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

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

Oceanography ◽

10.5670/oceanog.2021.103 ◽

2021 ◽

Vol 34 (1) ◽

Author(s):

Dwi Susanto ◽

◽

Jorina Waworuntu ◽

Windy Prayogo ◽

Agus Setianto

Keyword(s):

Indian Ocean ◽

Southern Oscillation ◽

Flow Direction ◽

Open Pit ◽

Boreal Summer ◽

Boreal Winter ◽

Indonesian Throughflow ◽

Complete Evaluation ◽

Easterly Wind ◽

The Indian Ocean

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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Recent Atmospheric Variability at Kibo Summit, Kilimanjaro, and Its Relation to Climate Mode Activity

Journal of Climate ◽

10.1175/jcli-d-17-0551.1 ◽

2018 ◽

Vol 31 (10) ◽

pp. 3875-3891 ◽

Cited By ~ 5

Author(s):

Emily Collier ◽

Thomas Mölg ◽

Tobias Sauter

Keyword(s):

Indian Ocean ◽

Current Knowledge ◽

Southern Oscillation ◽

Strong Association ◽

Atmospheric Modeling ◽

High Mountain ◽

Atmospheric Variability ◽

Rain Season ◽

The Indian Ocean ◽

The Impact

Abstract Accurate knowledge of the impact of internal atmospheric variability is required for the detection and attribution of climate change and for interpreting glacier records. However, current knowledge of such impacts in high-mountain regions is largely based on statistical methods, as the observational data required for process-based assessments are often spatially or temporally deficient. Using a case study of Kilimanjaro, 12 years of convection-permitting atmospheric modeling are combined with an 8-yr observational record to evaluate the impact of climate oscillations on recent high-altitude atmospheric variability during the short rains (the secondary rain season in the region). The focus is on two modes that have a well-established relationship with precipitation during this season, El Niño–Southern Oscillation and the Indian Ocean zonal mode, and demonstrate their strong association with local and mesoscale conditions at Kilimanjaro. Both oscillations correlate positively with humidity fluctuations, but the association is strongest with the Indian Ocean zonal mode in the air layers near and above the glaciers because of changes in zonal circulation and moisture transport, emphasizing the importance of the moisture signal from this basin. However, the most anomalous conditions are found during co-occurring positive events because of the combined effects of the (i) extended positive sea surface temperature anomalies, (ii) enhanced atmospheric moisture capacity from higher tropospheric temperatures, (iii) most pronounced weakening of the subsiding branch of the Indian Ocean Walker circulation over East Africa, and (iv) stronger monsoonal moisture fluxes upstream from Kilimanjaro. This study lays the foundation for unraveling the contribution of climate modes to observed changes in Kilimanjaro’s glaciers.

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Impact of Indo-Pacific Feedback Interactions on ENSO Dynamics Diagnosed Using Ensemble Climate Simulations

Journal of Climate ◽

10.1175/jcli-d-11-00287.1 ◽

2012 ◽

Vol 25 (21) ◽

pp. 7743-7763 ◽

Cited By ~ 49

Author(s):

A. Santoso ◽

M. H. England ◽

W. Cai

Keyword(s):

Indian Ocean ◽

Climate Model ◽

Southern Oscillation ◽

Ocean Basin ◽

Climate Feedback ◽

Enso Events ◽

Thermocline Feedback ◽

Enso Dynamics ◽

The Indian Ocean ◽

The Impact

The impact of Indo-Pacific climate feedback on the dynamics of El Niño–Southern Oscillation (ENSO) is investigated using an ensemble set of Indian Ocean decoupling experiments (DCPL), utilizing a millennial integration of a coupled climate model. It is found that eliminating air–sea interactions over the Indian Ocean results in various degrees of ENSO amplification across DCPL simulations, with a shift in the underlying dynamics toward a more prominent thermocline mode. The DCPL experiments reveal that the net effect of the Indian Ocean in the control runs (CTRL) is a damping of ENSO. The extent of this damping appears to be negatively correlated to the coherence between ENSO and the Indian Ocean dipole (IOD). This type of relationship can arise from the long-lasting ENSO events that the model simulates, such that developing ENSO often coincides with Indian Ocean basin-wide mode (IOBM) anomalies during non-IOD years. As demonstrated via AGCM experiments, the IOBM enhances western Pacific wind anomalies that counteract the ENSO-enhancing winds farther east. In the recharge oscillator framework, this weakens the equatorial Pacific air–sea coupling that governs the ENSO thermocline feedback. Relative to the IOBM, the IOD is more conducive for ENSO growth. The net damping by the Indian Ocean in CTRL is thus dominated by the IOBM effect which is weaker with stronger ENSO–IOD coherence. The stronger ENSO thermocline mode in DCPL is consistent with the absence of any IOBM anomalies. This study supports the notion that the Indian Ocean should be viewed as an integral part of ENSO dynamics.

