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ARRL Propagation Bulletin ARLP034 (2010)

ARLP034 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 34  ARLP034
From Tad Cook, K7RA
Seattle, WA  August 27, 2010
To all radio amateurs 

ARLP034 Propagation de K7RA

As I was writing the bulletin overnight my desktop PC was hit by a drive-by
virus that downloaded itself automatically when viewing sunspot images on
an infected website.  Unable to remove the malware by morning, the bulletin
was rewritten on another PC, and some of the topics that were planned had
to be skipped for now.  The image was of a large sunspot in sunspot group
1084, from the New Solar Telescope at Big Bear Solar Observatory in
California.  The infected site was one of many news sites carrying the
image. provides a nice uninfected image file at

This week saw three days (August 21-23) with no sunspots, and the average
daily sunspot numbers for the week (August 19-25) declined over 28 points
to 8, compared to the previous week.  Average daily solar flux was down
more than 8 points to 75.3.  The last period of three days or more with
zero sunspots ended on May 20, 2010, around 100 days ago.

Sunspot group 1100 disappeared on August 21 and returned August 25. In this
case, the sunspot group didn't transit the non Earth facing side of the
sun, but it just faded from view, returning just as it is about to rotate
off of the sun's western limb.  Sunspot group 1101 appeared on August 24,
and on August 25 had grown to three times its initial size.  Daily sunspot
numbers for August 24-26 were 11, 23 and 23.

Remember that the sunspot number is not the same as the number of sunspots.
The smallest non- zero sunspot number is 11, and gets 10 points for being a
sunspot group, and one point for containing one sunspot.  The sunspot
number of 23 on August 25-26 represents two sunspot groups, at ten points
each, one containing one sunspot (1 point) and the other containing two
sunspots (2 points).  On August 25 it appears that a new smaller sunspot
may be emerging between the eastern horizon and sunspot group 1101.

A stiff solar wind from a coronal hole increased geomagnetic activity, and
the planetary A index for August 21-26 was 3, 4, 7, 18, 20 and 11.  The
latest projection shows this decreasing, with the planetary A index on
August 27-28 at 10 and 8, followed by a quiet reading of 5 until September
19.  Solar flux for the same period is expected to be 75 for August 27 to
September 3, then 85 on September 4-5.  Several weeks from now is the fall
equinox, which is a good time for HF propagation.  The autumnal equinox
will be at 0309 UTC on September 23, 2010.

David Moore of Morro Bay, California sent in another article about the weak
sun and solar conveyor belt, this time from the National Science
Foundation.  Read it at

Jeff Hartley, N8II of Shepherdstown, West Virginia sent this on August 23:
"Lots of great over and near-the-pole propagation was a daily occurrence on
17 and 20 meters since Thursday the 19th here.  The RDA Russian contest was
a blast with many new Russian vanity calls in many areas of Asia worked
here.  It's interesting to note that around 0100 local (2100Z) in European
Russia there was a nice opening from UA1 to UA6 into here on 20 meters,
whereas only UA6 was workable in the 2-3 hours before that.  I love the
calls like RG8U, RG6G, R7AA, R9DX, etc.  Around 0140Z I actually had a very
nice run of Russian Asians from Zone 17-18 at around 80-100 per hour for
about 25-30 minutes.  UA0YAY in Zone 23 was loud on CW.  Signals from the
big guns were S9+.  17 meters has been open daily to SE Asia around
1300-1430Z.  Over the past few days I have heard YB4IR, and worked VR2XMT,
9M6NRO, 9V1DE, UA0SV and some JAs, most with good signals.  15 was pretty
punk until today when a few Europeans were finally heard around 1500Z".
If you would like to make a comment or have a tip for our readers, email
the author 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  Find more good
information and tutorials on propagation 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 19 through 25 were 11, 11, 0, 0, 0, 11, and 23
with a mean of 8.  10.7 cm flux was 77.9, 77.1, 75.5, 74.6, 74.9, 73.6 and
73.5 with a mean of 75.3.  Estimated planetary A indices were 5, 4, 3, 4,
7, 18 and 20 with a mean of 8.7.  Estimated mid-latitude A indices were 3,
1, 3, 0, 5, 13 and 15 with a mean of 5.7.


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