資料10-H

Commission H (Waves in Plas mas) Activity Report( Ver1.3)

March 10th, 2009
T. Okada and Y. Omura

Rese arch Topics<Magnetosphe ric Observations>
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 agood condition at least until the next long eclipse in 2009. 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, andhttp://www.stp.isas.jaxa.jp/geotail. Further, Ｓｉｎｃｅ 2005, the PWI team has started to open theaccess to all of 2 hour plots of the observed spectra. One can easily access the PWI 2 hour plots throughthe above web page.
The role of the PWI Principal Investigator has been taken over from Professor emeritus of Kyoto
Univ. H. Matsumoto, who is the current president of Kyoto University to Dr. H. Kojima of Kyoto Univ.
Nagayama et al. [2008] analyzed the frequency sweep rates of rising chorus emissions. They
performed the statistical analys is of chorus emissions observed by WFC onboard GEOTAIL from
October 1992 to December 2007. Figure 1 shows the analytical results: (a) amplitudes vs. L values, and(b) frequency sweep rates vs. L values. Both chorus amplitudes and frequency sweep rates become
smaller as the L-value becomes larger. This indicates that the frequency sweep rate would become large
as the chorus wave amplitude grows, which is consistent with the simulation results reported by
Hikishima et al. [2008a, b; 2009a].
10 000df/dt [Hz/sec]

Amplitude [pT]

100 0

10 0

10

1000

100

10

1
7

8

9

10

11

12

13

7

14

8

9

10

11

12

13

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L-valueL-value(a) Amplitudes(b) Frequency sweep rates
Figure 1: The amplitudes and frequency sweep rates of the chorus emissions depending on the L-value.
The mechanism for formation of the Earth’s radiation belt has been an outstanding issue for
utilization of the geospace environment. Kasahara et al. (2009) presented a typical magnetic storm
event which occurred from 9 to 19 October, 1990, in which there is a clear correlation amongcontinuous injection of hot electrons, generation of chorus, geomagnetic AE activity (all for ~8 days)
and the acceleration of electrons to relativistic energies. They also showed the frequency characteristics
of chorus elements that are important for non-linear wave particle interactions. They proposed afollowing scenario to explain the observations: the continuous injection of hot electrons associated with1

the continuous AE activity. The hot electrons with Tperp /T para > 1 temperature anisotropies excite
whistler-mode chorus waves. The chorus interacts with energetic electrons accelerating them to MeV
energies forming a flux of ‘‘
killer electrons’’
in the outer radiation belt.

Figure 2:
Satellite and ground based data
during the magnetic storm, October
1990: a, ~30 keV energetic electron
fluxes measured by NOAA-10 from 9
to 19 October 1990. The Dst index isshown by a solid line. b and c,
Relativistic ~2.5 MeV electron fluxes
and intensity of 1-10kHz VLF waves
observed by Akebono, respectively. d,
The AE index during the magnetic
storm

Knowledge of the characteristics of wire antennas in space plasmas used as sensors for electric fieldobservations by scientific satellites in geospace is necessary to determine the absolute intens ity and thephase of the electric field waves, because the observation data for the electric fields are available asvoltage signals.
Akebono satellite was launched in 1989 to observe electromagnetic waves in geospace. Higashi etal. [2008] analyzed the data acquired from 1989 to 1995 for the antenna impedance measured by thevector impedance measuring instrument (VIP) for the electric field sensors onboard Akebono satellite.
It was found that the resistance component of the antenna impedance has the frequency dependence.
By correcting the data of the antenna impedance measurement in consideration of the secular change
of VIP, the resistance values became normal as shown in Figure 3 [Kamei and Higashi, 2008].

Figure 3: Correction of the resistance component of the antenna impedance(Left: Before correction, Right: After correction)

