ARRL

ARRL Propagation Bulletin ARLP043 (2001)

SB PROP @ ARL $ARLP043
ARLP043 Propagation de K7VVV

ZCZC AP43
QST de W1AW  
Propagation Forecast Bulletin 43  ARLP043
From Tad Cook, K7VVV
Seattle, WA  October 19, 2001
To all radio amateurs 

SB PROP ARL ARLP043
ARLP043 Propagation de K7VVV

Sunspot numbers and solar flux values rose this week. Average daily
sunspots were up nearly 18 points, and average solar flux rose
almost 40 points. Solar flux was mostly in the 170s for a couple of
weeks, until this week when it went above 190, and then 200.

Solar flux for the next few days should continue this rise, with
values of 235, 240, 245 and 250 predicted for Friday through Monday.
Unless new sunspots emerge, the solar flux is expected to decline
below 200 by the end of this month.

You can see a difference in sunspots corresponding to the sudden
change in solar flux. Look at a photo for October 13, when the flux
was still below 180, at web site
http://spaceweather.com/images2001/13oct01/midi512_blank.gif .

Then take a look at an image from another day, at
http://spaceweather.com/images2001/18oct01/midi512_blank.gif , which
shows the October 18 photo when the flux was 228.7. Notice how the
big sunspot group that was off to the side is now in the middle,
aimed more toward earth.

Thursday and Friday, October 11 and 12, had unsettled to active
geomagnetic conditions, but geo-indices have been quiet since. This
was expected to continue, with A indices below 10, until today at
0105z when a large solar flare erupted from sunspot region 9661, the
big spot seen in the center of the solar disk in the October 18
photo referenced above. The energy from this flare caused a radio
blackout across Asia and Australia, and is expected to fully affect
earth on Sunday, October 21.

Sunspot numbers for October 11 through 17 were 174, 179, 166, 178,
176, 168 and 171 with a mean of 173.1. 10.7 cm flux was 174.8,
179.2, 179.5, 191.9, 192.9, 207.2 and 217.4, with a mean of 191.8,
and estimated planetary A indices were 17, 27, 10, 9, 11, 8 and 4
with a mean of 12.3.
NNNN
/EX