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1. Variability of Sea Level and Upper-Ocean Heat Content in the Indian Ocean: Effects of Subtropical Indian Ocean Dipole and ENSO

   https://doi.org/10.1175/JCLI-D-19-0167.1  

   Zhang, Lei ; Han, Weiqing ; Li, Yuanlong ; Lovenduski, Nicole S. ( September 2019 , Journal of Climate)

   In this study, the Indian Ocean upper-ocean variability associated with the subtropical Indian Ocean dipole (SIOD) is investigated. We find that the SIOD is associated with a prominent southwest–northeast sea level anomaly (SLA) dipole over the western-central south Indian Ocean, with the north pole located in the Seychelles–Chagos thermocline ridge (SCTR) and the south pole at southeast of Madagascar, which is different from the distribution of the sea surface temperature anomaly (SSTA). While the thermocline depth and upper-ocean heat content anomalies mirror SLAs, the air–sea CO2 flux anomalies associated with SIOD are controlled by SSTA. In the SCTR region, the westward propagation of oceanic Rossby waves generated by anomalous winds over the eastern tropical Indian Ocean is the major cause for the SLAs, with cyclonic wind causing negative SLAs during positive SIOD (pSIOD). Local wind forcing is the primary driver for the SLAs southeast of Madagascar, with anticyclonic winds causing positive SLAs. Since the SIOD is correlated with ENSO, the relative roles of the SIOD and ENSO are examined. We find that while ENSO can induce significant SLAs in the SCTR region through an atmospheric bridge, it has negligible impact on the SLA to the southeast of Madagascar. By contrast, the SIOD with ENSO influence removed is associated with an opposite SLA in the SCTR and southeast of Madagascar, corresponding to the SLA dipole identified above. A new subtropical dipole mode index (SDMI) is proposed, which is uncorrelated with ENSO and thus better represents the pure SIOD effect.

    

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2. Intraseasonal rainfall variability in the Bay of Bengal during the Summer Monsoon: coupling with the ocean and modulation by the Indian Ocean Dipole: Intraseasonal rainfall in Bay of Bengal

   https://doi.org/10.1002/asl.729  

   Jongaramrungruang, Siraput ; Seo, Hyodae ; Ummenhofer, Caroline C. ( February 2017 , Atmospheric Science Letters)
3. ENSO Explains the Link Between Indian Ocean Dipole and Meridional Ocean Heat Transport

   https://doi.org/10.1029/2021GL095796  

   McMonigal, K. ; Larson, Sarah M. ( January 2022 , Geophysical Research Letters)

   Indian Ocean meridional heat transport (MHT_IO) drives climate and ecosystem impacts, through changes to ocean temperature. Improved understanding of natural variability in tropical and subtropical MHT_IOis needed to contextualize observations and future projections. Previous studies suggest that El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) can drive variability in MHT_IO. However, it is unclear whether internally generated IOD can drive variability in MHT_IO, or if the apparent relationship between IOD and MHT_IOarises because both are modulated by ENSO. Here, we use a model experiment which dynamically removes ENSO to determine the role of internally forced IOD on MHT_IO. We find that IOD is not linked to anomalies in MHT_IO. Nevertheless, internal atmospheric variability drives significant MHT_IOvariability. There is little evidence for decadal or multidecadal variability in MHT_IO, suggesting this may be a region where an anthropogenic trend rises above the level of internal variability sooner.

    

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4. Impact of the Indian Ocean Dipole on Evolution of the Subsequent ENSO: Relative Roles of Dynamic and Thermodynamic Processes

   https://doi.org/10.1175/JCLI-D-20-0487.1  

   Yue, Zhang ; Zhou, W. ; Li, Tim ( May 2021 , Journal of Climate)

   Abstract The complex interaction between the Indian Ocean dipole (IOD) and El Niño–Southern Oscillation (ENSO) is further investigated in this study, with a focus on the impacts of the IOD on ENSO in the subsequent year [ENSO(+1)]. The interaction between the IOD and the concurrent ENSO [ENSO(0)] can be summarized as follows: ENSO(0) can trigger and enhance the IOD, while the IOD can enhance ENSO(0) and accelerate its demise. Regarding the impacts of IOD(0) on the subsequent ENSO(+1), it is revealed that the IOD can lead to anomalous SST cooling patterns over the equatorial Pacific after the winter following the IOD, indicating the formation of a La Niña–like pattern in the subsequent year. While the SST cooling tendency associated with a positive IOD is attributable primarily to net heat flux (thermodynamic processes) from autumn to the ensuing spring, after the ensuing spring the dominant contribution comes from oceanic processes (dynamic processes) instead. From autumn to the ensuing spring, the downward shortwave flux response contributes the most to SST cooling over the central and eastern Pacific, due to the cloud–radiation–SST feedback. From the ensuing winter to the ensuing summer, changes in latent heat flux (LHF) are important for SST cooling, indicating that the release of LHF from the ocean into the atmosphere increases due to strong evaporation and leads to SST cooling through the wind–evaporation–SST feedback. The wind stress response and thermocline shoaling verify that local Bjerknes feedback is crucial for the initiation of La Niña in the later stage. 

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5. Palaeoclimate perspectives on the Indian Ocean Dipole

   https://doi.org/10.1016/j.quascirev.2020.106302  

   Abram, Nerilie J. ; Hargreaves, Jessica A. ; Wright, Nicky M. ; Thirumalai, Kaustubh ; Ummenhofer, Caroline C. ; England, Matthew H. ( June 2020 , Quaternary Science Reviews)