ARLP034 Propagation de K7RA:
August 22, 2003

Propagation Forecast Bulletin 34 ARLP034
From Tad Cook, K7RA
Seattle, WA August 22, 2003
To all radio amateurs

ARLP034 Propagation de K7RA

Sunspot numbers down 19%, solar flux down 7%, and the planetary A index up 42%; Could it be any worse for HF operators? Well yes, it could, but those percentages reflect the change in average daily indices from last week to this week. What could be worse of course are zero sunspots with solar flux around 70 or lower, which is what we were seeing about seven years ago at the bottom of the solar cycle.

For an example of this, look back to Propagation Forecast Bulletin ARLP042 dated October 11, 1996 at The sunspot number was a flat 0 for every day of that week, and average solar flux was 68.6.

What does that mean for HF propagation? Run the free W6ELprop software available from Run one copy for August 22 with a solar flux of 68.6, and another copy with a flux value of 121.7. In my comparison, in each instance I ran a path from Dallas to Germany. The signal strength on the path with the lower values showed about the same signal levels for 40 meters, but the path reliability rating was much lower. Looking at 20 meters, the path seems to close about 90 minutes earlier on the one using the lower flux value. It is fun to run these comparisons over different paths and seasons.

Without any doubt the day most disturbed by geomagnetic storms this week was Monday, August 18, when the planetary A index was 86 and the planetary K index was 8 during one three-hour period, 7 during another, and 6 during three other periods. This indicates a severe geomagnetic storm. This kind of thing gets worse as one goes toward either pole, and in Fairbanks, Alaska the College A index was 132. The College K index was 8 during two periods, 7 during three periods, and 4, 5 and 6 in the other three. This is why many Alaskan amateur radio operators complain of long periods when they can't seem to hear or work anyone or anything.

The Monday storm began around 0100z when the interplanetary magnetic field tipped to the south near earth. This makes the earth vulnerable to the effects of any solar wind or flare activity. A solar flare erupted on the sun on August 19 at 2005z, and this pushed a strong coronal mass ejection toward earth. The forecast from the U.S. Air Force for planetary A index was adjusted upward on Thursday, August 21 after the initial one at 2104z. That earlier one predicted a planetary A index of 30 for Friday, which is quite high.

Six hours and twenty minutes later a new forecast was released which predicts Friday's planetary A index at 50. Saturday is predicted at 30, and Sunday, Monday and Tuesday all show the same planetary A index of 25. Predicted solar flux for Friday, August 22 is 115, and 110 is the value for Saturday through Tuesday, after which the number is expected to head higher.

I received several emails last week asking about any correlation between the widespread power blackout and space weather. This seems unlikely because conditions were actually rather mild during that time. But a solar flare is a natural thing to consider during a massive power outage, since a big flare on March 6, 1989 brought down an electric power grid in Canada. One who wrote to ask about this was Tim Anderson, AG4XM of Covington, Kentucky. He sent this article about space weather and the effects upon power grids:

David Moore of Morro Bay, California sent an article about an 11-year cycle in which the sun's magnetic poles reverse. Read all about it at

For more information on propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at

Sunspot numbers for August 14 through 20 were 108, 86, 92, 113, 104, 77, and 62, with a mean of 91.7. 10.7 cm flux was 129.7, 131.4, 126.9, 119.3, 115.9, 116.7, and 111.8, with a mean of 121.7. Estimated planetary A indices were 18, 14, 11, 15, 86, 21, and 15, with a mean of 25.7.