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ARRL Propagation Bulletin ARLP046 (2007)

ARLP046 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 46  ARLP046
From Tad Cook, K7RA
Seattle, WA  November 9, 2007
To all radio amateurs 

ARLP046 Propagation de K7RA

A single sunspot (number 973) appeared briefly toward the end of
Wednesday, November 6, then quickly faded.  This broke a 29-day
stretch of no sunspots, beginning after October 6-7, when a single
spot emerged for just two days.  Spot 973 was never visible in a
geo-effective (squarely facing earth) position, appearing only in
the southwest of the solar disk, destined to shortly rotate away
from Earth's view.

This sunspot is barely visible in a series of images at  Go to,, the
solar image for November 6.  The spot is not visible in this image
because the spot only appeared late in the day, probably after this

In the URL window of your web browser, look for the /06nov07/ string
and change the 6 to a 7, then an 8, hitting your Enter key after
each change.  Now you can use your browser's Forward and Back arrows
to quickly shift between the three images.

Can you see the sunspot?  It is in the west-southwest area, which is
the lower right.  You can't see it in the November 6 image, but it
is there on November 7, and almost rotated off the disk on November
8.  It is not a dark area, but a subtle white instead.  It is so
subtle that it may seem as if your mind is trying to comprehend a
pattern in noise.

We think of the lower right on maps as being southeast, but for a
solar image this is based on Earth's point of view, so it is a
mirror image relationship.  It works like this: Imagine that it is a
Summer's day at noon, and you are lying on a grassy field with your
arms stretched out to either side of you, your head pointed to
north, and feet toward south.  Your right arm is on your west side
and left is east.  So as you face the Sun, the right side of the
Sun's image is referred to as west, while left is east, the opposite
of the way we normally view maps.

I was actually a bit disappointed to see a sunspot this week,
because I would rather see us move beyond the bottom of the cycle,
and the more days in a row that we see no sunspots, the more I would
be convinced that we are ready to move beyond the cycle bottom, that
the bottom really is here.  One source I've been checking is the
monthly table of predicted smoothed sunspot numbers appearing in
every fourth or fifth edition of the Preliminary Report and Forecast
of Solar Geophysical Data at,

If you click on PRF 1679 and look at the table on page 9, you can
compare this with the previous table from a month earlier in PRF
1674.  Note that the bottom has moved again, just slightly.  In PRF
1674, the predicted smoothed sunspot numbers for January through
December 2007 are 12, 12, 11, 11, 11, 11, 12, 13, 15, 17, 20 and 23.
This suggests the minimum was broadly between March through June.
But in PRF 1679 the same months have 12, 12, 11, 10, 9, 10, 10, 11,
13, 16, 19 and 21, suggesting a May bottom.

They changed because a month later there is one more month of real
data to average to yield a smoothed sunspot number.  The smoothed
number is based on a year of data, and note that in the earlier
table the numbers are in bold typeface for April through December,
and the later table has May through December bold.  In these tables,
only the regular typeface numbers represent 100% real data.  So a
month earlier, the last month with a smoothed number based on no
predicted data at all was March, because there was real sunspot
number data stretching from mid-September 2006 through mid-September
2007 to calculate the March smoothed sunspot number, midway between
the two Septembers.  But April still needed data from October 2007,
which at that time was only forecast, not actually measured yet, so
it is a bold number.

In the past the forecast in this table always stretched a few years
into the future.  In fact, this table has ended in December 2007 for
some time now.  Why hasn't the forecast been extended through 2008
and 2009?  The reason is because the panel of scientists who met in
April 2007 to come up with predicted values for the next solar cycle
were unable to reach any consensus.  You can see their statement at  But they agreed that the
solar minimum is predicted for March 2008, plus or minus six months.

The two scenarios are Cycle 24 peaking at sunspot number 140 in
October 2011, or peaking at 90 on August 2012.  If you click on the
"Solar Cycle 24 Consensus Prediction" link, this brings up a
PowerPoint presentation summarizing the report.  If you don't have
PowerPoint, you can download a free viewer at,

The panel does not expect to reach a consensus for a Cycle 24
prediction until solar minimum has passed.  Until then, an average
of the two scenarios calls for a peak in January 2012 with a
smoothed sunspot number of 113, several points lower than the peak
of the current cycle.

In last week's bulletin, Carl Luetzelschwab K9LA said the closest
measurement we have to radiation that ionizes the F2 region is the
GOES X-ray data at 0.1 to 0.8 nm.  K9LA says that is not correct -
he received an e-mail from Michael Keane, K1MK, with the following

"There does exist an instrument that measures solar EUV flux
directly.  That is the SOHO Solar EUV Monitor (SEM) at One SEM channel covers solar EUV in
the 17-70 nm range. The other channel monitors just the 30.4 nm
resonance line of singly ionized helium. In most models, this 30.4
nm line by itself represents 25-50% of the energy input to the

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 November 1 through 7 were 0, 0, 0, 0, 0, 11 and
0 with a mean of 1.6.  10.7 cm flux was 67.3, 67.9, 67.6, 67.7,
67.4, 68.5, and 68.1 with a mean of 67.8.  Estimated planetary A
indices were 3, 2, 2, 3, 3, 1 and 1 with a mean of 2.1. Estimated
mid-latitude A indices were 4, 1, 2, 2, 1, 0 and 0, with a mean of


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