Updated on 2021/03/31

写真a

 
IWAI Kazumasa
 
Organization
Institute for Space-Earth Environmental Research Division for Heliospheric Research Associate professor
Graduate School
Graduate School of Science
Title
Associate professor
Contact information
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Profile
名古屋大学 宇宙地球環境研究所 太陽圏研究部 准教授。福井県武生市出身。2012年、東北大学大学院理学研究科博士後期課程終了。博士(理学)。国立天文台野辺山太陽電波観測所、情報通信研究機構、米国国立電波天文台を経て2017年4月より現職。専門は、太陽圏物理学、電波天文学。特に電波観測を用いた太陽圏の観測的研究や宇宙天気予報に関する研究をしている。また次世代電波望遠鏡の開発研究も推進している。
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Degree 1

  1. 博士(理学) ( 2012.3   東北大学 ) 

Research Interests 8

  1. Solar Wind, Sun, Space Weather, Space, Radio telescope, Digital devices

  2. Radio telescope

  3. Space

  4. Space Weather

  5. Solar Wind

  6. Sun

  7. Data assimilation

  8. Digital devices

Research Areas 3

  1. Natural Science / Space and planetary sciences

  2. Natural Science / Astronomy

  3. Social Infrastructure (Civil Engineering, Architecture, Disaster Prevention) / Disaster prevention engineering

Research History 4

  1. Nagoya University, Institute for Space-Earth Environmental Research   Division for Heliospheric Research   Associate professor

    2017.4

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    Country:Japan

  2. National Radio Astronomy Observatory   Guest Researcher

    2017.1 - 2017.3

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    Country:Japan

  3. National Institute of Information and Communications Technology (NICT)   Applied Electromagnetic Research Institute   JSPS research fellow

    2015.4 - 2017.3

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    Country:Japan

  4. National Astronomical Observatory of Japan   Nobeyama Solar Radio Observatory   Researcher

    2012.4 - 2015.3

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    Country:Japan

Education 2

  1. Tohoku University   Graduate School, Division of Natural Science

    2007.4 - 2012.3

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    Country: Japan

  2. Tohoku University   Faculty of Science

    2003.4 - 2007.3

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    Country: Japan

Professional Memberships 4

  1. The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)

  2. The Astronomical Society of Japan

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  3. JAPAN GEOSCIENCE UNION

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  4. International Astronomical Union (IAU)

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Committee Memberships 3

  1. 文部科学省 科学技術・学術政策研究所 科学技術予測センター   専門調査員  

    2020.4   

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    Committee type:Government

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  2. 日本天文学会   天文月報編集委員  

    2019.6   

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    Committee type:Academic society

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  3. 国立天文台 研究交流委員会   研究交流委員  

    2018.7   

Awards 4

  1. Obayashi Early Career Scientist Award

    2020.11   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   Studies on solar atmosphere and heliosphere based on the development of leading-edge radio telescopes

    Kazumasa Iwai

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  2. Sensyuu-kai Early Career Scientist Award

    2020.10   Alumni Association, Tohoku University Department of Physics  

    Kazumasa Iwai

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  3. Student Presentation Award (Aurora Medal)

    2012.5   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   Fine spectrum structures of solar radio type-I burst

    Kazumasa Iwai

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  4. Student Presentation Award (Aurora Medal)

    2009.5   Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)   The development of wide band solar radio polarization spectrograph

    Kazumasa Iwai

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Papers 31

  1. BepiColombo Science Investigations During Cruise and Flybys at the Earth, Venus and Mercury

    Mangano Valeria, Dosa Melinda, Franz Markus, Milillo Anna, Oliveira Joana S., Lee Yeon Joo, McKenna-Lawlor Susan, Grassi Davide, Heyner Daniel, Kozyrev Alexander S., Peron Roberto, Helbert Joern, Besse Sebastien, de la Fuente Sara, Montagnon Elsa, Zender Joe, Volwerk Martin, Chaufray Jean-Yves, Slavin James A., Krueger Harald, Maturilli Alessandro, Cornet Thomas, Iwai Kazumasa, Miyoshi Yoshizumi, Lucente Marco, Massetti Stefano, Schmidt Carl A., Dong Chuanfei, Quarati Francesco, Hirai Takayuki, Varsani Ali, Belyaev Denis, Zhong Jun, Kilpua Emilia K. J., Jackson Bernard V., Odstrcil Dusan, Plaschke Ferdinand, Vainio Rami, Jarvinen Riku, Ivanovski Stavro Lambrov, Madar Akos, Erdos Geza, Plainaki Christina, Alberti Tommaso, Aizawa Sae, Benkhoff Johannes, Murakami Go, Quemerais Eric, Hiesinger Harald, Mitrofanov Igor G., Iess Luciano, Santoli Francesco, Orsini Stefano, Lichtenegger Herbert, Laky Gunther, Barabash Stas, Moissl Richard, Huovelin Juhani, Kasaba Yasumasa, Saito Yoshifumi, Kobayashi Masanori, Baumjohann Wolfgang

    SPACE SCIENCE REVIEWS   Vol. 217 ( 1 )   2021.2

  2. Validation of coronal mass ejection arrival-time forecasts by magnetohydrodynamic simulations based on interplanetary scintillation observations

