Updated on 2022/03/24

写真a

 
FUJIKI, Ken'ichi
 
Organization
Institute for Space-Earth Environmental Research Division for Heliospheric Research Assistant Professor
Graduate School
Graduate School of Science
Title
Assistant Professor
Contact information
メールアドレス

Degree 1

  1. Ph.D.

Research Areas 2

  1. Others / Others  / Space Physics

  2. Others / Others  / Solar Physics

Current Research Project and SDGs 2

  1. Global Structure of Solar Wind Speed

  2. Development of Large UHF Antenna for IPS Observation

Research History 1

  1. Nagoya University   Institute for Space-Earth Environmental Research Division for Heliospheric Research   Assistant Professor

    2015.10

Education 1

  1. The Graduate University for Advanced Studies   Graduate School, Division of Mathematical and Physical Science

    1994.4 - 1997.9

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    Country: Japan

Professional Memberships 6

  1. 地球電磁気・地球惑星圏学会

  2. 日本物理学会

  3. 日本天文学会

  4. 日本物理学会

  5. 日本天文学会

  6. 地球電磁気・地球惑星圏学会

▼display all

 

Papers 90

  1. A Study of an Equatorial Coronal Hole Observed at the First Parker Solar Probe Perihelion Reviewed

    Karna Nishu, Berger Mitchell A., Asgari-Targhi Mahboubeh, Paulson Kristoff, Fujiki Ken'ichi

    ASTROPHYSICAL JOURNAL   Vol. 925 ( 1 )   2022.1

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

    DOI: 10.3847/1538-4357/ac3c46

    Web of Science

  2. Global Distribution of the Solar Wind Speed Reconstructed from Improved Tomographic Analysis of Interplanetary Scintillation Observations between 1985 and 2019 Reviewed

    Tokumaru Munetoshi, Fujiki Ken'ichi, Kojima Masayoshi, Iwai Kazumasa

    ASTROPHYSICAL JOURNAL   Vol. 922 ( 1 )   2021.11

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

    DOI: 10.3847/1538-4357/ac1862

    Web of Science

  3. 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:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1007/s11207-019-1487-6

    Web of Science

  4. 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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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1186/s40623-019-1019-5

    Web of Science

  5. Rarefaction of the Very Slow (<350 km/s) Solar Wind in Cycle 24 Compared With Cycle 23 Reviewed

    Munetoshi Tokumaru, Tomoya Shimoyama, Ken'ichi Fujiki, Kazuyuki Hakamada

    Journal of Geophysical Research: Space Physics   Vol. 123 ( 4 ) page: 2520 - 2534   2018.4

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Blackwell Publishing Ltd  

    We investigate long-term variation of the very slow solar wind (VSSW), whose speed is less than 350 km/s, during the period between 1997 and 2015, that is, Cycles 23 and 24, using interplanetary scintillation measurements, which enable determination of the global distribution of the flow speed and the electron density fluctuation level ΔNe. We find that the occurrence rate of VSSW increases in the maximum phase of the solar cycle, and it was mostly associated with high ΔNe in Cycle 23. However, the VSSW is found to be more associated with low ΔNe in Cycle 24. This fact is consistent with an increased occurrence of the low-density VSSW observed in situ in Cycle 24. These facts, which are considered to be a manifestation of weak solar activity in this cycle, suggest that the VSSW has become significantly rarefied in recent years. We identify the source region of the VSSW on the photosphere using a potential field analysis and examine the magnetic field properties of the VSSW source. We find that the low-ΔNe VSSW is associated with a smaller expansion factor and possibly a slightly weaker photospheric field strength than the high-ΔNe VSSW. The results obtained here may suggest that more open magnetic field areas producing the VSSW in Cycle 24 are formed in the quiet Sun region, which is associated with a lower mass flux supply into the corona, than those in Cycle 23.

    DOI: 10.1002/2017JA025014

    Web of Science

    Scopus

  6. High-latitude Conic Current Sheets in the Solar Wind Reviewed

    Olga V. Khabarova, Helmi V. Malova, Roman A. Kislov, Lev M. Zelenyi, Vladimir N. Obridko, Alexander F. Kharshiladze, Munetoshi Tokumaru, Justyna M. Sokol, Stan Grzedzielski, Ken'ichi Fujiki

    ASTROPHYSICAL JOURNAL   Vol. 836 ( 1 )   2017.2

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

    We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2-3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of coniclike magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

    DOI: 10.3847/1538-4357/836/1/108

    Web of Science

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

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

    EARTH PLANETS AND SPACE   Vol. 73 ( 1 )   2021.1

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1186/s40623-020-01345-5

    Web of Science

  8. A Daily Determination of B-Z Using the Russell-McPherron Effect to Forecast Geomagnetic Activity Reviewed

    Jackson B. V, Yu H-S, Buffington A., Hicks P. P., Tokumaru M., Fujiki K., Kim J., Yun J.

    SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS   Vol. 17 ( 4 ) page: 639 - 652   2019.4

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1029/2018SW002098

    Web of Science

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

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

    Solar Physics     2019.3

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

    DOI: https://doi.org/10.1007/s11207-019-1418-6

    arXiv

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

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

    Solar Physics   Vol. 294 ( 3 )   2019.3

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1007/s11207-019-1418-6

    Web of Science

    arXiv

  11. Solar cycle 24: An unusual polar field reversal Reviewed

    Janardhan, P, Fujiki, K, Ingale, M, Bisoi, S.~K, Rout, D

    Astronomy and Astrophysics   Vol. 618   2018.8

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

    DOI: 10.1051/0004-6361/201832981

  12. Relation Between Coronal Hole Areas and Solar Wind Speeds Derived from Interplanetary Scintillation Measurements

    Munetoshi Tokumaru, Daiki Satonaka, Ken'ichi Fujiki, Keiji Hayashi, Kazuyuki Hakamada

    SOLAR PHYSICS   Vol. 292 ( 3 )   2017.3

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

    We investigate the relation between coronal hole (CH) areas and solar wind speeds during 1995 - 2011 using the potential field (PF) model analysis of magnetograph observations and interplanetary scintillation (IPS) observations by the Institute for Space-Earth Environmental Research (formerly Solar-Terrestrial Environment Laboratory) of Nagoya University. We obtained a significant positive correlation between the CH areas (A) derived from the PF model calculations and solar wind speeds (V) derived from the IPS observations. The correlation coefficients between them are usually high, but they drop significantly in solar maxima. The slopes of the A-V relation are roughly constant except for the period around solar maximum, when flatter or steeper slopes are observed. The excursion of the correlation coefficients and slopes at solar maxima is ascribed partly to the effect of rapid structural changes in the coronal magnetic field and solar wind, and partly to the predominance of small CHs. It is also demonstrated that V is inversely related to the flux expansion factor (f) and that f is closely related to A(-1/2); hence, V alpha A(1/2). A better correlation coefficient is obtained from the A(1/2) - V relation, and this fact is useful for improving space weather predictions. We compare the CH areas derived from the PF model calculations with He I 1083 nm observations and show that the PF model calculations provide reliable estimates of the CH area, particularly for large A.

