日本地球惑星科学連合2023年大会

講演情報

[E] オンラインポスター発表

セッション記号 P (宇宙惑星科学) » P-EM 太陽地球系科学・宇宙電磁気学・宇宙環境

[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

2023年5月22日(月) 10:45 〜 12:15 オンラインポスターZoom会場 (2) (オンラインポスター)

コンビーナ:Liu Huixin(九州大学理学研究院地球惑星科学専攻 九州大学宙空環境研究センター)、大塚 雄一(名古屋大学宇宙地球環境研究所)、Chang Loren(Institute of Space Science, National Central University)、Yue Deng(University of Texas at Arlington)


現地ポスター発表開催日時 (2023/5/21 17:15-18:45)

10:45 〜 12:15

[PEM12-P34] Variability of the effective recombination coefficient during energetic particle precipitation events

*村瀬 清華1片岡 龍峰1,2西山 尚典1,2小川 泰信1,2田中 良昌1,2、佐藤 達彦3 (1.総合研究大学院大学、2.国立極地研究所、3.日本原子力研究開発機構)

キーワード:大気電離、太陽X線

Energetic particle precipitation (EPP) is one of the major sources of energy deposition into the Earth's middle atmosphere. It is essential to accurately reproduce the energy deposition from observable electron density profiles for a quantitative understanding of the EPP impact on the atmosphere. The effective recombination coefficient, αeff, represents an efficiency of electron loss due to collisions with ions in an equation of the time evolution of the electron density, dNe/dt = q - αeff Ne2, where Ne is the electron density and q is ionization rate by EPP. The coefficient is known to vary with the ion density ratio to the electron density. The purpose of the study is to re-examine the variability of this coefficient and to discuss the limitation of how accurately we can determine the EPP energy inputs.
In this study, the altitude profiles of ionization rate q were calculated with a particle transport simulation, PHITS, using EPP fluxes observed by satellites as the input. The coefficient αeff was estimated from the calculated ionization rate and electron densities obtained from the EISCAT radar observations in Tromsø (Norway) and Longyearbyen (Svalbard). We found 8 events of X-ray enhancements associated with X-class solar flares in 1982-2022 in which at least one of the EISCAT radars was in operation and a solar zenith angle was < 90° at the radar site. We estimated the coefficient for an altitude range of 60-100 km, since enhanced X-rays during solar flares deposit most of their energies at the altitudes. The estimatied coefficient αeff agrees with the values estimated in previous studies (Gledhill, 1986) within an error of ~30 %. In this presentation, we will briefly discuss the validity and predictability of the variability in αeff, including the effect of the ion density ratio estimated using a chemical model.