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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, A09304, doi:10.1029/2005JA011142, 2005

Generation and evolution of density irregularities due to self-focusing in ionospheric modifications

N. A. Gondarenko

Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland, USA


S. L. Ossakow

Plasma Physics Division, Naval Research Laboratory, Washington, D. C., USA


G. M. Milikh

Department of Astronomy, University of Maryland, College Park, Maryland, USA


Abstract

Simulations of the generation and evolution of ionospheric density irregularities due to thermal self-focusing are presented. A nonlinear, self-consistent development of the self-focusing instabilities (SFI) is studied with a two-dimensional model of HF radio wave propagation in inhomogeneous magnetized plasmas. The full-wave model is coupled with the electron temperature and plasma density equations. In these studies, the pump beam is incident vertically or tilted to the magnetic zenith direction. Our results demonstrate that irregularities generated and developed due to a local heating of the anisotropic ionosphere plasma are density depletions/striations with a strong enhancement of electron temperature inside depletions elongated along the magnetic field lines. For the ordinary mode (O mode) heating the reflection point is shifted upward with decreasing electron concentration. During the nonlinear evolution of the SFI instability the bunching of striations is observed. A number of the bunch-scale irregularities increase when the beam is tilted to the magnetic zenith direction. The presented results are consistent with the experiments carried out at the midlatitude SURA HF heating facility.

Received 18 March 2005; accepted 16 June 2005; published 17 September 2005.

Keywords: HF radio wave propagation; ionospheric density irregularities; thermal self-focusing instability.

Index Terms: 2439 Ionosphere: Ionospheric irregularities; 2487 Ionosphere: Wave propagation (0689, 3285, 4275, 4455, 6934); 2467 Ionosphere: Plasma temperature and density; 2411 Ionosphere: Electric fields (2712); 2443 Ionosphere: Midlatitude ionosphere.

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Citation: Gondarenko, N. A., S. L. Ossakow, and G. M. Milikh (2005), Generation and evolution of density irregularities due to self-focusing in ionospheric modifications, J. Geophys. Res., 110, A09304, doi:10.1029/2005JA011142.