Study of rain events over the South China Sea by synergistic use of multi-sensor satellite and ground-based meteorological data

Rain cells and rain bands over the South China Sea off the coast a Hong Kong are studied by using multi-sensor satellite and ground-based meteorological data. These include synthetic aperture radar (SAR) images acquired by the Advanced Synthetic Aperture Radar (ASAR) onboard the European ENVISAT satellite, weather radar images from the Hong Kong Observatory (HKO), rain rate data acquired by the Special Sensor Microwave Imager (SSM/I) sensor onboard the F15 satellite of the American Defense Meteorological Satellite Program (DMSP) and the rain sensors onboard the Tropical Rainfall Measurement Mission (TRMM) satellite, cloud image of GOES-9 satellite, sea surface wind maps acquired by the scatterometer onboard the QUIKSCAT satellite, and meteorological data from weather stations in Hong Kong. Three rain events, typical of Hong Kong, are studied. The first event consists of a cluster of rain cells associated with the summer monsoon, the second one of rain cells aligned in a rain bond generated by an upper-air trough, and the third one consists of small rain cells embedded in a cold front. It is shown that ASAR images, which have a resolution of 30 m in the Image Mode (IM) and 150 m resolution in the Wide Swath Mode (WSM), yield much more detailed information on the spatial structure of rain events over the ocean than data obtained from SSSM/I and the rain sensors onboard the TRMM satellite. The precipitation radar (PR) onboard TRMM, which is the rain measuring instrument flown in space with the next best resolution, has a resolution of only 4 km. However, the disadvantage of SAR is that it is sometimes difficult to identify SAR signatures visible on SAR images of the sea surface unambiguously as caused by rain events. By comparing SAR images with simultaneously acquired weather radar images of the Hong Kong Observatory, a better knowledge of radar signatures on SAR images resulting from rain events over the ocean is obtained. This knowledge then helps greatly in detecting rain events on SAR images which are acquired over ocean areas, which are not in the reach of weather radar stations. SAR images containing radar signature of rain events allow a much more detailed study of fine-scale structures of rain events over the World's ocean, in particular of clusters of rain cells, than any other sensor presently flown in space.