Investigate Blocking effect on snow event of heavy and continuous in Iran

Each heavy snow event may be not caused by blocking phenomenon, but Occurrence ofpersistent and heavy snow (4 days or more) can be associated with the occurrence of blockingphenomenon. In order to understand and evaluate the effectiveness of the heavy snowfall andpersistent blocking patterns Iran, Daily data of 500 hPa height, For the cold season (Octoberto March); A period of 60 years in a horizontal grid with a spatial resolution 5/2 * 5/2, fromNCEP-NCAR sites, was extracted to 40 degrees west and 100 degrees east longitude and 20to 80 degrees north latitude. In order to extract the blocking event, data Based on quantitativeindex climatology, the name of the two-dimensional detector, in MAT LAB softwareenvironment, were programmed to detect the occurrence. Then all blocking events continuedfor 4 days and further extracted. Due to the volume of data, through principal component andclustering techniques, extracted the prevailing patterns blocking. The dominant patterns ofprecipitation were effective in blocking 4 models on which of these four models, only onemodel is effective on snow and severe persistent. Results showed that the effects onprecipitation patterns, Only Omega blocking pattern, Right trough was recognized as aneffective blocking pattern on snow, because the cold air from above to strengthen widths rainsystem. The results showed if other conditions such as the availability of synoptic Strongpressure level ground, Position of zero degrees C isotherm at 850 hPa and The thickness ofthe layer thickness of 500 to 1000 Maps Leading to heavy snowfall continued to be in thepresence of blocking occurrence.