2

In Morioka et al. (2008), the dynamical behavior of auroral k ilometric radiation (AKR) is
investigated in connection with auroral particle acceleration at substorm onsets using
high-time-resolution wave spectrograms provided by Polar/PWI electric field observations. AKR
develops explosively at altitudes above a preexisting low-altitude AKR source at substorm onsets. This``AKR breakup'' suggests an abrupt formation of a new field-aligned acceleration region above thepreexisting acceleration region. The formation of the new acceleration region is completed in a very
short time (amplitude increases 10,000 times in 30 seconds), suggesting that the explosive development
is confined to a localized region. AKR breakups are usually preceded (1-3 minutes) by the appearance
and/or gradual enhancement of the low-altitude AKR. This means that the explosive formation of thehigh-altitude electric field takes place in the course of the growing low-altitude acceleration. The
development of the low-altitude acceleration region is thus a necessary condition for the ignition of thehigh-altitude bursty acceleration. The dH/dt component from a search-coil magnetometer at groundshows that a few minutes prior to substorm onsets, the quasi-DC component begins a negative
excursion that is nearly synchronized with the start of the gradual enhancement of the low-altitude
AKR, indicating a precursor-like behavior for the substorm. This negative variation of dH/dt suggests
an exponentially increasing ionospheric current induced by the upward field-aligned current. At
substorm onsets, the decrease in the quasi-DC variation of dH/dt further accelerates, indicating asudden reinforcement of the field-aligned current.

Figure 4. Relationship between global auroral activity and AKR development around a
substorm onset. Upper panels: Polar/UVI images in dark hemisphere on 3 Apr il 1996
showing an auroral breakup around 15:35 UT (image e). The small horizontal
rectangles under images indicate exposure times. Lower panel: a-t diagram indicating
AKR breakup at 15:35 UT after gradual enhancement of the low-altitude AKR.
Morioka et al. (2009) describes the onset process of auroral substorms in connection with the verticalevolution of auroral particle acceleration, on the basis of auroral kilometr ic radiation ( AKR) dynam ics.
We show that the auroral acceleration process at substorm onset basically consists of two stages: (1)appearance/intensif ication of a low-altitude acceleration region at 4000–5000 km accompanied byinitial brightening and (2) breakout of high-altitude field-aligned acceleration above the pre-existing
low-altitude acceleration region at 6000–12 000 km, which is followed by auroral breakup andpoleward expansion. It is also revealed that this two-stage evolution of auroral acceleration corresponds
to the two-step reinforcement of field-aligned current.

3

Figure 5. Schematic illustrations of time sequence for substorm on 3 April 1996.
Vertical axes for UV aurora, Pi2, and AKR in each panel correspond to activity,
amplitude, and altitude, respectively. Horizontal arrows indicate time tolerance
for determining start time of each substorm step.
Miyoshi et al.(2008) showed for the first time evidence that electromagnetic ion cyclotron (EMIC)
waves can cause the loss of relativistic electrons into the atmosphere. The process has been predicted
theoretically since 1970’s, but it has not been confirmed yet. Their conjunction observation fromground and satellite showed coincident precipitation of ions with energies of tens of KeV and of
relativistic electrons into an isolated proton aurora. The coincident precipitation was produced bywave-particle interactions with EMIC waves near the plasmapause. The numerical calculation on the
diffusion coefficients supported that the observed EMIC waves caused coincident precipitation of bothions in the ring current and relativistic electrons in the outer radiation belt.

Figure 6 : (left) Photograph of isolated proton aurora in the southern sky ofAthabasca, Canada, on September 5, 2005. Coincidence precipitations of both tens
keV ions and relativistic electrons were observed inside this aurora. (right)
Waveform of EMIC waves observed at Athabasca, when the isolated proton aurora
was observed. Bottom panel indicates the power spectral density of EMIC waves.
Helium-band EMIC waves are signif icantly detected.

4Kitamura et al. (2008) have statistically studied meridional electron density distributions above 45
degree invariant latitude during geomagnetically quiet periods using the electron density data obtained
from plasma waves observed by the Akebono satellite from March 1989 to February 1991, near solar
maximum, in an altitude range of 274-10,500 km. They have found the largest seasonal variation andsolar zenith angle (SZA) dependence of the electron density at an altitude of 2000 km with a factor of
50 in the trough, auroral and polar cap regions. The seasonal variation and SZA dependence are smaller,
about a factor of 5-10, above 5000 km. Day-night asymmetries in each season are smaller than theseasonal variation. The scale height is larger in the dayside than in the nightside in each season. These
results indicate that photoionization processes in the ionosphere strongly control electron density
distributions up to at least 5000 km in the trough, auroral, and polar cap regions.

Figure 7: Electron density distribution models in a region of ILAT>45 degree in an
altitude range of 1000-10,500 km. Meridional electron density distribution
models fitted by the sum of exponential and power law functions in the (a)summer, (c) equinox, and (e) winter seasons. The number of orbit passes in eachbin are shown in the (b) summer, (d) equinox, and (f) winter seasons. The dipole
magnetic field lines at ILAT of 45, 60, 70, and 80 degree are shown in eachpanel.

