In a complex contest of climate change, we observe the evolution of extreme events that greatly challenge many areas of human life. Although the Mediterranean Sea is a relatively mild basin, it is however characterized by, occasionally intense cyclones with tropical-like characteristics known as Tropical-Like Cyclones (TLC). Many studies have highlighted that sea surface temperature (SST) distribution play a crucial role in modulating the intense air-sea exchange, hence controlling both development and evolution of TLCs. However, given the complex interplay among ocean mixed layer, heat content and temperature, the role of the mixed layer depth (MLD) and SST Anomaly is of paramount importance. In this study we investigated the role of both SST anomaly, horizontal gradients and MLD profile on the origin and evolution of a recent record-breaking TLC (named IANOS and DANIEL). IANOS and DANIEL are originated over the southern Ionian Sea. The first made landfall over Greece mainland coast and DANIEL made landfall over Libyan coasts. These TLCs developed over a basin where a positive SST anomaly up to 4 °C was detected, which coincided with the sea area where it reached the maximum intensification and strength. We conducted a series of experiments using an atmospheric model (WRF - Weather Research and Forecasting system) driven by underlying SST (standalone configuration), either with daily update or coupled to a simple mixed-layer ocean model (SLAB ocean), with SST calculated at every time step using the SLAB ocean for a given value of the MLD. Sensitivity tests were performed increasing or decreasing MLD depth by 10 m, 30 m, 50 m, 75 m, 100 m, removing the horizontal gradients, removing the SST anomaly. Then, possible past and future climatological scenarios of MLD thickness were identified and tested. Preliminary results show that the MLD influences not only the intensity of the cyclone but also the structure of the precipitation field both in terms of magnitude and location. The fundamental role of the SST anomaly was also found to be essential to provide intense characteristics to IANOS and DANIEL. Results deserve further investigation in the context of climate change scenarios that can provide useful insights into impact on coastal civil and economics in the whole Mediterranean region.

How to cite: Redaelli, G., Liguori, G., Cavicchia, L., Miglietta, M. M., Bonaldo, D., Carniel, S., Calvo-Sancho, C., Martin, M. L., Gonzalez-Aleman, J. J., Ferretti, R., and Ricchi, A.: Exploring how a warmer Mediterranean Sea affects the origin and development of destructive Tropical-Like Cyclones IANOS and DANIEL, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19563, https://doi.org/10.5194/egusphere-egu24-19563, 2024.

Extreme sea levels can result in catastrophic flooding of coastal regions, endangering the lives of residents and destroying coastal infrastructure. Due to climate change they are becoming more frequent and therefore more dangerous. Extreme sea levels occur on different temporal and spatial scales, including sub-hourly scales, which we have only recently been able to assess due to the recent enhancement of the temporal resolution of the tide gauge measurements.

To quantify the contribution of sub-hourly sea level oscillations to positive sea level extremes, raw sea level data from 288 tide gauges along the European coasts, with a sampling resolution of less than 20 minutes, were obtained from: (1) the IOC-SLSMF website (263 stations); (2) National agencies (Portugal, Finland, Croatia – 24 stations). Large portions of the raw dataset had numerous data quality issues (i.e., spikes, shifts, drifts), thus quality control procedure was required. Out of range values and spikes were automatically removed, remaining data were visually examined, and spurious data were removed manually. After quality control, all data series were de-tided, and residuals were split into a low-frequency (T > 2 h) and a high-frequency (T < 2 h) component.

The five highest positive sea level extremes per year were extracted from the residual series and the high-frequency series. These were defined as residual extremes and high-frequency extremes, respectively. The contribution of the high-frequency sea level oscillations to the total sea level extremes along the European coasts was estimated. The contribution was shown to be significantly geographically and station-dependent, and it is important to take it into account when estimating flooding levels.

How to cite: Balić, M. and Šepić, J.: Contribution of high-frequency sea level oscillations to the sea level extremes along European coasts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16424, https://doi.org/10.5194/egusphere-egu24-16424, 2024.

In the afternoon of July 22, 2023, a very intense thunderstorm developed over the central Po Valley. It  quickly cross the Adriatic sea traveling from the center of the Po Valley to the Croatian coast, moving in the direction northwest-southeast. The thunderstorm  speed ranged between 50 and 80km/h, with  a downdraft exceeding 100 km/h, wind gust up to 120 km/h, which led to the formation of intense hailstorms with hail larger than 8 cm. The pressure difference between the front and central regions of storm,  reaced  6 hPa, with peaks up to 10 hPa. As the supercell moved towards the coast, the combined effects of the downdraft and the pressure variation, along with the storm's speed, likely triggered a meteotsunami. Both amateur evidences and instrumental observations showed the propagation of a  wave along the Adriatic coast, from North to South, with an amplitude of about 40 cm and a period of approximately 20 minutes. This phenomenon was observed from Ravenna (where the stormcell moves from land to sea) to Ancona, San Benedetto del Tronto, and Ortona with a propagation speed comparable with the storm  speed thus, in good agreement with a possible Proudman resonance. Physical analysis and numerical simulations of the atmosphere and ocean were performed  using numerical models: WRF (Weather Research and Forecasting System), ICON (Icosahedral Numerical Model), and ROMS (Regional Oceanographic Modeling System), coupled with SWAN (Simulating Waves in Nearshore) at 1 km horizontal resolution. The atmospheric results accurately reproduced  the storm's structure and evolution. The coupled ROMS and SWAN model was performed to assess the individual impacts of the downdraft, the vertical component of the downdraft, the pressure surge, and the overall storm surge. This work presents the outcomes and key factors contributing to the generation and amplification of this phenomenon.

