Multi-year current time series in the eastern North Atlantic Ocean

Müller, Thomas J.; Siedler, Gerold

doi:10.1357/002224092784797755

Cited by 121 publications

(69 citation statements)

References 29 publications

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“…When convective mixing is switched off, statically unstable stratification occurs, but the gross density and overturning structures only change marginally. This marks a sharp contrast with threedimensional models that show a reverse cell at high latitudes and a substantially lower abyssal density when convective mixing is switched off (Zhang et al, 1992;Marotzke and Scott, 1999).…”

Section: Introductioncontrasting

confidence: 61%

“…Another process that is essential for overturning dynamics is convective mixing (Zhang et al, 1992;Marotzke and Scott, 1999): as the water column becomes statically unstable, rapid mixing occurs, removing the instability and rendering the stratification neutral (Marshall and Schott, 1999). This process is parameterized here by a convective adjustment scheme, which is discussed in more detail in Appendix A1.…”

Section: The Governing Equationsmentioning

confidence: 99%

“…We hence cast THC dynamics based on boundary mixing and geostrophy into a conceptual model capable of explaining salient features such as narrow high-latitude downwelling and distinct density structures at eastern and western boundaries. By formulating and solving the equations of our model, we make quantitative the purely qualitative conceptual picture put forward by Colin de Verdière (1993) and Zhang et al (1992), which, in addition to boundary mixing, had been the conceptual starting point of Marotzke (1997). In turn, we here make the Marotzke (1997) framework fully self-consistent.…”

Section: Introductionmentioning

confidence: 99%

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A simple and self-consistent geostrophic-force-balance model of the thermohaline circulation with boundary mixing

Callies

Marotzke

2012

Ocean Sci.

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Abstract. A simple model of the thermohaline circulation (THC) is formulated, with the objective to represent explicitly the geostrophic force balance of the basinwide THC. The model comprises advective-diffusive density balances in two meridional-vertical planes located at the eastern and the western walls of a hemispheric sector basin. Boundary mixing constrains vertical motion to lateral boundary layers along these walls. Interior, along-boundary, and zonally integrated meridional flows are in thermal-wind balance. Rossby waves and the absence of interior mixing render isopycnals zonally flat except near the western boundary, constraining meridional flow to the western boundary layer. The model is forced by a prescribed meridional surface density profile.This two-plane model reproduces both steady-state density and steady-state THC structures of a primitive-equation model. The solution shows narrow deep sinking at the eastern high latitudes, distributed upwelling at both boundaries, and a western boundary current with poleward surface and equatorward deep flow. The overturning strength has a 2/3-power-law dependence on vertical diffusivity and a 1/3-power-law dependence on the imposed meridional surface density difference. Convective mixing plays an essential role in the two-plane model, ensuring that deep sinking is located at high latitudes. This role of convective mixing is consistent with that in three-dimensional models and marks a sharp contrast with previous two-dimensional models.Overall, the two-plane model reproduces crucial features of the THC as simulated in simple-geometry threedimensional models. At the same time, the model selfconsistently makes quantitative a conceptual picture of the three-dimensional THC that hitherto has been expressed either purely qualitatively or not self-consistently.

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Section: Introductioncontrasting

confidence: 61%

Section: The Governing Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A simple and self-consistent geostrophic-force-balance model of the thermohaline circulation with boundary mixing

Callies

Marotzke

2012

Ocean Sci.

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“…This shows that Storms can start evolving as far east as 22.58W. Eddy energy, or rather meridional motion, of this period is evident in long current meter records in the region near 228W (MÏller & Siedler, 1992) and westward moving cyclonic structures are already present near 188W (33^348N) (¢gure 4 of Pingree (1997)). Some early initial infrared signatures may even be observed east of Madeira $ 12^138W.…”

Section: Selected Composite Image Showing Subtropical Front Cold Cycmentioning

confidence: 87%

Position and structure of the Subtropical/Azores Front region from combined Lagrangian and remote sensing (IR/altimeter/SeaWiFS) measurements

