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ARRL Propagation Bulletin ARLP050 (2011)

ARLP050 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 50  ARLP050
From Tad Cook, K7RA
Seattle, WA  December 9, 2011
To all radio amateurs 

ARLP050 Propagation de K7RA

What happened to that new "grand minima?"  Cycle 24 just keeps
rolling along, and for the first seven days in December, there were
eight new sunspot groups.  December 5 had the largest sunspot
coverage over the past week, with a daily sunspot number of 185.
Average daily sunspot number for the week rose over nine points to
133.9, and average daily solar flux values rose exactly 19 points to

NW7US has a graph at comparing
Cycle 24 progress with the upswing of Cycle 23.

It is based on the RI or monthly mean Brussels International Sunspot
number, which is lower than the SWPC Space Weather Operations
sunspot numbers we use in our bulletin.  The data source is This
doesn't reflect the upswing since the start of each cycle, and does
not show the long quiet period at the start of the current cycle. It
just shows the monthly mean data over the 25 months ending in
September 2011, compared to the 25 months ending in June 1998. The
graph appears on

The latest forecast from USAF/NOAA has solar flux at 145 on December
9-12, 140 on December 13-16, 160 on December 17-18, and 155 on
December 19-22.

Planetary A index for the same dates is expected to be 5 on December
9-10, 8 on December 11, and 5 on December 12-22.

The solar flux values in the above forecast changed quite a bit from
what was reported in the ARRL Letter on Thursday.  That was based on and this
forecast is based on

Geophysical Institute Prague sees a quiet week ahead, with quiet
conditions December 9-11, quiet to unsettled December 12, and quiet
again on December 13-15.

Conditions should be good for the ARRL 10 Meter Contest this

Every new month brings a slight upward revision in the smoothed
sunspot forecast. Note the differences between the table on page 19
in and page 17 in

An article from the Royal Observatory of Belgium concerning rising
solar activity appears at,

Brian Machesney reported some interesting multipath echoes on
December 5. He writes, "Strong 17m CW signals from A71EM to FN34 are
suffering from what sound like multipath echoes at 13:30Z on 5 Dec
11. There seem to be at least three, distinct paths of nearly equal

Jon Jones, N0JK sent comments about the winter sporadic-E season:
"The winter Es season is underway. On December 3, KB3RHR EN90 was
into Kansas on 50 MHz at 2315 UTC. This was E-skip. The Winter Es
season tends to peak around Christmas. This year with the higher
solar flux the Es can link to F2 and TEP openings."

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 December 1 through 7 were 89, 106, 138, 154,
185, 143, and 122, with a mean of 133.9. 10.7 cm flux was 152.2,
157.3, 164.1, 163.6, 158.1, 151.1, and 148.9, with a mean of 156.5.
Estimated planetary A indices were 7, 4, 9, 4, 2, 1, and 1, with a
mean of 4. Estimated mid-latitude A indices were 7, 4, 7, 4, 4, 0,
and 1, with a mean of 3.9.


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