In this study, we use in situ observations and high-resolution coupled ocean-atmosphere simulations to investigate the mechanical coupling between the ocean and the atmosphere (referred to as Current Feedback, CFB) at the oceanic submesoscale (O(10 km)) and wind roll scales. First, we show that while the CFB remains active at the submesoscale with a stronger effect on the surface stress during the winter, its effect on submesoscale energetics is weaker than at the mesoscale. This effect is further weakened by energy contributions from thermal feedback and the highly transient nature of submesoscale flow. In addition, using in situ observations from DopplerScat and very high resolution (dx = 80 m) coupled simulations, we show that wind rolls can obscure the imprint of surface currents on surface stress and low-level winds. This interaction induces an energy transfer from the atmosphere to the ocean that overwhelms the energy transfer from submesoscale currents to the atmosphere, and generates currents coherent with the wind rolls down to 20 m depth.
How to cite: Renault, L., Rodriguez, E., Conejero, C., Uchoa, I., Marchesiello, P., Contreras, M., and Wenegrat, J.: Mechanical Air-Sea Interactions at submesoscale and Wind Rolls Scales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6892, https://doi.org/10.5194/egusphere-egu25-6892, 2025.
How to cite: Borg, A., Renault, L., Lapeyre, G., Morvan, G., Jouanno, J., and Jean-Baptiste, S.: Toward a better understanding of the effects of mesoscale air-sea interactions on the Antartic Circumpolar Current dynamics using coupled ocean-atmosphere models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5682, https://doi.org/10.5194/egusphere-egu25-5682, 2025.
Advances in uncrewed surface vehicles (USVs) enable expanded observations in the Southern Ocean, a region vital for global heat uptake yet critically undersampled. Using data from three USVs that sampled the Pacific sector of the Southern Ocean in both summer and winter, we evaluate processes and decorrelation scales driving sensible heat flux variability. High flux variability is linked to synoptic-scale southwesterly winds, with sensible heat flux decorrelation scales of 40–60 km and 6–10 hours, consistent across seasons and variables. Fine-scale (<1–10 km) oceanic processes, including fronts, filaments, and boundaries, further influence flux variability: Our datasets reveal over 8,000 temperature fronts ranging from <1 km to >20 km in width. While wind-related variability dominates sensible heat flux changes across the smallest fronts, the ocean’s role becomes increasingly significant with front width, reaching parity at ~4 km. However, due to their abundance, the total change of sensible heat flux over smaller (~1 km) fronts is an order of magnitude greater than that of larger (>4 km) fronts. These results highlight the role of fine-scale atmosphere-ocean interactions in driving heat flux variability in the Southern Ocean, offering valuable insights for enhancing flux estimates in this critical region.
How to cite: Edholm, J., Rosenthal, H., Biddle, L., Gille, S., Mazloff, M., du Plessis, M., and Swart, S.: Drivers of sensible heat flux in the Southern Ocean and their relationship to submesoscale fronts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-283, https://doi.org/10.5194/egusphere-egu25-283, 2025.
To do so, we compare 5 air-sea fluxes parametrizations within the IPSL General Circulation Model (GCM) [2] based on the new DYNAMICO atmospheric dynamical core [3] and the ocean engine NEMO [4]. We show that the spread in AMOC is more than 2 Sv, confirming the high sensitivity to air-sea fluxes. Furthermore, we manage to explain these discrepancies by assessing (i) winter time buoyancy fluxes in DWF area and (ii) subtropical and subpolar gyres intensity which drives the circulation. We also analyse the ocean-atmosphere feedbacks (mainly wind and sea surface temperature) that may be responsible for changes in AMOC, hence paving the way to a better representation in GCMs.
How to cite: Dehondt, C., Braconnot, P., Fromang, S., and Marti, O.: AMOC sensitivity to air-sea fluxes parametrization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8009, https://doi.org/10.5194/egusphere-egu25-8009, 2025.
How to cite: Delpech, A. and Tréguier, A.-M.: The role of small-scale ocean mixing processes in regional sea surface temperature, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16290, https://doi.org/10.5194/egusphere-egu25-16290, 2025.
Submesoscale eddies in the ocean surface layer are known to cause the restratification of the mixed-layer by converting the potential energy stored in the outcropping isopycnals into kinetic energy. Evidence of entrainment and subduction is found associated to submesoscale eddies, suggesting their importance for the biogeochemistry of the global ocean. Submesoscale eddies cannot be resolved in today’s global ocean models and existing parameterizations for baroclinic mixed-layer instabilities (MLIs), which are proven to reproduce the restratification quite well, are not capable to fully capture the vertical exchange of passive tracers across the mixed-layer. In this study, high resolution numerical simulations show the inadequacy of the MLI parameterization of Fox-Kemper, Ferrari, and Hallberg (2008, ‘FFH’) for the entrainment problem. A method for tracer inversion is then used to gain insights on the tracer transport in order to inform the parameterization. Parameter dependence is explored by considering different ocean initial conditions. Finally, the results show that a diffusive (symmetric) component needs to be included to the streamfunction (anti-symmetric) to entirely represent the transport induced by MLIs: the parameterization for entrainment is an update to the FFH parameterization.
How to cite: Lo Piccolo, A., Fox-Kemper, B., Brett, G. J., Chor, T. L., Wenegrat, J. O., and Zheng, Z.: Parameterizing Entrainment Induced by Submesoscale Eddies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18874, https://doi.org/10.5194/egusphere-egu25-18874, 2025.
Coastal breezes are mesoscale meteorological phenomena primarily driven by the thermal contrast between land and sea surfaces, creating a dynamic system that influences local circulation. These phenomena, common in coastal regions, have a significant impact on various environmental aspects, such as regulating extreme temperatures, transporting atmospheric pollutants, and modifying coastal surface ocean currents. This study aims to characterize the sea breeze system along the southwest coast of Spain, using a combination of observational data to provide a more detailed understanding of these phenomena in the region.
The analysis of sea breeze events focused on the summers of 2023 and 2024, using data obtained from coastal meteorological stations and radiosondes launched specifically in the study area to gather vertical information on the breezes. To detect breeze events, an objective algorithm based on the work of Borne et al. (1988), Arrillaga et al. (2018), and Román-Cascón et al. (2019) was used. This algorithm facilitated the identification of breeze events based on atmospheric conditions, providing a basis for further analysis.
A key contribution of this study is the proposal of a new classification of breeze types, enabling a more accurate characterization of different breeze events, by considering variables such as intensity, duration, and associated synoptic conditions. Furthermore, statistics of the recorded events are presented, offering a deeper insight into the frequency, intensity, and temporal characterization of breezes in the study area. The study also explored the relationship between turbulent variables during breeze events and different tidal moments, which is particularly relevant due to the large intertidal zone affecting one of the stations used. This observational approach enhances the understanding of the coastal breeze system in the study area and contributes to the broader knowledge of these phenomena.
How to cite: Luján-Amoraga, E., Román-Cascón, C., Bolado-Penagos, M., Ortiz-Corral, P., Jimenez-Rincón, J. A., Izquierdo, A., Bruno, M., and Yagüe, C.: Dynamics of sea breezes: Analysis of recent events in Southwest Spain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9247, https://doi.org/10.5194/egusphere-egu25-9247, 2025.
