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Electron trapping in shear Alfvén waves that power the aurora
Clare E J Watt1, Robert Rankin
1University of Alberta, Edmonton, Alberta, Canada. cwatt@phys.ualberta.ca
Physical Review Letters
|March 5, 2009
Summary
Auroral electrons are accelerated by shear Alfvén waves in Earth's plasma sheet. These waves trap and then release electrons, matching observational data and linking wave dynamics to aurora formation.
Area of Science:
- Plasma Physics
- Space Physics
- Geophysics
Background:
- Auroral electrons are accelerated along Earth's geomagnetic field.
- The precise mechanisms and locations of this acceleration are not fully understood.
- Shear Alfvén waves are a potential candidate for accelerating these particles.
Purpose of the Study:
- To investigate the role of shear Alfvén waves in the acceleration of auroral electrons.
- To determine the spatial regions where electron acceleration occurs.
- To establish a self-consistent link between wave dynamics and observed electron distributions.
Main Methods:
- One-dimensional (1D) Vlasov drift-kinetic plasma simulations were employed.
- Simulations tracked electron interactions within shear Alfvén waves.
- Key plasma parameters, including electron temperature (Te) and Alfvén velocity (vA), were analyzed.
Main Results:
- Electrons were observed to become trapped in shear Alfvén waves within the warm plasma sheet.
- Wave damping was prevented by this trapping mechanism.
- As waves propagated to regions with increasing v(Te)/v(A), their parallel electric fields decreased, allowing electrons to escape.
Conclusions:
- The study demonstrates a self-consistent mechanism for auroral electron acceleration.
- Shear Alfvén waves play a crucial role in trapping and releasing electrons.
- Simulation results align well with in situ observations of electron distribution functions, validating the proposed mechanism.
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