Cheryl Ann Blain

Seasonal mean circulation in the Yellow Sea } a model-generated climatology

The three-dimensional climatological circulation is computed for the Yellow and Bohai Seas in a series of six bimonthly realizations. The model (QUODDY, Lynch et al., Continental Shelf Res. 16(7) (1996) 875) is nonlinear, tide-resolving, and baroclinic with level 2.5 turbulence closure. Data inputs include seasonal hydrography, seasonal mean wind and river input, and oceanic tides. Results for winter and summer exhibit two distinct circulation modes. In winter, strongnortherly wind drives southward flow at the surface and alongboth Korean and Chinese coasts. This is compensated by deep return flow } the Yellow Sea Warm Current } in the central trough of the Yellow Sea, penetrating to the Bohai. The Changjiang discharge exits to the southwest in winter, trapped alongthe Chinese coast. In summer, a water mass produced by winter cooling } the Yellow Sea Cold Water } is isolated in the deep central trough, setting up cyclonic circulation over the eastern Yellow Sea. Summer winds from the south drive northeastward flow alongthe Chinese coast. The net result is a qualitative reversal of the winter pattern. The Changjiang discharge is driven offshore toward the Korean Strait by the summer wind. The winter and summer circulations are partitioned dynamically amongtidal rectification, baroclinic pressure g radients, wind response, and river input from the Changjiang. Wind dominates the winter pattern. In summer, baroclinic pressure gradients dominate the eastern Yellow Sea; with wind, tidal rectification, and input from the Changjiang dominant to the west of the cyclonic gyre. The seasonal cycle indicates that January and March exhibit the same basic winter pattern. May is quiescent, followed by July which defines the summer mode. September shows the same general summer pattern, with features shifted westward. November is a transition period followed by winter conditions. # 2001 Elsevier Science Ltd. All rights reserved.

The origin and preservation of a major hurricane event bed in the northern Gulf of Mexico: Hurricane Camille, 1969

Cores collected from Mississippi Sound, in the Gulf of Mexico, were studied using 210 Pbxs and 137 Cs geochronology, X-radiography, granulometry, and a multi-sensor core logger. Our results indicate the presence of a widespread sandy event layer that we attribute to Hurricane Camille (1969). An initial thickness of more than 10 cm is estimated from the cores, which is large compared to the time-averaged apparent accumulation rate of 0.29^0.47 cm y 31 . Physical and biological post-depositional processes have reworked the sandy layer, producing a regional discontinuity and localized truncation, and resulting in an imperfect and biased record of sedimentary processes during the storm. The oceanographic and sedimentological processes that would have produced an event bed during Hurricane Camille are simulated using a series of numerical models, i.e. (1) a parametric cyclone wind model, (2) the SWAN third-generation wave model, (3) the ADCIRC 2D finite-element hydrodynamic model, and (4) a wave^ current bottom boundary layer model that is coupled to transport and bed conservation equations (TRANS98). The simulated bed ranges from 5 cm to over 100 cm within a tidal channel near the barrier islands. Seaward of the islands, the bed is more than 10 cm in thickness with local variability. The magnitude and local variability of the storm bed thickness are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barriers. @ 2002 Elsevier Science B.V. All rights reserved.

The CI-Flow Project: A System for Total Water Level Prediction from the Summit to the Sea

The objective of the Coastal and Inland Flooding Observation and Warning (CI-FLOW) project is to prototype new hydrometeorologic techniques to address a critical NOAA service gap: routine total water level predictions for tidally influenced watersheds. Since February 2000, the project has focused on developing a coupled modeling system to accurately account for water at all locations in a coastal watershed by exchanging data between atmospheric, hydrologic, and hydrodynamic models. These simulations account for the quantity of water associated with waves, tides, storm surge, rivers, and rainfall, including interactions at the tidal/surge interface. Within this project, CI-FLOW addresses the following goals: i) apply advanced weather and oceanographic monitoring and prediction techniques to the coastal environment; ii) prototype an automated hydrometeorologic data collection and prediction system; iii) facilitate interdisciplinary and multiorganizational collaborations; and iv) enhance techniques and techn...

