Commission H (Waves in Plasmas) Activity Report
March 11th, 2005
T. Okada, Y. Omura, and H. MatsumotoResearch Topics<AKEBONO>
Based on the plasma wave data by AKEBONO spacecraft more than one solar cycle, the spatial andtemporal mapping of VLF wave activity in the inner geospace has been elucidated (Kasahara et al., 2004).
An example of such time variation of electric wave intensity during the geomagnetic storm time in thefrequency range from 1kHz to 10kHz is shown in Figure 1. The plasma wave data obtained by the
instruments
PWS
and
VLF
are
availableonrequest[forfurther
information:
http://www.stp.isas.jaxa.jp/akebono].

Figure: The vertical axis indicates the L-value of theobservation point, and the horizontal axis indicatesthe relative time from the beginning time of thestorm recovery (Kasahara et al., 2004).

Particle Acceleration by Plasma Wave
One of the hot topics in the inner magnetosphere physics is the origin of relativistic electrons in theouter radiation belt. One of the plausible mechanisms is wave-particle resonant diffusion by whistler
mode chorus during recovery phase of the magnetic storm. Using Akebono VLF and RDM data, Hikishima,
M. et al., presented the theoretical analysis and particle simulation results which indicate that the resonant
electrons with initially large pitch-angle anisotropy are rapidly pitch-angle diffused by a generated whistler
mode wave, and the subsequent anisotropy decreases and saturates the wave growth, (Computer experimentof cyclotron interaction for chorus generation, 2004 Asia-Pacific Radio Science Conference (AP-RASC
2004), pp.563-566, Qingdao, China, 2004).

<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 2005.The 24 hour plots of the observed wave spectrum data are openedin the PWI web site http://www.rish.kyoto-u.ac.jp/gtlpwi, and http://www.stp.isas.jaxa.jp/geotail.
ULF Waves in the Lunar Wake
GEOTAIL detected left-handed, circularly polarized ULF waves propagating along the backgroundmagnetic field when it was magnetically connected with the lunar wake. It is explained by polarity reversalof right-handed, sunward-propagating electron whistler waves, which were excited through the interaction

with electron beams flowing in anti-sunward direction downstream of the lunar wake with energy of about
1 keV (Nakagawa et al., GEOTAIL observation of upstream ULF waves associated with lunar wake, Earth
Planets Space, 569-580, 2003). The anti-sunward flow of electron beam was explained by filtering effect ofthe potential drop at the boundary of the lunar wake. After the passage through the electric field, theelectrons obtain significant perpendicular component of velocity, which can account for the cyclotron
resonance with sunward-propagating whistler mode waves detected by GEOTAIL (Nakagawa et al., Pitch
angle diffusion of electrons at the boundary of the lunar wake, submitted to Earth Planets Space 2004).

Figure: The dynamic spectrum of the IMF Bz
component during the period from 16:20 to 17:10 on
October 25, 1994. The wave activity associated withlunar wake was observed between 0.3 to 1.1 Hz
during the period from 16:45 to 17:00.

MHD Waves in Solar Wind
Hada,T. et al. have developed a method to quantitatively evaluate phase coherence among waves
included in time series data, by comparing structure functions of original data and its phase-shuffled/phase-unified surrogates. Application of the method to magnetic field data obtained by Geotail spacecraft,
it is revealed that the large amplitude MHD waves in the foreshock are phase correlated, and the correlationis stronger as the turbulence level is increased. Furthermore, the origin of the phase coherence is discussed
using wavelet-filtering technique (T. Hada, D. Koga, E. Yamamoto, Phase coherence of MHD waves in thesolar wind, Space Sci. Rev., 107, 463-466, 2003;
D. Koga, T. Hada, Phase coherence of foreshock MHD
waves: wavelet analysis, Space Sci. Rev. 107, 495-498,
2003; D. Koga, Phase coherence among MHD waves in theearth's foreshock region, Doctoral thesis, Kyushu
University, 2005.
Figure: The phase coherence among waves froma given turbulence time series. The vertical axis isthe ‘
phase coherence index’, which indicates how
strongly the wave phases are synchronized. It is
positively correlated with the turbulence level,
implying that the nonlinear interaction between
the waves generate the phase coherence.
Plasma Measurements
An empirical formula correlating the
Geotail spacecraft potential measured by
the single probe and the electron number
density as determined by the plasma wave
observations in the solar wind and broader
magnetosphere have been obtained. Using
this formula and plasma particle
measurements, the problem how muchand how the low-energy plasma exist inthe magnetosphere is investigated.
The figure in the previous page shows the density profile and energy-time (E-t) spectrogram during theperiod from 15:00 UT to 21:00 UT, November 26, 1995. Top panel is the density profile. Ns/c and NLEP are
shown as solid lone and Npwi is shown as open circles. Middle and bottom panels are omni-directional E-t
spectrogram of electrons and ions (K. Ishisaka, et al., Application of spacecraft potential to investigate the
distribution of low-energy plasma in magnetosphere, COSPAR COLLOQUIA SERIES Vol.16, Frontiers in
Magnetospheric Plasma Physics, pp.75-78, 2005).

