ZCZC AP33
QST de W1AW
Propagation Forecast Bulletin 33 ARLP033
From Tad Cook, K7VVV
Seattle, WA August 18, 2000
To all radio amateurs
SB PROP ARL ARLP033
ARLP033 Propagation de K7VVV
Last week's Propagation Forecast Bulletin ARLP032 predicted unsettled to active conditions for the weekend, but an interplanetary shock wave struck the earth's magnetosphere on August 12, triggering a powerful geomagnetic storm. As this was near the peak of the Perseid meteor shower, many observers witnessed the rare spectacle of an aurora as the backdrop for a meteor display. Planetary A index reached 60 last Friday and 109 on Saturday. The K index went as high as 8.
The subject of geomagnetic activity at the peak of the solar cycle figures into a question posed this week by W8GF. He wondered why 15 meter conditions to Central Asia are worse this summer than last, even though solar flux and sunspot numbers are higher. The question was passed around, and K9LA mentioned that geomagnetic activity is higher at the peak of the solar cycle, and from W8GF in Michigan it is a polar path toward Central Asia. Polar paths are severely degraded when there is high geomagnetic activity, and K9LA notes that July 1999 had eighteen days where the planetary A index was 7 or less, but July 2000 had only 8. A look at the W8GF log shows a correlation between lower A indices and better signals from Central Asia.
Over the past week average sunspot numbers were higher than the previous week by over 36 points, and average solar flux was up by nearly 33 points. Solar flux peaked this week for the short term at 1700z on Saturday when it was 195.3, although the official number for the day was the 2000z reading of 189.3. There was another peak on Tuesday when the morning, noon and afternoon readings were 192.5, 193.9 and 195. This is a bit short of last week's forecast, which called for a later and higher peak near 215 on Thursday. The previous week it looked like this week's flux would be closer to 240.
For this weekend, Friday through Monday, predicted flux values are 175, 175, 170 and 170, and expected planetary A index is 10 through the next week. Flux values are expected to meet minimum near 150 around August 27-29, then peak again near September 8-10. This is getting on toward the fall equinox, which should be an exciting time for HF operators at the peak of this solar cycle.
Thanks this week to Jean Bastien of Canada's Dominion Radio Astrophysical Observatory for providing the solar flux data.
Sunspot numbers for August 10 through 16 were 141, 170, 186, 196, 266, 209 and 244 with a mean of 201.7. 10.7 cm flux was 181, 187.3, 189.3, 186, 189.5, 193.9 and 185.6, with a mean of 187.5, and estimated planetary A indices were 23, 60, 109, 16, 12, 12 and 11 with a mean of 34.7.