Seasonal Variation of the Indonesian Throughflow in Makassar Strait

2012 ◽  
Vol 42 (7) ◽  
pp. 1099-1123 ◽  
Author(s):  
Toshiaki Shinoda ◽  
Weiqing Han ◽  
E. Joseph Metzger ◽  
Harley E. Hurlburt
Keyword(s):  
Seasonal Variation ◽  
Indian Ocean ◽  
Wind Stress ◽  
General Circulation ◽  
Ocean Currents ◽  
Upper Ocean ◽  
Indonesian Throughflow ◽  
Subsequent Recovery ◽  
Model Experiments ◽  
The Pacific

Abstract The seasonal variation of Indonesian Throughflow (ITF) transport is investigated using ocean general circulation model experiments with the Hybrid Coordinate Ocean Model (HYCOM). Twenty-eight years (1981–2008) of ⅓° Indo-Pacific basin HYCOM simulations and three years (2004–06) from a global HYCOM simulation are analyzed. Both models are able to simulate the seasonal variation of upper-ocean currents and the total transport through Makassar Strait measured by International Nusantara Stratification and Transport (INSTANT) moorings reasonably well. The annual cycle of upper-ocean currents is then calculated from the Indo-Pacific HYCOM simulation. The reduction of southward currents at Makassar Strait during April–May and October–November is evident, consistent with the INSTANT observations. Analysis of the upper-ocean currents suggests that the reduction in ITF transport during April–May and October–November results from the wind variation in the tropical Indian Ocean through the generation of a Wyrtki jet and the propagation of coastal Kelvin waves, while the subsequent recovery during January–March originates from upper-ocean variability associated with annual Rossby waves in the Pacific that are enhanced by western Pacific winds. These processes are also found in the global HYCOM simulation during the period of the INSTANT observations. The model experiments forced with annual-mean climatological wind stress in the Pacific and 3-day mean wind stress in the Indian Ocean show the reduction of southward currents at Makassar Strait during October–November but no subsequent recovery during January–March, confirming the relative importance of wind variations in the Pacific and Indian Oceans for the ITF transport in each season.

scholarly journals Seasonal Variation of the Seychelles Dome

2008 ◽  
Vol 21 (15) ◽  
pp. 3740-3754 ◽  
Author(s):  
Takaaki Yokoi ◽  
Tomoki Tozuka ◽  
Toshio Yamagata
Keyword(s):  
Seasonal Variation ◽  
Indian Ocean ◽  
Wind Stress ◽  
Zonal Wind ◽  
General Circulation ◽  
Indian Monsoon ◽  
Circulation Model ◽  
The Other ◽  
Boreal Summer ◽  
Zonal Wind Stress

Abstract Using an ocean general circulation model (OGCM), seasonal variation of the Seychelles Dome (SD) is investigated for the first time. The SD is an oceanic thermal dome located in the southwestern Indian Ocean, and its influence on sea surface temperature is known to play an important role in the Indian monsoon system. Its seasonal variation is dominated by a remarkable semiannual cycle resulting from local Ekman upwelling. This semiannual nature is explained by different contributions of the following two components of the Ekman pumping: one term that is proportional to the planetary beta and the zonal wind stress and the other term that is proportional to the wind stress curl. The former is determined by the seasonal change in the zonal component of the wind stress vector above the SD; it is associated with the Indian monsoon and causes downwelling (upwelling) during boreal summer (boreal winter). The latter, whose major contribution comes from the meridional gradient of the zonal wind stress, also shows a clear annual cycle with strong upwelling during boreal summer and fall. However, it remains almost constant for 5 months from June to October, even though the zonal wind stress itself varies significantly during this period. The above overall feature is due to the unique location of the SD; it is located between the following two regions: one is dominated by the seasonal variation in wind stress resulting from the Indian monsoon, and the other is dominated by the southeasterly trade winds that prevail throughout a year. The above uniqueness provides a novel mechanism that causes the strong semiannual cycle in the tropical Indian Ocean.

