Analysis of the Placement of Pressure Systems in the “Afria” Zone during the Last Fifty Years of Dust Days in Iran

Pressure systems are one of the most important factors in forming the general circulation of the atmosphere and air circulation and one of the determining factors in the land's temperature rate. In the present study, the hourly codes "06" were obtained from the collection of dust codes for 38 cities in Iran during the last half century (1970 to 2020) from the Meteorological Organization of Iran. These codes were arranged as daily tables to identify 561 dust waves based on the frequency of stations with dust (in short-written style: Eder). The first results showed that during the last half-century, among the 38 selected cities of Iran, three cities Bandar Abbas, Bandar Genaveh, and Dezfool have been the dustiest in Iran with a clear difference from other cities. In the synoptic section, the pressure systems, including low-pressure and high-pressure during the peak days of dust waves, were located in the first step "with a separation into hot and cold periods of the year" and in the second step "separated into two periods of 25 years". This work revealed the northward movement of the subtropical high-pressure belts and their departure from the tropical low-pressure belt along the orbital of deserts, especially between the Sahara and the Hijaz desert. The expansion of this zone, which is the source of the strong northeast winds and a major part of the "Headley cell – one of the three cells of the planetary circulation of the atmosphere", indicates the northward expansion of this cell. The western border of this expanding zone with the waters of the Atlantic Ocean is closed at once, but its eastern border is slowly narrowing from the interior of the Hejaz to the interior of Iran. Therefore, the fear of this eastward expansion is raised over the desert belt of Afria (Africa-Asia) and from Iran to Central Asia. Some expected consequences of the expansion of the Hadley cell over Iran are the increase in the share of dust arising from higher latitudes, specifically the deserts of Central Asia (Tooran); the increase in the number of warm months of the year; and the decrease in the presence of westerly rainy winds. Pressure systems are one of the most important factors in forming the general circulation of the atmosphere and air circulation and one of the determining factors in the land's temperature rate. In the present study, the hourly codes "06" were obtained from the collection of dust codes for 38 cities in Iran during the last half century (1970 to 2020) from the Meteorological Organization of Iran. These codes were arranged as daily tables to identify 561 dust waves based on the frequency of stations with dust (in short-written style: Eder). The first results showed that during the last half-century, among the 38 selected cities of Iran, three cities Bandar Abbas, Bandar Genaveh, and Dezfool have been the dustiest in Iran with a clear difference from other cities. In the synoptic section, the pressure systems, including low-pressure and high-pressure during the peak days of dust waves, were located in the first step "with a separation into hot and cold periods of the year" and in the second step "separated into two periods of 25 years". This work revealed the northward movement of the subtropical high-pressure belts and their departure from the tropical low-pressure belt along the orbital of deserts, especially between the Sahara and the Hijaz desert. The expansion of this zone, which is the source of the strong northeast winds and a major part of the "Headley cell – one of the three cells of the planetary circulation of the atmosphere", indicates the northward expansion of this cell. The western border of this expanding zone with the waters of the Atlantic Ocean is closed at once, but its eastern border is slowly narrowing from the interior of the Hejaz to the interior of Iran. Therefore, the fear of this eastward expansion is raised over the desert belt of Afria (Africa-Asia) and from Iran to Central Asia. Some expected consequences of the expansion of the Hadley cell over Iran are the increase in the share of dust arising from higher latitudes, specifically the deserts of Central Asia (Tooran); the increase in the number of warm months of the year; and the decrease in the presence of westerly rainy winds.