ARRL Propagation Bulletin ARLP005 (2008)

ARLP005 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 5  ARLP005
From Tad Cook, K7RA
Seattle, WA  February 1, 2008
To all radio amateurs 

ARLP005 Propagation de K7RA

Sunspots have returned.  After nearly three weeks with nothing
visible (January 9-28), sunspot group 982 emerged on January 29.
The very quiet geomagnetic conditions of the past week may be ending
with some moderate to unsettled activity.  US Air Force predicts a
planetary A index for February 1-6 at 12, 10, 15, 10, 8 and 5.  The
next active period could be around February 9-10, with a planetary A
index of 15.  The period of February 16-26 is likely to see no
spots, and for February 27 through March 1 we may see sunspots

Geophysical Institute Prague predicts unsettled to active conditions
for February 1-2, unsettled February 3-4, quiet to unsettled
February 5, and quiet on February 6-7.

Last year we began calculating and tracking a 3-month moving average
of daily sunspot numbers.  This was done to try to spot trends.  A
three month period seemed like it might give us some smoothing of
the often volatile daily numbers, but much shorter than the official
12-month smoothed values used to calculate the solar minimum some
time after it actually occurs.

Now that January is done, we can calculate the 3-month moving
average centered on December, 2007.  The sum of all the daily
sunspot numbers from November 1 through January 31 is 749, and
divided by 92 days, this gives a 3-month average of 8.1.

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
May 07 15.8
Jun 07 18.7
Jul 07 15.4
Aug 07 10.2
Sep 07  5.4
Oct 07  3
Nov 07  6.9
Dec 07  8.1

A three-month moving average may be too short to spot the actual
bottom of Cycle 23, but with the steady decline from 2006 until
October 2007, and a 3-month average rising from 3 to 6.9 then 8.1
since then, this suggests a cycle minimum during the Fall of last

Four years ago in Propagation Forecast Bulletin ARLP005, for January
30, 2004 (see N6QYS
(now W6JP) wondered if Cycle 23 was near minimum, and if conditions
would soon improve.  I looked at the weekly Preliminary Report and
Forecast, and the table of predicted smoothed sunspot numbers ended
in December 2007.  I could see that values were expected to be lower
a year from then, in January 2005.  Based on this, I wondered at the
time if sunspot levels might return to the predicted January 2005
level in 2008, and promised to set an alarm in my PDA for four years
into the future.

The actual average of daily sunspot numbers for January 2004 was
62.3, and January 2005 was 52.  The following Januarys through this
one had average sunspot numbers of 25.7, 28.2 and 5.1.

Based on the predicted smoothed sunspot table on page 8 at,, it could be some
time before we are back to the 2004 and 2005 levels.

So what is the difference those sunspot numbers make between 2004
and 2008?  In 2004, the 20 meter path from San Francisco to Japan
should stay open 2130-0500z, with best signals toward the end of
that period.  But for tomorrow, that path would probably open
between 2230-0030z.  15 meters would open 2200-0200z in 2004, but
perhaps 2300-2330z.

Similarly, Chicago to Germany in those days on 15 meters was
probably open 1530-1830z, but today not open at all.  On 20 meters
today the path would likely open 1530-1730z, but in 2004 it was

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,

Sunspot numbers for January 24 through 30 were 0, 0, 0, 0, 0, 13 and
14 with a mean of 3.9.  10.7 cm flux was 71.3, 71, 72.5, 72, 71.3,
71.6, and 72.7 with a mean of 71.8.  Estimated planetary A indices
were 5, 11, 5, 2, 2, 4 and 2 with a mean of 4.4.  Estimated
mid-latitude A indices were 3, 8, 6, 2, 2, 3 and 1, with a mean of