A CGCM Study on the Interaction between IOD and ENSO

Abstract

An atmosphere-ocean coupled general circulation model known as the Scale Interaction Experiment Frontier version 1 (SINTEX-F1) model is used to understand the intrinsic variability of the Indian Ocean dipole (IOD). In addition to a globally coupled control experiment, a Pacific decoupled noENSO experiment has been conducted. In the latter, the El Niño-Southern Oscillation (ENSO) variability is suppressed by decoupling the tropical Pacific Ocean from the atmosphere. The ocean-atmosphere conditions related to the IOD are realistically simulated by both experiments including the characteristic east-west dipole in SST anomalies. This demonstrates that the dipole mode in the Indian Ocean is mainly determined by intrinsic processes within the basin. In the EOF analysis of SST anomalies from the noENSO experiment, the IOD takes the dominant seat instead of the basinwide monopole mode. Even the coupled feedback among anomalies of upper-ocean heat content, SST, wind, and Walker circulation over the Indian Ocean is reproduced.As in the observation, IOD peaks in boreal fall for both model experiments. In the absence of ENSO variability the interannual IOD variability is dominantly biennial. The ENSO variability is found to affect the periodicity, strength, and formation processes of the IOD in years of co-occurrences. The amplitudes of SST anomalies in the western pole of co-occurring IODs are aided by dynamical and thermodynamical modifications related to the ENSO-induced wind variability. Anomalous latent heat flux and vertical heat convergence associated with the modified Walker circulation contribute to the alteration of western anomalies. It is found that 42% of IOD events affected by changes in the Walker circulation are related to the tropical Pacific variabilities including ENSO. The formation is delayed until boreal summer for those IODs, which otherwise form in boreal spring as in the noENSO experiment.

Impact of Indo-Pacific Feedback Interactions on ENSO Dynamics Diagnosed Using Ensemble Climate Simulations

“…5c). The ENSO period also becomes slightly longer in DCPL, which is qualitatively consistent with some of the previous studies (Wu and Kirtman 2004;Dommenget et al 2006;Behera et al 2006). The increases in ENSO variability are not constant across the experiments, which range from 5% up to 30% (Fig.…”

“…By switching off air-sea coupling over the Pacific, we find that IOD variability is largely retained (figure not shown). This result is consistent with that of Behera et al (2006) and Fischer et al (2005), suggesting that the IOD arises from a Bjerknes feedback that can be excited by processes other than ENSO. The simulated IOD appears to be stronger when compared with observations over the last 60 yr (Figs.…”

Relative role of El Niño and IOD forcing on the southern tropical Indian Ocean Rossby waves

“…The SINTEX model has been extensively used in the past to study tropical climate variability, and the predictability of ENSO and IOD [e.g., Yamagata et al, 2004;Luo et al, 2005aLuo et al, , 2005bBehera et al, 2005Behera et al, , 2006. Figure 3a shows the correlation between SODA and CTL run (3 month lead prediction) SSH anomaly for the period of .…”

Can Indian Ocean SST anomalies influence South American rainfall?

“…Whether the IOD is an oscillatory mode of intrinsic variability of the Indian Ocean that is independent of ENSO is still under debate (e.g. Baquero-Bernal et al 2002;Dommenget and Latif 2002;Fischer et al 2005;Behera et al 2006). Regardless of the debate on the origin of the IOD, previous studies have shown that after the SST dipole is formed in the Indian Ocean, it has the potential to modulate the monsoon regime over South Asia (e.g.…”