Study on the Ultraviolet Radiation Environment and Influencing Factors in Near Space

Most of the research on Ultraviolet (UV) radiation are based on the reanalysis data or atmospheric model data due to the limitation of observation altitude and the lack of the observation data in the near space. These methods lead to a fact that UV radiation research are highly susceptible to extremes in atmospheric constituent concentrations. Meanwhile, the analysis results are delayed and do not meet the timeliness needs of related applied research. So, the research of the change in UV radiation and influencing elements are analyzed which use the Chinese region as an example. Ozone is the most dominant source of OH in the near space. The photochemical reactions of both are controlled by the UV radiation. The photochemical relationship between OH and ozone and the principle of direct and indirect modification of ultraviolet radiation by photochemical action are the research bases in the near space. In this study, the GEOS-Chem model is used to simulate the distribution of monthly mean OH and ozone concentrations from 0 to 80 km altitude with a horizontal resolution of 2 degrees x 2.5 degrees in China. The MERRA-2 reanalysis data is used as the meteorological data. The default emission data are configured by the HEMCO module. The relationships of concentration changing between OH and ozone are summarized under the simulated conditions which are close to the actual atmospheric environment. On the one hand, a negative correlation is shown between OH and ozone concentration due to the steady state properties of the near space itself and the influence on the photolysis of ozone by UV radiation. For example, the region of high OH concentration decreases gradually with increasing latitude in summer. While the characteristics of high ozone concentration is in contrast to the OH features. On the other hand, the complex deviating radiative equilibrium state of near space itself and its sensitivity to external forcing perturbations lead to a positive correlation between OH and ozone concentration. These phenomena are inconsistent with the theory. For instance, the high values of OH and ozone concentrations in winter occur in the south-western region simultaneously. These results indicate that the relationship between the changes of OH and ozone concentration are both regularity and complexity. The changes in ozone concentration, which is influenced by OH, alter the irradiance in the UV-B band. The TUV radiation transfer model is used to simulate and calculate the radiation. The results of TUV show the monthly variation conditions of irradiance at different representative altitudes and reveal that the irradiance varies widely which is from 3.43 W center dot m(-2) to 16.15 W center dot m(-2) from 22 km to 42 km. The minimum value is at 22 km in the northwest region in May. The maximum irradiance is at 42 km in the Central and South China region in January. The irradiance exhibits a combination of bimodal and oscillatory characteristics in North China, Central and South China, South China Sea region and other region. The maximum and minimum of irradiance appear in different months depending on the regions. However, the maximum value occurs in November and the minimum value appears in May mostly. Besides, the maximum annual difference of irradiance is at 32 km for different region. The maximum annual difference of irradiance is 2.29 W center dot m(-2) in the North China region, while the minimum annual difference of irradiance is 0.53 W center dot m(-2) at 42 km in the South China sea region. The irradiance has the most dramatic change at the 22 km, which is from 2.42% to 32.79%. These variations mean that there are great differences in the impact and effect of ultraviolet radiation on astrobiology, aircraft materials and some others in different regions, altitudes and periods. The targeted considerations are necessary in the program design and analysis of the results in the related study areas.