scholarly journals Convective activity in the Labrador Sea: Preconditioning associated with decadal variability in subsurface ocean stratification

2003 ◽  
Vol 108 (C10) ◽  
Author(s):  
Ken-ichi Mizoguchi
Keyword(s):  
Decadal Variability ◽  
Labrador Sea ◽  
Convective Activity ◽  
Ocean Stratification ◽  
Subsurface Ocean

scholarly journals North Atlantic Modeling of Low-Frequency Variability in Mode Water Formation

2002 ◽  
Vol 32 (9) ◽  
pp. 2666-2680 ◽  
Author(s):  
Afonso M. Paiva ◽  
Eric P. Chassignet
Keyword(s):  
North Atlantic ◽  
Potential Vorticity ◽  
General Circulation ◽  
Decadal Variability ◽  
Sea Water ◽  
Maximum Amplitude ◽  
Circulation Model ◽  
Labrador Sea ◽  
Convective Activity ◽  
Mode Water

Abstract The generation of interannual and near-decadal variability in the formation of mode waters in the western North Atlantic is investigated in the realistic framework of an isopycnic coordinate ocean model forced with atmospheric data from 1946 to 1988. At Bermuda, the model reproduces quite well the observed potential vorticity and isopycnal depth anomalies associated with the subtropical mode water (STMW). Heat storage and preconditioning of the convective activity are found to be the important factors for the generation of STMW variability, with persistence of cold (warm) conditions, associated with anomalous heat loss (gain) over the western subtropics, being more significant for the generation of the simulated variability than are strong anomalous events in isolated years. In the Labrador Sea, the model captures the phase and order of magnitude of the observed near-decadal variability in the convective activity, if not its maximum amplitude. The simulated potential vorticity anomalies are, as observed, out-of-phase with those in the western subtropics and correlate well with the North Atlantic Oscillation (NAO) at near-decadal timescales, with the oceanic response lagging the NAO by ∼2–3 years. These results support the idea that the variability in water mass formation in the western North Atlantic can be attributed, to a large extent, to changes in the pattern of the large-scale atmospheric circulation, which generate sensible and latent heat flux variability by modifying the strength and position of the westerly winds and the advection of heat and moisture over the ocean. To the authors' knowledge, this is the first time that the interannual and near-decadal subsurface variability associated with STMW and Labrador Sea Water, and its relationship to the NAO, has been simulated in an ocean general circulation model.

Some Climatological Aspects of the Madden–Julian Oscillation (MJO)

2015 ◽  
Vol 28 (15) ◽  
pp. 6039-6053 ◽  
Author(s):  
Donald M. Lafleur ◽  
Bradford S. Barrett ◽  
Gina R. Henderson
Keyword(s):  
Seasonal Variability ◽  
Cycle Length ◽  
Decadal Variability ◽  
Low Frequency ◽  
The Other ◽  
Activity Levels ◽  
Atmospheric Response ◽  
Convective Activity ◽  
Madden Julian Oscillation ◽  
Annual Basis

Abstract One of the most commonly used metrics for both locating the Madden–Julian oscillation (MJO) geographically and defining the intensity of MJO convective activity is the real-time multivariate MJO (RMM) index. However, a climatology of the MJO, particularly with respect to the frequency of activity levels or of consecutive days at certain activity thresholds, does not yet exist. Thus, several climatological aspects of the MJO were developed in this study: 1) annual and 2) seasonal variability in MJO intensity, quantified using four defined activity categories (inactive, active, very active, and extremely active); 3) persistence in the above-defined four categories; 4) cycle length; and 5) low-frequency (decadal) variability. On an annual basis, MJO phases 1 and 2 occurred more often, and phase 8 occurred less often, than the other phases throughout the year. Notable seasonality was also found, particularly in the frequency of extremely active MJO in March–May (8% of days) compared with June–August (only 1% of days). The MJO was persistent in time and across intensity categories, and all activity categories the following day had at least an 80% chance of maintaining their amplitudes. Implications of this climatology are discussed, including length of complete MJO cycles (the shortest of which was 17 days) and correlations between MJO amplitude and atmospheric response.

