資料7-G

Commission G Report
March 26, 2014
1. Research Report
1.1. Report from Planetary Plasma and Atmospheric Research Center, Tohoku University(Yasumasa Kasaba, Tohoku University)=== Report from recent papers ===(1) Jupiter’s sodium nebula showed an enhancement in late May through the beginning of June 2007.
This means Io’s volcanic activity and the magnetosphere’s plasma content increased during this period.
On the other hand, Jupiter’s radio emission called HOM became quiet after the sodium nebulaenhancement. The HOM emission is considered to be related to the activity of aurorae on Jupiter.
These observation results therefore suggest that the increase in plasma supply from Io into Jupiter’smagnetosphere weakens its field-aligned current, which generates the radio emissions and aurorae on
Jupiter. By comparing our observation results to recent model and observation results, we add
supporting evidence to the possibility that Io’s volcanism controls Jupiter’s magnetospheric activity.
(2) Observations of [OI] 630 nm emission in the Enceladus torus around Saturn have been made at thesummit of Mt. Haleakala in Hawaii using a high-dispersion echelle spectrograph coupled to a 40 cm
telescope in the period of 13 May through 19 June 2011. A slit of the spectrograph was aligned
perpendicular to the equatorial plane of Saturn and placed at a distance of 4 Saturn's radii (Rs) fromthe planetary center in the dawn side to put the Enceladus torus within the field of view. As a result,[OI] 630 nm torus emission was detected with S/N ~ 7 for summed exposure of 20 h during theobserving period. The observed brightness has a maximum value of 4.1 ± 0.6 Rayleighs (R) near theequator, and it extends to north-south (N-S) direction with a full width at half maximum of 0.8 Rs. We
made estimation to explain mechanism of the observed brightness taking into account an excitation of[OI] 630 nm by electron impact and photodissociation of water group molecule (OH and H2O).
Densities of electron, O, OH, and H2O and electron temperature derived from data taken by Cassiniand Hubble telescope were used for the estimation. The observed brightness is reasonably explained,taking into account an uncertainty of estimation depending on N-S distributions of species and quiet
solar activity conditions. The estimation also suggests that [OI] 630 nm emission is excited byphotodissociation of OH and H2O and by electron impact of O with their contributions of 50%, 30%,
and 20%, respectively, for quiet solar activity. We also note that the intensity due to photodissociation
has considerable variability depending on the level of solar activity by a factor of 2.5.
(3) Auroral kilometric radiation (AKR) is known to be transient emissions generated by rapidly
accelerated electrons together with sudden auroral activation in the polar magnetosphere of the earth.
In contrast, the characteristics and relationship with the auroral acceleration of rather continuous AKR
emissions are not well understood. We examine the emission using long-term data and report that thecontinuous AKR emission frequency changes with universal time (UT) as the Earth rotates, indicatingthat the Earth is a spin-modulated variable radio source. The observed UT variation of AKR frequency
means that the acceleration altitude changes periodically with planetary rotation. The observations
indicate that the diurnal wobble of the tilted geomagnetic field in the solar wind flow alters themagnetosphere-ionosphere (M-I) coupling state in the polar magnetosphere, giving rise to periodic
variation of auroral particle acceleration altitude. These observations of planetary radio wave
properties provide insight into the physics of planetary particle acceleration(4) Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations withthe radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a307

