ARRL

ARRL Propagation Bulletin ARLP018 (2000)

SB PROP @ ARL $ARLP018
ARLP018 Propagation de K7VVV

ZCZC AP18
QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7VVV
Seattle, WA  May 5, 2000
To all radio amateurs 

SB PROP ARL ARLP018
ARLP018 Propagation de K7VVV

It seems odd to view the solar disk at the peak of the solar cycle
and see few sunspots, but that was the case this week. Solar flux, a
measure of 2.8 GHz energy from the sun which correlates roughly with
sunspots and the ionization of the particles which reflect HF radio
waves, were down sharply this week. On Thursday, when this bulletin
was written, the thrice daily solar flux numbers were 133, 134.5 and
134.7. Solar flux has not been this low since January.  Average
solar flux for this week dropped over thirty points, and average
sunspot numbers were down over seventy points, when compared to the
previous week.

Geomagnetic conditions were fairly unsettled as well, with planetary
A indices in the double-digits throughout the week, and K indices
often as high as 4. There weren't any severe geomagnetic storms, but
geomagnetic conditions were rarely quiet.

Looking at monthly trends, the average monthly solar flux for
January through April was 159, 174.1, 208.2 and 184.2.

The lower activity should continue for the next few days. Predicted
solar flux for Friday, May 5 through the following Tuesday is 130,
130, 135, 145 and 150. The predicted planetary A index for those
days is 10, 15, 12, 10 and 10.

KA5WQM wrote to remark on poor 10 meter conditions. He said that in
central Oklahoma the band has been unusable since last Thursday.
There are a couple of influences to consider. One is the season.
Ten meters is much better right around the equinox, and we are
moving every day closer to summer conditions when occasional short
skip via sporadic E-layer propagation will be the norm.

Of course the other factor is the lower sunspot activity and solar
flux. Doing a path projection from Oklahoma to Hawaii with a solar
flux of 230, there is a good bet for strong openings on 10 meters
from 1800 to 2230z. Lower the solar flux to 170, and the period in
which strong signals are likely over that path shrinks to 1930 to
2130z. With the solar flux at 130, communication is possible, but
strong openings are much less likely. During this month 15 meters
should be far better for long distance HF communications than 10.

Sunspot numbers for April 27 through May 3 were 163, 238, 142, 126,
121, 108 and 113 with a mean of 144.4. 10.7 cm flux was 183.5,
183.4, 174.9, 169.5, 157.7, 152.8 and 137.3, with a mean of 165.6,
and estimated planetary A indices were 13, 17, 12, 11, 14, 18 and
15, with a mean of 14.3.

Path projections for this weekend are from Hawaii.

To the East Coast of the United States, 80 meters 0430-1030z, 40
meters 0400-1130z, 30 meters 0330-1230z, 20 meters 0230-0730z and
1000-1330z, 17 meters 1500-1600z and 0100-0500z, 15 meters possibly
0200-0330z.

To the center of the continental United States (somewhere in
Kansas), 80 meters 0430-1230z, 40 meters 0330-1330z, 30 meters
0300-1430z, 20 meters 0130-1530z, 17 meters 1400-1800z and
0030-0800z, 15 meters 1600-0630z, 12 meters and 10 meters possibly
2030-2230z.

To the West Coast of the United States, 80 meters 0430-1400z, 40
meters 0300-1600z, 30 meters open all hours, strongest 0530-1300z,
weakest 1900-0000z, 20 meters 1330-0730z, 17 meters 1700-0730z, 15
meters possibly 1930-0600z.

To Australia, 80 meters 0830-1630z, 40 meters and 30 meters
0730-1700z, 20 meters 0630-1700z, 17 meters 0430-1000z, 15 meters
2130-2330z and 0300-0900z, 12 meters 2200-0830z, 10 meters
2230-0730z.

To Japan, 80 meters 0900-1630z, 40 meters 0800-1730z, 30 meters
0700-1800z, 20 meters 0530-1900z, 17 meters open all hours, best
0930-1300z, weakest 2230-0230z, 15 meters 2000-1230z, 12 meters
2130-1100z, 10 meters 2330-0930z.
NNNN
/EX