Investigating the atmospheric mechanism of severe dust events in southeast Iran

1. Introduction



Dust is one of the common phenomena in arid and semi-arid regions. This phenomenon annually introduces several million tons of soil into the atmosphere (Broumandi and Bakhtiarpour, 2015).

which has an important role in the climate system, atmospheric radiation, and hydrological cycle Alizadeh (Choobari et al., 2014; Shao et al., 2011).

A dust storm is a complex process that is under the interaction of atmospheric systems and is caused by conditions such as high wind speed, bare soil, and dry air (Broghani et al., 2016).

In recent years, pollution caused by dust particles has become an environmental problem, especially in developing countries.

Investigations of the meteorological statistics of Zabul, Zahedan, Mirjaveh, and Khash stations, which are located in the northern half of Sistan and Baluchistan province, showed that whenever there is a thermal low-pressure system in the Sistan plain region, it leads to the occurrence of dust storms and Sand has increased rapidly and dust particles from the dry and clay soils of Sistan region remain suspended for hours in the skies of Zahedan, Mirjaveh and Khash cities (Shahriari and Mohammadi, 2014).









2. Research Methodology



To investigate dusty days in the southeast of Iran, the data from 12 synoptic stations located in the region from 2000 to 2020 were used. The World Meteorological Organization definition was used to determine dusty days.

According to the definition of this organization, the occurrence of dust in terms of horizontal visibility is divided into four categories: weak dust with visibility less than 10 km, moderate dust with visibility between 1 and 10 km, severe storm with visibility between 200 and 1000 meters and very severe storm with less visibility. It is divided into 200 meters (Kaskautis, 2007).

Since the data collected in the mentioned stations are monitored for 3 hours and 8 times a day, first, in general, in all hours in the mentioned period, the frequency of all the dust particles reported by the meteorological stations is recorded and then the storm Those whose horizontal visibility was below 200 and 100 meters and were reported in more than 70% of the stations were classified.

3. Results and discussion

The obtained results have shown that, in the first pattern, a deep trough with a northeast-southwest axis has been established over central Iran, and at the same time, a strong positive eddy current has covered the east and center of Iran.

The existence of such a strong instability in the region has caused a strong pressure gradient to occur in the lower levels of the atmosphere, and as a result, it has led to the rise of dust from the dry areas and its flow into the hole of central Iran.

In the second model, a ridge with a height of 5,760 geopotential meters is located in central Iran, which caused the negative flow to occur from the southern slopes of Alborz to the southern Oman Sea.

The support of this eddy current in the region is associated with the eddy current located in the eastern half of the country, which continues from the east of Razavi Khorasan to the northeast of Sistan and Baluchistan. On the western side of the mentioned ridge, a 15-degree geographical trough has been created, which covers western Iran with a north-south axis.

This situation plays an important role in intensifying the counterclockwise flow over central Iran. The third pattern can also be recognized by the high ridge formed in the country.

In this system, the dominance of negative convection flow has caused the transfer of dust particles from areas with maximum negative convection.

In this way, with the increase of negative convection, which is associated with a small core over the northeast of Kerman, the currents entering the Jazmurian hole have become northeast, and this has played a key role in the transfer of particles from desert areas to the region.

Also, by examining the wind vector, it was observed that most of the currents are from north to south, which affects most of the western areas of Pakistan.

On the west side of Khorasan, a core of maximum velocity has been formed, which is determined by checking the direction of the airflow, which is associated with the intensity of this wind and its convergence in the central Iran region, the Jazmorian crater with periodic dust clouds with low horizontal visibility.

4. Conclusion

Dust centers can be divided into four areas based on AOD values and air mass tracking.

Thus, in the first pattern, the main dust transferred to the region can be referred to as the deserts of central Iran the southern regions of Khorasan, and the desert plain.

In the second pattern, most of the dust enters the region from the north and northwest of Afghanistan.

The third pattern is a pair, so that two northerly currents originate from Afghanistan and its northern regions, and the other enters the region from the Arabian Peninsula, in the southeastern parts of Iran, these two air masses converge, and dust flows and accumulates. accept

Based on the research of Lotfi Nesab et al. (1400) and Soleimani Sardo et al. (1400), the dust in the southeast of Iran has a different atmospheric structure such as northern currents. It has a border and cross-border origin, which was well mentioned in the present research.