資料7-G

two-dimensional auto burst detection algorithm that can distinguish each type-I burst element fromcomplex noise storm spectra that include numerous instances of radio frequency interference (RFI).
This algorithm removes RFI from the observed radio spectra by applying a moving median filter along
the frequency axis. Burst and continuum components are distinguished by a two-dimensional
maximum and minimum search of the radio dynamic spectra. The analysis result shows that each typeI burst element has one peak flux without double counts or missed counts. The peak flux distributionof type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and
5.
(5) Black aurora is a small-scale (typically a few to 10 km) black structure seen in diffuse aurora, andits generation process has been studied with immense interest. We report the precise characteristics ofblack aurora based on simultaneous image and particle measurement data and possible generation
process. Thirteen black auroral events are identified from the Reimei satellite data, and the relationshipbetween particle and auroral images around the satellite's magnetic footprints is investigated in detail.
We found that a number of small-scale deficiencies were embedded in precipitating electrons from thecentral plasma sheet with energies greater than 2–7 keV and that each deficiency corresponded exactly
to black arcs and black patches at the magnetic footprint. Therefore, black arcs and black patches are
not associated with a field-aligned potential (such as a divergent potential structure) but probably
originate from the suppression of pitch angle scattering. In the black auroral region, low-energy (2–5
keV) inverted-V-type downward electrons (spanning channels that are several tens of kilometers wide)
often appear to overlap with high-energy (several keV) plasma sheet electrons.
(6) This paper examines AKR spectra using the long-term observation from the Polar satellite to provethe comprehensive features of field-aligned auroral acceleration and to give observational constraints
to the theoretical mechanisms for acceleration at substorm. The remote observations of substorm
phenomena through auroral radio waves from the high altitude polar magnetosphere disclosed somefundamental characteristics of the vertical auroral acceleration region and provided new informationon the formation process for field-aligned electric field at substorm onset. Furthermore, we reveal new
aspect of the relationship between the plasma state in the plasma sheet and the formation of auroral
acceleration.
(7) In order to monitor space environment and its temporal variations, JAXA Space Environment
Group has been developing space radiation detectors as well as magnetometers and installing them on
Low Earth Orbit (LEO) satellites, Geostationary Orbit (GEO) satellites, Geostationary Transfer Orbit(GTO) satellite, Quasi Zenith Orbit (QZO) satellite and Japanese Experimental Module (JEM) of theInternational Space Station (ISS). We are using these space environment data to know the situation of
space environment and to provide warning messages to the satellite operators as well as ISS/JEM
manager, when the space environment will be harmful. Based on our observation data, we also haveconstructed an advanced electron belt model for the use in satellite manufacturing. With spaceradiation data obtained by JAXA satellites and ISS, some findings related to the space radiation
environment have been obtained. We will review our activities related to the space environment
research and development in JAXA.
(8) The Space Environment Data Acquisition equipment (SEDA), which was mounted on the Exposed
Facility (EF) of the Japanese Experiment Module (JEM, also known as “Kibo”) on the International
Space Station (ISS), was developed to measure the space environment along the orbit of the ISS. This
payload module, called the SEDA-Attached Payload (AP), began to measure the space environment inAugust 2009. This paper reports the mission objectives, instrumentation, and current status of theSEDA-AP.

