Detection of large-scale ocean circulation and tides

1983 ◽  
Vol 309 (1508) ◽  
pp. 361-370 ◽  
Keyword(s):  
Heat Flux ◽  
Surface Topography ◽  
Ocean Circulation ◽  
Satellite Altimetry ◽  
Large Scale ◽  
Precise Measurement ◽  
Ocean Surface ◽  
Ocean Topography ◽  
Tidal Signal ◽  
Nearly Continuous

As emphasized recently by Munk & Wunsch, the traditional methods of monitoring the ocean circulation give data too hopelessly aliased in space and time to permit a proper assessment of basin-wide dynamics and heat flux on climatic timescales. The prospect of nearly continuous recording of ocean-surface topography by satellite altimetry with suitable supporting measurements might make such assessments possible. The associated identification of the geocentric oceanic tidal signal in the data would be an additional bonus. The few weeks of altimetry recorded by Seasat gave a glimpse of the possibilities, but also clarified the areas where better precision and knowledge are needed. Further experience will be gained from currently projected multi-purpose satellites carrying altimeters, but serious knowledge of ocean circulation will result only from missions that are entirely dedicated to the precise measurement of ocean topography.

scholarly journals Improving the Altimeter-Derived Surface Currents Using High-Resolution Sea Surface Temperature Data: A Feasability Study Based on Model Outputs

2016 ◽  
Vol 33 (12) ◽  
pp. 2769-2784 ◽  
Author(s):  
M.-H. Rio ◽  
R. Santoleri ◽  
R. Bourdalle-Badie ◽  
A. Griffa ◽  
L. Piterbarg ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Ocean Circulation ◽  
Large Scale ◽  
Spatial Scales ◽  
Ocean Surface ◽  
Sea Surface ◽  
High Temporal Resolution ◽  
Surface Currents ◽  
Ocean Surface Currents

AbstractAccurate knowledge of ocean surface currents at high spatial and temporal resolutions is crucial for a gamut of applications. The altimeter observing system, by providing repeated global measurements of the sea surface height, has been by far the most exploited system to estimate ocean surface currents over the past 20 years. However, it neither permits the observation of currents moving away from the geostrophic balance nor is it capable of resolving the shortest spatial and temporal scales of the currents. Therefore, to overcome these limitations, in this study the ways in which the high-spatial-resolution and high-temporal-resolution information from sea surface temperature (SST) images can improve the altimeter current estimates are investigated. The method involves inverting the SST evolution equation for the velocity by prescribing the source and sink terms and employing the altimeter currents as the large-scale background flow. The method feasibility is tested using modeled data from the Mercator Ocean system. This study shows that the methodology may improve the altimeter velocities at spatial scales not resolved by the altimeter system (i.e., below 150 km) but also at larger scales, where the geostrophic equilibrium might not be the unique or dominant process of the ocean circulation. In particular, the major improvements (more than 30% on the meridional component) are obtained in the equatorial band, where the geostrophic assumption is not valid. Finally, the main issues anticipated when this method is applied using real datasets are investigated and discussed.

scholarly journals Ocean Surface Currents in the northern Nordic Seas from a combination of multi-mission satellite altimetry and numerical modeling

2020 ◽  
Author(s):  
Felix L. Müller ◽  
Denise Dettmering ◽  
Claudia Wekerle ◽  
Christian Schwatke ◽  
Marcello Passaro ◽  
...  
Keyword(s):  
Sea Ice ◽  
Satellite Altimetry ◽  
Barents Sea ◽  
Ocean Surface ◽  
Ocean Model ◽  
Main Step ◽  
Surface Currents ◽  
Data Set ◽  
Ocean Surface Currents ◽  
Ocean Topography

