KN4LF:
>As K9LA alludes to, absorption of a MF RF signal extends well south
>of the visible aurora oval. To look at the visible aurora oval only,
>in trying to determine if a higher latitude propagation path is
>blocked or open will leave one scratching his head when the path
>turns out to be closed.
The pmap plots are not "visible aurora". They are measurements
of energy levels in the auroral zone which can affect signals at all
frequencies and at all times. The auroral zones are always there
because of the earth's constant magnetic field and because of the sun's
constant emission of particles (solar wind). The plots are simply
a measurement of the intensity of the energy...sometimes we see it when
it is strong enough to excite atoms in the Earth's atmosphere but
most of the time it is invisible. References to the dynamic nature
of visible aurora were meant only as a visual example of how dynamic
the auroral zone is at ALL times...even when we cannot see it...which
is the usual case.
73, Bill W4ZV
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