Variability of Intraseasonal Kelvin Waves in the Equatorial Pacific Ocean

2008 ◽  
Vol 38 (5) ◽  
pp. 921-944 ◽  
Author(s):  
Toshiaki Shinoda ◽  
Paul E. Roundy ◽  
George N. Kiladis
Keyword(s):  
Wind Stress ◽  
General Circulation ◽  
Phase Speed ◽  
Circulation Model ◽  
Kelvin Waves ◽  
Upper Ocean ◽  
Equatorial Pacific Ocean ◽  
Model Experiments ◽  
Stress Changes ◽  
Background State

Abstract Previous observational work has demonstrated that the phase speed of oceanic equatorial Kelvin waves forced by the Madden–Julian oscillation (MJO) appears to vary substantially. Processes that are responsible for systematic changes in the phase speed of these waves are examined using an ocean general circulation model. The model was integrated for 26 yr with daily wind stress derived from the NCEP–NCAR reanalysis. The model is able to reproduce observed systematic changes of Kelvin wave phase speed reasonably well, providing a tool for the analysis of their dynamics. The relative importance of the upper ocean background state and atmospheric forcing for phase speed changes is determined based on a series of model experiments with various surface forcings. Systematic changes in phase speed are evident in all model experiments that have different slowly varying basic states, showing that variations of the upper ocean background state are not the primary cause of the changes. The model experiments that include and exclude intraseasonal components of wind stress in the eastern Pacific demonstrate that wind stress changes to the east of the date line can significantly alter the speed of Kelvin waves initially generated over the western Pacific, which often results in a phase propagation faster than the free wave speed. These faster waves contribute to the systematic changes of phase speed evident in observations. Similar results are also obtained using a linear stratified model, eliminating nonlinearity as a possible cause of the phase speed changes.

scholarly journals Impact of the Madden–Julian Oscillation on the Indonesian Throughflow in the Makassar Strait during the CINDY/DYNAMO Field Campaign

2016 ◽  
Vol 29 (17) ◽  
pp. 6085-6108 ◽  
Author(s):  
Toshiaki Shinoda ◽  
Weiqing Han ◽  
Tommy G. Jensen ◽  
Luis Zamudio ◽  
E. Joseph Metzger ◽  
...  
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Indonesian Throughflow ◽  
Madden Julian Oscillation ◽  
Field Campaign ◽  
Eastern Boundary ◽  
The Indian Ocean ◽  
Velocity Anomalies

Abstract Previous studies indicate that equatorial zonal winds in the Indian Ocean can significantly influence the Indonesian Throughflow (ITF). During the Cooperative Indian Ocean Experiment on Intraseasonal Variability (CINDY)/Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign, two strong MJO events were observed within a month without a clear suppressed phase between them, and these events generated exceptionally strong ocean responses. Strong eastward currents along the equator in the Indian Ocean lasted more than one month from late November 2011 to early January 2012. The influence of these unique MJO events during the field campaign on ITF variability is investigated using a high-resolution (1/25°) global ocean general circulation model, the Hybrid Coordinate Ocean Model (HYCOM). The strong westerlies associated with these MJO events, which exceed 10 m s−1, generate strong equatorial eastward jets and downwelling near the eastern boundary. The equatorial jets are realistically simulated by the global HYCOM based on the comparison with the data collected during the field campaign. The analysis demonstrates that sea surface height (SSH) and alongshore velocity anomalies at the eastern boundary propagate along the coast of Sumatra and Java as coastal Kelvin waves, significantly reducing the ITF transport at the Makassar Strait during January–early February. The alongshore velocity anomalies associated with the Kelvin wave significantly leads SSH anomalies. The magnitude of the anomalous currents at the Makassar Strait is exceptionally large because of the unique feature of the MJO events, and thus the typical seasonal cycle of ITF could be significantly altered by strong MJO events such as those observed during the CINDY/DYNAMO field campaign.

scholarly journals On the Indonesian throughflow in the OCCAM 1/4 degree ocean model

