On Fri, 18 Oct 2002, DF2PY wrote:
> The statement was made on the reflector that a full moon does
> influence the propagation on topband eventually. I am not a physicist
> by profession
Well, I happen to be an astrophysicist by training and profession so let
me interject a couple of relevant comments.
> First,the amount of reflected radiation is pretty low to what the
> direct solar radiation is.
True enough. The reflectively of the lunar surface is extremely low in
the UV, less than 0.1% at the relevant wavelengths.
But there's a much more fundamental weakness with this physical
explanation. In the extreme ultraviolet (EUV) portion of the spectrum
that is responsible for production of the F-layer, the moon ends up
blocking more of the relevant ionizing radiation from background
astronomical sources (primarily from the diffuse background) than it
contributes in reflected solar radiation.
In marked contrast to the optical region, in the EUV the full moon is
>>darker<< than the surrounding sky.
> Second,the part of the electromagnetic spectrum that contributes
> most to ionization is the Gamma rays.
For the F-layer it is the EUV region of the spectrum (wavelengths of 100
nm - 10 nm) that generate the ionization. Gammas do not contribute
significantly to producing any of teh ionospheric layers because gammas
are energetic enough to penetrate deep into the atmosphere below the
D-layer, almost to the ground.
So what might be a more plausible possible explanation for the observed
"full moon" effect?
Well, the quiet geomagnetic conditions which are typically associated
with good low band propagation originate in features on the sun. As a
result quiet geomagnetic condition do tend to repeat each solar
rotation.
The synodic period of the moon (from full moon to full moon) is 29.5
days. The synodic period of solar rotation varies (with solar latitude)
from about 27 to 34 days.
As a result, whenever good low band conditions happen to coincide with a
full moon, there's going to be a good chance that those conditions will
also recur on the next full moon and the next and ...
Of course this is also true for any lunar phase not just full moon and
for bad conditions as well as good. It's one of those serendipitous
coincidences of nature.
73,
Mike K1MK
Michael Keane K1MK
k1mk@arrl.net
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