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ARRL Propagation Bulletin ARLP035 (2011)

ARLP035 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7RA
Seattle, WA  September 2, 2011
To all radio amateurs 

ARLP035 Propagation de K7RA

The bulletin comes to you this week dispatched from another session
of Camp Blues, this time in Portland, Oregon.

Sunspot activity rose again this week, with the average daily
sunspot number up nearly 18 points to 83.6.  Geomagnetic indices
(both planetary and mid-latitude) were each down slightly.  High
sunspot number for the week was recorded on Wednesday, August 31, at
121.  The last time the sunspot number was higher was on July 31 and
August 1, at 128 and 130.  Prior to that on July 18 it was 127.

If you check the Daily Sun image at,
currently there are quite a number of spots on the Sun.

Predicted solar flux is 110 on September 2-5, 105 on September 6,
100 on September 7-8, 95, 90, 92, and 95 on September 9-12, 100 on
September 13-15, then peaking at 105 on September 18-22.

The solar flux values for the next few days are slightly higher than
the prediction in yesterday's ARRL Letter.

Predicted planetary A index is 5 on September 2, 8 on September 3-4,
5 on September 5-10, then 8, 12, and 8 on September 11-13, and 5 on
September 14-17.

As always, the Czech Republic has a slightly different view, and the
Geomagnetic Department of Geophysical Institute Prague says
September 2 should be quiet, September 3 unsettled, September 4
quiet to unsettled, and September 5-8 quiet again.

Looking back at the three-month moving average of sunspot numbers,
we now have the data for June through August, which gives us the
three-month average centered on July.  At 63, it is only slightly
above the average centered on June, 61.5.  The 3 month averages for
this year, centered on January through July were 35.3, 55.7, 72.3,
74.4, 65.9, 61.5 and 63. For 2010 three-month averages, the high was
35.6, centered on October, and the low was 16.4, centered on May.

Utah State University has a Space Weather Center web site, where
they have been posting frequency availability related to
communications with the National Hurricane Center in Miami.  You can
see current and projected NVIS (Near Vertical Incidence Skywave)
coverage across the Eastern Seaboard, as well as worldwide
propagation maps for 75, 40 and 20 meters centered on Miami.

Take a look at

Thanks to Thomas Otterbein, DG8FBV of Babenhausen Germany, for
noticing that in the last bulletin we referred to the NOAA
Preliminary Report and Forecast as a good source for smoothed
sunspot numbers.  That is true as a general statement, and you can
see the past and predicted progress of the current sunspot cycle.
But Thomas points out that this is not the smoothed sunspot number
you should use with VOACAP propagation prediction software.  He

"For VOACAP, VOAAREA users and for users of prediction programs such
as GUI which uses VOACAP the predicted SSN should be taken from:

"For this see also:"

For some nice photos of Thomas and his station, check (which now requires a login with a free
account on that site), and also

We are only a few weeks away from the Autumnal Equinox in the
Northern Hemisphere - September 23, 2011 - and the transition occurs
at 0904z.  We are transitioning out of Summer HF propagation to the
more favorable Fall conditions.  To get an idea of how much better
Fall propagation is, try using W6ELprop or a similar propagation
program (see with some dates such as
July 15 compared to September 23. You can have two of these running
at the same time, to make it easy to switch back and forth for

I did one from the center of the contiguous 48 United States to
Germany, and used a sunspot number of 120 (slightly optimistic) for
both dates.  The propagation is radically different between those
two dates, and so much better for the Fall date.  Give it a try.

Frank Donovan, W3LPL of Glenwood, Maryland pointed out that a new
monthly prediction for the solar cycle was released by NASA in early
August.  You can read it at But it isn't really
a new forecast, as the only thing that changed was the date from
July 1 to August 2, which was why we didn't mention it in the
bulletin.  But on September 1 a new forecast was released with a
slightly revised prediction for the sunspot cycle maximum.  Instead
of the smoothed sunspot number peaking at 69 in June-July 2013, it
is now predicted to peak at 70 in May 2013.  These forecasts are not
archived, and the same URL is used every month, so a personal record
must be kept to note changes.

Frank also sent this note on September 1: "Trans-polar HF
propagation has significantly picked up in the last week on 20, 17
and 15 meters.  This is the usual seasonal change, as well as solar
flux consistently above 100 and K indexes mostly 2 and below."

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 an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at Find more good
information and tutorials on propagation at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of ARRL
bulletins are at

Sunspot numbers for August 25 through 31 were 97, 76, 63, 73, 66,
89, and 121, with a mean of 83.6. 10.7 cm flux was 104.2, 104.6,
103.8, 101, 101.2, 101.3, and 109, with a mean of 103.6. Estimated
planetary A indices were 4, 3, 5, 6, 9, 4, and 2, with a mean of
4.7. Estimated mid-latitude A indices were 4, 3, 3, 4, 7, 2, and 1,
with a mean of 3.4.


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