scholarly journals The Central Role of Ocean Dynamics in Connecting the North Atlantic Oscillation to the Extratropical Component of the Atlantic Multidecadal Oscillation

2017 ◽  
Vol 30 (10) ◽  
pp. 3789-3805 ◽  
Author(s):  
Thomas L. Delworth ◽  
Fanrong Zeng ◽  
Liping Zhang ◽  
Rong Zhang ◽  
Gabriel A. Vecchi ◽  
...  
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Atlantic Multidecadal Oscillation ◽  
Ocean Dynamics ◽  
The North ◽  
Decadal Scale ◽  
The North Atlantic ◽  
Slab Ocean ◽  
The North Atlantic Oscillation ◽  
Sst Anomalies

Abstract The relationship between the North Atlantic Oscillation (NAO) and Atlantic sea surface temperature (SST) variability is investigated using models and observations. Coupled climate models are used in which the ocean component is either a fully dynamic ocean or a slab ocean with no resolved ocean heat transport. On time scales less than 10 yr, NAO variations drive a tripole pattern of SST anomalies in both observations and models. This SST pattern is a direct response of the ocean mixed layer to turbulent surface heat flux anomalies associated with the NAO. On time scales longer than 10 yr, a similar relationship exists between the NAO and the tripole pattern of SST anomalies in models with a slab ocean. A different relationship exists both for the observations and for models with a dynamic ocean. In these models, a positive (negative) NAO anomaly leads, after a decadal-scale lag, to a monopole pattern of warming (cooling) that resembles the Atlantic multidecadal oscillation (AMO), although with smaller-than-observed amplitudes of tropical SST anomalies. Ocean dynamics are critical to this decadal-scale response in the models. The simulated Atlantic meridional overturning circulation (AMOC) strengthens (weakens) in response to a prolonged positive (negative) phase of the NAO, thereby enhancing (decreasing) poleward heat transport, leading to broad-scale warming (cooling). Additional simulations are used in which heat flux anomalies derived from observed NAO variations from 1901 to 2014 are applied to the ocean component of coupled models. It is shown that ocean dynamics allow models to reproduce important aspects of the observed AMO, mainly in the Subpolar Gyre.

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 Impact of Anomalous Ocean Heat Transport on the North Atlantic Oscillation

2005 ◽  
Vol 18 (23) ◽  
pp. 4955-4969 ◽  
Author(s):  
Fabio D’Andrea ◽  
Arnaud Czaja ◽  
John Marshall
Keyword(s):  
North Atlantic Oscillation ◽  
Heat Transport ◽  
Time Scales ◽  
North Atlantic ◽  
Ocean Dynamics ◽  
Ocean Heat Transport ◽  
The North ◽  
The North Atlantic ◽  
Wind Driven Circulation ◽  
The North Atlantic Oscillation

Abstract Coupled atmosphere–ocean dynamics in the North Atlantic is studied by means of a simple model, featuring a baroclinic three-dimensional atmosphere coupled to a slab ocean. Anomalous oceanic heat transport due to wind-driven circulation is parameterized in terms of a delayed response to the change in wind stress curl due to the North Atlantic Oscillation (NAO). Climate variability for different strengths of ocean heat transport efficiency is analyzed. Two types of behavior are found depending on time scale. At interdecadal and longer time scales, a negative feedback is found that leads to a reduction in the spectral power of the NAO. By greatly increasing the efficiency of ocean heat transport, the NAO in the model can be made to completely vanish from the principal modes of variability at low frequency. This suggests that the observed NAO variability at these time scales must be due to mechanisms other than the interaction with wind-driven circulation. At decadal time scales, a coupled oscillation is found in which SST and geopotential height fields covary.

