SEICHES AT THE COASTAL STATIONS ALONG THE NORTH COAST OF SOUTH CHINA SEA
南海北部沿岸海洋站的假潮

The seiche data from 15 coastal stations along the north coast of South China Sea are collected These data,especially those of the typical seiche events with relatively large amplitude,are examined by using statistics,natural period analysis and spectrum analysis to study the mechanism Among those 15 coastal stations,seiches with an amplitude of no less than 20cm were found in 9 of them The average occurring frequency is from almost once per month to almost once per 33 months These seiches occur mostly in February,March and April Among the total 327 seiche events,there are 10 sets (or events)with amplitude greater than 50cm,and the greatest amplitude is 102cm It is found that,the greatest amplitude of each seiche event occurs mostly during the high or low tides The natural period of fundamental mode of the bay calculated by the Merian's formula coincides well with the period estimated from the curve of observational water level, as well as with the period derived from the power spectrum This result shows that the seiches with relatively large amplitudes mostly occur in spring and summer,and they are all related to rapid changes in wind speed and direction as well as air pressure These atmospheric perturbations are south going cold airs in spring time and tropical cyclones in summer time This study shows that the occurrence of these seiches is likely the result of coupling and resonance between atmospheric perturbation and free mode oscillation of the bay,which has the oscillation of offshore surface wave as an intermediate media