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 system (UKC4) and M & eacute;t & eacute;o-France's atmosphere-ocean regional coupled system (AROBASE) to capture and predict meteotsunamis. Configured at km-scale and with 10-min coupling frequency, the systems 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 systems are able to represent the meteotsunami: the Met Office system is more successful in the Celtic Sea around the UK, Ireland and the English Channel and the M & eacute;t & eacute;o-France system 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 represent this meteotsunami event.

In 2025, Météo-France implemented a new version of its climate prediction system for seasonal and subseasonal forecasting: System 9. This system belongs to the generation of Météo-France climate prediction systems based on the global coupled climate model CNRM-CM6-1 \citep{Voldoire2019}, developed at the Centre National de Recherches Météorologiques (CNRM). Building on its predecessor System 8, System 9 includes substantial changes in terms of ocean and sea-ice modeling, radiation scheme and initialization procedure. The article documents the configuration of System 9 and provides a comparative evaluation with System 8 in terms of model biases and predictive skill. First, System 9 often exhibits reduced biases, especially for surface temperatures over land and sea. Second, it demonstrates improved predictive skill for key parameters at seasonal timescales, such as Arctic sea-ice area around the September minimum and the Indian Ocean Dipole during its peak season. Third, it is also significantly more skillful at subseasonal timescales in the first forecast weeks, an improvement likely due to the revised initialization procedure. In the meantime, only a limited number of parameters, locations, and seasons show a clear degradation in bias or skill compared to System 8. Overall, the evaluation demonstrates that System 9 outperforms System 8 on several key metrics. This publication serves as the reference for the Météo-France operational seasonal forecasts provided to the Copernicus Climate Change Service (C3S) since 1 May 2025. It also establishes the baseline for the third generation of CNRM subseasonal forecasts feeding the Subseasonal-to-seasonal (S2S) database since 20 November 2025.

Ocean Reanalyses Workshop of the European Copernicus Marine Service What: Gather together ocean reanalyses users and producers to identify users' needs of ocean reanalyses and design the strategy to improve ocean reanalyses to fulfill users' needs When: 10-12 October 2023 Where: Toulouse, France, and online

Research and development activities around the current Météo-France operational seasonal forecasting system (System 8) are underway to upgrade it to the next version (System 9), along with efforts to improve the initialization of its components. Among these components, sea ice is particularly challenging to initialize. At present, a coupled-nudged initialisation strategy, based on a high-resolution configuration of the CNRM-CM6 climate model, is employed to initialise the System 8, except for the sea-ice. In order to get initial states of sea ice that are consistent with the forecasting model, our procedure consists in making a preliminary continuous run where the ocean and sea ice models are integrated in stand-alone mode, with forcing at the surface from an atmosphere reanalysis.However, in the current operational System 8 – based on the NEMO 3.6 ocean model and the GELATO sea ice model – the initial states of sea ice generated with this procedure are not fully realistic. Results show that the sea ice thickness over the Arctic region in the System 8 initial states is underestimated compared to the reference data. Numerous sensitivity experiments were carried out with the current NEMOv3.6-GELATO system, leading to some minor improvements. Thus, an upgraded version of the ocean model (NEMO version 4.2) coupled to a new sea-ice component (SI3) has been tested (in stand-alone mode, not coupled to the atmosphere) to see if the use of more recent versions of ocean and sea-ice models leads to some improvements in the Arctic sea ice representation. The results are encouraging as the representation of sea ice variables in the Arctic is improved compared to the old version.This incites our team to foresee that System 9 will indeed incorporate the NEMO4.2 and SI3 models, and that the same initialization procedure as before (using these new models) will provide sea-ice initial states closer to those observed.

