What Determines the Lagged ENSO Response in the South‐West Indian Ocean?

Abstract

Oceanic Rossby waves can propagate climate signals over considerable distances over long timescales. Using a long simulation from a coupled climate model, we examine oceanic and mixed atmosphere‐ocean teleconnections to the south‐western Indian Ocean (SWIO) associated with Rossby waves excited by the El Niño‐Southern Oscillation (ENSO). Reconstruction of propagating ENSO‐induced sea‐level anomalies from the simulation using an optimized linear wave model with dissipation highlights the prominent role of baroclinic, rather than barotropic, Rossby waves in modulating sea‐surface heights. Between 9.5° and 18.5°S, El Niño‐associated anomalous anticyclonic wind‐stress fields initiate downwelling Rossby waves, potentially influencing SWIO regional climate around 1–4 seasons after El Niño peak, while also destructively interfering with upwelling waves triggered on the eastern boundary by oceanic teleconnections. Further south, weaker ENSO winds, dissipation, non‐linear processes, and interference from higher‐mode Rossby waves limit ENSO influences in the SWIO. In the model, ENSO‐associated predictability is therefore constrained by the “atmospheric” rather than “oceanic” bridge.

Interannual variability of the thermocline depth in the south‐central Indian Ocean: Respective influences of IOD and ENSO

“…Because of their slower propagation speed, these anomalies hardly reach the western boundary of the Indian Ocean by the end of spring (Figure 4b). Consistent with previous studies (Zhang and Han, 2020;Eabry et al, 2021), these results indicate the more delayed but longer-lasting influence of ENSO on D20 variations in the SWIO than IOD.…”

“…As the IOD‐related wind signal dissipates quickly during early winter, the ENSO wind signal reaches its maximum in November but continues to exist until the following March (Figures 3 and 4). Previous studies have argued that, owing to this wind forcing, downwelling Rossby waves form and propagate westward from the southeastern Indian Ocean, causing a deepening of D20A in the SWIO (Hermes and Reason, 2009; Trenary and Han, 2012; Deepa et al ., 2018;Zhang and Han, 2020; Eabry et al ., 2021). Due to the faster speed of Rossby waves at lower latitudes, these deep D20A signals extend northwestward during winter and spring, consistent with a stronger Rossby wave signal but originating from further south (~15°S) than the corresponding IOD anomalies (e.g., Masumoto and Meyers, 1998; Chambers et al ., 1999; Birol and Morrow, 2001; Huang and Kinter III, 2002; Xie et al ., 2002; Rao and Behera, 2005; see also Figure 3h).…”

Surface Heating Over the Tibetan Plateau Associated With the Antarctic Oscillation

“…Therefore, the TCEI may be the key region as a medium of May AAO influencing the Northern Hemisphere, independent of ENSO. While the SST in western Australia may be dominated by the lagged response of ENSO through atmospheric and oceanic bridges (Eabry et al., 2021). Previous studies also indicate that the SST anomaly in the Indian Ocean is a remarkable medium connecting the AAO and the Northern Hemisphere climate (Dou & Wu, 2018; Dou et al., 2016; Nan & Li, 2003; Nan et al., 2009).…”

Drivers and characteristics of the Indo-western Pacific Ocean capacitor

“…In climatology, the SWTIO thermocline dome is maintained by the upwelling induced by negative wind stress curl between the weak equatorial westerlies and the southeasterly trades over the TIO (Hermes and Reason, 2008;Yokoi et al, 2008Yokoi et al, , 2012. The thermocline depth exhibits large variability, associated with the anomalous wind stress curl induced by ENSO (Masumoto and Meyers, 1998;Jury and Huang, 2004;Tozuka et al, 2010;Yang et al, 2019;Eabry et al, 2021;Wu et al, 2021). During the developing and mature phase of El Niño, the anomalous anticyclonic wind stress curls force downwelling oceanic Rossby waves in the southeast TIO, which propagate slowly westward and reach the SWTIO within one or two seasons (Figure 3).…”