Physics – Plasma Physics
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000jgr...10525191d&link_type=abstract
Journal of Geophysical Research, Volume 105, Issue A11, p. 25191-25204
Physics
Plasma Physics
2
Magnetospheric Physics: Magnetopause, Cusp, And Boundary Layers, Magnetospheric Physics: Numerical Modeling, Space Plasma Physics: Charged Particle Motion And Acceleration
Scientific paper
On May 13, 1996, as the Polar spacecraft was traveling at high invariant latitudes (~78°-79°) in the prenoon sector (~1050 magnetic local time), the Thermal Ion Dynamics Experiment on board recorded successive injections of protons with clear energy-time dispersion. These dispersion structures spread over several minutes and extend from several hundreds of eV down to a few tens of eV. During this pass, simultaneous measurements from the Wind spacecraft revealed little variation of the solar wind dynamical pressure but a gradual turning of the interplanetary magnetic field (IMF) from an essentially dawn-to-dusk orientation (i.e., predominant positive BY component and slightly negative BZ) to a north-to-south one (predominant negative BZ). We show that the observed injections result from magnetosheath particle entry at higher and higher latitudes in the dawn sector. Using test particle calculations in a simple model of reconnected interplanetary and magnetospheric field, we show that the injection modulation likely follows from changes in the dynamical regime experienced by the ions upon traversal of the magnetopause current sheet. That is, as the IMF gradually rotates, the time-varying BY and BZ lead to changes in the adiabaticity parameter κ in the region of entry and affect particle access to the Polar location. In the morning sector where magnetosheath plasma accelerates downtail, such an access to the inner magnetosphere requires magnetic moment damping and is thus favored during nonadiabatic episodes. The flux variations obtained numerically are in qualitative agreement with those observed, both in terms of characteristic energy and overall time evolution. This supports our interpretation of the modulated ion injections in terms of intermittent nonadiabatic entry from the magnetosheath followed by time of flight dispersion between the magnetopause and the spacecraft.
Delcourt Dominique C.
Fok Mei Ching
Giles Barbara L.
Moore Thomas Earle
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