Studying and Determination the Freezing Indexes and its Beginning of Autumnal Freezing in Iran (Case Study Ekbatan Station)

In this research, in order to consider the freezings which occurred in Ekbatan (Hamedan) station, minimum daily temperatures of this station were studied. that in generally freezings were divided to 3 levels: weak-freezing, middlefreezing and intense-freezing. Then, we determined the range of temporal changes and the abundance of the freezing. Also we have tried to introduce a model which can forecast the date of first autumnal freezing according to the date of last spring freezing. By calculating different statistical parameters, probability of occurrence the temperature thresholds between –15 to 0 (oc) were determined for different months. In addition to this, by dividing the year to 36 different periods of ten days, we have tried to calculate temperature of different probability percents. The result indicate that the minimum temperature in this station has been increasing during past two decades and Isfand and Ordibehesht have shown the most and the least rate of temprature, respectively. Sever freezing periods in day and bahman, the moderate ones during Mehr, Aban, Bahman and Esfand and the mild ones during Aban take place. In order to predict freezing during autumn amodel has been proposed by which an appropriate linear correlation between freezing in autumn and the one in spreang is shown. By means of spring freezing the history of autumn freezing can be predicted. This model is meaningful at the level of 5%.