ARRL Propagation Bulletin ARLP001 (2007)

ARLP001 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 1  ARLP001
From Tad Cook, K7RA
Seattle, WA  January 5, 2007
To all radio amateurs 

ARLP001 Propagation de K7RA

This is the first bulletin of 2007, the year we'll likely see the
end of sunspot cycle 23, the beginning of cycle 24, and the minima
between cycles.

A few days now into this new year, we can look at sunspot and solar
flux averages for 2006 compared with previous years.

Average daily sunspot numbers for the years 1999 through 2006 were
136.3, 173, 170.3, 176.6, 109.2, 68.6, 48.9 and 26.1. Average daily
solar flux for the same years was 153.7, 179.6, 181.6, 179.5, 129.2,
106.6, 91.9 and 79.9.

The numbers above show a very clear decline, which is easier to
perceive when the numbers are averaged over relatively long periods,
such as a year. Looking at quarterly averages, we see a little more
variability, but the same definite decline over time. Comparing
those yearly numbers to a decade ago when the cycle was near the
bottom, average daily sunspot numbers for 1995-1997 were 28.7, 13.2
and 30.7.

From the first quarter of 2004 through the fourth quarter of 2006,
the average daily sunspot number was 72.9, 71.3, 69.3, 61, 46.1,
55.7, 58, 36, 18.1, 39.7, 23.5 and 23.1.

The average daily solar flux for the same period was 111.1, 99.5,
111, 104.8, 96.4, 93.1, 93.6, 84.5, 78.5, 82.1, 77.5 and 81.6.

Recently this bulletin commented that the prediction for the low
point between cycles had recently slipped out a couple of months, so
instead of the low smoothed sunspot numbers predicted for March
2007, May looked more likely. Now a new forecast from NOAA has been
released, and it shows a flat yet relatively high minimum for this
year, spread out over many months. Take a look at page 9 of the
Preliminary Report and Forecast for January 3, 2007 at,

Now compare that to just a month earlier, December 5, 2006, on page
11 at, The one from
last month shows the minimum centered around May 2007 with a
smoothed sunspot number of 7, but the current issue shows a minimum
smoothed sunspot number of 10 stretching from December 2006 through
July 2007. Remember that the smoothed sunspot number for any month
is the average of the monthly averages from five-and-a-half months
before that month with five-and-a-half months after the month. So
these are not just predicted sunspot numbers, but predicted smoothed
sunspot numbers. In other words, the predicted smoothed sunspot
number of 10 for December 2006 represents the average of December's
daily numbers averaged with the months going back from the last half
of June 2006 averaged with the predicted average monthly numbers
through mid-June 2007.

A similar prediction, found on the web at,, is updated weekly.

Last week's bulletin mentioned an article in Space News on diverging
predictions for the upcoming solar cycle, but we reported that the
whole text of the piece is not available online. But Steve Sala,
K7AWB of Nine Mile Falls, Washington sent us this link,, which
links to the entire article.

The JAPY DX Group in Brazil has a VHF/UHF expedition for the first
week of 2007 to Comprida Island (IOTA SA-024) through January 7.
This is a 70 km long barrier island, part of the state of Sao Paulo,
and the grid locator is GG64bx. This is around 25.028 degrees south
latitude, 47.875 degrees west longitude. They are hoping to work
trans-equatorial propagation into the Caribbean, and will be on SSB
and CW on 50.11, 144.2 and 432.1 MHz, and FM on 144.54 and 433.1 MHz
after 2200z daily using calls PY2OC, PY2ENO and PY2ZX.

For the next few days, expect geomagnetic conditions to be from
quiet to unsettled. Solar flux should stay around 90, and sunspot
numbers below 50. Geophysical Institute Prague predicts unsettled
conditions for today, January 5, quiet to unsettled January 6-7, and
quiet conditions January 8-11.

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 December 28 through January 3 were 0, 0, 11, 28,
28, 31 and 38 with a mean of 19.4. 10.7 cm flux was 76.3, 78.4, 80,
83.3, 86.9, 90, and 87.7, with a mean of 83.2. Estimated planetary A
indices were 2, 2, 2, 0, 7, 19 and 20 with a mean of 7.4. Estimated
mid-latitude A indices were 1, 1, 2, 1, 7, 12 and 11, with a mean of