Cloud Electrification and Lightning Questions and Answers

Q: The energy dissipated in a typical lightning flash is of the order of

Correct answer: one gigajouleA typical flash transfers a few tens of coulombs through a potential difference of tens or hundreds of megavolts, giving an energy of the order of a gigajoule - roughly the chemical energy in thirty litres of petrol. Most of it goes into heating and expanding the channel, into light and into radio emission, and the fraction available at the strike point is small. It is far too diffuse and too brief to be worth capturing.

61.

Assertion (A): Intracloud flash rate responds to updraught intensification sooner than the cloud to ground rate.
Reason (R): Charging begins aloft in the mixed phase region before the lower charge centre develops.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

Both are true and the reason gives the sequence, and this is why total lightning is preferred for nowcasting. Cloud to ground activity lags the intracloud signal noticeably. Total lightning is therefore the more useful measurement.

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62.

Ball lightning is

A.the glow around a lightning rod just before a strike
B.a rarely observed luminous sphere of uncertain physical origin
C.the standard appearance of an ordinary return stroke
D.another name for a sprite high above a storm

Answer: B

Correct answer: a rarely observed luminous sphere of uncertain physical origin

Ball lightning is reported as a glowing sphere of tens of centimetres persisting for seconds, sometimes moving against the wind or passing through windows. Reports are numerous and consistent enough to be taken seriously, laboratory reproduction has been at best partial, and no accepted physical explanation exists. It is quite distinct from Saint Elmo’s fire, which is a well-understood corona discharge.

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63.

Saint Elmo's fire is

A.the lingering afterglow of a lightning channel
B.the reflection of a flash from the cloud base
C.a corona discharge from pointed objects in a strong field
D.a particular form of cloud to ground lightning

Answer: C

Correct answer: a corona discharge from pointed objects in a strong field

In the strong field beneath a thundercloud, the field concentrates at pointed conductors - masts, aerials, aircraft extremities, the horns of cattle - until it exceeds the local breakdown strength and a continuous glow discharge forms. It is a warning that the field is high and a strike is possible, though the discharge itself is harmless and carries only a small current.

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64.

Three of the following are electrical phenomena occurring below the cloud base. Which is the odd one out?

A.cloud to ground lightning
B.Saint Elmo's fire
C.the fair weather conduction current
D.a sprite in the mesosphere

Answer: D

Sprites occur tens of kilometres above the storm rather than below it. The other three all take place between the cloud base and the ground. Transient luminous events belong to the upper atmosphere. Sprites sit tens of kilometres above the cloud top.

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65.

Charge separation requires work to be done because

A.opposite charges attract and must be pulled apart
B.like charges attract and so resist being separated
C.charge cannot be separated without strong heating
D.the atmosphere behaves as a perfect conductor

Answer: A

The updraught supplies the mechanical energy, which is ultimately derived from latent heat release. A thunderstorm is therefore a heat engine driving an electrical generator. Convection supplies the mechanical work required.

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66.

Assertion (A): A thunderstorm can be regarded as an electrical generator driven by convection.
Reason (R): The updraught does mechanical work against the electrostatic attraction between charges.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both are true and the reason gives the energetics, and the ultimate source is latent heat released by condensation. The electrical energy is a small fraction of the total energy the storm processes. Latent heat dwarfs the electrical output entirely.

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67.

The energy dissipated in a typical lightning flash is of the order of

A.one kilojoule
B.one petajoule
C.one gigajoule
D.one joule

Answer: C

Correct answer: one gigajoule

A typical flash transfers a few tens of coulombs through a potential difference of tens or hundreds of megavolts, giving an energy of the order of a gigajoule - roughly the chemical energy in thirty litres of petrol. Most of it goes into heating and expanding the channel, into light and into radio emission, and the fraction available at the strike point is small. It is far too diffuse and too brief to be worth capturing.

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68.

State whether the following is true or false.
The electrical energy in lightning is a small fraction of a thunderstorm's total energy budget.

A.False
B.True only at large scales
C.False only at small scales
D.True

Answer: D

Latent heat release dwarfs the electrical output by many orders of magnitude. Lightning is a conspicuous but energetically minor product of the storm. Visibility and energy are quite unrelated here. The storm's heat output exceeds its electrical output vastly.

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69.

Volcanic lightning is thought to arise chiefly from

A.frictional charging of ash particles in the plume
B.the same graupel ice mechanism as in thunderstorms
C.the electrical conductivity of molten lava
D.cosmic ray ionisation above the volcano

Answer: A

Correct answer: frictional charging of ash particles in the plume

Volcanic plumes generate lightning at heights and temperatures where no ice exists, so the graupel mechanism cannot apply. Charging is attributed instead to fracto-emission as the magma shatters and to triboelectric charging as ash particles collide in the turbulent plume. Where the plume rises above the freezing level the ice mechanism may then contribute as well, giving a second lightning maximum higher up.

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70.

Consider the following statements about volcanic lightning.
1. Frictional charging of ash contributes near the vent.
2. Ice charging can operate higher in a tall plume.
3. It requires no particles in the plume at all.

A.All of them
B.1 and 2 only
C.3 only
D.1 only

Answer: B

The first two are correct and describe the two regimes. The third is nonsensical, since charge separation requires particles to collide and separate in the first place. No particles means no charge separation of any kind.

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