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Features of ion trajectories in the polar magnetosphere
Author(s) -
Horwitz J. L.
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/gl011i011p01111
Subject(s) - magnetosphere , physics , convection , polar , ionosphere , field line , geophysics , plasma sheet , pitch angle , ion , electric field , polar wind , computational physics , atomic physics , plasma , magnetopause , mechanics , astronomy , nuclear physics , quantum mechanics
The trajectories of mainly low‐energy ionospheric ions injected near the polar cusp into the polar magnetosphere are presented for a model polar magnetosphere including the effects of convection electric fields and gravitation. The trajectories display the ion mass and energy differentiation which has been seen in recent satellite observations of low‐energy ionospheric ions injected into the polar magnetosphere, and indicate that for reasonable ranges of injection energy, pitch angle and convection electric field: 1. Transport of low‐energy ‘polar cusp’ O + to the ∼1 Re altitude nightside auroral acceleration region is feasible; and 2. Preferential trapping of energetic O + relative to H + and He + energetic ions occurs in the closed field line region of the magnetotail plasma sheet. Two interesting classes of polar region very low‐energy heavy ion trajectories are noted: 1. ‘Parabolic’ trajectories, in which heavy ions injected at the polar cusp at small pitch angles rise then fall into the polar cap atmosphere, and 2. ‘Hopping’ trajectories, in which heavy ions injected at large pitch angles at the polar cusp mirror between the gravitational stopping location and magnetic mirror point as they convect at low to intermediate altitudes across the polar cap. It is also illustrated how during conditions of sunward convection in the central polar cap, a pronounced ‘spray’ of ions injected on the nightside may occur, in which such ions may appear in the nightside or dayside magnetosphere depending upon injection characteristics and dusk‐to‐dawn convection electric field magnitude; such ion dynamics may be of interest in connection with theta auroras.