Bibliography update on the California current system and related mesoscale ocean modeling

This bibliography updates the following publication: Mooers, C.N.K., R.G. Williams, K.C. Vierra and G.R. Halliwell, Jr., 1980. Bibliogrphy for the Coastal Circulation of the Eastern North Pacific. College of Marine Studies, University of Delaware, 77 pp.This bibliography has been prepared for use in the Ocean Prediction Through Observation, Modeling and Analysis (OPTOMA) program. It updates the 1980 publication "Bibliography for the Coastal Ciruclation of the Eastern North Pacific." In addition, mesoscale ocean modeling references related to the California Current System has been included.Prepared for: Office of Naval Research, Environmental Sciences Directorate (Code 420) Arlington, VAhttp://archive.org/details/bibliographyupda00batt61153N N0001484 WR24051NAApproved for public release; distribution is unlimited

Wind-forced modeling studies of currents, meanders, and eddies in the California Current system

This process-oriented study of the California Current system( CCS) uses a high-resolution, multilevel, primitive equation ocean model on a/3 plane to isolate the response of that eastern boundary oceanic regime to temporal and spatially varying wind forcing. To study the generation, evolution, and maintenance of many of the observed features such as currents, meanders, and eddies in the CCS, the model is forced from rest with seasonal climatological winds. In response to the prevailing wind direction, surface equatorward currents develop, along with upwelling of cooler water along the coast and a poleward undercurrent. Baroclinic/barotropic in stabilities in the equatorward surface current and poleward undercurrent result in the generation of meanders near the coast. As the meanders intensify, cold upwelling filaments develop along the coast and subsequently extend farther offshore. In time, the meanders form both cyclonic and anticyclonic eddies, which subsequently propagate farther offshore

Modeling Studies of the Leeuwin Current off Western and Southern Australia

The Leeuwin Current strengthens considerably from February to May each year, following the slackening of southerly coastal winds; strong eddies develop. A high-resolution, multilevel, primitive equation ocean model is used to examine this eddy development in an idealized way, by considering the development of flow from rest when temperatures are initially given the observed longshore gradients. The system is allowed to geostrophically adjust in the absence of longshore winds and of any surface heat flux. Two types of experiments are conducted. The first type uses the Indian Ocean climatological temperature gradient forcing (case 1 and 2), while the second type repeats the first experiment with the added contribution of the North West Shelf (NWS) temperature profile (cases 3 and 4). To investigate the additional effects of coastline irregularities, cases 1 and 3 use an ideal coastline, while cases 2 and 4 use an irregular (realistic) coastline. In all cases, maximum surface velocities occur at Cape Leeuwin, where the Leeuwin Current changes direction, and off Southern Australia. Maximum undercurrent velocities occur off Western Australia. In case 1, Cape Leeuwin and the Western Australian coast are the preferred locations for the development of warm, anticyclonic eddies, which are generated due to a mixed instability mechanism. In case 2, the warm, anticyclonic eddies occur in the vicinity of coastal promontories and at Cape Leeuwin. While advection of warm water is present along the entire coast in case 1, the irregular coastline geometry limits the extent of warm water in case 2. The added contribution from the NWS water in cases 3 and 4 augments the onshore geostrophic inflow to produce a model Leeuwin Current and undercurrent that are more vigorous and unstable than in the previous cases. In case 3, the NWS water adds strong horizontal shear to the coastal equatorial region of the domain and vertical shear to the inshore current. It also advects warmer water along the entire coast. In case 4, the addition of both the NWS water and the irregular coastline results in the establishment of a stronger surface current and undercurrent than in the previous cases; however, the irregular coastline limits the extent of the advection of the NWS warmer water along the Australian coast

On reducing the slope parameter in terrain-following numerical ocean models

The article of record as published may be found at http://dx.doi.org/10.1016/j.ocemod.2006.01.003Sigma coordinate ocean models, such as the Princeton Ocean Model, are a type of terrain-following model, which are currently being used in regions with large topographic variability such as entire ocean basins, shelf breaks, continental shelves, estuaries and bays. The main concern when using a terrain-following ocean model is to reduce the pressure gradient force error (PGFE). Regardless of the method of calculation of the pressure gradient, the PGFE will not be reduced to an acceptable value without first reducing the slope parameter, defined by the absolute value of the ratio of the difference between two adjacent cell depths and their mean depth. Here two methods for reducing the slope parameter are compared: a traditional two-dimensional smoothing with Gaussian filters and an alternative one-dimensional robust direct iterative technique. While both methods efficiently smooth the bottom topography so that the pressure gradient errors are reduced to acceptable levels, the alternative method is shown to have a unique advantage of maintaining coastline irregularities, continental shelves, and relative maxima such as seamounts and islands

