Propagation News – 7 May 2023

| May 5, 2023

Next week will see the Sun presenting with four large sunspots groups that are rotating to be Earth-facing, so look out for trouble. Just as the UK weather takes a turn for the worse, we expect the space weather to be unpredictable too!

Active regions 3293, 3294, 3296 and 3297 look dark and are looming large on the Sun’s face. Region 3293 emitted an M7.2 class solar flare on 3 May, which the Space Weather Prediction Centre reported was likely due to an intensification of the magnetic field within the spot group.

The flare caused some degradation of the ionosphere, but nothing too serious. However, the Space Weather Prediction Centre now predicts that further flares could follow, perhaps even a strong X-class flare, which could have more serious effects.

If an X-class flare occurs in daylight over the UK, we can expect the HF bands to be affected in what is known as a sudden ionospheric disturbance or Dellinger fadeout. This could see the lower HF bands shut down due to extreme ionisation in the D-layer, only for the band to return to normal over a period of minutes to an hour.

More worrying is the fact that the flare could spark a coronal mass ejection, or CME, which, if Earth-directed, could cause the Kp index to rise, MUFs to drop and bring auroral activity a few days after the CME. So, keep an eye on solarham.net for updates.

Meanwhile, the solar flux index, or SFI, remains in the 150s and this looks set to continue. The US Air Force predicts the SFI will start the week at 152, then dip slightly, before reaching 170 by 12 May.

It also predicts that geomagnetic conditions will be settled once we get past this weekend, which could see the Kp index rise to four. These unsettled conditions may be due to a coronal hole, which became Earth-facing on Thursday.

Propagation-wise, F2-layer maximum usable frequencies over a 3,000km path have struggled to exceed 21 to 24MHz during daylight hours as we head towards summer.

The season is characterised as having lower MUFs during the day, but these tend to be maintained into the hours of darkness. Meanwhile, Sporadic-E might spring some surprises for paths over 800 to 2,200km on 14 to 28MHz, with very strong signals and rapid fading.

VHF and up

The weather pattern is taking a change to unsettled as we move through this first May weekend, with low pressure dominating the charts and throwing active weather fronts across the country.

This will produce some quite heavy rain at times and perhaps even some thundery activity. This bodes well for rain scatter on the GHz bands.

This pattern extends well into next week, eventually changing from a south-westerly to a north-westerly followed by a building ridge of high pressure to bring a temporary hint of Tropo to end the week.

This opens the more exotic modes to consideration, such as meteor scatter and possible aurora, but these are very much outliers to the main interest at this time of year, which is Sporadic-E. The season has nominally started, and daily blogs are being added to the website Propquest.co.uk, which describe the more likely regions to find Sporadic-E opportunities.

This unsettled weather pattern brings a useful bonus in that it is often associated with jet stream activity. The whole period offers several jet streams across Europe, a positive for the start of the new Sporadic-E season, since jet streams are often associated with the location of Sporadic-E activity.

Moon declination is low and falling, reaching minimum next Tuesday. EME Moon windows will be short. Perigee is Thursday, so when you do have a view of the Moon, path losses will be low. 144MHz sky noise is high, reaching over 3200K late on Monday.

Category: GB2RS Propagation News