On the Evidences of the Gulf Stream in High Latitudes in the North Atlantic

Vegetation in the northern high latitudes shows a characteristic pattern of persistent changes as documented by multi-decadal satellite observations. The prevailing explanation that these mainly increasing trends (greening) are a consequence of external CO2 forcing, i.e., due to the ubiquitous effect of CO2-induced fertilization and/or warming of temperature-limited ecosystems, however does not explain why some areas also show decreasing trends of vegetation cover (browning). We propose here to consider the dominant mode of multi-decadal internal climate variability in the north Atlantic region, the Atlantic Multidecadal Variability (AMV), as the missing link in the explanation of greening and browning trend patterns in the northern high latitudes. Such a link would also imply potential for decadal predictions of ecosystem changes in the northern high latitudes.An analysis of observational and reanalysis data sets for the period 1979-2019 shows that locations characterized by greening trends largely coincide with warming summer temperature and increasing precipitation. Wherever either cooling or decreasing precipitation occurs, browning trends are observed over this period. These precipitation and temperature patterns are significantly correlated with a North Atlantic sea surface temperature index that represents the AMV signal, indicating its role in modulating greening/browning trend patterns in the northern high latitudes.Using two large ensembles of coupled Earth system model simulations (100 members of MPI-ESM-LR Grand Ensemble and 32 members of the IPSL-CM6A-LR Large Ensemble), we separate the greening/browning pattern caused by external CO2 forcing from that caused by internal climate variability associated with the AMV. These sets of model simulations enable a clean separation of the externally forced signal from internal variability. While the greening and browning patterns in the simulations do not agree with observations in terms of magnitude and location, we find consistent internally generated greening/browning patterns in both models caused by changes in temperature and precipitation linked to the AMV signal. These greening/browning trend patterns are of the same magnitude as those caused by the external forcing alone. Our work therefore shows that internally-generated changes of vegetation in the northern lands, driven by AMV, are potentially as large as those caused by external CO2 forcing. We thus argue that the observed pattern of greening/browning in the northern high latitudes could originate from the combined effect of rising CO2 as well as the AMV.

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The North Atlantic Eddy Heat Transport and Its Relation with the Vertical Tilting of the Gulf Stream Axis

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0172.1 ◽

2017 ◽

Vol 47 (6) ◽

pp. 1281-1289 ◽

Cited By ~ 6

Author(s):

A. M. Treguier ◽

C. Lique ◽

J. Deshayes ◽

J. M. Molines

Keyword(s):

Numerical Model ◽

Heat Transport ◽

North Atlantic ◽

Gulf Stream ◽

Mean Flow ◽

The North ◽

Spatial Shift ◽

Eddy Heat Flux ◽

Eddy Heat Transport ◽

The North Atlantic

AbstractCorrelations between temperature and velocity fluctuations are a significant contribution to the North Atlantic meridional heat transport, especially at the northern boundary of the subtropical gyre. In satellite observations and in a numerical model at ⅞° resolution, a localized pattern of positive eddy heat flux is found northwest of the Gulf Stream, downstream of its separation at Cape Hatteras. It is confined to the upper 500 m. A simple kinematic model of a meandering jet can explain the surface eddy flux, taking into account a spatial shift between the maximum velocity of the jet and the maximum cross-jet temperature gradient. In the Gulf Stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth. The numerical model suggests that the meandering of the Gulf Stream could account, at least in part, for the large eddy heat transport (of order 0.3 PW) near 36°N in the North Atlantic and for its compensation by the mean flow.

