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ARRL Propagation Bulletin ARLP037 (2004)

ARLP037 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7RA
Seattle, WA  September 10, 2004
To all radio amateurs 

ARLP037 Propagation de K7RA

Sunspot numbers and solar flux rose over the past week. The average
of the daily sunspot number for this week compared to the earlier
seven days rose nearly 30 points to 57. Average daily solar flux was
up over 16 points to 106.1. Solar flux is predicted to rise over the
next few days. Predicted solar flux is 135 for Friday, September 10,
and is expected to remain around 140 for the next four days or so.
Fortunately, the planetary A index is expected to remain low, with
predicted values over the weekend, from September 10-13 at 5, 8, 8
and 10.

Bill Burrows, WA7NCL wrote in this week saying he likes to use the K
index as an indicator of whether conditions will be good when he
wants to operate. You can get the current mid-latitude K index from
Boulder via WWV, and it is updated every three hours.

The broadcast is at 18 minutes past each hour on WWV and 45 minutes
after the hour on WWVH. You can also hear it on the phone any time
at, 303-497-3235, or on the web at, I checked it just now,
and the mid-latitude K index at 0600z on September 10 was 0. It
doesn't get any quieter than that.

Bill sent along a great resource for predictions of the K index. It
is from NOAA, and is on the web at There are several
text links on the left of the page for the predictions and also some
graphs for comparing recent predictions with actual conditions. The
prediction itself is on the text link called "Output List." Ideally,
we would like to see a low K index along with higher sunspot and
solar flux values.

This weekend is the Worked All Europe DX Contest. Conditions should
be good. And don't forget the autumnal equinox in less than two
weeks. As we approach Fall, HF propagation will be getting
seasonally better.

If you would like to comment or have a tip, email me 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 2 through 8 were 25, 25, 28, 59, 82,
95 and 85 with a mean of 57. 10.7 cm flux was 93.9, 96.7, 99.3,
103.2, 106.5, 118.9 and 124.5, with a mean of 106.1. Estimated
planetary A indices were 9, 3, 4, 7, 14, 16 and 9, with a mean of
8.9. Estimated mid-latitude A indices were 8, 1, 2, 5, 9, 11 and 4,
with a mean of 5.7.


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