Moored Observations of Current and Temperature in the Alas Strait: Collected for Submarine Tailing Placement, Used for Calculating the Indonesian Throughflow

Newly released current velocity and temperature measurements in the Alas Strait collected from November 2005 to February 2007 permit calculation of the mean and variable transport of the Indonesian Throughflow (ITF) in this region. These data were collected by the Environmental Division of the Amman Mineral Nusa Tenggara mining company to serve as a guide for the deep submarine placement of tailings produced by the Batu Hijau open pit copper-gold mine. Ocean currents, temperatures, and winds in the Alas Strait region exhibit intraseasonal and seasonal variability, with modulation at interannual timescales that may be associated with intraseasonal Kelvin waves, the regional southeast monsoon, the El Niño Southern Oscillation, and the Indian Ocean Dipole (IOD). Currents in the Alas Strait were found to flow steadily southward not only during the boreal summer from mid-April to October but also when a prolonged anomalously easterly wind associated with positive IOD extended this flow direction through the end of December 2006. A steady shear between the northward-flowing upper layer and the southward-flowing layer beneath was recorded from November 2005 to early April 2006 and from January to February 2007. The 2006 annual transport was –0.25 Sv toward the Indian Ocean and varied from 0.4 Sv in early April 2006 to –0.75 Sv in August 2006. Hence, Alas Strait transport plays a dual role in the total ITF, increasing it during boreal summer and reducing it during boreal winter. Northward flows tend to carry warmer water from the Indian Ocean to the Flores Sea, while the southward ITF flow carries cooler water to the Indian Ocean. Although the Alas Strait is located next to the Lombok Strait—one of the major ITF exit passages—they have different current and temperature characteristics. For a more complete evaluation of the ITF, the Alas Strait must be included in any future monitoring.

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Impact of the April–May SAM on Central Pacific Ocean sea temperature over the following three seasons

Climate Dynamics ◽

10.1007/s00382-021-05738-4 ◽

2021 ◽

Author(s):

Ting Liu ◽

Jianping Li ◽

Cheng Sun ◽

Tao Lian ◽

Yazhou Zhang

Keyword(s):

Indian Ocean ◽

Cold Water ◽

Southern Oscillation ◽

Equatorial Pacific ◽

Boreal Winter ◽

Central Pacific ◽

Sea Temperature ◽

Easterly Wind ◽

The Indian Ocean ◽

The Impact

AbstractAlthough the impact of the extratropical Pacific signal on the El Niño–Southern Oscillation has attracted increasing concern, the impact of Southern Hemisphere Annular Mode (SAM)-related signals from outside the southern Pacific Basin on the equatorial sea temperature has received less attention. This study explores the lead correlation between the April–May (AM) SAM and central tropical Pacific sea temperature variability over the following three seasons. For the positive AM SAM case, the related simultaneous warm SST anomalies in the southeastern Indian Ocean favor significant regulation of vertical circulation in the Indian Ocean with anomalous ascending motion in the tropics. This can further enhance convection over the Marine Continent, which induces a significant horizontal Kelvin response and regulates the vertical Walker circulation. These two processes both result in the anomalous easterlies east of 130° E in the equatorial Pacific during AM. These easterly anomalies favor oceanic upwelling and eastward propagation of the cold water into the central Pacific. The cold water in turn amplifies the development of the easterly wind and further maintains the cold water into the boreal winter. The results presented here not only provide a possible link between extratropical climate variability in the Indian Ocean and climate variation in the equatorial Pacific, but also shed new light on the short-term prediction of tropical central Pacific sea temperature.

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Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-11973-2018 ◽

2018 ◽

Vol 18 (16) ◽

pp. 11973-11990 ◽

Cited By ~ 5

Author(s):

Alina Fiehn ◽

Birgit Quack ◽

Irene Stemmler ◽

Franziska Ziska ◽

Kirstin Krüger

Keyword(s):

Indian Ocean ◽

Summer Monsoon ◽

Tropical Indian Ocean ◽

Boreal Summer ◽

Boreal Winter ◽

The West ◽

West Pacific ◽

Mixing Ratios ◽

The Indian Ocean ◽

Oceanic Emissions

Abstract. Oceanic very short-lived substances (VSLSs), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Indian summer monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. We compare results between two emission scenarios: (1) monthly averaged and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean reasonably well. Using monthly resolved emissions, the main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric injection in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric injection of bromoform is in the same range whether using monthly averaged or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in the highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary by up to 50 % between using monthly averaged and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine injection from the tropical Indian Ocean and west Pacific critically depend on the seasonality and spatial distribution of the VSLS emissions.

