The K7RA Solar Update

SEATTLE, WA, Aug 22, 2003--Sunspot numbers are down 19 percent, solar flux is down 7 percent and the planetary A index is up 42 percent: 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 saw about seven years ago at the bottom of the solar cycle.

For example, look back to Propagation Bulletin No 42 from October 11, 1996. The sunspot number was a flat zero for every day of that week, and average solar flux was 68.6. What did that mean for HF propagation? Run the free W6ELprop software--one copy for August 22 with a solar flux of 68.6 and another with a flux value of 121.7.

In my own comparison--for a hypothetical 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 seemed to close about 90 minutes sooner on the one using the lower flux value. It is fun to run these comparisons over different paths and seasons.

Without a doubt the day most disturbed by geomagnetic storms this week was Monday, August 18, when the planetary A index was 86. 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. 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 0100 UTC when the interplanetary magnetic field tipped to the south near Earth. This makes Earth vulnerable to the effects of any solar wind or flare activity. A solar flare erupted on August 19 at 2005 UTC, and this pushed a strong coronal mass ejection toward Earth. The forecast from the US Air Force for planetary A index was adjusted upward on Thursday, August 21, after the initial one at 2104 UTC. 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 that predicted 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 up.

I received several e-mails last week asking about any correlation between the widespread power blackout and space weather, but this seems unlikely because conditions were actually rather mild during that time. A solar flare is a logical thing to consider during a massive power outage, however, since a big flare on March 6, 1989, did bring down a power grid in Canada. Tim Anderson, AG4XM, of Covington, Kentucky, sent an article about space weather and the effects upon power grids.

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

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

Sunspot numbers for August 14 through 20 were 108, 86, 92, 113, 104, 77 and 62, with a mean of 91.7. The 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.

Amateur solar observer Tad Cook, K7RA, Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday and an abbreviated version also appears in The ARRL Letter. Readers may contact the author via k7ra@arrl.net.

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