Northern Hemisphere Stratospheric Pathway of Different El Niño Flavors in Stratosphere-Resolving CMIP5 Models

Abstract

The Northern Hemisphere (NH) stratospheric signals of eastern Pacific (EP) and central Pacific (CP) El Niño events are investigated in stratosphere-resolving historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), together with the role of the stratosphere in driving tropospheric El Niño teleconnections in NH climate. The large number of events in each composite addresses some of the previously reported concerns related to the short observational record. The results shown here highlight the importance of the seasonal evolution of the NH stratospheric signals for understanding the EP and CP surface impacts. CMIP5 models show a significantly warmer and weaker polar vortex during EP El Niño. No significant polar stratospheric response is found during CP El Niño. This is a result of differences in the timing of the intensification of the climatological wavenumber 1 through constructive interference, which occurs earlier in EP than CP events, related to the anomalous enhancement and earlier development of the Pacific-North American pattern in EP events. The northward extension of the Aleutian low and the stronger and eastward location of the high over eastern Canada during EP events are key in explaining the differences in upward wave propagation between the two types of El Niño. The influence of the polar stratosphere in driving tropospheric anomalies in the North Atlantic European region is clearly shown during EP El Niño events, facilitated by the occurrence of stratospheric summer warmings, the frequency of which is significantly higher in this case. In contrast, CMIP5 results do not support a stratospheric pathway for a remote influence of CP events on NH teleconnections.

Stratospheric role in interdecadal changes of El Niño impacts over Europe

“…This would agree with previous studies (e.g. : Iza and Calvo 2015;Calvo et al 2017). However, it is worthy highlighting that our work is not simply repeating the different CP versus EP results as documented in those previous studies.…”

“…Thus, the SST pattern found in the P period resembles an EP EN pattern, whereas it is similar to the CP EN in N period. This is confirmed by Calvo et al 2017). We have investigated if this is also the case for the EN effects in the two different periods of our study and if the contribution of this stratospheric pathway could then be added to the tropospheric results of López-Parages et al (2016a) to explain the differences in the European precipitation response detected in Fig.…”

“…In contrast, for centrally located EN events, Central Pacific EN (CP EN), such stratospheric pathway is missing (e.g. : Zubiaurre and Calvo 2012;Sung et al 2014;Iza and Calvo 2015;Calvo et al 2017). Indeed, the tropospheric teleconnections generated by these two types of events are different, in particular, the change in the strength of the Aleutian low, which is, in general, stronger in winter for EP EN than CP EN (Yu and Kim 2011).…”

Response of O<sub>2</sub> and pH to ENSO in the California Current System in a high-resolution global climate model

“…Each ENSO event evolves differently (e.g., Capotondi et al, 2015) and the variability between events, including the timing, strength, and location of temperature anomalies, can influence atmospheric teleconnections over the North Pacific (e.g., Calvo et al, 2017) and the propagation of coastally trapped waves (e.g., Frischknecht et al, 2015Frischknecht et al, , 2017. Atmospheric teleconnections, and the associated winds and air temperatures over the CalCS, are influenced by SSTs in other basins, including the Indian Ocean (e.g., Annamalai et al, 2007;Han et al, 2013) and the Kuroshio-Oyashio extension in the western North Pacific (e.g., Smirnov et al, 2015) and potentially by Arctic seaice concentrations (e.g., Alexander et al, 2004;Screen et al, 2014).…”

Long‐Term Trends in the Low‐Latitude Middle Atmosphere Temperature and Winds: Observations and WACCM‐X Model Simulations

“…(1972-1976 to 2001-2005) during winter solstice. In the stratosphere cooling was attributed to the reduction in the ozone together with increase in the vortex strength (Calvo et al, 2017;Randel et al, 2017). Negative (positive) contours are shown blue (red).…”