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ARRL Propagation Bulletin ARLP036 (2008)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  August 29, 2008
To all radio amateurs 

ARLP036 Propagation de K7RA

Our Sun is still very quiet, but last week's Propagation Forecast
Bulletin ARLP035 mentioned a new sunspot emerging on August 21-22. showed the sunspot number on those days as 11,
which is the smallest non-zero sunspot number.  Because of the way
the daily sunspot number is calculated, one sunspot gets ten points
for one group, and one point for one sunspot within that group.
Five sunspots in three groups yields a daily sunspot number of 35.

But the official sunspot number from NOAA showed zero on both days.
You can see it for yourself at,  It seems that this
little spot that tried to emerge never grew large enough to be
counted as a sunspot.  Instead it was just a little magnetic
wrinkle, but one interesting aspect was the polarity indicated a
Cycle 24 event, not Cycle 23 as we reported last week.  John
Andrews, W1TAG of Holden, Massachusetts wrote, "Your current report
on the ARRL website indicates that the tiny sunspot presently
visible is from the old solar cycle. The current Mt. Wilson
magnetogram data shows a dipole with the south pole leading the
north, which in the northern hemisphere indicates a new cycle spot."

In a subsequent message, John wrote, "On the other hand, those of us
playing at 505 and 137 kHz are quite delighted with the quiet Sun! A
little kick every now and then to recharge the supply of free
electrons, and we're all set. The transatlantic stuff is MUCH easier
than it was 4-5 years ago.  Oh well, the pendulum will swing the
other way with a vengeance, I'm sure. Then you'll be happy, and I'll
be sad."

If we don't see any sunspots this weekend, Sunday will mark 42
consecutive days with no sunspots.  This will also bring the 3-month
moving average for daily sunspot numbers (that we present monthly)
clear down to 1.76, the lowest on this side of Cycle 23.  This would
be the three month average centered on July.

That makes the 3-month moving average for the past 14 months look
like this:

Jun 07 18.7
Jul 07 15.4
Aug 07 10.2
Sep 07  5.4
Oct 07  3
Nov 07  6.9
Dec 07  8.1
Jan 08  8.5
Feb 08  8.4
Mar 08  8.4
Apr 08  8.9
May 08  5
Jun 08  3.7
Jul 08  1.8

We calculated the July 2008 average by adding together all daily
sunspot numbers from June 1 through August 31, then dividing by 92,
the number of days in that period.  Likewise, the June 2008 average
used the sum of all sunspot numbers from May 1 through July 31.

You can see why many thought the minimum was last October, but we've
instead reached a new low for the recent period.

The forecast for the next week is a planetary A index of 5 on every
day, indicating more of the same quiet and stable geomagnetic
conditions.  The prediction for September 5 is a planetary A index
of 18, probably from a recurring coronal hole and associated solar

Geophysical Institute Prague predicts quiet conditions August 29 to
September 3, and quiet to unsettled September 4.

Jim Henderson, KF7E of Queen Creek, Arizona notes that over the past
few days (August 25-27) at 1400z-1600z during his local morning
hours, conditions on 20 meters to Europe, across UA3/4/9/0 and Asia
have been great.  With no sunspots, he sees good effects from solar
wind streams energizing these paths.

But on Thursday, August 28 he noted an upswing in solar wind at, and reinforced the
observation with data at,  This caused a
decline in conditions, but at 1445z he noted copyable signals from
EY8/K4ZW in Tajikistan on 14.2176 MHz.  He noted that HS0ZEE (Chiang
Mai, Thailand) seemed to be coming strongest from the northeast, 90
degrees away from normal headings and with pronounced echo and rapid
auroral flutter.

Randy Crews, W7TJ of Spokane, Washington, offered this on August 27
in a message titled "Bumping along the bottom":

"I see we have been spotless now for 37 straight days, which I think
exceeds the number of spotless days in October of 2007 and could
possibly exceed the 6 week period of spotless days we had in
Sept/Oct of 1996. Possibly this month could set a double minimum in
Cycle 23. One thing that has really helped the Bands in the last few
days along with A and K indices of 0-2 is that the Sun is void of
any Coronal disturbances....BIG difference!  If we could get some
Cycle 24 spots, we would surely be off and running!  As it has been
said, it's darkest just B4 dawn."

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 a detailed
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 this
bulletin are at

Sunspot numbers for August 21 through 27 were 0, 0, 0, 0, 0, 0, and
0 with a mean of 0.  10.7 cm flux was 67.1, 67.6, 67.9, 67.1, 66.6,
66.9, and 66.6 with a mean of 67.1.  Estimated planetary A indices
were 4, 4, 2, 4, 2, 3 and 3 with a mean of 3.1.  Estimated
mid-latitude A indices were 4, 2, 2, 2, 1, 1 and 2 with a mean of 2.


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