Aeneas said:
[...] To illustrate the point about sound and observers position, one can look at the big event on the 22nd of September, found
here, which was reported by 162, 12 of whom reported a delayed sound and only 5 a concurrent sound. It was mentioned on SOTT at the times whether there were not possibly several fireballs, which then got lumped together as only one event. The puzzling thing is that one person in Norway heard a sound, where as all the others who heard a sound were in Britain. So perhaps there were more fireballs than one.
Good point, we might be able to separate two events by investigating the reports of sounds reported as associated with the fireballs and then look at the distance between them. As you suggest it a bit unlikely that sound from the same event should be heard in both Norway and England.
In general I gather that observing a fireball along with an associated sound phenomena would mean that the object is quite close to the observer, whereas a sound that follows later indicates that the distance to the event is further away.
The analogy is the the time lapse between a flash of lightening and the thunder, which when nearby follows shortly after the flash, whereas more time passes before the rumble is heard when the actual location of the strike is further away. And sometimes we only se the lightening as the sound is too far away to be heard. To explain a bit about the physics of sound the speed of sound in air can be approximated as:
V= 331.5 m/s + 0.6*(m/(s*degrees Celcius))*temperature in degrees Celcius,
(Formula adapted from _www.sengpielaudio.com/SpeedOfSoundPressure.pdf)
It therefor takes about 3 seconds per kilometer from the time we see a flash of lightening until we hear the sound. Or if we count 9 seconds from we se the flash until the sound arrives then it will correspond to a strike happening at about 3 km from us.
What I wonder about in the case of this event over Britain and Ireland, which I witnessed, is that if the whole show lasted maybe 30 seconds. How could sound then reach some observers if the object was that high up in the atmosphere as some calculations estimated. Lets say it broke up at an altitude of 55 km, which is the upper limit of the stratopause in the boundary area between the
stratosphere and the mesosphere, where the air pressure is about 1/1000th of what it is at sealevel, then the sound, if it really originated or could be generated at that altitude, would take about 165 seconds to reach Earth. It seems to me that the object would be gone by the time the sound reached the observer. Add to this that one will usually see it at an angle. This fact should make the sound reach the observer after more than 165 seconds although this difference will be less for angles closer to vertical. And then we have not even taken into considerations the distortion caused by wind speeds. A sound that enters the jet steam no doubt gets a bit carried away :)
In other words if a sound is heard along with a fireball observation then it is probably close or big. A distinct loud sound would mean it is fairly close, or caused by a big object as was the case at the Tunguska event, and if it is only a low rumble, probably it is further away.
