Physics
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000cosre..38..547v&link_type=abstract
Cosmic Research, v. 38, Issue 6, p. 547-556 (2000).
Physics
Scientific paper
A new population of dispersed suprathermal ions descending into the ionosphere is discovered in the cusp region from the INTERBALL-2 measurements at altitudes of 2-3R_E. The proton energies of the population are below the low energy cut-off of the main dispersed proton population of the magnetosheath origin, and its intensity and density are also much lower. For IMF B_z <= 2 nT the region of the population observations is located partly coincident with (or sometimes poleward from) the main proton population of the ``cusp proper.'' The pitch-angle velocity dispersion in the population during a 2-min satellite rotation manifests itself as a typical ``pitch-angle V'' together with a velocity dispersion due to poleward convection. The satellite passes chosen for the detailed analysis and modeling lay approximately along the cusp/cleft band from afternoon till prenoon MLT sectors, thus emphasizing the pitch-angle dispersion role with respect to the dispersion due to convection. This allows one to observe the suprathermal proton population during several tens of minutes over the MLT range of ~3 h around noon, i.e., similarly to the MLT extension of the ``cusp proper.'' A remarkable space/time stability of this new population is due to its low velocity (tens of km/s) and/or velocity diffusion in the flux tubes of the ``cusp proper.'' We have performed both backward tracing of proton trajectories in the Tsyganenko-96 model, and kinetic modeling of the kinematic variations of the distribution function for protons along their way from the bi-Maxwellian source in the form of a ``heating wall'' till the satellite. The parameters of the model were adjusted to the observed energy-time spectrograms. They consistently indicate the origin of the descending suprathermal proton population at intermediate altitudes of ~5R_E, i.e., within cusp flux tubes but well below the magnetopause. Some published measurements from the POLAR satellite in the cusp region at altitudes of 4-5R_E seem to be consistent with the supposition of crossing the source region of this population, variable in space and time (though these measurements were interpreted in a different manner).
Chugunin D. V.
Dubouloz Nicolas
Gal'perin Yu I.
Vovchenko V. V.
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