宇宙科学広報・普及主幹付

Atsushi Yamazaki

  (山﨑 敦)

Profile Information

Affiliation
Associate Professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency

Researcher number
00374893
J-GLOBAL ID
202001008895424436
researchmap Member ID
R000011885

Papers

 83
  • Takeshi Horinouchi, Toru Kouyama, Masataka Imai, Shin‐ya Murakami, Yeon Joo Lee, Atsushi Yamazaki, Manabu Yamada, Shigeto Watanabe, Takeshi Imamura, Javier Peralta, Takehiko Satoh
    Journal of Geophysical Research: Planets, Mar, 2024  
  • Tomoya Suda, Takeshi Imamura, Yeon Joo Lee, Atsushi Yamazaki, Takehiko Satoh, Takao M. Sato
    Journal of Geophysical Research: Planets, Oct, 2023  Peer-reviewed
  • J. Peralta, A. Cidadão, L. Morrone, C. Foster, M. Bullock, E. F. Young, I. Garate-Lopez, A. Sánchez-Lavega, T. Horinouchi, T. Imamura, E. Kardasis, A. Yamazaki, S. Watanabe
    Astronomy & Astrophysics, 672 L2-L2, Mar 28, 2023  
    Context. First identified in 2016 by the Japan Aerospace eXploration Agency (JAXA) Akatsuki mission, the discontinuity or disruption is a recurrent wave observed to propagate over decades at the deeper clouds of Venus (47–56 km above the surface), while its absence at the top of the clouds (∼70 km) suggests that it dissipates at the upper clouds and contributes to the maintenance of the puzzling atmospheric superrotation of Venus through wave-mean flow interaction. Aims. Taking advantage of the campaign of ground-based observations undertaken in coordination with the Akatsuki mission from December 2021 until July 2022, we undertook the longest uninterrupted monitoring of the cloud discontinuity to date to obtain a pioneering long-term characterisation of its main properties and to better constrain its recurrence and lifetime. Methods. The dayside upper, middle, and nightside lower clouds were studied with images acquired by the Akatsuki Ultraviolet Imager (UVI), amateur observers, and SpeX at the NASA Infrared Telescope Facility (IRTF). Hundreds of images were inspected in search of the discontinuity events and to measure key properties such as its dimensions, orientation, and rotation period. Results. We succeeded in tracking the discontinuity at the middle clouds during 109 days without interruption. The discontinuity exhibited properties nearly identical to measurements in 2016 and 2020, with an orientation of 91° ±8°, length of 4100 ± 800 km, width of 500 ± 100 km, and a rotation period of 5.11 ± 0.09 days. Ultraviolet images during 13–14 June 2022 suggest that the discontinuity may have manifested at the top of the clouds during ∼21 h as a result of an altitude change in the critical level for this wave, due to slower zonal winds.
  • Hiromu Nakagawa, Satoki Tsukada, Takashi Katagiri, Yasumasa Kasaba, Isao Murata, Yasuhiro Hirahara, Yuji Matsuura, Atsushi Yamazaki
    Applied Optics, 62(6) A31-A31, Jan 17, 2023  
    We demonstrate a newly designed, to the best of our knowledge, hollow optical fiber coupler for a mid-infrared (IR) laser heterodyne spectrometer that mixes a targeted light source with local oscillator (LO) light. The hollow fiber achieves a high transmission efficiency , not only for a coherent laser source but also for an incoherent blackbody source. The branching characteristics of the hollow optical fiber coupler are found to be strongly dependent on the curvature and length of the input port fiber, indicating that the branching ratio could be designed independently for each input port. Our laboratory measurements demonstrate that the branching ratio and transmittance of the coupler can be varied by coupling a flexible fiber to the input side owing to the excitation of higher-order modes. Using the hollow optical fiber coupler, a high-resolution emission spectrum of the quantum cascade laser at 10.3 µm for our laser-based heterodyne spectrometer is successfully achieved. Using a laser with a hollow fiber and a blackbody as a direct input signal in free space, we obtain the sensitivity performance of IR laser heterodyne spectrometer as 2000–3000 K of the system noise temperature. This suggests that the transmission of a coherent LO laser through a hollow optical fiber has almost the same sensitivity for the IR heterodyne detection as that without a fiber.
  • Kei Masunaga, Naoki Terada, Nao Yoshida, Yuki Nakamura, Takeshi Kuroda, Kazuo Yoshioka, Yudai Suzuki, Hiromu Nakagawa, Tomoki Kimura, Fuminori Tsuchiya, Go Murakami, Atsushi Yamazaki, Tomohiro Usui, Ichiro Yoshikawa
    Nature communications, 13(1) 6609-6609, Nov 3, 2022  
    Dust storms on Mars play a role in transporting water from its lower to upper atmosphere, seasonally enhancing hydrogen escape. However, it remains unclear how water is diurnally transported during a dust storm and how its elements, hydrogen and oxygen, are subsequently influenced in the upper atmosphere. Here, we use multi-spacecraft and space telescope observations obtained during a major dust storm in Mars Year 33 to show that hydrogen abundance in the upper atmosphere gradually increases because of water supply above an altitude of 60 km, while oxygen abundance temporarily decreases via water ice absorption, catalytic loss, or downward transportation. Additionally, atmospheric waves modulate dust and water transportations, causing alternate oscillations of hydrogen and oxygen abundances in the upper atmosphere. If dust- and wave-driven couplings of the Martian lower and upper atmospheres are common in dust storms, with increasing escape of hydrogen, oxygen will less efficiently escape from the upper atmosphere, leading to a more oxidized atmosphere. These findings provide insights regarding Mars' water loss history and its redox state, which are crucial for understanding the Martian habitable environment.

Misc.

 18
  • 今井 正尭, 神山 徹, 安藤 紘基, 佐川 英夫, 佐藤 隆雄, 原田 裕己, 山崎 敦, 佐藤 毅彦, 今村 剛
    日本惑星科学会誌遊星人, 31(2) 146-152, Nov, 2022  
  • 江副祐一郎, 船瀬龍, 船瀬龍, 三好由純, 石川久美, 笠原慧, 山崎敦, 長谷川洋, 三谷烈史, 松本洋介, 藤本正樹, 上野宗孝, 川勝康弘, 岩田隆浩, 沼澤正樹, 細川敬祐
    地球電磁気・地球惑星圏学会総会及び講演会(Web), 150th, 2021  
  • 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), Dec 1, 2017  
    © 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.]
  • 田口真, 神山徹, 今村剛, 堀之内武, 福原哲哉, 二口将彦, はしもと じょーじ, 岩上直幹, 村上真也, 小郷原一智, 佐藤光輝, 佐藤隆雄, 鈴木睦, 高木聖子, 上野宗孝, 渡部重十, 山田学, 山崎敦, 中村正人
    地球電磁気・地球惑星圏学会総会及び講演会(Web), 140th, 2016  

Research Projects

 9