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1.
The International Nusantara Stratification and Transport (INSTANT) program measured currents through multiple Indonesian Seas passages simultaneously over a three-year period (from January 2004 to December 2006). The Indonesian Seas region has presented numerous challenges for numerical modelers — the Indonesian Throughflow (ITF) must pass over shallow sills, into deep basins, and through narrow constrictions on its way from the Pacific to the Indian Ocean. As an important region in the global climate puzzle, a number of models have been used to try and best simulate this throughflow. In an attempt to validate our model, we present a comparison between the transports calculated from our model and those calculated from the INSTANT in situ measurements at five passages within the Indonesian Seas (Labani Channel, Lifamatola Passage, Lombok Strait, Ombai Strait, and Timor Passage). Our Princeton Ocean Model (POM) based regional Indonesian Seas model was originally developed to analyze the influence of bottom topography on the temperature and salinity distributions in the Indonesian seas region, to disclose the path of the South Pacific Water from the continuation of the New Guinea Coastal Current entering the region of interest up to the Lifamatola Passage, and to assess the role of the pressure head in driving the ITF and in determining its total transport. Previous studies found that this model reasonably represents the general long-term flow (seasons) through this region. The INSTANT transports were compared to the results of this regional model over multiple timescales. Overall trends are somewhat represented but changes on timescales shorter than seasonal (three months) and longer than annual were not considered in our model. Normal velocities through each passage during every season are plotted. Daily volume transports and transport-weighted temperature and salinity are plotted and seasonal averages are tabulated.  相似文献   

2.
The Indonesian seas provide a sea link between the tropical Pacific and Indian Oceans. The connection is not simple, not a single gap in a ‘wall’, but rather composed of the intricate patterns of passages and seas of varied dimensions. The velocity and temperature/salinity profiles Indonesian throughflow (ITF) are altered en route from the Pacific into the Indian Ocean by sea–air buoyancy and momentum fluxes, as well as diapycnal mixing due to topographic boundary effects and dissipation of tidal energy. The INSTANT program measured the ITF in key channels from 2004 to 2006, providing the first simultaneous view of the main ITF pathways. The along-channel speeds vary markedly with passage; the Makassar and Timor flow is relatively steady in comparison to the seasonal and intraseasonal fluctuations observed in Lombok and Ombai Straits. The flow through Lifamatola Passage is strongly bottom intensified, defining the overflow into the deep Indonesian basins to the south. The 3-year mean ITF transport recorded by INSTANT into the Indian Ocean is 15 × 106 m3/s, about 30% greater than the values of non-simultaneous measurements made prior to 2000. The INSTANT 3-year mean inflow transport is nearly 13 × 106 m3/s. The 2 × 106 m3/s difference between INSTANT measured inflow and outflow is attributed to unresolved surface layer transport in Lifamatola Passage and other channels, such as Karimata Strait. Introducing inflow within the upper 200 m to zero the water column net convergence still requires upwelling within the intervening seas, notably the Banda Sea. A layer of minimum upwelling near 600 m separates upwelling within the thermocline from a deep water upwelling pattern driven by the deep overflow in Lifamatola Passage. For a steady state condition upwelling thermocline water is off-set by a 3-year mean sea to air heat flux of 80 W/m2 (after taking into account the shoaling of thermocline isotherms between the inflow and outflow portals), which agrees with the climatic value based on bulk formulae sea–air flux calculations, as well as transport weighted temperature of the inflow and outflow water. The INSTANT data reveals interannual fluctuations, with greater upwelling and sea to air heat flux in 2006.  相似文献   

3.
Annual variation of the southern boundary current in the Banda Sea   总被引：1，自引：0，他引：1  
ADCP measurements in the southern Banda Sea, obtained with the bulk carrier “MS First Jupiter” from 1997 until 2000, have been analysed. The observations reveal the presence of an eastward flowing southern boundary current, bringing water from the Indonesian throughflow towards the connections with the Indian Ocean in Ombai Strait and the Timor Sea. The mean transport in the upper 300 m is estimated to be about 5 Sv, over 50% of the outflow towards the Indian Ocean in this layer through the eastern passages near Timor. The velocity in the boundary current shows a clear annual variation, more or less in phase with the annually varying inflow through Makassar Strait and the outflow near Timor. The phase of the annual variation cannot be explained by the monsoonal variation of the local winds. Therefore this annual variation of the throughflow is probably generated by large-scale forcing. A considerable reduction of the strength of the boundary current was observed in 1998, following the 1997–1998 El Niño with a delay of about half a year. On shorter time scales, Kelvin waves, entering the Banda Sea from the Indian Ocean, cause flow reversals of the boundary current.  相似文献   

