Cloud Seeding and Weather Modification Questions and Answers

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.

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.

Answer: C

The first two are correct and describe the usual arrangement. The third confuses permission with endorsement, which regulators are generally careful to keep distinct. A licence records an activity rather than approving a claim.

Answer: D

Nothing in the technique commands the weather; at best it nudges a marginal process. The change in vocabulary reflects the retreat from mid twentieth century optimism. Language followed the evidence over several decades.

Answer: A

Both are true and the reason gives the cause of the change, and the shift is visible across the literature of the period. Present claims are correspondingly more modest. The change in vocabulary tracked the change in expectation.

Answer: B

Gauges are adequate for the purpose; the difficulty lies in the comparison rather than the measurement. The other three are the genuine obstacles. Measurement is adequate; comparison is what fails. The missing counterfactual is the central obstacle.

Answer: C

Additional nuclei add nothing where the cloud is already converting its water. Seeding is only plausible where the natural nucleus supply is the limiting factor. Where something else limits the cloud, nuclei cannot help.

Answer: D

Correct answer: True

Seeding supplies nuclei, so it can only help where nuclei are the limiting factor. A cloud with ample natural nuclei and no supercooled water to spare will do what it was going to do, and adding more can even reduce the precipitation by dividing the water among too many particles.

Answer: A

Saharan dust reaching the Atlantic and beyond is a documented natural nucleus source. Such natural variation in nucleus supply complicates the interpretation of seeding trials. Dust episodes can change a cloud's seedability overnight.

Answer: B

Both are true and the reason gives the difficulty, and dust transport episodes can change the picture within a day. Seedability is therefore not a fixed property of a region. The same cloud may be seedable one day and not the next.