Can the Subtropical North Atlantic permanent thermocline be observed from space?

The analysis of remotely sensed altimeter data and in situ measurements shows that ERS 2 radar can monitor the ocean permanent thermocline from space. The remotely sensed sea level anomaly data account for ∼2/3 of the temperature variance or vertical displacement of isotherms at a depth of ∼550 m in the Subtropical North Atlantic Ocean near 32·5°N. This depth corresponds closely to the region of maximum temperature gradient in the permanent thermocline where near semi-annual internal vertical displacements reach 200 to 300 m. The gradient of the altimeter sea level anomaly data correlates well with measured ocean currents to a depth of 750 m. It is shown that observations from space can account for ∼3/4 of the variance of ocean currents measured in situ in the permanent thermocline over a 2-y period. The magnification of the permanent thermocline displacement with respect to the displacement of the sea surface was determined as −×650 and gives a measure of the ratio of barotropic to baroclinic decay scale of geostrophic current with depth. The overall results are used to interpret an eight year altimeter data time series in the Subtropical North Atlantic at 32·5°N which shows a dominant wave or eddy period near 200 days, rather than semi-annual and increases in energy propagating westward in 1995 (west of 25°W). The effects of rapid North Atlantic Oscillation climate change on ocean circulation are discussed. The altimeter data for the Atlantic were Fourier analysed. It is shown how the annual and semi-annual components relate to the seasonal maximum cholorophyll-a SeaWiFS signal in tropical and equatorial regions due to the lifting of the thermocline caused by seasonally varying ocean currents forced by wind stress.

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North Atlantic Ocean Circulation and Decadal Sea Level Change During the Altimetry Era

Scientific Reports ◽

10.1038/s41598-018-37603-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 21

Author(s):

Léon Chafik ◽

Jan Even Øie Nilsen ◽

Sönke Dangendorf ◽

Gilles Reverdin ◽

Thomas Frederikse

Keyword(s):

Atlantic Ocean ◽

Sea Level ◽

Ocean Circulation ◽

North Atlantic ◽

North Atlantic Ocean ◽

Sea Level Change ◽

Level Change

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A shift in the ocean circulation has warmed the subpolar North Atlantic Ocean since 2016

Communications Earth & Environment ◽

10.1038/s43247-021-00120-y ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Damien Desbruyères ◽

Léon Chafik ◽

Guillaume Maze

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

Large Scale ◽

North Atlantic Ocean ◽

Temperature Trends ◽

Global Impacts ◽

Meridional Overturning ◽

Near Future ◽

Ocean Observing

AbstractThe Subpolar North Atlantic is known for rapid reversals of decadal temperature trends, with ramifications encompassing the large-scale meridional overturning and gyre circulations, Arctic heat and mass balances, or extreme continental weather. Here, we combine datasets derived from sustained ocean observing systems (satellite and in situ), idealized observation-based modelling (advection-diffusion of a passive tracer), and a machine learning technique (ocean profile clustering) to document and explain the most-recent and ongoing cooling-to-warming transition of the Subpolar North Atlantic. Following a gradual cooling of the region that was persisting since 2006, a surface-intensified and large-scale warming sharply emerged in 2016 following an ocean circulation shift that enhanced the northeastward penetration of warm and saline waters from the western subtropics. The long ocean memory of the Subpolar North Atlantic implies that this advection-driven warming is likely to persist in the near-future with possible implications for the Atlantic multidecadal variability and its global impacts.

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A New Method for Tracking Meddies by Satellite Altimetry

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00080.1 ◽

2014 ◽

Vol 31 (6) ◽

pp. 1434-1445 ◽

Cited By ~ 8

Author(s):

Federico Ienna ◽

Young-Heon Jo ◽

Xiao-Hai Yan

Keyword(s):

Remote Sensing ◽

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Saline Water ◽

Ensemble Empirical Mode Decomposition ◽

Altimeter Data ◽

In Situ Techniques ◽

The North ◽

The North Atlantic

Abstract Subsurface coherent vortices in the North Atlantic, whose saline water originates from the Mediterranean Sea and which are known as Mediterranean eddies (meddies), have been of particular interest to physical oceanographers since their discovery, especially for their salt and heat transport properties into the North Atlantic Ocean. Many studies in the past have been successful in observing and studying the typical properties of meddies by probing them with in situ techniques. The use of remote sensing techniques would offer a much cheaper and easier alternative for studying these phenomena, but only a few past studies have been able to study meddies by remote sensing, and a reliable method for observing them remotely remains elusive. This research presents a new way of locating and tracking meddies in the North Atlantic Ocean using satellite altimeter data. The method presented in this research makes use of ensemble empirical mode decomposition (EEMD) as a means to isolate the surface expressions of meddies on the ocean surface and separates them from any other surface constituents, allowing robust meddies to be consistently tracked by satellite. One such meddy is successfully tracked over a 6-month time period (2 November 2005 to 17 May 2006). Results of the satellite tracking method are verified using expendable bathythermographs (XBT).