    Iwai Kazumasa, Shiota Daikou, Tokumaru Munetoshi, Fujiki Ken'ichi, Den Mitsue, Kubo Yuki

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.1

  3. Estimating the Temperature and Density of a Spicule from 100 GHz Data Obtained with ALMA Reviewed

    Masumi Shimojo, Tomoko Kawate, Takenori J. Okamoto, Takaaki Yokoyama, Noriyuki Narukage, Taro Sakao, Kazumasa Iwai, Gregory D. Fleishman, Kazunari Shibata

    The Astrophysical Journal   Vol. 888 ( 2 )   2020.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.3847/2041-8213/ab62a5

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  4. Spectral Structures of Type II Solar Radio Bursts and Solar Energetic Particles Reviewed International coauthorship International journal

    Iwai, Kazumasa, Yashiro, Seiji, Nitta, Nariaki, V, Kubo, Yuki

    ASTROPHYSICAL JOURNAL   Vol. 888 ( 1 )   2020.1

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

    We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SEPs). To examine the statistical relationship between type II bursts and SEPs, we selected 26 coronal mass ejection (CME) events with similar characteristics (e.g., initial speed, angular width, and location) observed by the Large Angle and Spectrometric Coronagraph, regardless of the characteristics of the corresponding type II bursts and the SEP flux. Then, we compared associated type II bursts observed by the Radio and Plasma Wave Experiment on board the Wind spacecraft and the SEP flux observed by the Geostationary Operational Environmental Satellite orbiting around the Earth. We found that the bandwidth of the hectometric type II bursts and the peak flux of the SEPs has a positive correlation (with a correlation coefficient of 0.64). This result supports the idea that the nonthermal electrons of type II bursts and the nonthermal ions of SEPs are generated by the same shock and suggests that more SEPs may be generated for a wider or stronger CME shock with a longer duration. Our result also suggests that considering the spectral structures of type II bursts can improve the forecasting accuracy for the peak flux of gradual SEPs.

    DOI: 10.3847/1538-4357/ab57ff

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  5. Coordinated Interplanetary Scintillation Observations in Japan and Russia for Coronal Mass Ejection Events in Early September 2017 Reviewed

    Tokumaru, Munetoshi, Fujiki, Ken'ichi, Iwai, Kazumasa, Tyul'bashev, Sergey, Chashei, Igor

    SOLAR PHYSICS   Vol. 294 ( 7 )   2019.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    Interplanetary (IP) shocks traveling between the Sun and the Earth's orbit were clearly detected in interplanetary scintillation (IPS) observations made at Toyokawa (Japan) and Pushchino (Russia), in association with two halo coronal mass ejections (CMEs) that occurred on 04 and 06 September 2017. Since the observation times at Toyokawa and Pushchino differ by about six hours, a combined analysis of the IPS data obtained at these sites enabled high-cadence tracking of the IP shock for one of the CME events. The plane-of-sky locations where the IP disturbances were observed at Toyokawa were generally consistent with those at Pushchino. The propagation speeds of IP shocks inferred from IPS observations were higher than the average speeds derived from the occurrence time of IP shocks at Earth. This difference was ascribed to the deceleration of the CME-driven shocks during propagation. The east-west asymmetry of the propagation speed of IP shocks was also revealed from IPS observations. Solar-wind disturbances moving at a speed significantly slower than the average speed of the IP shock were identified from the IPS observations of the 06 September 2017 halo CME event. A wide longitudinal extent of these slow disturbances was suggested by the fact they were observed not only west but also east of the Sun; i.e. the opposite side to the flare/CME site. The origin of the slow disturbances is considered to represent either wing portions of the highly warped IP shock or the post-shock dense materials.

    DOI: 10.1007/s11207-019-1487-6

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  6. Development of a coronal mass ejection arrival time forecasting system using interplanetary scintillation observations Reviewed

    Iwai Kazumasa, Shiota Daikou, Tokumaru Munetoshi, Fujiki Ken'ichi, Den Mitsue, Kubo Yuki

    EARTH PLANETS AND SPACE   Vol. 71   2019.4

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  7. Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles Reviewed

    Fujiki Ken'ichi, Shibasaki Kiyoto, Yashiro Seiji, Tokumaru Munetoshi, Iwai Kazumasa, Masuda Satoshi

    SOLAR PHYSICS   Vol. 294 ( 3 )   2019.3

  8. Solar Polar Brightening and Radius at 100 and 230GHz Observed by ALMA Reviewed

    Selhorst Caius L, Simoes Paulo J. A, Brajsa Roman, Valio Adriana, Gimenez de, Castro C. G, Costa Joaquim E. R, Menezes Fabian, Pierre Rozelot Jean, Hales Antonio S, Iwai Kazumasa, White Stephen

    ASTROPHYSICAL JOURNAL   Vol. 871 ( 1 )   2019.1

  9. Detection of Propagating Fast Sausage Waves through Detailed Analysis of a Zebra-pattern Fine Structure in a Solar Radio Burst Reviewed

