Propagation News – 19 February 2023
Last week was interesting as we had an X-class solar flare, and a significant geomagnetic disturbance, as well as good HF conditions at times.
An impulsive X1.1 solar flare was observed around active region 3217 in the southeast quadrant of the Sun at 1548UTC on the 11 February. The flare did not appear eruptive, so we had no associated coronal mass ejection.
Nevertheless, the flare caused a fade-out as its X-rays penetrated deep into the D-layer of the ionosphere.
There were other lesser M-class and C-class flares throughout the week.
The Kp index rose to five on Wednesday 15 February and conditions continued to be geomagnetically unstable throughout Thursday. Nevertheless, the ionosphere remained relatively stable with daytime MUFs over 3,000km generally staying above 28MHz all week.
The critical frequency is generally remaining well above 4MHz until midnight, meaning 80m is open around the UK and also to DX. After midnight it can decline, meaning only longer paths are open.
NOAA has updated its coronal mass ejection forecast model to predict a stronger-than-anticipated solar wind passing Earth by late Friday 17 February and into Saturday 18 February. A moderate G2 level storm watch was officially added, beginning on Friday, so aurora sky watchers and VHF enthusiasts should be alert this weekend.
Next week, the Space Weather Prediction Centre forecasts that the SFI will fall back, perhaps to 130 by next Friday. Once we get past this weekend’s geomagnetic disturbance, the Kp index is predicted to remain settled all week, although a single coronal mass ejection could soon spoil that.
VHF and up
After some good tropo for the 70cm UK Activity Contest last Tuesday, it will be a return to more unsettled weather that ends this week and starts this weekend. High pressure will then quickly return and take up residence over the south and west of the country, eventually ending up west of Ireland.
This will mean that tropo will again offer some enhanced conditions on VHF and UHF and may prove useful for the 1.3GHz UK Activity Contest on Tuesday evening.
After midweek, it will tend to favour paths within the UK and to the south into France. From midweek there will be low pressure to the east of the British Isles with a showery northerly flow down the North Sea. This will cut off the eastern half of Europe from any Tropo prospects, but it may offer some rain scatter from eastern areas.
There may continue to be some good chances of auroral propagation, which you can explore by checking the Kp index for values higher than five. In the absence of major meteor showers, random meteor scatter is always an option and likely to be most profitable around the dawn period.
For EME operators, Moon declination is negative but increasing, going positive again on Wednesday. The week will therefore see Moon availability windows increasing and path losses increasing from their lowest with perigee, the point where the Moon is closest to Earth, occurring today Sunday 19 February.
The Sun and Moon are close to an eclipse later today and throughout all of Monday’s moon window, so sky noise will be high due to the Sun being in the beamwidth of most antennas. After that, 144MHz sky noise is low for the rest of the week.
Category: GB2RS Propagation News
