An Interpretation of Supra-Arcade Downflows as Reconnection Onset Bursts

Supra-arcade downflows, also known as tadpoles, are low-density plasma voids that propagate sunward during solar flares. These events are important because they potentially provide insight about the spatiotemporal evolution of reconnection at the laptops, but there is disagreement about their cause. Supra-arcade downflows (SADs) have been interpreted as flux tubes or plasmoids from bursty reconnection. Recently, it was suggested that they are not plasmoids themselves, but wakes behind plasmoids as they descend toward the sun. We investigate an alternate interpretation of supra-arcade downflows which we call "reconnection onset bursts" (ROBs). These are low-density bursts occurring when reconnection rapidly onsets that penetrate the high density arcade, analogous to dipolarization fronts in the magnetotail. This differs from previous models in that the reconnection does not have to be short lived nor manifestly three-dimensional. Large-scale two-fluid numerical simulations confirm their existence and are used to investigate their parametric dependence. Observational signatures will be discussed.