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ARRL Propagation Bulletin ARLP028 (2000)

ARLP028 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7VVV
Seattle, WA  July 14, 2000
To all radio amateurs 

ARLP028 Propagation de K7VVV

Solar activity rose substantially this week.  Average sunspot
numbers compared to the previous week rose nearly 68 points to
244.6, and average solar flux rose nearly 39 points to 207.5.  A
strong solar flare around 1037z on Wednesday sent a bubble of
electrified gas, or plasma, toward the earth at more than 2 million
miles per hour.  Effects of the blast are being felt on Thursday,
and a second more powerful wind is expected to arrive on Friday.
This could be bad news for the Pacific 160 Meter Contest this
weekend, although possible aurora could prove interesting for the 6
Meter Sprint.  There is a good chance that any geomagnetic upset may
decline through the weekend though.

These flares originate in sunspot group 9077, which is large and
magnetically complex.  It harbors energy for powerful solar flares
which could erupt on Thursday or Friday.  For late updates, visit

Another URL that bears checking is  Dan has put
together some great links of interest to propagation and sun
watchers, including a chart which compares solar cycles 19 through
23.  Go to and click on ''Cy
19-23 Comparison.''  You will see that the current cycle is not as
bad as cycle 20, but weaker than cycles 21 or 22, and of course
nowhere near the biggest one of all, cycle 19.  The author suffered
through cycle 20 as a teenaged ham in the 1960s, but as a small
child heard the effects of cycle 19, which peaked in the late 1950s.
Father's low band VHF FM business radio in the company car brought
in unfamiliar voices from all over the country to our home in
California's San Joaquin Valley.

The three daily 2000z flux values reported by the Penticton
observatory for July 10-12 were 244.5, 241.6 and 314.6.  Because
they were flare enhanced, the NOAA Space Environment Center and the
U.S. Air Force collaborated to come up with more realistic solar
flux numbers, which were 215, 225 and 230.  The lower numbers are
the ones used here in our weekly summary.

The latest prediction shows solar flux peaking on Friday around 230,
then drifting down below 200 by July 18, and reaching a short term
minimum around 165 from July 23-26.  The next expected peak in solar
flux is around August 6-9.  Expect geomagnetic conditions to remain
active.  Based on the previous solar rotation, there are no
predicted days over the next month when the planetary A index is
expected to be in the single digits.

Sunspot numbers for July 6 through 12 were 210, 226, 260, 262, 232,
281 and 241 with a mean of 244.6. 10.7 cm flux was 174.3, 187.1,
210, 211.3, 215, 225 and 230, with a mean of 207.5, and estimated
planetary A indices were 7, 8, 7, 7, 19, 31 and 12, with a mean of


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