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Commission G Report
July 29, 2015
1. News=== PANSY in full operation===A full system PANSY radar operation with 520 kW peak-envelope transmitting power was
successfully conducted at Syowa, Antarctica for continuous 40 days through April to May, 2015, forthe observations of troposphere, stratosphere and mesosphere. (Yasunobu Ogawa, NIPR)
2. Meeting announcement/report•

26th IUGG (International Union on Geodesy and Geophysics) General Assembly was held at
Plague, Czech on June 22 – July 2, 2015. Detailed information is found in the following web-page.
http://www.iugg2015prague.com/•

International Symposium on the Whole Atmosphere (ISWA) will be held at Ito Hall, The
University of Tokyo, Tokyo, Japan, on 14-16 September 2016. Detailed information can be foundin the following web-page. http://pansy.eps.s.u-tokyo.ac.jp/iswa/•

14th International Symposium on Equatorial Aeronomy (ISEA) will be held at Bahir Dar
University, Bahir Dar, Ethiopia on October 19-23, 2015. Detailed information can be found in thefollowing web-page. http://www.bdu.edu.et/isea14/•

Internataional Reference Ionosphere (IRI) 2015 Workshop will be held on November 9-13, 2015.
Also there is Capacity Building Event on November 2-6, 2015. Both events are held at King
Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok, Thailand. Abstract
submission is open until the end of July. Detailed information can be found in the following webpage. http://www.iri2015.kmitl.ac.th/=== Commission-G meeting ===•MU radar and Equatorial Atmosphere Radar Symposium 2015 will be held at Research Institutefor Sustainable Humanosphere, Kyoto University on September 10-11, 2015.

3. Research Report
3.1. Report from National Institute for Polar Research (NIPR)(Yasunobu Ogawa, NIPR)=== Recent papers===
Ishida, T., Y. Ogawa, A. Kadokura, K. Hosokawa, and Y. Otsuka, Direct observations of blob
deformation during a substorm, Ann. Geophys., 33, 525-530, doi:10.5194/angeo-33-525-2015,
May 2015.
Ionospheric blobs are localized plasma density enhancements, which are mainly produced by thetransportation process of plasma. To understand the deformation process of a blob, observationsof plasma parameters with good spatial-temporal resolution are desirable. Thus, we conducted
the European Incoherent Scatter radar observations with high-speed meridional scans (60-80S)
during October and December 2013, and observed the temporal evolution of a blob during a

