Lower hybrid to whistler mode conversion on a density striation

TL;DR

This paper investigates how density striations in the ionosphere facilitate the linear conversion of lower hybrid waves into whistler waves, demonstrating effective energy transfer and establishing criteria for maximizing conversion efficiency.

Contribution

It introduces a scalar-field formalism to model mode conversion in cold plasma and provides a criterion for optimizing density striation parameters for maximum efficiency.

Findings

Mode conversion effectively transfers energy from short to long wavelength waves.

Conversion efficiency depends on striation width and amplitude.

A general criterion for striation width maximizes mode conversion efficiency.

Abstract

When a wave packet composed of short wavelength lower hybrid modes traveling in an homogeneous plasma region encounters an inhomogeneity, it can resonantly excite long wavelength whistler waves via a linear mechanism known as mode conversion. An enhancement of lower hybrid/whistler activity has been often observed by sounding rockets and satellites in the presence of density depletions (striations) in the upper ionosphere. We address here the process of linear mode conversion of lower hybrid to whistler waves, mediated by a density striation, using a scalar-field formalism (in the limit of cold plasma linear theory) which we solve numerically. We show that the mode conversion can effectively transfer a large amount of energy from the short to the long wavelength modes. We also study how the efficiency scales by changing the properties (width and amplitude) of the density striation. We present a general criterion for the width of the striation that, if fulfilled, maximizes the conversion efficiency. Such a criterion could provide an interpretation of recent laboratory experiments carried out on the Large Plasma Device at UCLA.