فصلنامه پژوهش های جغرافیای طبیعی
پیاپی 123 (بهار 1402)

Vision usually refers to the horizontal distance at which the contrast between a target and its sky background is equal to the threshold of the human eye. In an atmosphere that is standard and without pollution, visibility often varies in the range of 145-225 kms. However, in polluted places, atmospheric visibility is reduced by air pollutants through the dispersion and absorption of fine particles and gases in the atmosphere. In some highly polluted areas, the horizontal visibility can be as low as one kilometer. Due to the adverse effects of air pollution on human life, horizontal visibility has been one of the main concerns in air pollution and climatology studies. The trend of changes in horizontal vision as well as the effects of air pollution on the vision process has attracted the attention of all researchers. The results of many studies have also shown that horizontal vision has a negative correlation with public health, especially in developing countries. One study also found that horizontal vision was associated with an increase in deaths and cardiovascular disease in Shanghai, China. One of the effective climatic phenomena in horizontal view is dust. This meteorological-environmental phenomenon is called a mass of fine dust particles and sometimes smoke emitted into the atmosphere, which increases aerosols and reduces horizontal visibility. The location of southwestern Iran at the top of the basin of dusty winds known as the north wind, which spread dust from the deserts of Syria and Iraq to southwestern Iran, frequently reduces the horizontal visibility in these areas. The aim of this study is to use horizontal vision data, mean values of aerosol optical depth and atmospheric extinction coefficient to study the trend of horizontal vision changes in southwestern Iran between 2000-2020; Therefore, by reviewing the available resources in this field, it is clear that relatively limited methods have been used to study and analyze the process of horizontal vision, among which Ridit analysis is the most widely used and efficient method in this field.Given the importance of the issue, the need for such a study in this area becomes apparent. The study area is southwestern Iran, which includes the political boundaries of the provinces of Khuzestan, Ilam, Lorestan, Chaharmahal and Bakhtiari, Kohkiluyeh and Boyer-Ahmad. The highest point of this region with an altitude of 4283 meters is located along the northwest-southeast, which is part of the Zagros folds, while the lowest point with a height of -105 is located in the southwest of this region, which (leads to) stretches the Persian Gulf. Also, the area of the study area is 28199 / 42 square kilometers. The data consists of two different types of climatic data, including observational data from meteorological stations and satellite data. Observational data are daily horizontal data of synoptic stations in Ilam, Khuzestan, Chaharmahal Bakhtiari, Kohgiluyeh, Boyer-Ahmad and Lorestan provinces in the period 1998 to 2020. This information is often reported at three-hour intervals. Ridit statistical technique was used to study the horizontal vision trend. Ridit analysis is a useful statistical technique that is widely used in trend study. Ridit indicates the possibility that observation of vision over a period of time is better than distribution of reference vision. Aerosol optical depth index (AOD) and extinction coefficient were also used. Because the aerosol optical depth (AOD) is one of the important parameters in the study of dust and affects the horizontal viewing process. Also, the amount of optical depth can vary with the density of the number of aerosols and the properties of those particles. First, the frequency value of each horizon floor was determined and then the annual Ridit value was calculated for each of the stations studied and the relevant graphs were drawn. By studying the Ridit diagrams of the studied stations, it is clear that in Masjed-e-Soliman, Aligudarz, Dehloran, Khorramabad and Yasuj horizons, the horizon is increasing. Also, in these stations, the trend line is below the reference line until 2009, but from 2009 to 2020, the trend line is above the reference line. But in Shahrekord, Koohrang, Ilam, Do Gonbadan, Boroujerd, Borujen, Ramhormoz, Omidieh, Dezful, Bandar Mahshahr, Bostan, Ahvaz and Abadan stations, the horizontal visibility is decreasing. While in Ilam stations and two domes, there is no change in horizontal vision in the studied years. AOD diagram of the studied stations shows that in Ahvaz, Abadan, Borujen, Boroujerd, Bostan, Dezful, Do Gonbadan, Ilam, Bandar Mahshahr, Koohrang, Omidieh, Ramhormoz and Shahrekord stations, the amount of aerosols is increasing. Unlike 13 previous stations in Aligudarz, Dehloran, Khorramabad and Masjed Soleiman stations, the amount of aerosol has a decreasing trend. By examining and comparing the blackout coefficient diagrams in the studied stations, it was found that the blackout coefficient values decrease in Masjed Soleiman, Aligudarz, Dehloran, Yasuj and Khorramabad stations. But in the next 13 stations of the study area, the rate of blackout increases. After reviewing and studying the Ridit values, the aerosol optical depth index and calculating the extinction coefficient to determine the condition of the horizon in southwestern Iran Horizon was classified into five quality groups: very good, good, medium, bad and very bad. In this study, the trend of horizon vision changes based on daily horizontal data of 18 synoptic stations in southwestern Iran, the amount of AOD changes based on Modis satellite data and also by calculating the extinction coefficient in the mentioned stations were studied. The results showed that in Masjed-e-Soleiman, Aligudarz, Dehloran, Khorramabad and Yasuj stations, in the studied years, instead of decreasing the horizontal vision, we are facing a situation of improving the horizontal vision. While in Shahrekord, Koohrang, Ilam, Do Gonbadan, Boroujerd, Borujen, Ramhormoz, Omidieh, Dezful, Mahshahr, Bostan, Ahvaz and Abadan stations, the horizontal visibility is decreasing. And in these stations, we are faced with a decrease in horizontal visibility, with the difference that this decrease in Bostan, Bandar Mahshahr, Koohrang, Omidieh and Boroujerd stations has a sharp trend and compared to Ahvaz, Abadan, Borujen, Shahrekord, Ramhormoz and Dezful stations have worse conditions. Also, in Ilam and Do Gonbad stations, no change in the horizontal visibility status was observed in the studied years. AOD study in the studied stations showed that in Ahvaz, Abadan, Borujen, Boroujerd, Bostan, Dezful, Do Gonbadan, Ilam, Bandar Mahshahr, Koohrang, Omidieh, Ramhormoz and Shahrekord stations, the amount of aerosol increases. While in other stations, AOD decreases, which indicates an increase in horizontal visibility in these areas. Also, in Masjed-e-Soliman, Aligudarz, Dehloran, Yasuj and Khorramabad stations, the values of the extinction coefficient are reduced. This indicates that in these areas, the horizontal visibility conditions are better than other stations. But in other stations, the values of the blackout coefficient increase and show that in these areas the horizontal visibility is not in the desired condition; Therefore, it can be concluded that in general, in the southwest of Iran, the horizontal visibility trend is decreasing. It is also suggested that this statistical technique be used in other parts of the country to better determine its efficiency.