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substorm on 4 December 2013. This paper is the first report of direct observations of blob
deformation during a substorm. The blob deformation arose from an enhanced plasma flow shear
during the substorm expansion phase, and then the blob split into two smaller-scale blobs, whose
scale sizes were more than ~100 km in latitude. Our analysis indicates that the Kelvin-Helmholtz
instability and dissociative recombination could have deformed the blob structure.
Taguchi, S., K. Hosokawa and Y. Ogawa, Investigating the particle precipitation of a moving cusp
aurora using simultaneous observations from the ground and space, Progress in Earth andPlanetary Science, 2:11, doi:10.1186/s40645-015-0044-7, 2015.
Using observations of a moving cusp aurora from a high-sensitivity all-sky imager atLongyearbyen, Svalbard, and in situ observations of the precipitating particles from a spacecraftthat flew over the aurora, we examined the particle precipitation features in the early and final
stages of the moving cusp aurora. We focused on two auroral structures created near noon,
separated by approximately 3 min, during a southwestward interplanetary magnetic field (IMF)
condition on 17 December 2012. The second auroral structure occurred when the IMF turned
further southward. Immediately after the appearance of the latter structure, the two auroral
structures were adjacently situated, and the DMSP F18 spacecraft passed through these regions.
Hosokawa, K. and Y. Ogawa, Ionospheric variation during pulsating aurora, J. Geophys. Res.,
doi:10.1002/2015JA021401, in press, 2015.
Data from the European Incoherent SCATter (EISCAT) UHF/VHF radars in Tromso (69.60N,
19.20E), Norway were statistically analyzed to reveal how the occurrence of pulsating aurora(PsA) modifies the electron density profile in the ionosphere. By checking 5 winter seasons(2007-2012) observations of all-sky aurora cameras of National Institute of Polar Research(NIPR) in Tromso, we have extracted 21 cases of PsA. The results can be summarized asfollows: (1) hmE is lower (the energy of precipitation electrons is higher) during the periods of
PsA than that in the surrounding interval, (2) When NmE is higher (flux of PsA electrons islarger), hmE tends to be lower (precipitation is harder), (3) hmE is lower and NmE is larger inthe later magnetic local time, (4) When the AE index during the preceding substorm is larger,hmE is lower and NmE is larger.
Takahashi, T., S. Nozawa, T. T. Tsuda, Y. Ogawa, N. Saito, T. Hidemori, T. D. Kawahara, C. Hall, H.
Fujiwara, N. Matuura, A. Brekke, M. Tsutsumi, S. Wada, T. Kawabata, S. Oyama, and R. Fujii,
A case study on generation mechanisms of a sporadic sodium layer above Tromso (69.6N)
during a night of high auroral activity, Ann. Geophys., in press, 2015.
McCrea, I. W., A. Aikio, L. Alfonsi, E. Belova, S. Buchert, M. Clilverd, N. Engler, B. Gustavsson, C.
Heinselman, J. Kero, M. Kosch, H. Lamy, T. Leyser, Y. Ogawa, K. Oksavik, A. PellinenWannberg, F. Pitout, M. Rapp, I. Stanislawska, and J. Vierninen, The science case for the
EISCAT_3D radar, Progress in Earth and Planetary Science, PEPS-D-14-00016R1, in press,
2015.
3.2. Report from Solat-Terrestrial Environmental Laboratory, Nagoya University(Satonori Nozawa, Nagoya University)=== Recent papers===

Shiokawa, K., Y. Otsuka, K. J. Lynn, P. Wilkinson and T. Tsugawa, Airglow-imaging
observation of plasma bubble disappearance at geomagnetically conjugate points, Earth
Planets Space, 67:43, dio:10.1186/s40623-015-0202-6, 2015.

資料5-GThe first observation of the disappearance of a plasma bubble over geomagneticallyconjugate points was reported using airglow imagers at Darwin, Australia (magnetic
latitude: 22N) and Sata, Japan (21N) on 8 August 2002. It is suggested that the polarizationelectric field associated with equatorward neutral wind during a traveling atmosphericdisturbance drives plasma drift across the magnetic field line to cause the observed bubble
disappearance.
Ohya, H., K. Shiokawa, and Y. Miyoshi (2015), Daytime tweek atmospherics, J. Geophys. Res.
Space Physics, 120, 654–665, doi:10.1002/2014JA020375.
The first observation of daytime tweek atmospherics was reported based on measurements at
Moshiri (44.37N, 142.27E) and Kagoshima (31.48N, 130.72E), Japan, during nonsolar
eclipse days for 5 months in 1980-1994. The daytime tweeks had clear frequency dispersion
with an average duration of 12 ms, which was shorter than that in the nighttime(~50m/s). The average occurrences of the daytime tweeks at Moshiri and Kagoshima were
0.6 and 0.1 tweeks per minute during 10:00-15:00 LT, respectively. Daytime tweeks up to
the second-order mode were visible.
Fukushima, D., K. Shiokawa, Y. Otsuka, M. Nishioka, M. Kubota, T. Tsugawa, T. Nagatsuma, S.
Komonjinda, and C. Y. Yatini, Geomagnetically conjugate observation of plasma bubbles
and thermospheric neutral winds at low latitudes, J. Geophys. Res. Space Phys., 120, 2222–
2231, doi:10.1002/2014JA020398, 2015.
The first was reported on simultaneous observations of zonal drift of plasma bubbles and thethermospheric neutral winds at geomagnetically conjugate points in both hemispheres at
Kototabang, Indonesia (geomagnetic latitude (MLAT): 10.0S), and Chiang Mai, Thailand(MLAT: 8.9N) at 13-20 UT on 5 April 2011. The observed plasma bubble drift velocity wascompared with the velocity calculated from the observed neutral winds and the model
conductivity, to investigate the F region dynamo contribution to the bubble drift velocity.
The estimated drift velocities were 60-90% of the observed velocities of the plasma bubbles,
suggesting that most of the plasma bubble velocity can be explained by the F region dynamo
effect.
Miyoshi, Y., S. Oyama, S. Saito, H. Fujiwara, R. Kataoka, Y. Ebihara, C. Kletzing, G. Reeves, O.
Santolik, M. Cliverd, C. Rodger, E. Turunen, and F. Tsuchiya, Energetic electron
precipitation associated with pulsating aurora: EISCAT and Van Allen Probes observations,J. Geophys. Res. Space Phys., 120, 2754–2766, doi:10.1002/2014JA020690, 2015.
The paper reports that sub-relativistic electrons precipitate into the atmosphere during thepulsating aurora. The EISCAT measurement indicated the significant ionization at themesosphere associated with the pulsating aurora. The ground network observations forriometer and VLF radio waves confirmed that energetic electron precipitations occurred atwide area. A simulation study using the Van Allen Probes satellite data confirmed that thewhistler mode chorus waves can cause wide energy electron precipitations associated withthe pulsating aurora, which has been proposed by Miyoshi et al. [2010].
Abadi, Prayitno, Yuichi Otsuka, and Takuya Tsugawa (2015), Effects of Pre-reversal Enhancement of
ExB drift on the Latitudinal Extension of Plasma Bubble in Southeast Asia, Earth, Planets andSpace, 67:74, doi:10. 1186/s40623-015-0246-7.

