scholarly journals Reconstructing the Ocean's Interior from Surface Data

2013 ◽  
Vol 43 (8) ◽  
pp. 1611-1626 ◽  
Author(s):  
Jinbo Wang ◽  
Glenn R. Flierl ◽  
Joseph H. LaCasce ◽  
Julie L. McClean ◽  
Amala Mahadevan
Keyword(s):  
North Atlantic ◽  
Surface Density ◽  
Three Dimensional ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The North ◽  
Surface Data ◽  
Pressure Anomaly ◽  
Using Data ◽  
Baroclinic Modes

Abstract A new method is proposed for extrapolating subsurface velocity and density fields from sea surface density and sea surface height (SSH). In this, the surface density is linked to the subsurface fields via the surface quasigeostrophic (SQG) formalism, as proposed in several recent papers. The subsurface field is augmented by the addition of the barotropic and first baroclinic modes, whose amplitudes are determined by matching to the sea surface height (pressure), after subtracting the SQG contribution. An additional constraint is that the bottom pressure anomaly vanishes. The method is tested for three regions in the North Atlantic using data from a high-resolution numerical simulation. The decomposition yields strikingly realistic subsurface fields. It is particularly successful in energetic regions like the Gulf Stream extension and at high latitudes where the mixed layer is deep, but it also works in less energetic eastern subtropics. The demonstration highlights the possibility of reconstructing three-dimensional oceanic flows using a combination of satellite fields, for example, sea surface temperature (SST) and SSH, and sparse (or climatological) estimates of the regional depth-resolved density. The method could be further elaborated to integrate additional subsurface information, such as mooring measurements.

Estimated Global Hydrographic Variability

2007 ◽  
Vol 37 (8) ◽  
pp. 1997-2008 ◽  
Author(s):  
Gaël Forget ◽  
Carl Wunsch
Keyword(s):  
Ocean Circulation ◽  
Large Fraction ◽  
World Ocean ◽  
Three Dimensional ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The North ◽  
Salinity Variability ◽  
Vertical Displacements ◽  
Diffusive Processes

Abstract An estimate is made of the three-dimensional global oceanic temperature and salinity variability, omitting the seasonal cycle, both as a major descriptive element of the ocean circulation and for use in the error estimates of state estimation. Historical hydrography, recent data from the World Ocean Circulation Experiment, and Argo profile data are all used. Root-mean-square vertical displacements in the upper 300 m of the ocean are generally smaller than 50 m, except in energetic boundary currents and in the North Atlantic subpolar gyre. Variability in temperature and salinity is strongly correlated below the top 100 m. Salinity contributions to sea surface height variability appear more significant at low latitudes than expected, possibly resulting from advective and diffusive processes. Results are generally consistent with altimetric variability under two simple kinematic hypotheses, and much of the observed structure coincides with known dynamical features. A large fraction of the sea surface height variability is consistent with the hypothesis of dominance of the first baroclinic mode.

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.

scholarly journals Temporal and spatial characteristics of sea surface height variability in the North Atlantic Ocean

Ocean Science ◽  
2006 ◽  
Vol 2 (2) ◽  
pp. 147-159 ◽  
Author(s):  
D. Cromwell
Keyword(s):  
North Atlantic ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Altimeter Data ◽  
Atlantic Basin ◽  
North Atlantic Basin ◽  
The North ◽  
Second Mode ◽  
Leading Mode ◽  
The North Atlantic

Abstract. We investigate the spatial and temporal variability of sea surface height (SSH) in the North Atlantic basin using satellite altimeter data from October 1992–January 2004. Our primary aim is to provide a detailed description of such variability, including that associated with propagating signals. We also investigate possible correlations between SSH variability and atmospheric pressure changes as represented by climate indices. We first investigate interannual SSH variations by deriving the complex empirical orthogonal functions (CEOFs) of altimeter data lowpass-filtered at 18 months. We determine the spatial structure of the leading four modes (both in amplitude and phase) and also the associated principal component (PC) time series. Using wavelet analysis we derive the time-varying spectral density of the PCs, revealing when particular modes were strongest between 1992–2004. The spatial pattern of the leading CEOF, comprising 30% of the total variability, displays a 5-year periodicity in phase; signal propagation is particularly marked in the Labrador Sea. The second mode, with a dominant 3-year signal, has strong variability in the eastern basin. Secondly, we focus on the Azores subtropical frontal zone. The leading mode (35%) is strong in the south and east of this region with strong variations at 3- and 5-year periods. The second mode (21%) has a near-zonal band of low variance between  22°–27° N, sandwiched between two regions of high variance. Thirdly, we lowpass filter the altimeter data at a cutoff of 30 days, instead of 18 months, in order to retain signals associated with propagating baroclinic Rossby waves and/or eddies. The leading mode is the annual steric signal, around 46% of the SSH variability. The third and fourth CEOFs,  11% of the remaining variability, are associated with westward propagation which is particularly dominant in a "waveband" between 32°–36° N. For all three cases considered above, no significant cross-correlation is found between the North Atlantic Oscillation index and the amplitude of the leading four PCs of interannual SSH variability. The only exception is an anti-correlation found over the North Atlantic basin between the NAO and the 4th PC. In the subtropical front, the East Atlantic Pattern index is anti-correlated with the leading PC for SSH variations lowpass filtered at 30 days. Further investigation of forcing mechanisms is suggested using hindcasts from ocean general circulation models.

