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Drift mirror Mode waves in the distant (X ≃ 200 R e ) magnetosheath
Author(s) -
Tsurutani B. T.,
Richardson I. G.,
Lepping R. P.,
Zwickl R. D.,
Jones D. E.,
Smith E. J.,
Bame S. J.
Publication year - 1984
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl011i010p01102
Subject(s) - magnetosheath , physics , magnetosphere , plasma , solar wind , ion , atomic physics , proton , gyroradius , magnetopause , magnetohydrodynamics , geophysics , nuclear physics , quantum mechanics
Drift mirror waves have been detected 207 R e downstream in the distant magnetosheath by instrumentation onboard ISEE‐3. The MHD structures have estimated scale sizes of 4.6 × 10 4 to 2.3 × 10 5 km or 130 to 700 proton gyroradii, assuming 1 keV protons. Simultaneous measurements on IMP‐8 indicate that at the time of the events, the earth's magnetosphere was enveloped by a solar flare‐associated interplanetary shock and driver gas. The (shocked) driver gas was characterized by an unusually low plasma density with a β (plasma pressure/magnetic pressure) of ∼ 0.2. From the instability criterion, β ⊥ /β 11 >1+1/β ⊥ , the magnetosheath plasma should not go mirror‐mode unstable unless the anisotropy, β ⊥ / β 11 is large, >6. These unusual conditions are met by the demonstrated presence of highly anisotropic, energetic 35‐384 keV ions with P ⊥ /P 11 ≃ 30. It is calculated that most of the plasma energy density can be due to >1 keV ions. The source of the ions is not well understood, but an appealing possibility is magnetic annihilation of the northward magnetosheath fields with southern hemisphere polar cusp magnetic fields.