Nonlinear coupling between density structures, field-aligned ion flows, ULF electromagnetic waves, and ionospheric feedback in the auroral zone
Abstract
Results from a numerical study of the nonlinear interaction between ultra-low-frequency (ULF) shear Alfvén waves, slow MHD waves, and the high-latitude magnetospheric and ionospheric plasmas are presented. The basic hypothesis motivating this study is that heavy ion acceleration observed in the topside auroral and subauroral ionosphere and low-altitude magnetosphere, and associated inhomogeneities in density including plasma cavities and ducts (magnetic field-aligned density striations), can be produced by intense ULF electromagnetic waves standing and/or propagating along geomagnetic field lines in these regions. This study is based on a novel two-fluid MHD model describing ULF MHD waves in the cold, low-altitude magnetospheric plasma. The model includes nonlinear coupling between shear and slow MHD modes (parallel ion dynamics) as well as effects of E-region ionospheric activity leading to feedback instability. Numerical simulations of the model equations have been performed in dipole magnetic field geometry with realistic parameters of the ambient plasma. The simulations show that the ionospheric feedback is one of the major mechanisms responsible for formation of intense electromagnetic and plasma structures.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2007
- Bibcode:
- 2007AGUSMSM42A..05S
- Keywords:
-
- 2704 Auroral phenomena (2407);
- 2721 Field-aligned currents and current systems (2409);
- 2736 Magnetosphere/ionosphere interactions (2431);
- 2752 MHD waves and instabilities (2149;
- 6050;
- 7836);
- 2753 Numerical modeling