Abstract
Abstract. A statistical approach in order to study fog event characteristics occuring at the airport of Thessaloniki, Northern Greece is presented in this work. To achieve this, the seasonal and diurnal characteristics of fog are investigated using 35 years (1971–2005) of observations of meteorological parameters such as: visibility, air temperature, dew point temperature, air relative humidity, wind vector, precipitation, and cloud base height and coverage. Hourly surface observations of fifteen (15) years (1991–2005) are used to identify fog events induced by various physical mechanisms. Fog events are classified into fog types through the application of objective criteria that are derived upon fog formation processes and under the influence of various physiographic features. The temporal variability of different fog type occurrences are examined and the events are characterized according to their duration and intensity. The results are somehow affected by regional and local factors. Fog is mainly formed in winter time (~64%) with an enhanced likelihood to appear also in late autumn (19%). The highest frequency of the fog events occurs around sunrise or 1 to 2 h before of it. The mean duration of the events is about 4.5 h. Most of them (75%) are dense (visibility <400 m). The overall fog phenomenon is a combination of various types, such as: advection fog, radiation fog, cloud-base lowering fog and precipitation fog. Advection fog (30%) and radiation fog (29%), which are the most common types, occur predominantly in winter and early spring time. With respect to the former type, it seems that, in many cases, already formed fog is advected from the nearby Anthemountas valley. Moreover, a considerable number of fog events (22%) result from cloud-base lowering, and they frequently occur in late autumn and mid winter.
Highlights
The limited visibility associated with the appearance of fog is responsible for several losses in time, money and even human life in all forms of transportation, including navigation, aviation and land transportation
Studying the climatology of fog, serves as a basis for the better understanding of the various conditions that led to fog formation in the past, so fog occurrences may be predicted in the future when similar conditions are met
Contributing to this direction, synoptic scale features give a better insight in the synoptic conditions that prevail before fog formation, adding to the knowledge that is needed in aiding the forecasting of fog
Summary
The limited visibility associated with the appearance of fog is responsible for several losses in time, money and even human life in all forms of transportation, including navigation, aviation and land transportation. Our understanding of the physics of fog remains incomplete though, due to the time and space scales involved in numerous processes influencing fog formation, development and dissipation Because of this complexity the accurate forecasting of fog always remains a difficult task (Gultepe, 2007). Studying the climatology of fog, serves as a basis for the better understanding of the various conditions that led to fog formation in the past, so fog occurrences may be predicted in the future when similar conditions are met Contributing to this direction, synoptic scale features give a better insight in the synoptic conditions that prevail before fog formation, adding to the knowledge that is needed in aiding the forecasting of fog
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