Evidence of the South Tropical Counter-Current in the Coral Sea

In the Coral Sea, the mean dynamic topography of the sea surface indicates virtually zonal circulation with one westward flow and two eastward flows at 163� E. and two westward flows and one eastward flow at 158� E. One of the eastward flows may be defined as the South Tropical Counter-Current and its position suggests it originates in the western Coral Sea rather than north of New Guinea. However, the data of the abnormal years 1958 and 1972 point out only westward flow.

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Impact of Multiple Altimeter Data and Mean Dynamic Topography in a Global Analysis and Forecasting System

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-18-0236.1 ◽

2019 ◽

Vol 36 (7) ◽

pp. 1255-1266 ◽

Cited By ~ 2

Author(s):

Mathieu Hamon ◽

Eric Greiner ◽

Pierre-Yves Le Traon ◽

Elisabeth Remy

Keyword(s):

Data Assimilation ◽

Sea Surface ◽

Global Ocean ◽

Altimeter Data ◽

Dynamic Topography ◽

Mean Dynamic Topography ◽

Ocean Data Assimilation ◽

The Mean ◽

Data Assimilation System ◽

Assimilation System

AbstractSatellite altimetry is one of the main sources of information used to constrain global ocean analysis and forecasting systems. In addition to in situ vertical temperature and salinity profiles and sea surface temperature (SST) data, sea level anomalies (SLA) from multiple altimeters are assimilated through the knowledge of a surface reference, the mean dynamic topography (MDT). The quality of analyses and forecasts mainly depends on the availability of SLA observations and on the accuracy of the MDT. A series of observing system evaluations (OSEs) were conducted to assess the relative importance of the number of assimilated altimeters and the accuracy of the MDT in a Mercator Ocean global 1/4° ocean data assimilation system. Dedicated tools were used to quantify impacts on analyzed and forecast sea surface height and temperature/salinity in deeper layers. The study shows that a constellation of four altimeters associated with a precise MDT is required to adequately describe and predict upper-ocean circulation in a global 1/4° ocean data assimilation system. Compared to a one-altimeter configuration, a four-altimeter configuration reduces the mean forecast error by about 30%, but the reduction can reach more than 80% in western boundary current (WBC) regions. The use of the most recent MDT updates improves the accuracy of analyses and forecasts to the same extent as assimilating a fourth altimeter.

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Impacts of mean dynamic topography on a regional ocean assimilation system

Ocean Science ◽

10.5194/os-11-829-2015 ◽

2015 ◽

Vol 11 (5) ◽

pp. 829-837 ◽

Cited By ~ 5

Author(s):

C. Yan ◽

J. Zhu ◽

C. A. S. Tanajura

Keyword(s):

Data Assimilation ◽

Sea Surface Height ◽

Sea Surface ◽

Dynamic Topography ◽

Altimetry Data ◽

Mean Dynamic Topography ◽

Mean Sea Surface ◽

The Mean

Abstract. An ocean data assimilation system was developed for the Pacific–Indian oceans with the aim of assimilating altimetry data, sea surface temperature, and in situ measurements from Argo (Array for Real-time Geostrophic Oceanography), XBT (expendable bathythermographs), CTD (conductivity temperature depth), and TAO (Tropical Atmosphere Ocean). The altimetry data assimilation requires the addition of the mean dynamic topography to the altimetric sea level anomaly to match the model sea surface height. The mean dynamic topography is usually computed from the model long-term mean sea surface height, and is also available from gravimetric satellite data. In this study, the impact of different mean dynamic topographies on the sea level anomaly assimilation is examined. Results show that impacts of the mean dynamic topography cannot be neglected. The mean dynamic topography from the model long-term mean sea surface height without assimilating in situ observations results in worsened subsurface temperature and salinity estimates. Even if all available observations including in situ measurements, sea surface temperature measurements, and altimetry data are assimilated, the estimates are still not improved. This proves the significant impact of the MDT (mean dynamic topography) on the analysis system, as the other types of observations do not compensate for the shortcoming due to the altimetry data assimilation. The gravimeter-based mean dynamic topography results in a good estimate compared with that of the experiment without assimilation. The mean dynamic topography computed from the model long-term mean sea surface height after assimilating in situ observations presents better results.

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Impacts of mean dynamic topography on a regional ocean assimilation system

Ocean Science Discussions ◽

10.5194/osd-12-1083-2015 ◽

2015 ◽

Vol 12 (3) ◽

pp. 1083-1105

Author(s):

C. Yan ◽

J. Zhu ◽

C. A. S. Tanajura

Keyword(s):

Sea Surface Height ◽

Sea Surface ◽

Dynamic Topography ◽

Altimetry Data ◽

Mean Dynamic Topography ◽

Mean Sea Surface ◽

In Situ Observations ◽

The Mean

Abstract. An ocean assimilation system was developed for the Pacific-Indian oceans with the aim of assimilating altimetry data, sea surface temperature, and in-situ measurements from ARGO, XBT, CTD, and TAO. The altimetry data assimilation requires the addition of the mean dynamic topography to the altimetric sea level anomaly to match the model sea surface height. The mean dynamic topography is usually computed from the model long-term mean sea surface height, and is also available from gravimeteric satellite data. In this study, different mean dynamic topographies are used to examine their impacts on the sea level anomaly assimilation. Results show that impacts of the mean dynamic topography cannot be neglected. The mean dynamic topography from the model long-term mean sea surface height without assimilating in-situ observations results in worsened subsurface temperature and salinity estimates. The gravimeter-based mean dynamic topography results in an even worse estimate. Even if all available observations including in-situ measurements, sea surface temperature measurements, and altimetry data are assimilated, the estimates are still not improved. This further indicates that the other types of observations do not compensate for the shortcoming due to the altimetry data assimilation. The mean dynamic topography computed from the model's long-term mean sea surface height after assimilating in-situ observations presents better results.

