Curriculum Vitaes

Hitoshi Fujiwara

  (藤原 均)

Profile Information

Affiliation
Professor, Faculty of Science and Technology Department of Science and Technology , Seikei University
Degree
Doctor(Tohoku University)

J-GLOBAL ID
200901087510189600
researchmap Member ID
1000283407

External link

<<研究分野と背景>>
大気上端に位置する熱圏・電離圏領域(高度、およそ100-800 kmの領域)は、人工衛星やスペースシャトルが飛翔しオーロラが乱舞する、宇宙空間と大気との境界領域である。上方(磁気圏)からの太陽風起源のエネルギーと、下方(対流圏・成層圏・中間圏)からの大気波動等のエネルギー・運動量流入によって、熱圏・電離圏が激しく変動する様子が近年の観測・数値シミュレーションから明らかとなってきた。また、熱圏・電離圏の変動予測は、GPS 測位に代表される通信システムの高度な宇宙利用の結果、その安全な運用のために情報・通信、航空宇宙分野においても重要な研究課題となっている。

<<主な研究テーマ>>
1. 地球大気全域大循環モデル開発とシミュレーション
九州大学グループとの共同により、地表から大気上端までを計算可能な数値モデルの開発に世界で初めて成功した[Miyoshi and Fujiwara, 2003]。高度約 300 km の領域でオーロラエネルギー流入によって極域で励起される大規模波動に加えて、昼夜境界や真夜中の温度異常帯でも地球の自転にともなって伝搬性の大気擾乱が励起される可能性がはじめて示された[Fujiwara and Miyoshi, 2006]。さらに、高度300 kmの高高度においても対流圏起源と考えられる大気変動が見つかっており、次々と新しい成果が生まれつつある[例えば、Fujiwara and Miyoshi, 2009, 2010]。

2. 欧州非干渉散乱レーダー観測研究
極域熱圏・電離圏での大気運動やエネルギー収支を調べるため、国際共同で北欧に設置されている欧州非干渉散乱(European incoherent scatter: EISCAT)レーダー・データの解析を行ってきた。
下部熱圏では、強い鉛直シアー(> 50 m/s/km)を伴った水平風がしばしば観測されるが、その成因や熱圏での運動量・エネルギー収支に果たす役割については理解が及んでいない。EISCATデータから水平風プロファイルを高時間分解能で導出し、(シアー不安定に起因する)乱流エネルギー散逸量と磁気圏から流入する電磁エネルギー散逸量の同時推定にはじめて成功した [Fujiwara et al., 2004]。また、地磁気擾乱時の極冠域で電離圏・熱圏加熱現象についても新たな知見が得られている [Fujiwara et al., 2007; Fujiwara et al., 2014]。2010-2017年度にはEISCAT特別実験が採択され、極冠域での熱圏・電離圏変動について詳細を調べている。

3. 大気圏・電離圏統合モデル開発
衛星通信等の宇宙通信が我々の生活に不可欠となった結果、熱圏・電離圏変動による通信障害は航空機や船舶のGPS測位を不能とし重大事故を引き起こす可能性を伴うようになった。しかしながら、モデリング研究の遅れと基礎データの不足などからここでの変動予測は天気予報のレベルにはほど遠い。熱圏・電離圏の数値予報のためのシステム構築と観測データに基づく素過程のモデリングを実施している。本研究では、九州大学、情報通信研究機構、国立極地研究所、名古屋大学、京都大学グループとの共同によって研究を進めている。(Jin et al., 2011など)

4. 宇宙機軌道データ等からの熱圏大気質量密度の推定
人工衛星や他の宇宙機の軌道データや加速度計データを用いることにより、熱圏領域の大気質量密度が推定できる。しかしながら、現状では、広範囲にわたっての高時空間分布の推定は困難であり、これまで観測が十分ではなかった高度200-300kmでの密度推定のための研究を進めている(JAXA、九州大学との共同研究)。本研究課題は、宇宙機に働く大気摩擦力の推定(予測)にもつながるものであり、宇宙機の安全な運用において重要と考えられる。

