Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm53a..05l&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM53A-05
Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2748] Magnetospheric Physics / Magnetotail Boundary Layers, [2790] Magnetospheric Physics / Substorms
Scientific paper
A critical question in resolving the timing of events during magnetospheric substorms is the relationship between tail phenomena observed by satellites and the auroral signatures that can be seen from the ground. Such auroral phenomena are often considered to be simply the "mapping" of these magnetotail events to the ionosphere. This mapping can be very uncertain during the rapidly evolving conditions in substorms, when statistical magnetic models are not likely to adequately represent the actual conditions. Moreover, the communication between these different regions is not instantaneous and is largely carried by the propagation of MHD waves, with fast mode waves transmitting total pressure fluctuations and shear Alfven waves carrying magnetic stresses in the form of field-aligned currents. This wave propagation from the tail to the ionosphere requires time scales of several minutes, comparable to the time scales on which the tail itself is evolving. Furthermore, this wave energy must be converted to the energy of the particles that impact the ionosphere to create the auroral emissions. Thus, an understanding of wave propagation through the inhomogeneous magnetospheric plasma and the mechanisms by which they accelerate auroral particles is critical for understanding the ionospheric signatures of transient magnetotail phenomena. Fast magnetotail flows generate fast mode waves at their leading edge where they compress the plasma, and drive shear Alfven waves due to the velocity shear on their transverse boundaries. These two waves modes are coupled due to the gradients in the Alfven speed that are present throughout the magnetosphere, but especially where these gradients are strong such as at the plasma sheet boundary layer and at the inner edge of the plasma sheet. Thus, the wave propagation cannot be simply described using ray tracing techniques, and full wave modeling is required. In addition, we will consider the regions at which particles can be accelerated, due to the development of parallel electric fields due to electron inertia, electron pressure and Landau damping of the kinetic Alfven waves that can be formed at such boundaries. These considerations will lead to a more comprehensive picture of the flow of energy from magnetotail transients into the inner magnetosphere and the production of energetic particles that create the auroral signatures.
Lin Nan
Lysak Robert L.
Song Yushu
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