We investigate numerically the interaction between ionospheric magneticfield-aligned density striations and a left-hand circularly polarized ()-mode wave. The -mode wave is scattered into upper hybrid (UH) waves whichare partially trapped in the striations, but leak energy toelectromagnetic waves in the -mode branch. For small-amplitude (1 %)striations, this loss mechanism leads to a significant reduction in amplitudeof the UH waves. For several striations organized in a lattice, the leakingof -mode waves is compensated by influx of -mode radiation from neighboringstriations, leading to an increased amplitude of the weakly trapped UH waves.For large-amplitude (10 %) striations the trapped UH waves rapidly increasein amplitude far beyond the threshold for parametric instabilities, and the -mode leakage is less important.The results have relevance for the growth of striations and the onset of UHand lower hybrid turbulence during electromagnetic high-frequency pumping ofionospheric plasma, which require large-amplitude UH waves.
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