scholarly journals Investigating the relationship between volume transport and sea surface height in a numerical ocean model

2018 ◽  
Author(s):  
Estee Vermeulen ◽  
Björn Backeberg ◽  
Juliet Hermes ◽  
Shane Elipot
Keyword(s):  
Sea Surface Height ◽  
Volume Transport ◽  
Ocean Model ◽  
Sea Surface ◽  
Linear Regression Models ◽  
Current Time ◽  
Agulhas Current ◽  
Modelling Framework ◽  
Long Time ◽  
The Relationship

Abstract. The Agulhas Current Time-series mooring array (ACT) measured transport of the Agulhas Current at 34° S for a period of 3 years. Using along-track satellite altimetry data directly above the array, a proxy of Agulhas Current transport was developed based on the relationship between cross-current sea surface height (SSH) gradients and the measured transports. In this study, the robustness of the proxy is tested within a numerical modelling framework, using a 34-year long regional-hindcast simulation from the Hybrid Coordinate Ocean Model (HYCOM). Two reference proxies were created using HYCOM data from 2010–2013, extracting model data at the mooring positions and along the satellite altimeter track for; (1) the box transport (Tbox) and (2) the jet (southwestward) transport (Tjet). Next, sensitivity tests were performed where the proxy was recalculated from HYCOM for (1) a period where the modelled vertical stratification was different compared to the reference proxy, and (2) different lengths of periods: 1, 3, 6, 12, 18 and 34 years. Compared to the simulated (native) transports, it was found that the HYCOM proxy was more capable of estimating the box transport of the Agulhas Current compared to the jet transport. The HYCOM configuration in this study contained exaggerated levels of offshore variability in the form of frequently-impinging baroclinic anticyclonic eddies. These eddies consequently broke down the linear relationship between SSH slope and vertically-integrated transport, resulting in stronger correlations for the inshore linear regression models compared to the ones offshore. Vertically-integrated transport estimates were therefore more accurate inshore than those offshore or when the current was in a meandering state. Results showed that calculating the proxy over shorter or longer time periods in the model did not significantly impact the skill of the Agulhas transport proxy, suggesting that 3-years was a sufficiently long time-period for the observation based transport proxy.

scholarly journals Investigating the relationship between volume transport and sea surface height in a numerical ocean model

Ocean Science ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 513-526
Author(s):  
Estee Ann Vermeulen ◽  
Björn Backeberg ◽  
Juliet Hermes ◽  
Shane Elipot
Keyword(s):  
Sea Surface Height ◽  
Volume Transport ◽  
Ocean Model ◽  
Sea Surface ◽  
Current Time ◽  
Agulhas Current ◽  
Modelling Framework ◽  
Modelling Studies ◽  
Time Periods ◽  
The Relationship

Abstract. The Agulhas Current Time-series Experiment mooring array (ACT) measured transport of the Agulhas Current at 34∘ S for a period of 3 years. Using along-track satellite altimetry data directly above the array, a proxy of Agulhas Current transport was developed based on the relationship between cross-current sea surface height (SSH) gradients and the measured transports. In this study, the robustness of the proxy is tested within a numerical modelling framework using a 34-year-long regional hindcast simulation from the Hybrid Coordinate Ocean Model (HYCOM). The model specifically tested the sensitivity of the transport proxy to (1) changes in the vertical structure of the current and to (2) different sampling periods used to calculate the proxy. Two reference proxies were created using HYCOM data from 2010 to 2013 by extracting model data at the mooring positions and along the satellite altimeter track for the box (net) transport and the jet (southwestward) transport. Sensitivity tests were performed where the proxy was recalculated from HYCOM for (1) a period where the modelled vertical stratification was different compared to the reference proxy and (2) different lengths of time periods: 1, 3, 6, 12, 18, and 34 years. Compared to the simulated (native) transports, it was found that the HYCOM proxy was more capable of estimating the box transport of the Agulhas Current compared to the jet transport. This was because the model is unable to resolve the dynamics associated with meander events, for which the jet transport algorithm was developed. The HYCOM configuration in this study contained exaggerated levels of offshore variability in the form of frequently impinging baroclinic anticyclonic eddies. These eddies consequently broke down the linear relationship between SSH slope and vertically integrated transport. Lastly, results showed that calculating the proxy over shorter or longer time periods in the model did not significantly impact the skill of the Agulhas transport proxy. Modelling studies of this kind provide useful information towards advancing our understanding of the sensitivities and limitations of transport proxies that are needed to improve long-term ocean monitoring approaches.

