We study various time series of surface-layer wind velocity at different locations and provide evidences for the intermittent nature of the wind fluctuations in mesoscale to large-scale range. By means of the magnitude covariance analysis, which is shown to be a more efficient tool to study intermittency than classical scaling analysis, we find that all wind series exhibit similar features than those observed for laboratory turbulence. Our findings suggest the existence of a "universal" cascade mechanism associated with the energy transfer between synoptic motions and turbulent microscales in the atmospheric boundary layer.

In this paper we revisit an idea originally proposed by Mandelbrot about the possibility to observe "negative dimensions" in random multifractals. For that purpose, we define a new way to study scaling where the observation scale τ and the total sample length L are respectively going to zero and to infinity. This "mixed" asymptotic regime is parametrized by an exponent χ that corresponds to Mandelbrot "supersampling exponent". In order to study the scaling exponents in the mixed regime, we use a formalism introduced in the context of the physics of disordered systems relying upon traveling wave solutions of some non-linear iteration equation. Within our approach, we show that for random multiplicative cascade models, the parameter χ can be interpreted as a negative dimension and, as anticipated by Mandelbrot, allows one to uncover the "hidden" negative part of the singularity spectrum, corresponding to "latent" singularities. We illustrate our purpose on synthetic cascade models. When applied to turbulence data, this formalism allows us to distinguish two popular phenomenological models of dissipation intermittency: We show that the mixed scaling exponents agree with a log-normal model and not with log-Poisson statistics.

We study various hourly surface layer wind series recorded at different sites in the Netherlands by the "Royal Netherlands Meteorological Institute." By reporting all velocity magnitude correlation coefficients, associated with the available couples of locations, as a function of their spatial distance, we find that they fall on a single curve. This curve turns out to be remarkably well described by a logarithmic shape, characteristic of continuous cascades with an intermittency coefficient λ2 ≃ 0.04 and an integral scale L ≃ 600 km. Along the same line, we study the scaling properties of spatial velocity increment structure functions. This allows one to estimate the ζ(q) spectrum and to confirm an intermittent nature of mesoscale fluctuations similar to the one observed in fully developed turbulence.