First results of artificial stimulation of the ionospheric Alfvén resonator at 78°N

H C Scoffield,T R Robinson,T Turunen,L J Baddeley,D M Wright,T Raita,R S Dhillon,T K Yeoman

doi:10.1029/2006gl027384

Abstract

[1] On 2 December 2005 a modulated X-mode ionospheric modification experiment was carried out using the Space Plasma Exploration by Active Radar (SPEAR) high power facility on Svalbard (78.15°N, 16.05°E), with the intention of artificially stimulating the Ionospheric Alfven Resonator (IAR). A modulation frequency of 3 Hz was superimposed on a 20 minute on/off cycle. Local ionograms showed an E region ionosphere of sufficient plasma density for the SPEAR beam to strongly interact with the low-altitude ionospheric plasma. The Barentsburg pulsation magnetometer monitored the resulting wave activity in the 0.5–5 Hz frequency range. Clear enhancements of the spectral power at 3 Hz were observed in the D component data, when SPEAR was transmitting and there was little natural Pc1 wave activity. During part of the interval, when high power substorm-associated Pc1 waves occurred, the polarisation of the artificially-stimulated wave rotated from the D to the H component.

Highlights

[1] On 2 December 2005 a modulated X-mode ionospheric modification experiment was carried out using the Space Plasma Exploration by Active Radar (SPEAR) high power facility on Svalbard (78.15°N, 16.05°E), with the intention of artificially stimulating the Ionospheric Alfven Resonator (IAR)
Natural IAR resonance features appear as multiple maxima and minima in magnetic power spectra, which are stable for several hours and usually end by fading out or being masked by more intense wave activity of magnetospheric origin
During the first SPEAR ‘‘on’’ the ionospheric conditions were favourable for a strong interaction between the SPEAR pump wave and the D and E regions of the ionosphere (60 km – 130 km altitude), resulting in a 3 Hz modulation of the ionospheric current systems

Summary

Introduction

[2] The existence of the Ionospheric Alfven Resonator (IAR) was first proposed by Polyakov [1976]. Tions result in the formation of an Alfven wave, with the same frequency as the modulation of the pump wave Such magnetic field variations in the ULF/ELF/VLF frequency range have been generated by the high power facility at Tromsø, Norway (L = 6– 7) [Stubbe, 1996]. Bosinger et al [2000] attempted to excite waves in the 0.1– 3Hz range, and observed the ground signatures of artificial waves during 10% of the heating time They used a variety of stepwise frequency sweeps at modulation frequencies between 0.1 and 2 Hz. They used a variety of stepwise frequency sweeps at modulation frequencies between 0.1 and 2 Hz This method helped to identify the resonant frequencies of the cavity, which showed a higher power response.

Instrumentation

Observations

Findings

Discussion and Conclusions