308

資料7-G(9) We have carried out ground-based observations, optimized to temporal and spatial characteristics
of pulsating auroras (PAs) in the micro/meso scale, using an electron multiplying charge coupleddevice (EMCCD) camera with a wide field of view corresponding to 100 × 100 km at an altitude of
110 km and a high sampling rate up to 100 frames per second. We focus on transient PAs propagating
southward around 1100 UT, in the early recovery phase of the substorm, on 4th March 2011. Three
independent patches (PA1–3) each with different periods between 4 and 7 s were observed, whichmeans that the periodicity was not explained by the electron bounce motion and strongly depended on
local plasma conditions in the magnetosphere or in the ionosphere. One more insight is that only PA1
had also a sharp peak of modulations around 1.5 Hz, with a narrow frequency width of 0.30 Hz, andthe strong modulations existed as a small spot in the center of PA1. We have also conducted crossspectrum analysis and have obtained coherence and phase distributions for auroral variations between
0.1 and 3.0 Hz. The results indicated that low frequency variations from 0.2 to 0.5 Hz inside PA1–3
propagated as a collective motion in well-defined directions. The estimated horizontal propagation
velocities ranged from 50 to 120 km/s at the auroral altitude. The velocities are almost consistent with
the Alfven speed at the magnetic equator, which suggests that compressional waves have an effect on
PA via modulations of the ambient plasma environment.
(10) A new radio spectropolarimeter for solar radio observation has been developed at Tohoku
University and installed on the Iitate Planetary Radio Telescope (IPRT) at the Iitate observatory inFukushima prefecture, Japan. This system, named AMATERAS (the Assembly of Metric-band
Aperture TElescope and Real-time Analysis System), enables us to observe solar radio bursts in thefrequency range between 150 and 500 MHz. The minimum detectable flux in the observation
frequency range is less than 0.7 SFU with an integration time of 10 ms and a bandwidth of 61 kHz.
Both left and right polarization components are simultaneously observed in this system. These
specifications are accomplished by combining the large aperture of IPRT with a high-speed digital
receiver. Observational data are calibrated and archived soon after the daily observation. The databaseis available online. The high-sensitivity observational data with the high time and frequency
resolutions from AMATERAS will be used to analyze spectral fine structures of solar radio bursts.
(11) The first coordinated observations of an active region using ground-based radio telescopes and theSolar Terrestrial Relations Observatory (STEREO) satellites from different heliocentric longitudes
were performed to study solar radio type-I noise storms. A type-I noise storm was observed between
100 and 300 MHz during a period from 2010 February 6 to 7. During this period the two STEREO
satellites were located approximately 65° (ahead) and –70° (behind) from the Sun-Earth line, which iswell suited to observe the earthward propagating coronal mass ejections (CMEs). The radio flux of thetype-I noise storm was enhanced after the preceding CME and began to decrease before thesubsequent CME. This time variation of the type-I noise storm was directly related to the change of theparticle acceleration processes around its source region. Potential-field source-surface extrapolationfrom the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) magnetograms
suggested that there was a multipolar magnetic system around the active region from which the CMEs
occurred around the magnetic neutral line of the system. From our observational results, we suggestthat the type-I noise storm was activated at a side-lobe reconnection region that was formed after
eruption of the preceding CME. This magnetic structure was deformed by a loop expansion that led tothe subsequent CME, which then suppressed the radio burst emission.
(12) The relationships between solar radio type-I bursts and soft X-ray activities were investigatedusing Hinode/XRT and a ground-based radio telescope belonging to Tohoku University. Although a
type-I burst is thought to be generated by high energy non-thermal electrons in the solar corona, thecounterpart of this radio burst in X-rays or EUV have yet to be identified. In this study, we found somesmall scale soft X-ray activities on the XRT images around the onset time of the type-I burst when 10
percent of the soft X-ray flux enhancement around the onset time of the radio burst is defined as a309

