Effects of tropical cyclones on underwater sound propagation

Abstract

Environmental data collected near the continental shelf and the shelfbreak in the Southern East China Sea around Taiwan are utilized to study sound propagation effects of tropical cyclones (typhoons). These data were from the Conductivity-Temperature-Depth (CTD) profiling casts conducted during the Quantifying, Predicting, Exploiting (QPE) Uncertainty experiments in both 2008 and 2009. These CTD surveys provided observations for the normal physical oceanographic conditions in the area and, most importantly, the extreme conditions induced by a tropical cyclone Typhoon Morakot in the summer of 2009. Strong upwelling currents near the shelfbreak in the experiment area were observed after the typhoon past by, and the water-column stratification was changed. A sound speed variation of 10 m/s over 50 km in distance was measured in the upwelling area, and this can produce significant effects on sound propagation. Numerical models using parabolic-equation and ray tracing methods will be presented to demonstrate the underlying physics of the sound field variability. [Work supported by the Office of Naval Research.]