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Propagation News – 28 February 2021

We had a slightly better week in terms of solar activity, but the consensus is that HF propagation is still in the doldrums. Two sunspot groups made an appearance last week, although by now they may have vanished around the Sun’s edge again. Groups 2804 and 2805 pushed the solar flux index to 81 by Thursday, with a sunspot number of 33. Although group 2804 was quite large and also responsible for several low-level B-class solar flares, 2805 never really managed to appear as much more than a pinprick on the solar surface.

Last week was dominated by geomagnetic disturbances, with the Kp index staying at four for a lot of the time. This was mainly caused by the arrival of matter from a coronal mass ejection that was launched from the Sun on the 20th of February, and ongoing high-speed solar wind streams from coronal holes. The solar wind speed has been dropping, which suggests a return to more settled geomagnetic conditions this weekend. The US Air Force predicts the solar flux index will start at 82 on Sunday, but then decline to 74 as the week progresses. This reflects the lack of future sunspot activity currently being seen on the STEREO Ahead spacecraft.

Geomagnetic conditions are likely to start settled but become unsettled on the first, second and sixth of March, with a potential Kp index of five. This is due to matter arriving from a very large coronal hole on the solar surface. So it looks like a reasonable weekend for HF, but conditions and MUFs may decline early next week.

And note that we are now entering March. Spring is typically a time when HF favours North-South paths, such as the UK to South Africa and South America. Make the most of the next couple of months, before we enter the Summer season, which is characterised by lower F2-layer maximum usable frequencies. However, the bands will stay open longer, perhaps even 24 hours on 20 metres by mid Summer.

Short-skip Sporadic-E on 7 to 28MHz can make up for decreasing F2-layer propagation and activity, but we are still a couple of months away from the start of the Sporadic-E season.

VHF and up:

As we ended the week, an area of high pressure extended towards southern Britain from the southwest. It should have become firmly established over the country by now and should produce a welcome return of Tropo conditions for the VHF and UHF bands.

This should dominate into next week, but during Tuesday a more summer-like area of low pressure drifts north from Biscay, and may produce some heavy spring showers over southern England, so possible rain scatter conditions coming up for midweek.

The high doesn’t go away and should bring further Tropo after this showery interlude, but eventually an Atlantic cold front will move into northwest Britain at the end of the week, starting a spell of unsettled, windy weather there, but leaving southern Britain under the Tropo ridge for another day or so.

We are now in an extended period where lowest EME path losses coincide with low Moon declination and hence short Moon visibility windows. This week, declination goes negative on Monday so Moon visibility windows and peak Moon elevations will reduce. Path losses continue to fall this week as we get to the Moon’s closest approach to Earth, called perigee, on Tuesday.

There are no major meteor showers until mid March, so pre-dawn continues to be the best time for random meteor scatter contacts. (