QST de W1AW
Propagation Forecast Bulletin 43 ARLP043
From Tad Cook, K7VVV
Seattle, WA October 22, 1999
To all radio amateurs
SB PROP ARL ARLP043
ARLP043 Propagation de K7VVV
Solar flux had a spectacular increase over the past week, with values around 200. The official solar flux number is taken from the Penticton, British Columbia observatory at 2000z, but there are actually three measurements daily. The highest value for the week was at 2300z on Thursday, October 14, when the flux reached 200.6. Flux values stayed above 190 for the thrice-daily readings until 2000z on Saturday, when the flux was 189.0.
Geomagnetic conditions were quite stormy from October 10-17, when the planetary A index ranged from 21 to 34. This was caused by a series of coronal holes and flares, streaming charged particles in a high speed solar wind. From October 18-20 the planetary A index was in the single digits, with many periods having a K index of 1. On October 21, the effects of a coronal mass ejection a couple of days earlier could be seen, with K indices back up above 4. You can see geomagnetic indices in three hour intervals for planetary, mid and high latitudes at gopher://sec.noaa.gov/00/indices/DGD.
Earlier in the week the forecast for planetary A index for this coming weekend showed a value of 20. The latest forecast for the A index for Friday is 25 to 30, 10 for Saturday, and 15 to 20 on Sunday, due to a coronal hole. The predicted solar flux is 150, 145 and 140 for the same period. After the weekend the solar flux is expected to bottom out around 125 from October 26-29, then rise back to 200 around November 10 or 11. Geomagnetic indices are expected to be mostly low until November 6, when recurring coronal holes are expected to keep conditions unsettled or stormy through November 13.
On October 12 and 13, the Solar and Heliospheric Observatory (SOHO) detected two large coronal mass ejections from the sun over an eight hour period. You can see photos, an article and even an animation of this event if you look on the NASA web site at http://science.msfc.nasa.gov/newhome/headlines/ast15oct99_1.htm.
Last week NASA released an article about solar cycle progress at http://science.msfc.nasa.gov/newhome/headlines/ast14oct99_1.htm. It quotes work by David Hathaway, a solar physicist at the Marshall Space Flight Center indicating that the peak of the current solar cycle should be around the middle of next year.
''Our predictions have consistently targeted 2000 as the beginning of solar maximum,'' said Hathaway, ''but the latest numbers suggest that the peak sunspot count in 2000 will be a bit lower than expected. The projected peak is comparable to, but lower than the peaks of the last two maxima (in 1989 and 1978). That would put all three of the recent sunspot maxima in the same class -- above average compared to all the sunspot cycles since the mid 1700's.'' He went on to state that the peak of the solar cycle is actually a broad peak, not an event centered around a certain date. He predicts that solar activity should be highest in 2000 and 2001, and then perhaps in 2002 it will decline to where it is now in October 1999.
Sunspot numbers for October 14 through 20 were 206, 130, 189, 169, 135, 169 and 193 with a mean of 170.1. 10.7 cm flux was 199.8, 198.2, 189, 178, 172.7, 169.6 and 158.8, with a mean of 180.9, and estimated planetary A indices were 24, 24, 21, 26, 6, 7 and 4, with a mean of 16.
The path projection for this weekend is for Saturday, from San Francisco, California.