Lobe Trapped Continuum Radiation
Lobe trapped continuum radiation (LTCR) has been observed onboard the Geotail spacecraft, at
frequencies as low as 1 kHz in the distant geomagnetic tail region. By comparing the waveform
observations of the LTCR with the 3-d ray-tracing analysis, the possible source regions of the LTCR is
identified as the plasma sheet boundary layer away from the nominal tail axis and the low latitude boundary
layer (H. Takano, et al., Lobe trapped continuum radiation generated in the distant magnetotail, COSPARCOLLOQUIA SERIES Vol.16, Frontiers in Magnetospheric Plasma Physics, pp.224-227, Elsevier, 2004).

Antenna in Space Plasma
The characteristics of dipole antenna or probe antenna, namely the antenna impedance and effective
length have been studied using the AKEBONO and GEOTAIL observation data. The impedance of thewire dipole antennas onboard the Akebono satellite is estimated by using the electromagnetic fieldobservations for Omega navigational signals. The estimated capacitance and resistance exhibit specific spin
variation, which would be caused by the plasma sheath formation around the antenna wires depending on
the angle between the antenna direction and the geomagnetic field line. The figure shown below indicates adependence of antenna impedance to the angle on the geomagnetic field (R. Higashi et al., Estimation ofimpedance of wire antennas onboard the Akebono satellite, Proceedings of 2004 International Symposium
on Antennas and Propagation (ISAP 2004), Vol.1, pp.269-272, Sendai (Japan), 2004). The effective
lengths of two orthogonal sets of wire dipole antennas are estimated. The estimated effective length of each
dipole is nearly the half of its tip-to-tip length of 60 m, which is consistent with the conventional
assumption of the effective lengths of the dipole antennas (R. Higashi, et al., The characteristics of crossed
wire antennas onboard the Akebono satellite, IEICE Trans. Commun, Vol.J88-B, No.2, pp.442-450, 2005.
Imachi,T. et al., have conducted a “rheometry”experiment, and found the frequency dependence ofeffective height for DC (static) and AC (wave) electric fields ( Characteristics of electric wire antennas
onboard scientific spacecraft, 2004 Asia-Pacific Radio Science Conference (AP-RASC 2004), pp.558-561,
Qingdao ,China, 2004).

Figure: Experimental results
showing the dependence ofantenna
impedanceonthegeomagnetic field (Higashi et al.,2004).

<SELENE>
Present state of SELENE spacecraft: Development of the onboard software was almost finished and the
instrument is now in the final adjustment stage for the 2nd system function and EMC (ElectroMagnetic
Compatibility) tests which are scheduled to start in March 2005. The Lunar Radar Sounder (LRS)
experiment onboard the SELENE consists of three subsystems; SDR (sounder), NPW (natural plasmawave) and WFC (waveform capture).
SDR will provide subsurface stratification andtectonic features in the shallow part (several km
depth) of the lunar crust, by using an FM/CW radar
technique in HF frequency range. NPW and WFC
will observe natural plasma waves in the frequency
range from 20kHz to 30MHz and from 100Hz to
1MHz, respectively.
The left picture shows the SELENE in the 1st
EMC test at Tsukuba Space Center in March 2004.

