Ionospheric Erosion by Alfven Waves

Details Ionospheric Erosion by Alfven Waves Ionospheric Erosion by Alfven Waves

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm41c1190c&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM41C-1190

Physics

7829 Kinetic Waves And Instabilities, 7845 Particle Acceleration, 7846 Plasma Energization, 7857 Stochastic Phenomena (3235, 3265, 4475), 7867 Wave/Particle Interactions (2483, 6984)

Scientific paper

Using observations from the FAST small explorer spacecraft we present fields and plasma observations above the dayside auroral oval showing the erosion of ionospheric plasmas from the topside ionosphere by the action of Alfven waves. Using interferometric techniques the waves are shown to approximately obey the expected dispersion for Alfven waves with transverse scales extending from greater than electron inertial lengths down to ion gyro-radii. Measurements of the plasma density where these waves are observed show that over latitudinal widths exceeding 100 km total depletion of the cold ionospheric plasma can occur. The plasma within these depleted regions or cavities is composed of magnetosheath ion and electron distributions and upgoing transversely accelerated ions and downgoing field-aligned electrons distributed as conics and field-aligned beams respectively. Poynting flux observations on the density gradients comprising the cavity walls show that these waves are directed downwards and focused inwards towards regions of lower density. The wave phase velocity measurement in the plasma frame, while subject to significant uncertainty, is directed transversely outwards from the cavity. These observations suggest a feedback model for Alfven wave focusing and ion heating on density gradients that can lead to intense ion outflow from the ionosphere and subsequent depletion of ionospheric plasmas.

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