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ARRL Propagation Bulletin ARLP028 (2018)

ARLP028 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7RA
Seattle, WA  July 13, 2018
To all radio amateurs 

ARLP028 Propagation de K7RA

As of Thursday, July 12, there have been no sunspots visible for 16
days consecutively. pointed out that to find an equally long stretch of
no sunspots, we have to look back to November 2009 when we were
emerging from the deepest solar minimum in a century.  At the lowest
of the low activity in 2008, the sun was blank for 52 consecutive
days, they reported, and that seems to be from July 21, 2008 through
September 10, 2008, as shown here:

However my own record shows a slight break in that period, with a
sunspot number of 11 on August 21 and 22, 2008.  Where did I get
this, nearly ten years ago?  Although NOAA did not report this (as
seen in the link above), did.  If you look in their
archive for those dates, you will see it reported.  They
characterized it as a "relatively small spot".

I asked Dr. Tony Phillips of about this, and he
replied:  "Good point!  To get those 52 days, I went through the
official NOAA sunspot records and ironically did not check  They might have considered the 'spot a "pore" and
not a fully developed sunspot.  At any rate, the overall picture is
still the same:  If this solar minimum is anything like the last
one, we will eventually look back on 15 day stretches of
spotlessness as relatively brief intervals."

Was it so small that NOAA didn't record it?  It was there for two
days, so I decided to include it in my record.  My personal record
of solar flux and sunspots is preserved and updated in the Solar
Data Plotting Utility created by Scott Craig, WA4TTK:

Note he has a recent update for the data, and you can continue to
automatically update your copy weekly using a copy of this bulletin.

Although there were no sunspots last week, we did see an increase in
solar flux, from an average of 68.2 in the previous week to 71.5 in
the July 5 to 11 period.  This is not a large difference.

Average daily planetary A index increased from 4 to 7.3, while
average daily mid-latitude A index increased from 4 to 7.9.

Predicted solar flux is 72 on July 13 to 19, then 73, 74, 72, 72,
and 70 on July 20 to 24, then 68 on July 25 through August 2, 70 on
August 3, 72 on August 4 to 6, 74 on August 7, 76 on August 8 to 16,
then 74, 72, 72, and 70 on August 17 to 20, and 68 on August 21 to

Not long ago I thought sunspots may return by July 17 to 19, when
solar flux was predicted to rise to 80, but after July 7 that more
optimistic forecast was scaled back to what we have now.

Predicted planetary A index is 5 on July 13 to 19, then 15, 8, 10,
18 and 8 on July 20 to 24, then 5 again on July 25 through August 4,
then 12 and 8 on August 5 and 6, 5 again on August 7 to 10, 16 and 8
on August 11 and 12, 5 on August 13 to 15, then 15, 8, 10, 18 and 8
on August 16 to 20, and 5 on August 21 to 26.

Franta, OK1HH is back with his geomagnetic forecast after his
previously announced absence:

"Geomagnetic activity forecast for the period July 13 to August 8,

Geomagnetic field will be: 
Quiet on July 13, 25 to 29, August 6 
Quiet to unsettled on July (15 to 18, 21,) 30 and 31, August 4 
Quiet to active on July 20, 23, August 1, 3, (5, 7 and 8) 
Unsettled to active on July (14, 19,) 24 
Active to disturbed on July 22, August 2 

Solar wind will intensify on July 13 to 15 and 20 to 23 

- Parenthesis means lower probability of activity enhancement. 
- Beware of paraskavedekatriafobia today!"

OH6BG has created a VOACAP tool for WRTC 2018, currently in progress:

Also see:

Also this weekend, the IARU HF Championship:

Paul Merrill, W7IV of Templeton, California wrote:  "So, what do you
think about all the theories of 6m propagation in light of this
fantastic summer and the new mode of FT8?  Was this propagation
around all along and we just didn't have the gain or sensitivity to
make use of it?"

I'm certain this is the case.  FT8 is amazingly powerful, and
seemingly has the ability to peel back layers of noise and
uncertainty that human ears cannot.

On July 8, Dr. Skov wrote:

"Dear Tad,

After nearly two weeks of quiet, our Sun graces us with a much
needed boost in activity.  I took this bit of down time to celebrate
the American fourth of July with family, and to reflect on where the
fireworks of the Sun will lead us once we pass through this solar
minimum. I have some ideas.  In the coming several weeks, I will ask
for voluntary feedback on my Patreon project, set for pre-launch
later this month.  I want to ensure I am creating content that most
suits your needs and leads us in the right direction as a community
towards the future.  Your participation means the world to me.

The forecast this week is a bright one.  We have two solar storms,
albeit weak ones, on their way to Earth now.  With some luck, they
will bring aurora down to high-latitudes and possibly even lower! 
We also have a returning active region (that will likely be numbered
2716), which has already boosted solar flux back into the marginal
levels for radio propagation.  It is a low-level flare producer, but
GPS users shouldn't worry, reception should remain decent on Earth's
day side, and at low latitudes, thanks to the weak influence of
these solar storms.  However, GPS reception might get just a little
glitchy near aurora and around dawn and dusk.  Be sure to enjoy the
conditions while they last!

Cheers, Tamitha"

Max White, M0VNG sent this interesting article about tubes of plasma
in the sky:

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 July 5 through 11, 2018 were 0, 0, 0, 0, 0, 0,
and 0, with a mean of 0.  10.7 cm flux was 68.1, 70.5, 72, 71.6,
72.9, 72.1, and 73.3, with a mean of 71.5.  Estimated planetary A
indices were 17, 7, 5, 4, 3, 7, and 8, with a mean of 7.3.
Estimated mid-latitude A indices were 11, 8, 6, 6, 5, 11, and 8,
with a mean of 7.9.


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