Thunder

[Harry]

There are things regarding thunder which I have detected time and time again but have never really understood why.

Has anyone ever noticed these before, and if so is there any explanations for why?

1. I've noticed thunder at night tends to be louder than during the day. Is this because there is less background noise (planes, road traffic, building work, children's noise, birds etc) or does lightning tend to be more powerful at night, or bear different characteristics?

2. Sometimes, when you get close CG lightning bolts - one will cause a crackle and loud BANG/BOOM - the other one will just crackle and nothing more. Is the type of thunder caused purely determined by the strength of the bolt, number of 'strokes' etc, or are there other factors?

Thanks in advance for any suggestions

Edited April 20, 2009 by Harry

[Gilz]

Hi Harry

I will give this an attempt.

You are right in that at night there is less ambient noise making it seem louder and more intense

The variance in the sound we hear is caused by the distance we are from the lightning.

The speed of light travels at 299792458 m/s where as the speed of sound is 340 m/s, the closer the lightning strike the louder the thunder, add to that the fact that lightning never follows a straight path to the ground giving it the characteristic rumbling sound, also you have to take in to consideration the geographical circumstances, the sound wave will be deflected of the surroundings and echo hence making the rumble seem to last a lot longer.

Hope that is off help to you, however there is far more to it and there will be someone who will be able to go in to more detail.

Gill

[Chris Knight]

There are things regarding thunder which I have detected time and time again but have never really understood why.

Has anyone ever noticed these before, and if so is there any explanations for why?

1. I've noticed thunder at night tends to be louder than during the day. Is this because there is less background noise (planes, road traffic, building work, children's noise, birds etc) or does lightning tend to be more powerful at night, or bear different characteristics?

2. Sometimes, when you get close CG lightning bolts - one will cause a crackle and loud BANG/BOOM - the other one will just crackle and nothing more. Is the type of thunder caused purely determined by the strength of the bolt, number of 'strokes' etc, or are there other factors?

Thanks in advance for any suggestions

These are really interesting questions, and I bet that no-one really knows the full answers. Acoustics - the understanding of how sound changes in response to the environment - is an art, mainly relating to the interior of man-made structures. Buildings, loudspeaker enclosures and the like. When we get to the great outdoors, acoustics is usually relegated to the nuisance value of noise - how loud is the approaching plane under the flight track, why does this curved building focus London Underground noise on 47 Hammersmith Grove etc.

Clouds are both denser and cooler than the surrounding air - if they were just water droplets, they should both refract sound from below upwards, and absorb and attenuate sound. Observational evidence says that clouds reflect sound from below, and within the entire cloud structure.

I am sticking my neck out here. Much of the water, even in cumulus clouds, is actually ice, and not fluffy snowflakes, but little, and not so little solid frozen accreted raindrops. Not hail - which is refrozen ice and rain that has existed through several circuits through the up- and down-draughts in the cumulonimbus clouds in which hail forms. Occasionally this frozen rain falls in winter - it has the texture of the ice that collects on the interior of your freezer - not solid clear ice, but little pellets of white, crushable ice. Despite being constructed of ice with pockets of air, they reflect sound quite well, unlike either snowflakes, or water mist droplets.

OK, back to thunderstorms. thunderclouds contain about 90% ice, maybe more. At cloud base there is a large temperature differential from temperatures of -20C within to near freezing below with a steady adiabatic temperature gradient down to the surface. Due to the turbulence within the cloud, much of the water exists as hail, solid, lumps of ice containing very little enclosed gas pockets. This is a great reflector of sound, and of course, large bodies of hailstones are being shifted up and down within the tower by the strong up and downdrafts, creating Doppler effects to any reflected sounds, both increasing and decreasing the frequency of the echo.

So here is a hypothesis to explain why sometimes there is a crackle, and sometimes a crackle and boom:

If there is above the CG strike an updraft, where rain is being sucked upwards, then there is no solid ice surface to reflect the echo of the sound of the strike back to the ground, only the absorptive effects of the raindrops, traveling upwards.................................. Crackle only.

