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Rudi Kiefer: 'Environmental lapse rate' responsible for vast temperature changes
Rudi Kiefer

“Environmental lapse rate” sounds almost as scary as “polar vortex”, although both are processes known for many decades, and not a new development. The lapse rate doesn’t predict total collapse of the environment in some kind of global disaster.  It simply indicates how much colder it gets when you climb to a higher altitude.

Right now, daytime temperature can reach a mild 60 degrees in Gainesville.  At the shores of Lake Lanier we’re about 1,072 feet above sea level. Looking down on Hiawassee from the tower at Brasstown Bald’s beautiful visitor center sounds intriguing. But the platform there is at 4,780 feet elevation.  This is where the environmental temperature lapse becomes very noticeable. The higher you climb, the colder it gets. A common rate for this area is 20 Fahrenheit degrees difference for every mile of altitude. Being 3,708 feet above Gainesville therefore makes for a 14-degree temperature difference.  Not counting any wind, though it’s likely to be blowing there, Brasstown Bald will be at only 46 degrees.  Leave the town in chilly weather, say 40 degrees.  At the mountaintop it’ll be 26 Fahrenheit. Wind cools the human body considerably, so if there’s a 20 mph wind at the tower, it’ll drop those 26 degrees down to 11.

All this has to do with the fact that the air is most densely packed at the level of the oceans, and gets increasingly thinner higher up. That commercial airliner you may be observing high in the sky is probably flying at 35,000 feet altitude, where it’s 60 below zero.

High altitude road travel can present unexpected challenges, too. As a teenager, I was riding a motorcycle high up on a Swiss mountain road. It was August but sunset still seemed to come quickly. Conditions quickly changed from balmy temperatures down at Lake Brienz to a serious chill on top of the Grimsel Pass.

My front wheel suddenly found a patch of ice on the road and slid out.  Rear wheel and rider soon followed, and the whole conveyance crashed loudly into a gravel pile, thoughtfully placed on the shoulder by the Swiss highway department.  My first learning experience about the environmental temperature lapse rate was thus completed.  Why a teen is adventure-touring on a 7,000-ft. mountain pass at night, in a foreign country, and on a motorcycle, is a different question.

 

Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.
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