ARRL Propagation Bulletin ARLP032 (2007)

ARLP032 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 32  ARLP032
From Tad Cook, K7RA
Seattle, WA  August 3, 2007
To all radio amateurs 

ARLP032 Propagation de K7RA

Average daily sunspot numbers rose very little this week, less than
6 points to 7.3.  There were no major geomagnetic upsets, only
slightly unsettled conditions on the first day of August.

We saw eight straight days of no sunspots, then a spot or two over
four days, then no spots on the first two days of August.  A week
from now, August 10, we may see the beginning of several days with a
few sunspots every day.  Expect unsettled geomagnetic conditions
centered on August 7 and again on August 10.

Geophysical Institute Prague predicts quiet conditions August 3-5,
quiet to unsettled August 6, unsettled to active August 7, and back
to quiet August 8-9.

There were six and two meter reports this week.  On Sunday, July 29
Dick Bingham, W7WKR, who lives in the very remote mountain village
of Stehekin, Washington (reached by boat) reports that he began
hearing six meter beacons around 1800z, and until 2300z he worked 22
grids, including HR9BFS in EK66 (Honduras) as well as
WA/CA/ID/MT/CO/TX/UT.  Dick is blocked by a high ridge running
northwest to southeast, with takeoff elevations in excess of 25
degrees, so he doesn't hear the northeastern United States and

WB4SLM reported interesting E-skip on 2 meters, and from EM82 he
worked EM14, EM15 and EM25, all around 2100z on Sunday.  He lives in
Georgia, and during a 30 meter QSO with his father, W9JNH in Texas,
around 2133-2135z he heard long delayed echoes on his CW signal.

Four days earlier on June 25, Roger Lapthorn, G3XBM reported his
best 6-meter DX ever when he worked K1TOL in Maine on CW.  Roger was
running just a few watts into a vertical mounted on the side of his
house.  Roger says the distance was over 5000 kilometers.

With July over, we can spin some numbers and look for trends.

Monthly averages of daily sunspot numbers for April 2006 through
July 2007 were 55.2, 39.6, 24.4, 22.6, 22.8, 25.2, 14.7, 31.5, 22.2,
28.2, 17.3, 9.8, 6.9, 19.8, 20.7 and 15.6.  Monthly averages of
daily solar flux for the same period were 88.9, 80.9, 76.5, 75.8,
79, 77.8, 74.3, 86.3, 84.4, 83.5, 77.7, 72.2, 72.4, 74.4, 73.7 and

Looking at 3-month smoothed sunspot numbers, now the July numbers we
can add to May and June to show the three-month average centered on
June.  These numbers are based on data from the past 21 months,
November 2005 through July 2007:

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
Jan 07 22.7
Feb 07 18.5
Mar 07 11.2
Apr 07 12.2
May 07 15.8
Jun 07 18.7

These numbers are calculated like this:  April 1 through June 30 is
91 days.  Add all the daily sunspot numbers over those three months,
then divide by 91, and the result is approximately 15.8, centered on
May, the middle month.  Likewise, May 1 through July 31 has 92 days,
and the sum of daily sunspot numbers over that period divided by 92
is 18.7.

If the average of daily sunspot numbers for the 31 days of August
turns out to be more than 20 (meaning the sum of all the sunspot
numbers for the month exceeds 620), we should see the three-month
average centered on July rise above the June average.  We will see
that result in ARLP037, on September 7.

This 3-month moving average of sunspot numbers is turning out to be
a nice indicator of cycle trends, with the average smoothly
declining from December through March, and increasing since.  We'll
know some day, perhaps in a year or two, if the low number in March
is a good indicator of cycle minimum or not.  Users of Scott Craig's
Solar Data Plotting Utility (available free from may have noticed that this
cycle minimum so far doesn't look as long as the previous minimum
around 1995-1997.  But of course, if we are at the minimum or just
passed it, then we are only looking at probably half of its eventual
length on the graph.  I hope the upturn comes soon, and is dramatic.

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 July 26 through August 1 were 0, 0, 13, 14, 13,
11 and 0 with a mean of 7.3.  10.7 cm flux was 68.4, 68.7, 69.9, 69,
68.9, 68, and 68.8, with a mean of 68.8.  Estimated planetary A
indices were 9, 8, 4, 14, 10, 6 and 17 with a mean of 9.7.
Estimated mid-latitude A indices were 6, 6, 3, 11, 10, 4 and 15,
with a mean of 7.9.