"Rain" vs. "Drizzle"
[I was looking through Posthaste for the Why Things Are on perceptions of weather and couldn't find it, but found instead this item about raindrops. From Style, March 10, 1995.]
James and Marie Elise Underwood of Morganza, Md., ask, "Why are
raindrops sometimes heavy, fat drops that splat across the windshield,
yet other times fine, small drops that, even in a heavy rain, seem to
Dear Jimmy and Marie: We've always wondered if rain has ever come
down so hard that it was fatal. Because we think killed-by-rain would be
a really poetic way to go.
The big hairy raindrops usually come from thunderheads, those tall
cumulus clouds common in summer. The wind currents force the droplets up
and down and they grow bigger and bigger, with the biggest drops being
about the size of a pea, a fifth of an inch across, according to Allan
Eustis, a meteorologist with the National Weather Service.
The larger the drop, the greater its terminal velocity. This is not
because gravity "pulls" it harder. It's because air pressure has more
effect on a small drop. It can't cut through the atmosphere as well.
A pea-sized drop can reach a terminal velocity of about 30 feet per
second. It hits your windshield with all that force because it's big and
fast, like a pro football linebacker.
The smaller drops tend to form in horizontally organized, layered
clouds, without all the convection and turbulence and drama. A typical
raindrop is 0.06 inches, or about one-seventeenth of an inch, across. At
that size it can't go much faster than about 13 feet per second. It just
Eustis points out that raindrops aren't teardrop-shaped. They have
flattened bottoms, because of the air pressure.
"They kind of look like hamburger buns," he said.
Eustis says that if the drops are less than 0.02 inches in
diameter, the precipitation is no longer considered rain. By definition
it's drizzle. (Before you tell anyone it's drizzling outside, please
verify the droplet diameter.)
Posted by: Phil from Brussels | July 18, 2005 2:49 PM | Report abuse
Posted by: jw | July 18, 2005 3:05 PM | Report abuse
Posted by: firsttimeblogger | July 18, 2005 3:10 PM | Report abuse
Posted by: Phil from Brussels | July 18, 2005 3:21 PM | Report abuse
Posted by: Sara | July 18, 2005 3:31 PM | Report abuse
Posted by: lamb | July 18, 2005 5:58 PM | Report abuse
The comments to this entry are closed.