Contrasting Development and Decay Processes of Indian Ocean Dipoles in the 2000s

Horii, Takanori; Ueki, Iwao; Ando, Kenji

doi:10.2151/sola.2013-041

Cited by 7 publications

(4 citation statements)

References 31 publications

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“…The erosion of the initially thick barrier layer in this region is driven by the decrease in thermocline depth, rather than the reduction in the surface freshwater flux due to decreased precipitation [ Qiu et al ., ]. The thermocline shoaling is in turn the result of horizontal advection and wind‐induced upwelling of cooler waters [e.g., Du et al ., ; Halkides and Lee , ; Horii et al ., ], which may be related to the same upwelling Kelvin waves that produce anomalous cooling south of Java.…”

Section: Discussionmentioning

confidence: 99%

“…While cooling in the larger eastern EqIO in August–October has been attributed to a variety of mechanisms, including anomalous upwelling/advection and feedbacks with the atmosphere [ Murtugudde et al ., ; Vinayachandran et al ., ; Du et al ., ; Halkides and Lee , ; Horii et al ., ; Wang et al ., ], less is known about the specific processes for producing the earlier cool SST anomalies south of Java in May–July. In addition to alongshore wind‐induced seasonal SST cooling south of Java in austral winter, a variety of other processes contribute to mixed layer temperature changes in the region and may control the interannual variability of Java SST.…”

Section: Introductionmentioning

confidence: 99%

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Anomalous Java cooling at the initiation of positive Indian Ocean Dipole events

et al. 2016

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Anomalous sea surface temperature (SST) cooling south of Java, initiated during May–July, is an important precursor to positive Indian Ocean Dipole (pIOD) events. As shown previously, the Java SST anomalies are spatially and temporally coincident with seasonal upwelling induced locally by southeasterly trade winds. However, we confirm earlier findings that interannual variability of the Java cooling is primarily driven by remote wind forcing from coastal Sumatra and the equatorial Indian Ocean (EqIO); we also find an influence from winds along the Indonesian Throughflow. The wind forcing in the EqIO and along coastal Sumatra does not initiate SST cooling locally due to a deep thermocline and thick barrier layer, but can force upwelling Kelvin waves that induce substantial surface cooling once they reach the seasonally shallower thermocline near the coast of Java. Satellite altimetry is used to obtain a Kelvin wave coefficient that approximates Kelvin wave amplitude variations along the equator. All pIOD years in the satellite record have anomalous levels of upwelling Kelvin wave activity along the equator during April–June, suggesting that upwelling waves during this season are necessary for pIOD event development. However, a change to wind‐forced downwelling Kelvin waves during July–August can abruptly terminate cool Java SST anomalies and weaken the pIOD event. Upwelling Kelvin wave activity along the equator and wind stress anomalies west of Sumatra are both robust predictors of the IOD index later in the calendar year, while values of the Kelvin wave coefficient are the most reliable predictor of pIOD events specifically.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Anomalous Java cooling at the initiation of positive Indian Ocean Dipole events

et al. 2016

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“…Although we found a slight tendency for more SLD events before the onset of a positive IOD, the short period of reliable in situ data (2007–2012) prevented us from obtaining significant statics. In addition, only minor and moderate IOD events occurred during 2007–2012 [ Du et al ., ; Horii et al ., ], and in situ sea level data for the southern coast of Java were missing during significant IOD events such as those in 1994, 1997, and 2006. We are currently attempting to reconstruct the coastal upwelling signal using neighboring sea level data and will present the statistical analysis of the coastal upwelling signal and the occurrence of IOD in future reports.…”

Section: Discussionmentioning

confidence: 99%

Intraseasonal coastal upwelling signal along the southern coast of Java observed using Indonesian tidal station data

Horii

Ueki

Syamsudin³

et al. 2016

JGR Oceans

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Sea level variations along the coasts of Sumatra and Java were investigated to determine the coastal upwelling signal that is linked to local sea surface temperature (SST) variability. We used Indonesian tidal station data together with satellite SST data and atmospheric reanalysis data. The sea level variations along the southern coast of Java have a significant coherence with remote wind, local wind, and local SST variations, with an intraseasonal time scale of 20–50 days. Assuming that a coastal upwelling signal would appear as a sea level drop (SLD), we focused on intraseasonal‐scale SLD events in the data. Significant upwelling signals are frequently observed during both the boreal summer and winter. To evaluate the impact of the coastal upwelling on local SST, we examined statistical relationships between sea level and SST variations. The results demonstrated that events that occurred during April–August were associated with local SST cooling. The horizontal distribution of the SST cooling was analogous with annual mean SST, suggesting the importance of intraseasonal‐scale coastal upwelling in forming the climatic conditions of the southeastern tropical Indian Ocean.

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“…Given the key roles that the Java and Sumatra upwelling zones play in the onset and evolution of the IOD, the area has been the focus of numerous upper ocean and mixed layer temperature budget studies derived from observations (Horii et al, ), ocean general circulation models (OGCMs; Chen et al, ; Vinayachandran et al, ; Wang et al, ), and data assimilation reanalysis products (Du et al, ; Halkides & Lee, ). From composites of pIOD events, Du et al () attributed anomalous cooling south of Java to net surface heat fluxes (presumably from latent heat loss) and vertical entrainment (mostly associated with local wind forcing), but the weak correlations to local wind stress found by Chen et al () and Delman et al () are inconsistent with this explanation.…”

Section: Introductionmentioning

confidence: 99%

Process‐Specific Contributions to Anomalous Java Mixed Layer Cooling During Positive IOD Events

et al. 2018

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Negative sea surface temperature (SST) anomalies associated with positive Indian Ocean Dipole (pIOD) events first appear in the seasonal upwelling zone along the southern coast of Java during May–July. The evolution of anomalous SSTs in this coastal region is analyzed by computing a temperature budget using output from a strongly eddy‐active ocean general circulation model. The seasonal cooling south of Java in May–July is driven by a reduction in incoming shortwave radiation and by vertical mixing, consistent with earlier studies in the region; however, the model budget also shows an advective contribution that drives anomalous cooling at the onset of pIOD events. To identify which process(es) are responsible for the anomalous advective cooling during pIOD events, a novel process index regression method is used to estimate the contributions of wind stress, equatorial Kelvin waves, mesoscale eddies, and Lombok Strait flow to anomalous cooling south of Java. Using this method, wind stress forcing along the west coast of Sumatra is found to make the most substantial contribution to anomalous cooling south of Java, with lesser contributions from equatorially sourced Kelvin waves and local wind stress. Mesoscale eddies redistribute heat from the Lombok Strait outflow, and have an anomalous warming effect on the eastern side of the upwelling region. The process‐specific temperature budget south of Java highlights the importance of wind stress forcing west of Sumatra relative to equatorial and local forcing, and explains most of the mixed layer temperature anomaly evolution associated with advection during pIOD events.

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Contrasting Development and Decay Processes of Indian Ocean Dipoles in the 2000s

Cited by 7 publications

References 31 publications

Anomalous Java cooling at the initiation of positive Indian Ocean Dipole events

Anomalous Java cooling at the initiation of positive Indian Ocean Dipole events

Intraseasonal coastal upwelling signal along the southern coast of Java observed using Indonesian tidal station data

Process‐Specific Contributions to Anomalous Java Mixed Layer Cooling During Positive IOD Events

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