    DOI: 10.1007/s11207-017-1066-7

    Web of Science

  13. LONG-TERM TREND OF SOLAR CORONAL HOLE DISTRIBUTION FROM 1975 TO 2014 Reviewed

    K. Fujiki, M. Tokumaru, K. Hayashi, D. Satonaka, K. Hakamada

    Astrophysical Journal Letter   Vol. 827   page: 41-45   2016.8

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    We developed an automated prediction technique for coronal holes using potential magnetic field extrapolation in the solar corona to construct a database of coronal holes appearing from 1975 February to 2015 July (Carrington rotations from 1625 to 2165). Coronal holes are labeled with the location, size, and average magnetic field of each coronal hole on the photosphere and source surface. As a result, we identified 3335 coronal holes and found that the long-term distribution of coronal holes shows a similar pattern known as the magnetic butterfly diagram, and polar/low-latitude coronal holes tend to decrease/increase in the last solar minimum relative to the previous two minima.

  14. A Prolonged Southward IMF-Bz Event of May 02-04, 1998: Solar, Interplanetary Causes and Geomagnetic Consequences Reviewed

    Bisoi, Susanta Kumar, Chakrabarty, D., Janardhan, P., Rastogi, R. G., Yoshikawa, A., Fujiki, K., Tokumaru, M., Yan, Y.

    Journal of Geophisical Research (space)     page: in press   2016

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  15. Relationship Between Solar-Wind Speed and Coronal Magnetic-Field Properties Reviewed

    K. Fujiki, M. Tokumaru, T. Iju, K. Hakamada, M. Kojima

    Solar Physics   Vol. 290   page: 2491-2505   2015.9

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

    DOI: 10.1007/s11207-015-0742-8

  16. A 20 year decline in solar photospheric magnetic fields: Inner-heliospheric signatures and possible implications

    Janardhan, P., Bisoi, Susanta Kumar, Ananthakrishnan, S., Tokumaru, M., Fujiki, K., Jose, L., Sridharan, R.

    Journal of Geophysical Research: Space Physics   Vol. 120 ( 7 ) page: 5306-5317   2015.7

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

    DOI: 10.1002/2015JA021123

  17. North-south asymmetry in global distribution of the solar wind speed during 1985-2013

    Tokumaru, Munetoshi; Fujiki, Ken'ichi; Iju, Tomoya

    Journal of Geophysical Research: Space Physics   Vol. 120 ( 5 ) page: 3283-3296   2015.5

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  18. A Study of Density Modulation Index in the Inner Heliospheric Solar Wind during Solar Cycle 23 Reviewed

    Bisoi, S.K.; Janardhan, P.; Ingale, M.; Subramanian, P.; Ananthakrishnan, S.; Tokumaru, M.; Fujiki, K.

    Astrophysical Journal   Vol. 795   page: 69   2014.11

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

    DOI: 10.1088/0004-637X/795/1/69

  19. Kinematic Properties of Slow ICMEs and an Interpretation of a Modified Drag Equation for Fast and Moderate ICMEs Reviewed

    Iju, T.; Tokumaru, M.; Fujiki, K.

    Solar Physics   Vol. 289   page: 2157-2175   2014.6

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

    DOI: 10.1007/s11207-014-0472-3

  20. MHD analysis of the velocity oscillations in the outer heliosphere Reviewed

    Fujiki, K. ; Washimi, H.; Hayashi, K.; Zank, G.P.; Tokumaru, M.; Tanaka, T.; Florinski, V.; Kubo, Y.

    Geophysical Research Letter   Vol. 41   page: 1420-1424   2014.3

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    DOI: 10.1002/2014GL059391

  21. Radial Speed Evolution of Interplanetary Coronal Mass Ejections During Solar Cycle 23 Reviewed

    Iju, T.; Tokumaru, M.; Fujiki, K.

    Solar Physics   Vol. 288 ( 1 ) page: 331-353   2013.11

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

    DOI: 10.1007/s11207-013-0297-5

  22. Heliolatitude and Time Variations of Solar Wind Structure from in situ Measurements and Interplanetary Scintillation Observations Reviewed

    Sokół, J. M.; Bzowski, M.; Tokumaru, M.; Fujiki, K.; McComas, D. J.

    Solar Physics   Vol. 285 ( 1-2 ) page: 167-200   2013.7

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

    DOI: 10.1007/s11207-012-9993-9

  23. Kinematics of interplanetary coronal mass ejections in the inner heliosphere Reviewed

    Iju, Tomoya; Tokumaru, Munetoshi; Fujiki, Ken'ichi

    SOLAR WIND 13: Proceedings of the Thirteenth International Solar Wind Conference. AIP Conference Proceedings   Vol. 1539   page: 183-186   2013.6

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

    DOI: 10.1063/1.4811018

  24. Evolution of global distribution of the solar wind from cycle 23 to the early phase of cycle 24 Reviewed

    Tokumaru, Munetoshi; Fujiki, Ken'ichi; Kojima, Masayoshi

    SOLAR WIND 13: Proceedings of the Thirteenth International Solar Wind Conference. AIP Conference Proceedings   Vol. 1539   page: 275-278   2013.6

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

    DOI: 10.1063/1.4811041

  25. Scintillation Measurements of the Solar Wind Velocity in Strong Scattering near the Sun

    M. Kojima, W. A. Coles, M. Tokumaru, K. Fujiki

    Solar Physics   Vol. 283 ( 2 ) page: 519-540   2013.1

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

    DOI: 10.1007/s11207-012-0207-2

  26. The First Three Years of IBEX Observations and Our Evolving Heliosphere Reviewed

    D. J. McComas, M. A. Dayeh, F. Allegrini, M. Bzowski, R. DeMajistre, K. Fujiki, H. O. Funsten, S. A. Fuselier, M. Gruntman, P. H. Janzen, M. A. Kubiak, H. Kucharek, G. Livadiotis, E. Möbius, D. B. Reisenfeld, M. Reno, N. A. Schwadron, J. M. Sokół, and M. Tokumaru

    The Astrophysical Journal Supplement Series   Vol. 203 ( 1 )   2012.10

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    DOI: doi:10.1088/0067-0049/203/1/1

  27. Global Observations of Evolving 3D Solar Wind Structure Reviewed

    Tokumaru, M.; Fujiki, K.; Itoh, H.; Iju, T.; Kojima, M.

