Yinglong J. Zhang

Seasonal and interannual variability of the Columbia River plume: A perspective enabled by multiyear simulation databases

[1] As integral capability within an end-to-end observatory for the Columbia River estuary-plume-shelf system, we routinely create simulation databases of 3-D baroclinic circulation with unstructured grid models SELFE (Semi-implicit Eulerian-Lagrangian Finite Element) and ELCIRC (Eulerian-Lagrangian Circulation). Here, 1999―2006 SELFE simulations are used to study plume variability at multiple temporal scales: interannual, seasonal, and event scale. Time series of plume metrics, together with climatology and anomalies of surface salinity, suggest that simulations usefully capture key features of plume dynamics. In particular, simulations capture seasonal variability around two known trends: a coastally attached northward winter plume and a detached southward summer plume. Results show significant interannual variability of the plume orientation and extent, with potential implications on the variability of productivity in the system. An empirical orthogonal function analysis confirms that a bidirectional plume is prevalent in summer, showing that the result holds true regardless of interannual variability. Short-term bidirectional plumes, previously observed or modeled only in summer, can also occasionally develop in winter as a result of episodically strong upwelling-favorable winds. Across years, the predominantly coastal attached northward plume in late fall and winter is found to separate frequently from the coast, during wind relaxation events or weak wind reversals. Multiple skill scores are used to evaluate the quality of the simulations against earlier circulation databases and data. Analysis of root-mean-square error and bias suggests overall superiority of SELFE-generated over ELCIRC-generated simulation databases, but the generality of the conclusions is limited by (1) models not being the only difference between simulation databases and (2) no model prevailing across all error metrics.

Simulated tsunami inundation for a range of Cascadia megathrust earthquake scenarios at Bandon, Oregon, USA

Characterizations of tsunami hazards along the Cascadia subduction zone hinge on uncertainties in megathrust rupture models used for simulating tsunami inundation. To explore these uncertainties, we constructed 15 megathrust earthquake scenarios using rupture models that supply the initial conditions for tsunami simulations at Bandon, Oregon. Tsunami inundation varies with the amount and distribution of fault slip assigned to rupture models, including models where slip is partitioned to a splay fault in the accretionary wedge and models that vary the updip limit of slip on a buried fault. Constraints on fault slip come from onshore and offshore paleoseismological evidence. We rank each rupture model using a logic tree that evaluates a model’s consistency with geological and geophysical data. The scenarios provide inputs to a hydrodynamic model, SELFE, used to simulate tsunami generation, propagation, and inundation on unstructured grids with w 8.7–9.2. Simulated tsunami inundation agrees with sparse deposits left by the A.D. 1700 and older tsunamis. Tsunami simulations for large (22–30 m slip) and medium (14–19 m slip) splay fault scenarios encompass 80%–95% of all inundation scenarios and provide reasonable guidelines for land-use planning and coastal development. The maximum tsunami inundation simulated for the greatest splay fault scenario (36–44 m slip) can help to guide development of local tsunami evacuation zones.

MODEL PREDICTIVE NEURAL CONTROL OF A HIGH-FIDELITY HELICOPTER MODEL

In this paper we present a method for optimal control of a nonlinear highly realistic helicopter model based on a combination of a neural network (NN) feedback controller and a state-dependen t Riccati equation (SDRE) controller. Optimization of the NN is performed within a receding horizon model predictive control (MPC) framework, subject to dynamic and kinematic constraints. The SDRE controller utilizes a simplified 6DOF rigid body dynamic model, and augments the NN controller by providing an initial feasible solution and improving stability. While the SDRE control provides robustness based on a pseudo-linear formulation of the dynamics, the MPNC utilizes the highly accurate numerical helicopter model.

Benchmarking a new open-source 3D circulation model (ELCIRC)

Released recently as an open source code, ELCIRC ( E ulerian- L agrangian Cir culation) solves the primitive shallow-water Navier-Stokes equations with turbulence closure submodels. Numerically it uses a semi-implicit finite-difference/volume method on unstructured horizontal grids and structured grids in the unstretched vertical direction. An Eulerian-Lagrangian method (ELM) is used to treat the advection, and wetting and drying is a natural part of the algorithm. The model has low-order accuracy, but is very flexible, computationally efficient, and robust. Overall, it has shown excellent ability to address complex river-to-ocean systems, and is currently used as the computational engine for our observation and forecasting system for the Columbia River estuary and plume. As a part of the development of ELCIRC, we carefully assessed its performance against a wide set of controlled benchmark problems: wave propagation on a slope, geostrophic flow in a straight channel, and adjustment under gravity, etc. In this paper we report on these benchmark studies, which provide very useful insights on the capabilities and limitations of the model. Using carefully defined error metrics, convergence studies are carried out. Compared against well-established higher-order models (in particular, ADCIRC and ROMS), ELCIRC has the capability of compensating for its low-order accuracy through inexpensive high resolution. Benchmarks will be made available electronically before the publication of the conference proceedings.

