Bob G3REP asked me to post the following to the reflector:
-----------------------------------------------------------.
As mentioned by K9LA, I had discussions with Emma Woodfield of Liverpool
University last year and the conclusions were that Solar and lunar tides
contribute to geomagnetic fields, but the lunar component is only a few
percent of the strength of the solar contributions. This was written up
in Low Band Monitor; November 2004 (edited and published by K0CS)
Appleton's biography (by R Clark - fascinating read) described the
experiments at the Cavendish Field Laboratory where they discovered a
regular lunar tide as well as a solar one with the height of the E-Layer
rising and falling over a distance of about 1km (approx 1%) and
attaining its maxima about 45minutes before the Lunar transits.
According to Earth, Radio and the Stars by Harlan True Stetson (McGraw
Hill, 1934, pages 187-204) the following may be of interest:
Investigations by Kenrick and Pickhard of WBBM-Boston series from 1926
to 1931 that were reported to the American Geophysical Union in 1932
have yielded a further confirmation of the Lunar period with emphasis,
according to these investigations, on the semi-lunar period of 14.75
days, the second harmonic of the 29.5 day period. It appears signals are
enhanced when the moon is 30 deg below the horizon, and depressed when
the moon is above the horizon at an average altitude of 45 deg.
The text is not specific on what frequencies were used but it was
studied over a period of years and correlation of signal strength made
with lunar altitude.
Further discussion is covered by Matsushita (circa 1962) in a book
titled Ionospheric Sporadic E - International Series of Monographs on
Electromagnetic Waves edited by Smith and Matsushita 1962, Pergamon
Press. It's all a bit over my head, but it has interesting references to
lunar tides and its effect on foEs at different magnetic latitudes.
The other aspect to remember is that there are 25 Solar hours in a Lunar
day so any effect of the two on the ionosphere, whether it is f, E, or
Es or geomagnetic fields will shift progressively in and out of phase.
In summary: There are a multiplicity of events affecting what is going
on and the moon is just one of them. However the moon could marginally
affect any geomagnetic influences (which are varying greatly anyway), it
also affects the height of the E-layer (albeit 1%!), the critical
frequency of the E being dependent of electron density (with the
gravitational pull of Lunar & Solar tides), etc. One wonders if we will
ever find a conclusive answer.
73 de Bob G3REP
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