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CRRES electric field data during substorms have been analyzed by Nishimura et al. (2008) toinvestigate intense electric fields in the inner magnetosphere associated with dipolar izations. Substorm
injections during 13:00 - 15:00 UT on 7 March 1991 exhibit many large-scale electric fields andshort-duration electric field spikes. Large-scale electric fields with durations of 1 min are identified as
spatial structures associated with the region 1 field-aligned currents. Amplitudes of electric fields reach
30 mV/m with a high correlation with variations of the magnetic field, and the Poynting fluxes are2
directed toward the ionosphere with magnitudes of more than 0.5 mW/m . 16-Hz high-resolution data
2
show intense electric field spikes with amplitudes of 100 mV/m with durations of 1 s. Most of the
spikes are electromagnetic with Poynting fluxes of 0.1 mW/m directed toward the ionosphere. The
electric field spikes are identified as right-handed whistler waves with a size of 1000 km withfrequencies just below the ion cyclotron frequency. A nearly simultaneous measurement by the
DMSP-F9 satellite shows intense plasma flows with durations of 1 s and inverted-V electron
precipitation. An estimation of the wave and particle energy fluxes shows that about half of the
Poynting flux of the electric field spikes is consumed accelerating auroral particles, and 1% of the
Poynting flux dr ives the fast plasma flows at the ionosphere. It is suggested that the electromagnetic
spikes provide sufficient energy for auroral particle acceleration.

Figure 8: CRRES field and particle data between 13 and 15 UT on 7 March 1991.
Figures a-c and d-e show low-pass filtered magnetic and electric field data. Figure 2f
shows the high-resolution electric field with a period of less than 20 s. Figures g andh show the electron and ion energy flux. The intense electric fields labeled as A and B,
and the spikes  ,  , and  have been analyzed by Nishimura et al. (2008).

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Shiraishi et al. developed a nautomatic analyzer to measure the lower cut-off frequency ofContinuum Radiation (CR), which has been used to estimate an electron density around the Geotail
spacecraft. So far, the lower cut-off frequency is detected by human's eyes, it takes a long time toobtain the lower cut-off frequency, and it is difficult to avoid subjective factors. In there study, they
introduce a new scheme to detect the lower cut-off frequency of CR in signal analysis as shown in
Figure 9. An example of such an analysis result is shown in Figure 10.

Intensity[dBV/m/Hz^0.5]

(a)

CR

remarkable point
f cut

11/13

threshold-166 dBV /m/√Hz
11/14

1 0 1 1 1 1 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1 1 1 1 1
Low frequency 13 points

High frequency 14 points

Frequency [H z]

Intensit y[dBV/m/Hz^0.5 ](b)remarkable point
f cut

CR

threshold-166 dBV/m/√Hz

11/13

11/14

1 0 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 0 1
Low frequency 13 points

High frequency 14 points

Frequency [Hz]Fig.9 A new scheme to detect the lower cutoff frequency of CR. Examples ofbinar ization process applied to model spectra: (a) A model spectrum which have asequence of 「1」away from the remarked frequency. (b) A model spectrum
which have a sequence of 「1」in the vicinity of the remarked frequency.

Fig.10Detected cut-off frequencies at 10:00 UT –12:00 Jan. 15, 1995.

<Jupiter Observations>
In Kimura et al. (2008), Ulysses had a “
distant encounter”with Jupiter in February 2004. The
spacecraft passed from north to south, and it observed Jovian radio waves from high to low latitudes(from +80° to +10°) for few months during its encounter. In this study, we present a statistical7

investigation of the occurrence characteristics of Jovian quasi-periodic bursts, using spectral data fromthe unified radio and plasma wave experiment ( URAP) onboard Ulysses. The latitudinal distribution ofquasi-periodic bursts is derived for the first time. The analysis suggested that the bursts can be roughly
categorized into two types: one having periods shorter than 30 min and one with periods longer than 30
min, which is consistent with the results of the previous analysis of data from Ulysses’first Jovian
flyby [MacDowall, R.J., Kaiser, M.L., Desch, M.D., Farrell, W.M., Hess, R.A., Stone, R.G., 1993.
Quasi-periodic Jovian radio bursts: observations from the Ulysses radio and plasma wave. Experiment.
Planet. Space Sci. 41, 1059 1072]. It is also suggested that the groups of quasi-periodic bursts showed adependence on the Jovian longitude of the sub-solar point, which means that these burst groups are
triggered during a particular rotational phase of the planet. Maps of the occurrence probability of thesequasi-periodic bursts also showed a unique CML/MLAT dependence. We performed a 3D ray tracing
analysis of the quasi-periodic burst emission to learn more about the source distribution. The results
suggest that the longitudinal distribution of the occurrence probability depends on the rotational phase.
The source region of quasi-periodic bursts seems to be located at an altitude between 0.4 and 1.4 Rj
above the polar cap region (L>30).

