A LAGRANGIAN DESCRIPTION OF THE WESTERN EQUATORIAL PACIFIC RESPONSE TO THE WIND BURST OF DECEMBER 1992 - HEAT ADVECTION IN THE WARM POOL

During the Tropical Oceans Global Atmosphere (TOGA) Coupled Ocean-Atmo sphere Response Experiment (COARE) intensive observing period (IOP), s ustained westerly winds were observed between 20 December 1992 and 10 January 1993 in the area between 155 degrees E and 180 degrees. The oc eanic response to this event was monitored by 33 Lagrangian mixed laye r drifters, six of which were equipped with SEACAT salinity sensors. T he drifters were distributed over several hundred kilometers meridiona lly and over a zonal extent of 2400 km. During the wind event, the dri fters accelerated eastward and formed a strong equatorial jet that was relatively independent of longitude. Following the drifters, the wate r parcels cooled and became more saline; Sea surface temperature (SST) maps suggest that evaporative cooling occurred. In order to consider the dynamics and thermodynamics of this jet in more detail, wind stres s and buoyancy forcing along the track of each individual drifter were constructed from the TOGA COARE European Centre for Medium-Range Weat her Forecasts analysis. The mixed layer depth scale and the zonal pres sure gradient were calculated from a linear regression between the acc eleration and the wind stress. In the meridional direction, the wind s tress was smaller and not coherent with the acceleration at any period . During the December wind burst, the entire western equatorial Pacifi c cooled and a large-scale zonal temperature gradient with cooler wate r to the west was established west of the date line. Cooled water was advected to the: east during this episode. A 4-yr-long TOGA-Tropical A tmosphere Ocean (TAO) current meter record at 165 degrees E and the hi storical dataset from 250 drifters in the western Pacific within 3 deg rees of the equator, together with temperature gradients computed From the National Meteorological Center (renamed the National Centers or E nvironmental Prediction) SST analysis along the equator, were used to compute a time ensemble average heat advection. On average, cooled wat er was advected along the equator eastward from the ''warm'' pool, and this occurred when equatorial currents were to the east.