Session OS4.10

OS4.10 | Ocean modelling: numerical development and data assimilation

Ocean modelling: numerical development and data assimilation

Convener: Doroteaciro Iovino | Co-conveners: Marco Bajo, Katherine HutchinsonECSECS, Julien le Sommer, Jiping Xie, Jérôme Chanut, Andrea Storto

Orals

| Mon, 24 Apr, 08:30–10:15 (CEST)

Room L2

Posters on site

| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)

Hall X5

Posters virtual

| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)

vHall CR/OS

Over the last few years, there have been many evolutions in oceanographic models (e.g., NEMO), as well as in data assimilation used in marine environments.
NEMO (Nucleus for European Modelling of the Ocean) is a state-of-the-art modelling framework of the ocean that includes components for the ocean dynamics, sea-ice and biogeochemistry, along with a nesting package allowing for zooms, and versatile data assimilation interfaces (see https://www.nemo-ocean.eu/). The past few years have seen a great expansion in code functionality and capability. Additionally, the H2020 project IMMERSE and others have seen a multitude of new uses and exciting research coming out of the NEMO academic and operational oceanography community.
This session provides a platform for communication of NEMO and data assimilation developments in tandem with advertising the variety of applications (e.g., co-ocean dynamics at high latitudes; ocean biogeochemistry, climate projections: CMIP7 and beyond, coupling with data assimilation systems). This session aims to facilitate a lively exchange between developers and users, and together to identify gaps in our understanding.
Presentations of results based on new NEMO and data assimilation functionalities and new model configurations are welcome.

Orals: Mon, 24 Apr | Room L2

Chairpersons: Doroteaciro Iovino, Marco Bajo, Julien le Sommer

08:30–08:35

5-minute convener introduction

08:35–08:45

EGU23-14196

OS4.10

On-site presentation

Evaluating remedies for numerical mixing in a ¼° global NEMO configuration

Alex Megann

08:45–08:55

EGU23-5606

OS4.10

Virtual presentation

Effects of improved tidal mixing in NEMO one-degree global ocean model

Casimir de Lavergne, Saurabh Rathore, Gurvan Madec, Jean-Baptiste Sallée, Christian Ethe, and Antoine Nasser

08:55–09:05

EGU23-14980

OS4.10

ECS

On-site presentation

Reducing uncertainty in climate models through improved parameterizations of small scale processes

David Kamm and Julie Deshayes

The NEMO modelling framework finds application in numerous climate models. Simulating Earth’s climate and how it is changing means to solve a complex set of equations for a long period, usually hundreds of years. Given the small time scales of the processes involved and the limited available computational resources, this imposes numerical constraints on the spatial resolution of the simulation. Consequently, processes with a smaller physical length scale than the model grid can not be explicitly resolved, for example mesoscale eddies. The effects of these subgrid-scale processes on the larger scale climate system need to be approximated through parameterisations. Recent studies propose new methods to find and formulate parameterisations using machine learning tools, which promise improvements in the predictive skill of the model. With the prospect of introducing these into future versions of NEMO, their potential benefit is yet to be determined. We propose a new configuration to be used as a test protocol for subgrid-scale parameterisations. The configuration is of intermediate complexity and with an idealised basin geometry of the Atlantic and Southern Ocean. This allows for relatively cheap simulations even at very high horizontal resolution, while crucial aspects of the system like the meridional overturning circulation (MOC) or the antarctic circumpolar current (ACC) are still maintained. Effects of the subgrid-scale processes on the large-scale circulation are then diagnosed to evaluate the performance of their parameterisation.

How to cite: Kamm, D. and Deshayes, J.: Reducing uncertainty in climate models through improved parameterizations of small scale processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14980, https://doi.org/10.5194/egusphere-egu23-14980, 2023.

09:05–09:15

EGU23-3762

OS4.10

On-site presentation

Mesoscale eddy parameterisation in numerical "grey zone" ocean models

Julian Mak, James Maddison, David Marshall, Xi Ruan, and Wang Yan

It is known that ocean models at eddy permitting horizontal resolutions, while being the target for the next generation Earth System Models, suffer from several known deficiencies that lead to rather significant biases in the physical response particularly in the Southern Ocean. One cause of such deficiencies is attributed to the weak mesoscale eddies that are permitted, leading to weaker feedbacks onto the large-scale ocean circulation, with resulting consequences for other components of a Earth System Model. Without a parameterisation active, the eddy feedback is too weak and under-counted, but if a parameterisation is active then there is a double-counting issue, and explicit eddies may be severely damped by the parameterisation. Two existing approaches are to employ a resolution function, or to accept the damping introduced by the parameterisation but backscatter some energy/momentum into the modelled flow in some way.

Here we propose an alternative approach that reduces the damping of explicit eddies by the parameterisation in the first place, and instead of a resolution function asks for a definition of the "large-scale" state. We test the procedure in an idealised channel and gyre model in NEMO 4.0.5, in combination with the GEOMETRIC parameterisation for the eddy induced advection. Impacts to the explicitly resolved variability, total (explicit and parameterised) eddy energy levels, modelled mean state and its sensitivity, as well as biogochemical responses are discussed.

(Sample output: see https://imgur.com/ifM1SPQ for full resolution images. Showing surface relative vorticity, for (a) no parameterisation, (b) standard GM parameterisation applied as is, (c) GEOMETRIC applied as is, (d) GEOMETRIC applied in the new way.)

How to cite: Mak, J., Maddison, J., Marshall, D., Ruan, X., and Yan, W.: Mesoscale eddy parameterisation in numerical "grey zone" ocean models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3762, https://doi.org/10.5194/egusphere-egu23-3762, 2023.

