  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.