4.
A 50-year record of the Indonesian throughflow (ITF) was obtained using the Simple Ocean Data Assimilation (SODA) dataset to calculate a timeseries of Pacific-to-Indian Ocean pressure differences, which were calibrated to transport profiles using ARLINDO (1997) and INSTANT (2004–2006) observational data. The 50 year SODA based ITF transport average is 10.4 Sv; the transport weighted temperature (TWT) is 14.6 °C and the internal energy transport (IET) is 0.53 PW. The different configurations of the ITF transport and temperature profiles result in a dissimilarity in the variability of the IET and the TWT, with the IET more closely correlated with both the depth of the 18 °C isotherm in the western equatorial Pacific and the NINO3.4 index. As with the transport, the IET increases during La Niña and decreases during El Niño. The TWT is only weakly correlated with NINO3.4, suggesting that the El Niño-Southern Oscillation signal is transmitted from the Pacific to the Indian Ocean via changes in pressure and thus in transport rather than by changes in temperature.  相似文献   

5.
Pathways of intraseasonal variability in the Indonesian Throughflow region   总被引：2，自引：0，他引：2  
The recent INSTANT measurements in the Indonesian archipelago revealed a broad spectrum of time scales that influence Indonesian Throughflow (ITF) variability, from intraseasonal (20–90 days) to interannual. The different time scales are visible in all transport and property fluxes and are the result of remote forcing by both the Pacific and Indian Ocean winds, and local forcing generated within the regional Indonesian seas. This study focuses on the time-dependent three-dimensional intraseasonal variability (ISV) in the ITF region, in particular at the locations of the INSTANT moorings at the Straits of Lombok, Ombai and Timor. Observations from the INSTANT program in combination with output from the Bluelink ocean reanalysis provide a comprehensive picture about the propagation of ISV in the ITF region. The reanalysis assimilates remotely sensed and in situ ocean observations into an ocean general circulation model to create a hindcast of ocean conditions. Data from the reanalysis and observations from the INSTANT program reveal that deep-reaching subsurface ISV in the eastern Indian Ocean and ITF is closely linked with equatorial wind stress anomalies in the central Indian Ocean. Having traveled more than 5000 km in about 14 days, the associated Kelvin waves can be detected as far east as the Banda Sea. ISV near the Straits of Ombai and Timor is also significantly influenced by local wind forcing from within the ITF region. At the INSTANT mooring sites the ocean reanalysis agrees reasonably well with the observations. Intraseasonal amplitudes are about ±1.0 °C and ±0.5 m/s for potential temperature and velocity anomalies. Associated phases of ISV are very similar in observations and the reanalysis. Where differences exist they can be traced back to likely deficits in the reanalysis, namely the lack of tidal dissipation, insufficient spatial resolution of fine-scale bathymetry in the model in narrow straits or errors in surface forcing.  相似文献   

