What About Thunder?

I have heard that prior to a lightning strike, one can smell the ozone forming(near)--I don't know if I buy it, but worth throwing out here.

This is an amazing thing--That is why I always listen to the possibilities of power being harnessed from the ocean or air. Lightning is real and no one(no matter their education) can do anything with it(yet). I am not so sure we have a perfect definition of what it is, even.

Amazing stuff and I love a good storm. I just wanted to get something in here so I can read the following posts and discussions.

Nice CJ, thanks, K T

"I have heard that prior to a lightning strike, one can smell the ozone forming(near)"

Well, that makes a lot of sense. In order to have lightning, first you need an ionized channel through which the lightning current can flow. Ozone is ionized oxygen.

One of the common misconceptions about lightning is how much energy is involved. People calculate the breakdown potential of air at somewhere around one million Volts per meter, multiply that by a few kilometers, and multiply that by 200 kA, and it appears that you have a lot of power.

In fact, you never have the million Volt per meter electric field gradient at the same time as the 200 kA current. The air breaks down before the current can flow. Thus the large electric field gradient is an electrostatic field that facilitates the flow of current, but the very flow of that current negates the field. So you either have the field, or the current, but not both at the same time.

Of course lightning is powerful and dangerous. But you aren't going to use it to power the electrical grid, even if you had a way to harness it.

Wow--Thanks emc c.

I haven't really tried to understand it, but this helps a lot.

Can you address the effect of the DC on the floating water mass? Is there no effect? Water comes in 3 states, solid, liquid, and gas. Are you saying that there is no division of elements and immediate recombination along the DC line of flow through water as a gas?

Could it be one of several functions that occur during the brief phenomenon?

Trust me, I am not working on a theory of a different nature, I truly have a curiosity about this one amazing work of nature. What really strikes me is the sudden increase in rainfall immediately after a clap of thunder overhead. This I have ovserved myself many times. Is it just me?

I cannot answer your question conclusively or authoritatively, because I have never seen this question discussed.

It seems reasonable to assume that the same electric field which ionizes the air could indeed separate water molecules into hydrogen and oxygen, and then the lightning current flowing immediately thereafter could serve as an ignition source so that the hydrogen and oxygen could reform into water.

However, it isn't obvious to me how this would result in locally more rain. The phenomenon hypothesized doesn't create more water, it just uses energy to dissociate water molecules and then recombine them.

Also there is the question of timing. The rain falling on you at the time you hear the thunder is not necessarily the rain that was near the lightning waveform when it discharged. The delay in when you hear the thunder would have to line up with how much time it took to get the rain formed by the lightning waveform to reach you.

Thanks for your candor, I have greater respect for this type of input.

As to the timing. This is also one of the elements that seems to be odd. I see lightening and hear radio interference of about the same time and duration, but the thunder, delayed by distance and sound speed of course, last noticeably longer and varies in intensity not in any noticeable pattern related to what my eyes tell me.

These are points of interest for me in this discussion. These are the clues that have worked at my brain for these many years. I don't see the expansion/contraction of momentarily heated air and the extended rolling and rumbling of thunder as correlating.

I will be OK with no authoritative answer. I am more comforted that there is room to wonder.

Greater respect for what kind of input? And greater respect than for what else?

Here is a simple thought experiment that may help with rolling thunder. The lightning current heats the air very rapidly and you get essentially an explosion in the channel. That is thunder. It is an impulsive phenomenon.

Now consider a tuning fork. You strike it against a solid object, and it rings. The striking is an impulsive event, but the sound resulting is at a specific tuned frequency. This is the impulse response of the tuned fork.

You take your small child to the park. You place the child in a swing, and you give them a push: an impulse. The resulting motion is sinusoidal: the impulse response of another tuned system.

You drop a rock in your bathtub. The rock hitting the water drives a circular waveform outward that is a pressure wave, just like sound. When the wave hits the bathtub walls, it reflects inward, and bounces back in the direction it came from. Rolling thunder...

