Precipitation Formation Mechanisms Questions and Answers

Answer: A

Condensation warms the air and drives updraughts rather than downdraughts. The other three each make the descending air denser than its surroundings. Density contrast is what drives any downdraught. Buoyancy works the same way downward as it does upward.

Answer: B

Rainbands are prominent in frontal systems and in tropical cyclones alike. Their organisation reflects the dynamics of the parent system rather than the microphysics within them. The same microphysics operates in bands of very different origin.

Answer: C

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

Each system’s precipitation reflects how steeply it lifts the air. A warm front has a gentle slope, so it lifts a deep layer slowly over a wide area and gives widespread stratiform rain ahead of it. A cold front lifts abruptly, giving a narrow band of convective showers along the boundary. A tropical cyclone organises its convection into spiral rainbands around the eye, and a sea breeze front produces a line of shallow convection where it penetrates inland.

Answer: D

Both are true and the reason gives the geometry, and the shallow frontal slope places the cloud far in advance. Rain can begin many hours before the front itself arrives. The frontal surface slopes at roughly one in a hundred.

Answer: A

The warm tropical atmosphere places the zero degree isotherm well above the boundary layer. Much of the precipitation in such systems nevertheless involves the ice phase above that level. Eyewall convection extends far above the freezing level.

Answer: B

Deep convection in the eyewall extends far above the freezing level and glaciates. Both routes operate, with the shallower rainbands contributing warm rain specifically. The two routes operate at different heights simultaneously.

Answer: C

Snowflake density and shape vary far more than raindrop shape does. The resulting spread in the reflectivity relationship makes quantitative snowfall estimation notably less reliable. Errors of a factor of two are not unusual for snow.

Answer: D

Both are true and the reason gives the difficulty, and horizontal drift of the slowly falling snow adds a further error. Both effects are absent or much smaller for rain. Rainfall estimation is correspondingly better constrained.

Answer: A

Drop oblateness is a property of rain and is in fact exploited to improve rainfall estimates. The other three are all genuine difficulties specific to snow. Snow measurement lags rain measurement in accuracy considerably.

Answer: B

Fog droplets intercepted by leaves and needles can supply a substantial input in cloud forests. It is not recorded by a conventional gauge, which is why the name refers to something hidden. Cloud forests may receive much of their water in this way.