[P-EM11] Space Weather and Space Climate

[PEM11-P06] Characteristics of Solar Hydrogen Lyman Lines and Their Influences
on the Earth's Ionosphere

*Ryosuke Okubo¹, Kyoko Watanabe¹, Shinnosuke Kitajima¹, Satoshi Masuda², Akimasa Ieda², Hidekatsu Jin³, Chihiro Tao³, Michi Nishioka³ (1.National Defense Academy of Japan, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.National Institute of Information and Communications Technology)

Keywords:solar chromosphere and transition region, solar EUV emission, Lyman lines, Earth’s ionosphere, GAIA model

X-rays and extreme ultraviolet (EUV) emissions from the Sun contribute to the formation of the Earth’s ionosphere. The Lyman-α line (121.6 nm; Ly α ) is the strongest line emission in solar EUV emission, accounting for 56% of the EUV irradiance in the chromosphere and transition region (Fontenla et al., 1991), and thus are considered to contribute significantly to the formation of the Earth's ionosphere. However, other Lyman-series of line emissions, including the Lyman-β line (102.6 nm; Ly β ), have smaller irradiance than Ly α , but because of their shorter wavelength, the energy of the line emission is higher than Ly α. Therefore, there is a possibility that these Lyman series emissions may have more impact on the Earth’s ionosphere than Ly α. Lemaire et al. (2012) investigated the relationship between Ly α and Ly β lines during part of the solar cycle 23 (2002-2008) and found that the Ly α / β ratio varies between the maximum and minimum of solar cycle. In this study, we investigate the relationship between Ly α and Ly β observed by TIMED/EGS-SEE during the solar cycle 24 as in Lemaire et al. (2012), and their effects on the electron density variations in the Earth's ionosphere. On the other hand, Lemaire et al. (2012) did not mention the relationship between Ly α and β during solar flares. Therefore, in this study, we also investigate the variation of the Ly α / β ratio of 41 solar flares using the SDO/EVE and GOES/EUVS-E observations. In addition, to verify the effect of these solar emissions on the Earth's ionosphere, we calculated the altitude distribution of ion production rates at each EUV wavelength using the GAIA model (Jin et al., 2011). which can simulate the effect of solar emission on the Earth's ionosphere. In this paper, we will discuss the effects of Hydrogen Lyman-series line emissions on the Earth's ionosphere using the results of these analysis and calculations.