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ARRL Propagation Bulletin ARLP036 (2004)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 3, 2004
To all radio amateurs 

ARLP036 Propagation de K7RA

Thanks so much to Carl Luetzelschwab, K9LA who did a wonderful job
filling in and writing the bulletin last week. It was an excellent
piece, and you can read it in the archives of all our propagation
bulletins on the ARRL web site at,

Sunspot numbers and solar flux values declined this week compared to
last. The average daily sunspot number dropped by nearly 50 to 27.7
and the average daily solar flux was down over 23 points.
Geomagnetic activity increased on August 30 and 31. A moderate solar
wind stream sparked this.

Returning sunspot 649 has begun a transit across the solar surface.
It has shrunk in size, but, along with returning sunspot 656, is
expected to increase sunspot numbers and solar flux over the near

Solar flux is rising, and the predicted values for Friday through
Monday, September 3-6 are 100, 105, 110 and 115. Solar flux is
expected to peak around 130 on September 9. The planetary A index
predicted over September 3-6 is 15, 10, 10, and 10. The planetary A
index may rise higher around September 5 due to a solar wind stream
from a coronal hole, possibly producing unsettled to active
geomagnetic conditions.

The rising flux and sunspot numbers this weekend should be good news
for the All Asian DX Phone Contest this weekend, especially if
geomagnetic activity is quiet.

The days are getting shorter as the earth moves toward the Autumnal
Equinox on September 22. The long days in the far northern latitudes
are receding, so when there is geomagnetic activity, auroras are
more visible up north at nighttime. The start of Fall is a great
time for HF propagation, even past the peak of the cycle.

Just as we did a month ago, we should now look at the latest monthly
averages for daily sunspot numbers and solar flux, and compare them
with data from the past year. August's average daily sunspot number
was 69.6, and the average daily solar flux was 110. The monthly
averages show the steady decline of solar cycle 23.

The monthly average of daily sunspot numbers, October 2003 through
August 2004 were 118.9, 103.0, 75.7, 62.3, 75.6, 81.0, 59.3, 77.3,
77.0, 87.8 and 69.6.

The monthly averages of solar flux for the same period were 155.5,
140.8, 116.1, 114.1, 107.0, 112.1, 101.2, 99.8, 97.4, 119.8 and

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

Sunspot numbers for August 26 through September 1 were 44, 33, 28,
36, 30, 11 and 12 with a mean of 27.7. 10.7 cm flux was 97.5, 90.5,
87.2, 86.1, 89.9, 88.1 and 89.9, with a mean of 89.9. Estimated
planetary A indices were 7, 8, 12, 8, 34, 28 and 9, with a mean of
15.1. Estimated mid-latitude A indices were 4, 4, 6, 5, 27, 14 and
5, with a mean of 9.3.


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