Lianyuan Zheng

Hurricane storm surge simulations for tampa bay

Using a high resolution, three-dimensional, primitive equation, finite volume coastal ocean model with flooding and drying capabilities, supported by a merged bathymetric-topographic data set and driven by prototypical hurricane winds and atmospheric pressure fields, we investigated the storm surge responses for the Tampa Bay, Florida, vicinity and their sensitivities to point of landfall, direction and speed of approach, and intensity. All of these factors were found to be important. Flooding potential by wind stress and atmospheric pressure induced surge is significant for a category 2 hurricane and catastrophic for a category 4 hurricane. Tide, river, and wave effects are additive, making the potential for flood-induced damage even greater. Since storm surge sets up as a slope to the sea surface, the highest surge tends to occur over the upper reaches of the bay, Old Tampa Bay and Hillsborough Bay in particular. For point of landfall sensitivity, the worst case is when the hurricane center is positioned north of the bay mouth such that the maximum winds associated with the eye wall are at the bay mouth. Northerly (southerly) approaching storms yield larger (smaller) surges since the winds initially set up (set down) water level. As a hybrid between the landfall and direction sensitivity experiments, a storm transiting up the bay axis from southwest to northeast yields the smallest surge, debunking a misconception that this is the worst Tampa Bay flooding case. Hurricanes with slow (fast) translation speeds yield larger (smaller) surges within Tampa Bay due to the time required to redistribute mass.

How estuaries work: A Charlotte Harbor example

We consider the time-averaged, estuarine circulation through a control volume analysis of its mechanical energy balance; hence the title of our paper: How estuaries work. The venue is the Charlotte Harbor on Floridas west coast, and the analysis medium is the primitive equation ECOM3D-si model. We are motivated by an estuary classification dilemma. Being that estuarine circulation is buoyancy driven by the horizontal salinity gradient, and that the gradient increases with increasing vertical mixing as the salinity isolines rotate from horizontal to vertical, it follows that an increase in mixing should lead to an increase in circulation. Yet, at some point, intermediate between partial and well mixed, the estuarine circulation decreases. We explore this conundrum by considering the sources and sinks of mechanical energy, derived from river, tide, and wind forcing, through analyses of pressure work, work by stresses operating on the surface and the bottom, work against buoyancy through mixing and advection, and turbulence energy production by velocity component shears. How the energy partitions between work against buoyancy (that sets the driving force) and turbulence production (that serves as a brake) provides an answer. Depending on tides and winds, if the incremental rate of turbulence production exceeds that of buoyancy work, the estuarine circulation slows. A useful measure is the ratio of buoyancy work to turbulence production. As this ratio increases so does the circulation, and conversely. For the Charlotte Harbor, tides alone cause peak circulation. Weak, oscillatory winds may add to this, but with increasing wind stress the tide and wind-averaged estuarine circulation decreases. Further exploration of these effects across Rayleigh number space with varying estuarine geometries and forcing functions may lead to improved understandings of estuary workings in general.

Basic Tenets for Coastal Ocean Ecosystems Monitoring

Describing and understanding how the coastal ocean works requires a systems science approach, including long-term observations and model simulations. These are prerequisites to predicting the outcomes of either natural or human-induced occurrences. Applications to societally relevant issues such as ecology, coastal resiliency, and alternative energy resources all have the coastal ocean circulation as their starting point. Ecology provides an example. The circulation is what unites nutrients with light, fueling primary productivity and higher trophic level interactions, and the circulation largely determines the water properties in which organisms reside. Ecology, in essence, integrates all processes responsible for organism success. A rationale and a design are developed for a comprehensive coastal ocean observing and modeling system off Floridas west coast. Applications are provided demonstrating the utility of such a coastal ocean observing and modeling system for addressing problems of societal importance.

Combining Numerical Ocean Circulation Models with Satellite Observations in a Trajectory Forecast System: A Rapid Response to the Deepwater Horizon Oil Spill

The Deepwater Horizon oil spill presented an unprecedented threat to the Gulf of Mexico coastline and living marine resources, and possibly to that of the southeastern USA. Needed for mitigation efforts and to guide scientific investigations was a system for tracking the oil, both at the surface and at depth. We report on such system, implemented immediately upon spill onset, by marshaling numerical model and satellite remote sensing resources available from existing coastal ocean observing activities. Surface oil locations inferred from satellite imagery were used to initialize the positions of the virtual particles in an ensemble of trajectory models, and the particles were tracked using forecast surface currents, with new particles added to simulate the continual release of oil from the well. Three dimensional subsurface tracking were also performed from the well site location at several different depths. Timely trajectory forecasts were used to plan scientific surveys and other spill response activities.

