scholarly journals Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

2012 ◽  
Vol 9 (2) ◽  
pp. 421-442
Author(s):  
A. Olita ◽  
S. Dobricic ◽  
A. Ribotti ◽  
L. Fazioli ◽  
A. Cucco ◽  
...  
Keyword(s):  
Sea Level ◽  
Qualitative Evaluation ◽  
Regional Model ◽  
Qualitative Comparison ◽  
Sea Level Anomalies ◽  
Mesoscale Structures ◽  
Sicily Channel ◽  
Altimetric Measurements ◽  
Along Track ◽  
The Impact

Abstract. The impact of the assimilation of MyOcean Sea Level Anomalies along track data on the analyses of the Sicily Channel Regional Model was studied. The numerical model has a resolution of 1/32° degrees and is capable to reproduce mesoscale and sub-mesoscale features. The impact of the SLA assimilation is studied by comparing a simulation (SIM, which does not assimilate data) with two analyses, AN0 and AN1, assimilating different reprocessing versions (V0 and V1) of the same set of Along Track altimetric measurements. The quality of the analyses was evaluated by computing RMSE of the misfits between analyses background and observations (sea level) before assimilation. A qualitative evaluation of the ability of the analyses to reproduce mesoscale structures is accomplished by comparing model results with Ocean Color and SST satellite data, able to detect such features on the ocean surface. CTD profiles allowed to evaluate the impact of the SLA assimilation along the water column. We found a significant improvement for AN1 solution in terms of SLA rmse in respect to SIM (the averaged RMSE of AN1 SLA misfits over 1.5 years is about 0.5 cm smaller than SIM) and a weaker improvement in respect to the assimilation of the V0 dataset (0.1 cm average over the same period). Comparison with CTD data shows a questionable improvement produced by the assimilation process in terms of vertical features: AN1 is better in temperature while for salinity it get worse than SIM at the surface. The qualitative comparison of simulation and analyses with synoptic satellite independent data proves that SLA assimilation of V1 data allows to correctly reproduce some dynamical features (above all the circulation in the Ionian portion of the domain) and mesoscale structures otherwise misplaced or neglected both by SIM and AN0.

scholarly journals Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 485-496 ◽  
Author(s):  
A. Olita ◽  
S. Dobricic ◽  
A. Ribotti ◽  
L. Fazioli ◽  
A. Cucco ◽  
...  
Keyword(s):  
Sea Level ◽  
Qualitative Evaluation ◽  
Regional Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Qualitative Comparison ◽  
Mesoscale Structures ◽  
Sicily Channel ◽  
Along Track ◽  
The Impact

Abstract. The impact of the assimilation of MyOcean sea level anomalies along-track data on the analyses of the Sicily Channel Regional Model was studied. The numerical model has a resolution of 1/32° degrees and is capable to reproduce mesoscale and sub-mesoscale features. The impact of the SLA assimilation is studied by comparing a simulation (SIM, which does not assimilate data) with an analysis (AN) assimilating SLA along-track multi-mission data produced in the framework of MyOcean project. The quality of the analysis was evaluated by computing RMSE of the misfits between analysis background and observations (sea level) before assimilation. A qualitative evaluation of the ability of the analyses to reproduce mesoscale structures is accomplished by comparing model results with ocean colour and SST satellite data, able to detect such features on the ocean surface. CTD profiles allowed to evaluate the impact of the SLA assimilation along the water column. We found a significant improvement for AN solution in terms of SLA RMSE with respect to SIM (the averaged RMSE of AN SLA misfits over 2 years is about 0.5 cm smaller than SIM). Comparison with CTD data shows a questionable improvement produced by the assimilation process in terms of vertical features: AN is better in temperature while for salinity it gets worse than SIM at the surface. This suggests that a better a-priori description of the vertical error covariances would be desirable. The qualitative comparison of simulation and analyses with synoptic satellite independent data proves that SLA assimilation allows to correctly reproduce some dynamical features (above all the circulation in the Ionian portion of the domain) and mesoscale structures otherwise misplaced or neglected by SIM. Such mesoscale changes also infer that the eddy momentum fluxes (i.e. Reynolds stresses) show major changes in the Ionian area. Changes in Reynolds stresses reflect a different pumping of eastward momentum from the eddy to the mean flow, in turn influencing transports through the channel.

