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1.
Origin and mechanism of Subantarctic Mode Water formation and transformation in the Southern Indian Ocean 总被引：1，自引：0，他引：1
The sources and pathways of mode waters and lower thermocline waters entering the subtropical gyre of the Indian Ocean are
examined. A Lagrangian analysis is performed on an eddy-admitting simulation of the Global Ocean performed by the DRAKKAR
Group (NEMO/OPA), which captures the main observed features. We trace the subducted mode water’s pathways, identify their
formation regions and trace whether their source waters come from the Atlantic, Pacific or Indian sectors of the Southern
Ocean. Three main sites for mode waters ventilation in the Indian sector are identified with different circulation pathways
and source water masses: (a) just north of Kerguelen, where 4.2 Sv of lighter Subantarctic Mode Waters (SAMW); σ
0 ∼ 26.5) are exported—originating in the Atlantic and Agulhas Retroflection regions; (b) SW of Australia, where 6.5 Sv of
medium SAMW (σ
0 ∼ 26.6) are ventilated—originating in the southern and denser Agulhas Retroflection region; (c) SW of Tasmania and along
the South Australian coast, where 3 Sv of denser SAMW (σ
0 ∼ 26.75) are ventilated—originating from three sources: Leeuwin Current waters, Tasman Sea (Pacific) waters and Antarctic
Surface Waters. In all cases, modelled mode waters were last ventilated in the Indian Ocean just north of the deepest winter-mixed
layers. For the waters subducted SW of Australia, the last ventilation site extends even further north. Waters ventilated
in the deepest mixed layers north of the Subantarctic Front are then re-ventilated 5 years later southwest of Australia. The
model results raise new hypotheses that revisit the classical picture of the SAMW formation and transformation, where a large
homogeneous mixed layer is subducted and ‘slides’ equatorward, essentially maintaining the T/S characteristics acquired at
the surface. Firstly, the last ventilation of the modelled mode waters is not in the region of the deepest mixed layers, as
previously thought, but further north in regions of moderate meso-scale eddy activity. Secondly, the model shows for the first
time a significant source region for Indian Ocean mode waters coming from deep winter-mixed layers along the south Australian
coast. Finally, this analysis shows how the mode water characteristics are modified after subduction, due to internal eddy
mixing. The simulation shows that resolved eddies have a strong impact on the mixed layer properties and that isopycnal eddy
mixing also contributes to the generation of more homogeneous mode water characteristics in the interior. 相似文献
2.
ARGO hydrographic profiles, two hydrographic transects and satellite measurements of air–sea exchange parameters were used
to characterize the properties and seasonal heat budget variations of the Surface Mixed Layer (SML) south of Africa. The analysis
distinguishes the Subtropical domain (STZ) and the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ)
of the Antarctic Circumpolar Current. While no Subantarctic Mode Water forms in that region, occurrences of deep SML (up to
∼450 m) are observed in the SAZ in anticyclones detached from the Agulhas Current retroflection or Agulhas Return Current.
These are present latitudinally throughout the SAZ, but preferentially at longitudes 10–20° E where, according to previous
results, the Subtropical Front is interrupted. Likely owing to this exchange window and to transfers at the Subantarctic Front
also enhanced by the anticyclones, the SAZ shows a wide range of properties largely encroaching upon those of the neighbouring
domains. Heat budget computations in each zone reveal significant meridional changes of regime. While air–sea heat fluxes
dictate the heat budget seasonal variability everywhere, heat is mostly brought through lateral geostrophic advection by the
Agulhas Current in the STZ, through lateral diffusion in the SAZ and through air–sea fluxes in the PFZ and AZ. The cooling
contributions are by Ekman advection everywhere, lateral diffusion in the STZ (also favoured by the ∼10° breach in the Subtropical
Front) and geostrophic advection in the SAZ. The latter likely reflects an eastward draining of water warmed through mixing
of the subtropical eddies. 相似文献
3.
The subduction and export of subantarctic mode water (SAMW) as part of the overturning circulation play an important role
in global heat, freshwater, carbon and nutrient budgets. Here, the spatial distribution and export of SAMW is investigated
using Argo profiles and a climatology. SAMW is identified by a dynamical tracer: a minimum in potential vorticity. We have
found that SAMW consists of several modes with distinct properties in each oceanic basin. This conflicts with the previous
view of SAMW as a continuous water mass that gradually cools and freshens to the east. The circulation paths of SAMW were
determined using (modified) Montgomery streamlines on the density surfaces corresponding with potential vorticity minima.
