The polarity conversion of oceanic internal solitary waves (ISWs) in the South China Sea (SCS) is studied using
synthetic aperture radar (SAR) images. Eight SAR images which have oceanic internal wave polarity conversion
information in the SCS are selected from about 300 oceanic internal wave SAR images between 1998 and 2008. It is
found that the elevation ISWs mainly occur in the area from 114°E to 115°E longitude and from 20°N to 22°N latitude
during summer and early autumn. All the ISWs propagate westwards with the wavelengths between 300m and 800m.
The polarity conversion is analyzed using one SAR image which contains successive elevation internal waves and the
two-layer KdV theory. Studies with in situ data show that the occurrence of polarity conversion of ISWs in the SCS is
related to a thicker upper mixed layer compared with the lower layer on the continental shelf.