North Atlantic Circulation Regimes and Heat Transport by Synoptic Eddies

2020 ◽  
Vol 33 (11) ◽  
pp. 4769-4785 ◽  
Author(s):  
Paolo Ruggieri ◽  
M. Carmen Alvarez-Castro ◽  
Panos Athanasiadis ◽  
Alessio Bellucci ◽  
Stefano Materia ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
North Atlantic ◽  
High Latitude ◽  
Polar Regions ◽  
Mean Flow ◽  
Dynamical Interaction ◽  
Weather Regimes ◽  
Eddy Heat Flux ◽  
Synoptic Eddies

AbstractMeridional transport of heat by transient atmospheric eddies is a key component of the energy budget of the middle- and high-latitude regions. The heat flux at relevant frequencies is also part of a dynamical interaction between eddies and mean flow. In this study we investigate how the poleward heat flux by high-frequency atmospheric transient eddies is modulated by North Atlantic weather regimes in reanalysis data. Circulation regimes are estimated via a clustering method, a jet-latitude index, and a blocking index. Heat transport is defined as advection of moist static energy. The focus of the analysis is on synoptic frequencies but results for slightly longer time scales are reported. Results show that the synoptic eddy heat flux is substantially modulated by midlatitude weather regimes on a regional scale in midlatitude and polar regions. In a zonal-mean sense, the phases of the North Atlantic Oscillation do not significantly change the high-latitude synoptic heat flux, whereas Scandinavian blocking and the Atlantic ridge are associated with an intensification. A close relationship between high-latitude (midlatitude) heat flux and Atlantic jet speed (latitude) is found. The relationship between extreme events of synoptic heat flux and circulation regimes is also assessed and reveals contrasting behaviors in the polar regions. The perspective that emerges complements the traditional view of the interaction between synoptic eddies and the extratropical flow and reveals relationships with the high-latitude climate.

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

2017 ◽  
Vol 47 (6) ◽  
pp. 1281-1289 ◽  
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.

scholarly journals Dominant Anomaly Patterns in the Near-Surface Baroclinicity and Accompanying Anomalies in the Atmosphere and Oceans. Part I: North Atlantic Basin

2009 ◽  
Vol 22 (4) ◽  
pp. 880-904 ◽  
Author(s):  
Mototaka Nakamura ◽  
Shozo Yamane
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Spatial Scales ◽  
Storm Track ◽  
Lower Troposphere ◽  
Mean Flow ◽  
Atlantic Basin ◽  
Near Surface ◽  
North Atlantic Basin ◽  
Eddy Heat Flux

Abstract Variability in the monthly mean flow and storm track in the North Atlantic basin is examined with a focus on the near-surface baroclinicity, B = Bxi + Byj. Dominant patterns of anomalous B found from empirical orthogonal function (EOF) analyses generally show patterns of shift and changes in the strength of B. Composited anomalies in the monthly mean wind at various pressure levels based on the signals in the EOFs display robust accompanying anomalies in the mean flow up to 50 hPa in the winter and up to 100 hPa in other seasons. Anomalous eddy fields accompanying the anomalous Bx patterns exhibit, broadly speaking, structures anticipated from linear theories of baroclinic instabilities and suggest a tendency for anomalous wave fluxes to accelerate/decelerate the surface westerly accordingly. Atmospheric anomalies accompanying By anomalies have patterns different from those that accompany Bx anomalies but are as large as those found for Bx. Anomalies in the sea surface temperature (SST) found for the anomalous patterns of Bx often show large values of small spatial scales along the Gulf Stream (GS), indicating that a meridional shift in the position of the GS and/or changes in the heat transport by the GS may be responsible for the anomalous Bx and concomitant tropospheric and lower-stratospheric anomalies. Anomalies in the net surface heat flux, SST in preceding months, and meridional eddy heat flux in the lower troposphere support this interpretation.

Eddy Modulation of Air–Sea Interaction and Convection

2008 ◽  
Vol 38 (1) ◽  
pp. 65-83 ◽  
Author(s):  
Ivana Cerovečki ◽  
John Marshall
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Formation Rate ◽  
Mean Flow ◽  
Mode Water ◽  
Ocean Eddies ◽  
Eddy Heat Flux ◽  
Water Formation ◽  
Transformed Eulerian Mean

