Abstract
Surface currents in the Alboran Sea are characterized by a very fast evolution that is not well captured by altimetric maps due to sampling limitations. On the contrary, satellite infrared measurements provide high resolution synoptic images of the ocean at high temporal rate, allowing to capture the evolution of the flow. The capability of Surface Quasi-Geostrophic (SQG) dynamics to retrieve surface currents from thermal images was evaluated by comparing resulting velocities with in situ observations provided by surface drifters. A difficulty encountered comes from the lack of information about ocean salinity. We propose to exploit the strong relationship between salinity and temperature to identify water masses with distinctive salinity in satellite images and use this information to correct buoyancy. Once corrected, our results show that the SQG approach can retrieve ocean currents slightly better to that of near-real-time currents derived from altimetry in general, but much better in areas badly sampled by altimeters such as the area to the east of the Strait of Gibraltar. Although this area is far from the geostrophic equilibrium, the results show that the good sampling of infrared radiometers allows at least retrieving the direction of ocean currents in this area. The proposed approach can be used in other areas of the ocean for which water masses with distinctive salinity can be identified from satellite observations.
Highlights
The Strait of Gibraltar is the natural connection of the Mediterranean Sea with the world ocean, being a hot spot area in many senses
These images unveil the presence of at least three different water masses: the warm waters associated to the WAG and EAG, a very warm water filling the northeast part of the Alboran Sea as well as the nearby Algerian basin, and a tongue of cold water newly entered from the Strait of Gibraltar that separates the previous ones
This study provides further evidence that the Surface Quasi-Geostrophic (SQG) approach is able to reconstruct velocities in the Alboran Sea
Summary
The Strait of Gibraltar is the natural connection of the Mediterranean Sea with the world ocean, being a hot spot area in many senses. The model is free-surface, and has both a hydrostatic and a non-hydrostatic forare able to reprodaauntidocnce.onIttssehqsueuebnsotelyqbuvseeneetrrsivmtoeptidhnegespmouehnthyt dsaugieacitnaosltthpteherCooAricforeliicssanascecceoslae,sr-tas mwuTlahateiosmno(tdMhealerdsohmcalalaienstecaol.v,oe1r9fs9t7ht,eh).GeulfMof CEadDizEanSd Sth-eGAlbIoBraneSxeaperiment, a way to igmivesprrisoe vtoeatnhewe WsuAGb, swehqichuienntutrnfodirspelaccaessttheisoldtoWhAGave(firnomit9i.a37l°Wcoton1d.59i°tEi)o, anndshaasnbdeenadniscareltyizzedewdithfiaecludrvsilina-s close as further east This process of gyre generation is well known and ear grid of variable resolution. We went further by validating the reliability of using a time series of ocean velocity fields from SST covering the full area between the Strait of Gibraltar and the Alboran Sea. In particular, we analyzed the performance of the SQG approach when applied to infrared satellite measurements and compared to velocities derived from surface drifters. SMOS SSS daily L3 maps at 1/4◦ × 1/4◦ resolution were produced by means of a successive corrections analysis applied over time periods of nine days using influence radii adapted to the Mediterranean Sea, see [32] and reference therein
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