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ARRL Propagation Bulletin ARLP052 (2007)

ARLP052 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 52  ARLP052
From Tad Cook, K7RA
Seattle, WA  December 14, 2007
To all radio amateurs 

ARLP052 Propagation de K7RA

Sunspot 978 made a strong showing this week, and daily sunspot
numbers are up as a result.  The average daily sunspot number for
this week rose over 25 points to 36.7, and average daily solar flux
rose over 14 points to 87.2.  The sunspot numbers on December 9-11
were 42, 43 and 44.  Sunspot numbers haven't been nearly this high
since July 14-15 of 2007, when it was 41 both days.  The daily
sunspot number hasn't been higher since June 2 to June 8 of this
year, when it was 45, 58, 58, 63, 47, 59 and 51.

You can make your own animation of the emergence and movement of
sunspot 978 with photos on  Just click
on and in the URL field change /06dec07/ to
/07dec07/, hit the Enter key, then change it to /08dec07/, hit
Enter, and repeat until you reach /13dec07/ (14dec07 will probably
also work by the time you read this bulletin).  Now you can use your
browser's forward and back keys to animate the sunspot and watch it
move.  It is a big sunspot.

Geomagnetic activity was very low, although it was slightly
unsettled around December 11-12 at northern latitudes.  But take a
look at the table at,  Note the absence of
any geomagnetic activity in the far north, represented by the
strings of zeros for Alaska's College A and K index from November 30
to December 9.  The K index is measured every three hours, or eight
times per day.  Notice in the 64 readings from 1200z December 1 to
0900z December 9, the College K index rose from 0 to 1 only twice.

Tim Goeppinger, K6GEP of Orange, California wondered why, with the
higher sunspot numbers, he didn't see better propagation last
weekend in the ARRL 10 Meter Contest.  Recently this bulletin
mentioned unexpected 10 meter propagation when there were no
sunspots.  This may be a case where this week's sunspot activity
wasn't enough to support F layer propagation at 28 MHz, but perhaps
recent 10 meter DX was actually supported by sporadic E propagation.

The US Air Force and the NOAA Space Weather Prediction Center
forecast solar flux at 95 for December 14-16, and 90 on December
17-19.  This suggests a possible continuation of recent sunspot
activity, because sunspot numbers this week were 39-44 while solar
flux was 89-94.

They also predict a planetary A index for December 14-20 at 5, 5,
10, 20, 15, 15 and 10, so expect unsettled to active geomagnetic
conditions on Monday, December 17.  Geophysical Institute Prague
predicts quiet conditions December 14-16, active December 17, and
unsettled December 18-20.

This week there are a slew of new articles from various sources on
solar science and Hinode.  Rather than give you a multiple links,
let's try something new.  Copy and paste or just type to your web browser's URL field and hit the
Enter key to read the first article.  For the second, paste again,
but change sunmem1 to sunmem2.  Keep up that process through sunmem7
to read all seven articles.

Next week is Winter Solstice in the Northern Hemisphere, on
Saturday, December 22.  After that the hours of daylight will
gradually grow longer, and the increased sunlight will improve
propagation on the higher bands.  Three months away is the Spring
Equinox, and if we have more sunspots by then, so much the better.

In the interim, we can take advantage of the long nights and low
geomagnetic activity to enjoy the low bands, 160 and 80 meters.

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 December 6 through 12 were 29, 24, 36, 42, 43,
44 and 39 with a mean of 36.7.  10.7 cm flux was 78.2, 82.2, 86.9,
88.9, 86.9, 93.4, and 93.9 with a mean of 87.2.  Estimated planetary
A indices were 1, 1, 0, 2, 8, 12 and 7 with a mean of 4.4.
Estimated mid-latitude A indices were 1, 0, 1, 1, 5, 9 and 7, with a
mean of 3.4.


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