    K. Kaneda, H. Misawa, K. Iwai, S. Masuda, F. Tsuchiya, Y. Katoh, T. Obara

    Astrophysical Journal Letters   Vol. 855 ( 2 )   2018.3

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    Publishing type:Research paper (scientific journal)   Publisher:Institute of Physics Publishing  

    Various magnetohydrodynamic (MHD) waves have recently been detected in the solar corona and investigated intensively in the context of coronal heating and coronal seismology. In this Letter, we report the first detection of short-period propagating fast sausage mode waves in a metric radio spectral fine structure observed with the Assembly of Metric-band Aperture Telescope and Real-time Analysis System. Analysis of Zebra patterns (ZPs) in a type-IV burst revealed a quasi-periodic modulation in the frequency separation between the adjacent stripes of the ZPs (Δf ). The observed quasi-periodic modulation had a period of 1-2 s and exhibited a characteristic negative frequency drift with a rate of 3-8 MHz s-1. Based on the double plasma resonance model, the most accepted generation model of ZPs, the observed quasi-periodic modulation of the ZP can be interpreted in terms of fast sausage mode waves propagating upward at phase speeds of 3000-8000 km s-1. These results provide us with new insights for probing the fine structure of coronal loops.

    DOI: 10.3847/2041-8213/aab2a5

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  10. Solar ALMA Observations: Constraining the Chromosphere above Sunspots Reviewed

    Maria A. Loukitcheva, Kazumasa Iwai, Sami K. Solanki, Stephen M. White, Masumi Shimojo

    ASTROPHYSICAL JOURNAL   Vol. 850 ( 1 )   2017.11

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    We present the first high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a sunspot at wavelengths of 1.3 and 3 mm, obtained during the solar ALMA Science Verification campaign in 2015, and compare them with the predictions of semi-empirical sunspot umbral/penumbral atmosphere models. For the first time, millimeter observations of sunspots have resolved umbral/penumbral brightness structure at the chromospheric heights, where the emission at these wavelengths is formed. We find that the sunspot umbra exhibits a radically different appearance at 1.3 and 3 mm, whereas the penumbral brightness structure is similar at the two wavelengths. The inner part of the umbra is similar to 600 K brighter than the surrounding quiet Sun (QS) at 3 mm and is similar to 700 K cooler than the QS at 1.3 mm, being the coolest part of sunspot at this wavelength. On average, the brightness of the penumbra at 3 mm is comparable to the QS brightness, while at 1.3 mm it is similar to 1000 K brighter than the QS. Penumbral brightness increases toward the outer boundary in both ALMA bands. Among the tested umbral models, that of Severino et al. provides the best fit to the observational data, including both the ALMA data analyzed in this study and data from earlier works. No penumbral model among those considered here gives a satisfactory fit to the currently available measurements. ALMA observations at multiple millimeter wavelengths can be used for testing existing sunspot models, and serve as an important input to constrain new empirical models.

    DOI: 10.3847/1538-4357/aa91cc

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  11. Variation of the Solar Microwave Spectrum in the Last Half Century Reviewed

    Masumi Shimojo, Kazumasa Iwai, Ayumi Asai, Satoshi Nozawa, Tetsuhiro Minamidani, Masao Saito

    ASTROPHYSICAL JOURNAL   Vol. 848 ( 1 )   2017.10

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    The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed continuously from 1957 to 1994 at Toyokawa, Japan, and from 1994 until now at Nobeyama, Japan, with the current Nobeyama Radio Polarimeters. We examined the multi-frequency and long-term data sets, and found that not only the microwave solar flux but also its monthly standard deviation indicate the long-term variation of solar activity. Furthermore, we found that the microwave spectra at the solar minima of Cycles 20-24 agree with each other. These results show that the average atmospheric structure above the upper chromosphere in the quiet-Sun has not varied for half a century, and suggest that the energy input for atmospheric heating from the sub-photosphere to the corona have not changed in the quiet-Sun despite significantly differing strengths of magnetic activity in the last five solar cycles.

    DOI: 10.3847/1538-4357/aa8c75

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  12. OCTAD-S: digital fast Fourier transform spectrometers by FPGA Reviewed

    Kazumasa Iwai, Yuki Kubo, Hiromitsu Ishibashi, Takahiro Naoi, Kenichi Harada, Kenji Ema, Yoshinori Hayashi, Yuichi Chikahiro

    EARTH PLANETS AND SPACE   Vol. 69   page: 95   2017.7

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    We have developed a digital fast Fourier transform spectrometer made of an analog-to-digital converter (ADC) and a field-programmable gate array (FPGA). The base instrument has independent ADC and FPGA modules, which allow us to implement different spectrometers in a relatively easy manner. Two types of spectrometers have been instrumented: one with 4.096 GS/s sampling speed and 2048 frequency channels and the other with 2.048 GS/s sampling speed and 32,768 frequency channels. The signal processing in these spectrometers has no dead time, and the accumulated spectra are recorded in external media every 8 ms. A direct sampling spectroscopy up to 8 GHz is achieved by a microwave track-and-hold circuit, which can reduce the analog receiver in front of the spectrometer. Highly stable spectroscopy with a wide dynamic range was demonstrated in a series of laboratory experiments and test observations of solar radio bursts.

