Abstract
The upper circulation in the southern Bay of Biscay is analysed over winter and fall 2004 using a coastal altimetric dataset, moorings, sea surface temperature (SST) observations and a regional simulation from the SYMPHONIE model. The aim is to determine whether altimetric data can detect occurrences of a slope current (the Iberian Poleward Current, IPC). We first analyse in situ and SST data. The results show pulses of a warm surface poleward flow (IPC) limited to the westernmost part of the northern Spanish coast. Along-track TOPEX/Poseidon and Jason-1 data are analysed over three ‘events’ (Jan., Feb., and Oct. 2004). Altimetric data can depict the main pulses. They provide some information on their spatial variability but the present in situ dataset is not dense enough to assess this information. Local inconsistencies between neighbouring tracks may be related to uncertainties in altimetric corrections. The simulated fields are consistent with the in situ observations. They allow us to better understand the IPC subsurface properties and its signature in altimetric data. The ability of altimetry to monitor IPC pulses under any atmospheric conditions or when the SST signature is weak makes it an essential component for the IPC observing system in addition to satellite SST and moorings data.
Highlights
The circulation in the southern part of the Bay of Biscay (North-East Atlantic) results from the complex combination of currents over the shelf and slope, characterised by a strong baroclinicity over the slope, mesoscale eddies further offshore, local upwellings and internal tide generation in the west (Pingree and Le Cann, 1989, 1990, 1992; Van Haken, 2002; Pichon and Corréard, 2006)
As the wind measured at the buoys (Fig. 4) is eastward at Bares while highly variable at Villano and Silleiro until Feb. 1, we suggest that the eastward flow at Bares is the signature of two distinct mechanisms: Ekman current until Feb. 1 and, from Feb. 1 Ekman current combined with the intrusion of the Iberian Poleward Current (IPC) from the south
The event of October 2004 is an interesting case as it can illustrate further the benefit of using altimetric data. In this example where no clear sea surface temperature (SST) signal is observed, we have shown that the altimetric data allow us to identify a slope current with warm subsurface anomalies that can be considered as an intrusion of the IPC into the Bay of Biscay
Summary
The circulation in the southern part of the Bay of Biscay (North-East Atlantic) results from the complex combination of currents over the shelf and slope, characterised by a strong baroclinicity over the slope, mesoscale eddies further offshore, local upwellings and internal tide generation in the west (Pingree and Le Cann, 1989, 1990, 1992; Van Haken, 2002; Pichon and Corréard, 2006) It shows a large seasonal and interannual variability due to the development of the Iberian Poleward Current (IPC) in late fall and winter along the western Iberian coast (Haynes and Barton, 1990; Frouin et al, 1990). An experimental XTRACK dataset has been recently used by Le Hénaff et al (2010) to study a 10-year time series of altimetric data along the TOPEX/ Poseidon track #137 intercepting the northern Spanish coast close to 6.5°W over the period 1992–2002 Their objectives were to identify and characterise the signature of Navidad events and of their variability at interannual time scales on this single track.
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