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1.
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2.
Effect of River Discharge on Bay of Bengal Circulation   总被引：1，自引：1，他引：1  
The seasonal circulation and mixed layer depths in Bay of Bengal is modeled using the three-dimensional Princeton Ocean Model (POM). Along the coastal boundaries a higher resolution is accomplished using the curvilinear orthogonal grid. Model uses a free-surface and terrain following sigma coordinates. The initial climatological salinity and temperature fields for the model are derived from the World Ocean Atlas-2001(WOA01). The Model is forced with wind stress derived from COADS wind climatology. Bilinear interpolation is used to obtain the initial fields and wind stress to the required model specification. Using the seasonal fields and wind stress the model is integrated for simulating Bay of Bengal circulation. The numerical simulations on climatological scale for monsoon months were conducted to study the evolution of dynamics. The simulations bring out not only the typical characteristic features of fresh water plume along the coast but also intensification of the flow over the monsoon period. The increase in the fresh water flow found to affect only the western parts of the BoB. The opposing currents due to monsoon winds and southward flowing fresh water discharge (FWD) were also delineated. The model results show that the wind stress induced turbulence process is subdued in the presence of strong vertical salinity stratification due to the influence of FWD. The simulated mixed layer depths are in agreement with the reported analytical energy required for mixing values.  相似文献   

3.
Seventeen models participating in the Coupled Model Intercomparison Project phase 5（CMIP5） activity are compared on their historical simulation of the South China Sea（SCS） ocean heat content（OHC） in the upper 300 m. Ishii＇s temperature data, based on the World Ocean Database 2005（WOD05） and World Ocean Atlas 2005（WOA05）, is used to assess the model performance by comparing the spatial patterns of seasonal OHC anomaly（OHCa） climatology, OHC climatology, monthly OHCa climatology, and interannual variability of OHCa. The spatial patterns in Ishii＇s data set show that the seasonal SCS OHCa climatology, both in winter and summer, is strongly affected by the wind stress and the current circulations in the SCS and its neighboring areas. However, the CMIP5 models present rather different spatial patterns and only a few models properly capture the dominant features in Ishii＇s pattern. Among them, GFDL-ESM2 G is of the best performance. The SCS OHC climatology in the upper 300 m varies greatly in different models. Most of them are much greater than those calculated from Ishii＇s data. However, the monthly OHCa climatology in each of the 17 CMIP5 models yields similar variation and magnitude as that in Ishii＇s. As for the interannual variability, the standard deviations of the OHCa time series in most of the models are somewhat larger than those in Ishii＇s. The correlation between the interannual time series of Ishii＇s OHCa and that from each of the 17 models is not satisfactory. Among them, BCC-CSM1.1 has the highest correlation to Ishii＇s, with a coefficient of about 0.6.  相似文献   

4.
The North Indian Ocean exhibits profound impact of variation in lower tropospheric winds. In the present study climatological monthly winds are used to force a nonlinear reduced gravity model of the North Indian Ocean to simulate climatological surface circulation and sea level anomaly for all 12 months of the year. The sea level anomalies agree reasonably well with satellite altimeter derived sea level anomalies. The model successfully simulates the varying eddy structure and current pattern of the North Indian Ocean. Finally, the kinetic energy variation in the North Indian Ocean with special reference to equatorial region and the boundaries is analyzed in detail.  相似文献   

5.
The North Indian Ocean exhibits profound impact of variation in lower tropospheric winds. In the present study climatological monthly winds are used to force a nonlinear reduced gravity model of the North Indian Ocean to simulate climatological surface circulation and sea level anomaly for all 12 months of the year. The sea level anomalies agree reasonably well with satellite altimeter derived sea level anomalies. The model successfully simulates the varying eddy structure and current pattern of the North Indian Ocean. Finally, the kinetic energy variation in the North Indian Ocean with special reference to equatorial region and the boundaries is analyzed in detail.  相似文献   

