The Tropospheric Pathway of the ENSO–North Atlantic Teleconnection

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.

The Impact of Strong El Niño and La Niña Events on the North Atlantic

“…Consistent with existing studies noted in section , the main regions of RWS generation (during both El Niño and La Niña events) are the Caribbean and the tropical Atlantic. There is also a region of negative RWS in the north Pacific (Graf & Zanchettin, ; Jiménez‐Esteve & Domeisen, ), but the magnitude of the correlation to this region is smaller (with simulated values of the correlation peaking at −0.67 in the Caribbean, 0.58 in the tropical Atlantic, and −0.39 in the north Pacific). Hence, we now focus on the tropospheric pathway as defined based on the difference in the area‐averaged RWS in the Caribbean/tropical Atlantic regions, shown by orange rectangles in Figures a and b.…”

“…In the case of El Niño events, the stratospheric pathway (Bell et al, ; Brönnimann et al, ; Cagnazzo & Manzini, ; Domeisen et al, ; Ineson & Scaife, ) is via an intensification and eastward shift of the Aleutian low (Cagnazzo & Manzini, ; García‐Herrera et al, ; Hu et al, ; Kang & Tziperman, ; Kren et al, ; Niebauer, ; Polvani et al, ; Yang et al, ), which causes an increased planetary wave flux into the stratosphere (Braesicke & Pyle, ; Manzini et al, ), leading to a weaker than average December‐January‐February (DJF) stratospheric polar vortex strength (Butler & Polvani, ; Garfinkel et al, ) and the downward projection of this onto an anomalously negative North Atlantic Oscillation (NAO; see Figure 2 of review by Kidston et al, ). The identified tropospheric pathways are via excitation of Rossby Wave trains in the North Pacific which traverse North America (Graf & Zanchettin, ; Jiménez‐Esteve & Domeisen, ) and via excitation of Rossby Waves in the tropical Atlantic (Rodríguez‐Fonseca et al, ) which then propagate northward and eastward to impact on the North Atlantic (Robertson et al, ; Scaife, Comer, Dunstone, Knight, et al, ; Toniazzo & Scaife, ). Highly correlated to the source of Rossby Waves in the tropical Atlantic, and therefore also of importance, is a Rossby wave source (RWS) in the Caribbean region (Figure 7 of Fereday et al, ).…”

Weakening of the Teleconnection From El Niño–Southern Oscillation to the Arctic Stratosphere Over the Past Few Decades: What Can Be Learned From Subseasonal Forecast Models?

“…We have examined wave activity fluxes following Takaya and Nakamura () for EN and LN in both reanalysis data and S2S models, and there does not appear to be any wave train that originates in the tropical Pacific and ends in the eastern European sector (cf. Jiménez‐Esteve & Domeisen, ). Consistent with this, the general circulation model simulations of Shaman and Tziperman () with an idealized ENSO forcing find little evidence of a wave train into this region.…”

“…This leads to differences in the precipitation response over Europe to ENSO (Ayarzagüena et al, ). The frequency of extreme transient wave activity flux events from the North Pacific to the North Atlantic also changed after 1978 (Jiménez‐Esteve & Domeisen, ).…”

Global Search for Autumn‐Lead Sea Surface Salinity Predictors of Winter Precipitation in Southwestern United States

“…Additionally, Branstator and Teng () find that jets, which act as waveguides for Rossby wave propagation, are circumglobal in the winter but confined to certain regions during the summer. Indeed, Jiménez‐Esteve and Domeisen () conclude that the stratosphere can modulate transient Rossby wave propagation across North America during the winter, therefore bridging Pacific and North Atlantic through the troposphere. Hu et al () found a connection between large‐scale Rossby wave breaking and atmospheric rivers (ARs) making landfall on U.S. West Coast.…”