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1.
The circulation of the Southern Ocean is studied in the eddy-resolving model POP (Parallel Ocean Program) by an analysis
of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to include topography and continental
boundaries, thus deviations from a zonally integrated state involve transient and standing eddies. The meridional circulation
is presented in terms of the Eulerian, eddy-induced, and residual streamfunctions. It is shown that the splitting of the meridional
circulation into Ekman and geostrophic transports and the component induced by subgrid and Reynolds stresses is identical
to a particular form of the zonally integrated balance of zonal momentum. In this balance, the eddy-induced streamfunctions
represent the interfacial form stresses by transient and standing eddies and the residual streamfunction represents the acceleration
of the zonal current by density fluxes in a zonally integrated frame. The latter acceleration term is directly related to
the surface flux of density and interior fluxes due to the resolved and unresolved eddies. The eddy-induced circulation is
extremely vigorous in POP. In the upper ocean a shallow circulation, reversed in comparison to the Deacon cell and mainly
due to standing eddies, appears to the north of Drake Passage latitudes, and in the Drake Passage belt of latitudes a deep-reaching
cell is induced by transient eddies. In the resulting residual circulation the Deacon cell is largely cancelled and the residual
advection of the zonal mean potential density is balanced by diapycnal eddy and subgrid fluxes which are strong in the upper
few hundred meters but small in the ocean interior. The balance of zonal momentum is consistent with other eddy-resolving
models; a new aspect is the clear identification of density effects in the zonally integrated balance. We show that the wind
stress and the stress induced by the residual circulation drive the eastward current, whereas both eddy species result in
a braking. Finally, we extend the Johnson–Bryden model of zonal transport to incorporate all relevant terms from the zonal
momentum balance. It is shown that wind stress and induction by the residual circulation carry an eastward transport while
bottom form stress and the stress induced by standing eddies yield westward components of transport.
Received: 26 June 2001 / Accepted: 2 November 2001 相似文献
2.
The inertial coupling approach for the momentum transfer at the ocean–atmosphere interface, which is based on the assumption
of a similarity hypothesis in which the ratio between the water and air reference velocities is equal to the square root of
the ratio between the air and water densities, is reviewed using a wave model. In this model, the air and water reference
velocities are identified, respectively, with the spectrally weighted phase velocity of the gravity waves and the Stokes velocity
at the water roughness length, which are evaluated in terms of the dimensionless frequency limits in Toba's equilibrium spectrum.
It is shown that the similarity hypothesis is approximately satisfied by the wave model over the range of wave ages encountered
in typical sea states, and that the predicted values of the dimensionless surface drift velocity, the dimensionless water
reference velocity, and the Charnock constant are in reasonable agreement with observational evidence. The application of
the bulk relationship for the surface shear stress, derived from the inertial coupling hypothesis in general circulation modeling,
is also discussed.
Received: 6 January 2001 / Accepted: 28 June 2001 相似文献
3.
The response of phytoplankton communities to changing lake environments 总被引:10,自引:0,他引:10
Colin S. Reynolds 《Aquatic Sciences - Research Across Boundaries》1987,49(2):220-236
In this paper, empirical relationships between the mean phytoplankton biomass and limiting nutrient availability and between
the underwater extinction of light and the biomass are used to define some of the physical aspects of lake environments subject
to cultural eutrophication or to corrective restoration measures. The distinctive floristic distributions of different algae
among such environments are shown to be closely related to general morphological and physiological properties of the algae
themselves and that species sharing similar size- and shape-adaptations also share similar ecological growth and survival
strategies. From these general predictions of the responses of phytoplankton to changing lake environments, it is deduced
that deep lakes are slower to respond than shallow ones but that the transition between nutrient-and light-limitation is relatively
abrupt: ‘resilience’ of the system to restoration measures may be an expression of their progress towards the transition.
Presented at the International Conference on Lake Restoration in Zürich, 3–4 November 1986 相似文献
4.
Effects of mesoscale eddies on the marine ecosystem in the Kuroshio Extension (KE) region are investigated using an eddy-resolving
coupled physical-biological model. The model captures the seasonal and intra-seasonal variability of chlorophyll distribution
associated with the mesoscale eddies, front variability, Kuroshio meanders, and upwelling. The model also reproduces the observed
interannual variability of sea surface height anomaly (SSHA) in the KE region along a zonal band of 32–34°N from 2002 to 2006.
