Reciprocity in the Indian Ocean: Intraseasonal Oscillation and Ocean Planetary Waves

Rydbeck, Adam V.; Jensen, Tommy G.; Flatau, Maria

doi:10.1029/2021jc017546

Cited by 5 publications

(29 citation statements)

References 65 publications

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“…These results are consistent with the synchronization between ocean dynamics (seen from sea level anomalies) and the MJO. The synchronization between OHC modulated by ocean dynamics and intraseasonal variability supports previous studies for example (Rydbeck et al., 2021; Webber et al., 2010, 2012), and suggests that ocean dynamics may be an important component of the MJO.…”

Section: Discussionsupporting

confidence: 88%

“…The maximum amplitude of these anomalies are below the mean mixed layer (depicted as the black contour), which is where the maximum anomalies associated with equatorial waves from low-order baroclinic modes would be seen. While the temperature response is largely consistent with processes driven by Kelvin waves along the equator and Rossby waves in the off-equatorial section, this cannot be explicitly confirmed without doing more sophisticated analysis, such as those used by Pujiana and McPhaden (2020) and Rydbeck et al (2021) to isolate Kelvin waves and Rossby waves, respectively; this is beyond the scope of this study. Here, we are interested in variability on S2S timescales and not in the specific decomposition and effect of equatorial waves.…”

Section: Ohc and Physical Processes Associated With The Mjomentioning

confidence: 79%

“…The upper OHC is hypothesized to have a delayed feedback on the MJO via oceanic equatorial waves. Webber et al (2010) and Rydbeck et al (2021) describe one mechanism by which the interaction between OHC and the MJO occurs. Momentum forcing from the westerly wind stress associated with Intraseasonal Oscillations (ISOs) such as the MJO forces eastward propagating downwelling Kelvin waves.…”

Section: Introductionmentioning

confidence: 99%

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Processes Driving Subseasonal Variations of Upper Ocean Heat Content in the Equatorial Indian Ocean

Chandra,

Keenlyside,

Svendsen

et al. 2024

JGR Oceans

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In the equatorial Indian Ocean, the largest subseasonal temperature variations in the upper ocean are observed below the mixed layer. Subsurface processes can influence mixed layer temperature and consequently air‐sea coupling. However, the physical processes driving temperature variability at these depths are not well quantified. During the boreal winter, the Madden–Julian Oscillation (MJO) partly drives upper ocean heat content (OHC) variations. Therefore, to understand processes driving subseasonal OHC variability in the equatorial Indian Ocean, we use an observationally constrained, physically consistent ocean state estimate from the Estimating the Circulation and Climate of the Ocean (ECCO) Consortium. Using a heat budget analysis, we show that the main driver of subseasonal OHC variability in the ECCO ocean state estimate is horizontal advection. Along the equator, OHC variations are driven by zonal advection while the role of meridional advection becomes more important away from the equator. During the active phase of the MJO, net air‐sea heat fluxes damp OHC variability along the equator, while away from the equator net air‐sea heat fluxes partly drive OHC variability. Equatorial OHC variations are found to be associated with processes driven by Kelvin and Rossby waves consistent with previous studies. By quantifying the physical processes, we highlight the important role of ocean dynamics in contributing to the observed variations of subseasonal OHC in the equatorial Indian Ocean.

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Section: Discussionsupporting

confidence: 88%

Section: Ohc and Physical Processes Associated With The Mjomentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

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Processes Driving Subseasonal Variations of Upper Ocean Heat Content in the Equatorial Indian Ocean

Chandra,

Keenlyside,

Svendsen

et al. 2024

JGR Oceans

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“…It is pertinent to mention that EOF analysis, which effectively captures coherent variations, is particularly suited for studies involving planetary scale phenomenon and were extensively used to observe and analyze atmospheric and oceanic planetary scale activity [33 -36]. [37] has used EOF analysis of SSHA to characterize equatorial Rossby waves.…”

