# Search Results

## You are looking at 1 - 10 of 14 items for :

- Author or Editor: Robert L. Haney x

- Article x

- Refine by Access: All Content x

## Abstract

A multilevel primitive equation, ocean circulation model with surface layer physics is used to study the interannual variability of sea surface temperatures (SST) in the central midlatitude North Pacific Ocean. Results from a 10-year model simulation (hindcast) driven by observed winds are analyzed and compared with observations.

The hindcast SSTs exhibit a significant amount of nonseasonal variability despite being damped toward a regular annual cycle by the thermal boundary condition at the surface. This variability is due to the horizontal and vertical redistribution of heat by currants and by parameterized turbulence processes caused by the winds. The resulting hindcast SST anomalies are correlated with observed SST anomalies at a statistically significant level over a large part of the central midlatitude North Pacific Ocean. This suggests that wind forcing by itself, through the mechanisms noted before, makes an important contribution to the development of SST anomalies in this area. The hindcast and observed SST anomalies do not compare well in the northwest and in the southeast part of the midlatitude North Pacific, suggesting that local wind forcing by itself is relatively unimportant for SST anomaly generation in these locations.

Throughout the midlatitude North Pacific, however, the hindcast SST anomalies are only about one-third as intense as the observed anomalies. It is suggested that this discrepancy is due to the absence of forcing by anomalous surface heat fluxes in the model hindcast.

## Abstract

A multilevel primitive equation, ocean circulation model with surface layer physics is used to study the interannual variability of sea surface temperatures (SST) in the central midlatitude North Pacific Ocean. Results from a 10-year model simulation (hindcast) driven by observed winds are analyzed and compared with observations.

The hindcast SSTs exhibit a significant amount of nonseasonal variability despite being damped toward a regular annual cycle by the thermal boundary condition at the surface. This variability is due to the horizontal and vertical redistribution of heat by currants and by parameterized turbulence processes caused by the winds. The resulting hindcast SST anomalies are correlated with observed SST anomalies at a statistically significant level over a large part of the central midlatitude North Pacific Ocean. This suggests that wind forcing by itself, through the mechanisms noted before, makes an important contribution to the development of SST anomalies in this area. The hindcast and observed SST anomalies do not compare well in the northwest and in the southeast part of the midlatitude North Pacific, suggesting that local wind forcing by itself is relatively unimportant for SST anomaly generation in these locations.

Throughout the midlatitude North Pacific, however, the hindcast SST anomalies are only about one-third as intense as the observed anomalies. It is suggested that this discrepancy is due to the absence of forcing by anomalous surface heat fluxes in the model hindcast.

## Abstract

A 10-level primitive equation ocean circulation model is used to investigate the formation and evolution of large-scale thermal anomalies in the central North Pacific Ocean during the fall and winter of 1976–77. A simplified parameterization of the effects of turbulent vertical mixing produced by wind stirring and surface cooling is included in the model. The numerical experiments consist of prescribed change experiments in which monthly mean ocean temperature anomalies, observed down to 400 m by the North Pacific Experiment (NORPAX), are used to define the prescribed changes (anomalies) in the initial conditions and observed monthly mean anomalies of surface winds, and surface heat fluxes are used to define the prescribed changes in the atmospheric forcing.

Oceanic processes are investigated by comparing several prescribed change experiments with observations. With anomalous wind forcing, horizontal advection by anomalous wind-driven surface (Ekman) currents and anomalous wind mixing contribute to the development of a large-scale cold anomaly in the upper 100 m of the central North Pacific in qualitative agreement with the observed anomaly development. The effects of anomalous horizontal advection are primarily confined to the upper 50 m while anomalous wind mixing produces strong cooling down to 125 m and warming below that. The inclusion of anomalous surface heat fluxes improves the simulation and is especially important for the development of a shallow warm anomaly to the east of the large-scale cold anomaly. In all the experiments the pattern correlation between simulated and observed temperature anomalies is greatest near the surface (r≈0.88) and decreases with depth (r≈0.25 at 262 m).