ASSIMILATION OF SEA SURFACE HEIGHT ANOMALIES INTO HYCOM WITH AN OPTIMAL INTERPOLATION SCHEME OVER THE ATLANTIC OCEAN METAREA V

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Clemente Augusto Souza Tanajura ◽  
Filipe Bitencourt Costa ◽  
Renato Ramos da Silva ◽  
Giovanni Abdelnur Ruggiero ◽  
Victor Bastos Daher
Keyword(s):  
Interpolation Method ◽  
Maximum Error ◽  
Sea Surface Height ◽  
Volume Transport ◽  
Ocean Model ◽  
Sea Surface ◽  
Height Anomaly ◽  
Optimal Interpolation ◽  
Sea Surface Height Anomaly ◽  
The Impact

Along-track sea surface height anomaly (SSHA) data from the Jason-1 and Jason-2 satellites were assimilated into the ocean model HYCOM from July 1, 2009 until December 31, 2009. A new and simple approach to overcome the bias between the model and observed SSHA was proposed. It focuses on the meso-scale differences between the data and the model along each satellite track. An optimal interpolation method and the Cooper and Haines (1996) scheme (C&H) were employed to produce a SSHA analysis field and to adjust model layer thicknesses over the Atlantic METAREA V. The corrected model state was used as initial condition for the next assimilation cycle. SSHA data with a 7-day window were assimilated in 3-day intervals centered in the SSHA data window and the C&H scheme was applied taking the SSHA analysis. A control run without assimilation was also performed. The results showed that the model SSHA was completely reorganized by the end of the experiment. The modifications of SSHA were compared to the American Navy HYCOM+NCODA system and AVISO data. Maximum error was reduced from 0.7 m to 0.2 m by assimilation. Comparisons were also made with the Argo temperature and salinity vertical profiles. Improvements in the currents and volume transport were also produced by assimilation. The impact in temperature was in general positive, but there was no substantial modification in salinity.

scholarly journals ASSIMILATION OF SEA SURFACE HEIGHT ANOMALIES INTO HYCOM WITH AN OPTIMAL INTERPOLATION SCHEME OVER THE ATLANTIC OCEAN METAREA V

2013 ◽  
Vol 31 (2) ◽  
pp. 257 ◽  
Author(s):  
Clemente Augusto Souza Tanajura ◽  
Filipe Bitencourt Costa ◽  
Renato Ramos da Silva ◽  
Giovanni Abdelnur Ruggiero ◽  
Victor Bastos Daher
Keyword(s):  
Interpolation Method ◽  
Maximum Error ◽  
Sea Surface Height ◽  
Volume Transport ◽  
Ocean Model ◽  
Sea Surface ◽  
Height Anomaly ◽  
Optimal Interpolation ◽  
Ocean Data Assimilation ◽  
The Impact