09:15–09:25

EGU23-17579

OS4.10

Virtual presentation

Simplified Kalman smoother and ensemble Kalman smoother for improvingocean forecasts and reanalyses

Bo Dong, Keith Haines, and Yumeng Chen

Dong et al. 2021 presented a post processing smoothing method for application in
operational ocean reanalysis products using the archive of sequential filter
increments. This simple smoother, based on a temporal decay parameter, is
capable of effectively reducing errors in global ocean reanalyses, especially where or
when no observations are being assimilated (through assessment against
independent data). Here we further exploit this smoothing method by implementing
it in the Kalman filter (KF) and ensemble Kalman filter (EnKF), and comparing it’s
performance with traditional extended Kalman smoother (KS) and ensemble
Kalman smoother (EnKS) in the Lorenz 1963 model.
We demonstrate that our smoothing algorithm is equivalent to the KS and EnKS
except that the cross-time error covariances in the Kalman smoothers are modified
as the Kalman filter error covariance multiplied by a cross-time decay term. The
simplified KS and EnKS provide substantial improvement over the KF and EnKF with
smaller RMSE, while incurring very little computational or additional storage cost,
such that there is significant potential of implementing these methods in
operational ocean forecasts and reanalyses.

How to cite: Dong, B., Haines, K., and Chen, Y.: Simplified Kalman smoother and ensemble Kalman smoother for improvingocean forecasts and reanalyses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17579, https://doi.org/10.5194/egusphere-egu23-17579, 2023.

09:25–09:35

EGU23-11718

OS4.10

ECS

On-site presentation

Generating ocean initial condition for coupled forecasts through nudged NEMO experiments

Charles Pelletier, Christopher D. Roberts, Frederic Vitart, Magdalena A. Balmaseda, Kristian Mogensen, and Irina Sandu

Accurate ocean initial conditions are beneficial to coupled ocean - atmosphere forecasts in several ways depending on context. On short time scale (days), some extreme, societally high-impacting meteorological events such as tropical cyclones are associated with exceptionally intense air-sea exchanges, thus requiring good knowledge of the initial state of the upper ocean layers. As the forecast evaluation time scale gets longer (seasonal, decadal), the information contained within the atmospheric initial conditions becomes virtually ineffective to the advantage of that contained within the ocean’s.

In phase one of the Destination Earth (DestinE) initiative of the European Union, ECMWF is responsible for delivering the first two digital twins, on weather extremes and climate change adaptation. These will rely on the fusion of observations and cutting-edge, high-resolution versions of Earth system models. Developing a cheap, affordable method for generating realistic high-resolution ocean initial conditions is particularly critical to both these forthcoming digital twins developed in DestinE. In this presentation, we thus introduce a new ocean initial condition generation method built to meet these specific needs.

This method consists in running preliminary nudged ocean-standalone experiments, using the NEMO ocean model, which is part of the ECMWF’s Integrated Forecasting System. Its main technical novelty is the adaptation of a former sea-ice nudging scheme to NEMO’s multicategory SI3 sea-ice model, and it can be significantly cheaper than relying on ocean data assimilation, particularly at high resolutions. However, this method touches on several matters related to the ability of ocean models to be diverted from their natural equilibrium by being constrained towards increasingly realistic states. We investigate the criteria for obtaining realistic ocean initial condition using distinct combinations of model and nudging dataset resolutions, and evaluate the resulting skill of coupled ocean - atmosphere forecasts.

How to cite: Pelletier, C., Roberts, C. D., Vitart, F., Balmaseda, M. A., Mogensen, K., and Sandu, I.: Generating ocean initial condition for coupled forecasts through nudged NEMO experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11718, https://doi.org/10.5194/egusphere-egu23-11718, 2023.

09:35–09:45

EGU23-14291

OS4.10

On-site presentation

A hybrid data assimilation and machine learning approach for improving forecast skill in models strongly driven by boundary conditions

Clemens Cremer, Jesper Mariegaard, and Henrik Andersson

Data assimilation (DA) has shown to be a powerful method to improve hydronumeric models by integration of observations. However, in systems which are strongly governed by boundary conditions, the benefits of DA are typically limited to improvements of hindcast and quickly fade in forecasts where no observations are available. Where sufficient historical observations are available, machine learning (ML) models can be an attractive alternative for providing accurate forecasts of hydrodynamic conditions.

With the goal to improve the forecast, we propose a hybrid approach combining a physics-based numerical model with a machine learning approach via data assimilation. The ML model delivers accurate forecasts in a few points where historical observations are available. These results are then treated as synthetic observations by data assimilation which transfers the improvements to surrounding positions and other model variables.

This approach is illustrated with a case-study from the Elbe Estuary. Here, an operational two-dimensional hydronumeric model, strongly driven by boundary conditions, is used to compute the hydraulic conditions in the estuary with the main purpose of ensuring safe nautical navigation. The existing model is extended with an Ensemble Kalman Filter data assimilation approach where an ensemble is created by stochastic perturbation of model forcings.

During hindcast, data from two stations of the estuary are assimilated to improve numerical model results and initial conditions for the forecast. To maximize forecasting skill, a Long-short-term-memory machine learning approach is used to provide synthetic observations at assimilation stations during the forecast.

Results from the hybrid model compared to a baseline model, without assimilation, at independent validation stations show that the hybrid model can reduce forecast errors by 40% for water levels and prolongs the positive influence of data assimilation significantly.

How to cite: Cremer, C., Mariegaard, J., and Andersson, H.: A hybrid data assimilation and machine learning approach for improving forecast skill in models strongly driven by boundary conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14291, https://doi.org/10.5194/egusphere-egu23-14291, 2023.

