11:00 〜 13:00
[PEM11-P08] Are Pi2 pulsations an oscillating motion of field line dipolarization?
キーワード：Pi2型地磁気脈動、磁場双極化、ポロイダル的振動モード
Dawn-dusk flow shears in the nightside magnetosphere associated with field line dipolarization produce tangential discontinuities in the midnight sector and the KH instability generate periodic displacement of the discontinuity surface at Pi2 cadence [Saka et al., 2010].
Wave polarizations of Pi2 pulsations thus produced in the magnetosphere by the boundary displacement are generally reversed in the polar ionosphere [Saka et al., 2012]. The polarization reversal cannot be understood through the reconfiguration of geomagnetic field lines in terms of the fundamental harmonics in the meridian planes but rather by considering the third harmonics. We show that the field line deformations associated with third harmonics matched those of field line dipolarization. The dipolarization as well as Pi2 pulsations are a result of field-aligned propagation of poloidal wave (guided poloidal mode [Radoski, 1967]) that rotated the field lines in the meridian plane.
References
Radoski, H., Highly asymmetric MHD resonances: the guided poloidal mode, J. Geophys. Res., 72, 4026, 1967.
Saka,O., Hayashi, K., and Thomsen, M., First 10 min intervals of Pi2 onset at geosynchronous altitudes during the expansion of energetic ion regions in the nighttime sector, J. Atmos. Solar Terr. Phys., 72, 1100, 2010.
Saka, O., K. Hayashi, and D. Koga, Excitation of the third harmonic mode in meridian planes for Pi2 in the auroral zone. J. Geophys. Res., 117, A12215, doi:10.1029/2012JA018003, 2012.
Wave polarizations of Pi2 pulsations thus produced in the magnetosphere by the boundary displacement are generally reversed in the polar ionosphere [Saka et al., 2012]. The polarization reversal cannot be understood through the reconfiguration of geomagnetic field lines in terms of the fundamental harmonics in the meridian planes but rather by considering the third harmonics. We show that the field line deformations associated with third harmonics matched those of field line dipolarization. The dipolarization as well as Pi2 pulsations are a result of field-aligned propagation of poloidal wave (guided poloidal mode [Radoski, 1967]) that rotated the field lines in the meridian plane.
References
Radoski, H., Highly asymmetric MHD resonances: the guided poloidal mode, J. Geophys. Res., 72, 4026, 1967.
Saka,O., Hayashi, K., and Thomsen, M., First 10 min intervals of Pi2 onset at geosynchronous altitudes during the expansion of energetic ion regions in the nighttime sector, J. Atmos. Solar Terr. Phys., 72, 1100, 2010.
Saka, O., K. Hayashi, and D. Koga, Excitation of the third harmonic mode in meridian planes for Pi2 in the auroral zone. J. Geophys. Res., 117, A12215, doi:10.1029/2012JA018003, 2012.