ZCZC AP40
QST de W1AW
Propagation Forecast Bulletin 40 ARLP040
From Tad Cook, K7VVV
Seattle, WA October 4, 1999
To all radio amateurs
SB PROP ARL ARLP040
ARLP040 Propagation de K7VVV
There was a delay in putting out the bulletin this week due to an unannounced change in servers at the Penticton Observatory. This delayed getting some of the data for this bulletin.
Last week, which we report as Thursday through Wednesday, we saw marginal HF conditions and a declining solar flux. The average sunspot number was down over 56 points and average solar flux was off by over 22 points compared to the previous week. The really active geomagnetic day was September 27, when the planetary A index was 37 and the highest planetary K index was 5. The higher latitudes had the worst conditions, with the College A index from Alaska at 66 for the day with the K index up to 7.
Solar flux probably bottomed out on Friday, October 1 at 121.6. It has been rising since then, and two days later on October 3 it was 141.3 for the morning reading at Penticton and 134.5 for the noon reading, which is the official number for the day.
The predicted solar flux for the next week, beginning Monday, October 4 is 138, 140, 142, 145, 148, 150 and 152. Unless new activity appears, solar flux will probably peak above 155 around the middle of the month. Predicted planetary A index for the same period is 15, 12, 12, 12, 10, 15 and 15. These predictions which go out a week are fairly rough beyond the first few days.
The beginning of October marks the end of the third quarter of the calendar year. Average solar flux for the month of September was 135.7, the lowest since April, when it was 117.2. Average monthly solar flux for May, June, July and August was 148.4, 169.8, 165.6 and 170.7. Average solar flux for the first quarter of 1999 was 136.7, actually one point higher than it was for the month of September and nine points higher than the average for last week. Flux for the second quarter was 145, and for the quarter just ended it was 157.6. This indicates a steady upward trend for cycle 23, although a peek at the graph at http://www.dxlc.com/solar/ looks like recent trends over the last few solar rotations are down. The predicted peak for this cycle is some time next year. You can see charts of the forecast data in Acrobat format by scrolling to the last few pages at http://www.sec.noaa.gov/weekly/pdf/prf1253.pdf. Also check the page which leads to this report, which can be found at http://www.sec.noaa.gov/weekly/index.html. This has the weekly NOAA SESC Preliminary Report and Forecast.
JA7SSB sent an interesting URL for a solar activity chart which is very beautifully done with lots of rich detail. You can see it at http://crlgin.crl.go.jp/sedoss/solact3/.
Sunspot numbers for September 23 through 29 were 78, 86, 38, 44, 49, 52 and 84 with a mean of 61.6. 10.7 cm flux was 136.9, 131.6, 125.4, 122.7, 123.8, 126 and 124.8, with a mean of 127.3, and estimated planetary A indices were 24, 6, 4, 15, 37, 20 and 19, with a mean of 17.9.
The path projection this time is for mid-week from St. Louis, Missouri.