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ARRL Propagation Bulletin ARLP006 (2007)

ARLP006 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 6  ARLP006
From Tad Cook, K7RA
Seattle, WA  February 9, 2007
To all radio amateurs 

ARLP006 Propagation de K7RA

Average daily sunspot numbers and solar flux were up this week,
while average daily geomagnetic indices were down, which is a nice
combination. Our reporting week hasn't had better geomagnetic
stability (lower average A index) since November 16-22, 2006,
reported in last year's Propagation Forecast Bulletin ARLP049. That
week the planetary and mid-latitude A indices were 3.6 and 2.1,
while this week's numbers are 5.6 and 4.3.

Conditions won't remain quiet, and geomagnetic activity should
increase until next Tuesday, February 13. Geophysical Institute
Prague predicts quiet to unsettled conditions for today, February 9,
quiet conditions on February 10, unsettled to active February 11,
unsettled February 12, active geomagnetic conditions on February 13,
unsettled to active on February 14, and February 15 unsettled.

The US Air Force predicts a planetary A index for February 9-15 at
5, 5, 20, 20, 20, 15 and 5. For those same days they predict solar
flux values of 80, 83, 83, 81, 80 and 80.

We keep mentioning the bottom of the sunspot cycle, and by some
accounts, we are probably there, or very close. NOAA Space
Environment Center has a new prediction in this week's Preliminary
Report and Forecast of Solar Geophysical Data at, Look at the table on
page 10, and compare it with the table on page 9 in the report from
five weeks earlier,
These are predicted smoothed sunspot numbers, averaged over a year,
going six months prior and six months into the future for each

Notice in the most recent report that the latest smoothed sunspot
number not in bold lettering is July 2006. That is because the real
sunspot data actually exists for six months after that month, and
this is the actual smoothed sunspot number, an average of averages,
made up from the monthly averages for January 2006 through January
2007. If you check the report from five weeks ago, July 2006 is
bold, because there was one month for which actual sunspot numbers
weren't actually yet known, January 2007. So in the latest report,
the number for October 2006 factors in three predicted but as yet
unconfirmed monthly averages, February through April 2007, and
December includes predicted numbers for five months, February
through June 2007.

So in the early January report, you can see that the numbers for
October 2006 through August 2007 were 13, 11, 10, 10, 10, 10, 10,
10, 10, 10 and 11. The most recent prediction for those same months
was 14, 12, 12, 11, 11, 11, 11, 11, 11, 12 and 11. Both reports seem
to place us at the bottom. The other clue is at, where the predicted
smoothed sunspot number is 10.9 for March 2007, with 11 for both
this month and April. March 2007 would be the lowest predicted
smoothed sunspot number shown in this table.

Randy Crews, W7TJ of Spokane, Washington wrote to comment after last
week's summary of monthly sunspot averages in Propagation Forecast
Bulletin ARLP006 (see Randy thinks that
the actual low for cycle 23 was last year, in February 2006, when
the average sunspot number for the month was only 5.3. Another way
to look at this is with a 3-month moving average based on an average
of the daily sunspot numbers, instead of an average of averages, as
the 13 month smoothed number is. So for December 2006 we would get
an average of 27.2 by summing all of the sunspot numbers from
November 1 through January 31, which yields 2507, and dividing by
the number of days, which is 92.

Here is a table of the 3-month average of daily sunspot numbers for
a 13-month period:

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

The number shown for each month is the average for the daily numbers
for that month combined with the month preceding and the following
month. This still shows a low minimum centered on February 2006.
W7TJ says he likes the sunspot minimum because there are very few
days with disturbed conditions. He says, "What I am looking forward
to is a quiet Sun, absent of CMEs, coronal holes, X-Ray radiation
etc, that ruin propagation." And of course, since the MUF is lower
because of the lower solar activity, this really is the best time
for 80 and 160-meter propagation.

Now as we move toward mid-February, we are further from the darkest
day of the year, and half way toward the Spring equinox, which is a
good time for HF propagation. What will HF propagation be like from
your location today? This will vary according to which amateur band
you use and what part of the world you are targeting.

This bulletin has mentioned W6ELprop in the past, and you can use
this software to come up with unique propagation projections from
your location, much better than we could do in this bulletin by
generalizing for a region. You can get the software from, A good method is to take an average of
the three most recent sunspot numbers, and use that figure with
W6ELprop. You can get those numbers from,

So if it is Friday morning, February 9, the average would be based
on the sunspot numbers from February 6-8, which were 23, 23 and 22.
That averages to about 22.7. When you enter that number into
W6ELprop, whether you have it set to take sunspot number or solar
flux, you can always get the right choice by preceding the sunspot
number with the letter S. So that would be S22.7 for today.

W6ELprop will also work with the K index, and you can get the
current mid-latitude K index from WWV. The current WWV numbers are
always available at,

Of course, you will want to customize the program for your own
location, based upon latitude and longitude. There are a variety of
ways to find these coordinates, but one easy method that gets you
close enough is to do a ZIP Code search at, Be careful when
you enter the numbers, because W6ELprop expects west longitude as a
positive number, and on this web site they use the common standard
in which east longitude is positive. So for those of us west of
Greenwich, England, the prime meridian, we would turn that negative
longitude into positive for the W6ELprop software.

Given the average sunspot number for the previous few days, suppose
we are in Atlanta, Georgia, and want to know what the bands will be
like toward Brazil. If this is the first time using the program, we
can set up our location by clicking on Options at the top.

To make a projection, bring up the program, click on Predictions at
the top, then select On-Screen from the drop-down menu, and then use
the tab key to navigate through the various fields, entering PY for
Brazil in the Prefix or Locator field. When the calculation is made,
we can see that as the MUF rises above 22 MHz, 15 meters would
likely open around 1330z. Signals should stay strong during the day,
and get stronger before dropping out around 2300z when the MUF drops
below the 15-meter band.

A great propagation program is ACE HF Pro, which gives some very
fine graphic visualizations of propagation. You can learn about it
from, or from, That first link was from Tomas Hood,
NW7US, who in addition to editing the monthly propagation column for
CQ Magazine, has a fine web site devoted to radio propagation. It
has been offline for several months, but is back on 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 February 1 through 7 were 31, 36, 35, 28, 25, 23
and 23 with a mean of 28.7. 10.7 cm flux was 89.9, 90.3, 87.3, 83.7,
83, 81.9, and 82, with a mean of 85.4. Estimated planetary A indices
were 8, 2, 3, 2, 6, 8 and 10 with a mean of 5.6. Estimated
mid-latitude A indices were 7, 2, 1, 2, 4, 6 and 8, with a mean of


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