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Commission G Report
November 26, 2013
1. Research Report
1.1. EISCAT activities (Takuji Nakamura, National Insititute of Polar Research)(1) Using a simultaneous and common-volume observation by a European incoherent scatter(EISCAT) VHF radar and a sodium lidar at Tromso, Norway (69.6 deg N, 19.2 deg E), the effect ofpure particle precipitation, excluding that of the electric field, on sodium density variations has been
observed for the first time (Tsuda et al., 2013). The observation on 24-25 January 2012 showed that
sodium atom density decreased when there was no ion temperature enhancement (indicating a weakelectric field ) and the electron density increased (indicating strong particle precipitation). From theresults we have concluded that auroral particle precipitation induced sodium atom density decrease inthis event. Furthermore, a discussion is provided regarding the time response of the decrease in sodium
density.
(2) Ionospheric ion upflow during an auroral substorm has been investigated using simultaneous
EISCAT radar and IMAGE satellite data (Ogawa et al., 2013). Approximately 6 minutes after an
initial brightening identified with data from the IMAGE WIC instrument, ion upflow was seen and theelectron temperature became enhanced, too. The ion upflow, with a velocity of about 150 m/s, and theelectron temperature enhancement lasted for about 25 minutes. During the poleward expansion phasesurges of large upward ion velocity and flux, and high ion and electron temperatures occurred overLongyearbyen. The upward ion flux reached 2×10^14 m-2s-1. Naturally enhanced ion-acoustic lines(NEIALs) were seen near the poleward edge of the expanded auroral oval both near the end of
expansion phase 17 minutes after onset and also later in the recovery phase. The NEIALs seemed to beaccompanied by another type of enhanced echoes, obliquely to the local geomagnetic field. Data fromthe LENA instrument on the IMAGE satellite show that energetic neutral oxygen reaches the IMAGE
satellite about 40 minutes after the initial brightening, and oxygen continues to get detected during therecovery phase. Ion upflow at the poleward edge of the auroral oval during the expansion phase wasproved to be related to ion/neutral outflow with energy below 18-27 eV, whereas during the recovery
phase of a substorm upward ions are accelerated up to about 60 eV and flow out in the entire polar
region.
(3) Updates on EISCAT results are found at
http://polaris.nipr.ac.jp/~eiscat/results.html
References
Ogawa, Y., M. Sawatsubashi, S. C. Buchert, K. Hosokawa, S. Taguchi, S. Nozawa, S. Oyama, T. T.
Tsuda, and R. Fujii, Relationship between auroral substorm and ion upflow in the nightside polar
ionosphere, J. Geophys. Res., in press, 2013. (Accepted in October)
Tanaka, Y., A. Shinbori, T. Hori, Y. Koyama, S. Abe, N. Umemura, Y. Sato, M. Yagi, S. UeNo,
Satoru, A. Yatagai, Y. Ogawa, and Y. Miyoshi, Analysis software for upper atmospheric data
developed by the IUGONET project and its application to polar science, Advances in Polar Science, inpress, 2013.
Tsuda, T. T., S. Nozawa, T. D. Kawahara, T. Kawabata, N. Saito, S. Wada, Y. Ogawa, S. Oyama, C.
M. Hall, M. Tsutsumi, M. K. Ejiri, S. Suzuki, T. Takahashi, and T. Nakamura, Decrease in sodium

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資料7-Gdensity observed during auroral particle precipitation over Tromso, Norway, Geophys. Res. Lett., inpress, 2013. (Accepted in August)1.2. PANSY: Program of the Antarctic Syowa MST/IS Radar(Takuji Nakamura, National Insititute of Polar Research )PANSY (Program of the Antarctic Syowa MST/IS Radar) is a project which was started in 2000 tocomprehensively study the polar atmosphere with a large aperture atmospheric radar as the main
instrument combined with complementary observation techniques and also with numerical modelingand theoretical works.
The PANSY project has been supported internationally by resolutions from international scientificbodies such as IUGG, URSI, SPARC, SCOSTEP, and SCAR. The scientific research objectives andtechnical developments have been frequently discussed at international and domestic conferences. The
project was authorized in 2008 as one of the main observation plans for the 6 year period of Japanese
Antarctic Research Expedition program (2011-2016), and funded by Japanese government in 2009.