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We investigated the effects of the F region bottomside altitude (h'F) maximum upward ExB drift
velocity, duration of pre-reversal enhancement and the integral of upward ExB drift on thelatitudinal extension of equatorial plasma bubbles in the Southeast Asian sector using theobservations recorded by three GPS receivers and two ionosondes. The GPS receivers are
installed at Kototabang (0.2S, 100.3E; MLAT 9.9S), Pontianak (0.02S, 109.3E; MLAT 9.8S)
and Bandung (6.9S, 107.6E; MLAT 16.7S) in Indonesia. The ionosondes are installed atmagnetically equatorial stations, Chumphon (10.7N, 99.4E; MLAT 0.86N) in Thailand and Bac
Lieu (9.3N, 105.7E; MLAT 0.62N) in Vietnam. We analysed those observations acquired in theequinoctial months (March, April, September and October) in 2010-2012, when the solar activity
index F10.7 was in the range from 75 to 150. Assuming that plasma bubbles are the major sourceof scintillations, the latitudinal extension of the bubbles was determined according to the S4index. We have found that the peak of h'F, maximum upward ExB drift and the integral of
upward ExB drift during the pre-reversal enhancement period are positively correlated with the
maximum latitude extension of plasma bubbles, but that duration of pre-reversal enhancement
does not show correlation.
3.3. Report from National Institute for Information and Communications Technology (NICT)(Minoru Kubota, NICT)=== Recent papers===
Maruyama, T., J. Uemoto, M. Ishii, T. Tsugawa, P. Supnithi, and T. Komolmis (2014), Low-latitude
ionospheric height variation as observed by meridional ionosonde chain: Formation ofionospheric ceiling over the magnetic equator, J. Geophys. Res. Space Physics, 119, 10,595–
10,607, doi:10.1002/2014JA020215.
A multipoint ionosonde observation campaign was conducted along the magnetic meridional
plane in Southeast Asia to study ionosphere-thermosphere coupling. One station was near themagnetic equator and two of the other stations were at off-equatorial latitudes (approximately 10
deg magnetic latitude). The daytime ionospheric peak height (hmF2) was analyzed for eachseason during the solar minimum years, 2006-2007 and 2009. The peak height increased forapproximately 3 h after sunrise at the magnetic equator and off-equatorial latitudes, as expectedfrom the daytime upward ExB drift. The apparent upward drift at the magnetic equator ceased
before noon, while the drift at the off-equatorial latitudes continued upward and the layer heightexceeded the equatorial height around noon. The noontime limited layer peak height at themagnetic equator, which was termed the ionospheric ceiling, did not depend on the season, while
the maximum peak height at the off-equatorial latitudes largely varied with each season.
Numerical modeling using the SAMI2 code was conducted and the features of the ionosphericceiling were reproduced quite well. The dynamical parameters provided by the SAMI2 modelingruns showed that the ionospheric ceiling is formed by the field-aligned plasma diffusion, which
is a part of the fountain effect.
Yokoyama, T., H. Shinagawa, and H. Jin, Nonlinear growth, bifurcation and pinching of equatorial
plasma bubble simulated by three-dimensional high-resolution bubble model, J. Geophys. Res.
Space Physics, 119, 10,474-10,482, doi:10.1002/2014JA020708, 2014.
A new three-dimensional high-resolution numerical model to study equatorial plasma bubble(EPB) has been developed. The High-Resolution Bubble (HIRB) model is developed in amagnetic dipole coordinate system for the equatorial and low-latitude ionosphere with a spatial
resolution of as fine as 1 km. Adopting a higher-order numerical scheme than those used in theexisting models, the HIRB model is capable of reproducing the bifurcation, pinching, and資料5-G

