Results of forward fitting and spatial seismology inversion for the oscillation event on 2013 April 11. Panel a: asymmetric fundamental mode derived from forwardly solving the governing equation. The dashed line denotes the numerical solution of the fundamental mode and the solid points with error bars refer to the amplitude profile measured in Guo et al. (2015), multiplied by a coefficient of 0.11 Mm⁻¹. Panel b: comparison of the magnetic field derived from spatial seismology inversion and potential field extrapolation. The red dashed line denotes the inversion result by spatial seismology and the solid points with error bars represent the extrapolated field.