We present an assessment of the water mass dynamics in a reanalysis of the Mediterranean Sea with a focus on the Algero-Provencal basin. We use a theta-S-based algorithm to compute the fractions of the main western Mediterranean water masses: Atlantic and modified Atlantic Waters (AW and mAW), Western and Eastern Intermediate Waters (WIW and EIW), Tyrrhenian and Western Mediterranean Deep Water (TDW and WMDW). The reanalysis retains the known mean characteristics of the water masses, their seasonal to interannual variabilities, and main circulation patterns when compared with the literature. The imprint of winter mixing is particularly obvious with coherent variations of water mass volumes, mainly the yearly creation of WIW from mAW on northernmost shelves and of WMDW from all surface and intermediate layers during years of deep water formation (DWF). The results also highlight some unrealistic events of variability of the WMDW volume that are likely due to the data assimilation process. Recomputation of water mass volumes and transports without these altered years allowed to highlight the possible disruption of large-scale barotropic cyclonic circulation in the East Algerian basin in response to major DWF events over the Gulf of Lion and the induced surface consequence on Algerian Eddies' trajectories.

Research and development activities around the current Météo-France operational seasonal forecasting system (System 8) are underway to upgrade it to the next version (System 9), along with efforts to improve the initialization of its components. Among these components, sea ice is particularly challenging to initialize. At present, a coupled-nudged initialisation strategy, based on a high-resolution configuration of the CNRM-CM6 climate model, is employed to initialise the System 8, except for the sea-ice. In order to get initial states of sea ice that are consistent with the forecasting model, our procedure consists in making a preliminary continuous run where the ocean and sea ice models are integrated in stand-alone mode, with forcing at the surface from an atmosphere reanalysis. However, in the current operational System 8 – based on the NEMO 3.6 ocean model and the GELATO sea ice model – the initial states of sea ice generated with this procedure are not fully realistic. Results show that the sea ice thickness over the Arctic region in the System 8 initial states is underestimated compared to the reference data. Numerous sensitivity experiments were carried out with the current NEMOv3.6-GELATO system, leading to some minor improvements. Thus, an upgraded version of the ocean model (NEMO version 4.2) coupled to a new sea-ice component (SI3) has been tested (in stand-alone mode, not coupled to the atmosphere) to see if the use of more recent versions of ocean and sea-ice models leads to some improvements in the Arctic sea ice representation. The results are encouraging as the representation of sea ice variables in the Arctic is improved compared to the old version. This incites our team to foresee that System 9 will indeed incorporate the NEMO4.2 and SI3 models, and that the same initialization procedure as before (using these new models) will provide sea-ice initial states closer to those observed.

The AROBASE (AROme-BAsed coupled SystEm) project aims to develop a coupled kilometre-scale numerical forecasting system incorporating ocean, waves, aerosols/chemistry and land surface models around the fine-scale AROME (Application of Research to Operations at MEsoscale) numerical weather prediction model. The AROBASE modelling system aims to improve : 1. our understanding of meteorological processes and interactions between the different environmental components; 2. the realism of the simulations by precisely and consistently representing these phenomena and by taking into account the complexity of the exchange processes between components; 3. the forecast of severe meteorological events by improving the representation of interactions at fine scale.One important step is the evaluation of ocean-atmosphere-waves-coupling in AROBASE in the frame of Météo-France's coastal wave warning system. To assess the ability of AROBASE to better represent meteorological extremes leading to such coastal hazards, various modelling configurations are tested using the SURFEX (SURface EXternalisée) surface model, the MFWAM wave model of Météo-France derived from WAM (WAve Model) and the NEMO (Nucleus for European Modelling of the Ocean) ocean model. Different combinations of these models and different momentum flux parametrisations are used to evaluate the coupling impact and the improvement of both the marine and numerical weather forecasts.The first case study is the Eunice storm, which impacted the British Islands and Northern France on February 18, 2022, causing extensive damages due to strong winds. Eunice is also characterised by a high swell combined with a high tidal coefficient that caused large flooding locally. The modelling results will be compared to satellite and in situ observations, as well as operational outputs of AROME and MFWAM.

