venerdì 14 gennaio 2022

Propagation News – 16 January 2022

We had a week of relatively low, but stable, sunspot numbers, which affected the maximum usable frequencies available. Having said that, the SFI was above 100 all week, but we didn’t get the surge in numbers that we really needed for good reliable ionospheric propagation. MUFs over a 3,000km path often exceeded 28MHz, but this mainly occurred over the lunchtime period. And critical frequencies often exceeded 7MHz, again mainly over lunchtime, which makes 40 metres a good inter-G band when this occurs. So if you have got used to ignoring 7MHz for around-the-UK contacts, you could be in for a nice surprise. Forty metre skip often starts long but gets progressively shorter as the critical frequency increases. Keep an eye on the website for a graph of how propagation during the day develops.

If NOAA’s predictions are to be believed we could soon get that much-needed surge in activity. From 17 January the SFI is predicted to go up to 120 for around eight days. This may give a much-needed uplift in HF propagation. However, it does also bring the risk of solar flares, coronal mass ejections and geomagnetic disturbances. A large coronal hole is also threatening to cause a disturbance this weekend with a Kp index of five. If that happens expect degraded MUFs and poor DX, especially on northerly paths for the following two to three days.

VHF and up:

It’s been a while since there was a long-lasting region of high pressure over the country and this current period of high pressure seems likely to hang around for the whole of the coming week and produce some good prospects for Tropo. This will either be due to an elevated temperature inversion due to the high, and extending over long distances for Tropo DX; or due to regional surface night-time inversions when night frost and fog forms, and can produce local and somewhat temporary tropo enhancements.

These things are not that simple in reality, since the high centre tends to drift around; this alters the flow over the British Isles from a moist southwesterly, which is good for Tropo, to a colder north westerly, which is bad for Tropo, when the high is displaced a little west. This may happen in the second half of next week.

We are just leaving the midwinter window for Sporadic-E, so all that remains are some chance auroras and random meteor scatter to play with during the coming week. The Moon is at maximum declination today, but path losses are still high and falling after Friday’s apogee. 144MHz sky noise is low all week. (