## Abstract

A 10-level primitive equation ocean circulation model is used to investigate the formation and evolution of large-scale thermal anomalies in the central North Pacific Ocean during the fall and winter of 1976–77. A simplified parameterization of the effects of turbulent vertical mixing produced by wind stirring and surface cooling is included in the model. The numerical experiments consist of prescribed change experiments in which monthly mean ocean temperature anomalies, observed down to 400 m by the North Pacific Experiment (NORPAX), are used to define the prescribed changes (anomalies) in the initial conditions and observed monthly mean anomalies of surface winds, and surface heat fluxes are used to define the prescribed changes in the atmospheric forcing.

Oceanic processes are investigated by comparing several prescribed change experiments with observations. With anomalous wind forcing, horizontal advection by anomalous wind-driven surface (Ekman) currents and anomalous wind mixing contribute to the development of a large-scale cold anomaly in the upper 100 m of the central North Pacific in qualitative agreement with the observed anomaly development. The effects of anomalous horizontal advection are primarily confined to the upper 50 m while anomalous wind mixing produces strong cooling down to 125 m and warming below that. The inclusion of anomalous surface heat fluxes improves the simulation and is especially important for the development of a shallow warm anomaly to the east of the large-scale cold anomaly. In all the experiments the pattern correlation between simulated and observed temperature anomalies is greatest near the surface (r≈0.88) and decreases with depth (r≈0.25 at 262 m).

## Abstract

By employing a heat budget analysis appropriate to zonally and time averaged conditions within the atmosphere, it is shown that the net downward heat flux *Q* at the ocean's surface can be expressed as *Q* = *Q*
_{2} (*T _{A}
**–

*T*), where

_{s}*T** is an apparent atmospheric equilibrium temperature,

_{A}*T*the sea surface temperature, and

_{s}*Q*

_{2}a coefficient determined from the zonally and time averaged data. The latter coefficient, which is of the order of 70 ly day

^{−1}(°C)

^{−1}, varies with latitude by as much as 20%. It is suggested that the use of the above relation as a flux-type thermal boundary condition would allow for large-scale thermal coupling of ocean and atmosphere. The more common use of specified

*T*as a boundary condition clearly does not allow for such coupling.

_{s}## Abstract

By employing a heat budget analysis appropriate to zonally and time averaged conditions within the atmosphere, it is shown that the net downward heat flux *Q* at the ocean's surface can be expressed as *Q* = *Q*
_{2} (*T _{A}
**–

*T*), where

_{s}*T** is an apparent atmospheric equilibrium temperature,

_{A}*T*the sea surface temperature, and

_{s}*Q*

_{2}a coefficient determined from the zonally and time averaged data. The latter coefficient, which is of the order of 70 ly day

^{−1}(°C)

^{−1}, varies with latitude by as much as 20%. It is suggested that the use of the above relation as a flux-type thermal boundary condition would allow for large-scale thermal coupling of ocean and atmosphere. The more common use of specified

*T*as a boundary condition clearly does not allow for such coupling.

_{s}## Abstract

The coefficients *A _{n}
* and

*B*, and the percentage of the total height variance accounted for by each harmonic were computed for the first three longitudinal harmonics of 5-day mean 500-mb. height-contour charts at each 10° of latitude from 20° N. to 80° N. from December 1, 1959, to May 31, 1960. The phase angles and amplitudes of the first three harmonics were computed at 30° N., 50° N., and 70° N. and plotted as a function of time. Retrogression of the waves was found at high and low latitudes, while relatively stationary conditions prevailed at middle latitudes. The correlation coefficient between the contribution of the sum of the first three harmonics and the entire wave train was found to be almost +0.9.