Representation Error of Oceanic Observations for Data Assimilation

2008 ◽  
Vol 25 (6) ◽  
pp. 1004-1017 ◽  
Author(s):  
Peter R. Oke ◽  
Pavel Sakov
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Standard Technique ◽  
Original Data ◽  
Sea Level Anomalies ◽  
Ocean Data Assimilation ◽  
Representation Error ◽  
The Difference ◽  
Along Track ◽  
The Given

Abstract A simple approach to the estimation of representation error (RE) of sea level (η), temperature (T), and salinity (S) observations for ocean data assimilation is described. It is assumed that the main source of RE is due to unresolved processes and scales in the model. Therefore, RE is calculated as a function of model resolution. The methods described here exploit the availability of mapped sea level anomalies (mSLAs) and along-track sea level anomalies (atSLAs). The mSLA fields or atSLA observations are regarded as the true ocean state. Here, they are averaged according to the resolution of the model grid, and the averaged field is taken as a representation of the true state on the given grid. The difference between the original data and the averaged field is then regarded as the RE for η. Subsequently, the RE is projected for η over depth using a standard technique, giving an estimate of the RE for T and S. Examples of RE estimates for an intermediate- and high-resolution global grid are presented. It is found that there is significant spatial variability in the RE for η, T, and S, with values that are typically greater than or comparable to measurement error, particularly in regions of strong mesoscale variability.

scholarly journals Mean Dynamic Topography of the Black Sea, computed from altimetry, drifter measurements and hydrology data

Ocean Science ◽  
2011 ◽  
Vol 7 (6) ◽  
pp. 745-753 ◽  
Author(s):  
A. A. Kubryakov ◽  
S. V. Stanichny
Keyword(s):  
Sea Level ◽  
Black Sea ◽  
The Black Sea ◽  
Climatic Data ◽  
Dynamic Topography ◽  
Mean Dynamic Topography ◽  
Sea Level Anomalies ◽  
Temporal Features ◽  
Geostrophic Velocities ◽  
Along Track

Abstract. Mean Dynamic Topography (MDT) is a crucial parameter for estimating dynamic topography, and, therefore, geostrophic circulation from satellite altimetry measurements. In this work we use drifting buoy measurements, hydrographic profiles and along-track Sea Level Anomalies (SLA) to reconstruct MDT of the Black Sea by the "synthetic" method. Obtained MDT shows a lot of mesoscale features, which are not present in previous MDT fields of the Black Sea, mostly based on climatic data. Moreover, gradients of sea level in the synthetic MDT are significantly higher compared to other fields, which is evidence of more intense currents in the basin. Validation of determined MDT field with independent dynamic heights and drifter buoy velocities shows good quantitative and qualitative coincidence over all Black Sea basin and improvements compare to previous fields. New Black Sea MDT will improve quality of altimetry-derived geostrophic velocities and lead to better understanding of the spatial and temporal features of the upper layer dynamics.

scholarly journals Accuracy of the mean sea level continuous record with future altimetric missions: Jason-3 vs. Sentinel-3a

2015 ◽  
Vol 12 (4) ◽  
pp. 1511-1536 ◽  
Author(s):  
L. Zawadzki ◽  
M. Ablain
Keyword(s):  
Sea Level ◽  
Regional Scale ◽  
Mean Sea Level ◽  
Level Data ◽  
Continuous Record ◽  
Climate Evolution ◽  
The Mean ◽  
Altimetric Measurements ◽  
The Impact

Abstract. The current mean sea level (MSL) continuous record, essential for the understanding of climate evolution, is computed with the altimetric measurements of the TOPEX/Poseidon mission, succeeded by Jason-1 and later Jason-2. The accurate continuity of the record is ensured by the conservation of the "historical" TOPEX orbit, but also by calibration phases between the successive missions which enable a rigorous computation of their relative biases. In order to extend the current MSL record, Jason-3 will be the natural successor of Jason-2: on the same orbit with a calibration phase. Shortly after Jason-3, another altimetric climate-oriented mission, Sentinel-3a, will be launched on a different orbit. In this paper, simulated altimetric sea level data is used to study the sensitivity of the MSL continuous record to the change of the "historical" orbit for the new Sentinel-3a orbit. By estimating the impact of the absence of calibration phase on the MSL continuous record trend accuracy at global and regional scale and the impact of the orbit change on the long-term continuity of this MSL record, this study shows that linking Sentinel-3a data instead of Jason-3 to the MSL continuous record would prevent from meeting climate users requirements regarding the MSL trend accuracy.