How to cite: Ferretti, R., Memmola, F., Coluccelli, A., Brocchini, M., Corvaro, S., Penna, P., and Falco, P.: On the generation of a meteotsunami, the case study of supercell storm, over Adriatic Sea., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18075, https://doi.org/10.5194/egusphere-egu24-18075, 2024.

Coastal ecosystems are under climate and anthropogenic pressures. Extreme events as Marine Heatwaves (MHW) directly impact environmental conditions necessary to sustain biodiversity in coastal oceans. Recent results showed increasing occurrence and intensity of MHW in the Bay of Biscay and the English Channel based on surface temperature observations.

Combining satellite and in situ observations with recent high resolution numerical simulations, the impact of MHW on the whole water column is investigated to evaluate potential impacts on pelagic and benthic ecosystems. Special attention is given to the last two years, 2022 and 2023, as unprecedent warm years.

The last two decades have been observed (in situ and from satellites) and simulated (using CROCO coastal ocean model with 1km resolution) allowing to identify and characterize MHW (occurrence, duration, intensity). The propagation in the water column of observed heating is investigated with regard to the local dynamics (e.g. tides, constrained shallow waters, river plume dynamics). Depending on hydrodynamical conditions, impacts of MHW on the water column are contrasted and sensitive to characteristics from this type of extreme events.

Those first results are designed to pave the way for an assessment of the MHW impact on the coastal ecosystem during the last two decades with a focus on 2022 and 2023.

How to cite: Charria, G., Poppeschi, C., Simon, A., Gaymard, A., Martinez Almoyna Carlhand, M., Savoye, N., Lienart, C., Ulses, C., Pairaud, I., Couvelard, X., Theetten, S., and Le Roux, J.-F.: Impact of Marine Heatwaves over the water column in a coastal ocean: a case study in the Bay of Biscay and the English Channel , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12709, https://doi.org/10.5194/egusphere-egu24-12709, 2024.

Typhoons in the northwestern Pacific induce strong oceanic responses. Using 17 years of satellite observations, the impacts of typhoons on sea surface temperature (SST) and chlorophyll-a (Chl-a) are investigated. The SST time series shows that the SST begins to decrease 2 days before the typhoon’s arrival and continues to decrease until 2 days following the typhoon’s passage. The Chl-a has a weak peak 2 days prior to the typhoon’s arrival, rapidly increases after the typhoon arrives, reaches the strongest response on the third day of the typhoon, and gradually decreases to a value slightly higher than the pre-typhoon level. Prominent responses are associated with typhoons that have stronger intensity and slower translation speed. The pre-typhoon upper ocean structure plays a dominant role in determining oceanic responses. Surface cooling is generally stronger where the pre-typhoon mixed layer depth (MLD) is shallow. However, the change in Chl-a shows a contrasting response in that the response prominently increases only when the depth of typhoon-induced mixing exceeds the pre-typhoon MLD. This study poses a quantitative approach to assess the influence of typhoons on the upper ocean from a statistical perspective with consideration of the upper ocean structure.

How to cite: Wang, Y.: Determination of ocean structure on response of sea surface temperature and chlorophyll to typhoon in NW Pacific Ocean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1462, https://doi.org/10.5194/egusphere-egu24-1462, 2024.

   For the study of the marine heatwave that occurred from mid-May to late summer 2023, data provided by AEMET (Spanish Meteorological Agency) for the Gran Canaria Airport and Sea Surface Temperature from Copernicus (products METOFFICE-GLO-SST-L4-REP-OBS-SST and METOFFICE-GLO-SST-L4-NRT-OBS-SST-V2) have been utilized. The employed data include the daily records of meteorological and oceanographic variables from 1982 to 2023.

   A climatological normal year has been computed based on wind speed and Sea Surface Temperature (SST) data, calculating the mean value and smoothing the result with a moving average. A drop in wind speed has been observed in periods when the usual Trade winds are active over the eastern margin of the Atlantic ocean, decreasing from 13.8 m/s in early May, to only 3.0m/s in June, falling 5.8 m/s below the calculated average for that time of year. Associated with this decrease in wind intensity, there is a delayed increase in SST, reaching an average of 2.3 ºC above normal throughout the summer. Even after a subsequent increase in wind intensity, SST does not drop below normal values for the rest of the year. This relationship between a decrease in the wind intensity and an increase in the SST would suggest that the heat is being accumulated in the sea surface. We hypothesize that winds did not facilitate heat transfer from the sea surface in the form of sensible heat during a period when sensible heat is usually released from the ocean to the atmosphere.