Ocean-surface vector winds, currents, and their interaction play critical roles in shaping many aspects of the Earth’s environment (e.g., weather, climate, marine ecosystems, and ocean health), affecting human safety and wellbeing both on land and at sea. However, there are significant capability gaps in observing winds, currents, and their interaction. At present, global gridded products of surface currents have coarse (~150 km) feature resolutions and rely on theoretical assumptions that break down near the equator. Moreover, there is no satellite that provides simultaneous wind-current measurements that are important for studying wind-current coupling and its impact on weather and climate. The “Ocean DYnamics and Surface Exchange with the Atmosphere” (ODYSEA) satellite mission concept is designed to alleviate these capability gaps. ODYSEA, proposed to NASA’s Earth System Explorers program in mid-2023, aims to provide the first-ever global measurements of total surface currents and simultaneous winds with 5-km data postings and near-daily coverage of the global ocean. ODYSEA builds on NASA’s heritage of scatterometry and the success of the airborne Doppler scatterometer flown as part of the Sub-Mesoscale Ocean Dynamics Experiment (S-MODE), NASA’s Earth Venture Suborbital-3 (EVS-3) mission. ODYSEA also leverages strong domestic and international partnerships. Here we present ODYSEA’s objectives, anticipated capabilities, and expected contributions to advance the understanding of surface current dynamics and air-sea interaction.
How to cite: Lee, T., Gille, S., Ardhuin, F., Bourassa, M., Chang, P., Cravatte, S., Dibarboure, G., Farrar, T., Fewings, M., Girard-Ardhuin, F., Jacobs, G., Jelenak, Z., Lyard, F., May, J., Rémy, E., Renault, L., Rodriguez, E., Ubelmann, C., Villas Bôas, B., and Wineteer, A.: ODYSEA: a satellite mission to advance knowledge of ocean dynamics and air-sea interaction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2211, https://doi.org/10.5194/egusphere-egu25-2211, 2025.
Advances in satellite microwave remote sensing have demonstrated an unprecedented capability to observe global ocean sea surface salinity (SSS) from space since 2009. Satellite-based SSS observations provide a unique monitoring capability for the interfacial water exchanges between the atmosphere and the upper ocean, as well as salinity redistribution due to climate and global water cycle variability, and land-ocean interactions.
Satellite measurements of sea surface salinity (SSS) started in November 2009 with the Soil Moisture and Ocean Salinity (SMOS) mission launched by the European Space Agency (ESA). The Aquarius/SAC-D, launched in June 2011 by NASA and the Argentinean Space Agency (CONAE), was the first satellite mission designed to measure SSS. Meanwhile, the Soil Moisture Active and Passive (SMAP) was launched by NASA in January 2015, and it provides SSS as a derived product. SMAP is configured with a larger swath coverage, providing a higher spatial resolution (~40 km) than that (~100 km) in Aquarius.
Satellite remote sensing of SSS encounters many challenges, such as contamination of microwave signals near coastal areas or dependance of SSS accuracy on the quality of temperature and wind speed measurements. As such, the satellite-derived SSS data needs to be validated against in-situ measurements.
Here we used in-situ measurements of salinity and temperature from ARGO data for three oceanic basins i.e., Bay of Bengal (BOB), South China Sea (SCS), and Western North Pacific Ocean (WNPAC). The ARGO data from Sep 2011 to Dec 2022 were utilized for analysis due to the consistency of the period with the available satellite-derived salinity data. The number of ARGO profiles varies significantly among these three oceanic basins with the largest profiles available in the WNPAC and the least number of profiles in the SCS.
ARGO SSS climatology, although available at a coarser resolution than the satellite-derived SSS, captured the spreading of the low salinity water in the BOB during Oct-Dec. This feature is consistent with the satellite-derived SSS spatial distribution. For the BOB, the agreement between ARGO and satellite SSS data is reasonably good with an RMSE of 0.58 psu. In comparison, the SCS and WNPAC achieve RMSE of 0.22 psu and 0.14 psu, respectively. It should be noted that the number of near-surface ARGO observations is much higher in the WNPAC (37,207) compared to that in the BOB (15,305) and in the SCS (9,722) from Sep 2011 to Dec 2022. The BOB reveals strong seasonality and the largest variation in SSS from ~25-35 psu. Whereas, the SCS and WNPAC recorded variations in the range ~32-35 psu. The SCS and WNPAC exhibit freshening and salinification in specific years. The monthly mean SSS from ARGO and satellite data are highly correlated and show consistent variation in salinity in all three oceanic basins. Therefore, the satellite-derived SSS data could provide great insight for understanding ocean dynamics, circulation, water cycle, and could be useful for validating ocean models.
How to cite: Sasmal, K., Dandapat, S., Xu, X., Tkalich, P., Thompson, B., Kumar, R., Furtado, K., and Zhang, H.: Assessment of satellite-derived sea surface salinity using in-situ measurements in the Southeast Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13975, https://doi.org/10.5194/egusphere-egu25-13975, 2025.
Near-inertial internal waves (NIWs) are among the primary drivers of turbulence that sustains the ocean stratification. To propagate downward into the ocean interior, NIWs typically need horizontal scales L∼100 km. Therefore, it is commonly held that NIWs generated by basin-scale midlatitude storms depend on refraction by background vorticity gradients to become horizontally compact and then propagate into the thermocline. This contrasts with NIWs generated by tropical cyclones (TCs), which can rapidly propagate downward regardless of background ocean conditions. Here, we study the upper ocean response to midlatitude storms and TCs using a dynamical framework whose equations of motion are written in terms of vorticity and divergence rather than velocity vectors. We show that patterns of wind stress curl and convergence that are inherently linked to atmospheric convection necessarily generate NIWs that are horizontally compact and can induce substantial downward energy fluxes within the first inertial cycle after storm passage. The vorticity-divergence dynamical framework elucidates this because it allows us to account for spatial wind patterns even when solving motion linearly and for a single point in space. With this, we argue that the morphology of mesoscale convective systems allows them to drive downward propagation of NIWs in their wakes, whether ocean storms take the shape of a TC or a midlatitude storm.
How to cite: Brizuela, N. and D'Asaro, E.: Morphology of atmospheric convective systems facilitates rapid transmission of near-inertial energy into the ocean thermocline, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11271, https://doi.org/10.5194/egusphere-egu25-11271, 2025.
Deep-cycle turbulence (DCT) is a critical mechanism driving vertical mixing in the equatorial Pacific, playing a pivotal role in modulating heat and nutrient transport within the Pacific Cold Tongue. DCT arises from diurnal variations in stratification and shear, leading to turbulence that extends below the mixed layer. DCT generates significant heat fluxes into the ocean, averaging O(100 W m⁻²) and peaking at ~1000 W m⁻² during nighttime bursts, which contribute to surface cooling and thermocline warming. This process helps maintain cool sea surface temperatures (SSTs) and net heat uptake in the eastern Pacific Cold Tongue, influencing SST dynamics on interannual, seasonal, and subseasonal timescales. These dynamics significantly impact air-sea interactions, as DCT regulates the exchange of heat, momentum, and gases, which play a critical role in shaping tropical weather patterns and global climate variability.
Despite previous studies elucidating the temporal variability and mechanisms of DCT on the equator, its spatial extent and variability across the equatorial Pacific remain poorly understood due to limited observations.
