Study On The Oceanic Intraseasonal Variability In The Indonesian Throughflow Region And Its Surrounding Waters

The Indonesian Throughflow, which flows from the Pacific to the Indian Ocean through the Indonesian Seas, is not only the unique passage for water and heat transport between the two oceans at low latitude, but also an integral part of the global climate system and thermohaline circulation. Previous observations have revealed significant intraseasonal variability of sea level, sea surface temperature and currents with the periods ranging from 20 to 90 days in the Indonesian Throughflow and its surrounding seas. These oceanic intraseasonal oscillations are found to have notable influences on the Indonesian throughflow transport. In this study, the intraseasonal variability of sea level and its propagation in this region is investigated based on the data from satellite altimeter and NCEP/NCAR reanalysis using statistical methods. The results show that the intraseasonal variability of sea level in the study area is derived from the intraseasonal Kelvin waves in the equatorial Indian Ocean which is forced by the zonal wind anomalies over the equatorial Indian Ocean. The equatorial Kelvin waves propagate eastward and are trapped by the east boundary of the Indian Ocean. After that, they propagate along the Sumatra and Java Island chain as costal Kelvin waves and penetrate into the Indonesian Seas subsequently at the straits of the Lesser Sunda Islands and reach as far as the Makassar and Ombai Straits. The pathways of the intraseasonal Kelvin waves can be summarized as:(1) propagating eastward along the Lesser Sunda Island chain to reach the Ombai Strait.(2) propagating eastward along the Sumatra coast and then travelling northward along the east coast of Sumatra after passing through Sunda Strait, these signals, however, cannot arrive at the Karimata Strait.(3) propagating eastward along the Sumatra-Java coast and penetrating into the Java Sea through Lombok Strait, part of which propagating northward and further reach Makassar Strai.(4) propagating westward along the north coast of Java Island to Java Sea after passing through Lombok Strait.