scholarly journals Interannual variability of the Madden-Julian Oscillation and its impact on the North Atlantic Oscillation in the boreal winter

2015 ◽  
Vol 42 (13) ◽  
pp. 5571-5576 ◽  
Author(s):  
Hai Lin ◽  
Gilbert Brunet ◽  
Bin Yu
Keyword(s):  
North Atlantic Oscillation ◽  
Interannual Variability ◽  
North Atlantic ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

scholarly journals The Long- and Short-Lived North Atlantic Oscillation Events in a Simplified Atmospheric Model

2019 ◽  
Vol 76 (9) ◽  
pp. 2673-2700 ◽  
Author(s):  
Jie Song
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Early Stage ◽  
Atmospheric Model ◽  
Boreal Winter ◽  
Geophysical Fluid Dynamics Laboratory ◽  
The North ◽  
Northern Hemisphere Annular Mode ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract This study investigates the North Atlantic Oscillation (NAO) events with relatively long and short lifetimes based on an 8000-day perpetual-boreal-winter [December–February (DJF)] run result of the idealized Geophysical Fluid Dynamics Laboratory (GFDL) dynamical core atmospheric model. We identify the so-called long- and short-lived positive and negative NAO events from the 8000-day model output. The composite 300-hPa geopotential height anomalies show that the spatial patterns of the composite long-lived NAO events closely resemble the Northern Hemisphere annular mode (NAM) because the NAO dipole is accompanied with a statistically significant North Pacific meridional dipole (NPMD) at similar latitudes as that of the NAO dipole. The composite short-lived NAO events exhibit the locally confined canonical NAO. Twelve sets of modified initial-value experiments indicate that an absence (a presence) of the NPMD-type perturbations at the early stage of the long (short)-lived NAO events will decrease (increase) their intensities and naturally shorten (lengthen) their lifetimes. Thus, the preceding NPMD is an early factor that is conducive to the emergence of the long-lived NAO events in the model. We argue that through directly modulating the synoptic eddy forcing over the North Atlantic region, the preceding NPMD can gradually arouse the NAO-like circulation anomalies on the following days. That is the reason why the preceding NPMD can modulate the intensities and lifetimes of the NAO events.

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 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.

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