Relative importance of the processes contributing to the development of SST anomalies in the eastern pole of the Indian Ocean Dipole and its implication for predictability

AbstractThe Indian Ocean Dipole (IOD) is an interannual climate mode of the tropical Indian Ocean. Although it is known that negative sea surface temperature (SST) anomalies in the eastern pole during the positive IOD are stronger than positive SST anomalies during the negative IOD, no consensus has been reached on the relative importance of various mechanisms that contribute to this asymmetry. Based on a closed mixed layer heat budget analysis using a regional ocean model, here we show for the first time that the vertical mixing plays an important role in causing such asymmetry in SST anomalies in addition to the contributions from the nonlinear advection and the thermocline feedback proposed by previous studies. A decomposition of the vertical mixing term indicates that nonlinearity in the anomalous vertical temperature gradient associated with subsurface temperature anomalies and anomalous vertical mixing coefficients is the main driver of such asymmetry. Such variations in subsurface temperature are induced by the anomalous southeasterly trade winds along the Indonesian coast that modulate the thermocline depth through coastal upwelling/downwelling. Thus, the thermocline feedback contributes to the SST asymmetry not through the vertical advection as previously suggested, but via the vertical mixing.

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Impact of the South China Sea Summer Monsoon on the Indian Ocean Dipole

Journal of Climate ◽

10.1175/jcli-d-17-0815.1 ◽

2018 ◽

Vol 31 (16) ◽

pp. 6557-6573 ◽

Cited By ~ 7

Author(s):

Yazhou Zhang ◽

Jianping Li ◽

Jiaqing Xue ◽

Juan Feng ◽

Qiuyun Wang ◽

...

Keyword(s):

Indian Ocean ◽

South China Sea ◽

Summer Monsoon ◽

South China ◽

Indian Ocean Dipole ◽

The South China Sea ◽

The South ◽

China Sea ◽

The Indian Ocean ◽

Sst Anomalies

This paper investigates the impact of the South China Sea summer monsoon (SCSSM) on the Indian Ocean dipole (IOD). The results show that the SCSSM has a significant positive relationship with the IOD over the boreal summer [June–August (JJA)] and fall [September–November (SON)]. When the SCSSM is strong, the enhanced southwesterly winds that bring more water vapor to the western North Pacific (WNP) lead to surplus precipitation in the WNP, inducing anomalous ascending there. Consequently, the anomalous descending branch of the SCSSM Hadley circulation (SCSSMHC) develops over the Maritime Continent (MC), favoring deficit precipitation in situ. The precipitation dipole over the WNP and MC as well as the enhanced SCSSMHC leads to intensification of the southeasterly anomalies off Sumatra and Java, which then contributes to the negative sea surface temperature (SST) anomalies through the positive wind–evaporation–SST and wind–thermocline–SST (Bjerknes) feedbacks. Consequently, a positive IOD develops because of the increased zonal gradient of the tropical Indian Ocean SST anomalies and vice versa. The SCSSM has a peak correlation with the IOD when the former leads the latter by three months. This implies that a positive IOD can persist from JJA to SON and reach its mature phase within the frame of the positive Bjerknes feedback in SON. In addition, the local and remote SST anomalies in the tropical Indian and Pacific Oceans have a slight influence on the relationship between the SCSSM and precipitation dipole over the WNP and MC.

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Phytoplankton blooms induced/sustained by cyclonic eddies during the Indian Ocean Dipole event of 1997 along the southern coasts of Java and Sumatra

Biogeosciences Discussions ◽

10.5194/bgd-5-3905-2008 ◽

2008 ◽

Vol 5 (5) ◽

pp. 3905-3918 ◽

Cited By ~ 3

Author(s):

P. Rahul Chand Reddy ◽

P. S. Salvekar

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

State Of The Art ◽

Sea Surface ◽

Phytoplankton Blooms ◽

Indian Ocean Dipole Event ◽

Indonesian Archipelago ◽

The Indian Ocean ◽

The Tropics ◽

Sst Anomalies

Abstract. The Indonesian archipelago is the gateway in the tropics connecting two oceans (Pacific and the Indian Ocean) and two continents (Asia and Australia). During the Indian Ocean Dipole 1997, record anomalous and unanticipated upwelling had occurred along the southern coasts of Java and Sumatra causing massive phytoplankton blooms. But the method/mode/process for such anomalous upwelling was not known. Using monthly SeaWifs chlorophyll-a anomalies, TOPEX Sea Surface Height (SSH) anomalies, Sea Surface Temperatures (SST) and currents from a state-of-the-art OGCM, we report the presence of a series of cyclonic eddies along southern coasts of Sumatra and Java during November, December 1997 and January 1998. Upwelling caused by these cyclonic eddies, as also supported by the SSH and SST anomalies, has been responsible for the phytoplankton blooms to persist and dissipate during the 3 months (November, December 1997 and January 1998).