ABSTRACT. Along-track sea surface height anomaly (SSHA) data from the Jason-1 and Jason-2 satellites were assimilated into the ocean model HYCOM from July 1, 2009 until December 31, 2009. A new and simple approach to overcome the bias between the model and observed SSHA was proposed. It focuses on the meso-scale differences between the data and the model along each satellite track. An optimal interpolation method and the Cooper & Haines (1996) scheme (C&H) were employed to produce a SSHA analysis field and to adjust model layer thicknesses over the Atlantic METAREA V. The corrected model state was used as initial condition for the next assimilation cycle. SSHA data with a 7-day window were assimilated in 3-day intervals centered in the SSHA data window and the C&H scheme was applied taking the SSHA analysis. A control run without assimilation was also performed. The results showed that the model SSHA was completely reorganized by the end of the experiment. The modifications of SSHA were compared to the American Navy HYCOM+NCODA system and AVISO data. Maximum error was reduced from 0.7 m to 0.2 m by assimilation. Comparisons were also made with the Argo temperature and salinity vertical profiles. Improvements in the currents and volume transport were also produced by assimilation. The impact in temperature was in general positive, but there was no substantial modification in salinity.   Keywords: ocean data assimilation, Jason-1 and Jason-2 satellites, Argo. RESUMO. Dados de anomalia da altura da superfície do mar (AASM) dos satellites Jason-1 e Jason-2 foram assimilados no modelo oceânico HYCOM de 1 de julho de 2009 a 31 de dezembro de 2009. Um nova e simples abordagem foi proposta para superar o viés entre os dados observados de AASM e o campo do modelo. Ela enfoca as diferenças entre o modelo e as observações na mesoescala ao longo de cada trilha dos satélites. Um método de interpolação estatística e o esquema de Cooper & Haines (1996) (C&H) foram empregados para produzir um campo de análise de AASM e ajustes nas espessuras das camadas do modelo sobre a METAREA V do Atlântico. O estado corrigido do modelo foi usado como condição inicial para o próximo ciclo de assimilação. Dados de AASM em uma janela de 7 dias foram assimilados a cada 3 dias em data centrada na janela de dados e o método de C&H foi aplicado com a análise de AASM. Os resultados mostraram que a AASM do modelo foi completamente reorganizada no final do experimento. As modificações de AASM foram comparadas com análises globais do sistema Americano HYCOM+NCODA e com dados do AVISO. Erros máximos foram reduzidos de 0,7 m para 0,2 m com a assimilação. Comparações foram também feitas com perfis verticais de temperatura e salinidade do Argo. Melhorias nas correntes e no transporte de volume foram produzidas em relação à rodada de controle. O impacto na temperatura foi em geral positivo, mas não houve modificação substancial na salinidade.   Palavras-chave: assimilação de dados oceanográficos, satélites Jason-1 e Jason-2, Argo.

scholarly journals On the Relationship between Regional Ocean Heat Content and Sea Surface Height

2017 ◽  
Vol 30 (22) ◽  
pp. 9195-9211 ◽  
Author(s):  
John T. Fasullo ◽  
Peter R. Gent
Keyword(s):  
Time Scales ◽  
Low Frequency ◽  
Heat Content ◽  
Sea Surface Height ◽  
Ocean Heat Content ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Altimeter Data ◽  
Model Control ◽  
The Relationship

Abstract An accurate diagnosis of ocean heat content (OHC) is essential for interpreting climate variability and change, as evidenced for example by the broad range of hypotheses that exists for explaining the recent hiatus in global mean surface warming. Potential insights are explored here by examining relationships between OHC and sea surface height (SSH) in observations and two recently available large ensembles of climate model simulations from the mid-twentieth century to 2100. It is found that in decadal-length observations and a model control simulation with constant forcing, strong ties between OHC and SSH exist, with little temporal or spatial complexity. Agreement is particularly strong on monthly to interannual time scales. In contrast, in forced transient warming simulations, important dependencies in the relationship exist as a function of region and time scale. Near Antarctica, low-frequency SSH variability is driven mainly by changes in the circumpolar current associated with intensified surface winds, leading to correlations between OHC and SSH that are weak and sometimes negative. In subtropical regions, and near other coastal boundaries, negative correlations are also evident on long time scales and are associated with the accumulated effects of changes in the water cycle and ocean dynamics that underlie complexity in the OHC relationship to SSH. Low-frequency variability in observations is found to exhibit similar negative correlations. Combined with altimeter data, these results provide evidence that SSH increases in the Indian and western Pacific Oceans during the hiatus are suggestive of substantial OHC increases. Methods for developing the applicability of altimetry as a constraint on OHC more generally are also discussed.