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Drivers of oceanic exchange through the Indonesian Throughflow since the late 1800s – a synthesis of coral δ18O and high-resolution ocean models

10.5194/egusphere-egu2020-11181 ◽

2020 ◽

Author(s):

Sujata Murty ◽

Caroline Ummenhofer ◽

Markus Scheinert ◽

Erik Behrens ◽

Arne Biastoch ◽

...

Keyword(s):

Indian Ocean ◽

Mixed Layer ◽

Mixed Layer Depth ◽

Heat Content ◽

Phase Changes ◽

Boreal Winter ◽

Indonesian Throughflow ◽

Layer Depth ◽

Ocean Variability ◽

The Indian Ocean

The Indonesian Throughflow (ITF) serves as an important oceanic teleconnection for Indo-Pacific climate, altering heat and buoyancy transport from the Pacific to the Indian Ocean. Equatorial Pacific wind forcing transmitted through the ITF impacts interannual to interdecadal Indian Ocean thermocline depth and heat content, with implications for preconditioning Indian Ocean Dipole events. Yet the modulation of Indian Ocean thermal properties at seasonal timescales is still poorly understood. Here we synthesize coral &#948;18O records, instrumental indices (El Ni&#241;o Southern Oscillation (ENSO), Asian Monsoon), and simulated ocean variability (sea surface salinity (SSS) and temperature (SST), heat content, mixed layer depth) from state-of-the-art NEMO ocean model hindcasts to explore drivers of seasonal to multi-decadal variability. All coral sites are located within main ITF pathways and are influenced by monsoon-driven, buoyant South China Sea (SCS) surface waters during boreal winter that obstruct surface ITF flow and reduce heat transport to the Indian Ocean. Makassar and Lombok Strait coral &#948;18O co-varies with simulated SSS, subsurface heat content anomalies (50-350m) and mixed layer depth at the coral sites and in the eastern Indian Ocean. At decadal timescales, simulated boreal winter ocean variability at the coral sites additionally indicates a potential intensification of the SCS buoyancy plug from the mid- to late-20th century. Notably, the variability in these coral and model responses reveals sensitivity to phase changes in the Interdecadal Pacific Oscillation and the East Asian Winter Monsoon. These results collectively suggest that the paleoproxy records are capturing important features of regional hydrography and Indo-Pacific exchange, including responses to regional monsoon variability. Such proxy-model comparison is critical for understanding the drivers of variability related to changes in ITF oceanic teleconnections over the 19th and 20th centuries.

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Rainfall Teleconnections with Indo-Pacific Variability in the WCRP CMIP3 Models

Journal of Climate ◽

10.1175/2009jcli2694.1 ◽

2009 ◽

Vol 22 (19) ◽

pp. 5046-5071 ◽

Cited By ~ 46

Author(s):

Wenju Cai ◽

Arnold Sullivan ◽

Tim Cowan

Keyword(s):