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An Observation-Based Assessment of Nonlinear Feedback Processes Associated with the Indian Ocean Dipole

Journal of Climate ◽

10.1175/jcli-d-12-00483.1 ◽

2013 ◽

Vol 26 (9) ◽

pp. 2880-2890 ◽

Cited By ~ 29

Author(s):

Wenju Cai ◽

Yun Qiu

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Shortwave Radiation ◽

Heating Process ◽

Evaporative Heat Loss ◽

Damping Effect ◽

Temperature Feedback ◽

The Indian Ocean ◽

Sst Anomalies

Abstract A well-known feature of the Indian Ocean dipole (IOD) is its positive skewness, with cold sea surface temperature (SST) anomalies over the east pole (IODE) exhibiting a larger amplitude than warm SST anomalies. Several mechanisms have been proposed for this asymmetry, but because of a lack of observations the role of various processes remains contentious. Using Argo profiles and other newly available data, the authors provide an observation-based assessment of the IOD skewness. First, the role of a nonlinear dynamical heating process is reaffirmed, which reinforces IODE cold anomalies but damps IODE warm anomalies. This reinforcing effect is greater than the damping effect, further contributing to the skewness. Second, the existence of a thermocline–temperature feedback asymmetry, whereby IODE cold anomalies induced by a shoaling thermocline are greater than warm anomalies associated with a deepening thermocline, is the primary forcing of the IOD skewness. This thermocline–temperature feedback asymmetry is a part of the nonlinear Bjerknes-like positive feedback loop involving winds, SST, and the thermocline, all displaying a consistent asymmetry with a stronger response when IODE SST is anomalously cold. The asymmetry is enhanced by a nonlinear barrier layer response, with a greater thinning associated with IODE cold anomalies than a thickening associated with IODE warm anomalies. Finally, in response to IODE cool anomalies, rainfall and evaporative heat loss diminish and incoming shortwave radiation increases, which results in damping the cool SST anomalies. The damping increases with IODE cold anomalies. Thus, the IOD skewness is generated in spite of a greater damping effect of the SST–cloud–radiation feedback process.

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Impact of the South China Sea summer monsoon on the Indian Ocean dipole in CMIP5 models

Journal of Climate ◽

10.1175/jcli-d-20-0582.1 ◽

2020 ◽

pp. 1

Author(s):

Yazhou Zhang ◽

Jianping Li ◽

Fei Zheng ◽

Miao Yu ◽

Juan Feng ◽

...

Keyword(s):

Indian Ocean ◽

South China Sea ◽

Summer Monsoon ◽

South China ◽

Indian Ocean Dipole ◽

Cmip5 Models ◽

Physical Processes ◽

Low Level ◽

The Indian Ocean ◽

Sst Anomalies

AbstractThe impact of the South China Sea summer monsoon (SCSSM) on the Indian Ocean dipole (IOD) has been systematically investigated in observations. This study focuses on the ability of climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) to reproduce the observed relationship between the SCSSM and IOD, and the relevant physical mechanisms. All 23 models reproduce significant correlations between the SCSSM and IOD during boreal summer (June–July–August, JJA), whereas the influence of the SCSSM on the IOD varies considerably across the CMIP5 models. To explore the causes, all models are divided into two groups. Models that successfully simulated both the correlations between the SCSSM and JJA IOD and of the SCSSM and JJA IOD with precipitation over the western North Pacific and Maritime Continent are classified as Type-I, and these produce stronger low-level wind anomalies over the tropical southeastern Indian Ocean. The stronger low-level wind anomalies enhance local sea surface temperature (SST) anomalies via positive wind–evaporation–SST (WES) and wind–thermocline–SST (Bjerknes) feedbacks. This corresponds to a strengthening of IOD events due to the increased zonal gradient of SST anomalies over the tropical Indian Ocean. In contrast, Type-II models perform poorly in representing the relationship between the SCSSM and JJA IOD or relevant physical processes, corresponding to weaker WES and Bjerknes feedbacks, and produce weaker IOD events. These results demonstrate that the better the model simulation of the critical physical processes, the larger contribution of the SCSSM to the IOD.

