Three-Dimensional Magnetic Reconnection Spreading in Current Sheets of Non-Uniform Thickness

Abstract

We derive a theory of three-dimensional spreading of collisionless anti-parallel reconnection in current sheets with non-uniform thickness.• Spreading from a thinner to a thicker current sheet occurs slower than local electron and Alfvén speeds, a key prediction of the theory.• We apply the theory to reconnection spreading in Earth's magnetotail and discuss potential implications for solar flare ribbons.