بررسي روند تعداد روزهاي يخبندان در استان خراسان شمالي

Studing of the trend of the number of frost days in the northern Korasan

In resently years in the world scientific circles have been discussed the subject of climate changes, in this research, the changes of time oscilation of the number of frost days in duration 1978-2005 in the nortern Khorasan. In first researches or specifying the trend of data have used of Kendal mean and then clear that the number of frost days have descending trend. This trend have conformity to increasing trend of annual temperature mean. In later stage for fitting a suitable time series model to data used of Box-Jenkins method. First, data series becom stationary to using of difference transformation. Then have been drawn Autocorrelation and Partial Autocorrelation curves and studied stationary particulars and omission of variance. At the end, the model of ARIMA(0,0,2) have been distincted suitably. Calculated data in confidence level have been confirmed. For test of fitting, with to using of Regression method distinguished that the time series model has fitness to data in confident level. This model shows that the number of frost days in coming years will have descending trend with oscilation.