Propagation News – 8 June 2025
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 coronal mass ejection, or CME for short, followed a solar flare from sunspot 4100 on the 31 May at 0005UTC. The explosion lasted more than three hours. Type 2 radio emissions from shock waves within the CME cloud suggested it was travelling at 1,938 kilometres per second, or 4.3 million miles per hour!
Eventually the Bz swung south. This meant that the interplanetary magnetic field more easily coupled with the Earth’s magnetic field. The result was that the Kp index got up to 7.67 on the 1 June.
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 7 or more for four three-hour periods. This pushed the maximum usable frequency over a 3,000km path below 14MHz at times, which wasn’t conducive to good DXing.
On Thursday 5 June, it looked like we were 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 the 31 May, to a low of 134 on the 5 June. HF propagation was being driven by the geomagnetic conditions, with a general lowering of the maximum usable frequency.
Next week, NOAA predicts that the solar flux index 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 6 on the 13 June.
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
Last week has offered an example of what a good Sporadic-E season should look like. On Tuesday the 3 June in particular, the 6m band sounded like the 20m band and, at its peak, activity extended all the way up to the 2m band.
This coming week has an unsettled flavour with several areas of low pressure and weather fronts involved, together with heavy showers in between. This means rain scatter will be a supported mode on the GHz bands.
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 the coming week. So, there is a chance of Tropo propagation for the 2nd 144MHz Backpackers Contest on Sunday 15 June.
Meteor scatter is always interesting in June with four showers to play with during the month. The early ones are the Arietids, which peaked on Saturday 7 June – good news for the 50MHz UK Activity Contest on Thursday 12 June.
The Zeta Perseids peaks tomorrow, the 9 June, and there will be a couple of other showers later in the month. This is probably also why the Sporadic-E prospects improve about now.
Aurora has also been much in evidence recently. 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 5.
The advice for some who have not yet worked Sporadic-E is to check the 6m band around teatime.
There are, of course, usually two primary periods when Sporadic-E is more likely: one in the morning, and 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 at propquest.co.uk by following the Sporadic-E blog tab. The daily commentary will highlight the important directions each day. You can hopefully test out the system on Thursday 12 June in the 50MHz UK Activity Contest.
EME path losses were at their maximum with apogee, when the Moon is at its furthest from the Earth, on Saturday 7 June. Declination reaches minimum on Wednesday 11 June so Moon windows are short and peak elevation low. 144MHz sky noise peaks around the 11 and 12 June. EME conditions were classed as poor this weekend and are classed as poor-to-moderate on the 14 and 15 June.
Category: GB2RS Propagation News