QST de W1AW
Propagation Forecast Bulletin 19 ARLP019
From Tad Cook, K7VVV
Seattle, WA May 12, 2000
To all radio amateurs
SB PROP ARL ARLP019
ARLP019 Propagation de K7VVV
Solar flux and sunspot numbers were sharply lower over the past ten days, but are now heading higher. Solar flux reached a low on Saturday, May 6, when the three readings for the day were 126.3, 126.8 and 126.7. The noon 126.8 reading is the official flux for the day. Daily solar flux values have not been this low since October 2, 1999, when it was 126.3. Average solar flux for the past week was off by over 30 points when compared to the previous week, and average sunspot numbers were down by nearly 13.
Another interesting number to look at is the total sunspot area visible on the solar disk. These numbers are expressed as millionths of a hemisphere, and you can see the daily value along with the solar flux and sunspot numbers online at gopher://sec.noaa.gov/00/indices/DSD. We reached a low of 130 for visible sunspot area on May 7. Sunspot area has not been this low since September 30 and October 1, 1999. This value represents a nearly spotless sun, and is actually equivalent to .013 percent of the visible surface. Contrast this with a short time back, April 23, when the sunspot area number was 2860, representing 22 times the visible area of the May 7 value.
All of this does not mean that we have passed the peak of the solar cycle, however. Activity jumps around quite a bit, even during a peak year of the cycle such as this one. It is only later when viewing smoothed numbers on a graph that the progress of a cycle looks steady. For more information, read Solar Ups and Downs at http://science.nasa.gov/headlines/y2000/ast09may_1m.htm.
As this bulletin is written on Thursday evening, the solar flux seems to be ramping upward. It is measured three times per day in Penticton, British Columbia at 1700, 2000 and 2300z, and the last four values measured, from 2300z Wednesday through 2300z Thursday are 167.7, 177.7, 177.7 and 186.5. The predicted solar flux for the next five days, Friday through Tuesday, are 190, 195, 200, 200, and 205. Solar flux is expected to peak for the short term around 220 on May 18, then drop down around 130 from June 1-3.
Unfortunately, this weekend there may be effects from a coronal mass ejection that occurred on May 8. Predicted planetary A index for Friday through Tuesday is 20, 20, 15, 8, 8 and 8.
Sunspot numbers for May 4 through 10 were 105, 122, 111, 130, 131, 149 and 174 with a mean of 131.7. 10.7 cm flux was 134.5, 129.8, 126.8, 130.9, 137, 149.5 and 179.2, with a mean of 141.1, and estimated planetary A indices were 8, 14, 12, 7, 6, 11 and 7, with a mean of 9.3.
Path projections for this week are from Chicago, Illinois and are all to DX locations from this week's ARRL DX Bulletin ARLD020.