Precipitation Formation Mechanisms Questions and Answers

Answer: C

The first two are correct and are the basis of flood warning. The third ignores the timing entirely, which is the single most important factor in a flash flood event. Antecedent conditions modify the threshold considerably.

Answer: D

Shallow maritime cumulus warmer than freezing throughout rain regularly. Satellite radar has shown that such clouds contribute a large share of tropical oceanic rainfall. Such clouds are far too shallow to reach the freezing level.

Answer: A

Both are true and the reason gives the observational gap, and shallow warm rain had been systematically underestimated. Space based measurement gave the first uniform coverage of the oceans. Gauges cannot be placed across the open ocean at all.

Answer: B

Correct answer: drizzle from a shallow maritime stratocumulus

Shallow maritime stratocumulus is warmer than freezing throughout, so its drizzle forms by collision and coalescence alone - the warm rain process. The other three all pass through the ice phase: rain that began as snow, snow that reached the ground unmelted, and hail grown by riming in a convective updraught.

Answer: C

Latent heat is absorbed from the air and water vapour is added to it. The cooling drives downdraughts and the moistening reduces the evaporation of subsequent rain. The layer therefore becomes progressively more favourable.

Answer: D

Earlier rain moistens the sub-cloud layer and reduces further evaporation. This is why the onset of surface rainfall can lag the onset of precipitation aloft considerably. Radar sees the rain long before any gauge records it.

Answer: A

Both are true and the reason gives the delay, and the lag is greatest when the layer is initially dry. Radar frequently shows precipitation aloft before any gauge responds. The lag is longest in a deep and initially dry layer.

Answer: B

Cooled dense air reaches the ground and spreads as a density current. Its leading edge, the gust front, frequently triggers new convection and so propagates the system. Cold pool dynamics govern how a squall line advances.

Answer: C

The first two are correct and describe how convection propagates. The third reverses the sign, since a cold pool is by definition cooler than the air it displaces. That density contrast is what makes it a current at all.

Answer: D

A high concentration of condensate adds appreciably to the density of the air. Together with evaporative cooling it drives the strongest downdraughts observed in convective storms. Loading and cooling reinforce one another directly.