09:45–09:55

EGU23-15509

OS4.10

On-site presentation

Benchmark of the high-resolution Nemo-SI3-XIOS configuration SEDNA on an ARM-based HPC system, Fugaku.

Tina Odaka, Gilles Gouaillardet, Claude Talandier, Camille Lique, Julien Dérouillat, and Yann Meurdesoif

We have developed the ocean-sea ice Arctic regional configuration SEDNA (Sea ice - EDdy resolving ocean paN-Arctic configuration) at ultra-high resolution (800 m in the horizontal and 150 vertical levels) based on the NEMO-SI3 numerical platform, in order to investigate how the dynamics of mesoscale turbulent eddies in the Arctic Ocean interplay with sea ice.

The configuration was initially developed on the AMD-based HPC system Joliot-Curie ROME based at CEA in France, which has achieved a Linpack performance of 12 PFlop/s ranked number 33 of June 2020 TOP500 list (https://top500.org/system/179700/).

Thanks to a European PRACE allocation of nearly 40 million CPU hours, we were able to run a 8 year-long simulation. Although promising to understand part of the small-scale dynamics at play, this length of simulation will likely be a limiting factor in the investigation of the eddy dynamics which is known to equilibrate over several decades.

To overcome this limitation, here we investigate the feasibility of running SEDNA over several decades but at a realistic time cost. To that aim, a benchmark has been performed on the ARM based HPC system Fugaku based at RIKEN in Japan, which has archived a Linpack performance of 442 PFlop/s ranked number 1 of November 2020 TOP500 list (https://www.top500.org/system/179807/). Such a benchmark has required adaptation of the compiling and placements of NEMO and XIOS MPI processes in order to fit on the Fugaku architecture compared to standard X86_64 based HPC systems like Joliot-Curie ROME. In this presentation we will share the tips and lessons learned from our benchmarks and will report the benchmark results. Our insights on model MPI placements for efficient post processing of huge models will be discussed as well.

How to cite: Odaka, T., Gouaillardet, G., Talandier, C., Lique, C., Dérouillat, J., and Meurdesoif, Y.: Benchmark of the high-resolution Nemo-SI3-XIOS configuration SEDNA on an ARM-based HPC system, Fugaku., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15509, https://doi.org/10.5194/egusphere-egu23-15509, 2023.

09:55–10:05

EGU23-5916

OS4.10

ECS

On-site presentation

Recent data assimilation developments in the Mediterranean Sea Analysis and Forecasting System (MedFS)

Ali Aydogdu, Jenny Pistoia, Pietro Miraglio, Andrea Cipollone, Alessandro Grandi, Massimiliano Drudi, Emanuela Clementi, Simona Masina, and Nadia Pinardi

The Mediterranean Sea Analysis and Forecasting System (MedFS) is continuously under development to provide improved ocean state estimates and daily forecasts through the Copernicus Marine Service. Since the beginning of the second phase of Copernicus Marine Service, there have been various upgrades in the data assimilation (DA) component of the MedFS and assimilated observations. MedFS consists of a NEMO-based modelling system coupled with WW3 for improved hydrodynamic representation and it is interfaced to OceanVar, the CMCC 3D variational ocean data assimilation scheme to incorporate observations. Here we present the most important novelties recently included in the operational system which consist in the use of a new observation-based Mean Dynamic Topography (MDT) and a new set of Empirical Orthogonal Functions (EOFs) computed from 35 years of Mediterranean high-resolution reanalysis both covering also the Atlantic side of the domain, as well as the ingestion of Sentinel-6A Sea Level anomaly (SLA) altimeter data. An initial assessment of the assimilation of 5 Hz (~1 km) SLA observations will be presented. Moreover, we will show the impact of the assimilation of glider observations in the Mediterranean Sea with a focus on the western basin. Finally, we will outline our future plans for this phase of the Copernicus Marine Service towards higher-frequency assimilation with an improved background representation and observation operators for satellite products.

How to cite: Aydogdu, A., Pistoia, J., Miraglio, P., Cipollone, A., Grandi, A., Drudi, M., Clementi, E., Masina, S., and Pinardi, N.: Recent data assimilation developments in the Mediterranean Sea Analysis and Forecasting System (MedFS), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5916, https://doi.org/10.5194/egusphere-egu23-5916, 2023.

10:05–10:15

EGU23-3468

OS4.10

On-site presentation

Ensemble Data Assimilation in NEMO using PDAF

Lars Nerger, Yuchen Sun, Wibke Düsterhöft-Wriggers, Yumeng Chen, and Dale Partridge

NEMO itself does not provide full functionality for data assimilation. To enable data assimilation with NEMO, it was coupled with the Parallel Data Assimilation Framework (PDAF, https://pdaf.awi.de). PDAF is open source software providing generic functionality for data assimilation (ensemble filters and smoothers, and variational schemes) as well as ensemble simulations, related diagnostics and tools. For computational efficiency the coupling to NEMO was performed by inserting a few subroutines in higher-level routines of NEMO, which call functions of PDAF. This scheme allows for an in-memory exchange of model fields with the data assimilation software in order to avoid excessive file outputs and model restarts. Alternatively, an offline-coupling using disk files is possible. Next to the NEMO ocean physics, also components like the sea ice or biogeochemical models can be handled, which allows for fully multivariate data assimilation.
We discuss the structure and functionality of the implementation with a focus on ensemble filters. The application is exemplified using two setups; NEMO with the biogeochemistry model ERGOM configured at high resolution for the Baltic Sea, and a global eORCA1 configuration coupled with the FABM-MEDUSA biogeochemistry model.

