SB PROP @ ARL $ARLP018
ARLP018 Propagation de K7VVV
QST de W1AW
Propagation Forecast Bulletin 18 ARLP018
From Tad Cook, K7VVV
Seattle, WA May 5, 2000
To all radio amateurs
It seems odd to view the solar disk at the peak of the solar cycle and see few sunspots, but that was the case this week. Solar flux, a measure of 2.8 GHz energy from the sun which correlates roughly with sunspots and the ionization of the particles which reflect HF radio waves, were down sharply this week. On Thursday, when this bulletin was written, the thrice daily solar flux numbers were 133, 134.5 and 134.7. Solar flux has not been this low since January. Average solar flux for this week dropped over thirty points, and average sunspot numbers were down over seventy points, when compared to the previous week.
Geomagnetic conditions were fairly unsettled as well, with planetary A indices in the double-digits throughout the week, and K indices often as high as four. There weren't any severe geomagnetic storms, but geomagnetic conditions were rarely quiet.
Looking at monthly trends, the average monthly solar flux for January through April was 159, 174.1, 208.2 and 184.2.
The lower activity should continue for the next few days. Predicted solar flux for Friday, May 5 through the following Tuesday is 130, 130, 135, 145 and 150. The predicted planetary A index for those days is 10, 15, 12, 10 and 10.
KA5WQM wrote to remark on poor 10 meter conditions. He said that in central Oklahoma the band has been unusable since last Thursday. There are a couple of influences to consider. One is the season. Ten meters is much better right around the equinox, and we are moving every day closer to summer conditions when occasional short skip via sporadic E-layer propagation will be the norm.
Of course the other factor is the lower sunspot activity and solar flux. Doing a path projection from Oklahoma to Hawaii with a solar flux of 230, there is a good bet for strong openings on 10 meters from 1800 to 2230 UTC. Lower the solar flux to 170, and the period in which strong signals are likely over that path shrinks to 1930 to 2130 UTC. With the solar flux at 130, communication is possible, but strong openings are much less likely. During this month 15 meters should be far better for long distance HF communications than 10.
Sunspot numbers for April 27 through May 3 were 163, 238, 142, 126, 121, 108 and 113 with a mean of 144.4. 10.7 cm flux was 183.5, 183.4, 174.9, 169.5, 157.7, 152.8 and 137.3, with a mean of 165.6, and estimated planetary A indices were 13, 17, 12, 11, 14, 18 and 15, with a mean of 14.3.
Path projections for this weekend are from Hawaii.