Ice Nucleation and Ice Crystal Growth Questions and Answers

Answer: C

Correct answer: dust deposition on aircraft windscreens

Dust deposition has nothing to do with the liquid phase and would occur just as readily in clear dry air. The other three are all direct consequences of supercooled water freezing on contact with a surface: freezing rain loading power lines and trees, rime accreting on masts and towers, and airframe icing, which remains one of the more serious hazards in flight.

Answer: D

Large droplets carry more mass and impinge further back along the wing before freezing. Freezing drizzle sized droplets are recognised as a particularly dangerous condition. Runback ice forms behind the protected leading edge surfaces.

Answer: A

Both are true and the reason gives the danger, and de-icing systems protect only the forward surfaces. Ice forming behind them disrupts the airflow where nothing can remove it. Certification standards now address these larger droplet sizes.

Answer: B

Correct answer: has been heavily rimed by supercooled droplets

Graupel is a crystal or aggregate that has collected so many frozen supercooled droplets that the original crystal is no longer recognisable, giving a soft, opaque, roughly conical pellet. A snowflake has grown by deposition and by aggregation with other crystals and retains its open, low-density structure. Both form above the freezing level, so it is the riming, not the altitude, that separates them.

Answer: C

The first two are correct and follow from the process. The third is contradictory, since a glaciated region contains no supercooled droplets for the particle to accrete. Riming ceases as soon as the cloud has fully glaciated.

Answer: D

The vapour pressure difference gives them a growth advantage no droplet has. Combined with riming and aggregation, this carries them to precipitation size far faster than coalescence alone would. This is why most mid-latitude precipitation takes the ice route.

Answer: A

A lower fall speed delays removal but is not a growth advantage. The other three each let an ice particle gain mass faster than a droplet can. Fall speed governs removal rather than growth. A slow particle simply stays in the cloud for longer.

Answer: B

The process is accretion (riming).

When an ice crystal falls through a cloud of supercooled droplets, the droplets it hits freeze on contact and stick to it. This growth by accretion produces rime and, carried far enough, graupel and hail.

The Bergeron process is growth of ice crystals by vapour diffusion at the expense of droplets, without collisions. Coalescence is the merging of liquid drops, not freezing on ice, and nucleation is the initial formation of a droplet or crystal.