Integrating a Circulation Model and an Ecological Model to Simulate the Dynamics of Zooplankton

Zooplankton plays a fundamental role in the estuarine food web. Thus, understanding the factors that affect the distribution of estuarine zooplankton is of major concern for the management of estuaries. An integrated modeling approach, coupling a hydrodynamics and an ecological model, is presented here to simulate the three-dimensional dynamics of zooplankton. The hydrodynamics is computed with SELFE, a 3D baroclinic circulation model. The ecological model is based on an extension of EcoSim 2.0, which allows the simulation of several ecological state variables, to account for zooplankton dynamics. Some test cases are presented that validate the changes made in the EcoSim 2.0 and the integration of the hydrodynamic and ecological models. A sensitivity analysis is also performed to check the influence of the input parameters of the ecological model in the final results, showing the phytoplanktons temperature-dependent growth parameters as the most important, for phytoplankton, inorganic nutrients and DIC pools.

The origins of the anomalous warming in the California coastal ocean and San Francisco Bay during 2014–2016

During 2014 exceptionally warm water temperatures developed across a wide area off the California coast and within San Francisco Bay (SFB) and persisted into 2016. Observations and numerical model output are used to document this warming and determine its origins. The coastal warming was mostly confined to the upper 100 meters of the ocean and was manifested strongly in the two leading modes of upper ocean (0-100 m) temperature variability in the extra-tropical eastern Pacific. Observations suggest that the coastal warming in 2014 propagated into nearshore regions from the west while later indicating a warming influence that propagated from south to north into the region associated with the 2015-16 El Nino event. An analysis of the upper ocean (0-100 m) heat budget in a Regional Ocean Modeling System simulation confirmed this scenario. The results from a set of sensitivity runs with the model in which the lateral boundary conditions varied supported the conclusions drawn from the heat budget analysis. Concerning the warming in the SFB, an examination of the observations and the heat budget in an unstructured-grid numerical model simulation suggested that the warming during the second half of 2014 and early 2016 originated in the adjacent California coastal ocean and propagated through the Golden Gate into the Bay. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance.

Tidal Response to Sea-Level Rise in Different Types of Estuaries: The Importance of Length, Bathymetry, and Geometry: Tidal Response to Sea-level Rise

Tidal response to sea-level rise (SLR) varies in different coastal systems. To provide a generic pattern of tidal response to SLR, a systematic investigation was conducted using numerical techniques applied to idealized and realistic estuaries, with model results cross-checked by analytical solutions. Our results reveal that the response of tidal range to SLR is nonlinear, spatially heterogeneous, and highly affected by the length and bathymetry of an estuary and weakly affected by the estuary convergence with an exception of strong convergence. Contrary to the common assumption that SLR leads to a weakened bottom friction, resulting in increased tidal amplitude, we demonstrate that tidal range is likely to decrease in short estuaries and in estuaries with a narrow channel and large low-lying shallow areas.

Modeling mixing processes in the Columbia River estuary: A model-data comparison

Columbia River estuary is a macro-tidal estuary, shallow except for two narrow channels through which most of the salt transport takes place. Mixing processes in the two channels are strongly affected by Spring-Neap variations in the tidal range, river discharges (which typically exceed 10,000 m3/s during spring freshets) and coastal winds. The interactions between these forcings controls residual flows inside the estuary, which in turn impacts the extent of salt intrusion into the estuary. Using a new 3D baroclinic circulation model (ELCIRC, [12]) , a year long database of numerical simulations has been developed and contrasted against data from a network of in situ instruments which form a part of CORIE. CORIE is a long term coastal-margin observatory system for the Columbia River. In this paper we (a) show that ELCIRC simulations are able to reproduce some but not all key complex interactions observed in the field, (b) study the spatial and temporal variations circulation patterns using a combination of simulations and observations, and (c) use simulations to quantify the role played by each of the forcings (tides, winds, and discharge) on the residual circulation and salinity intrusion patterns.