Study of the mechanism and source of dust in Khorasan Razavi province by RegCM4 and HYSPLIT model: a case study (July 1, 2014)

The dust has affected most parts of Khorasan Razavi in July 1, 2014. The purpose of this study is ‎to simulate this event by RegCM model and validate its results with observation and remote sensing ‎data. For this purpose, horizontal visibility were prepared from the Iran Meteorological ‎Organization and AOD of Aqua and Merra-2 satellites from Giovanni web.‎ The result shows that the development of low heat pressure on Pakistan along with north and ‎northeast winds of 20 m/s in the east of the Razavi province leads to the transfer of dust to the ‎region. The HYSPLIT model and the output of the RegCM model show the dust source in ‎Turkmenistan and western Afghanistan.‎ The optical depth of aerosol obtained from the RegCM model is in good agreement with the ‎visibility in the east and south stations of the Razavi province, So that the correlation coefficient in ‎Gonabad was -0.98, Torbat Jam -0.66 and Sarakhs -0.61. In addition, the correlation coefficient of ‎the RegCM model and the Merra-2 optical thickness of aerosol obtained in Sarakhs and Torbat-e ‎Jam located in in the east of the province, including, were -0.45 and -0.78, respectively.‎ The result of comparing the time series showed the model output in three-hour intervals is in good ‎consistency with the visibility, the Aqua optical depth aerosol, and the Merra-2 optical thickness ‎aerosol in the east and south stations of the Razavi province. However, the RegCM model does not ‎estimate dust and has a time delay of 6 to 9 hours in the central and western stations.‎