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ARRL Propagation Bulletin ARLP041 (2010)

ARLP041 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 41  ARLP041
From Tad Cook, K7RA
Seattle, WA  October 15, 2010
To all radio amateurs 

ARLP041 Propagation de K7RA

Solar activity dropped again this week, although it is now gradually
strengthening.  Average daily sunspot numbers declined nearly 16
points to 11.7, and average daily solar flux dropped over five
points to 75.8.  Over the next two weeks solar flux is expected to
gradually increase, from 80 on October 15-16, 82 on October 17, 84
on October 18-22, 80 on October 23-25, and 85 on October 26-29.

The reporting week (the data at the end of this bulletin) runs
through Wednesday, October 13, and on Thursday, October 14 the
sunspot number rose from 24 to 34, and solar flux increased from
78.1 to 80.4.

The increase is expected from sunspot group 1112, emerging on
October 9, and group 1113, which appeared on October 13 rotating
over the eastern limb.  On October 14 new sunspot group 1114
appeared.  The STEREO mission at shows a
series of magnetically active areas on our Sun's far side, which
will gradually rotate into view.

A very rough estimate of the transit time involved can be made by
assuming that a full rotation of the Sun is about 27.5 days.  Each
of those 12 longitudinal divisions on the rotating solar globe at
the STEREO site therefore each represent approximately 55 hours, or
about 2.29 days.  This can be used as a rough guide to the time it
takes for any area of interest to move over the eastern horizon.

Geomagnetic activity is expected to be stable, with planetary A
index moving between five and eight.  Predicted planetary A index is
7 on October 15, 8 on October 16-17, 5 on October 18, 7 on October
19-20, 5 on October 21-23, 8 on October 24-25, and 5 on October

The Geomagnetic Department of Geophysical Institute Prague predicts
quiet conditions on October 15, quiet to unsettled October 16, quiet
October 17-20, and quiet to unsettled again on October 21.

Note the solar flux and A index data in the first and fifth
paragraphs is updated from similar data in yesterday's ARRL Letter.
You can see daily updates of this predicted data at

Over the past week the most active geomagnetic day was Monday,
October 11, when the planetary A index was 20 and the planetary K
index went as high as 5.  Alaska's College A index was 49, based on
a College K index as high as 7.  This activity was pushed by a
strong solar wind.

There is an interesting and educational web page devoted to
heliophysics from the University Corporation for Atmospheric
Research in Boulder, Colorado.  See it at

Richard Dowty, W7EET of St. Paul, Oregon isn't sure what to do with
the data presented in this bulletin.  He would rather see reports
that predict the MUF for the next week, tell him which bands will be
good or bad, and information of a more practical nature.

One problem with this is that MUF (Maximum Usable Frequency) is
different for different paths and at different times.  Generally MUF
should be higher when there are more sunspots.  We could make very
general statements such as "West coast stations should be able to
hear Japan on 20 meters from 2000-0230z and again at 0400-0430z,
with best signals from 2030-0030z, and 17 meters at 2130-0130z," but
that projection was actually done for Seattle.

A similar prediction for San Diego (two extremes) should say 20
meters to Japan from 2030-0330z, with signals 5-10 dB lower than the
path from Seattle, and 17 meters from 2100-0300z.  One could pick a
mid-point, such as around Red Bluff or Garberville, California, but
this produces a third set of data that doesn't really apply to the
north and south west coast extremes.

Years ago this bulletin would pick some point somewhere in North
America, and make projections toward different continents.  An
example is in Propagation Forecast Bulletin ARLP016 from 1999, which
you can see in the archive of propagation bulletins at  This sort
of information was very popular, but the bulletin wasn't big enough
to handle all of the permutations of predictions for many locations
to many other locations.

But now we have some good free tools for doing this, such as
W6ELprop, which you can download at
This way you can see what likely propagation might be from your
location to anywhere else, and this works better than reading a
generalization in this bulletin.  Another approach is to look at the
monthly propagation charts linked toward the end of this bulletin.

Propagation programs are designed to use the projected smoothed
sunspot number for the month, which you can find in about every
fourth issue of the Preliminary Report and Forecast at  For example, if you
look in issue 1831, on page 10 it shows a predicted smoothed sunspot
number for October 2010 of 33.  The smoothed number is actually an
average of monthly sunspot numbers for one year, six months forward
and six months back, so half the data that goes into this average is
the predicted data for the next six months, while the rest is the
record of sunspot numbers for the last six months.

Propagation programs then make a prediction that basically says half
the time conditions will be better than this value, and half the
time worse.

W6ELprop can handle either sunspot numbers or solar flux, and for a
more recent set of data some have suggested just averaging the past
five days of solar flux from and using that
number.  W6ELprop also uses K index, and you can get the most recent
mid-latitude K index from  But no propagation
program is designed to make predictions based on daily fluctuations
of either solar flux or sunspot number.

To find the latitude/longitude coordinates for you location, just go
to and enter an address.  In this example, I
will use 2832 SE Indiana Ave, Topeka, KS, and click "Search Maps."
Just above the upper right corner of the map click on Link and hit
Ctrl-C to copy the link displayed, then paste it into Notepad or
some other editor by hitting Ctrl-V.

Find the address in the link you've just pasted, and note that the
coordinates are just to the right, listing latitude first, longitude
second.  In this case it is 39.015909 and -95.660564, which can be
expressed as 39.02 or 39.016 degrees north latitude, and 95.66 or
95.661 degrees west longitude.  Note the convention is for longitude
to be expressed in degrees east, so west longitude appears as a
negative number.  W6ELprop uses the opposite convention, so west
longitude is a positive number.

You can use this method to find coordinates for any location of
interest, and enter it into the atlas portion of W6ELprop for future

For a good tutorial, check the link toward the end of this bulletin
for and look for the title
"An Introductory Tutorial to W6ELprop."

In closing, check the November 2010 issue of QST on page 30 for an
article about using WSPR for studying propagation paths.

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 October 7 through 13 were 0, 11, 12, 13, 11, 11,
and 24, with a mean of 11.7. 10.7 cm flux was 75.1, 74.9, 76.4,
75.9, 75.3, 75.2 and 78.1 with a mean of 75.8. Estimated planetary A
indices were 4, 4, 4, 2, 20, 10 and 4 with a mean of 6.9. Estimated
mid-latitude A indices were 2, 3, 3, 1, 10, 7 and 3 with a mean of


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