Reconstructing the subsurface ocean decadal variability using surface nudging in a perfect model framework

2014 ◽  
Vol 44 (1-2) ◽  
pp. 315-338 ◽  
Author(s):  
Jérôme Servonnat ◽  
Juliette Mignot ◽  
Eric Guilyardi ◽  
Didier Swingedouw ◽  
Roland Séférian ◽  
...  
Keyword(s):  
Decadal Variability ◽  
Model Framework ◽  
Subsurface Ocean ◽  
Perfect Model ◽  
Surface Nudging

scholarly journals Decadal variability of eddy temperature fluxes in the Labrador Sea

2021 ◽  
Author(s):  
Christopher Danek ◽  
Patrick Scholz ◽  
Gerrit Lohmann
Keyword(s):  
Decadal Variability ◽  
Labrador Sea

scholarly journals The Nature of Eddy Kinetic Energy in the Labrador Sea: Different Types of Mesoscale Eddies, Their Temporal Variability, and Impact on Deep Convection

2019 ◽  
Vol 49 (8) ◽  
pp. 2075-2094 ◽  
Author(s):  
Jan K. Rieck ◽  
Claus W. Böning ◽  
Klaus Getzlaff
Keyword(s):  
Kinetic Energy ◽  
Temporal Variability ◽  
Decadal Variability ◽  
Deep Convection ◽  
Deep Ocean ◽  
Temporal Variations ◽  
Heat Fluxes ◽  
Eddy Kinetic Energy ◽  
Labrador Sea ◽  
Boundary Current

AbstractOceanic eddies are an important component in preconditioning the central Labrador Sea (LS) for deep convection and in restratifying the convected water. This study investigates the different sources and impacts of eddy kinetic energy (EKE) and its temporal variability in the LS with the help of a 52-yr-long hindcast simulation of a 1/20° ocean model. Irminger Rings (IR) are generated in the West Greenland Current (WGC) between 60° and 62°N, mainly affect preconditioning, and limit the northward extent of the convection area. The IR exhibit a seasonal cycle and decadal variations linked to the WGC strength, varying with the circulation of the subpolar gyre. The mean and temporal variations of IR generation can be attributed to changes in deep ocean baroclinic and upper-ocean barotropic instabilities at comparable magnitudes. The main source of EKE and restratification in the central LS are convective eddies (CE). They are generated by baroclinic instabilities near the bottom of the mixed layer during and after convection. The CE have a middepth core and reflect the hydrographic properties of the convected water mass with a distinct minimum in potential vorticity. Their seasonal to decadal variability is tightly connected to the local atmospheric forcing and the associated air–sea heat fluxes. A third class of eddies in the LS are the boundary current eddies shed from the Labrador Current (LC). Since they are mostly confined to the vicinity of the LC, these eddies appear to exert only minor influence on preconditioning and restratification.

The Origins of Late-Twentieth-Century Variations in the Large-Scale North Atlantic Circulation

2014 ◽  
Vol 27 (9) ◽  
pp. 3222-3247 ◽  
Author(s):  
Stephen Yeager ◽  
Gokhan Danabasoglu
Keyword(s):  
Twentieth Century ◽  
North Atlantic ◽  
Decadal Variability ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Overturning Circulation ◽  
The North ◽  
Late Twentieth ◽  
The North Atlantic ◽  
Late Twentieth Century

Abstract Surface forcing perturbation experiments are examined to identify the key forcing elements associated with late-twentieth-century interannual-to-decadal Atlantic circulation variability as simulated in an ocean–sea ice hindcast configuration of the Community Earth System Model, version 1 (CESM1). Buoyancy forcing accounts for most of the decadal variability in both the Atlantic meridional overturning circulation (AMOC) and the subpolar gyre circulation, and the key drivers of these basin-scale circulation changes are found to be the turbulent buoyancy fluxes: evaporation as well as the latent and sensible heat fluxes. These three fluxes account for almost all of the decadal AMOC variability in the North Atlantic, even when applied only over the Labrador Sea region. Year-to-year changes in surface momentum forcing explain most of the interannual AMOC variability at all latitudes as well as most of the decadal variability south of the equator. The observed strengthening of Southern Ocean westerly winds accounts for much of the simulated AMOC variability between 30°S and the equator but very little of the recent AMOC change in the North Atlantic. Ultimately, the strengthening of the North Atlantic overturning circulation between the 1970s and 1990s, which contributed to a pronounced SST increase at subpolar latitudes, is explained almost entirely by trends in the atmospheric surface state over the Labrador Sea.

