Investigation of the origin and spatial distribution of high dust concentrations and its synoptical analysis in Gavkhooni basin

In recent years, the crisis caused by dust in the southeastern regions of the country has been one of the natural-human events affecting the daily lives of citizens and the economy of the region. Increasing access to various data processing sources has expanded dust modeling at various levels, including local, regional, and global levels, and has helped to understand the mechanism of complex natural systems. dust Modeling helps to identify the main factors that create it and the importance of each factor. One of these models that are used to detect the concentration and intensity of dust in the atmosphere and the range of this phenomenon and determine its origin is the dust model (NMMB / BSC). The purpose of this paper is to identify and monitor dust from the Gavkhoni basin by two methods of visual interpretation and tracking in satellite images using the mentioned model. Identifying areas with the possibility of dust and its synoptical study can be an important step in managing this phenomenon in the region.

In order to determine the potential areas of high concentrations of dust in the region, first in the period of 2016-2016, pervasive storms in the region were determined on a monthly basis based on the Aerosol optical depth parameter (AOD). Then, by the parameter of the minimum visibility and continuity of dust events obtained from the information of synoptic stations of the Meteorological Organization, the days with the lowest field of view and the highest continuity in the specified months (months with the highest AOD concentration) were selected. The Aerosol optical depth was calculated by using the Modis sensor and the Deep Blue algorithm. The MMB / BSC-Dust model was used to identify the most dust suscribted areas in the Gavkhoni basin. With the help of this model, dust transfer routes were monitored for three hours within 72 hours after the occurrence. Accordingly, in the next step of 25 model output maps for each time period, a map with the highest dust concentration in the basin was determined. To test the relationship of these parameters to the high concentrations of dust the output was then compared with the Synoptical maps and dust images of the Modis sensor dust storm from the Worldview database. In Synoptical studies, the goal is explaining the key relationships between the atmosphere and the environment. In order to determine the atmospheric patterns in the basin on the studied dates, the geographical range of 20 to 50 degrees north and 40 to 65 degrees east to receive digital data was determined. The hourly data of winds of different atmospheric levels of 100, 500, 700 and 850 hectopascals for days with the highest dust concentration were obtained from NCEP / NCAR center and the obtained maps were compared and analyzed with each of the dust concentration patterns.

The selected image of the 72-hour period on 4/6/2014 shows that the basin is affected by the southwestern regions of the country, especially the dust centers of Khuzestan and Iraq, which gradually affect the basin during the movement towards the central regions of the country. Images of the Modis sensor also confirmed the presence of this dust mass on the southwestern regions of the country and affected the basin on this date. The image of 4/25/2015 proved the existence of a dense dust mass in the southwestern regions of the country and the impact of the Gavkhoni basin from this mass. On this date, parts of the basin, including the eastern part of Gavkhoni Wetland and the center of the Little Spring Basin, have been producing dust. On this date, parts of the basin, including the eastern part of Gavkhoni Wetland and the center of the basin, have been a small source of dust. The dust event that occurred on 1/10/2016 shows that the basin is affected by dust sources in the Central Desert so that by moving the dense masses of dust from the central desert and the Black Desert, the basin was affected by them. And the central areas of the basin acted as a source of dust and contributed to the intensification of dust concentrations. As can be seen in the dust analysis, due to the low pressure in the center of Iran due to cyclonic rotation (counterclockwise in the northern hemisphere) on the north and south sides, the east wind and the west wind have dominated, respectively. The dominance of the western wind with orbital motion in dust storm events has been proven in most of the identified dates. In the most recent case, in 2016, we witnessed the expansion of a high-pressure center across the country and the change of this trend and the dominance of the east wind in the high levels of the atmosphere. An examination of the condition of the winds that took place on 13/3/2014 at 0-06 GMT shows the formation of centers with speeds higher than 12 m/s in the formation of dust centers. The winds blow from west to east and the dust passing through the basin originates from the western parts of the country, including the dust centers of Khuzestan and Iraq provinces. In this case, we have witnessed the dominance of unstable low-pressure centers on the surface of the basin, which can be one of the main factors in aggravating the dust phenomenon on the surface of the basin. Examination of omega winds (vertical winds on the ground) indicates the formation of an air ascent center on the range of the formation of high-speed wind nuclei and dust centers. The second incident occurred on 2/2/2015 at 3:00 PM GMT. Examination of wind direction maps shows the formation of centers with a speed of more than 25 meters per second with west-east direction on the surface of the western regions of the country and Gavkhoni basin, which aggravates dust production in sensitive areas such as Khuzestan and its movement Towards the Gavkhooni basin and affecting the basin. Examination of wind conditions to high atmospheric levels also showed that the wind regime was constant while increasing its speed at all atmospheric levels. An examination of the maps of omega winds (vertical winds on the ground) and sea surface pressure indicates the formation of an airborne and unstable (low pressure) center on the region, thus helping to aggravate the dust situation in the region. An examination of the dust storm that took place on 1/10/2016 at 6:00 PM GMT showed the formation of high wind speeds above 17 m/s in the eastern regions of the country, which are in the east-west direction at 850 ha Pascal level. he formation of these high-speed nuclei and the blowing of winds from the east to the basin have affected the Gavkhoni basin from the dust produced from the central desert and the black desert. Vertical winds also indicate the rising and falling currents and the movement of winds from high pressure (east) to low pressure (west) and the formation of east-west currents.

The results of this study showed that the source of dust occurrence in Gawkhuni basin is the Khuzestan and Iraq dust production centers, central desert and small parts of the basin center and around Gavkhuni Wetland. In addition, a synoptic examination of suitable areas of dust occurrence revealed that at the dates of the dust storms, low-pressure zones and high-velocity cores are formed at different levels of the atmosphere over the area, which is associated with the direction of the winds and the movement of dense masses of dust toward the basin.