Dear Tom,
How fast and how much do soil temperatures change a few feet down in response to temperature changes in the air?
Richard Povey
Dear Richard,
The short answers: very slowly and very little.
Internationally acclaimed geophysicist Dr. J. Tuzo Wilson (1908-1993) has written, “One of the most remarkable facts about the Earth’s heat is the extreme slowness with which it travels through the soil and rocks by conduction. A meter (39.4″) below the surface of the ground the daily variations of temperature are hardly felt, seldom producing a change of more than 1(degrees)C (1.8(degrees)F) in the ground at that depth, and the effect arrives there from half a day to a day late.”
And consider this: Only seasonal temperature changes can be detected 25 feet down, arriving literally several months afterward.
———-
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.
