2020年度 太陽系科学研究系 STPセミナー
■場所 ：Online (変更の場合は赤字)■時刻 ：月頭金曜日 16:00-17:00
■連絡先 ：齋藤研D2 滑川 拓 (namekawa [AT] stp.isas.jaxa.jp)
■備考 ：発表時間は一人当たり45分程度
| 開催日時・場所 | 発表者 (所属・身分) |
|---|---|
| 5/8(金) | 自己紹介 山本 |
| 5/15(金) | 自己紹介 大谷,Yang |
| 5/22(金) | 西野 |
| 5/29(金) | お休み |
| 6/5(金) | STP seminar O'Donoghue |
| 6/12(金) | 村上 |
| 6/19(金) | お休み |
| 6/26(金) | 長谷川 |
| 7/3(金) | STP seminar 児山 |
| 7/8(水) | JpGU発表練習 石城,滑川 |
| 7/17(金) | 浅村 |
| 7/24(金) | お休み |
| 7/31(金) | STP seminar 野和田 |
| 8/7(金) | お休み |
| 8/14(金) | お休み |
| 8/21(金) | お休み |
| 8/28(金) | お休み |
| 9/4(金) | お休み |
| 9/11(金) | お休み |
| 9/18(金) | 齋藤 |
| 9/25(金) | お休み |
| 10/2(金) | 大場 |
| 10/9(金) | 坂倉（本郷M2） |
| 10/16(金) | 森（本郷M2） |
| 10/23(金) | 甲斐（本郷M2） |
| 10/30(金) | 新井（本郷M2） |
| 11/6(金) | 江川（M2） |
| 11/13(金) | 島田（本郷M2） |
| 11/20(金) | 横山（本郷M2） |
| 11/27(金) | 西貝（本郷M2） |
| 12/4(金) | お休み |
| 12/11(金) | お休み |
| 12/18(金) | お休み |
| 12/25(金) | お休み |
| 1/1(金) | お休み |
| 1/8(金) | お休み |
| 1/15(金) | お休み |
| 1/22(金) | 修士論文発表練習 江川（M2） |
| 1/29(金) | お休み |
| 2/5(金) | 坂上 |
| 2/12(金) | 篠原 |
| 2/19(金) | お休み |
| 2/26(金) | 桑原 |
| 3/2(火) | 菅原 |
| 3/12(金) | 松田 |
| 開催日時・場所 | 発表者 (所属・身分) |
|---|---|
| 5/8(金) | 山本 |
| Development of a new method for in situ cosmic-ray exposure age measurements using laser ablation | |
| 概要： Cosmic-ray exposure (CRE) ages can be an indicator of the duration for which the sample is subject to the severe environment. Thus, developing a method for in situ CRE age measurement would be important. In situ CRE age measurements are also useful for choosing samples that should be brought back to the Earth. We develop a new method that combines laser-induced breakdown spectroscopy (LIBS) and quadrupole mass spectroscopy (QMS). This study focuses on the noble gas analysis with QMS. In our preliminary CRE age measurements, noble gases of ~10-16 mol were detected although the signal-to-blank ratios were small (<5). Our noble gas analyses demonstrate that even very small amounts of cosmogenic noble gases can be measured with this method, suggesting the capability of in situ CRE age measurement based on laser ablation. | |
| 5/15(金) | 大谷 |
| あらせ衛星の観測データ解析に基づく磁気圏内部起源Pc5波動(ULF波動)の特性の研究 | |
| 概要： 直近のシミュレーション研究によりリングカレント起源のULF波の一種（Pc5 ）がドリフト共鳴による周波数特性をもつことが明らかになった。そこで本研究では、当該周波数特性を持つイベントをあらせという衛星の観測データからとってきて統計解析したところ、ほかの生成起源のPc5はほとんど観測されなかった。よって過去に観測されたリングカレント起源のPc5の励起機構にドリフト共鳴が重要な役割を果たしている可能性が高いことが観測からもいうことができた。またこのイベントの空間分布と起こっているときの地磁気指数をそれぞれ統計解析したところ、それらへの依存性も確認された。 | |
| 5/15(金) | Yang |
| Analysis of salinity remote sensing algorithm | |
| 概要： Since the 1970s, with the rapid development of satellite remote sensing and satellite oceanography, it has caused a profound change in oceanographic research. Because the ocean data obtained by satellite remote sensing has the characteristics of large, space-time synchronization and continuous observation, the ocean can be studied from the whole, which greatly deepens the understanding of various ocean processes. This includes the inversion of ocean parameters. This paper aims to use satellite remote sensing technology to summarize the development of salinity remote sensing technology of sea surface. Based on the experience of scientists' different algorithms for inversion of sea surface salinity, this paper proposes a new idea, which uses remote sensing information Mechanism and marine spectral characteristics, including mathematical models related to salinity of sea surface, remote sensing image processing, independent algorithm for salinity inversion of sea surface, and make a basic oceanographic judgment on its reasonable degree. | |
| 5/22(金) | 西野 |
| MMS衛星による地球磁気圏尾部の低温高密度プラズマシートの観測例 | |
| 概要： 地球磁気圏にはプラズマシートと呼ばれる比較的密度が高い領域があり、そのプラズマの起源や輸送は磁気圏ダイナミクスにも大きく関与する。惑星間空間磁場(IMF)が北向きの時には磁気圏は静穏であるが、磁気圏境界面付近で太陽風から磁気圏へのプラズマ輸送が起きていることが知られている。ところが、磁気圏境界面からさらに内側でも太陽風起源と思われる冷たいプラズマが観測されることがあり、その輸送過程は不明である。我々は、MMS衛星の磁気圏尾部の観測により、IMF北向き時に磁気圏尾部プラズマシートで磁力線平行方向・反平行方向に低エネルギーイオンのエネルギー分散が起きることを発見した。そこで、Time-of-flight効果を仮定してイオンの加速地点と飛行経路を推定し、輸送メカニズムを考察する。具体的には、加速源から磁力線に沿って電離層に向かう成分と、電離層付近でミラー反射して磁気圏尾部に戻ってきた成分であると考えられる。これらのイオンが静穏時の磁気圏・電離圏結合に果たす役割を考察する。 | |
| 6/5(金) | O'Donoghue |
| Global maps of Jupiter's ionosphere: temperature, density and emissions | |
