A decomposition of ENSO’s impacts on the northern winter stratosphere: competing effect of SST forcing in the tropical Indian Ocean

Abstract

propagation of stationary waves in the extratropics mainly lies over the western coast of North America during warm ENSO, which is mainly associated with the TPO-induced positive PNA response and is partially suppressed by the effect of the accompanying TIO SST forcing.

Impacts of the ENSO Lifecycle on Stratospheric Ozone and Temperature

“…During ENSO's transition phases, there are strong SST anomalies in Indian Ocean and Atlantic Ocean although SST anomalies are weak in tropical Pacific Ocean (Figures S1c and S1g). Modelling studies have shown that Indian Ocean and Atlantic Ocean SST anomalies can drive strong responses in the stratosphere (Fletcher & Kushner, ; Omrani et al, ; Rao & Ren, ; Garfinkel et al, ). Our results suggest that the Indian Ocean and Atlantic Ocean SST anomalies during the transition phases of ENSO may be more efficient in affecting the southern hemisphere stratosphere including the southern branch of Brewer‐Dobson circulation and planetary wave activities.…”

Tracking the delayed response of the northern winter stratosphere to ENSO using multi reanalyses and model simulations

“…In a subsequent paper, we will also demonstrate the possible asymmetries of ENSO's delayed effects on the stratosphere in the next winter after mature ENSO. Based on the decomposition of ENSO's effects in the concurrent winter, as reported by Rao and Ren (2016), we may attribute the weaker and earlier occurrence of the stratospheric responses in CESM-WACCM to the stronger cancelling effects by, on average, the greatly overestimated SST forcing in the tropical Indian Ocean since the spring of the ENSO-decay years (Fig. 1d, f).…”

“…The much stronger SST anomalies in the tropical eastern Pacific in CESM than those in HadISST are associated with the much stronger SST anomalies in the tropical Indian Ocean in the winter-to-spring of the ENSO decay year in CESM (Fig. 1e, f vs. b, c; also see Li et al 2012;Rao and Ren 2016). As shown in Table 1, the number of QQ ENSO events recorded over the past 60 years is similar to the number of QB ENSO events recorded (i.e., warm: seven and nine; cold: six and seven, respectively).…”

“…WACCM has been used to study long-term changes caused by increasing levels of greenhouse gases , the development and recovery of the ozone hole (Eyring et al 2007(Eyring et al , 2010a, and the atmospheric response to the solar cycle and the flux of energetic particles (e.g., Marsh et al 2007;Jackman et al 2009;Matthes et al 2010). In particular, it has been used to investigate the atmospheric response of the stratosphere to tropical ENSO forcing (Sassi et al 2004;Calvo et al 2010;Rao and Ren 2016). In essence, version 4 of WACCM (WACCM4) is a superset of the Community Atmospheric Model version 4 (CAM4) and includes all of the physical parameterizations in CAM4 (Neale et al 2013).…”

“…We also use the "high top" Whole Atmosphere Community Climate Model (WACCM), which has been successfully used to investigate the stratospheric response to ENSO forcing (Sassi et al 2004;Calvo et al 2010;Rao and Ren 2016), and to perform a series of sensitivity experiments to further verify the existence of ENSO's delayed effects on the extratropical stratosphere, as well as to clarify the related physical processes. The results will further advance our knowledge of the influence of ENSO on the stratosphere and improve our understanding of the interannual variability of the extratropical stratosphere.…”