Speaker
Description
A mechanism for the proliferation of large numbers of slow shocks upstream of
reconnecting current layers during impulsive flares is explored. A surprising result of recent macro-scale kinetic simulations of electron energy gain during reconnection was the discovery of the generation of large numbers of slow shocks that extend far upstream of the reconnecting current layer (Arnold et al., 2021). The formation mechanism of these shocks and their role in producing the hot thermal electrons in impulsive flares are being explored with the macroscale simulations (kglobal and ARMS codes) and supporting PIC simulations. The formation of these slow shocks upstream is a consequence of the rapid growth, merging, and ejection of plasmoids in reconnecting current layers. The Alfvénic motion of plasmoids in current layers produces fast flows in the upstream region as plasma moves to fill in the low-pressure regions created by plasmoid motion. These high-speed flows steepen into slow shocks that heat the plasma upstream of reconnecting current layers. Global simulations of CMEs with ARMS also reveals the proliferation of these slow shocks as CME launch leads to Alfvénic downflows and the resulting formation of slow shocks. The mechanism of electron and ion heating of these slow shocks is being explored with local PIC simulations with parameters relevant to flare energy release: high sonic Mach number but with low Alfvénic Mach number. The goal is to fully understand the driver of hot thermal electrons and ions beyond those produced by evaporation in impulsive flares.