Numerical study of anomalous absorption of O mode waves on magnetic field‐aligned striations

B Eliasson,K Papadopoulos

doi:10.1002/2015gl063751

Abstract

AbstractSimple expressions that describe mode conversion and anomalous absorption of ordinary (O) mode waves injected at angles between the vertical and magnetic zenith to upper hybrid (UH) oscillations in the presence of field‐aligned density striations are presented. The absorption takes place in a region above the UH resonance layer where the striations allow trapped eigenmodes, leading to excitation of large‐amplitude UH waves. The derivation of the expressions is guided by dimensional analysis and numerical simulations. The results are relevant in interpreting high‐latitude heating experiments where anomalous absorption due to striations plays a crucial role.

Highlights

The interaction of HF radio waves with the ionospheric plasma in the vicinity of the upper hybrid (UH) resonance layer plays a critical role in the physics of ionospheric modifications and artificial ionospheric turbulence
The observations are consistent with the formation of smallscale magnetic field-aligned striations, followed by mode conversion of the O mode pump and test waves to UH waves trapped in the striations [Graham and Fejer, 1976; Vas’kov and Gurevich, 1976; Dysthe et al, 1982; Jones et al, 1984; Mjølhus, 1985; Gurevich et al, 1995, 1996]
The O mode wave injected from the bottom side is continuously converted to UH waves, and the UH wave amplitude gradually increases with time

Summary

Introduction

The interaction of HF radio waves with the ionospheric plasma in the vicinity of the upper hybrid (UH) resonance layer plays a critical role in the physics of ionospheric modifications and artificial ionospheric turbulence. It has been observed that when the electromagnetic beam is directed along the magnetic zenith (MZ), parallel to the magnetic field lines [Gurevich et al, 2002], or between the MZ and the Spitze angle [Rietveld et al, 2003; Honary et al, 2011], there is an increase of the electron temperature in the heated region. The observations are consistent with the formation of smallscale magnetic field-aligned striations, followed by mode conversion of the O mode pump and test waves to UH waves trapped in the striations [Graham and Fejer, 1976; Vas’kov and Gurevich, 1976; Dysthe et al, 1982; Jones et al, 1984; Mjølhus, 1985; Gurevich et al, 1995, 1996]. The results have implications on the electron heating at the UH layer and on the fraction of the electromagnetic wave energy that reaches the critical layer of the O mode where it can excite Langmuir turbulence

Optimal Angle of Incidence

Simulation Setup

Numerical Results

Scaling Analysis