The new Black Sea Reanalysis System within CMEMS

2021 ◽  
Author(s):  
Leonardo Lima ◽  
Stefania Angela Ciliberti ◽  
Ali Aydogdu ◽  
Romain Escudier ◽  
Simona Masina ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Black Sea ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Black Sea ◽  
Freshwater Flux ◽  
Sea Level Anomaly

<p>Ocean reanalyses are becoming increasingly important to reconstruct and provide an overview of the ocean state from the past to the present-day. These products require advanced scientific methods and techniques to produce a more accurate ocean representation. In the scope of the Copernicus Marine Environment Monitoring Service (CMEMS), a new Black Sea (BS) reanalysis, BS-REA (BSE3R1 system), has been produced by using an advanced variational data assimilation method to combine the best available observations with a state-of-the-art ocean general circulation model. The hydrodynamical model is based on Nucleus for European Modeling of the Ocean (NEMO, v3.6), implemented for the BS domain with horizontal resolution of 1/27° x 1/36°, and 31 unevenly distributed vertical levels. NEMO is forced by atmospheric surface fluxes computed via bulk formulation and forced by ECMWF ERA5 atmospheric reanalysis product. At the surface, the model temperature is relaxed to daily objective analysis fields of sea surface temperature from CMEMS SST TAC. The exchange with Mediterranean Sea is simulated through relaxation of the temperature and salinity near Bosporus toward a monthly climatology computed from a high-resolution multi-year simulation, and the barotropic Bosporus Strait transport is corrected to balance the variations of the freshwater flux and the sea surface height measured by multi-satellite altimetry observations. A 3D-Var ocean data assimilation scheme (OceanVar) is used to assimilate sea level anomaly along-track observations from CMEMS SL TAC and available in situ vertical profiles of temperature and salinity from both SeaDataNet and CMEMS INS TAC products. Comparisons against the previous Black Sea reanalysis (BSE2R2 system) show important improvements for temperature and salinity, such that errors have significantly decreased (about 50%). Temperature fields present a continuous warming in the layer between 25-150 m, within which there is the presence of the Black Sea Cold Intermediate Layer (CIL). SST exhibits a positive bias and relatively higher root mean square error (RMSE) values are present in the summer season. Spatial maps of sea level anomaly reveal the largest RMSE close to the shelf areas, which are related to the mesoscale activity along the Rim current. The BS-REA catalogue includes daily and monthly means for 3D temperature, salinity, and currents and 2D sea surface height, bottom temperature, mixed layer fields, from Jan 1993 to Dec 2019.  The BSE3R1 system has produced very accurate estimates which makes it very suitable for assessing more realistic climate trends and indicators for important ocean properties.</p>

scholarly journals Climate Signals in the Black Sea From a Multidecadal Eddy-Resolving Reanalysis

2021 ◽  
Vol 8 ◽  
Author(s):  
Leonardo Lima ◽  
Stefania Angela Ciliberti ◽  
Ali Aydoğdu ◽  
Simona Masina ◽  
Romain Escudier ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Level ◽  
Black Sea ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean Modeling ◽  
Sea Surface ◽  
The Black Sea

Ocean reanalyses are becoming increasingly important to reconstruct and provide an overview of the ocean state from the past to the present-day. In this article, we present a Black Sea reanalysis covering the whole satellite altimetry era. In the scope of the Copernicus Marine Environment Monitoring Service, the Black Sea reanalysis system is produced using an advanced variational data assimilation method to combine the best available observations with a state-of-the-art ocean general circulation model. The hydrodynamical model is based on Nucleus for European Modeling of the Ocean, implemented for the Black Sea domain with a horizontal resolution of 1/27°× 1/36°, and 31 unevenly distributed vertical levels. The model is forced by the ECMWF ERA5 atmospheric reanalysis and climatological precipitation, whereas the sea surface temperature is relaxed to daily objective analysis fields. The model is online coupled to OceanVar, a 3D-Var ocean data assimilation scheme, to assimilate sea level anomaly along-track observations and in situ vertical profiles of temperature and salinity. Temperature fields present a continuous warming in the layer between 25 and 150 m, where the Black Sea Cold Intermediate Layer resides. This is an important signal of the Black Sea response to climate change. Sea surface temperature shows a basin-wide positive bias and the root mean square difference can reach 0.75°C along the Turkish coast in summer. The overall surface dynamic topography is well reproduced as well as the reanalysis can represent the main Black Sea circulation such as the Rim Current and the quasi-permanent anticyclonic Sevastopol and Batumi eddies. The system produces very accurate estimates of temperature, salinity and sea level which makes it suitable for understanding the Black Sea physical state in the last decades. Nevertheless, in order to improve the quality of the Black Sea reanalysis, new developments in ocean modeling and data assimilation are still important, and sustaining the Black Sea ocean observing system is crucial.

