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ARRL Propagation Bulletin ARLP012 (2003)

ARLP012 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 12  ARLP012
From Tad Cook, K7RA
Seattle, WA  March 21, 2003
To all radio amateurs 

ARLP012 Propagation de K7RA

This has been quite a week for geomagnetic storms. The average daily
planetary A index, a measure of geomagnetic activity averaged over
24 hours from the planetary K indices in the same period, was about
20 points higher this week than last. This was caused by a near
constant strong solar wind accompanied by solar flares.

The worst or most active day was Monday when the planetary A index
was 39 and the higher latitude college A index (measured in Alaska)
was 78. The college K index was as high as 8, indicating a severe
geomagnetic storm near the polar region.

For an explanation of the relationship between K and A indices,
check Looking at
the chart you can see that if the K index of 8 persisted for 24
hours, this would produce an A index of 207, almost unheard of.
Fortunately mid-latitude numbers weren't as bad.

Solar flux and sunspot numbers declined this week over last.
Average daily sunspot numbers dropped nearly 82 points to 92, and
solar flux was down by over 14 points. This is expected to continue,
with solar flux below 100 through the middle of next week.

Unsettled to active geomagnetic conditions also should continue, at
least over the next few days. Solar flux and sunspot numbers were
better over the last few years around this date. Average daily
sunspot numbers were 134.3 in 2002, 101.7 in 2001 and 183.3 in 2000
during this week. Average daily sunspot numbers were 180.9 in 2002,
144.2 in 2001 and 207.8 in 2000.

The spring equinox begins today. Spring is a great time for HF
propagation, with all points on the earth today getting about 12
hours of sunlight. There actually is some variation in day length on
this day, dependent on the observer's latitude. This is explained by
the U.S. Naval Observatory 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 March 13 through 19 were 88, 114, 124, 121, 80,
64, and 53, with a mean of 92. 10.7 cm flux was 134.2, 138.9, 130.7,
128.6, 164.1, 118.4, and 108.2, with a mean of 131.9. Estimated
planetary A indices were 15, 25, 24, 23, 39, 26, and 14, with a mean
of 23.7.


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