turbulent structures of EPB. From a seeding perturbation resembling large-scale wave structure(LSWS), EPB grows nonlinearly from the crest of LSWS upwelling, bifurcates at the top of EPB,
then becomes turbulent at the topside of the F region.
M Buhari, S., M. Abdullah, A. Hasbi, Y. Otsuka, T. Yokoyama, M. Nishioka, and T. Tsugawa,Continuous generation and two-dimensional structure of equatorial plasma bubbles observed byhigh-density GPS receivers in Southeast Asia, J. Geophys. Res. Space Physics, 119, 10,56910,580, doi:10.1002/2014JA020433, 2014.
High-density GPS receivers located in Southeast Asia (SEA) were utilized to study the twodimensional structure of ionospheric plasma irregularities in the equatorial region. The
longitudinal and latitudinal variations of tens of kilometer-scale irregularities associated withequatorial plasma bubbles (EPBs) were investigated using two-dimensional maps of the rate of
total electron content change index (ROTI) from 127 GPS receivers with an average spacing ofabout 50-100 km. The longitudinal variations of the two-dimensional maps of GPS ROTI
measurement on 5 April 2011 revealed that 16 striations of EPBs were generated continuously
around the passage of the solar terminator. The separation distance between the subsequent onset
locations varied from 100 to 550 km with 10 min intervals. The lifetimes of the EPBs observedby GPS ROTI measurement were between 50 min and over 7 h.
Wongcharoen, P., P. Kenpankho, P. Supnithi, M. Ishii, T. Tsugawa (2015), Comparison of E layer
critical frequency over the Thai station Chumphon with IRI, Adv. Space Res., 55, 2131-2138,
doi:10.1016/j.asr.2015.01.031.
In this research, as a part of working towards improving the IRI over magnetic equatorial region,
the critical frequency of E layer in the ionosphere (foE) derived from the ionogram at Chumphon
station (10.72 deg N, 99.37 deg E), Thailand, during 2005-2008 is analyzed. The Chumphon
station is located in the magnetic equatorial region at the magnetic latitude of 3.22 deg N. The
seasonal variation of the foE measurements is compared to the IRI foE predictions with theoptional input in the sunspot number (Rz12) and the solar radio noise flux (F10.7).
Klinngam, S., P. Supnithi, S. Rungraengwajiake, T. Tsugawa, M. Ishii, and T. Maruyama (2015), The
occurrence of equatorial spread-F at conjugate stations in Southeast Asia, Adv. Space Res., 55,
2139-2147.
In this study, the probability of equatorial spread-F (ESF) occurrence at the conjugate stations inSoutheast Asia: Chiangmai station (CMU), Thailand, and Kototabang station (KTB), Indonesia,
and near the magnetic equator, Chumphon station (CPN), Thailand, is presented. We analyze theionogram data recorded by the Frequency Modulated Continuous Wave (FM/CW) ionosondes
for the periods of minimum solar activity from September 2008 to April 2009 and in theequinoctial months (March and April) from 2006 to 2013. The spread-F signatures are manuallycategorized into three types: the frequency spread-F (FSF), the range spread-F (RSF) and themixed spread-F (MSF) and the monthly average percentage of the occurrence of each ESF typeis presented. The results show that the percentage of RSF occurrence at CPN, which is locatedaround the magnetic equator, is higher than at other stations and the RSF mostly occurs during
the equinoctial months.

