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[Phys-L] Re: Rime on the Windshield



The truck's windshield probably slopes so that the sky subtends a large
solid angle at smaller angles of incidence. The clear sky is quite cold,
and glass is nearly black in IR. The air temperature was probably above
freezing, but the windshield was colder than the air. Water condensed on
the windshield and froze. The other windows "saw" a higher radiation
temperature environment and thus did not get cold enough to accumulate
ice.

Here in colder country we see this phenomenon often when the temperature
is above zero. It is also a major annoyance when using a telescope with
a front optic. We don't have to worry about it lately however; it has
been raining for more than three weeks here. Carports are quite
effective in preventing windshield icing.

Leigh (a recovering Californian)

On 13-Jan-06, Brian Whatcott wrote:

It was warm out yesterday, but the sky was clear last night, and by
today's early light, there was a light coat of ice on my truck
windshield
- but only the windshield, but not either of the side windows or
the rear window.
The truck was facing south east, into a sailboat, and was sheltered
by the house front too. It's a black '94 GMC truck. The prevailing
winds are either south which is warm, or north which is cool.
I think I know why it iced that way - can you guess?
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