عنوان مقاله [English]
Today, one of the most important issues in the field of climatology is air pollution and its relationship to the general circulation of the atmosphere. The atmosphere around the planet Earth is made up of gases called fixed atmosphere gases. Humans and all living things are accustomed to this composition of the atmosphere and have adapted to it. Any changes in the quality and quantity of these elements can be considered as air pollution. Therefore, since the main cause of all changes in the characteristics of the human environment is related to changes in atmospheric pressure, so in all climate-related studies, the first step is to identify patterns of air masses. Anti-cyclonic circulation patterns, both at the Earth's surface and in the upper atmosphere, create sunny weather, leading to temperature inversion and subsequent air pollution, especially in densely populated and industrial cities. In winter, when these inversions are stronger, hot air on the cold air acts like a cap that prevents air mixing. Thus, urban areas have a strong potential to face serious problems of air pollution as a result of a combination of limited conditioning of air and emission of pollutants from high atmospheric levels. Atmosphere in terms of temperature inversion is associated with minimum air mixture and stable conditions. So the highest density in the direction of the wind extends from the source of diffusion.
For the recognition and extraction of the synoptic patterns affecting the temperature inversion in Tabriz city, we initially prepared the data records on the temperature inversion for the time period of 2001-2010 by the use of upper atmosphere station data. This was followed by the utilization of digital data on sea surface pressure as daily mean from the reanalyzed data series of NCEP/NCAR in the eastern longitudes of 10°-60° and the latitudes of 10°-90° in 651 pixels of 2.5/2.5 degrees. With the PCA analysis on the data of sea surface data pressure in the days having temperature inversion, we reduced their volume and carrying out cluster analysis on the obtained components we recognized the most important atmospheric patterns and through which the map of each pattern was drawn.
Results and discussion
Based on the results of cluster analysis on the matrix of factor scores in this study, the occurrence of temperature inversion in the city of Tabriz is due to the domination of four consecutive patterns. The general characteristics of these patterns are as follows. 1- In general, in the hot period of the year, the high-pressure pattern of Migrant Europe is the most important system in the formation of temperature inversions. In this pattern, languages from the highlands to the western shores of the Caspian Sea are advancing, and due to the presence of a mid-level ridge, it is possible to strengthen the anticyclone core at sea level and thus create a stable atmosphere.
With the dominance of the downward process of air, the stability of the earth's surface air and the possibility of inversion formation in the warm period of the year intensify. Two summer patterns, which have been associated with the establishment of a high-pressure pattern on the northwest and in some cases with a low pressure on the Persian Gulf, have caused the upheavals of this period of the year.2 - In other patterns that have occurred more in the cold season, the surface stable layer due to the penetration of the tabs of Anti-cyclonic systems including high-pressure Siberian and European Migrant Europe high-pressure is done alone or in combination and in some cases with high-pressure Migrant Europe. North pressure is also present on the map, which is exacerbated by the Convection of cold weather. Despite the process of air fall due to the dominance of the convergence region of the mid-level convergence creates deep inversions and sometimes double-layer. In these patterns, the thickness of the inversion layer is low and the temperature difference between the peak and the base is high, which indicates the acute conditions of inversion to create air pollution. This phenomenon is likely to occur in any season. But its severity, which depends on synoptic factors.
The most important factor in causing temperature inversion in most cases is how to arrange the dominant pressure patterns, In this Patterns the cold weather due to the presence high pressure system expanded in the surface with the establishment Left side of a deep trough over the region, the cold air has diffused from higher latitudes on Tabriz and strong sustainability has been created in vertical column of the atmosphere. In cases of being cause the Northern low pressure along with pressure-immigrant Europe for the spread of a cold into the region. The warm air of lower latitudes has been placed over the cold air of ground by domination of a deep ridge over the region. Therefore the intensity of stability increased and severe temperature inversion into the air near the surface formed.