Search Results
You are looking at 1 - 7 of 7 items for :
- Author or Editor: John R. Bennett x
- Journal of Physical Oceanography x
- Refine by Access: All Content x
Abstract
A simple nonlinear model of the generation of Kelvin waves is presented and applied to internal Kelvin waves in Lake Michigan. It is shown that a Kelvin wave which has a wavelength longer than the Rossby radius of deformation steepens. This may explain “warm fronts” in records of nearshore temperature in Lake Michigan.
Abstract
A simple nonlinear model of the generation of Kelvin waves is presented and applied to internal Kelvin waves in Lake Michigan. It is shown that a Kelvin wave which has a wavelength longer than the Rossby radius of deformation steepens. This may explain “warm fronts” in records of nearshore temperature in Lake Michigan.
Abstract
A two-layer circular lake model is used to study the mean flow of Lake Ontario during midsummer. By computing the model only to the second order of amplitude, it is shown that the observed cyclonic circulation of Lake Ontario during summer is due to the rectified effects of the large, transient, wind-driven currents. This effect is strongly influenced by model grid resolution and friction.
Abstract
A two-layer circular lake model is used to study the mean flow of Lake Ontario during midsummer. By computing the model only to the second order of amplitude, it is shown that the observed cyclonic circulation of Lake Ontario during summer is due to the rectified effects of the large, transient, wind-driven currents. This effect is strongly influenced by model grid resolution and friction.
Abstract
Observations of Lake Ontario during the International Field Year for the Great Lakes are used to develop a. three-dimensional numerical model for calculating temperature and current. The model has a variable grid resolution and a horizontal smoothing which filters out small-scale vertical motion caused by truncation error but has little effect on the strong currents of the coastal boundary layer. Resolution of the shore zones and reduced horizontal smoothing improve simulation of both long-term mean flow and current reversals due to low-frequency waves.
Abstract
Observations of Lake Ontario during the International Field Year for the Great Lakes are used to develop a. three-dimensional numerical model for calculating temperature and current. The model has a variable grid resolution and a horizontal smoothing which filters out small-scale vertical motion caused by truncation error but has little effect on the strong currents of the coastal boundary layer. Resolution of the shore zones and reduced horizontal smoothing improve simulation of both long-term mean flow and current reversals due to low-frequency waves.
Abstract
Two time-dependent “vertical cross section models” are analyzed and applied to wind-driven currents in Lake Ontario. The models are: 1) a linear frictionless, two-level model, and 2) a numerical model which includes both friction and nonlinear terms. They predict current and temperature under the assumption that all variables except pressure are independent of the longshore coordinate. The longshore pressure gradient is computed from the condition that the volume transport normal to the cross section is zero.
First, the quasi-static response of the linear frictionless model is studied to isolate the effects of topography and stratification on the structure of the coastal currents. It predicts that the vertically averaged longshore current is independent of both rotation and stratification, being in the direction of the wind where the water is shallower than average and opposite the wind in the deep water. Under homogeneous conditions, the strongest currents are confined to a thin (∼3 km wide for Lake Ontario) region near the shore. The effect of stratification is to increase the width of this “costal jet” region and cause the flow to be more confined to the surface layer.
These qualitative results of the linear model are also true for the numerical model, but the latter gives more realistic current magnitudes. The main differences between the two models are due to friction which has a relatively straightforward damping effect on both the quasi-geostrophic and inertial oscillation components of the flow. The damping of the geostrophic mode, however, is smaller in cases where stratification is important, because it decreases the effect of bottom friction.
The models give realistic magnitudes for both horizontal and vertical motion in Lake Ontario and can explain many of the differences between the spring and summer current regimes.
Abstract
Two time-dependent “vertical cross section models” are analyzed and applied to wind-driven currents in Lake Ontario. The models are: 1) a linear frictionless, two-level model, and 2) a numerical model which includes both friction and nonlinear terms. They predict current and temperature under the assumption that all variables except pressure are independent of the longshore coordinate. The longshore pressure gradient is computed from the condition that the volume transport normal to the cross section is zero.
