Coincident Observations of Dye and Drifter Relative Dispersion over the Inner Shelf

AbstractCoincident Lagrangian observations of coastal circulation with surface drifters and dye tracer were collected to better understand small-scale physical processes controlling transport and dispersion over the inner shelf in the Gulf of Mexico. Patches of rhodamine dye and clusters of surface drifters at scales of O(100) m were deployed in a cross-shelf array within 12 km from the coast and tracked for up to 5 h with airborne and in situ observations. The airborne remote sensing system includes a hyperspectral sensor to track the evolution of dye patches and a lidar to measure directional wavenumber spectra of surface waves. Supporting in situ measurements include a CTD with a fluorometer to inform on the stratification and vertical extent of the dye and a real-time towed fluorometer for calibration of the dye concentration from hyperspectral imagery. Experiments were conducted over a wide range of conditions with surface wind speed between 3 and 10 m s−1 and varying sea states. Cross-shelf density gradients due to freshwater runoff resulted in active submesoscale flows. The airborne data allow characterization of the dominant physical processes controlling the dispersion of passive tracers such as freshwater fronts and Langmuir circulation. Langmuir circulation was identified in dye concentration maps on most sampling days except when the near surface stratification was strong. The observed relative dispersion is anisotropic with eddy diffusivities O(1) m2 s−1. Near-surface horizontal dispersion is largest along fronts and in conditions dominated by Langmuir circulation is larger in the crosswind direction. Surface convergence at fronts resulted in strong vertical velocities of up to −66 m day−1.

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Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

Oceanography ◽

10.5670/oceanog.2021.117 ◽

2021 ◽

Vol 34 (1) ◽

pp. 58-75

Author(s):

Michel Boufadel ◽

◽

Annalisa Bracco ◽

Eric Chassignet ◽

Shuyi Chen ◽

...

Keyword(s):

Gulf Of Mexico ◽

Physical Environment ◽

Large Scale ◽

Transport Processes ◽

Small Scale ◽

Surface Mixed Layer ◽

Physical Processes ◽

Mixing Processes ◽

Near Surface ◽

Wide Range

Physical transport processes such as the circulation and mixing of waters largely determine the spatial distribution of materials in the ocean. They also establish the physical environment within which biogeochemical and other processes transform materials, including naturally occurring nutrients and human-made contaminants that may sustain or harm the region’s living resources. Thus, understanding and modeling the transport and distribution of materials provides a crucial substrate for determining the effects of biological, geological, and chemical processes. The wide range of scales in which these physical processes operate includes microscale droplets and bubbles; small-scale turbulence in buoyant plumes and the near-surface “mixed” layer; submesoscale fronts, convergent and divergent flows, and small eddies; larger mesoscale quasi-geostrophic eddies; and the overall large-scale circulation of the Gulf of Mexico and its interaction with the Atlantic Ocean and the Caribbean Sea; along with air-sea interaction on longer timescales. The circulation and mixing processes that operate near the Gulf of Mexico coasts, where most human activities occur, are strongly affected by wind- and river-induced currents and are further modified by the area’s complex topography. Gulf of Mexico physical processes are also characterized by strong linkages between coastal/shelf and deeper offshore waters that determine connectivity to the basin’s interior. This physical connectivity influences the transport of materials among different coastal areas within the Gulf of Mexico and can extend to adjacent basins. Major advances enabled by the Gulf of Mexico Research Initiative in the observation, understanding, and modeling of all of these aspects of the Gulf’s physical environment are summarized in this article, and key priorities for future work are also identified.

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Small-Scale Dispersion in the Presence of Langmuir Circulation

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0107.1 ◽

2019 ◽

Vol 49 (12) ◽

pp. 3069-3085 ◽

Cited By ~ 4

Author(s):

Henry Chang ◽

Helga S. Huntley ◽

A. D. Kirwan Jr. ◽

Daniel F. Carlson ◽

Jean A. Mensa ◽

...

