ARRL

ARRL Propagation Bulletin ARLP036 (1997)

SB PROP @ ARL $ARLP036
ARLP036 Propagation de K7VVV

ZCZC AP36
QST de W1AW
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7VVV
Seattle, WA  September 5, 1997
To all radio amateurs

SB PROP ARL ARLP036
ARLP036 Propagation de K7VVV

Solar activity continues another week of good conditions with
heightened sunspot numbers and solar flux.  There are a number of
good indicators, and one is that the average solar flux for the
previous ninety days rose two points this week to 75, while the
solar flux on every day this week was high above this average.
Solar flux above the moving average indicates a positive trend, and
this has been the case for a month now.  The last day that the solar
flux was below the ninety day average was back on August 4, so this
is a good indication that cycle 23 may finally be under way.

Along with the increased solar activity came geomagnetic instability
caused by coronal mass ejections.  The planetary A index has been 19
for the past two days, and was also in the teens at the end of
August.  Look for possible instability again around September 24 and
25.

Based on the previous solar rotation, solar flux may dip below 80
after September 10, then above 80 ten days later, and above 90 after
September 25.  Over Friday, Saturday and Sunday this week it is
expected to be around 93, 90 and then 85.

An August 28 news article on the Reuters wire service detailed some
findings from the Michelson Doppler Imager--which is aboard the
Solar and Heliospheric Observatory--watching the Sun from almost one
million miles from Earth.  The article mentioned complex patterns of
currents below the Sun's surface which produce sunspots when they
contact plasma.  These streams can rub against each other and the
opposing forces shoot out material in the form of solar flares.

In other news NASA launched the new Advanced Composition Explorer
solar observatory, which is on a five year mission to study solar
flares and provide earlier warning of solar storms.  It will monitor
particles streaming from the Sun, and scientists hope to be able to
predict geomagnetic storms an hour earlier than at present.

Sunspot Numbers for August 28 through September 3 were 61, 67, 69,
80, 90, 67 and 55 with a mean of 69.9.  10.7 cm flux was 90.5, 91.5,
92, 96.4, 93.4, 91.7 and 93.1, with a mean of 92.7, and estimated
planetary A indices were 16, 15, 11, 4, 4, 5, and 19, with a mean of
10.6.
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/EX