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ARRL Propagation Bulletin ARLP041 (2006)

ARLP041 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 41  ARLP041
From Tad Cook, K7RA
Seattle, WA  October 6, 2006
To all radio amateurs 

ARLP041 Propagation de K7RA

Daily sunspot numbers and solar flux were higher this week. Average
daily sunspot numbers rose nearly 22 points to 34.6. Average daily
solar flux was up nearly six points to 76.7.

September 30 ended the third quarter of 2006, so now is a good time
to review quarterly averages of daily sunspot numbers and solar
flux, to examine the current solar cycle's downward trend.

From the first quarter of 2004 through the third 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 and 23.5.

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 and 77.5.

That still looks like a steady downward slope. The Space Environment
Center forecast still predicts a low point for sunspot numbers
during March and April of next year. This is based on a smoothed
sunspot number, so those daily values are averaged over six months
to produce a smoothed value centered in the middle of the period.

So when we are in the middle of it, because of daily variation, it
may not be immediately apparent that we have reached minimum. But if
it is anything like the last minimum--ten years ago this month--we
should observe at least several weeks of no sunspots at all.

We are nearing the end of sunspot cycle 23, and earlier this year we
read about the predictions of Mausumi Dikpata, who said that cycle
24 may be a big one. She used observations of the Great Conveyor
Belt, a huge circulating current of hot plasma inside the sun, which
takes about 40 years to complete a full rotation. The speed of this
belt seems to correlate well with solar activity 20 about years in
the future. The movement has slowed considerably, leading NASA solar
physicist David Hathaway to predict weak activity for cycle 25,
peaking around the year 2022. You can read about it at,

Eric Hall, K9GY mentioned the California QSO Party this weekend in a
recent email. You can find the at rules on the web at,

Here are some projections using W6ELprop (free at to see what propagation to California
from various locations may be like this weekend.

From Boston, 15-meter propagation may be possible, especially if
sunspot numbers stay steady or increase. The best times would be
1600-2100z. Check 20 meters 1430-0030z, with stronger signals late
in the period. 40 meters looks strongest from 0030-1130z, and 80
meters over about the same period.

From Atlanta, 10 meter chances look slim, but most likely openings
are around 1600-2300z, and 15 meter chances look very good over the
same period. Check 20 meters 1300-1400z and 1545-0300z, with
strongest signals in the last four hours of that period. 40 meters
looks good 2200-0130z, and excellent 0200-1200z, and still good
around 1230-1600z. 80 meters should be good after dark, but best

From the center of the 48 contiguous United States, check 20 meters
1500-0200z, and 40 meters should be open around the clock, with
strongest signals 0130-1300z, and weakest around 1630-2130z. 80
meters looks best 0230-1230z.

From Chicago, 10 meters has a small chance of openings in the
1730-2130z time slot. 15 meters looks very good 1630-2230z and
possibly later. 20 meters looks best 1330-1530z, and 2230-0230z.  40
meters may be open all day and night, with the best signals
0130-1200z and weakest 1700-2030z. 80 meters looks best 0330-1130z.

From Dallas, check 15 meters 1730-2200z, 20 meters 1400-0230z. 40
meters should be good over a 24 hour period, with best chances
0100-1300z and weakest around 1730-2030z. 80 meters looks strongest

From Salt Lake City, 80 meters should be open all day and night.
Best 80-meter signals 0130-1330z and weakest 1700-2200z. 40-meter
best bet is 1430-0300z.

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, .

Sunspot numbers for September 28 through October 4 were 36, 51, 38,
35, 36, 23 and 23 with a mean of 34.6. 10.7 cm flux was 73, 76.5,
77.7, 78.4, 77.9, 76.6, and 76.7, with a mean of 76.7. Estimated
planetary A indices were 2, 3, 12, 25, 7, 5 and 3 with a mean of
8.1. Estimated mid-latitude A indices were 2, 3, 9, 14, 6, 6 and 2,
with a mean of 6.


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