Simply Science: Weather impacts planes, ground noise

6:32 PM, Jul 19, 2012   |    comments
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GOLDEN VALLEY - A viewer email raised a good question about the impact that weather has on something as simple as how loud airplanes sounded to us on from the ground.

Jason from Plymouth emailed KARE 11 to tell us he noticed more plane noise recently. So we looked into whether the weather is having any impact on the noise.

To take off, an airplane relies on air to create lift, and because of this, air density can affect the rate of climb for the plane after takeoff, said Krishnan Mahesh, of the University of Minnesota's Department of Aerospace Engineering and Mechanics.

Cool dry air is denser than humid air so airplanes can climb more efficiently. There are more air molecules to support the plane's weight, Mahesh said.

Hot and moist air is less dense, so the plane can't climb through the air as efficiently and the plane can't climb as fast, Mahesh said.
So in conditions like our recent heat wave, an airplane remains closer to the ground longer, before reaching flight altitude, making it audible at the surface further from the airport than usual.

The weather also has an effect on how the sound from the plane's engine travels.

Sound from airplanes gets absorbed into the atmosphere. The amount of absorption, in part, depends on the air temperature and humidity level, along with the frequency of the sound waves. Hot air absorbs less of the sound, so a plane could sound louder in a heat wave than at other times.

Humid air, on the other hand, absorbs more of the sound so on a really humid day, the heat and humidity could cancel each other out.

Big thanks to Krishnan Mahesh in the University of Minnesota's Department of Aerospace Engineering and Mechanics for his help on answering Jason's Question!

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