Ice Nucleation and Ice Crystal Growth Questions and Answers

Answer: A

Both are true and the reason gives the vapour pressure difference driving the transfer. The droplets supply the vapour that the crystals consume, so the cloud glaciates over time. The transfer runs one way only, from liquid towards ice.

Answer: B

The two curves coincide at zero and converge again at very low temperatures. The maximum difference near minus twelve is where the Bergeron process transfers water most rapidly. This is also where dendritic crystals grow most readily.

Answer: C

Without liquid droplets there is no reservoir of vapour to transfer, and without ice there is nothing to grow. A fully glaciated cloud can no longer operate the process at all. Glaciation therefore extinguishes the very process that caused it.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: a mixed phase cloud contains both, and it is thermodynamically unstable for exactly the reason given by the Wegener–Bergeron–Findeisen process - the ice grows at the liquid’s expense. Statement 3 contradicts the second. Such clouds persist only where a continuing supply of liquid, usually from an updraught, replaces what the ice consumes, and once that supply fails the cloud glaciates.

Answer: A

Both are true and the reason gives the sustaining mechanism, and Arctic stratocumulus are the classic long lived example. Without that supply the cloud would glaciate within minutes. Persistent mixed phase cloud requires continual droplet formation.

Answer: B

Growth depends on the electrostatic capacitance of the shape, and a plate or dendrite exceeds a sphere considerably. The larger vapour excess over ice adds to the advantage. Both geometry and thermodynamics favour the crystal over the drop.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the justification. Steady-state vapour diffusion to a crystal obeys Laplace’s equation with a fixed value on the surface, which is exactly the electrostatic problem of a charged conductor, so the geometry enters through the electrical capacitance of that shape. It is why a branched dendrite grows faster than a compact crystal of the same mass: capacitance depends on shape, not merely on volume.

Answer: D

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

The habit changes with temperature in a sequence that reverses twice. Plates form near minus 2, needles near minus 5, dendrites near minus 15, and columns again below about minus 22, near minus 30. The alternation between plate-like and column-like growth arises from which crystal face grows faster at each temperature, and it means the shape of a snow crystal records the temperature it grew at.

Answer: A

Correct answer: minus 15 degrees Celsius

Around minus 15 the difference between the saturation vapour pressures over water and ice is near its maximum, so a crystal in a water-saturated cloud grows fastest there and does so along the branching, dendritic habit. That combination - rapid growth and a large capacitance from the branches - makes the dendritic growth zone the layer where most snow mass is produced.

Answer: B

Both are true and the reason gives the mechanism, and the rapid growth at that temperature produces the branched shapes. Aggregation efficiency depends strongly on habit as well as on temperature. Dendrites interlock in a way that compact crystals cannot.