RSGB
rsgb | July 19, 2024
We had another great week in terms of HF propagation. The solar flux index was at a remarkable 224 on Thursday, the 18th, and the Kp index had been consistently in the ones and twos all week.
It doesn’t get much better than this, HF-wise, although it’s a shame it’s not autumn with the associated good HF autumnal propagation.
Given that we are in the summer HF doldrums, there has been a lot of DX on the bands. 15m has been very good during late afternoons, and open to all continents, with Australia, Asia, Africa, North America and South America all workable on FT8 at the same time.
On Thursday, the 18th, there were 17 active sunspot regions visible, which are contributing to the high solar flux index. Two X-class solar flares brought short-term solar fadeouts on the 14th and the 16th, but any associated coronal mass ejection has been mainly directed away from Earth.
For those new to HF propagation, this is good news. Remember, a high solar flux index is generally good, while a high, perhaps more than four, Kp index is generally bad.
Daytime maximum usable frequencies (MUFs) over a 3,000km path have been consistently above 21MHz. Nighttime MUFs have been more than 14MHz, and often 18MHz, at times.
But will this continue? Probably not.
Of the 17 visible sunspot groups, six are classed as ‘growing’. There have been coronal mass ejections from sunspots on the edge of the Sun, but they have not been Earth-directed. But, as these spots rotate to be Earth-facing, a coronal mass ejection could be more problematic.
Next week, NOAA predicts that the solar flux index may fall, perhaps into the 170s to 180s range.
The Kp index is predicted to be around 2, but if we do have an Earth-facing coronal mass ejection that could easily climb to 4 or 5, with an associated drop in the maximum usable frequency.
So, will it be another week without a high Kp index? Maybe that is too much to hope for!
VHF and up propagation news from G3YLA and G4BAO :
Last week ended with a decaying high over Germany and fronts pushing in across western Britain. With such warm air over the UK at first, even temporarily, there will be a reasonable chance of tropo over nearby cooler waters around our coasts, especially along the English Channel and southern North Sea.
Incidentally, for anyone taking a VHF rig with them on holiday to the Mediterranean resorts, you can expect typical summer semi-permanent, very strong maritime tropo ducts over any sea path to neighbouring islands or countries.
Returning to the UK, we have a series of fronts and lows lined up for the coming week. In summer months these can often have a showery element to them, so expect some heavy rain and thunder at times, but at least there’ll be rain scatter to make up for it!
Meteor scatter is again a random experience, with no major showers this week. Try around, or just before, dawn for best results. The solar conditions have been all over the place with flares and weak auroral responses, but nothing dramatic for VHF radio.
Sporadic E, on the other hand, has done fairly well for digital mode activity, especially for transatlantic paths, but is slightly subdued where higher signal levels are required for SSB and CW. Although the weather is expected to be unsettled, the jet stream activity is less widespread than recently. If anything, the western side of Europe seems in the better spot with quite good options for paths to Iberia.
Remember, most years will see activity into the first week of September, so don’t give up yet.
The Moon is at minimum declination on Friday, the 19th so we start the week with short Moon windows and falling path losses as we approach perigee on the 24th. Perigee is the point at which the Moon is closest to the Earth. 144MHz sky noise starts very high but declines to medium next week.
(Mike Terry/BDXC)