عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Many countries around the world use many various methods of climatic classification and zoning, but a few standards are being used in Iran therefore it can be said that solid precipitations including snowfall have been paid too little attention in discussing the nation ‘s precipitation. Thus, in the present research, the frequency of days having the snowfall phenomenon was studied for 50 Iranian synoptic stations using 3 graphic, statistical and surfacing methods during the 1970-2000 period. The results of the present research indicate Zanjan station has the most frequent snowy days while such stations as Jask and Chabahar lack snowy days in the study period, total average of snowy days is between 8 and 9 also the trend of snowy days was increasing during the period, which was more visible from 1980 to 1993. After which it was decreasing again. During this period, the year of 1992 with an average of 15-16 snowy days. And year of 1973 with an average of 2-3 snowy days had the most and the fewest snowy days, respectively. Due to the phenomenon of thermal delay, the month of Bahman had the largest number of snowy days for coastal station while this was the case in month of day for off coastal stations. Given multivariate regression calculations, it was found that the relationship between altitude and latitude with the number of snowy days is a significant, direct one while it is significant and inverse between alteration coefficients and latitude. surfacing pattern of observed and calculated snowy days in Iran was displayed by using surfer software ,in which variables of longitude, latitude ,and number of snowy days were employed, which confirmed compatibility between the calculated and observed surfacing pattern of regression equations. On the basis of surfacing pattern of snowy day’s frequencies, maximum frequency is observed in northwestern part of our country.