Since one of my previous job responsibilities was figuring out how to protect aircraft from the effects of lightning, I have a pretty good idea of what happens.
Lightning is best described as "pulsed DC". The leader that initially establishes the discharge path is, in simple terms, a static charge which has reached sufficient potential to ionize a path through the air. This ionized path is what eventually carries the actual lighting discharge. There is very little current associated with the leader, and as far as how lightning affects people, buildings, etc., the leader can be ignored.
Once an ionized path is established, the part of the discharge that we see (and that creates thunder) occurs. This is an initial high current pulse, called the first return stroke, which may reach 100,000 amperes in a severe strike. This current decays rapidly (on the order of milliseconds)to a much lower level. Most of the actual charge transfer occurs during this longer lower level discharge, which is limited by how fast the charge can move to replace what was originally discharged. If 100,000 amperes isn't current, I don't know what is!!!
Sometimes the initial discharge is followed by repeated discharges when enough charge flows into the vicinity of the ionized path before the path dissipates, and creates a second (or third, or fourth, etc.) flash. This phenomenon is why lightning sometimes appears to flicker - it really is a series of discharges.
In a single strike, current only flows in one direction. Cloud-to-ground strikes generally originate in a pocket of negative charge in the cloud, i.e., the cloud is negative with respect to the earth. Cloud-to-ground strikes can also originate in a positively charged area of a cloud, in which case the earth is negative with respect to the cloud. A positive charge is simply a lack of electrons, a negative charge is a surplus of electrons. In a cloud-to-cloud strike, the leader can initiate in either a positive or negative pocket of charge.
I've attached a link to a NASA website with a good discussion of lightning.
To answer the original question, yes, lightning is in fact a very large pulse of electrical current. Any individual strike is DC, as charge only moves in one direction. A single lightning strike may contain multiple discharges, but they will all be of the same polarity. Other strikes may be the opposite polarity, but the polarity does not change during an individual discharge.
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]
Today's Featured Article - Oil Bath Air Filters - by Chris Pratt. Some of us grew up thinking that an air filter was a paper thing that allowed air to pass while trapping dirt particles of a particles of a certain size. What a surprise to open up your first old tractor's air filter case and find a can that appears to be filled with the scrap metal swept from around a machine shop metal lathe. To top that off, you have a cup with oil in it ("why would you want to lubricate your carburetor?"). On closer examination (and some reading in a AC D-14 service manual), I found out that this is a pretty ingenious method of cleaning the air in the tractor's intake tract.
... [Read Article]
Latest Ad:
1964 I-H 140 tractor with cultivators and sidedresser. Starts and runs good. Asking 2650. CALL RON AT 502-319-1952
[More Ads]
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
