Effect of heavy ions on coupling between density structures and electromagnetic waves in the auroral zone

Abstract

This paper presents the results from a numerical study of the effects of multiple ion species on the development of small-scale, intense electromagnetic waves and density structures that are frequently observed in the auroral ionosphere in the vicinity of discrete auroral arcs. The study is based on a multifluid MHD model describing nonlinear coupling between shear and slow ultra-low-frequency MHD waves in cold, low-altitude plasma containing several ion species. Simulations reveal that these waves can be generated by the ionospheric feedback instability in the downward current channels adjacent to the upward currents, causing aurora, when heavy ionospheric ions (in particular, O2+) provide the "matching impedance" condition between the ionosphere and the magnetosphere. The ponderomotive force associated with these waves moves ions along the ambient magnetic field from the ionosphere. Different ion species exhibit different dynamics, depending on their masses and initial distributions. The strongest variations in density of -14% and +23% of the background values occur in the F region and are produced by the dynamics of O+ ions. These density variations can be detected by ground radars and low-orbiting satellites in the auroral zone. Copyright © 2011 by the American Geophysical Union.