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Magnetic & Radio Observations
Magnetic Storms
Construct a simple magnetometer as described in the BAA journal Vol. 93, No. 1, December 1982 page 17. Measure the differential movements of the magnet by about hourly intervals. If large changes are detected in the evening increase the frequency of reading. Record the date and time of each reading. If rotation westwards is followed by a rapid movement eastwards visual auroral activity may be detected. Local experience will soon teach the observer the differences between the diurnal variation, storm conditions and the effects of local magnetic interference.
Radio Aurorae
Auroral displays occur because of high energy electrons ionising the atmosphere down to around 100 km, which we recognise as the E-region (formerly the Kennelly-Heaviside layer). This is the region from which radio reflections take place, because of the peak in ionisation at this level.
Because these reflections can be detected during daylight and when the night sky is cloudy, they have the advantage of giving us a much more complete picture of auroral activity. In addition, those in the south of Britain, who rarely see a visible aurora, can contribute, as aurorae can be detected by radio as far north as the Faroe Islands. As they can be observed before visual observation is possible, this can also give an alert for visual aurorae.
There are also questions to be answered. Reports have been made of Radio Aurorae without visual observations, and vice versa. It would be nice to understand if and why these occur.
So how to make these observations. You will need a radio receiver covering the appropriate frequencies (SSB/CW mode, not FM), and a suitable antenna (directional, typically a multi-element yagi), pointing north, as high and as clear as possible. Auroral reflections are strongest from 30 to 150 MHz (10m to 2m), and have been detected up to 900 MHz, but very weak. My suggestion is to use one of the amateur radio bands, because the receiving equipment is plentiful and relatively cheap, the antennas also easily obtainable, and there are reliable beacons on those bands to monitor. The reflections are strongest on the 50 and 70 MHz bands (6m and 4m), but most of my observations have been on the 144 MHz (2m) band. This has the advantage of smaller and hence higher gain antennas, and is perhaps less subject to the interference from computers and suchlike, which is a real problem these days.
You will need to tune to a beacon to the north, such as GM3ANG (Angus); lists are available on-line. These generally emit an unmodulated keyed signal, so you need to listen in CW or SSB mode. An aurora will result in a significant increase in signal strength, but this is not the only indication. The signal will sound like a hiss, quite unmistakable from other causes of increase. This is due to Doppler shift from the rapidly moving electrons. Now record the time, and immediately email the Director of the Aurora Section, through whom all reports should be channelled.
I realise this must leave many questions to be answered; it is only intended as an introduction. I will try and answer as many questions as I can, but please first do a little reading yourself. I recommend you refer to the VHF/UHF DX Book (ed. I.F. White), now free to download. My Chapter 2 contains a section on Auroral Propagation, and you will also find a lot of information about radio equipment and antennas, written in the 1990s, but much still applicable. If you wish to know yet more, I refer you to Radio Auroras by C. Newton, published by and available from the RSGB.
Dr Geoffrey H. Grayer (geoffgrayer@gmail.com), Assistant Director, BAA Aurora Section
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