The AROBASE (AROme-BAsed coupled SystEm) project of CNRM aims to assemble a multi-coupled regional modelling platform of the physico-chemical atmosphere, the ocean (including sea ice and marine biogeochemistry), the waves and the continental surfaces (soil, vegetation, cities, snow, lakes and rivers), at kilometric scale.In this context, a new high-resolution regional ocean configuration of the NEMO model has been developed. Named FRA36, it covers the maritime domain around mainland France with a resolution of ~2.5 km (ORCA 1/36° grid).In order to prepare the future ocean-atmosphere coupled system, FRA36 is first used in a configuration forced by the operational analyses of the AROME-France atmospheric model, at a horizontal resolution of 1.3 km and a 3h temporal resolution. FRA36 uses the global Copernicus Marine Service operational oceanographic productions with data assimilation (GLO12 analyses product) for initialisation and boundary conditions.We use this configuration to reproduce and analyse the summer 2022 succession of marine heatwave events around mainland France (English Channel, Bay of Biscay, North-Western Mediterranean Sea), using a continuous 3-month ocean simulation initialised the 1st of June 2022.First, the spatial and temporal evolution of the Sea Surface Temperature (SST) in this simulation is validated using satellite products. FRA36 reproduces well the succession of observed long-lasting warming periods, interspersed with sudden cold spells. Then, heat budgets in the ocean mixed layer are used to separate atmospheric (solar and non-solar fluxes) and oceanic (advection, mixing, entrainment) contributions to surface and sub-surface temperature variations. Following on from the Guinaldo et al. 2023 study, we here take advantage of the added value of having a 3D oceanic component, including explicit tides, and the atmospheric forcing at high spatio-temporal resolution from AROME-France, to characterise the respective atmospheric and oceanic contributions in the occurrences, maintenances and ends of this succession of high-stakes events.

We present an assessment of the water mass dynamics in a reanalysis of the Mediterranean Sea with a focus on the Western basin. We use a θ-S based algorithm to compute the fractions of the main western Mediterranean water masses : Atlantic and modified Atlantic Waters (AW, mAW), Western and Levantine Intermediate Waters (WIW and LIW)and Western Mediterranean Deep Waters (WDW). The reanalysis retains the known mean characteristics of the water masses, their seasonal to interannual variability and main circulation patterns when compared with the literature. The imprints of winter mixing is particularly obvious with coherent variations of water mass volumes, mainly the yearly creation of WIW from mAW on northernmost shelves and of WMDW from all surface and intermediate layers during years of deep water formation. The results also highlight some unrealistic events of variability of the WMDW volume that are likely due to the data assimilation process. Re-computing the water mass volumes and transports without these altered years allowed to highlight the possible disruption of the large-scale barotropic cyclonic circulation in the Eastern Algerian basin in response to major DWF events over the Gulf of Lion. The reanalysis also showsan overtopping ofWMDW in the Sardinia Channel in 2009 leading to a major backward flow of mAW from the Tyrrhenian to the Algero-Provençal basin. Both processes affects the circulations of AW and mAW over the whole western Mediterranean.

The AROBASE project aims to assemble a kilometre-scale limited-area multi-coupled modelling system of the physico-chemical atmosphere, the ocean (including sea-ice and marine biogeochemistry), waves and land surfaces (soil, vegetation, cities, snow, lakes and rivers) with important development criteria that are i) the transportable nature of the regional multi-coupled model and ii) the modular aspect to couple the relevant environmental components according to different applications. The AROBASE platform that will combine the AROME atmospheric model (with online chemistry and interactive aerosols) with the external surface model SURFEX, CTRIP for hydrological routing, NEMO and MFWAM for ocean and waves respectively, is built in the line of a seamless continuum of coupled modelling systems developed and used at CNRM, LACY and Météo-France. AROBASE will first help to improve the understanding and representation of the exchange processes between the compartments of the meteorological and environmental system at fine scale. It is also a new tool for high-resolution numerical weather prediction, which makes it particularly necessary to guarantee its performance in the forecast mode and its relevance for monitoring and anticipating meteorological phenomena and their consequences. AROBASE is finally an important step to prepare the new generation of the regional climate model (CNRM-RCSM) towards a kilometre resolution with new integrated components. The first results of the AROBASE platform will be presented during the conference, with a focus on the ocean-atmosphere-wave coupling, the air-sea interactions implied during severe meteorological situations over France metropolitan area and over-seas domains and impacts on numerical weather prediction.