Figure 11. A map of occurrence probability of the QP burst groups. (a) The horizontal axis
in each panel indicates the CML of Ulysses. The upper panel shows the CML distributionof the probability of the QP burst groups. The lower panel is the CML vs. the magnetic
latitude map of the occurrence probability. The color indicates the occurrence probability.
The black regions correspond to the lack of observation, whereas the blue regions
indicate the lowest probability. (b) has a similar format to that of (a), but the horizontal
axis is the sub solar longitude (SSL).
In Kimura et al. (2008b),Ulysses had a “
distant encounter”with Jupiter when it was within 0.8 AU of
the planet during February, 2004. The passage of the spacecraft was from north to south, andobservations of the Jovian radio waves were carried out for a few months from high to low latitudes(+80° to +10°) of Jupiter. The statistical study performed during this “
distant encounter”event provided
the occurrence characteristics of the Jovian broadband kilometric radiation (bKOM), including thehigh-latitude component as follows: (1) the emission intensity of bKOM was found to have a sinusoidal
dependence with respect to the central meridian longitude (CML), showing a broad peak at 1̃80°, (2)bKOM was preferably observed in the magnetic latitudinal range from +̃30° to +90°, and the emission
intensities at the high latitudes were found to be two times larger than that at the equatorial region, and(3) the emission intensity was controlled possibly by the sub solar longitude (SSL) of Jupiter. The
intensity had a sharp peak around SSL 2̃10°. A 3D ray tracing approach was applied to the bKOM in

8order to examine the source distribution. It was suggested that: (1) the R-X mode waves generated
through the Cyclotron Maser Instability process would be unable to reproduce the intense high- latitude
component of the bKOM, (2) the L-O mode, which was assumed to be generated at frequencies near
the local plasma frequency, was considered to be the dominant mode for past and present observations
at mid- and high-latitudinal regions, and (3) the high-latitude component of bKOM was found to have asource altitude of 0.9 1.5 Rj (Rj: Jovian radii), and to be distributed along magnetic field lines having
L>10.

Figure 12. Intensity map of the bKOM. Hor izontal axis in F ig. (a) indicates the CMLof Ulysses as seen from Jupiter. Upper panel of Fig. (a) shows CML distribution of
the average intensity. Lower panel of Fig. (a) depicts CML vs. magnetic latitude
map of the average intensity. The color contours show integrated electric field
intensity from 40–45 kHz. The white lines show the level of 0.035 m V/m. Fig. (b)is almost similar in format to that of Fig. (a), but for the horizontal axis, whichshows the SSL.
< KAGUYA (SELENE)>
The purposes of the Lunar Radar Sounder (LRS) on-board the Kaguya (SELENE) spacecraft are (1)to perform radar sounding of the lunar subsurface structures which provide clues to understand theorigin and evolution of the Moon, and (2) to observe natural radio waves from the Earth, Sun, andJupiter and plasma waves associated with lunar wake and mini-magnetosphere due to crustal magnetic
anomaly (Ono et al., 2008, Kumamoto et al., 2008, Kasahara et al., 2008).
LRS started the observation just after the extension of dipole antennas on Oct. 29. Through theoperation from October 29, 2008 to September 10, 2008, 98 days worth of radar sounder data and 270
days worth of plasma wave data have been obtained.
Subsurface radar sounding of the Moon using LRS/SELENE
The Lunar Radar Sounder (LRS) on-board the Kaguya (SELENE) spacecraft started the lunar
surface and subsurface soundings since November 2007 in order to understand the origin and evolutionof the Moon. Kaguya is in circular orbit with an altitude of 100 km and an inclination of 90 degrees.
Orbital period is about 2 hours. The LRS system transmits a radar signal modulated from 4 MHz to
6MHz with a pulse width of 200 microseconds and a peak power of about 800 Watts. The range
resolution of LRS is 75 m in free space. The pulse repetition frequency of pulse transmission is 20Hz.
After the operation for 10 month, the radar sounder observation covered almost whole area of the lunar

9

surface.
Ono et al. (2009) discovered prominent reflectors lying at the apparent depths of a few hundred
meters in the nearside maria of the Moon. The age of subsurface layer can be determined by crater
chronology of outcrop region. The prominent echoes found in Mare Selenitatis are probably fromburied regolith layers accumulated during the depositional hiatus of mare basalts between 3.55 and 3.44
billion years ago. The mare ridges in the southern part of Selenitatis basin were formed after 2.84
billion years ago, which suggests that global cooling probably dom inated the tectonics after 2.84 billion
years ago.

