Investigation of Tidal Exchange and the Formation of Tidal Vortices at Aransas Pass, Texas, USA

Laboratory and field measurements are presented as part of a study of tidal exchange through Aransas Pass, Texas. At the mouth of Aransas Pass, the input of circulation by the ebb tide forces the formation of a starting-jet dipole vortex. These vortices are believed to play an important role in the flushing of coastal regions, and affect the transport of passive tracers, such as nutrients and sediment, from the estuary to the ocean and vice versa. Tidal vortex formation was first measured in the laboratory to gain knowledge of the vortex structure and movement. This information was subsequently used to design and conduct a field campaign to measure these large-scale vortices. A combination of measurements from a towed acoustic Doppler current profiler (ADCP), CTD (conductivity, temperature, depth) and Lagrangian surface drifters were implemented for field data acquisition during ebb and flood tide. Drifter trajectories were used to estimate the size of each observed vortex as well as the statistics of relative diffusion offshore of Aransas Pass. The size of the rotational core of the vortex was shown to be approximated physically by the inlet width or by 0:02UT, where U is the maximum velocity through the inlet channel and T is the tidal period, and confirms results found in previous laboratory experiments. Additionally, the scale of diffusion was approximately 1–15 km and the apparent diffusivity was between 2–130 m2=s following Richardsons law. During flood tide, tidal vortices do not form due to the bay configuration. Instead, flow is distributed into three bay channels. Through the CTD vertical profiles, the data indicate that the system is generally well-mixed over the course of diurnal flood tide. For measurements taken during a semi-diurnal tide, a freshwater event was detected in the profile and confirmed with USGS gauge data. For currents during flood, the Lagrangian drifter data suggest that there is a narrow region to the north of the inlet by which passive tracers are transported through the inlet from offshore. Generally, the majority of the flow from the inlet continues through the Corpus Christi Ship Channel (50-80%) followed by the Lydia Ann Channel ( 20-40%) and the remainder flows through Aransas Channel

Laboratory Analysis of Vortex Dynamics For Shallow Tidal Inlets

Estuaries depend on the transport of nutrients and sediments from the open sea to help maintain a prosperous environment. One of the major transport mechanisms is the propagation of large two dimensional vortical structures. At the mouth of an inlet, tidal flow forces the formation of two dimensional vortical structures whose lateral extent is much greater than the water depth. After the starting jet vortex dipole detaches from the inlet, secondary vortices shed due to separation from the inlet boundary and eventually reach the starting-jet dipole. An idealized inlet con figuration was utilized for laboratory experiments detailing the formation and propagation of the vortex structures with water depths of 3, 5, and 9 centimeters and flow Froude scaled to inlets along the Texas coast. Using surface particle image velocimetry, the entrainment of the secondary structures into the vortex system are shown as well as variations in characteristics such as trajectory, size, vorticity, and circulation for the vortices as they move downstream

On the dynamics of the Zanzibar Channel

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 6091–6113, doi:10.1002/2015JC010879.The Zanzibar Channel lies between the mainland of Tanzania and Zanzibar Island in the tropical western Indian Ocean, is about 100 km long, 40 km wide, and 40 m deep, and is essential to local socioeconomic activities. This paper presents a model of the seasonal and tidal dynamics of the Zanzibar Channel based on the Regional Ocean Modeling System (ROMS) and a comparison of the model and observations. The seasonal dynamics of the channel is forced by remote processes and the local wind. Remote forcing creates the East African Coastal Current, a portion of which flows through the channel northward with a seasonally varying magnitude. The local wind enhances this seasonality in the surface Ekman layer, resulting in a stronger northward flow during the southwest monsoon season and a weak northward or occasionally southward flow during the northeast monsoon season. The tidal flows converge and diverge in the center of the channel and reduce the transport in the channel. The remotely forced, wind-forced, and tidal dynamics contain 5%, 3%, and 92% of the total kinetic energy, respectively. Despite their low kinetic energy, the remotely forced and wind-forced flows are most relevant in advecting channel water to the open ocean, which occurs in 19 days at the peak of the southwest monsoon season. The channel is well mixed, except during brief periods in the two rainy seasons, and temporarily cools between December and February. The dispersion of passive tracers is presented as an example of potential model applications.National Science Foundation Grant Numbers: OISE-0827059 , OCE-0550658 , OCE-0851493 , OCE-09274722016-03-1

