Introduction

Solar radiation with a solar spectral band of 0.4 to 0.7 micrometers is called short wavelength, which plays a significant role in the earth's climate system, dynamic and thermodynamic processes of the atmosphere and oceans, the photocenter of plants, the hydrological cycle of snow, and evaporation and transpiration. Therefore, its spatial and temporal changes can have consequences for humans the ecosystem, and the entire biosphere in different ways. Consequently, it is necessary to investigate the temporal-spatial distribution, the spatial changes of net short wavelength solar radiation.

Materials & Methods

The study method in this research is analytical-spatial. For this purpose, in the first step, satellite data based on the FLDAS global radiation model was obtained from 1984 to 2023 with a high spatial resolution (0.1 x 0.1 degree and approximately equivalent to 1 km) and daily and monthly time resolution. In the second step, after performing the pre-processing operation, to analyze the behavior of the mentioned variable in the desired period, the spatial distribution map of the average and the spatial distribution of the trend and the coefficient of variation were applied to each cell with statistical operations in the form of a matrix for a better view. Be obtained from the behavior of the desired variable. In the third step, the spatial autocorrelation of the data was analyzed using spatial statistics such as the spatial autocorrelation of the global Moran's index and the local Moran's insulin index.

Research Findings

According to the spatial distribution map, the average incoming net shortwave radiation is the maximum of the incoming shortwave net radiation during 12 months in the southeast of Iran, i.e. parts of Sistan-Baluchistan, Hormozgan, and Kerman. The geographical location of these provinces, i.e. proximity to the equator, low altitude above sea level, and clear skies have led to these areas becoming the center of concentration of net short-wavelength radiation entering Iran in January. The minimum radiation is mainly in the northern half of the country. An examination of the geographical location of these regions indicates that factors such as distance from the equator, cloudy skies, and the presence of chemical pollutants in the metropolises (north and northwest regions) have led to these regions receiving less radiant energy. The spatial distribution of the trends of each cell was tested with the linear regression method and found that there is no significant spatial distribution of trends anywhere in Iran in April and November. Spatial distribution maps of the trend showed that in the cold months of the year (January, February, March, and December), the incoming net short wavelength radiation in the northern half of the country had an increasing trend with a confidence level of 95%. He pointed out that the reduction of cloudiness and precipitation in these areas caused the amount of incoming short-wavelength net radiation to increase in the long term compared to the surrounding areas. However, in the hot months of the year (June, July, August, September) mainly in the southern half of the country, in May in the eastern half, and in October in the southeast, the spatial distribution showed a negative trend with a confidence level of 95%. Considering that the southern half of the country is mainly composed of arid and semi-arid areas, the increase in the trend of dust rising from these surfaces can be one of the factors affecting the scattering and absorption of incoming shortwave radiation in these areas in the long term. As a result, the trend of the mentioned variable has decreased in these areas. Spatial autocorrelation analysis of net incoming short wavelength radiation with the help of the global Moran index showed that the highest and lowest spatial autocorrelation according to the global Moran index was related to December and June respectively. And its spatial distribution is a cluster pattern.

Discussion of Results & Conclusion

The results showed that the highest amount of incoming short-wavelength radiation was in June and the lowest was in December. Also, the examination of the average spatial distribution showed that the maximum net incoming short-wavelength radiation was in the southern latitudes of the country and its minimum was in the northern latitudes of the country. The significant spatial distribution of the trend also indicated that in April and December, the spatial distribution did not have a significant trend in any part of the country. But in January, February, March, and December, in parts of the northern half of the country, there was an increasing spatial trend, and in June, July, August, and September, there was a significant negative spatial trend in parts of the southern half of the country. These conditions indicate the existence of changes in the components affecting the scattering and absorption of short wavelength incoming radiation, including atmospheric compounds, amount of clouds, precipitation, and fine dust in the atmosphere during the period studied in these areas.