Propagation News – 23 April 2023

We had a surge in sunspot activity over the last week, pushing the solar flux index up to a maximum of 178, although it subsequently declined to 147.

Solar flare activity was quite subdued after a frantic period from the 13 to the 15 April that saw 40 C-class flares and two M-class flares erupt.

This activity was mostly centred around active region 3282 in the northwest quadrant.

Geomagnetic conditions were unsettled for a time around the 18 and 19 with the Kp index hitting a maximum of 4.3. This appears to have been due to enhanced activity from a coronal mass ejection and continuing coronal hole activity that saw the solar wind speed hit more than 600km/s and the Bz swing south.

The critical frequency was down below 7MHz on the morning of Wednesday 19  April which impacted near-vertical incidence skywave signals around the UK.

This impacted maximum useable frequencies, which struggled to exceed 21MHz over a 3,000km path on Wednesday, although by Thursday they were back over 28MHz again. A critical frequency of more than 10MHz meant the 40m band was once again suitable for close-in contacts around the UK.

There were many reports of DX being worked later on during the week, with Australia and New Zealand topping the bill on 18MHz and 28MHz.

Next week NOAA has put a more positive spin on sunspot activity. The Solar Flux Index is predicted to be in the range of 168 to 172 for the first half of the week, falling to around 160 in the second half.

But we could be in for a bumpy ride geomagnetically, with the Kp index predicted to hit five on Wednesday 26 April through to Monday 1 May. This may be due to the return of solar phenomena that occurred 27 days ago and saw the Kp index get up to 4.67.

Meanwhile, a very large solar coronal hole, albeit positioned very south on the Sun’s surface, and a much smaller one on its equator, threaten HF conditions this weekend.

Keep an eye on the real-time solar wind from the ACE spacecraft for signs of a rise in speed and a southward-pointing Bz interplanetary magnetic field on solarham.net  This could push to Kp index higher, perhaps to four.

VHF and up

The Sporadic-E season is nearly upon us. Remember it will usually activate on 28MHz and then higher bands will follow if the event intensifies. There have been some 50MHz FT8 paths flagged up on DXmaps.com, although some may have been tropo.

The recent large high pressure centred over Scandinavia has been a bit subdued as regards Tropo. Much of the time, the air nearer the surface has been fairly dry with little sign of banks of sea fog over the North Sea, which would suggest better ducting potential.

We are now entering a phase with low pressure on the charts, initially over the south of Britain, but edging north for a time before drifting out across the North Sea.

This could produce some rain scatter on the GHz bands, especially should any heavy April showers develop.

Early next week a ridge will edge south across the UK in a colder northerly weather pattern, so although high pressure returns, it may not be especially good for tropo.

The third changeover comes after midweek when a milder south-westerly returns with active fronts bringing rain and unsettled weather, especially to the north and west. This could mean further opportunities for rain scatter on the GHz bands and perhaps a hint of tropo in the Southeast towards the continent.

Aurora and meteor scatter are well worth considering, and the Lyrids shower peaks on Sunday 23 April. The message is to monitor meteor scatter frequencies and the clusters for signs of activity and, of course, try putting out a CQ call!

Moon declination is positive and rising, meaning increasing Moon time and increasing peak elevation until peak declination on Tuesday. Moon apogee is next Friday so path losses increase all week.

144MHz sky noise is moderate to low.

Category: GB2RS Propagation News