Ice Nucleation and Ice Crystal Growth Questions and Answers

Answer: C

The particle melts in a warm layer aloft and then supercools without refreezing in the shallow cold layer below. It freezes on impact with the ground, which is what makes it so hazardous. Accretion on roads, wires and aircraft follows almost immediately.

Answer: D

The distinction between freezing rain and ice pellets is the depth of the cold layer at the surface. A deep cold layer allows the drop to refreeze in the air rather than on contact. Forecasting the two apart is a matter of a few hundred metres.

Answer: A

Both are true and the reason gives the distinction, and forecasting which will occur turns on that depth. Small errors in the profile change the predicted precipitation type entirely. Winter forecasting turns on resolving these shallow layers.

Answer: B

Correct answer: the zero degree isotherm

Melting begins where the temperature reaches zero, so the melting level follows that isotherm. In practice the layer sits a little below it, because melting absorbs latent heat and a falling particle takes time to melt through, which is why the radar bright band appears just beneath the freezing level rather than at it.

Answer: C

Melting absorbs latent heat and takes time, so a flake can survive a shallow warm layer. Cooling of the air by the melting itself also helps the snow survive. Wet bulb temperature is a better predictor than dry bulb here.

Answer: D

The distance depends on the flake size, the humidity and the lapse rate below. Larger aggregates survive furthest because they carry more mass relative to their surface. Humidity below the melting level matters as much as temperature.

Answer: A

Deposition is the direct vapour to solid transition and its reverse is sublimation. It is the primary growth mechanism for crystals in the upper parts of mixed phase clouds. Riming takes over where supercooled liquid becomes abundant.

Answer: B

Sublimation removes mass from a crystal rather than adding it. The other three are the three standard growth routes for an ice particle in a cloud. Each dominates in a different part of the cloud. Deposition works highest and riming lowest in the column.

Answer: C

The first two are correct and reflect the availability of liquid water. The third is wrong, since aggregation is most effective near the melting level rather than at the coldest levels. Surface stickiness rather than temperature alone governs it.

Answer: D

It is a purely geometric quantity taken from the analogous electrostatic problem. A dendrite has a much larger capacitance than a compact crystal of the same mass, which is why habit matters to growth rate. Two crystals of equal mass may grow at quite different rates.