The patterns are created by intense heating from lightning arcs traveling just below or along the surface of the ground or pavement. Craters or trenches are sometimes created in sand, soil, or asphalt as moisture is explosively vaporized by the intense heat of the lightning discharge. Jump directly to the content. When the opposite charges build up enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning.
The actual breakdown process is still poorly understood. The air breakdown creates ions and free electrons that travel down the conducting channel. This current flow temporarily equalizes the charged regions in the atmosphere until the opposite charges build up again.
Lightning from thunderstorms begins in a strong electric field between opposite charges within the storm cloud, and can stay completely within the cloud intra-cloud lightning when the charge regions are similar strength balanced or can reach the ground cloud-to-ground lightning when one of the regions is much stronger than the other unbalanced.
Lightning is one of the oldest observed natural phenomena on earth. During a storm, colliding particles of rain, ice, or snow inside storm clouds increase the imbalance between storm clouds and the ground, and often negatively charge the lower reaches of storm clouds. Objects on the ground, like steeples, trees, and the Earth itself, become positively charged—creating an imbalance that nature seeks to remedy by passing current between the two charges. This heat causes surrounding air to rapidly expand and vibrate, which creates the pealing thunder we hear a short time after seeing a lightning flash.
Each bolt can contain up to one billion volts of electricity. A typical cloud-to-ground lightning bolt begins when a step-like series of negative charges, called a stepped leader, races downward from the bottom of a storm cloud toward the Earth along a channel at about , mph , kph. Each of these segments is about feet 46 meters long. When the lowermost step comes within feet 46 meters of a positively charged object, it is met by a climbing surge of positive electricity, called a streamer, which can rise up through a building, a tree, or even a person.
When the two connect, an electrical current flows as negative charges fly down the channel towards earth and a visible flash of lightning streaks upward at some ,, mph ,, kph , transferring electricity as lightning in the process.
Some types of lightning, including the most common types, never leave the clouds but travel between differently charged areas within or between clouds.
Other rare forms can be sparked by extreme forest fires, volcanic eruptions, and snowstorms. Ball lightning, a small, charged sphere that floats, glows, and bounces along oblivious to the laws of gravity or physics, still puzzles scientists. About one to 20 cloud-to-ground lightning bolts is "positive lightning," a type that originates in the positively charged tops of stormclouds.
These strikes reverse the charge flow of typical lightning bolts and are far stronger and more destructive. Positive lightning can stretch across the sky and strike "out of the blue" more than 10 miles from the storm cloud where it was born. About 2, people are killed worldwide by lightning each year. Hundreds more survive strikes but suffer from a variety of lasting symptoms, including memory loss, dizziness, weakness, numbness, and other life-altering ailments.
A "stepped leader" of negative charge descends from the cloud seeking out a path toward the ground. Although this phase of a lightning strike is too rapid for human eyes, this slow-motion video shows it happening. As the negative charge gets close to the ground, a positive charge, called a streamer, reaches up to meet the negative charge.
The channels connect and we see the lightning stroke. We may see several strokes using the same path, giving the lightning bolt a flickering appearance, before the electrical discharge is complete. That's five times hotter than the surface of the Sun!
The heated air expands explosively, creating a shockwave as the surrounding air is rapidly compressed. The air then contracts rapidly as it cools. If we are watching the sky, we see the lightning before we hear the thunder.
That is because light travels much faster than sound waves.
0コメント