Intermittency of near‐bottom turbulence in tidal flow on a shallow shelf

The higher‐order structure functions of vertical velocity fluctuations (transverse structure functions (TSF)) were employed to study the characteristics of turbulence intermittency in a reversing tidal flow on a 19 m deep shallow shelf of the East China Sea. Measurements from a downward‐looking, bottom‐mounted Acoustic Doppler Velocimeter, positioned 0.45 m above the seafloor, which spanned two semidiurnal tidal cycles, were analyzed. A classical lognormal single‐parameter ( μ ) model for intermittency and the universal multifractal approach (specifically, the two‐parameter ( C 1 and α ) log‐Levy model) were employed to analyze the TSF exponent ξ ( q ) in tidally driven turbulent boundary layer and to estimate μ , C 1 , and α . During the energetic flooding tidal phases, the parameters of intermittency models approached the mean values of ≈ 0.24, 1 ≈ 0.15, and ≈ 1.5, which are accepted as the universal values for fully developed turbulence at high Reynolds numbers. With the decrease of advection velocity, μ and C 1 increased up to μ ≈ 0.5–0.6 and C 1 ≈ 0.25–0.35, but α decreased to about 1.4. The results explain the reported disparities between the smaller “universal” values of intermittency parameters μ and C 1 (mostly measured in laboratory and atmospheric high Reynolds number flows) and those ( μ = 0.4–0.5) reported for oceanic stratified turbulence in the pycnocline, which is associated with relatively low local Reynolds numbers R λw . The scaling exponents ξ (2) of the second‐order TSF, relative to the third‐order structure function, was also found to be a decreasing function of R λw , approaching the classical value of 2/3 only at very high R λw . A larger departure from the universal turbulent regime at lower Reynolds numbers could be attributed to the higher anisotropy and associated intermittency of underdeveloped turbulence.