Propagation News – 10 March 2024
As predicted, a coronal mass ejection, or CME for short, affected the ionosphere last weekend, the 2 and 3 of March, pushing maximum usable frequencies down and sparking auroral displays that were visible as far south as Cornwall.
The plasma hit the Earth around midday on Sunday the 3 March, eventually pushing the Kp index to more than 5 for nine hours. It eventually started to settle again, dropping to 4 for six hours, before then moving back to background levels by the morning of the 4 March.
The solar wind speed was not that high, being around 350 kilometres per second, but the Bz component of the interplanetary magnetic field, or IMF, was pointing sharply south for a long period. This allowed the solar plasma to couple with the Earth’s magnetic field more easily, and it flooded in.
The maximum usable frequency was impacted, and it took until late morning on the 4 March before the 10m band was usable again over a 3,000km path. This probably impacted northerly paths the most with southerly paths being relatively unscathed.
The rest of the week was generally free from coronal mass ejection chaos with the Kp index remaining below 3.
Attention is now turning to active region 3599, which has expanded in size. It may therefore be a threat for an M-class solar flare and potential CME.
Next week, commencing Monday 11 March, NOAA predicts that the solar flux index will be around 135, but may then increase to 170 by the 15 March.
We are heading towards the equinox, which means that geomagnetic disturbances are likely to be more common and harsher. They are almost twice as likely in spring and autumn versus the winter and summer.
If the Kp index stays low, though, this can be a good time for HF.
VHF and up
This weekend, the 9 and 10 March, a strengthening south-easterly wind will develop over the country as low pressure moves into Biscay and a strong high builds over Scandinavia. Unfortunately, this may not be useful for Tropo since the high is a long way to the northeast and stronger winds usually prohibit the development of a quality inversion.
All this changes again over this second weekend of March, the 9th and 10th, as low pressure pushes fronts into southern Britain. It won’t last long though and a weak ridge will cross the country on Tuesday 12 March, which may bring some Tropo support for south-eastern Britain into the continent for the 432MHz UK Activity Contest on Tuesday evening.
On Wednesday, an Atlantic low will cross northern areas with rain and possible rain scatter options, but this will soon clear to leave a weak high over the country and it’s a return to Tropo conditions for the remainder of the week.
The upshot of all this is that Tropo will be an off-and-on affair, but nonetheless worth a look. The other modes, not so much. Although, as we said in the HF section, spring is a good time of the year for auroral activity and, after the recent visible aurora, we should definitely keep a watch for activity and a high Kp index.
There has been the odd fleeting pulse of Sporadic-E showing on the Propquest graphs recently. This has been noticeable on the LF bands sometimes but is not yet a big player for the usual Sporadic-E bands of 10m, 6m and beyond. However, on digital modes, UK stations have seen 50MHz trans-equatorial propagation, or TEP, to Africa last week – so check for that.
For EME operators, Moon declination is still negative but goes positive again on Monday. Path losses are approaching minimum with perigee today, Sunday 10 March. 144MHz sky noise is low all week except today, the 10 March, when the Sun is close to the Moon and in the beam width of antennas.
Category: GB2RS Propagation News