The distribution of high surface chlorophyll corresponds to low SSHA. Cyclonic eddies are found to detach from the KE jet
near 150°E and 158°E and propagate westward. The westward propagating cyclonic eddies lift the nutrient-rich thermocline into
the euphotic zone and maintain high levels of chlorophyll in summer. In the subsurface layer, the pattern in chlorophyll is
influenced by both lateral and vertical advection. In winter, convection inside the eddy entrains high levels of nutrients
into the mixed layer, increasing production, and resulting in high chlorophyll concentration throughout the surface mixed
layer. There is significant interannual variability in both the cyclonic eddy activity and the surface phytoplankton bloom
south of the KE jet, although whether or not there is a causal link is unclear. 相似文献
5.
Homogeneous, nonrotating flow over a backward-facing rounded step is simulated using the 2D vertical version of two general
circulation models, a z-coordinate model—the Massachusetts Institute of Technology general circulation model (MITgcm)—and a σ-coordinate model—the Bergen Ocean Model (BOM). The backward-facing step is a well-known testcase since it is geometrically
simple but still embodies important flow characteristics such as separation point, reattachment length, and recirculation
of the flow. The study compares the core of the two models and uses constant eddy viscosities and diffusivities. The Reynolds
numbers ranges from 2·102 to 2·106. The results correspond with previously published results having a relatively stationary separation point and a fluctuating
reattachment length due to downslope propagating eddies released from the reattachment zone for Reynolds numbers higher than
or equal to 2 · 104. For Reynolds number within the laminar regime, the flow is stationary. The discrepancies between the models increase by
enhancing Reynolds numbers. The σ-coordinate model experiences a reduction in eddy sizes with increasing resolution and Reynolds numbers in correspondence
with published experiments, while the size of the eddies are independent of the Reynolds number using the MITgcm. Due to mixing
generated by the staircase topography, the z-coordinate model gives a better convergence of the separation point and reattachment length compared with the BOM; however,
this conclusion might change with the inclusion of a relevant turbulence scheme. 相似文献
6.
The wind-driven circulation in the northwestern Pacific and the South China Sea (SCS) is simplified as a two-layer, quasi-geostrophic
model in two rectangular basins connected by an idealized strait. This model is used to investigate the impact of the western
boundary current (WBC) on the adjacent marginal sea. The variability of the circulation in the two basins is investigated
with a high resolution and at low viscosity, which allows the numerical solution to resolve mesoscale eddy forcing. The model
ocean is driven by the time-independent asymmetric wind stress acting on the idealized Pacific (large basin) only. Under the
reference parameters used in this study, the WBC can intrude into the idealized SCS (small basin) in the form of a loop current,
shedding eddies regularly. The rate of eddy shedding is nearly constant throughout the entire integration time of the model;
however, the intensity of the eddy-shedding exhibits multiple timescale variability ranging from quasi-biennial to decadal
timescale. A set of sensitivity experiments demonstrate that our results are robust against changes to model parameters and
geometry. Multivariate spectral analysis is used to extract the spatiotemporal feature of the variability. Joint analysis
for the two basins shows that the circulation in the idealized SCS is significantly impacted by the variability at decadal
(15-year), interannual (5–7-year and quasi-biennial), and quasi-annual timescales. The spatial structures of the modes of
variablility suggest that the variance in position of the WBC, combined with mesoscale activity, act to influence the low-frequency
modes of the idealized SCS. The structural differences between the modes strongly impacting the idealized SCS and those having
weak influence are also presented. 相似文献
7.
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
8.