2007 ◽  
Vol 4 (2) ◽  
pp. 325-370 ◽  
Author(s):  
U. W. Humphries ◽  
D. J. Webb
Keyword(s):  
Indian Ocean ◽  
Ocean Model ◽  
Global Ocean ◽  
Indonesian Throughflow ◽  
Island Rule ◽  
Near Surface ◽  
The North ◽  
The Pacific ◽  
The Indian Ocean ◽  
Pass Through

Abstract. The Indonesian Throughflow is analysed in two runs of the OCCAM 1/4 degree global ocean model, one using monthly climatological winds and one using ECMWF analysed six-hourly winds for the period 1993 to 1998. The long-term model throughflow agrees with observations and the value predicted by Godfrey's Island Rule. The Island Rule has some skill in predicting the annual signal each year but is poor at predicting year to year and shorter term variations in the total flow especially in El Nino years. The spectra of transports in individual passages show significant differences between those connecting the region to the Pacific Ocean and those connecting with the Indian Ocean. This implies that different sets of waves are involved in the two regions. Vertical profiles of transport are in reasonable agreement with observations but the model overestimates the near surface transport through the Lombok Strait and the dense overflow from the Pacific through the Lifamatola Strait into the deep Banda Sea. In both cases the crude representation of the passages by the model appears responsible. In the north the model shows, as expected, that the largest transport is via the Makassar Strait. However this is less than expected and instead there is significant flow via the Halmahera Sea. If Godfrey's Island Rule is correct and the throughflow is forced by the northward flow between Australia and South America, then the Halmahers Sea route should be important. It is the most southerly route around New Guinea to the Indian Ocean and there is no apparent reason why the flow should go further north in order to pass through the Makassar Strait. The model result thus raises the question of why in reality the Makassar Strait route appears to dominate the throughflow.

scholarly journals Bomb 14C in the Indian Ocean Measured by Accelerator Mass Spectrometry: Oceanographic Implications

Radiocarbon ◽  
1989 ◽  
Vol 31 (03) ◽  
pp. 510-522 ◽  
Author(s):  
Edouard Bard ◽  
Maurice Arnold ◽  
J R Toggweiler ◽  
Pierre Maurice ◽  
Jean-Claude Duplessy
Keyword(s):  
Mass Spectrometry ◽  
Indian Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Equatorial Indian Ocean ◽  
Equatorial Zone ◽  
Mode Water ◽  
Indonesian Archipelago ◽  
The Pacific ◽  
The Indian Ocean

AMS 14C measurements on samples collected in the tropical-equatorial Indian Ocean during the INDIGO program (leg II, 1986) are presented and compared with β-counting results obtained under both INDIGO program and GEOSECS expedition in the Indian Ocean (1978). The most significant observation is a doubling of the bomb-14C inventory and mean penetration depth in the equatorial zone. Based on hydrologic considerations, two hypotheses can be proposed: 1) direct influx of Pacific mid-latitude waters through the Indonesian archipelago and 2) advection and/or mixing with Mode Water from the southern gyre of the Indian Ocean. Results obtained with a general circulation model of the ocean suggest that the influx from the Pacific is important in the upper 300m and that below 500m the bomb-14C budget is dominated by Mode Water advection.

scholarly journals On the Indonesian Throughflow in the OCCAM 1/4 degree ocean model

Ocean Science ◽  
2008 ◽  
Vol 4 (3) ◽  
pp. 183-198 ◽  
Author(s):  
U. W. Humphries ◽  
D. J. Webb
Keyword(s):  
Indian Ocean ◽  
Ocean Model ◽  
Global Ocean ◽  
Indonesian Throughflow ◽  
Island Rule ◽  
Near Surface ◽  
The North ◽  
The Pacific ◽  
The Indian Ocean ◽  
Pass Through

