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ARRL Propagation Bulletin ARLP042 (2005)

ARLP042 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 42  ARLP042
From Tad Cook, K7RA
Seattle, WA  October 7, 2005
To all radio amateurs 

ARLP042 Propagation de K7RA

Solar activity was down for the week, in fact we saw several days of
no sunspots at all. October 1, 2 and 3 each had a daily sunspot
number of 0. Sunspot numbers are slowly rising as sunspot 813
rotates to face Earth, but the average for the week dropped over 18
points to 11.6. Sunspot numbers and solar flux may rise, but
probably not by much.

As last week's bulletin mentioned, were waiting to see what the
return of giant sunspot 798 would bring. But as that area shifts
into view, only a few wisps are visible, indicating the area is
magnetically much less complex than what came around the past two
rotations. Over the next year as this cycle 23 bottoms out, we will
see long stretches of days with no spots, maybe even weeks, judging
by the behavior of past solar cycles.

But with the lower solar activity came very little geomagnetic
activity. The numbers reported in last week's bulletin were low, but
the weekly average for planetary and mid-latitude A index dropped
even lower, by about one point each. If you can check within the next few
weeks, before the data disappears, you can see the days with reading
after reading of K index equal to 0.

With the K index moving between 0 and 1 and back, this results in a
daily A index of 2 or 4. If you view the nomograph at, you get an
illustration of how eight readings of the K index through the day
yield the daily A index. If you take the eight K index readings and
they average to 2, this gives you an A index for the day of 7. If
the average is around 2.333, then the A index is 9.

These periods of low geomagnetic activity are great for 160 and 80
meters. Atmospheric noise is also much lower than in summer, and
periods of darkness are getting longer.

This bulletin is prepared a day earlier than usual, early Thursday
morning West Coast time, instead of early Friday. Over the next week
expect sunspot activity to remain low, and solar flux should hover
around 85. Planetary A index for the next five days, October 6-10 is
predicted at 8, 10, 5, 8 and 12. The next period of moderately
active geomagnetic conditions is forecast for October 12, based on
the last solar rotation.

Sgt. Korey Chandler, YI9VCQ/KA5VCQ sent an email from Iraq last week
about propagation from that part of the world. On September 30 he
wrote, "I just wanted to comment that I've had very good luck on
12-meter CW for the past week. Conditions have been solid to
Germany, Bulgaria, Russia, and Ukraine at around 1000-1500z.
10-meters hasn't been as good, but 15 showed several nice openings
to Asia and Australia. 40-meters is showing a nice start towards
winter conditions since I'm now working stations with my low

The next day Korey wrote, "I normally start on whatever band
'should' be open and work my way up. Usually I start on whatever
band is open and work my way higher. I, too, use W6ELprop. Of
course, I'll throw out a few CQs on each band just to check for
surprises. Most of the native Iraqi ops here do not know CW so Iraq
is a hard one for me to confirm. Can you believe it? Only a few of
the American/Coalition guys run CW. 30-meters is one of my favorite
bands. Nothing but CW/Digital and I'm a CW lover. Over 8,000 of my
11,000 QSOs so far are CW. Hope to see you on the bands!"

Korey mentioned W6ELprop, which has been listed here many times
before. Probably the best way to use it is with the predicted
smoothed sunspot number for the month, or you can average the
previous several days of sunspot numbers, which you can get from

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
bulletins is found at,

Sunspot numbers for September 29 through October 5 were 22, 13, 0,
0, 0, 15 and 31 with a mean of 11.6. 10.7 cm flux was 73.8, 72.2,
72.1, 74.9, 74.3, 82.7, and 81.3, with a mean of 75.9. Estimated
planetary A indices were 6, 11, 13, 13, 7, 4 and 4 with a mean of
8.3. Estimated mid-latitude A indices were 5, 6, 10, 8, 5, 2 and 2,
with a mean of 5.4.


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