Field‐aligned currents in Saturn's southern nightside magnetosphere: Sub‐corotation and planetary period oscillation components

Hunt, G.J.; Cowley, S.W.; Provan, G.; Bunce, E.J.; Alexeev, I.I.; Belenkaya, E.S.; Kalegaev, V.V.; Dougherty, M.K.; Coates, A.J.

Авторы: Hunt G.J., Cowley S.W.H, Provan G., Bunce E.J., Alexeev I.I., Belenkaya E.S., Kalegaev V.V., Dougherty M.K., Coates A.J.
Журнал: Journal of Geophysical Research
Том: 119
Номер: 12 (December)
Год издания: 2014
Издательство: William Byrd Press for John Hopkins Press
Местоположение издательства: United States
Первая страница: 9847
Последняя страница: 9899
DOI: 10.1002/2014JA020506
Аннотация: We investigate magnetic data showing the presence of field-aligned magnetosphere-ionosphere coupling currents on 31 Cassini passes across Saturn's southern post-midnight auroral region. The currents are strongly modulated in magnitude, form, and position by the phase of the southern planetary period oscillations (PPOs). PPO-independent currents are separated from PPO-related currents using the anti-symmetry of the latter with respect to PPO phase. PPO-independent downward currents ~1.1 MA per radian of azimuth flow over the polar open field region indicative of significant plasma sub-corotation, are enhanced in an outer plasma sheet layer of elevated ionospheric conductivity carrying ~0.8 MA rad-1, and close principally in an upward-directed current sheet at ~17°-19° ionospheric co-latitude carrying ~2.3 MA rad-1 that maps to the outer hot plasma region in Saturn's magnetosphere (equatorial range ~11-16 Saturn radii (RS)) co-located with the UV oval. Subsidiary downward and upward currents ~0.5 MA rad-1 lie at ~19°-20.5° co-latitude mapping to the inner hot plasma region, but no comparable currents are detected at larger co-latitudes mapping to the cool plasma regime inside ~8 RS. PPO-related currents at ~17.5°-20° co-latitude overlap the main upward and subsidiary downward currents, and carry comparable rotating upward and downward currents peaking at ~1.7 MA rad-1. The overall current layer co-latitude is also modulated with 1° amplitude in the PPO cycle, maximum equatorward adjacent to the peak upward PPO current and maximum poleward adjacent to peak downward PPO current. This phasing requires the current system to be driven from the planetary atmosphere rather than directly from the magnetosphere.
Добавил в систему: Алексеев Игорь Иванович

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Field‐aligned currents in Saturn's southern nightside magnetosphere: Sub‐corotation and planetary period oscillation componentsстатья

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