_{n}## Abstract

The coefficients *A _{n}
* and

*B*, and the percentage of the total height variance accounted for by each harmonic were computed for the first three longitudinal harmonics of 5-day mean 500-mb. height-contour charts at each 10° of latitude from 20° N. to 80° N. from December 1, 1959, to May 31, 1960. The phase angles and amplitudes of the first three harmonics were computed at 30° N., 50° N., and 70° N. and plotted as a function of time. Retrogression of the waves was found at high and low latitudes, while relatively stationary conditions prevailed at middle latitudes. The correlation coefficient between the contribution of the sum of the first three harmonics and the entire wave train was found to be almost +0.9.

_{n}## Abstract

A numerical model of a 6-level, baroclinic ocean with a flat bottom and a regular coast line extending from 51.25S to 48.75N is integrated over 125 years of simulated time using a finite-difference analog of the primitive equations. The surface atmospheric conditions which drive the circulation, both mechanically and thermally, are prescribed and depend on latitude only. The numerical integration is done in two phases. In the first phase (100 years), the temperature is predicted from the complete thermal energy equation, while the equations of horizontal motion are linear and the vertical mean current is constant in time. In the second phase (25 years), the complete primitive equations are used, and the coefficients of eddy viscosity and eddy conductivity are reduced.

Integration of the first phase produces western boundary currents in both hemispheres, a surface counter-current at 7N, an eastward undercurrent at the equator, and a narrow band of cold surface water along the equator which is maintained by a narrow belt of strong vertical velocities of the order of 200 cm day^{−1} at the bottom of the first layer. However, the calculated undercurrent and western boundary current speeds are only 25% as strong as those observed, and in the equatorial region the calculated thermocline is too deep.

The most interesting differences in the results of the two phases occur in equatorial regions where the eastward transport by the model undercurrent nearly doubled in the second phase. By comparing the under-current transport predicted by Gill's theory, with that obtained in the first and second phases, respectively, it is shown that density stratification increases the eastward transport by a factor of 4 while increased baroclinity and nonlinear effects increase the transport an additional 75% over the stratified case.

A calculation of the different modes of poleward heat transport in the second phase shows that the mean meridional circulation transports most of the heat, and that the eddies in both the vertical shear current and the vertical mean current transport heat equatorward. An analysis of the energy balance in the second phase of the model shows that, in the mean, kinetic energy is transformed into potential energy and that this is related to the thickness of the thermal boundary layer in the vicinity of the western boundary. There is also a positive, though small, transformation from the kinetic energy of the vertical shear flow to the kinetic energy of the vertical mean flow, which is related to the relatively large lateral eddy viscosity required by the coarse grid.

## Abstract

A numerical model of a 6-level, baroclinic ocean with a flat bottom and a regular coast line extending from 51.25S to 48.75N is integrated over 125 years of simulated time using a finite-difference analog of the primitive equations. The surface atmospheric conditions which drive the circulation, both mechanically and thermally, are prescribed and depend on latitude only. The numerical integration is done in two phases. In the first phase (100 years), the temperature is predicted from the complete thermal energy equation, while the equations of horizontal motion are linear and the vertical mean current is constant in time. In the second phase (25 years), the complete primitive equations are used, and the coefficients of eddy viscosity and eddy conductivity are reduced.

Integration of the first phase produces western boundary currents in both hemispheres, a surface counter-current at 7N, an eastward undercurrent at the equator, and a narrow band of cold surface water along the equator which is maintained by a narrow belt of strong vertical velocities of the order of 200 cm day^{−1} at the bottom of the first layer. However, the calculated undercurrent and western boundary current speeds are only 25% as strong as those observed, and in the equatorial region the calculated thermocline is too deep.

The most interesting differences in the results of the two phases occur in equatorial regions where the eastward transport by the model undercurrent nearly doubled in the second phase. By comparing the under-current transport predicted by Gill's theory, with that obtained in the first and second phases, respectively, it is shown that density stratification increases the eastward transport by a factor of 4 while increased baroclinity and nonlinear effects increase the transport an additional 75% over the stratified case.

