Influence of Tropical Pacific Sea Surface Temperature on the Genesis of Gulf Stream Cyclones

2016 ◽  
Vol 73 (10) ◽  
pp. 4203-4214 ◽  
Author(s):  
Sebastian Schemm ◽  
Laura M. Ciasto ◽  
Camille Li ◽  
Nils Gunnar Kvamstø
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
Gulf Stream ◽  
El Nino ◽  
Tropical Pacific ◽  
Cp El Niño ◽  
The North ◽  
Sst Variability ◽  
Ep El Niño ◽  
The North Atlantic

Abstract This study investigates the relationship between tropical Pacific sea surface temperature (SST) variability and cyclogenesis over the Gulf Stream region of the North Atlantic. A cyclone identification scheme and Lagrangian trajectories are used to compare preferred cyclogenesis locations and precyclogenesis flow paths associated with three patterns of tropical Pacific SST variability: eastern Pacific (EP) El Niño, central Pacific (CP) El Niño, and La Niña. During EP El Niño and La Niña winters, the upper-level precyclogenesis flow takes a subtropical path over North America and Gulf Stream cyclogenesis predominantly occurs under the North Atlantic jet entrance, which is the climatologically preferred location. In contrast, during CP El Niño winters, when the warmest SST anomalies occur in the central tropical Pacific, the precyclogenesis flow takes a northern path across North America and Gulf Stream cyclogenesis tends to occur farther north under the jet exit. The shift in preferred cyclogenesis is consistent with changes in transient upstream flow perturbations, detected using potential vorticity (PV) streamer frequencies, which are associated with the stationary wave response. Compared to EP El Niño winters, CP El Niño winters exhibit fewer southward-extending streamers and cyclonic (LC2) flow behavior, resulting in precyclogenesis air bypassing the right entrance of the North Atlantic jet. Downstream, Gulf Stream cyclones penetrate deeper into high Arctic latitudes during CP El Niño winters than in other cases. The results highlight distinct signatures of tropical SST anomalies on synoptic-scale atmospheric features and could help constrain future changes in the North Atlantic storm track and the associated poleward heat transport.

scholarly journals Extratropical Cyclogenesis Changes in Connection with Tropospheric ENSO Teleconnections to the North Atlantic: Role of Stationary and Transient Waves

2018 ◽  
Vol 75 (11) ◽  
pp. 3943-3964 ◽  
Author(s):  
Sebastian Schemm ◽  
Gwendal Rivière ◽  
Laura M. Ciasto ◽  
Camille Li
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
Gulf Stream ◽  
El Nino ◽  
Rocky Mountain ◽  
Stationary Waves ◽  
The North ◽  
Northeastern Pacific ◽  
The North Atlantic ◽  
North Atlantic Jet

AbstractThis study investigates mechanisms for changes in wintertime extratropical cyclogenesis over North America and the North Atlantic during different phases of El Niño–Southern Oscillation (ENSO). Insights into the relationship between the ENSO–North Atlantic teleconnection and the cyclogenesis changes are provided by diagnosing the relative roles of stationary wave propagation and transient eddies in setting cyclogenesis-conducive large-scale circulation anomalies. During La Niña winters, Rocky Mountain and Greenland cyclogenesis are enhanced, while Gulf Stream cyclogenesis is reduced. Diagnostics suggest that stationary waves of tropical origin work in tandem with transient eddies to amplify the ridge over the northeastern Pacific, establishing background flow anomalies that favor Rocky Mountain cyclogenesis; downstream, more transient eddies with an anticyclonic tilt push the North Atlantic jet poleward, favoring cyclogenesis near Greenland, while contributions from stationary waves are small. During central Pacific El Niño winters, the cyclogenesis situation is essentially the opposite: Rocky Mountain and Greenland cyclogenesis are reduced, while Gulf Stream cyclogenesis is enhanced. The analyses are consistent with stationary waves and transient eddies acting to weaken the climatological ridge over the northeastern Pacific, creating a more zonal Pacific jet; downstream, transient eddies with a cyclonic tilt push the North Atlantic jet equatorward, favoring Gulf Stream cyclogenesis. Anomalies in cyclogenesis frequencies, and the relative roles of transient and stationary waves, during eastern Pacific El Niño winters are associated with larger uncertainties.

