ARRL

ARRL Propagation Bulletin ARLP037 (2000)

SB PROP @ ARL $ARLP037
ARLP037 Propagation de K7VVV

ZCZC AP37
QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7VVV
Seattle, WA  September 15, 2000
To all radio amateurs 

SB PROP ARL ARLP037
ARLP037 Propagation de K7VVV

The sun has been almost spotless this week, which seems odd for what
is supposed to be the peak period of activity for solar cycle 23.
The Boulder Sunspot Number went all the way down to 27 on Monday,
and the average sunspot number for this reporting week (Thursday
through Wednesday) was a tiny bit over half of last week's average.
Monday's index was the lowest sunspot number of this year.

The last time the average weekly sunspot numbers were lower than
this week's (88.7) was back at the new year, when our Propagation
Forecast Bulletin ARLP001 reported an average of 85.1 for the week
of December 30 through January 5, 2000. But the lowest sunspot
number during that week was 69, far higher than 27. A daily sunspot
number that low has not been recorded for 19 months. That was on
February 6, 1999, when it was also 27.

Many radio amateurs might be asking if we are past the peak of the
cycle, but this cannot really be determined until well after the
peak, when the experts can analyze a moving average of sunspot and
solar flux data.

But check out a new addition to the WM7D web site. If you go to
http://www.wm7d.net/hamradio/solar/ and then click on the text which
says ''Click here for charts reflecting the past 72 months,'' this
will bring your web browser to
http://www.wm7d.net/hamradio/solar/past_cycle.shtml , which shows
the past six years in separate one year charts. The recent chart
seems to show a general peak in solar flux and sunspot numbers some
time during spring and summer of this year.

Of course in a few months, this may appear quite different, since we
are now focusing on the recent drop in activity and more activity in
the future may change this perception. Some time in the future a
long moving average (where one plots the center point after
averaging a large number of days) will probably show a very broad
peak, and it is too early to determine where that peak will be
centered. What we are experiencing now is the wide variation in
activity that can be observed even at the peak of the solar cycle.

Activity for the past few days has been picking up, and the latest
solar flux forecast for Friday through next Thursday is 160 for
Friday and Saturday, and 170 for Sunday through Thursday. Keep in
mind that projections like this beyond three days are somewhat
questionable, and the further out they are, the more of a guess they
are likely to be. Solar flux is expected to stay above 150 until
October 5, then reach the next minimum around 125 on October 10 or
11.

Planetary A indices predicted for Friday through next Thursday are
45, 12, 12, 10, 12, 12 and 10. The high A index forecast for Friday
is probably due to the M-Class solar flare which erupted at 1213z on
Tuesday. Shortly after this flare, the Solar and Heliospheric
Observatory recorded a spectacular and fast-moving full-halo coronal
mass ejection. The result may be mid-latitude auroral displays,
along with a minor to major geomagnetic storm.

Next week is the autumnal equinox, a time when HF conditions should
be at their best. Let's hope that the sun cooperates, and gives us
more sunspots and less solar flares.

Sunspot numbers for September 7 through 13 were 160, 115, 116, 69,
27, 38 and 96 with a mean of 88.7. 10.7 cm flux was 173.2, 163.4,
150.9, 140.6, 134.9, 132.6 and 133.2, with a mean of 147, and
estimated planetary A indices were 16, 21, 7, 5, 5, 20 and 10 with a
mean of 12.
NNNN
/EX