Oscillations in Sunspot Umbra in He I 1083 nm

Magnetohydrodynamic waves are an important mechanism of solar atmospheric heating. Doppler velocity and intensity measurements are known to clearly show these waves. In recent years, observations of fluctuations in the magnetic field show this oscillatory behaviour in both the photosphere and the chromosphere. The reason for these observed oscillations in the magnetic field has been difficult to interpret over the years. In this work, to address this issue, we invert He I 1083 nm line using HAZEL to study these fluctuations in the magnetic field and we find that these fluctuations arise due to the opacity effect. The nature and origin were also validated with the support of numerical simulations.