This study examines the spatial and temporal variability of DCT in the Cold Tongue region using Large Eddy Simulations (LES), which explicitly resolve sub-grid-scale mixing processes. The LES cover a meridional array of seven latitudinal points (1.5°S to 4.5°N) along 140°W and a zonal array spanning the central to eastern Pacific (165°W to 100°W) along the equator during contrasting periods influenced by Tropical Instability Waves (TIWs) and the seasonal cycle. Complementary hourly turbulence outputs from a 20-year MITgcm simulation are utilized to examine parameterized turbulence at these locations, enabling a comparison between sub-grid-resolved turbulence in LES and parameterized turbulence in the MITgcm.
Diurnal composite analyses reveal that parameterized turbulence in the MITgcm overestimates diapycnal heat flux compared to LES-resolved turbulence. The relationship between Richardson number, shear, stratification, and mixing is explored to understand the transition from the marginally stable regime near the equator (0°N, 140°W) to more stable conditions farther from the equator. Preliminary findings illustrate spatial asymmetries in mixing-related variables, with notable differences between the northern and southern hemispheres. These results highlight the need for further exploration of hemispheric asymmetries and their implications for mixing processes.
This study sets the stage for a comprehensive evaluation of mixing representation in the Pacific Cold Tongue region across diurnal to longer timescales, leveraging a hierarchy of model outputs, from LES to regional and global high-resolution simulations.
How to cite: Joseph, J., Deppenmeier, A.-L., B Whitt, D., O. Bryan, F., S. Kessler, W., Thompson, L., and Thompson, E.: Spatial Extent and Variability of Equatorial Deep-Cycle Turbulence in the Pacific Cold Tongue, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14246, https://doi.org/10.5194/egusphere-egu25-14246, 2025.
Tropical instability waves (TIWs), one of the most prominent mesoscale oceanic phenomena in the tropical Pacific, play important roles in climate and ecosystem. Due to limited observations and the difficulty in estimating equatorial current velocity, long-term changes in TIWs remain unknown.
Rather than the geostrophic equilibrium (Bonjean and Lagerloef, 2002), the TIW currents exhibit a momentum balance between inertial forces (local accelerations and advections), the Coriolis force and the pressure gradient force. Using a shallow water diagnostic model that retains the inertial forces, we have produced the TIW surface currents since 1993 based on the satellite altimetry sea surface height observations. The results have been well validated with moored observations of ocean velocities in TAO array (Wang et al., 2020, https://doi.org/10.1175/JPO-D-20-0063.1).
The satellite altimetry-derived TIW currents (1993-2021) have shown that TIWs have strengthened during this period, with their eddy kinetic energy (EKE) increasing by 12% per decade (~10 J m-3 per decade). The trend has been corroborated by other three independent datasets: satellite-observed sea surface temperature (1982-2021), moored currents from TAO (1980s-2020), and a global eddy-resolving ocean circulation model data (OFES2, 1958-2021). They consistently imply that the intensification is concentrated on the equatorial Yanai-mode TIWs. EKE budget based on OFES2 model data suggests that the increased EKE is attributed to the increased barotropic (primary) and baroclinic (secondary) instabilities. The former is due to the strengthened south equatorial currents (SEC), and the latter is due to the decreased mixed layer stratification and increased equatorial buoyancy fronts. The underlying mechanism is an enhanced cross-equatorial asymmetric warming in the eastern tropical Pacific since the 1990s that forces the changes in the equatorial multiscale ocean dynamics. As a feedback effect on the heat budget of cold tongue SST, the intensified TIWs lead to increased eddy dynamic heating effects of ∼70% since the 1990s near the equator, with implications for predicting and projecting tropical Pacific climate changes. (https://doi.org/10.1038/s41558-023-01915-x)
How to cite: Wang, M., Xie, S.-P., Sasaki, H., Nonaka, M., and Du, Y.: Intensification of Pacific tropical instability waves over the recent three decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5858, https://doi.org/10.5194/egusphere-egu25-5858, 2025.
There is a large number of mesoscale eddies in the ocean, which play a significant role in ocean circulation and climate change. Recent studies have indicated that mesoscale eddy activity in most regions will become more active under the influence of global warming, but changes in the characteristics of these eddies remain unclear. This study utilizes satellite observational data and reanalysis datasets, focusing on the Agulhas Leakage region, which is rich in mesoscale eddies and has become a research hotspot due to its unique geographical position. The study finds that the changes in the characteristics of anticyclonic eddies in this region are related to variations in the Atlantic Meridional Overturning Circulation (AMOC). Some of the eddy characteristics exhibit dynamic adjustments, with a turning point around 2005, which may be associated with sea temperature differences between the South Indian Ocean and the South Atlantic, as well as changes in the local wind field. The findings of this study will provide insights for future predictions of AMOC variability.
How to cite: Wei, L. and Wang, C.: Why do warm anticyclonic eddies in the Agulhas Leakage undergo dynamic adjustments?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17915, https://doi.org/10.5194/egusphere-egu25-17915, 2025.
Mesoscale eddies are ubiquitous features of the global ocean circulation. Tradiontally, anticyclonic eddies are thought to be associated with positive temperature anomalies while cyclonic eddies are associated with negative temperature anomalies. However, our recent study found that about one-fifth of the eddies identified from altimeter data are surface cold-core anticyclonic eddies (CAEs) and warm-core cyclonic eddies (WCEs). Idealized numerical model experiments highlight the role of relative wind-stress-induced Ekman pumping, surface mixed layer depth, and vertical entrainment in the formation and seasonal cycle of these unconventional eddies. The abundance of CAEs and WCEs in the global ocean calls for further research on this topic.
How to cite: Zhai, X.: Cold anticyclonic eddies and warm cyclonic eddies in the ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5720, https://doi.org/10.5194/egusphere-egu25-5720, 2025.
Langmuir turbulence, arising from the nonlinear interaction between surface gravity waves and wind-driven shear currents, significantly contributes to ocean mixing and the air-sea transfer of mass, momentum, and energy. Previous studies have either prescribed surface wind stress in single-phase flow simulations or left surface waves indeterminate in two-phase flow simulations. To better understand the generation and evolution of Langmuir turbulence, and to quantify the momentum and energy transfer across the air-sea interface, a series of two-phase wave-resolved direct numerical simulations are conducted across various Langmuir numbers. In these simulations, fully developed pressure gradient-driven turbulence on the air side is acted upon prescribed surface gravity waves. The results reveal characteristic structures of Langmuir cells at varying scales, including pairs of counter-rotating vortices and elongated streamwise streaks on the water surface. By decomposing flow velocity into mean current, wave orbital motion, and turbulence fluctuation, the impact of wave-induced phase-dependent strain on underlying turbulence and the enhancement of streamwise vorticity are analyzed in detail. Additionally, the momentum flux across the air-sea interface is calculated and its transfer mechanism is discussed, providing insights for parameterization in climate models.
How to cite: Liu, Y. and Li, Q.: Resolving Langmuir Turbulence in a Coupled Wind-Wave System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14613, https://doi.org/10.5194/egusphere-egu25-14613, 2025.
