** Solar Cycle 25 Progress thread **

Propagation questions, answers and general information
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Jim (Bournemouth)
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** Solar Cycle 25 Progress thread **

Post by Jim (Bournemouth) »

I thought I would put this together to chart the progress of the new solar cycle.. I plan to update it every so often as and when.
This first post is long, future ones will be shorter...

Information on solar activity, and various charts and info I refer to can be found at www.solen.info/solar/index.html

Some of this post is a repeat of information I posted in Peter's (pe1etr) thread re: solar cycle forecast viewtopic.php?f=53&t=7913 - I include it here for completeness.

Cycle 24 ended and Cycle 25 began officially in December 2019.
This is when the 13 month smoothed sunspot number was at its lowest. Another measure, the 365-day average of 10.7cm solar flux centred 6 months either side of a given date, indicates that the minimum occured during mid-November last year. See https://solen.info/solar/images/Cycles_ ... inimum.png

Counting sunspots can be subjective, so I have always chosen to use the 10.7cm solar flux index (sfi) as this is easily quantifiable and shows a very close match to sunspot numbers and the effect on our ionopshere.
To give an idea of what these values mean/indicate... at solar minimum, sfi can fall as low as mid 60s solar flux units (sfu); at solar maximum, sfi can top 300sfu during bigger cycles. During the last maximum, sfi 365 day average peaked arund 145sfu with occasional peaks towards and occasionally exceeding 200sfu.

A short term average (perhaps1-2 weeks or so) of around 130 or more should give some good openings on low-VHF at mid-latitudes depending on the time of year.

The 365-day smoothed solar flux (as mentioned above) bottomed out at 69.13sfu in mid-May, placing the minimum on 17th November last year. This minimum was similar in duration and overall curve to the last one, but a couple of sfu less deep. In 2008/9, many days saw the solar flux parked around the 65-66 mark; this minimum saw only occasional days drop that low.

Since then, this value started to rise fairly quickly as some of the very low activity last summer and early autumn fell out of the reckoning, currently 71.8sfu.

The last month has seen a sizeable uptick in solar activity (highest since Sept 2017), bigger than I expected.
After bumping along at between just below 70 to mid 70s for much of this year, late October saw sfi increase to the mid 80's and then above 90. After falling briefly to the mid 70s earlier this month, activity increased again and last night saw a cycle high of 104sfu.
With more active regions about to rotate into view, a short term continuation of this renewed activity looks likely to continue.

It's very early in the new cycle yet, but for HF/low VHF users, this activity is encouraging.We are now into month 13 and we are seeing levels of solar flux only attained early in the 3rd year of the last cycle. Indeed, late in the second year of C24 (late 2010) we were only seeing peaks in activity to just about 90sfu.

At a similar stage in the previous two cycles (22/23) i.e. late in the 2nd year after solar min, Cycle 22 (a biggie) had already almost topped 200sfu. Cycle 23 (a mid-sized cycle) saw sfi values peaking 130-140 late in the second year after minimum. So, a couple of markers to bear in mind as this coming year progresses.

So what can we expect in the short term (next few months)? It is entirely possible, even likely, that activity will drop off somewhat and we will probably get some days with sfi back in the 70s and some more spotless days, between bigger peaks. The rise of a typical cycle will exhibit these surges of activity, followed by something of a dropoff perhaps for a few months before the next, higher surge.

As for how big this cycle will be.. see Peter's thread linked to above... but I would still expect, at this stage, C25 to be similar in size, perhaps marginally bigger than C24. If, however, we get regular peaks in activity topping 100sfu over the coming months, during year 2 of a new cycle, that ** could ** be a strong indicater of a rather bigger cycle this time, similar to C23.

We shall see !
Jim, Bournemouth, Dorset. IO90BR.

Elad FDM-S2, FDM S3, Perseus, Airspy HF+, SDRPlay, Funcube Dongle SDR Rx; 8-ele OP-DES for Band 2, 8-ele LFA 2m, 3 ele LFA for 6m, 10-40m fan dipole, VHF vert
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simbeav
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Re: ** Solar Cycle 25 Progress thread **

Post by simbeav »

Thanks Jim. Very interesting.

Jim (Bournemouth)
Posts: 456
Joined: 18 Sep 2014 05:59
Location: Bournemouth, Dorset IO90BR
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Re: ** Solar Cycle 25 Progress thread **

Post by Jim (Bournemouth) »

November stats:

Monthly Sunspot Number 34.0. This value not reached in Cycle 24 til Sept 2010, 21 months after solar minimum.

Monthly solar flux 90.1. This value not reached in Cycle 24 until Feb 2011, 26 months after solar minimum.

November was Month 12 of cycle 25. Too early to say whether this is a flash in the pan, or a pointer towards a substantially bigger cycle this time.

Some more notes on the current solar activity:

Cycle 24 (as was Cycle 23 just before) was a little strange in that it had 2 peaks.. the first peak was dominated by activity from the northern hemisphere, the second was dominated by activity from the southern hemisphere. Had the two hemispheres peaked together, we probably would have had a rather higher but sharper peak overall.....

Interestingly... the burst of activity in recent weeks has mostly come from the southern hemisphere.... given that SH activity has lagged behind (in terms of time) NH, one would expect NH to be leading the charge now. In fact, what has happened is that after the NH peak in 2011, activity from the north has been consistently weak and isnt yet showing much sign of recovery.

What this will mean for Cycle 25 is unclear....

See this graph from solen.info: https://solen.info/solar/images/cycle24.png
Jim, Bournemouth, Dorset. IO90BR.

Elad FDM-S2, FDM S3, Perseus, Airspy HF+, SDRPlay, Funcube Dongle SDR Rx; 8-ele OP-DES for Band 2, 8-ele LFA 2m, 3 ele LFA for 6m, 10-40m fan dipole, VHF vert
.

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Jim (Bournemouth)
Posts: 456
Joined: 18 Sep 2014 05:59
Location: Bournemouth, Dorset IO90BR
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Re: ** Solar Cycle 25 Progress thread **

Post by Jim (Bournemouth) »

December stats:

Monthly sunspot number 21.8
Monthly solar flux 87.3

both values being a little bit down on those for November. The rise in activity in December failed to pass the 100sfu mark.

The effect of the last 10 weeks of the year (a period containing only two spotless days) on the smoothed annual curves puts Cycle 25 significantly ahead of Cycle 24 at the same stage, but well behind Cycle 23, though that started from a much higher base with a shallower shorter minimum phase. Still VERY early days.

It now looks like we will have a quieter period over the next 2 weeks at least, with some spotless days likely and sfi dropping below 80 when the current regions slip away over the western limb, while we wait for the next burst of higher activity. Worth noting that even with a fairly flat xray flux curve, background solar flux remains in the eighties.. compared with a year ago when it was barely 70.
Jim, Bournemouth, Dorset. IO90BR.

Elad FDM-S2, FDM S3, Perseus, Airspy HF+, SDRPlay, Funcube Dongle SDR Rx; 8-ele OP-DES for Band 2, 8-ele LFA 2m, 3 ele LFA for 6m, 10-40m fan dipole, VHF vert
.

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