6.
The objective of the paper is to use the data collected along two meridional sections (45° E and 57°30′ E) during the austral summer (January–March) 2004 to understand the influence of seabed topography across the Madagascar and Southwest Indian Ridges on hydrographic parameters. The study was supplemented by World Ocean Circulation Experiment (WOCE) Conductivity-Temperature-Depth data collected during February–March 1996 along 30° E, as well as Levitus climatology. A southward shift of 2° latitude (between 45° E and 57°30′ E) was recorded for the two predominant frontal structures, i.e., the Agulhas Return Front and Southern Subtropical Front, which is attributed to the influence of seabed topography on hydrographic parameters. No significant spatial variation of these fronts was noted between the 30° E and 45° E meridional sections. Between latitudes 31° S and 42° S, the temperature and salinity structures show deepening over the ridges. The Antarctic Circumpolar Current core was detected between 40°15′ S and 43° S.  相似文献   

7.
The large-scale circulation of the Indian Ocean has several major components. There is a cyclonic gyre in the far southwest with its axis along about 60°S. It extends to the bottom. North of this the Circumpolar Current flows eastward south of 40°S to more than 3000 m. The axis of the great anticyclonic gyre lies along 35°S to 40°S down to about 2000 m. Below there the western end shifts northward and the axis lies along the central and southeast Indian ridges, with southward flow west of the ridges and northward flow on the east side.There is a westward flow along 10°S to 15°S, which includes water from the Pacific, through the Banda Sea. The flow near the equator is eastward down to the depth of the ridge near 73°E. Flow within both the Arabian Sea and Bay of Bengal is cyclonic down to great depth.There is a southward flow along the coast of Africa in the upper 2000 m joining the Circumpolar Current, and a southward flow along the coast of Australia that does not reach the Circumpolar Current.Below 2500 m there is a northward flow from the Circumpolar Current along the east coast of Madagascar and on into the Somali and Arabian basins.  相似文献   

8.
基于WOA18(World Ocean Atlas)温盐数据集,分析印度洋等密度面的气候态分布,而后选取1985—1994年、1995—2004年和2005—2017年3个时段,分析等密度面的年代际变化。研究给出了11个等密度面深度的气候态分布,其中σ0=26.00 kg/m3的等密度面(参考压强为0 dbar)在 40°S附近露头,随着位势密度的增大,等密度面露头区逐渐南移直至消失;位势密度大于σ0=26.95kg/m3且小于等于σ2=37.00kg/m3的等密度面最深处均位于马达加斯加南侧,在北印度洋的深度变化不大。重点分析了σ0=26.00 kg/m3,σ1=31.87 kg/m3(参考压强为1 000 dbar),σ2=36.805 kg/m3(参考压强为2 000 dbar)3个等密度面深度和盐度的年代际变化,研究表明两者均存在显著的年代际变化。对于σ0=26.00kg/m3等密度面,深度先变浅后加深,年代际变化主要位于30°S—40°S(等密度面深度快速变化区);等密度面盐度在1995—2004年和1985—1994年的差异与2005—2017年和1995—2004年的差异中基本呈现相反的变化。 σ1=31.87kg/m3和σ2=36.805kg/m3的等密度面深度年代际变化都集中于40°S—50°S海域;总体上盐度的年代际变化前者表现为减小,后者表现为增加。  相似文献   

9.
本文利用Argo盐度、SODA海流量、OAFlux蒸发量和TRMM降水量等数据,采用盐度收支方程定量给出了印度洋混合层盐度的收支,揭示了整个印度洋净淡水通量项、平流项、垂向卷夹项的分布、季节变化特征及其对混合层盐度变化的主要贡献。结果表明,就多年平均而言,平流项负贡献（15.14%）大于正贡献（9.89%）,说明平流输送把低盐水输送到高盐海域,导致印度洋高盐海域混合层的盐度降低。净淡水通量项的分布和季节变化与降水量基本一致,且正贡献（13.70%）大于负贡献（7.81%）,说明净淡水通量项使印度洋的混合层盐度升高（因为多年平均蒸发量大于降水量）。盐度季节变化显著海域的进一步分析表明,6?11月,西南季风漂流把赤道西印度洋的低盐水（相对阿拉伯海高盐水而言）输送到阿拉伯海西部海域,导致该海域的盐度降低。平流输送把孟加拉湾湾口和中部的高盐水带到北部海域,是导致北部海域盐度升高的主要原因。  相似文献   