Sea spray-mediated heat flux plays an important role in air-sea heat transfer. Heat flux integrated over droplet size spectrum can well simulate total heat flux induced by sea spray droplets. Previously, a fast algorithm of spray-flux assuming single-radius droplets (A15) was widely used since the full-size spectrum integral is computationally expensive. Based on the Gaussian Quadrature (GQ) method, a new fast algorithm (SPRAY-GQ) of sea spray-mediated heat flux is derived. The performance of SPRAY-GQ is evaluated by comparing heat fluxes with those estimated from the widely-used A15. The new algorithm shows a better agreement with the original spectrum integral. To further evaluate the numerical errors of A15 and SPRAY-GQ, the two algorithms are implemented into a coupled CFSv2.0-WW3 system, and a series of 56-day simulations in summer and winter are conducted and compared. The comparisons with satellite measurements and reanalysis data show that the SPRAY-GQ algorithm could lead to more reasonable simulation than the A15 algorithm by modifying air-sea heat flux. For experiments based on SPRAY-GQ, the sea surface temperature at mid-high latitudes of both hemispheres, particularly in summer, is significantly improved compared with the experiments based on A15. The simulation of 10-m wind speed and significant wave height at mid-low latitudes of the Northern Hemisphere after the first two weeks is improved as well. These improvements are due to the reduced numerical errors. The computational time of SPRAY-GQ is about the same as that of A15. Therefore, the newly-developed SPRAY-GQ algorithm has a potential to be used for calculation of spray-mediated heat flux in coupled models.
How to cite: Shi, R. and Xu, F.: Accelerated Estimation of Sea Spray-Mediated Heat Flux Using Gaussian Quadrature, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21343, https://doi.org/10.5194/egusphere-egu25-21343, 2025.
Gas exchange processes at the air-sea interface play a crucial role in regulating the climate and sustaining human and marine life. It is known that a large portion of anthropogenic carbon dioxide is absorbed by the ocean, which, in turn, releases nearly half of the oxygen we breathe through the photosynthesis of marine flora in the sunlit upper ocean layer.
Despite its relevance, the processes governing the gas transfer across the ocean surface are not fully understood. Although there is evidence that the bubbles generated by the wave breaking enhances significantly the gas transfer rate, in particular for low-solubility species, the parameterization of their contribution is inaccurate.
To investigate the phenomenon, the gas transfer occurring at the free surface of progressive waves is simulated by using high-fidelity simulations. A multiphase flow solver is employed to model the gas flux across the air-water interface and the diffusion processes in the air and water domains, making available data with a level of detail unattainable in experiments. Waves of different initial steepness leading to regular wave patterns, mild spilling, and intense plunging breakers are examined and comparisons in terms of the gas flux across the interface and the gas concentration in the two fluids are established.
It is shown that the amount of gas transferred from the air to the water domain increases remarkably when wave breaking occurs, particularly in the presence of bubble entrainment. The availability of such detailed information allows us to compute the gas transfer velocity. Critical in this respect is the availability of the air-water interface actual area, a quantity generally unavailable in experiments. The increase in the gas transfer velocity is higher than the increase in the interface area across which the exchange takes place, meaning that there is an additional effect related to the enhanced turbulence associated with the bubble entrainment and the subsequent fragmentation process. It is also observed that provided the actual air-water interface area is accounted for, the gas transfer velocity scales approximately as the one-fourth power of the dissipation rate of the energy content in water, consistently with previous theoretical predictions.
How to cite: Iafrati, A., Pirozzoli, S., and Di Giorgio, S.: Contribution of the air entrainment to the gas transfer processes in wave-breaking events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3214, https://doi.org/10.5194/egusphere-egu25-3214, 2025.
With the growth in computing power and the advancement in numerical algorithms, computational fluid dynamics (CFD) is playing an increasingly important role in the study of many fluid mechanics problems in geophysical sciences. Built on highly accurate numerical schemes and utilizing high-performance computing, high-fidelity CFD is especially valuable for faithfully capturing the flow physics of turbulence in complex environments, such as water waves. This talk will introduce some of our recent developments in numerical methods for nonlinear wave fields and turbulence in the wave environment. The flow physics of wave-turbulence interaction will be illustrated, focusing on the turbulent boundary layers and multiphase flows at the wave surface. Innovative theoretical analyses and modeling will be presented to reveal the underlying flow dynamics.
How to cite: Shen, L.: Simulation-Based Study of Turbulent Flows in Wave Environment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5153, https://doi.org/10.5194/egusphere-egu25-5153, 2025.
Posters on site: Thu, 1 May, 16:15–18:00 | Hall X4
Near-inertial oscillations (NIOs) are widely observed dynamic motions in the global ocean, with a frequency related to earth’s rotation. Using a particle trajectory model, we found the combined influence of mesoscale eddies and NIOs could produce distinctive flower-like trajectories, which are a special case of near-inertial trajectories and were observed by surface drifters released within an anticyclone eddy in the South China Sea in 2021. The energy budget indicates that wind and geostrophic eddy currents are crucial in generating near-inertial energy during the flower-like trajectories. Furthermore, the particle trajectory model revealed variations in periods and widths of the near-inertial trajectory with latitudes. The width of near-inertial trajectories can exceed 8km in the near-equatorial region and reach 3-6km in the mid-latitude region (20°-50°). The ratios of near-inertial velocity to background velocity, defined as NITSIs, lead to arc-shaped (0.5<NITSI<1.0), overlapping semi-circular (NITSI>1.0), and near-circular trajectories (NITSI>>1.0). Globally, approximately 1/3 of the drifters’ lifespan featured clear near-inertial trajectories, with a significant presence in most middle latitudes and the largest NITSI in the north Pacific westerly. These findings highlight the importance of NIOs and suggest their substantial impact on local surface matter distribution, trajectory prediction, and marine rescue operations.
How to cite: Zheng, Y., Wu, W., Wang, M., Zhang, Y., and Du, Y.: Different Trajectory Patterns of Ocean Surface Drifters Modulated by Near-inertial Oscillations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3897, https://doi.org/10.5194/egusphere-egu25-3897, 2025.
In this study, we identify regions across the Mexican Pacific waters where the high-frequency variability of daily sea surface temperature (SST) is diminishing and those in which the warm upper-layer thickness increases, analyzing changes in the upper layers' thermal structure along the tropical Pacific Ocean and their relationship with the variability of the upper-layer thickness in the so-called Warm Pool of the Mexican Pacific. Our results reveal a clear, direct relationship between the thickness increase of the warm, upper-ocean layer and the reduction of the high-frequency SST variability, which are related to the long-term trend of SST and ENSO variability. The implications are enormous since extreme positive SST anomalies and increasing warm, upper-layer thickness are optimal oceanic conditions for forthcoming hurricane development and intensification.
How to cite: Martinez-Lopez, B.: Otis intensification and its relationship to El Niño and Climate Change in the eastern Pacific Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20498, https://doi.org/10.5194/egusphere-egu25-20498, 2025.
Typhoons, as intense ocean-atmosphere interaction events, exert profound impacts on coastal regions. The path and intensity of typhoons are predominantly governed by oceanic and atmospheric processes. While extensive research has been conducted in deep ocean regions, the mechanisms of ocean-atmosphere heat exchange during typhoon events remain inadequately understood in shallow shelf regions. It’s particular in the East China Sea, which is distinguished by its expansive continental shelf, shallow depths, overlapping surface and bottom mixed layers, and the influences of shelf circulation and the Yangtze River plume. In this region, tides are one of the key driving forces influencing ocean dynamics, however, they are rarely considered in ocean-atmosphere coupling studies. Basing on these, we have developed a high-resolution ocean-atmosphere coupled model for the coastal waters of China using the COAWST (Coupled-Ocean-Atmosphere-Wave-Sediment Transport) modeling system. This effort builds upon our research group's established high-resolution ocean model. Through simulations and validations of typhoon events, preliminary results demonstrate that ocean-atmosphere coupling significantly improves the prediction of typhoon tracks and intensities. This study will further analyze the dynamics of ocean-atmosphere heat flux exchanges during typhoons under the influence of shelf processes and examines their impacts on typhoon paths and intensities, with particular attention to the role of tides. These findings provide new insights into the dynamic processes induced by typhoons in coastal shelf regions and advance our understanding of their interactions with shallow ocean systems.
