Articles | Volume 33, issue 8
Regular paper
19 Aug 2015
Regular paper |  | 19 Aug 2015

Numerical study of upper hybrid to Z-mode leakage during electromagnetic pumping of groups of striations in the ionosphere

B. Eliasson and T. B. Leyser

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.

Short summary
Large-amplitude radio waves lead to the structuring of the ionospheric plasma into groups magnetic field-aligned density cavities, or striations. A large part of the electromagnetic wave with ordinary mode polarization is then mode converted into upper hybrid waves trapped in the striations, further enforcing the striations. This simulation study investigates numerically this mode conversion and leakage of the the upper hybrid waves to back to electromagnetic waves in the Z-mode branch.