Introduction: Dust is a natural process in desert areas, which is caused by the effect of strong winds on the surface of the soil. The aim of this study is to investigate the conditions of the formation and expanding the dust storm formed in Iraq to the Khuzestan province in February, 2017.   Materials and methods: The synoptic analysis was conducted using meteo-rological parameters from ERA-interim and observation data from the Ahwaz station. In addition, the EUMETSAT image, the DREAM and the HYSPLIT model output were used.   Results: As the results show, regarding to the storm, dust in low- pressure area located over Iran is expanded toward the west associated with the tough 500 hPa . With the formation of the high-pressure area in Syria, a pressure gradient is formed in Iraq resulting the northwest wind with the wind speed of 28 knots s (14 m/s) in 925 hPa. These conditions have led to transport the dust from Iraq toward southwest of Iran. A jet stream is formed 12 h before entering the dust from Iraq to Iran, at 900 hPa. The HYSPLIT model predicts the particle’s motion along the northwest winds, and is matched with the wind field in synoptic structure.   Conclusion: According to this study, the most important factors in dust trans-port to the Persian Gulf are geographic location of the low- and high-pressure area and the formed northwest winds in Iraq.

A squall line was recorded in Dayyer port over southwest of Iran, on 19 Mar 2017. In the present paper, we have simulated the characteristic features associated with the squall line by Weather Research and Forecasting (WRF) model using five different microphysics (MP) schemes. For validating the simulated characteristics of the squall line, the latitude-height and longitude-height cross section reflectivity and precipitation value derived from observed reflectivity gathered by Doppler Weather Radar at Bushehr, synoptic weather station data at Dayyer port along with NCEP-NCAR and ERA-INTERIM reanalyzes data were used. To verify the simulated precipitation, the Fractions Skill Score (FSS) curve was calculated. Examining the simulation results for geopotential and sea level pressure show that the model simulations using different MP schemes, agree well with the verifying reanalyzes. Also, the spatial rainfall distribution of simulations and verifying observations did not show big differences. However, there are significant differences in the details of simulations such as the maximum reflectivity of the convective cells, vertical extent of the storm cells, speed and direction of the wind, rainfall values and FSS curves. Though, all of the simulations have shown convective cells over Dayyer port at the time of occurrence of the squall line, but, only the model simulation using Lin MP scheme is consistent with the corresponding radar reflectivity and vertical extent. The FSS chart showed that the skill changes with spatial scale. Results using Lin microphysics scheme crossed the FSSuniform line at lower scales when compared to other MP schemes.

Introduction: Recently, local dust events increased in Khuzestan province. Therefore, knowledge on its properties can have a crucial role in future prediction and planning. Materials and methods: This study investigated the effect of different boundary layer schemes for dust simulation by WRF_Chem model on March 14th 2012 in Khuzestan province. To validate the model, observation data such as horizontal visibility, 10-m wind speed and PM10 were provided. Results: The results indicated that the MYN scheme has the highest correlation between model outputs and observation for 10-m wind speed, PM10 and horizontal visibility. Due to the highest correlation of the 10 m wind speed, horizontal visibility, PM10 respectively with 0.83, -0.76 and 0.76 values and the highest consistency with the day-night variation of PM10, MYN scheme can be selected as the most suitable scheme. At the second level, UW scheme seems to be an appropriate option. In MYN and UW schemes, the maximum wind speed in 925 hPa level was estimated 24 m/s at 03 UTC, March 14th which caused an increase in the 10 m wind speed at 06 and 09UTC. Therefore, the dust emitted from the surface to the air. Although the results of MYJ scheme showed proper correlation and temporal variation with observed, but as it determined PM10 concentration with high difference, it can’t be considered as a suitable scheme for simulation dust concentration. Conclusion: Although the PM10 concentration obtained by WRF_Chem showed difference with the observation for all the selected boundary layer schemes, MYN scheme gives the most appropriate result.

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