The Indonesian throughflow's effect on global climate determined from the COLA coupled climate system

Blocking the Indonesian archipelago by a land bridge, and so preventing flo w from the western equatorial Pacific Ocean into the eastern Indian Ocean, causes a global readjustment in the coupled ocean-atmosphere's climate. Not able features found in 10-yr-averaged fields when compared with the control climate are an ENSO-like signal over the equatorial Pacific, with warmer S STs in the eastern basin, westerly anomalies in wind stress, and increased precipitation along the equator. The band of increased precipitation is fla nked by bands of decreased rainfall. Over the Indian Ocean, blocking of the throughflow results in signatures similar to those associated with the Ind ian Dipole Mode. In the eastern basin, there are cooler SSTs and heat conte nt anomalies. The southeast trades are increased with an associated increas e in latent heating. The precipitation belt is shifted northwestward to giv e decreased rainfall over southern Indonesia and increased rainfall to the north; there is a slight increase in rainfall over eastern Africa, and SSTs are warmer in the western half of the basin. The Atlantic, midlatitudes, a nd polar regions are affected via atmospheric teleconnections. Net surface heat flux differences in regions of significant SST difference in the equatorial Pacific and Indian Oceans are about 2 times as large as f ound previously in ocean-only simulations, indicating a positive feedback. Experiments with the atmospheric GCM component forced by the Indian Ocean S ST anomalies generated by blocking the throughflow reproduce the changes in surface heat flux and winds found in the coupled model simulations over th e southern Indian Ocean. In the equatorial Pacific, positive feedback is pr ovided by the Bjerknes mechanism. In the Indian Ocean, the positive feedbac k loop comprises a change in oceanic heat flux divergence, which changes SS T, and in turn net surface heat flux and surface winds, which further chang e the oceanic circulation and heat flux divergence; the primary effect is o n meridional advection. The feedback is sufficiently strong that the anticy clonic-cyclonic pair of Sverdrup gyres generated in the tropical southern I ndian Ocean with lateral viscous effects alter the path of the depth-integr ated throughflow transport from zonal across the Indian Ocean, then southwa rd along the east African coast, to southwesterly. The Island Rule indicate s another positive feedback in the coupled system, albeit weak, as the modi fication to the wind stresses (attributed to the zonal ones in the equatori al Pacific), which results from blocking the throughflow, acts to decrease further the throughflow. Interannual variability in the total throughflow t ransport is not well predicted by the Island Rule. Its seasonal cycle appea rs driven by the cycle in the equatorial Pacific, as both lead by two month s that found in stand-alone ocean GCMs.