Vertical variations of mixing lengths under neutral and stable conditions during CASES99

By comparing κz with the mixing lengths under neutral conditions calculated using the observations from CASES99, the vertical layer where Monin-Obukhov similarity theory (MOST) is was identified.

Here κ is the von Kármán constant and z is the height above the ground. On average, MOST is approximately valid between 0.5 m and 10 m. Above the layer, the observed mixing lengths under neutral conditions are smaller than the MOST κz and can be approximately described by Blackadar's mixing length, κz/(1+ κz/l∞), with l∞ = 15 m for up to z ~ 20 m for the mixing length for momentum, and up to the highest observation height for the mixing length for heat.