Submesoscale (1–200km) wavenumber spectra of kinetic and potential energy and tracer variance are obtained from in situ observations in theGulf Stream region and in the eastern subtropical North Pacific. In the Gulf Stream region, steep kinetic energy spectra at scales between 200 and 20km are consistent with predictions of interior quasigeostrophic–turbulence theory, both in the mixed layer an...

Predicting how much mixing occurs when a given amount of energy is injected into a Boussinesq fluid is a longstanding problem in stratified turbulence. Here we address this problem with the point of view of equilibrium statistical mechanics. Assuming random evolution through turbulent stirring, the theory predicts that the unforced, inviscid, adiabatic dynamics is attracted irreversibly towards...

where kd is Kolmogorov dissipation wave number, α1 and α2 are some constants and 1 ≤ n ≤ 2 (see, e.g., [1] and references therein). In the case of plasma turbulence existence of various kinetic mechanisms of dissipation makes the situation much more complicated. For instance, observations of the solar wind turbulence [10, 11, 12] strongly suggest steep power law spectrum of the magnetic field f...

Flaring release of magnetic energy in solar corona is only possible if the magnetic field deviates from a potential one. We show that the linear magnetohydrodynamic (MHD) modes excited on top of the non-potential magnetic field possess a non-zero kinetic helicity. Accordingly, this necessarily results in a noticeable kinetic helicity of the turbulence, composed of these linear modes with variou...

Turbulence is ubiquitous in the solar wind. Turbulence causes kinetic and magnetic energy to cascade to small scales where they are eventually dissipated, adding heat to the plasma. The details of how this occurs are not well understood. This article reviews the evidence for turbulent dissipation and examines various diagnostics for identifying solar wind regions where dissipation is occurring....

Decay in time of undriven weakly collisional kinetic plasma turbulence in systems large compared to the ion kinetic scales is investigated using fully electromagnetic particle-in-cell simulations initiated with transverse flow and magnetic disturbances, constant density, and a strong guide field. The observed energy decay is consistent with the von Kármán hypothesis of similarity decay, in a fo...

The equilibrium structure of homogeneous turbulent shear flow is investigated from a theoretical standpoint. Existing turbulence models, in apparent agreement with physical and numerical experiments, predict an unbounded exponential time growth of the turbulent kinetic energy and dissipation rate; only the anisotropy tensor and turbulent time scale reach a structural equilibrium. It is shown th...

WeakMHD turbulence consists of waves that propagate along magnetic field lines, in both directions. When two oppositely directed waves collide, they distort each other, without changing their respective energies. Each wave suffers many collisions before cascading; by contrast, in strong MHD turbulence, waves cascade on the same timescale at which they collide. ‘‘ Imbalance ’’ means that more en...