The stationarity of sub-mesoscale turbulence in the stable planetary boundary layer

This talk presents results of an analysis of the stationarity of sub-mesoscale turbulence within the stable boundary layer. Turbulence kinetic energy, e, is calculated over integral time scales of about 100 s using 20 Hz measurements made at 1.5 m and 11 m above ground surface from 0100 h to 0600 h on 5 nights during the JORNADA field experiment. In horizontally homogeneous flow, we expect turbulence stationarity. Thus, we attribute variations of e to changes in the mean flow due to sub-mesoscale turbulence. The duration of stationarity is determined by how long consecutive values of e remain within a set limit. The overall average stationarity ranged from about 160 s to about 570 s. It is shown that at 1.5 m, which we take to be within the surface layer, the average duration of stationarity of e, tends to correlate with the kurtosis of the local heat flux; however, at 11 m, which we take to be outside of the surface layer, the correlation between e and the kurtosis of the local heat flux is poorly approximated. It is also shown that a consistent measure of nightly stability based on first order terms was not found.