Pressure covariability over the Atlantic, Europe and N. Africa. application: Centers of action for temperature, winter precipitation and summer winds in Athens, Greece

SummaryThis paper deals with the surface pressure covariability over the Altantic/European sector of the Northern Hemisphere, using monthly grid point data for the 100 year period 1890–1989. Factor analysis is applied to 90 grid point time series for January, February, July, and August. The initial 90 pressure variables can be reduced to 7–8 factors in winter and 10 in summer. A winter teleconnection was identified, known as the seesaw phenomenon, between the Icelandic low and the Azores subtropical anticyclone. In order to define the centers of action for temperature, winter precipitation and summer northerly wind frequency (etesian days) in Athens and in the Aegean sea, the variability of the factor scores and of these weather elements is compared. It is shown that the center of action for temperature in Athens is found to be in north and northwest Europe (centered over southern Scandinavia). For winter precipitation, the center of action is located in the west and southwest Mediterranean and northwest Africa. Finally, for the etesian winds frequency variability, this center of action is found over the northern Adriatic and northern former Yugoslavia, while there is no evidence of influence by the southwest Asia thermal low.