    Hinode-3: The 3rd Hinode Science Meeting, Proceedings of the conference held 1-4 December 2009 at Hitotsubashi Memorial Hall, Tokyo, Japan. Edited by T. Sekii, T. Watanabe, and T. Sakurai. ASP Conference Series   Vol. 454   page: 413   2012.8

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  28. Long-term evolution in the global distribution of solar wind speed and density fluctuations during 1997-2009 Reviewed

    Tokumaru, Munetoshi; Kojima, Masayoshi; Fujiki, Ken'ichi

    Journal of Geophysical Research   Vol. 117 ( A6 )   2012.6

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

    DOI: 10.1029/2011JA017379

  29. Heliolatitude and Time Variations of Solar Wind Structure from in situ Measurements and Interplanetary Scintillation Observations Reviewed

    Sokół, J. M.; Bzowski, M.; Tokumaru, M.; Fujiki, K.; McComas, D. J.

    Solar Physics     2012.5

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    DOI: 10.1007/s11207-012-9993-9

  30. Solar wind evolution since 1990 and H ENA ionization rates and survival probabilities in the heliosphere Reviewed

    Sokol, J. M.; Kubiak, M. A.; Bzowski, M.; Tokumaru, M.; Fujiki, K.; McComas, D. J.; Bochsler, P.

    EGU General Assembly 2012, held 22-27 April, 2012 in Vienna, Austria     page: 4723   2012.4

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  31. Two-Station Interplanetary Scintillation Measurements of Solar Wind Speed near the Sun Using the X-band Radio Signal of the Nozomi Spacecraft Reviewed

    Tokumaru, M.; Fujimaki, S.; Higashiyama, M.; Yokobe, A.; Ohmi, T.; Fujiki, K.; Kojima, M.

    Solar Physics   Vol. 276   page: 315-336   2012.2

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

    DOI: 10.1007/s11207-011-9864-9

  32. Solar parameters for modeling interplanetary background Reviewed

    Bzowski, M.; Sokol, J. M.; Tokumaru, M.; Fujiki, K.; Quemerais, E.; Lallement, R.; Ferron, S.; Bochsler, P.; McComas, D. J.

    ISSI Scientific Report No 12   Vol. 12   2011.12

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    DOI: 2011arXiv1112.2967B

  33. The prelude to the deep minimum between solar cycles 23 and 24: Interplanetary scintillation signatures in the inner heliosphere Reviewed

    Janardhan, P.; Bisoi, Susanta Kumar; Ananthakrishnan, S.; Tokumaru, M.; Fujiki, K.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38   2011.10

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    DOI: doi:10.1029/2011GL049227

  34. Three-Dimensional Solar Wind Structures Obtained with MHD Simulation Model Using Observation-Based Time-Varying Inner Boundary Map Reviewed

    Hayashi, K.; Tokumaru, M.; Fujiki, K.; Kojima, M.

    5th International Conference of Numerical Modeling of Space Plasma Flows (ASTRONUM 2010)   Vol. 444   page: 111   2011.10

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  35. Two-Station Interplanetary Scintillation Measurements of Solar Wind Speed near the Sun Using the X-band Radio Signal of the Nozomi Spacecraft Reviewed

    M. Tokumaru, S. Fujimaki, M. Higashiyama, A. Yokobe, T. Ohmi, K. Fujiki and M. Kojima

    SOLAR PHYSICS     2011.8

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    DOI: DOI: 10.1007/s11207-011-9864-9

  36. Solar Mass Ejection Imager (SMEI) 3-D reconstruction of density enhancements behind interplanetary shocks: In-situ comparison near Earth and at STEREO Reviewed

    Jackson, B. V.; Hamilton, M. S.; Hick, P. P.; Buffington, A.; Bisi, M. M.; Clover, J. M.; Tokumaru, M.; Fujiki, K.

    Journal of Atmospheric and Solar-Terrestrial Physics   Vol. 73 ( 11-12 ) page: 1317-1329   2011.7

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    DOI: doi:10.1016/j.jastp.2010.11.023

  37. Three-dimensional reconstruction of heliospheric structure using iterative tomography: A review Reviewed

    Jackson, B. V.; Hick, P. P.; Buffington, A.; Bisi, M. M.; Clover, J. M.; Tokumaru, M.; Kojima, M.; Fujiki, K.

    Journal of Atmospheric and Solar-Terrestrial Physics   Vol. 73 ( 10 ) page: 1214-1227   2011.6

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    DOI: doi:10.1016/j.jastp.2010.10.007

  38. Three-dimensional Reconstructions and Mass Determination of the 2008 June 2 LASCO Coronal Mass Ejection Using STELab Interplanetary Scintillation Observations Reviewed

    Bisi, M. M.; Jackson, B. V.; Hick, P. P.; Buffington, A.; Clover, J. M.; Tokumaru, M.; Fujiki, K.

    The Astrophysical Journal Letters   Vol. 715 ( 2 ) page: L104-L108   2010.6

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  39. Solar cycle evolution of the solar wind speed distribution from 1985 to 2008 Reviewed

    Tokumaru, Munetoshi; Kojima, Masayoshi; Fujiki, Ken'ichi

    Journal of Geophysical Research   Vol. 115 ( A4 ) page: CiteID A04102   2010.4

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  40. Solar Wind Forecast by Using Interplanetary Scintillation Observations Reviewed

    Fujiki, K., Ito, H, Tokumaru, M.

    TWELFTH INTERNATIONAL SOLAR WIND CONFERENCE. AIP Conference Proceedings   Vol. 1216   page: 663-666   2010.3

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  41. Is the Polar Region Different from the Quiet Region of the Sun? Reviewed

    Ito, Hiroaki; Tsuneta, Saku; Shiota, Daikou; Tokumaru, Munetoshi; Fujiki, Ken'ichi

    TWELFTH INTERNATIONAL SOLAR WIND CONFERENCE. AIP Conference Proceedings   Vol. 1216   page: 88-89   2010.3

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  42. Large-Scale Heliospheric Structure during Solar-Minimum Conditions using a 3D Time-Dependent Reconstruction Solar-Wind Model and STELab IPS Observations Reviewed

    Bisi, M. M.; Jackson, B. V.; Hick, P. P.; Clover, J. M.; Hamilton, S.; Tokumaru, M.; Fujiki, K.

    TWELFTH INTERNATIONAL SOLAR WIND CONFERENCE. AIP Conference Proceedings   Vol. 1216   page: 355-358   2010.3

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  43. 3D Reconstruction of Density Enhancements Behind Interplanetary Shocks from Solar Mass Ejection Imager White-Light Observations Reviewed

    Jackson, B. V.; Hick, P. P.; Buffington, A.; Bisi, M. M.; Clover, J. M.; Hamilton, M. S.; Tokumaru, M.; Fujiki, K.

