  The magnetic field inside the sunspot umbra, as observed by the Full-disk
MagnetoGraph (FMG) onboard the Advanced Space based Solar Observatory (ASO-S),
was found to be experiencing a weakening. To address this issue, we employed a
method developed by Xu et al. (2021) to correct the weakening in the data of 20
active regions observed by FMG during the period spanning December 29, 2022, to
July 23, 2023. Research has revealed that the onset of magnetic field weakening
occurs at a minimum magnetic field strength of 705 G, with the peak strength
reaching up to 1931 G. We computed the change ratio (R1) of the unsigned
magnetic flux within the sunspot umbra, considering measurements both before
and after correction. The change ratio (R1) spans from 26% to 124%, indicating
a significant increase in the unsigned magnetic flux within sunspot umbrae
observed by FMG after correction. To illustrate this, we selected four active
regions for comparison with data from the Helioseismic and Magnetic Imager
(HMI). After correction, it is found that the unsigned magnetic flux in sunspot
umbrae measured by FMG aligns more closely with that of HMI. This supports the
effectiveness of the corrective method for FMG, despite imperfections,
particularly at the umbra-penumbra boundary.
