Mon Oct 24 21:25:54 EDT 2005
<<On Mon, 24 Oct 2005 18:12:39 -0700 (PDT), John Bolduc <firstname.lastname@example.org> said:
> In simple terms there is an electrical mirror way up in the sky. During
> the day the sun absorbs most of the mirror, but at night the electrical
> mirror comes back and reflects signals (skywave) back to earth. Sorry my
> wife is nagging me to go to the store, so I'll to end my explanation here!
Not quite correct.
There are multiple layers up in the ionosphere, which have different
properties for radio waves of different frequencies. One of these
layers reflects mediumwave ("AM broadcast") and shortwave signals.
However, during the day, solar radiation energizes the layer below it,
which causes that layer to absorb MW and some SW signals before they
can get up to the reflecting layer. (That's why shortwave stations
switch frequency during the day.) It takes a little while for that
layer to change completely, which is why skywave sometimes persists
for a while after sunrise. When the ionosphere is disturbed by
a geomagnetic event, the absorptive layer may remain energized all
night, producing what are commonly known as "auroral" conditions.
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