Keyword(s):

Structure Function ◽

Second Order ◽

Relative Dispersion ◽

Small Scale ◽

Cell Diameter ◽

Order Structure ◽

Near Surface ◽

Surface Dispersion ◽

Surface Drifters ◽

Langmuir Cells

AbstractWe present an analysis of ocean surface dispersion characteristics, on 1–100-m scales, obtained by optically tracking a release of bamboo plates for 2 h in the northern Gulf of Mexico. Under sustained 5–6 m s−1 winds, energetic Langmuir cells are clearly delineated in the spatially dense plate observations. Within 10 min of release, the plates collect in windrows with 15-m spacing aligned with the wind. Windrow spacing grows, through windrow merger, to 40 m after 20 min and then expands at a slower rate to 50 m. The presence of Langmuir cells produces strong horizontal anisotropy and scale dependence in all surface dispersion statistics computed from the plate observations. Relative dispersion in the crosswind direction initially dominates but eventually saturates, while downwind dispersion exhibits continual growth consistent with contributions from both turbulent fluctuations and organized mean shear. Longitudinal velocity differences in the crosswind direction indicate mean convergence at scales below the Langmuir cell diameter and mean divergence at larger scales. Although the second-order structure function measured by contemporaneous GPS-tracked surface drifters drogued at ~0.5 m shows persistent r2/3 power law scaling down to 100–200-m separation scales, the second-order structure function for the very near surface plates observations has considerably higher energy and significantly shallower slope at scales below 100 m. This is consistent with contemporaneous data from undrogued surface drifters and previously published model results indicating shallowing spectra in the presence of direct wind-wave forcing mechanisms.

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Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project

MRS Proceedings ◽

10.1557/proc-663-561 ◽

2000 ◽

Vol 663 ◽

Cited By ~ 2

Author(s):

J. Samper ◽

R. Juncosa ◽

V. Navarro ◽

J. Delgado ◽

L. Montenegro ◽

...

Keyword(s):

Large Scale ◽

Reference Model ◽

Numerical Models ◽

Full Scale ◽

Small Scale ◽

Model Parameters ◽

In Situ Test ◽

Wide Range ◽

Engineered Barrier

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.

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Experiments on wind-driven heat exchange processes over melting snow

10.5194/egusphere-egu21-10182 ◽

2021 ◽

Author(s):

Michael Haugeneder ◽

Tobias Jonas ◽

Dylan Reynolds ◽

Michael Lehning ◽

Rebecca Mott

Keyword(s):

Snow Cover ◽

Surface Wind ◽

Infrared Camera ◽

Snow Accumulation ◽

Internal Boundary ◽

Small Scale ◽

Snow Melt ◽

Two Dimensional ◽

Atmospheric Conditions ◽

Near Surface

Snowmelt runoff predictions in alpine catchments are challenging because of the high spatial variability of the snow cover driven by various snow accumulation and ablation processes. In spring, the coexistence of bare and snow-covered ground engages a number of processes such as the enhanced lateral advection of heat over partial snow cover, the development of internal boundary layers, and atmospheric decoupling effects due to increasing stability at the snow cover. The interdependency of atmospheric conditions, topographic settings and snow coverage remains a challenge to accurately account for these processes in snow melt models. In this experimental study, we used an Infrared Camera (VarioCam) pointing at thin synthetic projection screens with negligible heat capacity. Using the surface temperature of the screen as a proxy for the air temperature, we obtained a two-dimensional instantaneous measurement. Screens were installed across the transition between snow-free and snow-covered areas. With IR-measurements taken at 10Hz, we capture the dynamics of turbulent temperature fluctuations over the patchy snow cover at high spatial and temporal resolution. From this data we were able to obtain high-frequency, two-dimensional windfield estimations adjacent to the surface.Preliminary results show the formation of a stable internal boundary layer (SIBL), which was temporally highly variable. Our data suggest that the SIBL height is very shallow and strongly sensitive to the mean near-surface wind speed. Only strong gusts were capable of penetrating through this SIBL leading to an enhanced energy input to the snow surface.With these type of results from our experiments and further measurements this spring we aim to better understand small scale energy transfer processes over patch snow cover and it&#8217;s dependency on the atmospheric conditions, enabling to improve parameterizations of these processes in coarser-resolution snow melt models.

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Solar magneto-convection

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002329 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 95-106 ◽

Cited By ~ 4

Author(s):

Manfred Schüssler

Keyword(s):

Active Regions ◽

Small Scale ◽

Solar Photosphere ◽

Surface Layers ◽

Dynamo Action ◽

Near Surface ◽

Wide Range ◽

Recent Developments ◽

Mixed Polarity ◽

The Magnetic Field

AbstractAn overview is given about recent developments and results of comprehensive simulations of magneto-convective processes in the near-surface layers and photosphere of the Sun. Simulations now cover a wide range of phenomena, from whole active regions, over individual sunspots and pores, magnetic flux concentrations and vortices in intergranular lanes, down to the intricate mixed-polarity structure of the magnetic field generated by small-scale dynamo action. The simulations in concert with high-resolution observations have provided breakthroughs in our understanding of the structure and dynamics of the magnetic fields in the solar photosphere.

