ARLP043 Propagation de K7RA:
October 24, 2003

Propagation Forecast Bulletin 43 ARLP043
From Tad Cook, K7RA
Seattle, WA October 24, 2003
To all radio amateurs

ARLP043 Propagation de K7RA

Big news this week is a colossal sunspot that appeared on Sunday, October 19. It first emerged at about seven times the earth's diameter, but two days later on Tuesday, it had grown to around the size of Jupiter, which is equivalent to eleven earth diameters. This is one of the largest sunspot groups to appear during the current cycle 23. Along with this large spot have been coronal mass ejections, keeping the earth's magnetic field upset, and an additional spot by mid-week. An ejection caused a radio blackout on Sunday around 1650z.

This is a big change from the recently spotless sun. Now a large coronal mass ejection threatens, and the predicted arrival time is Friday, October 24. This is not good news for contesters who hoped to work the CQ Worldwide DX SSB Contest this weekend. Currently on Thursday evening, the forecast is for a planetary A index of 50 for Friday through Sunday, October 24-26, but this could be a modest projection. Solar flux has risen since October 14 when it was only 92, and should top 200 by the middle of the coming week.

The growing solar activity is dramatic enough that it is now national news. Check the following sites for articles.

The solar flux value of 191 shown below for October 22 is the value measured at the Penticton observatory. The number from the NOAA Space Environment Center was lowered to 154, probably because of a flare enhancement to the Penticton reading. Those who keep records may want to lower the value for that day to 154 from 191, which would make the week's average for the daily solar flux 123.4 rather than 128.7. Not shown here is the following day, October 23, when the observatory at Penticton measured 209.3 and the SEC reported it as 183. These seem to be estimates based upon the morning measurements made three hours before local noon, which were both around 154 and 183 for the two days.

Sean Blackburn, KB7OOH of Everett, Washington wrote to inquire about a source for sunspot numbers to use with the W6ELprop software for propagation prediction. The numbers are at,

It is probably best to average several days of sunspot numbers to use with this program. As always, it is available free at.

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

Sunspot numbers for October 16 through 22 were 28, 66, 91, 89, 113, 144 and 117, with a mean of 92.6. 10.7 cm flux was 95.2, 98.8, 108.6, 120.4, 135.1, 151.5 and 191, with a mean of 128.7. Estimated planetary A indices were 26, 31, 27, 32, 30, 39 and 33, with a mean of 31.1.