بررسی پتانسیل شدت طوفان گرد و غبار با استفاده از مقایسه داده‌های میدان دید افقی و شاخص DSI در استان یزد

1- Introduction

One of the main challenges currently facing arid and desert areas is the phenomenon of dust. Although most dust storms, especially dust storms in Iran, are often regional in nature, local hotspots play an important role in the dust belt, especially in Iran. Yazd province has been one of the most prone areas with dust in the country since ancient times, so that one of the origins of local dust in this belt is the city of Yazd and salt domes northeast of Ardakan.

Many studies have used the DSI index to evaluate the frequency and intensity of dust storms; Although more studies have used the DSI index to identify the intensity and frequency of dust, fewer studies have used the horizontal visibility to determine the intensity of the dust index. In this study, the behavior of dust phenomenon in Yazd province based on horizontal visibility and dust storm index (DSI) has been investigated. The DSI index is a convenient way to monitor wind erosion on a large scale using meteorological records that calculate the frequency and intensity of dust storms in the area. Using a horizontal visibility is also a way to evaluate and estimate the frequency and intensity of dust storms. In this research, it has been tried to reveal the compatibility of these two methods in estimating the frequency and intensity of dust storms, and in the absence of data from one method, data replacement and other methods have been used in conducting research projects.

2- Methodology

n order to study the dust phenomenon in Yazd province, a joint statistical period from 2000 to 2018 was selected. In this study, the aim is to investigate the compatibility of the two methods of using horizontal visibility and using dust storm intensity index to investigate the status of dust storms in an area. In order to extract the dust event from 100 phenomenon codes (0-99), the codes related to the dust event were extracted. After extracting the dust events, the horizontal visibility parameter related to each event was extracted and classified on the data. The classification was done and the dust events were divided into 5 floors based on the horizontal visibility and zoned in the GIS software environment.

The DSI index is a combination of the following three indices that were extracted for all synoptic stations in the study area.

SDS = days with Sever Dust Storm Days, Total Dust Code Observations Maximum Daily Code 35-33.

MDS = days with Meduim Dust Storm days, total observations of dust codes maximum daily 30, 32 and 98.

LDE = days with local dust, total observations of dust codes maximum daily 07 and 09.

Finally, the following equation was used to calculate the DSI index

To prepare maps of different classes of horizontal field of view, the statistics of hourly dust events and kriging method were used. Finally, based on the spatial distribution of dust storms using both methods, the degree of conformity and the possibility of replacing each method with another method was investigated and analyzed.

3- Results

Examination of the frequency map of the occurrence of a horizontal visibility of 100-200 meters in Yazd province showed that there are two maximum dust occurrence cores separately in Meybod and Bafgh areas. Occurrence of 1000 m horizontal visibility indicates critical conditions in a dusty area. Examination of the frequency map of the occurrence of 1000 meters horizontal visibility in Yazd province shows the existence of 2 maximum cores in the area of Meybod, Yazd and Bafgh. Check the frequency map of 3000 and 500 horizontal field of view. 900 meters in Yazd province shows that one core occurs in the area of Yazd and the second maximum area is located in Meybod. Minimal polynuclear cells with small surface area can be seen in Herat, Gariz and Mehriz. Central, western and northern have the highest frequency.

Spatial distribution of dust occurrence intensity using DSI index showed that the highest value of this index occurred in the wind corridor with northwest-southeast direction in Meybod-Yazd. The other core of this index is located in Bafgh. The maximum core of the DSI index in terms of spatial distribution corresponds to the spatial distribution of the horizontal visibility 100-200 meters (supercritical) and the horizontal visibility 1000 meters (critical). In general, the intensity of the DSI index in the west of the province is higher than in the east. The south of the province also has the minimum values of the DSI index.

4- Discussion & Conclusions

Although most dust storms, especially dust storms in Iran, are often regional in nature, local hotspots play an important role in the dust belt, especially in Iran. Yazd province is one of the central arid regions of the country and due to the presence of desert and desert areas, it is a region prone to dust. In order to evaluate the appropriate indicators for monitoring and evaluating the frequency and intensity of dust, two indices of horizontal visibility and dust storm intensity index were used. The results of the studies showed that the field of view of 100-200 meters, which represents the supercritical conditions, had the lowest frequency. The wider the field of view, the greater the frequency of occurrence. Comparison of dust storm intensity based on two indicators showed that the spatial distribution of the field of view related to severe dust with a field of view of 100-200 meters and also the field of view of 1000 meters and less is completely consistent with the spatial distribution of dust storm index resulting from DSI method. And monitoring the intensity of the dust storm. If the data related to the dust phenomenon code is not available, the horizontal visibility data can be used and vice versa