Indian Ocean ◽

Climate Models ◽

Southern Oscillation ◽

Equatorial Pacific ◽

Boreal Winter ◽

Small Subset ◽

Stochastic Noise ◽

Cold Tongue ◽

Eastern Equatorial Pacific ◽

The Indian Ocean

Abstract The present study assesses the ability of climate models to simulate rainfall teleconnections with the El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD). An assessment is provided on 24 climate models that constitute phase 3 of the World Climate Research Programme’s Coupled Model Intercomparison Project (WCRP CMIP3), used in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). The strength of the ENSO–rainfall teleconnection, defined as the correlation between rainfall and Niño-3.4, is overwhelmingly controlled by the amplitude of ENSO signals relative to stochastic noise, highlighting the importance of realistically simulating this parameter. Because ENSO influences arise from the movement of convergence zones from their mean positions, the well-known equatorial Pacific climatological sea surface temperature (SST) and ENSO cold tongue anomaly biases lead to systematic errors. The climatological SSTs, which are far too cold along the Pacific equator, lead to a complete “nonresponse to ENSO” along the central and/or eastern equatorial Pacific in the majority of models. ENSO anomalies are also too equatorially confined and extend too far west, with linkages to a weakness in the teleconnection with Hawaii boreal winter rainfall and an inducement of a teleconnection with rainfall over west Papua New Guinea in austral summer. Another consequence of the ENSO cold tongue bias is that the majority of models produce too strong a coherence between SST anomalies in the west, central, and eastern equatorial Pacific. Consequently, the models’ ability in terms of producing differences in the impacts by ENSO from those by ENSO Modoki is reduced. Similarly, the IOD–rainfall teleconnection strengthens with an intensification of the IOD relative to the stochastic noise. A significant relationship exists between intermodel variations of IOD–ENSO coherence and intermodel variations of the ENSO amplitude in a small subset of models in which the ENSO anomaly structure and ENSO signal transmission to the Indian Ocean are better simulated. However, using all but one model (defined as an outlier) there is no systematic linkage between ENSO amplitude and IOD–ENSO coherence. Indeed, the majority of models produce an ENSO–IOD coherence lower than the observed, supporting the notion that the Indian Ocean has the ability to generate independent variability and that ENSO is not the only trigger of the IOD. Although models with a stronger IOD amplitude and rainfall teleconnection tend to have a greater ENSO amplitude, there is no causal relationship; instead this feature reflects a commensurate strength of the Bjerknes feedback in both the Indian and Pacific Oceans.

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A CGCM Study on the Interaction between IOD and ENSO

Journal of Climate ◽

10.1175/jcli3797.1 ◽

2006 ◽

Vol 19 (9) ◽

pp. 1688-1705 ◽

Cited By ~ 174

Author(s):

Swadhin K. Behera ◽

Jing Jia Luo ◽

Sebastien Masson ◽

Suryachandra A. Rao ◽

Hirofumi Sakuma ◽

...

Keyword(s):

Indian Ocean ◽

General Circulation ◽

Southern Oscillation ◽

Walker Circulation ◽

Tropical Pacific ◽

Boreal Summer ◽

Enso Variability ◽

The Indian Ocean ◽

Sst Anomalies ◽

The Tropical Pacific

Abstract An atmosphere–ocean coupled general circulation model known as the Scale Interaction Experiment Frontier version 1 (SINTEX-F1) model is used to understand the intrinsic variability of the Indian Ocean dipole (IOD). In addition to a globally coupled control experiment, a Pacific decoupled noENSO experiment has been conducted. In the latter, the El Niño–Southern Oscillation (ENSO) variability is suppressed by decoupling the tropical Pacific Ocean from the atmosphere. The ocean–atmosphere conditions related to the IOD are realistically simulated by both experiments including the characteristic east–west dipole in SST anomalies. This demonstrates that the dipole mode in the Indian Ocean is mainly determined by intrinsic processes within the basin. In the EOF analysis of SST anomalies from the noENSO experiment, the IOD takes the dominant seat instead of the basinwide monopole mode. Even the coupled feedback among anomalies of upper-ocean heat content, SST, wind, and Walker circulation over the Indian Ocean is reproduced. As in the observation, IOD peaks in boreal fall for both model experiments. In the absence of ENSO variability the interannual IOD variability is dominantly biennial. The ENSO variability is found to affect the periodicity, strength, and formation processes of the IOD in years of co-occurrences. The amplitudes of SST anomalies in the western pole of co-occurring IODs are aided by dynamical and thermodynamical modifications related to the ENSO-induced wind variability. Anomalous latent heat flux and vertical heat convergence associated with the modified Walker circulation contribute to the alteration of western anomalies. It is found that 42% of IOD events affected by changes in the Walker circulation are related to the tropical Pacific variabilities including ENSO. The formation is delayed until boreal summer for those IODs, which otherwise form in boreal spring as in the noENSO experiment.

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Positive Indian Ocean Dipole events prevent anoxia along coast of India

10.5194/bg-2016-195 ◽

2016 ◽

Cited By ~ 1

Author(s):

V. Parvathi ◽

I. Suresh ◽

Matthieu Lengaigne ◽

Christian Ethé ◽

Jérôme Vialard ◽

...

