Steadiness of coronal heating

No hints of observable changes in magnetic topology are associated with such small variations. The larger-amplitude, more rapid, rarer, and less well organized changes are associated with flux emergence. It is suggested therefore that while magnetic reconnection drives the latter, most of the active corona is heated with no evidence of a role for large-scale (observable) reconnection.

Since most coronal emission-line widths are subsonic, the bulk of coronal heating, if driven by reconnection, can only be of tangentially discontinuous magnetic fields, with angles below about 0.5c S /c A similar to 0.3 beta, with beta the plasma beta parameter (similar to 0.01) and c S and c A the sound and Alfven speeds, respectively. If heated by multiple small flare-like events, then these must be less than or similar to 1021 erg, i.e., picoflares.

But processes other than reconnection have yet to be ruled out, such as viscous dissipation, which may contribute to the steady heating of coronal loops over active regions.