Understanding the origins of interannual thermocline variations in the tropical Indian Ocean

Yu, Weidong; Xiang, Baoqiang; Lin, Liu; Liu, Na

doi:10.1029/2005gl024327

Cited by 159 publications

(160 citation statements)

References 22 publications

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“…Chambers et al [1999] and Xie et al [2002] demonstrated that the STIO subsurface variations are mainly associated with ENSO forcing, while Rao and Behera [2005] showed that Rossby waves formed in the region 5 S-10 S are largely due to IOD. Yu et al [2005] showed that the Rossby waves associated with IOD dominate north of 10 S while ENSO forcing dominates south of 10 S. In the cooccurrence years, the southwest TIO shows a strong and sustained warming due to strong downwelling Rossby waves [Chakravorty et al, 2013]. However, the mechanisms for the generation/maintenance of these Rossby waves during the cooccurrence years are not yet clearly understood.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, in cooccurrence years the southwest TIO displays strong and sustained warming due to the presence of downwelling Rossby waves. According to the previous studies [Rao and Behera, 2005;Yu et al, 2005], wind stress curl associated with IOD events are responsible for westward propagating downwelling Rossby waves. Figure 1 illustrates the time-longitude composite of SSH and wind stress curl anomalies at different latitudinal belts for pure El Niño (left), cooccurrence (middle), and pure IOD (right) years.…”

Section: Observed Interannual Variability In the Stio Rossby Wavesmentioning

confidence: 99%

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Relative role of El Niño and IOD forcing on the southern tropical Indian Ocean Rossby waves

et al. 2014

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The role of local air-sea interactions over the tropical Indian Ocean (TIO) and remote forcing from the tropical Pacific Ocean in the formation and maintenance of southern TIO Rossby waves during El Niño and positive Indian Ocean Dipole (IOD) years is investigated. These Rossby waves are significantly intensified during the El Niño and IOD cooccurrence years, as compared to those during pure El Niño or IOD years. Coupled ocean-atmosphere model sensitivity experiments reveal that air-sea coupled processes in the TIO are responsible for the Rossby wave formation and its maintenance from boreal summer to fall, while remote forcing from the Pacific intensifies and maintains these waves up to the following spring. During the cooccurrence years, the Rossby waves are generated by both the persistent equatorial easterlies and off-equatorial wind stress curl. During pure El Niño years, however, only off-equatorial wind stress curl exists to drive weak Rossby wave. Asymmetric heating associated with IOD and the mean background easterly vertical wind shear (in the northern hemisphere) during summer and fall excite two symmetric anticyclones in both sides of the equator as atmospheric Rossby wave response, which are responsible for the anomalous equatorial surface easterlies. In contrast, symmetric heat sink over the Maritime Continent in winter associated with El Niño-induced subsidence and mean easterly vertical shear (in southern hemisphere) are responsible for strong anticyclone in the southern TIO, which supports off-equatorial wind stress curl.

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Section: Introductionmentioning

confidence: 99%

Section: Observed Interannual Variability In the Stio Rossby Wavesmentioning

confidence: 99%

Relative role of El Niño and IOD forcing on the southern tropical Indian Ocean Rossby waves

et al. 2014

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“…This downwelling Rossby wave propagates westward and suppresses the upwelling in the thermocline dome (e.g. Masumoto and Meyers 1998;Yu et al 2005). Through this mechanism, the SWIO SST warms up and persists to the summer even as El Niño decays (Xie et al 2002).…”