scholarly journals Dynamics of the seasonal variations in the Indian Ocean from TOPEX/POSEIDON sea surface height and an ocean model

1998 ◽  
Vol 25 (11) ◽  
pp. 1915-1918 ◽  
Author(s):  
Jiayan Yang ◽  
Lisan Yu ◽  
Chester J. Koblinsky ◽  
David Adamec
Keyword(s):  
Indian Ocean ◽  
Seasonal Variations ◽  
Sea Surface Height ◽  
Ocean Model ◽  
Sea Surface ◽  
The Indian Ocean

scholarly journals Assessment of Traditional and New Eigenfunction Bases Applied to Extrapolation of Surface Geostrophic Current Time Series to Below the Surface in an Idealized Primitive Equation Simulation

2012 ◽  
Vol 42 (1) ◽  
pp. 165-178 ◽  
Author(s):  
Robert B. Scott ◽  
Darran G. Furnival
Keyword(s):  
Phase Locking ◽  
Sea Surface Height ◽  
Basis Functions ◽  
Sea Surface ◽  
Surface Boundary ◽  
Baroclinic Mode ◽  
Primitive Equation ◽  
Current Time ◽  
Free Surface Boundary Condition ◽  
Baroclinic Modes

Abstract Three strategies were compared for extrapolating surface geostrophic velocities to below the surface: S1, using only the barotropic or first baroclinic mode; S2, using a fixed or “phase locked” linear combination of the first baroclinic mode and the barotropic mode; and S3, a strategy similar to S2 but using a new set of basis functions. For S2 and S3, the phase locking allows one to impose zero velocity at the seafloor. The new basis functions start from zero at the surface, are not degenerate with respect to the free-surface boundary condition, and represent the adjustment of the pressure at a given depth from density surfaces responding to sea surface height undulations. In idealized primitive equation simulations, strategy S3 had the least error and allowed extrapolation to deeper levels, suggesting the new basis functions performed significantly better than the traditional baroclinic modes. In contrast, strategies S1 and S2 made poor predictions by 400-m depth. Large temporal fluctuations in the fraction of energy in the barotropic and first baroclinic modes could explain the poor predictions by strategies S1 and S2. This brings into question the interpretation of the sea surface height gradients measured by satellite altimetry in terms of first baroclinic mode motions.

scholarly journals Changes in extreme regional sea surface height due to an abrupt weakening of the Atlantic meridional overturning circulation

Ocean Science ◽  
2014 ◽  
Vol 10 (6) ◽  
pp. 881-891 ◽  
Author(s):  
S.-E. Brunnabend ◽  
H. A. Dijkstra ◽  
M. A. Kliphuis ◽  
B. van Werkhoven ◽  
H. E. Bal ◽  
...  
Keyword(s):  
North Atlantic ◽  
Atlantic Meridional Overturning Circulation ◽  
Sea Surface Height ◽  
Ocean Model ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
Sea Level Changes ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning

Abstract. As an extreme scenario of dynamical sea level changes, regional sea surface height (SSH) changes that occur in the North Atlantic due to an abrupt weakening of the Atlantic meridional overturning circulation (AMOC) are simulated. Two versions of the same ocean-only model are used to study the effect of ocean model resolution on these SSH changes: a high-resolution (HR) strongly eddying version and a low-resolution (LR) version in which the effect of eddies is parameterised. The weakening of the AMOC is induced in both model versions by applying strong freshwater perturbations around Greenland. A rapid decrease of the AMOC in the HR version induces much shorter return times of several specific regional and coastal extremes in North Atlantic SSH than in the LR version. This effect is caused by a change in main eddy pathways associated with a change in separation latitude of the Gulf Stream.

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