Cloud Seeding and Weather Modification Questions and Answers

21.

The beneficial competition hypothesis in hail suppression holds that

A.adding embryos divides the water among more and smaller stones
B.seeding melts the hailstones before ever they land
C.seeding removes the updraught that supports the stones
D.seeding prevents any ice at all from forming anywhere in the storm

Answer: A

Correct answer: adding embryos divides the water among more and smaller stones

This is the beneficial competition hypothesis, and it is the only one of the four that is physically coherent. Seeding cannot melt stones, cannot remove an updraught, and certainly cannot prevent ice forming in a storm that is already producing hail.

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22.

Consider the following statements about hail suppression programmes.
1. Their theoretical basis is beneficial competition among embryos.
2. Rigorous evaluation has not established a clear effect.
3. Randomised trials have proved them reliably effective.

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

Answer: B

The first two are correct and reflect the assessments of national bodies. The third is not supported, and several major trials found no statistically significant reduction. National assessments have remained cautious throughout.

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23.

State whether the following is true or false.
Warm fog is more difficult to disperse than supercooled fog.

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

Answer: C

Supercooled fog can be seeded to glaciate and clear, whereas warm fog offers no such lever. Dispersing warm fog requires heating or mechanical mixing and is correspondingly expensive. Only a few major airports have ever operated such systems.

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24.

Supercooled fog at an airport can be cleared by

A.adding condensation nuclei to thicken it
B.cooling it further to below minus forty
C.waiting for the temperature to rise above zero
D.seeding it so that it glaciates and falls out

Answer: D

Seeding converts the droplets to ice crystals which grow and settle out, opening a hole. The technique is well established and is among the few uncontested successes of weather modification. The result is visible within minutes at the site.

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25.

Assertion (A): Cold fog dispersal is among the least contested weather modification techniques.
Reason (R): The effect is immediate, local and directly observable at the site.

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 why it convinces, and no statistical inference over many events is required. Rain enhancement offers no comparable directness of evidence. Fog dispersal needs no statistical inference at all.

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26.

All of the following are recognised aims of weather modification programmes EXCEPT

A.dispersing supercooled fog at an airfield
B.changing the prevailing wind direction over a region
C.enhancing the precipitation falling over a water supply catchment
D.suppressing hail over agricultural farmland

Answer: B

Nothing in the technology acts on the large scale circulation, which carries energy far beyond any seeding intervention. The other three are the standard operational objectives. All three act locally on cloud rather than on circulation.

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27.

The central difficulty in evaluating rain enhancement is that

A.seeding agents are quite impossible to deliver at all reliably
B.nobody understands how ice nucleation works in the first place
C.we can never see what that same cloud would have done unseeded
D.rainfall cannot be measured with any useful accuracy

Answer: C

There is no way to know what a seeded cloud would have done had it been left alone. Only randomised comparison over many events can address the question, and natural variability is large. The effect sought is small against that background.

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28.

Assertion (A): Randomised trials are necessary to evaluate seeding.
Reason (R): The natural variability of rainfall greatly exceeds any plausible seeding effect.

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

Answer: D

Both are true and the reason gives the statistical problem, and single case comparisons are worthless in consequence. Even randomised trials often require many seasons to reach a useful conclusion. Sample size is the binding constraint on such work.

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29.

Consider the following statements about evaluating seeding trials.
1. The seeding decision must be randomised in advance.
2. A target and control area design helps reduce variance.
3. A single well documented case can establish an effect.

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

Answer: A

The first two are correct and are standard trial design. The third is precisely the fallacy that has sustained unfounded claims, since a single cloud provides no counterfactual whatever. One case can never establish a causal effect.

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30.

A target and control design in a seeding experiment is used to

A.avoid the need for any randomisation altogether
B.reduce the variance by comparing against a nearby unseeded area
C.increase the quantity of agent delivered into the cloud being treated
D.guarantee that the seeding will produce more rainfall

Answer: B

Correlating the two areas before the trial allows natural variation to be partly removed. The design still requires randomisation, since the correlation alone does not establish causation. Design and randomisation must work together.

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