ZCZC AP39
QST de W1AW
Propagation Forecast Bulletin 39 ARLP039
From Tad Cook, K7VVV
Seattle, WA September 25, 1998
To all radio amateurs
SB PROP ARL ARLP039
ARLP039 Propagation de K7VVV
Solar activity was up somewhat over the past week. Average sunspot numbers increased by almost 27 points, but solar flux was up by just under three points. The geomagnetic field was quite a bit more active this week compared to last due to solar flares and coronal holes. The day with the most geomagnetic activity last week was September 18, when the planetary A index was 20 and the K index went as high as 6.
The trend for the short term is for more activity. Solar flux for September 25 to 27, Friday through Sunday is expected to be 150, 155 and 155, while the major geomagnetic storm is expected to continue with planetary A indices of 25, 30 and 20. As this is being written on Thursday night, the Boulder K index is six, indicating a major storm, and the planetary A index for the day was 28. The high latitude A index was 51.
Solar flux is expected to peak around September 29 and 30 at 165, then drop to 150 by October 3, and bottom out around 120 from October 12 to 14.
This solar cycle is continuing it's upward climb, and a nice graph which shows the general trend over the past year can be seen at the Northwest Research Associates site at www.nwra.com/nwra/spawx/ssne-year.html. Recent and predicted short term 10.7 cm flux is graphed at the same site at www.nwra.com/nwra/spawx/f10.html.
The most important event for the last week affecting HF propagation was the passage into the fall season, which always means an improvement in high frequency propagation. The other important news was the resurrection of the Solar and Heliospheric Observatory which is again facing the sun. Until recently the outlook for SOHO was bleak, but now scientists hope to restore much of it's capacity for solar observation.
Sunspot Numbers for September 17 through 23 were 100, 106, 133, 130, 151, 154 and 162 with a mean of 133.7. 10.7 cm flux was 117.4, 122.5, 126.9, 132.1, 138.3, 141.1 and 143.2, with a mean of 131.6, and estimated planetary A indices were 7, 20, 12, 8, 14, 10, and 14, with a mean of 12.1.