On the other hand if there is a downdraft at the time of the CG, forcing hail downwards at speed, the approaching solid front of descending ice reflects the advancing pressure front of the sound wave from the strike, enabling you to hear first the direct crackle, and then the reflected and amplified boom, as it focuses back towards you.

As far as the first question is concerned, doesn't the whole atmosphere collapse downwards at night, due to lack of solar input? This is felt at all levels - the different propagation characteristics of radio waves, the general drop in temperature, it gets dark, you stop getting sunburnt, etc. A cooler atmosphere has different characteristics for sound propagation too - cooler is more dense, so sound travels slower, and frequencies decrease.

Edited May 8, 2009 by Chris Knight

[stingrays4]

Hi certainly some interesting points there ,i just enjoy the sounds of diferent 'thunder'. Also i have noticed that if cloud to cloud lightning then the thunder is more rumbly than say cloud to ground,which seems more of a violent 'rumble/crackle'? Mind you its been awhile since we had a good storm .

[MP-R]

Another thing I have noted is how different thunder sounds in winter and summer.

In winter thunder is a lot louder with a crashing sound but then tails off very quickly. Whereas, in summer thunder seems to last a lot longer with a moderate build up, a thud then it carries on for ages.

Maybe that's just me but it seems that way looking back at thunderstorm videos of mine.

[Coast]

There are things regarding thunder which I have detected time and time again but have never really understood why.

Has anyone ever noticed these before, and if so is there any explanations for why?

1. I've noticed thunder at night tends to be louder than during the day. Is this because there is less background noise (planes, road traffic, building work, children's noise, birds etc) or does lightning tend to be more powerful at night, or bear different characteristics?

I suspect it is because of less background noise (inside and out), possibly that you are then more 'tuned in' to it.

[Harry]

Another thing I have noted is how different thunder sounds in winter and summer.

In winter thunder is a lot louder with a crashing sound but then tails off very quickly. Whereas, in summer thunder seems to last a lot longer with a moderate build up, a thud then it carries on for ages.

Maybe that's just me but it seems that way looking back at thunderstorm videos of mine.

I agree MPR - I've noticed the exact same thing with winter thunder, much like this video shot in Kent a couple of years ago

This was a VERY close strike (note the streamers above the guy's head on the slow motion replay), you get the normal crackling/fizzing, followed by the bang...but as noted in your post above, tailing off very quickly.

I wonder whether this has something to do with the resistance of air at different temperatures - does sound travel more quickly through air of a higher temperature? Does air have the same conductance at different temperatures? I.e does static electricity have to overcome greater resistance during colder weather as opposed to warmer weather? I haven't the time at the moment to look it up - I suspect that if electrical resistance increases during colder weather, but sound resistance decreases then this may explain the observations between winter and summer thunder and lightning - less sound resistance and the thunder will travel past more quickly - reduced conductance would also mean more powerful strikes as the amount of energy to overcome the resistance would be greater.

It could be something as simple as the nature of the preciptation - will sound resonate more easily with snowflakes in the air as opposed to water droplets?

The thesis you could write on this subject

Edited January 17, 2011 by Harry

[MP-R]

I agree MPR - I've noticed the exact same thing with winter thunder, much like this video shot in Kent a couple of years ago

This was a VERY close strike (note the streamers above the guy's head on the slow motion replay), you get the normal crackling/fizzing, followed by the bang...but as noted in your post above, tailing off very quickly.

I wonder whether this has something to do with the resistance of air at different temperatures - does sound travel more quickly through air of a higher temperature? Does air have the same conductance at different temperatures? I.e does static electricity have to overcome greater resistance during colder weather as opposed to warmer weather? I haven't the time at the moment to look it up - I suspect that if electrical resistance increases during colder weather, but sound resistance decreases then this may explain the observations between winter and summer thunder and lightning - less sound resistance and the thunder will travel past more quickly - reduced conductance would also mean more powerful strikes as the amount of energy to overcome the resistance would be greater.

It could be something as simple as the nature of the preciptation - will sound resonate more easily with snowflakes in the air as opposed to water droplets?

