QST de W1AW
Propagation Forecast Bulletin 17 ARLP017
From Tad Cook, K7VVV
Seattle, WA April 20, 2001
To all radio amateurs
SB PROP ARL ARLP017
ARLP017 Propagation de K7VVV
Solar flux and sunspot numbers have been declining, but still there is plenty of activity to keep geomagnetic conditions active. Mean daily sunspot numbers declined by nearly 60 points this week over last, and average solar flux was down nearly 44 points. Sunspot numbers were down to the double instead of triple digits this week, with Tuesday through Thursday sunspot numbers at 89, 63 and 85. Sunspot numbers were last in the double digits about a month ago.
That large sunspot that caused so much excitement a few weeks ago is now visible again, and about to rotate into full view. Daily solar flux probably reached a minimum on Monday at 123.4, and the latest forecast has solar flux for Friday through Monday at 155, 165, 175 and 185. Solar flux is expected to peak somewhere around April 27 or 28 at 230. Of course, new activity could change this. After all, when solar flux peaked at 273 and 274 on March 27 and 28, a week earlier the best guess was that solar flux would peak around 180 on those dates.
Last Friday a strong geomagnetic storm was triggered by an interplanetary shock wave. This followed a couple of days of similar effects from coronal mass ejections. Then on Sunday, one of the most powerful solar flares ever recorded was observed, but it was near the sun's western limb, and mostly aimed away from earth. But Gary, WB0FFI, was talking to a friend on 80 meters a little over 200 miles away in Colorado on Sunday morning when all signals on the band suddenly vanished. Gary reported that signals went from S9 to nothing, and all that was left were electrical noise and the buzz of television sweep oscillators. Gary wondered if the energy from this flare caused a sudden expansion of the D layer, absorbing radio waves, and I think he is probably right. The X14 class flare happened at 1350z, right during Gary's weekly 1330-1430z sked.
Another interplanetary shock wave struck earth on Tuesday. This has been quite a week for auroras. The most disturbed day this week was Wednesday, when the planetary A index was 50 and the planetary K index reached 7 over two periods. This came one week after another severe disturbance, when the planetary A index was 60 and the high latitude College A index was 100.
Still, through all this, HF contacts were possible. I spent the week playing with PSK31, working stations using low power, free software downloaded from the net, and my laptop's sound card as an interface. This reminds me of the eighties, when I was KT7H and active on AMTOR.
Sunspot numbers for April 12 through 18 were 159, 138, 149, 100, 107, 89 and 63 with a mean of 115. 10.7 cm flux was 149, 137, 138.7, 134.2, 123.4, 126.1 and 131.8, with a mean of 134.3, and estimated planetary A indices were 38, 36, 15, 13, 7, 7 and 50 with a mean of 23.7.