<p>Satellite altimetry is an important part of the Global Geodetic Observing System providing precise information on sea level on different spatial and temporal scales. Moreover, satellite altimetry-derived dynamic ocean topography heights enable the computation of ocean surface currents by applying the well-known geostrophic equations. However, in polar regions, altimetry observations are affected by seasonally changing sea-ice cover leading to a fragmentary data sampling.</p><p>In order to overcome this problem, an ocean model is used to fill in data gaps. The aim is to obtain a homogeneous ocean topography representation that enables consistent investigations of ocean surface current changes. For that purpose, the global Finite Element Sea-ice Ocean Model (FESOM) is used. It is based on an unstructured grid and provides daily water elevations with high spatial resolution.</p><p><span>The combination is done based on a Principal Component Analysis (PCA) after reducing both quantities by their constant and seasonal signals. In the main step, the </span><span>most dominant spatial patterns of the modeled water heights </span><span>as provided by the PCA are linked with the </span><span>temporal variability of </span><span>the estimated </span><span>dynamic ocean topography elevations</span><span> from altimetry. At the end, the seasonal signal as well as the absolute reference from altimetry is added back to the data set.</span></p><p><span>T</span><span>his </span><span>contribution</span><span> describes the combination process </span><span>as well as the generated final product: </span><span> a daily, more than 17 years covering dataset of geostrophic ocean currents. The combination is done for the </span><span>marine </span><span>region</span><span>s</span><span> Greenland Sea, Barents Sea and the Fram Strait and includes sea surface height observations of the ESA altimeter satellites ERS-2 and Envisat. In order to evaluate the </span><span>combination </span><span>results, independent </span><span>surface </span><span>drifter </span><span>observations</span><span>, </span><span>corrected for</span> <span>a-geostrophic velocity </span><span>components, are used.</span></p>

scholarly journals Studying Dynamic Ocean Topography in Indonesia Sea Based on Satellite Altimetry

2021 ◽  
Vol 925 (1) ◽  
pp. 012062
Author(s):  
Dina A Sarsito ◽  
Muhammad Syahrullah ◽  
Dudy D Wijaya ◽  
Dhota Pradipta ◽  
Heri Andreas
Keyword(s):  
Surface Topography ◽  
Sea Level ◽  
Satellite Altimetry ◽  
Physical Phenomenon ◽  
Sea Surface ◽  
Height Measurement ◽  
Steric Sea Level ◽  
Sea Surface Topography ◽  
Ocean Topography ◽  
Almost All

Abstract Dynamic Ocean Topography is a part of sea surface variabilities derived from Sea Surface Topography as a time-dependent component. The Dynamic Ocean Topography height in this study was determined using the geodetic method of instantaneous sea level height measurement from satellite altimetry technology. In the territory of Indonesia seas, a picture of the long-wavelength phenomenon from the Dynamic Ocean Topography ranges from 0-2.5 meters with three distribution zones of low, medium, and high value. At the same time, the correlation with the positive value of Steric Sea Level Rise was obtained in almost all parts of Indonesia except for the area in the southern part of Java Island around Longitude 1070E and in the Pacific Ocean region, where that is thought to be caused by the existence of several permanent marine high-frequency physical phenomenon but with an indefinite period which usually acts as a dominant time-independent component of the Sea Surface Topography. The results are expected to be used to study the characteristics of the Indonesian seas for scientific and engineering purposes.

scholarly journals From satellite altimetry to Argo and operational oceanography: three revolutions in oceanography

2013 ◽  
Vol 10 (4) ◽  
pp. 1127-1167 ◽  
Author(s):  
P. Y. Le Traon
Keyword(s):  
High Resolution ◽  
Real Time ◽  
Sea Level ◽  
Ocean Circulation ◽  
Satellite Altimetry ◽  
Large Scale ◽  
Global Ocean ◽  
Operational Oceanography ◽  
In Situ Observations

