Islamic Azad University, Science and Research Sector, P.O.Box 14515-775, Tehran
Meteorological and Atmospheric Research Center, P. O. Box 14155-6466,Tehran
Institute of Geophysics, University of Tehran, P.O. Box 14155-6466, Tehran, Iran
Islamic Republic of Iran Meteorological Organization, P. O. Box 14155-6466,Tehran
An attempt is made to calculate some important quantities, such as wind shear, related to clear air turbulence (CAT) and their associated turbulence indices. Thresholds of the indices are calculated for moderate and light to moderate cases of CATs over Iran for a five months period (from January to May 2004) and corresponding large scale atmospheric patterns at upper levels have been examined. Indices are calculated using AVN model outputs and compared with pilot reports for CAT. Results showed that occurrence of CAT with intensity more that moderate is very rare over the region. Threshold values of Elrod-2 and Dutton are in good agreement with values calculated over Europe and USA. Most of the turbulence occurs in 250-300 hPa layer. Also, it was seen that above the geopotential trough the condition is favorable for the formation of intense CATs.