Lightning is a massive electrostatic discharge between electrically charged regions within clouds, or between a cloud and the Earth's surface. The charged regions within the atmosphere temporarily equalize themselves through a lightning flash, commonly referred to as a strike if it hits an object on the ground. There are three primary types; from a cloud to itself (intra-cloud or IC); from one cloud to another cloud (CC) and finally between a cloud and the ground (CG). Although lightning is always accompanied by the sound of thunder, distant lightning may be seen but be too far away for the thunder to be heard.
Lightning occurs approximately 40–50 times a second worldwide, resulting in nearly 1.4 billion flashes per year.
Many factors affect the frequency, distribution, strength, and physical properties of a "typical" lightning flash to a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may also vary by season in middle latitudes.
Sound of a thunderstormBecause human beings are terrestrial and most of their possessions are on the Earth, where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types, even though IC and CC are more common. Lightning's unpredictability limits a complete explanation of how or why it occurs, even after hundreds of years of scientific investigation. A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 3 mi. The actual discharge is the final stage of a very complex process. A typical thunderstorm has three or more strikes to the Earth per minute at its peak.
How Lightning Develops Between The Cloud And The Ground
A moving thunderstorm gathers another pool of positively charged particles along the ground that travel with the storm. As the differences in charges continue to increase, positively charged particles rise up taller objects such as trees, houses, and telephone poles. Have you ever been under a storm and had your hair stand up? Yes, the particles also can move up you! This is one of nature's warning signs that says you are in the wrong place, and you may be a lightning target!
The negatively charged area in the storm will send out a charge toward the ground called a stepped leader. It is invisible to the human eye, and moves in steps in less than a second toward the ground. When it gets close to the ground, it is attracted by all these positively charged objects, and a channel develops. You see the electrical transfer in this channel as lightning. There may be several return strokes of electricity within the established channel that you will see as flickering lightning.
http://www.lightningsafety.noaa.gov/science.htm
COMMON MISCONCEPTIONS AND MYTHS
1. Lightning never strikes twice… it strikes the Empire State Building in NYC some 22-25 times per year!
2. Rubber tires or a foam pad will insulate me from lightning… it takes about 10,000 volts to create a one inch spark. Lightning has millions of volts and easily can jump 10-20 feet!
3. Lightning rods will protect my ropes course…lightning rods are "preferential attachment points" for lightning. You do not want to "draw" lightning to any area with people nearby.
4. We should get off the water when boating, canoeing or sailing…tall trees and rocky outcrops along shore and on nearby land may be a more dangerous place.
5. A cave is a safe place in a thunderstorm…if it is shallow cave, or an old mine with metallics nearby, it can be a deadly location during lightning.
2.0 Atmospheric Physics 101. At any one time around the planet, there are 2000 thunderstorms and 100 lightning strikes to earth per second. The frequency of lightning increases in the lower latitudes (closer to the equator), and in the higher altitudes (mountainous terrain). In the USA, central Florida experiences some 10-15 lightning strikes per sq. km./yr. The Rocky Mountain west has about two thirds this activity. Central Africa, parts of Southeast Asia, and the Latin American mountain regions can experience two to three times as much lightning as central Florida.
Lightning leaders from thunderclouds proceed in steps of tens of meters, electrifying ground-based objects as they approach the earth. Ground-based objects may launch lightning streamers to meet these leaders. Streamers may be heard (some say they "sound like bacon frying") and seen (we may notice our hair standing on end). A connecting leader-streamer results in a closed circuit cloud-to-ground lightning flash. Thunder accompanying it is the acoustic shock wave from the electrical discharge. Thus, thunder and lightning are associated with one another.
3.0 Flash/Bang. We all possess a first-class lightning detection device, built into our heads as standard equipment. By referencing the time in seconds from seeing the lightning (the FLASH, or "F" ) to hearing the accompanying thunder (the BANG, or "B"), we can range lightning's distance. A "1,001 to 1,005" of five seconds equals lightning distance being one mile away. A "1,001 to 1,010" of ten = two miles; a "1,001 to 1,020" of twenty = four miles; a "1,001 to 1,030" of thirty = six miles; etc.
New information shows successive, sequential lightning strikes (distances from Strike 1 to Strike 2 to Strike 3) can be some 6-8 miles apart. Taking immediate defensive actions is recommended when lightning is indicated within 6-8 miles. The next strike could be close enough to be an immediate and severe threat.
Lightning is a capricious and random event. It cannot be predicted with any accuracy. It cannot be prevented. Advanced planning in the form of a risk management program is the best defense for maximum safety.
4.0 Standard lightning defenses. The eco-tourism environment is different from situations where substantial buildings or fully enclosed metal vehicles are the recommended shelters. Lightning in remote terrain creates dangerous conditions. Follow these guidelines:
LIGHTNING SAFETY TIPS
AVOID: Avoid water. Avoid all metallic objects. Avoid the high ground. Avoid solitary tall trees. Avoid close contact with others - spread out 15-20 ft. apart. Avoid contact with dissimilar objects (water & land; boat & land; rock & ground; tree & ground). Avoid open spaces.
SEEK:Seek clumps of shrubs or trees of uniform height. Seek ditches, trenches or the low ground. Seek a low, crouching position with feet together with hands on ears to minimize acoujstic shock from thunder.
KEEP: Keep a high level of safety awareness for thirty minutes after the last observed lightning or thunder.
5.0 Medical treatment and symptoms. Treat the apparently dead first. Immediately administer CPR to restore breathing. Eighty percent of lightning strike victims survive the shock. Lightning strike victims do not retain an electric charge and are safe to handle. Common lightning aftereffects include impaired eyesight and loss of hearing. Electrical burns should be treated as other burns.
Treat lightning like a snake: if you see it or hear it, take evasive measures.
No comments:
Post a Comment