# Questions About Thunder



## Robert Zwilling (Aug 8, 2019)

I am trying to get a visual picture of what thunder looks like. Read several articles but none go into all the details. The explanation for thunder is stated as air channel created, shock wave created, thunder created. I did find one discouraging fact, lightning out of the blue is lightning from the rear of a thunder storm that can travel up to 25 miles before it gets tired of flying through the sky, at which point it starts angling for the Earth. 

Thunder starts off by the lightning bolt creating a super hot air channel around it as the bolt heads for the ground or to another cloud. The hot air blasts outward all along the lightning bolt creating a shockwave which turns into audible thunder.

NOAA says "Thunder can seem like it goes on and on because each point along the channel produces a shock wave and sound wave."

Each point along the channel produces a shock wave and sound wave. Does this mean the points are an inch apart, a foot apart, or is the channel the length between bends in the bolt.

The lightning bolt sets up in a millionth of a second. Does this mean that the resulting air channels and shockwaves are set up so quickly that they are just very simple outlines along the entire length.

Does the entire length of the shockwave head away from the lightning bolt at the same rate so it would look like a cylinder with parallel walls.

If it doesn't have parallel walls, is it expanding into the shape of a cone.

What happens at the places where the bolt bends, does the shockwave turn corners or does it create two shockwaves, one going in the original direction, the second one following the new direction the bolt has taken.

Does the shockwave dissipate uniformly along the entire length of the bolt all at once, or does it collapse starting at one end, or starts from both ends, or starts in the middle going to the ends.

How long does the super heated air channel last compared to the lightning or is it gone the moment the lightning stops and only the expanding shockwave is left.

The lightning we see travels from the ground to the air. The start of the lighting bolt is a test path from the cloud looking for the ground. If you are close enough to the lightning the first sound is a cracking sound before the thunder starts. Is that the first pop of sound from the initial strike before the shockwave starts, separate from the thunder sound. Or is it the leading edge of the shockwave before it starts "rolling."

Is there any reverberation in thunder or does the shockwave just create one wave of sound that dies out.

Thanks for any visualizations of what thunder looks like.


----------



## Alex The G and T (Aug 8, 2019)

Once upon a time, I was climbing Sheep Peak, deep in the back country of Yosemite on a balmy sunny day, with a half a dozen compadres.  We hadn't quite reached the peak when we arrived at a knife ridge; which delineated the final approach to the peak.
We peeked through crenelations in a granite wall and saw that, unlike the azure skies we'd been enjoying on the north side of the mountain; everything on the south side of the mountain was black with storm clouds.
Rocks above our heads began to sizzle with electrical potential.
We all bailed, poste haste, reckless to life and limb down a steep, barren scree slope.  When Lightening began to strike the peak, behind us; we hunkered down, under such cover of small boulders as we could find.
I witnessed a lightning bolt strike less than a hundred feet Downslope of me.  Saw the hail on that particular rock vaporize and the lightning bolt pulsating, up to the skies and back down to the ground... as big around as outspread arms and as high as the sky.  One of the most amazing things I've ever witnessed in all my life.

Maybe the trigger was a "Millionth of a second;" but this bugger pulsated for, at least, a full second or... maybe...almost... two.

But I digress.
Lightning looks.  Thunder sounds.

As you say, lightning is long, with many jagged changes in direction.  The sound of thunder cracks and sizzles when it's nearby, then exhibits doppler effects, and intermittent pulses in volume of roaring, as the distance and direction of atmospheric collapse flows through the ether.  Thunder "Rolls," as they say.

Further,  One stroke of lightning can trigger another, and another, in  different directions.

Then there's the whole bit about the disparity between the speed of light and the speed of sound.  Nearby lightning sounds immediately.  A distant flash can take seconds to sound.  A lengthy bolt of lightening, at a distance, can stretch out the sounding for five to ten seconds duration.  It doesn't take but a quarter mile to make a discernible lag between what one sees and what one hears.

Then, of course, if one is listening to thunder in a venue of granite mountains; the echoes compound  the direction and duration of the sound effects immensely.