OSDYN (Observations and Simulations of the DYNamics) is a Python library that proposes diagnostics to explore the dynamics of the ocean and its interactions with the atmosphere and waves. Its main strengths are its genericity concerning the different types of netCDF files and its ability to handle large volumes of data. Dedicated to large data sets such as in-situ, satellite, and numerical model observations, OSDYN is particularly powerful to manage different types of Arakawa-C grids and vertical coordinates (Nemo, Croco, Mars, Symphonie, WW3, MesoNH). Based on common Pangeo stack (xarray, dask, xgcm), OSDYN provides data readers that standardize the dimensions, coordinates, and variables names and properties of the datasets. Thus, all python diagnostics can be shared regardless of the model outputs. Thanks to progress made using kerchunk and efforts on transforming metadata of Ifremer’s HPC center (auto-kerchunk), the reading of a large amount of netCDF files is fast and the selection of sub-domains or specific variables is almost immediate. Jupyter notebooks will detail the implementation of three kinds of analyses. The first one focuses on climatologic issues. In order to compare modeled and satellite sea surface temperatures, the second one addresses spatial interpolation and comparison of data when some may be missing. Lastly, the third analysis provides an overview of how diagnostics describing the formation of deep water masses can be used from different data sets.

Abstract. To improve high-resolution numerical environmental prediction, it is essential to represent ocean-atmosphere interactions properly, which is not the case in current operational regional forecasting systems used in Western Europe. The objective of this paper is to present a new forecast-oriented coupled ocean-atmosphere system and its evaluation. This system uses the state-of-the-art numerical models AROME (cy43t2) and NEMO (v3.6) with a horizontal resolution of 2.5 km. The OASIS coupler (OASIS3MCT-4.0), implemented in the SurfEX surface scheme and in NEMO, is used to perform the communications between models. The evaluation of this system is carried out using 7-day simulations from 12 to 19 October 2018, characterised by extreme weather events (storms and heavy precipitation event) in the area of interest. Comparisons with in-situ and L3 satellite observations show that the fully coupled simulation reproduces quantitatively well the spatial and temporal evolution of the sea surface temperature and 10 m wind speed. Sensitivity analysis to OA coupling show that the use of an interactive and high resolution SST, in contrast to actual NWP where SST is persistent and at low resolution, modifies the atmospheric circulation and the location of heavy precipitation. When compared to the operational-like ocean forecast, simulated oceanic fields show a large sensitivity to coupling. Forced ocean simulations highlight that this sensitivity is mainly controlled by the change in the atmospheric model used to drive NEMO (AROME vs. ECMWF IFS operational forecast). The oceanic boundary layer depths can vary by more than 40%. This impact is amplified by the interactive coupling and is attributed to positive feedback between sea surface cooling and evaporation.

We focus on the characterization of thermohaline fronts in the Western Mediterranean, with a particular focus on the North Balearic Front (NBF), separating the Atlantic Waters that spread into the Algerian Basin from the saltier and colder waters of the Liguro-Provencal area. We use a simple gradient-based method of front detection applied to a 20-year (from June 1993 to June 2013) reanalysis of the Mediterranean. Statistics of daily frontal indices are used to identify areas of recurrent fronts, i.e., frontal zones. Comparisons with data from glider transects and remotely sensed sea surface temperature and altimetry data have been used to validate our approach from daily to seasonal and interannual time scales. Our method yielded two co-existing frontal zones in the area of the NBF. One with an almost permanent haline surface frontal zone extending southeastward from the Balearic Islands to Sardinia, representing the northern limit of the fresher Atlantic Water that spreads via instabilities of the Algerian Current and associated Algerian Eddies. Between years, its position shifts by about 1 degrees of latitude, possibly due to processes associated with both the deep water formation in the Provencal Basin and the spreading of southern Algerian Eddies. The second frontal zone is seasonal and thermally driven extending off the northeast of Menorca to the northwest of Corsica. The Pyrenees Front, a sharp thermal front off Cap de Creus which marks the boundary between the warm surface waters of the Balearic Sea and the cooler waters in the Gulf of Lion in late summer, appears to facilitate the formation of the aforementioned seasonal thermal front through the northeastward advection of its waters toward the West Corsican Current. The divergent eastward extensions of the two frontal zones, and their differences in nature, structure, and spatio-temporal variability, call for a revisit of the NBF appellation and a clarification of its dynamics.

