ENSO and meridional modes: A null hypothesis for Pacific climate variability

Abstract

Pacific low‐frequency variability (timescale > 8 years) exhibits a well‐known El Niño‐like pattern of basin‐scale sea surface temperature, which is found in all the major modes of Pacific decadal climate. Using a set of climate model experiments and observations, we decompose the mechanisms contributing to the growth, peak, and decay of the Pacific low‐frequency spatial variance. We find that the El Niño‐like interdecadal pattern is established through the combined actions of Pacific meridional modes (MM) and the El Niño–Southern Oscillation (ENSO). Specifically, in the growth phase of the pattern, subtropical stochastic excitation of the MM energizes the tropical low‐frequency variance acting as a red noise process. Once in the tropics, this low‐frequency variance is amplified by ocean‐atmospheric feedbacks as the pattern reaches its peak phase. At the same time, atmospheric teleconnections distribute the variance from the tropics to the extratropics, where the pattern ultimately decays. In this stochastic red noise model of Pacific climate, the timescale of the extra‐tropical/tropical interactions (1–2 years) permits the stochastic excitation of the ENSO‐like pattern of decadal and interdecadal variance.

Independent Subspace Analysis of the Sea Surface Temperature Variability: Non-Gaussian Sources and Sensitivity to Sampling and Dimensionality

“…That is consistent with the oceanic influence of ENSO on decadal timescales [73]. Moreover, that agrees with the dynamical interactions between ENSO, PDO, and NPGO which have been discussed by several authors [74][75][76]. The quite relevant EOF11 pattern in IC1 is mostly correlated with the El Niño SST composite (asymmetric with respect to La Niña) at mid-latitudes in all oceans, during the DecemberFebruary season [68,77], which explains the above referred coherence of PC1 and PC11 during strong El Niños.…”

Amazon Plume Salinity Response to Ocean Teleconnections

“…Below average rainfall covered the central and eastern areas of the basin, near the river mouth. It is known from previous work that on interannual timescales the ENSO system has a large variance in the Pacific (Yeh and Kirtman, 2004;Di Lorenzo et al, 2015). Jiménez-Muñoz As shown in Figure 1, the Pacific SST anomalies in the Pacific Ocean were most often present near the South American coast, dispersing westward through the ocean, with a pattern similar to El Niño 3.…”

Is El Niño really changing?

“…For example, westerly wind bursts over the western and central Pacific can excite eastward propagating oceanic Kelvin waves along the equator that deepen the thermocline in the eastern Pacific and initiate the Bjerknes feedback [McPhaden, 1999;Fedorov, 2002]. And lastly, extratropical influences, in the form of Pacific Meridional Modes [Chiang and Vimont, 2004;Zhang et al, 2014] that are themselves excited by higher latitude wind forcing, can also energize both interannual and longer term variations in the equatorial Pacific Ocean [Di Lorenzo et al, 2015]. And lastly, extratropical influences, in the form of Pacific Meridional Modes [Chiang and Vimont, 2004;Zhang et al, 2014] that are themselves excited by higher latitude wind forcing, can also energize both interannual and longer term variations in the equatorial Pacific Ocean [Di Lorenzo et al, 2015].…”