ZCZC AP18
QST de W1AW
Propagation Forecast Bulletin 18 ARLP018
From Tad Cook, K7VVV
Seattle, WA May 3, 2002
To all radio amateurs
SB PROP ARL ARLP018
ARLP018 Propagation de K7VVV
Both average solar flux and daily sunspot numbers dropped last week. Sunspot numbers were down over 30 points, and solar flux was down nearly 20 points. But now that April is over, let's look at monthly averages. Average sunspot numbers for October through April were 197.4, 178.6, 217.5, 189, 194.5, 153.1 and 194.9. Average solar flux values for the same seven months were 208.1, 212.7, 236.5, 227.3, 205, 179.5 and 189.8. From these numbers it is apparent that April had higher solar flux and sunspot counts than March, but it is down from previous months.
During the last half of April, three coronal mass ejections sent energy past earth, and the results were geomagnetic storms around April 17-20 and April 23. Energy from a coronal hole should sweep past us shortly, but it shouldn't cause the kind of upset that April's storms brought us.
Over the next few days expect moderate geomagnetic activity with a rising solar flux. Flux values are expected to rise above 180 by Sunday, and peak for the near term above 200 around one week from now.
Lower geomagnetic indices are generally good for HF propagation. The solar flux is rising, which is also good. 10-meters should be fading away as we move toward summer, but 15-meters should do quite well over the next month. This summer 20-meters should be excellent during nighttime.
WB6RIB sent along a URL for a fascinating web site devoted to the 50-foot solar tower at the Mount Wilson Observatory in California. You can point your web browser toward http://www.astro.ucla.edu/~obs/intro.html to see this. To me the most interesting feature of this site is the archive of hand-drawn pencil sketches of the sun's surface dating back to January 4, 1917.
The story of these drawings (which are really tracings) and how they are made may be seen at http://www.astro.ucla.edu/~obs/150_draw.html. There are many very old drawings, including sets from the years 1128 to 1800.
Next week Carl, K9LA takes over the bulletin while K7VVV leaves town.
Sunspot numbers for April 25 through May 1 were 208, 160, 173, 121, 124, 113 and 166 with a mean of 152.1. 10.7 cm flux was 167.3, 162.6, 156.9, 147.1, 153, 153.4 and 162.4, with a mean of 157.5, and estimated planetary A indices were 5, 6, 8, 19, 9, 8 and 5 with a mean of 8.6.