ARRL

ARRL Propagation Bulletin ARLP034 (2000)

SB PROP @ ARL $ARLP034
ARLP034 Propagation de K7VVV

ZCZC AP34
QST de W1AW  
Propagation Forecast Bulletin 34  ARLP034
From Tad Cook, K7VVV
Seattle, WA  August 25, 2000
To all radio amateurs 

SB PROP ARL ARLP034
ARLP034 Propagation de K7VVV

Solar activity took a big dive over the past week, with sunspot
numbers dropping to 84 on August 22 and 23. Although NASA's
Spaceweather.com reported that the Boulder sunspot number has not
been this low in this calendar year, our records from past bulletins
show that it has been lower than this several times in January.
Boulder sunspot numbers, which are the ones reported weekly in this
bulletin, were 69 on January 1 and 2, 77 on January 3, 81 on January
29 and 82 on January 31, 2000.

Does this drop mean that the peak for the current cycle has passed?
Not at all. There are many wild variations in solar activity over
the course of the average 11 year cycle, and the only real way to
determine the peak or the minimum is to look back at a moving
average many months later.

The quieter sun did present some advantages for HF operators,
because while the activity was lower, the earth's geomagnetic
conditions were quieter as well. The College A index, from
Fairbanks, Alaska, was mostly in the single digits, and there were
19 three-hour periods over the week when the College K index was
actually 0, lower than the planetary K index at any time. This is
significant because the higher latitudes have greater geomagnetic
instability at times of heightened solar activity. During this week
the area near the Arctic Circle, at least in Alaska, was quieter
than the average for the entire planet.

Conditions look quieter for the near term as well. Solar flux is
probably bottoming out over the next few days, with predicted values
for Friday through Tuesday at 128, 128, 130, 132, and 135.
Predicted planetary A index looks quiet as well, with unsettled
conditions possible for August 30 through September 3. Solar flux
for the next few weeks is expected to peak at only 175 near
September 7-9. This is based only on what is known about activity
during the previous rotation, and any new activity could change
this.

The fall equinox is less than one month away (September 22), and
soon we should see a transition from summer to fall conditions.
Daytime absorption on the upper bands and atmospheric noise on lower
frequencies should be lessened, and stronger signals should be the
rule for this equinox at the peak of solar cycle 23.

AE4TM sent along a web link for his experiments using Pactor with
ionospheric observations. Check out his web page at
http://home.earthlink.net/~ae4tm/hamradio.html and send him your
feedback. Another interesting link was received this week.  Check
http://www.discovery.com/cams/sun/uv.html to see a live webcam from
the Solar and Heliospheric Observatory which is updated every 12
minutes with a new ultraviolet solar image.

Sunspot numbers for August 17 through 23 were 252, 231, 209, 150,
132, 84 and 84 with a mean of 163.1. 10.7 cm flux was 177.1, 169.5,
157.1, 152.4, 151.4, 144.2 and 136.9, with a mean of 155.5, and
estimated planetary A indices were 11, 6, 6, 7, 12, 5 and 11 with a
mean of 8.3.
NNNN
/EX