Greater respect for candor about what is not known in comparison to authoritative statements that leave no room for other possibilities, and explaining when something is a highly educated guess.

Thanks for the things to consider about the 'rolling' thing, I see how that could apply.

I still have yet to go to the links suggested, but I Promise not to disappear as other OP's have. Thanks to you, and all contributors.

I remember a teacher stating something along the lines of a vaccuum being created where the lightning had dispersed everything out. Then as the vaccuum was filled a sonic boom occurred.

It is a slam dunk that once the lightning current has cleared the channel that air will rush back in to fill up the near vacuum that was left when the lightning blew all the air out of the channel.

However it is less than obvious that would create a sonic boom. The pressure differential is at most one atmosphere, and likely less than that at the altitude at which the lightning occurs (speaking cloud-to-cloud, not cloud-to-ground).

Furthermore, the heat due to the lightning bolt doesn't dissipate instantaneously, so that the pressure would not instantly go to zero as the bolt extinguished.

Imagine the following slight variation on an old experiment. Assume a a plastic or glass container such as a ketchup or syrup bottle, that has a wide bottom and a long narrow neck. Pour a little water in the bottom, and place it in the microwave on high, long enough to boil the water for a while. The water vapor will fill the container and push out the air. You cap the bottle and remove it from the microwave. Now if you let things stop there, what happens is that the container implodes as the water vapor cools, because now the outside air pressure exceeds the internal pressure as the vapor cools and condenses. That is the classical experiment demonstrating atmospheric pressure. But if instead you had a really stout container that could take the pressure, you could let the water vapor completely condense and generate a one atmosphere pressure differential between the inside and outside of the pressure vessel.

If you could then instantaneously create an opening in the vessel that would allow pressure equilibration without damage to the vessel, my instinct is you would hear a rushing or whistling sound, but no sonic boom.

Agree/disagree/other?

At 0.528 of atmosphere, it will reach sonic speed in the throat of the nozzle.

This won't generate a noticeable sonic boom.

If the nozzle now diverges, the flow will accelerate and at the end of the nozzle it will terminate in a shock way (I think it is called an oblique shock wave, but memory is hazy).

With only 1 atm to drive it, the "boom" generated wouldn't be especially loud.

In the case of lightning, there are several effects operating.

Once the air is ionized, the lightning travels well above the speed of sound. The heated air cannot get out of the road fast enough so it piles up into a shock wave.

The air is dramatically heated. This raises the local speed of sound, enabling the air to move aside faster than it would if at ambient temperature. As this displaced air cools, the local speed of sound decreases, but other heated air is "catching up". This piles the air up, intensifying and broadening the shock wave.

The range of temperatures and sonic speeds vary the time taken for the wave to travel and dissipate, lengthening the duration of the thunder.

Echoes from clouds and other "hot spots" and "cold spots" also extend the duration, while local temperature and density variations can also have a focusing effect, reflecting sound and making it more directional, with a variety of preferred directions into which sound is concentrated.

The rain following later can often come about because the turbulence generated by the lightning forces droplets into contact with one another, coagulating a small proportion of them until they become heavy enough to overcome the varying currents in the cloud and they fall. (If they all coalesced, the resultant deluge would be massive and difficult to survive)

You may notice that the drops from a thunderstorm are often quite large. One reason is the turbulence within the cloud is high. Another is that updrafts are stronger than in a normal rain cloud, so drops must be heavier to be able to fall.

The huge amount of DC current flowing would certainly split water into H2 and O which would recombine almost immediately, making it's own, probably small, contribution.

In addition, the heat ionizes the air (and water). This absorbs a lot of heat which is almost immediately released again as they recombine. The slight delay further extends the duration of the thunder.