The distribution of the potential vorticity minima revealed “hotspots” where the different SAMW modes subduct north of the
Subantarctic Front. The subducted SAMWs follow narrow export pathways into the subtropical gyres influenced by topography.
The export of warmer, saltier modes in these “hotspots” contributes to the circumpolar evolution of mode water properties
toward cooler, fresher and denser modes in the east. 相似文献
4.
H.J. Niebauer 《Continental Shelf Research》1982,1(1):49-98
A seasonal ice edge zone is a unique frontal system with an air-ice-sea interface. This paper is a report on the numerical results from a quasi-three dimensional, time dependent, non-linear numerical model of circulation at a continental shelf-seasonal ice edge zone. The purpose of the experiments is to model the hydrography and circulation, including upwelling, baroclinic geostrophic flow, and inertial oscillations, at the ice edge with emphasis on examining the driving forces of wind and melting ice. It is suggested that the non-linear acceleration terms and vertical density diffusion terms are negligible and that the horizontal density diffusion terms are of secondary importance within the time and space scales of the experiments. The vertical eddy viscosity terms are important in a spin-up time scale and for Ekman transport and a bottom Ekman layer. The effects of the horizontal eddy viscosity terms are observable (a long-ice jet is diffused away from the ice edge) by the end (72 h) of the model runs.Model results are compared with available oceanographic and meteorological data for verification. The observed and modeled features of melt water induced water column stability, frontal structure, and ice edge upwelling are briefly discussed relative to observed ice edge primary production. Because the model is relatively general in nature, it is readily applicable to other seasonal or marginal ice edge zones in either hemisphere. 相似文献
5.
The Southern Ocean (SO) transports heat towards Antarctica and plays an important role in determining the heat budget of the
Antarctic climate system. A global ocean data synthesis product at eddy-permitting resolution from the Estimating the Circulation
and Climate of the Ocean, Phase II (ECCO2) project is used to estimate the meridional heat transport (MHT) in the SO and to
analyze its mechanisms. Despite the intense eddy activity, we demonstrate that most of the poleward MHT in the SO is due to
the time-mean fields of the meridional velocity, V, and potential temperature, θ. This is because the mean circulation in the SO is not strictly zonal. The Antarctic Circumpolar Current carries warm waters
from the region south of the Agulhas Retroflection to the lower latitudes of the Drake Passage and the Malvinas Current carries
cold waters northward along the Argentinian shelf. Correlations between the time-varying fields of V and θ (defined as transient processes) significantly contribute to the horizontal-gyre heat transport, but not the overturning
heat transport. In the highly energetic regions of the Agulhas Retroflection and the Brazil-Malvinas Confluence the contribution
of the horizontal transient processes to the total MHT exceeds the contribution of the mean horizontal flow. We show that
the southward total MHT is mainly maintained by the meridional excursion of the mean geostrophic horizontal shear flow (i.e.,
deviation from the zonal average) associated with the Antarctic Circumpolar Current that balances the equatorward MHT due
to the Ekman transport and provides a net poleward MHT in the SO. The Indian sector of the SO serves as the main pathway for
the poleward MHT. 相似文献
6.
Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean 总被引：9，自引：0，他引：9
It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin… 相似文献
7.
Daisuke Takahashi Kazuo Kido Yoshinori Nishida Naoto Kobayashi Naoyuki Higaki Hideo Miyake 《Continental Shelf Research》2007
We conducted hydrographic observations in 2002 to investigate the anticyclonic eddy that emerges every summer in Funka Bay, Hokkaido, Japan, and elucidate dynamical structure and wind-driven upwelling within the eddy. The anticyclonic eddy has a vertical scale of 32 m and is characterized by a strong baroclinic flow and a sharp pycnocline with a concave isopycnal structure. The sharp pycnocline occurs below a warm and relatively low-salinity water termed summer Funka Bay water (FS), which is formed by heating from solar radiation and dilution from river discharge in summertime Funka Bay. Flow of the anticyclonic eddy rotates as a rigid body at each layer, and the horizontal scale and rotation period of the eddy in the surface layer are about 15 km and 2.2 days, respectively. The dynamical balance of the anticyclonic eddy is well explained by the gradient flow balance. The contribution of centrifugal force to the gradient flow balance is about 27%. Therefore, the effect of the nonlinear term associated with centrifugal force cannot be neglected in considering the dynamics of the anticyclonic eddy in summertime Funka Bay. In addition, upwelling of subsurface water was observed in the surface layer of the central part of the eddy. The formation mechanism of this upwelling is consistent with interaction between horizontal uniform wind and the eddy. This upwelling is driven by upward Ekman pumping velocity related to the horizontal divergence of Ekman transport. In summertime Funka Bay, there are two wind effects that affect the anticyclonic eddy: a decay effect of the upwelling of subsurface water resulting from horizontal uniform wind (mainly northwesterly wind), and a maintenance or spin-up effect of horizontal non-uniform wind (mainly southerly–southeasterly seasonal wind) with negative wind stress curl. 相似文献
8.
