Synoptic and Satellite Analyses of Dust Storms in West and Northwest of Iran (Case Study: Dust Storms of July 15-20, 2000, and June 17-22, 2012)

The Dust storm is one of the most important climatic phenomena of the present age in arid and semi-arid regions of the world. Due to its characteristics, this phenomenon can have various environmental and climatic effects in different atmospheric systems, oceans and continents. Dust storms play a very important role in the earth's atmospheric cycle, so that dust particles are one of the factors of atmospheric warming, as well as reducing air quality and affecting human health. Dust particles have direct effects on absorbing or scattering radiation waves, which results in a significant decrease in visibility. The west and the northwest of Iran are facing the dust storm phenomenon and its problems periodically.

In this study, the frequency of dust phenomenon and its occurrence causes have been analyzed in the northwest and west of Iran, including Ardabil, East Azerbaijan, West Azerbaijan, Kurdistan, Zanjan, Hamedan, Kermanshah and Ilam provinces. At First, the occurrence of dust in the study area was investigated. To identify the source of the dust storm, dust storms of 15-20 July 2000 & 17-22 June 2012 (as case study) were described using MODIS satellite images. Modis sensor images were used to detect and monitor the dust storms. The reason for choosing these days for analysis was the high intensity and concentration of dust in those days in most of the stations. For the synoptic analysis of dust storms, re-analyzed data of sea level pressure, geopotential height, vector wind, vorticity, wind direction and omega at 500mb level were used. These data were obtained from National Oceanic and Atmospheric Administration (NOAA) which was prepared by the National Center for Environmental Prediction (NECP). The maps were drawn and synoptically analyzed using Grads software.

The results showed that the highest frequency of dust storm codes occurred in the studied stations was related to code 6, which indicated the presence of dust in the sky. In terms of monthly distribution, June, July, April, and May has the dustiest days in the studied area. The occurrence of dust had an increasing trend from the early hours of the night to noon. The frequency of dusty days in different years indicated an increasing trend from 2000 to 2018. The frequency of dusty days was higher in 2008 and 2012 compared with other years. The results also showed that the main sources of dust in the west and northwest of Iran are the desert areas of Iraq, the Arabian Peninsula, and the African Sahara. At sea level, the most important cause of dust storms in the west and northwest of Iran was the existence of a low-pressure center in Saudi Arabia and Iraq. In other words, dust storms in the west of Iran were transitional and have originated from the western neighbors of Iran (Iraq, east of Syria, and northern Saudi Arabia), where in the most severe event, the dust has spread to central Iran. At 500 mb level, the most important factor in creating dust storms in the west and northwest of Iran was the rule of the Azores sub-tropical high-pressure tongue and the location of the region below it. Due to the high pressure of the Azores on Iran, migratory cyclones and troughs due to lack of penetration into the region, had little effect on the formation of instability and dust storms, which the main reason for this phenomenon should be found in surface pressure systems. The extreme warming of the earth's surface had caused the instability of the atmosphere of Iran in summer up to a height of 2-3 km above the earth's surface. The low-pressure thermal cell was stretched from Pakistan to the south of Iran, and from there to the deserts of Saudi Arabia, Iraq and Syria on all days under study. The Iran-Pakistan low-pressure system, which appeared as a focal point in the southeast of Iran, was a low-pressure, high-suction system that created dust storms in the region.

The results of dust storms monitoring in northwest and west of Iran using satellite images showed that remote sensing techniques due to extensive and continuous coverage in space, monitoring natural disasters and also monitoring dust storms, intensity and dynamic tracking, can play a major role in dust monitoring. The results also showed that the Aqua and Terra satellites have a high capability in detecting and tracking dust storms due to their high temporal, spatial, and spectral resolution.