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ARRL Propagation Bulletin ARLP052 (2006)

ARLP052 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 52  ARLP052
From Tad Cook, K7RA
Seattle, WA  December 15, 2006
To all radio amateurs 

ARLP052 Propagation de K7RA

Big solar and geomagnetic activity this week from sunspot 930, as it
moved across the center of the visible sun as we see it from earth.
On Wednesday December 13, there was a big X-class solar flare, and
Thursday's mid-latitude A index rose to 30, while the planetary A
index hit 63, indicating a severe geomagnetic storm. As this
bulletin is written after midnight Friday morning on the West Coast,
the planetary K index for the past 9 hours has been 8. A full day
with nothing but a K index of 8 would produce an A index over 200.
The planetary A index predicted for December 15-18 is 45, 20, 15 and

Carl Luetzelschwab, K9LA sent a chart from 1986 showing a day during
the low point between solar cycles when the A index suddenly shot to
200. Our sun doesn't always do as expected during low points of a
solar cycle. There is a tremendous amount of short-term variability.
You can see the graph at,, where it is the top
chart on the page.

Earlier Thursday evening the Australian Space Forecast Centre issued
a warning for a major to severe geomagnetic storm for December 15.
You can receive free emailed warnings of such events by subscribing
Geophysical Institute Prague also predicts a severe geomagnetic
storm for December 15, active conditions for December 16, unsettled
for December 17, and back to quiet on December 18.

Geomagnetic storms aren't all bad. Other than producing pretty
Aurora Borealis, there are some nice effects on VHF, too. Vince
Varnas, K7ZH of Aloha, Oregon (CN85) reports, "Fantastic aurora and
aurora-E opening today (Thursday night). I worked most of the
northern tier of states and southern Canada provinces from WA1T (New
Hampshire) to KL7NO (Fairbanks) on 50 MHz with 100 watts to a
popular 3 element commercial Yagi on SSB (mostly). The Aurora
commenced just before 0000 UTC for me and was mixed with auroral-E
skip, too."

For last week's 10-meter contest, most reports talked about
trans-equatorial propagation into South America, or sporadic-E skip.
Bob Griffiths, NE3I of Blue Bell, Pennsylvania reported the contest
operation was either with locals, or groups of stations worked in a
row when one area of the country or the other seemed to pop in for a
brief period.

Of course it helps to be further south. Ken Lappe, W1YO of Leesburg,
Florida reports that from Central Florida 10-meters was open to
South America both Saturday and Sunday. But the 10-meter contest was
much better last year, with more African, Canadian and U.S. stations
worked. By the way, both W1YO and NE3I were using simple vertical

It's time to wrap up the bulletin for this week, because in addition
to the geomagnetic storm, there is a huge wind storm blowing outside
here in Seattle, the lights keep flickering, and I need to turn this
in before the power goes out. There is also a final exam in a Perl
programming course this weekend. Perl gurus are welcome to email
advice and encouragement, or to help comment my code.

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, see the ARRL
Technical Information Service at, For a detailed
explanation of the numbers used in this bulletin see, An archive of past
propagation bulletins is at, .
Monthly propagation charts between four USA regions and twelve
overseas locations are at,

Sunspot numbers for December 7 through 13 were 48, 32, 13, 23, 28,
27 and 21 with a mean of 27.4. 10.7 cm flux was 96, 96, 92.4, 90,
92.2, 102, and 93.6, with a mean of 94.6. Estimated planetary A
indices were 25, 25, 7, 14, 15, 26 and 5 with a mean of 16.7.
Estimated mid-latitude A indices were 14, 17, 6, 8, 11, 15 and 5,
with a mean of 10.9.


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