Growth by Condensation Questions and Answers

Answer: A

Correct answer: different parcels experience different histories of growth

Entrainment brings drier air in through the cloud edges, and the mixing that follows is inhomogeneous: some droplets evaporate entirely while others in less diluted parcels continue growing. Different parts of the cloud therefore carry droplets with different growth histories, and when those parcels mix the resulting spectrum is far broader than adiabatic condensation alone would produce - which helps close the gap in the previous item.

Answer: B

The first two are correct and are the leading proposed mechanisms. The third is the opposite of what the growth equation predicts, since diffusional growth narrows a spectrum rather than widening it. Some process outside the growth equation has to supply the breadth.

Answer: C

Latent heat release slows diffusional growth rather than accelerating the approach to rain. The other three are all serious candidate mechanisms in the warm rain literature. None of them alone accounts for every observed case.

Answer: D

The sequence shows where the difficulty lies, since the third stage must somehow give way to the fourth. Everything interesting about warm rain formation happens at that transition. Models are judged largely on how well they reproduce it.

Answer: A

Correct answer: produce a few large droplets that can start collecting early

A giant nucleus - a sea salt particle of several micrometres, say - activates at once and starts far out along the size spectrum, so it reaches collecting size long before ordinary droplets do. A handful of such droplets per litre is enough to begin the coalescence chain, which is why marine clouds rich in sea salt produce warm rain far more readily than continental ones of the same depth.