Growth by Collision and Coalescence Questions and Answers

Answer: C

The first two are correct and follow from its definition. The third is incomplete, since the kernel is a function of both radii and the efficiency between that particular pair. Every pair of sizes has its own kernel value.

Answer: D

Identical droplets fall at identical speeds and have almost no relative motion. Only turbulence or some other source of differential motion could initiate collection in such a cloud. Uniform spectra are the least favourable case for rain.

Answer: A

Hydrostatic balance concerns the vertical pressure structure and has nothing to do with collection. The other three are all established approaches to the microphysical problem. Each trades resolution against computational expense.

Answer: B

Rain echoes forming in clouds entirely warmer than zero cannot involve the ice phase. Such observations in tropical maritime cumulus were among the earliest confirmations of the warm rain process. Ice cannot be responsible above the freezing level.

Answer: C

Shallow maritime cumulus produce a large share of the precipitation over tropical oceans. Satellite radar has confirmed that much of it comes from clouds too shallow to reach the freezing level. Shallow warm rain had been underestimated for decades.

Answer: D

Both are true and the reason gives the value of the observation, and shallow warm rain had been systematically underestimated before. The oceans are precisely where conventional rain gauges cannot be placed. Satellite radar filled a genuine observational gap.

Answer: A

Droplets a micrometre or two across have essentially zero collision efficiency. Diffusional growth must carry them to roughly twenty micrometres before collection becomes a productive route. That growth takes the greater part of the available time.

Answer: B

A raindrop's fall speed is set by its size and by aerodynamics, not by the aerosol it grew on. The other three are each direct consequences of the nuclei population. Aerosol acts on the beginning of the process, not its end.

Answer: C

It accounts for water retained in the cloud, evaporated below base or carried away by the wind. Values vary enormously between cloud types and are difficult to measure directly. Estimates rely on budgets rather than on direct observation.

Answer: D

The first two are correct and are the main losses. The third is far too optimistic, since a large fraction of the condensed water in many convective clouds never reaches the ground at all. Losses to evaporation and to shear are both substantial.