ZCZC AP07
QST de W1AW
Propagation Forecast Bulletin 7 ARLP007
From Tad Cook, K7VVV
Seattle, WA February 12, 1999
To all radio amateurs
SB PROP ARL ARLP007
ARLP007 Propagation de K7VVV
Last week's Propagation Bulletin ARLP006 noted that the sunspot number on January 30 was only 29, and that it had not been this low since October 4, 1998 when it was 21. Now we can report another low in solar activity this week. On February 6 the solar flux dipped below 100 to 99.3. It has not been this low since July 18, 1998 when it was 99.2. This is unexpected in this part of the solar cycle, which should be rising.
This lower activity has a negative effect on propagation in the upper HF bands. As an example, if one runs the predicted numbers for this Saturday on a popular propagation prediction program, for a path from the center of the U.S. to Japan it shows 15 meters with strong signals from 2130-0230z, 12 meters from 2200-0100z, and 10 meters from 2200-0000z. But plug in the numbers for last Saturday over the same path, and it shows only a weak opening around 2230z on 15 meters.
Fortunately that quiet portion of the sun has drifted past, and the predicted solar flux for the next few days is much higher. The solar flux for this weekend, Friday through Sunday, is expected to be 170, 175 and 175. The planetary A index is predicted to be 12 for those three days. Conditions should be good for the World Wide RTTY WPX Contest.
Beyond the weekend expect solar flux to drop below 170, then below 160 by February 20, and below 140 after February 23. Solar flux should start creeping higher again after the beginning of March.
The author has taken advantage of the new ARRL member privilege of a league email address. While still reachable at the old address, you can write with questions or comments to the easy to remember k7vvv@arrl.net.
Sunspot Numbers for February 4 through 10 were 20, 15, 27, 36, 75, 57 and 69 with a mean of 42.7. 10.7 cm flux was 107.3, 103.7, 99.3, 109.5, 124.5, 129.3 and 152.4, with a mean of 118, and estimated planetary A indices were 7, 8, 12, 12, 5, 5 and 6, with a mean of 7.9.