How to cite: Du, B. and Wu, H.: Ocean-Atmosphere Coupling Processes during Typhoons in the East China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5067, https://doi.org/10.5194/egusphere-egu25-5067, 2025.
This study examines the impact of dust on surface and radiative fluxes, as well as sea surface temperature (SST), over the Red Sea during the dust season (March to August) from 1980 to 2024 using reanalysis and satellite datasets. We first identfied the extreme dust days (EDDs) across the Arabian Peninsula using MERRA-2 reanalysis data, employing the mean and two-sigma standardized deviation method. A total of 1,083 EDDs were detected during the study period, with 394, 103, and 39 days exclusively affecting the southern Red Sea, northern Red Sea, and the entire Red Sea, respectively.
We analysed the key variables, including dust aerosol optical depth, wind patterns, surface fluxes (latent and sensible heat), radiative fluxes (longwave and shortwave), and SST anomalies for the Red Sea and its sub-regions during EDDs. Positive anomalies in dust aerosol optical depth were observed over all three regions during EDDs, and further identified the dust transport pathways based on wind analyses. The results show significant radiative impacts, including increased longwave radiation (+16 W/m²) and reduced shortwave radiation (-30 W/m²) with suppressed latent heat flux (-50 W/m²) and sensible heat flux (-10 W/m²), indicating substantial ocean heat loss through surface evaporation during EDDs.
The SST anomalies also revealed a notable cooling across the Red Sea, with the northern region cooling up to -1.4°C, and the southern region exhibited milder cooling ranging between -0.3°C and +0.2°C. The average cooling across the entire Red Sea is approximately -0.8°C reflects the combined effects of stronger cooling in the northern and moderate cooling in the southern Red Sea region during EDDs. These findings highlight the critical role of dust in modulating surface energy budgets and SST variability in the Red Sea under three different EDD scenarios.
Key words: Arabian Peninsula, Extreme Dust Days, The Red Sea, Suraface-Radiative Fluxes, and Sea Surface Temperature.
How to cite: Nukapothula, S., Dasari, H. P., Kunchala, R. K., Papadopoulos, V. P., Hoteit, I., and Abualnaja, Y.: Impacts of Dust on Surface-Radiative Fluxes, and Sea Surface Temperatures in the Red Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5418, https://doi.org/10.5194/egusphere-egu25-5418, 2025.
Observations of Argo profiles and TAO/TRITON array confirm the significant seasonality of the barrier layer (BL) and temperature inversion (TI) in the northeastern tropical Pacific (NETP). Statistical result of the occurrence based on the Argo profiles reveals a bimodal variability of the BL, with two peaks in July and October. This bimodal seasonality of BL is attributed to the out-of-phase variations of the eastern Pacific fresh and warm pools. The fresh and warm pools both expand westward from May to July, when the Inter-Tropical Convergence Zone (ITCZ) becomes intense and broad. Heavy rainfall is the dominant contributor to the extension of the fresh and warm pools, leading to a high frequency of thick BL (40%). This frequent thick BL provides a precondition for its another development after August. The fresh pool is stable from August to November, while the warm pool contracts sharply. The cold tongue becomes active due to a prevailing trade wind and horizontal advection transports surface cold water to the northeastern warm pool. This cold advection deepens the isothermal layer and contributes to a frequent TI (30%) and thick BL (46%). The results suggest that the ITCZ rainfall and northward cold advection from equator dominate the upper layer stratification of NETP in summer and autumn, respectively
How to cite: Chi, J.: The Impact of the Eastern Pacific Fresh and Warm Pools on the Bimodal Seasonality of Barrier Layers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5569, https://doi.org/10.5194/egusphere-egu25-5569, 2025.
Metre-scale boundary layer turbulence and kilometer-scale submesoscale mixed layer eddies play crucial roles in upper ocean stratification. It is well established that the former generates significant vertical fluxes that mix the upper ocean, while the latter acts to restratify it. However, the interaction between these two multi-scale processes is not well understood, particularly when atmospheric forces are non-negligible. MPAS-Ocean was firstly used to investigate the influence of boundary layer turbulence on submesoscale eddy-induced restratification under various initial conditions. Two parametrizations K-Profile Parametrization (KPP) and k-ε were used to represent different forms of turbulence-induced destratification under the same forcing conditions. Comparison analysis was carried out by comparing the resulting submesoscale eddy-induced restratification. Among all cases, KPP exhibited a larger magnitude of vertical buoyancy flux than k-, indicating stronger turbulence-induced destratification. This enhanced destratification can lead to more intense submesoscale eddy-induced restratification, which largely compensates the turbulence-induced destratification. Furthermore, the value of the mixed layer eddy-induced streamfunction strongly depends on the strength of boundary layer turbulence, suggesting that parameterizations of these two processes may need to consider their interactions. To further explore the bidirectional interactions between these two processes, we are currently employing large-eddy simulation to resolve both. A spatial filter is used to separate the flow into submesoscales and small-scale turbulence. Preliminary results of the large eddy simulations, aiming to elucidate the interactions between these two processes, will be discussed.
How to cite: Jiang, X. and Li, Q.: interaction between boundary layer turbulence and submesoscale mixed layer eddies and its influence on upper ocean stratification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7745, https://doi.org/10.5194/egusphere-egu25-7745, 2025.
Interannual variability of surface mixed-layer near-inertial energy (NIE, representing the intensity of near-inertial waves) in the South China Sea and western North Pacific (WNP) is investigated using satellite-tracked surface drifter data set. It is found that NIE in the study region correlates negatively with El Niño-Southern Oscillation (ENSO) with a correlation coefficient of R = −0.44 and a time lag of 5 months, mainly because the variation of local wind stress lags behind El Niño by 4 months. By separating summer and winter seasons, the correlation is significantly improved. The summer NIE correlates positively with El Niño (R = 0.62), since tropical cyclones over the WNP tend to be stronger and longer-lived during the El Niño developing phase. The winter NIE correlates negatively with El Niño (R = −0.65), since the winter monsoon is weakened by the ENSO-related WNP anomalous anticyclone. This is the first time that interannual variability of NIE is studied by direct current velocity observations.
How to cite: lu, H.: Interannual Variability of Near-Inertial Energy in the SouthChina Sea and Western North Pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10164, https://doi.org/10.5194/egusphere-egu25-10164, 2025.
