Relative contributions of heat flux and wind stress on the spatiotemporal upper-ocean variability in the tropical Indian Ocean

Yuan, Xu; Ummenhofer, Caroline C.; Seo, Hyodae; Su, Zhongbo

doi:10.1088/1748-9326/ab9f7f

Cited by 3 publications

(2 citation statements)

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“…The Indian Ocean has been characterized as one of the major heat accumulators in the ocean with a significant increase of ocean heat content (OHC) and sea level during the past 2 decades, in particular in the subtropical southern Indian Ocean (SIO) (Roemmich et al, 2015;Nieves et al, 2015;Volkov et al, 2017;Y. Zhang et al, 2018;Ummenhofer et al, 2020) (Fig. 1a).…”

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confidence: 99%

“…Besides the ocean tunnel effect, the variability of sea level and OHC in the SIO is also driven by local atmospheric forcing. Wind-driven ocean dynamics are the dominant contributor of the upper-ocean temperature variability in the equatorial Indian Ocean (Yuan et al, 2020). Wind stress curl induces Ekman pumping, and alongshore winds cause coastal upwelling and downwelling.…”

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Interannual variability of sea level in the southern Indian Ocean: local vs. remote forcing mechanisms

et al. 2022

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Abstract. The subtropical southern Indian Ocean (SIO) has been described as one of the world's largest heat accumulators due to its remarkable warming during the past 2 decades. However, the relative contributions of remote (of Pacific origin) forcing and local wind forcing to the variability of heat content and sea level in the SIO have not been fully attributed. Here, we combine a general circulation model, an analytic linear reduced-gravity model, and observations to disentangle the spatial and temporal inputs of each forcing component on interannual to decadal timescales. A sensitivity experiment is conducted with artificially closed Indonesian straits to physically isolate the Indian Ocean and Pacific Ocean, intentionally removing the Indonesian Throughflow (ITF) influence on the Indian Ocean heat content and sea level variability. We show that the relative contribution of the signals originating in the equatorial Pacific vs. signals caused by local wind forcing to the interannual variability of sea level and heat content in the SIO is dependent on location within the basin (low latitude vs. midlatitude and western side vs. eastern side of the basin). The closure of the ITF in the numerical experiment reduces the amplitude of interannual-to-decadal sea level changes compared to the simulation with a realistic ITF. However, the spatial and temporal evolution of sea level patterns in the two simulations remain similar and correlated with El Niño–Southern Oscillation (ENSO). This suggests that these patterns are mostly determined by local wind forcing and oceanic processes, linked to ENSO via the “atmospheric bridge” effect. We conclude that local wind forcing is an important driver for the interannual changes of sea level, heat content, and meridional transports in the SIO subtropical gyre, while oceanic signals originating in the Pacific amplify locally forced signals.

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Interannual variability of sea level in the southern Indian Ocean: local vs. remote forcing mechanisms

et al. 2022

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Modeling the Indian Ocean

Shinoda,

Jensen,

Lachkar

et al. 2024

The Indian Ocean and Its Role in the Global Climate System

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Late 20th Century Indian Ocean Heat Content Gain Masked by Wind Forcing

Ummenhofer

Ryan

England

et al. 2020

Geophysical Research Letters

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Rapid increases in upper 700-m Indian Ocean heat content (IOHC) since the 2000s have focused attention on its role during the recent global surface warming hiatus. Here, we use ocean model simulations to assess distinct multidecadal IOHC variations since the 1960s and explore the relative contributions from wind stress and buoyancy forcing regionally and with depth. Multidecadal wind forcing counteracted IOHC increases due to buoyancy forcing from the 1960s to the 1990s. Wind and buoyancy forcing contribute positively since the mid-2000s, accounting for the drastic IOHC change. Distinct timing and structure of upper ocean temperature changes in the eastern and western Indian Ocean are linked to the pathway how multidecadal wind forcing associated with the Interdecadal Pacific Oscillation is transmitted and affects IOHC through local and remote winds. Progressive shoaling of the equatorial thermocline-of importance for low-frequency variations in Indian Ocean Dipole occurrence-appears to be dominated by multidecadal variations in wind forcing. Plain Language Summary Indian Ocean surface waters have warmed more than the tropical Atlantic or Pacific over the last 60 years. In contrast, the amount of heat stored in the upper 700 m of the Indian Ocean did not exhibit strong increases between 1960 and 2000, which is counter to temperature trends in other ocean regions across the globe. Only since the 2000s was rapid warming down to 700 m observed for the Indian Ocean. Using ocean model simulations, our study demonstrates that the unusual behavior of Indian Ocean temperatures over the last 60 years was mainly due to wind conditions: Two different pathways how winds can impact the upper ocean temperature structure in the Indian Ocean, either through the atmosphere or via an oceanic connection from the Pacific, are highlighted. In fact, wind trends during 1960-2000 counteracted additional heat input into the Indian Ocean due to an overall warming climate. These long-term changes in the Indian Ocean temperature structure affect regional climate in surrounding countries; they are also of importance for predicting how the Indian Ocean will respond in the near future to a warming climate.

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Relative contributions of heat flux and wind stress on the spatiotemporal upper-ocean variability in the tropical Indian Ocean

Cited by 3 publications

References 57 publications

Interannual variability of sea level in the southern Indian Ocean: local vs. remote forcing mechanisms

Interannual variability of sea level in the southern Indian Ocean: local vs. remote forcing mechanisms

Modeling the Indian Ocean

Late 20th Century Indian Ocean Heat Content Gain Masked by Wind Forcing

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