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ARRL Propagation Bulletin ARLP027 (2011)

ARLP027 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 27  ARLP027
From Tad Cook, K7RA
Seattle, WA  July 8, 2011
To all radio amateurs 

ARLP027 Propagation de K7RA

Average daily sunspot numbers for the past week dropped less than a
point (from 42 to 41.6) compared to the previous week, and average
daily solar flux was down over 5 points to 86.2.
Predicted solar flux for the near term is lower than of late, with
values at 88 for July 8, 90 on July 9-11, 92 on July 12-13, 94 on
July 14 then 90 on July 15-17, then 88 on July 18-21 and 86 on July
Predicted planetary A index for July 8-13 is 7, 10, 5, 5, 7, and 7,
followed by 5 on July 14-18.  This is followed by a rise in
geomagnetic activity on July 19-24 with planetary A index at 7, 8,
12, 15, 10 and 7.
The latest smoothed sunspot number prediction on page 13 at shows the numbers
for December 2010 through December 2011 slightly lower. Last month's
prediction showed smoothed sunspot numbers for that period at 30,
34, 38, 41, 45, 49, 54, 59, 63, 66, 68, 71 and 74.  The latest has
the values for those same months changed to 29, 32, 36, 39, 43, 47,
52, 57, 61, 64, 66, 69 and 72.  The reason that in July we see last
December's number change is because the smoothed sunspot number
represents an average of data over one year.  The data for
approximately six months after December 2010 wasn't completely known
until the end of June, and each successive month after that contains
one more month of predicted data, instead of data that is actually
Geophysical Institute Prague predicts unsettled activity on July 8,
quiet July 9, unsettled July 10-11, quiet to unsettled July 12, and
quiet July 13-14.
NASA has a new (monthly) solar cycle prediction.  Because these are
not archived and the URL never changes, tracking the updates can be
a bit daunting, but here are the changes from a month ago.
In paragraph 9, this sentence: "We find a starting time of May 2008
with minimum occurring in December 2008 and maximum of about 59 in
June/July of 2013" in last month's prediction changed to "We find a
starting time of October 2008 with minimum occurring in December
2008 and maximum of about 69 in June/July of 2013" in this month's.
So they now believe the cycle started five months later than
previously reported, and that the smoothed sunspot peak will be 10
points or seventeen percent higher.  These are international sunspot
numbers, not the Boulder numbers used in this bulletin, which are
Also changed at the end of that same paragraph, from last month's
prediction: "At this phase of cycle 24 we now give 40 percent weight
to the curve-fitting technique of Hathaway, Wilson, and Reichmann
Solar Physics  151, 177 (1994).  That technique currently gives
highly uncertain (but smaller) values to Ohl's method" to "At this
phase of cycle 24 we now give 50 percent weight to the curve-fitting
technique of Hathaway, Wilson, and Reichmann Solar Physics  151, 177
(1994).  That technique currently gives somewhat uncertain (but
similar) values to Ohl's method" in the latest prediction.  So 40
percent was changed to 50 percent, and "smaller" was changed to
Joe Molon, KA1PPV of Stamford, Connecticut likes to play around with
lower power on digital modes, and was running 1.5 watts with PSK-31
at 0101z on July 1 when he worked Ukrainian station UX7MX on 20
meters.  I think he must use a simple wire antenna, because when I
look at an image of his QTH using the hi-resolution images on Bing
Maps, I don't see a tower and Yagi.  Or perhaps he uses a vertical.
Later that same evening he logged stations in Belarus and France.
You can see some nice photos of UX7MX if you log into and go
In the current July 2011 issue of CQ Magazine, Tomas Hood, NW7US for
his monthly Propagation column has this headline:  "Don't Believe
the Pessimistic Forecasts!" complete with exclamation point.  He
points out that predictions have been all over the place and are
revised frequently.  He also notes that some might be tempted to
just turn off the radio because of forecasts, but this is
self-defeating, because if stations aren't listening and
transmitting, then there is nothing to work.  I would also note that
while marvelous new tools for solar observation exist now that even
a decade ago we didn't have, there just hasn't been enough data
(only 23 sunspot cycles so far) to make predictions with complete
reliability.  Maybe after another millennia!
On his website ( NW7US has similar info to
material in his column about the importance of x-rays in enhancing
ionospheric propagation.  Just page down a little way to "More about
Background X-rays".
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 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 June 30 through July 6 were 34, 51, 54, 42, 44,
30, and 36, with a mean of 41.6. 10.7 cm flux was 89.2, 87.6, 85.6,
86.2, 85, 84.8, and 84.6, with a mean of 86.1. Estimated planetary A
indices were 6, 13, 6, 8, 11, 14, and 8, with a mean of 9.4.
Estimated mid-latitude A indices were 3, 7, 3, 6, 7, 8, and 7, with
a mean of 5.9.


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