ARRL

ARRL Propagation Bulletin ARLP047 (1996)

SB PROP @ ARL $ARLP047
ARLP047 Propagation de KT7H

ZCZC AP67
QST de W1AW
Propagation Forecast Bulletin 47  ARLP047
From Tad Cook, KT7H
Seattle, WA  November 15, 1996
To all radio amateurs

SB PROP ARL ARLP047
ARLP047 Propagation de KT7H

There was a rise in solar activity over the past few days, with
solar flux rising steadily above the three month average of 70.  It
is expected to top out in the mid seventies by Saturday, and then
drop to 70 by the middle of next week, and 68 at the 1st of
December.  After that flux values are expected to rise above 70
again after December 7.

Geomagnetic disturbances are rising, and should peak today and again
around the 19th.

Perhaps this period of days with solar flux above the recent
averages is a sign that the cycle is about to turn up from the
bottom.  When we start seeing weeks of solar flux numbers above the
previous 90 day average we will know that the wait is over.

A packet message came in this week from Dick Farman, K2QR, ARRL
Technical Coordinator from Western New York.  Dick wants to see some
VHF content in this bulletin, and here are his comments:

Although present HF propagation is not particularly exciting - as
evidenced by solar flux numbers around 70 - anything can happen on
VHF.  The astute VHF DXer usually ignores the reported solar flux
and concentrates on the A and K indices.

Geomagnetic field disturbances may be sufficient to cause aurora,
and the aurora can be reflective at VHF.  As pointed out in an
earlier propagation bulletin, the A and K indices provide an
indication of geomagnetic activity and, therefore, can provide a
band opening tip-off to VHF operators.

When the A index is about 20 and the K index is 4 or 5 (or
greater.), conditions are often good for VHF aurora.  Hollow
sounding signals on 80 meters mean it's time to fire up on VHF and
point the antennas north.

Phase variations in signals reflected from the auroral curtain make
this propagation mode suitable for CW and, perhaps, SSB contacts.
FM becomes too distorted for communication.  Contacts are most
likely on 10, 6, and 2 meters.  As the intensity of the geomagnetic
storm increases, higher frequencies are effected.

As electrons trapped in Earth's magnetic field spin down and lose
energy, they emit photons and the aurora becomes visible-sometimes
as streaks of light, sometimes as ''curtains.''  It's often a tough
decision whether to work the bands or go outside to watch the light
show.

Sunspot Numbers for November 7 through 13 were 0, 0, 11, 11, 14, 27
and 14, with a mean of 11.  10.7 cm flux was 68.5, 69.1, 70.2, 71,
71.5, 72.2 and 73.1, with a mean of 70.8.  Planetary A indices for
the same period were 5, 4, 11, 6, 3, 8, and 11, with a mean of 6.9.
NNNN
/EX