Wind Forcing Experiments in the California Current System
Wind Forcing Experiments in the California Current System

Author: Philip G. Renaud

Publisher:

Published: 1986

Total Pages: 88

ISBN-13:

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A high-resolution, multi-level, primitive equation ocean model is used to examine the response of an idealized, flat-bottom, oceanic regime off northern California to steady, equatorward, local wind-forcing during the upwelling season. The model has open boundaries on all but the eastern coastal boundary on which either free-slip or zero-slip boundary conditions are imposed. Time-invariant winds, either with or without a component of wind stress curl, are used as model forcing to spin-up a classical two-dimensional, upwelling-induced coastal jet and undercurrent. Since no eddies are generated, a stability analysis of the mean flow is conducted which explores both the necessary conditions of mixed (barotropic and baroclinic) instability, through calculations of potential vorticity, and the sufficient conditions for baroclinic instability, through an application of a simple two-layer stability model. Comparisons of model results with observations of the coastal jet in the California Current System indicate that the location and the horizontal and vertical current shear associated with the model coastal jet compare favorably with observations; however the modeled jet is stronger, deeper and wider than the observed jet. Finally, the inclusion of wind stress curl and the zero-slip boundary condition are demonstrated to be important elements in model simulations of the coastal jet.

A Numerical Study of Wind Forcing Effects on the California Current System
A Numerical Study of Wind Forcing Effects on the California Current System

Author: James R. Vann

Publisher:

Published: 1994

Total Pages: 0

ISBN-13:

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A high-resolution multi-level, primitive equation ocean model is used to examine the response of an idealized, flat-bottom, eastern boundary oceanic regime on a beta-plane to climatological average (1980-1989), individual year, and multiple year wind forcing. The focus of this study is the California Current System along the coastal region, from 35 deg N to 47.5 deg N, off the West Coast of North America. Two types of experiments are conducted. The first type forces the model from rest with climatological, 1981, and 1983 monthly winds to examine the generation phase of features such as currents, upwelling, meanders, eddies, and filaments. The second type continues the forcing from the previous years to examine the maintenance of these features. In the first type of experiments, the following features are observed: a poleward coastal surface current near the start and end of each year, and equatorward surface current, a poleward undercurrent, upwelling, meanders, and eddies. In the second type of experiments, meanders and eddies were already present at the start of the experiment. In addition to the features observed during the first type of experiment, filaments are generated. The results support the hypothesis that wind forcing is an important mechanism for the generation of many of the observed features in the California Current System.

NPS-OC-94-006
NPS-OC-94-006

Author: James R. Vann

Publisher:

Published: 1994

Total Pages: 212

ISBN-13:

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A high-resolution multi-level, primitive equation ocean model is used to examine the response of an idealized, flat-bottom, eastern boundary oceanic regime on a beta-plane to climatological average (1980-1989), individual year, and multiple year wind forcing. The focus of this study is the California Current System along the coastal region, from 35 deg N to 47.5 deg N, off the West Coast of North America. Two types of experiments are conducted. The first type forces the model from rest with climatological, 1981, and 1983 monthly winds to examine the generation phase of features such as currents, upwelling, meanders, eddies, and filaments. The second type continues the forcing from the previous years to examine the maintenance of these features. In the first type of experiments, the following features are observed: a poleward coastal surface current near the start and end of each year, and equatorward surface current, a poleward undercurrent, upwelling, meanders, and eddies. In the second type of experiments, meanders and eddies were already present at the start of the experiment. In addition to the features observed during the first type of experiment, filaments are generated. The results support the hypothesis that wind forcing is an important mechanism for the generation of many of the observed features in the California Current System.

A Numerical Study of Seasonal Wind Forcing Effects on the California Current System
A Numerical Study of Seasonal Wind Forcing Effects on the California Current System

Author: Ross P. Mitchell

Publisher:

Published: 1993

Total Pages: 136

ISBN-13:

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A high-resolution, multi-level, primitive equation ocean model is used to examine the response of an idealized, flat-bottomed, eastern boundary oceanic regime on a beta-plane to both steady and seasonally-varying climatological wind forcing. The focus of the study is the California Current System along the coastal region, from 35 deg N to 45 deg N, off the Western United States. With steady equatorward wind forcing, a surface equatorward current and poleward undercurrent develop. Eddies form around days 60 and 7 with initial development in the northern region of the domain. The strong meandering current continues to grow throughout the 360 days of model time and can produce eddies that have wavelengths up to 200 km and can propagate at least -200 km offshore. When the alongshore component of the temporally averaged seasonally varying climatological wind forcing is used, there is a weak poleward undercurrent and equatorward surface current. There is weak upwelling and very little eddy activity with the eddies only propagating to -100 km offshore. When alongshore component of the time-dependent wind forcing with spatial variability in latitude is used, a surface equatorward jet, poleward undercurrent and eddies are generated. The eddies form throughout the domain in this experiment due to a competition between the 0-plan effect and the continuous and stronger equatorward wind forcing in the southern portion of the domain. The eddies in this experiment propagate at least -150 km from shore.

