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ARRL Propagation Bulletin ARLP029 (2006)

ARLP029 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 29  ARLP029
From Tad Cook, K7RA
Seattle, WA  July 21, 2006
To all radio amateurs 

ARLP029 Propagation de K7RA

Solar activity remains low, and was lower this week than the week
before.  Average daily sunspot numbers dropped over six points to
19.4, and solar flux was down over five points to 70.7.

July 13 saw the solar flux dip just barely below 70 to 69.9.  During
extended periods with zero sunspots, we will see solar flux around
67 or 68.  I believe the solar flux hasn't been below 70 in almost
exactly nine years, back to July 17, 1997 when it was also 69.9.

Today the sun appears spotless, although the sunspot number is above
zero.  Expect continued low levels of solar activity.  For the next
few days expect solar flux around 70, rising to 75 after Sunday,
July 23.  This is not a big change.  It is roughly equivalent to the
sunspot number rising from 11 to 18.  This doesn't mean that solar
flux and sunspot numbers are completely independent.  This week we
saw average solar flux around 71 and average sunspot number around
19.  Five years ago with an average solar flux around 141, average
daily sunspot numbers were around 162.

Geomagnetic indices should be quiet, with a planetary A index of
five.  The next period of higher geomagnetic activity due to
recurring coronal holes rotating into view is some moderate activity
expected around Tuesday, July 25, and then some higher activity
centered on August 1.  This is a prediction from the U.S. Air Force
Space Weather Operations.  Geophysical Institute Prague predicts
quiet conditions for July 21-24, unsettled conditions July 25-26,
and quiet to unsettled July 27.

Check this article on Space Weather from The Industrial Physicist:  Note the nice
illustration of magnetic and solar convection patterns about half
way down the page.

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 .

Sunspot numbers for July 13 through 19 were 11, 15, 17, 20, 23, 26
and 24 with a mean of 19.4. 10.7 cm flux was 69.9, 70.9, 70.2, 70.8,
71, 71.2, and 71.1, with a mean of 70.7. Estimated planetary A
indices were 5, 14, 6, 4, 4, 3 and 2 with a mean of 5.4. Estimated
mid-latitude A indices were 3, 10, 5, 2, 2, 2 and 2, with a mean of


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