    DOI: 10.1186/s40623-017-0681-8

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  13. Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric Imaging Reviewed

    M. Shimojo, T. S. Bastian, A. S. Hales, S. M. White, K. Iwai, R. E. Hills, A. Hirota, N. M. Phillips, T. Sawada, P. Yagoubov, G. Siringo, S. Asayama, M. Sugimoto, R. Brajsa, I. Skokic, M. Barta, S. Kim, I. de Gregorio-Monsalvo, S. A. Corder, H. S. Hudson, S. Wedemeyer, D. E. Gary, B. De Pontieu, M. Loukitcheva, G. D. Fleishman, B. Chen, A. Kobelski, Y. Yan

    SOLAR PHYSICS   Vol. 292 ( 7 )   2017.7

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    Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low-contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations. We describe the commissioning efforts that enable the use of two frequency bands, the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA. Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar-commissioning campaign held in December 2015 are presented. Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities.

    DOI: 10.1007/s11207-017-1095-2

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  14. Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping Reviewed

    S. M. White, K. Iwai, N. M. Phillips, R. E. Hills, A. Hirota, P. Yagoubov, G. Siringo, M. Shimojo, T. S. Bastian, A. S. Hales, T. Sawada, S. Asayama, M. Sugimoto, R. G. Marson, W. Kawasaki, E. Muller, T. Nakazato, K. Sugimoto, R. Brajsa, I. Skokic, M. Barta, S. Kim, A. J. Remijan, I. de Gregorio, S. A. Corder, H. S. Hudson, M. Loukitcheva, B. Chen, B. De Pontieu, G. D. Fleishmann, D. E. Gary, A. Kobelski, S. Wedemeyer, Y. Yan

    SOLAR PHYSICS   Vol. 292 ( 7 )   2017.7

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    The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at lambda = 3 mm and 5900 K at lambda = 1.3 mm. These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about 25 '', the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images.

    DOI: 10.1007/s11207-017-1123-2

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  15. ALMA Discovery of Solar Umbral Brightness Enhancement at lambda=3 mm Reviewed International coauthorship International journal

    Kazumasa Iwai, Maria Loukitcheva, Masumi Shimojo, Sami K. Solanki, Stephen M. White

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 841 ( 2 ) page: L20   2017.6

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    We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a lambda = 3 mm (100 GHz) mosaic image obtained by ALMA that includes a large sunspot within the active region AR12470, on 2015 December 16. The 3 mm map has a 300 '' x 300 '' field of view and 4 ''.9 x 2 ''.2 spatial resolution, which is the highest spatial resolution map of an entire sunspot in this frequency range. We find a gradient of 3 mm brightness from a high value in the outer penumbra to a low value in the inner penumbra/outer umbra. Within the inner umbra, there is a marked increase in 3 mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightness in the 1330 and 1400 angstrom slit-jaw images of the Interface Region Imaging Spectrograph (IRIS), adjacent to a partial lightbridge. This lambda = 3 mm brightness enhancement may be an intrinsic feature of the sunspot umbra at chromospheric heights, such as a manifestation of umbral flashes, or it could be related to a coronal plume, since the brightness enhancement was coincident with the footpoint of a coronal loop observed at 171 angstrom.

    DOI: 10.3847/2041-8213/aa71b5

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  16. Polarization Characteristics of Zebra Patterns in Type IV Solar Radio Bursts Reviewed

    K. Kaneda, H. Misawa, K. Iwai, F. Tsuchiya, T. Obara, Y. Katoh, S. Masuda

    ASTROPHYSICAL JOURNAL   Vol. 842 ( 1 )   2017.6

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    The polarization characteristics of zebra patterns (ZPs) in type IV solar bursts were studied. We analyzed 21 ZP events observed by the. Assembly of Metric-band Aperture Telescope and Real-time Analysis System between 2010 and 2015 and identified the following characteristics: a degree of circular polarization (DCP) in the range of 0%-70%, a temporal delay of 0-70 ms between the two circularly polarized components (i.e., the right- and left-handed components), and dominant ordinary-mode emission in about 81% of the events. For most events, the relation between the dominant and delayed components could be interpreted in the framework of fundamental plasma emission and depolarization during propagation, though the values of DCP and delay were distributed across wide ranges. Furthermore, it was found that the DCP and delay were positively correlated (rank correlation coefficient R = 0.62). As a possible interpretation of this relationship, we considered a model based on depolarization due to reflections at sharp density boundaries assuming fundamental plasma emission. The model calculations of depolarization including multiple reflections and group delay during propagation in the inhomogeneous corona showed that the DCP and delay decreased as the number of reflections increased, which is consistent with the observational results. The dispersive polarization characteristics could be explained by the different numbers of reflections causing depolarization.

