資料6-GCommission G Report
April 10, 2015
1. Research Report
1.1. Report from National Institute for Polar Research (NIPR)(Yasunobu Ogawa, NIPR)=== Report from recent papers ===(1) Pulsating auroras show quasi-periodic intensity modulations caused by the precipitation ofenergetic electrons of the order of tens of keV. It is expected theoretically that not only theseelectrons but also sub-relativistic/relativistic electrons precipitate simultaneously into theionosphere owing to whistler-mode wave?particle interactions. The height-resolved electron
density profile was observed with the European Incoherent Scatter (EISCAT) Tromso VHF radaron 17 November 2012. Electron density enhancements were clearly identified at altitudes >68 km
in association with the pulsating aurora, suggesting precipitation of electrons with a broadband
energy range from ~10 keV up to at least 200 keV. The riometer and network of subionosphericradio wave observations also showed the energetic electron precipitations during this period.
During this period, the footprint of the Van Allen Probe-A satellite was very close to Tromso andthe satellite observed rising tone emissions of the lower-band chorus (LBC) waves near theequatorial plane. Considering the observed LBC waves and electrons, we conducted a computer
simulation of the wave?particle interactions. This showed simultaneous precipitation of electrons
at both tens of keV and a few hundred keV, which is consistent with the energy spectrum
estimated by the inversion method using the EISCAT observations. This result revealed thatelectrons with a wide energy range simultaneously precipitate into the ionosphere in association
with the pulsating aurora, providing the evidence that pulsating auroras are caused by whistler
chorus waves. We suggest that scattering by propagating whistler simultaneously causes both theprecipitations of sub-relativistic electrons and the pulsating aurora.
(2) The solar zenith angle (SZA) dependence of the conductance is studied and a simple theoreticalform for the Hall-to-Pedersen conductance ratio is developed, using the peak plasma production
height. The European Incoherent Scatter (EISCAT) radar observations at Tromso (67 MLAT) on
30 March 2012 were used to calculate the conductance. The daytime electric conductance isassociated with plasma created by solar extreme ultraviolet radiation incident on the neutral
atmosphere of the Earth. However, it has been uncertain whether previous conductance models are
consistent with the ideal Chapman theory for such plasma productions. We found that the SZA
dependence of the conductance is consistent with the Chapman theory after simple modifications.
The Pedersen conductance can be understood by approximating the plasma density height profile
as being flat in the topside E region and by taking into account the upward gradient of atmospherictemperature. An additional consideration is necessary for the Hall conductance, which decreases
with increasing SZA more rapidly than the Pedersen conductance. This rapid decrease ispresumably caused by a thinning of the Hall conductivity layer from noon toward nighttime. We
expressed this thinning in terms of the peak production height in the Chapman theory.
Reference(1) Miyoshi, Y., S. Oyama, S. Saito, S. Kurita, H. Fujiwara, R. Kataoka, Y. Ebihara, C. Kletzing, G.
Reeves, O. Santolik, M. Cliverd, C. J. Rodger, E. Turunen, and F. Tsuchiya, Energetic electron資料6-G

precipitation associated with pulsating aurora: EISCAT and Van Allen Probe observations, J.
Geophys. Res. Space Physics, in press, doi:10.1002/2014JA020690, 2015.
(2) Ieda, A., S. Oyama, H. Vanhamaki, R. Fujii, A. Nakamizo, O. Amm, T. Hori, M. Takeda, G. Ueno,
A. Yoshikawa, R. J. Redmon, W. F. Denig, Y. Kamide, and N. Nishitani, Approximate forms ofdaytime ionospheric conductance, J. Geophys. Res. Space Physics, 119, pages 10397-10,415,
doi:10.1002/2014JA020665, Jan. 2015.

1.2. Report from Solat-Terrestrial Environmental Laboratory, Nagoya University(Satonori Nozawa, Nagoya University)=== Report from recent papers ===(1) Possible generation mechanisms of Pc1 pearl structures were investigated using multi-point
induction magnetometers in Athabasca in Canada, Magadan in Russia, and Moshiri in Japan. Two
Pc1 pulsations that were simultaneously observed at the three stations were selected. Based onpolarization analysis, similarity of the pearl structures at differen stations, and model calculations,
it is suggested that beating processes in the ionosphere could be one of the generation mechanismsof Pc1 pearl structures.
(2) The characteristics of nighttime medium-scale traveling ionospheric disturbance (MSTID)
features observed over Yonaguni (24.5°N, 123.0°E; 19.3°N dip latitude), Japan are studied using
all-sky imaging of OI 630.0 nm airglow emission. Detailed investigation suggests that thepoleward propagating enhancement of airglow intensity, probably associated with themidnightpressure bulge, causes the MSTID features to disappear when they reach lower latitudes later inthe night. When the MSTIDs reach lower latitudes well before midnight, they are found to be
inhibited by the equatorial ionization anomaly crest region.
Reference(1) Jun, C.-W., K. Shiokawa, M. Connors, I. Schofield, I. Poddelsky, and B. Shevtsov, Study of Pc1
pearl structures observed at multi-point ground stations in Russia, Japan and Canada, EarthPlanets Space, 66, 140, doi:10.1186/s40623-014-0140-8, 2014.
(2) V. Lakshmi Narayanan, K. Shiokawa, Y. Otsuka, S. Saito, Airglow observations of nighttime
medium-scale traveling ionospheric disturbances from Yonaguni: Statistical characteristics andlow latitude limit, J. Geophys. Res., 119, doi: 10.1029/2014JA020368, 2014.