| 概要： In this online presentation I will present maps of Jovian ionospheric properties of near-global coverage. For context, the last time this was performed was with 1993 data and a 4 meter telescope, yielding 10,000s of km resolution per pixel from Earth. Generally, these have not been taken seriously in the field, owing to their low spatial resolution but also their high uncertainties in parameters (e.g. temperature). In the present work, I will show ~1000's of km spatial resolution data with uncertainties on the order of just a few % from the 10-meter Keck telescope (the largest infrared telescope). We reveal what the global pattern of Jupiter's ionosphere looks like in remarkable detail, in fact such detail cannot be seen on any other planet including (to the best of my knowledge) the Earth, so is much we can learn about ionospheres in general here. This project has taken perhaps 1.5 years of effort and generated 100s of figures, so the seminar will necessarily cover a wide range of topics. By writing this talk and observing your feedback, I hope to shape the work into 2 (maybe 3) papers in the next several months, as a single paper would be far too long and unfocussed. | |
| 6/12(金) | 村上 |
| On-going and future UV missions for solar and exosolar systems | |
| 概要： Ultraviolet (UV) observation has been a powerful tool for investigating plantary upper atmosphere, exosphere, and plasma environments in the solar system. For example, Japan’s UV space telescope Hisaki dedicated to planetary spectroscopy succeeded to monitor the variations of Io plasma torus and Jupiter’s aurora for long time and continuously. However, due to its low sensitivity and low spatial resolution, Hisaki cannot detect other Jupiter’s and Saturn’s moons, especially icy moons such as Europa and Ganymede. A UV telescope with higher sensitivity and spatial resolution is required to cover the observation capabilities in this spectral range after Hubble Space Telescope, especially in late 2020s when Europa Clipper and JUICE will arrive Jovian system. In addition, the UV observation techniques can be used for characterizing the upper atmosphere of Earth-sized exoplanets. Therefore, we are now studying the concept of future UV space telescope mission and participation to Russian space telescope, World Space Observatory-Ultraviolet (WSO-UV). Here we present on-going and future UV missions and our concept studies. | |
| 6/26(金) | 長谷川 |
| Magnetic-field annihilation and island formation in electron-scale current sheet in Earth's magnetotail | |
| 概要： Establishing the mechanism of magnetic-to-particle energy conversion through magnetic reconnection in current sheets is the key to understanding the impact of fast release of magnetic energy in many space and astrophysical plasma systems, such as during magnetospheric substorms. It is generally believed that an electron-scale diffusion region (EDR), where a magnetic-to-electron energy conversion occurs, has an X-type magnetic-field geometry around which the energy of anti-parallel magnetic fields injected is mostly converted to the bulk-flow energy of electrons by magnetic tension of reconnected field-lines. However, it is at present unknown exactly how this energy conversion occurs in EDRs, because there has been no observational method to fully address this problem. Here we present state-of-the-art analysis of multi-spacecraft observations during a weak substorm of an electron-scale current sheet in Earth's magnetotail, which demonstrates that contrary to the standard model of reconnection with an X-type EDR geometry, the fast energy conversion in the detected EDR was caused mostly by magnetic-field annihilation, rather than reconnection. Furthermore, we detected a magnetic island forming in the EDR itself, implying that the EDR had an elongated shape ideal for island generation and magnetic-field annihilation. The experimental discovery of the annihilation-dominated EDR reveals a new form of energy conversion in the reconnection process that can occur when the EDR has evolved from the X-type to planar geometry. | |
| 7/3(金) | 児山 |
| シミュレーションによる小型水チェレンコフ検出器の性能評価 | |
| 概要： 1998 年にスーパーカミオカンデ実験による大気ニュートリノの観測によってニュートリノ振動が発見された。現在はニュートリノの未知の性質を研究するために、加速器ニュートリノを用いた長基線ニュートリノ実 験が行われている。ニュートリノ振動の研究を行う上で振動前後のニュートリノの性質を精度良く観測することが非常に重要である。本論文では、振動前のニュートリノの性質を調べる前置検出器の将来計画について述べる。 2020年代後半の実験開始を目指しているハイパーカミオカンデは、現在稼働中のスーパーカミオカンデの約10倍の有効体積を持ち、ニュートリノ振動の観測ではスーパーカミオカンデを大幅に上回る統計のニュートリノデータを用いて、さらに精度の高い成果を生むことが期待される。ハイパーカミオカンデ計画では、ニュートリノ振動の測定精度をさらに向上し、ニュートリノにおける粒子・反粒子（CP）対称性の破れの発見を実現するため、振動が起こる前のニュートリノ生成点近傍でニュートリノビームのフラックスやニュートリノ反応の詳細を調べる中間距離水チェレンコフ検出器(Intermediate Water Cherenkov Detector, IWCD) の建設が検討されている。さらにIWCD の性能を実証するためにさらに小型の水チェレンコフ検出器(Water Cherenkov Test Experiment, WCTE) の建設が予定されている。本論文では、WCTE において検出器を回転させた場合や検出器内の水の透過率を変えた場合に、事象再構成の性能がどのように変わるかをシミュレーションを用いて評価した。 | |
| 7/8(水) | 石城 |
| P3T法を用いた惑星系形成のN体計算コードGPLUMの開発 | |