Fig. 13. Radargrams with obvious lunar subsurface echoes (red arrows). Observation groundtracks are plotted on the lunar topographic map of the Moon.

<Ionospheric Waves>
An Improved-Orion sounding rock et SRP-5 has been carried out. The rocket was launched from the
Poker Flat Research Range, Fairbanks, Alaska at 14:17 LT on January 10, 2009. The apex altitude isabout 98 km at 150 seconds after launch. The primary science objective of SRP-5 Project ISIS
(Ionospheric Science and Inertial Sensing) is to measure the plasma density structure of the highlatitude D region ionosphere above Poker Flat Research Range. This will be accomplished using aplasma probe, radio receivers, and other sensors. The objective of TPU (Toyama Prefectural University)
radio receiver is the investigation of the electron density profile in the high latitude D region at daytime.
The electron density profile in the lowest ionosphere is estimated from the measured absorption of
three radio waves (257 kHz, 660 kHz and 820 kHz) transmitted from navigation and broadcast stations
near Fairbanks, Alaska.
Three signals were successfully observed from an altitude 0 km - 98 km during the ascent flight10

(Figure 14 and Figure 15). The approximate electron density profile can be determined from thecomparison between these experimental results and propagation characteristics calculated by the fullwave method. Then the most probable electron density profile in the lowest ionosphere below 65 km
will be demonstrated in future work.

Figure 14

Measurement results of three radio wave intensities, 257 kHz ((a) Lo and (b)Hi), 660 kHz ((c) Lo and (d) Hi), and 820 kHz ((e) Lo and (f) Hi)

Figure 15

The spectrum from waveform measurement of 257 kHz (top panel), 660 kHz(middle panel) and 820 kHz (bottom panel).

<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 Magnetospheric Orbiter). Scientists in Japan andEurope 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 isProf. 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 launch is scheduled in 2014.
The PWI investigates plasma/radio waves and DC electric field in Mercury magnetosphere. It
consists of two components of receivers, two sets of electric field sensors, two kinds of magnetic fieldsensors, and the antenna impedance measurement system.
The development and tests of the BBMs have been done by each PWI component team and the PWI
has passed the Prelim inary Design Review by JAXA, which was conducted in October, 2007. After that,
the PWI team has moved to the phase of the development of the Engineering model (EM). The first EM
tests of the PWI have been conducted from August to November, 2008 in Kyoto university. The tests
have been conducted for both of the analogue parts and digital parts. Up to now, the PWI team has notfound any serious problems. The second EM tests will start from April, 2009 in Kyoto university. Afterthe second EM tests, the PWI will attend the EM system integration tests in JAXA, which is scheduled

11

in June, 2009.
<Polar Observations>
Ozaki et al. [2008a] analyzed the simultaneous ground-satellite observation of VLF waves in
Antarctica, and discussed quantitatively the VLF penetration characteristics down through the polar
ionosphere.
Ozaki et al. [2008b] estimated the polar ionospheric VLF exit point by using observation andfull-wave calculation results to consider the effects of the magnetized ionosphere and of the
Earth-ionosphere waveguide propagation. Firstly, to find the distinct exit point, they theoreticallycalculated the spatial distributions of the wave intensity and the polarization on the ground for VLF
whistler mode waves coming down from the magnetized ionosphere. Then, they compared thecalculated results with the observed data, to evaluate the plausible locations of the exit point for theauroral hiss events. Their results showed that the direction of the exit point for auroral hiss was foundto be consistent with a bright aurora region, but the estimated exit point was located a few hundred
kilometers equatorward of the associated aurora. Thus, they suggested that the ray paths for theauroral hiss could be different from the directions of the geomagnetic field lines for auroral particle
precipitation.
Sato et al. (2008) have installed an Auroral Radio Spectrograph (ARS) system at Husafell station in
Iceland in order to study the generation and propagation processes of MF auroral radio em issions,referred to as auroral roar and MF burst, in the polar ionosphere. In late 2006, the ARS detected one
auroral roar and two MF bursts, which were identified as left-handed polarized waves. Results of data
analysis, including other auroral data and particle spectra observed by the DMSP satellite, suggest that
the MF bursts are generated by electrons with an average energy of several keV associated with auroral
breakup. On the other hand, the auroral roar is generated as upper hybrid waves by relatively
low-energy electrons over the observation site and propagates downward, being converted into L-O
mode electromagnetic waves.