6.
Monthly averaged total volume transport of the Indonesian throughflow (ITF) estimated by 14 global ocean data assimilation (ODA) products that are decade to multi-decade long are compared among themselves and with observations from the INSTANT Program (2004–2006). The main goals of the comparisons are to examine the consistency and evaluate the skill of different ODA products in simulating ITF transport. The ensemble averaged, time-mean value of ODA estimates is 13.6 Sv (1 Sv = 106 m3/s) for the common 1993–2001 period and 13.9 Sv for the 2004–2006 INSTANT Program period. These values are close to the 15-Sv estimate derived from INSTANT observations. All but one ODA time-mean estimate fall within the range of uncertainty of the INSTANT estimate. In terms of temporal variability, the scatter among different ODA estimates averaged over time is 1.7 Sv, which is substantially smaller than the magnitude of the temporal variability simulated by the ODA systems. Therefore, the overall “signal-to-noise” ratio for the ensemble estimates is larger than one. The best consistency among the products occurs on seasonal-to-interannual time scales, with generally stronger (weaker) ITF during boreal summer (winter) and during La Nina (El Nino) events. The scatter among different products for seasonal-to-interannual time scales is approximately 1 Sv. Despite the good consistency, systematic difference is found between most ODA products and the INSTANT observations. All but the highest-resolution (18 km) ODA product show a dominant annual cycle while the INSTANT estimate and the 18-km product exhibit a strong semi-annual signal. The coarse resolution is an important factor that limits the level of agreement between ODA and INSTANT estimates. Decadal signals with periods of 10–15 years are seen. The most conspicuous and consistent decadal change is a relatively sharp increase in ITF transport during 1993–2000 associated with the strengthening tropical Pacific trade wind. Most products do not show a weakening ITF after the mid-1970s’ associated with the weakened Pacific trade wind. The scatter of ODA estimates is smaller after than before 1980, reflecting the impact of the enhanced observations after the 1980s. To assess the representativeness of using the average over a three-year period (e.g., the span of the INSTANT Program) to describe longer-term mean, we investigate the temporal variations of the three-year low-pass ODA estimates. The average variation is about 3.6 Sv, which is largely due to the increase of ITF transport from 1993 to 2000. However, the three-year average during the 2004–2006 INSTANT Program period is within 0.5 Sv of the long-term mean for the past few decades.  相似文献   

7.
Tides affect transport and mixing in the Indonesian Seas, impacting the throughflow and the return flow of the global thermohaline circulation. In a previous study, barotropic and baroclinic tides were simulated for the Indonesian Seas at 5 km resolution in order to characterize the tides of the region and to identify and quantify locations of tidal mixing. Baroclinic tidal velocities exceeded barotropic velocities except in shallow regions and their variability was on smaller scales. Model results agreed reasonably with observations and are consistent with the resolution. However, only four mooring locations were available for comparison. The new International Nusantara Stratification (INSTANT) data set enables a more comprehensive comparison. With the exception of Lombok Strait, the model replicated the observed INSTANT velocity spectra, falling within the 90% confidence limits of the observed spectra, both in regions of high and low baroclinic tidal activity for the band of frequencies from 0.02 cph to 0.33 cph (periods of 50–3 h, respectively), which includes the major semidiurnal and diurnal tides and several of their first harmonics. The model overestimated the semidiurnal baroclinic tides in the narrow Lombok Strait, which is not well resolved in the model. Comparisons of vertical profiles of the major axes of the tidal ellipses at the mooring sites generally reproduced the vertical pattern, although there were exceptions, such as Lombok and Ombai Straits. Rms differences between the model estimates and hourly observations for the major axes of the tidal ellipses were typically 1–8 cm s−1 in regions of high tidal activity, 1–5 cm s−1 in regions of low tidal activity, and 1–20 cm s−1 for the semidiurnal tides in Lombok and Ombai Straits. Rms errors of 1–6 cm s−1 are typical in regions of moderate baroclinic tidal activity at this model resolution (5 km). Many of the larger rms differences result from vertical discrepancies in the depths of the internal tidal beams. The local nature of the internal tides generation and beam propagation results in large differences from small vertical shifts in the beams or generation due to topographic differences between the model topography and the actual topography. In addition, the moorings experienced severe blowdown. The blowdown adds uncertainty to the depths of the instruments and introduces errors in the observational tidal analysis in magnitude of the tidal constituents, both of which contribute to rms differences. Tidal mixing was found to occur in intense local regions with strong internal tidal shear. The local regions of mixing were typically along the bottom in steep slopes and over sills. In conclusion, the tidal model was found to reproduce the kinetic energy distribution and transfer of energy from tides to other frequencies in the Indonesian Seas and to roughly replicate the observed structure and magnitude of the tidal currents. Improvements in the tidal simulations in reproducing observations are expected with increased resolution.  相似文献   