Section: Analysis Of Sshamentioning

confidence: 99%

Coastal Upwelling in the Bay of Bengal: Role of Local and Remote Windstress

Ray¹,

Swain²,

Ali³

et al. 2022

Preprint

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Monsoon winds drive upwelling along the eastern coast of India during the south-west (SW) monsoons. These winds also provide alongshore windstress (AWS) resulting in positive cross-shore Ekman transport (ET) from late May to the end of September. While instances of high ET and sea surface temperature (SST) based upwelling index (UI_SST) were observed along different parts of the coast, UI_SST was weaker in the northern section in the earlier part of monsoon. This was even in the presence of maximum AWS and ET during the 10 years analysis period spanning January-2009 to December-2018. Additionally, negative sea surface height anomalies (SSHAs), typically associated with coastal upwelling, were observed only along the southern-most coast. An empirical orthogonal function (EOF) analysis revealed two coherent modes of SSHA variation. The first principal component (PC) showed a SSHA signature coincident spatio-temporally with the first downwelling Kelvin wave, closely associated with the equatorial zonal winds that drive coastal Kelvin waves. The third PC with a coastal SSHA pattern similar to the second upwelling Kelvin wave was associated with offshore ET along the northern part of the Indian east coast. Time series of the two PCs exhibited suppression of coastal upwelling by downwelling Kelvin waves during May-July along the northeastern coast of India. Local AWS driven ET was the primary driver of coastal upwelling with the weakening of the remotely forced Kelvin waves in August. A coherent mode consisting of negative coastal SSHA signature was excited in response to local AWS driven ET during the upwelling period. This study examined the spatio-temporal variability of SW monsoon coastal upwelling along the east coast of India and illustrated the role of equatorial windstress forced first downwelling Kelvin wave in suppressing upwelling in the northern part of the coast during early SW monsoon season.

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“…It is pertinent to mention that EOF analysis, which effectively captures coherent variations, is particularly suited for studies involving planetary scale phenomenon and were extensively used to observe and analyze atmospheric and oceanic planetary scale activity [37 -40]. [41] has used EOF analysis of SSHA to characterize equatorial intraseasonal Kelvin waves, while [42] has used EOF analysis of SSHA to characterize equatorial Rossby waves.…”

Section: Ceof Analysismentioning

confidence: 99%

Coastal Upwelling in the western Bay of Bengal: Role of Local and Remote Windstress

Ray¹,

Swain²,

Ali³

et al. 2022

Preprint

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Monsoon winds drive upwelling along the eastern coast of India during the south-west (SW) monsoons. These winds also provide alongshore windstress (AWS) resulting in positive cross-shore Ekman transport (ET) from March to the end of September. While instances of high ET and sea surface temperature based upwelling index (UI_SST) were observed along two parts of the coast: between Kashinagara and Kakinada in the north, and between Kavali and Point Calimere in the south. The UI_SST illustrated a much poorer agreement with local ET in the northern section, where the onset of UI_SST preceded the rise of ET and the subsidence of UI_SST signals occurred during a period of rising ET. Additionally, negative sea surface height anomalies (SSHAs), typically associated with coastal upwelling, were also missing through most of the upwelling period. A complex empirical orthogonal function (CEOF) analysis revealed two coherent modes of SSHA variation. The first mode showed a SSHA signature spatio-temporally coincident with the first upwelling and downwelling Kelvin waves closely associated with the equatorial zonal winds that drive them. The second CEOF mode, with a coastal SSHA pattern similar to the SSHA signatures of coastal upwelling, was associated with local offshore ET along the Indian east coast. The CEOF analysis exhibited the triggering of coastal upwelling in April and its suppression from June by coastally trapped Kelvin waves along the northeastern coast of India, while local AWS driven ET was the primary driver of coastal upwelling along the southeastern coast. The second CEOF mode also exhibited a coherent negative coastal SSHA signature excited by local AWS driven ET during the upwelling period. This study examined the spatio-temporal variability of premonsoon and SW monsoon coastal upwelling along the western Bay of Bengal and its relation to remotely forced coastal Kelvin waves.

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Reciprocity in the Indian Ocean: Intraseasonal Oscillation and Ocean Planetary Waves

Cited by 5 publications

References 65 publications

Processes Driving Subseasonal Variations of Upper Ocean Heat Content in the Equatorial Indian Ocean

Processes Driving Subseasonal Variations of Upper Ocean Heat Content in the Equatorial Indian Ocean

Coastal Upwelling in the Bay of Bengal: Role of Local and Remote Windstress

Coastal Upwelling in the western Bay of Bengal: Role of Local and Remote Windstress

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