Propagation News – 16 March 2025

We’ve had another week of disturbed geomagnetic conditions with the Kp index at four or five for long periods. On the evening of the 12 March, Kp was five and, at the time of writing, has stayed there for a total of five three-hour periods.

This has taken its toll on the ionosphere with MUFs over a 3,000km path down to less than 24.7MHz during daylight.

Meanwhile, the solar flux index rose to 160 on Thursday 13 March after hitting a low of 147 on the 7 March.

The best HF propagation was last weekend, the 8 and 9 March, just in time for the Commonwealth Contest. This saw stations around the world romping into the UK, including signals from Australia, New Zealand, the Falkland Islands, Barbados, and many others.

As contacts were limited to Commonwealth countries, it meant the UK had little QRM to contend with and it was fairly easy to fill the log book on 40m to 10m.

Australia was still coming in at 59 after dark, and even British Columbia on the west coast of Canada could be worked with simple wire antennas and low power.

This may have been caused by a pre-auroral enhancement, as the Kp index rose late on the first day of the contest.

Next week, NOAA predicts the solar flux index may rise to 195 by the 21 March. It also suggests that we may be back into calmer geomagnetic conditions with a maximum Kp index of two. This will be a welcome change and, if it happens, will no doubt result in better HF conditions.

And remember, March is a good month for north-south contacts, such as the UK to South Africa and UK to South America.

But with the equinox just around the corner, auroras are twice as common due to the Russell-McPherron effect.

Just as when two bar magnets attract one another when they are oriented oppositely, so opposite Bz components attract. During the autumn and spring equinox, this orientation enables a ‘connection’ to the Sun, thereby allowing the solar wind to stream in.

VHF and up

The recent change to colder weather brought showers and potential rain scatter to the second half of last week. But this weekend we have lost the showers and gained a large region of high pressure to bring a hint of Tropo.

It’s not perfect, since in cold air highs like this, conditions are usually less than ideal, so don’t expect too much from this particular area of high pressure.

The high will last until midweek before it slips away into eastern Europe and, on its parting, may allow some moisture below the inversion and will improve the Tropo prospects briefly. The second half of the coming week will be dominated by low pressure and back to rain scatter as an option on the GHz bands.

The solar conditions have continued to provide a few weak auroral alerts and it’s worth continuing a watching brief on the Kp index for hints of activity; anything greater than a Kp of five is worth our interest.

Listen out for watery-sounding signals on the LF bands and then check out the 10m and 6m bands for auroral signals.

The next important meteor shower is the April Lyrids, but there’s always the chance of random meteor scatter activity, particularly in the pre-dawn hours.

It’s still a little early to mention Sporadic-E, but it’s always worth looking at the lower frequencies first, which means 10m and 6m. Check the graphs on Propquest for signs of spikes in the foEs, which is the critical frequency of the Es-layer.

EME path losses continue to rise until apogee on Monday evening. Moon declination is still falling, reaching a minimum on Saturday 22 March. So again, we have short Moon windows and reducing peak Moon elevation. 144MHz sky noise is moderate and rising to high by Friday 21 March.

Category: GB2RS Propagation News