Propagation News – 23 August 2015

| August 21, 2015

HF propagation conditions were very bad earlier this week. The culprit was a high-speed solar wind stream from coronal holes on the sun. The solar wind often exceeded 500 kilometres per second and had a south-facing Bz field at times. This meant that it more easily coupled with the Earth’s magnetic field – and plasma poured in. The net result was very poor conditions with a depleted F2 layer, lower maximum usable frequencies and rapid fading on the HF signals that could get through.

The Kp index hit seven last weekend, leading to visible aurora and rotten conditions for the International Lighthouse and Lightship event, thanks to the arrival of material from a coronal mass ejection. However, late-season Sporadic-E brought some extended 10 metre openings to Europe on Thursday the 20th.

The solar flux index has declined, staying just below 100 all week. Next week, it should remain in the range 90-95, according to NOAA, but HF conditions may again be dominated by the geomagnetic effects of the solar wind.

Predicting much more than three days ahead is hard, but looking at images from the GOES-12 X-ray imaging satellite suggests that coronal hole-enhanced solar wind effects may be less prevalent in the latter half of next week. This could mean HF conditions may improve as geomagnetic conditions become more settled. Time will tell if we are right!

Low pressure will be nearby for much of this week, mainly to the North and West of Britain, but with smaller lows tracking northeast across the country at times.

The nearest areas of high pressure are over the Continent, linking back to a large high near the Azores. Conditions are expected to be fairly flat for VHF tropo, except today and tomorrow may see some Northerly trans-North Sea paths. Later in the week occasional Southerly paths into the Continent or across Biscay to Spain may be possible.

The Sporadic-E season’s primary months, typically from May to August, are nearly over, so Sporadic-E openings are much less likely. But with such an unsettled weather pattern there will be some jet stream upper winds over Britain and the near Continent. These jet stream winds may give a chance of Sporadic-A patches, but since they are quite close-by, the geometry is more likely to favour paths from northern Britain into Europe.

For EME operators, the Moon reaches its lowest declination on Monday so bringing very short, low-elevation Moon windows this week, but with perigee will come the lowest losses next weekend.

There are daily updates on the RSGB propagation forum.

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

Category: GB2RS Propagation News