Revising the Effects of Local and Remote Atmospheric Forcing on the Atlantic Jet and Western Alboran Gyre Dynamics

Abstract

Atlantic and Mediterranean waters encounter in the Strait of Gibraltar (Figure 1), where the fresher and lighter Atlantic Water (AW) flows onto the saltier and denser Mediterranean Water (MW) (Lacombe & Richez, 1982). Both water masses create the Atlantic Mediterranean Interface (AMI) with a thickness of 60-100 m, which deepens on the western side (400 m) and is shallower (100 m) on the eastern side (Bray et al., 1995). At the easternmost side of the Strait, AMI has been related with the isohaline 37.2 (García-Lafuente et al., 2013), and its position helps describe the biological processes taking place across the Strait

Using a Combination of High-Frequency Coastal Radar Dataset and Satellite Imagery to Study the Patterns Involved in the Coastal Countercurrent Events in the Gulf of Cadiz

“…The highest value of the MSLP (equal to 1034.6 mbar) was found on February 15, which is in correspondence with the second strongest CCC event in the GoC. If we look at the entire series, during the three strongest events of westward flow in the Gulf of Cadiz, we can find a considerable high values of the mean pressure variation over the Ligurian Sea, which is in agreement with recent works that associate subinertial flow fluctuations in the Strait of Gibraltar with MSLP fluctuation in the Western Mediterranean Sea [33]. On the other hand, the wind velocity presents an alternative behavior with respect to the main CCC event during 2017.…”

“…The combination of these two particularly strong physical forces allows the development of the most intense westward alongshore current of the year. Even if we are still limited by the lack of HFR data in the proximity of Cape Santa Maria, the strength of the westward flow, which here firstly appears in the western part of the Gulf but clearly originates in the near Strait of Gibraltar, according to the results obtained by [33,51], suggests that the current may reach the Portuguese coast. The extension of this event, in fact, is clearly visible in the chlorophyll distribution (presented in the last six panels of the figure) in both the eastern and the western part of the basin.…”

“…Therefore, for each velocity component (separately), we applied the conventional EOFs algorithm and the missing data were replaced by the reconstructed time series truncated at the first mode. A low-pass Fast Fourier Transform (FFT) filter with a cutting period of 30 h was applied to the velocity time series in order to remove the tidal signal and isolate the contribution of the low-frequency processes mainly caused by atmospheric forcing [33,68]. The daily mean was then calculated and the missing days were linearly interpolated to cover the whole time series for the year 2017.…”

“…Ref. [33] shows that the effect of surges generated by the inverted barometer response of sea-level mean to atmospheric pressure (MSLP) variations over the Ligurian Sea area must be taken into account to explain the Atlantic inflow variability at the eastern mouth of the strait. Given that our study area is adjacent to the Strait of Gibraltar, we must also consider the possible contribution of these surges, which are remotely generated, to the Gulf of Cadiz CCC events.…”

“…During this CCC event, a persistent wind blowing from south-west is observed, which should hamper the development of the westward flow of the current (Figure 11). However, during the same days, the strongest fluctuation of the year for the mean sea-level pressure over the North-Western Mediterranean Sea is able to generate the variation in the subinertial current intensity, which results in a reduction in the intensity of the Atlantic inflow [33,36,71]. In these conditions, a great amount of water masses accumulate near the meridional Iberian coast with the help of the northward direction of the wind.…”