The purpose of this research is to determine the best deployment position and stretching pattern of the side-to-side jet to create tarsal in the southwest of Iran, as well as to select the most frequent synoptic pattern in this region.

The daily rainfall data of stations in the southwest of Iran (Khuzestan, Chaharmahal, Bakhtiari, Kohgiluyeh, and Boyer Ahmad) during the statistical period in three solar cycles (1986-1997), (1997-2008) and (2008-2019) were received from the National Meteorological Organization. Orbital and meridional wind component data, geopotential height at 250 and 300 hPa levels, slp, specific humidity and omega from the US National Center for Oceanography and Environment (NCEP/NCAR) with a spatial resolution of 2.5 × 2.5 degrees. received. Then, using factor analysis and visual inspection, the most frequent patterns were determined for all three solar cycles.

The examination of the maps of the lower, border and middle level of the troposphere showed that in the severe droughts of southwest Iran, the establishment of high pressure Arabia over the Arabian and Oman seas and the movement of moisture from these seas to the low-pressure eastern slope of Sudan and the formation of a deep trough in the west of Iran from Europe to southern Sudan and Cold subpolar advection on the western low pressure slope of Sudan is the most suitable pattern for heavy rains and its continuation for several days in the southwest of Iran. The best location of the subtropical jet to strengthen the rain systems is the area between Egypt and the western coast of the Persian Gulf in southern Iraq, if the core of the jet is located in northwestern Saudi Arabia. And the main source of system moisture in all precipitation samples is the Arabian, Oman and Mediterranean seas.