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ARRL Propagation Bulletin ARLP034 (2002)

ARLP034 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 34  ARLP034
From Tad Cook, K7VVV
Seattle, WA  August 16, 2002
To all radio amateurs 

ARLP034 Propagation de K7VVV

The sun shows renewed activity this week. There was a dip in solar
flux and sunspot numbers centered around August 6-8, but with the
appearance of giant sunspot number 69 and more than 10 smaller
groups, the indices are again on the rise. Mean daily sunspot
numbers were up 9.3 points this week over last, and average daily
solar flux rose by precisely the same amount. Solar flux reached a
recent peak of 241.5 on July 26, dropped over 100 to 134.6 on August
8, and may peak again above 240 around the middle of next week.

Geomagnetic numbers over the past week indicated unsettled to active
conditions, and this is expected to continue. On August 14 a coronal
mass ejection appeared that wasn't squarely earth-directed, but
there is a fair chance it will cause upset on earth. The predicted
planetary A index for August 16-18 is 30, 15 and 10, and there is a
10 to 20% chance of a severe geomagnetic storm.

Bob, NM7M had some comments concerning K3MIY's recent email about
heating and thinning of the ionosphere. Bob says that the summer
seasonal reduction in Maximum Usable Frequency isn't caused by
heating, but by a chemical difference in the F-layer during summer.
Bob wrote:

"It is really a chemical effect due to the differential lifting of
atomic oxygen with seasons, as compared to that of molecular
nitrogen and oxygen. The (n2+O2)/O ratio is greater in summer than
winter, increasing by 1.5X to 3.3X from 150 km to 400 km.

"The higher ratio means more recombination of electrons (with NO2+
ions) than production of electrons by photo-ionization of atomic
oxygen, the principal constituent of the F-region. That lowers the
MUF in the summer.

"Check it out with MINIPROP, taking a path from W7 to EU, summer and

Bob says this is covered in greater detail on page 55 of his book,
"Little Pistol's Guide to HF Propagation."

KN4LF passed along the URL for his web site,
and points out that he has a page concentrating on Medium Frequency
propagation at

N0JK from Kansas wrote saying that the summertime E-layer skip on 6
meters hasn't been very productive, but August 4 was fantastic. He
said 6 meters was open from the Midwest to the Caribbean and
northern South America from 2000z to after 2330z. 9Y4TL, CO8DM and
ZF1DC made hundreds of 6 meter contacts, and ZF1DC even made a few 2
meter contacts to the U.S.

Sunspot numbers for August 8 through 14 were 150, 164, 140, 180,
230, 214 and 254, with a mean of 190.3. 10.7 cm flux was 134.6,
140.1, 148.4, 172.3, 183.9, 191.8, and 208.1, with a mean of 168.5.
Estimated planetary A indices were 10, 15, 16, 15, 15, 13, and 15,
with a mean of 14.1.


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