Professor Emeitus

中村 正人

ナカムラ マサト  (Masato Nakamura)

基本情報

所属
国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 教授
学位
博士(理学)(1987年10月 東京大学)

通称等の別名
宇宙研
J-GLOBAL ID
200901098690652704
researchmap会員ID
1000161601

外部リンク

研究キーワード

 1

論文

 177
  • T. Nagai, I. Shinohara, Y. Saito, A. Ieda, R. Nakamura
    Journal of Geophysical Research: Space Physics 128(12) 2023年12月  
    The spacecraft Geotail surveyed the near-Earth plasma sheet from XGSM = −10 to −31 RE and YGSM = −20 to +20 RE during the period from 1994 to 2022. It observed 243 magnetic reconnection events and 785 tailward flow events under various solar wind conditions during plasma sheet residence time of over 23,000 hr. Magnetic reconnections associated with the onset of magnetospheric substorms occur mostly in the range XGSM = −23 to −31 RE. When the solar wind is intense and high substorm activities continue, magnetic reconnection can occur closer to the Earth. The YGSM locations of magnetic reconnections depend on the solar wind conditions and on previous substorm activity. Under normal solar wind conditions, magnetic reconnection occurs preferentially in the pre-midnight plasma sheet. Under conditions with intense (weak) solar wind energy input, however, magnetic reconnection can occur in the post-midnight (duskside) plasma sheet. Continuous substorm activity tends to shift the magnetic reconnection site duskward. The plasma sheet thinning proceeds faster under intense solar wind conditions, and the loading process that provides the preconditions for magnetic reconnection becomes shorter. When magnetic flux piles up during a prolonged period with a strongly northward-oriented interplanetary magnetic field (IMF) Bz, the time necessary to provide the preconditions for magnetic reconnection becomes longer. Although the solar wind conditions are the primary factors that control the location and timing of magnetic reconnections, the plasma sheet conditions created by preceding substorm activity or the strongly northward IMF Bz can modify the solar wind control.
  • Yeon Joo Lee, Antonio García Muñoz, Atsushi Yamazaki, Eric Quémerais, Stefano Mottola, Stephan Hellmich, Thomas Granzer, Gilles Bergond, Martin Roth, Eulalia Gallego-Cano, Jean-Yves Chaufray, Rozenn Robidel, Go Murakami, Kei Masunaga, Murat Kaplan, Orhan Erece, Ricardo Hueso, Petr Kabáth, Magdaléna Špoková, Agustín Sánchez-Lavega, Myung-Jin Kim, Valeria Mangano, Kandis-Lea Jessup, Thomas Widemann, Ko-ichiro Sugiyama, Shigeto Watanabe, Manabu Yamada, Takehiko Satoh, Masato Nakamura, Masataka Imai, Juan Cabrera
    The Planetary Science Journal 3(9) 209-209 2022年9月1日  
    Abstract We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns.
  • Kiichi Fukuya, Takeshi Imamura, Makoto Taguchi, Tetsuya Fukuhara, Toru Kouyama, Takeshi Horinouchi, Javier Peralta, Masahiko Futaguchi, Takeru Yamada, Takao M. Sato, Atsushi Yamazaki, Shin ya Murakami, Takehiko Satoh, Masahiro Takagi, Masato Nakamura
    Nature 595(7868) 511-515 2021年7月22日  
    Although Venus is a terrestrial planet similar to Earth, its atmospheric circulation is much different and poorly characterized1. Winds at the cloud top have been measured predominantly on the dayside. Prominent poleward drifts have been observed with dayside cloud tracking and interpreted to be caused by thermal tides and a Hadley circulation2–4; however, the lack of nightside measurements over broad latitudes has prevented the unambiguous characterization of these components. Here we obtain cloud-tracked winds at all local times using thermal infrared images taken by the Venus orbiter Akatsuki, which is sensitive to an altitude of about 65 kilometres5. Prominent equatorward flows are found on the nightside, resulting in null meridional velocities when these are zonally averaged. The velocity structure of the thermal tides was determined without the influence of the Hadley circulation. The semidiurnal tide was found to have an amplitude large enough to contribute to the maintenance of the atmospheric superrotation. The weakness of the mean meridional flow at the cloud top implies that the poleward branch of the Hadley circulation exists above the cloud top and that the equatorward branch exists in the clouds. Our results should shed light on atmospheric superrotation in other celestial bodies.
  • T. M. Sato, T. Satoh, H. Sagawa, N. Manago, Y. J. Lee, S. Murakami, K. Ogohara, G. L. Hashimoto, Y. Kasaba, A. Yamazaki, M. Yamada, S. Watanabe, T. Imamura, M. Nakamura
    Icarus 345 113682-113682 2020年7月15日  査読有り
    © 2020 Elsevier Inc. We describe the dayside cloud top structure of Venus as retrieved from 93 images acquired at a wide variety of solar phase angles (0–120°) using the 2.02-μm channel of the 2-μm camera (IR2) onboard the Venus orbiter, Akatsuki, from April 4 to May 25, 2016. Since the 2.02-μm channel is located in a CO2 absorption band, the sunlight reflected from Venus allowed us to determine the cloud top altitude corresponding to unit aerosol optical depth at 2.02 μm. First, the observed solar phase angle dependence and the center-to-limb variation of the reflected sunlight in the region equatorward of 30° were used to construct a spatially averaged cloud top structure characterized by cloud top altitude zc, Mode 2 modal radius rg,2, and cloud scale height H, which were 70.4 km, 1.06 μm, and 5.3 km, respectively. Second, cloud top altitudes at individual locations were retrieved on a pixel-by-pixel basis with an assumption that rg,2 and H were uniform for the entire planet. The latitudinal structure of the cloud top altitude was symmetric with respect to the equator. The average cloud top altitude was 70.5 km in the equatorial region and showed a gradual decrease of ~2 km by the 45° latitude. It rapidly dropped at latitudes of 50–60° and reached 61 km in latitudes of 70–75°. The average cloud top altitude in the region equatorward of 30° showed negligible local time dependence, with changes up to 1 km at most. Local variations in cloud top altitude, including stationary gravity wave features, occurred within several hundreds of meters. Although long zonal or tilted streaky features poleward of ~45° were clearly identifiable, features in the low and middle latitudes were usually subtle. These did not necessarily appear as local variations at the cloud top level, where mottled and patchy UV patterns were observed, suggestive of convection and turbulence at the cloud top level.
  • J. Peralta, T. Navarro, C. W. Vun, A. Sánchez‐Lavega, K. McGouldrick, T. Horinouchi, T. Imamura, R. Hueso, J. P. Boyd, G. Schubert, T. Kouyama, T. Satoh, N. Iwagami, E. F. Young, M. A. Bullock, P. Machado, Y. J. Lee, S. S. Limaye, M. Nakamura, S. Tellmann, A. Wesley, P. Miles
    Geophysical Research Letters 47(11) 2020年6月16日  査読有り