Section: Introduction Introduction Introduction Introductionmentioning

confidence: 99%

Indian Ocean Variability in the CMIP5 Multimodel Ensemble: The Basin Mode

Xie

Yang

et al. 2013

Journal of Climate

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This study evaluates the simulation of the Indian Ocean Basin (IOB) mode and relevant physical processes in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Historical runs from 20 CMIP5 models are available for the analysis. They reproduce the IOB mode and its close relationship to El Niño–Southern Oscillation (ENSO). Half of the models capture key IOB processes: a downwelling oceanic Rossby wave in the southern tropical Indian Ocean (TIO) precedes the IOB development in boreal fall and triggers an antisymmetric wind anomaly pattern across the equator in the following spring. The anomalous wind pattern induces a second warming in the north Indian Ocean (NIO) through summer and sustains anticyclonic wind anomalies in the northwest Pacific by radiating a warm tropospheric Kelvin wave. The second warming in the NIO is indicative of ocean–atmosphere interaction in the interior TIO. More than half of the models display a double peak in NIO warming, as observed following El Niño, while the rest show only one winter peak. The intermodel diversity in the characteristics of the IOB mode seems related to the thermocline adjustment in the south TIO to ENSO-induced wind variations. Almost all the models show multidecadal variations in IOB variance, possibly modulated by ENSO.

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“…For the POST epoch, thermocline depressions begin to develop and amplify in the eastern half of the basin during September(0) to December(0) in response to in situ downwelling Ekman pumping. The Ekman pumping is associated with an anomalous anticyclone that develops over the southeast TIO during the developing phase of El Niñ o and/or the Indian Ocean dipole (IOD) Yu et al 2005;Rao and Behera 2005). [The IOD is the zonal mode of the equatorial Indian Ocean involving Bjerknes feedback (Saji et al 1999;Webster et al 1999). ]…”

Section: Indian Ocean Responsementioning

confidence: 99%

Decadal Shift in El Niño Influences on Indo–Western Pacific and East Asian Climate in the 1970s*

et al. 2010

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El Niñ o's influence on the subtropical northwest (NW) Pacific climate increased after the climate regime shift of the 1970s. This is manifested in well-organized atmospheric anomalies of suppressed convection and a surface anticyclone during the summer (June-August) of the El Niñ o decay year [JJA(1)], a season when equatorial Pacific sea surface temperature (SST) anomalies have dissipated. In situ observations and oceanatmospheric reanalyses are used to investigate mechanisms for the interdecadal change. During JJA(1), the influence of the El Niñ o-Southern Oscillation (ENSO) on the NW Pacific is indirect, being mediated by SST conditions over the tropical Indian Ocean (TIO). The results here show that interdecadal change in this influence is due to changes in the TIO response to ENSO.During the postregime shift epoch, the El Niñ o teleconnection excites downwelling Rossby waves in the south TIO by anticyclonic wind curls. These Rossby waves propagate slowly westward, causing persistent SST warming over the thermocline ridge in the southwest TIO. The ocean warming induces an antisymmetric wind pattern across the equator, and the anomalous northeasterlies cause the north Indian Ocean to warm through JJA(1) by reducing the southwesterly monsoon winds. The TIO warming excites a warm Kelvin wave in tropospheric temperature, resulting in robust atmospheric anomalies over the NW Pacific that include the surface anticyclone. During the preregime shift epoch, ENSO is significantly weaker in variance and decays earlier than during the recent epoch. Compared to the epoch after the mid-1970s, SST and wind anomalies over the TIO are similar during the developing and mature phases of ENSO but are very weak during the decay phase. Specifically, the southern TIO Rossby waves are weaker, so are the antisymmetric wind pattern and the North Indian Ocean warming during JJA(1). Without the anchor in the TIO warming, atmospheric anomalies over the NW Pacific fail to develop during JJA(1) prior to the mid-1970s. The relationship of the interdecadal change to global warming and implications for the East Asian summer monsoon are discussed.

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Understanding the origins of interannual thermocline variations in the tropical Indian Ocean

Cited by 159 publications

References 22 publications

Relative role of El Niño and IOD forcing on the southern tropical Indian Ocean Rossby waves

Relative role of El Niño and IOD forcing on the southern tropical Indian Ocean Rossby waves

Indian Ocean Variability in the CMIP5 Multimodel Ensemble: The Basin Mode

Decadal Shift in El Niño Influences on Indo–Western Pacific and East Asian Climate in the 1970s*

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