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ARRL Propagation Bulletin ARLP037 (2008)

ARLP037 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7RA
Seattle, WA  September 5, 2008
To all radio amateurs 

ARLP037 Propagation de K7RA

We're still looking at a quiet Sun, but currently a solar wind is
disturbing Earth's magnetic field.  6 meter operators--after
enjoying a fine season of sporadic E propagation this Summer--may
see some added excitement from auroral propagation.  Check the site for updated indicators.

The planetary A index was 33 on Thursday, September 4, the highest
daily number in over a year.  I don't know when it was last that
high, but the closest recent numbers were 32 on April 23, and 31 on
March 27.  Planetary A index for September 5-10 is predicted to be
20, 15, 8, 5, 5 and 5.  It is expected to rise to 20 on September

Ken Tata, K1KT of Warwick, Rhode Island reported tropospheric
propagation on Thursday night, September 4.  He likes the VHF
propagation maps at, and notes
it showed a band of propagation extending all up and down the
Eastern seaboard.

There has been some news about the current solar minimum regarding
continuous days without spots.  August was the first calendar month
with no sunspots since 1913.  Of course, there have been periods
longer than 30 days, but generally over a two calendar-month period
in which there were some sunspots in each month.  As of Thursday,
September 4, there have been 46 continuous days with no spots.  That
is the seventh longest period of no spots, looking back over 150
years to the mid nineteenth century.  If there are no sunspots
through this Sunday, at 49 days this will be the fourth longest
spot-free period.

But not everyone is reporting zero sunspots for August.  If you go
to and to the archives on the upper
right side, change the date to August 21 and August 22.  On both
those days they show a sunspot number of 11 (look at the left side
of the page), indicating a single spot which had a magnetic
signature indicating a new Cycle 24 origin.  This is the same number
that Zurich shows, but not NOAA, which didn't assign it a number
because it was so short lived.

Both May and June 1913 were spotless, in a continuous spotless run
of 92 days from April 8 to July 8.  Cycle 19 was the biggest solar
cycle on record, and it is interesting to note that it was preceded
by long periods without spots.  There was a 26 day spotless run from
February 15 to March 4, 1953, followed by 27 days from January 12
through February 7, 1954, and 30 days beginning on June 3, 1954 and
running through July 2.

In case you've forgotten what a spotted Sun looks like, take a peek
at seven years ago, on September 1, 2001 at,

In a little over two weeks will be the Autumnal Equinox (September
22)--the start of the Fall season and a sweet spot for HF
propagation.  Without sunspots, HF is still useful for long distance
communication.  Plugging in 0 for sunspots with one of the popular
propagation programs shows 20 meters to be the best overall.
Figuring a path from Texas to Brazil, W6ELprop
( shows 20 meters at the Equinox begins
opening around 1800z, with signals steadily rising, then closing
around 0200z.  17 meters looks productive with rising signal
strength throughout the day, starting at 1600z with signals rising
until the band closes around 0000z.  40 and 30 meters also look
productive, with 40 opening around 2300z, and rising signals,
especially after 0000z.  It stays strong all night, dying out after
local sunrise.  30 meters looks good over that path from 2300-0700z.

Evan Rolek, K9SQG of Beavercreek, Ohio notes that although signal
levels are overall much lower because of lack of sunspots, there are
still big variations.  For instance, two months ago he worked an S9
station from India, on 40 meters with a wire loop at 12 feet.

Bud Frohardt, W9DY is mobile in Elgin, Illinois.  After being on the
air recently, he thought perhaps sunspots had returned.  On August
26 he was operating CW mobile on 20 meters, and says he was able to
work many more stations than in recent months.  In 37 minutes he
worked all continents.  He says European stations were all over the
band with excellent signals until he turned off the radio at 2215z.

Russ Ward, W4NI of Nashville, Tennessee sent in a tip on an
interesting article he read about geomagnetic events.  Titled
"Elusive Onset of Geomagnetic Substorms," it appeared in the August
15, 2008 issue of Science, volume 321, pages 920-921.

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 August 28 through September 3 were 0, 0, 0, 0,
0, 0, and 0 with a mean of 0.  10.7 cm flux was 66.1, 66.8, 67.1,
66.7, 65.8, 66, and 66.2 with a mean of 66.4.  Estimated planetary A
indices were 2, 3, 3, 3, 4, 3 and 7 with a mean of 3.6.  Estimated
mid-latitude A indices were 2, 2, 2, 2, 2, 2 and 7 with a mean of


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