The PANSY radar is the first Mesosphere-Stratosphere-Troposphere/Incoherent Scatter (MST/IS)
radar in the Antarctic region. It is a large VHF monostatic pulse Doppler radar operating at 47 MHz,consisting of an active phased array of 1,045 Yagi antennas and an equivalent number of transmitreceive modules with a total peak output power of 500 kW. Its first stage has been installed at Syowa
Station (69°00’S, 39°35’E) in early 2011, and is currently operating with 228 antennas and modules.
The radar aims to clarify the role of atmospheric gravity waves at high latitudes in the momentum
budget of the global circulation in the troposphere, stratosphere and mesosphere and the dynamical
aspects of unique polar phenomena such as polar mesospheric clouds (PMC) and polar stratosphericclouds (PSC). The katabatic winds as a branch of Antarctic tropospheric circulation and as animportant source of gravity waves are also of special interest. Moreover, strong and sporadic energy
inputs from the magnetosphere by energetic particles and field-aligned currents can be quantitatively
assessed by the broad height coverage of the radar extending from the lower troposphere to the upper
ionosphere.
Currently the radar is operating with about a quarter of the full system. Nevertheless, we have alreadyobtained interesting results on the Antarctic troposphere, stratosphere and mesosphere, such as
observation of gravity waves and multiple tropopauses associated with a severe snow storm in the
troposphere and stratosphere, and polar mesosphere summer echoes. The first paper of these initial
results was recently accepted and is now online [Sato et al., JASTP, 2013].
Reference
Sato, K., M. Tsutsumi, T. Sato, T. Nakamura, A. Saito, Y. Tomikawa, K. Nishimura, H. Yamagishi, T.
Yamanouchi, Program of the Antarctic Syowa MST/IS radar (PANSY), J. Atmos. Solar-Terr., Physics,
doi:10.1016/j.jastp.2013.08.022 , in print, 2013.
1.3. Airglow imaging experiment (Kazuo Shiokawa, Nagoya Univ.)
Statistical characteristics of occurrence rate, direction of motion, and wave parameters of high-latitudenighttime medium-scale traveling ionospheric disturbances (MSTIDs) were reported based on
observations by all-sky airglow imagers at Tromsoe (magnetic latitude: 67.1N), Norway and at
Athabasca (61.7N), Canada. The MSTIDs were observed mostly before midnight with an occurrence
rate of more than 30-50% of clear observation hours. The average wavelengths, phase velocities, andperiods of the observed MSTIDs were 150-200 km, 50-80 m/s, and 30-60 min, respectively. SomeMSTIDs at Tromsoe tend to show eastward motion in addition to the typical westward and361/384

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southwestward motion at middle latitudes. At both stations, some MSTIDs showed characteristicchanges of their phase velocity and directions in association with auroral activity, suggesting that they
are plasma structures affected by auroral electric field.
Reference
Shiokawa, K., M. Mori, Y. Otsuka, S. Oyama, S. Nozawa, S. Suzuki, and M. Connors, Observation ofnighttime medium-scale travelling ionospheric disturbances by two 630-nm airglow imagers near theauroral zone, J. Atmos. Solar-Terr. Phys., 103, 184-194, 2013. (published on September 7, 2013)
1.4. Remote-sensing of ionosphere and thermosphere with IMAP/VISI an ground-based all-sky imager(Takeshi Sakanoi, Tohoku University)
Airglow emissions at the lower-thermosphere (O2 762 nm, 95km alt.) and the upper-thermosphere (O630 nm, 250 km alt.) are measured with IMAP/VISI on the international space station. We find many
concentric gravity wave event in the O2 emission, and equatorial anomaly and plasma bubbles in
O630 nm emission. We are also conducting the ground-based all-sky imaging measurement at thesummit of Haleakala, Maui, Hawaii to carry out simultaneous measurement of airglow emissions with
IMAP/VISI.
1.5. Auroral polarization measurement (Takeshi Sakanoi, Tohoku University)
We will carry out the auroral polarization measurement at Pokar Flat, Alaska throughout this winter,and are now developing a new instrument for auroral meridional polarization spectrograph.
1.6. Planetary ionosphere and magnetosphere (Takeshi Sakanoi, Tohoku University)
We examine the faint emissions of sodium and sulfur ion around the Jupiter's satellite Io, and oxygen
atom emission around the Saturn's satellite Enceradas. We are also planning the Sprint-A/EXCEEDand ground-based telescope campaign this winter, of which targets are Jupiter's aurora and volcanoes
on Io, etc.