The bubbles formed by breaking waves are thought to play an important role in increasing gas transfer across the atmosphere-ocean surface during high wind conditions (>15 m/s). However, real world data on near-surface bubbles with sufficient resolution in space, time and bubble size to understand exactly how the transfer mechanisms work is rare. In addition, there are almost no data showing the relationship between bubble size distributions and the local flow and gas saturation conditions, although data from the HiWinGS cruise suggests that these structures could be very important for gas transfer. The BELS project data was collected during five weeks in November/December 2023, and includes tracer-based gas flux measurements, physical oceanography, and ocean chemistry. Hourly averaged wind speeds were 5-30 m/s, with maximum significant wave height of 11 m. Here, we will present early results from the part of the project monitoring near-surface bubbles and their relationship to flow patterns and dissolved gas concentrations in the top five metres of the ocean. Data will be presented from a free-floating buoy carrying specialised bubble cameras at 1m and 3m, ADCPs and oxygen optodes. We will show measured bubble size distributions, and the spatial relationship of these bubbles to Langmuir circulation patterns and dissolved oxygen concentrations. We will also present an early analysis of the relationships between gas carried by both the water itself and the bubbles, and how this relates to the advection of these two gas reservoirs in the top few metres of the ocean.
How to cite: Czerski, H., Ashraf, I., Brooks, I., and Gunn, S.: Near surface bubble, gas and flow measurements during the Bubble Exchange in the Labrador Sea (BELS) cruise – early results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12896, https://doi.org/10.5194/egusphere-egu25-12896, 2025.
In open channel flow (OCF), expressions and patterns at the water surface may represent underwater turbulent phenomena. In this study, we seek to connect the surface signatures with the turbulence beneath it through the prediction of the time and length scales of turbulent structures in second moment closure (SMC) models. In the simplest scenario, the unforced free surface OCF is driven by a uniform horizontal pressure gradient and the only source of turbulence is the bottom shear. Working with Neumann surface boundary conditions for turbulence quantities, the traditional ‘return-to-isotropy’ for turbulent kinetic energy (TKE) components is modified to decay – in the absence of local TKE production – to a specified anisotropy profile as a function of depth below the surface, rather than to isotropy. This gives rise to distinct vertical and horizontal length scales, formed from the TKE components and the turbulence decay timescale. It also results, through changes in the algebraic closure solution, in a modification of vertical diffusivity consistent with more ad-hoc proposals in other studies to address excessive flux predictions using depth-dependent damping functions. An examination of results from these model changes is presented for weak equilibrium k - ε SMC models. The weak equilibrium k - ε SMC model solves for turbulent second moments by combining prognostic equations for TKE (k) and dissipation (ε) with an algebraic model to obtain eddy viscosity and diffusivity. SMC predictions for TKE components, dissipation, and horizontal turbulent length scales at the free surface are compared with observations obtained in a tidally modulated river, as well as with published results from OCF lab experiments and direct numerical simulations.
How to cite: Tian, B., Chickadel, C. C., and Harcourt, R. R.: Relating surface signatures to modeled turbulence dynamics in open channel flow, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14006, https://doi.org/10.5194/egusphere-egu25-14006, 2025.
Tropical ocean-atmosphere coupling plays a pivotal role in regulating the global climate system. Variability and mechanisms of the coupling exhibit significant regional differences due to variations in the background states and thermodynamic processes across the tropical basins. While previous studies mostly focused on the specific time scales and localized regions, a broader view of the tropical air-sea coupling “picture” remains incomplete. This project first utilizes an energy balance model of the coupled ocean-atmosphere system to diagnose the coupling characteristics for each tropical grid point across timescales through the “heat flux—sea surface temperature” relationship. Subsequently, a clustering algorithm is used to classify spatial differences into distinct coupling regimes. Finally, decomposition of the flux calculation is applied to identify critical variables and processes underlying each regime. This approach progressively reveals the mechanisms behind the regional differences in tropical ocean-atmosphere coupling features. Our findings also highlight that current high-resolution climate models still face challenges in accurately reproducing the coupling characteristics of some regimes, which would further limit the accuracy of climate simulation and prediction.
How to cite: Chen, R.: Ocean-atmosphere coupling regimes in the tropical area, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14275, https://doi.org/10.5194/egusphere-egu25-14275, 2025.
In the tropical ocean, diurnal heating and the formation of atmospheric convection cells associated with local precipitation events, cold pools and wind bursts, have been shown to impact air-sea exchange and the structure of the ocean surface layer. Here, we use a high-resolution regional ocean model, forced by an atmospheric Large Eddy Simulation (LES) that explicitly resolves these processes in a realistic scenario in the tropical north-east Atlantic Ocean, to study their impact on the ocean surface layer and parameterized air-sea fluxes. We find that in our study area, located in the trade wind zone, the oceanic heat loss is, unexpectedly, reduced in the presence of cold pools by on average 30 W m-2 due to the higher air humidity, weaker mean winds, and increased cloud cover. Our results also show that the total non-solar heat flux is dominated by the diurnal cycle of the trade winds, rather than by diurnal heating. In the ocean surface layer, local wind bursts, rain layers, and cloud shading induce a strong lateral variability of Diurnal Warm Layers (DWLs), questioning the local applicability of available DWL bulk parameterizations. From a series of numerical tracer experiments, we identify a new shear-dispersion mechanism, induced by the diurnal jet, that is reflected in an extreme anisotropy of horizontal dispersion with diffusivities of order 10-100 m2 s-1. These findings are likely relevant also in other regions in the trade wind zone.
How to cite: Umlauf, L., Schmitt, M., Klingbeil, K., and Shevchenko, R.: Three-dimensional Ocean Surface Layer Response to Rain, Wind Bursts and Diurnal Heating, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16435, https://doi.org/10.5194/egusphere-egu25-16435, 2025.
Fine-scale turbulence in the upper ocean boundary layer (OSBL) governs ocean surface stratification, and vertical exchanges of heat, momentum and matter in the ocean, which are key in the response of the oceans to changing environmental conditions. However, these turbulent processes are not explicitly represented in ocean models and their parameterization remains a significant source of uncertainty in climate models and operational prediction systems. Increasingly, systematically leveraging diverse data sources is becoming standard practice for developing and assessing OSBL parameterizations. Over the past years, data-driven automated procedures have for instance been used for calibrating the parameters of physics-based models, for developing parameterizations embedding ML components, and for proposing pure ML-based parameterizations of OSBL processes.
This study explores the advantages of the emerging paradigm of differentiable programming for the calibration of OSBL parameterizations . We developed a benchmark tool, Tunax, implemented in JAX, a differentiable framework for Python. This benchmark includes a fully differentiable single-column model with various possible OSBL parameterizations, alongside a calibration module which tunes the coefficients of these parameterizations against a reference database. The differentiability of the model enables the application of variational techniques for parameter calibration. The reference database is a collection of Large Eddy Simulations (LES) covering a range of typical physical conditions.
Here, we focus on the k-ε closure (Umlauf and Burchard, 2005), widely used in global ocean circulation models, and calibrate its parameters using a dataset of LES. These simulations have been designed to model the evolution of the oceanic mixed layer under various surface conditions (wind, heat fluxes and rotation). This work highlights the potential of differentiable calibration techniques to address uncertainties inherent to turbulence closures by enabling more flexible and data-informed parameterizations. Although this approach does not yet consistently outperform traditional calibration methods, it provides a promising avenue for reducing model biases associated with sub-grid scale parameterizations.
How to cite: Mouttapa, G., Le Sommer, J., Cosme, E., Durif, A., Deremble, B., Legay, A., and LeClaire Wagner, G.: Leveraging automatic differentiation for calibrating vertical mixing parameterizations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17338, https://doi.org/10.5194/egusphere-egu25-17338, 2025.