Abstract. The launch of the US/French mission Topex/Poseidon (T/P) (CNES/NASA) in August 1992 was the start of a revolution in oceanography. For the first time, a very precise altimeter system optimized for large scale sea level and ocean circulation observations was flying. T/P alone could not observe the mesoscale circulation. In the 1990s, the ESA satellites ERS-1/2 were flying simultaneously with T/P. Together with my CLS colleagues, we demonstrated that we could use T/P as a reference mission for ERS-1/2 and bring the ERS-1/2 data to an accuracy level comparable to T/P. Near real time high resolution global sea level anomaly maps were then derived. These maps have been operationally produced as part of the SSALTO/DUACS system for the last 15 yr. They are now widely used by the oceanographic community and have contributed to a much better understanding and recognition of the role and importance of mesoscale dynamics. Altimetry needs to be complemented with global in situ observations. In the end of the 90s, a major international initiative was launched to develop Argo, the global array of profiling floats. This has been an outstanding success. Argo floats now provide the most important in situ observations to monitor and understand the role of the ocean on the earth climate and for operational oceanography. This is a second revolution in oceanography. The unique capability of satellite altimetry to observe the global ocean in near real time at high resolution and the development of Argo were essential to the development of global operational oceanography, the third revolution in oceanography. The Global Ocean Data Assimilation Experiment (GODAE) was instrumental in the development of the required capabilities. This paper provides an historical perspective on the development of these three revolutions in oceanography which are very much interlinked. This is not an exhaustive review and I will mainly focus on the contributions we made together with many colleagues and friends.

A dynamically based method for estimating the Atlantic overturning circulation at 26°N from satellite altimetry

2021 ◽  
Author(s):  
Alejandra Sanchez-Franks ◽  
Eleanor Frajka-Williams ◽  
Ben Moat ◽  
David Smeed
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
Satellite Altimetry ◽  
Large Scale ◽  
Vertical Structure ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Large Scale Circulation ◽  
Surface Ocean ◽  
Starting Point

<p>The large-scale system of ocean currents that transport warm surface (1000 m) waters northward and return cooler waters southward is known as the Atlantic meridional overturning circulation (AMOC). Variations in the AMOC have significant repercussions for the climate system, hence there is a need for long term monitoring of AMOC fluctuations. Currently the longest record of continuous directly measured AMOC changes is from the RAPID-MOCHA-WBTS programme, initiated in 2004. The RAPID programme, and other mooring programmes, have revolutionised our understanding of large-scale circulation, however, by design they are constrained to measurements at a single latitude.</p><p>High global coverage of surface ocean data from satellite altimetry is available since the launch of TOPEX/Poseidon satellite in 1992 and has been shown to provide reliable estimates of surface ocean transports on interannual time scales. Here we show that a direct calculation of ocean circulation from satellite altimetry compares well with transport estimates from the 26°N RAPID array on low frequency (18-month) time scales for the upper mid-ocean transport (UMO; r = 0.75), the Gulf Stream transport through the Florida Straits (r = 0.70), and the AMOC (r = 0.83). The vertical structure of the circulation is also investigated, and it is found that the first baroclinic mode accounts for 83% of the interior geostrophic variability, while remaining variability is explained by the barotropic mode. Finally, the UMO and the AMOC are estimated from historical altimetry data (1993 to 2018) using a dynamically based method that incorporates the vertical structure of the flow. The effective implementation of satellite-based method for monitoring the AMOC at 26°N lays down the starting point for monitoring large-scale circulation at all latitudes.</p>

scholarly journals Automated detection of coherent Lagrangian vortices in two-dimensional unsteady flows

2015 ◽  
Vol 471 (2173) ◽  
pp. 20140639 ◽  
Author(s):  
Daniel Karrasch ◽  
Florian Huhn ◽  
George Haller
Keyword(s):  
Satellite Altimetry ◽  
Large Scale ◽  
Strain Tensor ◽  
Unsteady Flows ◽  
Fluid Flows ◽  
Ocean Surface ◽  
Automated Detection ◽  
Two Dimensional ◽  
Green Strain ◽  
Closed Orbits

Coherent boundaries of Lagrangian vortices in fluid flows have recently been identified as closed orbits of line fields associated with the Cauchy–Green strain tensor. Here, we develop a fully automated procedure for the detection of such closed orbits in large-scale velocity datasets. We illustrate the power of our method on ocean surface velocities derived from satellite altimetry.

scholarly journals From satellite altimetry to Argo and operational oceanography: three revolutions in oceanography

