Fundamental Issues of Auroral Arc Formation (Invited)

Details Fundamental Issues of Auroral Arc Formation (Invited) Fundamental Issues of Auroral Arc Formation (Invited)

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm52b..01h&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM52B-01

Physics

[2704] Magnetospheric Physics / Auroral Phenomena, [2731] Magnetospheric Physics / Magnetosphere: Outer, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2790] Magnetospheric Physics / Substorms

Scientific paper

Auroral forms are not footprints of magnetospheric processes, but the product of an interaction of the source plasma in the outer magnetosphere and tail with the ionosphere. Alfvén waves, quasi-stationary or propagating, are the agent of this interaction. They transport magnetic shear stresses and energy towards the Earth. Two principles govern the creation of auroral forms, (1) magnetic stress release and (2) maximization of the energy deposition. The first has two channels, auroral particle acceleration above or in the topside ionosphere and ohmic dissipation through Pedersen currents in the lower ionosphere. Maximization of the energy conversion is achieved by impedance matching between the incoming Alfvén wave and the effective resistance of the auroral acceleration region. The latter has various forms, depending on current direction and background density. The typical narrow width of auroral forms is a direct result of the impedance matching. Even thinner forms can arise from cavity formation at the interface between ionosphere and lower magnetosphere. The motion of auroral rays is witness of the release of magnetic shear stresses. Auroral arcs can be classified as (1) embedded arcs, (2) Hall generator arcs, and (3) Alfvénic arcs. They are distinguished by the geometry of the generator forces and currents as well as by the types of closure currents in the ionosphere.

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