Various natural phenomena have had a significant impact on the quality of human life since long ago. One of these types of natural phenomena is the deformation and displacement of the earth's surface, including subsidence. Subsidence is a morphological phenomenon that occurs under the influence of the downward movement of the earth. The salient features of radar images and the acceptable accuracy of the radar interferometric method have provided a powerful tool for researchers in investigating land subsidence. For this reason, 35 radar images of the Sentinel 1 sensor in the ascending orbit and transit 174 in the period from 2016 (June) to 2021 (January) were used to investigate the land subsidence in the Kermanshah plain. To analyze the time series of these images to prepare the average annual subsidence map in the plain, the radar interferometric technique was used under PSI and SBAS approaches. The results show the maximum land subsidence of 100 mm in the SBAS method and 10 mm in the PSI method in the west and northwest of the plain for 6 years. Finally, the maximum range was investigated in terms of geology and geo-hydrology. The results of the investigations showed that the land use of the maximum land subsidence area includes irrigated and rainfed agricultural lands, with the highest amount of water withdrawal in the agricultural sector, along with an average drop in the water level of 8 meters in 20 years in wells with a large thickness of fine-grained sediments. Is. In general, land subsidence in the area is affected by human and natural factors

This paper analyses the characteristics of the tropical tropopause, mid-latitude, and polar tropopause based on the sounding temperature data at Mehrabad and Shiraz airport stations in January and July in the statistical period of 2000-2022. The results showed that the observed frequency of the tropical tropopause in Iran in January (41 and 59 present in Mehrabad and Shiraz, respectively) is less than in July January (95 and 94 present in Mehrabad and Shiraz, respectively), and the frequency of the observed tropical tropopause in July is more than that of the mid-latitudes. The reason for this difference can be found in the increased thermal energy of the atmosphere in the warm seasons. In July, due to the development of thermal low pressure over Iran, the thermal energy, the air temperature, and the thickness of the atmosphere increased. As a result, the tropopause elevates and approaches the level of the tropical tropopause. It was also found that the tropical and mid-latitude tropopauses have a higher height in the warm month and are placed in lower pressure levels. For this reason, the temperature of these two tropopauses in the warm month is lower than the corresponding value in the cold month. Based on the results, the average height and temperature in tropical tropopause levels were estimated between 16.5 to 17.4 kilometers and -65 to -78 degree Celsius, respectively, in different regions of Iran. Also, these parameters for mid-latitude tropopause level were estimated from 11.5 to 12.8 kilometers and -52 to -59 degree Celsius, respectively