Simulating wave-tide induced circulation in Bay St. Louis, MS with a coupled hydrodynamic-wave model

Because tidal inlets are important areas with respect to biodiversity, sediment transport, freshwater river outflow, and pollutant transport, a comprehensive understanding of their circulation patterns is necessary for their management. This study focuses on modeling the 2D, depth-averaged circulation of Bay St. Louis in the northeastern Gulf of Mexico that is driven by waves and tides using a coupled hydrodynamic-wave model. The wave-tide coupled circulation within the inlet is examined during the flood, slack, and ebb phases of the tidal cycle. The wave height field, current velocity and sea surface elevation are analyzed to determine the effects of wave-current interaction. The influence of the various forcings on bay/inlet circulation is further investigated by the introduction of Lagrangian tracers. Lagrangian tracers are a reasonable indicator of how circulation patterns affect the motion of sediment particles or passive biological organisms such as fish larvae. Wave-current interaction is simulated by iteratively coupling the depth-integrated ADCIRC-2DDI hydrodynamic model to the phase-averaged spectral wave model SWAN. ADCIRC-2DDI is a fully developed, 2-dimensional, finite element, barotropic hydrodynamic model capable o f including wind, wave, and tidal forcing as well as river flux into the domain. The wave-hydrodynamic model coupling is captured through the following approach. First, radiation stress gradients, determined from the SWAN wave field, serve as surface stress forcing in ADCIRC. Elevation and currents computed from ADCIRC are subsequently input into the SWAN model. Between these iterations, the ADCIRC model is run for some appropriately small time interval during which the wave field is held constant. Presently there are no shelf-scale hydrodynamic models that incorporate waves, therefore a coupled model approach is one way of simulating wave-current interaction in bays and inlets. This approach is very flexible, making it possible to couple different wave models to ADCIRC depending on the relevant physics of the domain being studied (e.g. monochromatic wave diffraction vs. multi-spectral wave effects).

Simple Methodology for Deriving Continuous Shorelines from Imagery: Application to Rivers

AbstractA methodology is developed to extract and process shoreline data, the interface between land and water, identified from imagery. Initially, image pixels containing water (water points) and pixel locations of the land/water interface (edge points) are extracted from an image using either a supervised, threshold approach or a newly developed, automated texture-based analysis. Both are described and demonstrated. Subsequently applied is a procedure for processing these edge and water point locations to obtain oriented and ordered shoreline coordinates. The described methodology has several advantages: (1) shoreline processing is independent of imagery source and resolution, that is, specification of search directions based on image resolution or desired shoreline resolution is unnecessary and (2) a need for additional postprocessing of remote-sensed data or extracted-edge data are obviated, that is, edge data need not be of high quality or vectorized. Details of the entire methodology, including algo...

Bathymetrically controlled velocity‐shear front at a tidal river confluence

Nonbuoyant front formation at the confluence of Nanjemoy Creek and the main Potomac River (MD) channel is examined. Terra satellite ASTER imagery reveals a sediment color front emerging from Nanjemoy Creek when the Potomac is near maximum ebb. Nearly contemporaneous ASTER and Landsat ETM+ imagery are used to extract surface velocities, which suggest a velocity shear front is collocated with the color front. In situ velocities (measured by RiverRay traverses near the Nanjemoy Creek mouth) confirm the shear fronts presence. A finite-element simulation (using ADCIRC) replicates the observed velocity-shear front and is applied to decipher its physics. Three results emerge: (1) the velocity-shear front forms, confined to a shoal downstream of the creek-river confluence for most of the tidal cycle, (2) a simulation with a flat bottom in Nanjemoy Creek and Potomac River (i.e., no bathymetry variation) indicates the velocity-shear front never forms, hence the front cannot exist without the bathymetry, and (3) an additional simulation with a blocked-off Creek entrance demonstrates that while the magnitude of the velocity shear is largely unchanged without the creek, shear front formation is delayed in time. Without the Creek, there is no advection of the M6 tidal constituent (generated by nonlinear interaction of the flow with bottom friction) onto the shoals, only a locally generated contribution. A tidal phase difference between Nanjemoy and Potomac causes the ebbing Nanjemoy Creek waters to intrude into the Potomac as far south as its deep channel, and draw from a similar location in the Potomac during Nanjemoy flood.

