عنوان مقاله [English]
During the recent years, the dust phenomenon has grown significantly around the world following the occurrence of dry periods and the average increase in global temperature. Therefore, the regions located in the dry belt of the world have been more affected by this extreme phenomenon than other regions.
The main goal of this research is to investigate the synoptic patterns and the role of regional circulation of the atmosphere in the production of local and regional dust in Qazvin province. It is internal and external, and in this research, it has been tried to investigate and analyze the different dimensions of regional and extra-regional dusts using methods and data with high resolution.
In order to analyze dusty days in Qazvin province, two environmental and circulation databases were used. In this way, first, according to the meteorological data recorded in the ground level stations, the number of dust days was determined and then the circulation patterns that generated them were identified. The formation of environmental databases was done in such a way that the number of dusty days in the province in a 20-year period (2002 to 2021) for 5 Hamdid stations using the code of current weather phenomena (WW) of the country's meteorological organization (codes 6 and 30 to 35, which are related to dusty days) ) was determined in MATLAB software.
In order to analyze synoptic patterns and the role of regional atmospheric circulation in local and regional dust production over Qazvin province in a 20-year period, the following results were obtained.
- Station surveys during the statistical period showed that the majority of local and regional dust occurrences in the province are related to the hot period of the year and especially the summer season, which accounts for the largest amount of dust transmission in the region. On the other hand, the cold period of the year, especially winter, has the lowest percentage of dusty days in the province.
- The results of the investigation of atmospheric circulation in the region for periods of intense and pervasive dust showed that 4 circulation patterns are the main cause of this phenomenon in Qazvin province. The mentioned patterns have a regional and extra-regional nature, and in this category, we can mention the high-altitude formation of a tropical front with a strong descent of air and an increase in negative relative humidity as a regional factor. Among the extra-regional factors, we can mention the downward expansion of the polar ice cap and the formation of deep troughs on the main sources of dust in the Middle East, which have created periods of intense and pervasive dust in the region.
- The circulation of the lower level also showed that for the formation of dust in the region, southern currents were the main ones, although in some patterns, northern currents also carried dust particles. The increase in wind speed over the main sources of dust and on the other hand the increase in wind speed over Qazvin province also showed the interaction of sub-level pseudo-jets in the formation and transfer of dust particles.
- The results of tracking dust particles indicated that the main source of dust in the region is Iraq and other dust producing sources in the region have a reinforcing effect. In such a way that the transport of particles with the monitoring of more than 48 hours in the region showed the existence of local currents which were at the heart of the circulation of the regional scale and caused the rise of dust from the country of Iraq. It is necessary to explain that sources such as the country of Turkmenistan have also played a role in the occurrence of intense and pervasive dust periods in the region, which aggravate the conditions during the combined process with the flow to the region. Among other sources of dust, we can mention the border areas of southwestern Iran, where the process of desertification in this area has caused it to become a focus for dust in the neighboring areas.
- The results of the dust transfer volume showed that the highest AOD value is observed in the third pattern, during which in the range of the regional circulation of the atmosphere, the high-tropospheric system prevails and the interaction between the trajectories and the intensity Relative humidity can be an efficient tool in predicting very intense dust storms in the region. The atmospheric system that has the lowest concentration of particles in dust periods is the southward expansion of the polar ice cap and the formation of deep troughs over the dust centers of the Middle East, which was less intense than other atmospheric patterns.
Based on the obtained results, it was observed that the internal foci also play an important role in the formation of dust periods, as mentioned by (Namdari et al., 2019). (Latfi Nasab et al., 1400) also showed that the formation of low-level jets played an important role in the transfer of dust in the region, and in this research it was also observed that the presence of strong low-level wind currents is one of the important factors in the formation of periods There is dust in the area.
The circulation database includes geopotential height data of 500 hectopascal level, orbital and meridional wind components, which were used to determine the circulation pattern of dusty days. The statistical period of the circulation database is in accordance with the environmental database and data extraction was done through programming in the software environment (GrADS). The geographical area of circulation data is 0 to 60 degrees of latitude and 10 to 90 degrees of longitude. The upper atmosphere data were obtained from the European Medium-Term Weather Forecast Database (ECMWF) from the ERA5 data series with a resolution of 0.125 degrees.
In order to extract dust generation patterns, factor analysis and cluster analysis were used to identify factors and categorize atmospheric patterns on geopotential height data of 500 hectopascals.