ZCZC AP28
QST de W1AW
Propagation Forecast Bulletin 28 ARLP028
From Tad Cook, K7VVV
Seattle, WA July 14, 2000
To all radio amateurs
SB PROP ARL ARLP028
ARLP028 Propagation de K7VVV
Solar activity rose substantially this week. Average sunspot numbers compared to the previous week rose nearly 68 points to 244.6, and average solar flux rose nearly 39 points to 207.5. A strong solar flare around 1037z on Wednesday sent a bubble of electrified gas, or plasma, toward the earth at more than 2 million miles per hour. Effects of the blast are being felt on Thursday, and a second more powerful wind is expected to arrive on Friday. This could be bad news for the Pacific 160 Meter Contest this weekend, although possible aurora could prove interesting for the 6 Meter Sprint. There is a good chance that any geomagnetic upset may decline through the weekend though.
These flares originate in sunspot group 9077, which is large and magnetically complex. It harbors energy for powerful solar flares which could erupt on Thursday or Friday. For late updates, visit http://www.spaceweather.com.
Another URL that bears checking is www.qsl.net/w3df. Dan has put together some great links of interest to propagation and sun watchers, including a chart which compares solar cycles 19 through 23. Go to http://www.qsl.net/w3df/sol_f0.html and click on "Cy 19-23 Comparison." You will see that the current cycle is not as bad as cycle 20, but weaker than cycles 21 or 22, and of course nowhere near the biggest one of all, cycle 19. The author suffered through cycle 20 as a teenaged ham in the 1960s, but as a small child heard the effects of cycle 19, which peaked in the late 1950s. Father's low band VHF FM business radio in the company car brought in unfamiliar voices from all over the country to our home in California's San Joaquin Valley.
The three daily 2000z flux values reported by the Penticton observatory for July 10-12 were 244.5, 241.6 and 314.6. Because they were flare enhanced, the NOAA Space Environment Center and the U.S. Air Force collaborated to come up with more realistic solar flux numbers, which were 215, 225 and 230. The lower numbers are the ones used here in our weekly summary.
The latest prediction shows solar flux peaking on Friday around 230, then drifting down below 200 by July 18, and reaching a short term minimum around 165 from July 23-26. The next expected peak in solar flux is around August 6-9. Expect geomagnetic conditions to remain active. Based on the previous solar rotation, there are no predicted days over the next month when the planetary A index is expected to be in the single digits.
Sunspot numbers for July 6 through 12 were 210, 226, 260, 262, 232, 281 and 241 with a mean of 244.6. 10.7 cm flux was 174.3, 187.1, 210, 211.3, 215, 225 and 230, with a mean of 207.5, and estimated planetary A indices were 7, 8, 7, 7, 19, 31 and 12, with a mean of 13.