資料５－H
Commission H (Waves in Plasmas) Activity Report
March 2 nd , 2010
T. Okada, and Y. Omura

Research Topics
GEOTAIL>GEOTAIL spacecraft has been operated since 1992. The Plasma Wave Instrument (PWI) is continuously
collecting spectrum data and high time-resolution waveform data. It is expected to be in a good condition atleast until the next long eclipse in 2010. The 24 hour plots of the observed wave spectrum data have been
opened in the PWI web site http://www.rish.kyoto-u.ac.jp/gtlpwi, and http://www.stp.isas.jaxa.jp/geotail.
Furthermore, one can easily also access the PWI 2 hour plots with full time and frequency resolution
through the above web page.
<BepiColombo>
The BepiColombo is the science mission to Mercury. It is the first collaborative science mission between
JAXA and ESA. The BepiColombo mission consists of two individual spacecraft called MPO (Mercury
Planetary Orbiter) and MMO (Mercury MagnetosphericOrbiter). Scientists in Japan and Europe jointly
proposed the plasma wave observation system calledPWI (Plasma Wave Investigation). The proposal was
successfully accepted and the development of the PWIcomponent started. The MMO launch is scheduled in2014. The Principal Investigator of the PWI is Prof.
Yasumasa Kasaba of Tohoku University.
The PWI investigates plasma/radio waves and DC
electric field in Mercury magnetosphere. It consists ofPWI engineering model installed on thetwo components of receivers, two sets of electric fieldvibration test facility.
sensors, two kinds of magnetic field sensors, and theantenna impedance measurement system.
The thermal vacuum test and the vibration test of the PWI have been completed by the beginning ofJanuary, 2010. We have not seen any serious problems in these tests. We have been summarizing the resultsof the EM tests, which have conducted for one year, and submit the report to the JAXA for the preparationof the Critical Development Review (CDR) process. The CDR of the PWI is now scheduled in the middleof April, 2010.

Prototype of the sensor node [Kojima et al., 2009]<Development of the small sensor node for thesensor network system in space>
The prototype of the small sensor node has beendeveloped by RISH, Kyoto University and Kanazawa
University. It will be used for the sensor network
system for monitoring the space electromagneticenvironment. The size of the body is 7cm x 7cm x 7cm.
The small sensors for picking up plasma waves ofelectric field and magnetic field components are
installed outside of the body. The preamplifiers forthese sensors and power supply units are contained
inside the cubic body. In the near future, the tiny plasma1wave receiver developed by RISH, Kyoto University will be installed inside the body.
Reference
Kojima, H., H. Fukuhara, Y. Mizuochi, S. Yagitani, H. Ikeda, Y. Miyake, H. Usui, H. Iwai, Y. Takizawa, Y.
Ueda and H. Yamakawa, Miniaturization of plasma wave receivers onboard scientific satellites and its
application to the sensor network system for monitoring the electromagnetic environments in space,
Accepted for publication in Advances in Geosciences, 2009.

< KAGUYA (SELENE) >The Japanese lunar explorer “KAGUYA” was launched on September, 14, 2007 and the operation wassuccessfully performed until KAGUYA was impacted to the south-east of near side of the moon on June 10,
2009. The Lunar Radar Sounder (LRS) is one of the scientific instruments onboard the KAGUYA mainorbiter (Ono et al., 2008; 2009).
The LRS consists of two orthogonal 30 m tip-to-tip antennas and three subsystems; the sounder observation(SDR), the natural plasma wave receiver (NPW), and the waveform capture (WFC). The SDR is designed
to investigate the surface and subsurface structures of the moon using an HF radar technique (Ono et al.,2009a; 2009), and the NPW and WFC are designed to measure natural plasma waves around the moon andin interplanetary space (Kumamoto et al. 2008; Kasahara et al., 2008). The Level-2 data has been disclosed
for scientific utilization from “SELENE data archive system” and several data analyses are now inprogress.
Reference
KAGUYA(SELENE) Data Archive System, https://www.soac.selene.isas.jaxa.jp/archive/
Kasahara, Y., Y. Goto, K. Hashimoto, T. Imachi, A. Kumamoto, T. Ono, and H. Matsumoto, Plasma
Wave Observation Using Waveform Capture in the Lunar Radar Sounder on board the SELENE
Spacecraft, Earth, Planets and Space, 60(4), 341-351, 2008.
Kumamoto, A., T. Ono, Y. Kasahara, Y. Goto, Y. Iijima, and S. Nakazawa, Electromagnetic Compatibility(EMC) Evaluation of the SELENE Spacecraft for the Lunar Radar Sounder (LRS) Observations, Earth,Planets and Space, 60(4), 333-340, (2008).
Ono, T., A. Kumamoto, Y. Yamaguchi, A. Yamaji, T. Kobayashi, Y. Kasahara, and H. Oya, Instrumentation
and Observation Target of the Lunar RadarSounder (LRS) Experiment on-board the SELENE Spacecraft, Earth, Planets and Space, 60(4), 321-332,(2008).
Ono, T., A. Kumamoto, H. Nakagawa, Y. Yamaguchi, S. Oshigami, A. Yamaji, T. Kobayashi, Y. Kasahara,and H. Oya, Lunar Radar Sounder Observationsof Subsurface Layers under the Nearside Maria of the Moon, Science, 323, 909-912,
doi:10.1126/science.1165988, 2009.

