The Coronal Heating Paradox

The "coronal heating problem" has been with us over 60 years, and hundreds of theoretical models have been proposed without an obvious solution in sight. In this paper we point out that observations show no evidence for local heating in the solar corona, but rather for heating below the corona in the transition region and upper chromosphere, with subsequent chromospheric evaporation as known in flares. New observational evidence for this scenario comes from (1) the temperature evolution of coronal loops, (2) the overdensity of hot coronal loops, (3) upflows in coronal loops, (4) the Doppler shift in coronal loops, (5) upward propagating waves, (6) the energy balance in coronal loops, (7) the magnetic complexity in the transition region, (8) the altitude of nanoflares and microflares, (9) the cross section of elementary loops, as well as (10) 3D MHD simulations of coronal heating. The phrase "coronal heating problem" is therefore a paradoxical misnomer for what should rather be addressed as the "chromospheric heating problem" and "coronal loop filling process." This paradigm shift substantially reduces the number of relevant theoretical models for coronal heating in active regions and the quiet Sun, but our arguments do not apply to coronal holes and the extended heliospheric corona.