A mesoscale eddy detection method of specific intensity and scale from SSH image in the South China Sea and the Northwest Pacific 总被引:2,自引:0,他引:2
Mesoscale eddies exist almost everywhere in the ocean and play important roles in the ocean circulation of the world. These eddies may cause sound spread singular regions and bring great influences to the upwater ship and underwater aircraft. Due to the lack of hydrographic survey datasets, study of mesoscale eddies has been greatly restricted. Fortunately, satellite altimeter provided an effective way to study mesoscale eddies. An automatic detection algorithm is introduced to detect mesoscale eddies of specific intensity and spatial/temporal scale based on satellite sea surface height (SSH) data and the algorithm is applied in a strong eddy activity region: the South China Sea and the Northwest Pacific. The algorithm includes four steps. The first step is preprocessing of the SSH image, which includes elimination of error SSH data and interpolation. The second step is to detect suspected mesoscale eddies from preprocessed SSH images by dynamic threshold adjustment and morphological method, and the suspected mesoscale eddy detection includes two procedures: suspected mesoscale eddy core region detection and suspected mesoscale eddy brim extraction. The third step is to pick out mesoscale eddies satisfied with specified criteria from suspected mesoscale eddies. The criteria include three items, that is, intensity criterion, spatial scale, criterion and temporal scale criterion. The last step is algorithm performance analysis and verification. The algorithm has the capability of adaptive parameter adjustment, and can extract mesoscale eddies of interested intensity and spatial/temporal scale. The paper can provide a basis for analyzing space-time characteristics of mesoscale eddy in the South China Sea and the Northwest Pacific. 相似文献
9.
Experiments on degassing of water-saturated granite melts with a pressure drop from 100 and 450 MPa to 40 and 120 MPa, respectively,
at temperatures close to feldspar liquidus (750–700 °C), were carried out to determine the modality of water exsolution and
vesicle formation at the liquidus temperature. Pressure-drop rates as small as approximately 100 bar/day were used. Uniform
space distributions of bubbles of exsolved water were obtained with starting glass containing a small fraction (≈0.5 vol.%)
of trapped air bubbles. Volume crystallization of feldspar was observed in degassed melts supplied with seeds. Bubble size
distributions (BSD) measured in granite glasses after degassing are presented. Data on vesicle characteristics (number, radius,
area, elongation) were acquired on images digitized with standard software, while the reconstruction of size distributions
was performed with the Schwartz-Saltikov "unfolding" procedure. Bubble size distributions of size classes in the range 5–1000 μm
were acquired with proper magnification and satisfactory statistical reliability of determined number densities. The BSDs
of the experimental samples are compared with the results of measurements of rapidly degassed products of Mt. Etna and Vulcano
Island. Many particular features of the bubble nucleation and growth can be distinguished in an individual BSD. However, the
general BSD of the whole data set, including natural ones, can be relatively well described with linear regression in bilogarithmic
coordinates. The slope of this regression is approximately 2.8±0.1. This dependence is in striking contrast with distributions
theoretically predicted with classical nucleation models based on homogeneous nucleation of vesicles. The theoretical distribution
requires the occurrence of strong maxima that are not observed in our experimental and natural samples, thus arguing for heterogeneous
nucleation mechanisms.
Received: 1 October 1998 / Accepted: 25 June 1999 相似文献
10.
The ocean takes up approximately 2 GT carbon per year due to the enhanced CO2 concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO2 into the atmosphere, and among these are CO2 storage in the deep ocean. Topographic effects of dissolution and transport from a CO2 lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ-coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in
order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect
from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom
and the CO2 lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical
studies of dissolution from a CO2 lake. When topography is introduced, it is shown that the z-coordinate model and the σ-coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm − 2 s − 1 for the scenario of a 20-m-deep trench using BOM and 0.005–0.02 μmol cm − 2 s − 1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO2 stored in geological formations and to the ocean. 相似文献
11.
William D. Smyth Eric D. Skyllingstad Gregory B. Crawford Hemantha Wijesekera 《Ocean Dynamics》2002,52(3):104-115
The K-profile parameterization of upper-ocean mixing is tested and extended using observations and large eddy simulations
of upper-ocean response to a westerly windburst. A nonlocal momentum flux term is added, and the amplitude of the nonlocal
scalar flux is recalibrated. Parameterizations of Stokes drift effects are added following recent work by McWilliams and Sullivan
(2001). These changes allow the parameterization to produce both realistic gradients of momentum and scalars in the nocturnal
boundary layer and enhanced mixing during stable conditions. The revised parameterization is expected to produce improved
representations of lateral advection and sea-surface temperature in large-scale models.
Received: 31 August 2001 / Accepted: 15 December 2001 相似文献
12.
