Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm31d..04j&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM31D-04
Physics
[2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems
Scientific paper
Recent data from the FREJA, FAST and CLUSTER satellites have greatly increased our understanding of the magnetic field-aligned (Birkeland) current system in the Earth’s magnetosphere. Quasi-steady electric fields parallel to the background geomagnetic field exist in both upward and downward Birkeland current regions above the aurora. These fields, together with the turbulence found on auroral field lines, energize the plasma particles as they flow either away from or toward the Earth. In general, these parallel electric fields are supported by: (1) one or more strong double layers; (2) the mirror force; (3) the generalized parallel pressure gradient; and (4) anomalous transport effects due to turbulence. Recently, and for the first time, we have developed a fully self-consistent, multi-moment fluid theory for the Birkeland current system that contains the effects of plasma turbulence [J. R. Jasperse et al. (2006), Phys. Plasmas 13, 072903, and J. R. Jasperse et al. (2006), Phys. Plasmas 13, 112902]. Applying the new theory to the observations in a downward-current sheet, we are able to assess the relative importance of the above-mentioned four contributions to the self-consistent, parallel electric field. We find that the anomalous resistivity itself makes a very small contribution to the parallel electric field; however the presence of electrostatic ion-cyclotron turbulence has a very large effect on the altitude dependence of the entire quasi-steady solution. The magnitude of the parallel electric field is enhanced by nearly a factor of 40 compared to its value when turbulence is absent. We also find that the potential increase associated with the strong double layer that forms in downward currents can be evaluated using satellite data and the multi-moment fluid theory.
Basu Baidyanath
Jasperse John R.
Lund Eric J.
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