The above is a presentation given online to the Mid Sussex Amateur Radio Society and the Galashiels Amateur Radio Society on the 12th November 2021. It gives an overview of radio auroras. The texts and pages below elaborate. Click the titles or links for more.
A radio aurora starts as a huge solar flare or other ejection of plasma from the Sun. If there’s enough energy, the plasma hits the Earth’s atmosphere three days later and tracks south and north from the poles. How, is complex. Again, if there’s enough energy, the result may be plasma roaring down to Earth, splatting round the atmosphere. Continuing earthwards, the result may be a visible aurora, and more rarely, a radio aurora. Here’s how.
Particles from the Sun are propelled towards Earth in the solar wind. They interact with the Earth and Sun’s interplanetary magnetic field. These particles track down the field lines, entering the Earth’s atmosphere at the poles. They interact with particles in the Earth’s atmosphere. The eventual result is spinning columns of plasma that support VHF backscatter. Here’s how.
Radio auroras are sporadic E Region events. They don’t happen often – indeed most radio amateurs would say that they’ve never participated in an auroral event, even though they are equipped for VHF DX operation. Unlike Sporadic E activity which happens annually, radio auroras are much rarer. And yet radio auroras do have a predictability and cadence too. Here’s how to tell when an aurora is likely.
An estimate of the strength of the aurora and hence how far south the radio auroral oval has sunk leads speculation about necessary beam angles. If it’s a strong aurora, beaming east from the UK will enable QSOs with northern European stations. Likewise, beaming west will enable QSOs with Greenland and Canada. Here’s how it works.
The pages on this site describe radio auroras and hence indicate what’s needed to optimise operating during a radio aurora. There’s also a video that gives an excellent summary of SSB operation during a radio aurora. In this case it’s on the 6m band but it could equally be on 2m. This page then goes on to describe the technical adjustments needed to exploit the enhanced propagation of an aurora.
Doppler shift is a phenomenon whereby the received signal frequency is perceived to be changed because of movement of either the sender or receiver, or the propagating medium. The latter case where the scattering medium is moving is of specific interest in amateur radio. This causes Doppler shift in frequencies and Doppler distortion from multiple scattered paths. Here’s how it works.
Here’s a list of papers, books and the like that have informed the pages about radio auroras.