1.7. Simulation of medium-scale Traveling Ionospheric Disturbances(Takuya Tsugawa, National Institute of Information and Communications Technology)(1) Hemisphere-coupled modelingAn intriguing aspect of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) is thatthey were simultaneously observed at magnetic conjugate locations in the Northern and Southern
Hemispheres. In order to study the hemisphere-coupled electrodynamics, the numerical model has
been upgraded to consist of two simulation domains for both hemispheres in which the electrostatic
potential is solved by considering electrodynamics in both hemispheres. The simultaneous occurrenceof MSTIDs at the magnetic conjugate stations has clearly been reproduced when the F-region neutral
wind satisfies the unstable condition in both hemispheres and a sporadic-E layer is given only at theNorthern (summer) Hemisphere.
Reference
Yokoyama, T., Hemisphere-coupled modeling of nighttime medium-scale traveling ionosphericdisturbances, Adv. Space Res., doi:10.1016/j.asr.2013.07.048, 2013.
(2) Scale dependence

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Scale dependence of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) is studied
with the midlatitude ionosphere electrodynamics coupling model by changing initial perturbation
scales. It is shown that both sporadic E (Es)-layer and Perkins instabilities have the scale dependence
that a shorter wavelength mode tends to stop growing within a shorter period, whereas a very longwavelength mode grows so slowly in the E region that it does not effectively seed the Perkins
instability in the F region. As a result, the typical wavelength of MSTIDs (100-200 km) can be
spontaneously generated without scale-dependent forcing. It is also shown that long frontal structuresof MSTIDs can be formed by the Pedersen polarization process along the wavefront of MSTIDs bywhich the wavefront is forced to be uniformly distributed.
Reference
Yokoyama, T., Scale dependence and frontal formation of nighttime medium-scale travelingionospheric disturbances, Geophys. Res. Lett., 40, doi:10.1002/grl.50905, 2013.
1.8. Earthquake-induced ionospheric variations(Takuya Tsugawa, National Institute of Information and Communications Technology)(1) Sudden TEC depletion near the epicenter
Unusual ionospheric variations were observed in the M9.0 Tohoku-oki earthquake on 11 March 2011.
Among various kinds of features in the ionosphere, significant depletion of TEC near the epicenter
was observed after the earthquake. Although previous studies have suggested that the coseismic
ionospheric variations are associated with atmospheric perturbation caused by vertical displacement of
the sea surface, the mechanism of the TEC depletion has not been fully understood. In this paper, atwo-dimensional nonlinear nonhydrostatic compressible atmosphere-ionosphere model is employed toinvestigate the ionospheric variations in the vicinity of the epicenter. The simulation results reveal thatan impulsive pressure pulse produced by a sudden uplift of the sea surface leads to local atmospheric
expansion in the thermosphere and that the expansion of the thermosphere combined with the effect of
inclined magnetic field lines in the ionosphere causes the sudden TEC depletion above the epicenterregion.
Reference
Shinagawa, H., T. Tsugawa, M. Matsumura, T. Iyemori, A. Saito, T. Maruyama, H. Jin, M. Nishioka,
and Y. Otsuka, A simulation study of ionospheric variations in the vicinity of the epicenter of the
Tohoku-oki earthquake on 11 March 2011, Geophys. Res. Lett., 40, 5009–5013,
doi:10.1002/2013GL057627, 2013.
(2) Acoustic resonanceThree rare occasions are introduced, where the excitation of vertical acoustic resonance between the
ground and the ionosphere, and the resultant generation of a field-aligned current, just after
earthquakes are observationally confirmed. In the case of two inland earthquakes, barometricobservations very close to the epicenters (i.e., only 30 km apart) were available, and they showed asharp spectral peak which appeared within one hour after the origin time and lasted a few hours. The
observed periods of the spectral peaks around 260 seconds are close to the period of the theoreticallyexpected fundamental mode of the resonance. On the other hand, magnetic observations on the groundshowed a dominant period at 220–230 seconds which corresponds to the first overtone among
theoretically-expected major resonance peaks. In the third case, i.e., during the 2010 Chile earthquake,a long-period magnetic oscillation in the east-west direction, which has two major resonance periods at
265 and 190–195 seconds, was observed on the night-side magnetic dip equator in Peru, where the363/384

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distance is more than 2600 km from the epicenter, under a very quiet geomagnetic condition. The
oscillation was interpreted as the effect of field-aligned current generated through a dynamo process in
the ionosphere over the epicenter caused by the resonance.
Reference
Iyemori, T., Y. Tanaka, Y. Odagi, Y. Sano, M. Takeda, M. Nose, M. Utsugi, D. Rosales, E. Choque, J.
