scholarly journals An Observed Connection between the North Atlantic Oscillation and the Madden–Julian Oscillation

2009 ◽  
Vol 22 (2) ◽  
pp. 364-380 ◽  
Author(s):  
Hai Lin ◽  
Gilbert Brunet ◽  
Jacques Derome
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Wave Train ◽  
Intraseasonal Variability ◽  
Winter Season ◽  
Tropical Indian Ocean ◽  
Madden Julian Oscillation ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Based on the bivariate Madden–Julian oscillation (MJO) index defined by Wheeler and Hendon and 25 yr (1979–2004) of pentad data, the association between the North Atlantic Oscillation (NAO) and the MJO on the intraseasonal time scale during the Northern Hemisphere winter season is analyzed. Time-lagged composites and probability analysis of the NAO index for different phases of the MJO reveal a statistically significant two-way connection between the NAO and the tropical convection of the MJO. A significant increase of the NAO amplitude happens about 5–15 days after the MJO-related convection anomaly reaches the tropical Indian Ocean and western Pacific region. The development of the NAO is associated with a Rossby wave train in the upstream Pacific and North American region. In the Atlantic and African sector, there is an extratropical influence on the tropical intraseasonal variability. Certain phases of the MJO are preceded by the occurrence of strong NAOs. A significant change of upper zonal wind in the tropical Atlantic is caused by a modulated transient westerly momentum flux convergence associated with the NAO.

scholarly journals The Effect of the Madden–Julian Oscillation on the North Atlantic Oscillation Using Idealized Numerical Experiments

2020 ◽  
Vol 77 (5) ◽  
pp. 1613-1635
Author(s):  
Sebastien Fromang ◽  
Gwendal Rivière
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Nonlinear Effects ◽  
Madden Julian Oscillation ◽  
The North ◽  
Budget Analysis ◽  
The North Atlantic ◽  
Quasigeostrophic Model ◽  
The North Atlantic Oscillation ◽  
The Tropics

Abstract The aim of the paper is to investigate the influence of the Madden–Julian oscillation (MJO) on the North Atlantic Oscillation (NAO) using a quasigeostrophic model on the sphere. A simplified forcing based on potential vorticity anomalies in the tropics is used to mimic the MJO. The idealized nature of our setup allows us to determine the distinct roles played by stationary and synoptic waves. This is done by means of several series of almost 10 000 short runs of 30 days. Ensemble averages and a streamfunction budget analysis are used to study the modifications of the flow induced by the MJO. We find that a stationary Rossby wave is excited in the tropics during MJO phase 3. The western part of the Pacific jet is displaced poleward, which modifies the transient eddy activity in that basin. These changes create a ridge south of Alaska, which favors equatorward propagation of synoptic waves and larger poleward eddy momentum fluxes from the eastern Pacific toward the Atlantic, increasing the frequency of occurrence of the positive NAO events. The situation is essentially reversed following phase 6 of the MJO and conducive to the negative phase of the NAO. For a realistic MJO forcing amplitude, we find increases in both NAO phases to be around 30%, in reasonable agreement with the observations given the model simplicity. Finally, we present a series of experiments to assess the relative importance of linear versus nonlinear effects.

scholarly journals The North Atlantic Oscillation Response to Large-Scale Atmospheric Anomalies in the Northeastern Pacific

2013 ◽  
Vol 70 (9) ◽  
pp. 2854-2874 ◽  
Author(s):  
Marie Drouard ◽  
Gwendal Rivière ◽  
Philippe Arbogast
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Wave Breaking ◽  
Large Scale ◽  
Wave Train ◽  
Low Frequency ◽  
The North ◽  
Northeastern Pacific ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Ingredients in the North Pacific flow influencing Rossby wave breakings in the North Atlantic and the intraseasonal variations of the North Atlantic Oscillation (NAO) are investigated using both reanalysis data and a three-level quasigeostrophic model on the sphere. First, a long-term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the NAO. Furthermore, a large-scale, low-frequency ridge anomaly is identified in the northeastern Pacific in the days prior to the maximum of the positive NAO phase both in the reanalysis and in the model. A large-scale northeastern Pacific trough anomaly is observed during the negative NAO phase but does not systematically precede it. Then, short-term linear and nonlinear simulations are performed to understand how the large-scale ridge anomaly can act as a precursor of the positive NAO phase. The numerical setup allows for analysis of the propagation of synoptic waves in the eastern Pacific in the presence of a large-scale ridge or trough anomaly and their downstream impact onto the Atlantic jet when they break. The ridge acts in two ways. First, it tends to prevent the downstream propagation of small waves compared to long waves. Second, it deflects the propagation of the wave trains in such a way that they mainly propagate equatorward in the Atlantic. The two modes of action favor the anticyclonic wave breaking and, therefore, the positive NAO phase. With the trough, the wave train propagation is more zonal, disturbances are more meridionally elongated, and cyclonic wave breaking is more frequent in the Atlantic than in the ridge case.

scholarly journals Asian Jet Waveguide and a Downstream Extension of the North Atlantic Oscillation

2004 ◽  
Vol 17 (24) ◽  
pp. 4674-4691 ◽  
Author(s):  
Masahiro Watanabe
Keyword(s):  
East Asia ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Wave Train ◽  
East Asian ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The North Atlantic Oscillation ◽  
Asian Jet Waveguide

