ARRL

ARRL Propagation Bulletin ARLP039 (2001)

SB PROP @ ARL $ARLP039
ARLP039 Propagation de K7VVV

ZCZC AP39
QST de W1AW  
Propagation Forecast Bulletin 39  ARLP039
From Tad Cook, K7VVV
Seattle, WA  September 21, 2001
To all radio amateurs 

SB PROP ARL ARLP039
ARLP039 Propagation de K7VVV

Solar flux and sunspot numbers are in a general upward trend since
the beginning of August. If you have WA4TTK's Solar Data Plotting
Utility (available free from http://www.craigcentral.com/sol.htm ),
check the lowerscale showing recent sunspot and solar flux numbers.
Another place to see this trend is at http://www.dxlc.com/solar/ .

The past week had numbers that were down a bit. Average daily solar
flux was down almost 23 points and sunspot averages were off nearly
43 points, when compared to the previous week.

The Autumnal Equinox is this Saturday, and right now is the best
time for HF propagation in many months. 10-meters is getting really
good at this time of year, and will get better (at least in the
Northern Hemisphere) in October and November.

Looking at average sunspot numbers for the past two weeks, this
could be the best Fall equinox of the current cycle for HF
propagation. Average daily sunspot numbers from September 6-19 were
220, but for the same period last year, it was only 113, and 132 in
1999. We haven't had sunspot counts this high prior to the Fall
equinox since the peak of the last solar cycle, when the average
daily sunspot number was 219 from September 6-19, 1989.

On September 18 a solar flare near sunspot 9620 hurled a cloud of
particles into space. This is not moving directly toward earth, but
could sweep past us early Friday. The predicted planetary A index
for Friday through Monday is 15, 12, 10 and 10. Predicted solar flux
for Friday through the middle of next week is around 230.

Holographic images of the sun's far side show a large
southern-hemisphere sunspot. Although this is too far off to predict
with great accuracy, based upon the previous solar rotation solar
flux may peak near 240 around October 7 or 8.

Sunspot numbers for September 13 through 19 were 223, 216, 183, 169,
159, 215 and 224 with a mean of 198.4. 10.7 cm flux was 239.7,
236.6, 219.3, 207.1, 199.1, 203.8 and 198.8, with a mean of 214.9,
and estimated planetary A indices were 18, 10, 15, 8, 10, 8 and 8
with a mean of 11.
NNNN
/EX