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ARRL Propagation Bulletin ARLP002 (2012)

ARLP002 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 2  ARLP002
From Tad Cook, K7RA
Seattle, WA  January 13, 2012
To all radio amateurs 

ARLP002 Propagation de K7RA

Average daily sunspot numbers were up this week by a tiny bit, from
88.1 to 90.6, and average daily solar flux was down slightly, from
136.2 to 134.9.

I'm looking at recent sunspot data since May 2011 using the WA4TTK
Solar Data Plotter (see and the
activity had a rising trend throughout 2011 and seemed to peak
around mid-November, but since then has softened.

The latest daily projection from NOAA/USAF shows solar flux about 20
points lower than the average for the week, at 115 on January 13-15,
120 on January 16-20, then a jump of 25 points to 145 on January
21-26. It declines again, to a minimum of 135 on January 31 to
February 6, then rises to a peak of 165 on February 17-21.

Predicted planetary A index is 5 on January 12, 8 on January 13-14,
5 on January 15-17, 8 on January 18-19, and back to 5 on January

Rulon Passey, W7QR of Ogden, Utah pointed out that the solar flux
and Ap index forecast were missing from last week's bulletin. But
you can get the same data, updated daily, at

It is a shame that archives of these forecasts going way back aren't
available. They are up for less than three weeks, or at least the
current ones are. But let's try something interesting. The predicted
solar flux of 165 for February 17-21 is rather extraordinary.  This
is a period of five days, and happens to be right in the middle of
what will be our data reporting period - February 16-22 - for
bulletin number 8 on February 24. If we are to take this forecast
literally, with a solar flux value of 160 predicted on both the
first and last days, that would be an average solar flux value for
that seven days of 163.6.

I was surprised when I searched for the last time our bulletin
reported an average at this level or higher.  The last time was in
Propagation Forecast Bulletin ARLP045, issued November 11, 2011 with
data from November 3-9.  Average solar flux was 173.7 and average
sunspot number was 153.4. But even more surprising was when I
searched for any previous bulletin that reported an average this
high or higher.

Way back on January 17, 2003, nearly nine years ago, Propagation
Forecast Bulletin ARLP003 reported an average solar flux of 173.6
and sunspot number of 200.9.  This was right before Cycle 23 plunged
toward the long quiet period we recently recovered from with the
upswing of Cycle 24.

So let's track this and see if the prediction for the period six
weeks from now changes, by how much, and when. I suppose this
prediction may be based on a return to norm, assuming that Cycle 24
peaks in 2013, with the fact that the recent activity for the past
few weeks has been lower than it was in the last months of 2011.

The current issue of Atlantic Magazine has an entertaining and
informative article about the Sun and space weather prediction. Read
it at,

Last week we mentioned adjustments to the geomagnetic indices.
Michael Husler of NOAA sent a link to a page describing the new
geomagnetic products, and you can see it at

Unfortunately, due to a staff retirement in Prague, we are no longer
getting the updates from Geophysical Institute Prague. These updates
began 34 years ago in January, 1978.

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 January 5 through 11 were 99, 118, 110, 90, 90,
63, and 64, with a mean of 90.6. 10.7 cm flux was 141.3, 135.5,
140.5, 135.8, 142.3, 128.8, and 120.1, with a mean of 134.9.
Estimated planetary A indices were 5, 5, 5, 4, 6, 4, and 5, with a
mean of 4.9. Estimated mid-latitude A indices were 6, 6, 5, 5, 7, 5,
and 5, with a mean of 5.6.


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