第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月16日（水） 統計数理研究所 3階リフレッシュフロ

Asamura Kazushi

Kataoka Ryuho

Katoh Yuto

Miyoshi Yoshizumi

Nishiyama Takanori

Okano Shoichi

Sakanoi Takeshi

Satoh Mitsuteru

National Institute of Polar Research Repository

Temporal and spatial variations of pulsating auroras in fine-scale obtained from ground-based observationsTakanori Nishiyama1, Takeshi Sakanoi1, Yoshizumi Miyoshi2, Ryuho Kataoka3, Yuto Katoh4, Kazushi Asamura5, Mitsuteru Satoh6 and Shoichi Okano11Planet. Plasma Atmos. Res. Cent., Tohoku Univ.2Solar-Terrestrial Environment Laboratory,, Nagoya Univ.3Interactive Research Center of Science, Tokyo Institute of Technology4Department of Geophysics, Graduate School of Science, Tohoku Univ.5ISAS/JAXA6Department of Cosmosciences, Hokkaido Univ.Pulsating Aurora(PA) is characterized by the periodically changing emission amplitudes with the rectangular pulses of a few seconds to a few tens of seconds [e.g., Oguti et al., 1981; Yamamoto, 1988]. PAs tend to appear in the recovery phase of substorm between postmidnight and dawn sector. The horizontal size of PAs are known to be 10-200 km, based on the optical observations. Recently, some ground-satellite coordinated observations suggested the generation mechanisms of PAs as a result of pitch angle scatterings due to whistler mode chorus waves and/or the electron cyclotron harmonics[Nishimura et al., 2010; Liang et al., 2010]. Time-varying field aligned potential was also suggested by Sato et al. [2004]. The dominant mechanisms and the origin of the periodicity remain unclear. Ground-based all-sky observations have been made for a long time, although they were not enough for a quantitative discussion about small-scale characteristics of PAs such as the shapes and dynamics due to their limited spatial resolutions. The fast temporal variations of intensity known as quasi-3Hz modulations, which was reported by a number of rocket/satellite observations about precipitating electrons[e.g., Sandahl et al., 1980], has been hardly discussed in detail using the ground instruments because of the limited temporal resolutions and sensitivities. We have carried out ground-based observations using a suit of instruments, consisting of an EMCCD camera, an all-sky video camera, a photometer, and a search coil magnetometer covering the frequency range of ELF-VLF. We installed the instruments at Poker Flat Research Range between November 2010 and March 2011. Our EMCCD camera has narrow field of view corresponding to 100km × 100km at altitude of 110 km and high sampling rate up to 100 frames per second. An initial analysis result of event on March 4th 2011 around 1100UT revealed two important features of PAs in small scale. One is PAs in the FOV can be categorized into three regions which showed different periods. There were 1-3Hz modulations with peak frequency of 1.5 Hz inside each patches, while there was no higher frequency modulations. In addition, simultaneous observations with the search coil demonstrated that modulations of PA ranged 1 to 3Hz correlated to ELF amplitudes integrated over frequency range of 1-10Hz. On the other hand, VLF emissions corresponding to whistler mode waves were not seen during this period. These results demonstrate that the temporal and spatial characteristics of PA, such as periodicity, modulation and micro-shapes, varies considerably in a narrow region corresponding to about 2000km × 2000km in the magnetosphere. It means that the generation processes depend greatly on local plasma conditions and the conditions are nonuniform in the source regions.                                                                    Figure 1.  Summary plot of the event on Mar. 04th, 2011100km100kmMultiple ArcAAMCGR(LAT=62.9)FYKN(LAT=66.5)GAKO(LAT=62,4)INUV(LAT=68.4)WHIT(LAT=61.0)PulsatioPulsationPulsationBBNorthEastReferences[1] Oguti, T., S. Kokubun, K. Hayashi, K. Tsuruda, S. Machida, T. Kitamura, O. Saka, and T. Watanabe (1981),  Latitudinally propagating on-off switching aurorae and associated geomagnetic pulsations: A case study of an event of  February 20, 1980, Can. J. Phys., 59, 1131-1136.[2] Yamamoto, T. (1988), On the temporal fluctuations of pulsating auroral luminosity, J. Geophys. Res., 93, 897– 911. [3] Nishimura, Y.  J. Bortnik, W. Li, R. M. Thorne, L. R. Lyons, V. Angelopoulos, S. B. Mende, J. W. Bonnell, O. Le  Contel, C. Cully, R. Ergun, and U. Auster (2010), Identifying the Driver of Pulsating Aurora , Science 330 (6000), 81.  [DOI: 10.1126/science.1193186] [4] Liang, J., V. Uritsky, E. Donovan, B. Ni, E. Spanswick, T. Trondsen, J. Bonnell, A. Roux, U. Auster, and D. Larson  (2010), THEMIS observations of electron cyclotron harmonic emissions, ULF waves, and pulsating auroras, J.  Geophys. Res., 115, A10235, doi:10.1029/2009JA015148. [5] Sato, N., D. M. Wright, C. W. Carlson, Y. Ebihara, M. Sato, T. Saemundsson, S. Milan, and M. Lester (2004),  Generation region of pulsating aurora obtained simultaneously by the FAST satellite and a Syowa-Iceland conjugate  pair of observatories, J. Geophys. Res., 109, A10201, doi:10.1029/2004JA010419.[6] Sandahl, I., L. Eliasson, and R. Lundin (1980), Rocket observations of precipitating electrons over a pulsating aurora,  Geophys. Res. Lett., 7, 309 – 312.

Temporal and spatial variations of pulsating auroras in fine-scale obtained from ground-based observations

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Temporal and spatial variations of pulsating auroras in fine-scale obtained from ground-based observations

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