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ARRL Propagation Bulletin ARLP033 (2005)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 5, 2005
To all radio amateurs 

ARLP033 Propagation de K7RA

Average daily sunspot numbers rose over 68 points this week to 83.7,
when compared to last week's numbers.  Note this is four weeks after
the recent large number of sunspots around the beginning of July,
which corresponds to the rotation of the sun relative to Earth.
That area of the sun is now back in view, but with sunspots

The reporting week began with heightened geomagnetic activity on
July 28, but it quieted down.  Prediction for the next few days is
for solar flux to remain above 100, which is expected until August
10.  Current geomagnetic conditions are slightly unsettled, but
after August 10 are predicted to be quiet.  Barring any unexpected
solar flare, expect good conditions, at least relative to recent HF
propagation at this lower spot on the solar cycle.  Also note that
the Northern Hemisphere is about half way between the longest day of
the year and the fall equinox, and fall is good for HF propagation.

July ended this week, so now is a good time to look at monthly
averages to see if we can spot trends.  What we see is a tremendous
variation from month-to-month, with a rise in average sunspot and
solar flux numbers for July, due to the unusually large number of
sunspots early in the month.

The average daily sunspot numbers for the months October 2004
through July 2005 were 77.9, 70.5, 34.7, 52, 45.4, 41, 41.5, 65.4,
59.8 and 68.7.  Average daily solar flux for the same months was
106, 113.7, 95, 102.3, 97.2, 89.9, 85.9, 99.5, 93.7 and 96.5.  
Looked at in isolation, the numbers since early 2005 almost suggest
a rising solar cycle.

The overall trend for the remainder of this sunspot cycle will be
down, and it becomes more obvious when we average the numbers over a
long period.  Currently we are looking to reach solar minimum around
the end of 2006.  Our bulletin has reported this for some time now,
and this is based on the table of predicted smoothed sunspot numbers
that appears occasionally in the back of the weekly Preliminary
Report and Forecast from NOAA Space Environment Center, found at  This week's copy number
1561 at contains that
table, but I noticed that looking back over the past few years shows
the predicted values out to the end of 2007, just as it does today.

Look at this table for predicted smoothed sunspot numbers from four
years ago, in August 2001, and compare it to the table in the latest
issue noted above:

Even back in 2001 the predicted low numbers for the end of next year
were the same as today's prediction.  What changed are the predicted
numbers for a few months from now, which are higher than predicted
four years ago, and of course the actual smoothed numbers for all
that time in between differ also.

We must go back to 2000 to find tables that end earlier than 2007.
Here is one from August 2000 which ends in 2005:

Until I rechecked this, I thought the table was perhaps updated
yearly, with another year in the future added on.  I have a question
in to the NOAA Space Environment Center about this, plus another
question about the July 18 report of a sunspot number of -1 that we
covered recently.  Perhaps next week's bulletin will have more on

Vic Woodling, WB4SLM wrote about recent VHF DX, but on the FM
broadcast band, about half way between our own six and two meter
bands.  Vic's girlfriend lives near Haysville, North Carolina, in
grid square EM85, and around noon local time on Tuesday, August 2
she heard KRKX in Billings, Montana on 94.1 MHz on her car radio.
The strong signal was full-quieting, and the KRXK transmitter site
is in grid square DN55, a little less than 1500 miles away.

If you would like to comment or have a tip, email the author at,

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
bulletins is found at,

Sunspot numbers for July 28 through August 3 were 29, 69, 62, 110,
102, 112 and 102 with a mean of 83.7. 10.7 cm flux was 95.8, 103.7,
105, 109.7, 111.2, 110.2 and 108.9, with a mean of 106.4. Estimated
planetary A indices were 28, 19, 16, 9, 16, 12 and 11 with a mean of
15.9.  Estimated mid-latitude A indices were 18, 14, 11, 10, 18, 9
and 6, with a mean of 12.3.


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