scholarly journals Accuracy of the mean sea level continuous record with future altimetric missions: Jason-3 vs. Sentinel-3a

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 9-18 ◽  
Author(s):  
L. Zawadzki ◽  
M. Ablain
Keyword(s):  
Sea Level ◽  
User Requirements ◽  
Mean Sea Level ◽  
Level Data ◽  
Continuous Record ◽  
Climate Evolution ◽  
The Mean ◽  
Altimetric Measurements ◽  
The Impact

Abstract. The current mean sea level (MSL) continuous record, essential to understanding the climate evolution, is computed with the altimetric measurements of the TOPEX/Poseidon mission, succeeded by Jason-1 and later Jason-2. The accurate continuity of the record is ensured by the conservation of the "historical" TOPEX orbit as well as by calibration phases between the successive missions which enable a rigorous computation of their relative biases. In order to extend the current MSL record, Jason-3 will be the natural successor of Jason-2: on the same orbit with a calibration phase. Shortly after Jason-3, another altimetric climate-oriented mission, Sentinel-3a, will be launched on a different orbit. In this paper, simulated altimetric sea level data are used to study the sensitivity of the MSL continuous record to the change of the "historical" orbit for the new Sentinel-3a orbit. By estimating the impact of the absence of calibration phase on the MSL continuous record trend accuracy at the global and regional scales and the impact of the orbit change on the long-term continuity of this MSL record, this study shows that linking Sentinel-3a data instead of Jason-3 to the MSL continuous record would not meet climate user requirements regarding the MSL trend accuracy.

scholarly journals Contribution of future wide-swath altimetry missions to ocean analysis and forecasting

Ocean Science ◽  
2018 ◽  
Vol 14 (6) ◽  
pp. 1405-1421 ◽  
Author(s):  
Antonio Bonaduce ◽  
Mounir Benkiran ◽  
Elisabeth Remy ◽  
Pierre Yves Le Traon ◽  
Gilles Garric
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Spatial Scales ◽  
European Space Agency ◽  
Ocean Currents ◽  
Instrumental Error ◽  
Altimetry Data ◽  
Along Track ◽  
The Impact ◽  
Wide Swath

Abstract. The impact of forthcoming wide-swath altimetry missions on the ocean analysis and forecasting system was investigated by means of OSSEs (observing system simulation experiments). These experiments were performed with a regional data assimilation system, implemented in the Iberian–Biscay–Ireland (IBI) region, at 1∕12∘ resolution using simulated observations derived from a fully eddy-resolving free simulation at 1∕36∘ resolution over the same region. The objective of the experiments was to assess the ability of different satellite constellations to constrain the ocean analyses and forecasts, considering both along-track altimeters and future wide-swath missions; consequently, the capability of the data assimilation techniques used in the Mercator Ocean operational system to effectively combine the different kinds of measurements was also investigated. These assessments were carried out as part of a European Space Agency (ESA) study on the potential role of wide-swath altimetry in future versions of the European Union Copernicus programme. The impact of future wide-swath altimetry data is evident for investigating the reliability of sea level values in OSSEs. The most significant results were obtained when looking at the sensitivity of the system to wide-swath instrumental error: considering a constellation of three nadir and two “accurate” (small instrumental error) wide-swath altimeters, the error in ocean analysis was reduced by up to 50 % compared to conventional altimeters. Investigating the impact of the repetitivity of the future measurements, the results showed that two wide-swath missions had a major impact on sea-level forecasting – increasing the accuracy over the entire time window of the 5-day forecasts – compared with a single wide-swath instrument. A spectral analysis underlined that the contributions of wide-swath altimetry data observed in ocean analyses and forecast statistics were mainly due to the more accurate resolution, compared with along-track data, of ocean variability at spatial scales smaller than 100 km. Considering the ocean currents, the results confirmed that the information provided by wide-swath measurements at the surface is propagated down the water column and has a considerable impact (30 %) on ocean currents (up to a depth of 300 m), compared with the present constellation of altimeters. The ocean analysis and forecasting systems used here are those currently used by the Copernicus Marine Environment and Monitoring Service (CMEMS) to provide operational services and ocean reanalysis. The results obtained in the OSSEs considering along-track altimeters were consistent with those derived from real data (observing system experiments, OSEs). OSSEs can also be used to assess the potential of new observing systems, and in this study the results showed that future constellations of altimeters will have a major impact on constraining the CMEMS ocean analysis and forecasting systems and their applications.

