence is estimated to be less than β-2. There exist dependences of β-3 and β-5, respectively in the midium range (0.13-0.64 cpm), representing finestructure or its mixture with internal waves, and the high range (0.64 cpm) indicating weak finestructure.