Keyword(s):

Indian Ocean ◽

Interannual Variability ◽

Indian Ocean Dipole ◽

Boreal Summer ◽

Low Oxygen ◽

Easterly Wind ◽

Positive Indian Ocean Dipole ◽

Subsurface Waters ◽

Anoxic Events ◽

The Indian Ocean

Abstract. The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, leading to very low oxygen concentrations at shallow depths during late boreal summer and fall. This yearly-recurring coastal hypoxia is sometimes more severe, leading to coastal anoxia that has strong impacts on the living resources. In the present study, we analyze a 1/4°-resolution coupled physical-biogeochemical regional oceanic simulation over the 1960–2012 period to investigate the physical processes influencing oxycline interannual variability off the WCI. Our analysis indicates a tight relationship between the oxycline and thermocline variations along the WCI at both seasonal and interannual timescales, thereby revealing a strong physical control of the WCI oxycline variability. As in observations, our model exhibits a shallow oxycline/thermocline along the WCI during fall that combines with interannual variability to create a window of opportunity for coastal anoxic events at this time of the year. We further demonstrate that boreal fall WCI oxycline fluctuations are strongly related to the Indian Ocean Dipole (IOD), with an asymmetric influence of positive and negative IOD phases. Positive IODs are associated with easterly wind anomalies near the southern tip of India. These winds force downwelling coastal Kelvin waves that propagate along the WCI and deepen the thermocline and oxycline there, thus preventing the occurrence of coastal anoxia. On the other hand, negative IOD events are associated with WCI thermocline and oxycline anomalies of opposite sign, but of smaller amplitude, and are hence a necessary, but not sufficient condition for coastal anoxia. As the IODs generally start developing in summer, these findings suggest some predictability to the occurrence of WCI coastal anoxia a couple of months ahead.

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Indo-Pacific Climate Interactions in the Absence of an Indonesian Throughflow

Journal of Climate ◽

10.1175/jcli-d-14-00114.1 ◽

2015 ◽

Vol 28 (13) ◽

pp. 5017-5029 ◽

Cited By ~ 12

Author(s):

Jules B. Kajtar ◽

Agus Santoso ◽

Matthew H. England ◽

Wenju Cai

Keyword(s):

Indian Ocean ◽

Climate Model ◽

Southern Oscillation ◽

Ocean Basin ◽

Climate System ◽

Indonesian Throughflow ◽

Enso Events ◽

The Pacific ◽

The Indian Ocean ◽

Mean Climate

Abstract The Pacific and Indian Oceans are connected by an oceanic passage called the Indonesian Throughflow (ITF). In this setting, modes of climate variability over the two oceanic basins interact. El Niño–Southern Oscillation (ENSO) events generate sea surface temperature anomalies (SSTAs) over the Indian Ocean that, in turn, influence ENSO evolution. This raises the question as to whether Indo-Pacific feedback interactions would still occur in a climate system without an Indonesian Throughflow. This issue is investigated here for the first time using a coupled climate model with a blocked Indonesian gateway and a series of partially decoupled experiments in which air–sea interactions over each ocean basin are in turn suppressed. Closing the Indonesian Throughflow significantly alters the mean climate state over the Pacific and Indian Oceans. The Pacific Ocean retains an ENSO-like variability, but it is shifted eastward. In contrast, the Indian Ocean dipole and the Indian Ocean basinwide mode both collapse into a single dominant and drastically transformed mode. While the relationship between ENSO and the altered Indian Ocean mode is weaker than that when the ITF is open, the decoupled experiments reveal a damping effect exerted between the two modes. Despite the weaker Indian Ocean SSTAs and the increased distance between these and the core of ENSO SSTAs, the interbasin interactions remain. This suggests that the atmospheric bridge is a robust element of the Indo-Pacific climate system, linking the Indian and Pacific Oceans even in the absence of an Indonesian Throughflow.

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Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere

10.5194/acp-2018-92 ◽

2018 ◽

Cited By ~ 2

Author(s):

Alina Fiehn ◽

Birgit Quack ◽

Irene Stemmler ◽

Franziska Ziska ◽

Kirstin Krüger

Keyword(s):

Indian Ocean ◽

Asian Monsoon ◽

Tropical Indian Ocean ◽

Boreal Summer ◽

Boreal Winter ◽

The West ◽

West Pacific ◽

Mixing Ratios ◽

The Indian Ocean ◽

Oceanic Emissions

Abstract. Oceanic very short-lived substances (VSLS), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Asian monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. We compare results between two emission scenarios: (1) monthly and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean well. Using monthly resolved emissions, main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric entrainment in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric entrainment of bromoform is in the same range whether using monthly or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary up to 50 % between using monthly and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine entrainment from the tropical Indian Ocean and west Pacific critically depends on the seasonality and spatial distribution of the VSLS emissions.

