PREVAILING CLOUD TYPES IN ATHENS

Prevailing cloud types and their daily, annual and interannual variati on in the region of Athens were examined. These cloud types were group ed into five major classes: cumuliform, stratiform, cirriform, medium altitude clouds and no cloud class, referred to in the study as clear skies. The results are expressed as frequency of occurrence of differe nt cloud classes. It is found that clear skies and prevailing cumulifo rm clouds both have summer maxima. Stratiform and medium altitude clou ds have winter maxima, while cirriform clouds exhibit a semiannual var iation, with maxima in May and October. In terms of interannual trends , the tendency of stratiform clouds to prevail decreases while the ten dency of cumuliform clouds to prevail increases, probably due to urban expansion and the increase in urban activity.