Publications

Abstract. Meteorological tsunamis, or meteotsunamis, are anomalous waves triggered by atmospheric disturbances such as thunderstorms, gravity waves, squalls, or cyclones. While meteotsunamis have been studied extensively in regions like the Mediterranean and the United States, research in the Northwest European shelf remains limited, as meteotsunamis were considered rare and low-risk until recently. New evidence suggests they are often undetected due to insufficient tide gauge resolution. Reports indicate that meteotsunamis pose risks to infrastructure and have caused fatalities in the United Kingdom. This study evaluates the capability of the Met Office's atmosphere-ocean-wave regional coupled model (UKC4) and Météo-France’s atmosphere-ocean regional coupled model (AROBASE) to capture and predict meteotsunamis. Configured at km-scale and with 10-minute coupling frequency, the models were tested on the strongest meteotsunami event (up to 1 m) recorded so far in Ireland, which occurred in June 2022. The whole event lasted for hours and significantly impacted Ireland, the UK and France. This case has been widely studied but the exact atmospheric drivers of such a widespread event remain unknown. The two models are able to represent the meteotsunami: the Met Office model is more successful in the Celtic Sea around the UK, Ireland and the English Channel and the Météo-France model captures a weak signal in the Bay of Biscay and English Channel. Analysis of the atmospheric situation suggests two slow-moving low-pressure systems, with colliding cold and dry Arctic air and extremely warm and dry continental air. This generates a shallow stable layer near the surface, which gets disrupted by convective downdrafts, generating gravity waves which propagate in the stable layer at the same speed as ocean disturbance, leading to Proudman resonance and to meteotsunamis in three different countries. Finally, for the first time for this region, we show that a km-scale regional coupled ensemble can successfully forecast this meteotsunami event.

Abstract Bubble plumes play a significant role in the air–sea interface by influencing processes such as air–sea gas exchange, aerosol production, modulation of oceanic carbon and nutrient cycles, and the vertical structure of the upper ocean. Using acoustic Doppler current profiler (ADCP) data collected off the west coast of Ireland, we investigate the dynamics of bubble plumes and their relationship with sea state variables. In particular, we describe the patterns of bubble plume vertical extension, duration, and periodicity. We establish a power-law relationship between the average bubble penetration depth and wind speed, consistent with previous findings. Additionally, the study reveals a significant association between whitecapping coverage and observed acoustic volume backscatter intensity, underscoring the role of wave breaking in bubble plume generation. The shape of the probability distribution of bubble plume depths reveals a transition toward stronger and more organized bubble entrainment events during higher wind speeds. Furthermore, we show that deeper bubble plumes are associated with turbulent Langmuir number Lat ∼ 0.3, highlighting the potential role of Langmuir circulation on the transport and deepening of bubble plumes. These results contribute to a better understanding of the complex interactions between ocean waves, wind, and bubble plumes, providing valuable insights for improving predictive models and enhancing our understanding of air–sea interactions. Significance Statement This research contributes to understanding bubble plume dynamics in the upper ocean and their relationship with sea state variables. The establishment of a power-law relationship between the bubble penetration depth and wind speed, along with the association between whitecapping coverage and acoustic backscatter intensity, contributes to improved predictive capabilities for air–sea interactions and carbon dioxide exchange. The identification of the potential influence of Langmuir circulation on bubble plume dynamics expands our understanding of the role of coherent circulations in transporting bubble plumes. Additionally, this study presents a clear methodology using commercial sensors such as an ADCP, which can be easily replicated by researchers worldwide, leading to potential advancements in our comprehension of bubble plume dynamics.

We explore instances of unusual long-wave activity of meteorological origin along the coastal waters of north-west Europe during the summer of 2022. These events include meteorological tsunamis, i.e. waves in the tsunami frequency band originated by sharp atmospheric pressure variations and amplified by multiple resonant effects, and wind-generated infragravity waves which can trigger local seiches in enclosed basins and harboursAnomalous "tidal surges" were observed on 18 June 2022 in Wales, followed by similar occurrences in Ireland, France, and Spain. Additionally, several anomalous long-wave events were reported in south England and Wales on the morning of 19 July 2022. Our investigation involved analysing surface and high-altitude air pressure fields, as well as sea level oscillations for both days.We determine that the events on 18 June were a series of meteorological tsunamis, spreading across several western European countries and initiated by localised pressure disturbances originating within a low-pressure system over the North Atlantic Ocean. A local examination of the southern coast of Ireland suggests that Proudman resonance played a key role in amplifying the meteotsunami as it travelled eastward in the afternoon of 18 June. Similarly, our analysis of the events on 19 July indicates that the tidal surge observed in the UK and anomalous signals recorded in Ireland and France were likely instances of seiching triggered by infragravity waves. We conducted numerical simulations of the 18 June event using Volna-OP2, which solves the non-linear shallow water equations employing a finite volume discretisation technique. We also examined the influence of atmospheric wave velocity on the amplification of sea surface elevation.