Abstract Eddy modulation of the air–sea interaction and convection that occurs in the process of mode water formation is analyzed in simulations of a baroclinically unstable wind- and buoyancy-driven jet. The watermass transformation analysis of Walin is used to estimate the formation rate of mode water and to characterize the role of eddies in that process. It is found that diabatic eddy heat flux divergences in the mixed layer are comparable in magnitude, but of opposite sign, to the surface air–sea heat flux and largely cancel the direct effect of buoyancy loss to the atmosphere. The calculations suggest that mode water formation estimates based on climatological air–sea heat flux data and outcrops, which do not fully resolve ocean eddies, may neglect a large opposing term in the heat budget and are thus likely to significantly overestimate true formation rates. In Walin’s watermass transformation framework, this manifests itself as a sensitivity of formation rate estimates to the averaging period over which the outcrops and air–sea fluxes are subjected. The key processes are described in terms of a transformed Eulerian-mean formalism in which eddy-induced mean flow tends to cancel the Eulerian-mean flow, resulting in weaker residual mean flow, subduction, and mode water formation rates.

scholarly journals Vertical Structure and Energetics of the Western Pacific Teleconnection Pattern

2016 ◽  
Vol 29 (18) ◽  
pp. 6597-6616 ◽  
Author(s):  
Sho Tanaka ◽  
Kazuaki Nishii ◽  
Hisashi Nakamura
Keyword(s):  
Heat Flux ◽  
North Pacific ◽  
Thermal Gradient ◽  
Far East ◽  
Storm Track ◽  
Lower Troposphere ◽  
Western Pacific ◽  
Mean Flow ◽  
Eddy Heat Flux ◽  
The Western Pacific

Abstract The western Pacific (WP) pattern, characterized by north–south dipolar anomalies in pressure over the Far East and western North Pacific, is known as one of the dominant teleconnection patterns in the wintertime Northern Hemisphere. Composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere. The anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong Pacific jet but also a westward heat flux across the climatological thermal gradient between the North Pacific and the cooler Asian continent. The resultant baroclinic conversion of available potential energy (APE) from the climatological-mean flow contributes most efficiently to the APE maintenance of the monthly WP pattern, acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effect of anomalous eddy heat flux under modulated storm-track activity. Kinetic energy (KE) of the pattern is maintained through barotropic feedback forcing associated with modulated activity of transient eddies and the conversion from the climatological-mean westerlies, both of which act against frictional damping. The net feedback forcing by transient eddies is therefore not particularly efficient. The present study suggests that the WP pattern has a characteristic of a dynamical mode that can maintain itself through efficient energy conversion from the climatological-mean fields even without external forcing, including remote influence from the tropics.

scholarly journals The Life Cycle of the North Atlantic Storm Track*

2015 ◽  
Vol 72 (2) ◽  
pp. 821-833 ◽  
Author(s):  
Lenka Novak ◽  
Maarten H. P. Ambaum ◽  
Rémi Tailleux
Keyword(s):  
Heat Flux ◽  
Life Cycle ◽  
North Atlantic ◽  
Storm Track ◽  
High Heat ◽  
High Heat Flux ◽  
Dominant Type ◽  
The North ◽  
Eddy Heat Flux ◽  
The North Atlantic

Abstract The North Atlantic eddy-driven jet exhibits latitudinal variability with evidence of three preferred latitudinal locations: south, middle, and north. Here the authors examine the drivers of this variability and the variability of the associated storm track. The authors investigate the changes in the storm-track characteristics for the three jet locations and propose a mechanism by which enhanced storm-track activity, as measured by upstream heat flux, is responsible for cyclical downstream latitudinal shifts in the jet. This mechanism is based on a nonlinear oscillator relationship between the enhanced meridional temperature gradient (and thus baroclinicity) and the meridional high-frequency (periods of shorter than 10 days) eddy heat flux. Such oscillations in baroclinicity and heat flux induce variability in eddy anisotropy, which is associated with the changes in the dominant type of wave breaking and a different latitudinal deflection of the jet. The authors’ results suggest that high heat flux is conducive to a northward deflection of the jet, whereas low heat flux is conducive to a more zonal jet. This jet-deflecting effect was found to operate most prominently downstream of the storm-track maximum, while the storm track and the jet remain anchored at a fixed latitudinal location at the beginning of the storm track. These cyclical changes in storm-track characteristics can be viewed as different stages of the storm track’s spatiotemporal life cycle.

scholarly journals Dominant Anomaly Patterns in the Near-Surface Baroclinicity and Accompanying Anomalies in the Atmosphere and Oceans. Part II: North Pacific Basin

2010 ◽  
Vol 23 (24) ◽  
pp. 6445-6467 ◽  
Author(s):  
Mototaka Nakamura ◽  
Shozo Yamane
Keyword(s):  
Heat Flux ◽  
North Pacific ◽  
Spatial Scales ◽  
Baroclinic Instability ◽  
Lower Troposphere ◽  
Pacific Basin ◽  
Mean Flow ◽  
Near Surface ◽  
Eddy Heat Flux ◽  
North Pacific Basin

