Abstract
Abstract. We investigate numerically the interaction between ionospheric magnetic field-aligned density striations and a left-hand circularly polarized (L)-mode wave. The L-mode wave is scattered into upper hybrid (UH) waves which are partially trapped in the striations, but leak energy to electromagnetic waves in the Z-mode branch. For small-amplitude (1 %) striations, this loss mechanism leads to a significant reduction in amplitude of the UH waves. For several striations organized in a lattice, the leaking of Z-mode waves is compensated by influx of Z-mode radiation from neighboring striations, leading to an increased amplitude of the weakly trapped UH waves. For large-amplitude (10 %) striations the trapped UH waves rapidly increase in amplitude far beyond the threshold for parametric instabilities, and the Z-mode leakage is less important. The results have relevance for the growth of striations and the onset of UH and lower hybrid turbulence during electromagnetic high-frequency pumping of ionospheric plasma, which require large-amplitude UH waves.
Highlights
Powerful electromagnetic high-frequency (HF) waves transmitted into the ionosphere excite geomagnetic field-aligned plasma density striations
An O-mode polarized continuous wave injected into the overhead ionosphere along the magnetic field lines will excite upper hybrid (UH) resonances at quantized heights (Mjølhus, 1998; Eliasson and Papadopoulos, 2015), where the transmitted frequency matches one of the local resonances of the UH waves trapped in the striations
The mode conversion of an L-mode wave to UH waves on small-scale striations has been investigated with numerical simulations
Summary
Powerful electromagnetic high-frequency (HF) waves transmitted into the ionosphere excite geomagnetic field-aligned plasma density striations. The small-scale striations result from pump-driven UH waves, which as the thermal instability develops, become self-localized in the density depletions of the striations (Vas’kov and Gurevich, 1976; Inhester et al, 1981; Vas’kov and Gurevich, 1984; Gurevich et al, 1995a; Istomin and Leyser, 1997). For a system of density cavities (Istomin et al, 2006; Hall et al, 2009), the scattering of the pump wave directly into Z-mode waves leads to the excitation of odd UH modes for an asymmetric distribution of one-dimensional cavities, the original pump field and the depletions are symmetric.
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