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| Titel |
MESSENGER observations of magnetopause structure at Mercury |
| VerfasserIn |
G. A. DiBraccio, J. A. Slavin, S. A. Boardsen, B. J. Anderson, H. Korth, T. H. Zurbuchen, J. M. Raines, R. L. Jr. McNutt, S. C. Solomon |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058865
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| Zusammenfassung |
| MESSENGER Magnetometer (MAG) data from the first series of “hot-season” orbits at
Mercury, when periapsis was positioned over the subsolar region, have been used to
augment our initial studies to characterize the magnetopause structure as a function of
local time. Minimum variance analysis (MVA) was applied to transform the MAG
data into boundary-normal coordinates in order to determine (1) the thickness of
the magnetopause, (2) the magnetic shear angle across the boundary, and (3) the
normal magnetic field, BN, across the current sheet and, by inference, the rate of
reconnection and the magnetosphere electric potential. We applied the MVA to all distinct
magnetopause crossings within the subsolar region between 0800 and 1600 local time
and within ± 25Ë latitude. A well-defined normal direction, specified by a ratio
of the eigenvalue for intermediate variance to that for minimum variance that is
greater than 8, was determined for 72 crossings. For this data set, 72.2% of the
magnetopause traversals had a substantial normal component (i.e., BN > 4 nT). For a mean
boundary motion velocity of 10 km s-1, the average current sheet thickness was 29 km,
which is comparable to 2 gyroradii for solar wind protons. The mean ratio of the
normal magnetic field component to the total field magnitude, a measure of the
reconnection rate, was 0.2 and is independent of magnetic field shear angle across the
magnetopause. We conclude that Mercury’s magnetopause structure is generally open to the
solar wind plasma under a wide range of interplanetary magnetic field shear angles. |
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