Non‐Linear Response of the Extratropics to Tropical Climate Variability

Abstract

The El Niño-Southern Oscillation (ENSO) and the quasi-biennial oscillation (QBO) are the most important modes of climate variability in the tropical troposphere and tropical stratosphere, respectively. Although they originate in the tropics, their teleconnections produce impacts in the mid to high latitudes in winter (Andrews

Nonlinear Effects of the Stratospheric Quasi‐Biennial Oscillation and ENSO on the North Atlantic Winter Atmospheric Circulation

“…A recent work by Walsh et al (2022) showed that the QBO-related SPV anomaly is stronger in El Niño winters in model simulations of HadGEM3-GC31-MM (see their Figure 2). Their results appear to be inconsistent with previous studies as well as with this study.…”

“…The possible reasons could be: (a) The HadGEM3-GC31-MM model they use cannot reproduce well the effects of the QBO on the STJ through a subtropical pathway; however, this process is crucial for the combined effect of the QBO and El Niño on the SPV . (b) The QBO phases are selected using different levels: Walsh et al (2022) use a 30-hPa 𝐴𝐴 𝑈𝑈 and we use a de-seasonal 50-hPa 𝐴𝐴 𝑈𝑈 (See Figure S3 in Supporting Information S1). Future work using large ensembles of models that are capable of resolving all of the QBO's pathways to influence surface climate (which currently do not exist; Rao et al, 2020) is therefore needed to confirm that the nonlinearity is similar to that shown in this work.…”

“…This nonlinearity was recently revisited by Walsh et al. (2022), who found that the total weakening of the SPV when El Niño and QBOE co‐occur is larger than would be expected if the individual responses added linearly. The sign of the nonlinearity in Walsh et al.…”

“…The correlation between the SPV and the QBO is modulated by ENSO, and specifically most studies find it is strong during La Niña winters and weak during El Niño winters (Calvo et al, 2009;Garfinkel & Hartmann, 2008;Hansen et al, 2016;Wei et al, 2007). This nonlinearity was recently revisited by Walsh et al (2022), who found that the total weakening of the SPV when El Niño and QBOE co-occur is larger than would be expected if the individual responses added linearly. The sign of the nonlinearity in Walsh et al (2022) appears to disagree with previous studies (e.g., Garfinkel & Hartmann, 2008;Wei et al, 2007), indicating that there remains a lack of consensus on the nature of nonlinearity of ENSO-QBO SPV teleconnections.…”

“…This nonlinearity was recently revisited by Walsh et al (2022), who found that the total weakening of the SPV when El Niño and QBOE co-occur is larger than would be expected if the individual responses added linearly. The sign of the nonlinearity in Walsh et al (2022) appears to disagree with previous studies (e.g., Garfinkel & Hartmann, 2008;Wei et al, 2007), indicating that there remains a lack of consensus on the nature of nonlinearity of ENSO-QBO SPV teleconnections. The implications of any possible nonlinearity of the ENSO-QBO SPV relationship for tropospheric variability, particularly in the North Atlantic sector, have not been thoroughly explored either.…”