پديد آورندگان :
يارمرادي، زهرا دانشگاه لرستان، خرم آباد , نصيري، بهروز دانشگاه لرستان - گروه اقليم شناسي، خرم آباد , محمدي، غلامحسن , كرم پور، مصطفي دانشگاه لرستان - گروه اقليم شناسي، خرم آباد
چكيده لاتين :
1- Introduction
A dust storm is one of the biggest serious environmental problems in the arid and semi-arid regions of
the world, causing irreparable damages to farms, facilities, roads, traffic and transportation every year and
respitory problems by contaminating the air. Due to the geographic location of Iran which is in the arid
and semi-arid belt of the world, the country is frequently exposed to local and synoptic dust systems.
Considering the increasing occurrence of dust in the coming years, drought and climate changes and the
emergence of desert zones, the study of this phenomenon is considered important and should be studied
by using scientific researches to identify the factors affecting the occurrence of this phenomenon and dust
source areas. The main purpose of this research is to identify the sources and also track the dust route
entering the east of Iran using the HYSPLIT model, satellite images and synoptic analysis .
2- Methodology
In this study, At first, warm season dust storms were studied by using weather data, phenomenal code
and horizontal visibility. Then, the storm from August 12 to 14, 2018, was recorded using weather data
for East stations and horizontal visibility. For more accuracy, MODIS images of the storm wave on this
day were identified and the surface dust concentration was confirmed using the AOD Index. Then, using
the European Center for Average Meteorological Data (ECMWF) with a spatial resolution of 0.25 * 0.25,
sea level pressure (SLP), temperature, direction and wind speed, and geopotential height At 850, 500 and
250 levels, jet streams were investigated and The synoptic factor of the dust storm was determined. In the
next step, using the HYSPLIT model, the path of motion of particles and their source were determined at
three levels of 500, 1000 and 1500 meters for 24 hours before the storm. The meteorological data of the
model was obtained from a 0.5 degreess GDAS.
3- Results
The intensity and extent of the dust storm from August 12 to 14, 2018 showed that its horizontal
visibility had been decreased to less than 200 meters across stations in eastern half areas of Iran. On
this day, the dry bed of Hamoun, Pozak, Saberi and Hirmand, Afghanistan's plains have been
contributed to nourish the storm. The results of synoptic studies showed that when there is a high
pressure independent cell in the north-east of Afghanistan and north-east of Iran as well as a lowpressure
cell in the southwestern part of Afghanistan, a severe gradient is made between these regions
that causes the wind speed at ground level to be more than 14 meters per second. The severe pressure
and temperature differences in the region, the lack of humidity and the high radiation angle have
drove the dust of deserts outside the northern and eastern borders toward the region, and this area has
been under the Azores subtropical high pressure, which its blockage at high levels leads the
persistence of dust for three days in eastern Iran. The results of the model also showed that more than
90% of the dust entry routes to the east enters the eastern part of Iran from the deserts of
Turkmenistan, Khazakhistan and Afghanistan.
4- Discussion & Conclusions
Due to 120-day winds, low humidity, poor vegetation and dry regional substrates, the eastern part
of Iran is prone to the frequent occurrence of dusty phenomena. Based on satellite images and AOD
index, the storm has formed in the desert region of Turkmenistan and has been expanding to eastern
Iran. According to the synoptic study of the warm period of the dust storm in the east, the upper
levels of the Iranian plateau are under the control of the Azores high pressure and on the ground
surface, the thermal low is also increasing in the eastern half. When two strong low-pressure nuclei
with a 990 hp center in southeastern Afghanistan and southeastern Pakistan were deployed so that its
tabs penetrated into the studied region and progressed to the Mediterranean, it created the appropriate
conditions for climbing a huge amount of dust into the air that in the case of dryness of the area and
north-northwestern and northeastern flow of the upper levels, this phenomenon intensified and
moved to the eastern part of Iran. At high atmospheric levels, due to air stability and blocking events,
as well as air stagnation, the dust is more durable temporally and the process of bringing it down to
the ground surface will last longer days. The results of the HYSPLITE modeling output also showed
that the source of dust of the eastern half of Iran in the storm studied enter the studied area from the
deserts of Turkmenistan and northwest of Afghanistan and Khazakhistan with the north, northwest
and northeastern directions up to 90 percent. In all cases, the results of the model are compared with
and confirmed by satellite and synoptic studies.
