The Photospheric Poynting Flux and Coronal Heating

Abstract

Some models of coronal heating suppose that convective motions at the photosphere shuffle the footpoints of coronal magnetic fields and thereby inject sufficient magnetic energy upward to account for observed coronal and chromospheric energy losses in active regions. Using high-resolution observations of plage magnetic fields made with the Solar Optical Telescope aboard the Hinode satellite, we investigate this idea by estimating the upward transport of magnetic energy --- the vertical Poynting flux, S_z --- across the photosphere in a plage region. To do so, we combine: (i) estimates of photospheric horizontal velocities, v_h, determined by local correlation tracking applied to a sequence of line-of-sight magnetic field maps from the Narrowband Filter Imager, with (ii) a vector magnetic field measurement from the SpectroPolarimeter. Plage fields are ideal observational targets for estimating energy injection by convection, because they are: (i) strong enough to be measured with relatively small uncertainties; (ii) not so strong that convection is heavily suppressed (as within umbrae); and (iii) unipolar, so S_z in plage is not influenced by mixed-polarity processes (e.g., flux emergence) unrelated to heating in stable, active-region fields. In this plage region, we found that the average S_z varied in space, but was positive (upward) and sufficient to explain coronal heating, with values near (5 +/- 1) x 10^7 erg/cm^2/s. We find the energy input per unit magnetic flux to be on the order of 10^5 erg/s/Mx. A comparison of intensity in a Ca II image co-registered with the this plage shows stronger spatial correlations with both total field, B, and unsigned vertical field, |B_z|, than either S_z or horizontal field, B_h. The observed Ca II brightness enhancement, however, probably contains a strong contribution from a near-photosphere hot-wall effect unrelated to atmospheric heating.

30 pages, 11 figures, accepted by Pub. Astron. Soc. Japan

References in corpus (9)

• The Interface Region Imaging Spectrograph (IRIS)
• The Solar Optical Telescope for the Hinode Mission: An Overview
• Non-linear force-free field modeling of a solar active region around the time of a major flare and coronal mass ejection
• Tracking Vector Magnetograms with the Magnetic Induction Equation
• Evidence of Wave Damping at Low Heights in a Polar Coronal Hole
• What is the relationship between photospheric flow fields and solar flares?
• A Magnetic Calibration of Photospheric Doppler Velocities
• Decorrelation Times of Photospheric Fields and Flows
• The coronal energy input from magnetic braiding

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• Magnetic Tornado Properties: A Substantial Contribution to the Solar Coronal Heating via Efficient Energy Transfer
• The Role of Magnetic Helicity in Coronal Heating
• The importance of horizontal Poynting flux in the solar photosphere
• Estimating the rate of field line braiding in the solar corona by photospheric flows
• Spectropolarimetric Inversion in Four Dimensions with Deep Learning (SPIn4D): I. Overview, Magnetohydrodynamic Modeling, and Stokes Profile Synthesis
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• Reconstruction of photospheric velocity fields from highly corrupted data
• Morphological variations of solar granules in the presence of magnetic fields
• Using the Stokes V widths of Fe I lines for diagnostics of the intrinsic solar photospheric magnetic field