Intraseasonal Variation of the Throughflow in the Lombok Strait and Ombai Strait and Its Driven Mechanism

Power spectrum analysis of INSTANT data shows that transport throughflow the Lombok and Ombai Straits at different depth are subjected to different significant periods, according to which the Lombok and Ombai transports can divided into independent layers. The Lombok transport is divided as 0-150 m and 150-300 m layers, with significant periods at 30-70 and 30-40 days, respectively. The Ombai transport is divided as four layers, with significant period at around 40 days and 50-75 days for the upper 300 m, 30-45 days and 55-75 days at 300-600 m layer, 30-40 days, quasi-50 and 60-75 days at 600-1000 m layer, and 30-40 days beneath 1 000 m. The ISVs in Lombok and Ombai Straits are attributed to the propagation of intraseasonal Kelvin waves that derived from the equatorial Indian Ocean. Since the Kelvin waves arrive at greater depth during the propagation, the vertical distribution of transport series at each straits show upward phase propagation. The phase speed of ISVs propagating from the equatorial Indian Ocean to Lombok and Ombai Straits are estimated between 1.59 and 2.95 m/s, which are composed of the first and second baroclinic modes of Kelvin wave. Along shore wind anomalies at intraseasonal band along the Lesser Sunda Islands are suggested to have influence on the propagation of the intraseasonal Kelvin waves.