A Fresh View of the Coronal Heating Problem from TRACE

Markus J. Aschwanden (LMSAL)
Solar & Astrophysics Laboratory
Lockheed Martin Advanced Technology Center

The heating of solar and stellar atmospheres,
which have coronae several orders of magntitude 
hotter than their photospheres, is still a
puzzling problem. However, progress has been
made with the localization of the heating function 
with recent TRACE and SoHO data, namely that the
heating seems to be concentrated in the lowest
10,000 km of the corona. There are now at least
three major observational constraints that the heating
of the corona results from chromospheric energization
processes: 1) the overdensity of coronal loops,
2) observed upflows of heated plasma, and 3) the
heating function with a scale height of s_H~10,000 km.
We review a representative selection of coronal
heating models (AC heating, DC heating, magnetic
reconnection heating, etc) in the light of these new
observational constraints, and discuss inconsistencies
between theoretical models and observations.