ARRL Propagation Bulletin ARLP028 (1998)

ARLP028 Propagation de K7VVV

Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7VVV
Seattle, WA  July 10, 1998
To all radio amateurs

ARLP028 Propagation de K7VVV

Average solar flux was up just slightly last week over the week
before, and geomagnetic conditions were fairly unsettled.  Solar
flux was above the ninety day average of 108 on every day, and the
flux peaked at 129.1 on July 4.  This was the highest recorded value
since two months earlier when the solar flux reached 133.4 on May 5.
The earlier peak was not followed by another one four weeks later,
which is usually expected because of the 27.5 day rotation of the
sun.  Sometimes the active region that produced the high flux and
improved propagation has faded by the next rotation.

Solar flux over the next few days, Friday through Sunday, is
forecast to be 112, 110 and 108, with planetary A indices around 5,
10 and 8.

Based on the previous solar rotation, flux values are expected to
slip to 100 early next week, holding steady until July 24 when they
are expected to rise again.  Solar flux should rise above 120 by
July 28, and near 130 at the end of the month.

For these summer months, 20, 17 and 15 meters offer the best
propagation during daylight, especially when flux values are higher.
From the author's home in the Pacific Northwest, 20 meters is open
to the South Pacific late into every evening.  On 10 meters, the
best hope is north-south propagation when that band opens, with
South American signals strong into North America, especially into
the southern parts of the continent.

Last week's bulletin reported on the problems with SOHO, the Solar
and Heliospheric Observatory.  Unfortunately, contact with SOHO has
not been established.  Even if contact could be restored, the
condition of the equipment inside is uncertain.  This is because
SOHO has a thermal design that allows some equipment to operate in
extreme heat while other gear on the other side of the craft is very
cold.  Since the craft is now believed to be rotating, the sun is
heating the previously cold part of the craft, a condition which
scientists refer to as ''barbecue mode.''  Stay up to date on the
latest developments and also observe some of the stunning pictures
and fascinating observations on the SOHO web site at

Sunspot Numbers for July 2 through 8 were 109, 123, 129, 137, 110,
92 and 56 with a mean of 108.  10.7 cm flux was 120.4, 127.6, 129.1,
123.5, 121.1, 114.6 and 112.4, with a mean of 121.2, and estimated
planetary A indices were 10, 11, 12, 15, 19, 6, and 5, with a mean
of 11.1.