Propagation News – 22 June 2025

Last week we mentioned a large coronal hole on the Sun that might cause problems. The hole is so large that it is still Earth-centric seven days later.

We had expected the hole to increase the Kp index due to the solar wind emanating from it. However, as of Thursday, 19 June, conditions remained quiet with a Kp index of 2. As geomagnetic conditions have remained calm this past week, it has been quite good for HF.

15m has been one of the better bands, with openings to both the east and west, depending on the time. As is the way nowadays, most of the activity has been on FT8, but it has opened up opportunities to work the Far and Middle East, as well as South America.

The solar flux index has generally been in the range of 130 to 150, with a peak of 161 on 15 June. The Sun has been active, with a near X-class solar flare being observed around sunspot region 4114. This peaked at 1805UTC on 15 June. There was also an X-class solar flare at 2149UTC on 17 June.

This latter event was late in the evening, so had little impact on the UK, other than to potential paths to the west.

Maximum useable frequencies (MUFs) declined a little during the past week, with openings on 21MHz becoming a little scarcer. It is useful to operate as close to the MUF as possible to minimise the effects of D-layer absorption and maximise the chances of working DX.

Next week, NOAA predicts the solar flux index will be in the range of 125 to 145. Unsettled geomagnetic conditions are forecast for the period from 24 to 27 June, with a maximum predicted Kp index of 5.

If the Kp index is low, then we have a good chance of 21MHz openings to South America in the evening. As we pass the summer solstice we may even expect 14MHz to remain open to DX throughout the night. We can also expect sporadic E to continue to provide short-skip openings on 28MHz, and even the lower HF bands, such as 14, 18, 21, and 24MHz.

And now the VHF and up propagation news from G3YLA and G4BAO

After a week of high pressure, this weekend returns to something more normal with showery rain and a series of weather fronts and showery interludes in the coming week. This will mean that rain scatter on the GHz bands is worth considering. Also, since we are into the summer season, the chances of some rain being heavy and thundery is a good signal for rain scatter.

This sequence of low-pressure weather suggests that high pressure and tropo will be less likely to make a big impact on the coming week’s operating log. Any sign of high pressure will tend to be towards the south of the UK and over the continent. In very hot weather, the conditions can be good for low-level surface ducts across cooler seas. So, if you are tempted, then go for coastal or maritime paths up the east coast or across Biscay, for example.

Meteor scatter may benefit from the late June Bootids, which peak on Friday, 27 June and the daytime Beta Taurids which peak on 28 June. These are small showers, but they can also be important for contributions to long-lived metallic ions which are the building blocks of sporadic E propagation.

Aurora continues to appear with occasional radio events, but there is too much daylight for anything visual. As an alternative, you might see glimpses of noctilucent clouds low down on the northern horizon. These form in the mesosphere, at about 80km, as ice crystals form on meteor dust and can exhibit complex wave patterns. These are both good omens for sporadic E.

The summer sporadic E season is well under way now. It is advisable to check the usual cluster maps and propquest.co.uk for daily updates. It’s also worth making use of the longer daylight and weather patterns over the polar regions for paths to the Far East.

The Moon reaches perigee, its closest point to Earth, on Sunday, the 23rd, so path losses are low. Moon declination also reaches a maximum positive value on 25 June. This will mean that there are long Moon windows. 144MHz sky noise is moderate, increasing to high by Sunday, the 23rd. The New Moon is on 25 June so expect high noise levels due to its proximity to the Sun.

Category: GB2RS Propagation News