Thunder & Lightning

Where Does Lightning Strike?


Lightning will not strike unless there certain conditions are met. Lightning is a circuit, for it to strike the circuit must be complete or the energy will just keep moving without going anywhere or doing anything. To close the circuit, there are three places that lightning may strike.
http://ellerbruch.nmu.edu/classes/cs...cts/img777.gif 1. Within the cloud Lightning does happen without us always seeing it. When the difference between the positive electrons in the upper part of the cloud and the negative electrons in the lower part is great enough, a discharge of energy in the form of electricity will take place and lightning strikes within the cloud. 2. From one cloud to another Again, when the difference of charges is great enough there will be a stroke of lightning to equalize the difference and regain equilibrium. In this situation, the charge difference is too great between adjacent clouds and the stroke is caused. [B] 3. From a cloud to Earth.Earth must obtain a charge before it can be the circuit connector for the process of lightning. This happens when a cloud above Earth's surface passes over and alters the charge of the ground. Earth acquires a positive charge from the passing cloud(s) and can then close the circuit; lightning strikes through the sky, from the cloud to the ground, completing the circuit. http://ellerbruch.nmu.edu/classes/cs...picts/anim.gif

Thunder


Thunder is a result of lightning. Although many people say "thunder and lightning" it is actually "lightning and thunder". Thunder occurs because a stroke or flash of lightning heats up the air around it so fast that the air expands very rapidly, or explosively. It is said that the air around a lightning bolt heats to five times hotter than the air on the sun's surface! Since heat makes things expand, like a marshmallow in a microwave, the air expands when the lightning heats it. Because the rate of expansion is so fast, the air actually vibrates, causing waves. These waves are the sound waves that we hear as sound, or thunder.
Thunder travels about one mile for every second you count after you see a stroke of lightning. This allows you to figure out how close the lightning struck to where you are. For example: let's say that you see a flash of lightning and then begin to count how many seconds before you hear the thunder. If you count 15 seconds this means that the lightning struck about 3 miles from you (divide 15 seconds by 5 seconds to figure the stroke was 3 miles away).

The Cloud to Ground Striking Process


A stroke of lightning only takes about 1/2 of a second to occur. There are two key ideas associated with the process of lightning stokes. They are termed as stepped leaders and return strokes. There is also a dart leader. With these three, the path of a lightning bolt can be covered from the place where it leaves the cloud to its connection with Earth.
A stepped leader is a very faint discharge of lightning inside a cloud. These discharges move toward the ground in series of steps; each step down is about 50 yards long. When the leader steps down to Earth and connects to the ground or a tree (for example) the circuit is complete and the lightning strikes. http://ellerbruch.nmu.edu/classes/cs...cts/img781.gif
A return stroke is a lightning stroke that originates from the ground. The stroke travels back to the cloud.
A dart leader happens when electrons are discharged, taking the initial path of the lightning stroke to the ground. This means that lightning can strike the same place more than once. Lightning has favorite sites to strike and is capable of following the same path twice, contrary to what some people believe.