I'm enjoying this exercise in synesthesia, visualizing a sound; but it's a bit difficult to put memories of rolling thunder into words. It sparkles and crackles and booms and rattles the windows and sometimes you can feel the bass notes tweak your bones and shake the house.


----------



## HareBrain (Aug 8, 2019)

Alex The G and T said:


> A distant flash can take seconds to sound.



I commented on this a few years ago, how surprising it is that received wisdom (from parents etc) is almost universally that you can work out the distance to a lightning strike by counting two seconds for every mile until the thunder, when reality is more like six.


----------



## chrispenycate (Aug 8, 2019)

The bit of atmosphere through which the lightning is traveling - thebit which is hot enough that it just wants to go somewhere else - is not gas, it is plasma, dissociated nuclei and electrons. Fully ionised.  How much of this is due to temperature, and how much the electricity passing I don't know - and nobody else did fifty years ago when I would occasionally hang around the plasma physics department (take your watch off first).

The shockwave is hypersonic - travels faster than sound in the particular medium. This gives the 'crack' of the thunderclap, while the rumbly  bits are largely vibrations reflected off solid bodies, but coming from the post shock air, and arriving later (and slower).

I very much doubt if the directionality of the wavefront varies much as the current zig and zags, taking the path of least electrical resistance. A shock wave is just about perfectly omnidirectional, so unless it actually strikes you working out where the energy is coning from is extremely difficult. 

Should lightning strike the surface of the sea (pretty common) it has to penetrate the layer of low conductivity distilled water at the surface (not yet mixed rain) before starting the spectacular bits in the conductive salt water.


----------



## Danny McG (Aug 8, 2019)

HareBrain said:


> I commented on this a few years ago, how surprising it is that received wisdom (from parents etc) is almost universally that you can work out the distance to a lightning strike by counting two seconds for every mile until the thunder, when reality is more like six.


The Poltergeist is the well known one with a scene like that


----------



## Robert Zwilling (Aug 8, 2019)

Alex The G and T said:


> I witnessed a lightning bolt strike less than a hundred feet Downslope of me.


Do you remember what kind of sounds you heard when the lightning struck close by. Did you hear thunder from it. Thanks for the information. I can see the lightning pulsating but I can't imagine what it sounded like.


----------



## Robert Zwilling (Aug 8, 2019)

I use thousand one, thousand two, with no real pause between each one, gives a good 1 second timer until you get to 2 syllable numbers. 5 counts is supposed to be a mile or a little farther. The longer I count the better it feels. I'll have to listen to the real sharp crack and the thunder to see if it is around the same time lapse each time. The other night there was a train of continual storms going by in the distance, lasted around 2 hours, thunder constantly rumbling in the background. Reminded me of a Frankenstein movie.


----------



## Alex The G and T (Aug 8, 2019)

Robert Zwilling said:


> Do you remember what kind of sounds you heard when the lightning struck close by. Did you hear thunder from it. Thanks for the information. I can see the lightning pulsating but I can't imagine what it sounded like.



Incredibly loud thunder, like Rock Concert loud; overlain with electrical sizzling and crackling. Instantaneously to the visual.
I don't recall that there were extended reverberations.  There was a steady barrage of additional strikes roaring and crackling farther up on the peak.


----------



## hitmouse (Aug 9, 2019)

Robert Zwilling said:


> Thunder starts off by the lightning bolt creating a super hot air channel around it as the bolt heads for the ground or to another cloud. The hot air blasts outward all along the lightning bolt creating a shockwave which turns into audible thunder.
> 
> NOAA says "Thunder can seem like it goes on and on because each point along the channel produces a shock wave and sound wave."
> 
> Each point along the channel produces a shock wave and sound wave. Does this mean the points are an inch apart, a foot apart, or is the channel the length between bends in the bolt.



This is a figure of speech. Or calculus, if you want to get mathematical. The lightning bolt is continuous, but like any line, it can be represented by a series of points, as close or far apart as you choose.



Robert Zwilling said:


> The lightning bolt sets up in a millionth of a second. Does this mean that the resulting air channels and shockwaves are set up so quickly that they are just very simple outlines along the entire length.



Large lightning bolts can take several seconds to form.



Robert Zwilling said:


> Does the entire length of the shockwave head away from the lightning bolt at the same rate...


