scholarly journals Contribution of Pacific wind stress to multi-decadal variations in upper-ocean heat content and sea level in the tropical south Indian Ocean

2011 ◽  
Vol 38 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
Franziska U. Schwarzkopf ◽  
Claus W. Böning
Keyword(s):  
Indian Ocean ◽  
Sea Level ◽  
Wind Stress ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
South Indian Ocean ◽  
Upper Ocean Heat Content ◽  
South Indian ◽  
Decadal Variations

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

2019 ◽  
Vol 32 (21) ◽  
pp. 7227-7245 ◽  
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.

scholarly journals Interannual variability of sea level in the South Indian Ocean: Local versus remote forcing mechanisms

2021 ◽  
Author(s):  
Marion Kersalé ◽  
Denis L. Volkov ◽  
Kandaga Pujiana ◽  
Hong Zhang
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Sea Level ◽  
Heat Content ◽  
Wind Forcing ◽  
Local Wind ◽  
South Indian Ocean ◽  
South Indian ◽  
Local Wind Forcing ◽  
And Sea Level

Abstract. The subtropical South Indian Ocean (SIO) has been described as one of the world's largest heat accumulators due to its remarkable warming during the past two decades. However, the relative contributions of the 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 and Pacific Oceans, thus, 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 versus 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 vs. mid latitude; western 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 Nino 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.

Dramatic reduction and quick recovery of the South Indian Ocean heat content and sea level in 2014-2019

2020 ◽  
Author(s):  
Denis Volkov ◽  
Michael Rudko ◽  
Sang-Ki Lee
Keyword(s):  
Sea Level ◽  
Rossby Waves ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Wind Forcing ◽  
Upper Ocean ◽  
Local Wind ◽  
Upper Ocean Heat Content ◽  
Local Wind Forcing ◽  
And Sea Level

<p>The interannual-to-decadal variability of heat content and sea level in the South Indian Ocean (SIO) is strongly influenced by its connection with the Pacific and large-scale climatic forcing in the Indo-Pacific region primarily associated with El Niño-Southern Oscillation (ENSO). Besides the advection by the Indonesian Throughflow, signals generated in the Pacific can enter the SIO as coastally trapped Kelvin waves and propagate along the coast of Western Australia. In the southeast tropical and subtropical Indian Ocean, these signals along the eastern boundary can radiate westward as Rossby waves and eventually impact sea level and heat content in the SIO interior and near the western boundary. Local wind forcing, through Ekman pumping over the open ocean and coastal upwelling, is also able to generate Rossby waves and/or modify those emanated from the eastern boundary.</p><p>As measured by Argo floats and satellite altimetry, a decade-long increase of the upper-ocean heat content and sea level in the SIO in 2004-2013 ended with a remarkable drop returning to the initial values in 2004. This basin-wide heat release was associated with one of the strongest on record El Niño events in 2014-2016. Surprisingly, the basin-averaged heat content and sea level quickly recovered during the weak La Niña event in 2017-2019. Here we present an analysis of the evolution and mechanisms of 2014-2016 cooling and subsequent warming in the SIO subtropical gyre. We show that the 2014-2016 El Niño did contribute to the reduced heat content in the eastern SIO, while the local wind forcing (via increased Ekman upwelling) largely contributed to the heat reduction in the western SIO. We find no evidence to support that the 2017-2018 warming was forced by the weak La Niña, because the upper-ocean heat content in eastern SIO was still below normal during 2016-2018. The recovery largely occurred in the western SIO due to local wind forcing (via increased Ekman downwelling) primarily associated with changes in the strength of the southeasterly trade winds.</p><p>Because sea level is a good proxy for the oceanic heat content in the SIO, we extend our analysis back to 1993 using satellite altimetry records. Using a simple model of wind-forced Rossby waves, we estimate the relative contributions of sea level signals propagating from the eastern boundary, the origin of which is strongly linked to ENSO, and the local wind forcing in the SIO interior to the observed sea level variability. The local wind forcing appears to dominate the sea level (and, hence, the upper-ocean heat content) variability in the western SIO, especially in 2013-2019, while the ENSO-related signals are dominant in the eastern SIO. The local wind forcing over the SIO interior effectively suppressed the cooling associated with the most recent 2014-2016 El Niño event. In contrast, the cooling associated with the strongest on record 1997-1998 El Niño was amplified by the local wind forcing in the basin’s interior.</p>

scholarly journals Wind-Driven Oceanic Rossby Waves in the Tropical South Indian Ocean with and without an Active ENSO