scholarly journals The recruitment of Atlantic salmon in Europe

2009 ◽  
Vol 66 (2) ◽  
pp. 289-304 ◽  
Author(s):  
Kevin D. Friedland ◽  
Julian C. MacLean ◽  
Lars P. Hansen ◽  
Arnaud J. Peyronnet ◽  
Lars Karlsson ◽  
...  
Keyword(s):  
Atlantic Salmon ◽  
North Atlantic ◽  
Atlantic Multidecadal Oscillation ◽  
Climate Forcing ◽  
Biological Interactions ◽  
Physical Forcing ◽  
The North ◽  
Decadal Scale ◽  
The North Atlantic Oscillation ◽  
Growth Analyses

Abstract Friedland, K. D., MacLean, J. C., Hansen, L. P., Peyronnet, A. J., Karlsson, L., Reddin, D. G., Ó Maoiléidigh, N., and McCarthy, J. L. 2009. The recruitment of Atlantic salmon in Europe. – ICES Journal of Marine Science, 66: 289–304. The stock complex of Atlantic salmon, Salmo salar, in Europe has experienced a multidecadal decline in recruitment, resulting in the lowest stock abundances observed since 1970. Here, physical forcing, biological interactions, and the resultant growth response of post-smolt salmon are examined with a view to understanding the mechanism controlling recruitment. Sea surface temperature (SST) has increased in the Northeast Atlantic, with the pattern and seasonal change in SST negatively correlated with post-smolt survival during summer and in a region that spatially matches the post-smolt nursery. Constituents of the pelagic foodweb, including potential post-smolt food and plankton that may affect post-smolt forage, have changed on a decadal scale and correlate with salmon survival. Retrospective growth analyses of eight stock/sea age components show that post-smolt growth during summer is positively correlated with salmon survival and recruitment. The Atlantic Multidecadal Oscillation appears to be a more closely aligned climate forcing index than the North Atlantic Oscillation with respect to salmon recruitment. European Atlantic salmon recruitment appears to be governed by factors that affect the growth of post-smolts during their first summer at sea, including SST and forage abundances; growth appears to mediate survival by the functional relationship between post-smolts and their predators.

Atlantic Multidecadal Oscillation (AMO) and sea surface temperature in the Bay of Biscay and adjacent regions

2011 ◽  
Vol 92 (2) ◽  
pp. 213-234 ◽  
Author(s):  
Carlos Garcia-Soto ◽  
Robin D. Pingree
Keyword(s):  
North Atlantic ◽  
Atlantic Multidecadal Oscillation ◽  
Sea Surface ◽  
Bay Of Biscay ◽  
The North ◽  
Sst Variability ◽  
The North Atlantic ◽  
Climate Mode ◽  
Sst Anomalies

The sea surface temperature (SST) variability of the Bay of Biscay and adjacent regions (1854–2010) has been examined in relation to the evolution of the Atlantic Multidecadal Oscillation (AMO), a major climate mode. The AMO index explains ~25% of the interannual variability of the annual SST during the last 150 years, while different indices of the North Atlantic Oscillation (NAO) explain ≤1% of the long-term record. NAO is a high frequency climate mode while AMO can modulate low frequency changes. Sixty per cent of the AMO variability is contained in periods longer than a decade. The basin-scale influence of NAO on SST over specific years (1995 to 1998) is presented and the SST anomalies explained. The period analysed represents an abrupt change in NAO and the North Atlantic circulation state as shown with altimetry and SST data. Additional atmospheric climate data over a shorter ~60 year period (1950–2008) show the influence on the Bay of Biscay SST of the East Atlantic (EA) pattern and the Scandinavia (SCA) pattern. These atmospheric teleconnections explain respectively ~25% and ~20% of the SST variability. The winter SST in the shelf-break/slope or poleward current region is analysed in relation to AMO. The poleward current shows a trend towards increasing SSTs during the last three decades as a result of the combined positive phase of AMO and global warming. The seasonality of this winter warm flow in the Iberian region is related to the autumn/winter seasonality of south-westerly (SW) winds. The SW winds are strengthened along the European shelf-break by the development of low pressure conditions in the region to the north of the Azores and therefore a negative NAO. AMO overall modulates multidecadal changes (~60% of the AMO variance). The long-term time-series of SST and SST anomalies in the Bay of Biscay show AMO-like cycles with maxima near 1870 and 1950 and minima near 1900 and 1980 indicating a period of 60–80 years during the last century and a half. Similar AMO-like variability is found in the Russell cycle of the Western English Channel (1924–1972). AMO relates at least to four mesozooplankton components of the Russell cycle: the abundance of the chaetognaths Parasagitta elegans and Parasagitta setosa (AMO −), the amount of the species Calanus helgolandicus (AMO −), the amount of the larvae of decapod crustaceans (AMO −) and the number of pilchard eggs (Sardine pilchardus; AMO +). In addition to AMO, the decadal to multidecadal (D2M) variability in the number of sunspots is analysed for the last 300 years. Several periodicities and a multi-secular linear increase are presented. There are secular minima near 1710, 1810, 1910 and 2010. The long term variability (>11 years) of the solar sunspot activity explains ~50% of the variance of the SST of the Bay of Biscay with periods longer than 11 years. AMO is finally compared with the Pacific Decadal Oscillation, the leading principal component of North Pacific SST anomalies.

