ARRL Propagation Bulletin ARLP014 (2006)

ARLP014 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 14  ARLP014
From Tad Cook, K7RA
Seattle, WA  April 7, 2006
To all radio amateurs 

ARLP014 Propagation de K7RA

Some renewed activity this week with the appearance of a crowd of
sunspots, 865, 866, 867, 868 and 869. On March 25-27 there were 0
sunspots, then these new spots appeared on March 28, 29, April 2, 5
and 6. The big one, sunspot 865, is about to rotate out of view.

The daily sunspot number reached a peak of 105 on April 6. To find a
daily sunspot number this high, one must look back to last summer,
when the sunspot number on August 2 was 112, over seven months ago.
But this is just another one of those little up-ticks as this solar
cycle gradually declines, probably reaching a minimum in less than a

You can see the projection for the next year and a half in the
current April 4 issue of the NOAA Preliminary Report and Forecast of
Geophysical Data, in PDF format. Look on page 9 of this issue at, You'll see that the
predicted smoothed sunspot number for April 2006 is 12, and that
this chart predicts a decline that won't rise again to the current
level until some time around August or September 2007. But after
that, the next solar cycle (based on past cycle behavior) should
rise faster than the current one declined.

With the first quarter of the calendar year ended, we should examine
the decline of quarterly averages for daily sunspot numbers. Three
months gives us slightly less than three and a third rotations of
the sun, and is enough time to smooth out daily or weekly variations
so we can see a more general trend.

From the first quarter of 2003 through the first quarter of 2006,
the average daily sunspot number was 120.3, 107.3, 110.2, 99.2,
72.9, 71.3, 69.3, 61, 46.1, 55.7, 58, 36 and 18.1.

The average daily solar flux for the same period was 134.3, 124.2,
120.8, 137.4, 111.1, 99.5, 111, 104.8, 96.4, 93.1, 93.6, 84.5 and

I think you'll agree the general trend is down. An average daily
sunspot number of 18.1 for the first quarter of the year can be
easily compared to the minimum between cycles 22 and 23. From the
fourth quarter of 1995 to the second quarter of 1997, the average
daily sunspot numbers for each quarter were 21.3, 13.1, 13, 12.4,
14.2, 11.3 and 25.4. You can see that our recent quarterly average
of 18.1 fits right in toward the bottom of the last cycle.

For the near term, expect sunspot numbers and solar flux to decline
gradually. Over the next week, U.S. Air Force Space Weather
Operations predict a planetary A index for April 7-13 of 10, 8, 20,
15, 12, 7 and 5. Over those same days they show a decline of solar
flux values from 100 to 80. Geophysical Institute Prague shows quiet
to unsettled conditions for April 7, April 8 with quiet conditions,
unsettled conditions on April 9, active conditions April 10,
unsettled to active on April 11, April 12 unsettled, and quiet to
unsettled on April 13. So Prague thinks the peak in geomagnetic
instability should occur around April 10, but US Air Force predicts
April 9.

Michael Shelly, WB2KKI of Pocono Summit, Pennsylvania wrote in to
ask about MUF charts. These used to appear in QST, and they showed
the predicted change in Maximum Usable Frequency over a variety of
paths (for instance, West Coast USA to Japan) for a typical 24 hour
period, based on the month, and the predicted smoothed sunspot
number for the period.

These moved to the web some time ago, and you can find links to them
on the ARRL web site at Note
that this page also has a link to QST articles by Jerry Hall, K1TD,
on how to use this tool.

We get mail asking us for more useful information about predicted
propagation. For instance, when is a good time to work Europe, and
on what band? This is a good general question, but the readers of
this bulletin are all over the world, so it is difficult to make
these generalizations. It is even difficult to make good general
statements if we just limit our area of interest to North America,
because it covers such a large area. What is true for the southern
part of the East Coast may not be true for the north, or Midwest, or
either end of the West Coast.

But given data from public sources, you can get some good general
custom projections of propagation from your location to most other
locations on just about any HF band.

First, get some propagation prediction software. A great one is
ACE-HF Pro, which you can find at If you want
to try a piece of free software, the one we've mentioned numerous
times in the past is W6ELprop, which you can download at This program works with either solar
flux or sunspot numbers, but your best bet is probably to use the
average sunspot number for the past few days, rather than the latest
number. You can find them listed at,

So if I were doing one now, the latest available data is through
April 6. So I would take the average by adding 100, 99 and 99, and
dividing by 3, which gives us 99.3. If you want to enter the K index
into the program, you can get the mid-latitude values from WWV
either off the air at 18 minutes after the hour, or over the web at, You can also look at
recent geomagnetic activity at,

And last, we depend on the National Oceanic and Atmospheric
Administration's Space Weather Service for our main source of data.
Funding for these services in the administration's 2007 budget was
expected to stay at the current level, but now it looks like severe
cuts may be coming. I put up some information about this on the web

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 and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
propagation bulletins is found at,

Sunspot numbers for March 30 through April 5 were 35, 39, 39, 68,
79, 62 and 88 with a mean of 58.6. 10.7 cm flux was 83.9, 86.3, 87,
91.1, 100.4, 99.5, and 99, with a mean of 92.5. Estimated planetary
A indices were 4, 4, 2, 1, 1, 7 and 29 with a mean of 6.9. Estimated
mid-latitude A indices were 2, 2, 1, 1, 1, 4 and 18, with a mean of