The K7VVV Solar Update

SEATTLE, WA, Aug 16, 2002--The sun showed 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 this week were up 9.3 points over last week, 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. Predicted planetary A index for August 16-18 is 30, 15 and 10, and there is a 10 to 20 percent chance of a severe geomagnetic storm.

Bob Brown, NM7M, offered some comments concerning K3MIY's recent e-mail 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 winter.

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

Tom Giella, KN4LF, passed along the URL for his Web site which includes a page that concentrates on Medium Frequency propagation.

Jon Jones, 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 2000 UTC to after 2330 UTC. 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. The 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.

Amateur solar observer Tad Cook, K7VVV Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version also appears in The ARRL Letter. Readers may contact the author via k7vvv@arrl.net.

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