scholarly journals A Decadal-Scale Teleconnection between the North Atlantic Oscillation and Subtropical Eastern Australian Rainfall

2015 ◽  
Vol 28 (3) ◽  
pp. 1074-1092 ◽  
Author(s):  
Cheng Sun ◽  
Jianping Li ◽  
Juan Feng ◽  
Fei Xie
Keyword(s):  
North Atlantic Oscillation ◽  
Linear Model ◽  
Time Scales ◽  
North Atlantic ◽  
Decadal Variability ◽  
Meridional Overturning Circulation ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Australian Rainfall

Abstract The time series of twentieth-century subtropical eastern Australian rainfall (SEAR) shows evident fluctuations over decadal to multidecadal time scales. Using observations from the period 1900–2013, it was found that SEAR is connected to the North Atlantic Oscillation (NAO) over decadal time scales, with the NAO leading by around 15 yr. The physical mechanism underlying this relationship was investigated. The NAO can have a delayed impact on sea surface temperature (SST) fluctuations in the subpolar Southern Ocean (SO), and these SST changes could in turn contribute to the decadal variability in SEAR through their impacts on the Southern Hemisphere atmospheric circulation. This observed lead of the NAO relative to SO SST and the interhemispheric SST seesaw mechanism are reasonably reproduced in a long-term control simulation of an ocean–atmosphere coupled model. The NAO exerts a delayed effect on the variation of Atlantic meridional overturning circulation that further induces seesaw SST anomalies in the subpolar North Atlantic and SO. With evidence that the NAO precedes SEAR decadal variability via a delayed SO bridge, a linear model for SEAR decadal variability was developed by combination of the NAO and Pacific decadal oscillation (PDO). The observed SEAR decadal variability is considerably well simulated by the linear model, and the relationship between the simulation and observation is stable. SEAR over the coming decade may increase slightly, because of the recent NAO weakening and the return of negative PDO phase.

scholarly journals Dynamical Response of the Oceanic Eddy Field to the North Atlantic Oscillation: A Model–Data Comparison

2004 ◽  
Vol 34 (12) ◽  
pp. 2615-2629 ◽  
Author(s):  
Thierry Penduff ◽  
Bernard Barnier ◽  
W. K. Dewar ◽  
James J. O'Brien
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic Oscillation ◽  
Time Scales ◽  
North Atlantic ◽  
Distribution Model ◽  
Altimeter Data ◽  
Dynamical Response ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Observational studies have shown that in many regions of the World Ocean the eddy kinetic energy (EKE) significantly varies on interannual time scales. Comparing altimeter-derived EKE maps for 1993 and 1996, Stammer and Wunsch have mentioned a significant meridional redistribution of EKE in the North Atlantic Ocean and suggested the possible influence of the North Atlantic Oscillation (NAO) cycle. This hypothesis is examined using 7 yr of Ocean Topography Experiment (TOPEX)/Poseidon altimeter data and three ⅙°-resolution Atlantic Ocean model simulations performed over the period 1979–2000 during the French “CLIPPER” experiment. The subpolar–subtropical meridional contrast of EKE in the real ocean appears to vary on interannual time scales, and the model reproduces it realistically. The NAO cycle forces the meridional contrast of energy input by the wind. The analysis in this paper suggests that after 1993 the large amplitude of the NAO cycle induces changes in the transport of the baroclinically unstable large-scale circulation (Gulf Stream/North Atlantic Current) and, thus, changes in the EKE distribution. Model results suggest that NAO-like fluctuations were not followed by EKE redistributions before 1994, probably because NAO oscillations were weaker. Strong NAO events after 1994 were followed by gyre-scale EKE fluctuations with a 4–12-month lag, suggesting that complex, nonlinear adjustment processes are involved in this oceanic adjustment.

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.

