Thermal Plumes and Internal Solitary Waves Generated in the Lombok Strait Studied by Ers Sar

The Lombok Strait separates the Indonesian islands Bali and Lombok and is the second most important strait through which water is exchanged between the Pacific Ocean and the Indian Ocean. The south end of the Lombok Strait is split by a small island and on each side of the island are rugged sills with an average depth of about 200 m. On the sill, tidal current speeds up to ±3.5 m/s are encountered. Variable southward flow of warm Pacific waters through the strait into the Indian Ocean forms a well-developed thermal plume south of the sill. The position of the front associated with this plume has been identified on several ERS SAR images. Its extent and shape are determined by the water transport through the strait and characteristics of the South Java Current which in turn depend both on the annual cycle of the monsoon winds and prolonged disturbances in wind field. Another oceanic phenomenon that has been detected on ERS SAR images is the internal solitary waves that are tidally generated at the sill and propagate in both directions. The waves propagating northward into the Java Sea have always a quite regular circular shape while the ones propagating southward into the Indian Ocean have a very irregular shape. Physical explanation for this behavior is presented. We attribute this mainly to the strongly horizontally varying current field south of the sill. Since the sea surface manifestations of the internal waves vary very strongly with time, we hypothesize that the internal wave characteristics south of the Lombok Strait depend on the stratification of the water body and the strength of the water flow through the strait. Thus, we suggest that ERS SAR imagery showing internal waves south of the strait may also be used for obtaining information on the throug-strait flow variations.