2005 ◽  
Vol 35 (5) ◽  
pp. 729-746 ◽  
Author(s):  
Astrid Baquero-Bernal ◽  
Mojib Latif
Keyword(s):  
Indian Ocean ◽  
Wind Stress ◽  
Time Scale ◽  
Rossby Waves ◽  
Heat Content ◽  
Kelvin Waves ◽  
South Indian Ocean ◽  
South Indian ◽  
Coastal Kelvin Waves ◽  
The Tropical Pacific

Abstract The interannual heat content variability in the tropical south Indian Ocean (SIO) and its relationship with El Niño–Southern Oscillation (ENSO) is studied. The baroclinic ocean response to stochastic wind stress predicted by a simple analytical model is compared with two integrations of the ECHO-G coupled general circulation model. In one integration, ocean–atmosphere interactions are suppressed in the tropical Pacific Ocean, so that this integration does not simulate ENSO. In the other integration, interactions are allowed everywhere and ENSO is simulated. The results show that basinwide variability in the SIO heat content can be produced by two mechanisms: 1) oscillatory forcing by ENSO-related wind stress and 2) temporally stochastic and spatially coherent wind stress forcing. Previous studies have shown that transmission of energy from the tropical Pacific to the southern Indian Ocean occurs through coastal Kelvin waves along the western coast of Australia. The results in this paper confirm the occurrence of such transmission. In the ECHO-G simulations, this transmission occurs both at the annual time scale and at interannual time scales. Generation of offshore Rossby waves by these coastal Kelvin waves at interannual time scales—and, in particular, at the ENSO time scale—was found.

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

Climate ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 71 ◽  
Author(s):  
Meer Ali ◽  
Neetu Singh ◽  
Manchikanti Kumar ◽  
Yangxing Zheng ◽  
Mark Bourassa ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Thermal Energy ◽  
Heat Content ◽  
North Indian Ocean ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Upper Ocean Heat Content ◽  
Modes Of Variability ◽  
The North ◽  
Ocean Atmosphere Interaction

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.

scholarly journals Can Tropical Pacific Winds Enhance the Footprint of the Interdecadal Pacific Oscillation on the Upper-Ocean Heat Content in the South China Sea?

2020 ◽  
Vol 33 (10) ◽  
pp. 4419-4437 ◽  
Author(s):  
Fuan Xiao ◽  
Dongxiao Wang ◽  
Lei Yang
Keyword(s):  
South China Sea ◽  
Wind Stress ◽  
South China ◽  
Heat Content ◽  
Equatorial Pacific ◽  
The South China Sea ◽  
Ocean Heat Content ◽  
Upper Ocean ◽  
Interdecadal Pacific Oscillation ◽  
Upper Ocean Heat Content

AbstractIn this study, an enhanced footprint of the interdecadal Pacific oscillation (IPO) on the upper-ocean heat content (OHC) in the South China Sea (SCS) since the 1990s is revealed. The negative OHC–IPO correlation is significant (r = −0.71) during 1990–2010 [period 2 (P2)], whereas it is statistically insignificant during 1960–80 [period 1 (P1)]. Analyses show that the scope of the equatorial Pacific wind anomalies is wider during P2 compared with that during P1 due to a larger east–west SST gradient and enhanced tropical warming in the Indian Ocean. When the IPO is negative during P2, a wider scope of the wind stress anomalies associated with the IPO could lead to 1) the southward migration of the North Equatorial Current bifurcation latitude (NECBL) by affecting the wind stress curl over the key region where it is near the climatological NECBL and 2) an increase in the interbasin pressure gradient (sea surface height difference) between the western Pacific and the SCS; these two processes strengthen the Kuroshio and weaken the Luzon Strait transport (LST) or SCS throughflow into the SCS. Also, 3) the equatorial Pacific wind anomalies are wide enough to directly weaken the LST in the SCS through the “island rule.” These three pathways finally change the oceanic gyre in the SCS and increase the OHC. Our results suggest that the scope of the tropical wind stress is the crucial factor when we consider the relationship between the upper ocean thermal conditions in the SCS and the Pacific variability.

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