The island rule with multiple islands and its application to the Indonesian Throughflow

The island rule theory in the case of complex geometry with multiple islands referring to the Indo-Pacific Maritime Continent is investigated on the basis of Godfrey's island rule theory. The bottom friction and lateral friction of multiple channels are considered by employing the Munk and Stommel boundary layer models. Five idealized cases with various spatial distributions of islands are designed to examine the influence of shape and size of the islands. The analytical solutions of the streamfunctions of the through-flows among the islands are obtained and the volume transport through each channel is estimated. The Indonesian Throughflow (ITF) transport is then calculated using the analytical solutions with wind stress and compared with observations and previous theoretical results. The ITF transport from the multiple island rule is about 14.5 Sv during 2004-2006, which is close to the observed ITF transport (about 15.0 Sv) from the International Nusantara Stratification and Transport. We find that the multiple islands rule reproduces well the mean value and interannual variability of the observed ITF transport, and inclusion of wind stress in the North Pacific Ocean may improve the estimate of ITF transport. Sensitivity experiments indicate that frictional boundary layer thickness and channel size influence the estimated ITF transport under the multiple island framework. These results imply that the multiple island rule shows improvements in estimating the ITF transport relative to previous studies, and the multiple island rule can be used to produce long time series of ITF transport and might have implications for paleo-ITF study.

Automated summary

The island rule theory is applied to investigate the influence of complex geometry with multiple islands referring to the Indo-Pacific Maritime Continent. Through the use of analytical solutions and sensitivity experiments, the study finds that the multiple island rule reproduces well the observed transport of the Indonesian Throughflow (ITF) and may have implications for paleo-ITF study. The inclusion of wind stress in the North Pacific Ocean improves the estimation of ITF transport.