Objective Classification of Sea Surface Temperature Evolution diversity of ENSO Cycle

Abstract

El Niño-Southern Oscillation （ENSO） is the most prominent interannual climate mode over the tropical Pacific， which is characterized by a periodic and phase-locked evolution of sea surface temperature anomalies （SSTA）.From the perspective of ENSO cycle， this study objectively classified the SSTA evolution of ENSO from 1961 to 2021 into two results using K-means clustering method （KMA）： 3 or 5 types of ENSO cycle.When it is classified into 3 types， the basic characteristics of ENSO cycle are warm-developing， warm-decaying， and cold-persistence.When it is classified into 5 types， the discrepancies of intensity and zonal distribution of the development and decay processes between super-strong and normal events are highlighted.To further explain these discrepancies， this study employed a KMA considering the Principal Component Analysis （Empirical Orthogonal Function）.Based on the two EOF leading modes which reflects the zonal symmetric and asymmetric development modes， the zonally symmetric and asymmetric development processes of the ENSO cycle are divided.Combined with the KMA clustering analysis， it is further found that zonally asymmetric development mode together with the zonally consistent development mode jointly lead to the zonal asymmetric development speed of ENSO cycle.Reconstruction of the zonally homogeneous and asymmetric evolution modes of ENSO reveals that wind and thermocline thickness anomalies may be key factors controlling the zonal asymmetric evolution of SSTA.This study objectively classified different types of ENSO evolution， providing reference for climate dynamics and impacts of ENSO diversity.

Keywords

• enso cycle
• k-means cluster analysis
• principal component analysis
• pacific sst