Abstract Knowledge of the directional distribution of a wave field is crucial for a better understanding of complex air–sea interactions. However, the dynamic and unpredictable nature of ocean waves, combined with the limitations of existing measurement technologies and analysis techniques, makes it difficult to obtain precise directional information, leading to a poor understanding of this important quantity. This study investigates the potential use of a wavelet-based method applied to GPS buoy observations as an alternative approach to the conventional methods for estimating the directional distribution of ocean waves. The results indicate that the wavelet-based estimations are consistently good when compared to the framework of widely used parameterizations for the directional distribution. The wavelet-based method presents advantages in comparison with the conventional methods, including being purely data-driven and not requiring any assumptions about the shape of the distribution. In addition, it was found that the wave directional distribution is narrower at the spectral peak and broadens asymmetrically at higher and lower scales, particularly sharply for frequencies below the peak. The directional spreading appears to be independent of the wave age across the entire range of frequencies, implying that the angular width of the directional spectrum is primarily controlled by nonlinear wave–wave interactions rather than by wind forcing. These results support the use of the wavelet-based method as a practical alternative for the estimation of the wave directional distribution. In addition, this study highlights the need for continued innovation in the field of ocean wave measuring technologies and analysis techniques to improve our understanding of air–sea interactions. Significance Statement This study presents a wavelet-based technique for obtaining the directional distribution of ocean waves applied to GPS buoy. This method serves as an alternative to conventional methods and is relatively easy to implement, making it a practical option for researchers and engineers. The study was conducted in a highly energetic environment characterized by high wind speeds and large waves, providing a valuable dataset for understanding the dynamics of marine environment in extreme conditions. This research has implications for improving our understanding of directional characteristics of ocean waves, which is crucial for navigation, offshore engineering, weather forecasting, and coastal hazard mitigation. This study also highlights the challenges associated with understanding wave directionality and emphasizes a need for further observations.

The directional distribution of ocean waves is of great importance for a better understanding of air-sea interactions. Countless applications in science and engineering, such as, offshore energy production, microseisms prediction, wave climate modelling, coastal erosion, among many others, require precise information about the wave directionality. However, in spite of its importance, this quantity is poorly understood and difficult to accurately model. This study presents observations of the directional spreading parameters obtained from a set of low-cost GPS-based buoys during highly energetic conditions. One of the buoys was anchored off the west coast of Ireland during the HIGHWAVE project. These observations are compared with the measurements of 20 freely drifting buoys deployed in the Bay of Biscay during the SUMOS campaign. Spreading parameters were compared in the framework of widely used parameterisation for the directional distribution. The directional spreading is narrower at the spectral peak and broadens as the frequency moves away towards higher and lower scales. There is a particularly sharp increase in the spreading for f < fp. The results showed that buoy-based observations significantly differ from spatial-based measurements for frequencies around half the spectral peak. The measruements obtained by the drifting buoys show that for 2 < f/fp < 6, the spreading appears to be approximately constant with the frequency and tends to increase again for f > 6fp. The results showed that the directional spreading seems to be independent of the wave age, roughly across the entire range of frequencies.  This may imply that the shape of the directional spectrum is primarily controlled by the non-linear wave-wave interactions rather by the wind forcing.  In the vicinity of the spectral peak, a weakly linear relationship between the directional spreading and the significant wave height was observed.  The results show that as the significant wave height increases by one meter, the spreading decreases by about 4.5°. The preliminary results presented here contribute to the understanding of the directional distribution of ocean waves. However, further observations and comparisons are needed to fully capture the complexity of this phenomenon. Despite being preliminary, these results provide valuable insights and add to the ongoing discussion on this topic. This work was funded by the European Research Council (ERC) under the EU Horizon 2020 research and innovation programme (grant agreement no. 833125-HIGHWAVE). We are very grateful to the scientific team behind the SUMOS campaign for providing the drifting buoys data.

We investigate occurrences of anomalous tidal activity in coastal waters of north-west Europe during Summer 2022. Sightings of an anomalous “tidal surge” occurred on 18 June 2022 in Wales, followed by similar observations in Ireland, France, and Spain. Several anomalous long-wave events were also reported in south England and Wales in the morning of 19 July 2022. We analyzed surface and high-altitude air pressure fields, and sea level oscillations for both days. Our detailed analysis reveals that the 18 June events were a series of meteotsunamis, propagating over several countries in Western Europe and triggered by localized pressure perturbations, originating within a low-pressure area over the North Atlantic Ocean. A local analysis of the southern coast of Ireland suggests that Proudman resonance was the determinant mechanism that amplified the meteotsunami traveling eastward in the afternoon of 18 June. A similar analysis of the 19 July events suggests that the tidal surge reported in the UK and anomalous signals recorded in Ireland and France were episodes of seiching triggered by infragravity waves, resonated subharmonically by wind waves. Numerical simulations of the 18 June event were performed with Volna-OP2, which solves the non-linear shallow water equations using a finite volume discretization. The influence of the atmospheric wave velocity on the amplification of the sea surface elevation is analyzed.