資料7-G

burst-related activity. However, the causal relationship between the observed soft X-ray activities andthe onset of the type-I burst are unclear, and more simultaneous observations of radio bursts and Xrays are needed to investigate the coronal counterpart of the type-I burst.
(13) A model of the martian exosphere is built for average solar conditions. A Chamberlain's approach(Chamberlain, J.W. [1963]. Planet. Space Sci. 11, 901) is used to describe the O, CO, CO2, and O2
thermal exospheric components. The average thermal oxygen density at 300 km in altitude varies by
about one order of magnitude with seasons. A Monte-Carlo test particle simulation is also developedin order to estimate the non-thermal oxygen component of the exosphere. The seasonal variation of the
non-thermal oxygen average density is much less than the thermal component but displays clear
seasonal variations of its spatial distribution. The neutral oxygen atomic escaping flux varies from 2.9
to 5.3 x 1025 s―1 in good agreement with Valeille et al. (Valeille, A., Combi, M.R., Bougher, S.W.,
Tenishev, V., Nagy, A.F. [2009a]. J. Geophys. Res. (Planets) 114, 11006; Valeille, A., Tenishev, V.,
Bougher, S.W., Combi, M.R., Nagy, A.F. [2009b]. J. Geophys. Res. (Planets) 114, 11005). Mars's
oxygen exosphere is thermal below 600 km and non-thermal above 700 km at all seasons. The typicalscale height is ∼45 km for thermal O and ∼500 km for the non-thermal oxygen density. The total
photoionization rate above 300 km corresponds to a CO•2 /O+ total production ratio between 0.004
and 0.02. When compared to the composition of the escaping flux measured by ASPERA-3/Mars
Express, this suggests that ions formed below 300 km should significantly contribute to the escaping
ion flux and/or that a significant part of the newly O+ ions reimpacts Mars. The simulated oxygen
density profile is also compared to the recent observed profile by Alice/Rosetta (Feldman, P.D. et al.
[2011]. Icarus 214, 394-399). Although the scale height of our simulated non-thermal oxygen
exosphere and the transition from thermal to non-thermal dominated exospheres are slightly higher
than suggested by Feldman et al. (Feldman, P.D. et al. [2011]. Icarus 214, 394-399), a good agreement
is found when taking into account the uncertainties of Alice/Rosetta observations.
=== Short notice of research facility ===(14) IPRT (Iitate Planetary Radio Telescope) is a ground-based VHF-UHF radio telescope developedby Tohoku University, which has been developed at the Iitate observatory in Fukushima prefecture
Japan since 2000 and dedicated for the observations of solar and planetary radio emissions. IPRT has
two distinctive radio receivers; one is a low noise and quite stable receiver tuned at 325MHz and
785MHz, and another one is a 100-500MHz spectro-polarimeter, named AMATERAS (the Assemblyof Metric-band Aperture TElescope and Real-time Analysis System). The former is mainly used forobserving Jupiter’s synchrotron emission with the sensitivity of 0.1Jy, and enables us to investigate
dynamical variations of Jupiter’s deep inner magnetosphere. The latter is used for observing solar
radio bursts with 10ms accumulation time and 61KHz bandwidth, and enables us to clarify various
micro structure of wave-particle or wave-wave interactions generated in the solar corona region.
References(1) Yoneda, M., F. Tsuchiya, H. Misawa, Bonfond B., Tao C., M. Kagitani and S. Okano (2013),
Io’s volcanism controls Jupiter’s radio emissions, Geophys. Res. Lett., 40, 671–675,
doi:10.1002/grl.50095.
(2) Kodama, K., M Kagitani, S. Okano and N. M. Schneider (2013), First detection of [OI] 630
nm emission in the Enceladus torus, Geophys. Res. Lett., 40, 4177-4181,
doi:10.1002/grl.50799.
(3) Morioka, A., Y. Miyoshi, S. Kurita, Y. Kasaba, V. Angelopoulos, H. Misawa, H. Kojima, andJ. P. McFadden (2013), Universal time control of AKR: Earth is a spin-modulated variable
radio source, J. Geophys. Res. Space Physics, 118, 1123?1131, doi:10.1002/jgra.50180.