How to cite: Nerger, L., Sun, Y., Düsterhöft-Wriggers, W., Chen, Y., and Partridge, D.: Ensemble Data Assimilation in NEMO using PDAF, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3468, https://doi.org/10.5194/egusphere-egu23-3468, 2023.

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall X5

Chairpersons: Doroteaciro Iovino, Marco Bajo, Katherine Hutchinson

X5.285

EGU23-15977

OS4.10

ECS

Observation-only learning of 4DVarNet neural schemes for the reconstruction of sea surface turbidity dynamics from gappy satellite images

Clément Dorffer, Frédéric Jourdin, David Mouillot, Rodolphe Devillers, and Ronan Fablet

Optical remote sensing is increasingly used to assess various sea surface biogeochemical parameters (e.g., Chl-a, turbidity). If today’s systems offer better spatiotemporal coverage, the space-time sampling depends on both the satellite orbit and the cloud cover. The resulting sea surface observations generally present large proportions of missing data, making their completion challenging.

Here, we explore neural interpolation schemes as an approach for image gap filling, and their training from observation-only datasets with large missing data rates (with a mean of 65% of missing data and up to 100% for the worst days of the time-series), i.e., when no reference gap-free data are available to run a classic supervised learning approach. We propose and assess different strategies based on real or simulated missing data patterns to discard parts of the available data for learning. We combine these learning strategies with 4DVarnet schemes, which are state-of-the-art neural interpolation schemes backed on a variational data assimilation formulation. The approach was tested in a turbidity reconstruction context, using a multi-modal satellite dataset (CMEMS product: oceancolour_med_bgc_l3_my_009_143) at 1km spatial resolution with daily images from year 2019 to 2021, off the French coast in the western Mediterranean Sea.

Our learned variational algorithm significantly outperforms state-of-the-art interpolation techniques, including optimal interpolation and DINEOF, with a 37% gain in RMSE reached in preliminary tests.

How to cite: Dorffer, C., Jourdin, F., Mouillot, D., Devillers, R., and Fablet, R.: Observation-only learning of 4DVarNet neural schemes for the reconstruction of sea surface turbidity dynamics from gappy satellite images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15977, https://doi.org/10.5194/egusphere-egu23-15977, 2023.

X5.286

EGU23-11007

OS4.10

Development of global ocean data assimilation system for weak coupling to the KIAPS atmospheric data assimilation system

Eunbyeol Ko, Adam Clayton, Hyeyeong Jang, and In-Hyuk Kwon

KIAPS (Korea Institute of Atmospheric Prediction Systems) leads the development of NWP systems for the Korea Meteorological Administration (KMA), and developed the global atmosphere-surface NWP system that was made operational at KMA in April 2020. The system is based on a new atmospheric model called KIM (Korean Integrated Model), and incorporates a hybrid-4DEnVar system for deterministic analyses, and an LETKF for updating perturbations in the 50-member ensemble. During the next 4 years, KIAPS is aiming to develop this atmosphere-surface system into a full Earth system NWP system, to support skillful forecasts out to 30 days.
KIM has been coupled with NEMO to provide the ocean component. Here, we report on our progress developing an ocean-only data assimilation for NEMO, configured for eventual use in a weakly-coupled atmosphere-ocean DA system. We focus on two aspects: (1) the impact of changing the surface forcing model from the Met Office Unified Model to KIM, and (2) the impact of reducing the ocean DA window from 24 to 6 hours, to match the atmospheric DA windows. This study will be preliminary results for the development of the coupled DA system.

How to cite: Ko, E., Clayton, A., Jang, H., and Kwon, I.-H.: Development of global ocean data assimilation system for weak coupling to the KIAPS atmospheric data assimilation system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11007, https://doi.org/10.5194/egusphere-egu23-11007, 2023.

X5.287

EGU23-12614

OS4.10

ECS

Changes in the global upper ocean with new NEMOv4 features

Francesco Cocetta, Doroteaciro Iovino, Aimie Moulin, and Simona Masina

New and updated physics and parameterizations implemented in the NEMO ocean model from version 4 onwards are tested in a global eddying ocean/sea ice configuration, specifically the GLOB16 system. Such configuration is at the base of the operational short-term Global Ocean Forecast System (GOFS) adopted at the Euro-Mediterranean Center on Climate Change (CMCC) and uses a nonuniform tripolar grid with 1/16° horizontal resolution (corresponding to 6.9 km at the Equator) and 98 vertical levels. We performed a set of short-term simulations forced by the ECMWF operational atmospheric fields at 1/10° spatial resolution.

Among all the recent functionalities of the NEMO model, this work focuses on the new features that could impact the ocean energy budget. The new formulation of tides, the parameterization of the mixing induced by breaking internal waves and the formulation of the surface wave-induced mixing are selected. Test simulations are compared against a control run employing a set of metrics computed on the global domain and regional ocean sectors. Additionally, model results are evaluated against available satellite estimates to provide a first validation of the variability of upper ocean energy budget.

In the simulation in which the surface wave-induced mixing is included, external input forcings are needed to provide an accurate representation of the surface wave processes. Here, integrated wave parameters from WAVEWATCH III model feed the NEMO ocean model, in the forced mode.

Our analysis shows that all new ocean implementations impact global and regional patterns of sea surface salinity and sea surface height; conversely, only enhanced surface mixing affects the sea surface temperature and the mixed layer depth. However, all experiments showed the tendency to reduce the surface and basin-averaged ocean energy with updated mixing processes.

How to cite: Cocetta, F., Iovino, D., Moulin, A., and Masina, S.: Changes in the global upper ocean with new NEMOv4 features, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12614, https://doi.org/10.5194/egusphere-egu23-12614, 2023.

