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ARRL Propagation Bulletin ARLP007 (2004)

ARLP007 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 7  ARLP007
From Tad Cook, K7RA
Seattle, WA  February 13, 2004
To all radio amateurs 

ARLP007 Propagation de K7RA

Solar flux and sunspot numbers were up slightly this week, and
average planetary A index was down a little.  Unfortunately, this
isn't likely a trend, at least over the long term.  The NOAA SEC
Preliminary Report and Forecast for February 10 (at still shows us a few
years past the peak of Cycle 23 and a few years until the bottom.
These charts are on pages 13 and 14.  Note the forecast still shows
the 10.7 cm solar flux minimum (a measure of energy at 2.8 GHz)
predicted for September 2006 through April 2007, and the sunspot
number minimum around December 2006 through January 2007.  Note that
a year from now we might see half the sunspots we see now, and the
next cycle isn't predicted to be back to the February 2005 level
until the end of 2007.  These are all guesses based on past cycles,
and the numbers are smoothed using a moving average.  We won't know
when the cycle minimum occurred until several years after it has

Over the next few days expect solar flux to stay around 110, then
gradually decline toward 100, where it should stay until around
February 22.  Due to a coronal hole and a solar wind stream,
geomagnetic conditions should remain unsettled to active.

Mike Caughran, KL7R asked about lousy 40 and 80 meter conditions in
Alaska during periods of high geomagnetic activity.  He has never
been active during a complete solar cycle, but recalls years ago as
a Novice working 80 meter CW all night long under quiet conditions.
(Note that at his QTH in Juneau, tonight will be 15 hours long and
around Christmas, it was nearly 18 hours from sunset to sunrise).
He thought perhaps by now the sun would have quieted down, and asks
when the lower HF frequencies will return to normal.

Normally geomagnetic conditions are quite active after a peak in the
sunspot cycle, although this time it seems to be holding up quite
long.  It should turn down some time soon, but there is really no
way to know exactly when.  Any guesses are based on past solar
cycles.  If you look at the link to the NOAA SEC site above, on page
15 you'll see a graph of planetary A index, an average of
geomagnetic indices from around the world.  The graph shows the past
ten years, and note that at the sunspot cycle peak around 2000 the
progression of the planetary A index was just getting ramped up.
Studying the graph, we can see that if the previous solar cycle
peaked around 1990-1991, the dramatic drop in Ap index must have
occurred about 3-4 years later.  Based on that, perhaps we are on
the way down already.  Just like with the peak or bottom of the
solar cycle, we won't know until it has passed and can study the

By the way, the gentleman who asked the question this week has a
nice page at that is largely devoted to
QRP.  Don't miss KL7R's photo of a QRP transceiver he built inside a
Microsoft mouse.

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the Propagation page on the
ARRL Web site at

Sunspot numbers for February 5 through 11 were 109, 98, 92, 74, 81,
78 and 91 with a mean of 89.  10.7 cm flux was 105.5, 106.7, 111.1,
116.2, 117.8, 116.5 and 114.2, with a mean of 112.6.  Estimated
planetary A indices were 14, 21, 11, 8, 8, 9 and 26, with a mean of


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