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The use of GlobCurrent products at CPTEC/INPE (Brazil)

Since 2011 the National Institute for Space Research (INPE), Brazil, has conducted an operational remote sensing monitoring of sea surface features along the Southeastern Brazilian Margin, on the western side of the S Atlantic based on daily optical, thermal-infrared and microwave satellite data. The shelf-break dynamics on this region is ruled by meanders and eddies associated with the Brazil Current (BC). The continental shelf is dominated by transient mesoscale variability induced by BC meandering, coastal upwelling and directly by the wind. In this complex panorama, the systematic extraction, identification and tracking of sea surface features, like ocean fronts, eddies, meanders and coastal plumes have been contributing to build up regional knowledge about Ocean Surface Currents (OSC). Figure 1 presents the accumulated position of BC inner front extracted throughout 57 months, in a total of 1,094 frontal detections.

Figure 1: Accumulated position of Brazil Current inner front extracted from January 2011 to September 2015. The colorbar represents the relative number of observations in a total of 1,094 daily frontal detections using SST or Chlorophyll-a images. The black lines are bathymetric contours indicating the shelf break. It is possible to highlight four areas related to permanent or semi-permanent cyclonic meanders.

To better understand the regional dynamics, OSC in the region of interest has been derived from altimetry and compared with the U.S. Navy Costal Ocean Model (NCOM) numerical model and remotely sensed sea surface temperature and chlorophyll concentration fields. In general, with NCOM data it is possible to observe a reasonable spatial characterization over the inner and middle shelf. This relatively higher richness of details allows a better representation of the oceanographic processes mainly on the shelf break and coastal regions. These observations are also corroborated by concomitant thermal and ocean color satellite images. However, at more offshore areas, monthly altimetry and NCOM OSC are better correlated representing relatively well the larger scale processes (Figure 2).

Figure 2: Two examples of synergy between modeled Ocean Surface Currents vectors and satellite images: (i) on the left: NCOM vectors over MODIS/Aqua Chl-a image - February 29th 2010; and (ii) on the right: NCOM vectors over AVHRR/NOAA SST image - April 7th 2011.

Many efforts and projects aiming to model global OSC have caveats over the shelf and shallow waters, since the dynamics in these areas have different regional characteristics and present a component of complex sub-mesoscale to mesoscale processes. More recently, the GlobCurrent project has brought an innovative approach using the synergy of different satellite sensors, merging different processing techniques in order to improve the understanding of spatial and temporal variability of global OSC. We tested the first version of combined Geostrophy + Ekman OSC product of GlobCurrent, comparing with our daily ocean feature extraction from satellite data. We observed a good spatial correlation over the major meanders of the BC, although the sub/mesoscale features are still not well described by the present OSC product (Figure 3). We expect that future versions of GlobCurrent products could better represent sub/mesoscale processes in our region of interest improving our monitoring capability for those coastal and shelf break regions.

Figure 3: Calculated daily mean OSC fields (February 10th, May 6th and November 5th 2011) from “Combined Geostrophic+Ekman Currents” GlobCurrent product, overlaid with regional ocean features (dark-green lines) extracted by CPTEC/INPE from orbital images. One may observe a good spatial correlation over the major meanders of the Brazil Current, although the sub/mesoscale features are still not well described by the present version of the GlobCurrent product.

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