Abstract Anomalous atmospheric fields associated with the North Atlantic Oscillation (NAO) are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the NAO is a regional phenomenon. Analyses on the interannual time scale reveal that the NAO signal is relatively confined to the Euro–Atlantic sector in December while it extends toward East Asia and the North Pacific in February. The difference is most clearly seen in the meridional wind anomaly, which shows a wave train along the Asian jet, collocated with an anomalous vorticity source near the jet entrance. Diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi-stationary Rossby waves trapped on the Asian jet waveguide, and effectively excited by the anomalous upper-level convergence over the Mediterranean Sea. It is found that, when the NAO accompanies the Mediterranean convergence (MC) anomaly, most frequently seen in February, the NAO indeed has a much wider horizontal structure than the classical picture, rather similar to the Arctic Oscillation. In such cases interannual variability of the NAO is tied to the East Asian climate variability such that the positive NAO tends to bring a surface warming over East Asia. Similar results are obtained from an analysis of individual NAO events based on low-pass-filtered daily fields, which additionally identified that the downstream extension occurs at the decay stage of the NAO event and the MC anomaly appears to be induced by the Ekman pumping associated with the NAO. The signal of the MC anomaly can be detected even at 5 days before the peak of the NAO, suggesting that the NAO influence to East Asia is predictable to some extent; therefore, monitoring the developing NAO event is useful to the medium-range weather forecast in East Asian countries.

Spatial differences in the impact of the North Atlantic Oscillation on the flow of rivers in Europe

2011 ◽  
Vol 42 (1) ◽  
pp. 30-39 ◽  
Author(s):  
Dariusz Wrzesiński ◽  
Rafał Paluszkiewicz
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Winter Season ◽  
Winter Period ◽  
The North ◽  
The North Atlantic ◽  
Positive Correlations ◽  
The North Atlantic Oscillation ◽  
River Profiles ◽  
The Impact

The article presents regional differences in the impact that the North Atlantic Oscillation (NAO) exerts on the flow of European rivers. The impact is determined by temporal variations in the strength of relations expressed by coefficients of correlation between monthly or seasonal NAO indices and discharges recorded at 510 river profiles. The results of the correlation analysis were arranged using Ward’s method of hierarchical grouping. The classification of river profiles thus obtained made it possible to distinguish seven regions differing in the nature of the dependence between streamflow and the intensity of the NAO. The most statistically significant positive correlations are displayed by the rivers of Fennoscandia, Denmark and the northwest part of the British Isles in the winter period, while the most significant negative correlations (also in winter) are recorded for streams of the Mediterranean Basin, western France and the southeast of England. In the southeast part of the Baltic Sea drainage basin, significant positive correlations of streamflow with the NAO indices can be observed in the winter season and negative correlations are observed in spring.

scholarly journals Influence of the North Atlantic Oscillation on the Winter Season in Cuba

2021 ◽  
Vol 8 (1) ◽  
pp. 45
Author(s):  
Graciela González ◽  
Amílcar Calzada ◽  
Alejandro Rodríguez
Keyword(s):  
Regression Analysis ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Winter Season ◽  
Tropical Climate ◽  
Negative Phase ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

There have been several advances in understanding the North Atlantic Oscillation (NAO), but there are still uncertainties regarding its level of influence on the tropical climate. That is why this work determines the influence of the NAO on the main hydrometeorological events that affected Cuba in the 1999–2016 period. To comply with this, a regression analysis is carried out in the CurveExpert software where the combined influence of the NAO and El Niño-Southern Oscillation on hydrometeorological events is also examined. It was found that the NAO exerts a greater influence on Cuba when it is in its negative phase during the winter season.

scholarly journals Impact of Ural Blocking on Winter Warm Arctic–Cold Eurasian Anomalies. Part II: The Link to the North Atlantic Oscillation

2016 ◽  
Vol 29 (11) ◽  
pp. 3949-3971 ◽  
Author(s):  
Dehai Luo ◽  
Yiqing Xiao ◽  
Yina Diao ◽  
Aiguo Dai ◽  
Christian L. E. Franzke ◽  
...  
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Southern China ◽  
Wave Train ◽  
Cold Event ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract In Part I of this study, the Ural blocking (UB)-induced amplification role of winter warm Arctic–cold Eurasian (WACE) anomalies has been examined. It was found that the long-lived UB together with the positive North Atlantic Oscillation (NAO+) significantly contributes to the amplification of the WACE pattern. The present study examines how the UB variability affects quasi-biweekly WACE (QB-WACE) anomalies and depends on the NAO+ and North Atlantic conditions by classifying the UB based on a case study of a cold event that occurred over southern China in January 2008. A composite analysis during 1979–2013 shows that the QB-WACE anomalies associated with the UB that often occur with the NAO+ are strong and influenced by the North Atlantic jet (NAJ) and zonal wind strengths over Eurasia. For NAO+-related UB, the QB-WACE anomaly depends strongly on the location of UB, and the UB anomalies lag the NAO+ by approximately 4–7 days. The strength of the NAJ determines whether the combined NAO+ and UB anomalies exhibit a negative East Atlantic/West Russia (EA/WR−) pattern, while the region of weak zonal winds over Eurasia and the zonal extent of the NAJ dominate the location of UB. For southward-, eastward-, and westward-displaced UBs associated with a strong NAJ, the NAO+ favors the UB with a southward-displaced QB-WACE anomaly through wave train propagation like an EA/WR− pattern. Eastward- and southward-displaced UB anomalies induce similarly displaced cold anomalies with intrusion into southern China. However, for a northward-displaced UB, this happens without pronounced EA/WR− patterns because of a weak NAJ and is accompanied by a northward-displaced QB-WACE anomaly.

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