ZCZC AP20
QST de W1AW
Propagation Forecast Bulletin 20 ARLP020
From Tad Cook, KT7H
Seattle, WA May 16, 1997
To all radio amateurs
SB PROP ARL ARLP020
ARLP020 Propagation de KT7H
Last week was very quiet in terms of solar and geomagnetic activity. Average solar flux was about the same last week as the week before, the average sunspot number was up about 10 points, and the average planetary A index was down by almost half. Conditions haven't stayed calm, however, because on May 16 the Boulder A index jumped to 33. This is an indication of a geomagnetic disturbance, which correlates with absorption rather than reflection of radio signals.
Geomagnetic conditions are already settling down, and should be quiet again this weekend and beyond. The next predicted upset should be centered around May 28. No increase in solar flux is foreseen, but that is because these predictions are based upon the rotation of the Sun, and there hasn't been any real sunspot or solar flux activity in the past month which might return and cause an improvement in conditions. As mentioned in ARLP019, conditions are unusually quiet, considering how long the solar minimum has lasted.
20 meters remains the best band for worldwide communications, with later openings to the west as daylight extends into the evening.
Sunspot Numbers for May 8 through 14 were 23, 14, 23, 26, 12, 15 and 17 with a mean of 18.6. 10.7 cm flux was 71.9, 71.6, 72, 72.3, 72.2, 73.8 and 73.5, with a mean of 72.5, and estimated planetary A indices were 5, 6, 5, 7, 3, 3, and 6, with a mean of 5.