ARLP037 Propagation de K7RA:
September 10, 2004

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.