MISC

 86
  • 今村剛, 佐藤隆雄, 神山徹, 今井正尭, 安藤紘基, 佐川英夫, 原田裕己, 山崎敦, 佐藤毅彦, 中村正人
    地球電磁気・地球惑星圏学会総会及び講演会(Web) 150th 2021年  
  • 中村正人, 山崎敦, 山城龍馬, 石井信明, 戸田知朗, 二穴喜文, LIMAYE Sanjay S., 寺田直樹, 安藤紘基, 神山徹, 佐藤毅彦, 今村剛, 田口真, 林祥介, 堀之内武, LEE Yeon Joo, 高木征弘, 今井正尭, 福原哲哉, 杉本憲彦, 樫村博基, 渡部重十, 佐藤隆雄, はしもと じょーじ, 村上真也, MCGOULDRICK Kevin, 阿部琢美, 廣瀬史子, 山田学, 小郷原一智, 杉山耕一朗, 大月祥子, PERALTA Javier, 高木聖子, 岩上直幹, 上野宗孝, 坂野井健, 亀田真吾, 笠羽康正, 高橋幸弘, 佐藤光輝, 松田佳久, 山本勝
    日本地球惑星科学連合大会予稿集(Web) 2020 2020年  
  • Takeshi Imamura, Hiroki Ando, Silvia Tellmann, Martin Pätzold, Bernd Häusler, Atsushi Yamazaki, Takao M. Sato, Katsuyuki Noguchi, Yoshifumi Futaana, Janusz Oschlisniok, Sanjay Limaye, R. K. Choudhary, Yasuhiro Murata, Hiroshi Takeuchi, Chikako Hirose, Tsutomu Ichikawa, Tomoaki Toda, Atsushi Tomiki, Takumi Abe, Zen Ichi Yamamoto, Hirotomo Noda, Takahiro Iwata, Shin Ya Murakami, Takehiko Satoh, Tetsuya Fukuhara, Kazunori Ogohara, Ko Ichiro Sugiyama, Hiroki Kashimura, Shoko Ohtsuki, Seiko Takagi, Yukio Yamamoto, Naru Hirata, George L. Hashimoto, Manabu Yamada, Makoto Suzuki, Nobuaki Ishii, Tomoko Hayashiyama, Yeon Joo Lee, Masato Nakamura
    Earth, Planets and Space 69(1) 2017年12月1日  
    © 2017 The Author(s). After the arrival of Akatsuki spacecraft of Japan Aerospace Exploration Agency at Venus in December 2015, the radio occultation experiment, termed RS (Radio Science), obtained 19 vertical profiles of the Venusian atmosphere by April 2017. An onboard ultra-stable oscillator is used to generate stable X-band downlink signals needed for the experiment. The quantities to be retrieved are the atmospheric pressure, the temperature, the sulfuric acid vapor mixing ratio, and the electron density. Temperature profiles were successfully obtained down to ~ 38 km altitude and show distinct atmospheric structures depending on the altitude. The overall structure is close to the previous observations, suggesting a remarkable stability of the thermal structure. Local time-dependent features are seen within and above the clouds, which is located around 48-70 km altitude. The H2SO4 vapor density roughly follows the saturation curve at cloud heights, suggesting equilibrium with cloud particles. The ionospheric electron density profiles are also successfully retrieved, showing distinct local time dependence. Akatsuki RS mainly probes the low and middle latitude regions thanks to the near-equatorial orbit in contrast to the previous radio occultation experiments using polar orbiters. Studies based on combined analyses of RS and optical imaging data are ongoing.[Figure not available: see fulltext.]
  • 中村 正人, 今村 剛
    日本物理学会誌 = Butsuri 72(2) 92-97 2017年2月  
  • 佐藤毅彦, 佐藤隆雄, 中村正人, 上野宗孝, 笠羽康正, はしもと じょーじ, 中串孝志, LIMAYE Sanjay, 堀之内武
    日本気象学会大会講演予稿集 (112) 2017年  

書籍等出版物

 5

共同研究・競争的資金等の研究課題

 23