Are Chromospheric Nanoflares a Primary Source of Coronal Plasma?

Abstract

It has been suggested that the hot plasma of the solar corona comes primarily from impulsive heating events, or nanoflares, that occur in the lower atmosphere, either in the upper part of the ordinary chromosphere or at the tips of type II spicules. We test this idea with a series of hydrodynamic simulations. We find that synthetic Fe XII (195) and Fe XIV (274) line profiles generated from the simulations disagree dramatically with actual observations. The integrated line intensities are much too faint; the blue shifts are much too fast; the blue-red asymmetries are much too large; and the emission is confined to low altitudes. We conclude that chromospheric nanoflares are not a primary source of hot coronal plasma. Such events may play an important role in producing the chromosphere and powering its intense radiation, but they do not, in general, raise the temperature of the plasma to coronal values. Those cases where coronal temperatures are reached must be relatively uncommon. The observed profiles of Fe XII and Fe XIV come primarily from plasma that is heated in the corona itself, either by coronal nanoflares or a quasi-steady coronal heating process. Chromospheric nanoflares might play a role in generating waves that provide this coronal heating.

14 pages, 6 figures, accepted by Astrophysical Journal

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• Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
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• The First Ionization Potential Effect from the Ponderomotive Force: On the Polarization and Coronal Origin of the Alfven Waves
• Upflows in the upper solar atmosphere
• A Microfilament-Eruption Mechanism for Solar Spicules
• Spectroscopic Observations of a Coronal Loop: Basic Physical Plasma Parameters Along the Full Loop Length
• Possible Production of Solar Spicules by Microfilament Eruptions
• Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron
• Contribution of spicules to solar coronal emission
• An in-depth analysis of quiet-Sun IRIS Brightenings
• Active region upflows in various coronal structures and their coupling to the lower atmosphere