Propagation News – 28 March 2021

| March 26, 2021

What a mixed week we had, with large geomagnetic storms interspersed with quiet periods. The first storm occurred last weekend, when the Kp index hit six on Saturday and then five on Sunday. This wasn’t unexpected and we did warn that it might happen in the last GB2RS broadcast.

A second storm occurred when a weak shock passage was detected at around 1920UTC on Wednesday evening. This was likely related to a coronal mass ejection coming off the Sun’s eastern limb, which was observed on the 20th of March. The solar wind increased from 375km/s to around 440km/s and the Bz Interplanetary Magnetic Field component tipped south.

Otherwise, it was relatively quiet on the sunspot front with the solar flux index climbing from 77 on Sunday to 84 on Thursday, reflecting the increased UV due to groups 2811 and 2812. Conditions have been a little lacklustre, with daytime maximum usable frequencies over a 3,000km path struggling to climb over 18MHz at times.

Next week NOAA has the solar flux index prediction at 78 all week. It also predicts unsettled geomagnetic conditions on Sunday, Monday, and Tuesday, with the Kp index set to rise to five thanks to a high-speed stream from a coronal hole. Expect depressed critical frequencies and MUFs until this clears later in the week and the Kp index returns to more normal values.

This might be a good time to check your antennas so that you are ready for the 10 metre Sporadic-E season in a few weeks!

VHF and up

After some welcome Tropo down to Atlantic France and Northern Spain early last week, we are in the midst of a very disturbed period of weather and this will continue into early next week.

Perhaps contrary to expectations there could be some more Tropo on the southern warm air side of a waving front over southern Britain. This will most likely be west-east paths from southern Britain into northern Europe. Otherwise, we can hope the frontal rain band may provide limited rain scatter options on the GHz bands.

From about Tuesday, a new high will establish a dominant position over the UK and this could make Tropo more likely again, but this will be a cold air high and usually, these are not the best providers of good Tropo.

As we enter April in the coming week, it’s worth dusting down the Sporadic-E equipment and consider looking at 10m or 6m digital modes for early signs of life.  If the locational trigger is jet streams, in this case it would favour Scandinavia and the Baltic region.

For EME enthusiasts, declination goes negative today, so peak Moon elevation will fall as the week progresses and Moon windows will shorten. Path losses are at their lowest with perigee coming up on Tuesday.

The Lyrids meteor shower will start to ramp up in about two weeks’ time, peaking on the 22nd of April, but until then, the best time for meteor scatter contacts is the pre-dawn random meteor enhancement.

Category: GB2RS Propagation News