Electric Fields, Currents, and Magnetic Fluctuations of the Photosphere and Solar Wind

Abstract:

In the (collisional) solar interior, the heat flux necessarily generates a radial electric field, integrating to a surface field eE_th(R_s)≅1.4eV/Mm, comparable to the proton weight m_pg = 2.8eV/Mm. In the (less collisional) plasma "sheath" of the photosphere and heliosphere, the outward photon flux Γ_γ = 60.MW/m² causes additional electron displacement, giving eE_γ(r) = σ_γe Γ_γ /c. Here, the main uncertainty is the photon cross-section σ_γe for electrons correlated with protons: H-minus and "rydberg" hydrogen states have σ_γe ≅ 0.5x10^-20m², whereas isolated electrons have Thompson cross-section σ_γe ≅ 0.7x10^-28m². A 1D-radial average cross-section σ_γe ≅ 3x10^-24m² will generate the observed solar wind, as "collisional runaway" protons accelerate out of the 2.keV gravity well and up to 1.3 keV kinetic energy within several R_s. This coherent proton/electron flow will glow as the K-Corona, obviating the traditional T=100eV hydrostatic models.

Analyzing spacecraft magnetic data from this perspective provides three insights into the fluctuating wind currents. 1) Variable-duration spectral analyses clearly show that there is no persistent magnetic "spiral" at 1AU, merely the integrated fluctuations of local currents. Similarly, spectral components B(f) above f~50.mHz clearly show the √N scaling of random noise.

2) Pervasive dynamical "arc" events are observed on time-scales 10^3< t < 10^5 sec, presumably related to spiky "switchbacks" observed by PSP at 0.1AU. The dynamics appears as Bθ-Bz, Br-Bz, and Br-Bθ temporal arcs, with occurrence rates differing by direction. The observed dynamics is closely modelled by finite-duration "pinched" +/- current filaments, representing fractional charge non-neutrality of 10^-5 over distances d~10^3Mm and times t~2000s.

3) The Br and Bθ (but not Bz) spectral components at the solar rotation frequency f_rot are quite exceptional, varying between 0% and 30% (average 17%) of the total Brms^2 magnetic energy. In only these variable components (with differing radial dependencies) is there a Br-Bθ anti-correlation, which is traditionally mis-interpreted as a persistent spiral. These f_rot components probably reflect variable z-currents, driven by θ- and z-dependent electric potentials from exceedingly small differences in e-/p+ ejection from the rotating solar surface.