ARRL Propagation Bulletin ARLP020 (2000)

ARLP020 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7VVV
Seattle, WA  May 19, 2000
To all radio amateurs 

ARLP020 Propagation de K7VVV

This has been an exciting week for sun-watching hams. In last week's
Propagation Forecast Bulletin ARLP019, the forecast said that solar
flux may peak around 220 on May 18. Instead, on May 17 the noon
solar flux reading at Penticton, BC was 262, which is a new high for
the current solar cycle 23. The previous high for this cycle was
248.5 on November 10, 1999. Prior to that the solar flux has not
been this high since the last gasp of high numbers for cycle 22,
when it was 271 on February 3, 1992. That was quite an active week
back in 1992, when the solar flux on January 29 through February 3
was 266, 280, 303, 284, 288 and 271.

Average solar flux for this week was up an astonishing 85 points
compared to last week, and average sunspot numbers were up nearly
140 points, more than double last week's average.

Last week's bulletin mentioned that the solar area number, counted
as millionths of the solar disk, was 130 on May 7. But this week
that number reached a new high for this cycle of 3510 on May 15.
Along with the high sunspot counts and solar flux came some
geomagnetic activity. The most active days were May 12 and 17, when
the planetary A index was 22 and the K index was as high as five.

This week's forecast shows solar flux values for Friday through
Tuesday rising higher, at 260, 265, 265, 270 and 270. It also looks
like we may experience some more days of unsettled geomagnetic
conditions, with a predicted planetary A index of 12, 15, 15, 12 and
10. Given this prediction, at this point the best days for HF
propagation will probably be Monday and Tuesday. Solar flux is
expected to bottom out around 130 between June 2 and 3, and reach
another peak around the middle of next month.

WA3KFT wrote this week asking about web sites that show plots of
solar indices. Some good ones are,,, and

In response to some questions I had about 10 meter propagation at
the equinox, K9LA, who writes about propagation for the National
Contest Journal as well as Worldradio, wrote back with results of
some path projections he did using MiniProp. He studied 10 meter
paths from New York, Chicago and California to Europe, Japan and
Australia (VK4), with both short paths and some long paths.

He found that New York to Europe was best in Winter, with Fall a
close second. To Japan over the short path, Fall and Spring are
best, and the same for the long path, but with Summer a close second
or third. To Australia Fall and Spring were best, with Winter
conditions very close.

For his Chicago to Europe 10 meter path, Winter was best with Fall a
close second. Short path to Japan showed Fall best with Winter a
close second, and for long path Fall and Spring were best with
Summer close behind. To Australia Fall, Winter and Spring were about

For the path from California, Fall and Winter were best to Europe
with Spring not far behind, and a long path projection to Italy
showed Fall and Spring were best, with Summer not far behind. To
Japan, Fall and Winter were best with Spring not far behind, and to
Australia, Fall, Winter and Spring were about equal.

Before Carl did the projections, his feeling was that 10 meters was
best in the Winter. But when he thought about it more, he realized
that his answer may have been based on his Midwest location and the
fact that most of the DX he works on 10 meters is in Europe.

For this week, with the solar flux at a new high, expect good
conditions on 10, 12 and 15 meters. Over many paths 15 meters will
be open during most of the day and part of the night. 10 meters
should be especially strong over north-south paths. Path projections
from Texas to Brazil, for instance, show 10 and 12 meters open from
just before sunrise in Texas until just a few hours before sunrise
in Brazil, which is late into the Texas night.

Sunspot numbers for May 11 through 17 were 213, 211, 260, 263, 302,
298 and 342 with a mean of 269.9. 10.7 cm flux was 177.7, 190.4,
217.3, 232.5, 244.4, 258.7 and 262, with a mean of 226.1, and
estimated planetary A indices were 6, 22, 15, 12, 16, 18 and 22,
with a mean of 15.9.