The Sound and the Fury: What Causes Thunder? Much Ado About Lightning
Hullo Mum,
It isn’t exactly an aviation question, but since it’s weather related I expect it’s close enough. I suppose you’d know what causes thunder? I know I had learned this when I was in school, but I don’t remember and I’ll bet a few other people will be interested, too.
Thanks,
The Latest Noisy Flasher Who Wants His Question Answered
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Whoa Flash,
How can a weather question NOT be aviation related? We’ll take it. So what is thunder? Let’s not put the airplane ahead of the towbar or the thunder ahead of the lightning. Can’t have thunder without lighting, after all, so what is it that causes said lightning? Well, thunderstorm updrafts, dangerously fast rising columns of air within a thunderstorm, cause a tremendous amount of turbulence inside and for quite a distance around the cloud (I shouldn’t have to tell you that you don’t want to be flying anywhere NEAR this type of stuff. You already knew that). While scientists still bicker over the precise mechanism, they do agree that with all that motion, electrons are sheared off the particles rising through that atmospheric mayhem. Those electrons then tend to gather on the descending particles within the roiling cloud, leaving us with a positive charge at the top and a negative charge at the bottom. As the storm rages on, the updrafts continue to increase the charge differential from the top of our cloud to the bottom.
Air provides a reasonably good insulator until the charge differential grows too large. The stepped leader is the invisible electrical tentacle that shoots down from our storm, zigging and zagging quickly as it searches out the best nearby conducting path. The return stroke from the ground, a neighboring cloud, or even from elsewhere within the same cloud provides the electric zap you see and call a lightning bolt. One “bolt” can be anywhere from 1- 20 return strokes.
OK, fine. We have lightning-where’s the thunder? Lightning suddenly increases the temperature of the air to about 30,000 degree Celsius, or about 54,000 degrees Fahrenheit. Yep, that’s hotter than the surface of the sun. The sudden, dramatic expansion of that superheated air followed by the rush of air to fill in the gap after the contraction provides the thunder clap. Actually, to be even more precise, the slight tearing sound you may notice just prior to the strike is the sound of the invisible stepped leader and the click just before the crash of the main bolt is the sound of the return stroke. As the speed of light will always trump the speed of sound, the lag time between seeing the lightning and hearing the thunder increases with increased distance.
What do you need to know about lightning and airplanes? They don’t mix well, though the larger the airplane, the safer you’ll be. Most airplanes are designed to withstand a lightning strike more or less gracefully, though lightning is far from the only thunderstorm hazard. The updrafts, downdrafts, icing, hail, downbursts, and tornadoes give you a whole slew of good reasons to stay on the ground until the storm has safely passed.
Hopefully we’ve managed to illuminate the issue for you. Now stay out of trouble. Check the weather, check it again, and watch out for pop up thunderstorms, all right?
Mom
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