scholarly journals A Nonstationary ENSO–NAO Relationship Due to AMO Modulation

2018 ◽  
Vol 32 (1) ◽  
pp. 33-43 ◽  
Author(s):  
Wenjun Zhang ◽  
Xuebin Mei ◽  
Xin Geng ◽  
Andrew G. Turner ◽  
Fei-Fei Jin
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Circulation Model ◽  
La Niña ◽  
Late Winter ◽  
The North ◽  
La Nina ◽  
The North Atlantic

Abstract Many previous studies have demonstrated a high uncertainty in the relationship between El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). In the present work, decadal modulation by the Atlantic multidecadal oscillation (AMO) is investigated as a possible cause of the nonstationary ENSO–NAO relationship based on observed and reanalysis data. It is found that the negative ENSO–NAO correlation in late winter is significant only when ENSO and the AMO are in phase (AMO+/El Niño and AMO−/La Niña). However, no significant ENSO-driven atmospheric anomalies can be observed over the North Atlantic when ENSO and the AMO are out of phase (AMO−/El Niño and AMO+/La Niña). Further analysis indicates that the sea surface temperature anomaly (SSTA) in the tropical North Atlantic (TNA) plays an essential role in this modulating effect. Because of broadly analogous TNA SSTA responses to both ENSO and the AMO during late winter, a warm SSTA in the TNA is evident when El Niño occurs during a positive AMO phase, resulting in a significantly weakened NAO, and vice versa when La Niña occurs during a negative AMO phase. In contrast, neither the TNA SSTA nor the NAO shows a prominent change under out-of-phase combinations of ENSO and AMO. The AMO modulation and the associated effect of the TNA SSTA are shown to be well reproduced by historical simulations of the HadCM3 coupled model and further verified by forced experiments using an atmospheric circulation model. These offer hope that similar models will be able to make predictions for the NAO when appropriately initialized.

Modulation of the Global Atmospheric Circulation by Combined Activity in the Madden–Julian Oscillation and the El Niño–Southern Oscillation during Boreal Winter

2010 ◽  
Vol 23 (15) ◽  
pp. 4045-4059 ◽  
Author(s):  
Paul E. Roundy ◽  
Kyle MacRitchie ◽  
Jonas Asuma ◽  
Timothy Melino
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
The North ◽  
The North Atlantic

Abstract Composite global patterns associated with the El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO) are frequently applied to help make predictions of weather around the globe at lead times beyond a few days. However, ENSO modulates the background states through which the MJO and its global response patterns propagate. This paper explores the possibility that nonlinear variations confound the combined use of composites based on the MJO and ENSO separately. Results indicate that when both modes are active at the same time, the associated patterns in the global flow are poorly represented by simple linear combinations of composites based on the MJO and ENSO individually. Composites calculated by averaging data over periods when both modes are present at the same time more effectively describe the associated weather patterns. Results reveal that the high-latitude response to the MJO varies with ENSO over all longitudes, but especially across the North Pacific Rim, North America, and the North Atlantic. Further analysis demonstrates that the MJO influence on indexes of the North Atlantic Oscillation is greatest during La Niña conditions or during periods of rapid adjustment in the phase of ENSO.

scholarly journals Tropospheric QBO–ENSO Interactions and Differences between the Atlantic and Pacific

2016 ◽  
Vol 29 (4) ◽  
pp. 1353-1368 ◽  
Author(s):  
Felicitas Hansen ◽  
Katja Matthes ◽  
Sebastian Wahl
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
La Niña ◽  
Quasi Biennial Oscillation ◽  
The North ◽  
La Nina ◽  
The North Atlantic ◽  
The North Pacific