One of the generators of the electric charge that becomes lightning, is the frictional charging of rapidly moving droplets within the cloud. As they fall and then are pulled up again by updrafts, considerable electrostatic charge is developed. Because of the huge volume being agitated and thereby charged, enormous power is generated, hence the observed effects of lightning.

I wonder if a normal cloud could be made to coalesce the droplets sufficiently by generating sonic standing waves within it? Could be a more productive approach than cloud seeding.

One of the first websites to look at for learning about weather science is http://www.theweatherprediction.com/. The man behind it is Jeff Haby, a meteorology instructor at Mississippi State Univ. The content there is presented at an introductory level, so you might be interested in something more advanced. In that case, check the American Meteorological Society. You can search their online journals here.

Other websites to check would be the National Severe Storms Laboratory, the National Center for Atmospheric Research, the University Corporation for Atmospheric Research, or some of the weather discussion groups such as the Eastern US Weather Forums.

You might also wish to discuss this with Ron Holle, a weather photographer and one time lightning researcher at the NSSL.

The current thinking (is there a pun here?) is that lightning heats the air rapidly to an extreme temperature and sets up a shock wave.

I doubt that the effect of lightning on water in the air, either vapor, rain or cloud drops has anything to do with thunder because I do remember hearing thunder, and plenty of it when no rain fell. The Storm Prediction Center on their Activity Chart will mark any areas of dry thunderstorms, if any are present or expected in their Fire Weather Outlook. On the Activity Chart, just put your pointer over the "Fire" tab at the right end to make the Day 1 Fire Wx Outlook appear. Clicking on the tab takes you to page where you can see both the Day 1 and Day 2 outlooks.

In case you are wondering why I know about all these websites, I am a certified storm spotter and have been since 1997. I once wanted to be a research meteorologist, and also wanted to be a storm chaser. I dont' want to be a chaser, but I do want to do some chasing when I can afford the equipment and the gas, and have the time when storms doing their thing.

CJ, are you trying to stir up my SDS?

Thanks, great stuff to work with. I must join my wife for bedtime now, but I will be looking these references over and I thank you all.

Also, on the point of lightening with no rainfall, I am aware that the dewpoint will have an effect on water being visible or invisible but present in the air mass, so I wasn't too concerned about whether I could see the H₂O or not.

'night now. Merci beaucoup

Doug, I've been pouring over countless thousands of words, many in high-tech terminology, and animations galore, but I wanted to take a break and share the Wikipedia text. This text sums up all of the ideas expounded in our thread so far, and concludes that there must be more to it.

(copied from Wikipedia, bold added by me.):

Cause

The cause of thunder has been the subject of centuries of speculation and scientific inquiry. The first recorded theory is attributed to the Greek philosopher Aristotle in the third century BC, and an early speculation was that it was caused by the collision of clouds. Subsequently, numerous other theories have been proposed. By the mid-19th century, the accepted theory was that lightning produced a vacuum. In the 20th century a consensus evolved that thunder must begin with a shock wave in the air due to the sudden thermal expansion of the plasma in the lightning channel. In a fraction of a second the air is heated to a temperature approaching 28,000 °C (50,000 °F)^[1]. This heating causes it to expand outward, plowing into the surrounding cooler air at a speed faster than sound would travel in that cooler air. The outward-moving pulse that results is a shock wave, ^[2] similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft. More recently, this consensus has been eroded by the observation that measured overpressures in simulated lightning are greater than what could be achieved by the amount of heating found. Alternative proposals rely on electrodynamic effects of the massive current acting on the plasma in the bolt of lightning.^[3]

Well, I was struck by the two details, that thermal expansion, the "latest theory, has been 'eroded' by observations. .", and that there are newer alternative proposals having to do with electrodynamic effects on the plasma" etc.

I have to admit that my vocabulary exceeds many folks I run into usually, but the reading of these many references was challenging me in ways I have not dealt with in a long time. I was growing weary and getting ready to throw in the towel when I came to this clear statement.

