State whether the following is true or false.
Snowpack augmentation programmes are motivated chiefly by water supply rather than by weather itself.
Answer: A
Mountain snowpack acts as a natural reservoir releasing water through the melt season. Water and hydroelectric agencies are consequently the principal funders. The motivation is hydrological rather than meteorological.
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A common design in operational orographic programmes is to
Answer: B
Criteria on temperature, wind direction and liquid water govern when generators are lit. The upslope flow then carries the agent into the supercooled part of the cap cloud. Wind direction determines whether the plume reaches the target.
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Consider the following statements about operational criteria in seeding.
1. Temperature and wind direction both enter the decision.
2. Liquid water content indicates whether the cloud is seedable.
3. Operations should proceed whenever any cloud is present.
Answer: C
The first two are correct and are typical operating criteria. The third would waste agent on clouds that cannot respond and would dilute any effect in the record. Criteria exist to concentrate effort where it can work.
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Microwave radiometers are used in seeding programmes to
Answer: D
Correct answer: measure the supercooled liquid water available in the cloud
A radiometer looking upward measures the liquid water in the column overhead, which is the resource seeding is meant to convert. If there is none, there is nothing to seed and the operation should not run - so the instrument answers both the targeting question and the go or no-go decision.
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Assertion (A): Liquid water path measurement has improved the selection of seeding opportunities.
Reason (R): It identifies directly whether supercooled water is available to convert.
Answer: A
Both are true and the reason gives the value, and earlier programmes had to rely on indirect indicators. Better selection concentrates the effort where it can plausibly work. Indirect indicators were all that earlier work had.
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Match each instrument with its role in a seeding programme.
List I
A. Microwave radiometer
B. Weather radar
C. Trace chemical analysis
D. Precipitation gauge network
List II
1. confirming the agent reached the target
2. measuring supercooled liquid water path
3. measuring the resulting surface fall
4. detecting ice produced in the seeded plume
Answer: B
Together these address different links in the causal chain from release to rainfall. A programme lacking any of them leaves a corresponding gap in the evidence it can offer. Each instrument addresses a different causal link.
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The strongest recent evidence for orographic seeding came from
Answer: C
Observing the plume from release through ice growth to snowfall closes the causal chain. This represented a considerable advance over purely statistical arguments. The chain from release to snowfall was observed throughout.
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State whether the following is true or false.
Statistical association alone cannot establish that seeding caused an increase in precipitation.
Answer: D
Correct answer: True
More rain after seeding may mean the seeding worked, or that the cases seeded were the more promising ones, or simply that it rained. Establishing cause needs randomisation, so that the comparison is between like and like, and a physical mechanism that predicts the result in advance.
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All of the following weaken a claimed seeding success EXCEPT
Answer: A
Correct answer: the seeding decision was randomised in advance
Randomisation is what makes a claim credible rather than weakening it: it removes the possibility that the seeded cases were the ones more likely to rain anyway. The other three each open exactly that possibility - selecting cases afterwards, choosing the control area afterwards, and never confirming the agent arrived.
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Weather modification is regulated in many jurisdictions by requiring
Answer: B
Registration allows operations to be tracked and downwind concerns to be addressed. It does not imply that the regulator has accepted the efficacy of the technique. Permission and endorsement are quite separate things.
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