عنوان مقاله [English]
نویسنده [English]چکیده [English]
Thunderstorms are one of the most important natural hazards which cause human annihilations every year in addition to destroying of many agricultural productions throughout the world. Recognizing the synoptic conditions of the creation of thunderstorms can be useful to predict the occurring times and to take the necessary actions when confronting this phenomenon. Since thunderstorms have occurred in the province of Ardabil especially in the spring & summer seasons, paying attention to them seems important.
Materials and methods
In this research, we have tried to use the data from the synoptic stations of thunderstorms occurrence days of Ardabil, Meshkin-Shahr, khalkhal & Pars-Abad with the statistics arrangement of 2, 11, 19, 21 years. After making sure of the correctness of the used data, analyzing the characteristics of the data statistics & determining the kinds of seasonal and monthly statistical distribution of the days of thunderstorms is done. In addition to statistical analysis, we used the trend of time series (trend line or order of 6 polynomials) in order to determine the time fluctuations & study the phenomenon. Monthly classification of the days along with thunderstorms is also done by multivariate method and cluster analysis method. For vividness and explanation of thunderstorms and showers, the condition of sea level pressure, 500 geopotential heights and the columnar perceptible water of 26 May 1985 is analyzed as a sample. As this day has involved the occurrence frequency of thunderstorms among others, it has been selected as the representative day.
Results and Discussion
The results indicate that in the synoptic stations of Ardabil, Meshkin-Shahr and khalkhal, the frequency occurrence of thunderstorms belongs to the month of May and to June in the station of Pars-Abad. In the stations of Ardabil, Pars Abad & Meshkin-Shahr, the least coefficient of variance belongs to the month of May and to April in the station of khalkhal. In the whole seasons and months, the thunderstorms skewness is positive, but the kurtosis of thunderstorms is different in the stations considered. The standard derivation of warm months is more than the cold ones. Monthly thunderstorms dendrogram in the investigated stations indicated that these storms form 3 clusters in the whole stations. Time fluctuations models and trend line or order of 6 polynomial thunderstorms of studied stations in the spring season and once a year showed that in the stations of Ardabil, khalkhal and Meshkin-Shahr, the thunderstorms occurrence has a rising trend. This trend is reduced in Pars-Abad station. The representative of thunderstorms occurrence in the investigated annual and seasonal limits showed that the most thunderstorms occurrence frequency, is in the spring & summer seasons. The situation of the spring thunderstorms occurrence from the characteristics of the statistics is more similar to the annual situation. This is of high significance for the occurrence of thunderstorms in this reason. The amount of coefficient of variance of thunderstorms occurrence indicates more constancy and less fluctuations of thunderstorms occurrence in springtime rather than in the other seasons. The correlation of good process of trend line and order of 6 polynomials of thunderstorms in spring & once a year indicates that the spring season exploits more than the other seasons. The process of the rising of the line of thunderstorms occurrence in summer is stronger than in the autumn. The accounted coefficient of correlation between spring & summer thunderstorms occurrence frequency has a close correlation with the annual degree. From the viewpoint of seasonal frequency, the good correlation between spring and summer, and spring and autumn is also observed here.
The range of the frequency of the accordance of thunderstorm occurrence in Ardabil synoptic station with probability distribution of 3- parameter weibull is the indication of thunderstorms parameter of this station with probability distribution of 3- parameter weibull in 95% confidence levels for the season of spring. Consideration of synoptic maps of sea level pressure, 500 geopotential and perceptible water of the representative day of May 26, 1985, showed that on this day, the condition of the sea level and upper atmosphere levels are suitable for the occurrence of the phenomenon of thunderstorms; as on the sea level, the Isobaric patterns show the suitable conditions for transmitting of the moisture of Caspian Sea to Ardabil province. In 500 mb geopotential level also, the arrangement of upper divergences of trough settled in east European & south of Turkey causes the creation of instable conditions for the creation or forming of thunderstorms on this day. Regarding the occurrence of thunderstorms in west north of Iran, especially in the province of Ardabil, it is necessary to have & perform the necessary schedules for confronting this phenomenon. In order to do so, it is necessary to have suitable arrangements & programs for future. Probably the assurance of agricultural & animal husbandry productions can be one of the useful ways.