Three of the following are glaciogenic seeding agents. Which is the odd one out?
Answer: C
Correct answer: coarse sodium chloride powder
Salt is hygroscopic: it attracts water and grows into a large droplet, which is warm rain seeding and works in clouds above freezing. The other three are glaciogenic, producing ice in supercooled cloud - silver iodide by nucleation, dry ice and propane by cooling.
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Match each delivery method with its usual application.
List I
A. Aircraft flare
B. Ground generator
C. Rocket or artillery
D. Ground propane dispenser
List II
1. rapid delivery into a developing hail storm
2. seeding directly in the supercooled cloud region
3. seeding a cap cloud on a mountain ridge
4. releasing agent into orographic upslope flow
Answer: D
Which method suits depends on how the agent must reach the supercooled region. Ground based release relies on the terrain flow carrying the agent up into the cloud. Without that lift the agent stays in the boundary layer.
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Ground based seeding generators are most useful in
Answer: A
The terrain provides the vertical transport the generator itself cannot supply. Over flat ground the agent tends to remain trapped in the boundary layer and never reaches the supercooled region. Flat terrain provides no mechanism to lift the agent.
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Consider the following statements about ground based generators.
1. They rely on the flow to carry the agent to cloud level.
2. They suit orographic programmes particularly well.
3. They deliver agent reliably into any cloud type.
Answer: B
The first two are correct and describe their proper use. The third is not so, and targeting failures in which the agent never reaches the intended volume are a recurrent difficulty in evaluation. A null result may reflect delivery rather than physics.
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The static seeding hypothesis proposes that seeding works by
Answer: C
It treats the cloud's dynamics as fixed and aims only at the microphysical conversion. Modest increases in precipitation are all that such a mechanism could in principle deliver. Nothing in it allows the cloud itself to grow.
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Under the dynamic hypothesis, the benefit of seeding comes from
Answer: D
Freezing a large mass of supercooled water releases heat and increases buoyancy. The cloud then grows deeper and may process considerably more water than it otherwise would have. The effect sought is far larger than the static one.
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Assertion (A): The dynamic hypothesis predicts larger seeding effects than the static one.
Reason (R): It allows the cloud itself to grow rather than only altering its microphysics.
Answer: A
Both are true and the reason gives the distinction, and the dynamic effect has proved much harder to demonstrate convincingly. Most operational programmes are justified on static grounds instead. Modest claims are easier to defend than ambitious ones.
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Consider the following statements about the two seeding hypotheses.
1. The static hypothesis leaves cloud dynamics unchanged.
2. The dynamic hypothesis invokes latent heat and added buoyancy.
3. The dynamic hypothesis is the better established of the two.
Answer: B
The first two are correct and set out the two ideas. The third overstates the evidence, since dynamic effects remain considerably more contested than static ones. Field demonstration has lagged the theoretical argument.
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Overseeding a cloud refers to
Answer: C
With too many crystals competing for the available vapour none grows large enough to fall. The idea underlies attempts at hail suppression as well as being a risk in rain enhancement. Too much agent can be worse than none at all.
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Assertion (A): Overseeding is proposed as a route to hail suppression.
Reason (R): Many small embryos compete for the water and none grows to damaging size.
Answer: D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. A storm holds a finite quantity of supercooled water, and hail size depends on how much each embryo can collect. Introducing far more embryos divides that water among them, so many small stones fall instead of a few large ones - and small stones do little damage.
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