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3.4. Report from Research Institute for Sustainable Humanosphere, Kyoto University (RISH)(Mamoru Yamamoto, Kyoto University)=== Recent papers===
Watthanasangmechai, K., M. Yamamoto, A. Saito, T. Maruyama, T. Yokoyama, M. Nishioka, and M.
Ishii, Temporal change of EIA asymmetry revealed by a beacon receiver network in Southeast
Asia, Earth Planets Space, 67:75, doi:10.1186/s40623-015-0252-9, 2015.
To reveal the temporal change of the equatorial ionization anomaly (EIA) asymmetry, amultipoint satellite-ground beacon experiment was conducted along the meridional plane of theThailand-Indonesia sector. The observation includes one station near the magnetic equator andfour stations at off-equator latitudes. This is the first EIA asymmetry study with high spatial
resolution using GNU Radio Beacon Receiver (GRBR) observations in Southeast Asia. GRBRtotal electron contents (TECs) from 97 polar-orbit satellite passes in March 2012 were analyzed
in this study. Successive passes captured rapid evolution of EIA asymmetry, especially during
geomagnetic disturbances. Instead, high background TEC associated with an intense electricfield empowers the neutral wind to produce severe asymmetry of the EIA. Such rapid evolutionof EIA asymmetry was not seen during nighttime, when meridional wind mainly controlled theasymmetric structures.
S. Tulasi Ram, K. K. Ajith, M. Yamamoto, Y. Otsuka, T. Yokoyama, K. Niranjan, and S. Gurubaran,Fresh and evolutionary-type plasma bubbles triggered by overshielding electric fields nearsunrise terminator, J. Geophys. Res. Space Phys., 120, doi:10.1002/2015JA021427, in press,
2015.
The evolution of fresh and intense equatorial plasma bubbles (EPBs) near sunrise terminator
which further sustained for > 90 minutes of post-sunrise period was observed by Equatorial
Atmosphere Radar (EAR) at Kototabang during a minor geomagnetic storm period. These EPBs
were initially observed around 250-350km altitudes, growing upward under eastward
polarization electric fields and fully depleted along the flux tube. The background low-latitude Flayer dynamics that lead to the development of these dawn-time EPBs have been investigatedfrom two ionosondes at magnetically conjugate low-latitude locations.
Tong Gan, Masayuki Yamamoto, Hashiguchi Hiroyuki, Hajime Okamoto, and Mamoru Yamamoto,Spectral parameters estimation in precipitation for 50-MHz band atmospheric radars, Radio
Science, 50, doi:10.1002/2014RS005643, in press, 2015.
50-MHz band Atmospheric Radars (ARs) can detect clear air echoes and hydrometeor echoes
simultaneously. However, in order to calculate spectral parameters (i.e., echo power, Doppler
velocity, and spectrum width) of the clear air echo accurately, the clear air echo must be
separated from the hydrometeor echo well. In this study, we propose methods (top method andtwo-echo method) for calculating the spectral parameters in precipitation region. The top method
is used when raindrops or solid hydrometeors with small echo intensities exist. The top method
sets an echo cut level by using the peak intensity of a clear air echo. The echo cut level is used
for separating clear air echoes from hydrometeor echoes. The results demonstrate that the top
method and two-echo method are useful for reducing the errors of spectral parameters.