Ishitsuka, S. Yamanaka, K. Nakanishi, M. Matsumura, and H. Shinagawa, Barometric and magnetic
observations of vertical acoustic resonance and resultant generation of field-aligned current associatedwith earthquakes, Earth Planets Space, 65, 901–909, doi:10.5047/eps.2013.02.002, 2013.
1.9. Ionospheric variations observed after a massive tornado(Takuya Tsugawa, National Institute of Information and Communications Technology)
We detected clear concentric waves and short-period oscillations in the ionosphere after the EF5
tornado hit Moore, Oklahoma, USA, on 20 May 2013 using a dense wide-coverage ionospheric total
electron content (TEC) observation in North America. These concentric waves were non-dispersive
waves with a horizontal wavelength of ~120 km and a period of ~13 minutes. They were observed formore than seven hours throughout North America. TEC oscillations with a period of ~4 minutes werealso observed in the south of Moore for more than eight hours. Comparison between the TEC
observation and the infrared cloud image from the GOES satellite indicates that the concentric waves
and the short-period oscillations are caused by supercell-induced atmospheric gravity waves andacoustic resonances, respectively. This observational result provides the first clear evidence of a severe
meteorological event causing atmospheric waves propagating upward in the upper atmosphere andreaching the ionosphere.
Reference
Nishioka, M., T. Tsugawa, M. Kubota, and M. Ishii, Concentric waves and short-period oscillations
observed in the ionosphere after the 2013 Moore EF5 tornado, Geophys. Res. Lett., 40,
doi:10.1002/2013GL057963, 2013.
1.10. Storm-induced plasma stream in the low-to-mid latitude(Takuya Tsugawa, National Institute of Information and Communications Technology)
Geomagnetic disturbances from 7 to 12 November 2004 were quite intense, and the maximum
excursion of Dst reached –374 nT. Unusual ionospheric phenomena have been observed around theworld that have been associated with successive magnetic storms during this period. The ionospheric
total electron content (TEC) was increased at the longitudes of Japan within a short time after sunset
on 8 November, from 20 TEC units at 1830 JST to 97 TEC units at 2015 JST (JST = UT + 9 h). The
enhanced TEC was significant over Hokkaido (43 deg N), and the center of the enhanced region was
well within the plasmasphere as an L value of approximately 1.5. The drift velocity of the plasma inthe density-enhanced region measured by the Defense Meteorological Satellite Program (DMSP)
satellite was westward with a peak value of 250 m/s in the Earth’s frame, demonstrating a positive
correlation between density and drift velocity. A similar TEC event was observed after sunset on 10
November: TEC was enhanced, from 15 TEC units at 1830 JST to 45 TEC units at 2030 JST. During
the second event, the ionosphere was highly structured and the rate of the TEC index (ROTI) increased.
The two-dimensional map of a ROTI-enhanced region exhibited the west to northwest transportationof plasma in which density irregularities were entrained. A physical mechanism is proposed to explainthese disturbances, i.e., storm-induced plasma stream, which is different from a phenomenon calledstorm-enhanced density at midlatitudes.

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Reference
Maruyama, T., G. Ma, and T. Tsugawa, Storm-induced plasma stream in the low-latitude to
midlatitude ionosphere, J. Geophys. Res. Space Physics, 118, doi:10.1002/jgra.50541, 2013.
1.11. A new format to promote international sharing of GNSS-TEC data
(Takuya Tsugawa, National Institute of Information and Communications Technology)
NICT, a delegate of Japan, proposed “GNSS-TEC exchange format (GTEX)” as a format to promoteinternational exchange and sharing of GNSS-TEC data in an input document to the meeting ofWorking Group 3L-3 (trans-ionospheric propagation) of ITU-R held in Geneva from 19 to 26 June
2013. The document was discussed in the larger context of the need to incorporate new digitalproducts and SG3DB databanks. As a result, the GTEX was included in a Chairman’s report towards
the definition of new digital products for transionospheric propagation.
1.12. Development of SDR (software-defined radio) based radar receiver(Mamoru Yamamoto, Research Institute for Sustainable Humanosphere, Kyoto University)
A receiver system for radars were developed based on the general-purpose software-defined radio
receiver referred to as Universal Software Radio Peripheral 2 (USRP2) under control of a PC. The
receiver is able to collect received signals at intermediate frequency (IF) of 130 MHz with a sample
rate of 10 MHz. USRP2 digitizes IF received signals, produces IQ time series, and then transfers theIQ time series to PC through the Gigabit Ethernet. PC receives the IQ time series, executes range
sampling, carries out filtering in the range direction, decodes phase-modulated received signals,
integrates the received signals in time, and finally stores processed data to the hard disk drive (HDD).
