Characterization of fall–winter upwelling recurrence along the Galician western coast (NW Spain) from 2000 to 2005: Dependence on atmospheric forcing

Upwelling events driving ENACW (Eastern North Atlantic Coastal Water) into the Galician western coast rias had been considered typical spring–summer processes, according to the research developed in this area. However, they can also be observed in fall or winter under northerly winds blowing at shelf. Six different upwelling events were analyzed in the Ria of Pontevedra during the wet season (NDJF) from 2000 to 2005. These events were characterized by means of the zonal Ekman transport (Q_x) at four control points in front of the western rias (locally known as Rias Baixas) and thermohaline variables measured at a fixed station in the main mouth of the Ria of Pontevedra. The duration of the upwelling events ranged from 27 days (during February and March 2002) to 69 days (during November–December 2004 and January 2005). Upwelling events studied in the Ria of Pontevedra from 2000 to 2005 showed the similarity in upwelling features during both seasons (similar wind forcing and upwelled water). Finally, Q_x was correlated with the most representative atmospheric patterns in the Northern Hemisphere (EA, NAO, EA/WR, POL and SCA) from 1966 to 2005. The winter EA pattern has the most influence on Q_x showing an annual evolution with a prevalence of the positive phase from 1976 on. This positive phase is directly correlated with a prevalence of positive values of Q_x which are upwelling unfavorable in the Rias Baixas.