Identification of Dust Centers in Birjand City

Climatic phenomena in different regions of the world are different in relation to the geographical characteristics of each region. Dust is one of the dominant atmospheric phenomena in desert and semi-desert regions of the world. This phenomenon is related to air pollution in most parts of Iran with dry climate, including Birjand in eastern Iran. The origin and direction of dust in this area are varied in the year, and knowing them helps urban risk management, forecasting and desertification. In this study, Landsat satellite images were used to determine the origin of dust in the period of 1955-2017. The dust day was defined based on the classification of Shao and Dong with code 06 and 07 with horizontal visibility of less than 10 km, and revealed with BTD and TDI index. To determine dust atmospheric patterns, grid data from NOAA was used, and dust trajectories were carried out with the HYSPLIT model. The results showed that the most dust days in 1963 and 2008 (45 years), with 148 and 128 days, respectively, which mainly occur in the warm season and July. The 120-day winds of Sistan in the east of Iran plays a major role in transporting dust particles and air pollution in Birjand from the east and northeast from the deserts of Central Asia, Turkmenistan, Afghanistan, Khorasan Razavi plains and interior plains. But in the cold period of the year, Siberian cold masses from the east, cold fronts (migrating anticyclone), occluded fronts and low pressures from the northwest, west and southwest by passing through the central plains of Iran and sometimes the deserts of Syria and Iraq causes dust in the upper levels of the atmosphere. In all these centers, the occurrence of particles and pollution of cities prevails during periods of drought.