| 概要： 一般に，惑星系は，中心星を取り巻く原始惑星系円盤から形成したと考えられている．固体惑星やガス惑星のコアは，原始惑星系円盤内でkmサイズの天体(微惑星)の集積により形成したとされている．微惑星の集積過程は，主に微惑星系の重力多体計算(N体計算)によって議論されている．しかし，N体計算の粒子数の制約により，現在の多くのN体計算は，完全合体のような簡単な衝突モデルや，惑星系円盤の動径方向に狭い領域によるものである．より現実的な衝突モデル，動径方向に広い領域による，十分な粒子数のN体計算による研究はあまり行われておらず，汎惑星系形成論となるモデルは未だ構築されていない． 本研究では，Particle-particle Particle-tree 法を用いた新しいN体計算コードGPLUMを開発した．GPLUMでは，カットオフ半径より近距離の粒子間の重力相互作用を4次エルミート法で計算し，それより遠距離の粒子間重力相互作用をツリー法を用いて計算する．従来のP3T法を用いたコードでは，全ての粒子について同じカットオフ半径を用いているため，系内の粒子について質量比が大きくつくと計算速度が低下するという問題がある．GPLUMでは，カットオフ半径を粒子間の相互作用ごとに質量と軌道長半径に基づいて定める新たなアルゴリスムを実装することで，従来のP3T法コードの問題点を解決している． GPLUMの性能は，従来のP3T法コードと比較して，大きな質量比のついた質量分布を持つ粒子系のシミュレーションに対しては大幅に改善される． GPLUMによって，N体計算で~106-107粒子を扱うことが可能となり，これまでN体計算で扱うことができなかった広範囲，高解像度のN体計算を行うことができる．さらに，計算コストが向上することで，N体計算によるパラメータサーベイなど，新たな議論も可能となることが期待される． | |
| 7/8(水) | 滑川 |
| PARM-HEP Observation of Microburst Precipitation over Pulsating Aurora | |
| 概要： The phenomenon called microburst in which radiation belt particles precipitate to the Earth’s atmosphere is thought to be largely related to the loss of high energy electrons in radiation belt. It is suggested that this phenomenon is caused by pitch angle scattering of the magnetospheric particles by plasma waves, which is a mechanism similar to the cause of the pulsating aurora observed in the Earth’s polar region. There is a possibility that the origin of microburst can be clarified by proving simultaneous occurrence of microburst and pulsating aurora, but observational verification has not been made yet. For that purpose, we have developed a high-energy electron detector (HEP) for the observation of sub-relativistic - relativistic energy electrons that make up the microburst. This instrument is installed as one of the core instruments of the PARM instrument package developed for the simultaneous observation of the pulsating aurora and microburst by the international student sounding rocket experiment RockSat-XN and LAMP (Loss through Auroral Microburst Pulsation) sounding rocket experiment. We have succeeded in obtaining the flight data on 13 January 2019 from RockSat-XN sounding rocket experiment. Since the rocket was unfortunately launched on the dayside under quiet condition, simultaneous observation with pulsating aurora was impossible and the significant microbursts cannot be detected, but we detect quasi-relativistic energy electrons that can be explained by pitch angle scattering by weak chorus waves in the quiet dayside magnetosphere. On the other hand, LAMP rocket experiments are prepared for launch in winter 2021. We load an anti-coincidence counter on HEP mounted on LAMP to eliminate the effects of penetrating particles such as galactic cosmic rays. In this presentation, we will show the outline and observation results of HEP as well as the current status of the preparation for the launch of LAMP. | |
| 7/17(金) | 浅村 |
| あらせ衛星で観測された低エネルギーイオンの垂直方向加熱と磁気音波 | |
| 概要： 磁気音波は磁気赤道付近に集中して観測されるプラズマ波動である。あらせ衛星では、10-500eV/q の低エネルギーイオンのフラックス増大とともに磁気音波が観測される例が多く見つかっている。このようなイベントについて、波動データと粒子観測データを用い、波動粒子相互作用 (WPIA) 解析を行った。その結果、磁気音波が低エネルギーイオンを加熱していること、また、加熱された低エネルギーイオンが EMIC 波動にエネルギーを供給していることが分かった。 | |
| 7/31(金) | 野和田 |
| On the Morphological Study of Sun-aligned Arcs | |
| 概要： The sun-aligned arcs (SAAs) are identified as “arc-shaped” aurora observed at high-latitudes of the polar cap region, and frequently appear in association with a usual “oval-shaped” aurora. One of the most representative SAAs is “Transpolar arcs” (TPAs), which are growing from the poleward edge of nightside main auroral oval to the dayside. TPA is a part of mysterious aurora (theta aurora), whose shape is a Greek letter “Θ”, but its formation mechanism has hotly been debated since the theta aurora had been found in early 80’s. It is well-known that SAAs frequently occur under the northward IMF conditions, and their locations and motions are controlled by the IMF-By polarity. Recently, based on the auroral imager data, various unique-shaped SAAs have been found. They do not have the shape of a simple straightforward bar. For example, the TPAs with the nightside ends distorted toward pre- and post-midnight (Nightside Distorted TPAs), the bending SAAs jointed the dawn and dusk main auroral oval (Bending Arcs), and several bar-shaped TPAs within the polar cap (Multiple SAAs/TPAs) are raised. In a series of recent studies, they start to be used as a diagnostic tool of the magnetospheric dynamics under the northward IMF conditions. The physical processes occurring in the magnetotail, the dayside magnetopause, and the magnetospheric boundary (e.g., magnetotail reconnection, tailward-of-cusp reconnection and Kelvin-Helmholtz instability) are observed in most cases when these SAAs occur. Furthermore, their occurrences and fundamental characteristics are determined by the IMF-By and -Bz polarities. Therefore, these unique-shaped SAAs well-reflect the complicated physical phenomena seen within Solar Wind-Magnetosphere-Ionosphere system. In this presentation, this speaker will introduce what kind of SAAs have been found based on the auroral imager data obtained from the space-based observations, and how they are linked with the magnetosphere/magnetospheric boundary processes, in order to discuss the formation mechanisms of these SAAs. | |
