Precipitation Formation Mechanisms Questions and Answers

Answer: A

The first two are correct and describe the standard approach. The third is wrong, since the radar measures a volume aloft and infers what reaches the ground indirectly. The beam samples aloft and may miss shallow precipitation.

Answer: B

Melting snowflakes are large and water coated but still falling slowly, so reflectivity peaks. The band is a reliable indicator of stratiform precipitation and is absent in convective cells. Its presence is used to classify the precipitation automatically.

Answer: C

Correct answer: 2 - 4 - 1 - 3

The sequence follows the temperature the particle passes through as it falls. It grows first by deposition of vapour in the cold cloud above, then aggregates with other crystals into a larger flake as it descends into warmer air where crystals stick more readily, then melts at the freezing level - producing the radar bright band - and finally arrives as a raindrop. Most mid-latitude rain has this history.

Answer: D

Vertical velocities of several metres per second support much larger particles. The mixing this produces prevents the sharp horizontal melting layer that gives the bright band. Vertical motion destroys the horizontal uniformity required.

Answer: A

Mesoscale convective systems typically have convective cells with a trailing stratiform area. Separating the two is a routine step in analysing such systems. The two regions contribute differently to the total rainfall.

Answer: B

Both are true and the reason gives the structure, and the stratiform region can cover several times the area of the cells. Both parts contribute substantially to the total rainfall. Neither part can be neglected in a rainfall budget.

Answer: C

The figure is the depth of water that would accumulate on a flat impermeable surface in an hour. It is independent of the area considered, which is what makes it a useful measure. The same rate over a larger area simply delivers more water.

Answer: D

Conventional thresholds place light rain below about two and a half millimetres per hour and heavy rain above about ten. Fifty is well beyond that and is associated with flash flood risk. Rates of this order overwhelm most urban drainage systems.

Answer: A

The thresholds are conventions rather than physical boundaries and vary slightly between services. They are used chiefly for the consistent reporting of observations and warnings. Consistency between stations matters more than exact boundaries.

Answer: B

Once the rate exceeds the infiltration capacity the excess runs off immediately. A given total falling slowly may cause no flooding at all while the same total in an hour is dangerous. Infiltration capacity is the quantity that actually matters.