[S-SS03] Seismological advances in the ocean

[SSS03-P05] Empirical Green's Function Retrieval of Infra-gravity Waves in the Pacific Ocean via Ambient Noise Interferometry

*Kun Chi Ho¹, Justin Yen-Ting Ko¹, Hou-Sheng Cheng¹, Shiann-Jong Lee², Hsin-Hua Huang² (1.Institute of Oceanography, National Taiwan University, Taipei, Taiwan, 2.Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan)

Keywords:Ambient noise interferometry, Empirical Green’s function, Infra-gravity waves, Tsunami

Infra-gravity waves (IGWs), longer periods gravity waves (20-300 seconds), arise from nonlinear interactions among wind, wave dispersion, coastal features, seabed topography, and various wave processes. In this study, ambient noise interferometry computed cross-correlation functions from a 10-year dataset obtained from the Deep-ocean Assessment and Reporting of Tsunami (DART) system in the Pacific Ocean, yielding empirical Green's functions (EGFs) corresponding to IGWs periods. The EGFs demonstrated significant propagating behavior, adhering to empirical wave dispersion relationships. Coherence analysis with observed tsunami data validated the EGFs' feasibility for tsunami warning systems, outperforming Cornell Multi-grid Coupled Tsunami Model (COMCOT). Power Spectral Density (PSD) and spectrogram analysis revealed seasonal patterns in North and Southeast Pacific Ocean stations, with winter intensity peaking in the former and summer in the latter, akin to IGW observations from WAVEWATCH III. We combined the ray path from Fast Marching Surface Tomography (FMST) to thoroughly explore the seasonal variation of IGWs in intensity and propagation direction, aiming to establish potential links to climate models and to identify the sources of IGWs. Our results reveal that during periods of heightened winter Westerlies, storm activity predominantly fuels the source energy of IGWs. This inference is supported by the west-to-east propagation direction of IGWs along the Aleutian Islands, aligning with the movement of storms. Conversely, when Westerlies weaken, whether in winter or summer, shoreline reflection emerges as the primary source energy for IGWs.