Abstract
Abstract. The combination of remotely sensed gappy Sea surface temperature (SST) images with the missing data filling DINEOF (data interpolating empirical orthogonal functions) technique, followed by a principal component analysis of the reconstructed data, has been used to identify the time evolution and the daily scale variability of the wintertime surface signal of the Iberian Poleward Current (IPC), or Navidad, during the 1981–2010 period. An exhaustive comparison with the existing bibliography, and the vertical temperature and salinity profiles related to its extremes over the Bay of Biscay area, show that the obtained time series accurately reflect the IPC-Navidad variability. Once a time series for the evolution of the SST signal of the current over the last decades is well established, this time series is used to propose a physical mechanism in relation to the variability of the IPC-Navidad, involving both atmospheric and oceanic variables. According to the proposed mechanism, an atmospheric circulation anomaly observed in both the 500 hPa and the surface levels generates atmospheric surface level pressure, wind-stress and heat-flux anomalies. In turn, those surface level atmospheric anomalies induce mutually coherent SST and sea level anomalies over the North Atlantic area, and locally, in the Bay of Biscay area. These anomalies, both locally over the Bay of Biscay area and over the North Atlantic, are in agreement with several mechanisms that have separately been related to the variability of the IPC-Navidad, i.e. the south-westerly winds, the joint effect of baroclinicity and relief (JEBAR) effect, the topographic β effect and a weakened North Atlantic gyre.
Highlights
The Bay of Biscay is located in the intergyre zone of the North Atlantic, between the Azores current in the northern part of the subtropical gyre and the North Atlantic current in the subpolar gyre
That means that only days with at least 5 % of available data were reconstructed for the two Pathfinder subsets
If strong enough evidence is collected to confirm such relation, the time series shown in Fig. 7 would be the longest estimation of the time evolution of the surface signal of the Iberian Poleward Current (IPC)
Summary
The Bay of Biscay is located in the intergyre zone of the North Atlantic, between the Azores current in the northern part of the subtropical gyre and the North Atlantic current in the subpolar gyre. The general circulation in the intergyre area is slack, especially in the Bay of Biscay. The water circulation is characterised by a weak anticyclonic flow in the oceanic area (Pingree, 1993), a poleward slope current, slope water oceanic eddies, coastal upwelling in the western Iberian Peninsula, tidal flows, wind-induced currents and buoyant plumes (Pingree and Le Cann, 1989; Koutsikopoulos and LeCann, 1996). The slope current is characterised by its baroclinicity, generating eddies, fronts, meanders, instabilities and other related processes (Pingree and Le Cann, 1990; Coelho et al, 1999; Gil, 2003; Peliz et al, 2005, among others).
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