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Gyro‐phase effects near the storm‐time boundary of energetic plasma
Author(s) -
Delcourt D. C.,
Moore T. E.,
Sauvaud J. A.
Publication year - 1991
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 - 10.1029/91gl01526
Subject(s) - substorm , adiabatic invariant , plasma sheet , physics , plasma , adiabatic process , atomic physics , ion , particle acceleration , magnetosphere , field line , gyroradius , computational physics , geophysics , quantum mechanics , thermodynamics
The non‐adiabatic acceleration of plasma sheet ions during the expansion phase of substorms is examined by means of single‐particle codes. It is shown that, in the near‐Earth plasma sheet, the gyration phase at substorm onset controls the net ion energization, as the gyro‐period is locally comparable to the field variation time scale. This can yield a particularly significant decrease of the particle magnetic moment. It is accordingly argued that, via adiabatic invariant violation, the dipolarization of magnetospheric field lines can induce a “de‐trapping” of inner plasma sheet populations and, hence, give rise to short‐lived precipitation enhancements over the auroral zone. As this effect depends upon cyclotron frequency, it is expected to occur at distinct latitudes for different ion species. This contrasts with non‐adiabatic ion behavior further out into the geotail, which is characterized by intense perpendicular heating and a likely collective trapping.