Cluster PEACE Observations of Uni- and Bi-Directional Beams at Mid Altitudes on the Nightside

Details Cluster PEACE Observations of Uni- and Bi-Directional Beams at Mid Altitudes on the Nightside Cluster PEACE Observations of Uni- and Bi-Directional Beams at Mid Altitudes on the Nightside

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm21b..10w&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SM21B-10

Other

2704 Auroral Phenomena (2407), 2708 Current Systems (2409)

Scientific paper

The Cluster PEACE instrument measures electrons from ≈ 0.5 to ≈ 30,000 eV with up to 7.5o angular resolution. In gyrotropic plasmas, spin-resolution (4 second) data is available from all four satellites. This allows the unprecendented capability of resolving, with high time resolution, space/time features. When combined with other Cluster data, insights heretofore unattainable are now possible. In early 2001, Cluster passed through the dusk nightside auroral region at mid-altitudes. PEACE observations show the presence of uni- and bi-directional beams that are sometimes associated with solitary wave structures observed by the Wide Band Data (WBD) instrument. These wave emissions, when viewed in the frequency domain, are referred to as Broadband Electrostatic Noise. The uni-directional beams and bi-directional beams of unequal amplitude are also associated with perturbations of the ambient magnetic field indicative of field aligned currents. The magnetometer signatures are reminiscent of the current systems observed at Jupiter in the vicinity of the Io flux tube. The equal-amplitude bi-directional beams do not show such field-aligned currents. Loss cone features, indicative of mirror height lifting by parallel electric fields, accompany the field-aligned beams, but are not equal in depth and width. Examination of the 3D plasma distributions shows that the field-aligned beams are not an acceleration of the pre-existing hot plasma sheet electrons, but of a very cold population. The angular and energy widths of the field-aligned beam are very narrow and the peak energy ebbs and grows within event regions. A fundamental question that arises is whether the electron beams originate from an interaction with the solitary wave structures, or, conversely, whether the solitary waves are generated by the electrons. We will use the four point Cluster measurements to attempt an answer to that question and to construct a three-dimensional model of the current systems.

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