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ARRL Propagation Bulletin ARLP043 (2003)

ARLP043 Propagation de K7RA

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.


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