8.
The upper layer, wind-driven circulation of the South China Sea (SCS), its through-flow (SCSTF) and the Indonesian through flow (ITF) are simulated using a high resolution model, FVCOM (finite volume coastal ocean model) in a regional domain comprising the Maritime Continent. The regional model is embedded in the MIT global ocean general circulation model (ogcm) which provides surface forcing and boundary conditions of all the oceanographic variables at the lateral open boundaries in the Pacific and Indian oceans. A five decade long simulation is available from the MITgcm and we choose to investigate and compare the climatologies of two decades, 1960–1969 and 1990–1999.The seasonal variability of the wind-driven circulation produced by the monsoon system is realistically simulated. In the SCS the dominant driving force is the monsoon wind and the surface circulation reverses accordingly, with a net cyclonic tendency in winter and anticyclonic in summer. The SCS circulation in the 90s is weaker than in the 60s because of the weaker monsoon system in the 90s. In the upper 50 m the interaction between the SCSTF and ITF is very important. The southward ITF can be blocked by the SCSTF at the Makassar Strait during winter. In summer, part of the ITF feeds the SCSTF flowing into the SCS through the Karimata Strait. Differently from the SCS, the ITF is primarily controlled by the sea level difference between the western Pacific and eastern Indian Ocean. The ITF flow, consistently southwestward below the surface layer, is stronger in the 90s.The volume transports for winter, summer and yearly are estimated from the simulation through all the interocean straits. On the annual average, there is a ∼5.6 Sv of western Pacific water entering the SCS through the Luzon Strait and ∼1.4 Sv exiting through the Karimata Strait into the Java Sea. Also, ∼2 Sv of SCS water enters the Sulu Sea through the Mindoro Strait, while ∼2.9 Sv flow southwards through the Sibutu Strait merging into the ITF. The ITF inflow occurs through the Makassar Strait (up to ∼62%) and the Lifamatola Strait (∼38%). The annual average volume transport of the ITF inflow from the simulation is ∼15 Sv in the 60s and ∼16.6 Sv in the 90s, very close to the long term observations. The ITF outflow through the Lombok, Ombai and Timor straits is ∼16.8 Sv in the 60s and 18.9 Sv in the 90s, with the outflow greater by 1.7 Sv and 2.3 Sv respectively. The transport estimates of the simulation at all the straits are in rather good agreement with the observational estimates.We analyze the thermal structure of the domain in the 60s and 90s and assess the simulated temperature patterns against the SODA reanalysis product, with special focus on the shallow region of the SCS. The SODA dataset clearly shows that the yearly averaged temperatures of the 90s are overall warmer than those of the 60s in the surface, intermediate and some of the deep layers and the decadal differences (90s − 60s) indicate that the overall warming of the SCS interior is a local effect. In the simulation the warm trend from the 60s to the 90s in well reproduced in the surface layer. In particular, the simulated temperature profiles at two shallow sites at midway in the SCSTF agree rather well with the SODA profiles. However, the warming trend in the intermediate (deep) layers is not reproduced in the simulation. We find that this deficiency is mostly due to a deficiency in the initial temperature fields provide by the MITgcm.  相似文献   

9.
Direct velocity measurements from 2004 through 2006 confirm the eastward flowing surface South Java Current (SJC) and its deeper Undercurrent (SJUC) crosses the Savu Sea to reach Ombai Strait, a main outflow portal of the Indonesian Throughflow (ITF). The extension of the South Java Current system into Ombai Strait was hinted at by earlier measurement and modeling studies, but the 3-year velocity time series from two moorings in Ombai Strait clearly show separate distinct cores of flow in the SJC and SJUC. The deeper SJUC is driven by Kelvin waves forced by intraseasonal and semi-annual winds in the equatorial Indian Ocean and, when present, is observed across the entire strait. Eastward flow in the surface SJC is near year-round, although it appears that the mechanisms responsible for this flow differ throughout the year. Both the wind-driven Ekman flow during the northwest monsoon and the strongest semi-annual Kelvin waves that have surface signatures can result in eastward surface layer flow across the entire strait. In contrast, during the southeast monsoon the SJC has a subsurface maximum eastward flow at 50–100 m depth in the northern part of Ombai Strait, while the westward ITF is at an annual maximum at the surface in the southern part of the strait. Surface temperature maps suggest the presence of a front during the southeast monsoon that seems to trap the SJC to within ∼10–15 km of the northern boundary of Ombai Strait. The SJC and the frontal location are related to a complex interplay between local wind-driven Ekman dynamics, the strong ITF flow and topography. Significant energy is found at short intraseasonal time scales (20–60 days) in the along-strait flow that is probably related to the short duration westerly wind bursts that drive the Kelvin waves into Ombai Strait. There is a distinct lack of energy at longer intraseasonal time scales (60–90 days) that is likely attributable to interannual climate variability.  相似文献   