Modeling studies of the effects of wind forcing and thermohaline gradients on the California Current System

This process-oriented study uses a high-resolution, multi-level, primitive equation model to study the combined effects of wind forcing and thermohaline gradients 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 forcing and thermohaline gradients. In the first experiment, the effects of thermohaline gradients 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 forcing and thermohaline gradients are investigated. The results from the combined experiment show that even though the effects of wind forcing dominate the CCS, the additional effects of thermohaline gradients result 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&125W 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

Process-oriented modeling studies of the 5500-km-long boundary flow off western and southern Australia

The article of record as published may be found at http://dx.doi.org/10.1016/j.csr.2008.11.011While the unique character of the coastal current system off the western and southern coasts of Australia has been recognized, this vast 5500-km-long boundary flow has been studied far less than other current systems of the world. Recent observational studies from satellite altimetry and climatology are consistent with a continuous current extending from its origin at the North West Cape to the southern tip of Tasmania. To date, coastal modeling studies have focused on either the western Australian coast to Esperance or on southern Australia. There has been no process-oriented modeling study of the entire region that would allow the systematic exploration of the two independent forcing mechanisms (i.e.,wind forcing and thermohaline gradients) and their interactions that have been noted to act in a synergistic manner to maintain the longest continuous coastal current system in the world

Modeling Studies of Eddies in the Leeuwin Current: The Role of Thermal Forcing

A high resolution, multilevel, primitive equation (PE) model is used to investigate the generation and stability of the Leeuwin Current and eddies off the west coast of Australia. Two numerical experiments are conducted to investigate the roles of the Indian Ocean temperature field and the North West (NW) Shelf waters in generating both the current and eddies. In the first experiment an alongshore temperature gradient, typical of the Indian Ocean temperature field, is imposed, while in the second experiment the additional effects of the NW Shelf waters are considered. In the first experiment, the meridional Indian Ocean temperature gradient is sufficient to drive a poleward surface flow (the Leeuwin Current) and an equatorial undercurrent. The surface flow is augmented by onshore geostrophic flow and accelerates downstream. In the second experiment, the inclusion of the NW Shelf waters completely dominates in the NW Shelf equatorial source region. The effects of the NW Shelf waters weaken away from the source region but they continue to augment the Indian Ocean forcing, resulting in a stronger flow along the entire coastal boundary. The currents generated by the model agree well with the Leeuwin Current Interdisciplinary Experiment (LUCIE) current meter observations obtained during the austral fall and winter, when the Leeuwin Current is observed, and other recent modeling studies. The current is unstable and has significant mesoscale variability. The current forced only by the alongshore temperature gradient is unstable toward the poleward end of the model domain. In this region, barotropic instability tends to dominate over baroclinic instability. When the NW Shelf waters are added to force the current, eddies are generated near the source of these waters (in the equatorward end of the model domain) through barotropic instability of the current. Farther downstream, the NW Shelf waters add strong baroclinicity, which weakens poleward, to the current. Eddies are subsequently generated downstream from the NW Shelf region through both baroclinic and barotropic instability processes. Several scales of eddies are found to be dominant. The forcing by the Indian Ocean leads to eddy growth on scales around l 50 km. With the inclusion of the NW Shelf waters, the wavelength associated with mesoscale variability is around 180 km. Both of these length scales are close to the wavelength associated with a low-mode Rossby radius of deformation. The eddies generated by the model compare well with available observations. This study shows that the Leeuwin Current can be successfully modeled using a PE model forced by the mean climatology. Consistent with the findings of recent modeling studies, a shelf is not required to produce and maintain the current. The mesoscale features which have been missing from previous modeling studies are produced by the model and at scales comparable with available observations

Bibliography update on the California current system and related mesoscale ocean modeling /

This bibliography updates the following publication: Mooers, C.N.K., R.G. Williams, K.C. Vierra and G.R. Halliwell, Jr., 1980. Bibliogrphy for the Coastal Circulation of the Eastern North Pacific. College of Marine Studies, University of Delaware, 77 pp.This bibliography has been prepared for use in the Ocean Prediction Through Observation, Modeling and Analysis (OPTOMA) program. It updates the 1980 publication "Bibliography for the Coastal Ciruclation of the Eastern North Pacific." In addition, mesoscale ocean modeling references related to the California Current System has been included.Prepared for: Office of Naval Research, Environmental Sciences Directorate (Code 420) Arlington, VAhttp://archive.org/details/bibliographyupda00batt61153N N0001484 WR24051NAApproved for public release; distribution is unlimited