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ARRL Propagation Bulletin ARLP050 (2006)

ARLP050 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 50  ARLP050
From Tad Cook, K7RA
Seattle, WA  December 1, 2006
To all radio amateurs 

ARLP050 Propagation de K7RA

The IMF, or Interplanetary Magnetic Field, dipped south early
Thursday UTC (Wednesday night, November 29 in North America) letting
in a blast of solar wind. The planetary K index throughout Thursday
UTC (which is 4:00 PM Wednesday to 4:00 PM Thursday here on North
America's West Coast) was 2, 4, 5, 5, 5, 5, 2 and 1, and the
resulting planetary A index was 28. This week saw more geomagnetic
activity overall than the last reporting week (it runs Thursday
through Wednesday), with the average daily planetary A index rising
8.7 points to 12.3. Average daily sunspot numbers declined more than
11 points this week over last.

The daily sunspot number was 0 on three days recently, November
22-24. Since that time the number has been rising (12, 12, 30, 34,
33 and 59) from November 25-30. There are two prominent and growing
sunspots in view (927 and 926) and a holographic image from November
26 shows a mid-sized sunspot on our Sun's far side. Not bad for a
low point in solar cycle 23. Current predictions show the sunspot
minimum to be 3-4 months from now, although by then I would expect
to see more spotless days, up to several weeks in a row at least.
The predicted minimum is based on predicted monthly smoothed sunspot
numbers, so we will see quite a bit of variation, since daily
reality is not "smoothed." To determine a true smoothed sunspot
number for any month, you need 13 months of daily readings, so
currently we could only know an actual smoothed sunspot number as
recently as May 2006.

The average daily solar flux for the past week was 80.6, and the
latest prediction shows that number rising to 85 for December 1-5,
90 for December 6-7, and 95 during December 8-13. Sunspot numbers
should rise also. Over this weekend the planetary A index is
expected to quiet down, with a value of 15 for December 1, and 5 for
December 2-5. The next period of geomagnetic disturbance is expected
around December 7, with a planetary A index of 25. This is just
prior to the ARRL 10 Meter Contest, December 9-10. Geophysical
Institute Prague predicts quiet to unsettled conditions December 1,
quiet conditions December 2-5, unsettled December 6, and active
geomagnetic conditions on December 7.

November is over, so we can calculate monthly averages and look at
where we are and where we've been.

The average daily sunspot numbers for the months November 2005
through November 2006 were 32.2, 62.6, 26.7, 5.3, 21.3, 55.2, 39.6,
24.4, 22.6, 22.8, 25.2, 14.7 and 31.5. Average daily solar flux for
the same months was 86.3, 90.8, 83.4, 76.5, 75.5, 88.9, 80.9, 76.5,
75.8, 79, 77.8, 74.3 and 86.3.

The numbers for November are a surprise, although not outside the
range of normal variation.

In Propagation Forecast Bulletin ARLP042 dated October 13, 2006
there was a description of how smoothed sunspot numbers are
calculated. From the monthly averages above, we can calculate our
own smoothed sunspot number for May 2006. We take half of the
November 2005 average and half of the November 2006 average, add
them to the monthly averages for the intervening 11 months, and
divide by 12. So that is 16.1 plus 15.75, plus the 11 month total of
320.4, which equals 352.25. This shows an unofficial smoothed
sunspot number of 29.4 for May, 2006. If we just average the daily
sunspot number over those 13 months, that average is 29.75.

Enough numbers, and a little about propagation. After last weekend's
CQ Worldwide CW DX Contest, Allan Mason, VK2GR in Sydney, Australia
noted that 10 meter trans-equatorial propagation was good over both
days between VK2 and Japan with little QSB. He also worked 9M8 and
UA9 on 10, but 80 and 40 meters were the best bands to work Europe
and North America. Allan used 100 watts and inverted vee antennas.

Ed Clulow, N7TL of Portland, Oregon reports he heard nothing on 10
meters over the weekend, "but 15 was sure inspiring both days." Paul
Gray, N0JAA of Satellite Beach, Florida was surprised to work EA8EQ
in the Canary Islands on 12 meter SSB around 1700z earlier in the
week. Paul was using a G5RV antenna, and EA8AQ was quite strong.
Paul believes this was sporadic-E skip.

Herb Anderson, K7GEX of Seattle, Washington wrote to ask about
different geomagnetic numbers. He uses the VE7CC packet cluster, and
noticed that postings of geomagnetic A and K index by different
parties show different results. On November 28 at 0000z, DK0WCY
reported A index of 12, and K of 2, but K3SKE reported A of 9 and K
of 1. "Why the difference?", Herb asks.

I used telnet to connect via the internet to VE7CC, and noticed that
K3SKE must have been reporting data from WWV. That would be the
local Boulder A and K index in Colorado. DK0WCY reports at, that he has his own
magnetometer, which perhaps is where he was getting the numbers that
he reported. Generally magnetometers in higher latitudes report
greater geomagnetic disturbances. For instance, if you look at, you'll see that the
numbers in Alaska are generally higher than the numbers from
Fredericksburg, Virginia. Boulder, Colorado is around 40 degrees
north latitude, while DK0WCY is in the far north of Germany at
Scheggerott with a latitude of 54.33 degrees north. Fredericksburg
is around 38.3 degrees north, while Herb in Seattle lives at 47.776
degrees north.

The link above also shows planetary A and K index, and these numbers
are derived from 13 magnetometers around the world. You can learn
more about them at,

I was watching the local late evening news on television in Seattle,
and saw a story about the new Japanese Hinode spacecraft, which
carries several high resolution telescopes. The news story showed
dramatic footage of solar prominences and sunspots. You can see
images from this new satellite at,

Last, Ward Silver, N0AX had a couple of fascinating items in the
latest issue of the ARRL Contest Rate sheet this week. One was a
story out of India about cooling in the upper ionosphere. Ward
commented that cooling in the lower layers should improve density,
which of course translates to higher MUF and better propagation at
higher frequencies. You can read about it at,

Also in the same issue was a link to a fascinating and useful online
tool for propagation prediction which shows the optimum ham band for
working anywhere in the world based on CQ DX Zones. It is at, If you're not sure which zones
are where, just click on the CQ DX Zones link on the left.

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 23 through 29 were 0, 0, 12, 12, 30, 34
and 33 with a mean of 17.3. 10.7 cm flux was 76.8, 77.4, 78.6, 78.2,
82.4, 85.5, and 85, with a mean of 80.6. Estimated planetary A
indices were 18, 21, 15, 15, 6, 5 and 6 with a mean of 12.3.
Estimated mid-latitude A indices were 8, 10, 10, 9, 7, 4 and 6, with
a mean of 7.7.


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