    TWELFTH INTERNATIONAL SOLAR WIND CONFERENCE. AIP Conference Proceedings   Vol. 1216   page: 659-662   2010.3

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  44. Evolution of the anemone AR NOAA 10798 and the related geo-effective flares and CMEs Reviewed

    Asai, Ayumi; Shibata, Kazunari; Ishii, Takako T.; Oka, Mitsuo; Kataoka, Ryuho; Fujiki, Ken'ichi; Gopalswamy, Nat

    Journal of Geophysical Research   Vol. 114 ( A12 ) page: CiteID A00A21   2010.2

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  45. From the Sun to the Earth: The 13 May 2005 Coronal Mass Ejection Reviewed

    Bisi, M. M.; Breen, A. R.; Jackson, B. V.; Fallows, R. A.; Walsh, A. P.; Mikić, Z.; Riley, P.; Owen, C. J.; Gonzalez-Esparza, A.; Aguilar-Rodriguez, E.; Morgan, H.; Jensen, E. A.; Wood, A. G.; Owens, M. J.; Tokumaru, M.; Manoharan, P. K.; Chashei, I. V.; Giunta, A. S.; Linker, J. A.; Shishov, V. I.; Tyul'Bashev, S. A.; Agalya, G.; Glubokova, S. K.; Hamilton, M. S.; Fujiki, K.; Hick, P. P.; Clover, J. M.; Pintér, B.

    Solar Physics   Vol. 265 ( 1-2 ) page: 49-127   2010

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  46. Is the Polar Region Different from the Quiet Region of the Sun? Reviewed

    Ito, Hiroaki; Tsuneta, Saku; Shiota, Daikou; Tokumaru, Munetoshi; Fujiki, Ken'ichi

    The Astrophysical Journal   Vol. 719 ( 1 ) page: 131-142   2010

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  47. Relation between loop-shaped interplanetary disturbances and the magnetic flux rope Reviewed

    Tokumaru, M., M. Kojima, K. Fujiki, K. Munakata, T. Kuwabara, and K. Marubashi

    Advances in Geoscience (World Scientific Publishing Co., USA)   Vol. 3   page: in press   2009

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  48. Non-dipolar solar wind structure observed in the cycle 23/24 minimum Reviewed

    Tokumaru, M., Kojima, M., Fujiki, K., Hayashi, K.

    Geophysical Research Letters   Vol. 36 ( p ) page: CiteID L09101   2009

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  49. Interplanetary scintillation observations of the solar wind for space weather modeling Reviewed

    Tokumaru, M., M. Kojima, and K. Fujiki

    Space Technology Japan   Vol. 8   page: in press   2009

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  50. Origins and properties of the quasi-stationary slow solar wind Reviewed

    Eselevich, M. V., Eselevich, V. G., Fujiki, K.

    Astronomy Reports   Vol. 52 ( 7 ) page: 576-589   2008

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  51. A solar neutron telescope in Tibet and its capability examined by the 1998 November 28th event Reviewed

    Y. Murakia, H. Tsuchiya, K. Fujiki, S. Masuda, Y. Matsubara, H. Menjyo, T. Sako, K. Watanabe, M. Ohnishi, A. Shiomi, M. Takita, T. Yuda, Y. Katayose, N. Hotta, S. Ozawa, T. Sakurai, Y.H. Tan and J.L. Zhang

    Astroparticle Physics   Vol. 28 ( 1 ) page: 119-131   2007.9

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    A new solar neutron telescope has been constructed at Yangbajing, Tibet (600 g/cm2) and has been successfully operated for 8 years. During this time several interesting events were observed in coincidence with large solar flares. In this paper the authors discuss a directional count rate enhancement 1998 November 28 as to whether it is related to solar phenomena or not. We use this event to evaluate the sensitivity of the solar neutron telescope and discuss the detection limit for solar neutrons and high energy solar protons of this detector.

  52. *What coronal parameters determine solar wind speed? Reviewed

    Kojima, M., M. Tokumaru, K. Fujiki, H. Itoh, T. Murakami, and K. Hakamada

    New Solar Physics with Solar-B Mission", ASP Conference Series,eds K. Shibata, S. Nagata, and T. Sakurai   Vol. 369   page: 549-555   2007

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    It is crucially important for modeling solar wind acceleration to find universal physical parameters which can determine velocities of all kinds of solar wind from various sources such as slow wind from a helmet streamer, slow wind from an equatorial small coronal hole, the fast wind from a polar coronal hole. One of the parameters is the coronal hole scale size. A large-scale polar coronal hole is a source of fast solar wind, and medium and slow speed streams originate in smaller coronal holes. Nolte et al. (1976) obtained a linear correlation between the solar wind speed and coronal hole scale size for equatorial coronal holes. Kojima et al. (2004) analyzed the dependence of the solar wind speed on the scale size of high latitude coronal holes and reported that the speed was independent of the scale size if it was larger than 5X1010 km2. Another property is a flux expansion rate (f), which has a good inverse relation with solar wind velocity (Wang and Sheeley, 1990), and the third parameter is the magnetic field (B) energy released by reconnection at the lower corona (Fisk et al., 1999).
    We have studied physical conditions of coronal magnetic field which determine solar wind velocity using an interplanetary scintillation method which can observe the solar wind at all latitudinal ranges. From studies in the solar minimum phase we found that the ratio of two parameters of B and f has a considerably higher correlation with the solar wind velocity than an individual parameter of f and B. This work gives the crucially important constraints for the solar wind acceleration models.

  53. IPS tomographic observations of 3D solar wind structure Reviewed

    Kojima, M., M. Tokumaru, K. Fujiki, K. Hayashi, and B. V. Jackson

    Astronomical and Astrophysical Transactions   Vol. 26   page: 467-476   2007

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  54. The source and propagation of the interplanetary disturbance associated with the full-halo coronal mass ejection on 28 October 2003 Reviewed

    Tokumaru, M., M. Kojima, K. Fujiki, M. Yamashita, and B. V. Jackson

      Vol. (10.1029/ 2006JA012043)   2007

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  55. Streamer belt and chains as the main sources of quasi-stationary slow solar wind Reviewed

    Eselevich, M., V. Eselevich, and K. Fujiki

    Solar Physics   Vol. 240 ( 135-151 )   2007

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    It has been known that periods of the low geomagnetic activity in near-earth environment coincide with arrival time of the “slow" solar wind (SW) at Earth's orbit. In this connection, sources of the “slow" SW on the Sun are significant issue in the space weather problem. In this work synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from interplanetary scintillation were studied. Regions with velocity V ≈ 300-450 km s-1 and increased density N > 10 cm-3, typical of the “slow" solar wind originating from the belt and chains of streamers, are shown to exist at Earth's orbit, between the fast solar wind flows (with a maximum velocity Vmax ≈ 450-800 km s-1). The belt and chains of streamers are the main sources of the “slow" solar wind. As the sources of “slow" solar wind, the contribution from the chains of streamers may be comparable to that from the streamer belt.