scholarly journals Arctic sea surface height maps from multi-altimeter combination

2021 ◽  
Author(s):  
Pierre Prandi ◽  
Jean-Christophe Poisson ◽  
Yannice Faugère ◽  
Amandine Guillot ◽  
Gérald Dibarboure
Keyword(s):  
Sea Level ◽  
Sea Surface Height ◽  
Open Ocean ◽  
Sea Surface ◽  
Optimal Interpolation ◽  
Independent Data ◽  
Interpolation Scheme ◽  
Sea Level Anomaly ◽  
Arctic Sea ◽  
The Cross

Abstract. We present a new Arctic sea level anomaly dataset, based on the combination of three altimeter missions using an optimal interpolation scheme. Measurements from SARAL/AltiKa, CryoSat-2 and Sentinel-3A are blended together providing an unprecedented resolution for this type of products. The final gridded fields cover all latitudes north of 50° N, on a 25 km EASE2 grid, with one grid every three days over three years from July 2016 to April 2019. We use the Adaptive retracker to process both open ocean and lead echoes on SARAL/AltiKa thus removing the need to estimate a bias between open ocean an ice covered areas. SARAL/AltiKa also provides the baseline for the cross-calibation of CryoSat-2 and Sentinel-3A data. When compared to independent data, the combined product exhibits a much better performance than previously available datasets based on the analysis of a single mission.

NUMERICAL SIMULATION OF THE SEMIDIURNAL TIDAL WAVE IMPACT ON THE BLACK SEA CLIMATIC CIRCULATION

2017 ◽  
Author(s):  
Anna Lukyanova ◽  
Anna Lukyanova ◽  
Andrei Bagaev ◽  
Andrei Bagaev ◽  
Vladimir Zalesny ◽  
...  
Keyword(s):  
Black Sea ◽  
Time Scale ◽  
General Circulation ◽  
Circulation Model ◽  
The Black Sea ◽  
Marine Hydrophysical Institute ◽  
Wave Impact ◽  
Ecological Processes ◽  
Short Period ◽  
The Impact

The Black Sea is an enclosed deep marine basin, where the structure of tidal movements is dominated by the direct influence of the tidal force on the proper water body. We investigated the spatial structure of its climatic circulation under the impact of tides. We developed a program module extending the numerical general circulation model of the Black Sea which was designed in the Institute of numerical mathematics, Moscow. It allows the lunar semidiurnal harmonics (M_2) influence to be taken into account explicitly via the discrete analogues of the differential equations of motion. Our work reflects the main results of the numerical experiment on the 4x4 km horizontal grid and 40 vertical σ-levels. It was a one-year model run using the CORE atmospheric climatology forcing. We compared the first and the last weeks of simulation and found out that the characteristics of a tidal mode M2 were established at a very short period of time (7 days), which is the estimate of the model’s energy redistribution time scale. The coastal areas where the tidal impact is substantial (~10 cm) were located mainly at the shallow-shelf inlets highly influenced by the climate change. Validation of the cotidal maps showed the reliability of our model at the climatological time scale. In future we will focus on the baroclinic tidal movements and validation with the Marine Hydrophysical Institute database in order to shed new light on physical and ecological processes at the frontal zone along the Rim Current.

NUMERICAL SIMULATION OF THE SEMIDIURNAL TIDAL WAVE IMPACT ON THE BLACK SEA CLIMATIC CIRCULATION

2017 ◽  
Author(s):  
Anna Lukyanova ◽  
Anna Lukyanova ◽  
Andrei Bagaev ◽  
Andrei Bagaev ◽  
Vladimir Zalesny ◽  
...  
Keyword(s):  
Black Sea ◽  
Time Scale ◽  
General Circulation ◽  
Circulation Model ◽  
The Black Sea ◽  
Marine Hydrophysical Institute ◽  
Wave Impact ◽  
Ecological Processes ◽  
Short Period ◽  
The Impact

