Solar flares detected by the new narrowband VLF receiver at SANAE IV

Hanna Dahlgren,Andrew B Collier,Torbjörn Sundberg,Stephen Meyer,Etienne Koen

doi:10.4102/sajs.v107i9/10.491

Hanna Dahlgren, Andrew B Collier + Show 3 more

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https://doi.org/10.4102/sajs.v107i9/10.491

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Abstract

A narrowband receiver was installed at the SANAE IV base in Antarctica to monitor specific very low frequency (VLF) radio signals from transmitters around the world. VLF waves propagating through the Earth–Ionosphere Waveguide are excellent probes of the varying properties of the lower region of the ionosphere. This paper describes the set-up of the narrowband system and demonstrates its capabilities with data from a set of solar flares on 08 February and 12 February 2010.

Highlights

Very low frequency (3 kHz – 30 kHz) radio waves propagate thousands of kilometres in the Earth-Ionosphere Waveguide (EIWG) formed between the conducting Earth and the ionosphere
The UltraMSK system described in this paper was previously installed on an omnidirectional whip antenna, but in February 2010 it was moved to a larger magnetic loop antenna, located at a greater distance from the SANAE IV base
The functionality of the system was illustrated by the analysis of several M-class solar flares on 08 February and 12 February 2010

Summary

Introduction

Very low frequency (3 kHz – 30 kHz) radio waves propagate thousands of kilometres in the Earth-Ionosphere Waveguide (EIWG) formed between the conducting Earth and the ionosphere. Estimates of D-region electron density have been determined via VLF propagation measurements.[2,3,4] Further information on the response of the D-region during ionospheric disturbances, such as solar flares and gamma ray bursts, can be retrieved by constantly monitoring single-frequency signals and their prompt response to changing conditions. As the second flare occurred around dusk, the associated VLF disturbance was superimposed onto terminator effects, which led to a general increase of the signal strength for the duration of the event. Because the event occurred near midday, the disturbance pattern was clearly visible in the signals of central European origin, at a similar longitude to SANAE IV For these transmitters the signal increased in power by 4 dB – 6 dB. The main increase was more prominent in the stations located at other longitudes, that is, NPM on Hawaii, NAA in Maine and TBB in Turkey, with an increase of 8 dB – 14 dB

12 Feb 2010 -48

Discussion

Summary