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ARRL Propagation Bulletin ARLP033 (2013)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 16, 2013
To all radio amateurs 

ARLP033 Propagation de K7RA

Again this week, solar activity was unchanged, with average daily
sunspot numbers slipping from 85.4 to 85, and average daily solar
flux increasing 4.4 points to 111.7.  Geomagnetic conditions were
The latest solar flux prediction from USAF/NOAA has flux values of
125 on August 16, 130 on August 17-18, 120 on August 19-20, 110 on
August 21-23, 105 on August 24, 110 on August 25-26, 115 on August
27-29, 110 on August 30, 105 on August 31 through September 6, then
110 and 115 on September 7-8 and 120 on September 9-11.
Predicted planetary A index is 12 and 8 on August 16-17, 5 on August
18-19, then 12 and 15 on August 20-21, 8 on August 22-23, 5 on
August 24-30, then 12, 15, and 10 on August 31 through September 2,
and 5 on September 3-7.
OK1HH issues his own weekly geomagnetic activity forecast, and he
sees mostly quiet geomagnetic conditions August 16-17, quiet to
active August 18, quiet on August 19, mostly quiet August 20, quiet
August 21, active to disturbed August 22, quiet to unsettled August
23, quiet to active August 24, quiet to unsettled August 25-28,
quiet August 29-30, active to disturbed September 1, quiet to
unsettled September 2, quiet on September 3-5, mostly quiet
September 6-8, active to disturbed September 9, quiet to active
September 10, and active to disturbed September 11.  OK1HH says "a
positive storm phase" is expected August 22, and a growing solar
wind may cause remarkable changes in the magnetosphere and
ionosphere on August 16, and 21-22, and September 1-2, 6-7, and 11.
At 0318 UTC on August 16, the Australian Space Forecast Centre
issued a geomagnetic warning, saying a high speed wind stream is
spewing from a coronal hole.  Unsettled to active geomagnetic levels
are expected today, August 16, and minor storm levels are possible.
Scientific American has a 60 second podcast explaining why the
changing magnetic polarity of the sun is nothing to worry about.
Listen at
We get our solar flux data directly from the observatory in
Penticton, British Columbia where they measure and report the
numbers.  It has been available at
but this week that server seemed unreachable.  I poked around for
quite some time and finally found the same data in html rather than
plain text format at
Al Kaiser, N1API of Meriden, Connecticut asked, "If you have two
flares at the same time from two different sunspot areas on the sun,
do they add up to give a bigger class of flare, or just end up as
one longer event?"
They are counted and rated separately.  And if the flares are on
different areas of the sun, they are probably pointing in different
directions, so one or both might not affect earth.
Randy Crews, W7TJ of Spokane, Washington has long been fascinated by
the idea that the current solar cycle 24 may turn out to have two
peaks, like the last few cycles.  He writes, "There have been
several predictions that cycle 24 might have a second peak.  Well
maybe - maybe not.  Cycle 21 had a definite single peak:  November
of 1979.  Cycle 22 had two peaks:  September of 1989 and January of
1991.  Cycle 23 also had two peaks:  April/July of 2000 and December
of 2001.  K9LA presented some interesting analysis regarding the
declining magnetic strength of sunspots since 1995 and especially
cycle 24."  See
Randy continues, "Anyone who brings up a NASA photo of sunspots
during Cycle 21-23 will see many large magnetically complex sunspots
vs. Cycle 24's 'freckles' of small magnetically simple spots.  So we
MAY see a second peak IF the magnetic strength of the sunspots
holds, or better yet increases.  If not, a second peak is doubtful,
and chances are the peak of activity has passed (as defined by the
average monthly solar flux and average monthly sunspot count).  The
Sun is always full of surprises.  During the CQWW Contest of October
2003 the solar flux punched up to 290!"
Ah, Randy, wouldn't that be nice to see again!  In fact, your
current author's stewardship of this bulletin began in 1991, not
because of any particular expertise regarding astrophysics, but due
to a similar sudden burst of solar activity, which happened to
coincide with the former (and only other) author of this bulletin
becoming too ill to write (see
The event was Thursday, January 31, 1991 when the solar flux reached
357.  Someone needed to write about this.  I had no idea when I
alerted folks in Newington that it would be me.
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 August 8 through 14 were 90, 51, 76, 90, 85, 98,
and 105, with a mean of 85. 10.7 cm flux was 104.4, 103.6, 102.5,
110.4, 114.1, 122, and 125.2, with a mean of 111.7.  Estimated
planetary A indices were 5, 9, 6, 6, 6, 9, and 10, with a mean of
7.3.  Estimated mid-latitude A indices were 4, 11, 7, 7, 6, 9, and
9, with a mean of 7.6.


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