Register Account

Login Help

ARRL Propagation Bulletin ARLP019 (2008)

ARLP019 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 19  ARLP019
From Tad Cook, K7RA
Seattle, WA  May 2, 2008
To all radio amateurs 

ARLP019 Propagation de K7RA

For several weeks we expected today, May 2 to have active
geomagnetic conditions.  For instance, if you look at a forecast
from April 23 at,, it
shows an expected planetary A index for May 1-3 of 10, 20 and 15.
The next day, April 24 (see this
changed to 8, 20 and 15, and on April 25 it was 10, 15 and 15.  For
May 1 we see the actual planetary A index for that day was 9, and
for the following two days, the predicted values are 10 and 12,
which are much more moderate.  So obviously as we moved closer to
this date, the return of a solar wind stream seemed less likely,
although earlier today the planetary K index rose as high as 4,
indicating unsettled to active geomagnetic conditions.

The IMF (Interplanetary Magnetic Field) pointed south when the K
index was high, which means our planet was vulnerable to radiation
from solar flares and wind streams.  Later the IMF pointed north,
and the K index dropped to 0, which is very quiet.  Nine planetary K
index readings from 1500z May 1 through 1500z May 2 went from quiet
to active to quiet again, 0, 1, 3, 3, 4, 4, 4, 3 and 0.

A solar wind stream flowing from a coronal hole is expected to reach
earth on May 5.  The expected planetary A index for May 2-11 is 10,
12, 12, 8, 10, 8, 5, 5, 5 and 5.  That forecast is from the NOAA
Space Weather Prediction Center and the U.S. Air Force.  Those
numbers are from the May 1 prediction.  You can see the May 2
prediction some time after 2100z today by changing the last element
of one of the URLs in the first paragraph from 042445DF.txt to

That same forecast from May 1 is now predicting a 10.7 cm solar flux
reading of 70 for the next 45 days.  But on April 28 they were
predicting solar flux to rise to 75 from May 20-28.

The Solar Department at the Ondrejov Observatory of the Prague
Astronomical Institute (part of the Academy of Sciences of the Czech
Republic) projects a 10.7 cm solar flux range of 66-73 and a sunspot
number range of 0-25 for May 2-8.

For the same period Geophysical Institute Prague predicts
geomagnetic activity of unsettled to active May 2, active on May 3,
unsettled May 4-6, quiet to unsettled May 7, and quiet May 8.

F.K. Janda, OK1HH of the Czech Propagation Interest Group predicts
for the next solar rotation (about four weeks), quiet conditions May
8, 11-12, 15-16, (17,) 18-19, (22, 24,) and 26, unsettled to active
conditions May 2, 6-7, 9, 13 and 23, and active to disturbed May
(3-5, 10, 14,) 20, (21, 25, and 27)  The dates in parenthesis are
days he expects a lower probability of solar activity enhancing

HF operators looking for good propagation like to see higher sunspot
and solar flux numbers, because the MUF (Maximum Usable Frequency)
is higher, and they want lower A and K index numbers (indicating
quiet geomagnetic conditions) because absorption of HF signals is
generally lower. The two don't always go together.  High sunspot
activity, which we haven't observed for several years, may often
result in higher geomagnetic activity.

Now that we have all the sunspot data for April, we can take our
monthly look at our 3-month moving average of daily sunspot numbers
to give us a hint on where this cycle may be heading.  The March 08
figures below are an average of daily sunspot data from February 1
through April 30.

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
Jan 08  8.5
Feb 08  8.4
Mar 08  8.4

We can see that a slight rise in sunspot activity from October
levels has flattened.  Although another digit isn't really
significant, for readers who prefer to parse their parameters more
precisely, the December through March averages may be expressed as
8.14, 8.52, 8.39 and 8.36.

An exciting email arrived earlier this week from Martin Ewing, AA6E
of Branford, Connecticut regarding a free ionosphere visualization
plug-in for Google Earth.  I am just beginning to play with this.
It allows users to view a multi-dimensional model of the
ionosphere's electron density in real time, anywhere on earth.
Follow the links from and for more information and to download the
free software.

Donald Casillo, KD5UGY of Moore, Oklahoma suggested that at the end
of our bulletin, we show the actual latitude of the magnetometer
that the A index comes from.  This is because higher latitudes
usually have greater geomagnetic activity.  But our planetary A
index is actually derived from a number of magnetometers, and the
mid-latitude index observatory is near Fredericksburg Virginia at
38.2 degrees north latitude.  You can see a directory of USGS
magnetometers at  When you
click on a link for a particular observatory on the right side of
the page, you can see the coordinates to locate it precisely on a
map or with one of the satellite imaging sites.

But look at the coordinates for FRD, the source of our mid-latitude
A index.  It says 51.8 degrees "co-latitude" and 282.63 degrees
longitude.  What does this mean?  By looking at a number of these
coordinates and comparing them with approximate locations on a
mapping program, by observation I was able to parse out the
conversion.  At least for the northern latitude in the western
hemisphere (I haven't verified this for other parts of the earth)
just subtract their given co-latitude from 90 to get the kind of
north latitude coordinate that you and I are familiar with, and the
given longitude from 360 for west longitude.  So this shows the
Fredericksburg magnetometer at 38.2 degrees north latitude, and
77.37 west longitude, which indicates a spot about 8 miles southeast
of Fredericksburg on the north side of Fort A.P. Hill.

Use that same method to find the locations for other magnetometers.
For instance, the College station is where the high-latitude A and K
indexes that we see at, come from.  You can
also see planetary and the Fredericksburg mid-latitude numbers on
that page.

When you tune to WWV at 18 minutes after the hour, they give a
mid-latitude A and K index from the Boulder magnetometer.  Figure
out the latitude of that station from that same observatory page
mentioned above, and you can compare numbers with the Fredericksburg
middle latitude numbers.  You can also read this latest forecast at,  This is updated
every three hours.

Jon Kreski, AB9NN of Appleton, Wisconsin requests more information
on how the numbers we report affect the bands he is interested in
from his location.  Because readers are in so many locations around
the world, we haven't made enough general statements about
propagation on different bands, because complicating this is the
number of locations that these many stations in many places may want
to communicate with.  You can use W6ELProp, the free propagation
prediction program from or one of many
other programs that you can buy or try out to customize a forecast
from your exact location at the time you want to operate on the band
you are interested in.  We review the use of this program from time
to time (you can check back issues of the bulletin, as described
below) and we will try to cover this in depth next week.  You can
also check the monthly propagation charts, as mentioned below for
more general forecasts from several regions.

The past two bulletins offered a document from Dr. Kenneth Tapping
of the Penticton Observatory, which provides us with our solar flux
data.  He was misquoted in several news items recently, giving the
impression that we might be headed for decades of little or no
sunspots.  This document attempts to correct the record.  You can
still get this by sending a blank email to,
and you will get a PDF of Dr. Tapping's notes in return.
The response has been tremendous, currently approaching 1,000

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

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for April 24 through 30 were 11, 0, 0, 0, 0, 0, and
0 with a mean of 1.6.  10.7 cm flux was 70.4, 69.8, 69, 68.1, 68.5,
68.6, and 67 with a mean of 68.8.  Estimated planetary A indices
were 18, 8, 10, 10, 11, 8 and 9 with a mean of 10.6.  Estimated
mid-latitude A indices were 13, 7, 5, 7, 9, 4 and 4, with a mean of


Instragram     Facebook     Twitter     YouTube     LinkedIn