Abstract This study investigates the interaction of the quasi-biennial oscillation (QBO) and the El Niño–Southern Oscillation (ENSO) in the troposphere separately for the North Pacific and North Atlantic region. Three 145-yr model simulations with NCAR’s Community Earth System Model Whole Atmosphere Community Climate Model (CESM-WACCM) are analyzed where only natural (no anthropogenic) forcings are considered. These long simulations allow the authors to obtain statistically reliable results from an exceptional large number of cases for each combination of the QBO (westerly and easterly) and ENSO phases (El Niño and La Niña). Two different analysis methods were applied to investigate where nonlinearity might play a role in QBO–ENSO interactions. The analyses reveal that the stratospheric equatorial QBO anomalies extend down to the troposphere over the North Pacific during Northern Hemisphere winter only during La Niña and not during El Niño events. The Aleutian low is deepened during QBO westerly (QBOW) as compared to QBO easterly (QBOE) conditions, and the North Pacific subtropical jet is shifted northward during La Niña. In the North Atlantic, the interaction of QBOW with La Niña conditions (QBOE with El Niño) results in a positive (negative) North Atlantic Oscillation (NAO) pattern. For both regions, nonlinear interactions between the QBO and ENSO might play a role. The results provide the potential to enhance the skill of tropospheric seasonal predictions in the North Atlantic and North Pacific region.

scholarly journals Nonlinearity in the Tropospheric Pathway of ENSO to the North Atlantic

2020 ◽  
Author(s):  
Bernat Jiménez-Esteve ◽  
Daniela I. V. Domeisen
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Atmospheric Model ◽  
La Niña ◽  
Winter Climate ◽  
The North ◽  
La Nina ◽  
The North Atlantic

Abstract. El Niño Southern Oscillation (ENSO) can exert a remote impact on North Atlantic and European (NAE) winter climate. This teleconnection is driven by the superposition and interaction of different influences, which are generally grouped into two main pathways, namely the tropospheric and stratospheric pathways. In this study, we focus on the tropospheric pathway through the North Pacific and across the North American continent. Due to the possible non-stationary behavior and the limited time period covered by reanalysis data sets, the potential nonlinearity of this pathway remains unclear. In order to address this question, we use a simplified physics atmospheric model forced with seasonally varying prescribed sea surface temperatures (SST) following the evolution of different ENSO phases with linearly varying strength at a fixed location. To isolate the tropospheric pathway the zonal mean stratospheric winds are nudged towards the model climatology. The model experiments indicate that the tropospheric pathway of ENSO to the North Atlantic exhibits significant nonlinearity with respect to the tropical SST forcing, both in the location and amplitude of the impacts. For example, strong El Niño leads to a significantly stronger impact over the North Atlantic Oscillation (NAO) than a La Niña forcing of the same amplitude. For La Niña forcings, there is a saturation in the response, with no further increase in the NAO impact even when doubling the SSTforcing, while this is not the case for El Niño. These findings may have important consequences for long-range predictions of the North Atlantic and Europe.

scholarly journals The Tropospheric Pathway of the ENSO–North Atlantic Teleconnection

2018 ◽  
Vol 31 (11) ◽  
pp. 4563-4584 ◽  
Author(s):  
Bernat Jiménez-Esteve ◽  
Daniela I. V. Domeisen
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Stationary Waves ◽  
The North ◽  
La Nina ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract El Niño–Southern Oscillation (ENSO) exerts an influence on the North Atlantic–European (NAE) region. However, this teleconnection is nonlinear and nonstationary owing to the superposition and interaction of a multitude of influences on this region. The stratosphere is one of the major players in terms of the influence of the ENSO signal on this sector. Nevertheless, there are tropospheric dynamical links between the North Pacific and the North Atlantic that are clearly influenced by ENSO. This tropospheric pathway of ENSO to the NAE has received less attention. In view of this, the present study revisits the tropospheric pathway of ENSO to the North Atlantic using ECMWF reanalysis products. Anomalous propagation of transient and quasi-stationary waves across North America is analyzed with respect to their sensitivity to ENSO. Transient (quasi-stationary zonal waves 1–3) wave activity flux (WAF) from the Pacific to the Atlantic increases during El Niño (La Niña) conditions leading to a negative (positive) phase of the North Atlantic Oscillation (NAO). This response is observed from January to March for El Niño and only visible during February for La Niña events. However, the stratosphere strongly modulates this response. For El Niño (La Niña) conditions a weaker (stronger) stratospheric vortex tends to reinforce the negative (positive) NAO with the stratosphere and troposphere working in tandem, contributing to a stronger and more persistent tropospheric circulation response. These findings may have consequences for the prediction of the NAO during times with an inactive stratosphere.