scholarly journals Contribution of future wide swath altimetry missions to ocean analysis and forecasting

2018 ◽  
Author(s):  
Antonio Bonaduce ◽  
Mounir Benkiran ◽  
Elisabeth Remy ◽  
Pierre Yves Le Traon ◽  
Gilles Garric
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Spatial Scales ◽  
European Space Agency ◽  
Ocean Currents ◽  
Instrumental Error ◽  
Altimetry Data ◽  
Along Track ◽  
The Impact ◽  
Wide Swath

Abstract. The impact of forthcoming wide-swath altimetry missions on the ocean analysis and forecasting system was investigated by means of OSSEs (Observing System Simulation Experiments) performed with a regional data assimilation system, implemented in the Iberian-Biscay-Ireland (IBI) region, at 1/12° resolution using simulated observations derived from a fully eddy-resolving free simulations at 1/36° resolution over the same region. The objective was to asses the contribution of different satellite constellations to constrain the ocean analyses and forecasts, considering both along-track altimeters and future wide-swath missions, and as consequence the capability of the data assimilation techniques used in Mercator Ocean operational system to effectively combine the different kind of measurements. This was carried out as part of a European Space Agency (ESA) study on the potential role of wide-swath altimetry for the evolution of the European Union Copernicus programme. The impact of future wide-swath altimetry data is clearly evident investigating the reliability of sea-level in the OSSEs. The most significant results were obtained looking at the sensitivity of the system to wide-swath instrumental error: considering a constellation of three nadir and two accurate (small instrumental error) wide-swath altimeters, the error in the ocean analysis was reduced up to the 50 %, with respect to conventional altimeters. Investigating the impact of the repetitivity of the future measurements, the results showed that two wide-swath missions had a major impact on the the sea-level forecasting increasing the accuracy over the entire time-window of the 5-day forecasts, with respect to a single wide-swath instrument. A spectral analysis underlined that the contributions of wide-swath altimetry data observed in the ocean analyses and forecasts statistics were mainly due to resolve more accurately (up to > 25 %), with respect to along-track data, the ocean variability at spatial scales smaller than 100 km. Considering the ocean currents, the results confirmed that the information provided by wide-swath measurements at the surface is propagated also in the vertical and has a considerable impact (30 %) on the ocean currents (up to 300 metres), with respect to the present constellation of altimeters. The ocean analysis and forecasting systems used here are currently adopted by Copernicus Marine Environment and Monitoring Service (CMEMS) to provide operational services and ocean re-analysis. The results obtained in the OSSEs considering along-track altimeters were consistent with those derived with real data (observing system experiments, OSEs). OSSEs also allow to evaluate the potential of new observing systems and in this study the results showed that future constellations of altimeters will have a major impact to constrain the CMEMS ocean analysis and forecasting systems and their applications.

scholarly journals The ECMWF Ocean Analysis System: ORA-S3

2008 ◽  
Vol 136 (8) ◽  
pp. 3018-3034 ◽  
Author(s):  
Magdalena A. Balmaseda ◽  
Arthur Vidard ◽  
David L. T. Anderson
Keyword(s):  
Real Time ◽  
Sea Level ◽  
Bias Correction ◽  
Seasonal Forecasts ◽  
Ocean Reanalysis ◽  
Historical Representation ◽  
Real Time Analysis ◽  
Sea Level Anomalies ◽  
Analysis System ◽  
The Impact