310

資料7-G(4) Iwai, K., S. Masuda, Y. Miyoshi, F. Tsuchiya, A. Morioka, and H. Misawa (2013), Peak flux
distribution of solar radio Type-I bursts from highly resolved spectral observations, Astrophys.
J., 768:L2, doi::10.1088/2041-8205/768/1/L2.
(5) Sakanoi, T. Y. Obuchi, Y. Ebihara, Y. Miyoshi, K. Asamura, A. Yamazaki, Y. Kasaba, M.
Hirahara, T. Nishiyama, and S. Okano (2012), Fine-scale characteristics of black aurora and its
generation process, in Auroral Phenomenology and Magnetospheric Processes: Earth and other
Planets, AGU Geophysical Monograph 197, edited by A. Keiling et al., Amer. Geophys. Union,
Washington, D. C., 271-278.
(6) Morioka, A., Y. Miyoshi, N. Kitamura, H. Misawa, F. Tsuchiya, J. D. Menietti, and F.
Honary (2012), Fundamental characteristics of field-aligned auroral acceleration derived from
AKR spectra, J. Geophys. Res., 117., A02213, doi:10.1029/2011JA017137.
(7) Obara,T. (2012), Space Environment Measurements by JAXA satellites and ISS, Acta
Astronautica, pp.1-10, doi:10.1016/j.actaastro.2011.08.009(8) Obara, T.(2012), Space Environment Measurement by ISS / SEDA-AP, Electronics andCommunications in Japan, Vol.95, Issue 9, pp.10-16, doi:10.1002/ecj.11418(9) Nishiyama, T., T. Sakanoi, Y. Miyoshi, R. Kataoka, D. Hampton, Y. Katoh, K. Asamura, andS. Okano (2012), Fine scale structures of pulsating auroras in the early recovery phase of
substorm using ground-based EMCCD camera, J. Geophys. Res., 117, A10229,
doi:10.1029/2012JA017921.
(10)Iwai, K., F. Tsuchiya, A. Morioka, H. Misawa (2012), IPRT/AMATERAS: A New MetricSpectrum Observation System for Solar Radio Bursts, Solar Phys., 277, 2, 447-457,
10.1007/s11207-011-9919-y(11)
Iwai, K., Y. Miyoshi, S. Masuda, M. Shimojo, D. Shiota, S. Inoue, F. Tsuchiya, A.
Morioka, and H. Misawa, Solar Radio Type-I Noise Storm Modulated by Coronal Mass
Ejections, ApJ 744 167 doi:10.1088/0004-637X/744/2/167, 2012(12)
Iwai, K., H. Misawa, F. Tsuchiya, A. Morioka, S. Masuda, and Y. Miyoshi (2012),
Survey of Accelerated Particles in a Solar Active Region Using Hinode/XRT and GroundBased Type-I Radio Burst Observations, Hinode-3, ASP Conference Series, Vol. 454, 249253(13)M. Yagi, F. Leblanc, J.Y. Chaufray, F. Gonzalez-Galindo, S. Hess, R. Modolo (2012), Mars
exospheric thermal and non-thermal components: Seasonal and local variations, Icarus,
Vol.221, Issue 2, pp. 682-693
1.2. Report from Department of Geophysics, Tohoku University(Yasumasa Kasaba, Tohoku University)=== Report from recent papers ===(1) We investigate the background magnetic field dependence of the saturated state of amagnetorotational instability (MRI) in an accretion disk by performing three-dimensional
magnetohydrodynamic simulations. We assume an unstratified disk by employing the local
shearing box approximation. Three different uniform background magnetic field configurations
are treated for a wide range of field intensities. These simulations indicate that the time variationsof the turbulent stress and the magnetic energy are altered by the presence of a poloidal
component of the background field. We find that the saturation amplitude of the turbulent stressand the magnetic energy are determined by both the poloidal and azimuthal components of the
field. In particular, when the poloidal component has the same intensity, the obtained turbulent
stress for β y0 200 becomes smaller than those for a purely poloidal field case. Despite the factthat the background field affects the MRI turbulence, the correlation between the obtained311

