Reconstructions of the line-of-sight component of the magnetic field (B_∥), inferred by applying the weak-field approximation to the Ca II 854.2 nm data. Upper-left panel: reconstruction performed with the unconstrained algorithm. Lower-left panel: reconstruction performed with a temporally regularised algorithm. Lower-right panel: reconstruction performed with a spatially regularised algorithm. Upper-right panel: reconstruction performed with full regularisation in space and time. A movie with the time series is available https://www.aanda.org/10.1051/0004-6361/202348810/olm. The red tick marks indicate the location of the cut shown in Fig. 4.