|MadSci Network: Physics|
Don't even try to play with lightning. Lightning kills, in a zillion different ways. It's unpredictable, and can cause death, injury, or property damage at rather incredible distances from the point where it strikes. You might think it would be neat to see lightning up close: most of the survivors of nearby lightning strikes will tell you it's not worth it.
In any case, the method you're describing won't be very effective. The amount of charge you could put on a sheet of tinfoil is absolutely miniscule compared to the amount of charge which is pulled up through the ground by the electric fields associated with an impending lightning stroke, and the amount of ozone you could send into the air with a Jacob's Ladder will be so small compared to the oxygen and nitrogen there that you won't change the breakdown voltage (the voltage at which a spark occurs) of the air at all -- and you're assuming that ozone has a lower breakdown voltage than air, which I can't verify.
Lightning occurs where the electric field is the greatest. The electric field is (roughly) the voltage difference between the cloud and the ground, divided by the distance from cloud to ground:
V(cloud)-V(ground) Field = ------------------ H(cloud)-H(ground)You proposed decreasing V(ground) (actually V(tinfoil)) using a Van de Graaf generator. This won't work very well: charge will bleed off the edges of the foil before the field changes much at all. In fact, depending on how your Van de Graaf generator works, you might actually increase V(tinfoil), making it less likely that lightning will strike.
A better way is to change the height of the ground H(ground). Because the field is stronger where the ground (or things electrically connected to the ground) are higher, lightning tends to strike hilltops, trees, and tall buildings. This is partly how a lightning rod works: it's electrically connected to the ground, and increases the field around it by being tall, causing lightning to strike the rod rather than the building.
Lightning rods also work by being pointy. Objects with sharp points tend to bleed off charge from their points, reducing the voltage difference and weakening the field. This is why Van de Graaf generators are round. When a lightning rod weakens the field by bleeding charge, lightning becomes less likely.
So, the best way to attract lightning is to put a rounded metal object very high in the air, connected by a wire to a plate buried in the ground.
Professional lightning researchers attract lightning by launching rockets with copper wires attached to them up into the storm. The wires lead down and are electrically connected to the ground. They can get lightning to strike at the spot where the copper wire is attached to the ground almost every time.
More warnings: don't do this. You'll kill yourself. But if you try it anyway, be sure to notice that model rocket launchers generally have an electrical ignition switch on the end of a long wire, which is a great way for lightning to travel from the launchpad to you. Launching using a very very long fuse would be better.
Last warning: don't play with lightning.
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