資料10-GCommission G Report
March 5, 2013
1. Research Report
1.1. Polar cap studies (Keisuke Hosokawa, Univ. of Electro-Communications)
A highly sensitive all-sky EMCCD airglow imager has been operative in Longyearbyen, Norway (78.2N,15.6E; AACGM latitude 75.3) since October 2011. The imager captures 630.0 nm all-sky images with anexposure time of 4 sec, which is about 10 times shorter than that achieved by conventional cooled CCD
imagers. This allows us to visualize the structure of polar cap patches without blurring effects and better
estimate their periodicities. Hosokawa et al. (2013) presented, as one of the first results from the imager,an event of successive appearance of patches on the night of December 21, 2011. A time-series of the
optical intensity at zenith showed modulations having two distinguished periods, one at 40 min and theother at 5--12 min. One possible explanation is that such a coexistence of two different periodicities is amanifestation of simultaneous occurrence of patch generation processes on the dayside. Namely, the 40
min periodicity was created by large-scale reconfiguration of the dayside convection pattern while the 512 min modulations were closely associated with mechanisms driven by pulsed reconnection on thedayside magnetopause. Such a combined effect of multiple patch generation processes may play a role instructuring patches; thus, it would be of particular importance for evaluating the space weather effects inthe trans-ionospheric communications environment in the polar cap.
1.2 EISCAT-radar related studies (Satonori Nozawa, Nagoya Univ.)
A physical process for the latitudinal motion of an auroral arc based on the four-side bound Cowlingchannel model is proposed. Assuming that an upward field-aligned current (FAC) is associated with theauroral arc that forms a Cowling channel with finite lengths not only latitudinally but also longitudinallyand that the upward FAC region is primarily embedded in a purely northward electric field, the primaryHall current driven by the northward electric field accumulates positive excess charges at the eastern edgeof the channel and negative charges at the western edge. The charges produce a westward secondary
electric field. This secondary electric field moves the arc with its magnetospheric source drifting together
with the magnetospheric plasmas equatorward and simultaneously produces the electric field outside thechannel that moves the downward FAC equatorward of the upward FAC region equatorward together withthe upward FAC. Thus, the whole 3-D current system is expected to move equatorward as often observedin the afternoon auroral zone.
Poleward-moving auroral forms (PMAF), the ionospheric signatures of flux transfer events (FTEs), areintermittent phenomena observed in the cusp during negative interplanetary magnetic field intervals. We
present initial results from a new high-sensitivity all-sky imager installed at Longyearbyen, Norway inOctober 2011. The 630.0-nm all-sky images taken with a time resolution of 4 s reveal that one of thePMAFs that occurred with such typical separation times on 29 December 2011 comprises two consecutive
auroral bursts. This observation provides evidence that one PMAF could reflect double FTEs—there is notalways a one-to-one correspondence between FTEs and PMAFs.

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New instrument: In order to investigate drift velocities of the ionospheric irregularities at high-latitudes,
three dual-frequency GNSS receivers with mutual distances of 172-242 m have been operated at EISCAT
Tromso radar site since September 2012. The receivers sample GNSS signals at a rate of 50 Hz. Weobserved the ionospheric scintillation associated with aurora activities.
1.3. Airglow imaging experiment (Kazuo Shiokawa, Nagoya Univ.)
The Solar-Terrestrial Environment Laboratory (STEL), Nagoya University, started routine observation ofVLF waves at Athabasca (54.72N, 246.69E, MLAT=61.3), Canada, using a loop antenna since February
16, 2012. The loop antennas measure east-west and north-south magnetic field variations with a sampling
rate of 100 kHz. Quick-look spectra are available at http://stdb2.stelab.nagoya-u.ac.jp/vlf/index.html
2. Meetings (future meetings)
Following big meetings scheduled in relation to URSI Commission-G. Both meetings recently opened theweb page for paper submission.
IAGA the XIIth Scientific General Assembly, Merida Yucatan, Mexico, August 26-31, 2013
Symposium web-page: http://www.iaga2013.org.mx/
Abstract deadline: April 13, 2013
International CAWSES-II Symposium, Nagoya, Japan, November 18-22, 2013
Symposium web-page: http://www.stelab.nagoya-u.ac.jp/cawses2013/
Abstract deadline: June 30, 2013
3. Publication list
Polar cap studies (Related to 1.1)
Hosokawa, K., J. I. Moen, K. Shiokawa, and Y. Otsuka, Decay of polar cap patch, Journal of GeophysicalResearch, 117, doi:10.1029/2012JA018165, 2013.
EISCAT radar related studies (Related to 1.2)
Fujii, R., O. Amm, H. Vanhamäki, A. Yoshikawa, and A. Ieda (2012), An application of the finite length
Cowling channel model to auroral arcs with longitudinal variations, J. Geophys. Res., 117, A11217,doi:10.1029/2012JA017953. (Article first published online: 22 NOV 2012)
Taguchi, S., K. Hosokawa, Y. Ogawa, T. Aoki, and M. Taguchi (2012), Double bursts inside a polewardmoving auroral form in the cusp, J. Geophys. Res., 117, A12301, doi:10.1029/2012JA018150. (Article
first published online: 5 DEC 2012)2