[HCARC] Solar Minimum

[Kerry]

Gary,

Solar minimum is not particularly easy to identify.  Often there will be 
entire months around solar minimum without a sunspot.  It is 
particularly difficult to identify solar minimum when it occurs since 
the sunspot number used is a running 12 month average. Often it is a 
year or more after minimum or maximum before we can accurately determine 
when it was not that it really means anything.

The solar output we really care about is the X-ray flux since that is 
what actually ionizes the ionosphere.  Unfortunately it can't be 
measured from the ground, only from space.  While we have some sunspot 
values going back many centuries, comprehensive sunspot numbers only go 
back to the time of Galileo.  2800 MHz solar flux measurements go back 
to 1947 or 1948.  X-ray measurements only go back to the late 50's when 
we have had satellites in orbit with X-ray sensors.  So at best we only 
have 2 or 3 complete 22 year solar cycles of X-ray data.  That is hardly 
enough data to really understand the X-ray cycle which is what we really 
care about for ionospheric radio propagation.

Predictions of the strength and timing of solar maximums based on 
observations of time and strength of solar minimum as determined by 
sunspots or solar flux with no real understanding of the physics of the 
sun is voodoo statistics at its worse.  The best we can do at the moment 
is keep track of solar activity from day to day including sunspot group 
characteristics and probability of flares over the next 2 or 3 days and 
be ready to operate when conditions are expected to be good for the next 
couple days.  Even with low solar activity there are days with 
interesting propagation.  We should be spending our efforts to make sure 
we recognize the good days and take advantage of them that worry about 
when the next min or max might be.

Kerry



On 4/13/2018 11:22 AM, Gary Johnson wrote:
> More Frequent Spotless Days Now, Can Signal Solar Activity in the Future, Top Contester Says
> 04/09/2018
>   
> [UPDATED: 2018-04-12 @ 2318 UTC] The sunspot numbers have not been good, and it does not seem they’ll be getting much better anytime soon. According to the April 6 “K7RA Solar Update,” only 2 days of the March 29 – April 4 reporting week saw sunspots, and that was at the bare minimum. No sunspots showed at all for the previous reporting week. Solar flux has been sitting in the 60s lately and are forecast to remain at that level for the next 45 days. Better days lie ahead — eventually. Top contester Frank Donovan, W3LPL, asserts that solar precursors like spotless days, which correlate physical solar phenomena with future solar activity levels, are much better indicators of progress toward a solar minimum — a broad phase of the solar cycle — than of a specific event, such as the bottom of a broad solar minimum. Not only that, these and other solar precursors are useful in predicting the likely strength of Cycle 25, although accurate predictions of the strength and timeframe of the Cycle 25 solar maximum aren’t possible until the new sunspot cycle is under way.
>
> “We entered the Cycle 24 solar minimum with the onset of 8 spotless days in June 2016,” Donovan pointed out. “We had only 32 spotless days in 2016. We had 15 spotless days in a row in March 2017, followed by relatively infrequent spotless days for the next 7 months.”
>
> The frequency of spotless days accelerated in early November 2017, with 13 spotless days in a row. That was followed by many more spotless days over the next 5 months. In all, 2017 experienced 104 spotless days (see chart).
>
> “The frequency of spotless days accelerated again last month, when we had 25 spotless days,” Donovan noted. “We’ve already had 54 spotless days during the first quarter of 2018. This data and comparisons to frequent spotless days during the last solar minimum suggests that we may have just begun a period of very frequent spotless days for approximately the next 2 years, similar to the period of September 2007 through January 2009.
>
> Donovan said the next solar precursor is frequent extended periods of spotless days. For example, 2016 saw 14 spotless days in a row, March 2017 had 15, November 2017 saw 13, and early March experienced 14.
>
> “Long periods of spotless days will become even more frequent as we go deeper into solar minimum,” Donovan predicted. Once extended periods of spotless days become more frequent, another solar precursor will become important, he said.
>
> “New high-latitude, opposite-polarity Cycle 25 sunspots will then begin to appear more frequently, perhaps by late next year,” Donovan said. “More frequent Cycle 25 sunspots will signal that we’re approaching the bottom of the [Cycle 24] solar minimum phase.”
>
> An ongoing solar precursor that could herald the future strength of Cycle 25 is the intensity of the solar polar magnetic fields prior to the Cycle 24 solar minimum, Donovan said. “The good news is that the solar polar magnetic field strength is already slightly stronger than it was prior to the last solar minimum,” he said. “This suggests that Cycle 25 will be somewhat stronger than Cycle 24.”
>
> Donovan said if the long periods of spotless days end in about a year, that will be a precursor of a stronger Cycle 25. If they take more than 2 years to end, however, it will portend a weaker Cycle 25.
>
> He takes issue with reports suggesting that the solar minimum has arrived, based entirely on the very frequent incidence of spotless days over the past 6 weeks. “More comprehensive physical evidence suggests it’s more likely that we’ve just begun a lengthy deep solar minimum phase — similar to late 2007 through late 2008 — that’s likely to last well into next year,” he told The Daily DX. He said solar polar magnetic field strength peaks at least 1 year before solar minimum, and, while the south polar region peaked last year, the north polar region has not yet done so, suggesting that solar minimum is not likely to occur until 2019 at the earliest.
> ______________________________________________________________
> HCARC mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hcarc
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:HCARC at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html