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Propagation News – 22 April 2018

The Sun remained spotless this week, other than the hint of a new sunspot coming around its limb as this report was being written.

The solar flux index reflected this, sitting around the high 60s, although it did reach 71 on Thursday morning. Geomagnetic conditions were quiet at the beginning of the week, but a solar wind stream from a large solar coronal hole was predicted to hit Earth later on Thursday, the 19th. This normally means noisy HF bands, and depressed maximum usable frequencies (MUFs) after a possible initial positive phase.

We are now seeing a shift towards more summer-like ionospheric conditions in the northern hemisphere. At this time there is a chemical change towards more diatomic molecules in the F2 layer and fewer monatomic species. The diatomic molecules are more difficult to ionise and as a result MUFs can suffer.

Coupled with the lack of sunspots, we are now seeing daytime MUFs struggling to get above 16-17 Megahertz at times, despite the quiet geomagnetic conditions.
The upside is that night-time MUFs are staying higher, with seven Megahertz possibly staying open to DX over a 3,000km path through the night. A phenomenon that has been spotted is that the MUF is sometimes rising again for a short period after sunset. It might be worth checking 14MHz around 2000hrs UTC as this has showed itself a few times on the ionosonde data.

Next week, NOAA predicts the solar flux index will remain around 69 and geomagnetic conditions are predicted to be quieter from Monday onwards after the weekend’s high K-indices.

These settled conditions could bring better DX from Tuesday or Wednesday, once the ionosphere has settled. As we’ll explain in the VHF section, you may still have to wait a week or two before the start of the summer sporadic E season.

VHF and up:

Last week ended with high pressure near southern areas declining during the weekend as low pressure moved in from the Atlantic towards northern areas.

There may be slightly enhanced tropo conditions around at first but these could weaken as the low takes over. This could introduce showery weather with a prospect for rain scatter on the Gigahertz bands.

The 2018 sporadic E season is nearly here! It usually starts with a few fleeting SSB and CW signals across southern Europe, possibly not within range of UK stations, but with new digital modes, we might be lucky this early.

Since the location of sporadic E geographically can be influenced by the position of the jet stream, there may be some possibility of paths from the UK to the south-east into the Balkans and east to the Baltic states. The other possibility, based on expected jet stream positions, might be from Spain down to the Canaries.

Anyway, before it all kicks off, it is worth making that list of useful beacons on 10m or 6m so that you can quickly find the openings—just Google “G3USF beacons”. Also, use propquest.co.uk to find the daily jet stream positions.

Now we are in April, meteor activity is picking up again. The first significant shower, the Lyrids, peaks Sunday, 22 April sometime between 1000 and 2100 UTC.

Moon declination is still positive, but decreases all week, going negative—that is, south—this coming Friday. Losses will also increase as the Moon heads out to apogee, its furthest point from Earth. It’s another good week for EME then, with long windows and high Moon elevations.

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