BISL 04-Weather and Climate

(^46) Brief Flash
ME
T
EORO
LOGICA
L P
H
ENOMENA
WEATHER AND CLIMATE
47

E

lectrical st

orms are produced in large cumulonimbus-type clouds, which typically

bring heavy rains in addition to lightning and thunder.

T

he storms form in areas

of low pressure, where the air is w

arm and less dense than the surrounding

atmosphere. Inside the cloud, an enormous electrical charge accumulates, which isthen discharged with a zigzag flash between the cloud and the ground, between thecloud and the air, or between one cloud and another.

T

his is how the flash of lightning

is unleashed. Moreover, the heat that is released during the discharge generates anexpansion and contraction of the air that is called thunder.

ELE

CTRICAL CHARGES

The cloud's negative charges are attractedto the positive charges of the ground.

The

difference in electrical potential betweenthe two regions produces the discharge.

INSIDE THE CLOUDElectrical charges are produced from thecollisions between ice or hail crystals.Warm air currents rise, causing thecharges in the cloud to shift.

ORIGINLightning originates within largecumulonimbus storm clouds.Lightning bolts can have negative orpositive electric charges.

The electricit

y

moves from thecloud toward an airmass of oppositecharge.

A lightning flashcan occur within acloud or betweentwo oppositelycharged areas.

Negative chargesof the cloud areattracted by thepositive charges ofthe ground.

8,700

miles

per second(140,000 km/s) speed100 million voltsIS THE ELECTRICAL POTENTIAL OF A LIGHTNING BOLT.

DI

SCHARGE

The discharge takes place from the cloudtoward the ground after the steppedleader, a channel of ionized air, extendsdown to the ground.

Lightning bolt: 8,7

00 miles per second (140,000 km/s)

Airplane: 0.2 mile per second (0.3 km/s)F1 car: 0.06 mile per second (0.1 km/s)

A windmillgener

ates 200

volts.

110 volts isconsumed bya lamp.

Lightning can be distinguished primarily b

y

T the path taken by the electrical charges thatcause them.

YPES OF LIGHTNING

Cloud-

to-ground

Cloud-to-cloud

Cloud-to-air

DI

SCHARGE SEQUENCE

INDUCED CHAR

GE

The negative charge of the base ofthe cloud induces a positive charge inthe ground below it.

The lightning boltpropagates through anionized channel thatbranches out to reachthe ground. Electricalcharges run along thesame channel in theopposite direction.

If the cloud has additionalelectrical charges, theyare propagated to theground through thechannel of the first stroke and generate asecond return stroketoward the cloud.

This discharge, as inthe second stroke,does not havebranches. When thereturn dischargeceases, the lightningflash sequence comesto an end.

The primary function o

f lightning rods is to facilitate

LI the electrostatic discharge, which follows the pathof least electrical resistance.

GHTNING RODS

1. 
   

2. 
   

4. 
   

THUNDERThis is the soundpr

oduced by the air when

it expands very rapidly,generating shock wavesas it is heated.

RETURN STROKE

In the final phase, the discharge

rises from the Earth to the cloud.

5. 
   

3. 
   

A

B

C

PO

INT OF IMPACT

65 feet

(20 m)

This is the r

adius of a lightning bolt's effective

range on the surface of the Earth.

A lightning rod is an instrument whose purpose is to attract alightning bolt and channel the electrical discharge to the ground so

that it does no harm to buildings or people. A famous experiment byBenjamin Franklin led to the invention of this apparatus. During alightning storm, he flew a kite into clouds, and it received a strongdischarge.

That marked the birth of the lightning rod, which consists of

an iron rod placed on the highest point of

the object to be protected and

connected to the ground by a metallic, insulated conductor.

The principle

of all lightning rods, which terminate in one or more points, is to attractand conduct the lightning bolt to the ground.

1st phase 1st r

eturn

2nd phase 2nd return

3rd phase 3rd return

Cold air

Warm air

SEP

ARATION

The char

ges become separated, with the

positive charges accumulating at the top of thecloud and the negative charges at the base.

Cold air

Very hot

air

Cold air

Very hotair

Tip o

f the

conductor Lightningrod

channel

For Evaluation Only.

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