Conditions for Photospherically Driven Alfvenic Oscillations to Heat the Solar Chromosphere by Pedersen Current Dissipation

Abstract

A magnetohydrodynamic model that includes a complete electrical conductivity tensor is used to estimate conditions for photospherically driven, linear, non-plane Alfvenic oscillations extending from the photosphere to the lower corona to drive a chromospheric heating rate due to Pedersen current dissipation that is comparable to the net chromospheric net radiative loss of $\sim 10^7$ ergs-cm${}^{-2}$-sec${}^{-1}$. The heating rates due to electron current dissipation in the photosphere and corona are also computed. The wave amplitudes are computed self-consistently as functions of an inhomogeneous background (BG) atmosphere. The effects of the conductivity tensor are resolved numerically using a resolution of 3.33 m. The oscillations drive a chromospheric heating flux $F_{Ch}\sim 10^7-10^8$ ergs-cm${}^{-2}$-sec${}^{-1}$ at frequencies $\nu \sim 10^2-10^3$ mHz for BG magnetic field strengths $B\gtrsim 700$ G and magnetic field perturbation amplitudes $\sim 0.01-0.1$ $B$. The total resistive heating flux increases with $\nu$. Most heating occurs in the photosphere. Thermalization of Poynting flux in the photosphere due to electron current dissipation regulates the Poynting flux into the chromosphere, limiting $F_{Ch}$. $F_{Ch}$ initially increases with $\nu$, reaches a maximum, and then decreases with increasing $\nu$ due to increasing electron current dissipation in the photosphere. The resolution needed to resolve the oscillations increases from $\sim 10$ m in the photosphere to $\sim 10$ km in the upper chromosphere, and is proportional to ${\nu }^{-1/2}$. Estimates suggest that these oscillations are normal modes of photospheric flux tubes with diameters $\sim 10-20$ km, excited by magnetic reconnection in current sheets with thicknesses $\sim 0.1$ km.

55 pages, 19 figures

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• Multi-fluid approach to high-frequency waves in plasmas: I. Small-amplitude regime in fully ionized medium
• Some glimpses from helioseismology at the dynamics of the deep solar interior