10.
A 2°×2° map of spreading centres and fracture zones surrounding the Indian Ocean RRR triple junction, at 25.5°S, 70°E, is described from a data set of GLORIA side-scan sonar images, bathymetry, magnetic and gravity anomalies. The GLORIA images show a pervasive fabric due to linear abyssal hills oriented parallel to the two medium-spreading ridges (the Central Indian Ridge (CIR) and Southeast Indian Ridge (SEIR)). A cuvature of the fabric occurs along fracture zones, which are also located by lows in the bathymetry and gravity data and by offsets between magnetic anomalies. The magnetic anomalies also record periods of asymmetric spreading marking the development of the fracture zones, including the birth, at anomaly 2A, of a short fracture zone 50 km north of the triple junction on the CIR, and its death near the time of the Jaramillo anomaly. In some localities, a fine-scale fabric corresponds to a coarser fabric on the opposite flank of the CIR, possibly indicating a persistent asymmetry in the faulting at the median valley walls if the fabric has a tectonic and not a volcanic origin. A plate velocity analysis of the triple junction shows that both the CIR and Southwest Indian Ridge (SWIR) are propagating obliquely; the CIR appears to form an oblique trend by segmenting into a series of almost normally-oriented segments separated by short-offset fracture zones. For the last 4 m.y., the abyssal hill lineations indicate that the CIR segment immediately north of the triple junction has been spreading with an average 10° obliquity. The present small 5 km offset of the centres of the CIR and SEIR median valleys (Munschy and Schlich, 1989) is shown to be the result of this obliquity and a 30% spreading asymmetry between anomaly 2 and the Jaramillo on the CIR segment immediately north of the triple junction.  相似文献   

11.
Ocean Model Simulation of Southern Indian Ocean Surface Currents   总被引：1，自引：0，他引：1  
The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N-60°S and 30°E-120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.  相似文献   

12.
The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N–60°S and 30°E–120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.  相似文献   

13.
Results of comparison exercises carried out between the state-of-the-art TOPEX/POSEIDON altimeter-derived ocean surface wind speed and ocean wave parameters (significant wave height and wave period) and those measured by a set of ocean data buoys in the North Indian Ocean are presented in this article. Altimeter-derived significant wave height values exhibited rms deviation as small as ±0.3 m, and surface wind speed of ±1.6 m/s. These results are found consistent with those found for the Pacific Ocean. For estimation of ocean wave period, the spectral moments-based semiempirical approach, earlier applied on GEOSAT data, was extended to TOPEX/POSEIDON. For this purpose, distributions of first four years of TOPEX/POSEIDON altimeter data and climatology over the North Indian Ocean were analyzed and a new set of coefficients generated for estimation of wave period. It is shown that wave periods thus estimated from TOPEX/POSEIDON data (for the subsequent two years), when compared with independent data set of ocean data buoys deployed in the North Indian Ocean, exhibit improved accuracy (rms ~ ±1.4 nos) over those determined earlier with GEOSAT data.  相似文献   

14.
We analyze the time-longitude structure of composite cases from model-assimilated ocean data in the period 1958–1998, following on from earlier work by Huang and Kinter (J. Geophys. Res. 107(C11) (2002) 3199) that studied east–west thermocline variability in the Indian Ocean. Our analysis focuses on the Rossby wave signal along the thermocline ridge in the tropical SW Indian Ocean (10°S, 60–80°E), where wind stress curl is important. Anomalous winds in the equatorial east Indian Ocean force successive Rossby waves westward at speeds of 0.1 m s−1±30%. With a wavelength of 7000 km, the period of oscillation is in the range 1.9–5.2 years. The Indian Ocean Rossby wave is partially resonant with the global influence of the El Nino–Southern Oscillation, except during quasi-biennial rhythm. The presence of the Rossby wave offers potential predictability for east–west atmospheric circulation systems and climate that affect resources in countries surrounding the Indian Ocean.  相似文献   

