Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 21/07/2007 18:19:15

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: neilep on 21/07/2007 18:19:15

Hi all..How are ewe today ?..I'm fine...kids are a nuisance !! *le sigh*..I luff them though of course !!..and it's still raining loads here !!

Lightning !!..it's like...well bright and made of cloud fairy dust.....

...when it strikes does it come down from the sky ?...or does it (as I think I have heard) start from the ground and work upwards ?..   

I just do not know !!...is there some ambiguity when it comes to lightning strikes ?...are there different types ?..and why does it strike the way it strikes ?...is it really a " Strike " ?



Hugs & Shmishes

neil
xxxxx

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: paul.fr on 21/07/2007 18:29:08

Dearest Neil of many topics (neil of plures thema)

When a storm cloud discharges electricity to Earth, a small "leader stroke" zigzags toward the ground in about one one-hundredth of a second. Once it touches something like a tree, a pole, a barn or the ground- the electrical circuit is complete and a vast surge of electricity, the lightning bolt, roars up the path established by the leader stroke. Thus the lightning stroke generally goes from the highest object on the ground up to the cloud. It looks as if it happens the other way around-from the cloud to the ground.

The human eye cannot follow the formation of a lightning stroke because it shoots skyward in about one-millionth of a second. What the eye sees is the electrical discharge of as much as 100 million volts of electricity, which heats the surrounding air to a temperature five times hotter than the surface of the sun - 30 000 degrees C (54,000°F).

Interesting fact:
A lightning bolt is just a few centimetres wide. Thunder is the sound caused by the instantaneous heating and expansion of air along the lightning bolt. The variety of thunder sounds is caused by the different shape of each bolt.

Is that Okay?

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: neilep on 21/07/2007 18:53:18

Dearest Paul of many answers (paul of plures explana)


THANK EWE Paul.

But if a little leader thingy does a scouting trip first, then where does the el biggo upwards strike come from ?
It has to get it's power from somewhere !...do ewe know what I mean ?

I bow down in deference to your knowledge of lots.

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: paul.fr on 21/07/2007 19:34:26

Dearest Neil, seekier of knowledge ( ovis peto scientia )

If my online sheep to English translator is correct, i think this may be the answer you seek.

A huge electrical charge builds up as the cloud particles become electrified and the charged particles separate. The positive charge fixes near the top of the cloud and the negative charge at the bottom.

A positive shadow charge builds up on the ground beneath. an electric current is then discharged, weak spark travels down from the cloud and a positive charge rises to meet it.

If dave was here, i'm sure he would explain all of this with nice pictures.

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: neilep on 21/07/2007 19:51:26

Dearest Paul, giver of answers of all good and true (humanis cleverus big-repectus)

I think I am beginning to understand. yes pictures woudl be nice, me likey piccys !


I am still just a little confuddled about how the positive charge in all it's glory, which heads back up to the cloud, where it gets it's power from !...surely the energy has to come form somewhere and not the weak spark !

Don't bust a gut over this one....it's not your explanation..it's my inability to grasp it !!

THANKS PAUL

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: paul.fr on 21/07/2007 20:15:00

Quote from: neilep on 21/07/2007 19:51:26

Don't bust a gut over this one....it's not your explanation..it's my inability to grasp it !!

THANKS PAUL

Dearest Neil, Confuddled sheep from the town of Dumbfounded on the wouds(confusus ovis)

Goes into non-gut busting mode and turns to "how stuff works" for answers.

This is what they say: http://science.howstuffworks.com/lightning.htm

In an electrical storm, the storm clouds are charged like giant capacitors in the sky. The upper portion of the cloud is positive and the lower portion is negative. How the cloud acquires this charge is still not agreed upon within the scientific community, but the following description provides one plausible explanation.

 


In the process of the water cycle, moisture can accumulate in the atmosphere. This accumulation is what we see as a cloud. Interestingly, clouds can contain millions upon millions of water droplets and ice suspended in the air. As the process of evaporation and condensation continues, these droplets encounter many collisions with other moisture that is in the process of condensing as it rises. Also, the rising moisture may collide with ice or sleet that is in the process of falling to the earth or located in the lower portion of the cloud. The importance of these collisions is that electrons are knocked off of the rising moisture, thus creating a charge separation.

The newly knocked-off electrons gather at the lower portion of the cloud, giving it a negative charge. The rising moisture that has just lost an electron carries a positive charge to the top of the cloud. Beyond the collisions, freezing plays an important role. As the rising moisture encounters colder temperatures in the upper cloud regions and begins to freeze, the frozen portion becomes negatively charged and the unfrozen droplets become positively charged. At this point, rising air currents have the ability to remove the positively charged droplets from the ice and carry them to the top of the cloud. The remaining frozen portion would likely fall to the lower portion of the cloud or continue on to the ground. Combining the collisions with the freezing, we can begin to understand how a cloud may acquire the extreme charge separation that is required for a lightning stroke.

When there is a charge separation in a cloud, there is also an electric field that is associated with the separation. Like the cloud, this field is negative in the lower region and positive in the upper region.

The strength or intensity of the electric field is directly related to the amount of charge build-up in the cloud. As the collisions and freezing continue to occur and the charges at the top and bottom of the cloud increase, the electric field becomes more and more intense -- so intense, in fact, that the electrons at the earth's surface are repelled deeper into the earth by the strong negative charge at the lower portion of the cloud. This repulsion of electrons causes the earth's surface to acquire a strong positive charge.

All that is needed now is a conductive path for the negative cloud bottom to contact the positive earth surface. The strong electric field, being somewhat self-sufficient, creates this path.

The link above, provides quite an amount of interesting information on all aspects of lightning.

Title: Lightning.....up or down...they're the main two !!...but which is true ?
Post by: neilep on 21/07/2007 20:29:03

WOO !!!

tres tres bon elaborativeness of answer giving joy and luff !

THANK EWE PAUL........great link too !!


I apprecaite your time in clearing this up for me !!

Wooly hugs !