Task: Class Definition Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes 'residual layer'?

A. For flow over a hill, the top layer in the boundary layer that accelerates relative to its upstream value due to the Bernoulli effect.
B. A layer of air tens of meters thick at the bottom of the atmosphere where the variation of vertical turbulent flux with altitude is less than 10% of its magnitude.
C. The middle portion of the nocturnal atmospheric boundary layer characterized by weak sporadic turbulence and initially uniformly mixed potential temperature and pollutants remaining from the mixed layer of the previous day.
D. A type of atmospheric boundary layer characterized by vigorous turbulence tending to stir and uniformly mix, primarily in the vertical, quantities such as conservative tracer concentrations, potential temperature, and momentum or wind speed.

Answer: The middle portion of the nocturnal atmospheric boundary layer characterized by weak sporadic turbulence and initially uniformly mixed potential temperature and pollutants remaining from the mixed layer of the previous day.