On the atmospheric circulation characteristics associated with fog in Ioannina, north-western Greece

The evolution of the atmospheric circulation over Europe and the Mediterranean during fog events in Ioannina, north-western Greece, is examined for the period 19572002. A 24-h period starting at 12:00 UTC is defined as a fog day, when at least one of the present and/or past weather codes of the corresponding SYNOPs refers to fog. A sequence of such fog days is defined as a fog event. In total, 1019 fog events are found during the period under study. A methodology scheme using S-mode factor analysis and K-means cluster analysis is applied to the patterns of 850 hPa air temperature and 1000 and 500 hPa geopotential heights for the day before the initiation, the first day of occurrence and the day after the dissipation of fog, resulting in the classification of the 1019 fog events into ten clusters. For each one of the ten clusters, the mean 00:00 UTC patterns of the above parameters are constructed for 3 days. These patterns correspond to the evolution of the atmospheric circulation associated with fog formation and dissipation in the Ioannina region. Most of the patterns are characterized by anticyclonic activity or a weak southerly flow over Greece. The differences among the ten clusters refer mainly to the position and the intensity of the surface and upper air synoptic systems involved. Copyright (c) 2011 Royal Meteorological Society