Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm42a..03w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM42A-03
Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2753] Magnetospheric Physics / Numerical Modeling, [2772] Magnetospheric Physics / Plasma Waves And Instabilities
Scientific paper
The term "Alfvénic aurora" refers to bursty, field-aligned electron fluxes with a broad energy spectrum extending up to a well-defined maximum energy (~1keV), and usually associated with low-frequency (Alfvénic) electromagnetic field fluctuations. Often, Alfvénically-accelerated electrons have low temperatures transverse to B, indicating they originate in the ionosphere as opposed to the plasma sheet. The most common interpretation of these electron populations is that they are accelerated through encounters with dispersive Alfvén waves that have been launched by an assumed source or generator. We explore an alternative scenario in which cold ionospheric electrons drifting into the inverted-V structure from one side are first accelerated as they fall through a portion of the quasi-static inverted-V potential, and subsequently generate Alfvén waves through inverse Landau damping as their field-aligned velocities approach the Alfvén speed. The energy transfer process between Alfvén waves and electrons, or indeed between electrons and Alfvén waves, relies on the presence of short perpendicular scales relative to the ambient magnetic field that allow parallel electric fields to develop. Short perpendicular scales can be inferred from optical observations of auroral displays, as well as in-situ observations of accelerated electrons, which demonstrate structure on scales from 1km-100km in directions perpendicular to the magnetic field. Using linear theory, we first predict which wave modes may be driven unstable due to the presence of accelerated ionospheric electrons. Then we engage a suite of self-consistent nonlinear numerical simulation models covering both low- and high-frequency waves to investigate electrostatic and electromagnetic wave growth in the presence of cold electron beams and perpendicular structure. We compare results between different types of numerical experiments to address the question of whether simultaneous measurements of low-frequency Alfvénic perturbations and accelerated electrons can unambiguously infer the acceleration of electrons by shear Alfvén waves, or whether they could also be a signature of the generation of shear Alfvén waves by accelerated electron beams.
Knudsen David J.
Rankin Robert
Watt C. E.
No associations
LandOfFree
Alfvén Waves in the Alfvénic Aurora: Cause or Effect? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Alfvén Waves in the Alfvénic Aurora: Cause or Effect?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Alfvén Waves in the Alfvénic Aurora: Cause or Effect? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1891261