Gas flux across the sea surface is proportional to the difference of partial pressure between the sea-water and the overlying atmosphere and also to a parameter called gas transfer velocity k, a measure of the, the measure of efficiency of the gas exchange. Although it depends mostly in in-water and atmospheric turbulence, the usual way to parametrize it is by the wind speed, the source of the turbulence which has the advantage of being easily available from ship base measurements and reanalyses. Unfortunately, measured values of gas transfer velocity at a given wind speed have a large spread in values. It has been long suspected that the coverage of the sea surface with variable amounts of surface-active substances (or surfactants). It has been shown that surfactants may decrease the CO2 air-sea exchange by up to 50%. However the labour intensive methods used for surfactant study make it impossible to collect enough data to map the surfactant coverage or even create a gas transfer velocity parametrization involving a measure of surfactant activity. This is why we decided check the possibility of using optical fluorescence as a proxy of surfactant activity.
We are in the third year of a 4-year research grant funded by the Polish National Science Centre, NCN (grant number 2021/41/B/ST10/00946). Our group has previously showed that fluorescence parameters allow estimation the surfactant enrichment of the surface microlayer, as well as types and origin of fluorescent organic matter involved. In order to study their possible usefulness in improving the parametrization of the gas transfer velocity k, we measure from the research ship of the Institute, R/V Oceania, all the variables needed for its calculation, namely CO2 partial pressure both in water (PiCCARO G2101-i) and in air (Licor 7200, semiclose path with heated tube and Licor 7500, open path) as well as vertical flux of this trace gas (with the GiLL WindMaster and WindMaster Pro for 3D air movement needed for eddy correlation) as well as meteorological conditions. The data are used to calculate gas transfer velocity values which are compared to ones calculated literature from parametrization functions. The differences between the two, together with the surfactant fluorescence parameters are be used to test the hypothesis that surfactants are main reason for the “noisiness” of k measurement results and hopefully to improve the k parametrization by adding a surfactant related variable to the wind speed which at present is the sole independent variable of most parametrizations.
After 3 years of the project we have data from six Baltic cruises and to three Atlantic ones, of which 2/3 have been already analysed. The poster will present the early results of the project and show progress towards the main goal of the research: finding a reliable optical proxy for surfactant to be used in gas transfer velocity parametrization.
How to cite: Piskozub, J., Drozdowska, V., Wróbel-Niedźwiecka, I., Kuliński, K., Makuch, P., Aguado Gonzalo, F., Markuszewski, P., and Kitowska, M.: On the way towards understanding the effect of sea-water surfactants on gas transfer velocity , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17994, https://doi.org/10.5194/egusphere-egu25-17994, 2025.
Wind-driven waves play a pivotal role in air-sea interactions, influencing processes such as energy dissipation and turbulent mixing. In this study, we employ a Color Imaging Slope Gauge (CISG) to measure surface wave slopes with high spatiotemporal resolution in the linear wind-wave tank at the University of Hamburg. Complementary techniques include a Laser Doppler Velocimetry (LDV) system for point-wise, two-dimensional velocity measurements; a wire gauge and a laser slope gauge for point measurements of wave height and slope, respectively; and an infrared radiometer capable of capturing surface temperature variations. These tools enable the investigation of thermal gradients and their correlation with wave dynamics.
This research aims to examine the statistical properties of wind-generated waves and reconstruct their three-dimensional profiles to better understand their physical and kinematic behavior. A particular focus is placed on the mechanisms of microbreaking, which contribute to energy dissipation and capillary wave generation. To explore surface tension effects, surfactants are introduced to dampen gravity-capillary waves, allowing for detailed investigations of energy fluxes between wave regimes and the suppression of high-frequency wave components.
The combined use of slope imaging, velocity measurements, and thermal detection enhances our ability to study the interplay of different physical processes at the air-sea interface. This work lays the groundwork for further investigations of wave behavior under varying environmental conditions. In particular, the findings of this study will provide critical insights into the small-scale processes driving wave dynamics and contribute to improved parameterizations for wave and climate models.
How to cite: Morales Meabe, J. M. and Gade, M.: Characterizing Wind-Generated Waves Using a Color Imaging Slope Gauge (CISG), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18385, https://doi.org/10.5194/egusphere-egu25-18385, 2025.
Based on a combination of over 20 years of satellite data with extensive in situ measurements from previous research expeditions, an initial step is taken to differentiate the impact of submesoscale processes and turbulent mixing on the Eastern Boundary Upwelling System (EBUS) off Senegal and Mauritania. EBUS are an essential part of the global carbon cycle and are of central importance for the sustainability of economic and food resources. In the tropical Senegalo-Mauritanian EBUS, sea surface temperatures and net primary production exhibits a pronounced seasonal cycle. It is characterized by coastal upwelling in late boreal winter and an abrupt end in late boreal spring with the onset and strengthening of the poleward Mauritania Current. At first glance, the temporal and spatial development follows the annual cycle of the wind stress curl. However, a closer look reveals a more complex picture with a pronounced spatiotemporal heterogeneity, characterized by the influence of (sub)mesoscale eddies and (non-linear) internal tides.
Integrated cross-shelf tidal energy fluxes towards the coast are locally estimated from observations of multiple short-term moorings. Such fluxes should result in increased mixing near the coast, which is in fact supported by assessment of over 800 microstructure turbulence observations. (Internal) tides are known to drive much of the mixing and vertical exchange on a rather narrow coastal strip. Besides, lateral density gradients which were induced by upwelling are regularly subject to conditions favorable for frontogenesis. The associated secondary circulations can induce strong vertical motions and instabilities and export chlorophyll offshore through frontal jets. A snapshot of ship-based measurements of turbulent kinetic energy dissipation rates indicates an order of magnitude larger dissipation on the cold, dense side of the front, whereby surface heat flux is known to play a crucial role. Spatially high-resolution measurements of sea level deflections from the SWOT satellite show considerable variability on scales smaller than 20 km, but the applicability for balanced motions is hampered by the regular occurrence of solitary waves and topographic effects. Given the significance of these observed small-scale processes for the redistribution and alteration in net primary production and expected general changes of submesoscale processes (e.g. due to changing mixed layer depths in the context of global warming), a more precise quantification of their net impact is essential.
Outlook: An interdisciplinary expedition in spring 2025 will supplement the existing data and will use an adaptive sampling strategy, e.g. to tackle the mutual interaction of tides and internal waves with density fronts. Observed tidal fluxes will be interpreted in the context of a high-resolution 3D baroclinic tidal model. These, as well as the work presented, serve as preparatory work for the unprecedented year-round “FUTURO” campaign, which aims to provide a detailed picture of the annual cycle for this important EBUS.
How to cite: Schulz, M., Schütte, F., Dengler, M., and Brandt, P.: Impact of Submesoscale Dynamics and Turbulent Mixing on the Senegalo-Mauritanian Upwelling System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18410, https://doi.org/10.5194/egusphere-egu25-18410, 2025.
