Is there any known kind of lightning flash that doesn't have
accompanying thunder?

I was camping out a few nights ago, and for about 45 minutes, during
the night, I saw intermittent lightning flashes, but saw no lightning
bolt and heard no thunder. The location was in the South West of
England in a rural area on the coast. The lightning flashes were
bright, white, and powerful and seemed in close proximity. It was the
sort of lightning flash that would normally be quickly followed by a
loud crack of thunder.

TIA

Al Deveron

Al Deveron wrote:

Is there any known kind of lightning flash that doesn't have
accompanying thunder?

I was camping out a few nights ago, and for about 45 minutes, during
the night, I saw intermittent lightning flashes, but saw no lightning
bolt and heard no thunder. The location was in the South West of
England in a rural area on the coast. The lightning flashes were
bright, white, and powerful and seemed in close proximity. It was the
sort of lightning flash that would normally be quickly followed by a
loud crack of thunder.

TIA

Al Deveron

Sound is refracted by for example temperature changes, and there
may be no path for it from the lightning to you.

You get a mathematical surface with sound on one side and no sound
on the other, the sound side hearing two different paths at once.
Called a caustic surface. What happens in its vicinity requires
a wave solution of the acoustic equations (rather than ray tracing).

The refraction is why a jet plane sounds intermittently loud and soft,
as rays of sound are focussed on you and then defocussed as the ray
passes various thermals refracting it.

--
Ron Hardin


On the internet, nobody knows you're a jerk.

On Tue, 25 Jul 2006 22:48:34 GMT, Ron Hardin
wrote:

Al Deveron wrote:

Is there any known kind of lightning flash that doesn't have
accompanying thunder?

I was camping out a few nights ago, and for about 45 minutes, during
the night, I saw intermittent lightning flashes, but saw no lightning
bolt and heard no thunder. The location was in the South West of
England in a rural area on the coast. The lightning flashes were
bright, white, and powerful and seemed in close proximity. It was the
sort of lightning flash that would normally be quickly followed by a
loud crack of thunder.

TIA

Al Deveron

Sound is refracted by for example temperature changes, and there
may be no path for it from the lightning to you.

You get a mathematical surface with sound on one side and no sound
on the other, the sound side hearing two different paths at once.
Called a caustic surface. What happens in its vicinity requires
a wave solution of the acoustic equations (rather than ray tracing).

The refraction is why a jet plane sounds intermittently loud and soft,
as rays of sound are focussed on you and then defocussed as the ray
passes various thermals refracting it.

And then there's what locals here in the Upper Great Lakes of the U.S.
call "heat lightning", where you see the flashes but don't hear the
thunder. "Heat lightning" is really just someone else's thunderstorm,
but you get to see the display and can't hear the cheer. Thunderheads
can be seen, at various latitudes, from in excess of 150km away, and
all of the lightning may be caught up in that after sunset. Pretty
obvious, as brilliant as these displays can be, that sound does not
travel with the same efficiency or distance as light.

Not disagreeing with the above poster, just offering a simpler
explanation.

wrote in message
...
| On Tue, 25 Jul 2006 22:48:34 GMT, Ron Hardin
| wrote:
|
| Al Deveron wrote:
|
| Is there any known kind of lightning flash that doesn't have
| accompanying thunder?
|
| I was camping out a few nights ago, and for about 45 minutes, during
| the night, I saw intermittent lightning flashes, but saw no lightning
| bolt and heard no thunder. The location was in the South West of
| England in a rural area on the coast. The lightning flashes were
| bright, white, and powerful and seemed in close proximity. It was the
| sort of lightning flash that would normally be quickly followed by a
| loud crack of thunder.
|
| TIA
|
| Al Deveron
|
| Sound is refracted by for example temperature changes, and there
| may be no path for it from the lightning to you.
|
| You get a mathematical surface with sound on one side and no sound
| on the other, the sound side hearing two different paths at once.
| Called a caustic surface. What happens in its vicinity requires
| a wave solution of the acoustic equations (rather than ray tracing).
|
| The refraction is why a jet plane sounds intermittently loud and soft,
| as rays of sound are focussed on you and then defocussed as the ray
| passes various thermals refracting it.
|
| And then there's what locals here in the Upper Great Lakes of the U.S.
| call "heat lightning", where you see the flashes but don't hear the
| thunder. "Heat lightning" is really just someone else's thunderstorm,
| but you get to see the display and can't hear the cheer. Thunderheads
| can be seen, at various latitudes, from in excess of 150km away, and
| all of the lightning may be caught up in that after sunset. Pretty
| obvious, as brilliant as these displays can be, that sound does not
| travel with the same efficiency or distance as light.
|
| Not disagreeing with the above poster, just offering a simpler
| explanation.

