From a window seat in coach it often seems like turbulence strikes for no reason. You’re flying through cloudless skies when suddenly the plane shakes and the seatbelt light dings on. It would be nice to think that at least the pilots saw the rough air coming, but often they’re caught by surprise, too.
But that may be about to change. A recent study by the National Center for Atmospheric Research (NCAR) proposes a new explanation for why turbulence crops up. It owes to something called atmospheric “gravity waves.”
Even if you've never heard of gravity waves, you’ve definitely seen them in action. Think of the ripples created when a rock is dropped into a pond: The force of the dropped rock propels the water upwards while gravity pulls the disturbed water back towards its equilibrium state. Or consider waves at the beach: They’re gravity waves, too, produced when the wind whips up the ocean surface and gravity pulls the water back down.
The same principle applies in the earth’s atmosphere. Robert Sharman, author of the NCAR study, explains that atmospheric gravity waves occur when air moving up and down through the atmosphere hits resistance. For example, clouds rise from the troposphere into the more stable air of the stratosphere and the collision, as it were, sends out waves of air around the clouds. Sometimes those waves peter into nothingness and sometimes they run into airplanes, breaking on the body of a 747 the same way ocean waves break when they hit the shore: turbulence happens and you spill your Diet Coke.
Sharman and his team are currently analyzing turbulence data from airplane flight recorders in order to build a model for forecasting gravity waves. If their model gets good enough, pilots will be able to steer around choppy air and you’ll find yourself with more time to move around the cabin.
(As a last point, I was initially confused by the term gravity waves. I assumed it referred to an Einsteinian spacetime phenomenon when it really describes an instance of plain old Newtonian mechanics at work. A little Googling reveals that what I had in mind are called gravitational waves as opposed to gravity waves and it turns out researchers are making progress on that front as well: A team of Princeton astrophysicists recently announced that gravitational waves—which are caused by mega-collisions of space bodies like neutron stars or black holes—are probably a lot more common than we (they) have thought.)
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