Why Was the Indian Ocean Dipole Weak in the Context of the Extreme El Niño in 2015?

Abstract

The Indian Ocean witnessed a weak positive Indian Ocean dipole (IOD) event from the boreal summer to autumn in 2015, while an extreme El Niño occurred over the tropical Pacific. This was different from the case in 1997/98, when an extreme El Niño and the strongest IOD took place simultaneously. The analysis here suggests that the unique sea surface temperature anomaly (SSTA) pattern of El Niño in 2015 might have contributed to the weak IOD that year. El Niño in 2015 had a complex SSTA pattern, with positive warming over the central and eastern tropical Pacific. Such a combination of the classic El Niño (also known as cold-tongue El Niño) and the recently identified central Pacific El Niño (also known as El Niño Modoki II) had opposite remote influences on the tropical Indian Ocean. The classic El Niño reduced the strength of the Walker circulation over the tropical Indian Ocean, but this was offset by El Niño Modoki II. This study points out that the IOD can be strongly modulated by combined El Niño types in some circumstances, as in 2015.

Unprecedented 2015/2016 Indo‐Pacific Heat Transfer Speeds Up Tropical Pacific Heat Recharge

“…Around 2007, there is a shift toward prevailing positive SLA in the Indian basin (Figure b), consistent with the pronounced increase of Indian OHC from 2006 onward (see supporting information Figure S8). The subsequent Indian basin SLA reduction during the 2015/2016 El Niño was modest compared to 1997/1998, consistent with the fact that the positive Indian Ocean Dipole (IOD; Saji et al, ) event was weak in 2015/2016 (L. Liu et al, ). It is noteworthy that the relationship between the proxy and ITF volume fluxes shows some indication of nonlinearity (especially in ORAS5; see Figure c), with excessive reduction of ITF volume flux when eastern Indian Ocean SLA is high enough.…”

“…Absence of this feedback in the case of a weakly stratified Indian Ocean with an anomalously deep thermocline has also been found in a climate model (Song et al, ). Atmospheric teleconnections from the central Pacific probably played an additional role in weakening the development of the 2016 IOD event (L. Liu et al, ).…”

Developing an Abundance Index of Skipjack Tuna (Katsuwonus pelamis) from a Coastal Drifting Gillnet Fishery in the Southern Waters of Indonesia

“…In addition, the low catch rate in 2016 was also thought to be influenced by the climate anomaly. After a strong El Niño event during 2015-2016 [34,35], during the latter half of 2016, extreme wet conditions hampered Indonesia and Australia, which is caused by the strong negative Indian Ocean Dipole (IOD) and weak La Niña [34]. This phenomenon inflicted a lower intensity of upwelling, followed by an increase in sea surface temperature (SST) and a decrease in chlorophyll-a concentration in Southern Java waters [36], which was negatively correlated with the abundance of skipjack [37,38].…”

Role of Local Air‐Sea Interaction in Fire Activity Over Equatorial Asia

“…The SSTA in recent 2015/2016 El Niño tied with 1997/1998 El Niño as the strongest; however, carbon emissions from equatorial fires in 2015, 0.40 PgC year −1 , were relatively less than the 1997/1998 case (Liu et al, ; Wang et al, ). Even though the 2015/2016 case had a similar tropical Pacific SSTA magnitude to 1997/1998, the IOD event was relatively weaker in 2015/2016 than 1997/1998 (Chen et al, ; Liu et al, ). Indeed, distinct El Niño types have been reported based on the spatial pattern of SSTA, such as Eastern Pacific El Niño and Central Pacific El Niño (Ashok et al, ; Kao & Yu, ; Kug et al, ).…”