Developing a Smart Semantic Web With Linked Data and Models for Near-Real-Time Monitoring of Red Tides in the Eastern Gulf of Mexico

In recent decades, the technology used to detect and quantify harmful algal blooms (commonly known as red tides) and characterize their physicochemical environment has improved considerably. A remaining challenge is effective delivery of the information generated from these advances in a user-friendly way to a diverse group of stakeholders. Based on existing infrastructure, we establish a Web-based system for near-real-time tracking of red tides caused by the toxic dinoflagellate Karenia brevis, which annually threatens human and environmental health in the eastern Gulf of Mexico. The system integrates different data products through a custom-made Web interface. Specifically, three types of data products are fused: 1) near-real-time ocean color imagery tailored for red tide monitoring; 2) K. brevis cell abundance determined by sample analysis; and 3) ocean currents from a nested and validated numerical model. These products are integrated and made available to users in Keyhole Markup Language (KML) format, which can be navigated, interpreted, and overlaid with other products in Google Earth. This integration provides users with the current status of red tide occurrence (e.g., location, severity, and spatial extent) while presenting a simple way to estimate bloom trajectory, thus delivering an effective method for near-real-time tracking of red tides.

A critique of alternative power generation for Florida by mechanical and solar means

The authors address the potential for electrical power generation for Florida by harnessing the natural energy sources of wind and solar, along with ocean currents and waves, using observations of surface winds, solar radiation, ocean currents and waves collected by the University of South Florida, Coastal Ocean Monitoring and Prediction System (COMPS), augmented by other data and numerical model simulations. They begin by identifying what nature offers. The authors use specifications from existing, commercially available devices to convert natures bounty to power generation estimates, for wind and solar. They draw upon physical principles to arrive at power generation estimates for these potential sources, in the absence of mature, commercially available devices for ocean currents and waves. The authors then make reasonable extrapolations on what these estimations may mean in a practical sense for supplying energy to society, on the basis of what nature offers and what machinery may be capable of producing. A means for supplementing power generation by conventional fuels may be provided by power generation from these naturally occurring, alternative energy sources, particularly wind and solar, but a replacement for conventional fuels is not provided.

West Florida shelf upwelling: Origins and pathways

Often described as oligotrophic, the west Florida continental shelf supports abundant fisheries, experiences blooms of the harmful alga, Karenia brevis, and exhibits subsurface chlorophyll maxima evident in shipboard and glider surveys. Renewal of inorganic nutrients by the upwelling of deeper ocean water onto the shelf may account for this, but what are the origins and pathways by which such new water may broach the shelf break and advance toward the shoreline? We address these questions via numerical model simulations of pseudo-Lagrangian, isopycnic water parcel trajectories. Focus is on 2010, when the west Florida shelf was subjected to an anomalously protracted period of upwelling caused by Gulf of Mexico Loop Current interactions with the shelf slope. Origins and pathways are determined by integrating trajectories over successive 45 day intervals, beginning from different locations along the shelf break and at various locations and depths along the shelf slope. Waters upwelling across the shelf break are found to originate from relatively shallow depths along the shelf slope. Even for the anomalous 2010 year, much of this upwelling occurs from about 150 m and above, although waters may broach the shelf break from 300 m depth, particularly in the Florida Panhandle. Such interannual renewal of west Florida shelf waters appears to have profound effects on west Florida shelf ecology.

