Propagation News – 29 October 2023
It was not a good week for the ionosphere with the Solar Flux Index, or SFI, falling to less than 130, plus some disturbed geomagnetic conditions as well.
On Wednesday the 24 October, the SFI fell to 121, while the following day the Kp index hit 4.33 thanks to a coronal mass ejection from a filament eruption. Minor to strong geomagnetic storms continued on Thursday afternoon and evening with a warning that Aurora sightings may have been possible in the north of the UK that evening.
So, does this mean that Solar Cycle 25 is over? Most definitely not!
NOAA’s Space Weather Prediction Center has just issued a revised prediction for solar activity during Solar Cycle 25, saying solar activity will increase more quickly and peak at a higher level than that predicted by an expert panel in December 2019. The updated prediction now shows Solar Cycle 25 peaking between January and October of 2024, with a maximum sunspot number between 137 and 173.
Meanwhile, the critical frequency remained relatively high at around 11 to 12MHz around lunchtime, which still gives a Maximum Useable Frequency, or MUF, for paths over 3,000km of more than 28MHz. October remains a good month for higher-band HF propagation with many reports of contacts into the Pacific on the 15, 12 and 10m bands.
The bad news is that this weekend’s CQ World Wide SSB Contest could be hit by poor geomagnetic conditions later on. Two large coronal holes on the Sun recently rotated into an Earth-facing position which could mean a raised Kp index and reduced MUFs.
A coronal hole is a cooler, less dense region of the Sun with open magnetic field lines that allow solar plasma to flood out.
We expect the solar material to hit the Earth today, the 29 October, either in the afternoon or evening, perhaps continuing into Monday, with an associated warning of aurora as the Kp index rises.
Looking to next week, NOAA predicts the SFI will increase, perhaps hitting the 140 to 145 mark by the end of the week. The ionosphere may also remain unsettled until around Wednesday 1 November, although the rest of the week should be better.
VHF and up
This autumnal weather pattern is keeping up its attack on the UK during the coming week.
This means that low-pressure systems will remain in control and it’s unlikely that Tropo will get much of a look-in! That leaves rain scatter as the best of a bad bunch with heavy rain, especially any heavy showers around the coasts, being the most likely to offer good reflection points for GHz band operators.
The remaining options for propagation are aurora, which is not entirely out of the question since we have a large coronal hole navigating its way into a favourable position, as was mentioned earlier.
There are many websites and widgets that show the latest Kp value and it’s definitely worth adding one to your favourites list.
The other mode of possible interest is that of meteor scatter and, although we have just passed the peak of the Orionids, it came along just right for the 6m Affiliated Societies Contest on Sunday 22 October, when some out-of-season Sporadic-E propagation made a welcome appearance with paths to Italy, Sardinia and Spain being reported. The slow decay of the Orionids means that we still have the coming week to enjoy the remnants until early November.
For EME operators, Moon declination is positive and rising this week with lengthening Moon windows and increasing Moon elevation. Path losses start low but are increasing. 144MHz sky noise is moderate, peaking at 500 Kelvin on Wednesday 1 November.
Category: GB2RS Propagation News