<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 spacecrafts called MPO (Mercury
Planetary Orbiter) and MMO (Mercury Magnetospheric Orbiter). Scientists in Japan and Europe jointly
proposed the plasma wave observation system called PWI (Plasma Wave Investigation) in the response to
the AO (Announce of Opportunity) for MMO. The Principal Investigator of PWI is Prof. Hiroshi
Matsumoto in Kyoto University, Japan. After reviewing the PWI proposal, the MMO Payload Review
Committee in JAXA selected the PWI for the science payload onboard MMO spacecraft. The MMO launchis scheduled in 2012.
The PWI investigates plasma/radio waves and DC electricfield in Mercury magnetosphere. It consists of two
components of receivers, two sets of electric field sensors, twokinds of magnetic field sensors, and the antenna impedance
measurement system. The PWI team has started the detailed
design of each component and interface. The
BepiColombo/MMO preliminary Requirement Review andfirst Science Working Team meeting was held on March 7 to 9
in ISAS/JAXA, Sagamihara, Japan.

<New Technology>
Development of Wave-Particle onboard Correlator
In the attempt of detecting wave-particle interaction processes based on spacecraft observation data, wealways meet the difficulty in a data analysis stage. That is due to the big difference of time resolutions
between wave data and plasma data. The breakthrough will be provided by the one-chip wave-particle
correlator. It has the capability to calculate the correlation
One-Chip Wave-Particleof wave and plasma measurement data onboard
Correlator(FPGA)
Plasma wave receiverspacecraft with very high time resolution. Allcomponents of correlator circuits are constructed within a
FPGA. We have been developing the engineering modelof the one-chip wave-particle correlator andperforming various function and efficiency tests (Reportby H. Kojima, RISH).

LVDS(Interface to Plasma detectors)

Development of Direction Finding System of Electromagnetic Pulses
Tsutsui M. et al (1994) have developed a new system for finding arrival directions of electromagnetic(EM) pulses which have frequency dispersion characteristics. The sensor system is composed of a verticalelectric dipole antenna and orthogonally-arranged two horizontal search coils. This system is applicable forboth space plasma waves, atmospheric and seismic-related radio emissions.
The application of the system to lightning pulses has shownthat the system could accurately point to thelocationsof the lightning clouds and could chase their moving
directions on real-time basis.
The figure shows the vertical electric field andorthogonal components of a horizontal magnetic field (fromtop to bottom at the left), and frequency-dependent arrival
direction lines (a sector form) drawn from the detection site(right). The wide sector was formed due to frequency
dispersion characteristics of a detected electromagnetic
pulse.

Conferences and Meetings ( November 2004 –February 2005)
1)
2)
3)
4)

Space Weather/Climate Symposium #5, STEL, Nagoya, November 24-26, 2004.
Symposium on Space Environment, JAXA, Tsukuba, November 25-26, 2004.
AGU Fall meeting: December 13-17, San Francisco, U.S.A., 2004.
Third International Symposium on the Arctic Research and eventh Ny-Alesund Scientific Seminar,
Tokyo, Japan, February 22-24, 2005

Future Conferences and Meetings
1)
2)
3)
4)
5)

International Workshop on Seismo Electromagnetics, Tokyo, Japan, 15-17 March, 2005.
Magnetospheric ULF Waves (Chapman), San Diego, CA, USA, March 21-25, 2005
7th International School/Symposium for Space Simulations, Kyoto, Japan, March 26-31, 2005
ISSS-7, Kyoto, March 26-31, 2005 http://www.rish.kyoto-u.ac.jp/isss7/
International Workshop on Space Weather - On the Causes of Southward Interplanetary Magnetic
Field (IMF), Tokyo, Japan, April 4, 2005.
6) 9th Spacecraft Charging Technology Conference, Tsukuba, April 4-8, 2005,
7) European Geosciences Union General Assembly , Vienna, Austria, April 24-29, 2005
8) Joint meeting for Earth and Planetary Science 2005, Chiba, Japan, May 22-26, 2005.
9) Spring AGU Meeting New Orleans, 23-27 May, 2005
10) AGU 2005 Joint Assembly, Louisiana, USA, May 23-27, 2005
11) Asia Oceania Geosciences Society's 2nd Annual Meeting (AOGS 2005), June 20-24, 2005,
Singaporean (http://www.asiaoceania-conference.org/)
12) IAGA 2005 Scientific Assembly, Toulouse, France, 18-29 July, 2005
13) International Symposium on Antenna and Propagation (ISAP2005), Seoul, Korea, August
3-5, 2005
14) Cluster and Double Star Symposium: 5th Anniversary of Cluster in Space, ESA/ESTEC,
Noordwijk, The Netherlands, 19-23 September 2005,