Cause of Chromospheric Opposite Polarity Intrusions Discovered in Sunrise III/SCIP Data: MURaM-ChE Simulations Point to Twisted Flux Ropes

The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) instrument on board the balloon-borne S unrise iii observatory provided new high-resolution observations of the solar chromosphere in the Ca ii λ 854.2 nm line. The Stokes V signal in magnetic network regions was found to show fine-structured details, which suggests the magnetic field above the network elements does not simply expand as a unipolar feature but displays opposite-polarity intrusions (OPIs). These features appear as elongated structures in Stokes V observations. In this work, we demonstrate that such features appear ubiquitously in a numerical simulation of the solar chromosphere. We use a simulation that is computed with the recently developed chromospheric extension of MURaM (MURaM-ChE) and resembles an enhanced network region. We find that OPIs appear ubiquitously in the vertical component of the magnetic field at around 1 Mm above the surface and are visible in the synthetic Stokes V signal of the Ca ii λ 854.2 nm line. The structures have lengths of ≈2–7 Mm and widths of approximately 1 Mm. The magnetic field configurations associated with the OPI features appear to belong to twisted flux ropes and are visible for most of the time in the presented 21 minutes time series. Our results show that the magnetic structure of the chromosphere is more complex than previously thought, with even seemingly simple flux tubes showing embedded twisted fields pointing in the opposite direction. This may help in explaining new high-resolution observations from the S unrise iii mission.