OS54B-01 INVITED 16:00h
SUBMESOSCALE COASTAL OCEAN SURFACE CURRENT VARIABILITY
Measurements of coastal ocean surface currents using High Frequency (HF) radars with phased array technology have revealed a broad spectrum of processes. During a series of ONR-sponsored experiments, both HF (16 and 25 MHz) and Very High Frequency (VHF: 50 MHz) radars have revealed energetic, coherent submesoscale processes that are affected by mesoscale currents. Flowing along the coast of southeastern Florida shelf (EFS), the Florida Current (FC) produces an environment of large mean vorticity with embedded, energetic mesoscale and submesocale flow features. These submesoscale features, defined here as flow features with length scales less than the internal deformation radius of 10-40 km, have been observed with an Ocean Surface Current Radar (OSCR) and Wellen Radar (WERA). These features are energetic and coherent over scales of 2 to 20 km. With amplitudes of up to 50 cm s-1, we have limited knowledge of the spectrum of processes within the submesoscale band, of their nature, interaction with other flow scales and energy cascades. Observations in radar and sun glint photos from the space shuttle also indicate that submesoscale vortices and spiral eddies on the free surface are highly nonlinear with Rossby numbers ranging from 5 f to as high as 10 f . These spiral-like images of the surface fields represent a challenge from both fluid dynamical and remote sensing viewpoints as they have a pronounced impact on the surface roughness and backscattered energy. As part of the ONR sponsored SEA-COOS program, a three-station WERA is providing near-real time mapping of the surface velocity field at ~1 km resolution over a range of 100 to 120 km. Sampling intervals range from minutes to hours to help resolve the gradients and high frequency submesoscale motions where RMS differences have been in the 6 to 10 cm s-1 range. Unlike mesoscale features, which are elongated in the along-shelf direction, submesoscale processes tend to be more isotropic with considerable cross-shelf flow where large horizontal gradients in properties occur due to the interactions between fresher riverine, estuarine and shelf water. This property provides a potential for generating significant Reynolds stresses, u'v', a processes completely unexplored. The isotropic nature of submesoscale processes is also relevant with respect to turbulent mixing embedded in the flow, especially in the bottom boundary layer ``slippery boundary layer'' concept. The Florida Straits is an optimal regime to study the 3-D aspects of these energetic currents associated with coherent submesoscale variability.
OS54B-02 INVITED 16:15h
Insights From a Coordinated Observing and Modeling System for the West Florida Shelf
A coordinated coastal ocean observing and modeling program is ongoing on the west Florida continental shelf. This Coastal Ocean Monitoring and Prediction System (COMPS) combines academic (USF) resources with those of federal and state agencies to increase the data and model product availability to all potential users (see http://comps.marine.usf.edu). Private sector interactions are also being sought. COMPS is a partner in the Southeast Atlantic Coastal Ocean Observing System (SEACOOS) that includes the states of NC, SC, GA, and FL (see http://www.seacoos.org). As nascent observing systems our goals are to provide data and model products of societal benefit across a broad range of applications. Since the coastal ocean responds to local atmosphere forcing through momentum and buoyancy fluxes and deep-ocean forcing through adjacent boundary current interactions, specifications of the state of the coastal ocean are dependent on specifications of these forcing fields. Following a brief description of the COMPS observations and models examples are provided on how COMPS-related science is leading to improvements in both the observational array and the model implementations. Coastal oceans, as complex, three-dimensional, time dependent, data poor regimes, require the coordination between observing and modeling programs to fill information gaps and to provide the basis, through research, for sound, ecologically-based stewardship.
OS54B-03 16:30h
Integrated Coastal Analyses in the Gulf of Mexico
Coastal management and research require real-time access to environmental data for analyses of changing ocean conditions. The coastal ocean is impacted by offshore mesoscale forcing as well as input from terrigenous land sources in response to human impact resulting from changing land uses. Monitoring and understanding the variability of the coastal ocean is critical for defining the dispersion of pollutants and chemical agents that impact our environment and potentially our homeland security. We will demonstrate the utility of integrating real-time satellite derived ocean properties, available observations along with numerical coastal and open ocean model output for characterizing the ocean environment to support research efforts and operational programs at the National Aeronautics and Space Administration's Earth Sciences Applications Directorate (NASA ESA) and the National Oceanographic and Atmospheric Administration (NOAA). Integrating and analyzing information derived from satellite and model properties of the Gulf of Mexico will focus on operational and research efforts that include Harmful Algal Blooms (HABs), fresh water outfall, and hypoxia initiatives. We will examine the physical model predictions relative to the observations in terms of model performance and validation. Additionally, examples of the research, including short-term chlorophyll advection, inferred 3-D chlorophyll profiles and correlations of local surface divergence to chlorophyll blooms, will be presented.
