Oscillations of the solar photospheric magnetic field caused by the m = 1 high-latitude inertial mode

Abstract: Periodic oscillations at 338 nHz in the Earth frame are observed at high latitudes in direct Doppler velocity measurements. These oscillations correspond to the $m=1$ high-latitude global mode of inertial oscillation. In this study, we investigate the signature of this mode in the photospheric magnetic field using long-term series of line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) and the Global Oscillation Network Group (GONG). Through direct observations and spectral analysis, we detect periodic magnetic field oscillations at high latitudes ($65^\circ$--$70^\circ$) with a frequency of 338 nHz in the Earth frame, matching the known frequency of the $m = 1$ high-latitude inertial mode. The observed line-of-sight magnetic field oscillations are predominantly symmetric across the equator. We find a peak magnetic oscillation amplitude of up to $0.2$~gauss and a distinct spatial pattern, both consistent with simplified model calculations in which the radial component of the magnetic field is advected by the mode's horizontal flow field.