After 3 April 2025 and the noticeable tropo duct mentioned in my last posting, there was a long lasting tropospheric event caused by a stable high pressure moist air system over the North Sea.
Long lasting stable high pressure systems are not always my favourite events, as it is normally alterations in pressure (usually downwards) which tend to produce openings. This was actually two systems, as when the first started to fill the second one moved in and merged. It appeared to be one high pressure system the whole time.
I worked 53 stations on 144 and 432MHz between 1 and 11 April. This despite being absent at the GMDX convention on 5 and 6 April. The pressure was raised but not very high, peaking here at at 1026hpa on 10 April, but it had maintained a steady level above 1015hpa all the time since 30 March. In an area much given to storms arriving from the South West this long period of high pressure is unusual.
What constitutes "DX" for this purpose is debatable. Let us not have that debate here right now.
I have tried to plot contacts against barometric pressure as this event progressed over two weeks.
Week One -
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| Barometric pressure at GM4FVM 31 March to 5 April 2025 |
As usual, click to enlarge images as required.
Where only a prefix is shown, just one station there was worked. Where a number is shown, e.g. 3xSM, this means three stations were reached in that prefix. A dotted line under the prefixes indicates that a contest was scheduled for one of the bands for a time during this period.
The barograph chart at GM4FVM shows the raised pressure during the week. Please have patience with me while I use up imperial measurement charts - I will properly calibrate the instrument once I have changed over to charts in hpa units.
The gentle rise in pressure up to the afternoon of 1 April produced no improved propagation. Then a very slight levelling out of the rise brought two OZ stations and a G who were all involved in the 144MHz NAC contest. The rise returned on the morning of 2 April but levelled out again in the evening. That level stretch brought a good opening to OZ during the 144MHz UKAC FT8 contest. Another slight dip in pressure coincided with the SM duct on 3 April (see last posting) and continued into an opening across the North Sea on the morning of 4 April. This ended with an short but steep rise in pressure, while the usual evening enhancement brought in mostly Gs and PAs towards the end of the day. On 4 April I worked 2 x LA, 3 x OZ and 3 x GM and one SM in the morning to afternoon period, plus 4xLA, 5 x G, 6 x PA and an OZ in the evening.
I was absent from the shack as I was away at GMDX on 5 April and almost all of 6 April. Actually I was home around lunchtime on the 6th but I then fell asleep - which must have shown the quality of the contributions I heard at the GM convention.
Week Two -
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| Barometric pressure at GM4FVM 6 to 12 April 2025 |
During Week 2 the pressure gradually rose to a peak on 10 April and then fell steadily until 12 April. It was possible to work OZ on many days, and during the 432MHz NAC contest on 8 April I worked 6 OZ and 2 SMs. The 432MHz FT8 UKAC on 9 April produced a better than usual number of contacts. Once the steep decline set in at around 10:00 on 10 April I only worked one more DX station when the fall levelled up slightly.
Looking at these charts I would suggest that things depend on three factors for maximum DX for me on 144 and 432MHz (and probably 1296 too)
EITHER
1) High pressure with moist air (ideally with gently declining pressure)
OR
2) Evening cooling after a day of moist air high pressure
OR Both
PLUS
3) A contest
It looks very much to me that either 1 or 2 or both is very desirable, but adding a contest really raises my DX performance. Not that I enter contests, but I do give away points. Mornings generally are not so good, and there are few morning contests except poorly supported ones at the weekends.
Basically, if the same opening had occurred at the end of the month when there are no contests on 2m and 70cm I think I would have fared much worse.
The fact that a contest makes so much difference was something I must have been aware of but I had never put into context. It seems to be a bigger influence than I would have expected.
By the way, the rather wobbly barometer trace is not due to the apparatus but due to my shaky hands. I went over the trace with a pen as the barometer leaves quite a faint mark. I am using a modern felt-tip pen on the barograph, but the line gets lost amongst the chart lines. Charts used to be in red ink so that you could see the trace more clearly ....
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| Dickson and Cargill Barograph at GM4FVM |
Mind you, the barograph is 100 years old. It came to me via my father and it had not worked for at least 60 years. Although of no value I restored it recently. It is a useful thing to have for a VHF-er. I do have a modern weather station with a pressure readout but that will never be the same.
And then on 16 April came an impressive aurora. The K number at GM4PMK's magnetometer briefly reached a rather impressive K=9 and the VHF bands sounded amazing.
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| GM4PMK's magnetometer chart for 16 April 2025 |
I did a lot of listening. I did not work many stations compared to some others. I stuck to Q65 and contacted 12 stations, 7 on 50MHz, 1 on 70MHz and 4 on 144MHz. It would seem that the trend is continuing for Q65-15C to be common on 6m while Q65-30B is gaining ground on 2m where the going is rather more difficult.
Based on the present stage of the sunspot cycle many crystal-ball gazers are predicting more aurora activity for the coming months.
73 Jim
GM4FVM
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