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ARRL Propagation Bulletin ARLP035 (2018)

ARLP035 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7RA
Seattle, WA  August 31, 2018
To all radio amateurs 

ARLP035 Propagation de K7RA

We just saw 15 straight days with visible sunspots, but it ended on
Wednesday, August 29 with a sunspot number of zero. There were also
no sunspots seen on Thursday, the following day.

According to, in 2018 so far we've seen 134 days
(55 percent) with no sunspots. For all of last year, in 2017 there
were 104 days (28 percent overall) with no sunspots. During the last
solar minimum, there were 528 days with no sunspots in 2008-2009, or
about 72.2 percent of the days over the entire two years with no

The past reporting week (August 23 to 29) saw the average daily
sunspot number rise to 17.7, from 13 over the prior week. Average
daily solar flux rose from 67.5 to 70.6. Average daily planetary A
index rose from 10.1 to 19.9, while average mid-latitude A index
rose from 10.4 to 13.4.

For HF operations, we want to see high solar flux and sunspot
numbers, and low A index, a measure of geomagnetic instability. On
Sunday, August 26 we saw high A index numbers from an unexpected
crack, opening in Earth's magnetic field. Solar wind spewed forth
and the planetary A index rose to 76. During this period the
planetary K index (a component of the A index) rose to 7 over a six
hour period. Seven is a big K index number.

The middle latitude A index for the day was 34. But Alaska felt the
full force of the geomagnetic storm, with an A index in Fairbanks
(the College A index) of 90, a very high number. The College A index
hasn't been that high since September 8, 2017 when it reached 110. reported new sunspot group 2720 is the first large
spot of the next solar cycle, cycle 25. The magnetic polarity is
reversed from the polarity of sunspots in cycle 24.

K9LA, Carl Luetzelshwab noted that the latest spot was not a high
latitude event, which would be expected for a new cycle spot. Carl
said there was a new spot possibly from the new cycle on April 10,
but it was very short duration. Way back on December 20, 2016 the
first spot from the new cycle appeared.

Predicted solar flux is 68 on August 31 through September 7, 67 on
September 8 and 9, 68 on September 10 and 11, 69 on September 12, 70
on September 13 to 22, 69 on September 23 to 25, 67 and 68 on
September 26 and 27, 67 on September 28 through October 6, then 68,
68 and 69 on October 7 to 9, and 70 on October 10 to 14.

Predicted planetary A index is 5 on August 31 through September 2, 8
on September 3 and 4, 5, 5, and 8 on September 5 to 7, 5 on
September 8 to 10, then 15 on September 11 and 12, 12 on September
13 and 14, then 10, 12 and 8 on September 15 to 17, 5 on September
18 to 21, then 12, 18, 12, 10, 8 and 5 on September 22 to 27, 8 on
September 28 and 29, 5 on September 30 through October 3, 8 on
October 4, 5 on October 5 to 7, then 18 on October 8, 15 on October
9 and 10, 12 on October 11, 10 on October 12 and 13, and 8 on
October 14.

Geomagnetic activity forecast for the period August 31 to September
26, 2018 from F. K. Janda, OK1HH.

"Geomagnetic field will be: 
Quiet on September 2, 9, 17, 26
Quiet to unsettled on September 5 and 6, 10, 18, 24 and 25
Quiet to active on August 31, September 1, 8, 13 to 16, 18 to 20,
Unsettled to active on September 3 and 4, 7, 11 and 12, 23,
Active to disturbed on September 21 to 22

Solar wind will intensify on September (10 and 11,) 14 to 17, (21,)
22 to 24, (25)

- Parenthesis means lower probability of activity enhancement.
- Reliability of predictions remains low.

I was asking around why no one (actually, myself, though I
hesitated) foresaw an immediate massive disturbance roughly one week
ago. The answer is simple. In the analysis I neglected the freshest
evolution on the Sun, especially the development in the active area
2720, which was much closer to the southern prick of north coronal
polar hole than the previously dominant group 2719.

F. K. Janda, OK1HH"

Interesting article on the possible transition to cycle 25:

I found a possible source of confusion in the fourth paragraph of
that article, "the transition period from Solar Cycle 24 to Solar
Cycle 25 was deep and profound" should say Cycle 23 to Cycle 24. I
believe we are currently about to enter the transition to Cycle 25.

The latest from Dr. Skov:

"Dear Tad,

It comes as no surprise that I have mixed feelings about the
collision of Space Weather and terrestrial weather this past week.
On the one hand, aurora photographers got an unforgettable show over
the weekend, with aurora views that rivaled the best from the
biggest solar storms of this solar cycle. Indeed, the pictures are
mesmerizing. On the other hand, however, I find myself squirming
when I return to the moment I realized this solar storm was going to
be worse than my worst-case predictions.  The radio communications
blackouts and poor GPS reception were painful to watch unfold during
the largest hurricane to threaten Hawaii in more than 25 years.

In the end, everyone seems to agree that Hurricane Lane was a close
call. Luckily, it didn't make landfall, but its slow speed and
intensity was enough to cause massive flooding on the big island,
leaving some people stranded and without the comforts of home. Had
the situation been worse, amateur radio operators would have been a
life line of communications, while GPS-enabled search and rescue
drones would have done life-saving reconnaissance. Thank goodness
that was not necessary. I remember last year when Hurricane Irma hit
Puerto Rico, a set of extreme Space Weather events made amateur
radio communications and satellite phones nearly inoperable for a
week.  We dodged a bullet this time. But we cannot count on that.
With hurricanes and cyclones on the rise, there is little doubt that
a 'perfect storm,' in which Space Weather exacerbates an already bad
situation, will return sooner than we think.

In this week's forecast, I do my best to highlight the beauty of
this recent solar storm, but also the danger. As the weather quiets
down again and things return to "business as usual," I hope the
memory of this perfect storm remains. It may not be all that often
that Space Weather and Earth weather conspire like this, but when
they do, we need to be sure we're ready.

Cheers, Tamitha"

For more information concerning radio propagation, see the ARRL
Technical Information Service at For an explanation of
numbers used in this bulletin, see

An archive of past propagation bulletins is at More good
information and tutorials on propagation are at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for August 23 through 29, 2018 were 15, 29, 31, 26,
12, 11, and 0, with a mean of 17.7. 10.7 cm flux was 69.5, 72.4,
71.6, 71.1, 69.6, 69.8, and 70.5, with a mean of 70.6. Estimated
planetary A indices were 5, 5, 11, 76, 26, 10, and 6, with a mean of
19.9. Estimated mid-latitude A indices were 5, 7, 12, 34, 20, 9, and
7, with a mean of 13.4.


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