Dominant Modes of Upper Ocean Heat Content in the North Indian Ocean

The thermal energy needed for the development of hurricanes and monsoons as well as any prolonged marine weather event comes from layers in the upper oceans, not just from the thin layer represented by sea surface temperature alone. Ocean layers have different modes of thermal energy variability because of the different time scales of ocean–atmosphere interaction. Although many previous studies have focused on the influence of upper ocean heat content (OHC) on tropical cyclones and monsoons, no study thus far—particularly in the North Indian Ocean (NIO)—has specifically concluded the types of dominant modes in different layers of the ocean. In this study, we examined the dominant modes of variability of OHC of seven layers in the NIO during 1998–2014. We conclude that the thermal variability in the top 50 m of the ocean had statistically significant semiannual and annual modes of variability, while the deeper layers had the annual mode alone. Time series of OHC for the top four layers were analyzed separately for the NIO, Arabian Sea, and Bay of Bengal. For the surface to 50 m layer, the lowest and the highest values of OHC were present in January and May every year, respectively, which was mainly caused by the solar radiation cycle.

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Near-Real-Time Availability of Ocean Heat Content Over the North Indian Ocean

IEEE Geoscience and Remote Sensing Letters ◽

10.1109/lgrs.2014.2375196 ◽

2015 ◽

Vol 12 (5) ◽

pp. 1033-1036 ◽

Cited By ~ 1

Author(s):

Neethu Chacko ◽

Dibyendu Dutta ◽

M. M. Ali ◽

Jaswant R. Sharma ◽

Vinay K. Dadhwal

Keyword(s):

Indian Ocean ◽

Real Time ◽

Heat Content ◽

North Indian Ocean ◽

Ocean Heat Content ◽

The North ◽

Time Availability

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Intrinsic oceanic decadal variability of upper-ocean heat content

Journal of Climate ◽

10.1175/jcli-d-20-0962.1 ◽

2021 ◽

pp. 1-42

Author(s):

Navid C. Constantinou ◽

Andrew McC. Hogg

Keyword(s):

Time Scales ◽

Climate Models ◽

Low Frequency ◽

Heat Content ◽

Ocean Heat Content ◽

Upper Ocean ◽

Climate Projections ◽

Upper Ocean Heat Content ◽

Modes Of Variability ◽

Low Frequency Variability

AbstractAtmosphere and ocean are coupled via air–sea interactions. The atmospheric conditions fuel the ocean circulation and its variability, but the extent to which ocean processes can affect the atmosphere at decadal time scales remains unclear. In particular, such low-frequency variability is difficult to extract from the short observational record, meaning that climate models are the primary tools deployed to resolve this question. Here, we assess how the ocean’s intrinsic variability leads to patterns of upper-ocean heat content that vary at decadal time scales. These patterns have the potential to feed back on the atmosphere and thereby affect climate modes of variability, such as El Niño or the Interdecadal Pacific Oscillation. We use the output from a global ocean–sea ice circulation model at three different horizontal resolutions, each driven by the same atmospheric reanalysis. To disentangle the variability of the ocean’s direct response to atmospheric forcing from the variability due to intrinsic ocean dynamics, we compare model runs driven with inter-annually varying forcing (1958-2019) and model runs driven with repeat-year forcing. Models with coarse resolution that rely on eddy parameterizations, show (i) significantly reduced variance of the upper-ocean heat content at decadal time scales and (ii) differences in the spatial patterns of low-frequency variability compared with higher resolution simulations. Climate projections are typically done with general circulation models with coarse-resolution ocean components. Therefore, these biases affect our ability to predict decadal climate modes of variability and, in turn, hinder climate projections. Our results suggest that for improving climate projections, the community should move towards coupled climate models with higher oceanic resolution.

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Decadal Variability of Upper-Ocean Heat Content Associated with Meridional Shifts of Western Boundary Current Extensions in the North Pacific

Journal of Climate ◽

10.1175/jcli-d-16-0779.1 ◽

2017 ◽

Vol 30 (16) ◽

pp. 6247-6264 ◽

Cited By ~ 7

Author(s):

Bunmei Taguchi ◽

Niklas Schneider ◽

Masami Nonaka ◽

Hideharu Sasaki

Keyword(s):

North Pacific ◽

Frontal Zone ◽

Heat Content ◽

Ocean Heat Content ◽

Upper Ocean ◽

Upper Ocean Heat Content ◽

Temperature Anomalies ◽

The North ◽

Subarctic Frontal Zone ◽

The North Pacific

Generation and propagation processes of upper-ocean heat content (OHC) in the North Pacific are investigated using oceanic subsurface observations and an eddy-resolving ocean general circulation model hindcast simulation. OHC anomalies are decomposed into physically distinct dynamical components (OHC ρ) due to temperature anomalies that are associated with density anomalies and spiciness components (OHC χ) due to temperature anomalies that are density compensating with salinity. Analysis of the observational and model data consistently shows that both dynamical and spiciness components contribute to interannual–decadal OHC variability, with the former (latter) component dominating in the subtropical (subpolar) North Pacific. OHC ρ variability represents heaving of thermocline, propagates westward, and intensifies along the Kuroshio Extension, consistent with jet-trapped Rossby waves, while OHC χ variability propagates eastward along the subarctic frontal zone, suggesting advection by mean eastward currents. OHC χ variability tightly corresponds in space to horizontal mean spiciness gradients. Meanwhile, area-averaged OHC χ anomalies in the western subarctic frontal zone closely correspond in time to meridional shifts of the subarctic frontal zone. Regression coefficient of the OHC χ time series on the frontal displacement anomalies quantitatively agree with the area-averaged mean spiciness gradient in the region, and suggest that OHC χ is generated via frontal variability in the subarctic frontal zone.

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

Journal of Climate ◽

10.1175/jcli-d-19-0167.1 ◽

2019 ◽

Vol 32 (21) ◽

pp. 7227-7245 ◽

Cited By ~ 5

Author(s):

Lei Zhang ◽

Weiqing Han ◽

Yuanlong Li ◽

Nicole S. Lovenduski

Keyword(s):

Indian Ocean ◽

Sea Level ◽

Indian Ocean Dipole ◽

Heat Content ◽

Ocean Heat Content ◽

Upper Ocean ◽

Thermocline Depth ◽

Upper Ocean Heat Content ◽

South Indian ◽

The Indian Ocean

Abstract 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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