Northwest of Iran

This research aim is to identify the dynamic and thermodynamic patterns of heavy and widespread rainfall in northwest of Iran in the period 2000-2019. The percentile method was used to determine heavy rainfall. In dynamic and thermodynamic patterning of heavy rains, factor analysis and hierarchical clustering methods were used. After determining heavy rainfall patterns, two representative days were selected and 500Hpa atmospheric maps were drawn and interpreted. Then, in the GIS software, the heavy rains in the northwest of Iran were zoned. The results showed that in the first pattern, the main factor of air ascent and the occurrence of heavy and widespread rainfall in the northwest of Iran is the Mediterranean cyclone. The presence of a short front in the studied area has increased the intensity of instability, and the establishment of blocking in the mid-level of the atmosphere has caused the strengthening and continuation of precipitation. The results also showed that the main sources of moisture supply for heavy rainfall in the northwest of Iran are the Black Sea and the Mediterranean Sea. The synoptic maps of the representative day of the second pattern showed that the primary cause of the rise of moist air and the occurrence of heavy rain in the northwest of Iran is the merging of the Sudanian cyclone and the Mediterranean cyclone. The existence of a short front and the blocking has caused the creation of a baroclinic atmosphere and, as a result, the rise of air in the studied area.