Turbulence in the nocturnal boundary layer: highly-structured, strongly-variable, but ubiquitous

We report the results of the analysis of some 100 hours of fine-scale in situ measurements of the turbulence dissipation rate (epsilon) obtained from the surface through the top of the nocturnal boundary layer (NBL), during five separate nights. The results show: (1) that turbulence is always and everywhere present, (2) intense variations in epsilon over a few seconds and/or a few meters vertically, and (3) that intensities can range over more than five orders of magnitude, from 10-7 to 10-2 m2 sec-3. Typically, the weaker epsilon values are not measurable by conventional techniques. Our analysis examines the characteristics of epsilon both in the stable boundary layer (SBL) as well as in the overlying residual layer (RL) that separates the stable boundary layer from the free atmosphere.