University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Friday, February 27th 2015
Speaker: Robert Lysak, Department of Physics and MIfA
Subject: Alfven Waves and the Aurora

The aurora is the visible manifestation of a electrical current system that couples the magnetosphere and ionosphere. This current system leads to the development of parallel electric fields that can accelerate the auroral particles. The "standard model" of auroral acceleration assumes that auroral particles are accelerated through a static potential drop associated with these fields. However, some auroral particle distributions do not conform to this scenario. Such distributions are thought to be accelerated through time-dependent parallel electric fields associated with Alfven waves, the analogue to waves on a string. These waves can be accompanied by parallel electric fields when the perpendicular scale size becomes small. There are two main regimes of this acceleration. At lower altitudes where the plasma is cold, electron inertial effects becomes important and can lead to the bulk acceleration of the cold plasma. At higher altitudes, the primary particle acceleration mechanism is Landau damping, which preferentially accelerates electrons with velocities near the Alfvén wave phase velocity. These mechanisms are favored in regions where there are sharp plasma gradients, such as at the plasma sheet boundary layer or on the edges of the auroral density cavity, since phase mixing is an efficient mechanism for reducing the perpendicular wavelength.

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