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ARRL Propagation Bulletin ARLP038 (2004)

ARLP038 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 38  ARLP038
From Tad Cook, K7RA
Seattle, WA  September 17, 2004
To all radio amateurs 

ARLP038 Propagation de K7RA

Solar flux and sunspot numbers rose over the past week. The average
daily sunspot number was over 20 points higher than the average for
the previous week, to 77.6. The highest sunspot count was 87 on
September 10 and 11, and before that, 95 on September 7. The daily
solar flux averaged 13 points higher at 119.1, and the highest
reading over the past two weeks was 131 on September 9.

Predicted solar flux for the near term is 110 for September 17-19,
and down to 100 by September 21-22. The predicted planetary A index
for the next few days is 20 and 15 for September 17-18, then around
10 for September 19-21. September 22-23 is supposed to be quieter.
The higher A index predicted for Friday, September 17 is because of
a weak coronal mass ejection. The high A index on September 14 was
from a solar flare coming out of sunspot 672 on September 12.
Currently sunspot 672 is squarely facing earth.

Dick Gird, K6PZE wrote a letter about conditions on 10-meters. He is
active on a 10-10 net in Southern California, and reports that
check-ins are down to near nothing due to the declining solar cycle.
Of course, interest in 10-meters isn't as high as it was during the
top of the cycle, when worldwide communication with modest power and
antennas ruled the day. But sometimes there are openings on
10-meters when you might not expect it. Even with the low solar
activity, the beginning of Fall should yield some openings, even
with modest sunspot numbers. If the sunspot number is around 80 for
a few days, next week shows good 10-meter propagation possible
between Richard's location in San Diego and Chicago, Illinois, for

Listen for the 10-meter beacons around 28.2 MHz and above if the
band sounds dead, or just give a call using your favorite mode.
Don't forget that right on 28.2 MHz the Northern California DX
Foundation operates a network of 18 precisely timed and power
controlled beacons around the world. A recently updated list of
10-meter beacons can be found on the web at,

The Autumnal equinox is less than a week away. This is a good time
for HF propagation, as the nights become longer in the northern
hemisphere and the hours of daylight are about equal all over the
world. Fall begins next Wednesday, September 22 at 1625z.

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

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 September 9 through 15 were 82, 87, 87, 85, 65,
70 and 67 with a mean of 77.6. 10.7 cm flux was 131, 130, 116.4,
114.6, 117.7, 114.7 and 109.6, with a mean of 119.1. Estimated
planetary A indices were 4, 5, 6, 4, 8, 28 and 14, with a mean of
9.9. Estimated mid-latitude A indices were 3, 1, 1, 1, 5, 17 and 9,
with a mean of 5.3.


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