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ARRL Propagation Bulletin ARLP049 (2010)

ARLP049 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 49  ARLP049
From Tad Cook, K7RA
Seattle, WA  December 10, 2010
To all radio amateurs 

ARLP049 Propagation de K7RA

Average daily sunspot numbers for the week were up over nine points,
to 35, and average solar flux rose over six points to 87.3. These
differences compare the dates December 2-8 with the previous seven
days. Average planetary A index declined 2.5 points to 2.1, while
average mid-latitude A index dropped 1.1 points to 1.6. These are
nice numbers, with higher sunspot numbers accompanied by lower
geomagnetic indices.

Predicted solar flux for the near term is right near or slightly
above the average for the past week, at 87, 87, 88, 88, and 88 for
December 10-14. Predicted planetary A index for December 10-14 is 8,
10, 10, 8 and 5.  Planetary A index is expected to remain around 5
from December 15-24.

Geophysical Institute Prague has a slightly different prediction for
the next seven days.  They predict unsettled conditions for December
10-11, quiet to unsettled December 12, unsettled December 13, quiet
December 14 and quiet to unsettled December 15-16.

Note the period of somewhat unsettled geomagnetic activity centers
around this weekend, the dates for the ARRL 10 Meter Contest,
December 11-12.  But only a mild increase in geomagnetic activity is
expected.  The Geminid meteor shower peaks December 13-14, and could
provide some ionized trails enhancing 10 meter propagation.

This year's 10 meter contest is the first time that Mexican states
will be counted as multipliers along with U.S. states and Canadian
provinces, as well as DXCC countries. You can see a map of the 32
Mexican states in PDF format at  Complete contest rules
are at

Ten meters offers many opportunities for working Mexico from other
North American locations this weekend. For instance, Distrito
Federal, which includes Mexico City, should be workable from Salt
Lake City from 1730-1900z, and possibly from 1700-2100z.  The path
from the San Francisco Bay Area looks even better, with the
possibility of strong signals from 1700-2130z. From the Chicago
area, a likely opening is 1700-1830z, possibly open as early as
1630z and as late as 2000z. From Ohio the path looks good 1630-1930,
extending possibly 30 minutes early and an hour later. From
Winnipeg, Manitoba (VE4) the possibilities look excellent
1730-1900z, very good 1630-2030, and possibly extending to

If you want to use the predicted smoothed sunspot number with a
propagation prediction program for this month or next, you can find
the latest predicted values in the table on page 11 in issue
PRF-1840 at  The values are updated
there about every 4-5 weeks.

You can also do a peek into the future, as this table shows a
predicted smoothed sunspot number for December 2010 of 38, 74 in
December 2011, and 89 in December 2012.  You can download W6ELprop
at and run several instances of the
program at once, and flip back and forth, comparing projections for
2010 with 2011 and 2012.  The 10 meter possibilities expand
dramatically during periods of higher solar activity.

During the weekend the STEREO craft will surpass 97.95% coverage of
the Sun.  You can calculate an approximation of the coverage by
looking at and noting
the number at the bottom, "Separation angle A with B." When I look
at this early Friday morning, the number is 172.234, which
corresponds to about 97.84% coverage.  Subtract the separation angle
from 180, then divide by 360, subtract the result from 1 and
multiply times 100.  Or skip the subtraction from 1 to determine the
percent gap in the coverage.

To calculate the coverage at some time in the future, use the
"STEREO Orbit Tool" at
Just use any date and time you want to test, and use the same method
described above.  At some point in early 2011 after STEREO reaches
100% coverage the gap will begin to grow again, but this time on the
earth-facing side of the Sun.  The image will be filled in with data
from the Solar Dynamics Observatory (SDO), which has a web page at In fact, the current
STEREO image (see already uses SDO data
for the Earth-facing side of our Sun, even though that may seem
redundant.  But this probably assures us that the transition to 100%
coverage will be seamless.

Randy Crews, W7TJ of Spokane, Washington lives 231 miles almost
directly east of my home in Seattle.  He's at the eastern end of
Washington state, 15 miles from the Idaho border.  Although his
latitude is slightly lower than mine, the exact beam heading is
slightly north of east at 89.3 degrees, instead of some fractional
amount south.  Why is this?  Because the shortest path is via the
great-circle route, and at 231 miles it is far enough to put the
path leaving my place just slightly north of east, even though he is
at 47.6017 degrees north latitude and I am at 47.6693 degrees north

Randy has looked over his old station logs recently, and has
observations about the progress of Solar Cycle 24.

"Most don't realize how low we went in the Cycle 23/24 low: Previous
cycles began with a Sunspot Number of 10-12. This cycle began with a
Sunspot Number of about 1.5!

"Usually the cycle bottoms and picks right up within 12-13 Months
from the low. Not the case with Cycle 24.

"This cycle has yet to see the Solar Flux above 100. By comparison,
Cycle 22's official bottom was September of 1986, and as early as
April of 1987, Solar Flux Values were above 100 on many days (about
6 months later).

"With Cycle 24 (if you measure from the low of the lows (July/August
of 2008) we are past the 2 year point, measuring from October of
2009 (when the number of Cycle 24 spots exceeded the old number of
Cycle 23 spots) we are out over a year.

"I am grateful for what we have thus far. The High Bands are open
(17 meters consistently) which is a nice improvement and the higher
bands from time to time also which is a huge step from the long dry
spell in 2008.

"However, the bands have not really stepped into high gear. Flux
values consistently above 100 (years 2004/2005) would really move us
into the fast lane."

Thanks, Randy!

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 December 2 through 8 were 32, 27, 48, 47, 35,
34, and 22, with a mean of 35. 10.7 cm flux was 86.5, 86.8, 87.4,
87.9, 88.5, 87.1 and 87.2 with a mean of 87.3. Estimated planetary A
indices were 3, 1, 1, 1, 2, 4 and 3 with a mean of 2.1. Estimated
mid-latitude A indices were 1, 0, 1, 0, 3, 3 and 3 with a mean of


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