10.
A Note on the South China Sea Shallow Interocean Circulation   总被引：14，自引：1，他引：14  
1. IntroductionThe South China Sea (SCS) has many channelsconnecting with the outer oceans/seas (Fig. 1). Thewidest and deepest channel is the Luzón Strait, whichis the main entrance to the SCS from the WesternPacific Ocean, having a sill depth of about 2500 m.On the north, the Taiwan Strait connects with theEast China Sea, with a sill depth of about 70 m. Inthe vicinity of Mindoro Island, there are a numberof channels connecting the SCS with the Sulu Sea.The main channel is the M…  相似文献   

11.
The SODA product is used to investigate three Indonesian throughflow (ITF) branches: the flow through the Makassar Strait; through the South China Sea; and through the eastern Indonesian basins. The results reveal strong interannual variation in the Makassar Strait and the eastern Indonesian basins throughflow. Inspection of vertically integrated dynamic height (0–1000 db), a proxy of transport function, suggests that this interannual variation can be traced to the New Guinea Coastal Current, indicative of a strong influence of the South Pacific. The vertically integrated dynamic height along the south Java coast is related to variation in the North Pacific and in particular near the east coast of Mindanao Island, whereas the vertically integrated dynamic height along the coast of West Australia is related to variation in the South Pacific, and in particular near the coast of New Guinea. The integrated dynamic height difference between the Java and New Guinea coast appears to be a good proxy of ITF transport on the interannual time scale. Regression analysis shows a phase dependence of the three ITF pathways on the Nino3.4 index. Decoupling of current anomalies between the surface and subsurface layers is identified in the developing and mature phase of El Nino, reflecting different effects of local and remote forcing through oceanic pathways at the Makassar Strait and eastern Indonesian basins.  相似文献   

12.
 This work concerns an analysis of inter-basin and inter-layer exchanges in the component ocean part of the coupled ECHAM4/OPYC3 general circulation model, aimed at documenting the simulation of North Atlantic Deep Water (NADW) and related thermohaline circulations in the Indian and Pacific Oceans. The modeled NADW is formed mainly in the Greenland– Iceland–Norwegian Seas through a composite effect of deep convection and downward cross-isopycnal transport. The modeled deep-layer outflow of NADW can reach 16 Sv near 30 °S in the South Atlantic, with the corresponding upper-layer return flow mainly coming from the “cold water path” through Drake Passage. Less than 4 Sv of the Agulhas “leakage” water contributes to the replacement of NADW along the “warm water path”. In the South Atlantic Ocean, the model shows that some intermediate isopycnal layers with potential densities ranging between 27.0 and 27.5 are the major water source that compensate the NADW return flow and enhance the Circumpolar Deep Water (CDW) flowing from the Atlantic into Indian Ocean. The modeled thermohaline circulations in the Indian and Pacific Oceans indicate that the Indian Ocean may play the major role in converting deep water into intermediate water. About 16 Sv of the CDW-originating deep water enters the Indian Ocean northward of 31 °S, of which more than 13 Sv “upwell” mainly near the continental boundaries of Africa, South Asia and Australia through inter-layer exchanges and return to the Antarctic Circumpolar Current (ACC) as intermediate-layer water. As a contrast, only 4 Sv of Pacific intermediate water is connected to “upwelling” flow southward across 31 °S while the magnitude of northward deep flow across 31 °S in the Pacific Ocean is significantly greater than that in the Indian Ocean. The model suggests that a large portion of the deep waters entering the Pacific Ocean (about 14 Sv) “upwells” continually into some upper layers through the thermocline, and becomes the source of the Indonesian throughflow. Uncertainties in these results may be related to the incomplete adjustment of the model’s isopycnal layers and the sensitivity of the Indonesian throughflow to the model’s geography and topography. Received: 12 August 1997/Accepted: 12 March 1998  相似文献   