Figure 16: Dynamic spectra of LH (panel (a)) and RH (panel (b)) components of ARS
data recorded 2121-2125 UT on September 23, 2006. The MF burst appeared at
2123:10 UT only in the LH component spectrum. The panel (c) shows a series of
427.8 nm auroral images recorded by the Conjugate Auroral Imager (CAI) instrument
located at the Husafell station.

12

<ULF waves>
Miyoshi et al. (2008) used a unique set of ground and satellite observations to show evidence thatleft-hand polar ised electromagnetic ion cyclotron (EMIC) waves near the plasmapause can precipitate
relativistic electrons and lower-energy ions (with energies of tens of keV) at the same time into an
isolated proton aurora. They backed up this interpretation by estimating the pitch angle diffusion
coefficients for their event. Their study clarified that ions with energies of tens of keV affect theevolution o frelativistic electrons in the radiation belts via cyclotron resonance with EMIC waves.
Maeda et al. (2009) selected 19 cases in which the Cluster spacecraft was located on the field line
running through the midpoint of two ground magnetometer stations belonging to the CPMN
(Circum-pan Pacific Magnetometer Network), Tixie (TIK) and Chokurdakh (CHD), when TIK and
CHD observed ULF waves caused by field line resonence (FLR). Then, for the 19 cases, they
compared the electron density (Ne) observed by the WHISPER (Waves of High frequency Sounder for
Probing the Electron density by Relaxation) instrument onboard the Cluster satellites with simultaneous
plasma mass density (rho) estimated from the FLR frequency observed by TIK and CHD, bothcorrected to the values on the magnetospheric equatorial plane along the same field line. As a result, theratio of Ne to rho falled into a realistic range for 15 out of the 19 events. It was also suggested that thecontribution of heavy ions tends to increase when the magnetosphere is disturbed.
<Seismic ELF Emissions>
Ozaki et al. [2009] evaluated amplitude of a current moment (created by a seismic activity) in the
conductive lithosphere from the viewpoint of possible detection of radiated waves with sensitivity of anelectromagnetic sensor. They showed that if a seismic dipole source is larger than 1 kAm/Hz1/2 placed
at 10 km underground, we can detect it by a search coil magnetometer on the ground. However, evenfor the 1 kAm/Hz1/2 dipole, we cannot observe it in the ionosphere. To detect it in the ionosphere, the
1/2−3
current moment over 2.5 MAm/Hz in the conductive medium of 10 S/m is required, which would
not be a realistic value. Thus, they suggested that the direct observation of the seismic-related
electromagnetic waves in the ionosphere would be quite difficult.

<Computer simulation>
The scattering process of energetic electrons by resonant interactions with whistler-mode chorus
waves in the magnetosphere is examined in a self-consistent electromagnetic full-particle simulation[Hikishima et al., 2009b]. The coherent whistler-mode rising chorus can effectively scatter theenergetic electrons through the cyclotron resonant interaction. With increasing the frequency of risingchorus, the distribution functions show a significant deformation along the decreasing resonance

Figure 17: Temporal variation of distribution function of energetic electrons. The whitecurves are the resonance velocities.

13

velocity as shown with the elapsed times (i) to (iii) in Figure 17. The scattering of resonant electrons
follows a nonlinear process. The nonlinear resonant interaction induces acceleration of trappedelectrons and deceleration of untrapped resonant electrons. The nonlinear behavior of resonant
electrons would contribute to the dynamics of magnetospheric electrons.
Katoh et al. (2008) have showed that in the simulation of chorus generation, some resonant electrons
are rapidly energized by the processes of relativistic turning acceleration (RTA) and ultra-relativistic
acceleration (URA). RTA and URA are particular forms of nonlinear wave trapping of resonant
electrons by coherent whistler-mode waves and constitute viable mechanisms for the generation ofrelativistic electrons in the radiation belts of magnetized planets.

