地球温暖化は宇宙通信環境を悪化させる～二酸化炭素濃度上昇でスポラディックE層は強まり低高度化～

2025-10-24 九州大学

左：CO₂濃度が３１５ppm 時のEs層形成状況、右：CO₂濃度が667ppm時のEs層形成状況

＜関連情報＞

• https://www.kyushu-u.ac.jp/ja/researches/view/1351
• https://www.kyushu-u.ac.jp/f/63743/25_1024_01.pdf
• https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL117911

CO2濃度の増加は電離層のスポラディックEの形成にどのような影響を与えるのでしょうか? How Does Increasing CO2 Concentration Affect the Ionospheric Sporadic-E Formation?

Farhan Naufal Rifqi, Huixin Liu, Lihui Qiu, Chihiro Tao, Hiroyuki Shinagawa
Geophysical Research Letters  Published: 23 October 2025
DOI:https://doi.org/10.1029/2025GL117911

Abstract

Increasing CO₂ concentration is known to cause global-scale changes throughout the atmosphere and ionosphere. However, how the global change affects smaller-scale ionospheric phenomena remains unclear. This study investigates for the first time the impact of increasing CO₂ on the formation of sporadic-E layer, a key space weather element links to HF/VHF communications. Using the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA), simulations were conducted for normal (315 ppm) and doubled CO₂ (667 ppm) levels to evaluate changes in the vertical ion convergence (VIC). Simulation results reveal that the VIC is enhanced in the 100–120 km altitude range globally. Furthermore, VIC hotspots shift downward by approximately 5 km and exhibit changes in their diurnal pattern. The reduction of the ion-neutral collision frequency alongside changes in the zonal wind shear contributes significantly to these changes. Our study suggests that, as CO₂ concentrations continue to rise, future Es layers may become more intense, last longer, and form at lower altitudes compared to present-day conditions. These changes could potentially challenge the reliability of HF communication systems in the future.

Plain Language Summary

In this study, we examine the effect of increasing greenhouse gas, particularly CO₂, on the formation of sporadic-E layers, a type of ionospheric irregularity and a key space weather factor links to HF/VHF communications. These layers consist of metallic ions and exist periodically at altitudes of around 95–120 km, potentially disrupting communication systems. Utilizing an atmospheric model with double CO₂ concentration, we found that the change in winds and neutral gas density leads to the enhancement of the metallic ion accumulation below 120 km. This may consequently cause the sporadic-E layers to be more intense, last longer, and exist at lower altitudes in the future.

Key Points

• Impacts of increasing CO₂ on the sporadic-E (Es) ionospheric irregularity are investigated for the first time
• Increasing CO₂ is found to significantly enhance the Es-driver, the vertical metallic ion convergence below 120 km
• Reduction of the ion-neutral collision frequency at higher CO₂ levels contributes equally to this enhancement as the wind shear changes