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ARRL Propagation Bulletin ARLP024 (2008)

ARLP024 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 24  ARLP024
From Tad Cook, K7RA
Seattle, WA  June 6, 2008
To all radio amateurs 

ARLP024 Propagation de K7RA

We had seven days of no sunspots this week, but a sunspot was
emerging on Thursday, June 5.  Helioseismic holography revealed a
high latitude sunspot on the opposite side of the Sun.  Until
recently, we had no idea what was happening on the far side of the
Sun, the side directed away from earth.  Go to and to for more
information on helioseismology.

Sorry about my mix-up last week, which some readers saw in some
versions of the bulletin regarding Labor Day.  No, it is not
celebrated in May.  If you didn't see it, then you read a version
edited by the very capable and wide awake staff at ARRL HQ.

As promised last week, here is an update to the three-month moving
averages of sunspot numbers.

Sep 05 39.3
Oct 05 28
Nov 05 36
Dec 05 40.6
Jan 06 32.4
Feb 06 18.1
Mar 06 27.7
Apr 06 38.5
May 06 39.7
Jun 06 28.9
Jul 06 23.3
Aug 06 23.5
Sep 06 21.2
Oct 06 24.1
Nov 06 23.1
Dec 06 27.3
Jan 07 22.7
Feb 07 18.5
Mar 07 11.2
Apr 07 12.2
May 07 15.8
Jun 07 18.7
Jul 07 15.4
Aug 07 10.2
Sep 07  5.4
Oct 07  3
Nov 07  6.9
Dec 07  8.1
Jan 08  8.5
Feb 08  8.4
Mar 08  8.4
Apr 08  8.9

I was able to calculate the value for April because we have all the
data for March, April and May.  The total of all daily sunspot
numbers for those three months was 818.  Divide that value by 92
days gives us approximately 8.891 as the average.

Note the average sunspot number has increased only slightly since
last Fall.

Jeff Lackey, K8CQ of St. Simons Island, Georgia noted that in the
table of zero-sunspot days presented last week, there was at least
one error.  They counted as 36 days the period from May 27 to July
31, 1996.  You can look at the whole website, not just the page we
linked to last week at,  Jeff
checked data in the table against an archive of sunspot data on the
ftp site,
He found that the 66 days they reported as 36 days were actually
over two periods, but neither was over 20 days.  Jeff wrote,
"Indeed, the run that ended on 31 July began on 8 July, thus it was
a 14 day run.  The beginning date of 27 May was for a run that ended
on 7 June.  Between 7 June and 8 July, the sunspot numbers were all

The NOAA Space Weather Prediction Center sees a constant and quiet
geomagnetic planetary A index of 5 through June 14.  Geophysical
Institute Prague predicts quiet conditions for June 6, quiet to
unsettled June 7-8, and quiet again June 9-12.

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 May 29 through June 4 were 0, 0, 0, 0, 0, 0, and
0 with a mean of 0.  10.7 cm flux was 68.1, 67.1, 66.9, 66.6, 67.1,
66.3, and 65.2 with a mean of 66.8.  Estimated planetary A indices
were 9, 11, 8, 8, 5, 4 and 4 with a mean of 7.  Estimated
mid-latitude A indices were 7, 7, 8, 6, 4, 3 and 2, with a mean of


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