QST de W1AW
Propagation Forecast Bulletin 20 ARLP020
From Tad Cook, K7VVV
Seattle, WA May 19, 2000
To all radio amateurs
SB PROP ARL ARLP020
ARLP020 Propagation de K7VVV
This has been an exciting week for sun-watching hams. In last week's Propagation Forecast Bulletin ARLP019, the forecast said that solar flux may peak around 220 on May 18. Instead, on May 17 the noon solar flux reading at Penticton, BC was 262, which is a new high for the current solar cycle 23. The previous high for this cycle was 248.5 on November 10, 1999. Prior to that the solar flux has not been this high since the last gasp of high numbers for cycle 22, when it was 271 on February 3, 1992. That was quite an active week back in 1992, when the solar flux on January 29 through February 3 was 266, 280, 303, 284, 288 and 271.
Average solar flux for this week was up an astonishing 85 points compared to last week, and average sunspot numbers were up nearly 140 points, more than double last week's average.
Last week's bulletin mentioned that the solar area number, counted as millionths of the solar disk, was 130 on May 7. But this week that number reached a new high for this cycle of 3510 on May 15. Along with the high sunspot counts and solar flux came some geomagnetic activity. The most active days were May 12 and 17, when the planetary A index was 22 and the K index was as high as five.
This week's forecast shows solar flux values for Friday through Tuesday rising higher, at 260, 265, 265, 270 and 270. It also looks like we may experience some more days of unsettled geomagnetic conditions, with a predicted planetary A index of 12, 15, 15, 12 and 10. Given this prediction, at this point the best days for HF propagation will probably be Monday and Tuesday. Solar flux is expected to bottom out around 130 between June 2 and 3, and reach another peak around the middle of next month.
WA3KFT wrote this week asking about web sites that show plots of solar indices. Some good ones are
In response to some questions I had about 10 meter propagation at the equinox, K9LA, who writes about propagation for the National Contest Journal as well as Worldradio, wrote back with results of some path projections he did using MiniProp. He studied 10 meter paths from New York, Chicago and California to Europe, Japan and Australia (VK4), with both short paths and some long paths.
He found that New York to Europe was best in Winter, with Fall a close second. To Japan over the short path, Fall and Spring are best, and the same for the long path, but with Summer a close second or third. To Australia Fall and Spring were best, with Winter conditions very close.
For his Chicago to Europe 10 meter path, Winter was best with Fall a close second. Short path to Japan showed Fall best with Winter a close second, and for long path Fall and Spring were best with Summer close behind. To Australia Fall, Winter and Spring were about equal.
For the path from California, Fall and Winter were best to Europe with Spring not far behind, and a long path projection to Italy showed Fall and Spring were best, with Summer not far behind. To Japan, Fall and Winter were best with Spring not far behind, and to Australia, Fall, Winter and Spring were about equal.
Before Carl did the projections, his feeling was that 10 meters was best in the Winter. But when he thought about it more, he realized that his answer may have been based on his Midwest location and the fact that most of the DX he works on 10 meters is in Europe.
For this week, with the solar flux at a new high, expect good conditions on 10, 12 and 15 meters. Over many paths 15 meters will be open during most of the day and part of the night. 10 meters should be especially strong over north-south paths. Path projections from Texas to Brazil, for instance, show 10 and 12 meters open from just before sunrise in Texas until just a few hours before sunrise in Brazil, which is late into the Texas night.
Sunspot numbers for May 11 through 17 were 213, 211, 260, 263, 302, 298 and 342 with a mean of 269.9. 10.7 cm flux was 177.7, 190.4, 217.3, 232.5, 244.4, 258.7 and 262, with a mean of 226.1, and estimated planetary A indices were 6, 22, 15, 12, 16, 18 and 22, with a mean of 15.9.