ENSO Modulation of MJO Teleconnections to the North Atlantic and Europe

R W Lee,A J Charlton‐Perez,S J Woolnough,F Vitart

doi:10.1029/2019gl084683

Abstract

AbstractThe teleconnection from the Madden‐Julian Oscillation (MJO) provides a source of subseasonal variability and predictability to the North Atlantic‐European (NAE) region. The El Niño‐Southern Oscillation (ENSO) modulates the seasonal mean state, through which the MJO and its teleconnection pattern propagates; however, its impact on this teleconnection to the NAE region has not been investigated. Here we find a robust dependence of the teleconnections from the MJO to NAE weather regimes on the phase of ENSO. We show that the MJO to NAO+ regime tropospheric teleconnection is strongly enhanced during El Niño years, via enhanced Rossby wave activity, and suppressed during La Niña. Conversely, the MJO to NAO− regime stratospheric teleconnection is enhanced during La Niña years and suppressed during El Niño. This dependence on the background state has strong implications for subseasonal predictability, including interannual variations in subseasonal predictive skill.

Highlights

Anomalous tropical meridional divergence associated with Madden‐Julian Oscillation (MJO) (Madden & Julian, 1994) convection acts as a Rossby wave source on the subtropical jet (Seo & Lee, 2017; Seo & Son, 2012; Tseng et al, 2019)
We find that the MJO–polar vortex–North Atlantic‐European (NAE) pathway is strongly active during La Niña years (Figure 3c), for the weakened vortex following MJO phases 8, associated with the low in the northwest Pacific following MJO phase 7, increasing vertical heat flux to the stratosphere
Our findings demonstrate that the subseasonal teleconnections from the MJO to the NAE weather regimes are strongly dependent on the El Niño‐Southern Oscillation (ENSO) background state

Summary

Introduction

Anomalous tropical meridional divergence associated with MJO (Madden & Julian, 1994) convection acts as a Rossby wave source on the subtropical jet (Seo & Lee, 2017; Seo & Son, 2012; Tseng et al, 2019). Subsequent downstream propagation and Rossby wave breaking (Franzke et al, 2004; Michel & Rivière, 2011; Swenson et al, 2017; Woollings et al, 2008) in the NAE region perturb the storm track, blocking, and jet position This teleconnection pattern (Black et al, 2017; Cassou, 2008; Garfinkel et al, 2014; Guo et al, 2017; Henderson et al, 2016; Jiang et al, 2017; L'Heureux & Higgins, 2008; Lin et al, 2009; Moon et al, 2011; Stan et al, 2017; Vitart, 2017; Yadav & Straus, 2017) from the tropics results in a lagged and asymmetrical relationship in the NAE region. These differences are likely due to a longer data period, adding to the sample size, and a different dataset

Impact of ENSO Background State

Modulation of Wave Propagation

Findings

Discussion