<AKEBONO>
Single Probe Application
Toomi (2010) investigated the relationship between the AKEBONO spacecraft potential and the electron
number density in the plasmasphere during the period from May 1989 to August 1990. The empiricalformula shown the relationship between the spacecraft potential and electron number density was obtained.
Figure 1 shows the approximate formula of relationship between spacecraft potential and electron numberdensity in the range of electron number density from 100 to 105 cm-3 each bias current (red: -0.67A, green:-0.059A, blue: -0.017A). We found that the characteristic is changed when the bias current is changed.
Therefore it is important to feed a proper bias current to the probe in order to be set nearly zero to the probe2

potential for the ambient plasma.

-0.059A, blue: -0.017A). We found that theFigure 1. Characteristic between spacecraft potential Figure 2. Spatial distribution of electron density andelectron number density each bias current
along the AKEBONO satellite orbit
Using this correlation, a map is drawn which shows the spatial distribution of electron density. Figure 2
shows spatial distribution of electron density in the period from May 1989 to August 1990 plotted on theX-Z plane of the terrestrial magnetism coordinate system. The amount of electron density is indicated bycolor code. From the distribution of the electron density, we find that the density is high near the earth
region, and that the regions of low-density are inside of the magnetosphere. Thus, we can determine theregions along the AKEBONO orbit from the spacecraft potential.
Reference
Toomi,H., Study on characteristic of relationship between Akebono satellite potential and electron density,
Toyama prefectural university Master’s thesis, 2010.

< Techniques of Data Analysis and Computer Experiments >As the total amount of data measured by scientific spacecraft is drastically increasing, it is necessary for
researchers to develop new computation methods for efficient analysis of these enormous datasets. A newalgorithm for similar data retrieval was proposed by Kasahara et al. (2010). They first discuss key
descriptors that represent characteristics of the VLF/ELF waves observed by the Akebono spacecraft. Basedon these key descriptors, an algorithm for similar data retrieval was introduced, and then they finallydemonstrated that the developed algorithm works well for the retrieval of the VLF spectrum with a small
amount of CPU load.
A general-purpose database (DB) system that manages and opens experimental and/or observational data
was introduced by Takata et al. (2010). This platform works as a web-DB management system in which
databases can be easily managed without special skills and facilities. By defining a group manager and datamanager, the proposed system defines a flexible access restriction for each user and each unit of datasets
under the control of these managers. They demonstrated how a variety of web-DBs are appropriately
integrated under one management system in such situations in which each web-DB has a different userinterface in its search and data distribution functions and is designed with a different language (or script)
and connection method to its DB. In spite of the diversity of web-DBs, the proposed system is highly
suitable for practical use.

3

Reference
Y. Kasahara, A. Hirano and Y. Takata, Similar Data Retrieval from Enormous Datasets on ELF/VLF
Wave Spectrum Observed by Akebono, Data Science Journal, (10pages, advance publication),doi:10.2481/dsj.SS_IGY-002, 2010.
Y. Takata, Y. Kasahara, and T. Matsuhira, Development of a Science Database System Applicable to
Various Access Restrictions, Data Science Journal, 8, IGY32-IGY43, doi:10.2481/dsj.SS_IGY-008,
2010.

<Lightning-generated sferics observations>

Current moment (kA km)Ozaki et al. [2010] have investigated the technique for estimating lightning current by using the sfericwave fields. They have successfully obtained information on the discharge duration of the return stroke thatwas impossible to know only from the conventional wave field observation. They have also found that it ispossible to estimate the waveform of the return stroke current by using a nonlinear least-squares method
applied to the wave field. Figure 1 shows the estimated current moment waveforms by using the direct
waveforms of the observed sferic wave field. As a result, their method has shown that the error in theestimation of the current moment is less than 10 % for the horizontal distances of the lightning over 100km.