The Black Sea is an enclosed deep marine basin, where the structure of tidal movements is dominated by the direct influence of the tidal force on the proper water body. We investigated the spatial structure of its climatic circulation under the impact of tides. We developed a program module extending the numerical general circulation model of the Black Sea which was designed in the Institute of numerical mathematics, Moscow. It allows the lunar semidiurnal harmonics (M_2) influence to be taken into account explicitly via the discrete analogues of the differential equations of motion. Our work reflects the main results of the numerical experiment on the 4x4 km horizontal grid and 40 vertical σ-levels. It was a one-year model run using the CORE atmospheric climatology forcing. We compared the first and the last weeks of simulation and found out that the characteristics of a tidal mode M2 were established at a very short period of time (7 days), which is the estimate of the model’s energy redistribution time scale. The coastal areas where the tidal impact is substantial (~10 cm) were located mainly at the shallow-shelf inlets highly influenced by the climate change. Validation of the cotidal maps showed the reliability of our model at the climatological time scale. In future we will focus on the baroclinic tidal movements and validation with the Marine Hydrophysical Institute database in order to shed new light on physical and ecological processes at the frontal zone along the Rim Current.

Evolution of the Black Sea Physical Analysis and Forecasting System within CMEMS

2021 ◽  
Author(s):  
Stefania Angela Ciliberti ◽  
Eric Jansen ◽  
Diana Azevedo ◽  
Murat Gunduz ◽  
Mehmet Ilicak ◽  
...  
Keyword(s):  
Black Sea ◽  
Mixed Layer Depth ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Danube River ◽  
Core Model ◽  
The Black Sea ◽  
Physical Analysis ◽  
Marmara Sea ◽  
Forecasting System

<p>The Black Sea physical analysis and Forecasting System (BSFS) is part of the Black Sea Monitoring and Forecasting Centre (BS-MFC) for the Copernicus Marine Service (CMEMS). It provides analysis every day analysis and 10 days forecast fields for the blue ocean variables (including temperature, salinity, sea surface height, mixed layer depth and currents) in the Black Sea region since. In this work, we present the new version of the operational system that will be part of the next CMEMS  release. The hydrodynamical core model is based on NEMO v4.0, solved on 1/40º horizontal resolution spatial grid (including the overall Black Sea, the Bosporus Strait and part of the Marmara Sea) and 121 vertical levels with z-star. The core model uses ECMWF analysis and forecast atmospheric forcing and GPCP monthly climatological precipitation for computing heat, water and momentum fluxes. A total number of 72 rivers is accounted, as monthly climatology provided by SESAME project. The model implements a new representation of the Danube River with interannual river discharge datasets provided by the National Institute of Hydrology and Water Management. One of the main innovations of this system is the opening of the Bosporus Strait by using a box-approach in a portion of the Marmara Sea: it is achieved thanks to high resolution temperature, salinity, sea surface height, zonal and meridional velocity solutions provided by a novel implementation of the Marmara Sea model including straits based on Shyfem: it represents the optimal interface between the Mediterranean and the Black Sea. The hydrodynamical model is online coupled to an upgraded version of the OceanVar, the CMCC data assimilation scheme, able to assimilate SLA L3 satellite data, T/S in-situ profiles and SST from CMEMS TACs. The contribution focuses on model setup description, processing system and validation. To evaluate BSFS pre-operational run and monitor the operational production, we provide metrics as proposed within GODAE/Oceanpredict and MERSEA/MyOcean (which includes CLASS 1, 2 and 4 metrics).</p>

scholarly journals Impact of Atmospheric and Model Physics Perturbations On a High-Resolution Ensemble Data Assimilation System of the Red Sea

2020 ◽  
Author(s):  
siva reddy sanikommu ◽  
Habib Toye ◽  
Peng Zhan ◽  
Sabique Langodan ◽  
George Krokos ◽  
...  
Keyword(s):  
High Resolution ◽  
Data Assimilation ◽  
Red Sea ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Massachusetts Institute Of Technology ◽  
Basin Scale ◽  
Subsurface Layers ◽  
The Impact

<p>The Ensemble Adjustment Kalman Filter of the Data Assimilation Research Testbed is implemented to assimilate observations of satellite sea surface temperature, altimeter sea surface height and in-situocean temperature and salinity profiles into an eddy-resolving 4km-Massachusetts Institute of Technology general circulation model (MITgcm) of the Red Sea. We investigate the impact of three different assimilation strategies (1) <em>Iexp</em>– inflates filter error covariance by 10%, (2) <em>IAexp</em>– adds ensemble of atmospheric forcing to Iexp, and (3) <em>IAPexp</em>– adds perturbed model physics toIAexp. The assimilation experiments are run for one year, starting from the same initial ensemble on 1<sup>st</sup>January, 2011 and the data are assimilated every three days.</p><p>Results demonstrate that the <em>Iexp</em> mainly improved the model outputs with respect to assimilation-free MITgcm run in the first few months, before showing signs of dynamical imbalances in the ocean estimates, particularly in the data-sparse subsurface layers. The <em>IAexp</em> yielded substantial improvements throughout the assimilation period with almost no signs of imbalances, including the subsurface layers. It further well preserved the model mesoscales features resulting in an improved forecasts for eddies, both in terms of intensity and location. Perturbing model physics in <em>IAPexp</em> slightly improved the forecast statistics. It further increased smoothness in the ocean forecasts and improved the placement of basin-scale eddies, but caused loss of some high-resolution features. Increasing hydrographic coverage helps recovering the losses and yields more improvements in <em>IAPexp</em> compared to <em>IAexp</em>. Switching off inflation in <em>IAexp</em> and <em>IAPexp</em> leads to further improvements, especially in the subsurface layers.</p>

