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Lightning: an electrical discharge in the atmosphere
Lightning Facts
•On average a lightning stroke is 5 km long and 2 to 3 cm in
diameter.
•Approximately 100 lightning strikes occur on the Earth every
second.
•The current in lighting strikes ranges from 15,000 to 30,000
amperes. (A typical household circuit is rated at 15 amperes, and a
typical house has 100-200 amp service.)
•The voltage in a lighting stroke ranges from 1 million to 3 million
volts / meter. A 5km long lighting stroke would have 5 to 15
billion volts. (A typical household appliance is on a 120 volt
circuit.)
Lightning Facts
•The temperature of a lightning stroke is 30,000 deg C (this is 5
times hotter than the surface of the Sun)
•A lighting bolt has enough energy to power a typical house
with for 2 to 22 months.
•20 million cloud-to-ground lightning strikes hit the US each
year.
•Approximately 70 people are killed and 200 to 300 people are
injured by lightning each year in the United States.
Electricity and Charge
Proton: positively charged particle
Electron: negatively charged particle
Ion: an atom with an unequal number of protons and
electrons
Electrical current: movement of an electrical charge
(typically due to the movement of electrons)
An electric field is present in any region where positive and
negative charges exist.
A charge will experience attractive and repulsive forces in
the presence of an electricfield.
What types of charges attract each other?
What types of charges repel each other?
Electricity and Charge
The magnitude of this force of attraction is measured
in volts (V).
The strength of the electric field is measured in volts
/ meter (V/m).
Current will move easily through conductors (such
as metal or water) and will move poorly (or not at
all) through insulators (such as plastic).
Is the atmosphere a good conductor or a good
insulator?
What does this mean about the strength of electric
fields that may build in the atmosphere?
Fair weather electric field:
The background electric
field that exists in the lower
atmosphere.
The strength of the field is
about 100 V/m
In general the atmosphere is
positively charged and the
surface of the earth is
negatively charged.
Charging Mechanisms in Thunderstorms
What is the charge distribution in and around a thunderstorm?
How does a thunderstorm become charged so that lightning can occur?
1. Interface (noninductive) charging
2. Inductance charging
3. Other methods may
also be important for
creating the electric
field in a
thunderstorm
Interface charging:
The transfer of electrical
charge from one conducting
object to another when the
objects are brought into
contact
Hail becomes negatively
charged
Ice crystals become
positively charged.
Induction charging:
A feedback mechanism in which
the background electric field
causes positive and negative
charges within a particle to
migrant to opposite ends of a
particle.
This enhances the transfer of
charge during collisions of
The net result is that hail becomes
even more negatively charged,
and ice crystals become even
more positively charged.
Screening layer:
Thin layer on the surface of thunderstorm of
opposite charge due to charged ions created by
cosmic rays.
Image charge:
The positively charged region on the ground
that lies beneath the negatively charged region
of a thunderstorm
The Lighting Stroke
Types of lightning strokes:
1. In-cloud lightning
2. Cloud-to-cloud lightning
3. Cloud-to-ground lightning
Stages of a Lightning Stroke:
(A) stepped leader:
electrons moving
towards the ground in a
series of steps
(A) return stroke: occurs
when downward
moving electrons meet
upward moving
positively charged
atoms This process can
be repeated multiple
times over the same
path.
(A) dart leader: leader that
occurs after the initial
lightning flash
Figure 20.6
Figure 20.7
Figure 20.8
Distribution of Lightening in the US
Approximately 14,000 forest fires are started by lightning each year
in the United States, burning roughly 2 million acres / year.
Figure 20.10
Other Interesting Atmospheric Electrical Phenomena
Lightning Safety
Deaths:
•28% occur in open fields
•14% under trees
•8% near water
•5% on golf courses
•3% on or near tractors
•2.5% on corded telephones
•40% unreported
84% are male
What should you do if a thunderstorm is approaching?
1.Go inside if possible
2.Stay away from electrical appliances and corded
telephones
3.Avoid taking a shower or coming in contact with indoor
water supplies
What should you do if you can’t go inside?
1.Crouch as close to the ground as possible and minimize the
amount of your body that is in contact with the ground by
staying on your toes or heels.
2.Do not go under trees (unless you are in a forest)
3.Do not lie on the ground
4.Remove metal objects if possible
5.A car with a metal frame is a very safe place in a
thunderstorm.
Figure 20.12
Figure 20A
Figure 20B
Figure 20C