By Courtesy of the Propagation team
G3YLA JIM
G0KYA STEVE
G4BAO JOHN
Its all about the weather
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Jim Bacon G3YLA
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and Nick Henwood
RSGB President.
Propogation News
6th June 2025
HF
3
Last week’s HF propagation was heavily influenced by unsettled geomagnetic conditions. This was caused by a combination of coronal mass ejections and a strong solar wind from a coronal hole.
The CME followed a solar flare from sunspot 4100 on May 31st at 00:05 UTC – the explosion lasted more than three hours. Type II radio emissions from shock waves within the CME cloud suggested it was travelling at 1,938 km/s, or approximately 4.3 million mph.
Eventually, the Bz swung south. This meant that the interplanetary magnetic field more easily coupled with the Earth’s magnetic field with the result that the Kp index got up to 7.67 on June 1st.
The auroral effects were reported as being due to a co-rotating interaction region or CIR – a region in space where fast and slow solar wind streams collide, creating a compressed area with enhanced plasma and magnetic fields.
The Kp index was actually seven or more for four three-hour periods. This took the MF over a 3,000km path below 14MHz at times, so wasn’t conducive to good DXing!
At the time of writing on Thursday June 5th, it looked like we could be past the worst and the Kp index was back to a more reasonable 2.33.
Meanwhile, the solar flux index declined from a recent high of 164 on May 31st, to a low of 134 on June 5th. HF propagation was being driven by the geomagnetic conditions, with a general lowering of the MUF.
Next week, NOAA predicts that the SFI will start the week at around 155 and remain around 150. More worryingly, geomagnetic conditions are again predicted to be unsettled after this weekend, with a maximum Kp index of six on June 13th.
So unsettled geomagnetic conditions, plus the HF summer doldrums, means HF DX via F2-layer propagation may be hard to find. So make the most of the 10m Sporadic-E short-skip openings instead!
VHF and up
The end of the previous week and this coming week all carry the unsettled flavour with several areas of low pressure and weather fronts involved, together with heavy showers in between. This means rain scatter is a supported mode on the GHz bands, particularly on Saturday 7th of National Field Day weekend.
There is a slight hint of a slow improvement during the week, but not really any high pressure showing up until right at the end of next week for a chance of Tropo for the 2nd 144MHz Backpackers on Sunday 15th.
Meteor scatter is always interesting in June with four showers to play with during the month. The early ones are the Arietids, which peaks on Saturday June 7th and is good news for the 6m contest, and the Zeta Perseids peaks on Monday June 9th, plus a couple of other showers later in the month. This is probably also why the Sporadic-E prospects get an uptick about now.
Aurora has also been much in evidence recently, so despite the light summer evenings and short nights, the chances of radio aurora continue to be important, so monitor for high Kp values above about Kp=5.
Now to Sporadic-E which has been very busy in the past week, doubtless fuelled by the uptick in meteor input and there is every reason to keep on the lookout.
In case there are some who have not yet worked Es, just employing the rule of checking 6m at tea-time when you get home from work will soon put that right.
There are, of course, usually two primary periods when Es is more likely: one in the morning, the second in late afternoon and evening. A morning opening may repeat in the afternoon in similar locations, although usually the weather trigger may have moved a little in the meantime.
Check the jet stream charts on http://www.propquest.co.uk, Es blog tab. The daily commentary will highlight the important directions each day. You can hopefully test out the system on Wednesday June 12th in the 50MHz UKAC.
EME path losses are at their maximum with apogee (Moon furthest from the Earth) on Saturday June 7. Declination reaches minimum on Wednesday the 11th so Moon windows are short and peak elevation low. 144MHz sky noise peaks around June 11 and 12. EME conditions are classed as poor on 07-08 and poor to moderate on June 14-15.
G3YLA JIM
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G0KYA STEVE
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