scholarly journals PRECIPITAÇÃO SOBRE A AMÉRICA DO SUL E SUAS RELAÇÕES COM A OSCILAÇÃO MULTIDECADAL DO ATLÂNTICO E A OSCILAÇÃO DO ATLÂNTICO NORTE (RAINFALL OVER SOUTH AND ITS RELATIONS WITH AMERICA SWING MULTIDECADAL ATLANTIC AND SWING THE NORTH ATLANTIC)

2016 ◽  
Vol 18 ◽  
Author(s):  
Nayara Arroxelas dos Santos ◽  
Anderlan Henrique Batista Siqueira ◽  
Maria Luciene Dias de Melo
Keyword(s):  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
The North ◽  
The North Atlantic

Este estudo teve como objetivo analisar e avaliar qual o grau de correlação entre a precipitação sobre a América do Sul e as oscilações que ocorrem sobre a região do atlântico norte, Oscilação Multidecadal do Atlântico (OMA), sobre o oceano, e Oscilação do Atlântico Norte (OAN), na atmosfera. Foram coletados os dados dos índices das oscilações e da precipitação que cobrem um períodos de janeiro de 1900 a dezembro de 2012 para os índices e de janeiro de 1900 a dezembro de 2008 para a precipitação. Para tal, fez o uso das técnicas estatísticas Análise Exploratória de Dados e Correlação ordinária de Pearson. Analisaram-se os índices e se observou que existem dois modos preponderantes da OMA, um positivo de 1927 a 1964 e um negativo de 1965 a 1995. Todas as análises foram feitas baseadas nesses dois modos. Observaram-se nas anomalias, levando em consideração os dois modos da OMA, da precipitação um padrão único e oposto entre os modos da OMA, isto é, as regiões que apresentaram aumento da precipitação no modo positivo e apresentaram redução da precipitação no modo negativo e vice-versa. Os coeficientes de correlação entre o índice da OMA e a precipitação sobre o continente apresentou o mesmo padrão em ambos os modos da OMA, mostrando que a maior parte do continente apresentou correlação negativa. Isso mostra uma relação inversa entre a OMA e a precipitação, quando a OMA se apresentou negativa/positiva, a precipitação sobre o continente aumentou/diminuiu. Já em relação a OAN, durante o modo positivo da OMA, observou-se o mesmo padrão da correlação com a OMA. Contudo, no modo negativo da OMA, a correlação da precipitação com OAN mostrou um padrão aleatório. Esse fato pode estar relacionado com as teleconexões com outros fenômenos, por exemplo, El Niño – Oscilação Sul. Notou-se que a interação entre os fenômenos que ocorrem na parte norte do oceano atlântico é evidente.

Contributions of Downstream Eddy Development to the Teleconnection between ENSO and the Atmospheric Circulation over the North Atlantic

2012 ◽  
Vol 25 (14) ◽  
pp. 4993-5010 ◽  
Author(s):  
Ying Li ◽  
Ngar-Cheung Lau
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Storm Track ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract The spatiotemporal evolution of various meteorological phenomena associated with El Niño–Southern Oscillation (ENSO) in the North Pacific–North American–North Atlantic sector is examined using both NCEP–NCAR reanalyses and output from a 2000-yr integration of a global coupled climate model. Particular attention is devoted to the implications of downstream eddy developments on the relationship between ENSO and the atmospheric circulation over the North Atlantic. The El Niño–related persistent events are characterized by a strengthened Pacific subtropical jet stream and an equatorward-shifted storm track over the North Pacific. The wave packets that populate the storm tracks travel eastward through downstream development. The barotropic forcing of the embedded synoptic-scale eddies is conducive to the formation of a flow that resembles the negative phase of the North Atlantic Oscillation (NAO). The more frequent and higher persistence of those episodes during El Niño winters contribute to the prevalence of negative NAO conditions. The above processes are further delineated by conducting a case study for the 2009/10 winter season, in which both El Niño and negative NAO conditions prevailed. It is illustrated that the frequent and intense surface cyclone development over North America and the western Atlantic throughout that winter are associated with upper-level troughs propagating across North America, which in turn are linked to downstream evolution of wave packets originating from the Pacific storm track.

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