ARRL

ARRL Propagation Bulletin ARLP045 (1997)

SB PROP @ ARL $ARLP045
ARLP045 Propagation de K7VVV

ZCZC AP45
QST de W1AW
Propagation Forecast Bulletin 45  ARLP045
From Tad Cook, K7VVV
Seattle, WA  November 7, 1997
To all radio amateurs

SB PROP ARL ARLP045
ARLP045 Propagation de K7VVV

Solar Cycle 23 showed renewed activity this week, as solar flux
values went well over 100.  Average solar flux for the week was up
about 19 points, and average daily sunspot numbers were up about 36
points.  The average solar flux for the previous 90 days went up
two points from 87 to 89 over the week, and daily values were above
this average on every day, indicating a strong upward trend.  Flux
values are measured three times per day at an observatory in
Penticton, British Columbia.  The one reported here is the noon
measurement at 2000 UTC, but the highest flux measured for the week
was actually 120.6 at 2200 UTC on November 4.

As solar activity was rising, geomagnetic conditions were very
quiet, especially on November 2 and 3, when K indices were at one
or zero most of the time.  This meant that absorption of radio
waves in the upper latitudes and over polar paths was minimized,
and conditions on higher HF bands improved.  These conditions did
not last, and as this bulletin is being written on Thursday
evening, the K index is six, and a major geomagnetic storm is
raging.  This is from a major flare that burst from the solar
surface at 0558 UTC on Tuesday.  Protons from this flare are slow
moving, so it takes a couple of days to affect the Earth.  There
was another major flare on Thursday morning at 1155 UTC, so poor
conditions may continue, although at this point it is uncertain if
the new flare will hit the Earth directly with protons or not.

In last week's bulletin ARLP044 it was mentioned that active
geomagnetic conditions created havoc in the recent CQ Worldwide DX
Contest.  Actually that was mostly true from a west coast
contester's perspective, since contest stations in that region use
a polar path to reach Europe.  The east coast was not affected
nearly as much, since that path to Europe is further to the east.
It is mainly high latitude paths which are bothered during periods
of geomagnetic activity.

For the short term, expect poor conditions until effects from these
solar flares pass.  If we are not affected by the latter flare,
conditions may be back to normal by the middle of next week.  Solar
flux is expected to drop below 100 by November 11, below 90 two
days later, and to the mid-eighties after the middle of the month.
It should rise above 90 again around November 23, and above right
after Thanksgiving.  Periods of unsettled to active geomagnetic
conditions are forecast around November 20-23, a recurrence of the
conditions during the recent DX contest.

For updates on the storm, check WWV at 18 minutes after the hour,
or call 303-497-3235.  Conditions should be back toward normal when
the K index is three or less, although the ionosphere may take some
time to recover.  Some good sites on the web to check for alerts
and information are Cary Oler's Solar Terrestrial Dispatch page at
http://holly.cc.uleth.ca/solar/ or NOAA's Space Environment Center
at http://solar.sec.noaa.gov.

Sunspot Numbers for October 30 through November 5 were 51, 55, 62,
74, 66, 68 and 51 with a mean of 61.  10.7 cm flux was 88.2, 90.5,
93, 97.8, 109.8, 117.9 and 113.8, with a mean of 101.6, and
estimated planetary A indices were 10, 4, 8, 3, 3, 9, and 9, with a
mean of 6.6.
NNNN
/EX