A numerical investigation of eddy-induced chlorophyll bloom in the southeastern tropical Indian Ocean during Indian Ocean Dipole—2006

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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Inter-basin and Multi-time Scale Interactions in generating the 2019 Extreme Indian Ocean Dipole

Journal of Climate ◽

10.1175/jcli-d-20-0760.1 ◽

2021 ◽

pp. 1-39

Author(s):

Lei Zhang ◽

Weiqing Han ◽

Zeng-Zhen Hu

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Intraseasonal Oscillation ◽

Tropical Indian Ocean ◽

Forecast Model ◽

Tropical Pacific ◽

Boreal Summer ◽

Indian Ocean Dipole Event ◽

Easterly Wind ◽

Western Tropical Pacific

AbstractAn unprecedented extreme positive Indian Ocean Dipole event (pIOD) occurred in 2019, which has caused widespread disastrous impacts on countries bordering the Indian Ocean, including the East African floods and vast bushfires in Australia. Here we investigate the causes for the 2019 pIOD by analyzing multiple observational datasets and performing numerical model experiments. We find that the 2019 pIOD is triggered in May by easterly wind bursts over the tropical Indian Ocean associated with the dry phase of the boreal summer intraseasonal oscillation, and sustained by the local atmosphere-ocean interaction thereafter. During September-November, warm sea surface temperature anomalies (SSTA) in the central-western tropical Pacific further enhance the Indian Ocean’s easterly winds, bringing the pIOD to an extreme magnitude. The central-western tropical Pacific warm SSTA is strengthened by two consecutive Madden Julian Oscillation (MJO) events that originate from the tropical Indian Ocean. Our results highlight the important roles of cross-basin and cross-timescale interactions in generating extreme IOD events. The lack of accurate representation of these interactions may be the root for a short lead time in predicting this extreme pIOD with a state-of-the-art climate forecast model.

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The Interdecadal Variations and Causes of the Relationship Between Autumn Precipitation Anomalies in Eastern China and SSTA Over the Southeastern Tropical Indian Ocean

10.21203/rs.3.rs-1150525/v1 ◽

2021 ◽

Author(s):

Liwei Huo ◽

Zhaoyong Guan ◽

Dachao Jin ◽

Xi Liu ◽

Xudong Wang ◽

...

Keyword(s):

Indian Ocean ◽

Eastern China ◽

Tropical Indian Ocean ◽

The Other ◽

Drought Event ◽

Low Level ◽

Rainfall Anomalies ◽

Precipitation Anomalies ◽

The Relationship ◽

Southeastern Tropical Indian Ocean

Abstract Eastern China has a large population with rapid development of the economy, where is the important crop producing region. In this region, the spatial and temporal distribution of autumn rainfall in Eastern China is uneven, which has important societal impact. Using the NCEP–NCAR reanalysis and other observational datasets, it is found that the spatial distribution of the first EOF mode of autumn rainfall anomalies in eastern China is consistent across the region, with significant interannual variabilities. Pronounced interdecadal variations are presented in the relationship between autumn rainfall anomalies in eastern China and sea-surface temperature anomalies (SSTA) over the southeastern tropical Indian Ocean (SETIO). The interdecadal changes have been analyzed by considering two epochs: one during 1979-2004 and the other during 2005-2019. It shows weak and insignificant correlations between the autumn rainfall anomalies in eastern China and SSTA over SETIO during the first epoch. On the other hand, they are remarkable and positively correlated with each other during the second epoch. The inter-decadal changes of the above relationship are related to the warming of SST over SETIO during the second epoch. It causes stronger low-level convergence and ascending motion over SETIO, with the co-occurrence of enhanced western Pacific subtropical high and anomalous abundant moisture over eastern China carried by a low-level southerly anomaly originating from the South China Sea. Simultaneously, the local Hadley circulation over eastern China becomes weak, corresponding to the anomalous ascending motion. The collaboration of anomalous water vapour transport and ascending motion strengthens the connection between the SETIO SSTA and the autumn precipitation anomalies in eastern China, and vice versa. In the boreal autumn of 2019, entire eastern China suffered extreme drought. It suggests that this drought event in eastern China is strongly affected by the negative SSTA over SETIO, which is consistent with the statistical results.

