Possible mechanisms for fog formation over Borg El Arab airport, Egypt
Sayad, Tarek ; Morsy, Mostafa
The main aim of this study is to identify the causes of fog formation over Borg El Arab International Airport in Egypt. The frequency of fog at this location was studied for the period 1990-2010 using a variety of statistical techniques. The relationships between fog and different meteorological factors were also studied alongside fog occurrence frequency data to determine the mechanisms and conditions which are most likely to result in the type of fog observed at the study site. Hourly ground observations of the visibility and other meteorological parameters for foggy days at the site were analysed for the period of study. The results show that the maximum frequency of fog events occurs during winter and autumn months, with the highest daily frequency in November and highest hourly frequency in December. Most of the fog events lasted for a considerable period of time, with a maximum observed event duration of 13 h in January 2007. The fog events over the study area tend to occur during the early morning, between 0100 h and 0700LT (utc + 02 h), with a peak at 0500 h. Over the period of study there is a decreasing trend in annual fog frequency over the study area. Moderate fog is the most commonly observed category of fog event for all seasons (and it occurs most frequently in November and December), while severe fog is the last commonly observed category for all seasons. Fog requires stability in the lower layer of the atmosphere, and it forms over the study area when there is a high pressure of between 1010 and 1021 hPa, a low wind speed of less than 3 ms−1, predominately northeasterly, southwesterly, southeasterly or northerly wind directions, relative humidity higher than 85%, and a dew-point deficit of less than 3 degC. Therefore, severe, moderate, and weak fog events are highly negatively correlated with wind speed (−0.82, −0.81 and − 0.81, respectively) and dew-point deficit (−0.69, −0.71 and − 0.66), but are positively correlated with relative humidity (0.76, 0.84 and 0.79).
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