پیش بینی میزان دید افقی سالیانه حاصله از گرد و غبار در منطقه کم فشار حرارتی سیستان

Introduction

Horizontal vision is a simple observational indicator of air quality. In clean atmosphere, the field of view is between 145 and 225 km and in normal atmosphere between 10 to 100 km and in polluted areas it is less than this amount. Preliminary research shows that the accumulation of air vents in the atmospheric column severely reduces horizontal visibility Today, with the increase of human activities in recent years and the increase in the concentration of suspended particles in the atmosphere, including: air conditioners affecting the depth of light, has caused a decrease in horizontal vision. In Sistan and Baluchestan province, dust storms are in critical condition, so that on January 5, 2015, wind speeds reached 102 kilometers per hour in Zahedan and Nusratabad and dust concentration (〖PM〗_2.5)increased to 115 μg / m3. Research shows that during the peak of dust storms, the concentration of pollutant particles in Zabol station increases and the wind speed reaches 70 km / h and the horizontal visibility is drastically reduced to even less than 100 meters. Therefore, considering the importance of the visual quantity in the low thermal pressure region of Sistan, the study and forecast of its annual average until 2022 with the help of spatio-temporal regression was considered in this study.

Materials and methods

In this study, in order to predict the annual horizontal visibility, the statistical method of spatio-temporal regression with the help of R software and using the package spdep, plotKML, RgoogleMaps, tseries and maptools has been used. For this purpose, the data autocorrelation, data Stationary were first examined to determine the type of regression, error normalization test, error non-correlation test and error variance homogeneity test. Then, the test of significance of the regression line equation and the variance inflation index and the coefficient of determination of the data were calculated. Then, in order to predict the average annual horizontal visibility in the low thermal pressure region of Sistan, the spatio-temporal regression model was defined as follows:



z_(s,t)=β_0+β_1 z_(s_1,t-1)+β_2 z_(s,t-1)+β_3 x_s+β_4 y_s+ε_(s,t)



Where z_(s,t) the horizontal is view at time t in position s, s_1Position of the station closest to the station with position s, y_s and x_s Latitude and Longitude and ε_(s,t) is a set of errors. Then the upper and lower limits of the average annual horizontal visibility with 95% confidence interval were calculated according to the following relationship:

A≡(z ̂_(s_0,t_0 )-1.96σ_(s_0,t_0 ),z ̂_(s_0,t_0 )+1.96σ_(s_0,t_0 ) )



Where σ_(s_0,t_0 )is the standard deviation of z ̂_(s_0,t_0 )

Results and discussion

The results of spatio-temporal regression coefficients of the data show that the P-value for all variables is less than 0.05 and is significant in the model. And the generalized spatio-temporal regression model can predict the horizontal visibility variable in the coming years in the low thermal pressure region of Sistan.Spatial-temporal analysis of the average annual horizontal visibility shows that Sistan region has the lowest horizontal visibility until 2022, which is 6 to 7 km, followed by Zahedan region between 8 to 9 km. Predicted horizontal visibility In Ghaenat area, it is between 9 and 10 km, which is in the third rank among the stations in the region. The average horizontal visibility in Birjand area is between 10 and 12 km. Nehbandan station has better conditions than Birjand station in the coming years. However, the highest annual horizontal visibility is related to Sarbisheh station, which is 12 to 14 km, which in this regard can be said to have better conditions in terms of clean and healthy air. The plot points in 2022 show that Sistan and its southern parts, due to its proximity to the Loot Desert and the low altitude of the region compared to the surrounding areas, increase the intensity of its 120-day winds, which is one of the main reasons for the region's critical Horizontal view is towards its northern regions.

Conclusion

The general situation of Sistan low pressure region during the statistical period shows that its horizontal visibility decreases so that in 1986 with an average of 14.8 km started in 2018 it reaches 9.5 km. numerical model shows that the lowest average annual horizontal visibility during 2019 to 2022 with the rates of 6.9, 0.7, 7.1 and 7.2 km is related to Zahak station and its forecast shows that by 2022, it will increase by almost 300 meters, after that, Zabol station is located at 0.7, 7.1, 7.3 and 7.4 km, respectively, which the forecast of this station indicates that the average annual horizontal visibility will increase during the coming years. Its incremental figure is approximately 400 meters and 100 meters more than Zahak station. Nusrat Abad station is also facing an increase in annual horizontal visibility which reaches from 9.9 to 0.9 km, in Zahedan station, the average horizontal visibility has a decreasing trend, so that its value in 2019 is equal to 8.7 km, which in 2022 will reach 8.6 km. Which adds to the criticality of this station. Therefore, considering the high risk of all stations in the study area, it should be said that stations located in Sistan and Baluchestan province will have more severe conditions. The results show that the annual horizontal visibility increases in Birjand and Ghaen stations, which shows in 2019 with 10.0 and 9.2 km, respectively. And in 2022 it will reach 10.5 and 9.8 km. Finally, the results show that the average annual horizontal visibility in the coming years in the low-pressure region of Sistan will decrease, which can challenge the economic and demographic changes in the region.