  56. Tracking heliospheric disturbances by interplanetary scintillation Reviewed

    Tokumaru, M., M. Kojima, K. Fujiki, and M. Yamashita

    Nonlin. Processes Geophys.   Vol. 13   page: 329-338   2006

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  57. Reconstructed global feature of interplanetary disturbance for the full-halo coronal mass ejection event on 1999 September 20 Reviewed

    Tokumaru, M., M. Yamashita, M. Kojima, K. Fujiki, and T. Nakagawa

    Adv. Space Res.   Vol. 38   page: 547-551   2006

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  58. Interplanetary consequences caused by the extremely intense solar activity during October-November 2003 Reviewed

    Tokumaru, M., M. Kojima, K. Fujiki, M. Yamashita

    J. Geophys. Res.   Vol. in press   page: doi:10.1029/2004JA010656   2005

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  59. *Relation between solar wind velocity and properties of its source region Invited Reviewed

    Fujiki, K., M. Hirano, M. Kojima, M. Tokumaru, D. Baba, M., Yamashita, K. Hakamada

    Advances in Space Research   Vol. 2005   page: doi:10.1016/i.asr.2005.05.057   2005

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    Different kinds of coronal holes are sources of different kind of solar winds. A successful solar wind acceleration model should be able to explain all those solar winds. For the modeling it is important to find a universal relation between the solar wind physical parameters, such as velocity, and coronal physical parameters such as magnetic field energy. To clarify the physical parameters which control the solar wind velocity, we have studied the relation between solar wind velocity and properties of its source region such as photospheric/coronal magnetic field and the size of each coronal hole during the solar minimum. The solar wind velocity structures were derived by using interplanetary scintillation tomography obtained at Solar-Terrestrial Environment Laboratory, Japan. Potential magnetic fields were calculated to identify the source region of the solar wind. HeI 1083 nm absorption line maps obtained at Kitt Peak National Solar Observatory were used to identify coronal holes. As a result, we found a relation during solar minimum between the solar wind velocity and the coronal magnetic condition which is applicable to different kind of solar winds from different kind of coronal holes.

  60. Resolving the enigmatic solar wind disappearance event of 11 May 1999 Reviewed

    Janardhan, P., K. Fujiki, M. Kojima, M. Tokumaru, and K. Hakamada

    Journal of Geophysical Research   Vol. 110   page: 10.1029/2005JA010535   2005

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    On 11 and 12 May 1999, the Earth was engulfed by an unusually low-density (<1 cm^-3) and low-velocity (<350 km s^-1) solar wind for a period of over 1 day. Extensive studies of this unusual event that occurred during Carrington rotation 1949 (CR1949), using both ground-based and space-based in situ observations, have not as yet been able to identify the cause or the solar source of this event. Using solar wind velocity measurements from the four-station IPS observatory of the Solar-Terrestrial Environment Laboratory (STEL), Toyokawa, Japan, we investigate the structure of the solarwind in May 1999 during CR1949. IPS observations from STEL were used to make tomographic velocity maps to identify and delineate the extent and morphology of the stable solar wind flows during CR1949 in the vicinity of the Earth. Combined with in situ measurements of the interplanetary magnetic field (IMF), potential field computations of the solar magnetic fields in the period, and HeI 10830A° observations of coronal hole boundaries during CR1949, we have identified the source region of the unusual flows and have shown that the flow responsible for the "disappearance event" was a stable unipolar flow originating in the vicinity of a large midlatitude active region AR8525, located at 18N and between heliographic longitudes 280 and 300. Earlier workers have speculated that such events may be caused by the large-scale restructuring of the solar magnetic field at the maximum of each solar cycle. However, by identifying the solar source and nature of this event, we believe that at least in this particular case, the association with global, large-scale solar phenomena like the periodic 11-year solar polar field reversal is most likely to be coincidental.

  61. Correlation between expansion rate of the coronal magnetic field and solar wind speed in a solar activity cycle Reviewed

    Hakamada, K., M. Kojima, T. Ohmi, M. Tokumaru, K. Fujiki

    Solar Physics   Vol. 227   page: 387-399   2005

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  62. Origin of the slow solar wind Reviewed

    Ohmi, T., M. Kojima, M. Tokumaru, K. Fujiki, and K. Hakamada

    Adv. Space Res.   Vol. 33   page: 689-695   2004

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    The origin of the slow solar wind is an interesting subject on its own, and is also important in relation to the origin of the solar wind including the fast solar wind, especially if the slow wind originates directly from a coronal hole. We have been studying the solar wind whose speed is comparable to, or slower than, that measured in the heliospheric plasma sheet. We derived solar wind velocity distribution maps on the source surface using an interplanetary scintillation tomography analysis, and low-speed regions in them were investigated in relation to a coronal hole using potential field magnetic field lines.
    We found the slow solar wind which originated from an equatorial coronal hole located in the vicinity of active regions and also from a polar coronal hole which was about to disappear at the solar activity maximum. The properties of the slow solar wind from an equatorial coronal hole were investigated using spacecraft in situ measurements. Magnetic polarity in this wind was uniform, as expected from a potential field analysis. The helium relative abundance was as large as the fast wind, and variances of density, velocity, and helium abundance were as small as the fast wind from a large coronal hole. In spite of the small equatorial coronal hole origin, the density and ion freeze-in temperature were as large as observed for the slow wind in the heliospheric plasma sheet.
    This study clearly showed one of the origins of the slow solar wind and solved the age-old puzzle as to why a potential neutral line does not tend to pass through the locus of a low-speed stream. We think this work provides crucial information to reveal what determines the acceleration efficiency of the solar wind: physical properties in the coronal base or/and flux expansion.

  63. Fast solar wind after the rapid acceleration Reviewed

    Kojima, M., A. R. Breen, K. Fujiki, K. Hayashi, T. Ohmi, and M. Tokumaru

    J. Geophys. Res.   Vol. 109   page: (10.1029/2003JA010247)   2004

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    Since Grall et al. (1996) reported the acceleration profile of the polar solar wind near the sun region, the acceleration of the polar wind has been thought to be rapid. However, their velocities measured with interplanetary scintillation (IPS) method have a large velocity spread with some measurements being over 1000 km/s. Coles and Harmon (2001) have shown that density fluctuations produced by oblique Alfve´n waves can cause a large overestimation of flow velocities in the IPS measurement especially within 20 Rs. They attributed the wide spread of radial velocities obtained in IPS measurements near the Sun to this biasing effect. Therefore, the acceleration profile of the fast solar wind, how it is accelerated and how it approaches asymptotically the final velocity, has not yet elucidated, and it is crucially important for the study of solar wind acceleration.
    We have studied the radial dependence of the velocity of high-latitude fast solar wind in the heliocentric distance range of 0.13–0.9 AU. The analysis was made for the IPS observations during 3 years, from 1995 to 1997, when solar activity was minimum. For this study a new IPS tomographic analysis method was developed to obtain velocity distribution maps on two reference spheres at 0.13 and 0.3 AU form IPS observations. From this analysis, average velocities of 770–780 km/s were obtained at distances of 0.13–0.3 AU, which were 19 ± 17 km/s lower than those at 0.3–0.9 AU. The results from this work, taken together with measurements of SOHO/LASCO, EISCAT and MERLIN [Breen et al., 2002], Helios [Schwenn et al., 1978], and Ulysses [McComas et al., 2000], indicate that the fast wind is accelerated almost to its final flow velocity within 20 Rs and a small but not negligible acceleration exists beyond 30 Rs which tends to become smaller at farther heliocentric distances.
    This work revealed that the so-called rapid acceleration does not mean the completion of the acceleration within 10 s

