Large-scale HF-induced ionospheric modifications - Experiments

Details Large-scale HF-induced ionospheric modifications - Experiments Large-scale HF-induced ionospheric modifications - Experiments

Jan 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992jgr....97..113h&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 97, Jan. 1, 1992, p. 113-122. Research sponsored by U.S. Navy, NSF, and L

Physics

12

High Frequencies, Incoherent Scattering, Ionospheric Disturbances, Ionospheric Heating, Atmospheric Temperature, Incoherent Scatter Radar, Nocturnal Variations, Radar Beams, Steady State

Scientific paper

Experimental investigations of large-scale modifications created by a high-power HF beam (effective radiated power of about 100 MW, frequency of 3-5 MHz) in the nighttime ionosphere above Arecibo Observatory are presented. The modifications consist of field-aligned temperature enhancements and density depletions and have length scales along the geomagnetic field of tens of kilometers. A two-stage time evolution of the modifications is documented; they start from a broad and symmetric perturbation and develop into a narrow, northward shifted universal steady state on a time scale of 15-30 min. It is found that nonlinear refraction i.e., the self-consistent bending of the O mode HF beam across the geomagnetic field lines and the reorientation of the HF reflection surface to a geometry parallel to the geomagnetic field, is the key process involved in the generation of the large modifications. Preconditioning results showing the immediate onset of the narrow late-stage behavior provide dramatic confirmation of the underlying nonlinear mechanism sustaining the large modifications.

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