Contributions of El Ni\~no Southern Oscillation (ENSO) Diversity to Low-Frequency Changes in ENSO Variance

TL;DR

This paper investigates how different types of ENSO events contribute to long-term changes in ENSO variability, revealing shifts in event likelihoods that impact climate prediction and understanding.

Contribution

It introduces a fuzzy clustering method to categorize ENSO events and links shifts in ENSO variance to changes in event types and intensities.

Findings

Identification of two La Ni ilde{n}a and three El Ni ilde{n}o categories.

Shift in ENSO variance in the 1970s linked to increased likelihood of strong La Ni ilde{n}a and extreme El Ni ilde{n}o events.

ENSO diversity significantly influences low-frequency climate variability.

Abstract

El Ni\~no Southern Oscillation (ENSO) diversity is characterized based on the longitudinal location of maximum sea surface temperature anomalies (SSTA) and amplitude in the tropical Pacific, as Central Pacific (CP) events are typically weaker than Eastern Pacific (EP) events. SSTA pattern and intensity undergo low-frequency modulations, affecting ENSO prediction skill and remote impacts. Yet, how different ENSO types contribute to these decadal variations and long-term variance trends remain uncertain. Here, we decompose the low-frequency changes of ENSO variance into contributions from ENSO diversity categories. We propose a fuzzy clustering of monthly SSTA to allow for non-binary event category memberships. Our approach identifies two La Ni\~na and three El Ni\~no categories and shows that the shift of ENSO variance in the mid-1970s is associated with an increasing likelihood of strong La Ni\~na and extreme El Ni\~no events.