[A-CG40] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG40-01] Recent Advances in Atmospheric Free Oscillation Studies

★Invited Papers

*Takatoshi Sakazaki¹, Kevin Peardon Hamilton², Michael Schindelegger³ (1.Graduate School of Science, Kyoto University, 2.University of Hawai'i, 3.University of Bonn)

Keywords:Normal mode, Free oscillation, Lamb mode, Pekeris mode

The atmosphere displays normal mode, resonant oscillations (free oscillations) occurring at discrete sets of eigen-frequency and zonal wavenumber. Earlier works attempted to find observational evidence of these modes in the real atmosphere. Due to their relatively large amplitudes and lower frequencies, Rossby modes were more easily identified with some well-known examples such as “5-day wave” and “10-day wave”. Recently, a much larger array of free modes was discovered by Sakazaki and Hamilton (2020) based on the 2D spectral analysis for surface pressure data from the latest reanalysis, ERA5. Notably, high-frequency modes such as Kelvin, Rossby-gravity and gravity modes have been established. Here note that these modes are all classified as so-called “Lamb modes”, which is characterized by the Lamb wave structure in vertical. In 2021, with the analysis of long-travelling pressure waves that are caused by an eruption on Hunga Tonga–Hunga Haʻapai, another type of normal modes, namely “Pekeris modes” have been first identified (Watanabe et al., 2022). This presentation will review these recent advancements in the study of normal mode detection, while also introducing our own recent progress.