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ARRL Propagation Bulletin ARLP019 (2004)

ARLP019 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 19  ARLP019
From Tad Cook, K7RA
Seattle, WA  May 7, 2004
To all radio amateurs 

ARLP019 Propagation de K7RA

Thanks to Carl Luetzelschwab, K9LA for writing last week's
propagation forecast bulletin.

Your regular author was without power or other overhead utilities
from Tuesday through Saturday after a localized squall in the city
took down a large tree. This yanked out the electrical service
mast, and all that plus the breaker panel had to be upgraded. Urban
camping for several days made us really appreciate cheap, plentiful
electric power.

Carl mentioned last week that the solar cycle continues to decline.
Average daily sunspot and solar flux further dropped from last week
to this week, with average daily sunspot numbers down by nearly 5
points. Average sunspot numbers for the past two weeks were 52.7
and 48.1. Compare this with the last week in April and first week
in May in 2003, when average daily sunspot numbers were 185.1 and
146. However, three years from now the cycle should begin to turn
up again. Of course, at that time (Spring 2007), sunspot counts at
the bottom of the cycle will be much lower than now.

For the short term we can expect quiet geomagnetic conditions, good
for HF propagation. Daily solar flux values are expected to stay
below 100 until around May 18. Geomagnetic conditions should stay
quiet until May 20. Currently there are two small sunspots facing
earth, and helioseismic holography reveals no substantial sunspots
on the sun's far side.

Quiet conditions seem favorable for this weekend's CQ-M
International DX Contest, although scant sunspots will likely make
20 meters the best overall band for worldwide DX, with less long
distance propagation on 15 meters.

For more information concerning propagation and an explanation of
the numbers used in this bulletin see the ARRL Technical Information
Service propagation page at,

If you use Scott Craig's Solar Data Plotting Utility, you'll need to
edit this bulletin into two versions for automatic insertion of
data. Just make one version with last week's numbers, and the other
file with this week's, so you don't confuse the software.

Sunspot numbers for April 22 through 28 were 90, 63, 64, 45, 47, 28
and 32 with a mean of 52.7. 10.7 cm flux was 117.1, 115.3, 111.6,
107.1, 99.6, 95.1 and 89.5, with a mean of 105. Estimated planetary
A indices were 4, 20, 11, 12, 7, 5 and 8, with a mean of 9.6.
Estimated mid-latitude A indices were 5, 34, 17, 17, 5, 2 and 7,
with a mean of 12.4.

Sunspot numbers for April 29 through May 5 were 25, 46, 65, 41, 50,
63 and 47 with a mean of 48.1. 10.7 cm flux was 88.5, 89.4, 94.2,
97.5, 91.3, 87.4 and 88.5, with a mean of 91. Estimated planetary A
indices were 4, 12, 13, 6, 7, 10 and 13, with a mean of 9.3.
Estimated mid-latitude A indices were 3, 9, 8, 4, 6, 6 and 12, with
a mean of 6.9.


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