Investigation of trapped atmospheric gravity waves over the South China Sea using Envisat Synthetic Aperture Radar images.

Atmospheric gravity waves (AGWs) trapped in the marine boundary layer leave fingerprints on the ocean surface, which are detectable by Synthetic Aperture Radar (SAR) on board polar-orbiting satellites. They are associated with varying wind speeds on the sea surface, which modulate the small-scale sea surface roughness and thus the backscattered radar power. We present three representative examples of SAR images acquired over the South China Sea by the Advanced Synthetic Aperture Radar (ASAR) on board the European Envisat satellite and show that different mechanisms are responsible for their generation and trapping in a wave duct (wave guide). For this we use, in addition to the ASAR images, satellite images acquired around the same time in the visible and infrared channels by the US polar orbiting satellite Terra and the Japanese geostationary satellite Multifunctional Transport Satellite (MTSAT)-1R, and in the microwave band by the Quick Scatterometer (QuikSCAT) satellite. In addition, we use synoptic weather information from which parameters relating to the trapping of atmospheric gravity waves in the lower troposphere are derived. Furthermore, we extract quantitative information on the sea surface wind speed induced by AGWs based on a wind scatterometer model. [ABSTRACT FROM AUTHOR]