13.
The South China Sea (SCS) interocean circulation and its associated heat and freshwater budgets are examined using the results of a variable-grid global ocean model. The ocean model has a 1/6° resolution in the SCS and its adjacent oceans. The model results from 1982 to 2003 show that the western Pacific waters enter the SCS through the Luzon Strait with an annual mean volume transport of 4.80 Sv, of which 1.71 Sv returns to the western Pacific through the Taiwan Strait and East China Sea and 3.09 Sv flows toward the Indian Ocean. The heat in the western Pacific is transported to the SCS with a rate of 0.373 PW (relative to a reference temperature 3.72 °C), while the total heat transport through the outflow straits is 0.432 PW. The net heat transport out of the SCS is thus 0.059 PW, which is balanced by a mean net downward heat flux of 17 W/m2 across the SCS air–sea interface. Therefore, the interocean circulation acts as an “air conditioner”, cooling the SCS and its overlaying atmosphere. The SCS contributes a heat transport of 0.279 PW to the Indian Ocean, of which 0.240 PW is from the Pacific Ocean through the Luzon Strait and 0.039 PW is from the SCS interior gained from the air–sea exchange. The Luzon Strait salt transport is greater than the total salt transport leaving the SCS by 3.97 Gg/s, implying a mean freshwater flux of 0.112 Sv (or 3.54 × 1012 m3/year) from the land discharge and P − E (precipitation minus evaporation). The total annual land discharge to the SCS is estimated to be 1.60 × 1012 m3/year, the total annual P − E over the SCS is thus 1.94 × 1012 m3/year, equivalent to a mean P − E of 0.55 m/year. The SCS freshwater contribution to the Indian Ocean is 0.096 Sv. The pattern of the SCS interocean circulation in winter differs greatly from that in summer. The SCS branch of the Pacific-to-Indian Ocean throughflow exists in winter, but not in summer. In winter this branching flow starts at the Luzon Strait and extends to the Karimata Strait. In summer the interocean circulation is featured by a north-northeastward current starting at the Karimata Strait and extending to the Taiwan and Luzon Straits, and a subsurface inflow from the Luzon Strait that upwells into the surface layer in the SCS interior to supply the outward transports.  相似文献   

14.
The ECCO–GODAE global estimate of the ocean circulation 1992–2007 is analyzed in the region of the Indonesian Throughflow (ITF), including the Southern Ocean flow south of Australia. General characteristics are an intense month-to-month noise, only weak trends, and an important annual cycle (which is not the focus of attention). Apart from the details of the unresolved flows within the various passages, and right on the equator, the region and its large-scale climate effects appears to be accurately diagnosed by large-scale geostrophic balance, so that the ITF can be calculated either from the upstream or the downstream balanced flow (but no simple reference level can be defined). The INSTANT program occurs during a more or less typical three-year period. Indications of response to the large 1997–1998 El Niño are weak.  相似文献   

15.
Impacts of the South China Sea Throughflow (SCST) on seasonal and interannual variations of the Indonesian Throughflow are studied by comparing outputs from ocean general circulation model (OGCM) experiments with and without the SCST. The observed subsurface maximum in the southward flow through the Makassar Strait is simulated only when the SCST, which is driven by the large-scale wind, is allowed in the model. The mean volume and heat transport by the Makassar Strait Throughflow are reduced by 1.7 Sv and 0.19 PW, respectively, by the existence of the SCST in the model. The difference is particularly remarkable during boreal winter when the SCST reaches its seasonal maximum. Furthermore, the SCST is strengthened during El Niño, leading to the weakening in the southward volume and heat transport through the Makassar Strait by 0.37 Sv and 0.05 PW, respectively. These findings from the OGCM experiments suggest that the SCST may play an important role in climate variability of the Indo-Pacific Ocean.  相似文献   