Figure 18: (Top) A fraction ofresonant
electrons
arenonlinear ly trapped by chorus
waves and are effectively
accelerated.
(Bottom) Wave packets ofwhistler-mode
waves
are
successively generated near themagnetic
equator,theiramplitudes increasing as they
propagate
intobothhemispheres.

Amano and Hoshino (2008) investigated electron acceleration mechanism in high Mach number
collisionless perpendicular shocks in a weakly magnetized plasma using two-dimensional
particle- in-cell simulations. They observe strong electron
acceleration associated with large amplitude electrostatic
waves in the shock transition region. Multidimens ional
effects as well as the self-consistent shock structure are
essential for the strong electron acceleration at high Mach
number shocks.
Figure 19: Snapshot of particle phase-space plots
and compressional magnetic field profile
averaged over the y-direction. Color represents
the logarithm of the particle count in each bin.
Note that the vertical scale of the electron energy
spectrum (the second panel from the bottom) is
shown on a logarithm ic scale.

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Saito et al.(2008) demonstrated two-dimensional electromagnetic particle-in-cell simulations inmagnetized, homogeneous, collis ionless electron-proton plasma to investigate the forward cascade ofwhistler turbulence. The turbulence displays magnetic energy spectra that are relatively steep functionsof wavenumber and are anisotropic with more energy in directions relatively perpendicular to thebackground magnetic field than at the same wavenumbers parallel to it, as shown in Figure.
Figure 20: Magnetic fluctuation energy spectrum
displaying the anisotropic turbulence. Bottom andleft axis are wavenumbers parallel andperpendicular to the background magnetic field.
The wavenumbers are normalized to electron
inertial length. As shown in the figure 1, thefluctuating energy preferentially cascades to theperpendicular wavenumbers. Since obliquely
propagating whistler wave tends to haveelectrostatic fluctuation, the whistlers
preferentially heat electrons parallel to thebackground magnetic field through Landau
resonance.
The anisotropic whistler turbulence interacts with electrons through Landau and cyclotron
resonance, and heats them in directions both parallel and perpendicular to the background magnetic
field, with stronger heating in the parallel direction. They show that whistler turbulence evolves
preferentially to oblique propagation, and electrons gain more energy in the parallel direction.
<Antenna Characteristics in Space Plasma>
Miyake and Usui (2008) studied effects of photoelectron on the impedance characteristics of anelectric field antenna by performing the electromagnetic Particle-In-Cell simulations. They modeled thephotoelectron emission from the antenna surface and the antenna charging caused by the photoelectron
emission. After an equilibr ium solution of a photoelectron sheath profile is obtained, they examined theantenna impedance. They confirmed that the impedance characteristics in the presence ofphotoelectrons are well described by a parallel equivalent circuit consisting of the resistance and thecapacitance.
Figure 7 shows the antenna conductance (inverse of the resistance) versus frequency for two cases ofthe photoelectron flux. The conductance value is greater for the case of the large photoelectron density.
An analytical derivation of the antenna conduction shows that the conduction value is determined by
the conduction current caused by the actual motion of photoelectrons. The result indicated that theantenna impedance can vary with the spacecraft spin, which causes the variation of the photoelectron
density around the antenna.
They also developed a simulation method of analyzing the behavior of the plasma-wave receiving by
an electric field antenna. The Langmuir or Whistler waves were set up as an initial condition, and thewaves propagate in the simulation region. As a preliminary result, it was confirmed that the effective
length of a simple dipole coincides with the half of its physical length in absence of sheath andphotoelectron effects. They also confirmed that the effective length of MEFISTO aboard the
BepiColombo is roughly equal to the distance between two separated sensor elements, which are
deployed to the opposite directions.

15

Figure 21: Antenna conductance as function of frequency for the cases of large andsmall photoelectron fluxes, which is obtained by the Particle-In-Cell simulations.
Imachi et al. [2008] have analyzed the impedance of the electric dipole antenna which is placed in
the conductive medium such as space plasma at low frequencies. Their analysis is based on the resultof Rheometry experiment to measure the relationship between the output voltage of a pair of dipole
wire antennas and the intensity of the electric field applied to them in water. They investigated theequivalent circuits of this experiment assuming the electric field to be virtual power suppliers which areconnected in parallel (see Figure 22), and found that the structure of the antenna including theinsulation coating around the antenna wire affects the sensitivity at very low frequencies when it isconnected to high impedance receivers. Additionally they performed computer simulation of the
distribution of electric potential around the antenna wire, and clarif ied the difference in the distribution
depending on the structure of the antennas (Figure 23).

