Physics
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11601209g&link_type=abstract
Journal of Geophysical Research, Volume 116, Issue A1, CiteID A01209
Physics
2
Magnetospheric Physics: Mhd Waves And Instabilities (2149, 6050, 7836), Magnetospheric Physics: Plasma Sheet, Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Magnetospheric Physics: Substorms, Magnetospheric Physics: Plasma Waves And Instabilities (2471)
Scientific paper
An examination of the magnetic field and plasma observed by the inner THEMIS-D spacecraft (P3) close to the equatorial plane at ˜11RE at local midnight reveals the occurrence of mirror-mode structures. These structures have the same characteristic waveform seen in other regions. The examination of the mirror-mode instability shows that inside these structures the threshold of mirror instability is marginally reached, while the surrounding plasma is mirror stable. The observed mirror structures occur in the dipolarized magnetic field following a substorm-related dipolarization. It is found that after the dipolarization front, the local ions become more anisotropic and initial magnetic holes form inside this anisotropic plasma before the fully-fledged mirror structures are observed. The ions become less anisotropic afterward, but the strong field depression in the magnetic holes enhances the effective plasma beta so that the mirror instability threshold is marginally reached. Thus, the dipolarization process provides the large-amplitude magnetic field fluctuations and the anisotropic plasma environment for mirror structures to grow. The isolated large-amplitude mirror-mode structures survive in the mirror-stable plasma even through the plasma becomes less anisotropic. It is also found that the width of magnetotail mirror-structures is smaller than one gyroradius of a plasma sheet proton, which is different from the width of mirror structures in other regions. These mirror structures appear to have a strong correlation with electron anisotropy changes. These observations suggest that electron kinetics may also play a role during the growth and saturation of mirror instability in the near-Earth tail.
Angelopoulos Vassilis
Constantinescu Dragos O.
Ge Yong-Shuai
Larson David
McFadden James P.
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