Plasma Processes due to Spatial Variability in the Field-Aligned Flows: Signatures in the Auroral Region

Details Plasma Processes due to Spatial Variability in the Field-Aligned Flows: Signatures in the Auroral Region Plasma Processes due to Spatial Variability in the Field-Aligned Flows: Signatures in the Auroral Region

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm51b0818g&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SM51B-0818

Physics

2407 Auroral Ionosphere (2704), 2471 Plasma Waves And Instabilities, 2772 Plasma Waves And Instabilities

Scientific paper

The linear and nonlinear effects of a transverse gradient in the plasma flow velocity parallel to the ambient magnetic field (Vz) are analyzed. It is shown that a velocity gradient in the parallel ion flow, even in small magnitude (i.e., dVz/dx is much smaller than the ion gyrofrequency), can increase the parallel phase speed of the ion acoustic waves sufficiently to degrade the ion Landau resonance and escape strong ion Landau damping. This results in a significantly lower threshold current for the current driven ion acoustic instability, which can fall below that of the current driven ion cyclotron instability. This also enables the ion acoustic waves to be generated when the ion temperature equals or exceeds the electron temperature. In addition, an ion flow gradient can also lower the threshold for the current driven ion cyclotron instability by reducing the ion cyclotron damping. For a sufficiently strong magnitude, the flow gradient can give rise to a new class of ion cyclotron waves via inverse cyclotron damping. A broadband wave spectrum with multiple cyclotron harmonics is possible. A combination of the multiple cyclotron harmonic waves can result in spiky electric field structures with their peaks separated by an ion cyclotron time. Nonlinear evolution of the waves results in substantial ion heating and cross-field transport, which can affect the meso-scale transport properties. Self-consistent electron flux intensifies with wave growth and indicates modulation at the wave frequency. Spatial gradient in the parallel electron flow is also considered but it is found that they play a minimal role in the low frequency regime. The relevance of these results to in situ observations from the FAST satellite will be discussed. * This work is supported by the Office of the Naval Research

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