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1.
A high resolution (3–8 km grid), 3D numerical ocean model of the West Caribbean Sea (WCS) is used to investigate the variability
and the forcing of flows near the Meso-American Barrier Reef System (MBRS) which runs along the coasts of Mexico, Belize,
Guatemala and Honduras. Mesoscale variations in velocity and temperature along the reef were found in seasonal model simulations
and in observations; these variations are associated with meandering of the Caribbean current (CC) and the propagation of
Caribbean eddies. Diagnostic calculations and a simple assimilation technique are combined to infer the dynamically adjusted
flow associated with particular eddies. The results demonstrate that when a cyclonic eddy (negative sea surface height anomaly
(SSHA)) is found near the MBRS the CC shifts offshore, the cyclonic circulation in the Gulf of Honduras (GOH) intensifies,
and a strong southward flow results along the reef. However, when an anticyclonic eddy (positive SSHA) is found near the reef,
the CC moves onshore and the flow is predominantly westward across the reef. The model results help to explain how drifters
are able to propagate in a direction opposite to the mean circulation when eddies cause a reversal of the coastal circulation.
The effect of including the Meso-American Lagoon west of the Belize Reef in the model topography was also investigated, to
show the importance of having accurate coastal topography in determining the variations of transports across the MBRS. The
variations found in transports across the MBRS (on seasonal and mesoscale time scales) may have important consequences for
biological activities along the reef such as spawning aggregations; better understanding the nature of these variations will
help ongoing efforts in coral reef conservation and maintaining the health of the ecosystem in the region. 相似文献
2.
A semi-empirical formulation is given of the rate of stellar mass loss by stellar winds. Evolutionary studies of stars in the pre-main sequence (T Tauri) stage are presented for a variety of rates of mass loss. It has been found that different mass loss rates produce only small changes in the positions of equal evolutionary time lines in HR diagrams. Thus it is concluded that the spread of points in HR diagrams of young clusters results from a spread in their times of formation. This is consistent with the initiation of star formation by violent hydrodynamic compression of a typical interstellar cloud. 相似文献
3.
Ocean Dynamics - Fast sea level rise (SLR) is causing a growing risk of flooding to coastal communities around the Chesapeake Bay (hereafter, CB or “the Bay”), but there are also... 相似文献
4.
Observations of currents aimed to study the flow near a spawning aggregation reef, Gladden Spit off the coast of Belize, reveal unusually strong currents on 19–20 October 2009 (the current speed was over 1?m?s?1, when the mean and standard deviation are 0.2?±?0.12?m?s?1). During this short time, the water level was raised by 60–70?cm above normal in one place, but lowered by 10–20?cm in another location just 2?km away. The temperature dropped by over 2°C within a few hours. Analyses of local and remote sensing data suggest that a rare combination of an offshore Caribbean cyclonic eddy, a short-lived local tropical storm, and a Spring tide, all occurred at the same time and creating a “perfect storm” condition that resulted in the unusual event. High-resolution simulations and momentum balance analysis demonstrate how the unique shape of the coral reef amplified the coastal current through nonlinear flow–topography interactions. The suggested mechanism for the water level change is different than the classical wind-driven storm surge process. The study has implications for the influence of external forcing on mixing processes and physical–biological interactions near coral reefs. 相似文献
5.
Tidal-driven dynamics and mixing processes in a coastal ocean model with wetting and drying 总被引：2，自引：2，他引：0
A three-dimensional sigma coordinate numerical model with wetting and drying (WAD) and a Mellor–Yamada turbulence closure
scheme has been used in an idealized island configuration to evaluate how tidally driven dynamics and mixing are affected
by inundation processes. Comprehensive sensitivity experiments evaluate the influence of various factors, including tidal
amplitudes (from 1- to 9-m range), model grid size (from 2 to 16 km), stratification, wind, rotation, and the impact of WAD
on the mixing. The dynamics of the system involves tidally driven basin-scale waves (propagating anticlockwise in the northern
hemisphere) and coastally trapped waves propagating around the island in an opposite direction. The evolutions of the surface
mixed layer (SML) and the bottom boundary layer (BBL) under different forcing have been studied. With small amplitude tides,
wind-driven mixing dominates and the thickness of the SML increases with time, while with large-amplitude tides, tidal mixing
dominates and the thickness of the BBL increases with time. The inclusion of WAD in the simulations increases bottom stress
and impacts the velocities, the coastal waves, and the mixing. However, the impact of WAD is complex and non-linear. For example,
WAD reduces near-coast currents during flood but increases currents during ebb as water drains from the island back to the
sea. The impacts of WAD, forcing, and model parameters on the dynamics are summarized by an analysis of the vorticity balance
for the different sensitivity experiments. 相似文献
6.
