Recognition of variety of the atmospheric configuration at mid- troposphere and the interaction between effective synoptic patterns over Iran

In this research, circulation configuration of atmosphere was studied at 500 hPa level. This study has been done using daily data of geo-potential height at 12 GMT in NCEP/NCAR database with spatial resolution of 2.5*2.5 degree in a 55 years period including 20089 days from January, 1st, 1951(Day, 11th, 1329) to December, 31st,2005(Day, 10th,1384). At First, the mean geo-potential height at 12 GMT is extracted for all days of solar calendar to analysis spatial configuration and relation of these patterns. Then, an agglomerative hierarchical cluster analysis on the basis of ward linkage method has been done in MATLAB soft¬ware. According to this analysis, five circulation configurations in the north hemisphere are recognized. The 1-1 pattern which is coincided with the cold period of year shows maximum weakening of subtropical high pressure and predominance of westerlies with Ross by waves over Iran. The 2-2-2 pattern which is coincided with the warm period of year shows maximum activity of subtropical high pressure. Occurrence of this pattern is coincided with the time of predominance of this system over Iran.