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Exploring the use of machine-learning techniques to integrate ground- and remote sensing-based observations for efficient near-surface soil moisture mapping

10.5194/egusphere-egu2020-9092 ◽

2020 ◽

Author(s):

Sarah Schönbrodt-Stitt ◽

Paolo Nasta ◽

Nima Ahmadian ◽

Markus Kurtenbach ◽

Christopher Conrad ◽

...

Keyword(s):

Machine Learning ◽

Soil Moisture ◽

Spatial Resolution ◽

Surface Soil ◽

Bare Soil ◽

Small Scale ◽

Surface Soil Moisture ◽

Near Surface ◽

Campania Region

Mapping near-surface soil moisture (&#952;) is of tremendous relevance for a broad range of environment-related disciplines and meteorological, ecological, hydrological and agricultural applications. Globally available products offer the opportunity to address &#952; in large-scale modelling with coarse spatial resolution such as at the landscape level. However, &#952; estimation at higher spatial resolution is of vital importance for many small-scale applications. Therefore, we focus our study on a small-scale catchment (MFC2) belonging to the &#8220;Alento&#8221; hydrological observatory, located in southern Italy (Campania Region). The goal of this study is to develop new machine-learning approaches to estimate high grid-resolution (about 17 m cell size) &#952; maps from mainly backscatter measurements retrieved from C-band Synthetic Aperture Radar (SAR) based on Sentinel-1 (S1) images and from gridded terrain attributes. Thus, a workflow comprising a total of 48 SAR-based &#952; patterns estimated for 24 satellite overpass dates (revisit time of 6 days) each with ascendant and descendent orbits will be presented. To enable for the mapping, SAR-based &#952; data was calibrated with in-situ measurements carried out with a portable device during eight measurement campaigns at time of satellite overpasses (four overpass days in total with each ascendant and descendent satellite overpasses per day in November 2018). After the calibration procedure, data validation was executed from November 10, 2018 till March 28, 2019 by using two stationary sensors monitoring &#952; at high-temporal (1-min recording time). The specific sensor locations reflected two contrasting field conditions, one bare soil plot (frequently kept clear, without disturbance of vegetation cover) and one non-bare soil plot (real-world condition). Point-scale ground observations of &#952; were compared to pixel-scale (17 m &#215; 17 m), SAR-based &#952; estimated for those pixels corresponding to the specific positions of the stationary sensors. Mapping performance was estimated through the root mean squared error (RMSE). For a short-term time series of &#952; (Nov 2018) integrating 136 in situ, sensor-based &#952; (&#952;insitu) and 74 gravimetric-based &#952; (&#952;gravimetric) measurements during a total of eight S1 overpasses, mapping performance already proved to be satisfactory with RMSE=0.039 m&#179;m-&#179; and R&#178;=0.92, respectively with RMSE=0.041 m&#179;m-&#179; and R&#178;=0.91. First results further reveal that estimated satellite-based &#952; patterns respond to the evolution of rainfall. With our workflow developed and results, we intend to contribute to improved environmental risk assessment by assimilating the results into hydrological models (e.g., HydroGeoSphere), and to support future studies on combined ground-based and SAR-based &#952; retrieval for forested land (future missions operating at larger wavelengths e.g. NISARL-band, Biomass P-band sensors).

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In-Situ Shadowgraph Imaging

Marine Technology Society Journal ◽

10.4031/mtsj.52.6.5 ◽

2018 ◽

Vol 52 (6) ◽

pp. 62-65

Author(s):

Adam T. Greer

Keyword(s):

Sampling Technique ◽

Imaging Systems ◽

Biological Information ◽

Small Scale ◽

Complex Data ◽

Ocean Science ◽

Wide Range ◽

Physical Changes ◽

Body Compositions

AbstractVarious imaging systems are producing complex data that improve our understanding of physical and biological coupling in the ocean. In-situ shadowgraph imaging is one sampling technique that captures detailed biological information for a wide range of plankton with differing body compositions (e.g., gelatinous to crustacean) in their natural orientations, as well as small-scale physical changes. When combined with rapidly advancing computer vision methods and high-resolution oceanographic observations, shadowgraph imagery holds promise for generating new discoveries in ocean science that are only limited by our creativity in asking new questions.