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

Monthly Weather Review ◽

10.1175/2010mwr3350.1 ◽

2011 ◽

Vol 139 (3) ◽

pp. 738-754 ◽

Cited By ~ 52

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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Variability and meandering of the East Australian Current jet at 27oS

10.5194/egusphere-egu21-13806 ◽

2021 ◽

Author(s):

Bernadette Sloyan ◽

Christopher Chapman ◽

Rebecca Cowley ◽

Thomas Moore

Keyword(s):

Continental Shelf ◽

South Pacific ◽

Sea Surface ◽

Western Boundary ◽

East Australian Current ◽

Boundary Current ◽

The South ◽

Buoyancy Forcing ◽

The Mean ◽

Southward Flow

The East Australian Current (EAC) is the complex and highly energetic western boundary current of the South Pacific Ocean gyre. Low frequency (>2 year) variability of the EAC reflects the changes in the wind and buoyancy forcing over the South Pacific. However, local and regional wind and buoyancy forcing drives higher frequency variability (< 1-2 year) of the EAC. Due to the narrow shelf, the EAC-jet&#160; meandering has an immediate impact on the continental shelf circulation. Here we use the IMOS EAC mooring array between May 2015 to September 2019 and satellite observational data to quantify the quantify the EAC variability and assess the potential drives and impact of the on-shelf meandering of the EAC jet on the properties of the Coral and Tasman Seas.&#160;We find that there is considerable variability of Sea Surface Height (SSH) and Sea Surface temperature (SST) that at times co-vary, but at&#160; other times the anomalies are opposed. We compare the surface anomalies with the EAC velocity and transport timeseries. The mean along-slope velocity vectors show poleward velocity dominates from 0-1500 m at the five mooring locations from the 500 m isobath to the deep abyssal basin with the strongest southward flow at the continental shelf. The variance ellipses show that the largest variability in EAC transport is in the along-shore direction. This indicates that the EAC variability is dominated by the movement of the EAC on- and off-shore. The EAC thus maintains its jet structure as it meanders onshore and offshore adjacent to the continental slope. While the mean along-shore velocity vectors provide a picture of the mean EAC, the time-series shows that the EAC has a complex and highly variable structure. Strong southward flow is associated with off-shore flow (positive across-slope velocity). While mostly measuring the EAC core we see times where the flow is northward (positive along-slope velocity). This northward velocity is due to the shelf flow extending from the coast to the shelf, and is generally associated with on-shore flow (negative across-slope velocity). These changes in the direction and strength of the velocity are driven by cyclonic eddies inshore of the jet, and have significant influence on the exchange between the open and shelf ocean.

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Application of the BEM approach for a determination of the regional marine geoid model and the mean dynamic topography in the Southwest Pacific Ocean and Tasman Sea

Journal of Geodetic Science ◽

10.2478/v10156-011-0019-6 ◽

2012 ◽

Vol 2 (1) ◽

pp. 8-14 ◽

Cited By ~ 1

Author(s):

R. Tenzer ◽

R. Čunderlík ◽

N. Dayoub ◽

A. Abdalla

Keyword(s):

Pacific Ocean ◽

Dynamic Topography ◽

Geoid Model ◽

Mean Dynamic Topography ◽

Southwest Pacific ◽

Tasman Sea ◽

Marine Gravity ◽

The Mean ◽

Local Vertical Datum

Application of the BEM approach for a determination of the regional marine geoid model and the mean dynamic topography in the Southwest Pacific Ocean and Tasman SeaWe apply a novel approach for the gravimetric marine geoid modelling which utilise the boundary element method (BEM). The direct BEM formulation for the Laplace equation is applied to obtain a numerical solution to the linearised fixed gravimetric boundary-value problem in points at the Earth's surface. The numerical scheme uses the collocation method with linear basis functions. It involves a discretisation of the Earth's surface which is considered as a fixed boundary. The surface gravity disturbances represent the oblique derivative boundary condition. The BEM approach is applied to determine the marine geoid model over the study area of the Southwest Pacific Ocean and Tasman Sea using DNSC08 marine gravity data. The comparison of the BEM-derived and EGM2008 geoid models reveals that the geoid height differences vary within -25 and 18 cm with the standard deviation of 6 cm. The DNSC08 sea surface topography data and the new marine geoid are then used for modelling of the mean dynamic topography (MDT) over the study area. The local vertical datum (LVD) offsets estimated at 15 tide-gauge stations in New Zealand are finally used for testing the coastal MDT. The average value of differences between the MDT and LVD offsets is 1 cm.

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