Fangli Qiao Yeli Yuan Tal Ezer Changshui Xia Yongzeng Yang Xingang Lü Zhenya Song 《Ocean Dynamics》2010,60(5):1339-1355
A theoretical framework to include the influences of nonbreaking surface waves in ocean general circulation models is established
based on Reynolds stresses and fluxes terms derived from surface wave-induced fluctuation. An expression for the wave-induced
viscosity and diffusivity as a function of the wave number spectrum is derived for infinite and finite water depths; this
derivation allows the coupling of ocean circulation models with a wave number spectrum numerical model. In the case of monochromatic
surface wave, the wave-induced viscosity and diffusivity are functions of the Stokes drift. The influence of the wave-induced
mixing scheme on global ocean circulation models was tested with the Princeton Ocean Model, indicating significant improvement
in upper ocean thermal structure and mixed layer depth compared with mixing obtained by the Mellor–Yamada scheme without the
wave influence. For example, the model–observation correlation coefficient of the upper 100-m temperature along 35° N increases
from 0.68 without wave influence to 0.93 with wave influence. The wave-induced Reynolds stress can reach up to about 5% of
the wind stress in high latitudes, and drive 2–3 Sv transport in the global ocean in the form of mesoscale eddies with diameter
of 500–1,000 km. The surface wave-induced mixing is more pronounced in middle and high latitudes during the summer in the
Northern Hemisphere and in middle latitudes in the Southern Hemisphere. 相似文献
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9.
Modeling and observations of high-frequency flow variability and internal waves at a Caribbean reef spawning aggregation site 总被引：2，自引：2，他引：0
The characteristics and forcing mechanisms of high-frequency flow variations (periods of minutes to days) were investigated
near Gladden Spit, a reef promontory off the coast of Belize. Direct field observations and a high-resolution (50-m grid size)
numerical ocean model are used to describe the flow variations that impact the initial dispersion of eggs and larvae from
this site, which serves as a spawning aggregation site for many species of reef fishes. Idealized sensitivity model experiments
isolate the role of various processes, such as internal waves, wind, tides, and large-scale flow variations. The acute horizontal
curvature and steep topography of the reef intensify the flow, create small-scale convergence and divergence zones, and excite
high-frequency oscillations and internal waves. Although the tides in this area are relatively small (∼10-cm amplitude), the
model simulations show that tides can excite significant high-frequency flow variations near the reef, which suggests that
the preference of fish to aggregate and spawn in the days following the time of full moon may not be coincidental. Even small
variations in remote flows (2–5 cm s−1) due to say, meso-scale eddies, are enough to excite near-reef oscillations. Model simulations and the observations further
suggest that the spawning site at the tip of the reef provides initial strong dispersion for eggs, but then the combined influence
of the along-isobath flow and the westward wind will transport the eggs and larvae downstream of Gladden Spit toward less
turbulent region, which may contribute to enhanced larval survival. 相似文献
10.
Sensitivity studies with a new generalized coordinate ocean model are performed in order to compare the behavior of bottom boundary layers (BBLs) when terrain-following (sigma or combined sigma and z-level) or z-level vertical grids are used, but most other numerical aspects remain unchanged. The model uses a second-order turbulence closure scheme that provides surface and BBL mixing and results in a quite realistic climatology and deep water masses after 100 year simulations with a coarse resolution (1° × 1°) basin-scale terrain-following grid. However, with the same turbulence scheme but using a z-level grid, the model was unable to produce dense water masses in the deep ocean. The latter is a known problem for coarse resolution z-level models, unless they include highly empirical BBL schemes.A set of dense water overflow experiments with high-resolution grids (10 and 2.5 km) are used to investigate the influence of model parameters such as horizontal diffusivity, vertical mixing, horizontal resolution, and vertical resolution on the simulation of bottom layers for the different coordinate systems. Increasing horizontal diffusivity causes a thinner BBL and a bottom plume that extends further downslope in a sigma grid, but causes a thicker BBL and limited downslope plume extension in a z-level grid. A major difference in the behavior of the BBL in the two grids is due to the larger vertical mixing generated by the turbulence scheme over the step-like topography in the z-level grid, compared to a smaller vertical mixing and a more stably stratified BBL in the sigma grid. Therefore, the dense plume is able to maintain its water mass better and penetrates farther downslope in the sigma grid than in the z-level grid. Increasing horizontal and vertical resolution in the z-level grid converges the results toward those obtained by a much coarser resolution sigma coordinate grid, but some differences remain due to the basic differences in the mixing process in the BBL. 相似文献