Propagation News – 25 April 2021

| April 23, 2021

Last week was marked by solar flares, perhaps giving us a taste of things to come as the solar cycle progresses. The Kp index hit four on Monday after the weekend’s high of five. But luckily things then calmed down and we have been seeing the Kp index down to two overall. There was even one three-hour period where it was zero.

We have had more sunspots this week, which are always welcome. Region 2817 has now rotated off the Sun’s visible disk, but regions 2816 and 2818 have been very active. They pushed the solar flux index to 86 on Monday, but it was back down to 78 by Thursday.

The first M-class solar flare since the 29th of November 2020 was observed around region 2816 in the Sun’s southeast quadrant at 2342UTC on the 19th of April. Luckily, this occurred at night so had zero effect on the ionosphere over the UK. A coronal mass ejection, or CME, associated with this flare has been assessed as passing just behind Earth, but the Met Office’s space weather team said there was a slight chance of a glancing blow in the coming days.

A long-duration C-class flare around the same region occurred at approximately 0415UTC on the 22nd and looks to have produced a possible Earth-directed CME. If this is the case, we may expect the Kp index to rise, perhaps early in the weekend, resulting in reduced maximum usable frequencies.

HF conditions have been relatively lacklustre this week, although there has been some activity on 10m FT8. EA has been copied, perhaps via early-season Sporadic-E, and Bob, VP8LP on the Falkland Islands has put in an appearance during the late afternoon, as have numerous South American stations.

Daytime MUFs over a 3,000km path have generally struggled to exceed 18MHz at times, although there have been the odd DX openings on 21, 24 and even 28MHz.

Next week NOAA predicts the SFI will remain low, perhaps even dropping into the high 60s. Geomagnetic conditions are predicted to be generally quiet with a maximum Kp index of three. But do look out for further solar flares, which could cause short-lived disturbances on HF and the strong possibility of coronal mass ejections that could impact the Earth one or two days later, depending on the solar wind speed.

VHF and up

Conditions are starting out with a Tropo frame of mind into this weekend, but there are hints of a small low tracking south across Scotland at the end of this weekend, and probably across the North Sea to establish low pressure to the east of the UK after midweek. This will probably mean that the Tropo period is weakened gradually and with further lows near southern Britain at the end of the week, there is likely to be a subtle shift to rain scatter propagation for the GHz bands.

We keep flagging up the forthcoming Sporadic-E season and clusters show it’s just getting under way in an FT8 sense. It will no doubt start to show up with 10m or 6m beacons soon, so worth checking your favourite beacon list regularly.

If you haven’t got one yet, this would be a very good time to save a list of half a dozen frequencies for each band in the rig memories to make sure you can check for openings easily. From a jet stream perspective, initially, paths to Scandinavia look promising and by midweek probably more towards south eastern Europe and Ukraine.

Moon declination went negative today, so Moon windows are short and the Moon is at low elevation. The upside is that we have low path losses with perigee tomorrow (Monday).

The April Lyrids meteor shower produced some good meteor scatter QSOs last week and with the Eta-Aquarids set to peak on the 5th of May, the new meteor scatter season is well under way. Look at the usual frequencies for the mainly digimode activity.

Category: GB2RS Propagation News