Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm32c..03p&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SM32C-03
Other
2712 Electric Fields (2411), 2724 Magnetopause, Cusp, And Boundary Layers, 2752 Mhd Waves And Instabilities, 2772 Plasma Waves And Instabilities, 7815 Electrostatic Structures
Scientific paper
The earth's cusp regions are known to be the seat of a wide range of ULF plasma instabilities and turbulence. At high and mid-altitudes, NASA's Polar satellite repeatedly encounters the cusp regions and detects such waves with both its vector electric and magnetic field detectors. The combination of the electric and magnetic field data help enable plasma modes, energy flow, and source regions to be identified, and electrostatic and electromagnetic turbulence to be distinguished. For example, for IMF Bz south conditions, data from Polar's DC electric field instrument typically reveal intense (5-10 mV/m rms), quasi-static electric fields that appear immediately poleward of the last closed field line, yet prior to the ion injections that more customarily characterize the cusp region. We identify such electric field signatures as those of irregularities associated with open magnetic field lines, for which the quasi-DC and ULF electric fields are a combination of both local and more distant (magnetosheath) processes. Within the region of the cusp ion injections, on the other hand, both electric and magnetic field ULF turbulent-like waveforms are common. Using minimum variance and Poynting flux calculations, we demonstrate that such waveforms appear to be related to Alfven and magnetosonic waves that are associated with the currents carried by the precipitating particles. The DC electric field instrument also provides a detailed picture of the relationship of the broader band (0.05-20 Hz) turbulent-like wave features with the lower frequency (DC-0.05) electric fields which frequently include "spikey" waveforms. Although the data suggest that the higher frequency waves are extensions of the lower frequency structures, the appearance of quasi-DC (less than 0.1 Hz) structures without higher frequency spectral extensions has strong implications for local generation and/or damping mechanisms. This talk presents an overview of recent findings.
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