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ARRL Propagation Bulletin ARLP015 (2010)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 16, 2010
To all radio amateurs 

ARLP015 Propagation de K7RA

Weakened sunspots faded this week, and we were buffeted with more
geomagnetic instability, but without the dramatic geomagnetic storms
of the previous week.  Average daily sunspot numbers fell more than
20 points to 12.1, and average solar flux dropped nearly three
points to 75.1.

April 11 saw no sunspots, with group 1061 appearing April 5-10, and
sunspot group 1062 showing April 12-14.  By Thursday group 1062 was
gone, and we may see still more days without sunspots.  Predicted
solar flux for April 16-24 is 75, 77, 78, 79, 80, 82, 84, 80 and 80.
Predicted planetary A index for those same days is 5, 7, 12, 8, 7,
8, 5, 5 and 5.

Geophysical Institute Prague predicts quiet conditions for April 16,
quiet to unsettled April 17, active conditions April 18, quiet to
unsettled April 19, quiet April 20-21, and quiet to unsettled April

The new ARRL web site is up, and the links to propagation
information appearing at the end of each weekly bulletin have
changed.  See the links toward the end of this bulletin.

Carl Luetzelschwab, K9LA, had comments about Jim Secan's
observations in last week's propagation forecast bulletin ARLP014.

Carl writes, "Your statement about your discussion with Jim Secan in
your last bulletin is really two issues.  Once you sort those out
and understand them, you'll see that I totally agree with Jim. I
can't speak for anyone else, though.

"Issue 1 - Due to the daily variation of the ionosphere, our model
of it was developed based on the correlation between the smoothed
sunspot number and monthly median ionospheric parameters. This gives
us a statistical model of the ionosphere over a month's time frame.
Unfortunately it's not a real-time model. Because of the high
correlation between the smoothed sunspot number and the smoothed
solar flux, either index can be used to properly use our prediction
software. This is what I've always preached - that you should use a
smoothed solar index (not that it matters, but I prefer smoothed
sunspot number for historical reasons), and understand that the
results are statistical in nature over a month's time frame. This is
how the developers of our predictions intended them to be used.

"Issue 2 - Jim is trying to derive a solar index that represents
what the ionosphere is doing real-time by forcing the model of the
ionosphere to agree with a bunch of ionosondes. His results indicate
that the average of solar flux over the last 7 days works best to
give the least error.  So the difference in the two issues is the
time frame being used. Issue one is a long-term effort (over one
month) to correlate a solar index to data from one ionosonde, and
issue two is a short-term effort (daily, hourly) to correlate a
solar index to data from many widely separated ionosondes that don't
agree very well with each other at the same time of day."

Steve Wamback, KK2W of Angola, New York wrote, "I just wanted to
report very strange 10 meter propagation conditions on Sunday
Evening at 10:18 Local EDT (GMT Monday 02:18Z) 2 hours past my local
sunset. I just happened to tune through the 10 meter band by chance
as I occasionally do.  I heard James, KH6CB in QSO. Tuning further,
28.4 MHz, I heard VK4TJF (also James) just finishing a QSO so I
threw in my call sign with my 100 watts and G5RV. He heard me and we
exchanged 5x6 reports and a short QSO. Signals on the band persisted
for about a half hour then dissipated. I find night time 10 meter
openings to be extremely rare. Worked a PJ4 after dark once during a
December contest. Meteor scatter?"

That is odd propagation.  Perhaps multi-hop sporadic-E?  The path is
over 9,000 miles.

Check out the longest listing I've ever seen, which happens
to be Steve's at,

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,

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 8 through 14 were 23, 11, 11, 0, 14, 14,
and 12 with a mean of 12.1.  10.7 cm flux was 75.7, 76, 75, 74.6,
74.5, 74.9 and 75.1 with a mean of 75.1. Estimated planetary A
indices were 11, 6, 3, 8, 22, 3 and 9 with a mean of 8.9. Estimated
mid-latitude A indices were 9, 4, 3, 8, 18, 2 and 8 with a mean of


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