QST de W1AW
Propagation Forecast Bulletin 37 ARLP037
From Tad Cook, K7VVV
Seattle, WA September 15, 2000
To all radio amateurs
SB PROP ARL ARLP037
ARLP037 Propagation de K7VVV
The sun has been almost spotless this week, which seems odd for what is supposed to be the peak period of activity for solar cycle 23. The Boulder Sunspot Number went all the way down to 27 on Monday, and the average sunspot number for this reporting week (Thursday through Wednesday) was a tiny bit over half of last week's average. Monday's index was the lowest sunspot number of this year.
The last time the average weekly sunspot numbers were lower than this week's (88.7) was back at the new year, when our Propagation Forecast Bulletin ARLP001 reported an average of 85.1 for the week of December 30 through January 5, 2000. But the lowest sunspot number during that week was 69, far higher than 27. A daily sunspot number that low has not been recorded for 19 months. That was on February 6, 1999, when it was also 27.
Many radio amateurs might be asking if we are past the peak of the cycle, but this cannot really be determined until well after the peak, when the experts can analyze a moving average of sunspot and solar flux data.
But check out a new addition to the WM7D web site. If you go to http://www.wm7d.net/hamradio/solar/ and then click on the text which says ''Click here for charts reflecting the past 72 months,'' this will bring your web browser to http://www.wm7d.net/hamradio/solar/past_cycle.shtml , which shows the past six years in separate one year charts. The recent chart seems to show a general peak in solar flux and sunspot numbers some time during spring and summer of this year.
Of course in a few months, this may appear quite different, since we are now focusing on the recent drop in activity and more activity in the future may change this perception. Some time in the future a long moving average (where one plots the center point after averaging a large number of days) will probably show a very broad peak, and it is too early to determine where that peak will be centered. What we are experiencing now is the wide variation in activity that can be observed even at the peak of the solar cycle.
Activity for the past few days has been picking up, and the latest solar flux forecast for Friday through next Thursday is 160 for Friday and Saturday, and 170 for Sunday through Thursday. Keep in mind that projections like this beyond three days are somewhat questionable, and the further out they are, the more of a guess they are likely to be. Solar flux is expected to stay above 150 until October 5, then reach the next minimum around 125 on October 10 or 11.
Planetary A indices predicted for Friday through next Thursday are 45, 12, 12, 10, 12, 12 and 10. The high A index forecast for Friday is probably due to the M-Class solar flare which erupted at 1213z on Tuesday. Shortly after this flare, the Solar and Heliospheric Observatory recorded a spectacular and fast-moving full-halo coronal mass ejection. The result may be mid-latitude auroral displays, along with a minor to major geomagnetic storm.
Next week is the autumnal equinox, a time when HF conditions should be at their best. Let's hope that the sun cooperates, and gives us more sunspots and less solar flares.
Sunspot numbers for September 7 through 13 were 160, 115, 116, 69, 27, 38 and 96 with a mean of 88.7. 10.7 cm flux was 173.2, 163.4, 150.9, 140.6, 134.9, 132.6 and 133.2, with a mean of 147, and estimated planetary A indices were 16, 21, 7, 5, 5, 20 and 10 with a mean of 12.