Progression of thunder and lightning
 

I'm sat at the moment at a desk in the south of england, in a thunderstorm. It has been raining continuously for a couple of hours, and looking at the weather chart I'm right under (or maybe up to 50nm in front of) a cold front with embedded CBs.

Nothing unusual in that, except that for once in my life, I'm happy to be sat at a desk instead of flying.


Anyhow, I happened to be looking at a clock when half an hour ago there was a lightning flash. 3ish seconds later I heard the thunder - which then carried on (decreasing in loudness steadily) for a good 45 seconds. It did the same several more times over the next ten minutes.

So what was happening here?

Is the lightning event rippling down the length of a chain of embedded CBs?, or is this some accoustic effect causing a steadily decreasing echo? Something else?

Anybody with greater met knowledge than mine have any idea?

G

Acoustics. The thunder first arrives from the closest point of the lightning bolt - but then the thunder arrives from the more distant parts of the bolt. After all, the lightning bolt is not an arc of a circle with centre exactly at you!

Sound of Thunder
 

The same storm .. or another has just arrived over my office in Dartford. The same effect is apparent, that the first sound appears 3 - 10 secs after the flash but the rumblings continue for up to 45 secs. Unless the lightning bolt is 10 miles long, (how long are they ??) I can but assume we are getting echos back from ground features.

If my recollection is correct : speed of sound = 760 mph = 760 miles in 3600 secs. So 1/760 x 3600 = 4.7 secs/ mile.

Or is it that the lightning starts a mile away, which I hear 5 seconds (ish) later but also the sound travels 5 miles and reflects back (from Thurrock Shopping centre or something) and between 5 seconds and 45 seconds I am also getting all the other noise from the middle and other end of the lightning flash plus all the other ground refections as well until they reduce in volume and I don't hear them.

Is there somthing in heavy rain bearing cloud that allows sound to reflect back and too inside them as well ?? because it is really pretty flat in these parts.

DGG:confused:

The sound travels at about 1 mile per 5 secs. In addition to the above, there may also be echoes from proximate hills/buildings. Also, the cell will have multiple lightning events crackling away one after the other, so you'll be receiving a chorus of claps. Thunder is heard up to about a max of 15 miles away. So you might hear the near one plus echoes, followed by one 5 miles away plus echoes (not as loud), followed by another 10 miles away etc.
Given that it was a cold front, then a squall line is probable, so you might have heard from more than one cell concurrently.
The total result reaching your ears depends on how God rolls the dice.
http://www.wvlightning.com/images/lp.gif

There was continuous CB activity here in West Berks for about 4 hours this morning - quite violent stuff for this time of the year in the UK.

I also experienced these very long rumbles of thunder, which seemed to rumble near then what sounds like further away. However, the amount of lightning (ie, closeness together timewise of flashes) would suggest there were multiple embedded cells and the thunder was from multiple strikes.

A friend approx 1 mile away had their house nigh on destroyed by a strike back in May, which makes one a little wary when it's flashing and crashing away like it was this morning :eek:

Same here in Widnes about 0620 this morning. Spectacular lightning everywhere with rolls of thunder which didnt tie in, and also samples of the old code "Lightning seen, no thunder heard". Nightmare for the Met Observer at 'Pool, loads of crud, no layers to speak of but must have been tons of embedded CBs in there covering a large area.

Agree with previous posting, not usual for this time of year.

How about multiple path lengths, with the direct sound being less attenuated than the later arrivals?

Dick

A lot of individual cells constantly developing, increasing in strength and dissipating over a period of 8 hours , and moving N along the system which itself was moving slowly E would have contributed to this effect.

With the numbers you quote, I feel confident that echoes, etc. from a single stroke can be excluded. Attenuation over the path lengths implied would be fearsome.
I've seen video taken from very high altitude (say 200-ish miles, as it was taken by astronauts) which clearly showed examples of highly correlated lightning behavior, but I've not read a good discussion on either the precise form of the non-randomness nor its cause.
I can't find video on the net matching my memory.
NASA shuttle lightning video
The three shuttle videos here show some correlation, but not the degree I remember, nor that required for the effect you heard. But if it did that every time, it would sound like that every time, which it does not.

Two weeks ago we flying early evening from CLN to REDFA to the west of line of CB's and it was obvious that when Cloud A "let one off" Cloud B next door would do the same, followed by the next, etc... This went on for eight or nine cells or so - what you might call a "ripple effect".

Can't offer any explanation (the more science investigates lightning, the more questions get raised!). But anyone who has lived in the Kimberley region of NW Australia will be familiar with the phenomena. The TS there produce some truely spectacular effects.

The thunder you describe was common during the dying phases of a cell. As the cell decays to mostly a midlevel stratiform type of cloud, the lightning strokes would run inter cloud tru this stratiform. The resulting thunder would roll on seemingly for ever, an extremely deep resonous type that shook the very foundations of our house. The thunder didn't seem to stop, instead only decreasing as it sounded to get so far away. Awesome stuff, best experienced from the ground, they were fearsome to aviate around!!!!

Rolling Thunder
 

Just thought this was fascinating:

Sprites @ Nasa.gov

More on Sprites

Piltdown Man - astronauts have reported the same ripple effect extending over hundreds of miles.

I was very close to one of those strikes a couple of days ago and experienced the same effect. I had flash-BANG!, with that noise like tearing cloth, then slowly decaying rumbles with one rumble about 10s after the initial strike that rattled the windows and front door! Very spectacular (pre-frontal trough I think).

On the subject of lightning in general, this link shows a photo of some strikes framed against power pylons. http://www.ees-group.co.uk/

I am puzzled about why the lightning seems to be avoiding the pylons, when logic would suggest that it would seek the nearest highest point as a route to earth.

Does anyone have a suggestion as to why this appears so ?

I suggested 15 years ago to a scientist on a BBC radio program, that Sprites were the result of the core of a lightning strike ‘lasing.' I will search for my notes on the subject, but in essence it was the sheer surfeit of energy that enabled a plasma / water droplet-filled core to form a crude lense. The collapse of fields are fairly obvious.

It seems that after all these years, no better idea has been put forward.

gyro is right. The Kimberly region of NW West Oz has some of the most violent storm cells and lightning, I have ever experienced.

I quite enjoy watching storms and lightning displays .. and have seen lightning strike with 200 metres of me, twice, in the SW of W.A. .. but I recall, camping out on the banks of the Oakover River, just SE of Shay Gap in 1994 .. and retreating to the back of my Landcruiser station wagon .. not only to avoid the rain .. but in real fear, as the most violent lightning I have ever seen, seemed to be hitting the ground dozens of times a minute, for an hour at least .. within very close range of our camping spot .. :(

Thread drift.
Atmospheric scientists now believe lightning is the result of charge transfer between ice crystals in clouds. Observations from NASA's TRIMM satellite show a direct correlation between the amount of ice particles in a cloud, and the number of lightning flashes, irrespective of whether over land or sea.
The amount of ice also determines the subsequent rainfall intensity.

Ref. Univ. of AL in Huntsville, Walt Petersen et al.

Ripple Effect
 

Similar to PM's observation, I was paxing along a cold front from Indiana to Texas to get around the corner. We were treated to quite the light show as the lightning pulsated from one cloud to the next.

The duration of one flash could be several seconds, but it would pulse a number of times.