16.
The dynamics of the seasonal surface circulation in the Philippine Archipelago (117°E–128°E, 0°N–14°N) are investigated using a high-resolution configuration of the Regional Ocean Modeling System (ROMS) for the period of January 2004–March 2008. Three experiments were performed to estimate the relative importance of local, remote and tidal forcing. On the annual mean, the circulation in the Sulu Sea shows inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the southern basin. A strong jet with a maximum speed exceeding 100 cm s−1 forms in the northeast Sulu Sea where currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the surface water of the western Pacific (WP) from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry the surface water from the WP near the San Bernardino Strait into the Sulu Sea via the Tablas Strait.These surface currents exhibit strong variations or reversals from winter to summer. The cyclonic (anticyclonic) circulation during winter (summer) in the Sulu Sea and seasonally reversing currents within the Archipelago region during the peak of the winter (summer) monsoon result mainly from local wind forcing, while remote forcing dominates the current variations at the Mindoro Strait, western Sulu Sea and Sibutu passage before the monsoons reach their peaks. The temporal variations (with the mean removed), also referred to as anomalies, of volume transports in the upper 40 m at eight major Straits are caused predominantly by remote forcing, although local forcing can be large during sometime of a year. For example, at the Mindoro Strait, the correlation between the time series of transport anomalies due to total forcing (local, remote and tides) and that due only to the remote forcing is 0.81 above 95% significance, comparing to the correlation of 0.64 between the total and local forcing. Similarly, at the Sibutu Passage, the correlation is 0.96 for total versus remote effects, comparing to 0.53 for total versus local forcing. The standard deviations of transports from the total, remote and local effects are 0.59 Sv, 0.50 Sv, and 0.36 Sv, respectively, at the Mindoro Strait; and 1.21 Sv, 1.13 Sv, and 0.59 Sv at the Sibutu Passage. Nonlinear rectification of tides reduces the mean westward transports at the Surigao, San Bernardino and Dipolog Straits, and it also has non-negligible influence on the seasonal circulation in the Sulu Sea.  相似文献   

17.
A nested numerical model system has been set up to realistically simulate more than 30 years of the Indonesian throughflow (ITF). A global circulation model delivered the boundary values for sea level, temperature and salinity distributions to a local model covering the region of the ITF. Both models were forced with NCEP data. Results of the regional model are in good agreement with measured data regarding velocity distribution and stratification, as well as transported water masses. Model results show a highly variable and very complex current system. The presence of a realistic throughflow has been simulated even with a barotropic pressure gradient directed from the Indian towards the Pacific Ocean. Furthermore, model experiences indicate that the intensity of the ITF is correlated with the seasonal wind system. It is concluded that the ITF is neither driven by a barotropic or baroclinic pressure gradient nor by local winds. The ITF seems to be, rather, the extension of the very strong tropical Pacific Ocean circulation system westward into the Indonesian seas, where the western boundary is not fully closed due to the passages between the Indonesian islands. A hypothesis for the physical reason is given to explain the existence of the Indonesian throughflow.  相似文献   

18.
Oceanic response to Madden–Julian Oscillations (MJOs) is studied with satellite data, mooring observations, and reanalysis products to demonstrate that oceanic intraseasonal variabilities are a direct response to the atmospheric intraseasonal forcing. They propagate eastward to the Sumatran coast and southward along the coast to the southeastern Indian Ocean (SEIO) and the maritime continent, as coastal Kelvin waves. MJOs contribute to about 20% of the intraseasonal variabilities in the SEIO and the maritime continent. In addition, MJOs reduce the annual mean Indonesian Throughflow (ITF) and the associated westward temperature advection. However, MJOs only have slight influences on the peak ITF in boreal summer. The importance of INSTANT data is obvious not only for understanding of ITF but also for improving ocean reanalysis and should eventually lead to improved predictive understanding of phenomena such as MJOs.  相似文献   

19.
Changes in the Indonesian Throughflow(ITF) and the South China Sea throughflow—measured by the Luzon Strait Transport(LST)—associated with the 1976/77 regime shift are analyzed using the Island Rule theory and the Simple Ocean Data Assimilation dataset.Results show that LST increased but ITF transport decreased after 1975.Such changes were induced by variations in wind stress associated with the regime shift.The strengthening of the easterly wind anomaly east of the Luzon Strait played an important role in ...  相似文献   

20.
A quasi-global eddy permitting oceanic GCM, LICOM1.0, is run with the forcing of ERA40 daily wind stress from 1958 to 2001. The modelled Indonesian Throughflow (ITF) is reasonable in the aspects of both its water source and major pathways. Compared with the observation, the simulated annual mean and seasonal cycle of the ITF transport are fairly realistic. The interannual variation of the tropical Pacific Ocean plays a more important role in the interannual variability of the ITF transport. The relationshipbetween the ITF and the Indian Ocean Dipole (IOD) also reflects the influence of ENSO. However, the relationship between the ITF transport and the interannual anomalies in the Pacific and Indian Oceans vary with time. During some years, (e.g., 1994), the effect of a strong IOD on the ITF transport is more than that from ENSO.  相似文献   

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