Propagation News – 7 November 2021

| November 5, 2021

What a roller coaster week we had. From great conditions on HF last weekend, to a severe geomagnetic storm this week, it has been hard to predict what’s coming next. The Kp index hit seven on Thursday, thanks to incoming plasma from a full halo coronal mass ejection produced by an M1.7 flare from active region 2891 on November 2nd. NOAA classed this as a strong G3 geomagnetic storm after the DSCOVR spacecraft clocked the incoming material at more than 700 kilometres per second. At this time the solar flux index had reduced from more than 100 to just 89.

The Propquest website shows just what effect this storm had on the ionosphere, with critical frequencies on Thursday morning down to the mid 3MHz range. This meant maximum usable frequencies over a 3,000km path were estimated to be down to around 11MHz. The day before at the same time, they were up above 6MHz with MUFs over 3,000km above 25MHz. This probably sets the scene for the rest of this solar cycle, as explained in Steve, G0KYA’s presentation Solar Cycle 25 – The good, the bad and the downright ugly during the recent RSGB conference, which is now available to view on YouTube.

Next week NOAA predicts that the solar flux index will remain in the high 80s to mid 90s. Geomagnetic conditions are predicted to remain calm, with a Kp index of two. However, as we warned last week this could well turn out to be over optimistic, as a solar flare and any associated CME could easily push this up to five or higher. The best advice is to work the DX while it is there. At this time of year, and with SFI figures up in the 90s, you can expect the upper HF bands to come into their own, but only if geomagnetic conditions remain calm.

VHF and up

It still looks like a changeable pattern for VHF, but there are a few chances in there. The main theme continues to be that of unsettled weather with periods of rain interspersed by brighter showery interludes. This should provide further options for rain scatter on the GHz bands. There are a few fleeting options for Tropo, as weak ridges develop from high pressure over Biscay and the near continent, particularly during this first weekend. This is most likely across southern Britain and will probably favour paths to the near continent and across Biscay to Spain.

Recent solar activity gave a nice 144MHz aurora last Thursday, showing that it’s always worth checking for this exotic mode by keeping an eye on the space weather sites. Meteor scatter should also be on your watch list, since we are approaching the November Leonids, which peak mid month around the 17th/18th. Now would be a good time to get some practice sessions going with digimodes if you’ve not tried it before. Until the shower peak, stick to the time around dawn to maximise your chances with random meteors.

For EME enthusiasts, path losses are low but rising after perigee last Friday, but with minimum declination today the Moon will be low in the sky at Zenith, getting higher as the week progresses.

Category: GB2RS Propagation News