    DOI: 10.3847/1538-4357/aa74c1

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  17. The First ALMA Observation of a Solar Plasmoid Ejection from an X-Ray Bright Point Reviewed International coauthorship International journal

    Masumi Shimojo, Hugh S. Hudson, Stephen M. White, Timothy S. Bastian, Kazumasa Iwai

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 841 ( 1 )   2017.5

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    Eruptive phenomena such as plasmoid ejections or jets are important features of solar activity and have the potential to improve our understanding of the dynamics of the solar atmosphere. Such ejections are often thought to be signatures of the outflows expected in regions of fast magnetic reconnection. The 304 angstrom EUV line of helium, formed at around 10(5) K, is found to be a reliable tracer of such phenomena, but the determination of physical parameters from such observations is not straightforward. We have observed a plasmoid ejection from an X-ray bright point simultaneously at millimeter wavelengths with ALMA, at EUV wavelengths with SDO/AIA, and in soft X-rays with Hinode/XRT. This paper reports the physical parameters of the plasmoid obtained by combining the radio, EUV, and X-ray data. As a result, we conclude that the plasmoid can consist either of (approximately) isothermal similar to 10(5) K plasma that is optically thin at 100 GHz, or a similar to 10(4) K core with a hot envelope. The analysis demonstrates the value of the additional temperature and density constraints that ALMA provides, and future science observations with ALMA will be able to match the spatial resolution of space-borne and other high-resolution telescopes.

    DOI: 10.3847/2041-8213/aa70e3

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  18. The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm Reviewed International coauthorship International journal

    Kazumasa Iwai, Masumi Shimojo, Shinichiro Asayama, Tetsuhiro Minamidani, Stephen White, Timothy Bastian, Masao Saito

    SOLAR PHYSICS   Vol. 292 ( 1 ) page: 22   2017.1

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor-insulator-superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is 7700 +/- 310 K at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations.

    DOI: 10.1007/s11207-016-1044-5

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  19. Microwave observations of a large-scale coronal wave with the Nobeyama radioheliograph Reviewed

    A. Warmuth, K. Shibasaki, K. Iwai, G. Mann

    ASTRONOMY & ASTROPHYSICS   Vol. 593   2016.9

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:EDP SCIENCES S A  

    Context. Large-scale globally propagating waves in the solar corona have been studied extensively, mainly using extreme ultraviolet (EUV) observations. In a few events, corresponding wave signatures have been detected in microwave radioheliograms provided by the Nobeyama radioheliograph (NoRH). Several aspects of these observations seem to contradict the conclusions drawn from EUV observations.
    Aims. We investigate whether the microwave observations of global waves are consistent with previous findings.
    Methods. We revisited the wave of 1997 Sep. 24, which is still the best-defined event in microwaves. We obtained radioheliograms at 17 and 34 GHz from NoRH and studied the morphology, kinematics, perturbation profile evolution, and emission mechanism of the propagating microwave signatures.
    Results. We find that the NoRH wave signatures are morphologically consistent with both the associated coronal wave as observed by SOHO/EIT and the Moreton wave seen in H alpha. The NoRH wave is clearly decelerating, which is typically found for large-amplitude coronal waves associated with Moreton waves, and its kinematical curve is consistent with the EIT wavefronts. The perturbation profile shows a pronounced decrease in amplitude. Based on the derivation of the spectral index of the excess microwave emission, we conclude that the NoRH wave is due to optically thick free-free bremsstrahlung from the chromosphere.
    Conclusions. The wavefronts seen in microwave radioheliograms are chromospheric signatures of coronal waves, and their characteristics support the interpretation of coronal waves as large-amplitude fast-mode MHD waves or shocks.

    DOI: 10.1051/0004-6361/201628591

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  20. CORONAL MAGNETIC FIELDS DERIVED FROM SIMULTANEOUS MICROWAVE AND EUV OBSERVATIONS AND COMPARISON WITH THE POTENTIAL FIELD MODEL Reviewed

    Shun Miyawaki, Kazumasa Iwai, Kiyoto Shibasaki, Daikou Shiota, Satoshi Nozawa

    ASTROPHYSICAL JOURNAL   Vol. 818 ( 1 )   2016.2

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    We estimated the accuracy of coronal magnetic fields derived from radio observations by comparing them to potential field calculations and the differential emission measure measurements using EUV observations. We derived line-of-sight components of the coronal magnetic field from polarization observations of the thermal bremsstrahlung in the NOAA active region 11150, observed around 3:00 UT on 2011 February 3 using the Nobeyama Radioheliograph at 17 GHz. Because the thermal bremsstrahlung intensity at 17 GHz includes both chromospheric and coronal components, we extracted only the coronal component by measuring the coronal emission measure in EUV observations. In addition, we derived only the radio polarization component of the corona by selecting the region of coronal loops and weak magnetic field strength in the chromosphere along the line of sight. The upper limits of the coronal longitudinal magnetic fields were determined as 100-210 G. We also calculated the coronal longitudinal magnetic fields from the potential field extrapolation using the photospheric magnetic field obtained from the Helioseismic and Magnetic Imager. However, the calculated potential fields were certainly smaller than the observed coronal longitudinal magnetic field. This discrepancy between the potential and the observed magnetic field strengths can be explained consistently by two reasons:. (1) the underestimation of the coronal emission measure resulting from the limitation of the temperature range of the EUV observations, and (2) the underestimation of the coronal magnetic field resulting from the potential field assumption.

