Growth by Collision and Coalescence Questions and Answers

Answer: C

The first two are correct and describe the two families of scheme. The third reverses their relationship, since bulk schemes deliberately sacrifice spectral detail for computational economy. The choice is a trade between fidelity and cost.

Answer: D

Both are true and the reason gives the cost, and the collection integral must be evaluated between every pair of bins. Bulk schemes remain the practical choice for large scale models. Bin schemes are reserved for process studies at small scale.

Answer: A

The sequence runs from least to most detailed and from cheapest to most expensive. Two moment schemes are the common compromise because they allow droplet number to respond to aerosol. Without that variable the indirect effects cannot appear.

Answer: B

Aerosol acts through droplet number, which a one moment scheme does not carry as a variable. Without it the scheme cannot represent the indirect effects at all. Droplet number is the variable through which aerosol acts.

Answer: C

Dividing the mass among the droplets gives a volume per droplet of about ten picolitres, and the corresponding radius is near thirteen micrometres. The figure is typical of maritime cumulus at middle levels. Continental clouds of the same water content hold smaller drops.

Answer: D

Both are true and the reason gives the cube root dependence, and a factor of eight in water content changes the radius by only two. Droplet number is much the more powerful influence on size. This is why aerosol changes droplet size so effectively.

Answer: A

It is a crude representation of the requirement that some droplets reach collector size. Modern formulations replace the sharp threshold with a smooth dependence on droplet number and water content. The smooth forms behave far better in a numerical model.

Answer: B

It is among the least constrained parameterisations in cloud modelling. Model intercomparisons regularly attribute a large part of their spread in precipitation to this one term. It remains among the least constrained parameterisations in use.

Answer: C

Correct answer: a high concentration of small aerosol particles

More nuclei means the available water is divided among more droplets, so every droplet is smaller, the spectrum is narrower and collection is slower. That is the microphysical basis of the aerosol effect on precipitation. The other three all broaden the spectrum or increase the collision rate.

Answer: D

Numerous small droplets fall at nearly equal speeds and collect inefficiently. Such clouds frequently precipitate only after glaciating, by the ice phase rather than the warm rain process. Depth and glaciation substitute for microphysical efficiency.