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10 November, 2007
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
Spaceweather.com. Go to, http://spaceweather.com/
images2007/06nov07/midi512_blank.gif, 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
shot.
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, http://www.swpc.noaa.gov/weekly/.
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 http://www.sec.noaa.gov/SolarCycle/SC24/.
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, http://tinyurl.com/6b6g5.
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 information:
"There does exist an instrument that measures solar EUV flux directly.
That is the SOHO Solar EUV Monitor (SEM) at
http://umtof.umd.edu/semflux/.
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 thermosphere/ionosphere."
If you would like to make a comment or have a tip for our readers, email
the author at, k7ra@arrl.net.
For more information concerning radio propagation, see the ARRL Technical
Information Service at,
http://www.arrl.org/tis/info/propagation.html.
For a detailed explanation of the numbers used in this bulletin see,
http://www.arrl.org/tis/info/k9la-prop.html.
An archive of past propagation bulletins is at, http://www.arrl.org/w1aw/prop.
Monthly propagation charts between four USA regions and twelve overseas
locations are at, http://www.arrl.org/qst/propcharts.
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 1.4.
Source: The
American Radio Relay League
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• All propagation
reports can be found at:
http://www.southgatearc.org/propagation
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