日本地球惑星科学連合2018年大会

講演情報

[EE] 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-EM15] Dynamics in magnetosphere and ionosphere

2018年5月21日(月) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:田中 良昌(国立極地研究所)、堀 智昭(名古屋大学宇宙地球環境研究所)、中溝 葵(情報通信研究機構 電磁波研究所、共同)、尾崎 光紀(金沢大学理工研究域電子情報学系)

[PEM15-P07] SuperDARN北海度-陸別短波レーダーによるサブオーロラ帯高速流の電気伝導度(太陽天頂角)依存性の研究

*張 玉テイ1西谷 望1堀 智昭1 (1.名古屋大学 宇宙地球環境研究所)

キーワード:サブオーロラ分極ストリーム、ペダーセン伝導度、太陽天頂角、SuperDARN北海度-陸別短波レーダー

In this study, we investigate characteristics of the subauroral polarization streams (SAPS), focusing on ionospheric conductivity dependence, especially the solar zenith angle(SZA) dependence, using the Super Dual Auroral Radar Network (SuperDARN) Hokkaido East radar, National Oceanic and Atmospheric Administration (NOAA) Polar Operational Environmental Satellites (POES) system and Meteorological Operational Satellite Program of Europe (MetOp) system data. The time span for the present study is from 2008/1/10 to 2016/12/31, which contains over 3180 days, and we limited the time range of the analysis to 3-8 UT (12-17 LT). We found 60 SAPS events over seasons except for summer, and for each event we examined the SZA and the peak Line-of-sight velocity observed in the SAPS, in order to identify the threshold of the possible SZA and illuminated ionospheric altitude for SAPS to be generated. We have determined location of the echo region based on the straight ray path geometry with empirical offset value for multiple-hop paths, whereas in order to investigate the effect of HF propagation geometry and achieve a more precise mapping of scattering locations, we are trying to apply a new empirical virtual height model to the SuperDARN Hokkaido East radar, which uses different coefficients based on range and elevation angle in the model when mapping backscatter targets propagate via different propagation paths. We also took into account the effect of EUV absorption in the atmosphere. As a result of the statistical study, we find that SAPS tend to appear when the SZA is larger than 98.5 degrees, and that the minimal threshold of illuminated ionospheric altitude for SAPS occurrence is estimated to be about 138 km, which is just above the altitude of the peak of Pedersen conductivity. This result suggests that the low background Pedersen conductivity plays an important role in the generation of SAPS through a positive feedback in which the enhanced electric filed drives frictional heating of the neutral atmosphere and thereby lowers the conductivity further. To the best of our knowledge, this is the first detailed study of SAPS-associated SZA, and shows quantitatively the importance of Pedersen conductivity for SAPS generation. We also investigated the seasonal dependence, MLT and MLAT dependence of SAPS, which shows how the solar radiation in different seasons affects SAPS.