Reflection and absorption of Alfvénic power in the low-altitude magnetosphere

Details Reflection and absorption of Alfvénic power in the low-altitude magnetosphere Reflection and absorption of Alfvénic power in the low-altitude magnetosphere

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.8016s&link_type=abstract

Journal of Geophysical Research (Space Physics), Volume 108, Issue A4, pp. COA 17-1, CiteID 8016, DOI 10.1029/2002JA009425

Physics

14

Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Mhd Waves And Instabilities, Magnetospheric Physics: Numerical Modeling, Ionosphere: Wave Propagation (6934)

Scientific paper

Results from a numerical study of the nonlinear interaction between large-amplitude Alfvén waves and the low-altitude auroral magnetosphere and ionosphere are presented. In the model the Alfvén wave encounters collisionless resistive dissipation when and where the effective parallel drift of electrons carrying the wave field-aligned current density exceeds a critical threshold corresponding to onset of current-driven microinstability. The resulting parallel electric field and parallel potential drop introduce frequency, amplitude, and perpendicular length-scale dependence in the absorption of Alfvén wave power. Analysis of the power flow shows that (1) most of the power generated by a constant-current source in the magnetosphere and carried by relatively small-amplitude, high-frequency, and short transverse wavelength Alfvén waves is reflected at low altitudes by the wave-induced collisionless resistive layer (RL); (2) Alfvén wave power is absorbed primarily in the RL except when stimulated by a constant-voltage generator, wherein ionospheric Joule heating dominates the absorption at large transverse length scales; (3) the absorption is high (~0.8) at length scales of 10-20 km (ionospheric projection) for constant voltage source conditions; and (4) the relation between the wave-induced parallel potential drop and wave field-aligned current is linear with proportionality constant of order 109 Ω-m2 over much of the range of interest. Correspondence between predicted properties and satellite observations is demonstrated.

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