Dynamically relevant alignments are used in order to show that regions with weak vorticity are not structureless, non-Gaussian and dynamically not passive. For example, the structure of vorticity in quasi-homogeneous/isotropic turbulent flows is associated with strong alignment between vorticity to and the eigenvectors of the rate of strain tensor 2i (especially -but not only -between to and 22) rather than with intense vorticity only. Consequently, much larger regions of turbulent flow than just those with intense vorticity are spatially structured. The whole flow field -even with the weakest measurable enstrophy is strongly non-Gaussian, which among other things is manifested in strong alignment between vorticity and the vortex stretching vector Wi-tojsij. It is shown that the quasi-two-dimensional regions corresponding to large cos(to, 22) are qualitatively different from purely two-dimensional ones, e.g. in that they possess essentially nonvanishing enstrophy generation, which is larger than its mean for the whole field. * Corresponding author. 1A brief presentation of some results of this paper was published in Tsinober et al. (1995b).

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Regions with large fluctuations of energy, rate of energy dissipation, enstrophy and enstrophy generation have been studied experimentally and theoretically. The main objects of this study are the moments of these quantities in turbulent grid flow, circular jet and boundary layer Dracos 1992, Kit, Tsinober, andDracos 1993). Some quantitative aspects of the experimental results are explained by introducing the idea of 'local cascades' of helicity, helicity generation and angular momentum.

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