Variability of sea surface height and circulation in the North Atlantic: Forcing mechanisms and linkages

2015 ◽  
Vol 132 ◽  
pp. 273-286 ◽  
Author(s):  
Zeliang Wang ◽  
Youyu Lu ◽  
Frederic Dupont ◽  
John W. Loder ◽  
Charles Hannah ◽  
...  
Keyword(s):  
North Atlantic ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The North ◽  
The North Atlantic ◽  
Forcing Mechanisms

scholarly journals Temporal and spatial characteristics of sea surface height variability in the North Atlantic Ocean

2006 ◽  
Vol 3 (3) ◽  
pp. 609-636 ◽  
Author(s):  
D. Cromwell
Keyword(s):  
North Atlantic ◽  
Principal Components ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Frontal Region ◽  
Altimeter Data ◽  
The North ◽  
Second Mode ◽  
Leading Mode ◽  
The North Atlantic

Abstract. We investigate the spatial and temporal variability of sea surface height (SSH) in the North Atlantic basin using altimeter data from October 1992–January 2004. Our primary aim is to provide a fuller description of such variability, particularly that associated with propagating signals. We also investigate possible correlations between SSH variability and climate indices. We first investigate interannual SSH variations by deriving the complex empirical orthogonal functions (CEOFs) of altimeter data lowpass-filtered at 18 months. We determine the spatial structure of the leading four modes (both in amplitude and phase) and also the associated principal components (PCs). Using wavelet analysis we derive the time-varying spectral density of the PCs revealing when particular modes are strongest between 1992–2004. The spatial pattern of the leading CEOF, comprising 30% of the total variability, has a 5-year period. Signal propagation with a 5-year period is also observed in the Labrador Sea. The second mode, with a dominant 3-year signal, has strong variability in the eastern basin. We next focus on the Azores subtropical frontal region. The leading mode (35%) is strong in the south and east of this region. The second mode (21%) has a near-zonal band of low variance between ~22°–27° N sandwiched between two regions of high variance. We then lowpass filter the altimeter data at a cutoff of 30 days, instead of 18 months, in order to retain signals associated with propagating baroclinic Rossby waves. The leading mode is the annual steric signal, around 46% of the SSH variability. The third and fourth CEOFs, 11% of the remaining variability, are associated with westward propagation which is particularly dominant in a ''waveband'' between 32°–36° N. No significant cross-correlation is found between the North Atlantic Oscillation index and the amplitude of the leading two principal components of interannual SSH variability. The East Atlantic Pattern index, however, is correlated with the principal components of the two leading modes of SSH variability, particularly with PC2 in the Azores subtropical frontal region. Further investigation of forcing mechanisms is suggested using hindcasts from ocean general circulation models.

scholarly journals A Preoperational Scheme for Calculating Sea Surface Height by Bernoulli Inverse of Argo Float Data in the North Atlantic

2005 ◽  
Vol 22 (9) ◽  
pp. 1416-1422 ◽  
Author(s):  
Steven G. Alderson ◽  
Peter D. Killworth
Keyword(s):  
North Atlantic ◽  
Input Data ◽  
Solution Method ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The North ◽  
Early Results ◽  
The North Atlantic ◽  
Height Fields ◽  
Good Agreement

Abstract A preoperational scheme has been implemented to calculate sea surface height fields at 7-day intervals over the North Atlantic. Input data from Argo floats is downloaded and processed in near–real time. The solution method is by Bernoulli inverse. Early results are encouraging. Features of the results are compared with both model and satellite data and show good agreement.

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