Because only sequential data transfer from USRP2 to PC is available, the range sampling is triggeredby transmitted pulse leaked to the receiver. In order to perform range imaging with multiple
frequencies, the digital receiver executes real-time signal processing for each of the time series
collected at different frequencies. Further, in order to implement oversampling, the receiver is able todecode phase-modulated oversampled signals by interleaving oversampled signals in the range
direction. Because program codes for real-time signal processing at PC is written in C++ language, thesignal processing executed by the digital receiver is easy to be implemented, reconfigured, and reused.
Using the measurement result from a 1.3-GHz range imaging atmospheric radar, we demonstrate thatthe digital receiver, which is capable of executing real-time signal processing for range imaging andoversampling, is useful for resolving fine-scale structure of atmospheric turbulence with a verticalscale as small as 100 m.
Reference
Yamamoto, M. K., T. Fujita, Noor Hafizah Binti Abdul Aziz, T. Gan, H. Hashiguchi, T.-Y. Yu, and M.
Yamamoto, Development of a digital receiver for range imaging atmospheric radar, J. Atmos. Sol.Terr. Phys., doi:10.1016/j.jastp.2013.08.023, in press, 2013.
1.13. Sounding rocket/ground-based observations of the ionosphere in July 2013
(Mamoru Yamamoto, Research Insitute for Sustainable Humanosphere, Kyoto University;
Keigo Ishisaka, Toyama Prefectural University)
There are number of waves in the mid-latitude ionosphere. One interesting phenomenon is mediumscale traveling ionospheric disturbance (MSTID) in the F-region. The MSTID is the wave structurewith a wavelength of 100-200 km. These horizontal structures can be observed by using the total
electron content (TEC) from GEONET, Japanese dense network of GPS receivers. We conducted an
intensive experiment to study generation mechanism of the MSTID by the combination of sounding

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rockets and ground observations. We monitored horizontal structures of the MSTID by using GPSTEC real-time monitor system. While active MSTID region appeared over south Kyushu, Institute ofSpace and Aeronautical Science of JAXA (JAXA/ISAS) launched sounding rockets S-310-42 and S520-27 from Uchinoura Space Center (USC) at 23:00 JST and 23:57 JST, respectively. Ionosphericparameters, i.e., plasma density, electric field, density fluctuations, were measured by in-situ
instruments on board of the S-520-27 rocket. TMA (Tri-Methyl Aluminum) and Lithium were released
from the S-31-42 and S-520-27 rockets, respectively, for measurement of the neutral winds. Theirluminescent clouds were imaged from the JAXA experimental jet "Hisho" and from three ground sites.
The Lithium experiment under the moonlight was the world first trial, and was successful. Bothrockets transmitted dual-band beacon signal which was received at five ground sites. Preliminary
analysis of from the experiment show that strong wind shear and sporadic-E layers co-existed ataround 100 km. Also the results infer large horizontal inhomogeneity of F-region plasma density as
well. Electric-field detector (EFD) on board of the rocket S-520-27 measured a waveform of electricfield at the frequency less than 6.4 kHz. Intensity from 4 kHz to 6 kHz are increased at the apex region
during the period from 210 sec to 350 s. In the low frequency components, we sound enhanced
intensity of 40 Hz or less is clearly seen during the time of most of rocket flight.
2. Meetings
Meetings scheduled in relation to URSI Commission-G were conducted as listed below.
IAGA the XIIth Scientific General Assembly, Merida Yucatan, Mexico, August 26-31, 2013
Symposium web-page: http://www.iaga2013.org.mx/
Mesosphere, Thermosphere, Ionosphere Research Meeting,National Institute of Information and Communications Technology, Koganei, Japan,
September 16-17, 2013
International CAWSES-II Symposium, Nagoya, Japan, November 18-22, 2013
Symposium web-page: http://www.stelab.nagoya-u.ac.jp/cawses2013/
NOTE: There were more than 250 participants from 32 countries.
Number of presentations reached 393.
Future meetings related to URSI Commission-G are as follows,
Japan Geoscience Union (JpGU) Meeting 2014
Pacifico Yokohama, Yokohama, Japan, April 28-May 2, 2014.
http://www.jpgu.org/meeting_e/
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.

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