The thesis you could write on this subject

Great video! All very interesting and entirely possible. I suppose it does have something to do with the nature of other weather conditions. i.e. thunder in winter often comes with the heaviest downpours, often with hail or in the case of a few events - very heavy snow. There also tends to be quite a bit of wind which may cause diversion in soundwaves - I have to say I'm rather ignorant to it all.

Summer of course, thunderstorms build up often in still conditions and go on for ages without any precipitation falling so perhaps that allows the thunder to roll on for longer with less sharp sound differences.

[Mesoscale]

Wow some really good answers there, and that guy didn't even flinch haha.

During snow storms etc lightning is almost always positive just to throw that out there. lol

If some one can ellaborate on that point?

Ive noticed the more dense the air is e.g. humidity. the queiter the thunder is.

a couple of examples of this when I was in mexico and florida the thunder is alot quieter then here in england, there was no wardrobe shakers. even some of the close ones wern't.

I agree most of the 'shake the house' thunder occures after dark, maybee its because humidity decreases during the night making the sound of thunder change.

Edited January 17, 2011 by Mesoscale

[Harry]

Wow some really good answers there, and that guy didn't even flinch haha.

During snow storms etc lightning is almost always positive just to throw that out there. lol

If some one can ellaborate on that point?

Ive noticed the more dense the air is e.g. humidity. the queiter the thunder is.

a couple of examples of this when I was in mexico and florida the thunder is alot quieter then here in england, there was no wardrobe shakers. even some of the close ones wern't.

I agree most of the 'shake the house' thunder occures after dark, maybee its because humidity decreases during the night making the sound of thunder change.

I've heard on a couple of documentaries, that there is a higher proportion of +ve to -ve bolts in NW Europe than anywhere else in the world...I cannot substantiate this as I cannot for the life of me remember which documentary I heard this - but I've heard it more than once.

By aural means only (check spelling before you all laugh lol) I have definitely detected thunder being louder generally, during night time storms than daytime, but as mentioned in an earlier post this COULD simply be the fact there's less background noise. It could be however the fact nighttime temperatures are cooler than daytime typically and therefore bolstering the argument that the more you decrease temperature the louder thunder tends to be...but then where does humidity fit in, as almost without question some our highest humidities (or relative humidities) occur during the night time periods, particularly during plume events, as the temperature falls to close to the dew point (this maybe totally inaccurate meteorology here - feel free to slam)

HOPEFULLY, we'll have many more storms this year whereby we can put these various theories to the test

Edited January 17, 2011 by Harry

[ZONE 51]

Interesting, what i do think is the that it depends on the route the strike/bolt of lightning takes through the air mass, also the length, whether it be a short bolt with a quick rapid expansion of the air giving a short loud crack, or a huge multi route fork CG taking more length and time to expand the air causing long deep rumbles lasting many seconds, and of course we have ppn type/intensity as said in other posts. what do you think then? i think im right on what i said at least some of it?

Edited January 18, 2011 by nimbilus

[Dom W]

http://www.weatherscapes.com/techniques.php?cat=lightning&page=thunder

This site is an interesting read

Thunder is such an amazing sound and can either be frightening when it is very close or a very relaxing sound especially when heavy rain is falling too.

I just read on the site about that click you hear during a lightning flash, which is internal electrical wiring.

[Coast]

Some more interesting facts on thunder here:

http://www.weatherimagery.com/blog/facts-about-thunder/

Why does thunder rumble?

Thunder rumbles for a few different reasons. The first being, a lightning bolt is very rarely a straight line and is never equally distant from you at all points. A lightning bolt on average is 4 miles long, it zig-zags all over the place, and can have many limbs that branch out in many different directions separated by many miles. As a result, the compression waves created by each part of the lightning bolt reach you at different times. The sound wave that has traveled a greater distance will be softer and arrive later than a compression wave created by a part of the lightning bolt that was closer to you, which will be louder.

The second thing is the compression waves (or the thunder) will bounce around and off the clouds, the terrain, and other objects. Much like your voice echoes in a canyon or large auditorium, so do the compression waves generated by lightning.

