Low level Jets (LLJets) play an important role in the formation and development of weather and climate events in regional scale. In this research the role of two summer LLJets over Middle East on the formation and development of summertime dust storms over southeast and southwest of Iran has been investigated. A regional climate model (RegCM4), coupled with a chemistry module has been used to clarify the characteristics of LLJets and the structure of dust storms. Using a 20-km resolution on a 23 sigma levels, RegCM4 has allowed us for investigating the LLJets involved on the formation and development of summer dust storms as well as enhancing the structure of LLJets over the Middle East. The results indicate that the initiation and development of both Shamal and Sistan jets is associated with the Inertial Oscillation of the ageostrophic wind by vanishing or abrupt decreasing of turbulence in the planetary boundary layer after the sunset and also the diurnal oscillation of the horizontal pressure field associated with heating and cooling of the sloping terrain. Theoretically, high mountains of Zagros, Khorasan and Afghanistan play an important role on the initiation and development of LLJets over west-side of Zagros and Sistan region, respectively. In this research, eliminating Zagros Mountains has been associated with a significant decrease in the Shamal wind intensity and also a change in its diurnal direction. On the other hand, the Sistan Jet is mainly a gap wind which can cause dust storms on its downward due to a favorable surface condition. Summer dust storms in both regions mainly initiate on mid-night to early morning when LLJets achieve their highest intensity over the area. This emphasis on the role of Shamal and Sistan Jets on the formation and development of summer dust storms. It is found that the direction, intensity and depth of summer dust storms are the function of direction, intensity and the height of LLJets over the Middle East. On this basis, summer dust storms form in a shallow layer in the lower troposphere by following the LLJets conditions.

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