Slow-mode shocks and Their Role in the Symmetric Magnetic Reconnection Based on 2.5D Hybrid Simulations

Abstract:

The process of breaking and reconnecting of magnetic field lines is known as magnetic reconnection. Petschek’s model predicts the presence of a structure called slow-shocks on both the sides of central diffusion region, which helps in acceleration of particles to achieve to fast reconnection. At the Earth's magnetosphere, the presence of slow-mode shocks has been reported at the magnetotail (symmetric reconnection) and at the magnetopause (asymmetric reconnection) to be 10% and 20%, respectively. The goal of our study is to find if this detection percentage accurate, and how does it change depending on the physical parameters such as, beta, angle of crossing. We also check whether these show-shocks break down into some other structure as we transition from magnetohydrodynamic (MHD) scale to ion diffusion region scale, and where and how do particles gain energy. We perform 2.5D hybrid simulations for magnetic reconnection for 3 different betas, and analyze the data obtained by Rankine-Hugoniot conditions, and 6 specific slow-shock conditions. We find that: [1] Detection probability of slow-mode shocks increases as the distance from X-point increases. [2] If the observations are performed close to X-point, slow-mode shocks might not be found, as the detection probability below 6 λ_i is < 20%. [3] Higher the beta, greater the chance to observe slow-shocks, and vice-versa. [4] Detection probability can be as low as 10% if the satellite crosses the neutral sheet at a very oblique angle. [5] A crescent-shaped accelerated population is seen in the slow-shock regions, whereas a meandering population is seen for non-slow shock region. [6] Accelerated beam particles from the neutral sheet contribute in the satisfaction of slow-shock conditions (high pressure in downstream). [7] The structural configuration of reconnection has slow-shocks but they are not the main driver of acceleration of the particles (fast reconnection).