The seasonal cycle of transport from the Pacific to the Indian Ocean via the Indonesian throughflow

A series of numerical model experiments were run to investigate the annual cycle of mass transport between the Pacific and Indian Oceans via the Indonesian throughflow (ITF). The 1{dollar}{lcub}1over 2{rcub}{dollar}-layer, reduced-gravity model used in this study, forced by climatological wind stress, produces a mean Indonesian throughflow which has an annual range of more than 8 Sv. The peak throughflow occurs from mid-April through July, and the minimum is in November and December. A linear version of this model gives a similar result indicating that the annual, wind-driven response of the throughflow is primarily linear.; Model experiments show that most of the annual throughflow signal is due to equatorial; variability generated by off-equatorial winds account for less than 1Sv and are out of phase with the baseline throughflow signal. The effects of wind forcing in the equatorial Indian Ocean cancel those due to winds in the Indonesian seas, and winds in the equatorial Pacific winds generate annual ITF variations nearly equivalent to those from the baseline run.; In this model, Rossby waves (formed by Ekman pumping in the eastern Pacific) propagate to the western boundary of the Pacific then form coastal Kelvin waves that propagate through the Indonesian seas. In northern spring (fall), a downwelling (upwelling) wave brings elevated (reduced) sea level to the Pacific side of the Indonesian seas, and the ITF is maximum (minimum). In the Indian Ocean, monsoon winds produce equatorial Kelvin waves which propagate east and form coastal waves along the southern coasts of Sumatra and Java. In this case, a downwelling (upwelling) wave increases (decreases) sea level on the Indian Ocean side of Indonesia in northern winter (spring), thus acting in opposition to the baseline ITF variability. The effect of winds in the Indonesian seas on the model upper layer thickness is opposite to the effects of the remotely forced Kelvin waves from the Indian Ocean. In northern winter, when the Indian Ocean winds cause a upwelling coastal wave, the local wind stress provides Ekman pumping. In northern spring, locally forced Ekman suction counters the downwelling Kelvin wave.