The other reason thunder rumbles is because higher frequencies tend to dissipate more quickly, unlike the lower frequencies that can travel much further before they dissipate. Think of a car with a lot of bass. You can hear the base long after the car has passed, even when the windows are up and doors closed. But the higher frequencies are much quieter.

[Mesoscale]

Have you heard of ducting, when a warm front comes through with elevated thunderstorms feeding on the warm air above the cold the difference between the two airmass causes the thunder to get trapped inside the cold air keeping the sound from escaping in all directions forcing it to the ground this causes the thunder to be alot louder then usual.

[Coast]

I've noticed thunder at night tends to be louder than during the day. Is this because there is less background noise (planes, road traffic, building work, children's noise, birds etc) or does lightning tend to be more powerful at night, or bear different characteristics?

What makes thunder louder on some occasions than others? Most of the time it has to do with how the temperature changes with height. The short answer is that thunder tends to be loudest when there is a cold pocket near the surface and warm air above it - an "inversion."

So, because temperatures tend to cool near the ground at night, thunder tends to be louder at night. But most thunderstorms form from warm, unstable conditions - NOT normally when it's cold at the ground - so I have to go a little deeper in my explanation!

Let's start with what's "normal." Most thunderstorms are "surface-based", like the one shown below. Warm, moist air from near the ground (surface of the Earth) rises and forms the thunderstorm. It's colder aloft, so this is an "unstable" temperature and moisture distribution.

In an unstable situation, not only does the air rise, but the sound of the thunder also can rise and disperse, some of it going horizontally near ground and much of it travelling upward toward outer space (like the "sound waves" depicted below). This "dilutes" the sound energy and the thunder isn't as loud.

In this inversion situation, the sound of thunder gets trapped by the inversion layer. This is because sound travels faster in warm air than in cold air. So the sound rays trying to angle upward and laterally away from the lightning near the ground get bent and travel almost horizontally instead. This is called "ducting", in the same sense as the heating/air conditioning ducting throughout your home carries air to your rooms.

Because the sound energy is trapped beneath the inversion, rather than much of it escaping higher into the atmosphere, you hear the thunder as a much louder sound. Winds and how they vary with height can also affect how sound travels and it's loudness.

If you are very distant from the lightning strike (usually more than 10 to 15 miles), you may not hear the thunder at all. That's because the thunder's sound energy can still travel out horizontally in all directions, even if it doesn't travel upward in inversion situations, and loses some of its intensity that way. But you can hear it farther on an inversion night than on other occasions

http://www.weather.com/blog/weather/8_24331.html

The Science of thunder:

http://www.lightningsafety.com/nlsi_info/thunder2.html

[chrisbell-nottheweatherman]

http://www.weather.c...er/8_24331.html

The Science of thunder:

http://www.lightning...o/thunder2.html

Thanks for those links, Coast - very interesting!

[Harry]

http://www.weather.com/blog/weather/8_24331.html

The Science of thunder:

http://www.lightningsafety.com/nlsi_info/thunder2.html

Thanks indeed! Am pleased there's a scientific explanation, or theory at least, as to why all these years thunder seems louder at night

[Mesoscale]

http://www.weather.c...er/8_24331.html

The Science of thunder:

http://www.lightning...o/thunder2.html

Thanks I always thought it was called Ducting.

Its just a shame us poor folks dont hear 'thunder' more often.

[Methuselah]

I like the booming sound caused by very short C-G strikes. Can sound like a war zone.

[Adi F]

2. Sometimes, when you get close CG lightning bolts - one will cause a crackle and loud BANG/BOOM - the other one will just crackle and nothing more. Is the type of thunder caused purely determined by the strength of the bolt, number of 'strokes' etc, or are there other factors?

The crack/bang can be explained relatively easily. The same principle as when you are hear a gun fire up close, you get a high pitched supersonic crack as the round passes you followed by the low pitch bang of the gun. With Lightning you hear the supersonic crack as the lightning passes the closest point to you then hear the bang of the lightning reverberating form the cloud and surrounding terrain.