  64. Solar cycle dependence of high-latitude solar wind Reviewed

    Fujiki, K., M. Kojima, M. Tokumaru, T. Ohmi, A. Yokobe, and K. Hayashi

    Solar Wind Ten, AIP Conference Proceedings   Vol. 679   page: 141-143   2003

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  65. Radial dependence of propagation speed of solar wind disturbance Reviewed

    Yamashita, M., M. Tokumaru, and M. Kojima

    Solar Wind Ten, AIP Conference Proceedings   Vol. 679   page: 754-757   2003

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  66. Global structure of interplanetary coronal mass ejections retrieved from the model fitting analysis of radio scintillation observations Reviewed

    Tokumaru, M., M. Kojima, K. Fujiki, and M. Yamashita

    Solar Wind Ten, AIP Conference Proceedings   Vol. 679   page: 729-732   2003

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  67. Toroidal-shape interplanetary disturbances associated with the halo coronal mass ejection event on July 14, 2000 Reviewed

    Tokumaru, M., M. Kojima, K. Fujiki, M. Yamashita, and A. Yokobe

    J. Geophys. Res.   Vol. 108   page: 1220   2003

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  68. Evidences for low-speed streams from small coronal hole Reviewed

    Ohmi, T., M. Kojima, K. Hayashi, A. Yokobe, M. Tokumaru, K. Fujiki, and K. Hakamada

    Solar Wind Ten, AIP Conference Proceeding   Vol. 679   page: 137-140   2003

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  69. Polar low-speed solar wind reappeared at the solar activity maximum of cycle 23 Reviewed

    Ohmi, T., M. Kojima, M. Tokumaru, K. Fujiki, K. Hayashi, and K. Hakamada

    Geophy. Res. Lett   Vol. 30   page: 1409-1412   2003

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  70. Time-dependent tomography of heliospheric features using interplanetary scintillation (IPS) remote-sensing observations Reviewed

    Jackson, B.V., P.P. Hick, A. Buffington, M. Kojima, M. Tokumaru, K. Fujiki, T. Ohmi, and M. Yamashita

    Solar Wind Ten, AIP Conference Proceedings   Vol. 679   page: 75-78   2003

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  71. MHD tomography using interplanetary scintillation measurement Reviewed

    Hayashi, K., M. Kojima, M. Tokumaru, and K. Fujiki

    Journal of Geophysical Research   Vol. 108   page: (10.1029/2002JA009567)   2003

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  72. Basic results of MHD tomography analysis method for IPS observation Reviewed

    Hayashi, K., K. Fujiki, M. Kojima, and M. Tokumaru

    Solar Wind Ten, AIP Conference Proceedings   Vol. 679   page: 144-147   2003

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  73. *How did the solar wind structure change around the solar maximum? - From interplanetary scintillation observation Reviewed

    Fujiki, K., M. Kojima, M. Tokumaru, T. Ohmi, A. Yokobe, K. Hayashi, D. J. McComas, and H. A. Elliott

    Annales Geophysicae   Vol. 21   page: 1257-1261   2003

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  74. Solar wind velocity structure around the solar maximum observed by interplanetary scintillation Reviewed

    Fujiki, K., M. Kojima, M. Tokumaru, T. Ohmi, A. Yokobe, K. Hayashi, D. J. McComas, and H. A. Elliott

    Solar Wind Ten, AIP Conference Proceedings   Vol. 679   page: 226-229   2003

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  75. Tomographic analysis of solar wind structure using interplanetary scintillation Reviewed

    Kojima, M., K. Fujiki, M. Tokumaru, T. Ohmi, Y. Shimizu, A. Yokobe, B.V. Jackson, and P.L. Hick

    COSPAR Colloquium Series   Vol. 12   page: 55-59   2002

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  76. Solar wind speed and expansion rate of the coronal magnetic field in solar maximum and minimum phases Reviewed

    Hakamada, K., M. Kojima, M. Tokumaru, T. Ohmi, A. Yokobe, and K. Fujiki

    Solar Physics   Vol. 207   page: 173-185   2002

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  77. Latitudinal velocity structures up to the solar poles estimated from IPS tomography analysis Reviewed

    Kojima, M., K. Fujiki, T. Ohmi, M. Tokumaru, A. Yokobe, and K. Hakamada

    Journal of Geophysical Research   Vol. 106   page: 15,677-15,686   2001

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  78. Polar Low-speed Solar Wind at the Solar Activity Maximum Reviewed

    Ohmi, T., M. Kojima, A. Yokobe, M. Tokumaru, K. Fujiki, and K. Hakamada

    Journal of Geophysical Research   Vol. 106   page: 24,923-24,936   2001

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  79. Microwave Observation of Eruptive Solar Events with and without Flare Activity(共著) Reviewed

    Astrophysical Journal   Vol. 533   page: 557   2000

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  80. Microwave Preflare Enhancement and Depletion in Long Duration Events Reviewed

    Advanced Space Research   Vol. 26 ( 3 ) page: 477   2000

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  81. Three-dimensional propagation of interplanetary disturbances detected with radio scintillation measurements at 327MHz(共著) Reviewed

    Journal of Geophysical Research   Vol. 105   2000

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  82. Low speed solar wind from the vicinity of solar active regions(共著) Reviewed

    Journal of Geophysical Research   Vol. 104   page: 16993   1999

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  83. The highest solar wind velocity in a polar region estimated from IPS tomography analysis(共著) Reviewed

    Space Science Review   Vol. 87   page: 237   1999

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  84. 17 and 34 GHz Observations of the Sun with the Nobeyama Radioheliograph Reviewed

    Proceedings of Nobeyama Symposium, NRO Report   Vol. 479   page: 249   1998

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    Authorship:Lead author   Language:English  

  85. Corotating Ion Events Associated with Cosmic Ray Modulation Reviewed

    J. Geomag. Geoelectr.   Vol. 47   page: 1333   1995

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  86. Energy Loss Straggling of Heavy Charged Particles in thick Silicon Absorbers Reviewed

    Journal of the Physical Society of Japan   Vol. 63 ( 1 ) page: 92   1994

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  87. Rapid Recovery of Anomalous Cosmic Ray Flux at 1 AU in Solar Cycle 22 Reviewed

    Geophysical Research letter   Vol. 21 ( 25 ) page: 3027   1994

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  88. The Energetic Particle Spectrometer HEP onboard the GEOTAIL Spacecraft Reviewed

    J. Geomag. Geoelectr.   Vol. 46   page: 713   1994

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  89. Determination of Charge and Energy for Particles Penetrating a Silicon △E×E Telescope in Space Radiation Reviewed