A calculation of the different modes of poleward heat transport in the second phase shows that the mean meridional circulation transports most of the heat, and that the eddies in both the vertical shear current and the vertical mean current transport heat equatorward. An analysis of the energy balance in the second phase of the model shows that, in the mean, kinetic energy is transformed into potential energy and that this is related to the thickness of the thermal boundary layer in the vicinity of the western boundary. There is also a positive, though small, transformation from the kinetic energy of the vertical shear flow to the kinetic energy of the vertical mean flow, which is related to the relatively large lateral eddy viscosity required by the coarse grid.

## Abstract

The role of surface-generated mixing in determining the seasonal variation of the ocean thermal structure is investigated using a one-dimensional numerical model. The model contains vertical eddy diffusion with a constant coefficient *K _{H}
* = 0.5 cm

^{2}s

^{−1}, an instantaneous convective adjustment mechanism as commonly used in oceanic general circulation models, and a simple parameterization of surface-generated wind and convective mixing based on recent mixed-layer theories. Forcing on the seasonal time scale is accomplished by prescribing the atmospheric solar radiation, longwave radiation, wind speed, temperature and dew point to vary sinusoidally with the annual period. Results of model integrations show that surface-generated wind and convective mixing are responsible for producing many features which are observed in the real ocean including the occurrence of two sea surface temperature maxima—one in summer and another in early fall.

## Abstract

The role of surface-generated mixing in determining the seasonal variation of the ocean thermal structure is investigated using a one-dimensional numerical model. The model contains vertical eddy diffusion with a constant coefficient *K _{H}
* = 0.5 cm

^{2}s

^{−1}, an instantaneous convective adjustment mechanism as commonly used in oceanic general circulation models, and a simple parameterization of surface-generated wind and convective mixing based on recent mixed-layer theories. Forcing on the seasonal time scale is accomplished by prescribing the atmospheric solar radiation, longwave radiation, wind speed, temperature and dew point to vary sinusoidally with the annual period. Results of model integrations show that surface-generated wind and convective mixing are responsible for producing many features which are observed in the real ocean including the occurrence of two sea surface temperature maxima—one in summer and another in early fall.

## Abstract

The generalized omega equation (ω equation) for hydrostatic, inviscid, isentropic, Boussinesq flow is interpreted in terms of the change of differential relative vorticity in a fluid parcel. A new formulation of the ω equation, consistent with this interpretation, is introduced. The formulation can be interpreted as the primitive equation (PE) counterpart of the **Q** vector formulation of the quasigeostrophic (QG) ω equation. This interpretation is equivalent to the interpretation of the differential horizontal divergence [(−*w _{z}
*)

_{ z }] equation as the PE counterpart of the QG differential vorticity equation. The generalized equations also show the role that the rate of change of differential ageostrophic vorticity and differential divergence play in forcing nonquasigeostrophic vertical velocity and nonquasigeostrophic vorticity, respectively. This is illustrated by a simple application of the theory for the circulation in a tropical cyclone. Finally, the necessary and sufficient conditions required to obtain the corresponding QG expressions are specified from the generalized equations.

## Abstract

The generalized omega equation (ω equation) for hydrostatic, inviscid, isentropic, Boussinesq flow is interpreted in terms of the change of differential relative vorticity in a fluid parcel. A new formulation of the ω equation, consistent with this interpretation, is introduced. The formulation can be interpreted as the primitive equation (PE) counterpart of the **Q** vector formulation of the quasigeostrophic (QG) ω equation. This interpretation is equivalent to the interpretation of the differential horizontal divergence [(−*w _{z}
*)

_{ z }] equation as the PE counterpart of the QG differential vorticity equation. The generalized equations also show the role that the rate of change of differential ageostrophic vorticity and differential divergence play in forcing nonquasigeostrophic vertical velocity and nonquasigeostrophic vorticity, respectively. This is illustrated by a simple application of the theory for the circulation in a tropical cyclone. Finally, the necessary and sufficient conditions required to obtain the corresponding QG expressions are specified from the generalized equations.