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Response of North Atlantic Ocean Circulation to Atmospheric Weather Regimes

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0217.1 ◽

2014 ◽

Vol 44 (1) ◽

pp. 179-201 ◽

Cited By ~ 31

Author(s):

Nicolas Barrier ◽

Christophe Cassou ◽

Julie Deshayes ◽

Anne-Marie Treguier

Keyword(s):

Atlantic Ocean ◽

Wind Stress ◽

Ocean Circulation ◽

North Atlantic ◽

North Atlantic Ocean ◽

Meridional Overturning Circulation ◽

Subpolar Gyre ◽

Wind Stress Curl ◽

Overturning Circulation ◽

Weather Regimes

Abstract A new framework is proposed for investigating the atmospheric forcing of North Atlantic Ocean circulation. Instead of using classical modes of variability, such as the North Atlantic Oscillation (NAO) or the east Atlantic pattern, the weather regimes paradigm was used. Using this framework helped avoid problems associated with the assumptions of orthogonality and symmetry that are particular to modal analysis and known to be unsuitable for the NAO. Using ocean-only historical and sensitivity experiments, the impacts of the four winter weather regimes on horizontal and overturning circulations were investigated. The results suggest that the Atlantic Ridge (AR), negative NAO (NAO−), and positive NAO (NAO+) regimes induce a fast (monthly-to-interannual time scales) adjustment of the gyres via topographic Sverdrup dynamics and of the meridional overturning circulation via anomalous Ekman transport. The wind anomalies associated with the Scandinavian blocking regime (SBL) are ineffective in driving a fast wind-driven oceanic adjustment. The response of both gyre and overturning circulations to persistent regime conditions was also estimated. AR causes a strong, wind-driven reduction in the strengths of the subtropical and subpolar gyres, while NAO+ causes a strengthening of the subtropical gyre via wind stress curl anomalies and of the subpolar gyre via heat flux anomalies. NAO− induces a southward shift of the gyres through the southward displacement of the wind stress curl. The SBL is found to impact the subpolar gyre only via anomalous heat fluxes. The overturning circulation is shown to spin up following persistent SBL and NAO+ and to spin down following persistent AR and NAO− conditions. These responses are driven by changes in deep water formation in the Labrador Sea.

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Assessing the sensitivity of the North Atlantic Ocean circulation to freshwater perturbation in various glacial climate states

Climate Dynamics ◽

10.1007/s00382-011-1043-z ◽

2011 ◽

Vol 37 (9-10) ◽

pp. 1909-1927 ◽

Cited By ~ 7

Author(s):

Cédric J. Van Meerbeeck ◽

Didier M. Roche ◽

Hans Renssen

Keyword(s):

Atlantic Ocean ◽

Ocean Circulation ◽

North Atlantic ◽

North Atlantic Ocean ◽

The North ◽

The North Atlantic ◽

Glacial Climate

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Shifting ocean circulation warms the Subpolar North Atlantic since 2016

10.5194/egusphere-egu21-940 ◽

2021 ◽

Author(s):

Damien Desbruyères ◽

Léon Chafik ◽

Guillaume Maze

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

Large Scale ◽

Deep Ocean ◽

Ocean Heat Uptake ◽

Driving Mechanisms ◽

Temperature Trends ◽

Meridional Overturning ◽

Ocean Observing

<p>The Subpolar North Atlantic (SPNA) is known for rapid reversals of decadal temperature trends, with ramifications encompassing the large-scale meridional overturning and gyre circulations, Arctic heat and mass balances, or extreme continental weather. Here, we combine datasets derived from sustained ocean observing systems (satellite and in situ), and idealized observation-based modelling (advection-diffusion of a passive tracer) and machine learning technique (ocean profile clustering) to document and explain the most-recent and ongoing cooling-to-warming transition of the SPNA. Following a gradual cooling of the region that was persisting since 2006, a surface-intensified and large-scale warming sharply emerged in 2016 following an ocean circulation shift that enhanced the northeastward penetration of warm and saline waters from the western subtropics. Driving mechanisms and ramification for deep ocean heat uptake will be discussed.</p>

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Decadal Polar Motion Connected with Atmospheric Pressure and Sea Level Patterns over the North Atlantic Ocean

