ARRL

ARRL Propagation Bulletin ARLP035 (1999)

SB PROP @ ARL $ARLP035
ARLP035 Propagation de K7VVV

ZCZC AP35
QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7VVV
Seattle, WA  August 27, 1999
To all radio amateurs 

SB PROP ARL ARLP035
ARLP035 Propagation de K7VVV

All solar indices were up this week, but so were geomagnetic
numbers.  This meant that although there was more ionizing radiation
from the sun to produce a reflective ionosphere for HF signals,
proton activity from flares and coronal holes kept conditions
unstable.

When protons strike charged particles in the ionosphere, their
positive charge neutralizes the negative ionization.  In addition,
the lower D layer, which tends to absorb HF radio signals expands,
and there is increased absorption in the polar regions as well.

Sunspot number averages for this week were up over 20 points
compared to last week, and solar flux averages were up by over 43
points.  The only really quiet day in terms of geomagnetic stability
was August 21, when the planetary A index was below 10 and the K
index over most periods was only 2.  The worst days were August 20
and 23, when the A index was 33, and the K index was 6.  As one
moves higher in latitude, these effects get worse, and the College A
index from Alaska on those days was 65 and 67, with K indices as
high as 7.  This is a severe geomagnetic storm toward the polar
regions.

Unsettled conditions are forecast for the next few weeks.  There are
frequent periods when the A index should be above 10, and around
September 12-16 an A index of 20 is predicted.  We have been in a
period of rising solar flux, and the values for this Friday through
Sunday are forecast at 220, 215 and 215.  Flux values should stay
above 200 through the end of August, then drop to below 170 around
September 3.  Solar flux should bottom out around 125 on September 9
or 10, then rise up above 170 by September 18.  Of course conditions
could get better if new sunspots rotate into view.

On August 21 at 0737 UTC KH6HME worked W1LP/MM on 2 meter SSB, a
distance of almost 3,000 miles.  W1LP was in grid DL51CE.

K8KZ wrote from Michigan to ask why propagation on 10 and 15 meters
disappears for the most part during summer months, and he wonders if
the late night 20 meter propagation will disappear this winter.

In the summer, heating takes place in the F layers of the
ionosphere, causing it to expand during daylight hours.  Since the
MUF (Maximum Usable Frequency) is based on the density of the
ionosphere, expansion by heating makes it less dense, so the MUF is
lower.  10 meters tends to get left out, but 20 does not.

But on 20 meters in the summer, propagation into the night
(particularly toward the west) is enhanced because the days are
longer.  During daylight the ionosphere is receiving more ionizing
radiation from the sun, so 20 is great from North America toward the
Pacific on summer nights.

In the winter, the days are shorter, so we don't get that long
propagation after sunset.  Also, because with less daylight the F
layers are not heated as much, MUFs are higher, as the layers are
more dense.

The bands are great for worldwide propagation in the Fall and Spring
because the conditions are more even between the southern and
northern hemispheres, providing more opportunities for worldwide
propagation of HF signals.  The equinox is coming up in less than a
month on September 22.  Look for great fall conditions, especially
if some new sunspots appear.

K8KZ is in Farmington Hills, Michigan, and he wonders if the solar
flux could go high enough this winter to allow evening propagation
on 20 meters.  Running some samples on a propagation program, we can
look at the path from K8KZ to KH6 on August 21, when the solar flux
was 172.7.  20 meter signals should have been very strong from
0100-0730 UTC, possibly through the night, and quite good again in
the morning from 1130-1600 UTC.

If we do another projection, this time in the fall on November 21
and assume a optimistic solar flux of 250, the signals are good
throughout the day, but fade quickly after 0200 UTC.  Projecting
forward to the last day of the year, and assuming a very optimistic
flux of 300, evening signals fade around the same time.  If the flux
is 200, they fade a little faster.  So the answer appears to be that
even with optimum conditions, the summertime seasonal effects don't
extend into winter.

Sunspot numbers for August 19 through 25 were 68, 65, 79, 78, 110,
103 and 127 with a mean of 90.  10.7 cm flux was 134.7, 151.6,
161.2, 172.7, 187.5, 202 and 208.4, with a mean of 174, and
estimated planetary A indices were 22, 33, 6, 11, 33, 29 and 8, with
a mean of 20.3.

The path projections for this week are from K8KZ in Farmington
Hills, MI.  This should still be good from anywhere nearby, such as
Detroit, Ann Arbor, Southfield, Pontiac, Lansing, Toledo, Ohio or
Southwest Ontario.

To Europe, 80 meters 0000-0600 UTC, 40 meters 2230-0730 UTC, 30
meters 2100-0830 UTC, 20 meters all hours, best 0030-0300 UTC,
weakest 1430-1600 UTC, 17 meters 1030-0200 UTC, 15 meters 1230-0030
UTC, 12 meters 1700-1930 UTC.

To Southern Africa, 80 meters 0000-0430 UTC, 40 meters 2330-0430
UTC, 30 meters 2300-0500 UTC, 20 meters 2100-0530 UTC, 17 meters
1930-0230 UTC, 15 meters 1730-0200 UTC, 12 meters 1630-0000 UTC, 10
meters possibly 1530-2200 UTC.

To the Caribbean, 80 meters 2330-1030 UTC, 40 meters 2200-1200 UTC,
30 meters open all hours, best 0030-0930 UTC, weakest 1600-1800 UTC,
20 meters open all hours, best 0000-0630 UTC, weakest 1600- 1800
UTC, 17 meters 1530-0500 UTC and 1030-1300 UTC, best 0000-0500 UTC,
15 meters 1100-0430 UTC, best 0000-0330 UTC, 12 meters 1200- 0230
UTC, 10 meters 1330-2330 UTC.

To South America, 80 meters 0000-1000 UTC, 40 meters 2330-1030 UTC,
30 meters 2300-1030 UTC, 20 meters 2130-0700 UTC and 0900-1200 UTC,
17 meters 1030-0530 UTC, 15 meters 1200-0400 UTC, 12 meters 1300-
0130 UTC, 10 meters 1530-2130 UTC.

To Hawaii, 80 meters 0500-1130 UTC, 40 meters 0400-1230 UTC, 30
meters 0300-1330 UTC, 20 meters 0130-0730 UTC and 1100-1530 UTC, 17
meters 1600-0600 UTC, 15 meters 1700-0300 UTC, 12 meters 2000-2200
UTC.

To Australia, 80 meters 0730-1130 UTC, 40 meters 0700-1200 UTC, 30
meters 0630-1230 UTC, 20 meters 0530-0900 UTC and 1100-1400 UTC, 17
meters 0400-0700 UTC and 1230-1530 UTC, 15 meters 0330-0600 UTC, 12
meters 0200-0400 UTC, 10 meters possiby 2100-0000 UTC.

To Japan, 80 meters 0930-1030 UTC, 40 meters 0900-1130 UTC, 30
meters 0800-1230 UTC, 20 meters 0600-0830 UTC and 1000-1430 UTC, 17
meters 1200-1500 UTC and 2100-2300 UTC and 0330-0630 UTC, 15 meters
1930-0430 UTC, 12 meters 2030-0100 UTC, 10 meters possibly 2030-
2330 UTC.
NNNN
/EX