Propagation News – 17 March 2024

What a difference a month makes. We’ve gone from a solar flux index up to almost 200, to one that is down in the 120s.

Over the past week, we have had only two M-class solar flares, which means we have had limited coronal mass ejection activity and therefore low Kp indices.

Last weekend’s Commonwealth Contest saw UK amateurs making plenty of HF contacts, some with Australia, but everyone agreed that HF propagation was a little lacklustre.

There is a daily chance of moderate-class solar flares from AR 3607, the largest sunspot region, but all remaining spots remain mostly small and simple.

The solar wind speed has been quite high with sporadic periods of a south-pointing Bz field. This is what has pushed the Kp index to three, but this isn’t a big threat to HF. There is a slight chance of unsettled intervals caused by a weak coronal hole near the south centre of the solar disc coupled with the fast solar wind.

NOAA reports that active region 3590 has been detected on the far side of the Sun using helioseismology. This may mean that it will still be active and a threat when it returns in a week or so. This region was the source of the X6 solar flare on the 22 February – the largest so far in solar cycle 25.

Next week, commencing the 18 March, NOAA predicts that the solar flux index will remain in the 120 to 130 range, although the US Air Force predicts it could reach 150. Geomagnetic conditions are likely to be mainly settled with a maximum Kp index of two or three.

So, this is a reasonable forecast for HF propagation, which should remain open up to 28MHz during daylight hours. This is also a good time for north-south paths, such as the UK to South Africa, and the UK to South America.

VHF and up

The continuing theme of unsettled weather will produce further spells of rain and heavy showers and once again provide some rain scatter options on the GHz bands.

Another thing to mention is that, as we move towards the latter part of the month, the intensity of showers becomes greater due to the additional warmth improving the effectiveness of the rain scatter process.

It is very hard to find any traditional Tropo until we get well into the coming week. It may occur on Thursday the 21 March when a high will develop a ridge from Biscay across southern Britain and the near continent. This should provide a chance of Tropo for the final few days of the coming week. Unfortunately, this is not in time for the UK Activity Contest on 1.3GHz on Tuesday 19 March, but the 70MHz UK Activity Contest on Thursday 21 March may be luckier.

The north of Britain may start to see the next low bringing rain over that weekend, so although it has an early exit from any Tropo, at least being well north gives Scottish stations a head start for any aurora, which tends to favour the spring months.

Meteor scatter still remains in the random territory – try just before sunrise for best results. But with the next major shower being the Lyrids in late April, we have a while to wait for an uptick in activity.

Lastly, a brief mention of Sporadic-E. It has popped up with some weak events on the Dourbes plots on Propquest, but the main season is still a little way off.

Maybe check next month for a heads-up on the lower bands like 28 and 50MHz. Of course, digital modes will get a head start, so best to check the clusters and chatrooms for signs of fleeting activity. Some UK stations reported 50MHz trans-equatorial propagation to Africa last week, so check for that.

For EME operators, Moon declination reaches a maximum on Sunday, but path losses are starting to increase again. 144MHz sky noise is moderate, falling to low on Wednesday.

Category: GB2RS Propagation News