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Variability of the Intertropical Convergence Zone recorded in coral isotopic records from the central indian Ocean (Chagos Archipelago)

Quaternary Research ◽

10.1016/j.yqres.2004.02.009 ◽

2004 ◽

Vol 61 (3) ◽

pp. 245-255 ◽

Cited By ~ 30

Author(s):

Miriam Pfeiffer ◽

Wolf-Christian Dullo ◽

Anton Eisenhauer

Keyword(s):

Indian Ocean ◽

Southern Oscillation ◽

Major Change ◽

Temporal Variations ◽

Oxygen Isotopic Composition ◽

Intertropical Convergence Zone ◽

Boreal Winter ◽

Convergence Zone ◽

The Indian Ocean ◽

Chagos Archipelago

We have analyzed the stable oxygen isotopic composition of two Porites corals from the Chagos Archipelago, which is situated in the geographical center of the Indian Ocean. Coral δ18O at this site reliably records temporal variations in precipitation associated with the Intertropical Convergence Zone (ITCZ). Precipitation maxima occur in boreal winter, when the ITCZ forms a narrow band across the Indian Ocean. The Chagos then lies within the center of the ITCZ, and rainfall is strongly depleted in δ18O. A 120-yr coral isotopic record indicates an alternation of wet and dry intervals lasting 15 to 20 yr. The most recent 2 decades are dominated by interannual variability, which is tightly coupled to the El Niño–Southern Oscillation (ENSO). This is unprecedented in the 120 yr of coral record. As the ITCZ is governed by atmospheric dynamics, this provides evidence of a major change in the coupled ENSO–monsoon system.

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The Indian Ocean Dipole

10.1093/acrefore/9780190228620.013.619 ◽

2018 ◽

Cited By ~ 7

Author(s):

Saji N. Hameed

Keyword(s):

Indian Ocean ◽

Forest Fires ◽

Indian Ocean Dipole ◽

Seasonal Cycle ◽

Southern Oscillation ◽

Equatorial Indian Ocean ◽

Eastern Indian Ocean ◽

Boreal Summer ◽

Ocean Atmosphere ◽

The Indian Ocean

Discovered at the very end of the 20th century, the Indian Ocean Dipole (IOD) is a mode of natural climate variability that arises out of coupled ocean–atmosphere interaction in the Indian Ocean. It is associated with some of the largest changes of ocean–atmosphere state over the equatorial Indian Ocean on interannual time scales. IOD variability is prominent during the boreal summer and fall seasons, with its maximum intensity developing at the end of the boreal-fall season. Between the peaks of its negative and positive phases, IOD manifests a markedly zonal see-saw in anomalous sea surface temperature (SST) and rainfall—leading, in its positive phase, to a pronounced cooling of the eastern equatorial Indian Ocean, and a moderate warming of the western and central equatorial Indian Ocean; this is accompanied by deficit rainfall over the eastern Indian Ocean and surplus rainfall over the western Indian Ocean. Changes in midtropospheric heating accompanying the rainfall anomalies drive wind anomalies that anomalously lift the thermocline in the equatorial eastern Indian Ocean and anomalously deepen them in the central Indian Ocean. The thermocline anomalies further modulate coastal and open-ocean upwelling, thereby influencing biological productivity and fish catches across the Indian Ocean. The hydrometeorological anomalies that accompany IOD exacerbate forest fires in Indonesia and Australia and bring floods and infectious diseases to equatorial East Africa. The coupled ocean–atmosphere instability that is responsible for generating and sustaining IOD develops on a mean state that is strongly modulated by the seasonal cycle of the Austral-Asian monsoon; this setting gives the IOD its unique character and dynamics, including a strong phase-lock to the seasonal cycle. While IOD operates independently of the El Niño and Southern Oscillation (ENSO), the proximity between the Indian and Pacific Oceans, and the existence of oceanic and atmospheric pathways, facilitate mutual interactions between these tropical climate modes.

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