An observational study has been employed to understand the structure of large scale atmospheric circulation over Southwest Asia (SWA). Long-term geopotential height, zonal and meridional wind, vertical velocity and relative vorticity have been used for all levels of troposphere.The results indicated that the summertime large scale circulation regime is settled over SWA during late May to early June, when the subtropical jet stream over the Middle East suddenly moves northward and Tropical easterly jet and Somali jet suddenly appear and reinforce in the west of Indian Ocean. The appearance of the Turkmenistan anticyclone, the Quasi-stationary Trough of east Turkey (QSTT) and Zagros trough, as well as the settlement of Pakistan low and Arabian high in their summertime normal position, are the main results of the changing of atmospheric circulation over the SWA in the same period. Each of these components will typically participate in the climate of SWA in summer. The investigations show that the Turkmenistan anticyclone plays the main role in the formation and maintenance of the QSTT and Northern winds over eastern Iran plateau. It is also one of the important components in the formation of Iran low. The results also indicated that the Zagros trough is formed over the Western Iran plateau due to the thermal forcing of Zagros Mountain. Moreover, the establishment of the Turkmenistan anticyclone and Pakistan low caused the 120 days winds of Sistan, and the development of Arabian high and Zagros trough resulted in the Shamal wind in Persian Gulf region.

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