Propagation News – 21 May 2023

After last week’s NOAA prediction that we would have settled geomagnetic conditions all week, it seems they were right! The Kp index never got above three – a miracle given the recent disruption due to coronal mass ejections and coronal holes.

The proton flux from the Sun has declined as well. However, an M9 solar flare on Tuesday from active region 3310, and numerous C-class flares, may be a precursor to more flare activity next week.

With a solar flux index in the 130s and 140s, HF conditions have been quite good. Daytime maximum usable frequencies over a 3,000km path have usually exceeded 21MHz, with 24MHz seeing occasional F2-layer openings, as well as sporadic-E propagation.

At the moment, the 10m band is mainly open to Sporadic-E propagation with more DX paths now locked out until the Autumn. This is in line with predictions, as the ionosphere changes in the Northern Hemisphere summer with a change to more diatomic elements, which are harder to ionise.

So, will our luck hold out next week?

The Space Weather Prediction Centre forecasts that the Solar Flux Index, or SFI, will decline slightly to the 120s and this weekend should be geomagnetically settled. However, it is predicting that the Kp index will rise again from the 23 May. It suggests that the Kp index may hit four or even five for a few days before becoming more settled again from the 30 May.

The US Air Force disagrees and thinks the SFI will be higher, perhaps hitting 145 and even 155 by the 28 May. It agrees that we are in for more unsettled geomagnetic conditions from the 24 to the 28 May, possibly due to a coronal hole rotating into an Earth-facing position.

So, expect MUFs to decline if the Kp index goes up, with poor overall HF conditions.

It is certainly looking like this weekend may see the best conditions for HF, so we suggest you get your DXing in right now, with 14 to 21MHz offering the best prospects.

 VHF and up

The upcoming weather week will be predominantly high-pressure driven, with an elongated region of high pressure from the Azores to Scandinavia.

However, there is still scope for a few blemishes and as we end the current week it comes as isolated showers, especially in the south and weakening fronts over north-western Britain. Early next week, a brief period with low pressure over the near continent will threaten some heavier rain for south-eastern areas.

Concentrating on the high-pressure part of the story, this means Tropo is a strong player and will hopefully be in attendance for the 144MHz May Contest and 144MHz Backpackers Contest this weekend.

Remember that, in the summer months, Tropo becomes much weaker over the land during the stronger heating of the daytime sunshine but can become quite widespread overnight and around coasts.

The rainfall component can lead to good rain scatter options, especially as the summer usually produces more intense rainfall, so performs better as a scatterer on the GHz bands.

The other primary propagation mode is going to be Sporadic-E as we move into the peak summer months. Follow the position of jet streams on the upper air charts, shown on propquest.co.uk and described in a daily blog.

Don’t forget there are always modes like aurora and meteor scatter, which can add to the excitement, but will need to be checked each day.

Moon declination is at its highest this weekend for the Dubus EME 10GHz and up SSB/CW contest, peaking on Monday. With apogee next Friday, path losses will continue to increase.

144MHz sky noise is moderate early next week becoming low by Thursday.

Category: GB2RS Propagation News