We present an analysis of specific water masses fluxes in the Western Mediterranean Sea issued from a twenty years (1992-2013) reanalysis (MEDRYS1V2). Water masses are identified on the base of salinity and potential density properties and computes; the fractions of each water mass involved in total flux are computed under the hypothesis assumptions of mixing lines schemes. It was first designed in order to avoid rough truncations between water masses on the T-S diagram when using fixed thermo-haline properties thresholds. The method does not use the temperature marker due to its high seasonal variability in near surface waters (0-200 m) and we consider that potential density is a better marker to discriminate deep and intermediate water masses. The algorithm discriminates successively five different water masses : the Atlantic Water (AW) incoming from the Gibraltar strait (salinity between 36,1 and 38,45 PSU), the Levantine Intermediate Waters (LIW) incoming from the Tunisia-Sicily strait (salinity between 38,45 and 39.1 PSU), the Modified Atlantic Waters (MAW) defined as near-surface waters (potential density less than 28,9 kg m-3) that are neither AW or LIW, while Western Intermediate Waters (WIW) are those remaining until the σθ = 29,10 kg m-3 threshold for Western Mediterranean Deep Waters (WMDW) is reached. Such computed fractions of each water mass, whose sum is constrained to unity, are then used to compute their water masses transports all along over twenty years of the reanalysis. The transport are assessed across computed on key transects delimiting known sub-basin entities (Ligurian Sea, Gulf of Lion, Balearic Sea...), with total transports showing balanced mass budget. The such computed total transport reveal marked differences in their seasonal to interannual variability, while the analysis of the water mass transports allows to identify those which mainly implied induced these variability. The results first show a low seasonal and no significant interannual variability at the exit of the Alboran Sea that results from the balance between the eastward AW/MAW outflow and the westward WIW and WMDW inflows. The Corsican strait, the Ligurian Sea line and Tunisia-Sardinia straits show a marked seasonal variability (0,37-0,39 Sv) mainly driven by the AW/MAW. By contrast, a strong interannual variability dominates the seasonal one (-2 to 1 Sv) between the Algerian Basin and the northern basin, correlated to the WMDW formation. The analysis of each specific water masses transport pointed out that shows this marked variability to be first driven by the intermediate and deep water masses transports. Similarly the interannual variability of the AW and MAW transports in the central part of the Western Mediterranean suggests some coupling between the deep, intermediate and surface water masses, even through the shallower Balearic Sea.

The Copernicus Marine Environment Monitoring Service (CMEMS; http://marine.copernicus.eu) is one of the six services of the European Copernicus Programme for Earth Observation (http://www.copernicus.eu). CMEMS was implemented by Mercator Ocean beginning in 2014, under a delegation agreement from the European Commission. The operational services of CMEMS were set up gradually as part of a series of European projects, starting with MERSEA (2004-2008), and followed by MyOcean (2009-2012) under FP7, and MyOcean2 (and its follow-on) from 2012 through 2015.

This study evaluates the Mediterranean Sea heat budget components from a set of forced and coupled simulations performed in the frame of the Med-CORDEX project. The simulations use regional climate system models (RCSMs) dedicated to the Mediterranean area and driven by the ERA40/ERA-Interim reanalyses. The study focuses on the period 1980–2010. Interannual variations of the average net heat flux at the sea surface are consistent among models but the spread in the mean values is large (from −4.8 to +2.2 Wm −2 ) with the coupled models showing the lowest heat loss from the sea. For the heat flux at the Strait of Gibraltar both interannual variations and mean values show a large intermodel spread. The basin average temperature shows positive trends with highest values in the coupled models; it also shows interannual variations that are in good agreement with observations. The heat content rate is calculated based on the derivative of the average temperature and is found to be significantly correlated for most models with the net heat flux at the sea surface (average correlation ~0.5) but not with the net heat flux through the Strait of Gibraltar (average correlation ~0.2), suggesting that in the considered RCSMs the interannual variability of the heat content rate is mainly driven by the surface heat fluxes. The resemblance between the simulated and observed heat content rates is stronger in the forced models than in the coupled ones. This is explained by the stronger constraint applied to the forced models by the use of the surface temperature relaxation to observations. The temperature of the outflowing water through the Strait of Gibraltar shows positive and significant trends, also higher in the coupled models. It is suggested that the Mediterranean Sea warming found in most models and in particular in the coupled ones, induces a change of the hydrographic conditions that affects the Strait of Gibraltar.

