Description: In normal mode seismology, the atmosphere and the solid Earth are generally considered to be decoupled, and the seismic wave energy from the Earth's interior is difficult to propagate into the atmosphere. However, a growing number of studies have shown that earthquakes, volcanoes and tsunamis can disturb the Earth's atmosphere due to various coupling effects. Therefore, it is an open question whether normal mode (especially in low frequency) signals can be detected in atmospheric observations. In our study, experiments were conducted to investigate the existence of normal mode signals in surface atmospheric observations using the improved multi-taper method, based on the seismographs and ground-based atmospheric observations of the Global Seismic Network before and after the 2021 Mw8.2 Alaska earthquake. Then, the results showed that the normal mode signal can be detected in the pressure observations by comparing the pre-earthquake, post-earthquake and theoretical calculations. However, since the signal-to-noise ratio varies greatly between stations and modes, direct correction of the barometric pressure by the admittance method may lead to large deviations in the estimation of normal mode parameters. Furthermore, we investigate the generation mechanism of seismic normal modes in surface atmospheric observations, which suggests that these signals originate from crust-atmosphere coupling in the same frequency band, and this possible coupling should be considered in normal mode seismology research.