ORIGINAL PAPER Changes in the zonal propagation of El Niño-related SST anomalies: a possible link to the PDO Pablo L. Antico 1,2,3 & Vicente R. Barros 1,4 Received: 19 February 2015 /Accepted: 7 March 2016 # Springer-Verlag Wien 2016 Abstract Long-term variability of El Niño (EN) cycle has been the topic of several studies, mainly because of its impacts on climate around the globe. This variability has been mainly described by changes in the intensity and frequency of EN events. In this study, interdecadal changes in the zonal evolu- tion of EN-related sea surface temperature anomalies (SSTA) and their possible link with a well-known mode of Pacific interdecadal variability are analyzed. EN events are classified according to the sense of zonal propagation of SSTA along the equatorial Pacific during the period 1900–2012. As a result, two types of EN are defined: eastward-directed and westward- directed EN. It is found that EN-related SSTA preferably evolves to the east (west) during the warm (cold) phase of the Pacific Decadal Oscillation. Hence, this study offers new insights into the possible causes of long-term EN changes. 1 Introduction The El Niño/Southern Oscillation (ENSO) phenomenon con- sists of an atmospheric component, the Southern Oscillation, and an oceanic component, named El Niño (EN) or La Niña during its warm and cold phases, respectively (Trenberth 1997). ENSO-associated wind and sea surface temperature (SST) anomaly patterns in the tropical Pacific produce chang- es in the main weather patterns and hence affect climate around most of the globe (Ropelewski and Halpert 1987, 1989; Halpert and Ropelewski 1992). Therefore, it is impor- tant to understand the nature of long-term changes of EN episodes. Although a considerable number of studies has been focused on the interdecadal variations of the EN intensity (Rasmusson and Carpenter 1982; Ashok et al. 2007; Kug and Jin 2009; Yeh et al. 2009) and EN frequency (Wang 1995; An and Wang 2000; Xu and Chan 2001; Horii and Hanawa 2004; Sooraj et al. 2009; Qian et al. 2011), less atten- tion has been devoted to the changes in zonal propagation of equatorial Pacific EN-related SST anomalies (SSTA), which is the focus of the present study. Fedorov and Philander (2000) analyzed the evolution of EN and La Niña since the 1950s and found variations in the zonal propagation of equatorial Pacific SSTA. Their results show that the Southern Oscillation has eastward phase propagation since 1976 in opposition to the more common westward phase propagation described by Rasmusson and Carpenter ( 1982) during the 1960s and 1970s. Later, Fedorov and Philander (2001) referred to decadal changes in the Pacific mean conditions that favor eastward phase propa- gation during the 1980s and 1990s. A similar change in the EN-related SST zonal sense of propagation since the 1980s was also described by Wang and An (2002) and Trenberth et al. (2002). Subsequently, McPhaden and Zhang (2009) em- phasized the asymmetry in BENSO SST anomaly phase Electronic supplementary material The online version of this article (doi:10.1007/s00704-016-1766-1) contains supplementary material, which is available to authorized users. * Pablo L. Antico antico@at.fcen.uba.ar 1 Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina 2 Departamento de Ciencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Intendente Güiraldes 2160, C1428EGA Buenos Aires, Argentina 3 Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, B1900FWA La Plata, Argentina 4 Centro de Investigaciones del Mar y de la Atmósfera, Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA Buenos Aires, Argentina Theor Appl Climatol DOI 10.1007/s00704-016-1766-1