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A classical non-linear quasi-geostrophic model of wind-driven ocean circulation is integrated by using new additional boundary conditions conceived to: a) preserve, as far as possible, the typical structure of the Sverdrup flow in the southern and eastern regions of an idealised sub-tropical gyre and b) eliminate any additional boundary conditions in the northern and western regions of the fluid domain. Numerical simulations produce current and transport values close to those found in the literature whereas instability occurs at relatively low values of non-linearity, consistently with the well-known Sverdrup-like behaviour of large-scale transport in the world-wide ocean. A strict correlation emerges between the stability and the persistence of the Sverdrup-like behaviour of the so obtained solutions. [ABSTRACT FROM AUTHOR]

Abstract Measurements of QuikScat for 2000–2009 and ASCAT scatterometers for 2009–2016 are used to describe the variability of the Black Sea wind velocity and wind curl. High-resolution (12.5 km) scatterometry data provide a possibility to investigate several small-scale features ("hot points") of the wind field in the basin related to the topographic effects. They include: the gap winds near the Bosphorus, the Kerch Strait, and Tuapse; tip jets at the south and west of the Crimean peninsula, several capes of the Anatolian coast; the Kolkheti valley winds; wind shadow zones at the eastern Turkey coast and the western Crimean coast. Driving factors and directional variability of wind in these "hot points" is discussed. QuikScat and ASCAT data are used to describe seasonal and interannual variability of wind characteristics in 2000–2016. Comparison with in-situ data shows that QuikScat noticeably overestimates wind magnitude during low winds conditions (<2 m/s). ASCAT winds are generally lower than QuikScat, but the ASCAT wind curl is higher. The amount of low winds values (<2 m/s) in the ASCAT data is 6% of the total data, and it is 1% in the QuikScat data. Overestimation of low winds decreases wind gradients near the wind shadows, which is the most possible reason of the underestimation of the wind curl in the QuikScat dataset. Wind curl has a different sign and a completely different interannual variability in the western and eastern parts of the sea. Near the eastern coast of the basin, high-resolution satellite measurements reveal three powerful small-scales maximums of cyclonic vorticity. These maximums are related to the wind jets flowing around topographic obstacles in the vicinity of the Kerch Strait, in the mountain gap near Tuapse, and from the Kolkheti valley. They are observed throughout the whole year, but are largest in winter. The contribution of these maximums to the overall cyclonic vorticity is essential (30% in the QuikScat data and 50% in the ASCAT data). In the western part of the basin, the wind curl is negative (anticyclonic) on average, with the highest anticyclonic curl observed in summer. Winds are decreasing in 2000–2016 in agreement with the data on the 20 century. At the same time the basin-average wind curl rises due to its increase in the eastern Black Sea. We speculate that these trends are associated with the displacement of the Siberian Anticyclone to the west. The related rise of pressure over the eastern Europe correlates significantly with the wind curl variability on interannual time scales. Highlights • High-resolution (12.5 km) scatterometry is used to study wind dynamics in 2000–2016. • Numerous small-scale topographic effects are described using satellite data. • Small-scale effects give up to 50% contribution in the average wind curl. • Seasonal and interannual wind velocity and wind curl variability are described. • Wind curl variability is related to displacement of the Siberian Anticyclone. [ABSTRACT FROM AUTHOR]

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period.

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period. [ABSTRACT FROM AUTHOR]