## Abstract

An oceanic baroclinic jet impinging on a coastal boundary represents a particular type of ocean–coast interaction. This specific oceanographic phenomenon is an example of the stagnation in line flows occurring in fluid dynamics with three additional features: rotation, stratification, and a sloping boundary. In this study the authors describe the density, vorticity, and deformation characteristics of an oceanic jet impinging on a sloping boundary. The case study corresponds to the impinging process of the Atlantic jet at the African coast (Alboran Sea).

In the impinging region, the acceleration field is divergent related to the fact that the magnitude of the deformation is larger than the magnitude of the rotation. It is also found that the stagnation streamsurface does not lie in a vertical plane but tilts in the opposite direction to the tilt of the isopycnals. The flow upstream of the stagnation point is characterized by backing, speed convergence, diffluence, and negative streamwise vorticity. The flow past the stagnation point is characterized by veering, speed divergence, confluence, and positive streamwise vorticity. The current can only be considered irrotational in a narrow part of the impinging region.

## Abstract

An oceanic baroclinic jet impinging on a coastal boundary represents a particular type of ocean–coast interaction. This specific oceanographic phenomenon is an example of the stagnation in line flows occurring in fluid dynamics with three additional features: rotation, stratification, and a sloping boundary. In this study the authors describe the density, vorticity, and deformation characteristics of an oceanic jet impinging on a sloping boundary. The case study corresponds to the impinging process of the Atlantic jet at the African coast (Alboran Sea).

In the impinging region, the acceleration field is divergent related to the fact that the magnitude of the deformation is larger than the magnitude of the rotation. It is also found that the stagnation streamsurface does not lie in a vertical plane but tilts in the opposite direction to the tilt of the isopycnals. The flow upstream of the stagnation point is characterized by backing, speed convergence, diffluence, and negative streamwise vorticity. The flow past the stagnation point is characterized by veering, speed divergence, confluence, and positive streamwise vorticity. The current can only be considered irrotational in a narrow part of the impinging region.

## Abstract

The circulation and dynamics of the Modified Atlantic Water have been studied using data from an intensive field experiment carried out between 22 September and 7 October 1992. Data included 134 CTD casts, ADCP, and satellite imagery. A well-defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern Alboran Sea. Smaller-scale cyclonic eddies were also observed. The front separates the more saline, older modified Atlantic water (*S*>38) in the northern region from the fresher, more recent modified Atlantic water (*S*<36.8) in the south. The associated baroclinic jet had a mean transport of 1 Sv and maximum geostrophic velocities of 1.0 ms^{−1}. The three-dimensional structure and spatial scales of both gyres were similar, that is, 90 km long and 220 m deep. In the eastern Alboran, northeast of Oran, the origin of the Algerian Current was also detected with an eastward transport of 1.8 Sv. The general picture can be presented as a structure formed by a wavelike front coupled with two large anticyclonic gyre-small cyclonic eddy systems.

The relative importance of stratification, relative vorticity, and Froude number in the distribution of Extel’s potential vorticity has been examined, and potential vorticity conservation is used to infer vertical motion. The vertical velocity forcing has been computed using the quasigeostrophic Q vector formulation of the omega equation. It is found that the differential vorticity advection due to mesoscale phenomena in the western Alboran plays a main role in this forcing. The vertical velocities associated with these mesoscale structures reach maximum absolute values of 15 m day^{−1}.

## Abstract

The circulation and dynamics of the Modified Atlantic Water have been studied using data from an intensive field experiment carried out between 22 September and 7 October 1992. Data included 134 CTD casts, ADCP, and satellite imagery. A well-defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern Alboran Sea. Smaller-scale cyclonic eddies were also observed. The front separates the more saline, older modified Atlantic water (*S*>38) in the northern region from the fresher, more recent modified Atlantic water (*S*<36.8) in the south. The associated baroclinic jet had a mean transport of 1 Sv and maximum geostrophic velocities of 1.0 ms^{−1}. The three-dimensional structure and spatial scales of both gyres were similar, that is, 90 km long and 220 m deep. In the eastern Alboran, northeast of Oran, the origin of the Algerian Current was also detected with an eastward transport of 1.8 Sv. The general picture can be presented as a structure formed by a wavelike front coupled with two large anticyclonic gyre-small cyclonic eddy systems.