scholarly journals Labrador Sea subsurface density as a precursor of multidecadal variability in the North Atlantic: a multi-model study

2021 ◽  
Vol 12 (2) ◽  
pp. 419-438
Author(s):  
Pablo Ortega ◽  
Jon I. Robson ◽  
Matthew Menary ◽  
Rowan T. Sutton ◽  
Adam Blaker ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Large Scale ◽  
Climate Model ◽  
Decadal Variability ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Western Boundary ◽  
Multidecadal Variability ◽  
Boundary Density

Abstract. The subpolar North Atlantic (SPNA) is a region with prominent decadal variability that has experienced remarkable warming and cooling trends in the last few decades. These observed trends have been preceded by slow-paced increases and decreases in the Labrador Sea density (LSD), which are thought to be a precursor of large-scale ocean circulation changes. This article analyses the interrelationships between the LSD and the wider North Atlantic across an ensemble of coupled climate model simulations. In particular, it analyses the link between subsurface density and the deep boundary density, the Atlantic Meridional Overturning Circulation (AMOC), the subpolar gyre (SPG) circulation, and the upper-ocean temperature in the eastern SPNA. All simulations exhibit considerable multidecadal variability in the LSD and the ocean circulation indices, which are found to be interrelated. LSD is strongly linked to the strength of the subpolar AMOC and gyre circulation, and it is also linked to the subtropical AMOC, although the strength of this relationship is model-dependent and affected by the inclusion of the Ekman component. The connectivity of LSD with the subtropics is found to be sensitive to different model features, including the mean density stratification in the Labrador Sea, the strength and depth of the AMOC, and the depth at which the LSD propagates southward along the western boundary. Several of these quantities can also be computed from observations, and comparison with these observation-based quantities suggests that models representing a weaker link to the subtropical AMOC might be more realistic.

scholarly journals A Decade of Ocean Changes Impacting the Ice Shelf of Petermann Gletscher, Greenland

2018 ◽  
Vol 48 (10) ◽  
pp. 2477-2493 ◽  
Author(s):  
P. Washam ◽  
A. Münchow ◽  
K. W. Nicholls
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Freshwater Flux ◽  
Ice Shelf ◽  
Hydrographic Data ◽  
Ocean Stratification ◽  
Freshwater Fluxes ◽  
Subsurface Ocean ◽  
Grounding Line ◽  
Seasonal Signal

AbstractHydrographic data collected during five summer surveys between 2002 and 2015 reveal that the subsurface ocean near Petermann Gletscher, Greenland, warmed by 0.015° ± 0.013°C yr−1. New 2015–16 mooring data from beneath Petermann Gletscher’s ice shelf imply a continued warming of 0.025° ± 0.013°C yr−1 with a modest seasonal signal. In 2015, we measured ocean temperatures of 0.28°C near the grounding line of Petermann Gletscher’s ice shelf, which drove submarine melting along the base of the glacier. The resultant meltwater contributed to ocean stratification, which forced a stronger geostrophic circulation at the ice shelf terminus compared with previous years. This increased both the freshwater flux away from the sub–ice shelf cavity and the heat flux into it. Net summertime geostrophic heat flux estimates into the sub–ice shelf cavity exceed the requirement for steady-state melting of Petermann Gletscher’s ice shelf. Likewise, freshwater fluxes away from the glacier exceed the expected steady-state meltwater discharge. These results suggest that the warmer, more active ocean surrounding Petermann Gletscher forces “non steady state” melting of its ice shelf. When sustained, such melting thins the ice shelf.

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