The Recognition of Synoptic and Local Scale Factors Influencing the Occurrence of the Dust Phenomenon in Ilam

Subject Areas : Regional Planning

mohahasein naserzadeh ¹ , hojat fatahi ²

1 - استادیار گروه جغرافیا و اقلیم شناسی، دانشگاه خوارزمی، تهران، ایران
2 - کارشناسی ارشد آب و هواشناسی کاربردی، دانشگاه خوارزمی، تهران، ایران

Received: 2014-11-12 Accepted : 2016-05-19 Published : 2016-04-20

Keywords: Ilam, Dust, thermal low pressure, synoptic analysis, instability indices,

Abstract :

The undesirable phenomenon of the dust storm is one of the natural disasters, which influences Ilam province due to its geographical location and adjacency to the large areas of desert. The study was performed after collecting 40 dust systems, and divided them into two cold and warm periods of the year, during the period 2000-2010, using geo-potential height maps of level 500, and sea level pressure, the wind vector maps, speed lines, and omega maps at 700 hPa level, ranging from 15 to 45 degrees North and 20 to 65 degrees East. In addition, to evaluate the situation in the upper atmosphere, by referring to the University of Wyoming weather database, Radiosonde data were received for days with dust storms in the Southwestern stations of Iran. Furthermore, by using software RAOB and SKEW-T diagrams, the data were drawn and analyzed daily. To study the stability and instability of the atmosphere, LI, SI, CAPE, and TT indices were used. Dust enhancement on MODIS images was performed using the features of the brightness temperature and Aerosol Optical Depth (AOD). The results indicated that during the cold era of the year, migratory systems of the west winds, and the along polar jet stream, and in the warm period of the year, the thermal low pressures of the earth surface are the most important factors in creating and shaping the phenomena of dust in Ilam province. When a deep landing occurs in the west part of the study area on the deserts of the adjacent countries, and the wind velocity reaches the jet stream speed, having the proper environmental conditions, by creating instability in the earth surface, they cause dust and its movement towards the province. During the warm era of the year, the thermal low pressures of the earth surface, and particularly low pressure of the Persian Gulf, by sucking the air of the surrounding desert (Arabian Peninsula) is an important cause of dust. The paths of dust waves, the deployment of the landing axis, the low pressure of the earth surface, and the used satellite images indicated that the most important sources of the entering dust to the province of Ilam are the Southern deserts of Iraq, northern deserts of Saudi Arabia, Southern deserts of Syria, and to some extend the Northern of the Sahara Desert.

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