Insight regarding the mean and eddy motion in the Skagerrak/northern North Sea area is gained through an analysis of model-simulated currents, hydrography, kinetic energy and relative vorticity for the 2 years 2000 and 2001. In this a -coordinate ocean model is used. Since the tidal currents are generally strong in the area, care is exercised to distinguish the mesoscale (eddy) motion from higher-frequency motion such as tides, before computing the mean and eddy kinetic energy. The model-simulated response is first compared with available knowledge of the circulation in the area, and when available, also with sea-surface temperature obtained from satellite imagery. It is concluded that the model appears to faithfully reproduce most of what is known, in particularly the upper mixed layer circulation. An analysis of the mean and eddy kinetic energy reveals that many of the mesoscale structures found in the area are recurrent. This is particularly true for the structures off the southern tip of Norway. Also in general, areas of strong mean and eddy kinetic energy are co-located. The exception is the area off the southern tip of Norway, where the eddy kinetic energy is much larger than its mean counterpart. An analysis of the relative vorticity reveals that the variability found is due to the occurrence of recurrent anticyclonic eddies. It is hypothesized that these eddies are generated due to an offshore veering of the Norwegian coastal current (NCC) as it reaches the eastern end of the Norwegian Trench plateau. Here it becomes a free jet, which is then vulnerable to either barotropic instability caused by the horizontal shear in the jet-like structure of the NCC at this point, or a baroclinic (frontal) instability. The latter may come into play when the NCC veers offshore and its relatively fresh water meets the inflowing saline water of Atlantic origin, a frontogenesis that may become strong enough for cyclogenesis to take place. Due to the depth-independent nature of the model-generated eddies, the barotropic instability is the most likely candidate. It remains to resolve the reason for the offshore veering of the NCC. The most likely candidate mechanisms are vortex squeezing or simply that the coastline curvature is large enough for the NCC to separate from the coast in a hydraulic sense.Responsible Editor: Phil Dyke 相似文献
13.
A complex and highly dynamical ocean region, the Agulhas Current System plays an important role in the transfer of energy, nutrients and organic material from the Indian to the Atlantic Ocean. Its dynamics are not only important locally, but affect the global ocean-atmosphere system. In working towards improved ocean reanalysis and forecasting capabilities, it is important that numerical models simulate mesoscale variability accurately—especially given the scarcity of coherent observational platforms in the region. Data assimilation makes use of scarce observations, a dynamical model and their respective error statistics to estimate a new, improved model state that minimises the distance to the observations whilst preserving dynamical consistency. Qualitatively, it is unclear whether this minimisation directly translates to an improved representation of mesoscale dynamics. In this study, the impact of assimilating along-track sea-level anomaly (SLA) data into a regional Hybrid Coordinate Ocean Model (HYCOM) is investigated with regard to the simulation of mesoscale eddy characteristics. We use an eddy-tracking algorithm and compare the derived eddy characteristics of an assimilated (ASSIM) and an unassimilated (FREE) simulation experiment in HYCOM with gridded satellite altimetry-derived SLA data. Using an eddy tracking algorithm, we are able to quantitatively evaluate whether assimilation updates the model state estimate such that simulated mesoscale eddy characteristics are improved. Additionally, the analysis revealed limitations in the dynamical model and the data assimilation scheme, as well as artefacts introduced from the eddy tracking scheme. With some exceptions, ASSIM yields improvements over FREE in eddy density distribution and dynamics. Notably, it was found that FREE significantly underestimates the number of eddies south of Madagascar compared to gridded altimetry, with only slight improvements introduced through assimilation, highlighting the models’ limitation in sustaining mesoscale activity in this region. Interestingly, it was found that the threshold for the maximum eddy propagation velocity in the eddy detection scheme is often exceeded when data assimilation relocates an eddy, causing the algorithm to interpret the discontinuity as eddy genesis, which directly influences the eddy count, lifetime and propagation velocity, and indirectly influences other metrics such as non-linearity. Finally, the analysis allowed us to separate eddy kinetic energy into contributions from detected mesoscale eddies and meandering currents, revealing that the assimilation of SLA has a greater impact on mesoscale eddies than on meandering currents. 相似文献
14.