| 9/18(金) | 齋藤 |
| Heavy Ion measurements around the Moon | |
| 概要： Interaction between the solar wind and a solar system object varies largely according to the object’s properties, such as the existence of a global intrinsic magnetic field and/or thick atmosphere. It is well known that the Moon has neither global intrinsic magnetic field nor thick atmosphere. Different from the Earth’s case where the intrinsic global magnetic field prevents the solar wind from penetrating into the magnetosphere, solar wind directly impacts the lunar surface. MAP-PACE on Kaguya made observations of low energy charged particles around the Moon at a circular lunar polar orbit of 100km altitude for about 1 year, at ~50km-altitude for about 2months, and some orbits had further lower perilune altitude of ~10km during the last 4 months. MAP-PACE-IMA (Moon looking ion energy mass spectrometer) is one of the four PACE analyzers. IMA detected mass discriminated heavy ions originating from the lunar surface/lunar exosphere with moderately high mass resolution for the first time. IMA data are the only in-situ measured ion data so far obtained around large non-magnetized airless bodies with mass range up to 60 (Fe). The knowledge obtained by IMA is quite useful for the ion measurements with higher mass resolution in the future missions including BepiColombo/Mio and MMX. I will briefly summarize the results of heavy ion measurements obtained by IMA and introduce our ongoing efforts to understand the heavy ions around the Moon. | |
| 10/2(金) | 大場 |
| 国際共同大気球実験「SUNRISE-3」/近赤外線偏光分光観測装置用スキャンミラー機構の開発 | |
| 概要： スキャンミラー機構は, スリット観測によって2次元空間上に広がる天体の物理量を診断するために必要な技術である. 国際共同大気球実験「SUNRISE-3」に搭載される近赤外線偏光分光観測装置は, スリット観測方式を採用しており, 太陽彩層大気の高精度な物理量診断を目指している. 彩層大気は, 一つ一つの微細な磁場が広く空間構造を形成しており, かつダイナミックであるため, 広視野を高精度・高速で走査するスキャンミラー機構が必須である. そこで, 電磁吸引式アクチュエータおよび静電容量センサを内蔵し, クローズドループ制御によって高精度なミラー制御を実現させることで, 上述の要求を満たすスキャンミラー機構を開発した. 光学試験によってスキャンミラー機構の性能を検証した結果, 「広いスキャン範囲(±1005″)」・「十分な安定度(3σ < 0.″1)」・「早いステップ移動時間(~26msec)」を保有していることを実証した. さらに, 気球フライト環境にて予想される低圧環境および低温/高温環境を再現した熱サイクル試験および熱真空試験を実施し, 問題なく要求性能を満たしていることを確認した. | |
| 10/9(金) | 坂倉（本郷M2） |
| Study of formation mechanisms of the molecular ion polar plume and its contribution to the ion escape from Mars | |
| 概要： Mars once had water on its surface about 4 billion years ago, but there is no liquid water on the surface at present. Escape of the neutral and ionized atmosphere to space is considered as the main cause of this climate change. Polar plume is one of the channels of the ion escape from Mars and the polar plume ions escape due to acceleration by the solar wind convection electric field. We recently reported a CO2+-rich plume event on August 28, 2015. Peak flux of CO2+ was 4.2x106 cm-2s-1, which is about one order of magnitude higher than the average flux of O+ in the polar plume reported by Dong et al. (2017). Such high escape flux is unexpected because CO2+ is a minor component at high-altitude ionosphere. To fully understand the mechanism of the polar plume, it is important to study the composition of the polar plumes. In order to investigate the relationship between a CO2+-rich plume event and solar wind (SW) conditions, we conducted a statistical study. We analyzed data obtained by STATIC, MAG and SWIA onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) from Nov. 28, 2014 to Oct. 11, 2019. The results show that CO2+ plume events tend to be observed under high solar wind dynamic pressure and strong electric field conditions. This result is consistent with the hypothesis that CO2+ plume is caused by deep penetration of the solar wind convection electric field due to the high solar wind dynamic pressure. On the other hand, observation frequency of O2+plume events does not show such dependences on the solar wind parameters. This is probably because O2+ is abundant near the ionopause enough to create O2+ plumes regardless of the solar wind conditions. The results also show that solar wind conditions affect escape rate and composition of the polar plume. Strong solar wind dynamic pressure lowers source altitude and therefore increases escape rate and changes the ion composition in the polar plume. References: Dong, Y., et al. (2017), J. Geophys. Res. Space Phys., 122, 4009-4022, doi:10.1002/2016JA023517 | |
