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Field‐aligned currents in Saturn's magnetosphere: Local time dependence of southern summer currents in the dawn sector between midnight and noonстатья
Статья опубликована в высокорейтинговом журнале
Информация о цитировании статьи получена из
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Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 2 декабря 2016 г.
- 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: 121
- Номер: 8
- Год издания: 2016
- Издательство: William Byrd Press for John Hopkins Press
- Местоположение издательства: United States
- Первая страница: 7785
- Последняя страница: 7804
- DOI: 10.1002/2016JA022712
- Аннотация: We examine and compare the magnetic field perturbations associated with field-aligned ionosphere-magnetosphere coupling currents at Saturn, observed by the Cassini spacecraft during two sequences of highly inclined orbits in 2006/7 and 2008 under late southern summer conditions. These sequences explore the southern currents in the dawn-noon and midnight sectors, respectively, thus allowing investigation of possible origins of the local time (LT) asymmetry in auroral Saturn kilometric radiation (SKR) emissions, which peak in power at ~8 h LT in the dawn-noon sector. We first show that the dawn-noon field data generally have the same four-sheet current structure as found previously in the midnight data, and that both are similarly modulated by “planetary period oscillation” (PPO) currents. We then separate the averaged PPO-independent (e.g., subcorotation) and PPO-related currents for both LT sectors using the current system symmetry properties. Surprisingly, we find that the PPO-independent currents are essentially identical within uncertainties in the dawn-dusk and midnight sectors, thus providing no explanation for the LT dependence of the SKR emissions. The main PPO-related currents are, however, found to be slightly stronger and narrower in latitudinal width at dawn-noon than at midnight, leading to estimated precipitating electron powers, and hence emissions, that are on average a factor of ~1.3 larger at dawn-noon than at midnight, inadequate to account for the observed LT asymmetry in SKR power by a factor of ~2.7. Some other factor must also be involved, such as a LT asymmetry in the hot magnetospheric auroral source electron population.
- Добавил в систему: Алексеев Игорь Иванович