This is the beginning of an apparently physics-unrelated question, which involves 1700-1800 Italian law, atmospheric processes, sound waves propagating through fluid and clouds, and lightning strikes burning down churches.
The core of the question is figuring out if and how a sound wave influences the formation / disruption of clouds and eventual thunderstorms.
Background and Context
I live next to the European Alps, in northern Italy. Here weather is often cloudy and thunderstorms are not rare. For religious purposes, every town in this area has a church with a tall bell tower alongside it. And of course, a huge bronze bell hangs in each tower to ring every hour.
I've talked to a local elderly (who happens to manage the bell tower) about thunderstorms, and I was told that when a thunderstorm approaches he rings the bell repeatedly and vigorously to try to "break up the storm", in order to supposedly avoid rain and thunder falling on the town. This is a practice still widely used to this day in this area. Me being a engineering student, I wanted to figure out if that really made sense and what effects ringing the bell really had.
A bronze bell ringing multiple times produces sound. The kinetic energy of the bronze clapper is cast on the bell, which converts it into sound energy. Specifically, the bronze bell vibrates and transfers the sharp vibration to the layer of air molecules wrapped around the bell, which initiates a chain transmission. This produces sound waves, which are longitudinal (compression) waves transmitted through a fluid (air).
Longitudinal waves are waves in which the vibration of the medium is parallel ("along") to the direction the wave travels and displacement of the medium is in the same (or opposite) direction of the wave propagation. Mechanical longitudinal waves are also called compressional or compression waves, because they produce compression and rarefaction when traveling through a medium, and pressure waves, because they produce increases and decreases in pressure. [source]
Those waves are then spread out more or less spherically (following the inverse square law) from the bell top point.
The natural questions to ask at this point are:
- What happens when the sound wave passes through the cloud?
- Does the wave have enough energy to reasonably alter the formation of the cloud and therefore prevent / allow the thunderstorm?
- Is there such thing as "breaking up the storm" or is it just a popular belief?
I genuinely have no idea since I have no first hand experience with this. Thunderstorm formation looks like a whole different process, and I can't seem to find a connection with sound waves.
Thunderstorms form when warm, moist air rises into cold air. The warm air becomes cooler, which causes moisture, called water vapor, to form small water droplets - a process called condensation. The cooled air drops lower in the atmosphere, warms and rises again. [source]
Historically relevant experiments
While doing my research I found papers from the late 1700s where Italian scientist were trying to answer one of our questions: does ringing the tower bell disrupt an incoming thunderstorm?
Their answer is the opposite of what I expected: they thought that ringing the bell actually amplified the storm.
You can find the original version of these papers here
Their results look extremely nonrigorous, but it can be a starting point to reflect on.
Note: I can do a full translation of the paper if someone is interested, right now I'll do my best to translate and summarize the key concepts (sparing you a ton of mid-1700 religious and legal drama)
Paper published in 1770
Key: Total nonsense
The vibration induced by the bell sharp sound has 2 effects on air: it rubs together different parts [of the cloud] and it thins out the mass [of the cloud]. The rubbing, as it is known, awakens the "electric fire" (I have no clue about what that is). The thinning out attracts it [the electric fire], diminishing air resistence. Vibrations in general unite instead of breaking up.
It is also said that the bell sound (while storming) attracts the lightning strikes on the tower bell (which is pure nonsense), instead of letting lightning target houses or fields, and it is thought to be a good thing.
Plus, the bell sound would warn locals that a storm is approaching.
Act of 1783
Key: Law prohibits ringing bells during storms
A series of sad experiences says that the tower bell ring, instead of dissipating the clouds and the storms, activates and puts in danger the towers and the churches, which have been subject to numerous strikes, fires and deaths during storms. It is therefore prohibited to ring bells during storms.
Paper published in 1787:
Key: Evaluation of air vibration effects on clouds
This paper exposes 2 reasons backing up the law against ringing bells during storms.
1: Atmospheric Sound Ondulations. Vibrations originated from percussion of objects propagate spherically, generating "compression and approachment of parts". Not heavy clouds break under this condition. But a cloud is a electrified conductor. It is known that the stress exercised from the electric fire is inversely proportional to its capacity, and its capacity is directly proportional to the surface area. If the cloud volume decreases, its surface area must decrease too. Therefore, the capacity will decrease and the intensity of the electric fire will increase. From this we can infer that vibrations, which compress the volume of a cloud, necessarily increase the intensity of the electric fire, which will discharge on the closest bodies, thus on the bell tower.
2: Air rarity around bell tower. Vibrations continuously remove air and turn it into thinner and thinner air. There is therefore an air current towards the sound source. The electric fire will follow that direction.
It ends with:
It is demonstrated that ringing the bell promotes the striking of a lightning and targets the strike on the source of the vibrations.