arXiv:1205.2090v1 [astro-ph.SR] 9 May 2012 Simulation of multiple supra–arcade downflows in solar flares M. C´ ecere 1,2 , M. Schneiter 1,3,4 , A. Costa 1,3,4 , S. Elaskar 1,4 and S. Maglione 5 ABSTRACT In later papers we have shown that sunward, generally dark, plasma features originated above posteruption flare arcades are consistent with a scenario where plasma voids are generated by the bounc- ing and interfering of shocks and expansion waves upstream of an initial localized deposition of energy which is collimated in the magnetic field direction. In this paper we analyze the multiple production and interaction of supra–arcade downflows (SAD) and the structure of individual SADs that make them rel- atively stable features while moving. We compare our results with observations and with the scenarios proposed by other authors. Subject headings: 1. Introduction Sunward dark moving trails with origin [40 - 60]Mm above posteruption flare arcades and decel- erating speed in the range ∼ [50 - 500]km s -1 were first detected with the Yohkoh Soft X–ray Telescope (SXT). Since then, they have been extensively reported using other instruments such as TRACE (Innes et al. 2003a,b), SOHO/SUMER (Innes et al. 2003b) and SDO/AIA (Savage et al. 2012). The lack of X–ray and extreme–ultraviolet (EUV) signatures in images and spectra has lead to consensus on that these down– moving structures ought to be voided flows generated by reconnection processes in a current sheet above the flare arcade. Besides the dark moving structures, bright supra–arcade downflowing features have also been reported during flares (McKenzie 2000). McKenzie and Savage (2009), Savage and McKenzie (2011) suggested that supra–arcade downflows (SAD) are the cross–sections of thin and empty flux tubes re- tracting from a reconnection site high in the corona. 1 Consejo Nacional de Investigaciones Cient´ ıficas y T´ ecnicas (CONICET), Argentina. 2 Facultad de Matem´ atica, Astronom´ ıa y F´ ısica, Universidad Na- cional de C´ ordoba (UNC), C´ ordoba, Argentina 3 Instituto de Investigaciones en Astronom´ ıa Te´ orica y Experi- mental IATE, C´ ordoba, Argentina. 4 Facultad de Ciencias Exactas, F´ ısicas y Naturales, Universidad Nacional de C´ ordoba (UNC), C´ ordoba, Argentina 5 Facultad de Ingenier´ ıa, Universidad Nacional de R´ ıo Cuarto, Ciudad Universitaria, R´ ıo Cuarto, C´ ordoba, Argentina According to these authors, the high enough inner magnetic pressure could be the reason the voids are able to resist being filled in immediately by the sur- rounding denser plasma. Linton et al. (2009) proposed a scenario where the dynamic of retracting magnetic fields is triggered by a localized reconnection event that produces up and down flowing reconnected flux tubes, which are slowed down by underlying magnetic arcade loops. The observed SAD speeds are lower than expected for reconnection outflows in regions of typical Alfv´ en speeds of 1000 km s -1 . Linton et al. (2009) suggested that drag forces could work against the reconnection outflow. Verwichte et al. (2005) analyzed TRACE SAD os- cillations transverse to the magnetic field. They found that the initial speeds and the displacement amplitudes, of kink–like type in the observational dark lanes of variable sizes (between [∼ 2 - 9]Mm), decrease as they propagate downwards, while the period remains fairly constant with height. Recently, after AIA observations with high reso- lution and cadence, Savage and McKenzie (2011) re– interpreted SADs as wakes created by the retraction of thin loops instead of the previous interpretation as flux tube cross–sections (renamed by the authors as SADLs). They interpreted SADLs as features of sizes [∼ 0.9 -1.3]Mm observed during the early phase of the eruptive event and SADs as features of sizes ∼ 9Mm that become apparent afterwards. They proposed that deceleration is expected due to the buildup of down- 1