Monday

MHD avalanches involve small, intensely localized instabilities that spread across neighbouring regions in a magnetic field.
Cumulatively, many small events release vast amounts of stored magnetic energy.
Straight cylindrical flux tubes, in Parker (1972)'s model of coronal loops, are liable to such avalanches: one unstable flux tube can cause instability to proliferate through reconnection, resulting in an ongoing chain of like events.
True coronal loops are curved, arching between different footpoints on one photospheric plane.
Using three-dimensional MHD simulations, we here verify the viability of MHD avalanches within the curved magnetic geometry of a multi-threaded coronal arcade.
Diverging from the behaviour of straight cylindrical models, a torus-like instability occurs, as flux tubes displace vertically and spread instability over a region wider than the original flux tubes, yet arguably more contained than that seen among straight flux tubes.
As a result, substantial and sustained heating is produced, contributing significantly to coronal heating.
Overwhelmingly dominant is viscous heating, from the shocks and jets produced around these small events.
Reconnection is not the greatest contributor to heating, but is the facilitator of those processes that are.
Localized and intermittent, the heating shows no strong spatial preference, except for a small bias away from footpoints.