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ARRL Propagation Bulletin ARLP012 (2006)

ARLP012 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 12  ARLP012
From Tad Cook, K7RA
Seattle, WA  March 24, 2006
To all radio amateurs 

ARLP012 Propagation de K7RA

There were no zero-sunspot days over the past week. In fact, the
average daily sunspot number was a little more than double the
previous week's numbers, rising over 17 points to 33.4. This was a
nice little up-tick toward the solar cycle minimum, coming with the
start of spring for the Northern Hemisphere.

Unfortunately for HF operators, the average geomagnetic numbers
doubled as well. This and the associated aurora were triggered by a
solar wind stream that hit Earth beginning on Saturday, March 18.
Maximal effects were felt the following day, when the College A
index, (measured less than two degrees latitude south of the Arctic
Circle), rose to 51 on Sunday.

Saturday's College A index was 39, but on Friday, March 17 it was
only 2, a very quiet number. The Planetary A index over those same
days was 3, 26 and 37, and the mid-latitude A index was 2, 15 and

This weekend is the CQ World Wide WPX SSB Contest, and there
shouldn't be any nasty surprises regarding propagation. The
predicted planetary A index for the next five days, March 24-28 is
12, 12, 10, 7 and 5.

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
propagation bulletins is found at,

Sunspot numbers for March 16 through 22 were 22, 24, 27, 40, 33, 39
and 49 with a mean of 33.4. 10.7 cm flux was 72.4, 72, 72.4, 75.2,
76.9, 76.7, and 75.9, with a mean of 74.5. Estimated planetary A
indices were 6, 3, 26, 37, 22, 13 and 10 with a mean of 16.7.
Estimated mid-latitude A indices were 4, 2, 15, 24, 14, 8 and 9,
with a mean of 10.9.


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