Propagation News – 6 April 2025

We had a week of mixed solar conditions, but it ended with an SFI of 182 and a Kp of 3.67 on Thursday 3 April.

The geomagnetic field declined to quieter levels following a prolonged period of active, Kp4 conditions earlier on Wednesday due to solar wind enhancements. This impacted propagation, with the critical frequency struggling to get much above 7MHz on Wednesday.

Compare this with the following day, when the critical frequency hit 10.4MHz by 0830UTC. Nevertheless, there was DX to be worked on Wednesday with FT8 allowing signals from Australia, Japan, Indonesia, China, and Surinam to get into the UK on 21MHz.

The solar proton flux was also high on Tuesday 1 April, affecting signals passing through the polar regions, but this had declined by Thursday and was heading back to normal levels. This was due to a large CME observed off the east limb of the Sun on Friday 28 March. If it had been Earth-directed, we may have seen a massive aurora.

Next week, NOAA predicts that the solar flux index will stay in the 175-185 region. A Kp of six was forecast for yesterday, Saturday 5 April, followed by a further period of unsettled geomagnetic conditions due to an enhanced solar wind.

If this is the case, we may not get more settled conditions until the 14 to the 16 April.

Nevertheless, this remains a good time for North-South HF paths, such as the UK to South Africa, and UK to South America.

VHF and up

The old forecasting maxim that the ‘longer a high lasts, the longer it will last’ is built upon the presence of blocked upper air weather patterns. When the jet stream gets so distorted into a high amplitude north/south wave, its lateral movement, from west to east, becomes very slow.

On the upper air charts this takes the shape of the Greek letter omega, and this is the current set-up. It means that the weather associated with it also lasts a long time.

In this case it’s the high pressure and its spell of fine weather that is likely to last for the whole of the coming week. The position of the high will change though, starting over the North Sea and ending over the UK and nearby Atlantic. This means that Tropo will be the mode of choice for the coming period, which includes the 70cm UK Activity Contest on Tuesday and the 6m UK Activity Contest on Thursday.

Rain scatter is unlikely during this extended period of dry weather.

The meteor scatter options are still mainly driven by random meteors for the coming period into next week, but the next important shower, the Lyrids, peaks on the 22 April. The auroral alerts continue to come through, raising interest. As usual, the clue will be fluttery sounding signals on the bands, particularly noticeable on CW, but they can also be pronounced on speech transmissions. Monitor the Kp index for values above Kp5.

There have been a few trans-equatorial openings to Southern Africa on 50MHz digital modes for the fortunate few who live in the extreme south and southwest of the UK, but it did extend up to Cambridgeshire and Suffolk briefly on some days last week.

The long drought of Sporadic-E will soon be over, but we’re still in the realms of very isolated events for 10m and 6m, which will be short-lasting. The jet stream, which can be a good clue as to potential locations, suggests looking to Scandinavia, the Baltic and northern Europe.

EME path losses are falling again, but Moon declination has been at its highest this weekend, so we have long Moon windows. 144MHz sky noise is low throughout the coming week.

Category: GB2RS Propagation News