Yes, but if the bolt takes time to form, the shockwave  will have moved farther away from the origin by the time the bolt terminates, so...


Robert Zwilling said:


> so it would look like a cylinder with parallel walls.
> 
> If it doesn't have parallel walls, is it expanding into the shape of a cone.


The cone is a good way of looking at it. But if the bolt has bends in it then the cone will be bendy, and if the bolt has forks in it then there will be a sort of branching bendy cone. Either way you will not get one big bang from a flat shockwave front, bit a more rumbly untidy drawn out noise.




Robert Zwilling said:


> How long does the super heated air channel last compared to the lightning or is it gone the moment the lightning stops and only the expanding shockwave is left.



The heat dissipates as fast as the air will conduct it away, and as fast as it radiates. Not instantaneous but pretty quick.



Robert Zwilling said:


> The lightning we see travels from the ground to the air.



Quite a lot of it never hits the ground but stays in the air/clouds.


----------



## BigBadBob141 (Aug 25, 2019)

Sitting up in bed the other night reading ( am an insomniac ), this was three in the morning, a thunder storm had been grumbling away for the past half-hour, but not very near, at least two or three miles away at nearest.
All of a sudden there was an enormous single, solitary bang, which felt as if it was right on top of me!
This must of been the storms parting shot, no idea where it landed but it must have been pretty damned close!!!


----------



## BigBadBob141 (Sep 23, 2021)

Turns out thunder and lightning is far more complex then scientists first thought.
Some lightning bolts are positively charged while some are negatively .
One type is rarer then the other and about ten times more destructive, why they don't know, can't remember which is which.
Also the space shuttle crew observed that lightening storms on earth are mirrored by what appear to be lightening  strikes going up into space at the same time, very, very odd.
At this time no one knows what causes this, so watch this space!


----------



## Robert Zwilling (Sep 23, 2021)

I think the lightning generator in storms is actually an atomic accelerator. Some of the stuff going up into the sky are called sprites, which is more like a light show than a destructive thunderbolt. Supposedly the sprites happen when a positive lightning bolt strikes the Earth. I didn't know there were positive and negative bolts.  Positive lightning is worse.

Apparently the bottom of the cloud is negative, the top is positive, and 95 percent of the lightning is from the lower negative section. I guess the Earth is negative, so there are a lot of sparks and just the brute force of the contained electrical energy in the negative lightning bolt.

The positive lightning comes from the top of the cloud and transfers some of the positive energy to the ground making a much more violent exchange. I guess beside the electrical energy in the individual bolt you also have the positive energy being transferred from the cloud to the ground, which increases the amount of energy at the point of contact.

Water dripping through a metal pipe without touching the edges will create an electrical charge between the pipe and the water droplet. Perhaps it is possible that hail going up and down in a thunderstorm several times before becoming too heavy to stay aloft can create a static charge similar to the way the rubber belt works in a Van de Graaff generator. Supposedly storms with a lot of ice in them produce more lightning than storms with less ice in them. Lighter weight hail can also blow sideways instead of dropping straight down like heavier hail. Maybe the hail isn't always seen.  Moving water creates electrical charge


----------



## BigBadBob141 (Sep 26, 2021)

There is a well known experiment where you have a stream of water, maybe coming out of a tap ( faucet for our american friends ) or something similar .
Then you approach the water stream with an electrically charged rod ( static electricity ), the water shies away from the rod if they share the same sign charge + or -, if it was opposites they would be attracted + and -, just like the poles of two magnets.
So yes moving water does seem to gain a charge.


----------



## hitmouse (Sep 27, 2021)

BigBadBob141 said:


> There is a well known experiment where you have a stream of water, maybe coming out of a tap ( faucet for our american friends ) or something similar .
> Then you approach the water stream with an electrically charged rod ( static electricity ), the water shies away from the rod if they share the same sign charge + or -, if it was opposites they would be attracted + and -, just like the poles of two magnets.
> So yes moving water does seem to gain a charge.


Isn't water a polar molecule such that a stream from a tap is attracted to the static rod whether it is positive or negatively charged? Please correct me if I am wrong. My school science lessons were a very long time ago.


----------