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 Oscillations: Cycle Times for the NAO, the AMO and the AMOC

Climate ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 43 ◽  
Author(s):  
Knut Lehre Seip ◽  
Øyvind Grøn ◽  
Hui Wang
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Atlantic Multidecadal Oscillation ◽  
Meridional Overturning Circulation ◽  
Cycle Times ◽  
The North ◽  
In Series ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

We show that oceanic cycle lengths persist across oceanic cyclic time-series by comparing cycles in series that come from “sister” measurements in the North Atlantic Ocean. These are the North Atlantic oscillation (NAO), the Atlantic multidecadal oscillation (AMO) and the Atlantic meridional overturning circulation (AMOC). The raw NAO series, which is an extremely noisy series in its raw format, showed cycles at 7, 13, 20, 26 and 34 years that were common with, or overlapped, the other two series, and across increasing degrees of smoothing of the NAO series. At the 1960 midpoint of the hiatus period 1943–1975, NAO was leading time-series to AMOC and AMO and AMO was a leading time-series to AMOC, but in 1975, at the end of the hiatus period, the leading relations were reversed.

scholarly journals Atmospheric and Ocean Dynamics May Explain Cycles in Oceanic Oscillations

Climate ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 77
Author(s):  
Knut L. Seip ◽  
Øyvind Grøn
Keyword(s):  
North Atlantic ◽  
Southern Oscillation ◽  
Distinct Pattern ◽  
Ocean Dynamics ◽  
Cyclic Pattern ◽  
The North ◽  
The Pacific ◽  
Cycle Lengths ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

What causes cycles in oceanic oscillations, and is there a change in the characteristics of oscillations in around 1950? Characteristics of oceanic cycles and their sources are important for climate predictability. We here compare cycles generated in a simple model with observed oceanic cycles in the great oceans: The North Atlantic Oscillation (NAO), El Niño, the Southern Oscillation Index (SOI), and the Pacific Decadal Oscillation (PDO). In the model, we let a stochastic movement in one oceanic oscillation cause a similar but lagging movement in another oceanic oscillation. The two interacting oscillations show distinct cycle lengths depending upon how strongly one oscillation creates lagging cycles in the other. The model and observations both show cycles around two to six, 13 to 16, 22 to 23, and 31 to 32 years. The ultimate cause for the distinct cycles is atmospheric and oceanic “bridges” that connect the ocean basins, but the distinct pattern in cycle lengths is determined by properties of statistical distributions. We found no differences in the leading or lagging strength between well separated basins (the North Atlantic and the Pacific) and overlapping ocean basins (both in the Pacific). The cyclic pattern before 1950 appears to be different from the cyclic pattern after 1950.

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