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From: Chris Luginbuhl (cbl_at_hidden_email_address.net)
Date: 07/02/1996



> > Marko,
> >
> > Your skies in the north might be more conducive to more colorful
> > displays since ice crystals should be (?) more common in your
area -
> > the mere fact that ice crystals exist here in the tropics raises
more
> > than a few eyebrows when I relate it to my officemates.
>
> Actually, the tropical tropopause is colder than polar tropopause.
This
> can be explained by the fact that the tropical tropopause is in
much
> higher altitude, near 15 kilometers, compared to about 8 kilometer
of
> polar tropopause.
>
> - Timo

But actually the answer must be more complicated than this, I think: first,
does sufficient water vapor for ice-xtal formation more often reach into the polar upper atmosphere than into the tropical? Colder may not be relevant if there is not enough water to form clouds.

Second, tropical conditions may more often result in extensive lower-atmosphere cloud development, which may then tend to obscure upper atmosphere halo-generating clouds.

I am just speculating: I myself do not know whether haloes are more frequent
in higher latitudes or in lower. I do however think the question is much more complicated than simply the temperature of the tropopause. The accumulating data on halo occurrences that is being accumulated might be helpful in this regard, though the important information about the visibility of upper clouds / obscuration by lower clouds is not easy to account for.

Chris

Christian B. Luginbuhl
U.S. Naval Observatory Flagstaff Station Flagstaff, Arizona USA
cbl_at_nofs.navy.mil