A new perspective on studying ENSO teleconnections

Traditionally we think that climate is a long term average of weather. It is true but only if the climate is stationary. However, in a changing climate, where one or more relevant system parameters are changing in time, there can be no stationarity by definition, whereas stationarity is crucial for the applicability of any temporal averaging techniques. To avoid this problem we redefine climate as the distribution of potential climate realizations characterized by the instantaneous statistics of an ensemble using the so-called snapshot attractor view. In this view, the relevant quantities of the climate system are the statistics taken over an ensemble of possible realizations evolved from various initial conditions. To illustrate the power and applicability of this method we investigate the changes in the El Niño–Southern Oscillation (ENSO) phenomenon and its precipitation-related teleconnections over the Globe under climate change in the Community Earth System Model’s Large Ensemble from 1950 to2100. For the investigation, a recently developed ensemble-based method, the snapshot empirical orthogonal function (SEOF) analysis is used. The instantaneous seasonal ENSO SST pattern is defined as the leading mode of the SEOF analysis carried out at a given time instant over the ensemble. The corresponding principal components (PC1s) characterize the ENSO phases. Considering regression maps, we find that the largest changes in the typical amplitude of SST fluctuations occur in the June–July–August–September (JJAS) season, in the Niño3–Niño3.4 region and in the western part of the Pacific Ocean. At the same time, the increase is also considerable along the Equator in December–January–February (DJF). The Niño3 amplitude shows also an increase of about 20% and 10% in JJAS and DJF, respectively. The strength of the precipitation-related teleconnections of the ENSO is found to be non-stationary, as well. For example, the anti-correlation with precipitation in Australia in JJAS and the positive correlation in Central and North Africa in DJF are predicted to be more pronounced by the end of the 21th century. Half-year-lagged correlations, aiming to predict precipitation conditions from ENSO phases, are also studied. The Australian, Indonesian precipitation and that of the eastern part of Africa in both JJAS and DJF seem to be well predictable based on ENSO phase, while the South Indian precipitation is in relation with the half-year previous ENSO phase only in DJF. The strength of these connections increases with time, especially from the African region to the Arabian Peninsula.