15.
本文基于海洋环流模式模拟的高分辨率欧拉场,利用拉格朗日追踪方法,评估了印尼贯穿流（ITF）对印度洋的热量贡献。通过计算ITF水体在印度洋的传输路径及伴随的温度变化来获取ITF水体在印度洋的热量传输过程。模拟结果表明ITF进入印度洋后主要向西流动并在到达马达加斯加后分叉,进入南、北印度洋。热收支分析表明ITF在北印度洋吸收0.41 PW热量,在南印度洋释放0.56 PW热量;这两个过程相互补偿,导致ITF对整个印度洋的净加热贡献并不显著,只有0.15 PW。进一步的检查ITF离开印度洋的出口（跨过34°S）,结果表明ITF主要随着位于西边界的奥古拉斯流和位于东边界的利文流离开印度洋。约89%的ITF水体沿着西边界离开印度洋,其余的11%主要沿着东边界离开印度洋;前者对整个印度洋的净加热贡献为0.10 PW,后者的净加热贡献为0.05 PW。  相似文献   

16.
The Rodriguez Triple Junction (RTJ) corresponds to the junction of the three Indian Ocean spreading ridges. A detailed survey of an area of 90 km by 85 km, centered at 25°30 S and 70° E, allows detailed mapping (at a scale of 1/100 000) of the bathymetry (Seabeam) and the magnetic anomalies. The Southeast Indian Ridge, close to the triple junction, is a typical intermediate spreading rate ridge (2.99 cm a-1 half rate), trending N140°. The Central Indian Ridge rift valley prolongs the Southeast Indian Ridge rift valley with a slight change of orientation (12°). The half spreading rate and trend of this ridge are 2.73 cm a-1 and N152° respectively. In contrast, the Southwest Indian Ridge close to the triple junction is expressed by two deep-valleys (4300 and 5000 m deep) which abut the southwestcrn flanks of the two other ridges, and appears to be a stretched area without axial neovolcanic zone. The evolution of the RTJ is analysed for the past one million years. The instantaneous velocity triangle formed by the three ridges cannot be closed indicating that the RTJ is unstable. A model is proposed to explain the evolution of the unstable RRF Rodriguez Triple Junction. The model shows that the axis of the Central Indian Ridge is propressively offset from the axis of the Southeast Indian Ridge at a velocity of 0.14 cm a-1, the RTJ being restored by small jumps. This unstable RRF model explains the directions and offsets which are observed in the vicinity of the triple junction. The structure and evolution of the RTJ is similar to that of the Galapagos Triple Junction located in the East Pacific Ocean and the Azores Triple Junction located in the Central Atlantic Ocean.  相似文献   

17.
Results of comparison exercises carried out between the state-of-the-art TOPEX/POSEIDON altimeter-derived ocean surface wind speed and ocean wave parameters (significant wave height and wave period) and those measured by a set of ocean data buoys in the North Indian Ocean are presented in this article. Altimeter-derived significant wave height values exhibited rms deviation as small as - 0.3 m, and surface wind speed of - 1.6 m/s. These results are found consistent with those found for the Pacific Ocean. For estimation of ocean wave period, the spectral moments-based semiempirical approach, earlier applied on GEOSAT data, was extended to TOPEX/POSEIDON. For this purpose, distributions of first four years of TOPEX/POSEIDON altimeter data and climatology over the North Indian Ocean were analyzed and a new set of coefficients generated for estimation of wave period. It is shown that wave periods thus estimated from TOPEX/POSEIDON data (for the subsequent two years), when compared with independent data set of ocean data buoys deployed in the North Indian Ocean, exhibit improved accuracy (rms ~ - 1.4 nos) over those determined earlier with GEOSAT data.  相似文献   