| 10/16(金) | 森（本郷M2） |
| Study of proton escape from Mars based on MAVEN observations | |
| 概要： Mars is considered to have had water on surface in ancient days, while there is no surface water at present. Escape of atmospheric gases to space is considered to play an important role in this climate change. Particularly, hydrogen loss is closely related to the water content on Mars. Its main mechanism is thought to be Jeans escape of hydrogen atoms, which are dissociated from hydrogen molecules, sourced from odd-hydrogen reactions with near-surface water vapor. Since the molecular hydrogen is long-lived, the seasonal variation of hydrogen escape is predicted to be typically less than a factor of two (Krasnopolsky, 2002). However, Halekas (2017) reported unexpectedly large (about one order of magnitude) seasonal variations in the hydrogen corona. The cause of the large seasonal variation is not understood. A candidate mechanism is rapid transport of water to upper atmosphere due to the Martian dust storms. The enhancement of the hydrogen corona will increase the proton escape originated from the neutral hydrogen. In order to assess the hypothesis, we investigated proton escape from Mars based on MAVEN (Mars Atmosphere and Volatile EvolutioN) observations from November 2014 to March 2019. We also investigated if the seasonal variation depends on size of the dust storms by comparing MY(Mars Year)32, 33 and 34, since Martian global dust storm occurred only in MY34. For this purpose, we implemented methods to separate planetary-origin protons from solar-origin protons, which utilize characteristics of phase space density (PSD) observed in the optical wake and solar wind regions, by STATIC (Supra Thermal and Thermal Ion Composition) instrument. For identification of each region, we used data from MAG (magnetometer) and SWIA (Solar Wind Ion Analyzer) onboard MAVEN. In the magnetotail wake region, the ions with the energy less than 20 eV were identified as planetary protons. In order to understand the cause of the large seasonal variation in the wake region, we investigated proton density in the ionosphere during the same period. In solar wind region, solar wind maxwell distributions derived from solar wind density and temperature observed by SWIA were removed and partial moments of picked up protons originated from hydrogen corona were calculated. To calculate partial moments, we identified regions where picked up protons should distribute. The result shows that planetary proton density in the optical wake region has a seasonal variability which is more than one order of magnitude and the proton density in the ionosphere also has the seasonal variation, which is consistent with the result in the wake region. It suggests that proton escape in the wake region reflects seasonal variations in the ionosphere, i.e., the source region of planetary protons in the wake region. The variations in the solar wind region are small and have fluctuations which are similar to solar wind density. It is possible that the variations are small because solar wind contamination cannot be eliminated enough. The variations in MY32, 33 and 34 are similar in the wake and solar wind regions. It suggests that the size of dust storm does not affect proton escape. References: Krasnopolsky (2002), J. Geophys. Res., doi:10.1029/2001JE001809. 5128. Halekas (2017), J. Geophys. Res. Planets, doi: 10.1002/2017JE005306 | |
| 10/23(金) | 甲斐（本郷M2） |
| アルベーン波乱流加熱を考慮したコロナループ加熱シミュレーション | |
| 概要： コロナ加熱は天文学において重要な課題であり、その加熱メカニズム、特に磁場のエネルギーがどのように熱に変わるかは未解明である。ある先行研究では、モード変換を介してアルベーン波から生成された圧縮波が散逸することでコロナループ加熱が達成されるというシミュレーションの結果がでている(Moriyasu et al. 2004)。しかしこの研究には(1) コロナ磁場が数Gと小さく仮定されている、(2) 計算結果として出てくる波の速度振幅(100 km s-1)が、観測されるスペクトル線の非熱幅(10 - 20 km s-1)を説明できない、という問題点があった。アルベーン波の散逸過程はモード変換だけではなく、他にもさまざまな過程が提唱されている。そのうちの１つに、逆行するアルベーン波が衝突することにより磁力線垂直方向にカスケードが生じて散逸する過程(アルベーン波乱流) があり、近年盛んに研究されている。 これを踏まえ本研究では、これまでのモデルにアルベーン波の散逸過程としてモード変換に加え、現象論的にアルベーン波乱流の効果(Shoda et al. 2018)を取り入れることで上記の問題点の解決を試みた。より現実に近いコロナ磁場強度(数十G)を用いて一次元MHDシミュレーションを行いコロナの再現に成功した。コロナ中の波動振幅は観測と整合的な値に抑えられ、コロナ磁場が10 G - 100 Gの範囲で磁場の-0.3乗に、100 G - 650Gでは-1乗に比例することがわかった。 | |
| 10/30(金) | 新井（本郷M2） |
| magnetic field amplification and cosmic ray acceleration in supernova ejecta | |