Abstract A new operational ocean analysis/reanalysis system (ORA-S3) has been implemented at ECMWF. The reanalysis, started from 1 January 1959, is continuously maintained up to 11 days behind real time and is used to initialize seasonal forecasts as well as to provide a historical representation of the ocean for climate studies. It has several innovative features, including an online bias-correction algorithm, the assimilation of salinity data on temperature surfaces, and the assimilation of altimeter-derived sea level anomalies and global sea level trends. It is designed to reduce spurious climate variability in the resulting ocean reanalysis due to the nonstationary nature of the observing system, while still taking advantage of the observation information. The new analysis system is compared with the previous operational version; the equatorial temperature biases are reduced and equatorial currents are improved. The impact of assimilation in the ocean state is discussed by diagnosis of the assimilation increment and bias correction terms. The resulting analysis not only improves the fit to the data, but also improves the representation of the interannual variability. In addition to the basic analysis, a real-time analysis is produced (RT-S3). This is needed for monthly forecasts and in the future may be needed for shorter-range forecasts. It is initialized from the near-real-time ORA-S3 and run each day from it.

scholarly journals Quality Assessment of a 1985–2007 Mediterranean Sea Reanalysis

2011 ◽  
Vol 28 (4) ◽  
pp. 569-589 ◽  
Author(s):  
Mario Adani ◽  
Srdjan Dobricic ◽  
Nadia Pinardi
Keyword(s):  
Mediterranean Sea ◽  
Sea Level ◽  
Root Mean Square ◽  
Three Dimensional ◽  
Optimal Interpolation ◽  
Mean Square ◽  
Sea Level Anomalies ◽  
Mean Fields ◽  
Along Track ◽  
Mean Square Errors

Abstract A simulation and two reanalyses from 1985 to 2007 have been produced for the Mediterranean Sea using different assimilation schemes: a reduced-order optimal interpolation [System for Ocean Forecast and Analysis (SOFA)] and a three-dimensional variational scheme (OceanVar). The observational dataset consists of vertical temperature and salinity in situ profiles and along-track satellite sea level anomalies; daily mean fields of satellite sea surface temperature are used for correcting the air–sea fluxes. This paper assesses the quality of the reanalyses with respect to observations and the simulation. Both the SOFA and OceanVar schemes give very similar root-mean-square errors and biases for temperature and salinity fields compared with the assimilated observations. The largest errors are at the thermocline level and in regions of large eddy field variability. However, OceanVar gives 20% better results for sea level anomaly root-mean-square error.

scholarly journals Major improvement of altimetry sea level estimations using pressure-derived corrections based on ERA-Interim atmospheric reanalysis

Ocean Science ◽  
2016 ◽  
Vol 12 (3) ◽  
pp. 825-842 ◽  
Author(s):  
Loren Carrere ◽  
Yannice Faugère ◽  
Michaël Ablain
Keyword(s):  
Shallow Water ◽  
Sea Level ◽  
Regional Scale ◽  
Atmospheric Correction ◽  
Deep Ocean ◽  
Global Ocean ◽  
Strong Impact ◽  
Global Mean Sea Level ◽  
Along Track ◽  
The Impact

Abstract. The new dynamic atmospheric correction (DAC) and dry tropospheric (DT) correction derived from the ERA-Interim meteorological reanalysis have been computed for the 1992–2013 altimeter period. Using these new corrections significantly improves sea level estimations for short temporal signals (< 2 months); the impact is stronger if considering old altimeter missions (ERS-1, ERS-2, and Topex/Poseidon), for which DAC_ERA (DAC derived from ERA-Interim meteorological reanalysis) allows reduction of the along-track altimeter sea surface height (SSH) error by more than 3 cm in the Southern Ocean and in some shallow water regions. The impact of DT_ERA (DT derived from ERA-Interim meteorological reanalysis) is also significant in the southern high latitudes for these missions. Concerning more recent missions (Jason-1, Jason-2, and Envisat), results are very similar between ERA-Interim and ECMWF-based corrections: on average for the global ocean, the operational DAC becomes slightly better than DAC_ERA only from the year 2006, likely due to the switch of the operational forcing to a higher spatial resolution. At regional scale, both DACs are similar in the deep ocean but DAC_ERA raises the residual crossovers' variance in some shallow water regions, indicating a slight degradation in the most recent years of the study. In the second decade of altimetry, unexpectedly DT_ERA still gives better results compared to the operational DT. Concerning climate signals, both DAC_ERA and DT_ERA have a low impact on global mean sea level rise (MSL) trends, but they can have a strong impact on long-term regional trends' estimation, up to several millimeters per year locally.

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