The ionosphere is high outer layer of the Earth's atmosphere, charged (ionised) by solar radiation. This charging allows radio signals to bounce off the ionosphere and propagate over long distance. The ionosphere is also sensitive to the impact of space weather, and when this happens we should see changes in the signal strength of radio transmissions. There are also signature markers for solar flare x-ray events, which are usually correlated with coronal mass ejections (CMEs).
At Dunedin Aurora we monitor:
The VLF antenna is a wire loop with approx 50 turns of wire. The signal is passed through a "SuperSID" filter and processed with Spectrum Lab software and custom software. Reception of long distance stations shows a diurnal variation in signal strength. This signal can be altered by space weather and x-rays generated by solar flares.
The GPS signal is recieved with a Sparkfun "SAM" GPS module and processed with custom software. The satellite signal can be affected by the uneven make-up of the ionosphere, causing it to scintillate (Similar to how the turbulent atmosphere causes stars to twinkle). This scintillation is worse during geomagnetic storms and should show as a surge. The S4 index measures the amplitude of this scintillation.