Late-Morning Jump in TKE in the Mixed Layer over a Mountain Basin

Abstract

The turbulence or “gustiness” of the winds new the surface in a mountain valley increases sharply after the nocturnal inversion layer dissipates, normally in the late morning or early afternoon. This increase—almost all in the horizontal wind components-results from an increase in the mixed-layer velocity scaling parameter w_*. The increase in w_*, in turn, results mostly from the rapid increase in the mixed-layer inversion height z_i which occurs as the nocturnal inversion layer dissolves. The consistency between the turbulent energy jump and the increase in w_* agrees with findings over flatter terrain. It suggests that at least some of the thermal eddies in the mountain mixed layer are transient, i.e., advected by the mean wind and not permanently attached to terrain features.