| 概要： The mechanism of cosmic ray acceleration has not been fully understood. It is widely accepted that supernova remnants (SNRs) are the main sources of galactic cosmic rays. SNR has two types of shock waves: forward shock waves passing through the ISM and reverse shock waves passing through the supernova ejecta. Diffusive shock acceleration (DSA) is a commonly adopted process to explain the origin of cosmic rays at astrophysical shocks. According to this process, the acceleration efficiency depends on the intensity of the magnetic turbulence at the shock wave. Recent X-ray observations (Uchiyama et al., 2008) imply that in a young SNR(100s yr) the accelerations occur at both forward shock waves and reverse shock waves. However, the ejecta is supposed to have a too weak magnetic field to explain the observations. In our research, we focus on the magnetic field amplification in the ejecta by shock waves before the ejecta expands into the ISM. We estimate the maximum magnetic field by the magnetic field amplification of the MHD dynamo effect (Fraschetti et al.,2013) Furthermore, observations of gamma rays from a very young SNR(1s yr) outside our galaxy were reported (Xi et al., 2020). The amount of gamma rays produced by CRs via pp interaction depends on the density of protons. In the SNRs at this stage, the density of the ejecta is greater than that of the ISM. Therefore, we compare the amount of gamma rays from forward shock waves and reverse shock waves and investigate the conditions under which CRs are accelerated. Reference: Uchiyama et al., 2008, ApJ, doi: 10.1086/588190 Fraschetti et al., (2013), ApJ,doi: 10.1088/0004-637X/770/2/84 Xi et al., 2020, ApJ, doi: 10.3847/2041-8213/ab982c | |
| 11/6(金) | 江川（M2） |
| 「かぐや」によって観測された 月起源二次イオンと月表面組成の関係 | |
| 概要： 月は十分な大気と全球的な固有磁場を持たないため、地球磁気圏外で月面は太陽風にさらされる。このとき太陽風イオンや太陽光により月面から二次イオンが放出される。放出される二次イオンは月面の情報を保持していると考えられる。しかしながら、衛星データを用いて二次イオンの分布と表面の元素組成などの関係について詳しく理解されていない。 月探査衛星「かぐや」に搭載されたイオン観測装置MAP-PACE-IMAは月起源のイオンのエネルギーと質量の分析を行った。本研究ではIMAのデータを用いて、太陽風イオンの月面衝突で生成されると考えられる二次イオンのうち、月表面の岩石を構成する主要な元素(Mg、Si、Fe)について、二次イオンの計測量の生成場所に対する依存性を調べた。また、太陽風強度の影響をできるだけ取り除くべく、ケイ素イオンに対するマグネシウムイオン(Mg+/Si+)や鉄イオン(Fe+/Si+)の相対量の比較を行った。Fe+/Si+がlunar prospectorのGRSで得られた表面の鉄の濃度と相関関係が見られた。また、一部の領域を除くが、Mg+/Si+も同様にマグネシウムの濃度と相関関係がみられた。 | |
| 11/13(金) | 島田（本郷M2） |
| 地球磁気シースにおける温度異方性によって作られる磁気ミラー構造のGradShafranovリコンストラクション手法 | |
| 概要： 地球磁気圏と惑星間空間の間には bow shock と呼ばれる衝撃波面が存在しており、その下流には磁気シースと呼ばれる領域が広がっている。シース内でも特に準垂直衝撃波の下流では選択的な粒子加熱によって、特にイオンにおいて磁場に垂直方向の温度が平行方向の温度よりも大きくなる温度異方性 (T⊥ > T‖) が発達していることが知られている。この温度異方性のある領域では磁気ミラー構造が発達し、ミラーモードと呼ばれる波動が励起される。このような場に特徴的な現象には lion roars と呼ばれる高周波ホイッスラー波動がある。lion roars を解析する場合に重要になるのは、磁気ミラー構造の中心付近で磁力線に沿った磁場の大きさが最も小さくなる場所 (minimum-B) である。しかしながら観測衛星が必ずしもミラー構造の中心を通るとは限らないため、衛星観測で得られる 1次元（時系列）データから minimum-B の空間分布を特定することはできない。衛星の観測データから磁場構造を再現するためにはGrad-Shafranov(GS)リコンストラクションという手法が必要になるが、温度異方性のある場における正しいモデルはまだ確立されていない。本研究では実際の磁気シースへのGS-リコンストラクションの適用とその妥当性を考える。 | |
| 11/20(金) | 横山（本郷M2） |
| Particle acceleration in a shock wave propagating to an inhomogeneous medium | |
| 概要： It is known that the energy spectrum of cosmic rays has a power law spectrum. Diffusive Shock Acceleration (DSA) is recognized as plausible acceleration mechanism to yield this power law spectrum. Although in the standard DSA theory the plasma in the shock upstream region is assumed to be uniform, in the real astrophysical phenomena, shock waves propagate through various scales of fluctuations. In this study, we take into account the inhomogeneity of plasma and investigate its influence on particle acceleration. | |
| 11/27(金) | 西貝（本郷M2） |
| Transition of dominant ion-scale instabilities in strong perpendicular shocks | |
| 概要： In high Alfven Mach number shock waves, various instabilities can be excited by the velocity difference between three particle species, i.e. the incoming electrons, ions and reflected ions. Some of these instabilities play a crucial role in generation of high energy particles. In this study, we investigate plasma instabilities in the perpendicular shock transition region. We focus on Alfven Ion Cyclotron (AIC) instability and Weibel instability, both of which are excited by an effective temperature anisotropy generated by the reflected ions and the exact relation between the two instabilities has not been fully understood. Recent studies have reported that the Weibel instability has been shown to generate folded current sheets, which eventually dissipate via magnetic reconnection to accelerate electrons (Matsumoto et al., 2015). We adopted the ring model focusing only on the transition layer and investigated the dependence of instability on upstream physical parameters. We performed linear analysis and Particle-in-cell simulations and found that (1) the AIC and Weibel instabilities both