Abstract
The availability of 5-year time series of velocity and temperature data from two sonic anemometers installed at Jang Bogo Station, Antarctica, allowed a systematic investigation of the turbulence features in a stable layer affected by submeso motions and characterized by the vertical divergence of some second-order moments for a large fraction of time (quite a non-ideal surface layer). The investigation of the effect of the averaging time interval on the statistics of the second-order moments showed that this is greater for the variances of the velocity components with respect to that for the vertical fluxes. This corresponds to a greater contribution from low-frequency motions. The turbulence statistics were investigated and compared with current literature results in terms of vertical structure, share of energy between horizontal and vertical components, skewness of the vertical velocity and turbulent velocities. As a general result, all the normalized second-order moments show a clear change passing from neutral to stable conditions, passing through the range of bulk Richardson number equal to 0.1–1.
Highlights
The stable boundary layers call for a number of exceptions in the application of the Monin–Obukhov similarity theory (MOST)
Grachev et al [2] noted that beyond a critical value of the gradient Richardson number, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out, and that this is a limit in the application of MOST
Sun et al [3,4,5] formulated the so-called hockey-stick transition (HOST) paradigm, suggesting that Equations (5) and (8) approximately hold for wind velocity less than a threshold VS, above which the turbulence scale velocities are a function of the local wind velocity, i.e., of the velocity bulk gradient U(z)/z: see for instance Sun et al [5], Equations 4 and 5)
Summary
The stable boundary layers call for a number of exceptions in the application of the Monin–Obukhov similarity theory (MOST) This is based on the hypothesis of the driving effect of vertical fluxes of momentum and heat, and of the empirical validity of the flux–gradient relationship. The share of the turbulent kinetic energy among vertical and horizontal components (or the ratio between the vertical and horizontal velocity variances) at the inertial scales changes with respect to the typical values in shear-dominated turbulence, the horizontal components being dominant with respect to the vertical one This topic is widely discussed for instance by Zilitinkevich et al [6] (Figures 4–6) and by Cheng et al [7] Comparing the results obtained using different averaging times, the influence of low-frequency (submeso) on the statistics was investigated
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