WeMO effects on the amount and the chemistry of winter precipitation in the north-eastern Iberian Peninsula

Abstract

The cluster classification of provenances at a site in the NE Iberian Peninsula indicated that in the period of extended winter (December to March, DJFM) fast Atlantic air flows correspond to positive WeMO index (WeMOi), while negative WeMOi are associated to Mediterranean circulations. The amount of winter precipitation was inversely correlated with winter WeMOi. Wet deposition fluxes of marine-derived (Na+, Mg2+ and Cl) and anthropogenic-derived (NO3 and K+) ions were significantly (and negatively) related to winter WeMOi. The negative phase of WeMO causes the entry of air masses from the Mediterranean into the Iberian Peninsula, that are enriched with marine ions. For NO3 this result suggests the advection over the Mediterranean of polluted air masses from southern Europe and the scavenging and deposition of this pollution by rain during WeMO negative phases. This will carry long-range pollutants to the NE Iberian Peninsula, but local pollutants may also contribute, as precipitation events from the Mediterranean (associated to negative WeMOi) may incorporate local anthropogenic emissions that build up during the winter anticyclonic episodes typical of the region.