Seasonal Variability of Total Cloud Cover in the Mediterranean Region for the Period 1948–2014

Abstract

The seasonal variability of total cloud cover in the Mediterranean region is studied, using NCEP/NCAR daily grid point data. The mean day to day intra-annual variations of total cloud cover during the hydrological year (1 October–30 September) are extracted for the 66-year period 1948–2014. A dimensionality reduction method is applied on the 324 time series and three main modes of seasonal variation of cloud cover over the Mediterranean region are found. The first one is simple, characterized by a maximum in winter and a minimum in summer, prevailing mainly over the sea. The second one is double showing maxima in early autumn and late spring and minima in late summer and winter and prevails over SW Europe and NW Africa inland regions. Finally, the third one shows a maximum in June and a minimum in October and prevails over the eastern part of central Europe. The main characteristics of these modes are attributed to the seasonal variation of the various thermal and dynamical factors affecting the region. An examination of the seasonal variability of cloud cover in the above core regions during sub-periods of the total period 1948–2014 reveals some long-term changes during the last 66 years.