On the problem of influence of the North Atlantic and Southern Oscillations on the variability of surface air temperature in the European-Mediterranean region in summer and autumn

Abstract

On the basis of reanalysis of the data of the European Center of Medium-Range Weather Forecasts for 1979–1993, the interannual and monthly variability of the surface air temperature (SAT) in the European-Mediterranean region for summer and autumn with regard for the influence of the North Atlantic (NAO) and Southern (SO) Oscillations have been studied. The NAO manifests itself on a significant level from August to October and is responsible for up to 55% of the variance of monthly average SAT in the north part of the European region. This phenomenon is caused by the intensification of zonal circulation and enhanced transport of warm Atlantic air masses to Northern Europe. A general trend toward a decrease in the variance of monthly average SAT in the mature phase of the NAO is observed over the most part of Europe. In this case, the NAO is responsible for up to 35% of monthly fluctuations of SAT in summer, up to 45% in September, and up to 65% in October. As the SO index sharply decreases and an event of El Nino develops in the Pacific, the maximum variance of SAT in the European-Mediterranean region in summer significantly increases within the two-week range of variability. Up to 25% of the variance of fluctuations of SAT in summer within the indicated range of variability are, in this case, induced by the SO.