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ARRL Propagation Bulletin ARLP035 (2002)

ARLP035 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7VVV
Seattle, WA  August 23, 2002
To all radio amateurs 

ARLP035 Propagation de K7VVV

Last week this bulletin reported renewed solar activity, and this
week the high activity continued. Average daily solar flux rose
nearly 57 points from last week and 66 points from the previous
week. Average daily sunspot numbers were up nearly 67 points from
last week and over 76 points from the week before.

The sunspot number rose to 308 on Sunday, the highest value since
late July when sunspot numbers reached a level not seen since March
2001. This activity was accompanied by energetic coronal mass
ejections, which caused aurora and geomagnetic disturbances. The
most disturbed days this week were Monday and Wednesday, when the
planetary A index reached 27 and 41. On Wednesday when the A index
was 41 we saw planetary K indices of 7. Seven was also the highest
College K index measured in Alaska, and the College A index for that
day was 50.

Over the next few days geomagnetic activity should decline, with
planetary A indices of 15, 20, 15 and 10 for Friday through Monday.
Keep in mind that HF operators usually prefer the A index to be 10
or lower for really great conditions. Solar flux will also decline
slightly, with Friday through Monday values of 215, 215, 210 and

The days are getting shorter, and HF conditions should improve as we
move toward the fall season. You can run some tests on seasonal
variations using W6ELprop, available for free from For instance, looking at 10 and 15
meters on a path from Seattle to Japan for today with a solar flux
of 215, 10 meters shows a D rating (small chance of propagation)
with signals 16-18 dB above noise if open, and only from 2030 to

15 meters varies from D to C to B and back to D over the 1900-0830z
period, with the best bet from 2100 to 0500z (B rating).  But now
run the same path for a month later, and make a guess of a slightly
lower 195 for the solar flux. On September 23 the Seattle to Japan
path on 10 meters varying from D to B and back to D rating over the
2030 to 0530z period, with the best signals (B rated) from 2130 to
0230z and a couple dB hotter. 15 meters shows possible propagation
from 1530-0700z, with an A rating from 2100-0430z. Try it yourself
on various paths and dates to get a rough idea what the shorter days
will bring.

Sunspot numbers for August 15 through 21 were 281, 247, 270, 308,
247, 209 and 238, with a mean of 257.1. 10.7 cm flux was 210.3,
213.8, 226.7, 241, 237, 227.5, and 219.9, with a mean of 225.2.
Estimated planetary A indices were 19, 17, 13, 18, 27, 23, and 41,
with a mean of 22.6.


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