Propagation News – 21 April 2024

Last week saw a welcome return of sunspots but, unfortunately, it also brought unsettled geomagnetic conditions.

By Thursday 18 April the solar flux index was back above 200, hitting 217. Compare that to the previous week’s 131 and you can see that there is a lot more activity. But, with 12 active regions visible, it looks like we could be in for a bumpy ride over the next seven days.

The Kp index hit five on the evening of Tuesday 16 April after the interplanetary magnetic field, or Bz, swung southwards, sparking visible aurora in the UK as far south as Dartmoor. This impacted the ionosphere, pushing MUFs over a 3,000km path down, with recovery not showing itself until 0930UTC on Wednesday 17 April.

The 10m band is struggling to open at times, although you may find FT8 still passing weak signals. SSB operators might be better advised to look at the 12 and 15m bands which may provide richer pickings.

Next week, NOAA predicts that the solar flux index may decline to be in the range of 170 at the beginning of the week, falling to between 135 and 140 at the end of the week. The risk of an M-class flare is currently at 75%, with an X-class event at 20%. Despite this, NOAA predicts the Kp index will be around 2 for all of next week. However, there is a chance that a flare and associated CME could scupper that completely.

If we do get a coronal mass ejection, or CME for short, we can expect the Kp index to rise roughly 48 hours after the event, perhaps hitting 5 or more and possibly sparking visible aurora from the UK again.

Overall then, it’s good news on the sunspot front, but not so good for geomagnetic activity, which could see MUFs fall if any solar flares and CMEs come to fruition.

VHF and up

The weather is likely to remain in an unsettled state, despite temporary high pressure moving across the country this weekend. This may bring some Tropo, but it’s a cold air high and probably not the best for enhanced VHF conditions, except for localised overnight or early morning temporary lifts.

The rest of the time, there will continue to be an unsettled flavour to the weather so this leads to the possibility of rain scatter on the GHz bands, especially if we get heavy April showers.

This first weekend coincides with the peak of the Lyrid meteor shower which peaks tonight, the 21 and 22 April, so it’s worth checking the usual meteor scatter frequencies. If you are not familiar with meteor rates and variations from day to day, then visit the excellent Radio Meteor Observing Bulletin at rmob.org  which gives an hourly display from various locations around the world. You can find many other useful links to meteor scatter resources by searching for ‘meteor scatter’ on the RSGB website

The Sun has woken up a little since last week, and a few auroral flutter signals on the LF bands suggest we shouldn’t give up yet for this spring. As usual, keep a watch for the Kp index going above 5.

The late April period can provide some fleeting early season Sporadic-E events, especially for the 10 and 6m bands. A couple of weak 5MHz Sporadic-E critical frequencies were noted during late afternoon on Wednesday 17 April on the Dourbes plot shown at propquest.co.uk

For EME operators, Moon declination goes negative again today, the 21 April, but path losses are falling as we passed apogee yesterday, the 20 April. 144MHz sky noise is low but rising to moderate by the end of next week.

Category: GB2RS Propagation News