Abstract. The Indonesian Throughflow is analysed in two runs of the OCCAM 1/4 degree global ocean model, one using monthly climatological winds and one using ECMWF analysed six-hourly winds for the period 1993 to 1998. The long-term model throughflow agrees with observations and the value predicted by Godfrey's Island Rule. The Island Rule has some skill in predicting the annual signal each year but is poor at predicting year to year and shorter term variations in the total flow, especially in El Niño years. The spectra of transports in individual passages show significant differences between those connecting the region to the Pacific Ocean and those connecting with the Indian Ocean. On investigation we found that changes in the northern transports were strongly correlated with changes in the position of currents in the Celebes Sea and off Halmahera. Vertical profiles of transport are in reasonable agreement with observations but the model overestimates the near surface transport through the Lombok Strait and the dense overflow from the Pacific through the Lifamatola Strait into the deep Banda Sea. In both cases the crude representation of the passages by the model appears responsible. In the north the model shows, as expected, that the largest transport is via the Makassar Strait. However this is less than expected and instead there is significant flow via the Halmahera Sea. If Godfrey's Island Rule is correct and the throughflow is forced by the northward flow between Australia and South America, then the Halmahers Sea route should be important. It is the most southerly route around New Guinea to the Indian Ocean and there is no apparent reason why the flow should go further north in order to pass through the Makassar Strait. The model result thus raises the question of why in reality the Makassar Strait route appears to dominate the throughflow.

scholarly journals Impact of Ocean Currents on Wind Stress in the Tropical Indian Ocean

2021 ◽  
Author(s):  
Neethu Chacko ◽  
M M Ali
Keyword(s):  
Indian Ocean ◽  
Wind Stress ◽  
Equatorial Indian Ocean ◽  
Tropical Indian Ocean ◽  
Ocean Currents ◽  
Study Region ◽  
Different Seasons ◽  
The Indian Ocean ◽  
Stress Estimation ◽  
Effect Of Surface

This study examines the effect of surface currents on the bulk algorithm calculation of wind stress estimated using the scatterometer data during 2007-2020 in the Indian Ocean. In the study region as a whole the wind stress decreased by 5.4% by including currents into the wind stress equation. The most significant reduction in the wind stress is found along the most energetic regions with strong currents such as Somali Current, Equatorial Jets and Aghulhas retroflection. A highest reduction of 11.5% is observed along the equator where the Equatorial Jets prevail. A sensitivity analysis has been carried out for the study region and for different seasons to assess the relative impact of winds and currents in the estimation of wind stress by changing the winds while keeping the currents constants and vice versa. The inclusion of currents decreased the wind stress and this decrease is prominent when the currents are stronger. This study showed that equatorial Indian Ocean is the most sensitive region where the current can impact on wind stress estimation. The results showed that uncertainties in the wind stress estimations are quite large at regional levels and hence better representation of wind stress incorporating ocean currents should be considered in the ocean/climatic models for accurate air-sea interaction studies.

scholarly journals Meridional Overturning Circulation in a multi-basin model. Part II: Sensitivity to diffusivity and wind in warm and cool climates

2021 ◽  
Author(s):  
Jonathan A. Baker ◽  
Andrew J. Watson ◽  
Geoffrey K. Vallis
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
General Circulation ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Buoyancy Forcing ◽  
The Pacific ◽  
Primary Determinant ◽  
Meridional Overturning

AbstractThe response of the meridional overturning circulation (MOC) to changes in Southern Ocean (SO) zonal wind forcing and Pacific basin vertical diffusivity is investigated under varying buoyancy forcings, corresponding to ‘warm’, ‘present-day’ and ‘cold’ states, in a two-basin general circulation model connected by a southern circumpolar channel. We find that the Atlantic MOC (AMOC) strengthens with increased SO wind stress or diffusivity in the model Pacific, under all buoyancy forcings. The sensitivity of the AMOC to wind stress increases as the buoyancy forcing is varied from a warm to a present-day or cold state, whereas it is most sensitive to the Pacific diffusivity in a present-day or warm state. Similarly, the AMOC is more sensitive to buoyancy forcing over the Southern Ocean under reduced wind stress or enhanced Pacific diffusivity. These results arise because of the increased importance of the Pacific pathway in the warmer climates, giving an increased linkage between the basins and so the opportunity for the diffusivity in the Pacific to affect the overturning in the Atlantic. In cooler states, such as in glacial climates, the two basins are largely decoupled and the wind strength over the SO is the primary determinant of the AMOC strength. Both wind- and diffusively-driven upwelling sustain the AMOC in the warmer (present-day) state. Changes in SO wind stress alone do not shoal the AMOC to resemble that observed at the last glacial maximum; changes in the buoyancy forcing are also needed to decouple the two basins.

