ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-27-1027-2009 Formation of lower-hybrid solitary structures by modulational interaction between lower-hybrid and dispersive Alfvén waves Hall J. O. 1 2 Stenberg G. 1 Eriksson A. I. 1 André M. 1 Swedish Institute of Space Physics, Uppsala, Sweden present address: Swedish Defence Research Agency, Stockholm, Sweden 02 03 2009 27 3 1027 1033 Copyright: © 2009 J. O. Hall et al. 2009 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/27/1027/2009/angeo-27-1027-2009.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/1027/2009/angeo-27-1027-2009.pdf

We investigate the possibility that lower-hybrid solitary structures (LHSS), which are frequently observed in the Earth's ionosphere and magnetosphere, are formed as a result of a modulational interaction between lower-hybrid and dispersive Alfvén waves of initially small amplitude. A large amplitude lower-hybrid pump wave can excite density structures with length scales transverse to the geomagnetic field of the order of the ion gyroradius via a modulational instability. The structure formation in the nonlinear stage of the instability is investigated by numerical solutions of the governing equations, using plasma parameters relevant for LHSS observations in the upper ionosphere and in the magnetosphere. The numerical solutions reveal that the lower-hybrid waves become self-localized inside cylindrically symmetric (with respect to the ambient magnetic field) density cavities, in qualitative agreement with observations. Our model includes thermal electron effects but shows no stabilization at the ion sound gyroradius, suggesting that any preference of observed LHSS for that perpendicular scale likely is due to processes arresting the cavity collapse.

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