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ARRL Propagation Bulletin ARLP023 (2007)

ARLP023 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 23  ARLP023
From Tad Cook, K7RA
Seattle, WA  June 1, 2007
To all radio amateurs 

ARLP023 Propagation de K7RA

The average daily sunspot number this week dropped nearly 23 points
to 3.3, while average daily solar flux declined exactly five points
to 68.8.  We saw five days in a row with a sunspot number of 0.  All
those zeroes combined with sunspot numbers of 11 and 12 are what
made the average only 3.3.  If there are any sunspots at all, the
sunspot number itself can't ever go that low, because there are no
sunspot numbers between 0 and 11, due to the way the number is
calculated.  It is not actually a count of the number of sunspots.

11 is the number you get if there is one sunspot, because a value of
10 is added for each group of sunspots.  So one sunspot counts for
only one group, so ten plus one sunspot equals eleven.  If there are
two sunspots in that group, then the sunspot number is 12, three is
13, and so on.  But if there are three sunspots divided into two
groups, then the number is 23, as it was on May 20.

If we didn't have any images of the Sun, and the sunspot number was
23, we might think there were thirteen sunspots in one group,
instead of three in two groups, which would be valid according to
the formula, but less likely.

The forecast is for continued one or zero sunspot conditions, with a
planetary A index for June 1-7 at 5, 5, 15, 15, 8, 5 and 5.
Geophysical Institute Prague predicts quiet conditions for today,
June 1, unsettled June 2-4, and quiet again on June 6-7.  For some
reason they didn't make any prediction for June 5, but I'll bet that
it is a quiet to unsettled day.

Just prior to the writing of this bulletin, at 0651z on June 1, an
M1 class X-ray flare was released from the Sun.  Thanks to NW7US and
his web site,, for this alert.  Now, the
interplanetary magnetic field points south, making earth vulnerable.
On June 3, a solar wind stream is expected to hit earth when a
coronal hole shifts into a critical position.  This is what the
planetary A index forecast of 15 for June 3-4 is based on.

Let's look at the average daily sunspot numbers and solar flux for
May, compared to previous months, to spot any trends.

Monthly averages of daily sunspot numbers for April 2006 through May
2007 were 55.2, 39.6, 24.4, 22.6, 22.8, 25.2, 14.7, 31.5, 22.2,
28.2, 17.3, 9.8, 6.9 and 19.8.  Monthly averages of daily solar flux
for the same period were 88.9, 80.9, 76.5, 75.8, 79, 77.8, 74.3,
86.3, 84.4, 83.5, 77.7, 72.2, 72.4 and 74.4.

We've recently been looking at 3-month smoothed sunspot numbers, so
knowing the May values, we can combine them with March and April to
produce a smoothed 3-month average sunspot number centered on April,
which turns out to be 12.2.

Here are the 3-month smoothed sunspot numbers for the past 19

Oct 05 28 
Nov 05 36 
Dec 05 40.6 
Jan 06 32.4 
Feb 06 18.1 
Mar 06 27.7
Apr 06 38.5 
May 06 39.7 
Jun 06 28.9 
Jul 06 23.3 
Aug 06 23.5 
Sep 06 21.2 
Oct 06 24.1 
Nov 06 23.1 
Dec 06 27.3 
Jan 07 22.7 
Feb 07 18.5 
Mar 07 11.2 
Apr 07 12.2

The moving average centered on April is just one point above March's
value, but the overall trend is consistent with a declining solar

Several people sent articles about new methods for predicting solar
radiation storms up to an hour or two prior to their commencement.
One involves detecting a swarm of electrons in advance of the
energetic ions.  Another refers to the "scream" of a coronal mass
ejection's advance front of radio energy.  See the two stories at, and

ARRL Field Day is coming up soon, and several readers, including
Wade Grimes, K0MHP of Elsberry, Missouri asked about conditions for
that weekend, now just three weeks away.

It is too early to tell, but I have been checking the daily updates
at,  The one
released on May 31 shows a solar flux of 65, possibly meaning no
sunspots, and coming off a period of higher geomagnetic activity,
based on the most recent solar rotation.  Field Day is always the
last full weekend in June, which this year is June 23-24, and the
planetary A index prediction for June 19-24 is 25, 20, 20, 20, 12
and 5.

But this weekend there are actually three other field day operating
events, not associated with the ARRL Field Day, and we can
participate in those too if we wish.

The first is the IARU Region 1 HF Field Day.  It actually is in two
parts, CW and SSB, and the CW weekend is this weekend, running from
1500z Saturday to 1500z Sunday, June 2-3.  IARU Region 1 covers
Europe, Africa, Middle East, and Northern Asia, but nothing in the
rules precludes North American stations from participating, and in
fact, those Region 1 stations get more points for working other
stations outside their continent.

There are some interesting differences between their Field Day and
the ARRL Field Day.  One is they have much more in the way of
logging requirements, and they score more points for working
stations in different places, whereas in the ARRL Field Day an
acceptable entry consists of a dupe sheet and summary form.  The
other interesting difference is that antennas can be only a single
element, such as a dipole, a longwire, or a trapped vertical.  No
part of that antenna can be more than 15 meters above ground level.
You can read the rules for the IARU Region 1 HF Field Day at,

This weekend is also the National Field Day for the Radio Society of
Great Britain.  Their rules are even more different from ARRL Field
Day than the IARU event.  They don't preclude North American
stations either, but to be eligible for awards, a club must register
with the RSGB, and expect to receive a site inspection from
representatives of the HF Contests Committee, possibly more than
once over the weekend.  The deadline for registration was May 13.
This one also runs from 1500z to 1500z, like the IARU event.  It is
CW only, and one class of entrants restricts antenna heights to 20
meters.  Another entry class permits "One antenna only which must be
a single element having not more than two elevated supports and not
exceeding 11 meters above ground at its highest point."  There is a
low power entry class, and they must run 10 watts or less, but can
only operate for 12 hours maximum.  You can read the rules yourself

An even more unusual field day is the "Look Around In the Field"
event, put on by NJ2OM.  In fact, there are bonus points for working
either NJ2OM, or his daughter, NJ2YL, and even more if you talk to
both of them and additional points for every band you work them on!
The objective of this event is, "To get outside, look around and
notice all the different wildlife around you, then exchange that
information with other amateur radio operators."  It only runs
Saturday, and only between 1600z-2159z (perhaps for the convenience
of NJ2OM!) and you can see the rules at,

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,

Sunspot numbers for May 24 through 30 were 0, 0, 0, 0, 0, 11 and 12
with a mean of 3.3. 10.7 cm flux was 69.9, 68.1, 67.7, 67, 68.7,
69.6, and 70.7, with a mean of 68.8. Estimated planetary A indices
were 28, 16, 16, 12, 5, 4 and 4 with a mean of 12.1. Estimated
mid-latitude A indices were 21, 9, 10, 10, 5, 5 and 3, with a mean
of 9.


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