analysis and recognition of thickness anomaly patterns during extreme cold days in iran

to doing this research daily interpolated temperature data from asfezari data base have been used. in order to recognition extreme cold days, the normalized temperature deviation index (ntdi) applied. then the index sorted according to extensive and severity and first 500 days selected for analysis. the geopotential height data extracted from www.esrl.noaa.gov data base. the thickness anomaly calculated for each day and classified by cluster analysis and ward method. the thickness mean and temperature anomaly maps has been showed during each pattern. the results showed that 5 thickness anomaly pattern observed during extreme cold day's occurrence in iran. the response of iran absolute temperature anomaly to thicknes anomaly are different. the coldest extreme low temperature on iran occurred when located negative anomaly in thicknes over siberian and northeastern parts of iran and observed positive anomaly over barents sea, groland and europe. the mean air temperature anomaly of iran accompany to this circumstance of thickness anomaly is -5.9â° centegrade.