Geomagnetic effects, 2018 October 01 - 02

With the advent of the dark months here in Wales, attention is turning to accumulating data on geomagnetic effects on WSPR propagation at 14MHz.

Already, just a few days past the Autumn Equinox, and with very low solar activity, propagation on 14MHz now tends to collapse by around 22UT (W4HOD is typically the last to hear me then).

Yesterday saw some moderately rough geomagnetic conditions. Here is how the Leirvogur magnetometer saw things:

Looking at the database of who had heard me overnight, I could see that only TF1A had done so.  This is how I was heard with time (the blue line at right indicates 00UT):

As you can clearly see, propagation to TF1A from my station had collapsed by quite early in the evening, the last spot timed at 17:56UT.  The ongoing disturbance may well have contributed to the early propagation cessation.  I confirmed TF1A was in fact operating during this period, and had not simply disconnected for a while, by looking at his reception reports for other stations, mostly from EA, as it happens.

Then, shortly after 00UT, TF1A starts hearing me again at quite strong levels, with two peaks of -13dB SNR and -10dB SNR at 00:52UT and 02:32UT, respectively.

If we mark those two peaks on the Icelandic magnetometer output, we can see that they coincide, as I have always found, with the field's 'H' (horizontal intensity) reaching the end of a 'rebound' (restoration) to levels typical of quiet conditions, although the field need not stay quiet for the effect to be realised.

The effect is probably the result of enhanced total electron density after a disturbance.  The link between field restoration and enhanced electron content after an, admittedly, much larger disturbance, was noted in a 1998 paper.

Where WSPR proves very valuable to these studies is in its continuous availability at many locations across the globe, although distribution is very skewed towards industrialised nations.  Even so, there are a good number of stations at high latitudes now, where in the past, studying polar effects required a lot of effort to organise, and typically relied on only a handful of transmitters and receivers operating for just a few hours.