Are Chromospheric Nanoflares a Primary Source of Coronal Plasma?

TL;DR

This study uses hydrodynamic simulations to evaluate if chromospheric nanoflares are the main source of hot plasma in the solar corona, finding they are unlikely to be the primary cause based on spectral line discrepancies.

Contribution

The paper provides the first detailed hydrodynamic simulation comparison showing chromospheric nanoflares cannot account for observed coronal plasma properties.

Findings

Simulated Fe XII and Fe XIV line profiles do not match observations.

Chromospheric nanoflares do not raise plasma to coronal temperatures.

Coronal heating likely occurs in the corona itself, not from chromospheric nanoflares.

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.