Abstract Variability in the monthly-mean flow and storm track in the North Pacific basin is examined with a focus on the near-surface baroclinicity. Dominant patterns of anomalous near-surface baroclinicity found from empirical orthogonal function (EOF) analyses generally show mixed patterns of shift and changes in the strength of near-surface baroclinicity. Composited anomalies in the monthly-mean wind at various pressure levels based on the signals in the EOFs show accompanying anomalies in the mean flow up to 50 hPa in the winter and up to 100 hPa in other seasons. Anomalous eddy fields accompanying the anomalous near-surface baroclinicity patterns exhibit, broadly speaking, structures anticipated from simple linear theories of baroclinic instability, and suggest a tendency for anomalous wave fluxes to accelerate–decelerate the surface westerly accordingly. However, the relationship between anomalous eddy fields and anomalous near-surface baroclinicity in the midwinter is not consistent with the simple linear baroclinic instability theories. Composited anomalous sea surface temperature (SST) accompanying anomalous near-surface baroclinicity often exhibits moderate values and large spatial scales in the basin, rather than large values concentrated near the oceanic fronts. In the midsummer and in some cases in cold months, however, large SST anomalies are found around the Kuroshio–Oyashio Extensions. Accompanying anomalies in the net surface heat flux, SST in the preceding and following months, and meridional eddy heat flux in the lower troposphere suggest active roles played by the ocean in generating the concomitant anomalous large-scale atmospheric state in some of these cases.

scholarly journals Estimates of Eddy Heat Flux Crossing the Antarctic Circumpolar Current from Observations in Drake Passage

2016 ◽  
Vol 46 (7) ◽  
pp. 2103-2122 ◽  
Author(s):  
D. Randolph Watts ◽  
Karen L. Tracey ◽  
Kathleen A. Donohue ◽  
Teresa K. Chereskin
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Antarctic Circumpolar Current ◽  
Baroclinic Instability ◽  
Drake Passage ◽  
Heat Fluxes ◽  
Poleward Heat Transport ◽  
Eddy Heat Flux ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe 4-yr measurements by current- and pressure-recording inverted echo sounders in Drake Passage produced statistically stable eddy heat flux estimates. Horizontal currents in the Antarctic Circumpolar Current (ACC) turn with depth when a depth-independent geostrophic current crosses the upper baroclinic zone. The dynamically important divergent component of eddy heat flux is calculated. Whereas full eddy heat fluxes differ greatly in magnitude and direction at neighboring locations within the local dynamics array (LDA), the divergent eddy heat fluxes are poleward almost everywhere. Case studies illustrate baroclinic instability events that cause meanders to grow rapidly. In the southern passage, where eddy variability is weak, heat fluxes are weak and not statistically significant. Vertical profiles of heat flux are surface intensified with ~50% above 1000 m and uniformly distributed with depth below. Summing poleward transient eddy heat transport across the LDA of −0.010 ± 0.005 PW with the stationary meander contribution of −0.004 ± 0.001 PW yields −0.013 ± 0.005 PW. A comparison metric, −0.4 PW, represents the total oceanic heat loss to the atmosphere south of 60°S. Summed along the circumpolar ACC path, if the LDA heat flux occurred at six “hot spots” spanning similar or longer path segments, this could account for 20%–70% of the metric, that is, up to −0.28 PW. The balance of ocean poleward heat transport along the remaining ACC path should come from weak eddy heat fluxes plus mean cross-front temperature transports. Alternatively, the metric −0.4 PW, having large uncertainty, may be high.

scholarly journals On the Role of Eddies and Surface Forcing in the Heat Transport and Overturning Circulation in Marginal Seas

2011 ◽  
Vol 24 (18) ◽  
pp. 4844-4858 ◽  
Author(s):  
Michael A. Spall
Keyword(s):  
Conceptual Model ◽  
Heat Transport ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Meridional Heat Transport ◽  
Overturning Circulation ◽  
Nordic Seas ◽  
Marginal Seas ◽  
Eddy Heat Flux ◽  
The Mean

Abstract The factors that determine the heat transport and overturning circulation in marginal seas subject to wind forcing and heat loss to the atmosphere are explored using a combination of a high-resolution ocean circulation model and a simple conceptual model. The study is motivated by the exchange between the subpolar North Atlantic Ocean and the Nordic Seas, a region that is of central importance to the oceanic thermohaline circulation. It is shown that mesoscale eddies formed in the marginal sea play a major role in determining the mean meridional heat transport and meridional overturning circulation across the sill. The balance between the oceanic eddy heat flux and atmospheric cooling, as characterized by a nondimensional number, is shown to be the primary factor in determining the properties of the exchange. Results from a series of eddy-resolving primitive equation model calculations for the meridional heat transport, overturning circulation, density of convective waters, and density of exported waters compare well with predictions from the conceptual model over a wide range of parameter space. Scaling and model results indicate that wind effects are small and the mean exchange is primarily buoyancy forced. These results imply that one must accurately resolve or parameterize eddy fluxes in order to properly represent the mean exchange between the North Atlantic and the Nordic Seas, and thus between the Nordic Seas and the atmosphere, in climate models.

