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ARRL Propagation Bulletin ARLP037 (2010)

ARLP037 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7RA
Seattle, WA  September 17, 2010
To all radio amateurs 

ARLP037 Propagation de K7RA

Average daily sunspot numbers this week dropped nearly 23 points to
15.6, and geomagnetic indices were quiet.  The average daily solar
flux was 78.1, but the latest prediction from USAF and NOAA is for
rising solar flux values.  The September 17-23 projection has solar
flux values at 85, 85, 86, 86, 86, 87, and 88, which is well above
last week's average.  Solar flux hasn't been to 88 or higher since
August 7 (90.5), and before that July 21 (89.1).

The same forecast shows planetary A index for the same period at 8,
5, 5, 5, 18, 18 and 15, which indicates rising geomagnetic activity
along with the increased solar activity. Geophysical Institute
Prague predicts quiet to unsettled conditions September 17, quiet
September 18-19, quiet to unsettled September 20, and unsettled
conditions September 21-23.

The Autumnal Equinox occurs Wednesday, September 22 at 11:09 PM EDT,
which is 0309 UTC on September 23.  With the northern and southern
hemispheres bathed in equal amounts of light, expect better
worldwide HF propagation, although solar activity continues at a low
level which does not support an MUF into the higher frequencies over
most paths.

By the way, the bulletin didn't mention this at the beginning of
September, but the monthly averages of daily sunspot numbers have
risen the past few months. For June, July and August the average
daily sunspot numbers for each month were 18, 23.1 and 28.2, and so
far in September the average for the first 16 days is 29.6.

Last Saturday, September 11, AC7SB, W7RDP and WE7X went to the
Suntop forest fire lookout station in the Cascade Mountains of
Washington State.  The location is 47.041 deg N, 121.5965 deg W,
While there they used a telescope and filter to view an emerging
sunspot, W7RDP and WE7X operated the ARRL VHF Contest, and AC7SB
worked 40 meter CW using a tape-measure dipole.  You can see a photo
album of their adventure at,

Scott Bidstrup, TI3/W7RI in Costa Rica sent an article about Tsunami
waves disrupting the ionosphere.  Read it at,

Mike Downing, KC0Y of Broomfield, Colorado is getting back on 6
meters after many years, and wonders how things have changed
regarding TVI?  He mentioned that most people are using cable TV and
the broadcasters have left Channel 2, which had a lot of the
problems in the past.  According to what I've heard, the situation
is much better than it was decades ago, for the reasons that Mike

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 September 9 through 15 were 0, 11, 11, 26, 17,
24, and 20 with a mean of 15.6. 10.7 cm flux was 73.7, 75.3, 78,
78.3, 79.5, 80.7 and 81.2 with a mean of 78.1 Estimated planetary A
indices were 4, 2, 1, 1, 2, 9 and 7 with a mean of 3.7. Estimated
mid-latitude A indices were 4, 2, 1, 1, 1, 7 and 4 with a mean of


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