資料7-G

turbulent stress and the magnetic energy in the nonlinear stage is independent of the field topology.
Our results indicate that the saturated turbulent stress has a stronger correlation with the power ofthe perturbed component of the magnetic field than with the power of the total magnetic field.
These results suggest that both the intensity and the direction of the background magnetic fieldsignificantly affect the turbulent motion of the MRI in accretion disks.
(2) Io-Jupiter interaction leads to auroral emissions and Jovian decametric radiations (Io-DAM). The
longitudinal distribution of the Io-DAM occurrence probability has been considered to becontrolled by the footprint magnetic intensity of each hemisphere. Recent observations revealed
that the brightness of the main auroral spot is mainly modulated by Io's magnetic latitude. In thepresent study, we propose that the Io-DAM occurrence probability is controlled by the north-south
asymmetry of the footprint magnetic intensity, in addition to Io's magnetic latitude. Hall
magnetohydrodynamic equations are solved in the corotating meridional plane, which includes the
Jovian ionosphere of finite thickness. We assume that the ionospheric Pedersen conductance isinversely proportional to the footprint magnetic intensity; the conductance is nearly the same forboth ionospheres at a longitude of 290°, while twice higher for the south than for the north at alongitude of 110°. Above the northern ionosphere, the parallel current density further than 20°
downstream of the main spot is estimated to be 1.5–2.0 times larger for 290° than for 110°. This
indicates that if the Io-DAM lead angle is large, the suppressed Io-DAM occurrence probability
for the northern hemisphere around 110° would be caused by the north-south asymmetry of the
footprint magnetic intensity. A large current density conducted into the south around 110° would
be the source of the Io-D component, radiated from the southern hemisphere. The observedbrightness of the Io-related auroras is discussed in the context of the intensity of the parallel
current density.
(3) We have investigated the geological conditions below two lava flow units through determining thebulk permittivity and porosity in the uppermost basalt layer to depths of a few hundred meters. We
use a newly developed method based on three data sets obtained by the Lunar Radar Sounder(LRS), Multiband Imager (MI), and Terrain Camera (TC) onboard the Selenological andEngineering Explorer (SELENE; Kaguya) spacecraft. The bulk permittivity of the uppermost
basalt layer is calculated as the ratio of the apparent radar depth to the thickness of the uppermost
basalt layer. Its thickness can be constrained from the excavation depths of two types of craters(haloed and nonhaloed craters). These craters are identified on the basis of FeO and/or TiO2 maps
created from the MI data. These excavation depths are determined based on the measurement of
the crater diameter using the TC data. The apparent radar depth is derived from the time delay
between the surface echo and subsurface echo measured by LRS near the craters. The bulk
permittivities are estimated to be 2.8–5.5 in a lava flow unit of Mare Humorum and 4.2–18.0 in alava flow unit of Mare Serenitatis. These bulk permittivities are indicative of porous basalt layerswith the porosities of 19%–51% in the unit of Humorum and 0%–33% in the unit of Serenitatis.
The estimated porosities would be mainly explained by two different sources: intrinsic voids oflava and impact-induced cracks.
(4) By a series of self-consistent electron hybrid code simulations, we study the effect of the
background magnetic field inhomogeneity on the generation process of whistler-mode chorus
emissions. Chorus with rising tones are generated through nonlinear wave-particle interactions
occurring around the magnetic equator. The mirror force plays an important role in the nonlinear
interactions, and the spatial inhomogeneity of the background magnetic field is a key parameter ofthe chorus generation process. We have conducted numerical experiments with different spatial
inhomogeneities to understand properties of the chorus generation process. We assume the same
initial condition of energetic electrons at the magnetic equator in all simulation runs. The
simulation results reveal that the spectral characteristics of chorus significantly vary depending on

