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ARRL Propagation Bulletin ARLP013 (2009)

ARLP013 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 13  ARLP013
From Tad Cook, K7RA
Seattle, WA  March 27, 2009
To all radio amateurs 

ARLP013 Propagation de K7RA

Every day I check the 45 day forecast of planetary A index and solar
flux from NOAA and the U.S. Air Force.  For quite some time now, the
solar flux forecast has been the same.  The projection shows 45 days
of solar flux at 70, with no variation.  I look at this because
there is so little sunspot activity, and I hope that any increase in
predicted solar flux values may coincide with renewed sunspot
activity.  But this method hasn't worked out very well in the past
year or so.

When I looked at this on Wednesday night, March 25, the 10.7 cm flux
forecast showed 70 for March 26-27, then bumping up to 72 for March
28-31, then back to 70 for all of April and beyond.  This is not
much increase in activity, but with such a quiet Sun for the past
few years, we become sensitive to small changes, and even optimistic
at times.

Last night, Thursday, March 26 the prediction was nearly the same,
except with the solar flux of 72 lasting two more days, through
April 2.

The forecasts are via,
click on "Alerts, Forecasts and Summaries," then "USAF 45-day Ap and
10.7 cm Flux Forecasts."  The new daily forecast is posted around
2100z, but often doesn't appear in the list at until later.

If you suspect this is the case, just click on the latest available
date, then edit the URL at the top of your web browser to reflect
the current date.  So if it is Friday, March 27, and the latest
listing you see is for March 26, just click on that link, and at the
end of the URL change /032645DF.txt to /032745DF.txt and hit the
Enter key.  If that day's forecast has been uploaded, it should pop
up when you hack the web address using these instructions.

Early on March 26 reported a new "proto-sunspot"
seen "struggling to emerge" at high latitude, making it a Cycle 24
spot.  The same site reported the Solar and Heliospheric Observatory
(SOHO) is monitoring "intense activity on the Sun's northeastern

The following day repeated a common refrain heard
lately after some activity begins to emerge: "Yesterday's
proto-sunspot failed to emerge. The Sun is blank."

The NASA STEREO (Solar TErrestrial RElations Observatory) mission
will eventually enable views of the entire Sun, so we will know in
advance about emerging solar activity that is outside Earth's view.

The two spacecraft orbit the Sun similar to earth, but one leads the
Earth and the other follows.  The leading spacecraft A travels
faster than the trailing spacecraft B, and because of this the angle
of the two relative to each other gradually increases over time.

The craft were launched October 26, 2006 and they reached
quadrature, or 90 degrees separation 62 days ago on January 24,
2009.  Spacecraft A takes 347 days to complete an orbit of the Sun,
and spacecraft B takes 387 days.  They separate from each other at a
rate of about 44 degrees per year.

View their current positions relative to Earth, the Sun, Venus and
Mercury updated hourly at
Click on the STEREO Orbit Tool link, and you can view a similar
image for any date and time from the launch date through the end of

NASA has a dense, single page pdf document describing the mission at, and while we can't
recommend Wikipedia as an always-reliable resource (its immediately
changeable nature drives teachers and reference librarians crazy),
the Wikipedia community seems to have a good information page on
STEREO at  Other NASA resources
are at and, and Johns Hopkins University Applied
Physics Laboratory has information at

Currently USAF and NOAA predict a planetary A index of 8 for today,
March 27, then leveling off at 5 (a very quiet, stable level) until
April 9-10, when it jumps to 15, then 10.  Geophysical Institute
Prague predicts quiet to unsettled conditions March 27, quiet March
28-29, quiet to unsettled March 30-31, and back to quiet for April

This weekend is the CQ World Wide WPX SSB Contest.  Perhaps we'll
get lucky with some worldwide propagation.  The chance of disruption
by any geomagnetic activity seems remote.

Finally, Kenneth Beck, WI7B of Kennewick, Washington responded to
last week's musings about east and west on the Sun.  Referencing an
image at,,
he wrote, "It always seemed to me to be clearer when I realize that
the Sun rotates around its axis in the same direction as the earth.
The is the 'right-hand rule,' with your thumb pointing towards the
'north.' With that perspective, look up at the sky (you can stand,
sit, or crawl on your knees for this thought experiment), hold up
your right hand with the thumb pointing up to the sky, and then
rotate it.  Sunspots will travel in the direction of your fingers,
counter-clockwise around your thumb."

He continues, "Better yet, hold a full mug of beer in your right
hand and turn it.  The bubbles in the beer will turn just like
sunspots.  Now drink!"

Thanks, Kenneth.  If you look up his call on, on his page
you'll see Kenneth in a kilt, hunched over and ready to launch a
Scottish Hammer, a Stone Put, or perhaps doubled over in pain after
a manly contest of Caber Toss.

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 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

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for March 19 through 25 were 0, 0, 0, 0, 0, 0, and 0
with a mean of 0.  10.7 cm flux was 69.1, 68.7, 70.1, 68.7, 68,
69.1, and 68.5 with a mean of 68.9.  Estimated planetary A indices
were 3, 4, 8, 4, 3, 8 and 10 with a mean of 5.7.  Estimated
mid-latitude A indices were 3, 2, 5, 4, 2, 6 and 7 with a mean of


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