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首页> 外文期刊>Journal of geophysical research >Magnetic Holes Upstream of the Martian Bow Shock: MAVEN Observations
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Magnetic Holes Upstream of the Martian Bow Shock: MAVEN Observations

机译：Magnetic Holes Upstream of the Martian Bow Shock: MAVEN Observations

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abstract_textpMagnetic holes (MHs) are pressure-balanced structures characterized by distinct decreases in the interplanetary magnetic field strength in otherwise unperturbed solar wind. In this paper we present an analysis of MHs upstream of the Martian bow shock based on 3 months of observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Plasma properties within and around these structures as well as their shape characteristics are examined. We find an occurrence rate of around 2.1 events per day. About 51% of all events are of linear type with magnetic field rotation across the hole less than 10 degrees. We observe linear MHs both as isolated events and as part of a train of MHs. The proton temperature anisotropy inside MHs increases, while alpha particles remain mostly isotropic. The average electron temperature inside MHs modestly increases with increasing hole depth. The duration of linear holes at 1.5 AU shows an increase compared to durations at smaller heliocentric distances, but the structures remain asymmetrical and ellipsoid. A case study of MHs accompanied by a population of heavy pickup ions is also discussed./ppPlain Language Summary The solar wind, a supersonic flow of electrons and ions flowing radially outward from the Sun, carries a magnetic field. Magnetic holes are structures with reduced magnetic field strength that last between a few seconds to a few minutes. These structures have been observed at many places throughout the solar system. A common formation mechanism for magnetic holes is a wave mode instability that converts magnetic energy into ion thermal energy, known as the mirror mode. Mirror mode instabilities grow when the temperature of ions moving perpendicular to the magnetic field is higher than that of ions moving in the parallel direction. Mirror waves alter the magnetic field and the spatial structure of the plasma. In this paper, we use observations from the Mars Atmosphere and Volatile EvolutioN spacecraft to study magnetic holes in the space environment around Mars./p/abstract_text

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