Development of theoretical probability density function (PDF) for MLD over the oceans is important, as such a function provides a novel avenue for diagnostics of the numerical experiments with ocean GCMs and for comparison of the model results with observational data such as Argo floats. We built a new PDF based upon the Censored Modified Fisher-Tippet distribution (CMFT PDF herein). CMFT PDF represents a 2.5 – parameter distribution with the shape and location parameters steering the PDF and a pre-defined minimum of sample. CMFT distribution provides explicit equations for the mean and variance and also allows for estimating extreme values of MLD corresponding to high percentiles. A newly developed CMFT PDF was applied to GLORYS12 reanalysis to diagnose the characteristics of MLD in terms of MLD statistics. For application we used 3-degree spatial averaging of GLORIS12 profiles to provide the results which can further analyzed and intercompared to different alternative MLD estimates. This provided quite a rich sample which was further used for computation of the PDF parameters and higher order percentiles over the global oceans. This analysis shows that characteristics of probability density distributions are quite different for different regions with e.g. Labrador Sea demonstrating much heavier tails compared to the Irminger Sea and the NAC. Extreme values of MLD for March can amount to more than 3000 meters in the Labrador Sea. This provides an effective diagnostic approach for intercomparison of different model experiments and also for validation of the model results against observational data, such as e.g. Argo buoys. We also provide the analysis of climate variability of MLD statistics derived from CMFT PDF demonstrating in particular different tendencies in the mean and extreme MLD values. Further we also discuss the links between the statistics of the ocean MLD with those of surface fluxes as well as atmospheric variability.
How to cite: Gulev, S., Kukushkin, V., and Treguier, A. M.: Development and evaluation of the probability density distribution for mixed layer depth over the global oceans, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5512, https://doi.org/10.5194/egusphere-egu25-5512, 2025.
Water mass transformations in the Southern Ocean serve as a lynchpin in the global overturning circulation. Among them, the transformation of Circumpolar Deep Water into Antarctic Winter and Surface Water is uniquely critical for the export of Intermediate Waters north of the Polar Front, the exchange of carbon dioxide between the atmosphere and the subsurface ocean, and the upwards flux of oceanic heat, which inhibits sea ice growth. However, our understanding of the processes responsible for the upwelling of Circumpolar Deep Water and its destruction remains incomplete. We hypothesize that shallow open-ocean convective plumes, only extending into or just below the pycnocline, are underrepresented in both the observational record and in global Earth System Models (ESMs), due to their elusive spatial and temporal scales and the hydrostatic approximation made by all ESMs. Therefore, they play a hitherto undervalued role in setting the water mass structure of the Southern Ocean. We present evidence from a unique year-round upper ocean mooring in the Weddell Sea of a shallow open-ocean convective plume extending into the pycnocline during winter 2021. Using the MITgcm ocean model, we simulate an analogous plume in both hydrostatic and non-hydrostatic configurations. Preliminary results suggest that the conditions necessary to form such plumes can be expected with some regularity in the Weddell Sea. We also note differences between the non-hydrostatic and hydrostatic simulations, highlighting the expected biases associated with the hydrostatic approximation in ESMs.
How to cite: Brown, R., Haumann, A., Losch, M., Rauch, C., and Janout, M.: Shallow open-ocean convection in the Weddell Sea: A case study using observations and modelling techniques, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6934, https://doi.org/10.5194/egusphere-egu25-6934, 2025.
Subduction in the Northwestern Pacific produces North Pacific Subtropical Mode Water (NPSTMW) and constitutes an important branch of the Subtropical Cell. Subduction in the Northwestern Pacific occurs typically during March and April. Based on ocean and atmosphere reanalysis products, the subduction of the NPSTMW is calculated using an Eulerian method. It is found that the averaged subduction time of NPSTMW, weighted by the daily detrainment rate, can vary more than two weeks every year. A composite analysis of the early and the late subduction shows that the subduction time is mostly affected by the strength of the surface zonal wind in the subduction region, which is found to be closely related to the strength and meridional shift of the Aleutian Low in March and April. When the Aleutian Low is stronger (weaker) or shifts southward (northward) in March and April, the surface westerly wind in the subduction region is stronger (weaker), which delays (expedites) the shoaling of the mixed layer and leads to a later (earlier) subduction of the NPSTMW.
How to cite: Zhang, X. and Xu, F.: The Interannual Variability of North Pacific Subtropical Mode Water Subduction Time Modulated by Aleutian Low, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21345, https://doi.org/10.5194/egusphere-egu25-21345, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot 4
EGU25-2306 | ECS | Posters virtual | VPS18
Deep learning for submesoscale surface flow retrieval from geostationary satellite observationsWed, 30 Apr, 14:00–15:45 (CEST) | vP4.7
A wide range of problems in oceanic mass and energy transport involve learning submesoscale surface flow fields from diurnal geostationary satellite observations. Yet, traditional methods, such as the Maximum Cross-Correlation (MCC) algorithm, suffer from limited spatiotemporal resolution and extensive post-processing. Here, we present the RAFT-Ocean architecture, a deep neural network-based approach for learning submesoscale flow fields in pixel-to-pixel manner, to retrieve submesoscale surface flow fields from geostationary satellite data. Compared to the MCC algorithm, the RAFT-Ocean architecture significantly improves these methods, reducing the end-point error (EPE) uncertainty by more than 65% and the absolute angular error (AAE) by more than 55%. The RAFT-Ocean architecture, when transferred to the geostationary ocean color satellite (GOCI/CMOS and GOCI-II/GK2B) sea surface chlorophyll-a products for diurnal hourly flow field retrieval, produced more realistic, continuous, and refined sea surface flow field data compared to geostrophic flow data from altimeter data. The refined diurnal hourly flow field matched well with the filamentous structure of surface phytoplankton, demonstrating an advantage in spatiotemporal resolution for kinetic energy transfer across scales. This approach enhances flow field retrieval quality and opens new avenues for real-time marine environment monitoring and modeling.
How to cite: Ding, X., Zhao, M., and Li, H.: Deep learning for submesoscale surface flow retrieval from geostationary satellite observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2306, https://doi.org/10.5194/egusphere-egu25-2306, 2025.
EGU25-11742 | Posters virtual | VPS18
Two-particle dispersion in the Gulf of Gabès using a high resolution nested ocean modelWed, 30 Apr, 14:00–15:45 (CEST) | vP4.15
Measuring relative dispersion in coastal ecosystems is important for both ocean health and society. Submesoscale dynamics interacting with mesoscale eddies influence mixing processes and phytoplankton blooms dispersion. Two-particle dispersion statistics over an initial spatial scale (0.7 - 1 km) are analysed in the Gulf of Gabès (central-southern Mediterranean Sea) using a high-resolution ocean model through a multiple nesting approach. The model is forced by ERA5 atmospheric fields, while the lateral boundary conditions and initial conditions are provided by daily fields from a Mediterranean Sea reanalysis. The analysis focuses on the turbulent fluid aspects of phytoplankton dispersion in coastal areas under bloom and non-bloom conditions. The results are presented in terms of kurtosis (normalized fourth moment of the pair separation distances), relative diffusivity (particles’ spreading velocity) and time scale-dependent pair separation rate (pair velocity scales normalized by separation distance). At the submesoscale (0.7 – 2km), the non-local exponential regime is absent in both bloom and non-bloom conditions, where the dispersion is locally driven by energetic submesoscale structures. For scales ranging 2-15 km, the two-particle statistics follow the theoretical Richardson regime, which is well detected in the case of a bloom. This regime implies the presence of an inverse energy cascade range where energy is transferred from small to large scales. The diffusive regime is absent for all scales and in both bloom and non-bloom conditions.
How to cite: Bouzaiene, M., Menna, M., Dilmahamod, A. F., Delrosso, D., Simoncelli, S., and Fratianni, C.: Two-particle dispersion in the Gulf of Gabès using a high resolution nested ocean model , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11742, https://doi.org/10.5194/egusphere-egu25-11742, 2025.
