Propagation News – 24 September 2023
Last week’s space weather was very disturbed from a geomagnetic point of view. The Kp index hit 6.67 on the 19 September, spawning reports of visible aurora from around the UK once again. This was the result of a coronal mass ejection passing Earth, which caused a period of strong G3 storming very early that morning.
The ionosphere was badly affected with MUFs over a 3,000km path down below 18MHz for most of the day. By Wednesday the 20 September, things began to improve and MUFs were back to 21MHz, and sometimes even 24MHz, by late morning. By Thursday the 21st, the Kp index was down to 2.67.
Meanwhile, we had numerous C- and M-class solar flares to contend with as well – a total of 39 from the 18th to the 20th.
So, last week was not exactly a good time for HF operations!
This week, commencing today the 24 September, NOAA predicts that the solar flux index will be in the range of 135 to 145 although, if the past month is anything to go by, it could easily be higher. The Kp index is forecast to be 2, apart from on the 28th and 29th when it could rise to 4.
In reality, with so many sunspots, we could have a solar flare and associated coronal mass ejection at any time, so take these predictions with a pinch of salt!
The good news is that we are now past the autumnal equinox, so the ionosphere is improving. Expect better worldwide HF conditions as we head towards October and November.
VHF and up
The recent unsettled weather seems to have set a trend for us with a likely repeat process through the coming week, although there may be a few drier interludes. The next low in the sequence will soon be arriving to keep the rather unsettled theme in play.
This means that rain scatter is a good choice for operators during the period.
There is usually some uncertainty in such a complex pattern, and recent model runs have been alternating between a return of high pressure during the next week, with a chance of Tropo, and the continuation of lows with fronts bringing rain and showers.
We are, however, in a ‘keep the lows coming’ mindset at the moment, so don’t build your hopes of Tropo too high. Such uncertainties in long lead-time forecasts are quite typical at this time of the year when ex-hurricanes can get involved in the Atlantic flow pattern and disrupt the forecasts very easily.
The other modes to monitor are aurora, which has been seen recently from southern Britain, so definitely one to keep in mind, and meteor scatter, which can be productive.
We are approaching the ‘busy season’ for meteors with several good showers between early October and December. However, the last week in September does not hold much promise. There are always random meteors to keep interest alive, but this week might be better used getting equipment ready for the next few months of activity.
Having reached its lowest declination of the lunar month, the Moon is now beginning its slow climb back up. With the Moon out of Sagittarius, sky noise will decrease and is at its lowest mid-week. Path loss, or degradation, will be lowest on the 27th with the Moon at perigee, its closest point to Earth. The full Moon is on the 29th.
Altogether, it looks like a good week for EME operations, especially if you can elevate your antenna or dish reflector.
Category: GB2RS Propagation News
