From the most recent ARRL Propagation Letter.
SB PROP @ ARL $ARLP019
ARLP019 Propagation de K7RA
ZCZC AP19
QST de W1AW
Propagation Forecast Bulletin 19 ARLP019
From Tad Cook, K7RA
Seattle, WA May 11, 2018
To all radio amateurs
SB PROP ARL ARLP019
ARLP019 Propagation de K7RA
Sunspots reappeared this week, after none on April 28 through May 3.
Average daily sunspot numbers increased from 3.6 (last week) to 14.6
(May 3-9).
So far in 2018 56% of days were spotless. For all of 2017 the rate
was about half or 28%, for the whole year, a total of 104 days.
These numbers are according to
http://www.spaceweather.com .
Seemingly counter-intuitively considering the slight rise in sunspot
numbers, yet not unusual, average daily solar flux declined one
point from 69.3 to 68.3.
Solar activity continues to decline, and we've been expecting (over
the past few years) solar minimum to arrive about two years from now
in 2020.
But some have suggested that perhaps the decline is currently faster
than anticipated. I like to imagine a sooner minima could precede a
faster rise in the next cycle! What if the upcoming Cycle 25 echoes
Cycle 19? Sorry, no scientific evidence, but I like to dream this
could happen.
Cycle 19 was the largest in recorded history, and I would be glad to
see another one, just so it isn't accompanied by a Carrington Event.
The Carrington Event happened in September 1859 and produced solar
flares so powerful that telegraph offices, connected by long lines
acting as antennas, caught fire. But the peak of Cycle 19 happened
about 100 years later.
Spaceweather.com reports this week that the American Geophysical
Union (agu.org) in a paper published May 10, researchers from the
University of Birmingham use Extreme Value Theory to estimate the
average time between "Carrington-like flares."
See
https://bit.ly/2G6J2sRTough to predict, but they estimate one every 100 years. Of course,
this means we are long overdue, but perhaps this is like the
gambler's fallacy: don't bet on red just because the last five spins
of the wheel landed on black:
https://en.wikipedia.org/wiki/Gambler%27s_fallacyAccording to
http://legacy-www.swpc.noaa.gov/weekly/pdf/prf2227.pdfon page 11, smoothed solar flux numbers around 63 are predicted
toward the end of 2019. But when we observe numbers around the last
solar minimum (right now I am looking at the 109 days ending on
October 9, 2008 as an example) there were numerous consecutive
periods of no sunspots (average daily sunspot number during that
time was only 1.046) but average daily solar flux was 66.4, several
points higher than values predicted for the end of 2019.
These long term predictions are updated about every four weeks, but
I have no idea when predictions for 2020 will appear.
Predicted solar flux is 69 on May 11-12, 68 on May 13-15, 67 on May
16-18, 72 on May 19-25, 70 on May 26, 68 on May 27 through June 8,
and 70 on June 9, 72 on June 10-21, 70 on June 22 and 68 on June
23-24.
Predicted planetary A index is 8 on May 11, 5 on May 12-16, 12 on
May 17-18, 8 on May 19, 5 on May 20-31, then 18, 25, 20, 16, 12 and
8 on June 1-6, 5 on June 7-12, then 42, 12, and 8 on June 13-15 and
5 on June 16-24.