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Forecasting the Gulf Stream Path using Buoyancy and Wind Forcing over the North Atlantic

Journal of Geophysical Research Oceans ◽

10.1029/2021jc017614 ◽

2021 ◽

Author(s):

Adrienne Silver ◽

Avijit Gangopadhyay ◽

Glen Gawarkiewicz ◽

Arnold Taylor ◽

Alejandra Sanchez‐Franks

Keyword(s):

North Atlantic ◽

Gulf Stream ◽

Wind Forcing ◽

The North ◽

The North Atlantic

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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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Reply to “Comments on ‘Reconstruction of the Gulf Stream from 1940 to the Present and Correlation with the North Atlantic Oscillation’”

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0191.1 ◽

2019 ◽

Vol 49 (10) ◽

pp. 2735-2737

Author(s):

Sylvain Watelet ◽

Jean-Marie Beckers ◽

Alexander Barth

Keyword(s):

North Atlantic Oscillation ◽

North Atlantic ◽

Gulf Stream ◽

The North ◽

The North Atlantic ◽

The North Atlantic Oscillation

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Instability-Driven Benthic Storms below the Separated Gulf Stream and the North Atlantic Current in a High-Resolution Ocean Model

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0261.1 ◽

2018 ◽

Vol 48 (10) ◽

pp. 2283-2303 ◽

Cited By ~ 3

Author(s):

René Schubert ◽

Arne Biastoch ◽

Meghan F. Cronin ◽

Richard J. Greatbatch

Keyword(s):

Energy Transfer ◽

High Resolution ◽

Kinetic Energy ◽

North Atlantic ◽

Gulf Stream ◽

Eddy Kinetic Energy ◽

North Atlantic Current ◽

The North ◽

The North Atlantic ◽

Atlantic Current

AbstractBenthic storms are important for both the energy budget of the ocean and for sediment resuspension and transport. Using 30 years of output from a high-resolution model of the North Atlantic, it is found that most of the benthic storms in the model occur near the western boundary in association with the Gulf Stream and the North Atlantic Current, in regions that are generally collocated with the peak near-bottom eddy kinetic energy. A common feature is meander troughs in the near-surface jets that are accompanied by deep low pressure anomalies spinning up deep cyclones with near-bottom velocities of up to more than 0.5 m s−1. A case study of one of these events shows the importance of both baroclinic and barotropic instability of the jet, with energy being extracted from the jet in the upstream part of the meander trough and partly returned to the jet in the downstream part of the meander trough. This motivates examining the 30-yr time mean of the energy transfer from the (annual mean) background flow into the eddy kinetic energy. This quantity is shown to be collocated well with the region in which benthic storms and large increases in deep cyclonic relative vorticity occur most frequently, suggesting an important role for mixed barotropic–baroclinic instability-driven cyclogenesis in generating benthic storms throughout the model simulation. Regions of the largest energy transfer and most frequent benthic storms are found to be the Gulf Stream west of the New England Seamounts and the North Atlantic Current near Flemish Cap.

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The Role of Extratropical Air–Sea Interaction in the Autumn Subseasonal Variability of the North Atlantic Oscillation

Journal of Climate ◽

10.1175/jcli-d-19-0060.1 ◽

2019 ◽

Vol 32 (22) ◽

pp. 7697-7712 ◽

Cited By ~ 5

Author(s):

Yu Nie ◽

Hong-Li Ren ◽

Yang Zhang

Keyword(s):