1999

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The position and structure of the North Atlantic Subtropical Front is studied using Lagrangian flow tracks and remote sensing (AVHRR imagery: TOPEX/POSEIDON altimetry: SeaWiFS) in a broad region (∼31° to ∼36°N) of marked gradient of dynamic height (Azores Current) that extends from the Mid-Atlantic Ridge (MAR), near ∼40°W, to the Eastern Boundary (∼10°W). Drogued Argos buoy and ALACE tracks are superposed on infrared satellite images in the Subtropical Front region. Cold (cyclonic) structures, called ‘Storms’, and warm (anticyclonic) structures of 100–300 km in size can be found on the south side of the Subtropical Front outcrop, which has a temperature contrast of about 1°C that can be followed for ∼2500 km near 35°N. Warmer water adjacent to the outcrop is flowing eastward (Azores Current) but some warm water is returned westward about 300 km to the south (southern Counterflow). Estimates of horizontal diffusion in a Storm (D=2.2×102 m2 s−1) and in the Subtropical Front region near 200 m depth (Dx=1.3×104 m2 s−1, Dy=2.6×103 m2 s−1) are made from the Lagrangian tracks. Altimeter and in situ measurements show that Storms track westwards. Storms are separated by about 510 km and move westward at 2.7 km d−1. Remote sensing reveals that some initial structures start evolving as far east as 23°W but are more organized near 29°W and therefore Storms are about 1 year old when they reach the MAR (having travelled a distance of 1000 km). Structure and seasonality in SeaWiFS data in the region is examined.

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“…The kinetic energy of the mesoscale variability in the ocean interior is much stronger than the kinetic energy of the large-scale mean circulation. According to M€ uller and Siedler [1992], anisotropic energy distributions are found for both current components at periods around 200 days based on the 9 year long 22 subsurface moorings in the Canary and Iberian Basins of the North Atlantic (their Figure 13). Therefore, the dominant period of 200 days that we found is related to the baroclinic instability from the sea surface into the ocean interior that influences the Meddy's horizontal and vertical movements.…”

Section: Horizontal and Vertical Displacement Of A Meddymentioning

confidence: 99%

An analysis of the evolution of Meddies in the North Atlantic using floats and multisensor satellite data

Ienna

Yan

2015

JGR Oceans

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Previous studies focusing on the remote detection of Mediterranean Eddies (Meddies) have reported that the isopycnal surface changes derived from satellite multisensor measurements at the approximate depth of 400 m can be used to sense the presence of underlying Meddies. While the isopycnal surface near that depth does indeed reveal the locations of Meddies, an analysis of isopycnal surface changes in response to the evolution of Meddies has yet to be made. Accordingly, this research focuses on analyzing the relationship between isopycnal surface changes and the evolution of Meddies. The vertical isopycnal surface variability of Meddies, which is directly related to contributions from rotational velocity, interior thermal variation, and vertical displacement of Meddies, is observed and studied using float observations from A Mediterranean Undercurrent Seeding Experiment (AMUSE). The contributions of each of the three aforementioned parameters are estimated, enabling us to understand their relative role in changing the isopycnal surface above Meddies. Furthermore, in order to further understand Meddies' evolution and their associated forcing, the dominant frequencies of their horizontal and vertical displacements, as well as the sea surface height variability above the Meddy, are analyzed using the Hilbert-Huang Transform. Finally, the horizontal and the vertical eddy viscosity dissipation of Meddies is computed and compared with a theoretical model. The empirical horizontal and the vertical eddy viscosities are found to be 7 3 10 6 cm 2 s 21 and 200 cm 2 s 21 , respectively. This study will therefore contribute to understanding how the isopycnal surface is related to the presence of Meddies, what frequencies dominate its variability, and the values of eddy viscosity which can be used for a numerical model.

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Multi-year current time series in the eastern North Atlantic Ocean

Cited by 121 publications

References 29 publications

A simple and self-consistent geostrophic-force-balance model of the thermohaline circulation with boundary mixing

A simple and self-consistent geostrophic-force-balance model of the thermohaline circulation with boundary mixing

Position and structure of the Subtropical/Azores Front region from combined Lagrangian and remote sensing (IR/altimeter/SeaWiFS) measurements

An analysis of the evolution of Meddies in the North Atlantic using floats and multisensor satellite data

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