Resampling of ENSO teleconnections: accounting for cold-season evolution reduces uncertainty in the North Atlantic

Martin P King,Stefan Sobolowski,Camille Li

doi:10.5194/wcd-2-759-2021

Abstract

Abstract. We re-examine the uncertainty of the El Niño–Southern Oscillation (ENSO) teleconnection to the North Atlantic following the investigation of Deser et al. (2017) (DES2017). Our analyses are performed on the November–December (ND) and January–February (JF) means separately and for a geographical area that covers a larger extent in the midlatitude North Atlantic than DES2017. The motivation for splitting the cold season in this way arises from the fact that the teleconnection patterns and underlying physical mechanisms are different in late fall compared to midwinter. As in DES2017, our main technique in quantifying the uncertainty is bootstrap resampling. Amplitudes and spatial correlations of the bootstrap samples are presented together effectively using Taylor diagrams. In addition to the confidence intervals calculated from Student's t tests and the percentiles of anomalous sea level pressure (SLP) values in the bootstrap samples, we also investigate additional confidence intervals using techniques that are not widely used in climate research but have different advantages. In contrast to the interpretation by DES2017, our results indicate that we can have confidence (at the 5 % significance level) in the patterns of the teleconnected SLP anomalies. The uncertainties in the amplitudes remain large, with the upper-percentile anomalies at up to 2 times those of the lower percentiles in the North Pacific and 2.8 times in the North Atlantic.

Highlights

During the 1980s–1990s, dynamical understanding of tropical–extratropical atmospheric teleconnections saw substantial progress, with observational analyses beginning in earnest as data from in situ and satellite measurements became available. Trenberth et al (1998) provide an excellent review of many foundational studies performed during this period establishing the idea that tropical sea surface temperature (SST) perturbations such as El Niño–Southern Oscillation (ENSO) can drive upper-tropospheric divergence, which in turn acts as a source for planetary-scale Rossby waves with far-reaching climate impacts
The observed sea level pressure (SLP) composites (Co described in Sect. 2) for ENSO are calculated for the period 1920–2013, the same period used in DES2017
As reported by DES2017 for DJF, we find that the SLP anomalies during El Niño and La Niña events in the November– December (ND) and JF seasons do not indicate any asymmetry in terms of the sign of the anomalies over the domains used in the Taylor diagrams; this is true for both the North Atlantic and North Pacific sectors

Summary

Introduction

During the 1980s–1990s, dynamical understanding of tropical–extratropical atmospheric teleconnections saw substantial progress, with observational analyses beginning in earnest as data from in situ and satellite measurements became available. Trenberth et al (1998) provide an excellent review of many foundational studies performed during this period establishing the idea that tropical sea surface temperature (SST) perturbations such as El Niño–Southern Oscillation (ENSO) can drive upper-tropospheric divergence, which in turn acts as a source for planetary-scale Rossby waves with far-reaching climate impacts. More recent efforts in the field include studies on the effects of ENSO SST diversity and amplitude, as well as nonlinearity of the teleconnections (e.g., Feng et al, 2017; Frauen et al, 2014; Garfinkel et al, 2013; Toniazzo and Scaife, 2006; TrascasaCastro et al, 2019; Weinberger et al, 2019; Zhang et al, 2018). The role of tropical–extratropical teleconnections in the predictability of Northern Hemisphere climate, and how prediction systems can be improved by including these processes correctly, was recognized early on. Attention to this aspect has intensified in recent years (e.g., Hardiman et al, 2020; Scaife et al, 2014, 2016). Establishing the teleconnection patterns and amplitudes as well as the physical mechanisms involved remains a challenge owing to large atmospheric internal variability in the extratropics

Objectives

Results

Conclusion