X5.288

EGU23-13120

OS4.10

ECS

Response of the Benguela upwelling system to four decades of global warming

Amr Talaat Salama, Marco Zavatarelli, Momme Butenschön, and Tomas Lovato

The Benguela upwelling system (BUS) is one of the most productive marine systems in the world oceans, with about 50 times the productivity per unit area compared to the global ocean average. Such high productivity is attributed to the upwelling process, in which Equatorward alongshore winds combined with the Coriolis effect force surface coastal water offshore, resulting in bringing deep, cold, nutrient-rich waters up to the photic layer, triggering the primary production. The BUS is highly likely to be affected by global warming. Nevertheless, it’s response seems complex because warming might affect the system by two counteracting ways. First, as warming proceeds, upwelling favorable winds might intensify leading to stronger upwelling events. On the other hand, increased stratification potentially counteracts the efficacy of upwelling to deliver nutrients to surface layers. Overall, such possible alterations could have drastic impacts on the physical and biogeochemical characteristics of the BUS and primarily the primary productions rates. Thus, investigating the response of the BUS to recent global warming is crucially important.

To this purpose, a coupled highly resolved 3D physical-biogeochemical model is implemented based on NEMO (Nucleus for European Modelling of the Ocean) and BFM (Biogeochemical flux model). The coupled model is being constructed via an online nesting approach to maintain high resolution for a small-scale process like the upwelling, but at the same time to provide the Benguela domain precise boundary conditions. The grid refinement has been conducted using AGRIF (Adaptive Grid Refinement in Fortran). A two-way online nesting has been applied, where information from the child is allowed to propagate back into the parent domain. With a tripolar ORCA025 grid, the nesting (parent) domain covers the global ocean with a horizontal resolution of 1/4°, while the nested (child) domain for the Benguela domain has a resolution of 1/16° and spatially extend from (7°W to 27°E) and from (15°S to 44°S). Both grids have 75 vertical layers. The coupled model is run over a hindcast simulation encompassing four decades starting from 1980 to 2020.

Regarding the model’s set-up, bottom topography is being derived from GEBCO, while the atmospheric forcing has been retrieved from ERA5, and due to the significance of river freshwater input in such simulation, the coupled model was forced with runoff data from the Global Flood Awareness System (GLOFAS). As for the BFM model configuration, it comprises multiple plankton functional groups, nutrients forms, and O2 dependent processes. BFM initial conditions were retrieved from The Global Ocean Data Analysis Project (GLODAP). Finally, the coupled model is validated using in situ and satellite observational data for physical and biogeochemical state-variables and processes.

How to cite: Talaat Salama, A., Zavatarelli, M., Butenschön, M., and Lovato, T.: Response of the Benguela upwelling system to four decades of global warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13120, https://doi.org/10.5194/egusphere-egu23-13120, 2023.

X5.289

EGU23-12031

OS4.10

ECS

The Danube River role in the Black Sea dynamics

Caterina Gianolla

The aim of this study is to investigate the mechanism of the estuarine water exchange and to offer a proper and useful representation of the riverine release into mesoscale-resolving ocean models.

In particular, this study focuses on the effects of the Danube River release (in terms of volume flux, temperature, and salinity) in the Black Sea circulation and dynamics, thus contributing to upgrade the current representation of the riverine release in the framework of the Copernicus Black Sea forecasting system (https://marine.copernicus.eu/about/producers/bs-mfc).

The mesoscale-resolving ocean models, that is few kilometer as horizontal resolution, cannot solve the estuarine dynamics because they cannot represent the estuary geometry due to their low resolution. However, they may produce a reliable representation of the river plumes if they are forced by a realistic estuarine water release.

A 2-layer box model, named CMCC EBM (https://www.estuaryboxmodel.org), is proposed as an intermediate-complexity solution encompassing the main estuarine dynamics processes averaged over the diurnal tidal cycle. The model solves the estuarine water exchange by two conservation equations for volume and salt fluxes and uses two parametric equations for the SWI length and the horizontal mixing along the estuary.

Minimal calibration and short CPU time make the EBM a powerful tool for coupling with ocean models and hydrology models to produce both operational forecasts and climate scenarios.

Verri et al. 2020; 2021 investigated the estuarine processes of the Po river delta system and the CMCC EBM is found to offer reliable estimates of runoff and salinity at the river mouths and to improve the representation of the buoyancy plume in coupled mode with a mesoscale ocean model over the Adriatic Sea based on NEMO code.

Here we propose a couple of twin experiments by the NEMO code over the Black Sea during 2020-2021: Experiment 1 considers observed river discharge for the five Danube branches coming from NIHWM dataset at daily frequency, and monthly climatological salinity from SeaDataNet; Experiment 2 replaces the discharge at the Danube mouths with the results of the EBM running over the same range 2020-2021 and forced by the daily observed runoff applied at the estuary heads and the entering salinity and volume flux at the river mouths provided by the NEMO model.

Comparison of the twin experiments is discussed to point out the added value of coupling the NEMO model with the EBM.

Moreover this study aims at investigating how the temperature gradient at the river mouths may affect the Regions Of Freshwater Influence (i.e., shelf areas adjacent to estuaries influenced by wind stress, the surface heating-cooling and the tidal currents) and the whole basin dynamics. Thus an additional conservation equation for the heat flux is added to the CMCC EBM and we evaluate the role of the temperature gradient at the river mouths.

Finally the Danube river-estuary-sea continuum is intended to be solved with a 3D finite element model in order to represent the estuarine dynamics in a seamless way and to provide a benchmark for validating the EBM+NEMO system.

How to cite: Gianolla, C.: The Danube River role in the Black Sea dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12031, https://doi.org/10.5194/egusphere-egu23-12031, 2023.

