ARRL

ARRL Propagation Bulletin ARLP031 (2001)

SB PROP @ ARL $ARLP031
ARLP031 Propagation de K7VVV

ZCZC AP31
QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7VVV
Seattle, WA  July 27, 2001
To all radio amateurs 

SB PROP ARL ARLP031
ARLP031 Propagation de K7VVV

It is summertime, but not too early to look forward to fall HF radio
conditions. F-layer propagation should return to 12 and 10 meters in
the fall, particularly for those of us operating in the higher
latitudes. The summer solstice was on June 21 this year, and the
autumnal equinox will be September 22. This places the mid-way point
between the longest day and the equinox about 10 days from now.

There aren't many sunspots currently visible, and a holographic
image of the far side of our star shows no substantial sunspot
groups.

Average daily sunspot numbers over the past week dropped ten points,
and average solar flux was down just over two points. Solar flux
values have been meandering, and this is expected to continue.
Solar flux values over the next week should be flat, around 120 from
July 28 through August 2. Solar flux could gradually rise after
that, but not much of a peak is expected, unless new activity
develops. The holographic image of the sun's far side gives us a
hint of things to come, since any activity exactly opposite from our
view should be back on earth side in about two weeks.

Although there hasn't been much sunspot activity, we have recently
been affected by a high speed solar wind emitted from a coronal
hole. This accounts for the planetary A index of 15 and 22 on
Tuesday and Wednesday. Current forecasts show the planetary A index
dropping to around 12 on Friday and below 10 on Sunday, then
possibly rising to around 15 on Tuesday and Wednesday.

Sunspot numbers for July 19 through 25 were 180, 193, 153, 153, 143,
143 and 96 with a mean of 151.6. 10.7 cm flux was 142.3, 142.6, 139,
140.4, 143.2, 132.5 and 133.3, with a mean of 139, and estimated
planetary A indices were 9, 8, 8, 11, 12, 15 and 22 with a mean of
12.1.
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/EX