18.
The realization of North Atlantic Deep Water (NADW) replacement in the deep northern Indian Ocean is crucial to the “conveyor belt” scheme. This was investigated with the updated 1994 Levitus climatological atlas. The study was performed on four selected neutral surfaces, encompassing the Indian deep water from 2000 to 3500 m. The Indian deep water comprises three major water masses: NADW, Circumpolar Deep Water (CDW) and North Indian Deep Water (NIDW). Since NADW flowing into the southwest Indian Ocean is largely blocked by the ridges (the Madagascar Ridge in the east and Davie Ridge in the north in the Mozambique Channel) and NIDW is the only source in the northern Indian Ocean that cannot provide a large amount of volume transport, CDW has to be a major source for the Indian deep circulation and ventilation in the north. Thus the question of NADW replacement becomes that of how the advective flows of CDW from the south are changed to be upwelled flows in the north—a water-mass transformation scenario. This study considered various processes causing motion across neutral surfaces. It is found that dianeutral mixing is vital to achieve CDW transformation. Basin-wide uniform dianeutral upwelling is detected in the entire Indian deep water north of 32°S, somewhat concentrated in the eastern Indian Ocean on the lowest surface. However, the integrated dianeutral transport is quite low, about a net of 0.2 Sv (1 Sv=106 m3 s-1) across the lowermost neutral surface upward and 0.4 Sv across the uppermost surface upward north of 32°S with an error band of about 10–20% when an uncertainty of half-order change in diffusivities is assumed. Given about 10–15% of rough ridge area where dianeutral diffusivity could be about one order of magnitude higher (10-4 m2 s-1) due to internal-wave breaking, the additional amount of increased net dianeutral transport across the lowest neutral surface is still within that error band. The averaged net upward transport in the north is matched with a net downward transport of 0.3 Sv integrated in the Southern Ocean south of 45°S across the lowermost surface. With the previous works of You (1996. Deep Sea Research 43, 291–320) in the thermocline and You (Journal of Geophysical Research) in the intermediate water combined, a schematic dianeutral circulation of the Indian Ocean emerges. The integrated net dianeutral upwelling transport shows a steady increase from the deep water to the upper thermocline (from 0.2 to 4.6) north of 32°S. The dianeutral upwelling transport is accumulated upward as the northward advective transport provided from the Southern Ocean increases. As a result, the dianeutral upwelling transport north of 32°S can provide at least 4.6 Sv to south of 32°S from the upper main thermocline, most likely to the Agulhas Current system. This amount of dianeutral upwelling transport does not include the top 150–200 m, which may contribute much more volume transport to the south.  相似文献   

19.
The annual subduction rate in the South Indian Ocean was calculated by analyzing Simple Ocean Data Assimilation(SODA) outputs in the period of 1950–2008. The subduction rate census for potential density classes showed a peak corresponding to Indian Ocean subtropical mode water(IOSTMW) in the southwestern part of the South Indian Ocean subtropical gyre. The deeper mixed layer depth, the sharper mixed-layer fronts and the associated relatively faster circulation in the present climatology resulted in a larger lateral induction, which primarily dominants the IOSTMW subduction rate, while with only minor contribution from vertical pumping.Without loss of generality, through careful analysis of the water characteristics in the layer of minimum vertical temperature gradient(LMVTG), the authors suggest that the IOSTMW was identified as a thermostad, with a lateral minimum of low potential vorticity(PV, less than 200×10~(–12) m~(–1)·s~(–1)) and a low d T?dz(less than 1.5°C/(100m)). The IOSTMW within the South Indian Ocean subtropical gyre distributed in the region approximately from25° to 50° E and from 30° to 39°S. Additionally, the average characteristics(temperature, salinity, potential density)of the mode water were estimated about(16.38 ± 0.29)°C,(35.46 ± 0.04),(26.02 ± 0.04) σ_θ over the past 60 years.  相似文献   

20.
热带印度洋偶极子事件和副热带印度洋偶极子事件的联系   总被引：6，自引：0，他引：6  
分别对热带印度洋偶极子事件和副热带印度洋偶极子事件的时间序列进行了周期分析。结果表明,热带印度洋偶极子事件的主要振荡周期为2 a和4 a,而副热带偶极子事件的主要振荡周期为8 a;对整个印度洋海区的海表温度距平进行2~8 a的带通滤波,发现未滤波之前,2个事件的相关性很低,而在进行了滤波之后,2个事件的相关性有很大的提高,并且当副热带印度洋偶极子事件超前热带印度洋偶极子事件9个月时,二者具有很强的相关性。通过对温度场和风场的分析,从物理上解释了2个事件之间的相互联系。  相似文献   

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