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The Impact of Indian Ocean Mean-State Biases in Climate Models on the Representation of the East African Short Rains

Journal of Climate ◽

10.1175/jcli-d-17-0804.1 ◽

2018 ◽

Vol 31 (16) ◽

pp. 6611-6631 ◽

Cited By ~ 11

Author(s):

Linda Hirons ◽

Andrew Turner

Keyword(s):

Indian Ocean ◽

Wind Stress ◽

Equatorial Indian Ocean ◽

East African ◽

Easterly Wind ◽

Low Level ◽

The Indian Ocean ◽

Short Rains ◽

The Impact ◽

Mean State

The role of the Indian Ocean dipole (IOD) in controlling interannual variability in the East African short rains, from October to December, is examined in state-of-the-art models and in detail in one particular climate model. In observations, a wet short-rainy season is associated with the positive phase of the IOD and anomalous easterly low-level flow across the equatorial Indian Ocean. A model’s ability to capture the teleconnection to the positive IOD is closely related to its representation of the mean state. During the short-rains season, the observed low-level wind in the equatorial Indian Ocean is westerly. However, half of the models analyzed exhibit mean-state easterlies across the entire basin. Specifically, those models that exhibit mean-state low-level equatorial easterlies in the Indian Ocean, rather than the observed westerlies, are unable to capture the latitudinal structure of moisture advection into East Africa during a positive IOD. Furthermore, the associated anomalous easterly surface wind stress causes upwelling in the eastern Indian Ocean. This upwelling draws up cool subsurface waters, enhancing the zonal sea surface temperature gradient between west and east and strengthening the positive IOD pattern, further amplifying the easterly wind stress. This positive Bjerknes coupled feedback is stronger in easterly mean-state models, resulting in a wetter East African short-rain precipitation bias in those models.

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ENSO response to changes in the tropical Indian ocean temperature

10.5194/egusphere-egu21-2881 ◽

2021 ◽

Author(s):

Brady Ferster ◽

Alexey Fedorov ◽

Juliette Mignot ◽

Eric Guilyardi

Keyword(s):

Indian Ocean ◽

Southern Oscillation ◽

Coupled Model ◽

Tropical Indian Ocean ◽

Equatorial Pacific ◽

Central Pacific ◽

Trade Winds ◽

Enso Variability ◽

The Mean ◽

Ensemble Experiments

Since the start of the 21st century, El Ni&#241;o-Southern Oscillation (ENSO) variability has changed, supporting generally weaker Central Pacific El Ni&#241;o events. Recent studies suggest that stronger trade winds in the equatorial Pacific could be a key driving force contributing to this shift. One possible mechanism to drive such changes in the mean tropical Pacific climate state is the enhanced warming trends in the tropical Indian Ocean (TIO) relative to the rest of the tropics. TIO warming can affect the Walker circulation in both the Pacific and Atlantic basins by inducing quasi-stationary Kelvin and Rossby wave patterns. Using the latest coupled-model from Insitut Pierre Simon Laplace (IPSL-CM6), ensemble experiments are conducted to investigate the effect of TIO sea surface temperature (SST) on ENSO variability. Applying a weak SST nudging over the TIO region, in four ensemble experiments we change mean Indian ocean SST by -1.4&#176;C, -0.7&#176;C, +0.7&#176;C, and +1.4&#176;C and find that TIO warming changes the magnitude of the mean equatorial Pacific zonal wind stress proportionally to the imposed forcing, with stronger trades winds corresponding to a warmer TIO. Surprisingly, ENSO variability increases in both TIO cooling and warming experiments, relative to the control. While a stronger ENSO for weaker trade winds, associated with TIO cooling, is expected from previous studies, we argue that the ENSO strengthening for stronger trade winds, associated with TIO cooling, is related to the induced changes in ocean stratification. We illustrate this effect by computing different contributions to the Bjerknes stability index. Thus, our results suggest that the tropical Indian ocean temperatures are an important regulator of TIO mean state and ENSO dynamics.

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Warming of the Indian Ocean weakens the Atlantic Niño - El Niño Southern Oscillation connection

10.5194/egusphere-egu21-13911 ◽

2021 ◽

Author(s):

Shreya Dhame ◽

Andréa Taschetto ◽

Agus Santoso ◽

Giovanni Liguori ◽

Katrin Meissner

Keyword(s):

