Atmosphere And Weather

How Lightning is Formed



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How Lightning is Formed

Although we do not realize it, we recreate lightning on a daily basis. How many of us have walked across the carpet, touched a door handle and jumped when we hear and feel the shock. Although it is shocking, we have just experienced lightning on a much smaller scale. How is lightning formed outside? Within a cloud, ice crystals bounce off each other creating charged particles.

Positively charged particles rise to the top of the cloud while the negatively charged particles sink to the bottom of the cloud. On the ground there is a negative charge but when a thunderstorm passes over, the ground becomes positively charged. If you were standing in a positively charged area, your hair would stand up and you would be in danger of being struck by lightning.

The first action from the lightning occurs when a “stepped leader” appears from the base of the cloud. This leader reaches the ground in one-hundredth of a second.

The second part is the action of “streamers”, positively charged ions that rush up to meet the stepped leader. When they meet the negative charge comes down to the ground and the return stroke begins, which only lasts a tenth of a second.

Once the connection is made, other stepped leaders may travel that same path, which to an observer would look like the bolt of lightning was pulsing or gives a strobe affect.

There are different types of lightning that occur. There is cloud to ground lightning and under that umbrella of cloud to ground lightning exists bead lightning, ribbon lightning, staccato lightning, and forked lightning.

Bead lightning is the breakup of cloud to ground lightning into short bright sections. Ribbon lightning occurs when high cross winds blow each return stroke, bright flash, and has branching off the main bolt. Forked lightning is just that, lightning that branches out.

There are several other types of lightning other than cloud to ground lightning. One of them is ground to cloud lightning. Ground to cloud lightning occurs when the negatively charged ions rise up from the ground to meet the stepped leader in the cloud, and then travel back to the ground as the return stroke.

Cloud to cloud lightning also referred to as intra-cloud lightning, occurs between the top of the cloud and the bottom. Another term for it is heat lightning because it can be seen from far away and the thunder does not travel that far and usually the ground temperature is warmer.

Another type of lightning is sheet lightning which is a path of the discharge that is hidden within the cloud, causing the whole cloud to light up. Dry lightning occurs when rain is not present at the surface. Dry lightning is the main cause of wildfires.

Rocket lightning is yet another form of lightning that is found at the cloud base and moves horizontally. The reason for the name “rocket” is because of the speed with which it moves through the cloud.

Positive lightning occurs during clear or partly cloudy skies and travels several miles horizontally before discharging. Positive lightning strikes are rare but are also one of the most dangerous because they carry 6 to 10 times the voltage of other types of lightning.

On December 8th, 1963 Pan Am flight 214 was flying from Baltimore/Washington International airport to Philadelphia International airport. While in a holding pattern the plane was struck by lightning, believed to positive lightning, which ignited fuel vapors, causing the wing to separate and ultimately killing all 81 passengers on board.

When the cause was determined to be lightning that brought down flight 214, all commercial aircraft were ordered to have static wicks added to the planes. The wicks would reduce damage by dissipating the charge if a strike did occur.

The last type of lightning that forms is a rare occurrence called ball lightning. The only reported instances of ball lightning come from eyewitness accounts, but no one has been able to record video or get a picture of ball lightning. It is reported as being spherical in shape and lasting for several seconds.

Lightning comes in many different types, but they all form the same way. Positive and negative charged ions rush to meet each other. So if you feel your hair stand up on your body and lightning is present, be prepared to be greeted by a stepped leader if you are the tallest object around. The best thing to do if this happens is to crouch down on the balls of your feet and make yourself the smallest possible target.


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