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ARRL Propagation Bulletin ARLP020 (2009)

ARLP020 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7RA
Seattle, WA  May 19, 2009
To all radio amateurs 

ARLP020 Propagation de K7RA

After weeks of little or no sunspots, it is nice to have something
to report.  Following multiple false starts, quick-fading spots and
knots of magnetic activity which never progressed into actual
darkened sunspots, new sunspot group 1017 emerged on Wednesday, May
13.  The daily sunspot number was 12, and the next day the size of
the group approximately doubled, raising the sunspot number to 18.
This is a cycle 24 sunspot group.

A week ago we expected active regions spotted by the STEREO mission
would emerge into sunspots over the weekend, but like many others in
the recent past, they faded away.  The new sunspot this week emerged
a few days later.

Last week's bulletin showed average daily solar flux at 68.5, and
this week it was 72.  The average solar flux for the last three days
prior to this bulletin (May 12-14) was 73.9, indicating a further
rise.  On May 14, the daily predicted 45 day 10.7 cm solar flux from
USAF/NOAA was raised to 75 for May 15-21.  By the way, we've
mentioned in the past that the link to the latest daily forecast at is sometimes
delayed until after the forecast is put up, and you can hack the URL
(web address) to the next date from the latest available forecast.
Thursday's must be the longest delay between the forecast time and
the time the link goes up on the web.  Right now the forecast done
at 2059z on May 14 is still not available at 1430z on May 15.  But
you can click on the latest link, which takes you to and then
change the date at the end of the URL to /051445DF.txt, which takes
you to
Over seventeen hours after it was written, this was still the only
way to read Thursday's forecast.

There seems to be more confusion regarding the difference between
number of sunspots and sunspot number.  Mike Khokhlov, UA9CIR of
Ekaterinburg in Asiatic Russia notes that the new Solar Cycle
Prediction update for cycle 24 from NOAA (see issued a week ago
said the cycle may peak four years from now ''with a maximum sunspot
number of 90''.  But in other reports, such as ARLS003
( this was changed to
''Solar Cycle 24 will peak in May 2013 with 90 sunspots per day on
average''. got it wrong also, saying ''The panel
predicts the upcoming Solar Cycle 24 will peak in May 2013 with 90
sunspots per day, averaged over a month'' (see  Update: Dr. Tony Phillips of said the error was corrected, but the link should
have been changed so that it ends in php instead of htm.  Edit that
URL and page back and forth to see the difference.

Note that Thursday and Friday of this week had one sunspot group,
but the sunspot numbers were 12 and 18.  As mentioned in past
bulletins, a good explanation for the arcane method for computing
daily sunspot number is at, a NOAA page about
the work of Johann Wolf.

The two references above to the ''90 sunspots'' error were actually
widespread.  Just Google the phrase ''90 sunspots per day'' and you
will get hundreds of hits.  Although NOAA was the source of the
original correct information, NOAA News got it wrong at

Dennis Eksten, W9SS tried to write in last week, but couldn't find
our email address, which is toward the end of each bulletin.  Or it
should be.  I was alarmed to find that it was missing from ARLP019,
and I shuddered to think how long the bulletin had been coming out
with no reference for contacting the author.  Fortunately, it was
only missing last week, and has been reinserted this week.

Dennis saw an Associated Press story last weekend titled ''Warning:
Sunspot cycle beginning to intensify''.  It was titled differently in
different publications (see
and note that this also has the ''90 sunspots per day'' error) but
Dennis wondered about the geomagnetic storm of 1859 and if it could
happen today with the dire results mentioned in the article.

As far as I know, the tales of telegraph wires starting fires and
aurora visible around the world were taken from contemporary
nineteenth century accounts, and are true.  I've heard this story
for a long time, and seen references to 1859 newspaper accounts.
This would make an interesting subject for historical research.  The
query was passed from W9SS to Tom Ciciora, KA9QPN, the Illinois SM,
who commented, ''We can all pretty much agree that most newspaper
accounts of natural phenomena were sensationalized back then in
order to assist the fledgling newspaper industry (kind of like
now.), but the question bears asking.  Is the scenario described
even possible?''

We really have no way to predict whether this will happen again,
just as we have no way to predict another cycle 19 or a Maunder
Minimum.  But the NAS predictions of 4-10 years recovery and
trillions in damages certainly gives one pause for reflection.  We
do have much more complex and concentrated infrastructure currently,
and seem more vulnerable.

This reminds one of the old stories about EMP (electromagnetic pulse
from a nuclear blast) in warfare, and the vulnerability of solid
state vs. old vacuum tube technology.  In the Cold War, one side
felt that their military hardware, in fighter jets for example, with
modern solid state electronics was far superior to the other side,
which may have used older designs with vacuum tubes.  But it was
pointed out that vacuum tubes are much less vulnerable to an EMP
blast.  The simpler, hardier design may be superior in a real life
battlefield environment that has escalated to the unthinkable level.
Thank goodness it was never tested with EMP in a real battle.

Much more to write about on some other topics, but we are out of

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 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 May 7 through 13 were 0, 0, 0, 0, 0, 0, and 12
with a mean of 1.7.  10.7 cm flux was 69.5, 70.8, 72.3, 71.8, 71.9,
73.9, and 73.8 with a mean of 72.  Estimated planetary A indices
were 10, 13, 6, 4, 4, 2 and 3 with a mean of 6.  Estimated
mid-latitude A indices were 7, 12, 6, 3, 2, 0 and 2 with a mean of


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