Internal wave observations in the northern South China Sea from satellite ocean color imagery

The northern South China Sea (SCS) including the Luzon Strait, from around 19 degrees to 22 degrees N latitude and from 114 degrees to 122 degrees E longitude, is an ocean area where energetic internal waves occur frequently. In this study, satellite ocean color products from SeaWiFS (Sea-viewing Wide Field-of-view Sensor) and MODIS (Moderate Resolution Imaging Spectroradiometer) including true color and chlorophyll images are used for the statistical analysis of internal wave occurrence. For spatial distribution, fewer internal waves distributed in the east of 118 degrees E obviously originate from the Luzon Strait, and more internal waves in the west of 118 degrees E may propagate from the east or evolve into solitons originating from the eastern boundary owing to the fission effect of the shoaling thermocline. No internal wave is found east of the Luzon Strait. The lunar daily observed internal wave occurrence frequencies show that more internal waves are found after full moon and new moon, that is the spring tide. This indicates that the generation of internal waves in the northern SCS may relate to the internal tide. The monthly distribution of internal wave occurrence frequencies reveals that the high frequencies are distributed from May to August and reach a peak in July with a maximum frequency of 21.5%. The low occurrence frequencies are found in winter from November to February with a minimum frequency of 0.5% in January.