Adiabatic Processes and Lapse Rates Questions and Answers

Answer: A

The roughness length is the height at which the extrapolated logarithmic profile reaches zero wind, ranging from a fraction of a millimetre over calm water to a metre over forest. The displacement height is a companion parameter needed over tall canopies, which makes it a reasonable alternative. Albedo and Bowen ratio describe radiative and energetic rather than aerodynamic properties. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: B

Calm water is aerodynamically very smooth, but the roughness length increases with wind speed as waves develop, which is the Charnock relation. This dependence on the wind itself makes the ocean surface unusual, since over land the roughness is fixed by the terrain and vegetation. It matters greatly for the drag coefficient in strong winds.

Answer: C

The bulk aerodynamic formula writes the stress as the density times a drag coefficient times the square of the wind speed at a reference height, usually ten metres. The drag coefficient depends on roughness and on stability, and over the ocean it depends on the wind speed itself because the waves grow with it. Squaring the wind means that a doubling of the speed quadruples the stress, which is why storm surges and wave heights respond so sharply to increases in wind.

Answer: D

Measurements in hurricanes show the drag coefficient saturating and even declining above about 33 metres per second, probably because sea spray and foam smooth the effective surface. This was an unexpected finding with important consequences for hurricane intensity prediction. Without it, models would predict weaker storms than are observed.

Answer: A

Reduced drag at extreme wind speeds means less frictional dissipation, so the ratio of enthalpy input to momentum loss rises and the maximum potential intensity increases. Emanuel's theory of maximum potential intensity depends explicitly on this ratio. The discovery reconciled theoretical intensity limits with the strongest storms actually observed.

Answer: B

The theory treats the storm as a Carnot engine drawing enthalpy from the warm ocean and rejecting heat at the cold outflow temperature, with the intensity set by the exchange coefficients and the air sea disequilibrium. Shear and rotation determine whether a storm can organise but not its thermodynamic ceiling. The theory gives an upper bound that few storms actually attain. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: C

Shear tilts and ventilates the storm, importing low entropy air into the core and preventing the warm core structure from being maintained. Most storms fall well short of their potential intensity for this reason. The other factors listed are genuine requirements for genesis rather than constraints on the intensity of an existing storm.

Answer: D

Evaporation from the warm ocean supplies the latent heat that drives the storm, and the enthalpy flux increases with wind speed, which is the positive feedback that allows intensification. The cold outflow at the tropopause is where heat is rejected, completing the cycle. Mid-level dry air is an obstacle rather than a source, and stratospheric penetration is incidental. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

The enthalpy flux from the ocean increases with wind speed, so a strengthening storm draws more energy from the surface and strengthens further, which is the WISHE feedback. Ocean cooling by mixing does act as a brake and is why slow moving storms weaken over their own cold wake. Frictional dissipation is a loss rather than a gain despite warming the air. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: B

Strong winds mix cold water up from beneath the thermocline, cooling the surface by several kelvin and reducing the enthalpy flux, and a slow moving storm sits over its own cold wake. Deep warm layers and warm core eddies suppress this effect and are associated with rapid intensification. Salinity matters through its effect on mixing but is a secondary influence. Framing the question as which quantity the change acts upon makes the answer follow without calculation.