Automated identification of rivers and shorelines in aerial imagery using image texture

A method has been developed which automatically extracts river and river bank locations from arbitrarily sourced high resolution (~1m) visual spectrum imagery without recourse to multi-spectral or even color information. This method relies on quantifying the difference in image texture between the relatively smooth surface of the river water and the rougher surface of the vegetated land or built environment bordering it and then segmenting the image into high and low roughness regions. The edges of the low roughness regions then define the river banks. The method can be coded in any language without recourse to proprietary tools and requires minimal operator intervention. As this sort of imagery is increasingly being made freely available through such services as Google Earth or Worldwind this technique can be used to extract river features when more specialized imagery or software is not available.

Development of a forecast capability for coastal embayments of the Mississippi Sound

The present work focuses on results from the second phase of development of a forecast system for coastal circulation in the Mississippi Sound and surrounding embayments in the northeast Gulf of Mexico. The basis of the forecast system is the 3-D finite element model, ADCIRC, driven by tides, river inflow, and wind. Sensitivity of the forecast model to wind stress and offshore boundary forcing is demonstrated. Limited area domain models of Bay St. Louis and the Pearl River highlight the influence of seasonal river flux.

The Role of River Discharge and Vertical Mixing Formulation on Barotropic Circulation in Bay St. Louis, MS

Nearshore urban runoff is known to adversely impact the fecal coliform levels in Bay St. Louis, MS, motivating the need for a three-dimensional (3-D) model of circulation and mixing for the region. Such a model is applied here to 1) understand role of river discharge as a long-term flushing mechanism for the bay, and 2) assess the sensitivity of the computed 3-D circulation to the parameterization of vertical mixing. Sea levels and currents in Bay St. Louis are simulated by ADCIRC, a 3-D barotropic finite element (FE) circulation model. The constructed computational model resolves bathymetry in Bay St. Louis to between 70–100 m. Tidal forcing is derived from a larger domain simulation of the Mississippi Bight and forcing from the Wolfe River is obtained from USGS stream gage data. Vertical profiles of the horizontal residual current in the inlet connecting Bay St. Louis to the Mississippi Sound demonstrate considerable sensitivity of the circulation to the vertical mixing parameterization. The across inlet flow is particularly affected. Pathways of numerical drifters after 15 days clearly indicate that the residual circulation associated with tides and an average spring river discharge are not a significant mechanism for exchange between the bay and offshore coastal waters. Only under extreme storm events discharge are particles in the bay flushed out into offshore waters.

Evaluation of Baroclinic ADCIRC using a process-oriented test along a slope

Abstract : Process-oriented tests, such as those suggested by Haidvogel and Beckmann (1999), are often utilized in the validation of baroclinic processes in shallow water models. In a previous analysis, the so-called lock-exchange or dam break problem on a flat slope, wherein a vertical barrier that separates water of different densities is removed at time zero, was utilized in the validation of the baroclinic additions to the shallow water ADCIRC (ADvanced CIRCulation) model (Kolar et al., 2009). More specifically, a laboratory-scale model was utilized to capture high-resolution data sets of the lock-exchange problem. These data sets allowed for direct comparison throughout the domain of the experimental and numerical results. Results showed good agreement between model and laboratory results, sans the shear instabilities along the interface. Using these same techniques, we analyzed a density front along a slope, the gravity adjustment test case suggested by Haidvogel and Beckmann (1999). In this analysis, water of different densities is separated by a vertical barrier that is removed at time zero, allowing the more dense water to travel down the slope. Data is captured every 0.2 seconds using high-resolution digital photography, with salt concentration extracted by comparing pixel intensity of the dyed fluid against calibration standards. Herein, experimental results are compared to numerical results for the location of the front, along with the average root mean square errors of the salinity field.