First, the quasi-static response of the linear frictionless model is studied to isolate the effects of topography and stratification on the structure of the coastal currents. It predicts that the vertically averaged longshore current is independent of both rotation and stratification, being in the direction of the wind where the water is shallower than average and opposite the wind in the deep water. Under homogeneous conditions, the strongest currents are confined to a thin (∼3 km wide for Lake Ontario) region near the shore. The effect of stratification is to increase the width of this “costal jet” region and cause the flow to be more confined to the surface layer.
These qualitative results of the linear model are also true for the numerical model, but the latter gives more realistic current magnitudes. The main differences between the two models are due to friction which has a relatively straightforward damping effect on both the quasi-geostrophic and inertial oscillation components of the flow. The damping of the geostrophic mode, however, is smaller in cases where stratification is important, because it decreases the effect of bottom friction.
The models give realistic magnitudes for both horizontal and vertical motion in Lake Ontario and can explain many of the differences between the spring and summer current regimes.
Abstract
An empirical forced wave model of currents and thermocline displacements in the coastal zone of Lake Ontario is derived from data from the International Field Year for the Great Lakes (1972). The model consists of three linear wave equations for predicting the depth of the thermocline, its slope and the longshore volume transport from the wind. The empirical phase speeds are consistent with internal Kelvin wave and topographic wave theory and the response to a unit longshore wind stress is consistent with cross-section models of long lakes.
Abstract
An empirical forced wave model of currents and thermocline displacements in the coastal zone of Lake Ontario is derived from data from the International Field Year for the Great Lakes (1972). The model consists of three linear wave equations for predicting the depth of the thermocline, its slope and the longshore volume transport from the wind. The empirical phase speeds are consistent with internal Kelvin wave and topographic wave theory and the response to a unit longshore wind stress is consistent with cross-section models of long lakes.
Abstract
The rectified flow induced by wind-driven internal seiches in a rotating lake is studied. Friction and nonlinearity combine to generate a secondary mean flow which is calculated analytically for the case of a uniform depth lake and numerically for variable depth.
The theory is applied to Lake Kinneret, the former Sea of Galilee, where the diurnal wind forcing produces a large internal Kelvin wave and which has a strong cyclonic mean flow. The uniform depth model reproduces the diurnal response adequately, but variable depth is required to reproduce the mean flow.
Abstract
The rectified flow induced by wind-driven internal seiches in a rotating lake is studied. Friction and nonlinearity combine to generate a secondary mean flow which is calculated analytically for the case of a uniform depth lake and numerically for variable depth.
The theory is applied to Lake Kinneret, the former Sea of Galilee, where the diurnal wind forcing produces a large internal Kelvin wave and which has a strong cyclonic mean flow. The uniform depth model reproduces the diurnal response adequately, but variable depth is required to reproduce the mean flow.
Abstract
We compare results from a simple parametric, dynamical, deep-water wave prediction model with two sets of measured wave height maps of Lake Michigan. The measurements were made with an airborne laser altimeter under two distinctly different wind fields during November 1977. The results show that the model predicted almost all of the synoptic features. Both the magnitude and the general pattern of the predicted wave-height contours compared well with the measurements. The model also predicts the direction for wave propagation in conjunction with the wave height map, which is useful for practical ship routing and can be significantly different form the prevailing wind direction.
Abstract
We compare results from a simple parametric, dynamical, deep-water wave prediction model with two sets of measured wave height maps of Lake Michigan. The measurements were made with an airborne laser altimeter under two distinctly different wind fields during November 1977. The results show that the model predicted almost all of the synoptic features. Both the magnitude and the general pattern of the predicted wave-height contours compared well with the measurements. The model also predicts the direction for wave propagation in conjunction with the wave height map, which is useful for practical ship routing and can be significantly different form the prevailing wind direction.
