Air transportation systems counted as one of the development ways of any area and more than other transportation systems communicates with weather conditions. Between various aerology phenomenon's, fog is one of the main reasons for cancellation, annulment and or flight deviation to other airports that don’t take into consideration so far. In Ardabil airport, according to special topographic situation, necessary factors and condition is prepared for occurrence of fog phenomenon and for this reason, in more days of year and different hours of day, various kinds of dense fog forms.
In this research, for statistical analysis of fog in Ardabil airport, recent five-year statistics (2004-2008) of Ardabil airport synoptic station with reading 24 hours at round- the- clock (night and day) with one-hour time distance are used. After extraction of days with fog and influential and communicating atmospheric parameters in fog formation like mean temperature, relative humidity, dew point temperature, direction and speed of wind, pressure, horizontal visibility and nightly radiation, maps of sea level pressure & 500 hectopascal geopotential heights for same days extracted. With analysis of maps and other effective atmospheric parameters in formation of fog, kinds of fogs separated together and investigated occurrence and duration of either one. Because winds of Ardabil airport are very important in fog formation especially frontal & advection fogs, so, speed & direction of these winds were investigated in seasonal scale. In drawing of wind roses, WRplot 3.5 software was used. To present of suitable model for fog forecast and also for investigation of correlation between fog and other atmospheric parameters, data of mean temperature, dew point temperature, relative humidity, speed of wind, amount of cloud and 24-hours changes of atmosphere pressure for days with fog at hours of 15 & 03 GMT and Pearson correlation coefficient and multiple regression were used. Then, kinds of fog graded to 2 - 4 grades and calculated its correlation with other atmospheric parameters by using of spearman method. Coefficients of multivariable regression to forecasting of visibility at 03 and 15 GMT extracted and equation of fog forecasting model calculated. So, sea level pressure & humidity, 500 hectopascal geopotential heights and vector wind maps for 500 hazy days investigated and synoptic patterns of fog formation were recognized. According to fog effect in decreasing visibility in various month of year, suitable flight hours at various month of year presented.
Results and Discussion
Results of this research represented that in spring, summer and autumn, prevailing wind in Ardabil airport is east wind that comes from Caspian Sea and mountains of Talesh. In winter, prevailing wind is southwest wind. This research also showed that between examined parameters, relative humidity has more correlation with visibility. This correlation in 03 & 15 GMT is -0.164 & -0.192 and both are significant at the 0.05 level. Correlation between visibility and relative humidity in 03 GMT is more than 15 GMT. In 15 GMT, visibility is more related to cloudiness in compare with 03 GMT, because in this time, advection fog has more frequency and accompany with clouds. By compare with correlation between dry temperature and relative humidity in 03 & 15 GMT, we see that this correlation in 03 GMT is significant but in 15 GMT, this correlation is weak & insignificant. In Ardabil airport, from all of fogs, 41 percent were radiation type, 31 percent were frontal type and 28 percent were advection type. Examination of fog synoptic patterns indicated that 4 effective synoptic patterns have role in formation of fog that mainly in earth surface is consist of influence of Siberia high pressure that spreads from northwest to northeast of Khazar sea, formed high pressure that spread upon eastern Europe and high pressure upon Khazar sea and at up of atmosphere, generally is consist of ascent and descent flows in 500 hectopascal geopotential heights. Number 2, 3, 4 & 1 synoptic pattern has the most important role in fog formation in Ardabil airport respectively.
The results show that the occurrence of this synoptic pattern provides essentially conditions for fog formation in this airport. Hours 15 & 03 GMT with 118 & 234 case respectively, allocated to own most fog occurrence and hour 09 GMT with 12 cases, allocated to own least fog phenomenon occurrence along of under consideration statistical period. In Ardabil airport, the best time for perform of flight operation at April, May, September & October is from 08 to 14 GMT and at November, December, January, February & march is 09 to 12 GMT and at June & July is from noon to dusk.