OS54B-04 16:45h
Poleward flow events around Pt. Conception, California: An analysis based on HF radar and moored time series
Following relaxations and reversals in the prevailing equatorward winds off the Central California coast, bands of warm water flow poleward alongshore around Point Conception. Satellite sea surface temperature images show the events as bands of warm water extending from the Santa Barbara Channel around the Point. We use time series of currents and temperature from an alongshore array of inner shelf moorings (15 m water depth), moorings on the mid-shelf (100 m water depth), and high frequency radar observations to determine the space and time scales of these poleward flow events. Comparison of moored time series between the inner and mid-shelf show that the events are often confined to the inner shelf where they occur frequently throughout the year. After equatorward winds relax or reverse, the events propagate northward at about 10-13 km/ day. As they pass along the coast, they raise inner shelf temperatures from 3-5 C for a few to several days. Some events propagate completely across the alongshore moored array while others stop within the array when upwelling favorable winds resume. We speculate that these events are important mechanisms for transporting organisms poleward, against the prevailing equatorward flow of the California Current System.
http://www.icess.ucsb.edu/iog/iog.html
OS54B-05 17:00h
Progress in the Application of Tangent Linear and Adjoint Models for Predictability Studies in the Coastal Ocean.
The non-linear nature of coastal ocean dynamics raises questions about the predictability limitations that may be encountered when using coastal observing systems for forecast purposes. Developing an understanding of the transient growth phenomena that may be associated with a given environment can lead to system designs that maximize the information content of the observations and enhance the forecast skill. Regional circulation models, such as the Regional Ocean Modeling System(ROMS), based on the fully non-linear primitive equations, should exhibit transient growth phenomena representative of those which develop in the real ocean. Leading singular vectors (optimal perturbations) may be determined for a specific model configuration using the forward and adjoint tangent linear models. These modes describe the initial spatial structures which maximize growth in some norm (energy, enstrophy, etc.) and can be utilized in ensemble generation and assessments of predictability. Tangent linear and corresponding adjoint tangent linear models have recently become available for ROMS along with drivers for calculating the normal modes, adjoint normal modes and singular vectors. As preliminary steps in the assessment of these tools and the study of disturbance growth in coastal ocean flows, normal modes, adjoint normal modes and singular vectors are calculated for several idealized flows and compared to solutions of the corresponding discretized eigenvalue problems.
OS54B-06 17:15h
Numerical Model Simulations of Circulation over the Continental Shelf off Northern California
The three-dimensional circulation on the continental shelf off northern California in the WEST (Wind Events and Shelf Transport) experiment region is studied using the primitive equation Regional Ocean Modeling System (ROMS). The simulations are performed with realistic topography and initial stratification in a limited-area domain with a high-resolution grid. Forcing consists of measured wind stress and heat flux values obtained during summer 2001. The general response shows a southward coastal upwelling jet of up to 1 m s$^{-1}$ and a weakening or reversal of currents inshore of the jet when upwelling winds relax. Model results are compared to WEST moored velocity and temperature measurements at five locations, to the CODAR region surface current observations, and to hydrographic measurements along shipboard survey lines. The model performs reasonably well, with the highest velocity correlations at the inshore mooring (40 m water depth) and below 70 m depth at the offshore moorings (90 m and 130 m water depth). The comparison of surface velocities with CODAR measurements shows good agreement in the mean velocity vectors and the first two EOF modes. The hydrography compares closely at the southern and northern edges of the survey region, with weaker correlations at the three interior survey lines. We examine the dynamics during an upwelling and subsequent relaxation event in May 2001 in which the WEST measurements show evidence of a strong flow response. Flow near Pt. Reyes during this event is complicated and the response to upwelling and relaxation north and south of Pt. Reyes is quite different. Analysis of term balances from both the three-dimensional and depth-averaged momentum equations help to clarify the event dynamics in different regions over the shelf.