SST, thermohaline structure, and circulation in the southern Gulf of California in June 2004 during the North American Monsoon Experiment

The thermohaline structure, circulation, and heat fluxes in the Gulf of California entrance during June 2004 are described based on conductivity-temperature-depth and Lowering Acoustic Doppler Current Profiler data collected in a 14-day survey, supported by satellite data. The AVHRR images show extensive mesoscale structures in the region, the most striking being (1) a cool filament extending from the California Current domain and (2) a warm intrusion along the mainland shelf. On the warm side of the thermal front created by the cool filament there was a strong current flowing into the Gulf, with speeds up to 0.70 ms(-1) in the surface; this current, which the SST images suggest was associated with a decaying eddy, carried 6 Sv into the Gulf. Associated with the second structure, there was an ingoing coastal current on the mainland shelf, with weak surface currents but with speeds similar to 0.25 ms(-1) at its core, between 70 and 200 m; this coastal current transported 2 Sv into the Gulf. The two ingoing currents appear to join inside the Gulf, forming a very strong (speeds 0.40-0.80 ms(-1)) narrow (similar to 30 km) coastal current between the surface and 500 m depth. Changes in the thermohaline structure of the upper layers observed by repeat sampling of three cross sections were dominated by advection. However, it was found that the advective heat flux is very variable in space and time. For the period of observation it was estimated that the lateral heat input was 4.8 +/- 3.0 x 10(5) Wm(-2) as estimated with LADCP currents and 5.7 +/- 2.20 x 10(5) Wm(-2) with geostrophic velocities.