О баллонной неустойчивости в токовых слоях
Автор: Леонович А.С., Козлов Д.А.
Журнал: Солнечно-земная физика @solnechno-zemnaya-fizika
Статья в выпуске: 2 т.1, 2015 года.
Бесплатный доступ
Решена задача неустойчивости азимутально-мелкомасштабных альфвеновских и медленных магнитозвуковых (ММЗ) волн в аксиально-симметричной модели геомагнитного хвоста с токовым слоем. Найденные решения описывают неустойчивые в присутствии токового слоя колебания и относятся к области вытянутых в хвост замкнутых магнитных силовых линий. Определены спектры собственных частот основных гармоник стоячих азимутально-мелкомасштабных альфвеновских и ММЗ-волн в локальном и ВКБ-приближениях и проведено их сравнение. Показано, что полученные в этих приближениях свойства рассматриваемых колебаний кардинально различаются. В локальном приближении альфвеновские волны оказываются устойчивыми во всем диапазоне рассматриваемых магнитных оболочек. ММЗ-волны на магнитных оболочках, проходящих через токовый слой, переходят в режим апериодической (баллонной) неустойчивости. В ВКБ-приближении как альфве-новские, так и ММЗ-волны на силовых линиях, проходящих через токовый слой, переходят в режим неустойчивости при конечной частоте собственных колебаний. Определена структура азимутально-мелкомасштабных неустойчивых альфвеновских волн поперек магнитных оболочек.
Мгд-волны, баллонная неустойчивость, токовый слой, геомагнитный хвост
Короткий адрес: https://sciup.org/142103561
IDR: 142103561 | УДК: 533.9, | DOI: 10.12737/6425
On ballooning instability in current sheets
The problem of instability of the magnetotail current sheet to azimuthally small-scale Alfvén and slow magnetosonic (SMS) waves is solved. The solutions describe unstable oscillations in the presence of a current sheet and correspond to the region of stretched closed field lines of the magnetotail. The spectra of eigen-frequencies of several basic harmonics of standing Alfvén and SMS waves are found in the local and WKB approximation, which are compared. It is shown that the oscillation properties obtained in these approximations differ radically. In the local approximation, the Alfvén waves are stable in the entire range of magnetic shells. SMS waves go into the aperiodic instability regime (the regime of the “ballooning” instability), on magnetic shells crossing the current sheet. In the WKB approximation, both the Alfvén and SMS oscillations go into an unstable regime with a non-zero real part of their eigen-frequency, on magnetic shells crossing the current sheet. The structure of azimuthally small-scale Alfvén waves across magnetic shells is determined.
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