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ARRL Propagation Bulletin ARLP015 (2012)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 13, 2012
To all radio amateurs 

ARLP015 Propagation de K7RA

The bulletin comes to you today from Olympia, Washington, where K7RA
is on a fortnight road trip down the West Coast.

Solar activity took a serious nosedive this week, with average daily
sunspot numbers dropping to a value less than half the previous
week's average, down nearly 43 points to 32.6.  Solar flux values
were also off, down nearly 12 points to 95.9.

The low point for sunspot numbers was April 9 and 10, with the daily
sunspot number at 24 for both days.  But subsequently we witnessed a
rise, hitting 28 and 50 on April 11 and 12.

The current prediction shows solar flux at 95 on April 13 to 19,
then suddenly jumping to 105 on April 20 and 21, 110 on April 22 to
25, then 105 on April 26 to 28, 100 on April 29 and 30 and 95 on May
1 to 9.  Predicted planetary A index is an unsettled 18 on April 13,
12 on April 14, 10 and 8 on April 15 and 16, 5 on April 17 to 23, 10
and 8 on April 24 and 25, 5 on April 26 to 29, 8 on April 30, and 5
on May 1 to 7.

This is an improvement from yesterday's forecast, which had solar
flux at 90 for the next few days. But you can keep up with the daily
revisions at

If you checked or recently, you
may have noticed missing geomagnetic mid-latitude K indices from
Fredericksburg, Virginia on April 7 to 9. They had a computer issue,
and that data is lost forever.  So the mid-latitude A index shown in
this bulletin for those days is the author's very rough and
unscientific wild guess.

for an interesting article on helioseismology and the next solar

check out an interesting article from the Naval Research Laboratory
about coronal cells.  See a similar article on the same subject at

Check out an internet connected Software Defined Radio in Walla
Walla, Washington at  I've just
been listening to 40 meter CW, and with a mouse click you can select
20 meters also. This can support multiple simultaneous users tuning
independently. Thanks to KD7PAJ for this.

Got this report on April 5 from WA9YSD, The Kite Flier's Radio Club:
"Today around 1730 UTC I was listening to some week state side CW
signals on 40 meters. I heard this strange QSB on the signal and
noticed the noise floor had QSB as well. So I switch to 17 meters
and observed more QSB on the background noise. I then went to and saw that the CME ejection was late or missed
us. Guess it was just late because I was amazed on hearing it hit

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 web page at For an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at Find more good
information and tutorials on propagation at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for April 5 through 11 were 50, 39, 38, 25, 24, 24,
and 28, with a mean of 32.6. 10.7 cm flux was 100.9, 97.4, 98.5,
93.3, 94.5, 93.3, and 93.4, with a mean of 95.9. Estimated planetary
A indices were 13, 4, 10, 5, 4, 8, and 5, with a mean of 7.
Estimated mid-latitude A indices were 11, 3, 6, 3, 2, 6, and 5, with
a mean of 5.1.


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