appear from a single dispersion relation in different limiting cases, (2) the maximum growth rate of waves propagating parallel to the ambient field depends largely on Alfven Mach number, sound Mach number and ring ion ratio among the upstream parameters, (3) the transition between the AIC and Weibel instabilities is around where the maximum growth rate reaches about ~7/ion cyclotron frequency, (4) this system saturates when the magnetic field gains a few percent of the ring ion energy and (5) magnetic reconnection is observed in the ring model, but only for extreme conditions. We will also see a little about the difference between the ring and beam (counter stream) models. Reference: Matsumoto et al. (2015), Science, doi: 10.1126/science.1260168 | |
| 1/22(金) | 江川（M2） |
| 月面生成二次イオンと月表面組成の関係 | |
| 概要： 月には、地球のように全球的な固有磁場や濃い大気が存在しない。そのため、地球磁気圏外に存在するとき、月固体表面は太陽風に曝されている。月周回衛星「かぐや」による月周辺プラズマの観測を行った結果、月固体表面に由来する月起源イオンが月周回軌道上で観測できることが明らかとなった。そのイオンの生成過程としては、過去の地上からの分光観測や地上実験の結果から、太陽光による光脱離（PSD: Photon Stimulated Desorption）と太陽風スパッタリングなどが考えられていたが、これまでの「かぐや」衛星による月周辺プラズマの観測データの解析によって、Na、KなどのアルカリイオンはPSDが主な成因で、太陽風スパッタリングも一定の割合で成因となっていることが明らかになった。しかしながら、これまでに月周辺プラズマを直接観測したデータと月表面組成を合わせて議論されることは殆どなく、その理解は未だ充分ではない。そこで本研究の目的は、月周回衛星「かぐや」搭載プラズマ観測装置MAP-PACEの観測データを用い、太陽風イオンと固体表面との相互作用で生成される二次イオンと月表面組成の関係について理解することである。特に、月表面を構成する岩石の主要元素であり、太陽風スパッタリングが主な生成過程だと考えられるSi、Fe、Mgに着目して、領域ごとにその比較を行った。本研究では月面生成イオンが生成されてから獲得するエネルギーを求め、IMAの観測データから月面生成成分のデータを抽出した。次に、抽出したデータからイオン種を同定し、太陽風の条件の変化の効果をできる限り除くためSi+で規格化した。その上で、月面をいくつかの領域に分け、地質的特徴に基づいて分類を行った。領域ごとにFe+/Si+とMg+/Si+を求め、比較した。また、Lunar Prospector搭載ガンマ線分光計GRSでの月表面のFe、Mg濃度との関係についても解析を行った。これらの解析結果より、領域ごとに月面生成二次イオンの分布に偏りが見られ、Fe+/Si+についてはSiに対するFe濃度との間に有意な正の相関のあることが初めて明らかになった。また、Siに対するMg濃度が高いとMg+/Si+が高いという傾向が見られた。太陽風スパッタリングやPSDによる固体表面からの粒子放出は、月と同様な固有磁場と濃い大気のない、太陽風と固体表面が直接相互作用をする天体において、普遍的に生じると考えられる。本研究で得られた固体表面から放出されたイオンの組成とその表面組成との関係に関する知見は、月周辺プラズマや月外圏大気と固体表面の関係の理解への鍵になるとともに、月と同様な環境の天体と太陽風との相互作用の理解、天体周回軌道における粒子観測による太陽風を利用した対象天体の表面情報の遠隔探査にもつながると考えられる。 | |
| 2/5(金) | 坂上 |
| 非線形Alfven波モデルに基づくM型主系列星彩層・コロナ・恒星風の物理量評価 | |
| 概要： 近年、惑星・惑星系進化や宇宙生物学的見地から、中心星大気からの紫外線・X線放射や恒星風が、惑星間空間・惑星大気に与える影響に関心が集まっている。とりわけ注目されているのは太陽よりも低温なM型主系列星 (M型星) である。M型星は、発達した対流層に由来する激しい磁気活動として、彩層・コロナの形成や磁場駆動形の恒星風の存在が観測されている。しかし、恒星大気 (彩層・コロナ)・恒星風の物理量を観測的に評価することは未だ難しく、対応する理論モデルも確立されていないため、議論の不定性は依然として大きい。こうした中、観測体制が整った太陽大気・太陽風に対する理論モデルを洗練し、恒星大気・恒星風に適用する研究が始められている。中でも有力なのは、恒星表層の対流運動で励起されたAlfven波が上層大気や惑星間空間まで伝播し、非線形過程を経て恒星大気を加熱、恒星風を駆動するモデルである。 そこで本研究では、Sakaue & Shibata 2020 の太陽大気・太陽風モデルをM型星の大気・恒星風に適用し、コロナの温度や恒星風速度、質量損失率の物理量を評価した (Sakaue & Shibata 2021)。Sakaue & Shibata 2020 では1次元磁気流体シミュレーションに基づいてAlfven波の非線形伝播と非定常な太陽大気・太陽風の形成過程との関係性を議論しており、本研究では数値計算上の下部境界として5つのM型星の光球を想定することで、M型星大気・恒星風への自然な拡張が図られている。計算の結果、M型星のコロナは太陽コロナよりも系統的に低温であり、M型星の恒星風は太陽風よりも高速かつ低質量損失率で特徴づけられることが分かった。本発表では、こうした太陽・M型星の大気・恒星風の物理量に見られる多様性を、解析的なアプローチから体系的に理解できることを示す。 | |
| 2/12(金) | 篠原 |
| Introduction to Particle Instrument for Nano-Satellite (PINO) onboard a cubesat | |
| 概要： Recently, the use of CubeSats for space science researches is no longer unusual. We expect that CubeSats will be a powerful platform for space environment observations. However, in Japan, more opportunities to install instruments onboard CubeSats are desired for future observations and development of new technologies. Fortunately, we have a chance to install a high-energy electron measurement onboard the BIRDS-5 satellite, which is the fifth satellite in Joint Global Multi-Nation Birds Satellite (BIRDS) Program of Kyushu Institute of Technology. The BIRDS-5 project was kicked off in July 2020. Thanks to the JSPS KAKENHI support, we have started to develop the high-energy electron analyzer, PINO: Particle Instrument for Nano-Satellite. In this presentation, we will present the outline of science and the latest status of PINO development. | |
| 2/26(金) | 桑原 |
| Development of the absorption cell filters for remote D/H observation | |
| 概要： The hydrogen atoms in the planetary exosphere scatter the solar Lyman-alpha radiation and produce a faint glow surrounding the planet. The brightest emission among the planetary coronas is hydrogen Lyman-alpha. Absorption cell technique is an efficient tool for remote sensing of the planetary coronas and allows us to measure not only an intensity distribution of the Lyman-alpha emission but also a temperature distribution in the planetary exosphere. These distributions are quite important to quantitatively estimate of the escape rate of the present planetary atmosphere. Since the absorption cell technique can be used as a light-weight ultra-high resolution filter, it will be crucial for realizing an