1. National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Beijing Key Laboratory of Space Environment Exploration, Beijing 100190, China
Abstract：Solar far-ultraviolet radiation is one of the main sources of energy input into near space, and the response of the near space environment to solar eruptions is an important scientific issue to be further studied. Studying the radiation characteristics of the solar far-ultraviolet in the middle and upper atmosphere is an important basis for studying atmospheric composition and density changes, photochemical reactions and dynamic processes in near space. In this paper, using the far-ultraviolet data calculated by the FISM2 flare model and the earth’s middle and upper atmosphere data provided by the MSIS-E-00 model, the solar far-ultraviolet radiation from 120 to 190 nm is divided into 7 bands, and numerical simulations were performed using an atmospheric radiative transfer method based on the Lambert-Beer law. A total of 150 sets of flare data in 11 years from January 2010 to December 2020 were selected, and time-lag cross-correlation (TLCC) was used to evaluate the flare peak time difference between solar far-ultraviolet radiation and soft X-rays, using least squares (LS) method to calculate their flare peak flow relationship. Atmospheric radiative transfer equations were used to calculate the spectral properties, flux changes, and heating rate changes of the solar far-ultraviolet in near space (20～100 km) during flares. Finally, the deposition of solar far-ultraviolet radiation in the earth’s atmosphere is calculated. The results show that in the process of solar flare eruption, the flux of far-ultraviolet radiation changes significantly, and the flux peak is about 240 s earlier than that of soft X-rays. The wavelength increases with the increase of the wavelength; in the near space range of 20～100 km, the solar far-ultraviolet spectrum is almost completely absorbed, but due to the special absorption window structure of the atmospheric composition, part of the spectrum in the 185~190 nm band can reach an altitude of 20 km. In the near space region, the ratios of the far-ultraviolet fluxes at the time of the solar flare eruption and before the eruption were all around 2.0 in the seven bands, and the ratios of the peak heating rates were 1.22, 1.88, 1.35, 1.42, 1.23, 1.08 and 1.11. This paper verifies the feasibility of using far-ultraviolet radiation to sense solar flares in near space, provides a theoretical basis for optical detection experiments in near space and provides a reference for related research fields such as atmospheric inversion.
Key words：Near space; Solar flare; Far ultraviolet radiation; Radiative transfer; Atmospheric absorption
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