THE EFFECT OF THE INDONESIAN THROUGHFLOW ON OCEAN CIRCULATION AND HEAT-EXCHANGE WITH THE ATMOSPHERE - A REVIEW

A new version of the island rule, which relates transport aound an isl and to wind and pressure forcing, provides a basis for comparing vario us published theoretical estimates of the long-term mean Indonesian th roughflow magnitude. It is found, among other things, that nonlinear e ffects near Halmahera and pressure gradients across New Zealand may mo dify the long-term throughflow magnitude. Recent theoretical estimates of interannual throughflow variations are in approximate agreement wi th observation; Indian Ocean Kelvin waves play an important role. On s till shorter timescales and for understanding flow details in differen t channels, consideration of the full details of the Indonesian region via numerical modeling becomes essential. Most of the throughflow ent ers from the Mindanao Current. The process by which the South Pacific waters eventually reach the Mindanao Current appears to involve some n onlinear retroflection process (particularly in northern summer) and s ubsequent freshening along long pathways in the North Pacific. Observe d water mass transformations in Indonesian waters demand a vertical ed dy diffusivity of about 10(-4) m(2) s(-1), large enough to generate tu rbulent heat fluxes of order 40 W m(-2) at the base of the mixed layer . According to numerical models, changes in ocean circulation associat ed with the throughflow are likely to affect patterns of heat exchange with the atmosphere in widely separated regions of the world ocean. I n particular, an increased throughflow will result in more heat loss t o the atmosphere in the subtropical Indian Ocean and less in the Pacif ic Ocean. Simple, physically reasonable mechanisms have been offered f or these model results. Observational evidence to support or refute th ese mechanisms is rather fragmentary but is reviewed here. Our present understanding of the throughflow permits some informed speculations a s to the possible role of the throughflow in coupled ocean-atmosphere phenomena such as the El Nino-Southern Oscillation (ENSO). Earlier est imates of western Pacific reflectivity seem largely confirmed by recen t observational results. However, it is suggested that tidal mixing in the Indonesian seas may generate ENSO-related sea surface temperature anomalies there, possibly affecting the development of westerly wind bursts.