Production of small-scale alfvén waves by ionospheric depletion, nonlinear magnetosphere-ionosphere coupling and phase mixing

Russell, A.J.B., Wright, A.N. and Streltsov, A.V. (2013) Production of small-scale alfvén waves by ionospheric depletion, nonlinear magnetosphere-ionosphere coupling and phase mixing. Journal of Geophysical Research: Space Physics, 118(4), pp. 1450-1460. (doi: 10.1002/jgra.50168)

Abstract

Rockets and satellites have previously observed small-scale Alfvén waves inside large-scale downward field-aligned currents, and numerical simulations have associated their formation with self-consistent magnetosphere-ionosphere coupling. The origin of these waves was previously attributed to ionospheric feedback instability; however, we show that they arise in numerical experiments in which the instability is excluded. A new interpretation is proposed in which strong ionospheric depletion and associated current broadening (a nonlinear steepening/wave-breaking process) form magnetosphereionosphere waves inside a downward current region and these oscillations drive upgoing inertial Alfvén waves in the overlying plasma. The resulting waves are governed by characteristic periods, which are a good match to previously observed periods for reasonable assumed conditions. Meanwhile, wavelengths perpendicular to the magnetic field initially map to an ionospheric scale comparable to the electron inertial length for the low-altitude magnetosphere, but become shorter with time due to frequency-based phase mixing of boundary waves (a new manifestation of phase mixing). Under suitable conditions, these could act as seeds for the ionospheric feedback instability.

• Item Type: Articles
• Keywords: Magnetosphere-ionosphere coupling; small-scale alfvén waves; ionospheric depletion; phase mixing; magnetosphere-ionoshere waves; ionospheric feedback instability
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Russell, Dr Alexander
• Authors: Russell, A.J.B., Wright, A.N., and Streltsov, A.V.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Journal of Geophysical Research: Space Physics
• Publisher: Wiley-Blackwell
• ISSN: 2169-9402
• Copyright Holders: Copyright © 2013 American Geophysical Union
• First Published: First published in Journal of Geophysical Research: Space Physics
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher