Growth by Collision and Coalescence Questions and Answers

Answer: A

The first two are correct and describe the classic maritime case. The third is wrong, since shallow maritime cumulus only a kilometre or two deep are among the most reliable warm rain producers. Depth matters less than the breadth of the droplet spectrum.

Answer: B

High droplet concentration is the continental case and works against warm rain. The other three describe the maritime microphysics that lets collection begin early. Few nuclei mean large droplets, and large droplets collect well.

Answer: C

The rain water term represents the collectors and the cloud water term the material collected. The product form is why accretion becomes dominant only once autoconversion has generated some rain. The two terms operate in sequence rather than in parallel.

Answer: D

Both are true and the reason gives the sequence, and this is why the timing of autoconversion controls the whole process. Once rain exists the conversion of cloud water proceeds far more rapidly. Rain production is therefore strongly non-linear in time.

Answer: A

The boundaries are conventional but the ordering reflects a real progression in fall speed and in growth mechanism. Drizzle is conventionally taken to begin near a hundred micrometres in diameter. Terminal velocity rises steeply across that boundary.

Answer: B

Correct answer: A-2, B-4, C-1, D-3

The four sizes span more than two orders of magnitude: a cloud droplet at about 20 micrometres, a drizzle drop at 200, a small raindrop at a millimetre and a large one at four. The gap between the first two is the one collection must bridge, and it is why the transition from cloud to rain is the central problem of the subject.

Answer: C

The diameter increases by a factor of one hundred and mass scales with the cube. A million cloud droplets are therefore required to make a single ordinary raindrop. The figure explains why collection must be efficient to work at all.

Answer: D

The cube law on a hundredfold increase in diameter gives exactly this figure. It conveys why the collection process must be efficient and why the initial collectors matter so much. A million merger events cannot occur one at a time by chance.

Answer: A

Spontaneous breakup limits the largest drops directly, while collisional breakup follows an energetic impact between two drops. Collisional breakup is the more frequent of the two in heavy rain. Drop concentrations there make energetic impacts commonplace.

Answer: B

Both are true and the reason gives the cause, and spontaneous breakup requires a drop already near the aerodynamic limit. The two together establish the equilibrium size distribution observed. Growth and fragmentation reach a statistical balance.