Propagation News 22 September 2013

| September 20, 2013

For the most part, last week followed the pattern of recent weeks. Solar activity mostly continued to be low or very low. However, C-class flares were reported on the 18th and 19th. Few sunspot groups were visible and those that were had little impact on propagation. Several coronal mass ejections were reported but none proved to be Earth-directed. The solar flux was down in the 90s for most of the week, but rose to 104 on the 18th and 108 on the 19th. The average over the week was 97 – a point higher than the previous week. However, the 90-day average lost two points to stand at 111. The X-ray flux declined to A7.9 units on the 12th – its lowest point so far this year. However, it rallied to B3.0 by the 19th. The geomagnetic field was mostly quiet but briefly reached ‘active’ level on the 15th under the influence of a high speed coronal stream, and became ‘unsettled’ on the 19th, again due to a high-speed stream. The Ap index was in single figures every day until the 19th, when it reached 11 units. Solar wind data from the ACE spacecraft saw solar wind speeds vary between 321 and 559 kilometres per second. Particle densities were low. Bz ranged between minus 5 and plus 10 nanoTeslas. While the dearth of solar activity continued to be disappointing, and there was renewed speculation that cycle 24 might prove to be two-peaked, with the second peak in 2014, low geomagnetic activity meant that HF MUFs generally reached or exceeded predicted levels.

Finally, the forecast for the week ahead. Prospects look a shade brighter. While solar activity is expected to be mostly low or very low occasional C-class flares look possible. Solar flux levels are expected to stay above the 100 mark and may well exceed 120. Geomagnetic activity is like to be up a bit on the 23rd and 24th, due to a recurring coronal hole, but quieter levels should then return. MUFs during daylight hours at equal latitudes are expected to be around 23MHz in the south and 20MHz in the north. Darkness lows are expected to be about 11MHz. As we pass through the equinox north-south propagation should be in good shape. Paths to South American should be particularly strong. The maximum usable frequency, where there should be a 50 per cent chance of success, will be around 26MHz. The optimum working frequency, with a 90 per cent chance of success, will be about 21MHz. The path should be at its best between 1000 and 1900UTC.

And that’s all for this week from the propagation team.

Category: GB2RS Propagation News

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