A Simple Model of the Response of the Atlantic to the North Atlantic Oscillation

2014 ◽  
Vol 27 (11) ◽  
pp. 4052-4069 ◽  
Author(s):  
Xiaoming Zhai ◽  
Helen L. Johnson ◽  
David P. Marshall
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Heat Content ◽  
Meridional Overturning Circulation ◽  
Wind Forcing ◽  
Western Boundary ◽  
Ekman Pumping ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract The response of an idealized Atlantic Ocean to wind and thermohaline forcing associated with the North Atlantic Oscillation (NAO) is investigated both analytically and numerically in the framework of a reduced-gravity model. The NAO-related wind forcing is found to drive a time-dependent “leaky” gyre circulation that integrates basinwide stochastic wind Ekman pumping and initiates low-frequency variability along the western boundary. This is subsequently communicated, together with the stochastic variability induced by thermohaline forcing at high latitudes, to the remainder of the Atlantic via boundary and Rossby waves. At low frequencies, the basinwide ocean heat content changes owing to NAO wind forcing and thermohaline forcing are found to oppose each other. The model further suggests that the recently reported opposing changes of the meridional overturning circulation in the Atlantic subtropical and subpolar gyres between 1950–70 and 1980–2000 may be a generic feature caused by interplay between the NAO wind and thermohaline forcing.

The North Atlantic Oscillation and related topics

2020 ◽  
Author(s):  
Richard Greatbatch
Keyword(s):  
North Atlantic Oscillation ◽  
Time Scales ◽  
North Atlantic ◽  
Climate Projections ◽  
Easterly Wind ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic ◽  
Set Up ◽  
The North Atlantic Oscillation

<p>We start with the severe European winter of 1962/63, a winter when the North Atlantic Oscillation (NAO) index was strongly negative with persistent easterly wind anomalies across northern Europe and the British Isles. We then note that the NAO is a manifestation of synoptic Rossby wave breaking. The positive feedback with which synoptic eddies act to maintain the atmospheric jet stream against friction turns out to also be the mechanism by which the equatorial deep jets in the ocean are maintained against dissipation. We were fortunate to be able to demonstrate this in both a simple model set-up that supports deep jets and directly from mooring data on, and on either side of, the equator at 23 W in the Atlantic Ocean. The deep jets offer some potential for prediction over the neighbouring African continent on interannual time scales. This then leads to a brief discussion of the importance of the tropics for prediction on both seasonal and decadal time scales and longer, linking back to the winter of 1962/63.  The models we use for prediction not only contain surprisingly large biases but also require the parameterization of unresolved processes and some brief discussion will be given on the representation of mesoscale eddies in ocean models, such as are used in prediction systems and for making future climate projections.</p><p> </p><p> </p>

scholarly journals TYPOLOGIA REŻIMU ODPŁYWU RZEK W POLSCE W RÓŻNYCH FAZACH OSCYLACJI PÓŁNOCNOATLANTYCKIEJ

1970 ◽  
pp. 249-261
Author(s):  
Dariusz Wrzesiński
Keyword(s):  
Spatial Distribution ◽  
North Atlantic Oscillation ◽  
Time Scales ◽  
North Atlantic ◽  
Annual Cycle ◽  
Similar Distribution ◽  
The North ◽  
The North Atlantic ◽  
Monthly Runoff ◽  
The North Atlantic Oscillation

The paper presents the spatial distribution of types of river regime in Poland according to the assumptions of Dynowska (1997) for three time scales: 1971–2010 and for years with high and low indices of the North Atlantic Oscillation and directions of their transformation in various phases of NAODJFM. The paper applied daily flow values from the period 1971–2010 for 516 stations located on 280 Polish rivers. In the examined time scales, five types of regime were designated including rivers characterised by a similar distribution and range of monthly runoff values in an average annual cycle. The designated groups, however, differ in terms of the number of rivers, which affects the image of spatial distribution of rivers representing the identified types of regime. The analysis shows that in the studied NAODJFM phases, transformations of the flow regime of many rivers in Poland are often observed. Compared to average conditions (1971–2010), in the negative phase of NAODJFM, the most stable is nival type well formed. The most common transformations relate to the nival regime moderately formed, which usually changes into a nival well formed or nival-pluvial regime. In the positive phase of NAODJFM, regime transformations are more frequent. The most stable type of regime is again nival well formed, and the most common transformation occurs in the case of the pluvio-nival regime (into the nival-pluvial regime) and nival-pluvial regime, which is transformed into well or moderately formed nival regimes.

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