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ARRL Propagation Bulletin ARLP031 (2013)

ARLP031 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7RA
Seattle, WA  August 2, 2013
To all radio amateurs 

ARLP031 Propagation de K7RA

The weekly averages of daily sunspot numbers and solar flux barely
changed at all compared to the previous week.  Average daily sunspot
numbers went from 73.4 to 79.6, while average daily solar flux
decreased from 110.6 to 109.7.
The weak peak of this solar cycle continues.  We are moving toward
the fall season, which is always seasonally better than summer for
HF propagation.  Let's hope for a rise in solar activity to
complement the seasonal change.
The latest prediction from NOAA/USAF for the near term has solar
flux at 115 on August 2-3, 110 on August 4-6, then 115, 120 and 115
on August 7-9, 105 on August 10-12, 100 on August 13, 105 on August
14-18, 100 on August 19-24, and 125 on August 25.  Flux values hit a
minimum around 100 on September 3-4, and rise to a peak of 135 on
September 11-12.
Expected planetary A index is 8, 12 and 8 on August 2-4, 5 on August
5-8, 8 on August 9-10, 5 on August 11-20, then 10, 15 and 10 on
August 21-23, 5 on August 24-26, 10 on August 27, 15 on August
28-31, 8 on September 1, and 5 after September 1.
Petr Kolman, OK1MGW presents a weekly geomagnetic prediction from
the Czech Propagation Interest Group.  He predicts active to
disturbed conditions for today, August 2, quiet to active August 3,
quiet to unsettled August 4, mostly quiet August 5, quiet to
unsettled August 6-7, mostly quiet August 8-11, quiet August 12-13,
quiet to active August 14-15, quiet to unsettled August 16-18,
mostly quiet August 19-20, quiet to active August 21-22, and mostly
quiet August 23-24.  Petr says that growth in the solar wind may
cause remarkable changes to the magnetosphere and ionosphere on
August 2-3 and 14-16.
NASA released their monthly solar cycle prediction, and there is no
change from last month.  You can read it at
At the beginning of each month we take a look at the latest numbers
from our 3-month moving average of daily sunspot numbers.  We do not
see any upward trend.  We see two peaks, one toward the end of 2011
and another smaller peak this spring.  In 2011, the 3 month periods
centered on October and November had average daily sunspot numbers
of 118.8 and 118.6.  This spring the 3-month periods centered on
April and May had averages at 106.4 each.  Could these be the
double-peaks of solar activity that some have predicted for this
sunspot cycle?
The 3-month moving averages of daily sunspot numbers centered on
January through June 2013 were 73.6, 80.7, 85.2, 106.4, 106.4, and
97.5.  Just to clarify, the 3-month period centered on June includes
sunspot numbers for all of the 92 days from May 1 through July 31.
The sum is 8,970.  Divide that total by 92, and the result is
exactly 97.5.
Jon Pollock, K0ZN of DeSoto, Kansas reported 17 meter observations
in last week's bulletin ARLP030, and this week has another report.
He wrote, "I won't keep reporting this, but I thought this was again
instructive since I am seeing this so frequently lately.  On Friday,
July 26 I was up late and again decided to give 17 meters a try at
Midnight CST.  Again 17 meters was very quiet, no signals at all.
i.e.  'Dead'.  Except that I heard some weak thunderstorm crashes in
the background.  My experience has been that often when you hear
that, the QRN source is a long way away.  I called CQ about five
times (400 watts CW into a ground mounted vertical with a large
radial system) and VK7CW in Burnie, Tasmania came back (now about
12:15 AM CST) with a nice signal, about S-6.  He was running 100
watts to a hexbeam.  We ended up having a rag chew, and ours were
the only signals either one of us could hear on the band over a
9,380 mile path from Eastern Kansas.  Again, 17 meters is more often
than not open when it seems dead, often for long haul contacts."
Rick Lindquist, WW1ME sent a link to yet another article about the
current solar cycle being the weakest in one-hundred years.  It also
mentions a July meeting of the American Astronomical Society Solar
Physics Division, which was in Bozeman, Montana.  You can read the
article at  
The American Astronomical Society promises to have downloadable
presentation files from the meeting, but nothing yet.  They will be
posted at

For more information concerning radio propagation, see the ARRL
Technical Information Service at  For an explanation of
the 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 25 through 31 were 71, 58, 64, 68, 97, 105,
and 94, with a mean of 79.6.  10.7 cm flux was 106.9, 109.5, 107.9,
109.4, 112.1, 113.1, and 108.7, with a mean of 109.7.  Estimated
planetary A indices were 11, 14, 11, 7, 6, 6, and 5, with a mean of
8.6.  Estimated mid-latitude A indices were 10, 23, 10, 8, 7, 6, and
5, with a mean of 9.9.


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