A three-dimensional model based on the Princeton Ocean Model (POM) has been implemented to study the circulation of the west coast of India. The model uses a curvilinear orthogonal horizontal grid with higher resolution near the coast (3–9 km) and a terrain following sigma coordinate in the vertical. The model is able to simulate Lakshadweep High and Lakshadweep Low (LL) during the winter and summer monsoons, respectively. During winter, the downwelling processes noticed along the coast help in the formation of temperature inversions. The inversions can be seen even up to the depths of ～50 m, which agrees with the available ARGO data in the region. Model simulations show that coastal upwelling off Kerala is at its peak in July. The intensity of upwelling reduces along the coast towards north. During the existence of LL, there is a cyclonic eddy in the sub-surface waters over the South-Eastern Arabian Sea, with vertical extent up to the depths of 100–150 m and it is strengthened due to the presence of northward counter current in the shelf region. The southerly coastal jet formed along the southern coast as a result of upwelling is noticed a westward shift along with LL. The location of the eddy off Kerala is tilted towards the open ocean with depth and our experiments suggest that this flow can be understood as a first baroclinic mode. 相似文献
9.
Interannual modulation of mesoscale eddy activity at the intraseasonal timescale in the southeastern tropical Indian Ocean
and its relation to the Indian Ocean dipole mode (IOD) events are investigated using results from a high-resolution ocean
general circulation model. The model reproduces observed characteristics of the intraseasonal variability and its interannual
modulation fairly well, with large variances of the intraseasonal variability during the 1994 and 1997/1998 IOD events. Large
negative temperature anomaly off the coasts of Java and the Lesser Sunda Islands in boreal summer, due to seasonal variation
and interannual anomaly, extended further to the east in 1994, and the associated strong Indonesian throughflow enhanced the
baroclinic instability in the upper layer, generating anomalously large mesoscale eddy activity. The eddy heat transport,
in turn, significantly affected decaying phase of the 1994 IOD event. On the other hand, the development of the cold region
off the Java Island associated with the 1997/1998 IOD event occurred in boreal winter, causing weaker baroclinic instability
and hence weaker eddy activity off Java. This led to little influence on the heat budget in the southeastern tropical Indian
Ocean for the 1997/1998 IOD event. 相似文献
10.
Sea surface temperature (SST) from a near real-time data set produced from satellites data has been assimilated into a coupled
ice–ocean forecasting model (Canadian East Coast Ocean Model) using an efficient data assimilation method. The method is based
on an optimal interpolation scheme by which SST is melded into the model through the adjustment of surface heat flux. The
magnitude and space–time variation of the adjustment depend on the depth of heat diffusion into the water column in response
to changes in surface flux, the correlation time scale of the data, and model and data errors. The diffusion depth is scaled
by the eddy diffusivity for temperature. The ratio of the model and data errors is treated as an adjustable parameter. To
evaluate the quality of the assimilation, the results from the model with and without assimilation are compared to independent
ship data from the Atlantic Zone Monitoring Program and the World Ocean Circulation Experiment. It is shown that the assimilation
has a significant impact on the modeled SST, reducing the root mean square difference (RMSD) between the model SST and the
ship SST by 0.63°C or 37%. The RMSD of the assimilated SST is smaller than that of the satellite SST by 0.23°C. This suggests
that model simulations or predictions with data assimilation can provide the best estimate of the true SST. A sensitivity
study is performed to examine the change of the model RMSD with the adjustable parameter in the assimilation equation. The
results show that there is an optimal value of the parameter and the model SST is not very sensitive to the parameter. 相似文献
11.
青海湖热力状况的模拟与未来情景之研究 总被引：5，自引：2，他引：3
运用基于湖泊热量收支与湍流扩散的湖泊热力学模型模拟了青海湖近３０年来湖水热力状况,内容包括湖泊水面温度,温度沿深度的垂直分布,冬季结冰与融冰的起迄时间,冰盖厚度;积雪深度与天数等。在此基础上,运用４个ＧＣＭｓ模型输出的ＣＯ２倍增情景下该地区的气候状况,评价了湖泊热力状况在未来的可能变化情况。 相似文献
12.
