Precipitation Formation Mechanisms Questions and Answers

Answer: A

The sixth power dependence means the largest drops dominate the return entirely. This is the root of the difficulty in converting reflectivity into a rainfall rate reliably. A single large drop can outweigh thousands of small ones.

Answer: B

It is an empirical power law whose coefficients depend on the precipitation type. Using an inappropriate pair of coefficients can produce errors of a factor of two or more in the estimated rainfall. Operational radars therefore switch coefficients by echo type.

Answer: C

The first two are correct and reflect operational practice. The third is not so, and misclassifying the echo type is among the larger sources of error in radar rainfall estimates. Classification algorithms run continuously for this reason.

Answer: D

Correct answer: revealing the shape and hence the size of the drops

A dual polarisation radar transmits and receives in both horizontal and vertical planes, and because a falling drop flattens in proportion to its size, the difference between the two returns reports the drop shape. That gives the size distribution the reflectivity alone cannot, so the rain rate can be estimated without assuming a single relationship, and hail, snow and melting particles can be told apart.

Answer: A

Both are true and the reason gives the physics, and small drops remain nearly spherical. The differential reflectivity therefore reports the characteristic drop size in the sampled volume. This is the principal advantage of dual polarisation.

Answer: B

Correct answer: False

The teardrop shape is an artistic convention with no basis in the physics. A small drop is held spherical by surface tension; a larger one is flattened on its underside by the air pressing on it as it falls, giving a shape like a hamburger bun with a rounded top and a flat or slightly dimpled base. Beyond about 5 mm the distortion grows until the drop breaks apart, which is what limits raindrop size.

Answer: C

Correct answer: a dust particle raised by the wind

A hydrometeor is a particle of condensed water in the atmosphere - a drop, a crystal, a flake, a hailstone. Blown dust is a lithometeor, a particle of solid matter that is not water. The distinction matters in radar work, since dust, insects and chaff all return a signal and must be recognised as non-meteorological echo.

Answer: D

The four are distinguished by the temperature profile and by the updraught the particle grew in. Correctly forecasting which will occur is among the harder problems in winter weather. A few hundred metres of profile decides between them.

Answer: A

Wet growth traps water that freezes slowly and clearly, while dry growth traps air and appears opaque. Sectioning a stone therefore reveals something of its history within the storm. The layering is a record of the trajectory it followed.

Answer: B

Both are true and the reason gives the origin of the banding, and it records the trajectory the stone followed. Counting the layers does not, however, count the number of circuits reliably. Modern trajectory modelling has complicated the older reading.