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Planes, car batteries and even trees take a beating in the heat

The current 100-degree-day streak is at seven days -- it'll likely be eight after today -- and forecasts don't indicate that any end is in sight.

As miserable as heat waves make animals feel, they also affect the vegetable and mineral crowds.

Trees can have heatstroke, airplanes find getting off the ground a little tougher, and car batteries give up the ghost faster under extreme heat.

Thin and thinner

The hotter it gets, the thinner air gets.

And that means airplanes with propellers must go faster to generate the lift necessary to take off, said Lynn Lunsford, a Federal Aviation Administration spokesman.

"As the air temperature increases, air molecules spread out and air density decreases," Lunsford said. "At an airport like Meacham, where the absolute altitude is 710 feet above sea level, the performance of aircraft may be equivalent to operation at 3,000 or 4,000 feet."

Lunsford said that means the plane needs a longer runway. Decreased air density affects not only the wings' lift but also the propellers' efficiency.

A plane's acceleration is affected because the engines' power output, which depends on oxygen, is reduced, Lunsford said. That all makes the aircraft climb slower once it's in the air and demand higher airspeed to keep it from stalling, he said.

Lunsford said jets aren't affected as significantly.

The worst sound ever

Lots of folks have heard the sickening staccato click when trying to start the car on a frozen morning. But Dan Ronan, a AAA Texas spokesman, said car batteries are more likely to die from extreme heat.

"With this heat over the last several days, we've noticed a 5 percent increase [statewide] in calls for towing service," Ronan said. "A lot of batteries, a lot of heating and air-conditioning systems."

Extra heat under the hood can push older belts and hoses over the edge and suddenly bring everything to a grinding halt, Ronan said. Batteries that are approaching their three-year mark are also susceptible to added heat.

"We've seen this because people are hanging on to their cars longer and deferring maintenance," he said. "Suddenly August comes up with 107 degrees and the unit says, 'I'm done. I ain't going to work anymore.'"

How hot did you say?

Aaron Pan, curator for Fort Worth's Museum of Science and History, said it's pretty common knowledge -- since the 1800s -- that listening to crickets and katydids can tell you the temperature.

"If you count the chirps of male crickets or katydids in 15 seconds and add 40, that's the temp in Fahrenheit," he said.

What's less commonly known is that this can't be done when the mercury tops 99, Pan said.

"A lot of crickets stop chirping when it's below 50 degrees or above 100 degrees," he said.

What, no shade?

Trees don't perform well in extreme heat, either. Pan said they can suffer heatstroke, especially the very young or very old.

Cooling themselves much the way humans do -- yes, they "sweat" -- trees open the stomata on their leaves so water inside the plant can evaporate, Pan said.

"Extremely high temps cause excessive moisture loss, so the trees close the stomata on the leaves," he said. "They no longer take in carbon dioxide for photosynthesis, and they're no longer cooling themselves. So the leaves heat up, and that's bad for the tissues. An internal temperature of 115 degrees is fatal."

Creating shade over a young tree can help save its life, Pan said. For an old tree, besides watering the roots, spraying water on the leaves will cool them.

Hot times in the city

Life is, indeed, hotter in the cities.

Streets, rooftops, parking lots and other man-made surfaces that have replaced nature create an "urban heat island," said Jesse Moore, a meteorologist with the National Weather Service in Fort Worth.

"Almost always the temps at the downtown areas are higher than rural areas," he said.

Moore said official temperature readings with the National Weather Service are taken at a standard height of 5 feet by instruments in shade.

Surface temperatures in the sunlight can be much hotter -- just ask any band member who has been out marching on pavement this week.

What might surprise people, Moore said, is that the situation reverses when the sun goes down.

"At night, the opposite happens," he said. "The temperature is cooler at ground level, because cold air sinks. That's why you can see frost on the ground even though the weather service says the temperature is 35 degrees."

Terry Evans, 817-390-7620

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