312資料7-G

the magnetic field inhomogeneity. Whistler-mode emissions are generated and propagate awayfrom the equator in all simulation runs, but distinct chorus elements with rising tones are only
reproduced in the cases of small inhomogeneities. In the simulation that had the smallest
inhomogeneity, we find excitation of broadband hiss-like emission (BHE) whose amplitudes arecomparable to discrete chorus elements found in other simulation runs. The BHE consists of many
wave elements with rising tones nonlinearly triggered in the region close to the magnetic equator.
We show that the small spatial inhomogeneity of the background magnetic field results in thesmall threshold amplitude for the nonlinear wave growth and allows the triggering process ofrising tone elements to emerge easily in the equatorial region of the magnetosphere.
=== Short notice of research facility ===(5) The Jovian and solar radio wave receiver system in HF range (15-40MHz) was continuously
operated at Iitate Observatory of Tohoku University. Spectrograms of Jovian and solar radio wave
with a time resolution of 0.5 sec were automatically archived and provided to the researchers
through the internet. The discussion on combining this data archive with that of Nancay
observatory has started between the researches of Paris Astronomical Observatory and Tohoku
University.
In addition, the operation of RF waveform recording receiver system for the observation of Jovian
decametric S-bursts was started at Iitate Observatory since October 2013. The data will be usefulfor the analysis of the repetition of S-bursts, which is caused by Jovian Ionospheric Alfven
Resonator (IAR).
Reference(1) Sai, K., Y. Katoh, N. Terada, and T. Ono, Effect of Background Magnetic Field on Turbulence
Driven by Magnetorotational Instability in Accretion Disks, Astrophys. J., 767, 165,
doi:10.1088/0004-637X/767/2/165, 2013.
(2) Matsuda, K., Y. Katoh, N. Terada, and H. Misawa, A simulation study of Io-related Jovian
decametric radiation: Control factor of occurrence probability, J. Geophys. Res. Space Physics,
118, 5082-5098, doi:10.1002/jgra.50493, 2013.
(3) Ishiyama, K., A. Kumamoto, T. Ono, Y. Yamaguchi, J. Haruyama, M. Ohtake, Y. Katoh, N.
Terada, and S. Oshigami, Estimation of the permittivity and porosity of the lunar uppermost
basalt layer based on observations of impact craters by SELENE, J. Geophys. Res. Planets, 118,
1453-1467, doi:10.1002/jgre.20102, 2013.
(4) Katoh, Y. and Y. Omura, Effect of the background magnetic field inhomogeneity on generation
processes of whistler-mode chorus and hiss-like broadband emissions, J. Geophys. Res. Space
Physics, 118, 4189-4198, doi:10.1002/jgra.50395, 2013.
1.2. Report from National Institute of Communications and Informatiion(Takuya Tsugawa, NICT)=== Comparison of meridional thermospheric winds observed by ionosondes and Fabry-Perot
interferometers ===We construct the first comparison of the estimated meridional wind velocities with meridional windobserved with FPIs. We analyzed data from the ionosondes and FPIs installed at Chiang Mai, Thailand,
and Kototabang, Indonesia, from 2010. We found that the estimated and observed wind velocities
were generally in good agreement on most nights, although on some nights, the wind velocities weredifferent. The assumption that the meridional wind is equal anywhere between the two ionosonde
stations would not be suitable for the days when the winds were not in good agreement. We also
investigated the seasonal dependence of the correlation between the estimated and observed313