Tommy G. Jensen Timothy J. Campbell Richard A. Allard Richard Justin Small Travis A. Smith 《Ocean Dynamics》2011,61(5):657-674
The coupled ocean atmosphere mesoscale prediction system that includes the Navy Coastal Ocean Model has been configured for
the Kuroshio Extension region using multiple one-way nested high-resolution grids. The coupled model system was used to simulate
a strong cold-air outbreak event from 31 Jan to 7 Feb 2005 in good agreement with meteorological data from a surface buoy
data and QuikSCAT scatterometer winds. Latent heat fluxes and sensible heat fluxes were computed during the event with daily
averages in excess of 1,500 W/m2 and 500 W/m2, respectively, and combined instantaneous turbulent heat fluxes up to 2,300 W/m2. The largest heat fluxes were found in two large meanders of the Kuroshio and along its southern flank. Strong gradients
in turbulent heat fluxes coincided with strong sea surface temperature gradients and were maintained during the cold-air outbreak
simulation. The large turbulent heat fluxes lead to significant subtropical mode water formation during the event at a rate
about 10 Sv in the cyclonic recirculation region south of the Kuroshio. This increased the volume of core layer mode water
within the temperature range 16°C to 18°C by 10% and increased the surface area of that layer directly exposed to the atmosphere
by a factor close to 5 in the model domain. 相似文献
13.
Ocean–atmosphere coupling in the Humboldt Current System (HCS) of the Southeast Pacific is studied using the Scripps Coupled Ocean–atmosphere Regional (SCOAR) model, which is used to downscale the National Center for Environmental Prediction (NCEP) Reanalysis-2 (RA2) product for the period 2000–2007 at 20-km resolution. An interactive 2-D spatial smoother within the sea-surface temperature (SST)–flux coupler is invoked in a separate run to isolate the impact of the mesoscale (～50–200 km, in the oceanic sense) SST field felt by the atmosphere in the fully coupled run. For the HCS, SCOAR produces seasonal wind stress and wind stress curl patterns that agree better with QuikSCAT winds than those from RA2. The SCOAR downscaled wind stress distribution has substantially different impacts on the magnitude and structure of wind-driven upwelling processes along the coast compared to RA2. Along coastal locations such as Arica and Taltal, SCOAR and RA2 produce seasonally opposite signs in the total wind-driven upwelling transport. At San Juan, SCOAR shows that upwelling is mainly due to coastal Ekman upwelling transport, while in RA2 upwelling is mostly attributed to Ekman pumping. Fully coupled SCOAR shows significant SST–wind stress coupling during fall and winter, while smoothed SCOAR shows insignificant coupling throughout, indicating the important role of ocean mesoscale eddies on air–sea coupling in HCS. Coupling between SST, wind speed, and latent heat flux is incoherent in large-scale coupling and full coupling mode. In contrast, coupling between these three variables is clearly identified for oceanic mesoscales, which suggests that mesoscale SST affects latent heat directly through the bulk formulation, as well as indirectly through stability changes on the overlying atmosphere, which affects surface wind speeds. The SST–wind stress and SST–heat-flux couplings, however, fail to produce a strong change in the ocean eddy statistics. No rectified effects of ocean–atmosphere coupling were identified for either the atmospheric or oceanic mean conditions, suggesting that mesoscale coupling is too weak in this region to strongly alter the basic climate state. 相似文献
14.
P. L. S. Rao 《Pure and Applied Geophysics》2001,158(5-6):965-988
—?In this paper, we examine the large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture over the Asian summer monsoon region. The five year (1986–1990) uninitialized daily analyses for the summer season comprising June, July and August (JJA), produced at the European Centre for Medium Range Weather Forecasts (ECMWF) under the aegis of Tropical Ocean and Global Atmosphere (TOGA) have been considered to carry out the study.¶The following features characterize the Asian summer monsoon domain. It acts as the source of kinetic energy as well as vorticity, and sink of heat and moisture. Kinetic energy and vorticity are produced in the monsoon region and transported horizontally. On the contrary, heat and moisture are transported into the monsoon region. The zonal and meridional components of adiabatic generation of kinetic energy contribute to the production of kinetic energy over the Arabian Sea and Bay of Bengal, respectively. The horizontal advection of relative vorticity is balanced by sub-grid scale generation. The angular momentum generated due to pressure torque (east-west pressure gradient) is balanced by the flux convergence of omega momentum. Further, the angular momentum budget delineates that flux convergence of relative momentum is necessary to maintain the surface westerlies against the friction. The horizontal convergence of heat and moisture facilitates enhancement of diabatic heating, and also leads to the formation of diabatic heat sources, which are crucial to sustain the summer monsoon circulation. 相似文献
15.
