Resonant signals in the lithosphere-atmosphere-ionosphere coupling.

A study in the lithosphere, atmosphere and ionosphere (LAI) coupling often troubles scientists due to a certain distance between distinct instruments, which monitor geophysical parameters in different spheres. An instrumental system was established in southwest China (Leshan; LESH) for monitoring vibrations and perturbations in LAI (MVP-LAI). A ground-based Global Navigation Satellite System (GNSS) receiver at the YADU station locates ~ 260 km away that continuously receives electromagnetic signals transmitted from the BeiDou navigation System (BDS) geostationary satellites to monitor the total electron content (TEC) at the ionospheric pierce point right over the MVP-LAI system. The employment of YADU TEC benefits in elimination of possible shaking effects happening on multiple instruments at the LESH station and mitigation the troubles due to the discrepancy in observation places. Through a stacking process on the retrieved data for increase of signal to noise ratios, a novel phenomenon of the resonant LAI coupling at a fundamental mode of ~ 3.4 mHz and its multiples persists in ground vibrations, atmospheric pressure and TEC retrieved from the MVP-LAI system and the YADU station. The retrieved data share frequencies during the operational period of 1.5 months that is irrelevant to obvious events in the lithosphere, atmosphere and ionosphere. The persistence of the resonant LAI coupling is essential in the Earth's system.

Large air pressure changes triggered by P-SV ground motion in a cave in northern Taiwan.

Acoustic-gravity waves are generally considered to be one of the major factors that drive changes of the total electron content in the ionosphere. However, causal mechanisms of couplings between sources in the lithosphere and responses in the atmosphere and the ionosphere are not fully understood, yet. A barometer in the cave of the SBCB station records an unusual phenomenon of larger amplitudes in air pressure changes inside than those at the Xinwu station (outside). Accordingly, the comparison between the recorded data at the SBCB and Xinwu station can drive investigations of potential sources of the unusual phenomenon. Analytical results of phase angle differences reveal that the air pressure outside the cave at the Xinwu station often leads air pressure changes inside at the SBCB station at relatively low frequency bands. In contrast, the larger pressure changes at frequencies > ~ 5 × 10-4 Hz inside the cave at the SBCB station lead smaller changes outside at the Xinwu station. To expose causal mechanisms of the unusual phenomenon, continuous seismic waveforms are further conducted for examination. When the horizontal and vertical ground velocities of ground vibrations yield a difference in the phase angle close to 90°, coherence values between the air pressure changes and ground vibrations become large. This suggests that the pressure-shear vertical ground vibrations can drive air pressure changes. Meanwhile, the results shed light on investigating the existence of acoustic waves near the Earth's surface using a partially confined space underground due to that the assumptions of the waves can propagate upward into the atmosphere driving changes in the ionosphere.