This research is an attempt to investigate the blocking systems over the Atlantic Ocean and especially over the Mediterranean sea, which leads to surface cyclogenesis in the east of the Mediterranean Sea, and the influence of their effects over the Iranian region. At the first step of study, Mediterranean topography, local Mediterranean winds and cyclogenesis have studied; then structure and types of existing blocking systems on the synoptic weather maps have been introduced with figures.
In the second step of the study, all of the blocking systems that were formed over the Atlantic Ocean were identified from 1989 to 1997, the results of which are shown in the table included in the paper. Of course this part of the work was done with the help of Prof. Colucci from USA and data are given from NCEP.
Atmospheric blocking systems can lead to a stagnation of weather patterns where the patterns remain for several days or even weeks at the same location during the blocking system. This case can lead to flooding, drought, above normal temperatures, below normal temperatures and other weather extremes. Therefore, it is important to recognize a blocking pattern in its initial development. With this awareness, one can forecast up to several days in advance with a high degree of accuracy.