X5.290

EGU23-10629

OS4.10

Regional Ocean model validation in simulating the low frequency variability over the Maritime continent

Johnson Zachariah, Daiane Faller, Nidheesh Gangadharan, Bijoy Thompson, and Pavel Tkalich

Resolving the regional ocean circulation is a key factor in the understanding of climate-driven oceanic variability. Accurate sea level simulation, in the areas at the interface between land and ocean, could help to mitigate the environmental, social and economic damages caused by sea level rise and extremes. This is particularly the case for the seas in the Southeast Asia region (SAR), where the ocean circulation is complex owing to unique geographic and oceanographic features of the region. In order to overcome the caveats due to sparse sampling of this domain regional configuration of the ocean model (NEMO) is set up for the SAR (90^oE-142^oE; 18^oS-26^oN) with 51 vertical sigma levels and hindcast simulations are performed for the period 1958–2021 using the downscaled ERA5 (surface forcings) and ECMWF global ocean reanalysis (ORAS5) data as lateral boundary conditions. This paper describes the dominant phenomena and model performance in simulating the low-frequency variability of the seas in the SAR with a focus on sea level, SST and ocean currents. The comparison of simulations with tide gauges and satellite altimetry observations yields good match. Correlation analysis between the simulations and air-sea coupled phenomena like El Nino southern Oscillation (ENSO) and Pacific decadal oscillation (PDO) reveals significant correlation which provides the confidence for further research of the low-frequency ocean variability in the SAR.

Keywords: Validation (SSH) with Tide-gauges, Satellite, SST with Reanalysis, Observation, Maritime Continent

How to cite: Zachariah, J., Faller, D., Gangadharan, N., Thompson, B., and Tkalich, P.: Regional Ocean model validation in simulating the low frequency variability over the Maritime continent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10629, https://doi.org/10.5194/egusphere-egu23-10629, 2023.

X5.291

EGU23-2216

OS4.10

Comparison of eddy permitting, eddy rich and sub-mesocale permitting global configurations based on NEMO 4.2 OGCM.

Clement Bricaud, Perrine Abjean, Jérôme Chanut, Romain Bourdallé Badie, and Gilles Garric

In the framework of the Copernicus Marine Environment Monitoring Service, Mercator Ocean International operates a global high-resolution forecasting systems at the resolution of 1/12°. Increasing resolution appears necessary to improve the quality of service and to satisfy the users’ needs in the operational application (Le Traon, 2019). Resolving scales below 100 kilometers, and in particular sub mesoscale processes (1-50 km), appears to be essential to better represent the circulation in the open ocean (Chassignet, 2017), and, to improve the large-scale representations thanks to a more explicit energy transfers between finer and larger scales (Fox-Kemper Baylor, 2019). A deeper understanding of their various contributions (geostrophic flows, tidal motions, waves, inertial currents) and their role in the global ocean kinetic energy budget will improve the knowledge of these energy transfers between different scales.

In 2019, it has been decided to go towards higher resolution and develop a new global sub mesoscale-permitting model. Benefiting from the context of the European H2020 IMMERSE project, a new 1/36° global configuration (2 to 3 km resolution), based on the NEMO 4.2 OGCM, has been developed. Thanks to the resolution increase, this model can resolve the Rossby radius in almost all open oceans areas at global scale quite everywhere and to span a large part of the internal wave spectrum.

In 2022, a hierarchy of multi-year simulations at 1/4°, 1/12° and 1/36° resolution and with/without explicit tide representation has been performed: for each resolution, after a 3-years spin up without tidal forcing, 2 twin 3-years runs have been realized: one without tidal forcing and one forced by the 5 tidal components K1, O1, S2, M2, N2. These models are driven at the surface by the 8km/1hour ECMWF IFS system. Atmospheric pressure forcing have been activated.

We propose a first evaluation of the benefits due to the resolution increase and tidal forcing. Circulation, energy, tidal representation and mixing of the experiments are compared to each other’s.

How to cite: Bricaud, C., Abjean, P., Chanut, J., Bourdallé Badie, R., and Garric, G.: Comparison of eddy permitting, eddy rich and sub-mesocale permitting global configurations based on NEMO 4.2 OGCM., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2216, https://doi.org/10.5194/egusphere-egu23-2216, 2023.

X5.292

EGU23-8057

OS4.10

The impact of 4D-Var data assimilation of HF-Radar and SST observations on the surface circulation of the northwestern Mediterranean Sea

(withdrawn)

Michele Bendoni, Andrew Moore, Maria Fattorini, and Carlo Brandini

X5.293

EGU23-2621

OS4.10

Assimilation of range-and-depth-averaged sound speed in Fram Strait

Florian Geyer, Ganesh Gopalakrishnan, Hanne Sagen, Bruce Cornuelle, Matt Mazloff, and Francois Challet

Acoustic thermometry measurements of ocean sound speed were used to improve state estimates of ocean temperature in Fram Strait. This is the first time that large-scale acoustic measurements have been assimilated into an ocean model in the Arctic. From September 2010 to July 2012 the Acoustic Technology for Observing the Interior of the Arctic Ocean (ACOBAR) experiment measured acoustic travel times between Greenland and Spitsbergen. These acoustic tomography measurements were taken along 167-301 km long sections between 3 bottom-mounted moorings. The measurements were inverted to yield time series of range-and-depth-averaged ocean sound speed for 0-1000 m ocean depth.