Indian Ocean ◽

Atlantic Ocean ◽

Southern Oscillation ◽

Warming Trend ◽

Equatorial Pacific ◽

Ocean Warming ◽

The West ◽

Indian Ocean Warming ◽

The Indian Ocean ◽

Mean State

The tropical Indian Ocean has warmed by 1 degree Celsius since the mid-twentieth century. This warming is likely to continue as the atmospheric carbon dioxide levels keep rising. Here, we discuss how the warming trend could influence the El Ni&#241;o Southern Oscillation (ENSO) via interaction with the Pacific and the Atlantic Ocean mean state and variability. The warming trend leads to the strengthening of easterlies in the western equatorial Pacific, subsequent downwelling and increase of the mixed later depth in the west, and an increase in the subsurface temperature gradient across the equatorial Pacific. In the eastern equatorial Pacific, the response of upwelling ocean currents to surface wind stress decreases, resulting in a weakening of ENSO amplitude. The Indian Ocean warming influences ENSO via the Atlantic Ocean as well. There, it is associated with the strengthening of equatorial easterly winds, and anomalous warming in the west and upwelling induced cooling in the east, especially in austral winter, during the peak of the Atlantic Ni&#241;o. Consequently, this results in a decrease of the amplitude of Atlantic Ni&#241;o events and weakening of the Atlantic Ni&#241;o-ENSO teleconnection, thereby hindering the transition of El Ni&#241;o events to La Ni&#241;a events. Thus, the Indian Ocean warming trend is found to modulate tropical Pacific and Atlantic mean state and variability, with implications for ENSO predictability under a warming climate.

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Indo-Pacific warm pool expansion modulates MJO lifecycle

10.5194/egusphere-egu2020-1039 ◽

2020 ◽

Author(s):

Panini Dasgupta ◽

Roxy Mathew Koll ◽

Michael J. McPhaden ◽

Tamaki Suematsu ◽

Chidong Zhang ◽

...

Keyword(s):

Life Cycle ◽

Indian Ocean ◽

Southern Oscillation ◽

Average Rate ◽

Warm Pool ◽

Dominant Mode ◽

Maritime Continent ◽

Pacific Warm Pool ◽

The Indian Ocean ◽

The Impact

The Madden&#8211;Julian Oscillation (MJO) is the most dominant mode of intraseasonal variability in the tropics, characterized by an eastward propagating zonal circulation pattern and rain bands. MJO is very crucial phenomenon due to its interactions with other timescales of ocean-atmosphere like El Ni&#241;o Southern Oscillation, tropical cyclones, monsoons, and the extreme rainfall events all across the globe. MJO events travel almost half of the globe along the tropical oceans, majorly over the Indo-Pacific Warm Pool (IPWP) region. This IPWP region has been warming during the twentieth and early twenty- first centuries in response to increased anthropogenic emissions of greenhouse gases and is projected to warm further. However, the impact of the warming of the IPWP region on the MJO life cycle is largely unknown. Here we show that rapid warming over the IPWP region during 1981&#8211;2018 has significantly changed the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3&#8211;4 days, and increasing over the Indo-Pacific Maritime Continent by 5&#8211;6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool. The warm pool has been expanding on average by 2.3 &#215; 105 km2 per year during 1900&#8211;2018 and at an accelerated average rate of 4 &#215; 105 km2 per year during 1981&#8211;2018. The accelerated warm pool expansion has increased moisture in the lower and middle troposphere over IPWP and thereby increased the gradient of lower-middle tropospheric moisture between the Indian Ocean and western Pacific. This zonal gradient of moisture between the Indian Ocean and west Pacific and the increased subsidence over the Indian ocean due to increased convective duration of MJO over maritime continent are likely the reasons behind the changing lifecycle of MJO.

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Inter-Annual Variability of Boreal Summer Intra-Seasonal Oscillation Propagation from the Indian Ocean to the Western Pacific

Atmosphere ◽

10.3390/atmos10100596 ◽

2019 ◽

Vol 10 (10) ◽

pp. 596

Author(s):

Zhang ◽

Wang ◽

Liu

Keyword(s):

Indian Ocean ◽

Equatorial Pacific ◽

Boreal Summer ◽

Central Pacific ◽

Mean Motion ◽

Annual Variability ◽

Seasonal Oscillation ◽

Central Pacific Warming ◽

The Indian Ocean ◽

The Western Pacific

The inter-annual variability of boreal summer intra-seasonal oscillation (BSISO) propagation from the Indian Ocean (IO) to the western Pacific (WP) is investigated for the boreal summers (May to September) of 1979–2018. It is shown that the interannual variability of BSISO mainly happens in its evolution, not in its strength over the IO. Here, we classify four distinctive modes for inter-annual variability of BSISO propagation: (i) northeast mode, propagating from the IO to the western equatorial Pacific (WEP) and the western North Pacific (WNP); (ii) north-only mode, only propagating to the WNP; (iii) east-only mode, only propagating to the WEP; and (iv) stationary mode, propagating to neither the WEP nor the WNP. It is found that the Maritime Continent (MC) and WEP are two key regions determining these four modes concerning mean state moisture and vertical motion. Associated with central equatorial Pacific cooling, the BSISO of northeast and north-only modes can reach the WP by passing over the MC due to positive mean moisture anomalies and upward mean motion anomalies over the MC. The strong negative mean moisture anomalies and downward mean motion anomalies over the WEP, related to strong central Pacific cooling, prevents the development of BSISO there, resulting in north-only mode. For the east-only and stationary modes associated with the central Pacific warming, their BSISO can hardly pass the MC due to negative mean moisture anomalies and downward mean motion anomalies. The positive mean moisture anomalies and upward mean motion anomalies over the WEP related to strong central Pacific warming, however, will reinitiate the BSISO in the WEP for the east-only mode.

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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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