    Jpn. J. Appl. Phys.   Vol. 33   page: 4106   1994

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  90. Geometric Factor of Geotail HEP-MI and-HI Telescopes

    Bulletin of Science and Engineering Research Laboratory, Waseda Univ.   ( 139 ) page: 1   1992

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    Language:English  

▼display all

Books 3

  1. An Upgrade of Nobeyama Radioheliograph to a Dual-Frequency (17 and 34 GHz)System (共著)

    Coronal Physics From Radio and Space Observation (Lecture Note in Physics)  1997 

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    Language:English

  2. Cross-Calibration of Far UV Spectra of Solar System Objects and the Heliosphere

    Bzowski, Maciej; Sokół, Justyna M.; Tokumaru, Munetoshi; Fujiki, Kenichi; Quémerais, Eric; Lallement, Rosine; Ferron, Stéphane; Bochsler, Peter; McComas, David J.( Role: Joint author)

    SPRINGER  2013.4 

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    Language:English

  3. Solar wind properties from IPS observations,in "The Sun and the Heliosphere as an Integrated System", Editors: Giannina Poletto and Steven T. Suess

    Kojima, M., K. Fujiki, M. Hirano, M. Tokumaru, T. Ohmi, and K. Hakamada( Role: Joint author)

    Kluwer Academic Publishers  2004 

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    Language:English

    The solar corona changes its structure dramatically with solar activity. As a consequence, the solar wind also changes dynamically. Coronal holes and physical parameters in the coronal play an important role in determining the solar wind speed and the solar wind structure. We have been studying several interesting solar wind features found in the latitudinal structure observed by Ulysses; namely, how they depend on the solar cycle and what coronal parameters determine it. We proposed a model to determine the solar wind velocity structure.
    Since Hewish et al. (1964) discovered the interplanetary scintillation (IPS) phenomena, the IPS method has been one of the few devices which can be used to observe solar wind in three-dimensional space. However, because of the line-of-sight integration effect of IPS, solar wind had to be studied with blurred images. In the late 1990s, we developed a new method of IPS observation and analysis which can deconvolve the line-of-sight integration effect. Today we can obtain unbiased solar wind images with high spatial resolution from IPS observations.
    The Ulysses spacecraft has been observing detailed structures of solar wind in three dimensions. However, Ulysses takes ten months even to make a rapid latitudinal scan from the south to north poles. IPS measurements have several advantages in comparison with spacecraft measurements. IPS can observe three-dimensional solar wind in a short time, and the observations can be carried out consistently over a solar cycle. Making use of these IPS advantages, we conducted the present study.
    In the ascending/descending phase, the latitudinal width of the low-speed region extends/shrinks, and the velocity gradient in the high-latitude high-speed region becomes steeper/gradual. On the other hand, the velocities in the polar region and the velocity gradient between low-speed and high-speed regions do not change. When, at solar maximum, the polar coronal hole area shrinks and nearly vanishes, the v

MISC 4

  1. Solar cycle 24: An unusual polar field reversal Reviewed

    Janardhan, P, Fujiki, K, Ingale, M, Bisoi, S.~K, Rout, D

    Astronomy and Astrophysics   Vol. 618   2018.8

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    DOI: 10.1051/0004-6361/201832981

  2. Rarefaction of the Very Slow (&lt;350 km/s) Solar Wind in Cycle 24 Compared With Cycle 23

    Munetoshi Tokumaru, Tomoya Shimoyama, Ken'ichi Fujiki, Kazuyuki Hakamada

    Journal of Geophysical Research: Space Physics   Vol. 123 ( 4 ) page: 2520 - 2534   2018.4

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    Language:English   Publishing type:Rapid communication, short report, research note, etc. (scientific journal)   Publisher:Blackwell Publishing Ltd  

    We investigate long-term variation of the very slow solar wind (VSSW), whose speed is less than 350 km/s, during the period between 1997 and 2015, that is, Cycles 23 and 24, using interplanetary scintillation measurements, which enable determination of the global distribution of the flow speed and the electron density fluctuation level ΔNe. We find that the occurrence rate of VSSW increases in the maximum phase of the solar cycle, and it was mostly associated with high ΔNe in Cycle 23. However, the VSSW is found to be more associated with low ΔNe in Cycle 24. This fact is consistent with an increased occurrence of the low-density VSSW observed in situ in Cycle 24. These facts, which are considered to be a manifestation of weak solar activity in this cycle, suggest that the VSSW has become significantly rarefied in recent years. We identify the source region of the VSSW on the photosphere using a potential field analysis and examine the magnetic field properties of the VSSW source. We find that the low-ΔNe VSSW is associated with a smaller expansion factor and possibly a slightly weaker photospheric field strength than the high-ΔNe VSSW. The results obtained here may suggest that more open magnetic field areas producing the VSSW in Cycle 24 are formed in the quiet Sun region, which is associated with a lower mass flux supply into the corona, than those in Cycle 23.

    DOI: 10.1002/2017JA025014

    Scopus

  3. Relation Between Coronal Hole Areas and Solar Wind Speeds Derived from Interplanetary Scintillation Measurements

    Munetoshi Tokumaru, Daiki Satonaka, Ken'ichi Fujiki, Keiji Hayashi, Kazuyuki Hakamada

    SOLAR PHYSICS   Vol. 292 ( 3 )   2017.3

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    We investigate the relation between coronal hole (CH) areas and solar wind speeds during 1995 - 2011 using the potential field (PF) model analysis of magnetograph observations and interplanetary scintillation (IPS) observations by the Institute for Space-Earth Environmental Research (formerly Solar-Terrestrial Environment Laboratory) of Nagoya University. We obtained a significant positive correlation between the CH areas (A) derived from the PF model calculations and solar wind speeds (V) derived from the IPS observations. The correlation coefficients between them are usually high, but they drop significantly in solar maxima. The slopes of the A-V relation are roughly constant except for the period around solar maximum, when flatter or steeper slopes are observed. The excursion of the correlation coefficients and slopes at solar maxima is ascribed partly to the effect of rapid structural changes in the coronal magnetic field and solar wind, and partly to the predominance of small CHs. It is also demonstrated that V is inversely related to the flux expansion factor (f) and that f is closely related to A(-1/2); hence, V alpha A(1/2). A better correlation coefficient is obtained from the A(1/2) - V relation, and this fact is useful for improving space weather predictions. We compare the CH areas derived from the PF model calculations with He I 1083 nm observations and show that the PF model calculations provide reliable estimates of the CH area, particularly for large A.

