Abstract
Abstract
Highlights
Taylor’s statistical theory of turbulence states that the turbulence is isotropic if the average value of any function of the velocity components, defined in relation to a given set of axes, is unaltered under axis rotation (Taylor 1935)
In the quadrant analysis method applied to the atmospheric surface layer (ASL), the momentum or heat flux fractions and time fractions from each quadrant of u -w or T -w are reported over smooth and rough surfaces (McBean 1974; Antonia 1977; Narasimha et al 2007; Zou et al 2017)
We discuss the general effect of stability on the Reynolds stress anisotropy associated with the 30-min averaged flow in an unstable ASL
Summary
Taylor’s statistical theory of turbulence states that the turbulence is isotropic if the average value of any function of the velocity components, defined in relation to a given set of axes, is unaltered under axis rotation (Taylor 1935). It becomes apparent that in an unstable ASL, the vertical velocity fluctuations associated with the coherent heat flux events could transport large amount of momentum in intermittent bursts, either in upward or downward direction. Since only the anisotropic part of the velocity fluctuations can carry momentum (Dey et al 2018; Könözsy 2019), it indicates that the Reynolds stress anisotropy associated with these coherent heat flux events must be different from the averaged whole flow. To the best of our knowledge, very few studies have addressed this problem by adopting an event-based approach This is pertinent in the context of ASL turbulence, where there are no comprehensive studies to quantify anisotropy concomitant with the intermittent heat flux events in convective conditions.
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