    DOI: 10.3847/0004-637X/818/1/8

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  21. Chromospheric Sunspots in the Millimeter Range as Observed by the Nobeyama Radioheliograph Reviewed

    Iwai Kazumasa, Koshiishi, Hideki, Shibasaki, Kiyoto, Nozawa, Satoshi, Miyawaki, Shun; Yoneya, Takuro

    The Astrophysical Journal   Vol. 816 ( 2 ) page: 91   2016.1

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    DOI: 10.3847/0004-637X/816/2/91

    arXiv

  22. FREQUENCY DEPENDENCE OF POLARIZATION OF ZEBRA PATTERN IN TYPE-IV SOLAR RADIO BURSTS Reviewed

    Kazutaka Kaneda, H. Misawa, K. Iwai, F. Tsuchiya, T. Obara

    ASTROPHYSICAL JOURNAL LETTERS   Vol. 808 ( 2 )   2015.8

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    We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZPs. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50%-70% right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50-70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double-plasma-resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.

    DOI: 10.1088/2041-8205/808/2/L45

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  23. SOLAR MICRO-TYPE III BURST STORMS AND LONG DIPOLAR MAGNETIC FIELD IN THE OUTER CORONA Reviewed

    A. Morioka, Y. Miyoshi, K. Iwai, Y. Kasaba, S. Masuda, H. Misawa, T. Obara

    ASTROPHYSICAL JOURNAL   Vol. 808 ( 2 )   2015.8

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    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 R-S. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

    DOI: 10.1088/0004-637X/808/2/191

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  24. Observation of Sunspot Brightness Temperature with the Nobeyama 45 m Telescope Reviewed

    Iwai Kazumasa, Shimojo, Masumi

    The Astrophysical Journal   Vol. 804 ( 1 ) page: 48   2015.5

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/0004-637X/804/1/48

    arXiv

  25. Coronal magnetic field and the plasma beta determined from radio and multiple satellite observations Invited Reviewed

    Iwai Kazumasa, Shibasaki, K., Nozawa, S., Takahashi, T., Sawada, S., Kitagawa, J., Miyawaki, S. and Kashiwagi, H.

    Earth Planets and Space   Vol. 66   page: 149   2014.11

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1186/s40623-014-0149-z

    arXiv

  26. Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts Reviewed

    Iwai Kazumasa, Miyoshi, Y., Masuda, S., Tsuchiya, F., Morioka, A., and Misawa, H.

    The Astrophysical Journal   Vol. 789 ( 1 ) page: 4   2014.7

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    DOI: 10.1088/0004-637X/789/1/4

    arXiv

  27. GENERATION MECHANISM OF THE SLOWLY DRIFTING NARROWBAND STRUCTURE IN THE TYPE IV SOLAR RADIO BURSTS OBSERVED BY AMATERAS Reviewed

    Y. Katoh, K. Iwai, Y. Nishimura, A. Kumamoto, H. Misawa, F. Tsuchiya, T. Ono

    ASTROPHYSICAL JOURNAL   Vol. 787 ( 1 )   2014.5

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    We investigate the type IV burst event observed by AMATERAS on 2011 June 7, and reveal that the main component of the burst was emitted from the plasmoid eruption identified in the EUV images of the Solar Dynamics Observatory (SDO)/AIA. We show that a slowly drifting narrowband structure (SDNS) appeared in the burst's spectra. Using statistical analysis, we reveal that the SDNS appeared for a duration of tens to hundreds of milliseconds and had a typical bandwidth of 3 MHz. To explain the mechanism generating the SDNS, we propose wave-wave coupling between Langmuir waves and whistler-mode chorus emissions generated in a post-flare loop, which were inferred from the similarities in the plasma environments of a post-flare loop and the equatorial region of Earth's inner magnetosphere. We assume that a chorus element with a rising tone is generated at the top of a post-flare loop. Using the magnetic field and plasma density models, we quantitatively estimate the expected duration of radio emissions generated from coupling between Langmuir waves and chorus emissions during their propagation in the post-flare loop, and we find that the observed duration and bandwidth properties of the SDNS are consistently explained by the proposed generation mechanism. While observations in the terrestrial magnetosphere show that the chorus emissions are a group of large-amplitude wave elements generated naturally and intermittently, the mechanism proposed in the present study can explain both the intermittency and the frequency drift in the observed spectra.

    DOI: 10.1088/0004-637X/787/1/45

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  28. Measurements of Coronal and Chromospheric Magnetic Fields using Polarization Observations by the Nobeyama Radioheliograph Reviewed

    Iwai Kazumasa, Shibasaki, K.

    Publications of the Astronomical Society of Japan   Vol. 65 ( SP1 ) page: S14   2013.12

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    DOI: 10.1093/pasj/65.sp1.S14

  29. Peak Flux Distributions of Solar Radio Type-I Bursts from Highly Resolved Spectral Observations Reviewed

    Iwai Kazumasa, Masuda, S., Miyoshi, Y.,Tsuchiya, F., Morioka, A., and Misawa, H.

    The Astrophysical Journal Letters   Vol. 768   page: L2   2013.5

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    DOI: 10.1088/2041-8205/768/1/L2

  30. Solar Radio Type-I Noise Storm Modulated by Coronal Mass Ejections Reviewed

    Iwai Kazumasa, Miyoshi, Y., Masuda, S., Shimojo, M., Shiota, D., Inoue, S., Tsuchiya, F., Morioka, A., and Misawa, H.

