Dear Tom,
You’re seldom wrong, but your mistaken use of “sublime” borders on the ridiculous.
Kurt Mathes, Gardner, Ill.
Dear Kurt,
Pun noted. Your criticism is technically valid because the column to which you refer used “sublimation” to describe the formation of frost, which actually is a deposition process. Read on.
Water exists in three phases: solid, liquid and gas. Sublimation is the transition from solid directly to gas without passing through the liquid phase. Deposition, the opposite process, is the change from gas directly to solid. Meteorologists use (some would say misuse) sublimation to refer to both processes.
When ice cubes in a freezer gradually shrink, that’s sublimation (analogous to the evaporation of a liquid). When frost forms on vegetation, that’s deposition (analogous to condensation).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
