Simultaneous Action of X- and O-Mode HF Pump Waves on the High-Latitude Upper (F-Region) Ionosphere at EISCAT

Nataly Blagoveshchenskaya,Ingemar Haggstrom,Alexey Kalishin,Tatiana Borisova,Tim Yeoman,Ivan Egorov

doi:10.3390/universe8020091

Abstract

We report experimental results from multi-instrument diagnostic tools related to phenomena in the high latitude ionosphere F-region, induced by the simultaneous action of powerful extraordinary (X-mode) and ordinary (O-mode) polarized HF radio waves at EISCAT (European Incoherent SCATter) during magnetically quiet background geophysical conditions. HF pump waves were injected towards the magnetic zenith at a frequency of 5.423 MHz, which was just below the critical frequency of the F2 layer when the excitation of X- and O-mode phenomena was possible. In the course of the experiment, the effective radiated power (ERP) of the X-mode wave was 130.5 MW, while the portion of the O-mode ERP was 29.9 MW (about 20% of the full ERP). It was found that simultaneous action of the X- and O-mode pump waves lead to the excitation of effects typical for both X- and O-mode HF pump waves. Namely, the excitation of small-scale field-aligned irregularities due to the thermal parametric (resonance) instability and a downshifted maximum (DM) component in the wideband stimulated electromagnetic emission (WSEE) spectra, typical for the O-mode HF pumping, was observed, together with multiple ion gyro-harmonic structures in the narrowband stimulated electromagnetic emission (NSEE) spectra. These latter results were recorded at a large (more than 1000 km) distance from the EISCAT/heating facility, typical only for an X-mode HF pumping. The results obtained are compared with “pure” O-mode heating and discussed in detail.

Highlights

Publisher’s Note: MDPI stays neu-The investigation of the interaction between powerful high frequency (HF) radio waves (HF pump waves) and ionosphere plasma is an actively developing problem in the physics of ionospheric plasmas
Over the last five decades, considerable efforts have been undertaken into the investigation of phenomena in the upper (F-region) ionosphere induced by HF pump waves by using ground-based HF transmitters with high effective radiated power, so-called HF heating facilities
The downshifted maximum (DM) is a commonly occurring spectral feature in the wideband stimulated electromagnetic emission (WSEE) spectrum, observed in the close vicinity of HF heating facilities under O-mode HF pumping at frequencies below the critical frequency frequency of the F2 layer (foF2) and away from the electron gyro-harmonics

Summary

Introduction

The investigation of the interaction between powerful high frequency (HF) radio waves (HF pump waves) and ionosphere plasma is an actively developing problem in the physics of ionospheric plasmas. Over the last five decades, considerable efforts have been undertaken into the investigation of phenomena in the upper (F-region) ionosphere induced by HF pump waves by using ground-based HF transmitters with high effective radiated power, so-called HF heating facilities. This provides the controlled investigations to explore in detail the nonlinear processes in the plasma, the excitation of turbulences and plasma waves, and the plasma and cyclotron resonances.

Results

Discussion

Conclusion