The Assessment and Determining of the Type of Frost in Khorasan Razav

Based on meteorological conditions and also topography, frost is divided into two types of radiative and advective. Province of Khorasan Razavi in north east of Iran, is one of the places which is affected by advection of cold weather and always its agricultural productions are faced to many losses. So, determining the kind of frost in this province is very important. The aim of this studyis to consider and determine the type of the early fall and late spring frost and their probability in province of Khorasan Razavi. The meteorological data of twelve synoptic stations were collected and the date of temperature falling to 0°C (threshold) or lower for the first time in the fall and last time in the spring were determined. Then, the date of frost was given withquantitative values. To determine the type of frost, all atmospheric parameters were considered at observation date, the days before and after the first fall and last spring frost and then the dates were separated based on the kind of the frost. A statistical period of 13 years was selected and then probability of date of occurrence with 25, 50 and 75 percent were calculated. Results show that the earlier and later average of the starting date of advective frost happened in 20 of November and 17 of December in Ghouchan and Boshrouye station, respectively. The results also show that, the advective frost finish in 11th of March and 7th of April in Boshrouye station (South) earlier and in Ghouchan (North) latest respect to the other stations.