   Under this scenario, with a lack of strong winds, mixing in the first layers of the water column is not effective, and the surface temperature measured from satellites is capturing a phenomenon that might mislead the deep-reaching extent of the anomaly. In ongoing analyses, we explore the impact on the water column affected by this abnormal increase in the sea surface temperature by using data provided by Argo floats profiling in the vicinity of the Canary Islands.

How to cite: Pereira, C., Aguiar-González, B., Carr, M., and Machín, F.: Wind-Speed Anomalies and SST Rise: Investigating the Mid-2023 Heatwave Propagation below the sea surface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13640, https://doi.org/10.5194/egusphere-egu24-13640, 2024.

Accurate sea surface height (SSH) forecasting is crucial for predicting coastal flooding and protecting communities. Recently, state-of-the-art physics-based numerical models have been outperformed by machine learning models, which rely on atmospheric forecasts and the immediate past measurements obtained from the prediction location. The reliance on past measurements brings several drawbacks. While the atmospheric training data is abundantly available, some locations have only a short history of SSH measurement, which limits the training quality. Furthermore, predictions cannot be made in cases of sensor failure even at locations with abundant past training data. To address these issues, we introduce a new deep learning method HIDRA3, that jointly predicts SSH at multiple locations. This allows improved training even in the presence of data scarcity at some locations and enables making predictions at locations with failed sensors. HIDRA3 surpasses the state-of-the-art model HIDRA2 and the numerical model NEMO, on average obtaining a 5.0% lower Mean Absolute Error (MAE) and an 11.3% lower MAE on extreme sea surface heights.

How to cite: Rus, M., Mihanović, H., Ličer, M., and Kristan, M.: HIDRA3: A Robust Deep-Learning Model for Multi-Point Sea-Surface Height Forecasting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3123, https://doi.org/10.5194/egusphere-egu24-3123, 2024.

Marine heatwaves (MHWs) have increased worldwide in recent decades and are considered one of the most pressing challenges of climate change due to their dramatic environmental and socio-economic impacts. This study examines the occurrence of MHW in the North Sea over more than four decades (1982-2023) by analyzing the long-term trends and interannual variations of MHW characteristics. The study also investigates the role of atmospheric and large-scale climate modes on MHW generation. We find that the accelerated SST warming trend (0.38 ± 0.04 °C/decade) was accompanied by an increase in MHW frequency by 1.0± 0.3 events/decade and in MHW days by 17± 6 days/decade over the entire period. In the summer of 2023, several extreme climate events were observed worldwide, including terrestrial and oceanic heatwaves. This triggered strong media interest and public concern about the causes and links to climate change. In the North Sea, the average SST value broke the record in June and September 2023 with several extreme MHWs. In June 2023, the northwestern part of the North Sea experienced the strongest MHW since 1982, which lasted three weeks (from June 13 to July 4, 2023) and was attributed to changes in atmospheric circulation.

Keywords: North Sea; SST; marine heatwaves; ERA5.

How to cite: Mohamed, B., Barth, A., and Alvera-Azcárate, A.: The summer marine heatwaves in the North Sea in 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8900, https://doi.org/10.5194/egusphere-egu24-8900, 2024.

In recent several years, sudden high swell waves have often occurred on the east coast of the Korean Peninsula, especially in the winter season, which caused many casualties and property damage. These sudden swells have the characteristics of suddenly generating high waves even though the wind does not blow strongly, sweeping away unwary people on breakwaters or causing property damage such as ports and fish farms located on the coast. This study develops a detection and warning system for sudden high swells that frequently occur on the Korean Peninsula's east coast in winter. Using the calculated swell-wind wave height difference, significant wave height, and wind speed, we developed a sudden high swell warning system in three stages (Warning, Watch, and Attention). Analysis reveals that this system successfully detected three recent swell-related accidents on the east coast of Korea. Further experiments by applying the system to the prediction results of the wave model showed that the method successfully issued a warning 24 hours before a sudden high swell reached the east coast of the Korean peninsula. The developed system can provide quantitative and consistent forecast information, which will significantly contribute to preventing accidents caused by sudden high swells along the east coast of the Korean Peninsula. Lastly, we investigated the meteorological conditions that trigger sudden high swell based on reanalysis data and synoptic weather charts.

Acknowledgement: This research was supported by the Korea Meteorological Administration Research and Development Program under Grant (RS-2023-00239702)

How to cite: Oh, Y. and Moon, I.-J.: Detection and Prediction for Sudden High Swells Along the East Coast of Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14475, https://doi.org/10.5194/egusphere-egu24-14475, 2024.