[1] The surface circulation and eddy field from the Azores Current system are studied here by analyzing surface drifters records and altimetry maps collected over more than 16 years. Clear differences in mean flow and eddy characteristics allow for a classification of the Azores Current in three zonal sectors: west of 30°W between the Mid-Atlantic Ridge and the Hyères-Atlantis seamount system, between 30°W and the longitude of Madeira, and east of Madeira. A detailed and quantitative characterization of each sector is given. The transition between the western and central parts is controlled by the Hyères-Atlantis ridge. In the transition to the eastern sector there is a change in the dynamics and the flow is forced by the cyclonic recirculation driven by the Mediterranean outflow. There is no clear expression of a continuous surface northern counterflow, but three distinct westward flows are seen: one along the southeastern border of the Azores plateau, another one southwest of Madeira, and a third one along 31°N west of the Hyères seamount. No clear tilt in the axis of the Azores Current is found in the calculated mean surface flow from surface drifters. Observations from both drifters and altimetry data show that anticyclonic features dominate in the northern region, whereas cyclonic ones dominate in the southern region. Overall, cyclones are more numerous, constituting 60% of large eddies. The eddy features detected in the west tend to be larger than those in the east, both in size and sea level anomaly. There is indication of different mean propagation speeds east and west of 25°W-30°W, with the mean speeds consistently increasing by 25%-45% in the west. Estimates for the rate of formation of strong eddies range from 1.4 to 2.4 year −1 for cyclones, and 1.2 to 1.7 year −1 for anticyclones.

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International audienceThe output from a high-resolution two-decade long Mediterranean Outflow simulation is analysed here to provide a census of Mediterranean Water eddies (aka Meddies), both anticyclones and cyclones. The formation rate of Meddies that survive for at least 90 days is of 12 Meddies yr−1 of which ∼12% are cyclones. The rate of formation reaches 40 Meddies yr−1 (30% cyclones) when considering all the Meddies living over 15 days. About 70% of the population is born along the southwestern Iberian slope, but several robust Meddies also originate in points of convergence of the main pathways into the open ocean. The longest-lived Meddies propagate northwestwards, but most of the anticyclones veer southwestwards after a while. As the Meddies drift away from their birthplace, their radius tends to increase gradually from 15 to 30 km. The thickness (depth-difference between isopycnals 27.2 and 27.5) of anticyclones born near Cape St. Vincent contracts by approximately 100 m, after travelling 1000 km from their source; their mean swirl velocities range from about 21 cm s−1 (at z = 1000 m) up to 27 cm s−1 (at z = 600 m). Mean salinity and temperature anomalies are significantly lower for cyclones, which in general are also more slowly rotating, shallower and thinner than anticyclones. Cyclones are more easily tracked at 600 m depth where longer trajectories are recorded. In the vicinity of Portimão Canyon, cyclones outnumber anticyclones while the reverse happens downstream of Cape St. Vincent

Funding informationESA.Measuring Sea-Surface Salinity (SSS) from space is a relatively recent technique that relies on L-band radiometry that has evolved to a point where useful information is provided every few days. The impact of assimilating satellite SSS data is investigated using the global FOAM ocean forecasting system. This system assimilates daily satellite SSS products from the ESA Soil Moisture and Ocean Salinity (SMOS), NASA Aquarius and Soil Moisture Active Passive (SMAP) missions equatorward of 40 • N/S, in addition to other observing systems. The data are assimilated using a 3D-Var scheme that includes an observation bias correction scheme to estimate spatially and temporally varying bias estimates for each SSS satellite. The SSS assimilation is tested over 2 years and 3 months covering the 2015/2016 El Niño with assessment focussed on the tropical regions, particularly in the Pacific. Consistent reductions in root-mean-square errors are found in all tropical regions from each of the satellite SSS datasets. The largest improvements of up to about 8% are found in the tropical Pacific from assimilating both the SMOS and SMAP datasets together. The largest impact is in the intertropical convergence zone (ITCZ) in the central Pacific during 2015 and early 2016 where the surface salinity is reduced by about 0.03 pss on average, correcting for too little precipitation. A smaller magnitude, large-scale reduction in the SSS is also seen in the tropical Pacific that increases the modelled surface stratification and leads to reduced vertical mixing. Changes to the SSS in the ITCZ lead to changes in the meridional gradients of SSS that affects the sea surface height and surface currents, both of which are improved in the SMOS assimilation experiment compared to externally produced observation-based datasets. The results suggest that assimilation of SMOS and SMAP satellite data is now of an appropriate quality for operational implementation. 1Ocean Assimilation Model (FOAM) system (Blockley et al., 2014) produces daily analyses and 7-day forecasts of the three-dimensional ocean and sea-ice state, including temperature, salinity and velocity. The same system is also used to produce reanalyses over the satellite altimeter era in order to calibrate seasonal forecasts (MacLachlan et al., 2015).The observing systems routinely assimilated in FOAM include in situ and satellite sea-surface temperature (SST) This article is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.

A collision of Mediterranean Water dipoles in the Gulf of Cadiz is studied here, using data from