Spatial and temporal scales of the Brazil-Malvinas Confluence region documented by MODIS high resolution simultaneous SST and color images

BARRE, N., C. PROVOST AND M. SARACENO

ADVANCES IN SPACE RESEARCH

Año: 2006 vol. 37 p. 770 - 786

0273-1177

The moderate resolution imaging spectroradiometer (MODIS) on board the Aqua satellite measures visible and infrared radiation in36 wavebands, providing simultaneous images of sea-surface temperature (SST) and chlorophyll-a (chl-a) concentration in the uppermeters of the sea. For the first time, truly synoptic SST and chl-a- concentration images are available. These images are daily and of1.1-km resolution.The strong contrasts in sea-surface temperature and surface chlorophyll-a concentration over the southwest Atlantic make satelliteinfrared and color images particularly appropriate tools for studying the Brazil–Malvinas (B/M) Current confluence. We examinetwo years (July, 2002–June, 2004) of Aqua/MODIS infrared and color images to document the precise structure of the B/M confluencesimultaneously in SST and chl-a.We first compared MODIS weekly data with simultaneous independent satellite data. Spatial and temporal distributions are similarfor both SST and color. Differences between MODIS and SeaWiFS (sea-viewing wide field-of-view sensor) are large in pigment-richregions along the coast and shelf. Here, we focused on the offshore region where differences are small.For each season, exceptionally cloud-free 1.1-km resolution MODIS images showed two thermal fronts, one corresponding to theBrazil Currents southernmost limit, the other, to the Malvinas Currents northernmost limit. These two fronts remained quite closeto each other (within 50 km) and were separated by water with an SST and chl-a concentration typical of the continental shelf waters.In spring, the water rich in chl-a from the platform is squeezed between the two currents and entrained away from the coast in betweenthe two thermal fronts. In the frontal region, SST gradient maxima trace the contour of the chl-a-rich water.Enlargements of the frontal region and of the turbulent region downstream of the frontal collision are presented and analyzed.MODIS documents in an unprecedented way the SST and chl-a filaments as they are distorted and mixed by meso- and sub-mesoscalestructures in the strain-dominated region of the B/M confluence. It is suggested that a substantial part of the chl-a local maximum in theMalvinas return flow is of continental-shelf origin.