Fluctuations of Turbulent Magnetic Field

The degree of linear polarization has recently been found to show wide random variations over the solar disk. These variations are presumably at least partly due to fluctuations in the flux density of turbulent photospheric magnetic fields and associated variations in the degree of Hanle depolarization. In order to understand the origin of such large scale fluctuations of the turbulent magnetic flux density we develop a phenomenological model to calculate the spatial Fourier spectrum of the fluctuations of turbulent magnetic fields in the solar photosphere and convective zone. It is found that if the model parameters are fitted to turbulence closure models and numerical experiments the characteristic scale of the fluctuations is by about an order of magnitude larger than the turbulence scale (the scale of the granulation), owing to the more effective quenching of small-scale fluctuations by turbulent diffusion.