A surface layer variance heat budget for ENSO

Abstract

Characteristics of the El Niño–Southern Oscillation (ENSO), such as frequency, propagation, spatial extent, and amplitude, strongly depend on the climatological background state of the tropical Pacific. Multidecadal changes in the ocean mean state are hence likely to modulate ENSO properties. To better link background state variations with low‐frequency amplitude changes of ENSO, we develop a diagnostic framework that determines locally the contributions of different physical feedback terms on the ocean surface temperature variance. Our analysis shows that multidecadal changes of ENSO variance originate from the delicate balance between the background‐state‐dependent positive thermocline feedback and the atmospheric damping of sea surface temperatures anomalies. The role of higher‐order processes and atmospheric and oceanic nonlinearities is also discussed. The diagnostic tool developed here can be easily applied to other tropical ocean areas and climate phenomena.

ENSO-driven energy budget perturbations in observations and CMIP models

“…The latter is important in coupling SSTs and subsurface ocean temperatures (Boucharel et al 2015). In the following sections, after examination of the local relationship between SSTs and OHC, we explore the energy budget variability associated with ENSO on a basin scale to investigate whether the underestimation of OHC variability is present in the area-average or spatial error compensation occurs.…”

The Defining Characteristics of ENSO Extremes and the Strong 2015/2016 El Niño

“…As the mean state has, in recent decades, switched back into a more negative IPO phase, which can explain the early 21st century global warming hiatus (England et al, ; Kosaka & Xie, ; see Medhaug et al, on hiatus controversies), ENSO variability consistently weakens (Hu et al, ), marked by more frequent emergence of weaker El Niño events that peak in the central Pacific (Lee & McPhaden, ; Xiang et al, )—often referred to as central Pacific (CP) El Niño (Kao & Yu, ), El Niño Modoki (Ashok et al, ), dateline El Niño (Larkin & Harrison, ), or warm pool El Niño (Kug et al, ). This has been associated with the declining role of the thermocline feedback (Boucharel et al, ; Guan & McPhaden, ; Lübbecke & McPhaden, ).…”

“…The component is, on the other hand, considered as part of a damping term by the mean currents. Studies that adopt such framework will tend to report stronger dominance of the thermocline feedback (e.g., Boucharel et al, ; Ren & Jin, ). Figure shows that the component is clearly larger than in both GODAS and ECCO2.…”

“…This is because ENSO can rectify onto the mean state through nonlinear dynamics (e.g., Sun et al, ) or redden through ocean and atmosphere teleconnections (e.g., Newman et al, ), thus giving rise to decadal variability, manifesting in modes such as the Interdecadal Pacific Oscillation (IPO) (Power et al, ) or its Northern Hemisphere analog, the Pacific Decadal Oscillation (PDO) (Mantua et al, ). Yet the impact of decadal mean state on ENSO can be readily explained through coupled dynamical frameworks (e.g., Boucharel et al, ; Choi et al, ; Jin et al, , ; Lübbecke & McPhaden, ). Research on this issue was particularly stimulated following the apparent climate shift around the mid‐1970s towards a more positive IPO phase until the late 1990s, as evident from an El Niño‐like decadal mean state with warming of the tropical Pacific and slackened Pacific Trade Winds (e.g., Trenberth & Hurrel, ).…”

Fokker–Planck dynamics of the El Niño-Southern Oscillation

“…nonlinear recharge oscillator model. Following previous studies on the role of NDH 15,30,31 in setting amplitude asymmetry 15 , we implemented NDH in the ROM, especially the dominant zonal and vertical NDHs 15,31 . Using the formulation of Jin et al 6 , the zonal and vertical components of NDH can be represented by combinations of T E and [h] , as follows:…”