The oceanic response to a typhoon, where mesoscale ocean circulations co-exist, was investigated by analyzing the independent
observations of profiling floats data at three different locations, satellite altimetry data near the eye of Typhoon Man-Yi
(2007) before and after its passage, and synthetic aperture radar data taken during the typhoon’s passage. In spite of the
nearly symmetric wind pattern around the eye, the distribution of mesoscale eddies had a major impact on the surface currents
and mixed layer (ML) depths. As a result, the entrainment of the water below the ML into the ML was affected by the mesoscale
circulation and became asymmetric, which accounted for most of the changes observed in the temperature profiles. Changes in
the isotherms were driven primarily by the westward propagation of the mesoscale pattern rather than by the typhoon-induced
shoaling. The typhoon-induced shoaling could have played a significant role in the generation of high-frequency (e.g., near-inertial)
oscillations and/or sub-mesoscale structures. Although a similar or even greater energy flux was observed at the surface,
the entrainment within the anticyclonic circulation was weaker than that within the cyclonic circulation and at the edge of
the anticyclonic circulation because of the thick pre-existing ML. A strong ocean response to Typhoon Man-Yi (2007) within
a cyclonic circulation or at the edge of an anticyclonic circulation, rather than within an anticyclonic eddy, has implications
for the role of mesoscale ocean circulations in better understanding and forecasting the typhoon intensity. 相似文献
15.
Jennifer L. Lewicki George E. Hilley Laura Dobeck Bruno D. V. Marino 《Bulletin of Volcanology》2012,74(1):135-141
Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO2 fluxes and quantify CO2 emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO2 flux were made during September–October 2010 and ranged from 85 to 1,766 g m−2 day−1. Comparative maps of soil CO2 flux were simulated and CO2 emission rates estimated from three accumulation chamber (AC) CO2 flux surveys. Least-squares inversion of measured eddy covariance CO2 fluxes and corresponding modeled source weight functions recovered 58–77% of the CO2 emission rates estimated based on simulated AC soil CO2 fluxes. Spatial distributions of modeled surface CO2 fluxes based on EC and AC observations showed moderate to good correspondence (R
2 = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO2 emissions over relatively large areas. 相似文献
16.
Vertical dynamics of summer phytoplankton in a stratified estuary (Gulf of Finland,Baltic Sea) 总被引:1,自引:1,他引:0
Urmas Lips Inga Lips Taavi Liblik Villu Kikas Kristi Altoja Natalja Buhhalko Nelli Rünk 《Ocean Dynamics》2011,61(7):903-915
We present the results of multiparametric observations designed to follow the phytoplankton dynamics and interrelated physical,
chemical and biological processes in the Gulf of Finland (Baltic Sea). Data were acquired by an autonomous moored water column
profiler, an acoustic Doppler current profiler, a flow-through system installed aboard a ferry and by profiling and discrete
water sampling aboard research vessels in July and August 2009. The main aim of the study was to investigate the processes
responsible for the formation and maintenance of sub-surface maxima of phytoplankton biomass. We suggest that the environmental
conditions caused by the prevailing atmospheric and oceanographic forcing (wind; vertical stratification; basin-wide, mesoscale
and sub-mesoscale processes) are preferred by certain species/taxonomic groups and explain the migration patterns of phytoplankton.
Nocturnal downward migration of phytoplankton with a swimming speed up to 1.6 m h−1 occurred when the community was dominated by the dinoflagellate Heterocapsa triquetra. The observed splitting of the population into two vertically separated biomass maxima suggests that the H. triquetra cells, which reached the sub-surface layers with high nutrient concentrations, experienced bi-diurnal or asynchronous (when
swimming upwards) vertical migration. The most intense sub-surface biomass maxima, on some occasions with the biomass much
higher than that in the surface layer, were detected in connection to the sub-mesoscale intrusions below the depth of the
strongest vertical density gradient. 相似文献
17.
Karin M. H. Huijts Huib E. de Swart George P. Schramkowski Henk M. Schuttelaars 《Ocean Dynamics》2011,61(8):1067-1091
An analytical and a numerical model are used to understand the response of velocity and sediment distributions over Gaussian-shaped
estuarine cross-sections to changes in tidal forcing and water depth. The estuaries considered here are characterized by strong
mixing and a relatively weak along-channel density gradient. It is also examined under what conditions the fast, two-dimensional
analytical flow model yields results that agree with those obtained with the more complex three-dimensional numerical model.
