Propagation News – 23 August 2020

Sunspot region 2772 was rotating off the Sun’s limb at the end of the week. As a result, the solar flux index declined from 74 down to 71 as the Sun’s surface cleared. There was some activity though. A solar storm cloud was hurled into space on 16 August by a slow-motion solar flare in the Sun’s southern hemisphere. The coronal mass ejection was due to sweep past Earth on the 20th. A group of three smaller coronal holes passed the Sun’s central meridian on Wednesday and Thursday, which could spell unsettled conditions at the weekend due to the solar wind emanating from them. NOAA predicts that the Kp index will rise to three until the threat passes. This is not really high enough to cause big problems, but keep an eye on the Kp index at solarham.com as a guide.

Next week, NOAA has the SFI pegged at 71 to 72, reflecting a lack of sunspots. The Kp index should also be pegged at two, at least until Sunday, 30 August when it could climb to four. Look out for a potential positive pre-auroral phase enhancement, followed by a decline in maximum usable frequencies (MUF) as any potential geomagnetic storm progresses.

Current daytime MUFs over a 3,000km path are still in the 14 to 18MHz range, with night-time MUFs covering 10 to 14MHz according to propquest.co.uk.

VHF and up

A deep low, and gales over the northern and western part of the British Isles, is not ideal summer holiday weather and not good for antennas either. In fact, this unsettled pattern will stay with us through to Thursday, when some models show temporary high pressure over the country to end the week.

It’s fair to say that not all models do this and instead of a high, it’s no more than a one day weak ridge before further lows arrive. In terms of propagation it’s looking like another period of weather more suitable for GHz bands rain scatter.

Tropo may put in an appearance later in the week, but it might only be a brief visit, and perhaps not with a well-developed inversion if it’s a temporary visit. As an aside, it’s a particularly good period of summer tropo over the Mediterranean at the moment, with potential for east to west paths, say from EA to IT9, or IT9 to SV or 5B4.

The sporadic E season is hanging on, particularly for digital modes, and next week should continue to offer several nicely placed jet streams for paths into Europe.

Note that propquest.co.uk, which contains a daily blog on where the weather triggers may be more active, now contains a single sporadic E probability index—EPI. This combines many of the contributory factors into one experimental index on a map showing where the chance of sporadic E is highest. Click on the map or enter your locator to overlay the ideal distance rings for sporadic E from your QTH.

Moon declination is now negative and falling all week, and as perigee was Friday, EME path losses are low but rising. Moon windows will shorten as the week progresses. 144MHz sky temperatures are rising, peaking at over 3000K on Thursday, so your masthead preamps won’t help you! Read G4BAO’s GHz bands column from the April 2020 RadCom for an explanation of why.

Category: GB2RS Propagation News