The separate roles played by the two geographical poles of the NAO in influencing winter precipitation over Spain

Abstract

In this article, the spatiotemporal relationship between winter (DJF) precipitation over Spain and sea level pressure fields is studied using the Center of Action (COA) approach. The COAs which make up the North Atlantic Oscillation (NAO), i.e., the Azores High (AH) and the Icelandic Low (IL), are considered separately, and we find that interannual variations in the strength and position of the AH explain a very high fraction of the variance of Spain winter precipitation. The correlation of AH properties with winter precipitation is strongest in the northwest of the country. A regression model was developed that explains 83 percent of the variance of the Spain precipitation over 1981–2011. We found that the positive extreme values of AH indices are related to droughts, and negative extremes to heavy rain. The westward and southward shifts of the AH encourage the presence of low pressure system over the Iberian Peninsula and high precipitation in Spain occurs due to the moisture transport off the North Atlantic impinging upon Peninsula Spain and France.