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ARRL Propagation Bulletin ARLP006 (2011)

ARLP006 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 6  ARLP006
From Tad Cook, K7RA
Seattle, WA  February 11, 2011
To all radio amateurs 

ARLP006 Propagation de K7RA

Seven different sunspot groups were visible over the past week.  The
high sunspot number in the past seven days was 71 on Tuesday, and
the average daily sunspot number more than doubled, rising over 24
points to 44.3.  Average daily solar flux was up nearly three points
to 83.5.

71 is the highest sunspot number since May 5, 2010 when it was 77.
Coincidentally, both February 8, 2010 and February 8, 2011 had a
sunspot number of 71, and between those dates it was never higher
except for 77 on May 5.

The NOAA/USAF prediction for solar flux for the near term improved
considerably from what was reported in yesterday's ARRL Letter.
Solar flux is predicted at 90 on February 11-18, then for February
19-25, 88, 88, 86, 84, 84, 80 and 80.  They predict a constant
planetary A index of 5 through the end of the month, then 7, 10, 10
and 7 on March 1-4.

Even though NOAA sees a constant and quiet geomagnetic environment
through the end of the month, Geophysical Institute Prague sees it a
little differently for February 11-17.  They predict quiet on
February 11-12, quiet to unsettled February 13, unsettled February
14-16, and quiet to unsettled February 17.

There are a couple of sobering items concerning progress of solar
Cycle 24 and predictions for the peak, now centered around February
through July in 2013.

The latest predicted smoothed sunspot numbers are in this week's
Preliminary Report and Forecast #1849 at

Dick Wiltgen, K8RBW of Chicago sent an article from NASA on the
latest solar cycle prediction. Read it at

Note they are using International Sunspot Numbers, which are lower
than the Boulder numbers we use in this bulletin, and reported in
the Preliminary Report and Forecast.  Also, at this stage in Cycle
24, predictions are more reliable.  Among others, the article cites
recent work by Joan Feynman, daughter of the remarkable Nobel Prize
winning physicist Richard Feynman.

Ray Perrin, VE3FN of Ottawa, Ontario sent in a very interesting
report of propagation at the start of high geomagnetic activity on
February 4.

Ray wrote, "Just before 2000Z on Feb 4, I was tuning across 15
meters and was surprised to hear a strong signal from a Finnish
station on CW.  I tuned up the band a bit and heard another Finnish
station -- Marko OH3XR -- working a station in Ohio.  I was
surprised that I was able to hear the Ohio station as it is very
short skip from my QTH (Ottawa) in eastern Ontario (grid FN25).  But
I noticed the signal from the Ohio station was not pure T9.  It also
had some slight hiss which I normally associate with auroral

"I then worked Marko OH3XR and he reported that there was a large
aurora in progress.  This seemed to confirm that I had indeed heard
the Ohio station via aurora -- besides, I believe the path was much
too short to have been F Layer.  Marko's signal was pure T9 and I am
unsure as to the mechanism that propagated our signals.  My first
assumption was that it was Auroral E.  However, I believe that
F-layer propagation can be enhanced after an aurora -- primarily on
north - south paths.  But my guess is that it was Auroral E.

"After our QSO, I checked the NOAA Space Weather Now site.  It was
still showing that the auroral zone was fairly quiet and the K index
was low.  But a little later, it showed an active auroral zone, a K
index of 6, and that there was a G1 storm in progress."

It is interesting to look at geomagnetic indices on that date,
particularly planetary A and K index, at

In last week's bulletin (see was a report
from Tamas, HA5PT and he sent along some links, including a sound
file to augment his report.  See and

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 February 3 through 9 were 32, 45, 26, 41, 28,
71, and 67, with a mean of 44.3. 10.7 cm flux was 80.4, 82.1, 81,
80.2, 82.3, 89.7 and 88.7 with a mean of 83.5. Estimated planetary A
indices were 1, 21, 13, 11, 3, 4 and 2 with a mean of 7.9. Estimated
mid-latitude A indices were 0, 12, 11, 8, 2, 3 and 1 with a mean of


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