Atmospheric deposition represents a significant source of nutrients at the Mediterranean basin scale. We apply aerosol deposition fields simulated from atmospheric models into the high resolution oceanic biogeochemical model NEMOMED12/PISCES with nutrient ratios used for plankton growth set to Redfield ratio. We perform 3 simulations to determine the impact of nutrients on productivity over the period 1997–2012: (i) without atmospheric deposition, (ii) with nitrogen deposition from anthropogenic and natural sources, and (iii) with deposition of both nitrogen (from anthropogenic and natural sources) and phosphate from desert dust. Time series of modeled deposition fluxes are compared to available measurements. This comparison with measurements shows that both variability and intensity ranges are realistic enough for our main purpose of estimating the atmospheric deposition impact on Mediterranean biogeochemical tracers such as surface nutrient concentrations, chlorophyll a and plankton concentrations. Our results show that atmospheric deposition is one of the major sources of nitrogen and phosphorus for some regions of the oligotrophic Mediterranean Sea. More than 18·109gNmonth−1 are deposited to the whole Mediterranean Sea. This deposition is responsible for an average increase of 30–50% in primary production over vast regions. Natural dust-derived deposition of phosphorus is sparser in space and time (0.5·109gmonth−1 on average over the entire basin). However, dust deposition events can significantly affect biological production. We calculate fertilizing effects of phosphate from dust to be low on average (6–10%) but up to 30% increase in primary productivity can be observed during the months when surface water stratification occurs. Finally, these fertilizing effects are shown to be transmitted along the biological chain (primary production, Chl a, phytoplankton, zooplankton, grazing). We also perform a preliminary study on the maximal biological response of the Mediterranean by simulating extreme deposition events throughout the basin over a full year period. We show that nitrogen deposition effects observed in our long-term simulations (1997–2012) are close to maximal effects (i.e. those produced by high intensity deposition events) whereas dust-derived phosphate effects are substantially weaker than the effect on productivity reached when an extreme deposition event occurs.

The north-western Mediterranean Sea is a key location for the thermohaline circulation of the basin. The area is characterized by intense air-sea exchanges favored by the succession of strong northerly and north-westerly wind situations (mistral and tramontane) in autumn and winter. Such meteorological conditions lead to significant evaporation and ocean heat loss that are well known as the main triggering factor for the Dense Water Formation (DWF) and winter deep convection episodes. During the HyMeX second field campaign (SOP2, 1 February to 15 March 2013), several platforms were deployed in the area in order to document the DWF and the ocean deep convection, as the air-sea interface conditions. This study investigates the role of the ocean-atmosphere coupling on DWF during winter 2012-2013. The coupled system, based on the NEMO-WMED36 ocean model (1/368 resolution) and the AROME-WMED atmospheric model (2.5 km resolution), was run during 2 months covering the SOP2 and is compared to an ocean-only simulation forced by AROME-WMED real-time forecasts and to observations collected in the north-western Mediterranean area during the HyMeX SOP2. The comparison shows small differences in terms of net heat, water, and momentum fluxes. On average, DWF is slightly sensitive to air-sea coupling. However, fine-scale ocean processes, such as shelf DWF and export or eddies and fronts at the rim of the convective patch, are significantly modified. The wind-current interactions constitute an efficient coupled process at fine scale, acting as a turbulence propagating vectors, producing large mixing and convection at the rim of the convective patch.

The HYdrological cycle in the Mediterranean Experiment (HyMeX) Special Observing Period 2 (SOP2, January 27–March 15, 2013) was dedicated to the study of dense water formation in the Gulf of Lion in the northwestern Mediterranean. This paper outlines the deep convection of winter 2012–2013 and the meteorological conditions that produced it. Alternating phases of mixing and restratification are related to periods of high and low heat losses, respectively. High-resolution, realistic, three-dimensional models are essential for assessing the intricacy of buoyancy fluxes, horizontal advection, and convective processes. At the submesoscale, vertical velocities resulting from symmetric instabilities of the density front bounding the convection zone are crucial for ventilating the deep ocean. Finally, concomitant atmospheric and oceanic data extracted from the comprehensive SOP2 data set highlight the rapid, coupled evolution of oceanic and atmospheric boundary layer characteristics during a strong wind event.