Large-scale lognormal fluctuations in turbulence velocity fields

Reconstruction of large-scale peculiar velocity fields

A reconstruction method for recovering the initial conditions of the Universe starting from the present galaxy distribution is presented which guarantees uniqueness of solutions. We show how our method can be used to obtain the peculiar velocities of a large number of galaxies, hence trace galaxies orbits back in time and obtain the entire past dynamical history of the Universe above scales whe...

Velocity fluctuations in forced Burgers turbulence.

We propose a simple method to compute the velocity difference statistics in forced Burgers turbulence in any dimension. Within a reasonnable assumption concerning the nucleation and coalescence of shocks, we find in particular that the ‘left’ tail of the distribution decays as an inverse square power, which is compatible with numerical data. Our results are compared to those of various recent a...

Large-scale velocity fluctuations in polar solar wind

The 3-D structure of the solar wind varies dramatically along the Sun’s activity cycle. In the present paper we focus on some properties of the polar solar wind. This is a fast, teneous, and steady flow (as compared to low-latitude conditions) that fills the high-latitude heliosphere at low solar activity. The polar wind has been extensively investigated by Ulysses, the first spacecraft to perf...

Scale-dependent angle of alignment between velocity and magnetic field fluctuations in solar wind turbulence

Large negative velocity gradients in Burgers turbulence.

We consider one-dimensional Burgers equation driven by large-scale white-in-time random force. The tails of the velocity gradients probability distribution function (PDF) are analyzed by saddle point approximation in the path integral describing the velocity statistics. The structure of the saddle-point (instanton), that is, the velocity field configuration realizing the maximum of probability,...