International Association of Geodesy Symposia - Gravity, Geoid and Marine Geodesy ◽

10.1007/978-3-662-03482-8_88 ◽

1997 ◽

pp. 666-673 ◽

Cited By ~ 2

Author(s):

Tetsuya Iwabuchi ◽

Kosuke Heki ◽

Isao Naito

Keyword(s):

Atlantic Ocean ◽

Sea Level ◽

North Atlantic ◽

Atmospheric Pressure ◽

Polar Motion ◽

North Atlantic Ocean ◽

The North ◽

The North Atlantic ◽

And Sea Level

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Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation

Ocean Science ◽

10.5194/os-11-425-2015 ◽

2015 ◽

Vol 11 (3) ◽

pp. 425-438 ◽

Cited By ~ 7

Author(s):

G. Candille ◽

J.-M. Brankart ◽

P. Brasseur

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Gulf Stream ◽

North Atlantic Ocean ◽

Altimeter Data ◽

Stochastic Perturbations ◽

The North ◽

Altimetric Data ◽

The North Atlantic ◽

Along Track

Abstract. A realistic circulation model of the North Atlantic ocean at 0.25° resolution (NATL025 NEMO configuration) has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on the model dynamics. The main motivation for this work is to develop ensemble data assimilation methods, assimilating altimetric data from past missions Jason-1 and Envisat. The assimilation experiment is designed to provide a description of the uncertainty associated with the Gulf Stream circulation for years 2005/2006, focusing on frontal regions which are predominantly affected by unresolved dynamical scales. An ensemble based on such stochastic perturbations is first produced and evaluated using along-track altimetry observations. Then each ensemble member is updated by a square root algorithm based on the SEEK (singular evolutive extended Kalman) filter (Brasseur and Verron, 2006). These three elements – stochastic parameterization, ensemble simulation and 4-D observation operator – are then used together to perform a 4-D analysis of along-track altimetry over 10-day windows. Finally, the results of this experiment are objectively evaluated using the standard probabilistic approach developed for meteorological applications (Toth et al., 2003; Candille et al., 2007). The results show that the free ensemble – before starting the assimilation process – correctly reproduces the statistical variability over the Gulf Stream area: the system is then pretty reliable but not informative (null probabilistic resolution). Updating the free ensemble with altimetric data leads to a better reliability with an information gain of around 30% (for 10-day forecasts of the SSH variable). Diagnoses on fully independent data (i.e. data that are not assimilated, like temperature and salinity profiles) provide more contrasted results when the free and updated ensembles are compared.

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Marine Wind and Wave Height Trends at Different ERA-Interim Forecast Ranges

Journal of Climate ◽

10.1175/jcli-d-14-00470.1 ◽

2015 ◽

Vol 28 (2) ◽

pp. 819-837 ◽

Cited By ~ 56

Author(s):

Ole Johan Aarnes ◽

Saleh Abdalla ◽

Jean-Raymond Bidlot ◽

Øyvind Breivik

Keyword(s):

Wind Speed ◽

Wave Height ◽

North Atlantic ◽

Wave Model ◽

Altimeter Data ◽

The North ◽

The Impact ◽

Global Reanalysis ◽

Made In

Abstract Trends in marine wind speed and significant wave height are investigated using the global reanalysis ERA-Interim over the period 1979–2012, based on monthly-mean and monthly-maximum data. Besides the traditional reanalysis, the authors include trends obtained at different forecast range, available up to 10 days ahead. Any model biases that are corrected differently over time are likely to introduce spurious trends of variable magnitude. However, at increased forecast range the model tends to relax, being less affected by assimilation. Still, there is a trade-off between removing the impact of data assimilation at longer forecast range and getting a lower level of uncertainty in the predictions at shorter forecast range. Because of the sheer amount of assimilations made in ERA-Interim, directly and indirectly affecting the data, it is difficult, if not impossible, to distinguish effects imposed by all updates. Here, special emphasis is put on the introduction of wave altimeter data in August 1991, the only type of data directly affecting the wave field. From this, it is shown that areas of higher model bias introduce quite different trends depending on forecast range, most apparent in the North Atlantic and eastern tropical Pacific. Results are compared with 23 in situ measurements, Envisat altimeter winds, and two stand-alone ECMWF operational wave model (EC-WAM) runs with and without wave altimeter assimilation. Here, the 48-h forecast is suggested to be a better candidate for trend estimates of wave height, mainly due to the step change imposed by altimeter observations. Even though wind speed seems less affected by undesirable step changes, the authors believe that the 24–48-h forecast more effectively filters out any unwanted effects.

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