Among the types of airborne particles, particles with a diameter of less than 10 microns have many adverse effects on human health. Meteorological parameters and the movement of a large volume of vehicles are considered the most important modulating factors in the distribution and concentration of atmospheric pollutants. In this study, in order to predict the concentration of PM-10 pollutant during a long-term interval in Tehran city, GA-ANFIS hybrid model was used. Wind speed, wind direction, temperature, relative humidity and traffic volume were considered as inputs and pollutant concentration PM_10 as the output of the model. The results of the calculation of the performance indicators showed that the combined GA-ANFIS model provides a better framework than the ANFIS model in predicting the pollutant concentration PM_10. In order to evaluate the spatio-temporal patterns of PM_10 pollutant concentration and to identify hot and cold spots in Tehran city, local Moran's statistic and Ard-J Gettys statistic were calculated. The results showed that there is a high level of clustering of PM_10 pollutant in Tehran (with 95% confidence level). The clusters of PM_10 have divided the city into two northern and southern parts so that most of the cold spots in the northern half and the hot spots in the south have spread to the center of the city

The height of the boundary layer is one of the most important determining factors, the extent of mixing of pollutants and suspended particles and the quality of air near the surface of the earth. The main goal of this research is to reveal the relationship between land cover changes and boundary layer height changes during the last 3 decades in Lorestan province. In this regard, two sets of data were used, which include the land cover classes of the MODIS sensor and the height of the boundary layer of the ECMWF climate database version ERA5. These data were selected on a monthly scale (January) to check the cold period and (July) to check the warm period and were checked in 7 time periods with 5-year steps during the statistical period of 1990-2020. In this research, the cross-matrix analysis technique was used in the ARC-GIS environment and the average height of the boundary layer on each land use was extracted and compared in 7 time steps of 5 years, separately from the cold and warm periods of the year. The results showed that firstly, the height of the boundary layer during the warm period is significantly higher than the cold period of the year, and secondly, the minimum and maximum spatial pattern of the boundary layer height in the cold and warm periods of the year is different in the province. In the cold period, the maximum height of the boundary layer is in the western parts. and southwest (low-altitude lands with forest cover), while in the warm period of the year, the maximum boundary layer is concentrated in the barren and mountainous lands of the east of the province. In addition, it was observed that in the hot period of the year, agricultural lands with a boundary layer height of 1263 and pasture lands with a boundary layer height of 1243 have the highest boundary layer height among the investigated use classes, while in the cold period of the year, urban and residential lands with a height of 192 meters, It has the highest boundary layer height and the spatial average of the boundary layer height of the province has had an increasing trend

In this research, the climatic variables of temperature and precipitation of Urmia Lake catchment area were evaluated and projected using CMIP6 models under two scenarios SSP1-2.6 and SSP5-8.5 in the future periods (2031-2055 and 2071-2095). First, the accuracy of the models for the base period (1990-2014) was evaluated using Taylor diagram and RMSE and NRMSE indices after downscaling with different methods of quantile mapping, and among the models, the MRI-ESM2-0 for temperature and INM-CM5-0 for precipitation using the SSPLIN downscaling method were selected to project the future climate, then the future temperature and precipitation data were produced. The results of comparing the temperature and precipitation of the future periods with the base period showed that the average annual temperature of the basin will increase under all scenarios. The average annual temperature increase of the basin in the near future in the optimistic and pessimistic scenarios will be 1.5 and 1.8 degrees Celsius, respectively, and in the far future, 1.4 and 4 degrees Celsius respectively. The average annual precipitation will decrease in all scenarios, in the near future it will decrease by 19.9 and 21.6 percent in the optimistic and pessimistic scenarios, respectively, and by 12 and 28.6 percent in the far future, respectively. Based on the spatial distribution of changes in temperature and precipitation in the future periods, the greatest increase in temperature and the greatest decrease in precipitation will occur in the northern areas of the basin.

This research aimed at investigating and predicting snowing changes in Hamedan region using MODIS satellite data and images, harmonic analysis and micro-scaled atmospheric data. The study used Hamadan station data, satellite images and the NDSI index during the 30 years (1992 to 2022), analyzed the trend of snowfall changes, and modeled and predicted for the next 20 years. The analysis of satellite images and the NDSI index showed that the snow cover in Hamadan city has significantly decreased. This amount, compared to the area of the city, has decreased from about 20% of the snow cover to about 7% over the decade. Also, the variance value in the first harmonic coefficient during the statistical period is about 75%, which refers to seventy-five percent of snowfall in the region. The variance of the second harmonic coefficient is 20 percent, which implies the effect of Alvand Mountain and the height of the region on snowfall. In recent years, this amount has reached 27 percent, indicating a decrease in large-scale synoptic systems' contribution. It also shows climate changes and warmer winters. The maximum snowfall in the first harmonic is 16.2 centimeters, which has decreased to 13.2 centimeters in recent years. In recent years, the phase angle or the time of maximum snowfall has changed from mid-fall to early winter. The LARS micro-scale model was used to predict and scale the data of the atmospheric general circulation model (HadGEM2-ES) and the Coupled Model Inter-comparison Project (CMIP5). The results showed that Hamadan has been facing a decrease in snowfall and warmer winters in recent years.