Abstract
Abstract. In this article, the benefits of using satellite imagery of different types (namely thermal infrared, visible-range, and synthetic aperture radar (SAR) images) for observing surface circulation of marine basins are being discussed. As a region of interest, we use the Western Mediterranean Basin. At first, the areas with sharpest thermal and chlorophyll-a gradients within the region of interest were defined on a seasonal base using the data provided by Aqua Moderate Resolution Imaging Spectrometer (MODIS). After that, mesoscale eddies were detected using different sea surface temperature (SST) products and, finally, submesoscale vortices were observed with Envisat Advanced SAR imagery. Thus found locations of eddies were compared with locations of the sharpest fronts discovered in the first part of the study, which showed that the biggest, mostly anticyclonic, eddies tended to correspond to locations of main surface currents; smaller cyclonic eddies were mostly attributed to thermal fronts, while submesoscale eddies were distributed quite homogeneous. The observations performed in that way revealed quite prominent basin-, meso- and submesoscale eddy activity in the region of interest. Additionally, significant seasonal variability in the type of surface water stirring was noted. Thus, the maximum of both meso- and submesoscale eddy activity seems to happen during the warm season, while during winter, presumably due to low Richardson numbers typical for the upper water layer, the turbulent features are still undeveloped and of the smaller spatial scale than during the warm period of year.
Highlights
1.1 General ProblematicsThe Mediterranean Sea is frequently considered a natural laboratory for studying oceanographic processes
Mesoscale eddies of the region of interest were highlighted by an analysis of satellite altimetry and numerical modelling data (Escudier et al, 2016; Isern-Fontanet et al, 2006), but it seems that only the biggest anticyclones can be adequately resolved by sea level anomaly (SLA) fields provided by conventional satellite altimetry (Karimova, 2016)
In this and similar figures, violet and blue shading correspond to low values of Chl-a, while yellow one, to high values of Chl-a. Such an impressive and detailed representation of surface turbulence in this image is explained by the occurrence of a seasonal phytoplankton bloom, due to which a great number of organic cells is presenting in surface waters
Summary
The Mediterranean Sea is frequently considered a natural laboratory for studying oceanographic processes. Despite significant attention paid to studying surface circulation in the Western Mediterranean and especially to anticyclonic gyres of the Alboran Sea and Algerian Basin, which have been intensively studied by satellite and in situ observations (Millot, 1999), in general a wealth of data provided by satellite imagery still stays unused. Thermal infrared imagery is traditionally used either for some descriptive analysis of surface circulation in the region of interest (Taupier-Latage, 2008) or for an interpretation of in situ measurements (e.g., Pascual et al, 2002). Due to such a limited usage of satellite imagery, general statistics on meso- and submesoscale eddies in the region of interest is still quite unknown. Mesoscale eddies of the region of interest were highlighted by an analysis of satellite altimetry and numerical modelling data (Escudier et al, 2016; Isern-Fontanet et al, 2006), but it seems that only the biggest anticyclones can be adequately resolved by sea level anomaly (SLA) fields provided by conventional satellite altimetry (Karimova, 2016)
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