Figure 22: Equivalent circuit of an antenna wire, assuming the electric field tobe virtual power suppliers which are connected in parallel.

Figure 23: S imulated distributions of electric potential. The left figure shows thecase that the antenna wires have no insulation coating. The right figure shows
the case that they have insulation coating on the side of the wires.

16

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Conferences and Meetings（August 2008〜Feburuary 2009）
1) XXIXth URSI General Assembly, Chicago, USA Aug. 9-16, 2008
2) IMAS/The International Radiation Symposium (IRS2008): Current Problems in Atmospheric
Radiation, Brazil Aug. 3-8, 2008
3) ICPP2008：International Congress on Plasma Physics, Fukuoka, Japan Sep. 8-12, 2008
4) BepiColombo(/Messenger) Science Working Team Meeting #3, Sendai, Japan Sep. 16-18, 2008
5) SGEPSS Fall Meeting, Sendai, Japan Oct. 9-12, 2008
6) European Microwave Week (EuMW) 2008, Amsterdam, Netherlands Oct. 27-31, 2008
7) International Symposium on Antennas , Propagation and Em Theory (ISAPE) 2008, Kunming,
China, Nov. 2-6, 20088) 1st International Symposium of Polar Research, Tokyo, Japan Nov. 4-6, 2008
9) International Symposium: F ifty Years after IGY -Modern Information Technologies and Earth andSolar Sciences-, Tokyo, Japan, Nov. 10-13,
10) 2008 ULTIMA (Ultra Large Terrestrial International Magnetometer Array)
General Meeting, Tsukuba, Japan, Nov. 13, 2008.
11) The 15th world congress on Intelligent Transport Systems (ITS) 2008, New York Nov. 16-20, 2008
12) AGU 2008 Fall Meeting, San Francisco Dec. 15-19, 2008
13) Asia-Pacific Microwave Conference (APMC) 2008, Hong Kong and Macau Dec. 16-20, 2008
The ICPP (International Congress on Plasma Physics) 2008 meeting was held in Fukuoka, Japan, on
Sep. 8-12, 2008. This meeting covered a wide area of plasma physics, including ULF waves, thus
many papers were presented related to ULF waves.
The 118th SGEPSS (Society of Geomagnetism and Earth, Planetary and Space Sciences) Fall
Meeting was held in Sendai, Japan, on Oct. 9-12, 2008. This meeting covered a wide area ofgeomagnetism and earth, planetary and space sciences, including ULF waves, thus many papers were
presented related to ULF waves.

19

The 2008 ULTIMA General Meeting was held in Tsukuba, Japan, On Nov. 13, 2008. ULTIMA(Ultra Large Terrestrial International Magnetometer Array) is an international consortium that aims at
promoting collaborating research on the magnetosphere, ionosphere, and upper atmosphere through theuse of ground-based magnetic field observations. ULTIMA is composed of individual magnetometer
arrays in different countries/regions.
The official webpage of ULTIMA is at:
http://www.serc.kyushu-u.ac.jp/ultim a/ultima.html At the 2008 ULTIMA General meeting, several
presentations were made on ULF waves observed by the magnetometer arrays.
Future Conferences and Meeting
1)
2)
3)
4)

3rd European Conference on Antenna and Propagation (EuCAP) 2009, Berlin March 23-27, 2009
IEEE MTT-S International Microwave Symposium 2009, Boston Massachusetts June 7-12, 2009
IEEE AP-S 2009, Charleston, South Carolina May 31-June 6, 2009
Modern Challenges in Nonlinear Plasma Physics: A conference honoring the career of Dennis
Papadopoulos"
June
15-19,
2009,
Sani
Resort,Halkidiki,
Greecehttp://www.astro.auth.gr/~vlahos/kp
5)
The 11th Scientif ic Assembly of IAGA, Hungary Aug. 23-30, 2009
6) JInternational Symposium on Antenna Technology and Applied Electromagnetics (ANTEM) andthe Canadian Radio Sciences Meeting (URSI/CNC), Banff, Canada uly 27-30, 20097) IEEE AP-S 2010, Toronto, Ontario, Canada July 10-17, 2010
Ack nowlegement
The editors thank to Dr. H. Kojima, Dr. Y. Kasahara, Dr. S.Yagitani, Dr. H. Kawano, Dr. Y. Miyoshi,
Dr. A. Kumamoto, and Dr. K. Ishisaka for their contribution to this report.

20