Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm33a1890n&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM33A-1890
Physics
[2487] Ionosphere / Wave Propagation, [2730] Magnetospheric Physics / Magnetosphere: Inner, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2752] Magnetospheric Physics / Mhd Waves And Instabilities
Scientific paper
Electromagnetic ion cyclotron (EMIC) waves excited in the equatorial region of the magnetosphere by the ion cyclotron instability propagate along magnetic field lines to the ionosphere and are observed as Pc1 geomagnetic pulsations (Pc1) with frequencies at 0.2-5Hz on the ground. These Pc1 waves propagate horizontally through the ionospheric duct. Magnetospheric ions are scattered by the resonance with EMIC waves and precipitate to the ionosphere to cause isolated proton auroras at subauroral latitudes. One-to-one correspondence between isolated proton auroras and Pc1 waves was found by Sakaguchi et al. [JGR, 2008]. The mechanism of ionospheric duct propagation of Pc1 has been studied theoretically for the polarization characteristics [Graifinger, JGR, 1972; Fujita and Tamao, JGR, 1988], and observationally for the possible Pc1 source [e.g., Fraser et al., JATP, 1976] and for the spatial distribution of polarization mode [Hayashi et al., Can J. Phys., 1981] using ground magnetometers. However, comparison between the actual position and size of ionospheric Pc1 sources and the polarization characteristics of Pc1 waves has not been done. In order to investigate this relation, we compare the spectral and polarization parameters of Pc1 waves observed by a 64-Hz sampling induction magnetometer and the position and area of isolated proton auroras observed by an all-sky imager at Athabasca (ATH, 54.7N, 246.7E, magnetic latitude: 61.7N), for 13 one-to-one correspondent events of Pc1 waves and isolated proton auroras reported by Sakaguchi et al. [JGR, 2008]. We found that the major axis direction of Pc1 polarization varies depending on the area of the isolated proton aurora and on the distance from ATH to the aurora. In the presentation, we will discuss these results based on a multi-event study using data from three years of 2005-2008 in the context of the model calculation by Fujita and Tamao [1988].
Connors Martin G.
Nomura Ryo
Otsuka Yoichi
Sakaguchi Kei
Shiokawa Kazuhiko
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