Ekman transport along the Galician coast (northwest Spain) calculated from forecasted winds

Abstract

Ekman transport is studied close to the Galician coast by means of forecasted winds provided by METEOGALICIA from November 2001 to October 2004. Three different coastal zones are identified: western coast from Miño River to Cape Finisterre, middle coast from Cape Finisterre to Cape Ortegal and northern coast, from Cape Ortegal to Cape Peñas. In addition to existence of long‐term variations, the periodicity of the transport signal is characterized by an annual component (365 days), a seasonal fluctuation (50 to 80 days) and a timescale related to passing storms (15–20 days). Although the periodicity of the signal is similar at the three zones owing to external meteorological forcing, the Ekman transport is modulated by the presence of the coast, in such a way that seasonal patterns vary in intensity and direction along the coast. Thus the autumn‐winter pattern is characterized by high transport at the northern and middle coast, pointing landward perpendicular to the shoreline, and moderate values at the western coast, pointing landward and oblique to the shoreline. On the other hand, the spring‐summer pattern is characterized by high transport at the western coast, pointing seaward perpendicular to the shoreline. The same orientation is observed at the middle coast although with a lower magnitude. Finally, Ekman transport at the northern coast points landward and oblique to the shoreline. The different transport orientations are shown to be responsible for the upwelling probability variation along the coast.