Enhanced Plasma Expansion in Auroral Plasma Cavities in the Upward Current Region

Details Enhanced Plasma Expansion in Auroral Plasma Cavities in the Upward Current Region Enhanced Plasma Expansion in Auroral Plasma Cavities in the Upward Current Region

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm54a..08d&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM54A-08

Physics

7815 Electrostatic Structures, 7839 Nonlinear Phenomena, 7843 Numerical Simulation Studies, 2704 Auroral Phenomena (2407), 2772 Plasma Waves And Instabilities

Scientific paper

The existence of deep density cavities extending from topside ionosphere to altitudes of several Earth's radii is now well established from several satellite observations. Observations from FAST and Polar also show that double layers form in the cavity at both low and high altitudes in the upward current plasma. Such double layers accelerate electrons downward and ionospheric ions upward. Since the early observations of ion beams from S3-3 at altitudes of about one RE , the Earth's radius, the supply of cold ionospheric ions to the double layers at such altitudes for large parallel accelerations forming in beams has been a problem. Suggestions for the supply range from wave-particle interaction resulting into ion heating at low altitudes to accelerations in different layers. We further suggest here that the ion supply could be facilitated by expansion of the ionospheric plasma. This is specially so because of the deep density cavity in combination with the generation of secondary and backscattered (SBS) electrons by the primary precipitating energetic electrons. The SBS electrons generate a warms electron population, which enhances the process of plasma expansion. The heating of the cold ionospheric electrons as well as of the SBS electrons by waves generated by the primary electrons further enhances the plasma expansion. The transport of the ionospheric plasma to high altitudes by means of the enhanced plasma expansion does not only supply ions for the ion beam formation at high altitudes, but it also generates an ion beam at low altitudes as well as supplies the trapped electron population needed for the formation of double layers at mid and high altitudes. We demonstrate these assertions by means of one-dimensional particle-in-cell simulations of long auroral flux tubes.

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