Current Sheets and Magnetic Reconnection statistics by Solar Orbiter at few to tens of Ion Inertial Lengths I: Energy Dissipation

Abstract

In this work, we study the turbulent origin of ion-scale Current Sheets (CSs) and the dissipation of energy via magnetic reconnection. We analyze 103 hours of high-cadence (4 samples/s) in-situ ion data from Solar Orbiter, collected between July 2020 and September 2022. We apply an automatic detection algorithm that finds current sheets (CSs) of thickness (length in the normal direction, $λ$) near the ion inertial length ($δ_i$), and classifies them as Alfvénic or reconnecting. We compile a catalog of 974 CSs of thickness in the range of few to 90 ion inertial lengths, of which 53 contain an ion reconnection jet. We estimate that Solar Orbiter spends $\sim 1 \%$ of the dwell time inside a CS of few to 90 $δ_i$ thickness, and 0.06\% inside a reconnecting CS of the same thickness range. By comparing these results with previous studies we estimate that the abundance of CSs and of Reconnecting CSs evolves with heliocentric distance ($r$) as $r^{-0.9}$ and $r^{-1.5}$, respectively. We estimate that magnetic reconnection dissipates $ε_{rec}\sim 30 \hspace{5pt} \text{J} \text{kg}^{-1} \text{s}^{-1},$ in the $\sim 1 - 40$ $δ_i$ scale-range, by assessing the amount of plasma that interacts with a reconnection exhaust. We show how the dissipation of turbulence energy cascade by magnetic reconnection at scales smaller than 90 $δ_i$ is more effective closer to the Sun, and decays as $r^{-3.6}$. The current density of Alfvénic CSs thicker than the ion inertial length presents scale invariance, obeying $J_0/J_A=0.9(λ/2δ_i)^{-0.71}$, suggesting that CSs generated locally from solar wind turbulence.