venerdì 8 gennaio 2021

Propagation News – 10 January 2021

We start by welcoming in 2021, and here’s hoping that it proves to be more fruitful than 2020 in terms of HF propagation. We’ve started the New Year with zero sunspots and a solar flux index back in the mid-70s on Thursday the 7th. The STEREO Ahead spacecraft is not showing anything of note around the back of the Sun, but we know that spots can suddenly appear.

HF propagation has been relatively poor, but with seasonal ionospheric changes mainly being responsible for an uplift in daytime critical and maximum usable frequencies. Daytime critical frequencies have generally been in the range of 4.5 to 5.5MHz, falling to below 3.5MHz by 1930UTC on most evenings. This means that 80m is ceasing to be suitable for local NVIS contacts as the evening progresses, which is normal for this time of year.

Daytime maximum usable frequencies over a 3,000km path have exceeded 18 and even 21MHz on most days, with winter Sporadic-E being the main DX mode on the higher 12 and 10 metre bands. There has been the odd F2-layer opening on 28MHz, but we will need some more sunspot activity to make band openings more reliable.

NOAA predicts the solar flux index will remain in the high 70s at the beginning of next week, reflecting the lack of sunspot activity. The Kp index is predicted to reach a maximum of only two, due to a lack of coronal hole and coronal mass ejection activity. This means we may have a more settled ionosphere, which may be good for HF DX.

So in summary, it’s more of the same in terms of HF propagation next week, with no real highlights. But don’t ignore the lower bands, such as 1.8, 3.5, and 7MHz, which can really come into their own in mid-winter.

VHF and up:

Despite no Tropo for a number of weeks, there has been high pressure to the west of Britain for some time. During the weekend and next week, it will become more dominant over much of the country, initially favouring Tropo for the south-western parts, but perhaps more generally later. This may be temporarily curtailed by frontal systems moving across the country around midweek and thus add some options for GHz rain scatter, but some models bring a ridge of high pressure back later in the week.

As hinted at in the last bulletin, a sudden stratospheric warming did indeed develop on the 4th of January 2021. As mentioned, it can have impacts on not just the stratospheric flow, but can influence weather patterns nearer the surface about a couple of weeks later.

In a related note, it appears the models, after a milder next week, are hinting at a colder northerly spell again after the following weekend.

Staying with the stratospheric wind flow changes, these may have a possible link to winter Sporadic-E events and it’s worth monitoring 10m and 6m for activity in the next couple of weeks or so, especially FT8, but CW and SSB are not impossible.

After the excitement of the Quadrantids meteor shower we are now entering the annual quiet period in meteor activity with just two significant showers between now and the April Lyrids, so back to pre-dawn random meteors for the best chance of DX.

The Moon was at perigee yesterday, so path losses are at their lowest, but it’s at minimum declination on Tuesday meaning Moon windows are short and low elevation. The Moon only reaches 12 degrees elevation on Tuesday, meaning horizon noise will be an issue all week at VHF.

And that’s all from the propagation team this week. (