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Ann. Geophys., 20, 1167-1179, 2002
www.ann-geophys.net/20/1167/2002/
© European Geosciences Union 2002
Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet
D. L. Hysell1,2,3 and J. L. Chau4
1Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
2On leave at the Radio Science Center for Space and Atmosphere, Kyoto University, Uji, Kyoto 611–011, Japan
3Now at the Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, USA
4Radio Observatorio de Jicamarca, Instituto Geof´isico del Per´u, Lima, Peru
Correspondence to: D. L. Hysell; (daveh@geology.cornell.edu)
Abstract. Large-scale (l
~ 1 km) waves in the daytime and night-time equatorial electrojet are
studied using coherent scatter radar data from Jicamarca. Images of plasma
irregularities within the main beam of the radar are formed using
interferometry with multiple baselines. These images are analyzed according to
nonlocal gradient drift instability theory and are also compared to nonlinear
computer simulations carried out recently by Ronchi et al. (1991) and Hu and
Bhattacharjee (1999). In the daytime, the large-scale waves assume a non-steady
dynamical equilibrium state characterized by the straining and destruction of
the waves by shear and diffusion followed by spontaneous regeneration as
predicted by Ronchi et al. (1991). At night, when steep plasma density
gradients emerge, slowly propagating large-scale vertically extended waves
predominate. Eikonal analysis suggests that these waves are trapped (absolutely
unstable) or are nearly trapped (convectively unstable) and are able to tunnel
between altitude regions which are locally unstable. Intermediate-scale waves
are mainly transient (convectively stable) but can become absolutely unstable
in narrow altitude bands determined by the background density profile. These
characteristics are mainly consistent with the simulations presented by Hu and
Bhattacharjee (1999). A new class of large-scale primary waves is found to
occur along bands that sweep westward and downward from high altitudes through
the E-region at twilight.
Key words. Ionosphere (equatorial
ionosphere; ionospheric irregularities; plasma waves and instabilities)
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