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El Niño-Southern Oscillation and Indian Ocean Dipole Modes: Their Effects on South American Rainfall during Austral Spring

Atmosphere ◽

10.3390/atmos12111437 ◽

2021 ◽

Vol 12 (11) ◽

pp. 1437

Author(s):

Mary T. Kayano ◽

Wilmar L. Cerón ◽

Rita V. Andreoli ◽

Rodrigo A. F. Souza ◽

Itamara P. Souza ◽

...

Keyword(s):

Indian Ocean ◽

El Niño ◽

Indian Ocean Dipole ◽

El Nino ◽

Southern Oscillation ◽

Tropical Indian Ocean ◽

El Niño Southern Oscillation ◽

El Nino Southern Oscillation ◽

Austral Spring ◽

Precipitation Anomalies

This paper examines the effects of the tropical Pacific Ocean (TPO) and Indian Ocean Dipole (IOD) modes in the interannual variations of austral spring rainfall over South America (SA). The TPO mode refers to the El Niño-Southern Oscillation (ENSO). The isolated effects between IOD and TPO were estimated, events were chosen from the residual TPO (R-TPO) or residual IOD (R-IOD), and the IOD (TPO) effects for the R-TPO (R-IOD) composites were removed from the variables. One relevant result was the nonlinear precipitation response to R-TPO and R-IOD. This feature was accentuated for the R-IOD composites. The positive R-IOD composite showed significant negative precipitation anomalies along equatorial SA east of 55° W and in subtropical western SA, and showed positive anomalies in northwestern SA and central Brazil. The negative R-IOD composite indicated significant positive precipitation anomalies in northwestern Amazon, central–eastern Brazil north of 20° S, and western subtropical SA, and negative anomalies were found in western SA south of 30° S. This nonlinearity was likely due to the distinct atmospheric circulation responses to the anomalous heating sources located in longitudinally distinct regions: the western tropical Indian Ocean and areas neighboring Indonesia. The results obtained in this study might be relevant for climate monitoring and modeling studies.

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Air–sea interactions in tropical Indian Ocean: The Indian Ocean Dipole

Tropical and Extratropical Air-Sea Interactions ◽

10.1016/b978-0-12-818156-0.00001-0 ◽

2021 ◽

pp. 115-139

Author(s):

Swadhin Kumar Behera ◽

Takeshi Doi ◽

J. Venkata Ratnam

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Tropical Indian Ocean ◽

The Indian Ocean

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Atmospheric energetics over the tropical Indian Ocean during Indian Ocean dipole events

Climate Dynamics ◽

10.1007/s00382-018-4510-y ◽

2018 ◽

Vol 52 (9-10) ◽

pp. 6243-6256 ◽

Cited By ~ 2

Author(s):

Yuehong Wang ◽

Jianping Li ◽

Yazhou Zhang ◽

Qiuyun Wang ◽

Jianhuang Qin

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Tropical Indian Ocean ◽

Atmospheric Energetics

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Realism of the Indian Ocean Dipole in CMIP5 Models: The Implications for Climate Projections

Journal of Climate ◽

10.1175/jcli-d-12-00807.1 ◽

2013 ◽

Vol 26 (17) ◽

pp. 6649-6659 ◽

Cited By ~ 45

Author(s):

Evan Weller ◽

Wenju Cai

Keyword(s):

Indian Ocean ◽

Indian Ocean Dipole ◽

Climate Models ◽

Tropical Indian Ocean ◽

Cmip5 Models ◽

Climate Projections ◽

Coupled Models ◽

Austral Spring ◽

Wide Range ◽

The Indian Ocean

Abstract An assessment of how well climate models simulate the Indian Ocean dipole (IOD) is undertaken using 20 coupled models that have partaken in phase 5 of the Coupled Model Intercomparison Project (CMIP5). Compared with models in phase 3 (CMIP3), no substantial improvement is evident in the simulation of the IOD pattern and/or amplitude during austral spring [September–November (SON)]. The majority of models in CMIP5 generate a larger variance of sea surface temperature (SST) in the Sumatra–Java upwelling region and an IOD amplitude that is far greater than is observed. Although the relationship between precipitation and tropical Indian Ocean SSTs is well simulated, future projections of SON rainfall changes over IOD-influenced regions are intrinsically linked to the IOD amplitude and its rainfall teleconnection in the model present-day climate. The diversity of the simulated IOD amplitudes in models in CMIP5 (and CMIP3), which tend to be overly large, results in a wide range of future modeled SON rainfall trends over IOD-influenced regions. The results herein highlight the importance of realistically simulating the present-day IOD properties and suggest that caution should be exercised in interpreting climate projections in the IOD-affected regions.

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