The conclusion I have come to with the assistance of this CR4 thread, and the exhaustive research done all day today, is this;

I am satisfied that my uncomfortableness with variances between my observations and the standard explanations I had been presented with is not unfounded, in that the many conflicts in explanations and observations and measurements so far have left even the experts in this field expecting to discover more about this amazing phenomenon.

Even more so since the 'electrodynamic effects on the plasma' was given as the direction that is being evaluated for future theories. One of which may include my hypothesis. Of course, maybe not also, but I can still be a bit excited to watch for developments in a field that I have always marveled at.

Not conclusive, but NOT disappointing results. Thank you all, I am content with the result of this thread in response to my query.

CJM.

CJ, you might want to concentrate on cloud electrification. I once had plans to research this area, but I haven't looked at it in quite a while. You might find something useful there.

Oh, and thanks for the compliments.

"Electrodynamic effects" sounds obvious when pointed out, but of course you would expect it to be significant.

Would be interesting to know exactly what, physically, these effects do.

Thanks CJ, you have given me something to think about.

In deserts you can have considerable lightning and thunder when the humidity is low, and no rain results.

It seems to come about because the heat of the day generates large updrafts which prevent dust in the air settling. This dust rises, often over 50,000 ft, then starts to fall as the updraft runs out of puff.

Because it doesn't fall directly back into the updraft, it can reach terminal velocity.

Because of eddy shedding, it doesn't fall in a straight line, and most will eventually be swept back into the updraft.

Air friction is meanwhile charging the dust, until the resultant charge leads to lightning, either between clouds or to earth.

All the while, humidity can be so low there is no hope of rain falling.

When you witness these clouds, they look so like the real thing, it is a huge disappointment when they turn out to be dry.

The clouds and lighning dissipates around sunset.

Now you have re-kindled my curiosity. I wonder if anyone has witnesses lightening, and thereby thunder, when no clouds were present?

Apparently even low levels of humidity (presence of water gas) are involved in the phenomenon when the charge is great enough.

The term 'dry' lightening means no rainfall hitting ground, but apparently some clouds are required.

"I wonder if anyone has witnesses lightening, and thereby thunder, when no clouds were present?"

Lightning is often observed in the clouds of a dust storm, but as far as I know, some sort of cloud is necessary, although it doesn't have to contain water.

Lightning has also been observed in volcanic eruptions. In that case, friction between pyroclastic particles probably electrifies them.

Lightning can reach up to 30 miles from a large storm. Thus the saying, "bolt out of the blue."

I have often wondered way water at normal temperature laying around on the floor evaporates, some may know the answer, but I have further wondered, does the water molecule rise up into the atmosphere as a water molecule, or does the hydrogen atom due to entropy throw it's self off and recombine with its neighbour, rising up into the atmosphere? (pH effect?), this then may give rise to a situation where you have a recombination of hydrogen and oxygen plus electrical unbalances occurring at the same time? Just a thought.

Regards JD.

The H2O water molecule remains intact regardless of state: solid, liquid or gaseous. Water evaporates due to entropy, but it remains a water molecule nonetheless. It requires a chemical reaction, not the mere addition or subtraction of heat energy, to dissociate the water molecule.

Thank you emc c:

I though in was not going to as simple as hydrogen rising by displacement, so a water molecule stays intact, and chemically evenly distribute itself though out the atmosphere, with the warmer air rising. carrying the water molecule with it. I was thinking along the lines of water ph, when there is an excess of hydrogen where are they? ionized molicules?

Regards JD.

H2O the water molecule is an extremely stable substance. It doesn't dissociate without a lot of activation energy. The way you get free H+ ions in aqueous solution is by dissolving an acid in the water. The water remains what it is, but the acid dissociates into H+ ions and the negative ion to which it was bonded prior to ionization. Example acids are HF (hydrogen fluoride), HNO3 (nitric acid), and H2SO4 (sulfuric acid).