| Autor: |
Matsuba, Yoshinao1 (AUTHOR) matsuba@edu.k.u-tokyo.ac.jp, Roelvink, Dano2,3 (AUTHOR), van Dongeren, Ap2,3 (AUTHOR) |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Oceans. Oct2024, Vol. 129 Issue 10, p1-18. 18p. |
| Abstrakt: |
Infragravity (IG) waves are important drivers of extreme run‐up, morphological changes, and seiches. While locally forced IG waves have been extensively investigated, recent studies have revealed the significance of free IG waves generated on distant beaches. This study focuses on free IG waves generated at a coast facing southeast in Japan during the passage of a typhoon. The relationship between incident short waves and free IG waves as well as their contributions to nearshore IG waves, in particular to seiches in a small port, are analyzed using unique measurement data and numerical experiments. During the typhoon passage, more than 75% of the observed IG wave energy originates from free IG waves at an observatory located at a depth of 23 m, and their peak direction is alongshore. Six‐year measurement data demonstrate that peak directions of free IG waves strongly depend on the incident wave angles of short waves and that swells from the south generate alongshore propagating free IG waves. A numerical model can reproduce the alongshore propagating free IG waves accurately when using a large computational domain. Moreover, numerical experiments performed using the model demonstrate that the alongshore propagating free IG waves are IG waves reflected from distant beaches. The free IG waves from distant beaches are small outside the port, but seiches in the port are amplified by more than 10%. The relationship between seiches and incoming free IG waves is further discussed based on the numerical experiments. Plain Language Summary: Infragravity (IG) waves are ocean waves with long wavelengths which are generated by short waves. They play an important role in coastal hazards during storm conditions. Previous studies have focused on IG waves which are generated close to shore in the wave shoaling and breaking process. However, the importance of IG waves, which are generated at distant beaches and propagate freely across the sea, is not yet well understood. This study analyzes unique observation data recorded at a coast facing southeast in Japan during the passage of a typhoon and investigates the characteristics of these free IG waves using a numerical model covering a large computational domain. The observation data suggest that the directions of free IG waves strongly depend on the wave angles of incident short waves and that short waves from the south generate free IG waves propagating in the alongshore direction at the coast. The numerical experiments demonstrate that the alongshore propagating free IG waves originate from distant beaches and that they amplify the water level changes in a small port by more than 10%. This suggests that accurate risk assessment in ports during storms requires the consideration of free IG waves originating from distant beaches. Key Points: Alongshore propagating free infragravity waves were observed during the passage of Typhoon LionrockThe alongshore propagating free infragravity waves originated from distant beaches more than 10 km awayThe alongshore propagating free infragravity waves amplified seiches in a small port by more than 10% [ABSTRACT FROM AUTHOR] |
| Databáze: |
GreenFILE |
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