導波管の分散効果を伴う特異な低緯度ホイッスラの伝播機構(<特集>「地球科学から見た磁気」)

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The purpose of the present paper is to discuss the propagation mechanism of very unusual whistlers with additional traces strongly influenced by the Earth-ionosphere waveguide propagation, which are observed simultaneously at Sakushima (geomag. lat. 24°N) and Kagoshima (20°N), on the basis of the simultaneous location of their causative atmospherics and their ionospheric exit regions in the Northern Hemisphere. This is the first simultaneous location of exit regions of whistlers and their causative atmospherics. The study is great potential in whistler studies. It is found that the causative atmospherics of very unusual whistlers are located exactly at the duct entrance and are trapped in a magnetospheric duct in the local sunrise meridian. Hence the additional traces of the Earth-ionosphere waveguide propagation are concluded to be due to the subionospheric propagation after leaving the ionosphere. The longitudinal gradient of the ionosphere at the duct exit enables the whistler wave energy to be concentrated in a restricted sector in azimuth (in this case, East to West) and to be received at our stations. Wave emergence from the ionosphere over a wide exit angle, together with the extremely small divergence loss, result in an efficient wave interference. This leads to the formation of conspicuous traces of the first and second order mode cut-offs of very unusual whistlers. On the other hand, atmospherics not accompanying any whistler are estimated to be located far from the duct entrance.
社団法人日本磁気学会の論文
2005-10-01

著者

島倉信
千葉大学大学院自然科学研究科

導波管の分散効果を伴う特異な低緯度ホイッスラの伝播機構(<特集>「地球科学から見た磁気」)

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