El Niño Impacts on Seasonal U.S. Atmospheric Circulation, Temperature, and Precipitation Anomalies: The OLR-Event Perspective*

Abstract

This study shows that, since 1979 when outgoing longwave radiation (OLR) observations became reliably available, most of the useful U.S. seasonal weather impact of El Niño events is associated with the few events identified by the behavior of outgoing longwave radiation (OLR) over the eastern equatorial Pacific (“OLR–El Niño events”). These events produce composite seasonal regional weather anomalies that are 95% statistically significant and robust (associated with almost all events). Results also show that there are very few statistically significant seasonal weather anomalies, even at the 80% level, associated with the non-OLR–El Niño events. A major enhancement of statistical seasonal forecasting skill over the contiguous United States appears possible by incorporating these results. It is essential to respect that not all events commonly labeled as El Niño events lead to statistically useful U.S. seasonal forecast skill.

Understanding ENSO Diversity

“…SSS indices were defined utilizing these differences in the western-to-central equatorial Pacific (Singh et al 2011) and in the southeastern Pacific (Qu and Yu 2014) to distinguish El Niño types. g) Outgoing longwave radiation (OLR) index method (Chiodi and Harrison 2013): An index was constructed using OLR anomalies over the eastern-to-central equatorial Pacific, to separate events into El Niños characterized by an OLR signal and those without an OLR signal. The two classes of events so identified were found to produce different remote climate impacts.…”

“…The characterization of ENSO diversity based on SST statistics and SST-based indices focuses on the oceanic signature of El Niño and does not necessarily account for the coupled ocean-atmosphere signature of ENSO. Other studies (e.g., Chiodi and Harrison 2013) have considered parameters that are more characteristic of ocean-atmosphere coupling, such as the eastern equatorial Pacific outgoing longwave radiation. An index combining coupled SSTA and precipitation anomalies may be a good indicator of the most extreme teleconnections of ENSO (Cai et al 2014).…”

State of the Climate in 2016

“…In the Northern Hemisphere, the enhanced westerlies reflected both an eastward extension of the East Asian jet stream well east of the date line, and an eastward shift in that jet's exit region to the eastern North Pacific. This wintertime jet stream pattern represents a fundamental manner in which El Niño's circulation impacts are communicated downstream and poleward into the extratropics (Ropelewski and Halpert 1986, 1989Harrison and Larkin 1998;Higgins et al 2002;Chiodi and Harrison 2013).…”

Observing and Predicting the 2015/16 El Niño

“…5, middle and bottom panels; Chiodi and Harrison 2013;L'Heureux et al 2015). The eastern Pacific OLR index is strongly skewed compared to the central Pacific index, reflecting nonlinearity in SSTs (e.g., Takahashi and Dewitte 2016), so the differences in evolution with 1997/98 and 1982/83 are more dramatic.…”