Analysis of synoptic patterns affecting the occurrence of dust storms in Kurdistan province

In recent years dust storms as one of the most damaging environmental phenomena has engulfed over large parts of Iran and many human activities in the region have been affected (Khoshkish et al., 2011; Azizi et al., 2011). Dust storm is one of the environmental-climate disasters that its occurrence causing air traffic, prevalence of respiratory, heart disease and damage to agronomy (Rasoli et al., 2010). There is documentary evidence that the mineral dust aerosols affected on cloud formation and amount of precipitation and even reduces the acidity of precipitation (Ichoku et al., 2004). Intensity of dust storm determinate by survival, spatial distribution and visual reduction, and depending on continuity divided to short term (up to half an hour) and long-term (several hours or one day) (Lashkari et al., 2008). Due to consequence dust storm occurrence and its role in the life and human activity, many studies have been conducted on this event (Merrifield et al., 2013; Carnevale et al., 2012; Meloni et al., 2008). In some studies, dust frequency, their trend in the long term period and statistical analysis was investigated. But among them, climate studies more inspected synoptic analysis. Natsagdorj et al (2003) studied dust storms in Mongolia and showed that dust storms often occur in the Gobi desert and most occurrences are observed in the spring. Engelstadler (2001) investigated dust storm frequencies and their relationships to land surface conditions. Orvlosky et al (2004) analyzed spatial distribution, frequency, seasonality and diurnal variation of the dust storms in Turkmenistan and show that the highest mean annual frequency of such storms is observed in the spring in the sandy Central Karakum Desert. Zolfaghari and Abedzade (2004) investigated dust storms synoptic analysis in west Iran. According to their results maximal duration of dust storms is recorded in June and minimum in December. As previous studies have shown that the occurrence of these storms has increased in recent years in the West of Iran. Thus, Synoptic study of this event properties could be the present of their formation. In this study, it is assumed relatively deep down on Syria deserts caused to create the dust in Sanandaj. To this purpose the main synoptic patterns of sea level pressure and thickness 500-1000 hectopascal influencing the occurrence of dust storms in Sanandaj city were studied in 2009 to 2012.
Data and In this paper, environmental and circulatory database were used to be analyzed synoptic dust days. Daily records of dust storm occurrence during 2009-2012 by the Department of Environment Kurdistan and atmospheric parameter (sea level pressure 500-hPa and geopotential height 500-100-hPa) were utilized for synoptic analysis. In order to close study of dust storm, aerosol data were divided to two groups consist of days without dust storms (particular matter less than 200 µg.m-3) and dust storm days (concentrations of PM10 ranging 200-3000 µg.m-3). According to dust storms creation zone located in an area outside of Iran, we selected extensive area (0-60o E and 0-70o N). Finally the dust days database (94 days) was formed as a 94*783 matrix in MATLAB software. Then, cluster analysis was performed using Ward Linkage method to determinate sea level pressure and geopotential height pattern. At last, selected one day as representative dust days and its circulation patterns in Surfer software was plotted.
Sea surface level investigation Results showed that the cluster analysis upon sea surface pressure data represent three patterns. In the first pattern, located low pressure on Persian Gulf and its landing on Syria and Iraq desert due to dust storm in west of Iran. In the other hand, on the west Russia high pressure situated that cause air flowing from low latitude to high latitude. In the second pattern, the position cyclone on Iraq makes dust transportation to the study region. This pattern included maximum dust days. Climate condition dominated on third pattern is different from other patterns.
Geopotntial height 500-1000 hPa surveying The obtained results of cluster analysis upon 500 hPa represent three patterns exist. Mediterranean high trough in the first and third pattern, black sea low pressure and Saudi Arabia high in the second pattern are reasons for dust storm occurrence.
Dust storm in Sanandaj mainly occurs in spring, especially in July. In general, dust occurs when the strong pressure gradient is formed over dry source regions between Syria, Iraq’s desert and Iran, giving rise to strong wind conditions for the lifting of dust particles. In general, existence of landing deeply on easternmost Mediterranean sea, spreads air from arid regions (deserts of Libya, Egypt, northern Saudi Arabia and Iraq) toward Iran, and high trough Arabia have important role in the creating dust storms in southern, south-western and west of Iran ( particularly Sanandaj). Dust storms in Sanandaj mainly occur in warm half of the year. These events have increasing trend since late winter and reaches a peak in July.