ARRL

ARRL Propagation Bulletin ARLP017 (2001)

SB PROP @ ARL $ARLP017
ARLP017 Propagation de K7VVV

ZCZC AP17
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.
NNNN
/EX