Is there any way to tell how far away a lightning strike is by how its thunder sounds? I thought one way might be by using the fact that higher frequencies travel faster than lower frequencies. Would you have to correct for the fact that thunder may not take a straight path? (If so, this would affect the distance calculation based on the time between lightning and thunder as well.)
[Physics] Without seeing the lightning, can you tell how far away it struck by how the thunder sounds
acousticslightningmeteorologyweather
Related Solutions
(1) To address your first question: you have to treat the cloud and the earth below it as forming as a capacitor. There's a good popular description of this at http://micro.magnet.fsu.edu/electromag/java/lightning/. A capacitor is described by it's capacitance, and this is related to the voltage and charge by:
$$C = \frac{Q}{V}$$
where $Q$ is the electric charge and $V$ is the voltage difference across the capacitor. You can approximate the cloud and earth as a parallel plate capacitor, and the capacitance is given by:
$$C = \frac{\epsilon A}{d}$$
where $A$ is the area of the cloud base, $d$ is the spacing between the cloud base and the earth, and $\epsilon$ is the permittivity of air ($8.854 \times 10^{-12}C^2N^{-1}m^{-2}$). Combining the two equations and a quick rearrangement gives:
$$V = \frac{Qd}{\epsilon A}$$
This is obviously a gross simplification, but should give you a rough idea of the potential difference.
(2) As to your second question: as you say, positive lightning requires a higher voltage to get it started. Looking at the equation for the voltage, assuming the cloud stays the same the only way the voltage can be higher is if the charge is higher. Current is defined as charge per unit time, and if the duration of the lightening strike is roughly constant a positive lightning bolt has to transfer more charge in the same time and therefore has a higher current.
Here is a model that pictures the electrostatics of the creation of a lightning bolt.
The usual cloud-to- ground discharge probably begins as a local discharge between the small pocket of positive charge at the base of the cloud (the p region) and the primary region of negative charge (the N region) above it. This local discharge frees electrons in the N-region that previously had been attached to water or ice particles. These electrons overrun the p-region, neutralize its small positive charge, and then continue on their trip to the ground.
The horizontal extent is kilometers thus the field is built up from the ground, and there is no possibility of running out of the area. It is a matter of probabilities of the square meter or so where most of the energy will be dissipated and that depends on the local field distributions. A conductor like a lightning rod has a sharp field around it and provides the easiest path, if the strike were to happen within some meters of its location: strikes have a limited area, about 20 feet variability.
A horse or a human may find themselves in the strikes path, there will be little difference except on the conductivity of the body, I have heard of lightning just burning the clothes. If the horse is with four feet in the air, again it is a matter of the random path of the strike and the conductivity of the horse.
All in all it is the large geography of the spot that will determine the region where the bolt will strike and the local conductivities for the details. Running would help if one entered a house or other solid shelter. Falling on the ground or sheltering at a ridge is good advice to lessen the probability of being struck, because of the electric fields built up around high points: do not become the lightning rod by being the highest point in the region.
Best Answer
This is an interesting question. Unfortunately, the answer is probably no for two reasons. There is a nice way of telling how far away a lightning strike was by counting the seconds before the thunder reaches you though. First let me tell you why your method probably won't work, then I'll tell you how to calculate the distance based on the time of arrival (a method which you might already know).
Why your method won't work without sensitive equipment.
What relatively simple method will work?
A trick I learned as a child (perhaps you did too) is to count down the seconds between the lightning flash and the thunder clap. From this you can calculate roughly how far away the lightning was. Since the speed of light is so fast as to be considered instantaneous in this situation, the time it took the sound to get to you tells you how far away the lightning struck. If the time for the sound to reach you is $\Delta t$, then the lightning was a distance $$d=\Delta t*v$$ away, where $v=0.21\tfrac{mi}{s}$ is the speed of sound in air. As an example, if you count $5\ \text{seconds}$ for the sound to reach you, then the lightning would be roughly $1\ \text{mile}$ away. You can remember to simply divide by $5$ as a rule of thumb. This calculation gives the distance to the source of the thunder which may be a couple of miles above the ground.