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Detailed Reference Information |
Potemra, T.A., Zanetti, L.J., Erlandson, R.E., Bythrow, P.F., Gustafsson, G., Acuña, M.H. and Lundin, R. (1987). Observations of large-scale birkeland currents with viking. Geophysical Research Letters 14: doi: 10.1029/GL014i004p00419. issn: 0094-8276. |
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The Viking spacecraft carries a high-resolution Magnetic Field Experiment that acquires approximately 53 vector samples per second. It has four automatically switchable ranges from ¿1024 to ¿65,536 nT (full scale) and resolutions commensurate with a 13 bit A/D converter in each range ( ¿0.125 to ¿8 nT). Data acquired on March 25, 1986 (just a month after Viking's launch) at ~ 13,000 km altitude over the morning sector near 08:30 MLT indicate that the large-scale (>0.5¿ invariant latitude wide) region 1 and region 2 Birkeland current systems can be readily identified. A narrow (~0.2¿ wide) upward flowing Birkeland current exists poleward of the region 1 (downward) flowing current. The density of the large-scale currents is about 0.1 &mgr;A/m2, which is the value expected from a mapping of the densities of 2 to 4 &mgr;A/m2 usually observed at ~800 km altitudes. Small-scale currents embedded in the region 1 system include an intense 8 &mgr;A/m2 earthward-flowing current that is only 8 km wide. That current can be associated with an upward flux of electrons with energies ≤1 keV that can account for nearly all of the current. Comparison of the magnetic fleld observations with particle measurements from the Hot Plasma Experiment confirms that the earthward-flowing large-scale region 1 system is carried primarily by upwardflowing low-energy (<10 eV) electrons. Embedded in this low-energy flux are smaller regions of more energetic electrons that produce the small-scale currents. The correlation of magnetic and particle observations supports previous suggestions that the region 1 currents in the morning sector have their source in the boundary layer and that the region 2 currents are associated with the plasma sheet. ¿American Geophysical Union 1987 |
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American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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