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ARRL Propagation Bulletin ARLP013 (2005)

ARLP013 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 13  ARLP013
From Tad Cook, K7RA
Seattle, WA  April 1, 2005
To all radio amateurs 

ARLP013 Propagation de K7RA

We saw a decline this week in average daily sunspot numbers and
solar flux. Average daily sunspot numbers were down over 10 points
to 34.1 when compared to the previous week, and average daily solar
flux declined almost 12 points to 80.2.

The short term prediction shows solar flux values rising slowly over
the next week, reaching 100 around April 8. The planetary A index
should rise over the next few days. The predicted planetary A index
for April 2-5 is 15, 25, 35 and 20.

Just completed is the first quarter of 2005. Now is a good time to
take some running averages of sunspot numbers and solar flux,
comparing this quarter to previous periods.

From the first quarter of 2003 through the first quarter of 2005,
the average daily sunspot numbers were 120.3, 107.3, 110.2, 99.2,
72.9, 71.3, 69.3, 61 and 46.1.

The average daily solar flux for the same period was 134.3, 124.2,
120.8, 137.4, 111.1, 99.5, 111, 104.8 and 96.4.

We see clearly that cycle 23 continues the fall toward solar
minimum, which is currently forecast roughly around October 2006 to
April 2007. Fortunately, the rise of a solar cycle is much more
rapid than its decline. But when comparing current smoothed sunspot
numbers to the predicted numbers once the next cycle turns up, the
predicted value for April 2005 is just slightly above the predicted
value for December 2007. So we shouldn't expect conditions to
improve beyond what we've had recently until early 2008, or a little
less than three years from now. Current sunspot numbers are lower
than they've been since 1997. The peak of the next cycle will
probably occur in 2010.

March 1965 was 40 years ago. I was still twelve years old, and when
riding the school bus home one day in that March, I saw that my mom
had hung her red sweater in the window. That was my signal. I
couldn't wait for the bus to drop me off so I could race back up the
hill. I ran into the house, grabbed the envelope from the FCC off
the dining room table, and ripped it open. Inside, there was my new
Novice call, WN7CSK. Hard to believe it's been 40 years.

If you would like to comment or have a tip, email the author at,

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at,

Sunspot numbers for March 24 through 30 were 57, 65, 41, 35, 15, 15
and 11 with a mean of 34.1. 10.7 cm flux was 87.1, 82.1, 77.7, 78.4,
79.7, 78.8 and 77.6, with a mean of 80.2. Estimated planetary A
indices were 6, 18, 16, 13, 4, 5 and 9 with a mean of 10.1.
Estimated mid-latitude A indices were 4, 15, 12, 8, 2, 3 and 6, with
a mean of 7.1.


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