imaging instrument for observation of planetary coronas with small spacecraft. Absorption performance of the cell strongly depends on parameters such as filament shape, filament temperature, applied power to the filament, filled gas pressure, optical path length, and position of the beam path. The hydrogen absorption cells have been developed to optimize the above parameters and evaluated using an ultra-high spectral resolution Fourier transform spectrometer installed at the DESIRS beamline of Synchrotron SOLEIL in France. In this presentation, the summary of the development and the remaining issues are presented. The basic design of an absorption cell imager and the application for the future space mission is also presented. | |
| 3/2(火) | 菅原 |
| Assessing the analytical accuracy for compound-specific isotope analysis of 15N-enriched amino acids | |
| 概要： Nitrogen consists of two stable isotopes (14N: 99.63% and 15N: 0.37%). In geochemical studies, the ratio of 15N/14N is often expressed as δ15N notation in per mill (‰) relative to the standard ratio in terrestrial atmospheric air (Air). The variation of δ15N in the terrestrial materials generally falls within ±20‰, but even such little variations tell us a lot of information for studying environmental and physicochemical processes that the molecules has experienced. Unlike the terrestrial materials, extraterrestrial materials, especially pristine solar system materials such as comets and chondrites, exhibit extremely high δ15N values more than +1000‰ (Furi & Marty, 2015, Nature Geosci) and even +5000‰ as a nanometer scale materials, which is called a hot spot (Briani et al., 2009, PNAS). The extreamely high δ15N values of the pristine solar system materialsraised a question regarding the analytical accuracy in calculating δ15N values, because the conventional δ15N analysis has been developed for the measurement of terrstrial materials that varies from -10 to +50‰ (Hoefs, 2015, Stable isotope geochemistry). In the δ15N analysis by gas chromatography / isotope-ratio mass spectrometry (GC/IRMS), the nitrogen in the organic materials are converted to N2. The possible combinations of the isotopes are 14N≡14N (m/z28), 15N≡14N (m/z 29), 15N≡15N (m/z30). However, the existance of 15N≡15N (m/z30) is ignored, because the amount of 15N on the Earth is very little compared with 14N. The applicability of this assumption has not been examined for 15N-enriched materials. If significant amount of 15N≡15N are produced during the analyis, the calculated δ15N values include a large uncertainty. In contrast, unlike nitrogen, the δ13C analysis converts organic carbon to CO2, i.e., no 13C-13C bound is produced. In order to examine the accuracy of the isotope analysis for 15N- and 13C-enriched materials, we evaluated the GC/IRMS results for several 15N-and 13C-labelled amino acid samples. The results revealed that the measured δ15N valuescertainly deviate from the original values and suggested the formation of 15N≡15N, whereas the measured δ13C valuesare identical with the original values. The topic of the presentaion is highly analytical chemistry, but I will try to explain politly. I will also give a short review about 15N/14N in the universe. | |
| 3/12(金) | 松田 |
| Direct Antenna Impedance Measurement for Quantitative AC Electric Field Measurement by Arase | |
| 概要： We developed the in-situ direct measurement technique for the electric field antenna impedance using onboard signal processing. Antenna impedance is an important parameter for observed electric field calibration. Because it changes depending on local plasma parameters, in-situ measurements along the orbit are essential to obtaining precise electric field calibration. We installed the onboard signal calibration function (SWCAL) as a part of the onboard software of the plasma wave experiment (PWE) aboard Arase, and we performed over 5500 measurements in the inner magnetosphere from March 2017 to March 2020. We successfully measured antenna capacitance along the orbit of Arase, which is important for AC electric field calibration. We found that the measured antenna capacitance varies between 70 and 160 pF depending on the ambient electron density. We evaluate the effect of antenna impedance for AC electric field calibration and found that the observed electric field data includes ambiguity up to 7.8 dB and 17 degrees in the main target frequency range of the waveform capture/onboard frequency analyzer (WFC/OFA) of PWE. This ambiguity can be calibrated by considering the real antenna impedance effects measured by SWCAL. | |
最終更新日 2019.04.08 <編集: 星>