Characterizing the weather band variability of the Texas shelf current

Considering the benefits of understanding the circulation patterns of the shelf, it is not surprising that there are numerous studies of the Texas Shelf circulation patterns. Given that previous studies were focused on the low-frequency variability of the circulation which is upcoast (northeast flow) in the summer and downcoast (southwest flow) especially on the inner shelf in the non-summer seasons, this study investigates the weather band (2–15 days) variability of the Texas Shelf near-surface circulation pattern. Current meter data at 1.5 m below the sea surface from the inner, mid, and outer shelves were analyzed. This study demonstrated that there are high-frequency current reversals within the weather band in each season. From the estimated persistence of the currents during reversals, the inner and mid shelf currents are predominantly downcoast in the non-summer seasons and upcoast in the summer season whereas the outer shelf currents are mostly upcoast all year round. The Wavelets analysis of the currents revealed that most of the variabilities on the inner and mid shelf regions were within the 4-12-day band whereas on the outer shelf the dominant variability was within the 3–8-day band. From the cross-spectra analysis of both the currents and wind data, it was determined that the influence of the wind was more dominant on the inner and mid shelf regions at the 8–15-day band than on the outer shelf where the contribution of the wind is prevalent at the 2–4-day band

Gulf of Mexico Hurricane Glider Operations in Support of Tropical Cyclone Intensification Forecasts

During the 2019 peak hurricane season, two gliders operated by Texas AM University (TAMU) and the University of Southern Mississippi (USM) and funded by Shell Exploration Production Company were deployed as part of the National Oceanic and Atmospheric Administration Hurricane Glider Program to collect near-real time subsurface ocean temperature and salinity measurements for data assimilation into global ocean and hurricane models. The missions were designed to resolve regional ocean features that can contribute to hurricane intensity and provide spatial coverage in the event of a tropical cyclone with the intent to capture potential intensification prior to landfall. For the Gulf of Mexico, the Mississippi River plume, Loop Current, and Loop Current Eddies are areas of interest that can contribute to hurricane intensity. Tropical Storms Nester and Olga were named storms during the 2019 season in the Atlantic Basin, and their trajectories passed by the USM and TAMU gliders, respectively. While changes in the sea surface temperature were more likely due to the presence of seasonal fronts rather than the passing of these tropical storms, the data did indicate pockets of subsurface warm water under a freshwater plume from the Mississippi River. Currently, multiple hurricane glider missions are underway in the Gulf of Mexico during a record breaking 2020 season with Hurricane Laura anticipated to make landfall early morning (local time) on Thursday, August 27, 2020 near the Texas/Louisiana border

Ocean Forests: Breakthrough Yields for Macroalgae

The US Department of Energy Advanced Research Projects Agency - Energy (ARPA-E) MacroAlgae Research Inspiring Novel Energy Research (MARINER) program is encouraging technologies for the sustainable harvest of large funding research of macroalgae for biofuels at less than $80 per dry metric ton (DMT). The Ocean Forests team, led by the University of Southern Mississippi, is developing a complete managed ecosystem where nutrients are transformed and recycled. The team\u27s designs address major bottlenecks in profitability of offshore aquaculture systems including economical moored structures that can withstand storms, efficient planting, managing and harvesting systems, and sustainable nutrient supply. The work is inspired by Lapointe [1] who reported yields of Gracilaria tikvahiae equivalent to 127 DMT per hectare per year (compared with standard aquaculture systems in the range of 20 to 40 DMT/ha/yr). This approach offers the potential for breakthrough yields for many macroalgae species. Moreover, mini-ecosystems in offshore waters create communities of macroalgae, shellfish, and penned finfish, supplemented by visiting free-range fish that can increase productivity, produce quality products, and create jobs and income for aquafarmers. Additional benefits include reduced disease in fish pens, cleaning contaminated coastal waters, and maximizing nutrient recycling. Cost projections for a successful, intensive, scaled system are competitive with current prices for fossil fuels

Uncrewed Ocean Gliders and Saildrones Support Hurricane Forecasting and Research

Miles et al focus on uncrewed ocean gliders and saildrones support hurricane forecasting and research. Components of the sustained ocean observing system are useful for understanding the role of the ocean in hurricane intensity changes. Here, the authors provide a broad overview of the ongoing US hurricane glider project and details of a new effort with the Saildrone USV during the 2021 hurricane season. While this article focuses on the US East Coast, Gulf of Mexico, and Caribbean Sea, similar efforts are underway in Korea, the Philippines, Japan, and China, among other countries