1.3. Report from Research Institute for Sustainable Humanosphere, Kyoto University (RISH)(Mamoru Yamamoto, Kyoto University)=== Report from recent papers ===(1) The pulsed, beamwidth-limited atmospheric radar suffers from a finite resolution volume, making
it difficult to resolve the small-scale irregularity structure of refractive index (or clear-airturbulence) in the scattering region. Multi-receiver and multi-frequency imaging techniques werethus proposed to improve the spatial resolution of the measurements in the finite resolution
volume. The middle and upper atmosphere radar (MUR; 34.85° N, 136.10° N) possesses thecapabilities of 5 frequencies, ranging from 46 MHz to 47 MHz, and up to 25 receivers to carry out
the imaging techniques. In this paper, we exhibit the three-dimensional (3-D) radar imaging
utilizing five frequencies and 19 receivers of the MUR. The Capon method was employed for theprocess of imaging, and examinations of a wavy layer and turbulent structures were made, in資料6-G

which the spatial weighting effect on the imaging were mitigated beforehand. Information such as
echo center and structure morphology in the resolution volume was then extracted. For example,
the location distribution of echo centers could imply the traveling orientation of the wavy layer,
which was correspondent with horizontal wind direction. Such information of wavy layer structure
was more difficult to disclose without removal of the spatial weighting effect. This paper
demonstrates an advanced application of 3-D radar imaging to some practical atmosphericphenomena.
(2) Using the fan sector backscatter maps of 47 MHz Equatorial Atmosphere Radar (EAR) at
Kototabang (0.2°S geographic latitude, 100.3°E geographic longitude, and 10.4°S geomagneticlatitude), Indonesia, the spatial and temporal evolution of equatorial plasma bubbles (EPBs) were
examined to classify the evolutionary-type EPBs from those which formed elsewhere and drifted
into the field of view of radar. A total of 535 EPBs were observed during the low to moderate
solar activity years 2010–2012, out of which about 210 (~39%) are of evolving type and theremaining 325 (~61%) are drifting-in EPBs. In general, both the evolving-type and drifting-inEPBs exhibit predominance during the postsunset hours of equinoxes and December solstices.
Interestingly, a large number of EPBs were found to develop even a few minutes prior to the apex
sunset during equinoxes. Further, the occurrence of evolving-type EPBs exhibits a clear secondary
peak around midnight (2300–0100 LT), primarily, due to higher rate of occurrence during thepostmidnight hours of June solstices. A significant number (~33%) of postmidnight EPBs
generated during June solstices did not exhibited any clear zonal drift, while about 14% of EPBs
drifted westward. Also, the westward drifting EPBs are confined only to June solstices. The
responsible mechanisms for the genesis of fresh EPBs during postmidnight hours were discussed
in light of equatorward meridional winds in the presence of weak westward electric fields.
References(1) Chen, J. S., J. Furumoto, M. Yamamoto, Three-dimensional radar imaging of atmospheric layer
and turbulence structures using multiple receivers and multiple frequencies Ann. Geophys., 32,899-909, DOI:10.5194/angeo-32-899-2014, 2014.
(2) Ajith, K. K., S. T. Ram, M. Yamamoto, T. Yokoyama, V. S. Gowtam, Y. Otsuka, T. Tsugawa,and K. Niranjan, Explicit characteristics of evolutionary-type plasma bubbles observed from
Equatorial Atmosphere Radar during the low to moderate solar activity years 2010-2012, J.
Geophys. Res. Space Physics, 120 (2), 1371-1382, doi:10.1002/2014JA020878., 2015.

2. News
2.1. PANSY in full operation (Yasunobu Ogawa, NIPR)
Program of the Antarctic Syowa MST/IS radar (PANSY) introduced the first MST/IS radar in theAntarctic. The radar started research observation in 2012 with 1/4 of the full array system, and hascollected almost continuous observational data in the troposphere, lower stratosphere and mesosphere
for about three years. Although the full system operation has been postponed due to limited
transportation in 2011/12 and 2012/13 seasons caused by a very thick sea-ice condition, full systemobservations have been successfully started in early 2015 with 520 kW transmitting power and 1045
array antennas.

資料6-G2.2. MU Radar is awarded IEEE Milestone (Mamoru Yamamoto, RISH)
IEEE, an association dedicated to advancing innovation and technological excellence for the benefit ofhumanity, is the world’s largest technical professional society. IEEE established the Milestones
Program in 1983 to recognize the achievements of the Century of Giants who formed the profession
and technologies represented by IEEE. Each milestone recognizes a significant technical achievementthat occurred at least 25 years ago in an area of technology and having at least regional impact. In
December 2014, IEEE decided to award Milestone to the MU (Middle and Upper atmosphere) radar as
the first large-scale MST (Mesosphere, Stratosphere, and Troposphere) radar with a two-dimensional
active phased array antenna system. The MU radar was established in 1984 by Kyoto University withcollaboration of Mitsubishi Electric Corporation, and enabled continuous and flexible observation of
the atmosphere, and has contributed to the progress of atmospheric science and radar engineering. Its
dedication ceremony will be held on May 13, 2015 at Shirankaikan, Kyoto University.

3. Publication list
Publications were listed in each section of research report.