    The Astrophysical Journal   Vol. 744 ( 2 ) page: 167   2012.1

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/0004-637X/744/2/167

  31. IPRT/AMATERAS: A New Metric Spectrum Observation System for Solar Radio Bursts Reviewed

    Iwai Kazumasa, Tsuchiya, F. Morioka, A. and Misawa, H.

    Solar Physics   Vol. 277 ( 2 ) page: 447–457   2012.1

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    DOI: 10.1007/s11207-011-9919-y

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MISC 7

  1. Database of Solar Radio Bursts Observed by Solar Radio Spectro-polarimeter AMATERAS Reviewed

    Tsuchiya, F, H. Misawa, T. Obara, K. Iwai, K. Kaneda, S. Matsumoto, A. Kumamoto, Y. Katoh, M. Yagi, B. Cecconi

    Planetary Radio Emission 8     page: 445 - 453   2017

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    Language:English   Publishing type:Article, review, commentary, editorial, etc. (international conference proceedings)  

    DOI: 10.1553/PRE8s445

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  2. An FFT Circuit for a Spectrometer of a Radio Telescope using the Nested RNS including the Constant Division. Reviewed

    Hiroki Nakahara,Hiroyuki Nakanishi,Kazumasa Iwai,Tsutomu Sasao

    SIGARCH Computer Architecture News   Vol. 44 ( 4 ) page: 44-49   2016

  3. An FFT Circuit Using Nested RNS in a Digital Spectrometer for a Radio Telescope Reviewed

    2016 IEEE 46TH INTERNATIONAL SYMPOSIUM ON MULTIPLE-VALUED LOGIC (ISMVL 2016)     page: 60-65   2016

  4. An RNS FFT Circuit Using LUT Cascades Based on a Modulo EVMDD. Reviewed

    Hiroki Nakahara,Tsutomu Sasao,Hiroyuki Nakanishi,Kazumasa Iwai

    2015 IEEE International Symposium on Multiple-Valued Logic, Waterloo, ON, Canada, May 18-20, 2015     page: 97-102   2015

  5. An AWF Digital Spectrometer for a Radio Telescope Reviewed

    Nakahara Hiroki, Nakanishi Hiroyuki, Iwai Kazumasa

    2014 INTERNATIONAL CONFERENCE ON RECONFIGURABLE COMPUTING AND FPGAS (RECONFIG)     2014

  6. A HIGH-SPEED FFT BASED ON A SIX-STEP ALGORITHM: APPLIED TO A RADIO TELESCOPE FOR A SOLAR RADIO BURST Reviewed

    Nakahara Hiroki, Iwai Kazumasa, Nakanishi Hiroyuki

    PROCEEDINGS OF THE 2013 INTERNATIONAL CONFERENCE ON FIELD-PROGRAMMABLE TECHNOLOGY (FPT)     page: 430-433   2013

  7. Survey of Accelerated Particles in a Solar Active Region Using Hinode/XRT and Ground-Based Type-I Radio Burst Observations

    Kazumasa Iwai, Hiroaki Misawa, Fuminori Tsuchiya, Akira Morioka, Satoshi Masuda, Yoshizumi Miyoshi

    HINODE-3: THE 3RD HINODE SCIENCE MEETING   Vol. 454   page: 249 - 252   2012

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    The relationships between solar radio type-I bursts and soft X-ray activities were investigated using Hinode/XRT and a ground-based radio telescope belonging to Tohoku University. Although a type-I burst is thought to be generated by high energy non-thermal electrons in the solar corona, the counterpart of this radio burst in X-rays or EUV have yet to be identified. In this study, we found some small scale soft X-ray activities on the XRT images around the onset time of the type-I burst when 10 percent of the soft X-ray flux enhancement around the onset time of the radio burst is defined as a burst-related activity. However, the causal relationship between the observed soft X-ray activities and the onset of the type-I burst are unclear, and more simultaneous observations of radio bursts and X-rays are needed to investigate the coronal counterpart of the type-I burst.

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Research Project for Joint Research, Competitive Funding, etc. 1

  1. Studies on solar storms by developing multi directional radio observation instruments

    2020.10

    DAIKO FOUNDATION 

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\4000000 ( Direct Cost: \4000000 )

KAKENHI (Grants-in-Aid for Scientific Research) 6

  1. Forecasting of space disasters using advanced ICT: Challenge to the speace meteorological radar

    Grant number:19K22028  2019.6

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)  Grant-in-Aid for Challenging Research (Exploratory)

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\6370000 ( Direct Cost: \4900000 、 Indirect Cost:\1470000 )

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  2. Investigation of solar storm propagation processes by development of next generation phased array radio telescope

    Grant number:18H01266  2018.4

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\17420000 ( Direct Cost: \13400000 、 Indirect Cost:\4020000 )

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  3. Construction of data-assimilation type solar storm arrival prediction model using radio observations

    Grant number:18H04442  2018.4 - 2020.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

    Kazumasa Iwai

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

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  4. Study of fine spectral structures of solar radio burst by developing a super high-speed digital spectrometer

    Grant number:16K17813  2016.4 - 2019.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)  Grant-in-Aid for Young Scientists (B)

    Iwai Kazumasa

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

    We have developed a digital fast Fourier transform spectrometer made of an analog-to-digital converter (ADC) and a field-programmable gate array (FPGA). High time and spectral resolutions, highly stable spectroscopy, and a wide dynamic range of the spectrometers were demonstrated in a series of laboratory experiments. The developed digital spectrometers were installed in the solar radio telescope of NICT. We detected many fine spectral structures of solar radio bursts from the test observations. These results are summarized in a paper published by the peer-refereed journal.