Many of the recent storms we have had in the UK have been due to mid-level
instability release (hot, humid air from the Mediterranean area running
under cooler westerlies aloft) with little or no convection from the surface
layers. These have been producing storms 2 to 3 miles up in altocumulus
castellanus and floccus - no low level Cb as you know them. The more
newsworthy storms have been formed when excessive heat has "broken the cap"
or convection from low levels has been triggered by convergence on outflow
winds from the high-level storms.

Such a storm can pass overhead and produce no more than muffled thunder if
all the strikes are intercloud. We have recently had such storms where I
live, which is probably about 150 miles from where the OP was on holiday.
You get the big flashes but a 10-15 second delay before the long, faint
rolls of thunder because the lightning is 2-3 miles away - straight up.

These storms can also produce quite bright reflections in other, inactive,
clouds. We also had a demonstration of that here a night or two back when
some very active storms passed over with the normal thunder and lightning.
An hour or so later the storms had moved away so the thunder was barely
audible but reflections from layer cloud to the SW gave the false impression
that more storms were coming.

Because of the shock wave caused by sudden heating in the lightning channel,
I do not think there is any kind of "normal" lightning (I am discounting
phenomena such as "ball" lighning and also the high-level "sprites" which
pass through a very rarefied atmosphere) which does not produce thunder,
even if refraction effects such as mentioned by another poster greatly
attenuate the sound.
--
- Yokel -
oo oo
OOO OOO
OO 0 OO
) ( I ) (
) ( /\ ) (
Yokel @ Ashurst New Forest
SU 336 107 17m a.s.l.

"Yokel" now posts via a spam-trap account.
Replace my alias with stevejudd to reply.

Yokel wrote:
Because of the shock wave caused by sudden heating in the lightning channel,
I do not think there is any kind of "normal" lightning (I am discounting
phenomena such as "ball" lighning and also the high-level "sprites" which
pass through a very rarefied atmosphere) which does not produce thunder,
even if refraction effects such as mentioned by another poster greatly
attenuate the sound.

The refractive effect that results in no path from lightning to you is pretty
attenuative, ie. no sound at all, except in exponential tails of bessel functions
from a wave solution across the caustic surface.

A stratified lower atmosphere makes it a lot more likely. I assume it's hotter
than othersise, to avoid an unstable lapse rate where it meets air above; which
makes sound travel faster. All the sound that comes down at a slant turns right
back up again as it meets the interface, and doesn't reach you at all.

--
Ron Hardin


On the internet, nobody knows you're a jerk.

Ron Hardin wrote:
A stratified lower atmosphere makes it a lot more likely. I assume it's hotter
than othersise, to avoid an unstable lapse rate where it meets air above; which
makes sound travel faster. All the sound that comes down at a slant turns right
back up again as it meets the interface, and doesn't reach you at all.

Being hotter wouldn't make it more stable at the interface, I guess, so that wouldn't
work.

--
Ron Hardin


On the internet, nobody knows you're a jerk.

Thanks to all for the replies. I'm afraid I'm not a meteorologist -
just a layman, so I won't attempt to understand everything that has
been said about this (bessel functions included ) although the
explanations sound fascinating..

On the night in question, I was lying on the ground and caught sight
of what I believe was the actual source of the lightning on one
occasion. I saw no typical jagged lines arcing through the sky. What I
saw looked more like a giant flashgun going off at one point in the
sky, almost directly above me. Does this lend further creedence to
Yokel's explanation?

It seemed absolutely uncanny that such a powerful bright flash
produced no audible sound.

Al Deveron