The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales. 相似文献
16.
本模式用以K半经验理论为基础的闭合方程组求解,引进了地形作用、动量、热量和水汽的侧向扩散和垂直湍流交换以及凝结加热等物理过程,其中湍流交换系数K是地表粗糙度、几何高度、大气稳定度及风速切变等因子的函数。本模式还考虑了山地、平原和水面在地形高度、地表粗糙度、辐射、蒸发及热交换等方面的差异,在下垫面上建立热平衡方程与边界层内控制方程耦合。将模式应用于太湖流域,计算得到的该流域边界层内温、压、湿、风的分布特征与实际情况相似,模式具有一定的实用性。 相似文献
17.
本模式用以K半经验理论为基础的闭合方程组求解,引进了地形作用、动量、热量和水汽的侧向扩散和垂直湍流交换以及凝结加热等物理过程,其中湍流交换系数K是地表粗糙度、几何高度、大气稳定度及风速切变等因子的函数。本模式还考虑了山地、平原和水面在地形高度、地表粗糙度、辐射、蒸发及热交换等方面的差异,在下垫面上建立热平衡方程与边界层内控制方程耦合。将模式应用于太湖流域,计算得到的该流域边界层内温、压、湿、风的分布特征与实际情况相似,模式具有一定的实用性。 相似文献
18.
The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales.
相似文献19.
Cyrus Karas Dirk Nürnberg Ralf Tiedemann Dieter Garbe-Schönberg 《Earth and Planetary Science Letters》2011,301(1-2):117-124
The transition from the early Pliocene “Warmhouse” towards the present “Icehouse” climate and the role of Gateway dynamics are intensively debated. Both, the constrictions of the Central American Seaway and the Indonesian Gateway affected ocean circulation and climate during the Pliocene epoch. Here, we use combined δ18O and Mg/Ca ratios of planktonic foraminifera (marine protozoa) from surface and subsurface levels to reconstruct the thermal structure and changes in salinities from the Southwest Pacific Deep Sea Drilling Project (DSDP) Site 590B from 6.5 to 2.5 Ma. Our data suggest a gradual cooling of ~ 2 °C and freshening of the sea surface during ~ 4.6–4 Ma with an increased meridional temperature gradient between the West Pacific Warm Pool and the Southwest Pacific when the closing of the Central American Seaway reached a critical threshold. After ~ 3.5 Ma, the restricted Indonesian Gateway might have amplified the East Australian Current, allowing enhanced heat transport towards the Southwest Pacific with reduced meridional temperature gradients when the global climate gradually cooled. At the same time our data suggest a cooling and freshening of Subantarctic Mode Water (SAMW) or/and an increased northward flow of SAMW towards Site 590B, possibly a first step towards the present Antarctic Frontal System. 相似文献
20.
J.K. Cochran M.P. Bacon S. Krishnaswami K.K. Turekian 《Earth and Planetary Science Letters》1983,65(2):433-452
Disequilibrium between210Po and210Pb and between210Pb and226Ra has been mapped in the eastern and central Indian Ocean based on stations from Legs 3 and 4 of the GEOSECS Indian Ocean expedition.210Po/210Pb activity ratios are less than 1.0 in the surface mixed layer and indicate a residence time for Po of 0.6 years.210Po and210Pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100–500 m, where Po may be returned to solution after removal from the surface water, and in samples taken near the bottom at a few stations.210Pb excesses relative to226Ra are observed in the surface water but these excesses are not as pronounced as in the North Pacific and North Atlantic. The difference is attributable to a lower flux of210Pb from the atmosphere to the Indian Ocean. Below the main thermocline,210Pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom. Departures from this pattern are especially evident at stations taken in the Bay of Bengal (where210Pb/226Ra activity ratios as low as 0.16 are observed) and near the Mid-Indian Ridge. The data suggest that removal of210Pb at oceanic boundaries, coupled with eddy diffusion along isopycnals, can explain gradients in210Pb near the boundary. Application of a simple model including isopycnal diffusion, chemical removal, production and radioactive decay produces fits the observed210Pb/226Ra gradients for eddy diffusion coeffients of ～ 107 cm2/s. High productivity in surface waters of the Bay of Bengal makes this region a sink for reactive nuclides in the northern Indian Ocean. 相似文献