Offshore forcing on the “pressure point” of the West Florida Shelf: Anomalous upwelling and its influence on harmful algal blooms

Gulf of Mexico Loop Current (LC) interactions with the West Florida Shelf (WFS) slope play an important role in shelf ecology through the upwelling of new inorganic nutrients across the shelf break. This is particularly the case when the LC impinges upon the shelf slope in the southwest portion of the WFS near the Dry Tortugas. By contacting shallow water isobaths at this “pressure point” the LC forcing sets the entire shelf into motion. Characteristic patterns of LC interactions with the WFS and their occurrences are identified using unsupervised neural network, self-organizing map, from 23 years (1993–2015) of altimetry data. The duration of the occurrences of such LC patterns is used as an indicator of offshore forcing of anomalous upwelling. Consistency is found between the altimetry-derived offshore forcing and the occurrence and severity of WFS coastal blooms of the toxic dinoflagellate, Karenia brevis: years without major blooms tend to have prolonged LC contact at the “pressure point,” whereas years with major blooms tend not to have prolonged offshore forcing. Resetting the nutrient state of the shelf by the coastal ocean circulation in response to deep-ocean forcing demonstrates the importance of physical oceanography in shelf ecology. A satellite altimetry-derived seasonal predictor for major K. brevis blooms is also proposed.

A Regional Testbed for Storm Surge and Coastal Inundation Models - An Overview

Since 2008, a Regional Testbed has been comparing storm surge models in terms of historical storm simulations and coastal inundation maps, e.g., Flood Insurance Rate Maps and Surge Atlas. The models include two structured grid (CH3D and POM) and two unstructured grid (ADCIRC and FVCOM) models. During 2008, the storm surge and coastal inundation in the Chesapeake Bay and the Outer Banks of North Carolina during Hurricane Isabel was simulated and the results compared in an independent but non-interoperable effort by partners. In 2009-2010, an additional model SLOSH was added, and all five models were used to simulate the storm surge and coastal inundation in southwest Florida during Hurricane Charley and the results compared. Model inputs and outputs were designed in an interoperable fashion, using common model input data, parameterization and coefficients, common model output formats using a common model data grid. Thirty scenarios were developed to test the sensitivity of the models to bathymetry, storm forcing, wind drag coefficient, bottom friction, Coriolis, 2D vs. 3D formulation, etc. Various types of model products, including time series of storm surge and maximum inundation over the entire model domain, were compared to each other and measured data. The detailed model simulations and comparisons required considerable computational and analysis time, but resulted in the discovery of how model features affected the model accuracy, leading to an overall improvement of all the models used. Testbed results showed differences in storm surge elevation and coastal inundation during both Isabel and Charley. While the simulated water level at the observed stations generally did not differ by more than 20% and no model appears to be consistently superior / inferior to any other model, there are more significant differences in the produced inundation maps. The computational efficiency differs considerably among the various models. Additional simulations of a large number (20+) of storms and domains are needed to better define the relative importance of different model parameters and to sort out the causes for subtle differences among the model results. More in-depth model inter comparison results will be forthcoming in a future paper.

More surprises in the global greenhouse: Human health impacts from recent toxic marine aerosol formations, due to centennial alterations of world-wide coastal food webs

Reductions of zooplankton biomasses and grazing pressures were observed during overfishing-induced trophic cascades and concurrent oil spills at global scales. Recent phytoplankton increments followed, once Fe-, P-, and N-nutrient limitations of commensal diazotrophs and dinoflagellates were also eliminated by respective human desertification, deforestation, and eutrophication during climate changes. Si-limitation of diatoms instead ensued during these last anthropogenic perturbations of agricultural effluents and sewage loadings. Consequently, ~15% of total world-wide annual asthma trigger responses, i.e. amounting to ~45 million adjacent humans during 2004, resulted from brevetoxin and palytoxin poisons in aerosol forms of western boundary current origins. They were denoted by greater global harmful algal bloom [HAB] abundances and breathing attacks among sea-side children during prior decadal surveys of asthma prevalence, compiled here in ten paired shelf ecosystems of western and eutrophied boundary currents. Since 1965, such inferred onshore fluxes of aerosolized DOC poisons of HABs may have served as additional wind-borne organic carriers of toxic marine MeHg, phthalate, and DDT/DDE vectors, traced by radio-iodine isotopes to potentially elicit carcinomas. During these exchanges, as much as 40% of mercury poisonings may instead have been effected by inhalation of collateral HAB-carried marine neurotoxic aerosols of MeHg, not just from eating marine fish. Health impacts in some areas were additional asthma and pneumonia episodes, as well as endocrine disruptions among the same adjacent humans, with known large local rates of thyroid cancers, physician-diagnosed pulmonary problems, and ubiquitous high indices of mercury in hair, pesticides in breast milk, and phthalates in urine.