Papers

 92
  • Ryuho Kataoka, Daikou Shiota, Hitoshi Fujiwara, Hidekatsu Jin, Chihiro Tao, Hiroyuki Shinagawa, Yasunobu Miyoshi
    Journal of Space Weather and Space Climate, 12 41-41, Dec 23, 2022  
    The accidental reentry of 38 Starlink satellites occurred in early February 2022, associated with the occurrence of moderate magnetic storms. A poorly understood structure of Coronal Mass Ejections (CMEs) caused the magnetic storms at unexpected timing. Therefore, a better understanding of minor CME structures is necessary for the modern space weather forecast. During this event, the “up to 50%” enhancement of air drag force was observed at ~200 km altitude, preventing the satellites’ safety operations. Although the mass density enhancement predicted by the NRLMSIS2.0 empirical model is less than 25% under the present moderate magnetic storms, the real-time GAIA simulation showed a mass density enhancement of up to 50%. Further, the real-time GAIA simulation suggests that the actual thermospheric disturbances at 200 km altitude may occur with larger amplitude in a broader area than previously thought.
  • Mamoru Ishii, Daikou Shiota, Chihiro Tao, Yusuke Ebihara, Hitoshi Fujiwara, Takako Ishii, Kiyoshi Ichimoto, Ryuho Kataoka, Kiyokazu Koga, Yuki Kubo, Kanya Kusano, Yoshizumi Miyoshi, Tsutomu Nagatsuma, Aoi Nakamizo, Masao Nakamura, Michi Nishioka, Susumu Saito, Tatsuhiko Sato, Takuya Tsugawa, Shigeo Yoden
    Earth, Planets and Space, 73(1), Dec, 2021  
    We surveyed the relationship between the scale of space weather events and their occurrence rate in Japan, and we discussed the social impact of these phenomena during the Project for Solar–Terrestrial Environment Prediction (PSTEP) in 2015–2019. The information was compiled for domestic users of space weather forecasts for appropriate preparedness against space weather disasters. This paper gives a comprehensive summary of the survey, focusing on the fields of electricity, satellite operations, communication and broadcasting, satellite positioning usage, aviation, human space activity, and daily life on the Earth’s surface, using the cutting-edge knowledge of space weather. Quantitative estimations of the economic impact of space weather events on electricity supply and aviation are also given. Some topics requiring future research, which were identified during the survey are also described. Graphic Abstract: [Figure not available: see fulltext.].
  • Kanya Kusano, Kiyoshi Ichimoto, Mamoru Ishii, Yoshizumi Miyoshi, Shigeo Yoden, Hideharu Akiyoshi, Ayumi Asai, Yusuke Ebihara, Hitoshi Fujiwara, Tada-Nori Goto, Yoichiro Hanaoka, Hisashi Hayakawa, Keisuke Hosokawa, Hideyuki Hotta, Kornyanat Hozumi, Shinsuke Imada, Kazumasa Iwai, Toshihiko Iyemori, Hidekatsu Jin, Ryuho Kataoka, Yuto Katoh, Takashi Kikuchi, Yûki Kubo, Satoshi Kurita, Haruhisa Matsumoto, Takefumi Mitani, Hiroko Miyahara, Yasunobu Miyoshi, Tsutomu Nagatsuma, Aoi Nakamizo, Satoko Nakamura, Hiroyuki Nakata, Naoto Nishizuka, Yuichi Otsuka, Shinji Saito, Susumu Saito, Takashi Sakurai, Tatsuhiko Sato, Toshifumi Shimizu, Hiroyuki Shinagawa, Kazuo Shiokawa, Daikou Shiota, Takeshi Takashima, Chihiro Tao, Shin Toriumi, Satoru Ueno, Kyoko Watanabe, Shinichi Watari, Seiji Yashiro, Kohei Yoshida, Akimasa Yoshikawa
    Earth, Planets and Space, 73(1), Dec, 2021  
    <title>Abstract</title>Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar–terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar–terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.
  • Hiroyuki Shinagawa, Chihiro Tao, Hidekatsu Jin, Yasunobu Miyoshi, Hitoshi Fujiwara
    Earth, Planets and Space, 73(1), Jan 27, 2021  
    Abstract A sporadic E layer has significant influence on radio communications and broadcasting, and predicting the occurrence of sporadic E layers is one of the most important issues in space weather forecast. While sporadic E layer occurrence and the magnitude of the critical sporadic E frequency (foEs) have clear seasonal variations, significant day-to-day variations as well as regional and temporal variations also occur. Because of the highly complex behavior of sporadic E layers, the prediction of sporadic E layer occurrence has been one of the most difficult issues in space weather forecast. To explore the possibility of numerically predicting sporadic E layer occurrence, we employed the whole atmosphere–ionosphere coupled model GAIA, examining parameters related to the formation of sporadic E layer such as vertical ions velocities and vertical ion convergences at different altitudes between 90 and 150 km. Those parameters in GAIA were compared with the observed foEs data obtained by ionosonde observations in Japan. Although the agreement is not very good in the present version of GAIA, the results suggest a possibility that sporadic E layer occurrence can be numerically predicted using the parameters derived from GAIA. We have recently developed a real-time GAIA simulation system that can predict atmosphere–ionosphere conditions for a few days ahead. We present an experimental prediction scheme and a preliminary result for predicting sporadic E layer occurrence.
  • N. Yoshida, H. Nakagawa, N. Terada, J. S. Evans, N. M. Schneider, S. K. Jain, T. Imamura, J.‐Y. Chaufray, H. Fujiwara, J. Deighan, B. M. Jakosky
    Journal of Geophysical Research: Planets, 125(12), Dec, 2020  

Misc.

 56

Books and Other Publications

 2

Presentations

 274

Teaching Experience

 24

Research Projects

 30