Power spectra of solar network and non-network fields

Abstract

We report new properties of solar magnetic fields in a quiet region as found from their magnetic power spectra. The power spectra of network and intranetwork fields (non-network fields) are separately calculated from a Big Bear magnetogram obtained with moderately high spatial resolution of 1.5 arc sec and a high sensitivity reaching 2 Mx cm⁻². The effect of seeing on the power spectrum has been corrected using Fried's (1966) Modulation Transfer Function with the seeing parameter determined in our previous analysis of the magnetogram. As a result, it is found that the two-dimensional power spectra of network and non-network fields appear in a form: Γ(k₀ ≲ k ≲ k₁) ∼ k⁻¹ and Γ(k ≳ k₁) ∼ k^(3.5). Here k₀ ≈ 0.47 Mm⁻¹ for network fields and k₀ ≈ 0.69 Mm⁻¹ for non-network fields, the latter of which corresponds to the size of mesogranulation; k₁ ≈ 3.0 Mm⁻¹ for both, which is about the size of a large granule. The network field spectrum below k₀ appears nearly flat, whereas that of non-network fields instead decreases towards lower wave numbers as Γ(k) ∼ k^(1.3). The turnover behavior of magnetic field spectra around k₁ coincides with that found for the velocity power spectrum, which may justify the kinetic approach taken in previous theoretical studies of the solar magnetic power spectra.