The relative importance of stratification, relative vorticity, and Froude number in the distribution of Extel’s potential vorticity has been examined, and potential vorticity conservation is used to infer vertical motion. The vertical velocity forcing has been computed using the quasigeostrophic Q vector formulation of the omega equation. It is found that the differential vorticity advection due to mesoscale phenomena in the western Alboran plays a main role in this forcing. The vertical velocities associated with these mesoscale structures reach maximum absolute values of 15 m day^{−1}.

## Abstract

The 3D velocity field in the Alboran Sea (Western-Mediterranean) is diagnosed through density dynamical assimilation in a primitive equation (PE) model with mesoscale resolution. The ageostrophic motion is computed from fields produced by short-term backward and forward integrations of the PE model initialized with quasi-synoptic CTD data. A weight function based on a low-pass digital filter (Digital Filter Initialization method) is applied to the resulting time series of model variables to obtain the final, dynamically balanced, density and 3D velocity fields. The diagnosed ageostrophic motion is interpreted by comparing the vertical velocity field with that obtained from the quasigeostrophic (QG) ω equation. The two methods produce very similar results with maximum vertical motions in the range of 10–20 md^{−1} associated with the differential advection of relative vorticity in small-scale jet meanders [upward (downward) motion upstream (downstream) of the ridges]. Small local differences between PE and QG vertical velocities (typically 1–2 md^{−1}) are attributed to known limitations of the QG theory and to differences between the analysed and the dynamically initialized density fields. The horizontal ageostrophic, motion in the western Alboran gyre (WAG) is in the same direction as the geostrophic motion above 100 m but in the opposite direction below 100 m. While the horizontal ageostrophic motion in the WAG can imply inflow or outflow depending on the position of local meanders, the gyre-scale ageostrophic circulation is characterized by convergence above 100 m and divergence below 100 m, implying an average downward motion of less than 1 md^{−1}. The general success of this assimilation approach could provide an alternative to QG diagnosis in mesoscale dynamics.

## Abstract

The 3D velocity field in the Alboran Sea (Western-Mediterranean) is diagnosed through density dynamical assimilation in a primitive equation (PE) model with mesoscale resolution. The ageostrophic motion is computed from fields produced by short-term backward and forward integrations of the PE model initialized with quasi-synoptic CTD data. A weight function based on a low-pass digital filter (Digital Filter Initialization method) is applied to the resulting time series of model variables to obtain the final, dynamically balanced, density and 3D velocity fields. The diagnosed ageostrophic motion is interpreted by comparing the vertical velocity field with that obtained from the quasigeostrophic (QG) ω equation. The two methods produce very similar results with maximum vertical motions in the range of 10–20 md^{−1} associated with the differential advection of relative vorticity in small-scale jet meanders [upward (downward) motion upstream (downstream) of the ridges]. Small local differences between PE and QG vertical velocities (typically 1–2 md^{−1}) are attributed to known limitations of the QG theory and to differences between the analysed and the dynamically initialized density fields. The horizontal ageostrophic, motion in the western Alboran gyre (WAG) is in the same direction as the geostrophic motion above 100 m but in the opposite direction below 100 m. While the horizontal ageostrophic motion in the WAG can imply inflow or outflow depending on the position of local meanders, the gyre-scale ageostrophic circulation is characterized by convergence above 100 m and divergence below 100 m, implying an average downward motion of less than 1 md^{−1}. The general success of this assimilation approach could provide an alternative to QG diagnosis in mesoscale dynamics.