North Atlantic Oscillation ◽

North Atlantic ◽

Gulf Stream ◽

Low Frequency ◽

Mean Flow ◽

The North ◽

Subseasonal Variability ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract Considerable progress has been made in understanding the internal eddy–mean flow feedback in the subseasonal variability of the North Atlantic Oscillation (NAO) during winter. Using daily atmospheric and oceanic reanalysis data, this study highlights the role of extratropical air–sea interaction in the NAO variability during autumn when the daily sea surface temperature (SST) variability is more active and eddy–mean flow interactions are still relevant. Our analysis shows that a horseshoe-like SST tripolar pattern in the North Atlantic Ocean, marked by a cold anomaly in the Gulf Stream and two warm anomalies to the south of the Gulf Stream and off the western coast of northern Europe, can induce a quasi-barotropic NAO-like atmospheric response through eddy-mediated processes. An initial southwest–northeast tripolar geopotential anomaly in the North Atlantic forces this horseshoe-like SST anomaly tripole. Then the SST anomalies, through surface heat flux exchange, alter the spatial patterns of the lower-tropospheric temperature and thus baroclinicity anomalies, which are manifested as the midlatitude baroclinicity shifted poleward and reduced baroclinicity poleward of 70°N. In response to such changes of the lower-level baroclinicity, anomalous synoptic eddy generation, eddy kinetic energy, and eddy momentum forcing in the midlatitudes all shift poleward. Meanwhile, the 10–30-day low-frequency anticyclonic wave activities in the high latitudes decrease significantly. We illustrate that both the latitudinal displacement of midlatitude synoptic eddy activities and intensity variation of high-latitude low-frequency wave activities contribute to inducing the NAO-like anomalies.

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Sensitivity of winter North Atlantic-European climate to resolved atmosphere and ocean dynamics

Scientific Reports ◽

10.1038/s41598-019-49865-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

Reindert J. Haarsma ◽

Javier García-Serrano ◽

Chloé Prodhomme ◽

Omar Bellprat ◽

Paolo Davini ◽

...

Keyword(s):

Atmospheric Circulation ◽

North Atlantic ◽

Gulf Stream ◽

Ocean Dynamics ◽

Small Scale ◽

Western Boundary ◽

The North ◽

The North Atlantic ◽

Mean Climate ◽

Meso Scale

Abstract Northern Hemisphere western boundary currents, like the Gulf Stream, are key regions for cyclogenesis affecting large-scale atmospheric circulation. Recent observations and model simulations with high-temporal and -spatial resolution have provided evidence that the associated ocean fronts locally affect troposphere dynamics. A coherent view of how this affects the mean climate and its variability is, however, lacking. In particular the separate role of resolved ocean and atmosphere dynamics in shaping the atmospheric circulation is still largely unknown. Here we demonstrate for the first time, by using coupled seasonal forecast experiments at different resolutions, that resolving meso-scale oceanic variability in the Gulf Stream region strongly affects mid-latitude interannual atmospheric variability, including the North Atlantic Oscillation. Its impact on climatology, however, is minor. Increasing atmosphere resolution to meso-scale, on the other hand, strongly affects mean climate but moderately its variability. We also find that regional predictability relies on adequately resolving small-scale atmospheric processes, while resolving small-scale oceanic processes acts as an unpredictable source of noise, except for the North Atlantic storm-track where the forcing of the atmosphere translates into skillful predictions.

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The spiralling North Atlantic Subtropical Gyre

10.5194/egusphere-egu2020-1459 ◽

2020 ◽

Author(s):

Kristofer Döös ◽

Sara Berglund ◽

Trevor Mcdougall ◽

Sjoerd Groeskamp

Keyword(s):

North Atlantic ◽

Gulf Stream ◽

Subtropical Gyre ◽

The South ◽

Spiral Flow ◽

The North ◽

Saline Waters ◽

Downward Spiral ◽

Meridional Overturning ◽

The North Atlantic

The North Atlantic Subtropical Gyre is shown to have a downward spiral flow beneath the mixed layer, where the water slowly gets denser, colder and fresher as it spins around the gyre. This path is traced with Lagrangian trajectories as they enter the Gyre in the Gulf Stream from the south until they exit through the North Atlantic Drift. The preliminary results indicate that these warm, saline waters from the south gradually becomes fresher, colder and denser due to mixing with waters originating from the North Atlantic. There are indications that there is also a diapycnal mixing, in the eastern part of the gyre due to mixing with the saline Mediterranean Waters, which would then be crucial for the Atlantic Meridional Overturning. The mixing in the rest of the gyre is dominated by isopycnic mixing, which transforms gradually the water into colder and fresher water as it spins down the gyre into the abyssal ocean before heading north.

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