Goodday all...
I'm looking for optimum (i.e. realistic) angle settings to define the twilight
terminator and sunlight angle parameters for use in Geoclock. This is what
Geoclock HELP has to say about twilight and sunlight angles:
>The value is the offset, in degrees, of the zone boundary from the edge of
the (geometric)
>sunlight part of the earth. Typical values of interest for shortwave
operating include:
>
>SUNLIGHT = -6.596 Boundary where sun starts/stops illuminating the D-layer.
This controls
>absorption on the lower frequency shortwave radio bands.
>
>TWILIGHT = -14.165 Boundary where sun starts/stops illuminating the F-layer.
These values
>are based on average D- and F- layer heights. They define the Ionospheric
Gray Line: a
>twilight zone where shortwave radio signals can pass through the D-layer
without absorption.
>Within this zone signals will encounter an illuminated F- layer whose
ionization level will be
>normally enhanced over that found in the night zone.
The values mentioned above are the default settings for the "HAM" map display,
which is a an equidistant- azimuth (great circle) map centered on one's QTH.
(Great circle day/night is very interesting viewing, by the way!). Other angle
values included in Geoclock are aimed more at visual observation of apparent
twilight and sunrise, such as -0.833 for SUNLIGHT, and -6 for TWILIGHT.
I would be interested to hear comments on these D- and F-layer illumination
angles.
73, Alex PA3DZN
----
Alex C.J. van Eijk
Email: DXIS@wxs.nl
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