Glaciogenic cloud seeding aims to
Answer: A
Many supercooled clouds contain too few natural ice nuclei to glaciate efficiently. Adding artificial nuclei is intended to start the Bergeron process and convert liquid water into precipitation. The cloud's own nuclei are the limiting factor being supplied.
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Assertion (A): Glaciogenic seeding can only work where supercooled liquid water is present.
Reason (R): The added nuclei have nothing to act upon in a cloud that has already glaciated.
Answer: B
Both are true and the reason gives the requirement, and identifying suitable clouds is a large part of any operational programme. Seeding a glaciated cloud accomplishes nothing whatever, however much agent is released.
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Silver iodide is most often dispersed for seeding by
Answer: C
Correct answer: burning it in an acetone solution to produce a fine smoke
A solution of silver iodide in acetone is burnt in a generator, and the vapour condenses into particles of a few hundredths of a micrometre. That is the size wanted: enough particles per gram to be worth releasing, and small enough to be carried into the cloud by the updraught.
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Silver iodide begins to nucleate ice at a temperature of approximately
Answer: D
Reported thresholds cluster between about minus four and minus eight depending on preparation. Nucleating at so modest a supercooling is precisely what makes the compound useful for seeding. Most natural mineral nuclei require far deeper supercooling.
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Match each seeding agent with what it does.
List I
A. Silver iodide
B. Solid carbon dioxide
C. Liquid propane
D. Sodium chloride
List II
1. produces intense local cooling on expansion
2. nucleates ice by lattice resemblance
3. acts as a large hygroscopic condensation nucleus
4. chills air enough for homogeneous freezing
Answer: A
The first three are glaciogenic and the fourth hygroscopic, so they suit quite different clouds. The delivery method and the cloud type together decide which is appropriate. No single agent suits every cloud that might be seeded.
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Dry ice seeding produces ice crystals by
Answer: B
A pellet of solid carbon dioxide is far colder than minus forty and freezes droplets in its wake. It leaves no residue in the cloud, which is one argument advanced in its favour. Nothing chemical remains in the cloud after the pellet has gone.
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Assertion (A): Dry ice seeding does not depend on any lattice match with ice.
Reason (R): It works by cooling the air below the temperature of homogeneous freezing.
Answer: C
Both are true and the reason gives the distinct mechanism, and this is why it leaves no chemical residue. Its disadvantage is that it must be released directly into the supercooled part of the cloud. Ground release is therefore not an option for it.
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Consider the following statements comparing silver iodide and dry ice.
1. Silver iodide nucleates ice by resembling the ice lattice.
2. Dry ice works by intense local cooling instead.
3. Both agents leave a chemical residue in the cloud.
Answer: D
Correct answer: 1 and 2 only
Statements 1 and 2 give the two mechanisms correctly: silver iodide has a crystal structure close enough to ice to act as a template, while dry ice at −78 degrees chills the air around it so sharply that ice forms spontaneously. Statement 3 is wrong for the dry ice, which sublimes to carbon dioxide and leaves nothing behind.
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Hygroscopic seeding is applied to
Answer: A
Large salt particles produce a few unusually large droplets that begin collecting early. The aim is to start the collision coalescence process sooner than it would otherwise begin. It is the warm cloud analogue of glaciogenic seeding.
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Assertion (A): Hygroscopic seeding targets the collision coalescence process.
Reason (R): Large salt particles create early collector drops in a warm cloud.
Answer: B
Both are true and the reason gives the mechanism, and it is the warm cloud counterpart of glaciogenic seeding. Neither approach helps a cloud that is already precipitating efficiently. Seedability depends on what is limiting the cloud.
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