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.