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ARRL Propagation Bulletin ARLP018 (2010)

ARLP018 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  May 7, 2010
To all radio amateurs 

ARLP018 Propagation de K7RA

Sunspots made a strong return this week, and so did geomagnetic
activity.  Average daily solar flux increased 4.2 points to 79.6,
and on Wednesday, May 5 the daily sunspot number reached 77, the
highest in nearly four years.  The sunspot number hasn't been as
high since May 28, 2006, when it was 78.

Last Friday, April 30, sunspot group 1064 appeared, and then faded
after the third day.  On Sunday groups 1065, 1066 and 1067 appeared,
and the next day 1063 made a reappearance, along with new group
1068.  1069 arose on May 4 and 1065 disappeared. 1070 appeared on
May 5.  1069 grew quickly, and the sunspot number rose from 61 to 70
and then 77 on Wednesday, but dropped to 45 on May 6, when 1066 and
1077 disappeared.

Solar flux rose steadily from 76.2 on April 29 to 83.2 on May 5, but
dropped over four points to 79.1 on May 6.  NOAA and USAF predict
solar flux to decline over the next few days, with the May 7-10 flux
values at 78, 76, 75, and 75.  This probably indicates another short
quiet period with little or no sunspot appearances.

A look at the STEREO mission image at
on Friday morning shows no bright spots (indicators of magnetic
activity and sometimes sunspots) coming up.  STEREO achieved 89%
coverage on May 6, and is expected to reach 90% on June 18, 2010.
Expect 95% coverage by October 12.

Along with increased sunspots came rising geomagnetic activity.  The
peak days were Sunday and Monday, when the planetary A index was 39
and 27, and the K index went as high as six over several three-hour

NOAA and USAF predict planetary A index for May 7-13 at 9, 12, 12,
8, 8, 5 and 5.  Geophysical Institute Prague predicts quiet
conditions for May 7, unsettled May 8, quiet to unsettled May 9-10,
unsettled May 11, and quiet May 12-13.

Now that April has ended, we can look at sunspot averages for the
past month and the past three month period.

Average daily sunspot number for April was only 11.2, down from
21.3, 31 and 25.2 for January through March.  The three-month moving
average centered on March was 22.3, close to the averages of 22.4
and 25.7 centered on January and February.

Look on page 10 of the NOAA Space Weather Operations Preliminary
Report and Forecast for May 4 at,  It shows the
current sunspot cycle peaking at a smoothed value of 90 in February
through July 2013.  Also note how the monthly sunspot numbers this
year as reflected in the graph decline from the projected values.

Tomas David Hood, NW7US, who edits the Propagation column in CQ
Magazine, has a propagation resource at
He also has a Facebook page that features frequent reports and
comments on solar activity and propagation.  On Facebook do a search
for "Space Weather and Radio Resources at"

Bob Kile, W7RH had a comment regarding this week's increasing
sunspot activity.  He writes, "Shucks Tad, I really enjoyed the last
minimum of 2007-2010. The activity level on 160m was superb and
conditions were fantastic even out west!"

Bob has been quite happy with the low solar activity and quiet
geomagnetic conditions over the past few years, as his main interest
is 160 meters.  He lives in Las Vegas, but operates a 160 meter HF
remote base station in a remote quarter of Northern Arizona.  Bob
has planted acres of antennas and controls the station remotely.  It
sits on a 20 acre piece of land that he purchased at a popular
online auction site.  See for
pictures and info.

Bill Echols, NI5F of Jackson, Mississippi had a comment on the 70
MHz propagation in Europe (where it is an amateur band) and aircraft
traffic, contrails, and volcanic ash.  Bill writes, "It very well
may be that jet contrails provide the normal mechanism for enhanced
70-MHz paths rather than the jet itself. Many years ago it was noted
in England that the U.S. stealth aircraft could be detected after
the fact by scanning for the moisture in jet contrails between
55-MHz and 70-MHz and comparing that 'signature' against the normal
metallic returns; obviously, if there had been stealth aircraft
during the observation window, the number of contrail returns would
be higher than the metallic returns."

"The jets on our stealth aircraft were modified in classified ways
to minimize, and in most cases, eliminate this method of detection.
I actually remember seeing something about this in amateur
literature once; if I remember correctly, it was in an RSGB
periodical somewhere in the early 1990s."

Robert Steenburgh, KA8JBY of Houston, Texas says that the annual
Space Weather Workshop at the Space Weather Prediction Center
concluded a week ago, and soon material presented there will be
available on the web at,  There is
also a link to past conferences, where there are slides and other
material presented from 1999-2009.  Until his recent retirement
Robert worked as the US Air Force Liaison to the Space Weather
Prediction Center in Boulder.  Now he is in Houston working for
NASA's Space Radiation Analysis Group, which has a web site 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 web page at, For an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is 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 April 29 through May 5 were 0, 12, 13, 47, 61,
70, and 77 with a mean of 40. 10.7 cm flux was 76.2, 78.6, 77.8,
79.5, 80.3, 81.7 and 83.2 with a mean of 79.6. Estimated planetary A
indices were 6, 4, 4, 39, 27, 10 and 8 with a mean of 14. Estimated
mid-latitude A indices were 4, 2, 1, 18, 19, 7 and 6 with a mean of


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