scholarly journals Enhanced atmospheric response to Gulf Stream SST anomalies in CAM6 simulations with 1/8-degree regional grid refinement over the North Atlantic

2021 ◽  
Author(s):  
Robert Jnglin Wills ◽  
Adam Herrington ◽  
Isla Simpson ◽  
David Battisti
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Atmospheric Response ◽  
Grid Refinement ◽  
The North ◽  
The North Atlantic ◽  
Sst Anomalies

scholarly journals Transient Atmospheric Response to Interactive SST Anomalies

2008 ◽  
Vol 21 (3) ◽  
pp. 576-583 ◽  
Author(s):  
David Ferreira ◽  
Claude Frankignoul
Keyword(s):  
North Atlantic ◽  
Initial Conditions ◽  
Maximum Amplitude ◽  
Atmospheric Response ◽  
The North ◽  
Winter Conditions ◽  
Initial Evolution ◽  
Sst Anomaly ◽  
The North Atlantic ◽  
Sst Anomalies

Abstract The transient atmospheric response to interactive SST anomalies in the midlatitudes is investigated using a three-layer QG model coupled in perpetual winter conditions to a slab oceanic mixed layer in the North Atlantic. The SST anomalies are diagnosed from a coupled run and prescribed as initial conditions, but are free to evolve. The initial evolution of the atmospheric response is similar to that obtained with a prescribed SST anomaly, starting as a quasi-linear baroclinic and then quickly evolving into a growing equivalent barotropic one. Because of the heat flux damping, the SST anomaly amplitude slowly decreases, albeit with little change in pattern. Correspondingly, the atmospheric response only increases until it reaches a maximum amplitude after about 1–3.5 months, depending on the SST anomaly considered. The response is similar to that at equilibrium in the fixed SST case, but it is 1.5–2 times smaller, and then slowly decays away.

scholarly journals The Relation between the North Atlantic Oscillation and SSTs in the North Atlantic Basin

2004 ◽  
Vol 17 (24) ◽  
pp. 4752-4759 ◽  
Author(s):  
Weile Wang ◽  
Bruce T. Anderson ◽  
Robert K. Kaufmann ◽  
Ranga B. Myneni
Keyword(s):  
North Atlantic Oscillation ◽  
Granger Causality ◽  
North Atlantic ◽  
Gulf Stream ◽  
Causal Relation ◽  
Causal Effect ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Sst Anomalies

Abstract The authors use the notion of Granger causality to investigate the relationship between the North Atlantic Oscillation (NAO) index and the sea surface temperatures (SSTs) over the Northern Hemisphere. The Granger causality analysis ensures that any apparent oceanic influence upon the atmosphere (as measured by the NAO) is provided by the ocean and is not related to preexisting conditions within the NAO itself (and vice versa when looking at the atmospheric influence upon the ocean). Although this statistical technique does not imply physical forcing of one field on the other, it is generally more reliable compared to the simple lead/lagged correlation. Using this technique, the authors find that on seasonal time scales, the preceding NAO anomalies' influence on the wintertime SST field is rather restricted. Conversely, preceding SST anomalies have a statistically significant causal effect on the wintertime NAO. However, the causal relation between preceding SSTs and the wintertime NAO is limited to the Gulf Stream extension; in contrast to the canonical tripole SST pattern typically associated with the NAO, the authors do not find that SST anomalies in either the Greenland or subtropical regions have a significant causal effect on the NAO. These results suggest that the Gulf Stream SSTs have an important influence in initiating disturbances of the atmospheric circulation over the wintertime North Atlantic.

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

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

scholarly journals Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation

Ocean Science ◽  
2015 ◽  
Vol 11 (3) ◽  
pp. 425-438 ◽  
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.

scholarly journals Observational Assessment of Nonlocal Heat Flux Feedback in the North Atlantic by GEFA

2013 ◽  
Vol 52 (3) ◽  
pp. 645-653 ◽  
Author(s):  
Na Wen ◽  
Zhengyu Liu ◽  
Qinyu Liu
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Wind ◽  
Turbulent Heat ◽  
Observational Assessment ◽  
The North ◽  
The North Atlantic ◽  
Flux Response ◽  
Sst Anomalies ◽  
Heat Flux Feedback

AbstractMost previous studies have proven the local negative heat flux feedback (the surface heat flux response to SST anomalies) in the midlatitude areas. However, it is uncertain whether a nonlocal heat flux feedback can be observed. In this paper, the generalized equilibrium feedback assessment (GEFA) method is employed to examine the full surface turbulent heat flux response to SST in the North Atlantic Ocean using NCEP–NCAR reanalysis data. The results not only confirm the dominant local negative feedback, but also indicate a robust nonlocal positive feedback of the Gulf Stream Extension (GSE) SST to the downstream heat flux in the subpolar region. This nonlocal feedback presents a strong seasonality, with response magnitudes of in winter and in summer. Further study indicates that the nonlocal effect is initiated by the adjustments of the downstream surface wind to the GSE SST anomalies.

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

2018 ◽  
Vol 48 (10) ◽  
pp. 2283-2303 ◽  
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.

Global Monsoon Responses to Decadal Sea Surface Temperature Variations during the Twentieth Century: Evidence from AGCM Simulations

2019 ◽  
Vol 32 (22) ◽  
pp. 7675-7695 ◽  
Author(s):  
Jie Jiang ◽  
Tianjun Zhou
Keyword(s):  
Twentieth Century ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Sea Surface ◽  
Monsoon Precipitation ◽  
The North ◽  
The North Atlantic ◽  
Sst Anomalies

Abstract Multidecadal variations in the global land monsoon were observed during the twentieth century, with an overall increasing trend from 1901 to 1955 that was followed by a decreasing trend up to 1990, but the mechanisms governing the above changes remain inconclusive. Based on the outputs of two atmospheric general circulation models (AGCMs) forced by historical sea surface temperature (SST) covering the twentieth century, supplemented with AGCM simulations forced by idealized SST anomalies representing different conditions of the North Atlantic and tropical Pacific, evidence shows that the observed changes can be partly reproduced, particularly over the Northern Hemisphere summer monsoon (NHSM) domain, demonstrating the modulation of decadal SST changes on the long-term variations in monsoon precipitation. Moisture budget analysis is performed to understand the interdecadal changes in monsoon precipitation, and the dynamic term associated with atmospheric circulation changes is found to be prominent, while the contribution of the thermodynamic term associated with humidity changes can lead to coincident wetting over the NHSM domain. The increase (decrease) in NHSM land precipitation during 1901–55 (1956–90) is associated with the strengthening (weakening) of NHSM circulation and Walker circulation. The multidecadal scale changes in atmospheric circulation are driven by SST anomalies over the North Atlantic and the Pacific. A warmer North Atlantic together with a colder eastern tropical Pacific and a warmer western subtropical Pacific can lead to a strengthened meridional gradient in mid-to-upper-tropospheric thickness and strengthened trade winds, which transport more water vapor into monsoon regions, leading to an increase in monsoon precipitation.

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

2019 ◽  
Vol 32 (22) ◽  
pp. 7697-7712 ◽  
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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