Williams, David
(2020)
Meteotsunami generation, amplification and occurrence in north-west Europe.
PhD thesis, University of Liverpool.
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Abstract
Meteotsunamis are atmospherically generated tsunamis with characteristics similar to all other tsunamis, and periods between 2–120 minutes. They are associated with strong currents and may unexpectedly cause large floods. Of highest concern, meteotsunamis have injured and killed people in several locations around the world. To date, a few meteotsunamis have been identified in north-west Europe. This thesis aims to increase the preparedness for meteotsunami occurrences in north-west Europe, by understanding how, when and where meteotsunamis are generated. A summer-time meteotsunami in the English Channel is studied, and its generation is examined through hydrodynamic numerical simulations. Simple representations of the atmospheric system are used, and termed synthetic modelling. The identified meteotsunami was partly generated by an atmospheric system moving at the shallow-water wave speed, a mechanism called Proudman resonance. Wave heights in the English Channel are also sensitive to the tide, because tidal currents change the shallow-water wave speed. To explain meteotsunami growth in a wider range of conditions, a generalised understanding of Proudman resonance is developed through idealised simulations and analytical models. Most surprisingly, wave amplification near predictions of Proudman resonance can occur even if the instantaneous forcing speed deviates from the mean forcing speed by 18%. This amplification can happen if the atmospheric forcing remains over the meteotsunami. Broader context is given to meteotsunami case studies in north-west Europe through an 8-yr climatology. In total, 349 meteotsunamis are identified and 256 associated mesoscale atmospheric systems are classified. Of meteotsunamis between 2010–2017, 79% were smaller than 0.5 m and about half occurred in winter. Of the classified atmospheric systems, 46% were quasi-linear systems and 33% were open-cellular convection. For 45 meteotsunamis in France, the mesoscale atmospheric systems occurred within well-documented synoptic atmospheric conditions, and there is evidence of repeated favourable conditions for Proudman resonance. Finally, a new explanation of how open-cellular convection generates meteotsunamis is developed through synthetic models. Open-cellular convection is modelled as a repeating field of individual cells moving at the shallow-water wave speed. Each individual cell generates an individual wave. When these individual waves form a linear superposition, constructive interference of repeating waves can lead to a larger meteotsunami than would be expected from single individual cells.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Engineering |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 05 Mar 2020 10:26 |
| Last Modified: | 19 Jan 2023 00:04 |
| DOI: | 10.17638/03073478 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3073478 |
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