On the Cause of Supra-Arcade Downflows in Solar Flares

Abstract

A model of supra-arcade downflows (SADs), dark low density regions also known as tadpoles that propagate sunward during solar flares, is presented. It is argued that the regions of low density are flow channels carved by sunward-directed outflow jets from reconnection. The solar corona is stratified, so the flare site is populated by a lower density plasma than that in the underlying arcade. As the jets penetrate the arcade, they carve out regions of depleted plasma density which appear as SADs. The present interpretation differs from previous models in that reconnection is localized in space but not in time. Reconnection is continuous in time to explain why SADs are not filled in from behind as they would if they were caused by isolated descending flux tubes or the wakes behind them due to temporally bursty reconnection. Reconnection is localized in space because outflow jets in standard two-dimensional reconnection models expand in the normal (inflow) direction with distance from the reconnection site, which would not produce thin SADs as seen in observations. On the contrary, outflow jets in spatially localized three-dimensional reconnection with an out-of-plane (guide) magnetic field expand primarily in the out-of-plane direction and remain collimated in the normal direction, which is consistent with observed SADs being thin. Two-dimensional proof-of-principle simulations of reconnection with an out-of-plane (guide) magnetic field confirm the creation of SAD-like depletion regions and the necessity of density stratification. Three-dimensional simulations confirm that localized reconnection remains collimated.

16 pages, 5 figures, accepted to Astrophysical Journal Letters in August, 2013. This version is the accepted version

References in corpus (4)

• Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows
• On the Distribution of Plasmoids In High-Lundquist-Number Magnetic Reconnection
• A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source
• Distribution Functions of Sizes and Fluxes Determined from Supra-Arcade Downflows

Cited by in corpus (17)

• Imaging and spectroscopic observations of magnetic reconnection and chromospheric evaporation in a solar flare
• The Origin of Underdense Plasma Downflows Associated with Magnetic Reconnection in Solar Flares
• Observations of supra-arcade fans: instabilities at the head of reconnection jets
• Plasma Heating Induced by Tadpole-Like Downflows in the Flaring Solar Corona
• Secondary Rayleigh-Taylor type Instabilities in the Reconnection Exhaust Jet as a Mechanism for Supra-Arcade Downflows
• Thermodynamical Evolution of Supra-Arcade Downflows
• Reconnection Properties of Large-Scale Current Sheets During Coronal Mass Ejection Eruptions
• Formation and Reconnection of Three-dimensional Current Sheets with a Guide Field in the Solar Corona
• A Model for Coronal Inflows and In/Out Pairs
• Evidence for Vortex Shedding in the Sun's Hot Corona
• Thermodynamics of supra-arcade downflows in solar flares
• Peristaltic Pumping near Post-CME Supra-Arcade Current Sheets
• Thermodynamic Evolution of Solar Flare Supra-arcade Downflows
• Saddle-shaped solar flare arcades
• Effects of supra-arcade downflows interacting with the post-flare arcade
• Statistical Investigation of the Kinematic and Thermal Properties of Supra-arcade Downflows Observed During a Solar Flare
• Statistical Investigation of the Widths of Supra-arcade Downflows Observed During a Solar Flare