ARRL

ARRL Propagation Bulletin ARLP050 (2000)

SB PROP @ ARL $ARLP050
ARLP050 Propagation de K7VVV

ZCZC AP50
QST de W1AW  
Propagation Forecast Bulletin 50  ARLP050
From Tad Cook, K7VVV
Seattle, WA  December 15, 2000
To all radio amateurs 

SB PROP ARL ARLP050
ARLP050 Propagation de K7VVV

Solar flux and sunspot numbers for the past week were down from the
previous week. Average sunspot numbers were off by nearly 40 points,
and average solar flux was down by almost 18.

Last week's Propagation Forecast Bulletin ARLP049 suggested that a
short term solar flux minimum of 140.2 was reached at 1800z on
December 6 (the official number for the day, at 2000z was 141), but
it actually went lower a few days later. After rising to 144.2 on
December 7, it dropped to 134.7 on Saturday, December 9. The lowest
reading in this period was actually at 1800z on that day, when it
was 130.3.

Last week's bulletin also predicted a planetary A index for the
10-Meter contest weekend of 25 and 15 for Saturday and Sunday, but
it wasn't that bad. Planetary A indices for the two days were 16 and
9, which was much more moderate. Mid-latitude K indices were only 2
or 3 for the whole weekend. There was plenty of activity on
10-Meters for the contest.

Current predictions for the next short term solar flux peak have
tightened up. The current data predicts a peak of 200 centered on
December 22-23 instead of 20-23. The next occurrence of unsettled
conditions is supposed to be December 23-24 with a planetary A index
of 15, but this is based on recurring conditions from active regions
rotating into view.

On Thursday sunspot groups 9267 and 9264 are fast growing, and 9267
lies toward the center of the visible disk, posing a potential
threat of solar flares pointed toward earth. If solar flares do not
erupt, the predicted planetary A index should stay at a nice stable
value around 8 through December 21. Solar flux is predicted to be
about 185 on December 15-16 and 190 for December 17-21.

With winter approaching, the polar region is dark and this makes
propagation from North America over polar paths into Europe and Asia
more difficult on the higher bands. Maximum Usable Frequencies are
much lower now than they were during the peak conditions at the fall
equinox. Night time activity should be shifting from 20 meters to 40
meters.

Sunspot numbers for December 7 through 13 were 125, 81, 73, 58, 101,
95 and 173 with a mean of 100.9. 10.7 cm flux was 144.2, 138.3,
134.7, 146.6, 143.6, 149.8 and 164.6, with a mean of 146, and
estimated planetary A indices were 13, 17, 16, 9, 7, 5 and 4 with a
mean of 10.1.
NNNN
/EX