Advection and diffusion of Indonesian throughflow water within the Indian Ocean South Equatorial Current.

摘要

Using WOCE WHP CTD and ADCP sections in Indian Ocean from 1995 and ARLINDO 1994 CTD data within the Timor Sea, the throughflow component of the SEC transport is investigated. Throughflow water is well represented by its nearly homogenous low salinity feature within the SEC thermocline, extending from 60 m to about 300–400 m (or 10°C isotherm). Over 80% of its initial T/S signature is still present half way across the Indian Ocean, with over 60% reaching well into the western Indian Ocean. While the transport of thermocline water within the SEC from 5°S to 20°S varies from 10 to 35 Sv (Sv = 1 × 106 m3 s−1), the throughflow portion varies from 3 to 12 Sv, probably in response to variations of the throughflow transport, which changing with the phase of the monsoon and ENSO, and of the Indian Ocean Equatorial recirculation cell between the Equatorial Counter Current (5°S) and the SEC in the Indian Ocean. The throughflow water low salinity signal within the SEC thermocline diminishes enroute across the Indian Ocean. Assuming this is accomplished by isopycnal mixing with adjacent thermocline water, an isopycnal mixing coefficient of the order of 10 4 m2 s−1, with average value of (1.1 ± 0.8) × 104 m2 s−1 , is determined, which is reduced to 103 m2 s−1 if there is no zonal equatorial recirculation.; Estimates of the eddy fluxes across I-2 are made using a filtering procedure which filters out the fields of mesoscale eddy components using an ideal pass filter. The total eddy heat flux across 12 section from about 57° to 90.5°E, over the 60–300 m depth range is towards the south, of approximately 0 (hull ADCP), 2.2 (LADCP), 6.1 (geostrophic reference to hull ADCP meridional velocity at 200 m) and 2.8 × 1012 W (geostrophic reference to LADCP meridional velocity at 1000 m), about 2 orders of magnitude less than the total heat flux. The eddy flux of salt is southward at 3.7, 1.7, 3.2 and 1.0 × 105 kg s−1. The geostrophic velocity field reference the ADCP at 200 m provides the best estimate of eddy heat and salt transports. These correspond to the diffusivity Ky of the order of 2.0–4.5 and 3.6–8.6 × 103 m2 s−1 for temperature and salinity, respectively, which is one order of magnitude smaller than the lateral mixing coefficient calculated by the method of stationary lateral mixing of the Indonesian Throughflow, but is consistent with the situation of no equatorial recirculation. (Abstract shortened by UMI.)