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ARRL Propagation Bulletin ARLP031 (2010)

ARLP031 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7RA
Seattle, WA  August 6, 2010
To all radio amateurs 

ARLP031 Propagation de K7RA

Sunspot numbers and solar flux declined this week, with average
daily sunspot numbers down over 15 points to 20.3, and average daily
solar flux down nearly 4 points to 81.4.  These are the numbers from
last Thursday through this Wednesday, July 29 through August 5.

A new sunspot group emerged Wednesday, and three more appeared on
Thursday.  Sunspot numbers for Wednesday and Thursday were 27 and

Geomagnetic activity has been high, due to a coronal mass ejection
which hit Earth at 1710z on Tuesday, sending Wednesday's planetary A
index to 42, but Thursday's (August 5) only to 10.  The predicted
planetary A index for August 6-7 is 12 and 8, then 5 on August 8-10,
then back to 8 on August 11, and 5 again for August 12-21.

Geophysical Institute Prague expects active geomagnetic conditions
August 6, quiet to unsettled August 7, quiet August 8-9, unsettled
August 10-11 and quiet August 12.

In last week's (July 29) ARRL Letter we promised a comparison of
sunspot activity during sporadic-e seasons in recent years, but
neglected to include it in ARLP030.  Steve Daniel, NN4T had a
question about comparing sunspot levels during June and July since
the turn of the century.  The average sunspot numbers for those
months from 1999-2010 were 188.4, 213.9, 160, 165, 125.8, 82.5,
64.3, 23.5, 18.1, 2.7, 5.8 and 20.6.  You can see they were highest
of all in 2000, and have increased a bit since 2007.

Since July has passed, we can take another look at our three-month
moving averages for sunspot numbers.

The averages for the past year, centered on July 2009 through June
2010 were 4, 4, 4.6, 7.1, 10.2, 15.2, 22.4, 25.7, 22.3, 18.5, 16.2
and 20.4.

The monthly average sunspot numbers for January through July of this
year were 21.3, 31, 25.2, 11.2, 20, 18, and 23.1.

In recent activity, Bob Karpinski, WB8B of Clinton Township,
Michigan reports that with 5 watts CW he worked ZL2IFB on 10 meters
at 0040z on August 4.

Marty, K3PBU brought to my attention the fact that on the recent
propagation chart at at
the bottom of the page it says the prediction is based on a solar
flux of 123.  This is not right, and should be corrected soon.

Mike Schaffer, KA3JAW likes to chase broadcast television DX in
Tampa, Florida.  He posted a video at
showing an August 4 1725-1805z signal from Ontario on channel 2,
about 1300 miles away.  He feels the coronal mass ejection enhanced

Charley Shaffer, K7NW asked about the book "Rebels on the Air" by
Jesse Walker, and if that was really me as a teenager, described in
the opening to a chapter.  Yes, that was me at age 15.  I was WA7CSK
back then, and a volunteer at the little listener supported FM
broadcast station described in the book.

Next week I will be out of town and I've asked Tomas Hood, NW7US to
write the bulletin.  He is propagation editor for CQ Magazine, and
has a web site devoted to HF propagation at  If you are on Facebook, check out his
very useful propagation page by searching for "Space Weather and
Radio Resources at".

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 July 29 through August 4 were 31, 29, 12, 13,
17, 13, and 27 with a mean of 20.3. 10.7 cm flux was 84.6, 83.2,
81.5, 79.7, 79.1, 80.6 and 80.8 with a mean of 81.4.  Estimated
planetary A indices were 7, 7, 6, 4, 5, 20 and 42 with a mean of 13.
Estimated mid-latitude A indices were 5, 5, 4, 2, 5, 14 and 26 with
a mean of 8.7.


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