LM method
Direct wave

100806040200020406080 100 120 140 160

Time (sec)
Figure 1: Estimated current moment waveforms (solid line) andthe direct waveforms of the observed sferics (dotted line).

Reference
Ozaki, M., S. Yagitani, T. Koide, and I. Nagano, "Estimation of lightning return stroke current
waveforms by nonlinear least squares method applied to sferics," IEICE Transactions onCommunications, Vol.J93-B, No.4, (in print), April 2010.

<ULF Waves>
By using MHD simulations, Ugai (2009) showed how reconnection jets drive ionospheric electrojets
and Pi 2 pulsations at substorms. When a large-scale plasmoid, directly generated by the reconnection jet,collides with the magnetic loop of the closed field lines in the inner magnetosphere, strong electrojets are
impulsively driven in a finite extent of the ionospheric footpoint of the magnetic loop. On the other hand,
Alfven waves, which were generated simultaneously with the plasmoid generation, reaches the ionosphericelectrojet layer and are reflected, interact (or resonate) with the waves traveling toward the footpoint,4

leading to impulsive Pi 2 pulsations.
Uozumi et al. (2009) examined Pi 2 wave oscillations that showed a high correlation between highand low-latitude MAGDAS/CPMN ground magnetometer stations. They examined the magnetic local time(MLT) dependence of the delay time from the low-latitude station to the high-latitude station; as a result,they found that the H-component delay time showed a remarkable MLT dependence, especially in thepremidnight sector: They found, in the premidnight sector, that the high-latitude H oscillation tends to delay
from the low-latitude H oscillation by ≤100s. On the other hand, the D-component delay time was not
significant (<10s) in the entire nighttime sector. They proposed a Pi 2 propagation model, which explained
these observed features. They also examined the spatial distribution of the Pi 2 events relative to the centerof auroral breakups; they found that the high-correlation Pi 2 events tend to occur away from the center ofauroral breakups by more than 1.5hr MLT. They suggested that the high-correlation H-component Pi 2
oscillations at high latitudes are a manifestation of forced Alfven waves excited by fast magnetosonicwaves.
References
Ugai M, Impulsive magnetic pulsations and electrojets in the loop footpoint driven by the fast reconnection
jet, Physics of Plasmas, 16(11), 112902, Nov. 2009.
Uozumi, T., S. Abe, K. Kitamura, T. Tokunaga, A. Yoshikawa, H. Kawano, R. Marshall, R. J. Morris, B. M.
Shevtsov, S. I. Solovyev, D. J. McNamara, K. Liou, S. Ohtani, M. Itonaga, and K. Yumoto (2009),
Propagation characteristics of Pi 2 pulsations observed at high and low latitude MAGDAS/CPMN
stations: A statistical study, J. Geophys. Res., 114, A11207, doi:10.1029/2009JA014163.
Kataoka, Ryuho, Yoshizumi Miyoshi, and Akira Morioka, Hilbert-Huang Transform of geomagnetic
pulsations at auroral expansion onset, The 33rd Symposium on Space and Upper Atmospheric Sciencesin the Polar Region, National Institute of Polar Research, Japan, Nov. 12-13, 2009.
H. Kawano, V. Pilipenko, S. Saita, K. Yumoto, and I. Mann, Application of the improved hodographmethod (to identify the field-line resonance) to ground magnetometer data, The 33rd Symposium onSpace and Upper Atmospheric Sciences in the Polar Region, National Institute of Polar Research, Japan,Nov. 12-13, 2009.
Conferences and Meetings
1) 126th SGEPSS (Society of Geomagnetism and Earth, Planetary and Space Sciences) Fall Meeting,Kanazawa, Japan, Sep. 27-30, 2009.
2) The 33rd Symposium on Space and Upper Atmospheric Sciences in the Polar Region, National
Institute of Polar Research, Japan, Nov. 12-13, 2009.
3) 2009 AGU Fall Meeting, 14–18 December San Francisco, California, USA4) MEETING: 19th Cluster Workshop, Multi-point Investigations of MagnetosphereIonosphere Coupling and Aurora, May 18-21, 2010, Poiana Brasov, Romania
5) 2010 Western Pacific Geophysics Meeting22-25 June 2010, Taipei, Taiwan
Meeting web site: http://www.agu.org/meetings/wp10/
6) Second International Symposium on Radio Systems and Space Plasma, August 25-27,
2010, Sofia, Bulgaria
Acknowlegement
The editors thank Dr. H. Kojima, Dr. Y. Kasahara, Dr. S.Yagitani, Dr. K. Ishisaka and Dr. H. Kawano,for their contribution to this report5