Ana Teles-Machado

Surface circulation in the Gulf of Cadiz: Model and mean flow structure

[1] The mean flow structure of the Gulf of Cadiz is studied using a numerical model. The model consists of a set of one-way nested configurations attaining resolutions on the order of 2.6 km in the region of the Gulf of Cadiz. In the large-scale configuration, the entrainment of the Mediterranean Water is parameterized implicitly through a nudging term. In medium- and small-scale nested configurations, the Mediterranean outflow is introduced explicitly. The model reproduces all the known features of the Azores Current and of the circulation inside the Gulf of Cadiz. A realistic Mediterranean Undercurrent is generated and Meddies develop at proper depths on the southwest tip of the Iberian slope. The hypothesis that the Azores Current may generate in association with the Mediterranean outflow (β-plume theories) is confirmed by the model results. The time-mean flow is dominated by a cyclonic cell generated in the gulf which expands westward and has transports ranging from 4 to 5 Sv. The connection between the cell and the Azores Current is analyzed. At the scale of the Gulf, the time-mean flow cell is composed by the westward Mediterranean Undercurrent, and by a counterflow running eastward over the outer edge of the Mediterranean Undercurrent deeper vein, as the latter is forced downslope. This counterflow feeds the entrainment at the depths of the Mediterranean Undercurrent and the Atlantic inflow at shallower levels. Coastward and upslope of this recirculation cell, a second current running equatorward all the way along the northern part of the gulf is revealed. This current is a very robust model result that promotes continuity between the southwestern Iberian coast and the Strait of Gibraltar, and helps explain many observations and recurrent SST features of the Gulf of Cadiz.

Surface circulation in the Gulf of Cadiz: 2. Inflow-outflow coupling and the Gulf of Cadiz slope current

[1] A study of the upper slope circulation in the Gulf of Cadiz is presented. Observations, both original and revisited, and realistic numerical modeling are used together to describe the structure and variability of the slope current system above the Mediterranean outflow. It is shown that the Mediterranean inflow-outflow coupling plays a stronger role than that of the atmospheric forcing in driving the upper slope currents. The Mediteranean outflow forces a surface open ocean current toward the Strait of Gibraltar. Part of it is entrained into the outflow and the remaining flows into the Mediterranean. This latter component does not suffice for the observed transport of the Atlantic inflow into the Mediterranean. A secondary contribution to the inflow is therefore needed to complement the transport. This contribution comes from a persistent equatorward current along the upper slope between Cape St. Vincent and the Strait of Gibraltar. The jet is 20–30 km wide and significant in the upper 200 m attaining subinertial maxima as much as 0.3–0.4 m/s and monthly means in the order of 0.1–0.15 m/s. This current shows a strong variability at time scales in the order of 2–8 days, and displays a significant vertical shear. The response of the upper slope current to synoptic and seasonal atmospheric variability is analyzed. Very low correlation was detected at synoptic scales and the response of the system to seasonal forcing is unclear. A cycle of intensification in June–July and a decrease in winter is apparent in the measurements, but is weak in the model results. It is speculated that the cycle in the observed currents is associated with variability in the inflow/outflow coupling system, rather than driven by seasonally changing wind forcing.

Evidence of time-mean cyclonic cell southwest of Iberian Peninsula: The Mediterranean Outflow-driven β-plume?

[1] First observational evidence of time-mean cyclonic recirculation southwest of Iberia is presented. Data sets of hydrography, satellite altimetry and surface drifters velocities are analyzed jointly in order to obtain an accurate time-averaged circulation in the mid-latitude northeast Atlantic off the Gulf of Cadiz. A cyclonic recirculation cell with characteristics similar to those predicted by theoretical and modeling studies is detected in all computed velocity fields. The cell in the upper 1000-m layer exhibits transports of 3 to 4 Sv that are only slightly smaller than the model transports. The cell is centered at approximately 36°N, 10°W, is elongated zonally and extends to 15°W westwards. Wind driven Sverdrup transport and β-plume dynamics are both suggested to play a role in the generation of the cyclonic cell, but the relative contribution of these effects is yet to be clarified. The core of the recirculation appears compact and the magnitude of the cell fades westwards much faster than predicted by the theoretical and modeling studies considered.

On the year‐to‐year changes of the Iberian Poleward Current

The results of a 20 year high-resolution simulation that spans from 1989 to 2008 are analyzed to study the year-to-year changes of the Iberian Poleward Current (IPC), and its effects on the temperature and salinity variability on the Western Iberian Margin. The model results are compared with satellite data and with data measured at two moored multiparametric buoys. The model reproduces the events of strong sea surface temperature (SST) anomalies described in the literature, for the northern and western coasts, and it helps to explain the connection between the IPC intensity, temperature, and salinity. By analyzing some specific winters, with different characteristics, it is confirmed that years of stronger IPC result in higher transport of heat and salt, and the development of positive anomalies of temperature and salinity. However, local air-sea fluxes are also important and explain the temperature and salinity anomalies observed in some of the winters. The interplay between the IPC transport, or advection, and the local heat and salt fluxes explain why the temperature and salinity anomalies may be in antiphase or uncorrelated with the IPC magnitude. It is shown that from November to January, the IPC magnitude depends mostly on the intensity of the southerly winds, and it has a significant negative correlation with the NAO index.