The power spectrum of the evolving solar wind shows evidence of a spectral break between an inertial range of turbulent fluctuations at higher frequencies and a “ 1 / f ” like region at lower frequencies .
In the ecliptic plane at \sim 1 AU , this break occurs approximately at timescales of a few hours , and is observed in the power spectra of components of velocity and magnetic field .
The “ 1 / f ” energy range is of more direct coronal origin than the inertial range , and carries signatures of the complex magnetic field structure of the solar corona , and of footpoint stirring in the solar photosphere .
To quantify the scaling properties we use generic statistical methods such as generalised structure functions and PDFs , focusing on solar cycle dependence and on anisotropy with respect to the background magnetic field .
We present structure function analysis of magnetic and velocity field fluctuations , using a novel technique to decompose the fluctuations into directions parallel and perpendicular to the mean local background magnetic field .
Whilst the magnetic field is close to “ 1 / f ” , we show that the velocity field is “ 1 / f ^ { \alpha } ” with \alpha \neq 1 .
For the velocity , the value of \alpha varies between parallel and perpendicular fluctuations and with the solar cycle .
There is also variation in \alpha with solar wind speed .
We have examined the PDFs in the fast , quiet solar wind and intriguingly , whilst parallel and perpendicular are distinct , both the B field and velocity show the same PDF of their perpendicular flucutations , which is close to gamma or inverse Gumbel .
These results point to distinct physical processes in the corona , and to their mapping out into the solar wind .
The scaling exponents obtained constrain the models for these processes .