Chuck Murcko wrote:
...
> And BTW, WTF is "black ice"? This term seems to have become popular last decade and I haven't noticed a new phase of water or anything, just the same stuff that's always been frozen on the roads. Or is it some kind of doofus mental aid?
It means a clear road covered by clear ice. The road loses it's
specularity and becomes much darker, hence 'black ice'. Imagine
starting with no snow, having a rain or very heavy mist, then the
temperature suddenly drops with no more precipitation. The standing
water can create a very smooth, hard ice layer that can remain wet.
Doesn't happen often, although I was very lucky to be going slowly in
Northern Ohio once as the temperature dropped from 34 to 28. The wet
road changed suddenly and was so slippery I could barely stand.
Specularity is the (typically) bell-curve random reflection of light.
Mirrors have zero specularity. Most surfaces have some specularity
which allows you to see them with light coming from non-incident angles
since some will get scattered in every direction.
In warmer states, like Virginia, the temperature tends to bounce over
and under freezing which gives more opportunities for this.
...
> Chuck Murcko
> Topsail Group
> http://www.topsail.org/
-- sdw@lig.net sdw@insta.com swilliams@Jabber.com Stephen D. Williams Insta, Inc./Jabber.Com, Inc./CCI http://sdw.st 43392 Wayside Cir,Ashburn,VA 20147-4622 703-724-0118W 703-995-0407Fax Dec2000
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