Propagation News – 10 December 2023

We dodged a bullet last week as a high-speed solar wind stream from a coronal hole sped past the Earth. Although the wind speed was often in excess of 600 kilometres per second, its Bz, or magnetic field, was pointing north. The net result was that most of this passed harmlessly away from Earth and the Kp index remained around three.

Meanwhile, the solar flux index declined to 130 by Thursday, which is quite a difference from the 194 we had on the 23 November.

Solar activity last week reached moderate levels thanks to multiple low-level M-class solar flares detected around active region 3513 in the northeast quadrant. This region also produced frequent C-class flares.

Daytime MUFs over a 3,000km path mostly remained over 28MHz, while nighttime MUFs over a similar path length remained around 10MHz.

As we head towards mid-winter, we may expect these nighttime MUFs to drop, with the result that the 80m band closes down for short-skip early on in the evening—the curse of the inter-UK 80m Club Championship contests!

However, the 80m band may still be open over long distances and we are now entering the best time of year for low-band DXing. Keep an eye on the top end of the 80m band, around sunrise, for transatlantic signals.

Next week NOAA predicts that the solar flux index may recover a little and be in the range of 130 to 150. Geomagnetic conditions will depend upon coronal mass ejections, but are predicted to be good, with a peak of Kp4 on 12 December. There is a slender coronal hole on the Sun that could cause the Kp index to rise this weekend, ending the 10th, due to its associated solar wind stream. However, it shouldn’t be too bad and any poor HF conditions are likely to be short-lived.

Finally, NOAA has updated its progression forecast for Solar Cycle 25. It now predicts that this cycle will peak somewhere between January and September 2024 with a solar flux index of around 167 to 201.

VHF and up

The present spell of unsettled weather at the end of the first week of December will run into the first half of next week.

This brings a limited chance of rain scatter on the GHz bands, but there is a strong signal in the models for a major change of weather patterns for the middle of next week.

This will be the arrival of high pressure around Wednesday, the 13th, that will probably last into the following weekend, although there is some model variation in how quickly it will move away.

The main result is that, although it begins as a cold air high pressure with frosts, it will probably develop surface temperature inversions, which will be useful for tropo. Towards the end of next week, as the centre of the high drifts east, it will allow more moist air at the surface and produce stronger ducting potential as well as develop an upper-level inversion for longer DX paths into the continent.

The evening of 14 December sees the peak of the biggest and most reliable meteor shower of the year. The Geminids has the potential for a zenithal hourly rate of 150. The higher 50MHz and 144MHz activity usually provides the best chances, and a reasonably quiet QTH with 100W and a beam will bring you plenty of digimode QSOs.

QSOs are even made by EME-class stations on the 70cm band and strong, long reflections on the lower bands can allow SSB QSOs if you’re persistent enough.

That said, MSK144 and FSK441 digimodes will be the most reliable.

Aurora remains a possibility, but the isolated out-of-season sporadic E blips on the Propquest NVIS plots last month have quietened down for now.

For EME operators, Moon declination is negative, falling further and reaching minimum on Thursday, the 14th. Path losses are falling towards a minimum at perigee on Saturday, the 16th. 144MHz sky noise is moderate until the 12th and 13th when the Moon and Sun are close in the sky.

Category: GB2RS Propagation News