The analytical model reproduces and explains the main velocity and sediment characteristics in large parts of the parameter
space considered (average tidal velocity amplitude, 0.1–1 m s − 1 and maximum water depth, 10–60 m). Its skills are lower for along-channel residual flows if nonlinearities are moderate to
high (strong tides in deep estuaries) and for transverse flows and residual sediment concentrations if the Ekman number is
small (weak tides in deep estuaries). An important new aspect of the analytical model is the incorporation of tidal variations
in the across-channel density gradient, causing a double circulation pattern in the transverse flow during slack tides. The
gradient also leads to a new tidally rectified residual flow component via net advection of along-channel tidal momentum by
the density-induced transverse tidal flow. The component features landward currents in the channel and seaward currents over
the slopes and is particularly effective in deeper water. It acts jointly with components induced by horizontal density differences,
Coriolis-induced tidal rectification and Stokes discharge, resulting in different along-channel residual flow regimes. The
residual across-channel density gradient is crucial for the residual transverse circulation and for the residual sediment
concentration. The clockwise density-induced circulation traps sediment in the fresher water over the left slope (looking
up-estuary in the northern hemisphere). Model results are largely consistent with available field data of well-mixed estuaries. 相似文献
18.
Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products. Enhanced productivity and a shift in the PSC were observed, which were likely due to upwelling of nutrient-rich water into the euphotic zone. The supply of nutrients promoted the growth of larger cells (micro- and nanoplankton), and the PSC shifted to greater sizes. However, the picoplankton were still important and contributed ∼48% to total chla concentration. In addition, PSC time series revealed a lag period of about three weeks between maximum eddy intensity and maximum chlorophyll, which may have been related to phytoplankton growth rate and duration of eddy intensity. 相似文献
19.
Two prognostic experiments taking into account real atmospheric forcing for 2006 and 2011 were carried out based on the eddy-resolving numerical model with a horizontal resolution of 1.6 km for the Black Sea. The main dynamic features such as the Rim Current, the Sevastopol, and Batumi anticyclones are reproduced in both experiments. The model results are confirmed via observation data. We accomplished the analysis of simulated circulation and energetics. The results demonstrate that both the vertical viscosity and vertical diffusion along with the energy inflow from the wind have been the main contributors to the annual and seasonal budgets of kinetic and potential energies of the Black Sea circulation. It is shown that two regimes of the Black Sea general circulation are implemented depending on a magnitude of wind contribution to the kinetic energy in winter. Intensive mesoscale eddy formation was observed along the Anatolian, Caucasian, and Crimean coasts. The analysis of the Black Sea circulation and eddy energetics allowed us to conclude that the generation and development of the mesoscale coastal eddies is associated with the barotropic instability in case of intensive coastal currents and is associated with both the barotropic and baroclinic instability in case of weak coastal currents. 相似文献
20.
U. Yalçın Kalyoncuoglu 《Journal of Seismology》2007,11(2):131-148
In this study, the spatial distributions of seismicity and seismic hazard were assessed for Turkey and its surrounding area.
For this purpose, earthquakes that occurred between 1964 and 2004 with magnitudes of M ≥ 4 were used in the region (30–42°N and 20–45°E). For the estimation of seismicity parameters and its mapping, Turkey and
surrounding area are divided into 1,275 circular subregions. The b-value from the Gutenberg–Richter frequency–magnitude distributions is calculated by the classic way and the new alternative
method both using the least-squares approach. The a-value in the Gutenberg–Richter frequency–magnitude distributions is taken as a constant value in the new alternative method.
The b-values calculated by the new method were mapped. These results obtained from both methods are compared. The b-value shows different distributions along Turkey for both techniques. The b-values map prepared with new technique presents a better consistency with regional tectonics, earthquake activities, and
epicenter distributions. Finally, the return period and occurrence hazard probability of M ≥ 6.5 earthquakes in 75 years were calculated by using the Poisson model for both techniques. The return period and occurrence
hazard probability maps determined from both techniques showed a better consistency with each other. Moreover, maps of the
occurrence hazard probability and return period showed better consistency with the b-parameter seismicity maps calculated from the new method. The occurrence hazard probability and return period of M ≥ 6.5 earthquakes were calculated as 90–99% and 5–10 years, respectively, from the Poisson model in the western part of the
studying region. 相似文献