QST de W1AW
Propagation Forecast Bulletin 34 ARLP034
From Tad Cook, K7VVV
Seattle, WA August 25, 2000
To all radio amateurs
SB PROP ARL ARLP034
ARLP034 Propagation de K7VVV
Solar activity took a big dive over the past week, with sunspot numbers dropping to 84 on August 22 and 23. Although NASA's Spaceweather.com reported that the Boulder sunspot number has not been this low in this calendar year, our records from past bulletins show that it has been lower than this several times in January. Boulder sunspot numbers, which are the ones reported weekly in this bulletin, were 69 on January 1 and 2, 77 on January 3, 81 on January 29 and 82 on January 31, 2000.
Does this drop mean that the peak for the current cycle has passed? Not at all. There are many wild variations in solar activity over the course of the average 11 year cycle, and the only real way to determine the peak or the minimum is to look back at a moving average many months later.
The quieter sun did present some advantages for HF operators, because while the activity was lower, the earth's geomagnetic conditions were quieter as well. The College A index, from Fairbanks, Alaska, was mostly in the single digits, and there were 19 three-hour periods over the week when the College K index was actually 0, lower than the planetary K index at any time. This is significant because the higher latitudes have greater geomagnetic instability at times of heightened solar activity. During this week the area near the Arctic Circle, at least in Alaska, was quieter than the average for the entire planet.
Conditions look quieter for the near term as well. Solar flux is probably bottoming out over the next few days, with predicted values for Friday through Tuesday at 128, 128, 130, 132, and 135. Predicted planetary A index looks quiet as well, with unsettled conditions possible for August 30 through September 3. Solar flux for the next few weeks is expected to peak at only 175 near September 7-9. This is based only on what is known about activity during the previous rotation, and any new activity could change this.
The fall equinox is less than one month away (September 22), and soon we should see a transition from summer to fall conditions. Daytime absorption on the upper bands and atmospheric noise on lower frequencies should be lessened, and stronger signals should be the rule for this equinox at the peak of solar cycle 23.
AE4TM sent along a web link for his experiments using Pactor with ionospheric observations. Check out his web page at http://home.earthlink.net/~ae4tm/hamradio.html and send him your feedback. Another interesting link was received this week. Check http://www.discovery.com/cams/sun/uv.html to see a live webcam from the Solar and Heliospheric Observatory which is updated every 12 minutes with a new ultraviolet solar image.
Sunspot numbers for August 17 through 23 were 252, 231, 209, 150, 132, 84 and 84 with a mean of 163.1. 10.7 cm flux was 177.1, 169.5, 157.1, 152.4, 151.4, 144.2 and 136.9, with a mean of 155.5, and estimated planetary A indices were 11, 6, 6, 7, 12, 5 and 11 with a mean of 8.3.