Conditional Sampling of Turbulence in the Atmospheric Surface Layer

Abstract

Conditional sampling and averaging techniques are used to obtain statistics of convectively-driven quasi-ordered structures at a height of 4 m within the atmospheric surface layer. The fraction of time 'y occupiedby these structures, and their frequency of occurrence I can depend on detection criteria parameters, suchas the threshold and hold time. The effect of these parameters on 'y and f is investigated for two conditionalsampling techniques. Both techniques indicate that y decreases continuously with increasing threshold,whereas there is a region in which I is independent of both parameters. When the parameters are suitablyselected, reasonable agreement for both 'y and f can be obtained between the techniques. This agreementdoes not depend on whether the velocity or the temperature fluctuation is used as the basis of detection forone of the techniques.