Ocean Science ◽  
2013 ◽  
Vol 9 (5) ◽  
pp. 901-915 ◽  
Author(s):  
P. Y. Le Traon
Keyword(s):  
High Resolution ◽  
Real Time ◽  
Sea Level ◽  
Ocean Circulation ◽  
Satellite Altimetry ◽  
Large Scale ◽  
Global Ocean ◽  
Operational Oceanography ◽  
In Situ Observations

Abstract. The launch of the French/US mission Topex/Poseidon (T/P) (CNES/NASA) in August 1992 was the start of a revolution in oceanography. For the first time, a very precise altimeter system optimized for large-scale sea level and ocean circulation observations was flying. T/P alone could not observe the mesoscale circulation. In the 1990s, the ESA satellites ERS-1/2 were flying simultaneously with T/P. Together with my CLS colleagues, we demonstrated that we could use T/P as a reference mission for ERS-1/2 and bring the ERS-1/2 data to an accuracy level comparable to T/P. Near-real-time high-resolution global sea level anomaly maps were then derived. These maps have been operationally produced as part of the SSALTO/DUACS system for the last 15 yr. They are now widely used by the oceanographic community and have contributed to a much better understanding and recognition of the role and importance of mesoscale dynamics. Altimetry needs to be complemented with global in situ observations. At the end of the 90s, a major international initiative was launched to develop Argo, the global array of profiling floats. This has been an outstanding success. Argo floats now provide the most important in situ observations to monitor and understand the role of the ocean on the earth climate and for operational oceanography. This is a second revolution in oceanography. The unique capability of satellite altimetry to observe the global ocean in near-real-time at high resolution and the development of Argo were essential for the development of global operational oceanography, the third revolution in oceanography. The Global Ocean Data Assimilation Experiment (GODAE) was instrumental in the development of the required capabilities. This paper provides an historical perspective on the development of these three revolutions in oceanography which are very much interlinked. This is not an exhaustive review and I will mainly focus on the contributions we made together with many colleagues and friends.

Impacts of Shortwave Penetration Depth on Large-Scale Ocean Circulation and Heat Transport

2005 ◽  
Vol 35 (6) ◽  
pp. 1103-1119 ◽  
Author(s):  
Colm Sweeney ◽  
Anand Gnanadesikan ◽  
Stephen M. Griffies ◽  
Matthew J. Harrison ◽  
Anthony J. Rosati ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Penetration Depth ◽  
Ocean Circulation ◽  
Mixed Layer ◽  
Large Scale ◽  
Sea Surface ◽  
Shortwave Radiation ◽  
Sea Surface Temperatures ◽  
Surface Temperatures

Abstract The impact of changes in shortwave radiation penetration depth on the global ocean circulation and heat transport is studied using the GFDL Modular Ocean Model (MOM4) with two independent parameterizations that use ocean color to estimate the penetration depth of shortwave radiation. Ten to eighteen percent increases in the depth of 1% downwelling surface irradiance levels results in an increase in mixed layer depths of 3–20 m in the subtropical and tropical regions with no change at higher latitudes. While 1D models have predicted that sea surface temperatures at the equator would decrease with deeper penetration of solar irradiance, this study shows a warming, resulting in a 10% decrease in the required restoring heat flux needed to maintain climatological sea surface temperatures in the eastern equatorial Atlantic and Pacific Oceans. The decrease in the restoring heat flux is attributed to a slowdown in heat transport (5%) from the Tropics and an increase in the temperature of submixed layer waters being transported into the equatorial regions. Calculations were made using a simple relationship between mixed layer depth and meridional mass transport. When compared with model diagnostics, these calculations suggest that the slowdown in heat transport is primarily due to off-equatorial increases in mixed layer depths. At higher latitudes (5°–40°), higher restoring heat fluxes are needed to maintain sea surface temperatures because of deeper mixed layers and an increase in storage of heat below the mixed layer. This study offers a way to evaluate the changes in irradiance penetration depths in coupled ocean–atmosphere GCMs and the potential effect that large-scale changes in chlorophyll a concentrations will have on ocean circulation.

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