    DOI: 10.1007/s11207-017-1066-7

    Web of Science

  4. High-latitude Conic Current Sheets in the Solar Wind

    Olga V. Khabarova, Helmi V. Malova, Roman A. Kislov, Lev M. Zelenyi, Vladimir N. Obridko, Alexander F. Kharshiladze, Munetoshi Tokumaru, Justyna M. Sokol, Stan Grzedzielski, Ken'ichi Fujiki

    ASTROPHYSICAL JOURNAL   Vol. 836 ( 1 )   2017.2

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    Language:English   Publishing type:Rapid communication, short report, research note, etc. (scientific journal)   Publisher:IOP PUBLISHING LTD  

    We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2-3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of coniclike magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

    DOI: 10.3847/1538-4357/836/1/108

    Web of Science

Presentations 18

  1. Distribution of Solar Wind Sources at the Solar Surface from 1985 to 2016

    Fujiki, K.; Tokumaru, M.; Iwai, K.

    SGEPSS 2021  2021.11.2  Society of Geomagnetism and Earth, Planetary and Space Sciences

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    Event date: 2021.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:online  

  2. Simple Estimation of the Global Solar Wind Structure

    Japan Geoscience Union Meeting 2021  2021.6.5  Japan Geoscience Union

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    Event date: 2021.5 - 2021.6

    Language:Japanese   Presentation type:Poster presentation  

    Venue:online  

  3. Reconstruction of Global Solar Wind Structure from 1975 to 2016 by Using Interplanetary Scintillation and Solar Magnetogram Observations International conference

    Ken'ichi Fujiki, Munetoshi Tokumaru

    AOGS 15th Annual Meeting 

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    Event date: 2018.6

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Honolulu, Hawaii, USA   Country:United States  

  4. Reconstruction of global solar wind structure from 1975 to 2016

    Ken'ichi Fujiki, Munrtoshi Tokumaru, Kazumasa Iwai

    JpGU 2018 

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    Event date: 2018.5

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  5. Solar Wind Structure and Coronal Hole Distribution International conference

    ISEE Founding Symposium 

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    Event date: 2015.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  6. Investigations of Inner- and Outer-Heliosphere Using STEL-IPS International conference

    FUJIKI, Ken'ichi, TOKUMARU, Munetoshi, KOJIMA, Masayoshi, IJU, Tomoya, Haruichi WASHIMI, Keiji HAYASHI

    AOGS 12th Annual Meeting 

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    Event date: 2015.8

    Language:English   Presentation type:Poster presentation  

    Country:Singapore  

  7. Test of Solar Wind Models Using Interplanetary Scintillation Data International conference

    FUJIKI, Ken'ichi TOKUMARU, Munetoshi, KOJIMA, Masayoshi, IJU, Tomoya

    AOGS 11th Annual Meeting 

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    Event date: 2014.7 - 2014.8

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Royton Sapporo Hotel, Japan   Country:Japan  

  8. Upgrade of STEL IPS system International conference

    Ken'ichi Fujiki

    IPS Worksiop 2013 

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    Event date: 2013.11

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Nagoya University, Japan   Country:Japan  

  9. Relationship between solar wind speed and coronal magnetic field properties (I) International conference

    Ken'ichi Fujiki, Masayoshi Kojima, Munetoshi Tokumaru, Tomoya Iju

    International CAWSES-II Symposium 

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    Event date: 2013.11

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Nagoya University, Japan   Country:Japan  

  10. Solar Wind Observations Using STEL 327-MHz Interplanetary Scintillation System International conference

    Ken'ichi Fujiki, Munetoshi Tokumaru, Masayoshi Kojima, Tomoya Iju

    2013 Asia-Pacific Radio Science Conference 

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    Event date: 2013.9

    Language:English   Presentation type:Poster presentation  

    Venue:Howard International House, Taipei, Taiwan   Country:Taiwan, Province of China  

  11. SOLAR WIND FORECAST BY USING STELAB-IPS International conference

    Ken'ichi Fujiki, Munetoshi Tokumaru, Tomoya Iju

    AOGS-AGU (WPGM) Joint Assembly 

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    Event date: 2012.8

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Resorts World Convention Centre, Singapore   Country:Singapore  

  12. Solar Wind Observations Using STELab-IPS Arrays In Japan International conference

    Ken'ichi Fujiki, Munetoshi Tokumaru, Masayosi Kojima

    ASJ-KAS Joint Sessions on Space Weather and Space Climate 

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    Event date: 2011.10

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Jeju, Korea   Country:Korea, Republic of  

  13. Global Solar Wind Structure Observed with STELab-IPS International conference

    Ken'ichi Fujiki, Munetoshi Tokumaru, Masayoshi Kojima

    AOGS 2011 

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    Event date: 2011.8

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Taipei International Convension Centre   Country:Taiwan, Province of China  

  14. Variation of Global Solar Wind Structure Observed with STELab-IPS International conference

    Ken'ichi Fujiki

    IPS Workshop 

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    Event date: 2011.6

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Aberystwyth University   Country:United Kingdom  

  15. SOLAR WIND FORECAST BY USING INTERPLANETARY SCINTILLATION OBSERVATION International conference

    Ken'ichi Fujiki, Hiroaki Ito, Munetoshi Tokumaru

    Solar Wind 12 

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    Event date: 2009.6

    Language:English   Presentation type:Oral presentation (general)  

    Venue:St Malo, France   Country:France  

  16. Solar wind studies with multi-station interplanetary scintillation observation International conference

    Ken'ichi Fujiki, Munetoshi Tokumaru, Masayoshi Kojima

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    Event date: 2008.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  17. Reconstruction of global solar wind structure from 1975 to 2016 International conference

    Ken'ichi Fujiki, Munrtoshi Tokumaru, Kazumasa Iwai

    JpGU 2018  2018.5.20 

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    Language:Japanese   Presentation type:Oral presentation (general)  

  18. Reconstruction of Global Solar Wind Structure from 1975 to 2016 by Using Interplanetary Scintillation and Solar Magnetogram Observations

    Ken'ichi Fujiki, Munetoshi Tokumaru

    AOGS 15th Annual Meeting  2018.6.3 

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    Language:English   Presentation type:Oral presentation (general)  

    Venue:Honolulu, Hawaii, USA  

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Works 1

  1. Development of imaging argolithm applied to Nobeyama radioheliograph

    1996
    -
    1997

KAKENHI (Grants-in-Aid for Scientific Research) 1

  1. Study of structural variation of the global heliosphere associated with the peculiar solar dynamo activity

    Grant number:25247079  2013.4 - 2018.3

    Tokumaru Munetoshi

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    We carried out interplanetary scintillation measurements using the improved multi-station system of the Nagoya University in order to elucidate the global distribution of the solar wind and its evolution during the Solar Cycle 24 associated with extremely weak activities. As the result, we find that the occurrence of the very slow (< 350 km/s) solar wind, whose density is as low as the fast wind, increases distinctly in this cycle, and that the relation between the speed and either the open field areas or the magnetic flux expansion factor does not show any clear response to the solar activity. These facts suggest that the mass supply or energy injection rate from the corona decreases in association with a marked decline of the solar activity, and the fact that this effect is most prominent for the very slow wind provides an important clue to the solar wind acceleration.