scholarly journals The dynamic connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

2015 ◽  
Vol 12 (5) ◽  
pp. 2231-2256
Author(s):  
E. Lambert ◽  
D. Le Bars ◽  
W. P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Coastal Current ◽  
Indonesian Throughflow ◽  
Boundary Current ◽  
South Indian Ocean ◽  
Leeuwin Current ◽  
South Indian ◽  
The Indian Ocean

Abstract. East of Madagascar, wind and surface buoyancy fluxes reinforce each other, leading to frontogenesis, outcrop and an eastward along-front flow: the South Indian Ocean Countercurrent (SICC). In the east the Leeuwin Current (LC) is a unique eastern boundary current which flows poleward along Australia. It is often described as a regional coastal current forced by an off-shore meridional density gradient or a sea surface slope, yet little is known of the forcing and dynamics that control these open ocean meridional gadients. To complete this understanding, we make use of both an ocean general circulation model and a conceptual two-layer model. The SICC impinges on west Australia and adds to a sea level slope and a southward geostrophic coastal jet: the Leeuwin Current. The SICC and the LC are thus dynamically connected. An observed transport maximum of the LC around 22° S is directly related to this impingement of the SICC. The circulation of the Indonesian Throughflow (ITF) through the Indian Ocean appears to be partly trapped in the upper layer north of the outcrop line and is redirected along this outcrop line to join the eastward flow of the SICC. Shutdown of the ITF in both models strongly decreases the Leeuwin Current transport and breaks the connection between the LC and SICC. In this case, most of the SICC was found to reconnect to the internal gyre circulation in the Indian Ocean. The Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current are thus dynamically coupled.

Indo-Pacific Climate Interactions in the Absence of an Indonesian Throughflow

2015 ◽  
Vol 28 (13) ◽  
pp. 5017-5029 ◽  
Author(s):  
Jules B. Kajtar ◽  
Agus Santoso ◽  
Matthew H. England ◽  
Wenju Cai
Keyword(s):  
Indian Ocean ◽  
Climate Model ◽  
Southern Oscillation ◽  
Ocean Basin ◽  
Climate System ◽  
Indonesian Throughflow ◽  
Enso Events ◽  
The Pacific ◽  
The Indian Ocean ◽  
Mean Climate

Abstract The Pacific and Indian Oceans are connected by an oceanic passage called the Indonesian Throughflow (ITF). In this setting, modes of climate variability over the two oceanic basins interact. El Niño–Southern Oscillation (ENSO) events generate sea surface temperature anomalies (SSTAs) over the Indian Ocean that, in turn, influence ENSO evolution. This raises the question as to whether Indo-Pacific feedback interactions would still occur in a climate system without an Indonesian Throughflow. This issue is investigated here for the first time using a coupled climate model with a blocked Indonesian gateway and a series of partially decoupled experiments in which air–sea interactions over each ocean basin are in turn suppressed. Closing the Indonesian Throughflow significantly alters the mean climate state over the Pacific and Indian Oceans. The Pacific Ocean retains an ENSO-like variability, but it is shifted eastward. In contrast, the Indian Ocean dipole and the Indian Ocean basinwide mode both collapse into a single dominant and drastically transformed mode. While the relationship between ENSO and the altered Indian Ocean mode is weaker than that when the ITF is open, the decoupled experiments reveal a damping effect exerted between the two modes. Despite the weaker Indian Ocean SSTAs and the increased distance between these and the core of ENSO SSTAs, the interbasin interactions remain. This suggests that the atmospheric bridge is a robust element of the Indo-Pacific climate system, linking the Indian and Pacific Oceans even in the absence of an Indonesian Throughflow.

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