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  5. 電波観測を用いたリアルタイム宇宙天気予報システムの構築

    Grant number:15J09524  2015.4 - 2017.3

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    岩井 一正

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    太陽の大気コロナでは、フレアに代表される爆発現象や、コロナ質量放出(以下CME)と呼ばれるプラズマ雲の放出現象が発生する。その過程では、強い電波放射(太陽電波バースト)が発生する。粒子の伝搬速度よりも電波の伝搬速度は速いため、電波バーストの検出は宇宙天気災害の有効な予報手段となる。
    山川望遠鏡は受け入れ研究機関であるNICTが新たに開発した太陽電波望遠鏡である。観測周波数帯域は70MHz - 9GHzであり、フレアに起因する太陽電波バーストの発生周波数帯域をほぼ全てカバーできる。本望遠鏡にはFPGAを用いた最新鋭のデジタル分光計OCTAD-Sが搭載され、観測する全帯域で8msの時間分解能で連続観測が可能である。本年度はこの新型分光計の性能評価および査読論文への投稿を行った。論文は現在査読中である。論文化と並行して山川望遠鏡を用いた太陽電波バーストの定常観測を行った。その結果、多数の電波バーストの受信に成功した。特に2016年4月18日に発生した太陽フレアに伴う電波バーストは、NICTが毎日行っている宇宙天気予報の直前に発生した。そのため関連する太陽フレアによって発生した高エネルギー粒子の地球への到来を、電波バーストの情報から到来前に予測し、予報発令に反映させることに成功した。この予報成功は本研究の重要な目的の達成を意味する。今後は電波バーストの自動認識システムを付加することで、粒子の到来前予測の例を増やすことが課題である。
    この他、山川望遠鏡と相補的な情報が得られるミリ波・サブミリ波の太陽観測を実現するために野辺山45m望遠鏡による太陽観測実験を行い、高度高度な較正手法を開発した。この技術を応用して日米欧の国際協力で建設された大型ミリ波・サブミリ波電波干渉計ALMAによる太陽観測国際チームに参画し、ALMAを用いた世界初の太陽観測実験を成功させることに大きく貢献した。

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  6. 太陽電波Type-Iに関する粒子加速過程の研究

    Grant number:09J03264  2009 - 2011

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    岩井 一正

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    太陽から最も頻繁に放射される電波バーストの一つにType-Iがある。この現象は他の太陽電波現象に比べて強度の弱い太陽電波現象である。Type-Iはコロナ中で高エネルギーに加速された電子から放射されると考えられているが、その電子を高エネルギーに加速する過程はいまだ明らかになっていない。これら高エネルギー粒子の生成過程は、太陽コロナの物理を議論する上で極めて重要であるとともに、未知の加速課程の発見につながる可能性がある。そこで本研究では微弱な太陽電波バーストType-Iを発生させる高エネルギー電子の加速過程を解明することを目的とし、地上電波観測を中心とした研究活動を行ってきた。その結果、本年度に以下の成果が得られた。
    1:観測システムの連続運用・データアーカイブ化
    本研究では微弱な電波強度で微細なスペクトル構造を伴い放射されるType-Iバーストを効果的に観測するための電波観測装置(IPRT/mmTERAS)を開発した。連続運用フェーズに移行した本年度は、全自動運用システムの開発・観測データのアーカイブ化・データ公開システムの構築と装置論文の執筆を行った。その結果、全自動での運用およびデータアーカイブ化に成功した。また観測データは観測日中にWebから公開することが可能となった。
    2:超微細Type-Iバーストの発見
    Type-Iには継続時間1秒未満の微細なスペクトル構造が多数含まれていることが知られている。本研究ではType-Iの微細なスペクトル構造に注目し、Type-Iの高分解スペクトル観測を行い、そのデータの解析を行った。その結果Type-Iには今まで連続成分とみなされた電波成分にも多量の微細バーストが含まれていることを発見した。加えてType-Iバースト成分の統計的特徴に注目し、電波強度の発生頻度解析を行った。その結果、バースト成分の電波強度は幕状分布し、その指数は-2から-3と通常のType-III電波バーストやフレア現象よりスペクトルが急峻であることが示唆された。

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Teaching Experience (On-campus) 3

  1. 物理学実験

    2019

  2. Space-Earth Radio Science

    2019

  3. 先端物理学特論

    2019

Teaching Experience (Off-campus) 3

  1. 物理学実験

    2019 名古屋大学 理学部)

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  2. Space-Earth Radio Science

    2018 Nagoya University)

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  3. 先端物理学特論

    2017 名古屋大学 理学部)

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