QST de W1AW
Propagation Forecast Bulletin 21 ARLP021
From Tad Cook, K7VVV
Seattle, WA May 26, 2000
To all radio amateurs
SB PROP ARL ARLP021
ARLP021 Propagation de K7VVV
Sunspots and solar flux numbers have dropped since their peak last week, although because the peak came at the end of the previous reporting period on Wednesday, May 17, the average solar flux number for this week is not much lower. Average solar flux is down less than 2 points this week, and average sunspot numbers are down about 37 points.
There was a big geomagnetic shock on Wednesday, when the planetary A index rose to 73, indicating severe storm levels. The planetary K index was either 6 or 7 for 15 hours. This was after a quiet week where the K index was often 1 or 2. Aurora was sighted as far south as Oklahoma and Missouri on May 23 and 24.
The K index is updated every 3 hours, and a 1 point change is very significant. The A index is updated every 24 hours, and represents the average K index for the previous day. A 1 point change in the A index is very small. For instance, if the K index were 2 for all of the eight 3-hour periods in a day, the A index for the day would be 7. But if the K index were always 3 throughout a day, the A index would be 15. A constant K index of 4 would result in an A index of 27, and a K index of 5 would mean an A index of 48. If the K index were 6 for all periods in a day, then the A index would be 80, and an A index of 132 would result if all periods had a K index of 7.
CW contesters concerned about the CQ Worldwide WPX test this weekend can relax. The latest projection shows geomagnetic conditions settling down. The predicted planetary A index for Friday through Tuesday is 10, 10, 12, 20 and 15. There is more upset seen for early next week, but Friday through Sunday does not look bad. The predicted solar flux for Friday through Tuesday is 165, 160, 150, 145 and 140.Near term solar flux should bottom out near 130 around June 2 or 3, then rise to a peak around the middle of June.
With longer days in the northern hemisphere along with higher sunspot counts and solar flux, look for greater worldwide propagation after dark on 20, 17 and 15 meters.
Sunspot numbers for May 18 through 24 were 297, 239, 282, 271, 207, 150 and 185 with a mean of 233. 10.7 cm flux was 252.9, 254.3, 245.6, 232.3, 214.9, 204.3 and 189.4, with a mean of 227.7, and estimated planetary A indices were 10, 9, 6, 7, 9, 22 and 73, with a mean of 19.4.
Here are some path projections for this weekend's contest, with the best bets for working major points on the globe from the USA.