The ocean sound speed time series was assimilated into a regional numerical ocean model using the Massachusetts Institute of Technology General Circulation Model-Estimating the Circulation and Climate of the Ocean four-dimensional variational (MITgcm-ECCO 4DVAR) assimilation system. The data assimilation improved the range-and-depth-averaged ocean temperatures at the independent 78°50’N oceanographic mooring section in Fram Strait (0-1000 m depth). The RMS error of the ocean state estimate (0.21°C) was comparable to the uncertainty of the interpolated mooring section (0.23°C). The lack of depth information in the assimilated ocean sound speed measurements caused an increased temperature bias at shallow depths (0-200 m). The temporal correlations with the mooring section were not improved because short-term variations in the mooring measurements and the ocean state estimate did not coincide in time. This was likely due to the small-scale eddying and non-linearity of the ocean circulation in Fram Strait. Furthermore, the horizontal resolution of the state estimate (4.5 km) was eddy-permitting, rather than eddy resolving. Therefore, the state estimate could not represent the full ocean dynamics of the region. This study demonstrates the usefulness of large-scale acoustic measurements for improving ocean state estimates at high latitudes.

How to cite: Geyer, F., Gopalakrishnan, G., Sagen, H., Cornuelle, B., Mazloff, M., and Challet, F.: Assimilation of range-and-depth-averaged sound speed in Fram Strait, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2621, https://doi.org/10.5194/egusphere-egu23-2621, 2023.

X5.294

EGU23-2044

OS4.10

Adaptive covariance hybridization for coupled climate reanalysis

(withdrawn)

Francois Counillon, Sebastien Barthelemy, and Yiguo Wang

X5.295

EGU23-7251

OS4.10

ECS

A new regional model of the Subpolar Gyre based on NEMO4

Polina Verezemskaya, Bernard Barnier, Sergey Gulev, Jean-Marc Molines, Alexander Gavrikov, Jean-Michel Lellouche, and Alexandra Verezemskaya

The investigation is devoted to the development of a regional eddy-resolving model of the ocean of the Subpolar North Atlantic in order to reliably reproduce the components and properties of the Subpolar Gyre and the Atlantic meridional overturning circulation. Using the tools of the NEMO4 model, a configuration was created and, based on the literature, new parametrizations were proposed and implemented in the model: correction of the friction stress (current feedback for forced models), cool skin and warm sublayer in surface turbilent fluxes scheme. Also we formulated the best scheme of horizontal impulse advection from the point of view of reproducing mesoscale vortices. Last but noe least the local-sigma coordinate was implemented in the area of underwater cascading (overflow). For the first time, the eddy-resolving global ocean reanalysis GLORYS12V1 was validated against the independent observational data. The implementation of the local sigma coordinate allowed to reproduce the flow function of the Atlantic meridional overturning circulation in a model with a stepped representation of bathymetry. All the parametrization and scheme innovations led to an improvement in the solution, with the exception of the cool skin parametrization. Physical processes representation in the model is discussed.

How to cite: Verezemskaya, P., Barnier, B., Gulev, S., Molines, J.-M., Gavrikov, A., Lellouche, J.-M., and Verezemskaya, A.: A new regional model of the Subpolar Gyre based on NEMO4, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7251, https://doi.org/10.5194/egusphere-egu23-7251, 2023.

X5.296

EGU23-7307

OS4.10

NEMO v4.2 in regional climate modelling - towards climate projections for the German coasts

Birte-Marie Ehlers, Janna Meyer, Wibke Düsterhöft-Wriggers, Vera Maurer, and Frank Janssen

The “German Strategy for Adaption to Climate Change” (DAS) is the political framework to climate change adaption in Germany. The DAS core service “Climate and Water” provides monitoring and projection data to evaluate requirements for climate change adaption. Using the state of the art ocean model NEMO v4.2 a setup is developed to provide projection data for the target regions North Sea and Baltic Sea with focus on the German coastal region and its estuaries.

The setup includes the entire North-West-Shelf to take into account the impact of the North Atlantic weather systems on the dynamics of the seas and the cross-shelf transport. An adjusted bathymetry based on up-to-date measurements of the sea floor from the EMODNET network is introduced and studied with regard to its tidal behaviour, especially in the German Bight. The setup is also tested for its response on the use of different data sets of boundary data for tides, temperature and salinity, providing insights into the influence of temporal resolutions of boundary data on projection results.

Validation work is presented with focus on the sea level at the German coasts and water exchange between the North Sea and the Baltic Sea through the Danish Straits. Furthermore special attention is payed to the thermal stratification and to the seasonality and thickness of sea ice.

First results and a short overview on the coupling of NEMO to the atmospheric model ICON for the EURO-CORDEX domain will complete the presentation. An outlook on further development steps towards high-resolution nested grids and the utilisation of a wetting-and-drying scheme will be given.

How to cite: Ehlers, B.-M., Meyer, J., Düsterhöft-Wriggers, W., Maurer, V., and Janssen, F.: NEMO v4.2 in regional climate modelling - towards climate projections for the German coasts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7307, https://doi.org/10.5194/egusphere-egu23-7307, 2023.

Posters virtual: Mon, 24 Apr, 14:00–15:45 | vHall CR/OS

Chairpersons: Andrea Storto, Jérôme Chanut, Jiping Xie

vCO.2

EGU23-12858

OS4.10

Performance evaluation of NEMO4.2 with Paraver

Francesca Mele, Italo Epicoco, Silvia Mocavero, and Jesus Labarta

The last release of the NEMO v4.2 ocean model includes many modifications that have a significant impact on the model performance. The goal of the work is to assess NEMO performance obtained due to the optimizations carried out during the last four years within the IMMERSE and IS-ENES3 projects. The computational analysis was conducted using Extrae and Paraver which are the performance tools developed at the Barcelona Supercomputing Center.