資料7-G

meridional winds. They were in good agreement from February to April and were not in good
agreement from May to July.
Reference
Michi Nishioka et al. (2014), Comparison of meridional thermospheric winds observed by ionosondes
and Fabry-Perot interferometers (in Japanese), Arctic Record (ISSN 0085-7289), 57(3), 357.
1.4. Report from Solat-Terrestrial Environmental Laboratory, Nagoya University(Kazuo Shiokawa, Nagoya University)
A campaign observation of auroras and VLF/ELF waves was carried out from January 28 to February
5, 2014 at Poker Flat, Alaska, in collaboration with an auroral rocket launch. Dual cameras were used
to determine the height of auroras. A loop antenna with a 20kHz-sampling portable recorder wastested for VLF/ELF wave measurement at remote site without power line.
1.5. Report from Research Institute for Sustainable Humanosphere, Kyoto University(Mamoru Yamamoto, Kyoto University)=== Report from recent papers ===(1) The so-called large scale wave structure (LSWS) at the base of F-layer is the earliest manifestationof seed perturbation for the Rayleigh-Taylor (R-T) instability. It has been found to playdeterministic role on the development of equatorial plasma bubbles (EPBs). Except for a few casestudies, a comprehensive investigation has not been conducted to determine the characteristics ofLSWS. One reason is that it is not straightforward with existing sensors to detect LSWS,
particularly, in the spatial domain. In this scenario, a comprehensive study was carried out, for the
first time, on the spatial and temporal characteristics of LSWS. Observations were made over the
African and Southeast Asian sectors during the year 2011. The observations confirm the findings
from case studies, that these wave structures can occur a few degrees west of E-region sunset
terminator, and can grow significantly in amplitude at longitudes east of sunset terminator. Withthe use of additional stations that are located on either side of dip equator, the phase fronts of these
spatial structures are shown to be aligned with geomagnetic field lines over a wide latitudinal beltof 5-6o (~500 - 600 km) centered on dip equator. The zonal wavelengths of these structures arefound to vary from 100 to 700 km which is consistent with the earlier reports. A new statisticalfinding is that EPBs were consistently observed when the amplitudes of LSWS were grown tosufficient strengths. These results provide better insights on the underlying physical processes
involved in excitation of LSWS in terms of important roles being played by the E-region electricalloading and the polarization electric fields that are induced via spatially varying dynamo current
due to neutral wind perturbations associated with Atmospheric Gravity Waves (AGWs).
(2) A new three-dimensional GPS ionospheric tomography technique is developed that uses total
electron content (TEC) data from the dense Global Position System (GPS) receiver network, GPS
Earth Observation Network (GEONET) in Japan, and it will not require an ionospheric model as
the initial guess that will bias the reconstruction of electron density. The GEONET is operated by
Geospatial Information Authority of Japan and consists of more than 1200 receivers; this highdensity and wide coverage helps to reconstruct the electron density distribution in the ionospherewith high spatial resolution. This tomography technique uses a constrained least squares fit toreconstruct the three-dimensional electron density distributions. This method is different to mostother techniques as they require a background ionospheric model as an initial guess that could bias
the reconstructed electron density. It rather uses a prior condition that the electron density should
not exceed a certain value that is determined by the restrain parameter, which is derived from the314

資料7-G

NeQuick model. Its independency of the initial guess from a model will make it useful even in
disturbed conditions. This paper presents results that are obtained by using this new tomographic
technique. The reconstruction of three-dimensional ionospheric tomograms is demonstrated using
the GPS data, and the reliability and robustness are checked with simulated tomograms obtainedusing the synthetic GPS-TEC data produced using NeQuick model.
Reference(1) S. Tulasi Ram, M. Yamamoto, R. T. Tsunoda, H. D. Chau, T. L. Hoang, B. Damtie, M. Wassaie,
C. Y. Yatini, T. Manik and T. Tsugawa, Characteristics of Large Scale Wave Structure (LSWS)
observed from African and Southeast Asian longitudinal sectors, J. Geophys. Res. Space Phys.,
doi:10.1002/2013JA019712R, in press, 2014.
(2) Gopi K. Seemala, Mamoru Yamamoto, Akinori Saito, and Chia-Hung Chen, Three-dimensional
GPS ionospheric tomography over Japan using constrained least squares, J. Geophys. Res. Space
Phys., doi:10.1002/2013JA019582, in press, 2014.
2. Meetings
Meetings scheduled in relation to URSI Commission-G were conducted as listed below.
Japan Geoscience Union (JpGU) Meeting 2014
Pacifico Yokohama, Yokohama, Japan, April 28-May 2, 2014.
http://www.jpgu.org/meeting_e/
14th International Workshop on Technical and Scientific Aspects of MST Radar- INPE - São José dos Campos/SP – Brazil, May 25-31, 2014
http://www2.inpe.br/climaespacial/MST14/
Asia Oceania Geosciences Society 11th Annual Meeting,
Royton Sapporo Hotel, Sapporo, Japan, July 28-August 1, 2014.
http://www.asiaoceania.org/aogs2014/
The 40th COSPAR Scientific Assembly
Moscow, Russia, August 2-10, 2014.
http://cospar2014moscow.com/
3. Publication list
Publications were listed in each section of research report.

315