Modeling Studies of Wind and Thermohaline Forcing on the California Current System
Modeling Studies of Wind and Thermohaline Forcing on the California Current System

Author: Philip W. Vance

Publisher:

Published: 1997-06-01

Total Pages: 89

ISBN-13: 9781423569930

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A high-resolution, multi-level, primitive equation model is initialized with climatological data to study the combined effects of wind and thermohaline forcing on the ocean circulation of the California Current System (CCS). The ocean circulation is generated by the model using a combination of climatological wind stress and thermohaline forcing. In the first experiment, the effects of thermohaline forcing alone are evaluated, in the second experiment, previously conducted, the effects of wind forcing are isolated, while in the third experiment, the combined effects of wind and thermohaline forcing are looked at. The results from the combined experiment show that even though the effects of wind forcing dominate the CCS, the additional effects of the thermohaline forcing results in the following: the seasonal development of a poleward surface current and an equatorward undercurrent in the poleward end of the model region; an onshore geostrophic component, which results in a temperature front and stronger surface and subsurface currents between Cape Mendocino and Point Arena; and a region of maximum eddy kinetic energy inshore of tilde 125 deg W between Cape Mendocino and Point Arena, associated with the temperature front. These model simulations are qualitatively similar to recent hydrographic, altimetric, drifter, and moored observations of the CCS.

The Effects of Climatological and Transient Wind Forcing on Eddy Generation in the California Current System
The Effects of Climatological and Transient Wind Forcing on Eddy Generation in the California Current System

Author:

Publisher:

Published: 1989

Total Pages: 0

ISBN-13:

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A high-resolution, multi-level, primitive equation ocean model is used to examine the response to transient and climatological wind forcing of an idealized, flat-bottomed oceanic regime on a beta-plane, along an eastern boundary. An annually periodic wind forcing function with zonal variability is used as transient forcing in several experiments using both winter and summer initializations. When the curl component of the forcing is stronger than the stress, as in the wintertime, a surface poleward flow develops in the nearshore region with an equatorward flow offshore. When wind stress dominates the forcing, as in the summertime, a coastal jet develops with an undercurrent. In other experiments, spatially varying one degree and two tenths degree steady wind stress data are used as climatological forcing. The one degree climatological wind stress data has positive curl at the coast which causes a poleward surface flow to develop. When two tenths degree wind stress data is used in the nearshore area, both positive and negative curl in the coastal region result in the formation of poleward and equatorward currents, respectively. As a result of convergence in the surface flow, eddies and a well defined cold filament develop. These results show that the interaction of diverse coastal currents driven by an equally diverse wind field can play an important role in the production of cold filaments and eddies. Theses. (jhd).

The Effects of Climatological and Transient Wind Forcing on Eddy Generation in the California Current System
The Effects of Climatological and Transient Wind Forcing on Eddy Generation in the California Current System

Author: Robert W. Edson

Publisher:

Published: 1989

Total Pages: 154

ISBN-13:

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A high-resolution, multi-level, primitive equation ocean model is used to examine the response to transient and climatological wind forcing of an idealized, flat-bottomed oceanic regime on a beta-plane, along an eastern boundary. An annually periodic wind forcing function with zonal variability is used as transient forcing in several experiments using both winter and summer initializations. When the curl component of the forcing is stronger than the stress, as in the wintertime, a surface poleward flow develops in the nearshore region with an equatorward flow offshore. When wind stress dominates the forcing, as in the summertime, a coastal jet develops with an undercurrent. In other experiments, spatially varying one degree and two tenths degree steady wind stress data are used as climatological forcing. The one degree climatological wind stress data has positive curl at the coast which causes a poleward surface flow to develop. When two tenths degree wind stress data is used in the nearshore area, both positive and negative curl in the coastal region result in the formation of poleward and equatorward currents, respectively. As a result of convergence in the surface flow, eddies and a well defined cold filament develop. These results show that the interaction of diverse coastal currents driven by an equally diverse wind field can play an important role in the production of cold filaments and eddies. Theses. (jhd).

Wind Forcing of Eddies and Jets in the California Current System
Wind Forcing of Eddies and Jets in the California Current System

Author: Terrance A. Tielking

Publisher:

Published: 1988

Total Pages: 118

ISBN-13:

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A high-resolution, multi-level, primitive equation ocean model is used to examine the response to wind forcing of an idealized flatbottomed oceanic regime along an eastern ocean boundary. A band of steady winds, either with or without a curl, is used as forcing on both an f-plane and a beta-plane. In addition, a stability analysis is made to determine if the necessary and sufficient conditions for instability processes to occur are satisfied. It is seen that when the wind driven coastal jet and undercurrent are unstable (which occurs in the cases of wind with no curl), eddies and jets are generated. In the case of wind with curl, since the Davidson Current develops rather than the coastal jet and undercurrent, no eddies develop. A comparison of model results with available observations shows that both the time-averaged and instantaneous model simulations of the coastal jet, undercurrent and eddies are consistent with available observational data. Study results support the hypothesis that wind forcing can be an important eddy generation mechanism for the California Current System. (edc).

A Numerical Study of Interannual Wind Forcing Effects on the California Current System, 1980-1983
A Numerical Study of Interannual Wind Forcing Effects on the California Current System, 1980-1983

Author: Robert T. Haines

Publisher:

Published: 1994

Total Pages: 124

ISBN-13:

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A high resolution, multi-level, primitive equation ocean model is used to examine the response of an idealized, flat-bottomed, eastern boundary oceanic regime on a beta-plane to climatological average (1980-1989) and individual yearly (1980-1983) wind forcing. The focus of this study is the California Current System (CCS) along the coastal region, from 35 deg N to 47.5 deg N, of the Western United States. Five experiments were initialized from a state of rest and two from the fields remaining at day 360 from the climatological average wind forcing. With the climatological average wind forcing, a surface equatorward jet and poleward undercurrent are generated. Eddies form along the entire eastern boundary and a field of cyclonic eddies approximately 200 km in diameter remain at day 360. Results for the non-El Nino (1980-1981) years are very similar to the results for the climatological average wind forcing. Early in the year, the El Nino wind fields for 1983 are more intense than the average and 1980-1982 winds, and they have a much stronger poleward component. A surface poleward current develops over an equatorward undercurrent.