Extrae provides a trace rich of information regarding the usage of the computational resources made by the model, these include measurements related to the memory subsystem, instruction cycles, vectorization level, communications among parallel processes and many others. Paraver provides a visual inspection of the trace and an insight of the computational features of the NEMO model; this allows to define easily a detailed quantitative evaluation of performance issues.

The performance analysis carried out on NEMO is based on the evaluation of different metrics each one related to a different aspect of the computational resource. The main aspects analyzed are the execution time, the communication time, the number of instructions per cycle and the cache hit rate. In addition, we combined these metrics to evaluate the parallel scalability and the global efficiency of the model when the number of core increases.

Our investigation was focused on evaluating the impact of the last HPC changes and namely: the use of collective neighbors communication pattern, available in MPI3, for the halo exchange; the use of the loop fusion technique to improve the data locality; the impact of the extended halo; the impact of the MPI+OpenMP version of NEMO obtained by means of PSyclone which is a DSL compiler developed at the STFC.

The analysis has been carried out on MareNostrum4 supercomputer at BSC with the NEMO source code available @commit 1d9676ff (a.k.a 68-summer-body-2022 branch) and using the Bench Test configured for ORCA12-like resolution. The evaluation of the MPI+OpenMP was carried out using NEMO 4.0 in ORCA025 configuration kindly provided by STFC as outcome of the PSyclone DSL compiler.

The use of the extended halo with 2 points provides a significant improvement on the performance with a factor of 13% due to a reduction of the number of exchanged messages.

The use of MPI3 communications does not introduce many benefits: a lower number of MPI point-to-point exchanges is compensated by the higher message size of MPI3 neighbors collective communications.

The use of loop fusion does not introduce many benefits: few routines with loop fusion and the little improvement registered in cache misses is compensated by the increase in the number of instructions due to the fusion of the loops.

The analysis of the traces on the hybrid MPI/OpenMP NEMO version processed by Psyclone doesn’t highlight many benefits when the number of OpenMP threads increases due to the part of the code not parallelized.

Finally, one of the most important HPC development, the tiling, has not been analyzed yet, since the last modifications have been merged recently and the resulting code is still under revision.

How to cite: Mele, F., Epicoco, I., Mocavero, S., and Labarta, J.: Performance evaluation of NEMO4.2 with Paraver, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12858, https://doi.org/10.5194/egusphere-egu23-12858, 2023.

vCO.3

EGU23-14046

OS4.10

Insights into the linear dynamics between sea ice and atmosphere through strong-coupled data assimilation

(withdrawn)

Jiping Xie and Laurent Bertino

vCO.4

EGU23-7036

OS4.10

ECS

Data driven stochastic primitive equations with dynamic modes decomposition

Francesco Tucciarone, Etienne Mémin, and Long Li

The full numerical resolution of planetary flows, with the complex interdependence of mesoscale and sub-mesoscale dynamics that characterize such large scale circulation, is beyond reach with nowadays technology. When performing a numerical simulation of the ocean or the atmosphere, great care must be put in the choice of the parametrization of all those scales that are too small to be efficiently resolved.
This work investigates the benefits of a stochastic decomposition of the Lagrangian trajectory into a smooth-in-time large scale velocity and a random fast-evolving uncorrelated part, ideally accounting for mesoscale and submesoscale processes. This approach, named Location Uncertainty (LU) [1], is built upon a stochastic version of the Reynolds Transport Theorem allowing us to cast the classical physical conservation laws into this scale-separated framework. This framework has been proven to be successful in several large-scale models for ocean dynamics [2,3,4,5].
The derivation and implementation (within the community model NEMO, https://www.nemo-ocean.eu) of the hydrostatic primitive equations in this stochastic framework has been outlined in [6] and it is tested in this work with a novel data-driven approach based on dynamical mode decomposition [7]. The flow prediction in an idealized double-gyre configuration is shown to be improved by this stochastic contribution.

[1], E. Mémin Fluid flow dynamics under location uncertainty,(2014), Geophysical & Astrophysical Fluid Dynamics, 108, 2, 119–146.
[1] W. Bauer, P. Chandramouli, B. Chapron, L. Li, and E. Mémin. Deciphering the
role of small-scale inhomogeneity on geophysical flow structuration: a stochastic approach. Journal of Physical Oceanography, 50(4):983-1003, 2020.
[2] W. Bauer, P. Chandramouli, L. Li, and E. Mémin. Stochastic representation of
mesoscale eddy effects in coarse-resolution barotropic models. Ocean Modelling, 151:101646, 2020.
[3] Rüdiger Brecht, Long Li, Werner Bauer and Etienne Mémin. Rotating Shallow
Water Flow Under Location Uncertainty With a Structure-Preserving Discretization. Journal of Advances in Modeling Earth Systems, 13, 2021MS002492.
[5] V. Resseguier, L. Li, G. Jouan, P. Dérian, E. Mémin, B. Chapron, (2021), New trends in ensemble forecast strategy: uncertainty quantification for coarse-grid computational fluid dynamics, Archives of Computational Methods in Engineering.

[6] F.L. Tucciarone, E. Mémin, L. Li, (2022), Primitive Equations Under Location Uncertainty: Analytical Description and Model Development, Stochastic Transport in Upper Ocean Dynamics, Springer.

[7] L. Li, E. Mémin, G. Tissot, Stochastic Parameterization with Dynamic Mode Decomposition, Stochastic Transport in Upper Ocean Dynamics, Springer.

How to cite: Tucciarone, F., Mémin, E., and Li, L.: Data driven stochastic primitive equations with dynamic modes decomposition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7036, https://doi.org/10.5194/egusphere-egu23-7036, 2023.