The Statistics and Structure of Subseasonal Midlatitude Variability in NASA GSFC GCMs

2005 ◽  
Vol 18 (16) ◽  
pp. 3294-3316 ◽  
Author(s):  
Dennis P. Robinson ◽  
Robert X. Black
Keyword(s):  
Three Dimensional ◽  
Storm Track ◽  
Storm Tracks ◽  
Dimensional Structure ◽  
Mean Flow ◽  
Weather Regimes ◽  
Three Dimensional Structure ◽  
Dynamical Characteristics ◽  
The North ◽  
Synoptic Eddies

Abstract A comprehensive analysis of midlatitude intraseasonal variability in extended integrations of NASA GSFC general circulation models (GCMs) is conducted. This is approached by performing detailed intercomparisons of the representation of the storm tracks and anomalous weather regimes occurring during wintertime in the Atmospheric Model Intercomparison Project (AMIP)-type simulations of both the NASA–NCAR and a version of the Aries model used in NASA’s Seasonal-to-Interannual Prediction Project (NSIPP) model. The model-simulated statistics, three-dimensional structure, and dynamical characteristics of these phenomena are diagnosed and directly compared to parallel observational analyses derived from NCEP–NCAR reanalyses. A qualitatively good representation of the vertical structure of intraseasonal eddy kinetic energy (EKE) is provided by both models with maximum values of EKE occurring near 300 hPa. The main model shortcoming is an underestimation of EKE in the upper troposphere, especially for synoptic eddies in the NSIPP model. Nonetheless, both models provide a reasonable representation of the three-dimensional structure and dynamical characteristics of synoptic eddies. Discrepancies in the storm-track structures simulated by the models include an anomalous local minimum over the eastern Pacific basin. However, both GCMs faithfully reproduce the observed Pacific midwinter storm-track suppression. Interestingly, the NSIPP model also produces a midwinter suppression feature over the Atlantic storm track in association with the anomalously strong upper-level jet stream simulated by NSIPP in this region. The regional distribution of anomalous weather regime events is well simulated by the models. However, substantial structural differences exist between observed and simulated events over the North Pacific region. In comparison to observations, model events are horizontally more isotropic, have stronger westward vertical tilts, and are more strongly driven by baroclinic dynamics. The structure and dynamics of anomalous weather regimes occurring over the North Atlantic region are qualitatively better represented by the models. The authors suggest that model deficiencies in representing the zonally asymmetric climatological-mean flow field (particularly the magnitude and structure of the Pacific and Atlantic jet streams) help contribute to model shortcomings in (i) the strength and seasonal variability of the storm tracks and (ii) dynamical distinctions in the maintenance of large-scale weather regimes.

scholarly journals Interhemispheric Asymmetry of Warming in an Eddy-Permitting Coupled Sector Model

2015 ◽  
Vol 28 (18) ◽  
pp. 7385-7406 ◽  
Author(s):  
David K. Hutchinson ◽  
Matthew H. England ◽  
Andrew M. Hogg ◽  
Kate Snow
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Ocean Circulation ◽  
High Latitude ◽  
Climate Model ◽  
Mean Flow ◽  
Surface Warming ◽  
Sector Model ◽  
Air Temperatures ◽  
Wide Sector

Abstract Climate model projections and observations show a faster rate of warming in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). This asymmetry is partly due to faster rates of warming over the land than the ocean, and partly due to the ocean circulation redistributing heat toward the NH. This study examines the interhemispheric warming asymmetry in an intermediate complexity coupled climate model with eddy-permitting (0.25°) ocean resolution, and results are compared with a similar model with coarse (1°) ocean resolution. The models use a pole-to-pole 60° wide sector domain in the ocean and a 120° wide sector in the atmosphere, with Atlantic-like bathymetry and a simple land model. There is a larger high-latitude ocean temperature asymmetry in the 0.25° model compared with the 1° model, both in equilibrated control runs and in response to greenhouse warming. The larger warming asymmetry is caused by greater melting of NH sea ice in the 0.25° model, associated with faster, less viscous boundary currents transporting heat northward. The SH sea ice and heat transport response is relatively insensitive to the resolution change, since the eddy heat transport differences between the models are small compared with the mean flow heat transport. When a wind shift and intensification is applied in these warming scenarios, the warming asymmetry is further enhanced, with greater upwelling of cool water in the Southern Ocean and enhanced warming in the NH. Surface air temperatures show a substantial but lesser degree of high-latitude warming asymmetry, reflecting the sea surface warming patterns over the ocean but warming more symmetrically over the land regions.

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