Coupled Data Assimilation and Ensemble Initialization with Application to Multiyear ENSO Prediction

2019 ◽  
Vol 32 (4) ◽  
pp. 997-1024 ◽  
Author(s):  
Terence J. O’Kane ◽  
Paul A. Sandery ◽  
Didier P. Monselesan ◽  
Pavel Sakov ◽  
Matthew A. Chamberlain ◽  
...  
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Optimal Interpolation ◽  
Tropical Ocean ◽  
Enso Prediction ◽  
Bred Vectors ◽  
Coupled Data Assimilation ◽  
The Impact

We develop and compare variants of coupled data assimilation (DA) systems based on ensemble optimal interpolation (EnOI) and ensemble transform Kalman filter (ETKF) methods. The assimilation system is first tested on a small paradigm model of the coupled tropical–extratropical climate system, then implemented for a coupled general circulation model (GCM). Strongly coupled DA was employed specifically to assess the impact of assimilating ocean observations [sea surface temperature (SST), sea surface height (SSH), and sea surface salinity (SSS), Argo, XBT, CTD, moorings] on the atmospheric state analysis update via the cross-domain error covariances from the coupled-model background ensemble. We examine the relationship between ensemble spread, analysis increments, and forecast skill in multiyear ENSO prediction experiments with a particular focus on the atmospheric response to tropical ocean perturbations. Initial forecast perturbations generated from bred vectors (BVs) project onto disturbances at and below the thermocline with similar structures to ETKF perturbations. BV error growth leads ENSO SST phasing by 6 months whereupon the dominant mechanism communicating tropical ocean variability to the extratropical atmosphere is via tropical convection modulating the Hadley circulation. We find that bred vectors specific to tropical Pacific thermocline variability were the most effective choices for ensemble initialization and ENSO forecasting.

Assimilating Along-Track Altimetric Observations through Local Hydrostatic Adjustment in a Global Ocean Variational Assimilation System

2011 ◽  
Vol 139 (3) ◽  
pp. 738-754 ◽  
Author(s):  
Andrea Storto ◽  
Srdjan Dobricic ◽  
Simona Masina ◽  
Pierluigi Di Pietro
Keyword(s):  
Sea Level ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Global Ocean ◽  
Dynamic Topography ◽  
Sea Level Anomaly ◽  
Mean Dynamic Topography ◽  
Skill Scores ◽  
The Mean ◽  
Along Track

Abstract A global ocean three-dimensional variational data assimilation system was developed with the aim of assimilating along-track sea level anomaly observations, along with in situ observations from bathythermographs and conventional sea stations. All the available altimetric data within the period October 1992–January 2006 were used in this study. The sea level corrections were covariated with vertical profiles of temperature and salinity according to the bivariate definition of the background-error vertical covariances. Sea level anomaly observational error variance was carefully defined as a sum of instrumental, representativeness, observation operator, and mean dynamic topography error variances. The mean dynamic topography was computed from the model long-term mean sea surface height and adjusted through an optimal interpolation scheme to account for observation minus first-guess biases. Results show that the assimilation of sea level anomaly observations improves the model sea surface height skill scores as well as the subsurface temperature and salinity fields. Furthermore, the estimate of the tropical and subtropical surface circulation is clearly improved after assimilating altimetric data. Nonnegligible impacts of the mean dynamic topography used have also been found: compared to a gravimeter-based mean dynamic topography the use of the mean dynamic topography discussed in this paper improves both the consistency with sea level anomaly observations and the verification skill scores of temperature and salinity in the tropical regions. Furthermore, the use of a mean dynamic topography computed from the model long-term sea surface height mean without observation adjustments results in worsened verification skill scores and highlights the benefits of the current approach for deriving the mean dynamic topography.

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