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Analysis of Drought-Sensitive Areas and Evolution Patterns through Statistical Simulations of the Indian Ocean Dipole Mode

Water ◽

10.3390/w11061302 ◽

2019 ◽

Vol 11 (6) ◽

pp. 1302 ◽

Cited By ~ 2

Author(s):

Qing-Gang Gao ◽

Vonevilay Sombutmounvong ◽

Lihua Xiong ◽

Joo-Heon Lee ◽

Jong-Suk Kim

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Diagnostic Techniques ◽

Eastern Coast ◽

Indochina Peninsula ◽

Indian Ocean Dipole Mode ◽

Sensitive Areas ◽

The Indian Ocean ◽

Long Term Trend

In this study, we investigated extreme droughts in the Indochina peninsula and their relationship with the Indian Ocean Dipole (IOD) mode. Areas most vulnerable to drought were analyzed via statistical simulations of the IOD based on historical observations. Results of the long-term trend analysis indicate that areas with increasing spring (March–May) rainfall are mainly distributed along the eastern coast (Vietnam) and the northwestern portions of the Indochina Peninsula (ICP), while Central and Northern Laos and Northern Cambodia have witnessed a reduction in spring rainfall over the past few decades. This trend is similar to that of extreme drought. During positive IOD years, the frequency of extreme droughts was reduced throughout Vietnam and in the southwestern parts of China, while increased drought was observed in Cambodia, Central Laos, and along the coastline adjacent to the Myanmar Sea. Results for negative IOD years were similar to changes observed for positive IOD years; however, the eastern and northern parts of the ICP experienced reduced droughts. In addition, the results of the statistical simulations proposed in this study successfully simulate drought-sensitive areas and evolution patterns of various IOD changes. The results of this study can help improve diagnostic techniques for extreme droughts in the ICP.

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Influence of the Indian Ocean Dipole on tree-ring δ18O of monsoonal Southeast Tibet

Climatic Change ◽

10.1007/s10584-016-1663-8 ◽

2016 ◽

Vol 137 (1-2) ◽

pp. 217-230 ◽

Cited By ~ 14

Author(s):

Philipp Hochreuther ◽

Jakob Wernicke ◽

Jussi Grießinger ◽

Thomas Mölg ◽

Haifeng Zhu ◽

...

Keyword(s):

Indian Ocean ◽

Tree Ring ◽

Indian Ocean Dipole ◽

The Indian Ocean ◽

Southeast Tibet

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Two Independent Triggers for the Indian Ocean Dipole/Zonal Mode in a Coupled GCM

Journal of Climate ◽

10.1175/jcli3478.1 ◽

2005 ◽

Vol 18 (17) ◽

pp. 3428-3449 ◽

Cited By ~ 114

Author(s):

Albert S. Fischer ◽

Pascal Terray ◽

Eric Guilyardi ◽

Silvio Gualdi ◽

Pascale Delecluse

Keyword(s):

Indian Ocean ◽

El Niño ◽

Indian Ocean Dipole ◽

El Nino ◽

Tropical Indian Ocean ◽

Sea Surface ◽

Dynamical Response ◽

Thermocline Depth ◽

Second Phase ◽

The Indian Ocean

Abstract The question of whether and how tropical Indian Ocean dipole or zonal mode (IOZM) interannual variability is independent of El Niño–Southern Oscillation (ENSO) variability in the Pacific is addressed in a comparison of twin 200-yr runs of a coupled climate model. The first is a reference simulation, and the second has ENSO-scale variability suppressed with a constraint on the tropical Pacific wind stress. The IOZM can exist in the model without ENSO, and the composite evolution of the main anomalies in the Indian Ocean in the two simulations is virtually identical. Its growth depends on a positive feedback between anomalous equatorial easterly winds, upwelling equatorial and coastal Kelvin waves reducing the thermocline depth and sea surface temperature off the coast of Sumatra, and the atmospheric dynamical response to the subsequently reduced convection. Two IOZM triggers in the boreal spring are found. The first is an anomalous Hadley circulation over the eastern tropical Indian Ocean and Maritime Continent, with an early northward penetration of the Southern Hemisphere southeasterly trades. This situation grows out of cooler sea surface temperatures in the southeastern tropical Indian Ocean left behind by a reinforcement of the late austral summer winds. The second trigger is a consequence of a zonal shift in the center of convection associated with a developing El Niño, a Walker cell anomaly. The first trigger is the only one present in the constrained simulation and is similar to the evolution of anomalies in 1994, when the IOZM occurred in the absence of a Pacific El Niño state. The presence of these two triggers—the first independent of ENSO and the second phase locking the IOZM to El Niño—allows an understanding of both the existence of IOZM events when Pacific conditions are neutral and the significant correlation between the IOZM and El Niño.

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