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Numerical Simulation of Near-Surface Wind during a Severe Wind Event in a Complex Terrain by Multisource Data Assimilation and Dynamic Downscaling

Advances in Meteorology ◽

10.1155/2020/7910532 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

De Zhang ◽

Luyuan Chen ◽

Feimin Zhang ◽

Juan Tan ◽

Chenghai Wang

Keyword(s):

Wind Speed ◽

Data Assimilation ◽

Surface Wind ◽

Wrf Model ◽

Surface Wind Speed ◽

Dynamic Downscaling ◽

Near Surface ◽

Wind Event ◽

Weak Wind

Accurate forecast and simulation of near-surface wind is a great challenge for numerical weather prediction models due to the significant transient and intermittent nature of near-surface wind. Based on the analyses of the impact of assimilating in situ and Advanced Tiros Operational Vertical Sounder (ATOVS) satellite radiance data on the simulation of near-surface wind during a severe wind event, using the new generation mesoscale Weather Research and Forecasting (WRF) model and its three-dimensional variational (3DVAR) data assimilation system, the dynamic downscaling of near-surface wind is further investigated by coupling the microscale California Meteorological (CALMET) model with the WRF and its 3DVAR system. Results indicate that assimilating in situ and ATOVS radiance observations strengthens the airflow across the Alataw valley and triggers the downward transport of momentum from the upper atmosphere in the downstream area of the valley in the initial conditions, thus improving near-surface wind simulations. Further investigations indicate that the CALMET model provides more refined microtopographic structures than the WRF model in the vicinity of the wind towers. Although using the CALMET model achieves the best simulation of near-surface wind through dynamic downscaling of the output from the WRF and its 3DVAR assimilation, the simulation improvements of near-surface wind speed are mainly within 1 m s−1. Specifically, the mean improvement proportions of near-surface wind speed are 64.8% for the whole simulation period, 58.7% for the severe wind period, 68.3% for the severe wind decay period, and 75.4% for the weak wind period. The observed near-surface wind directions in the weak wind conditions are better simulated in the coupled model with CALMET downscaling than in the WRF and its 3DVAR system. It is concluded that the simulation improvements of CALMET downscaling are distinct when near-surface winds are weak, and the downscaling effects are mainly manifested in the simulation of near-surface wind directions.

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Wave Energy Resource Assessment for Exploitation—A Review

Journal of Marine Science and Engineering ◽

10.3390/jmse8090705 ◽

2020 ◽

Vol 8 (9) ◽

pp. 705 ◽

Cited By ~ 1

Author(s):

Nicolas Guillou ◽

George Lavidas ◽

Georges Chapalain

Keyword(s):

Wave Energy ◽

Energy Resource ◽

Resource Assessment ◽

Wave Climate ◽

Maximum Efficiency ◽

Physical Processes ◽

Wide Range ◽

Technical Specifications ◽

Reduced Costs

Over recent decades, the exploitation of wave energy resources has sparked a wide range of technologies dedicated to capturing the available power with maximum efficiency, reduced costs, and minimum environmental impacts. These different objectives are fundamental to guarantee the development of the marine wave energy sector, but require also refined assessments of available resource and expected generated power to optimize devices designs and locations. We reviewed here the most recent resource characterizations starting from (i) investigations based on available observations (in situ and satellite) and hindcast databases to (ii) refined numerical simulations specifically dedicated to wave power assessments. After an overall description of formulations and energy metrics adopted in resource characterization, we exhibited the benefits, limitations and potential of the different methods discussing results obtained in the most energetic locations around the world. Particular attention was dedicated to uncertainties in the assessment of the available and expected powers associated with wave–climate temporal variability, physical processes (such as wave–current interactions), model implementation and energy extraction. This up-to-date review provided original methods complementing the standard technical specifications liable to feed advanced wave energy resource assessment.

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An Assessment of NASA’s GMAO MERRA-2 Reanalysis Surface Winds

Journal of Climate ◽

10.1175/jcli-d-19-0199.1 ◽

2019 ◽

Vol 32 (23) ◽

pp. 8261-8281 ◽

Cited By ~ 4

Author(s):

D. Carvalho

Keyword(s):

Surface Wind ◽

The Other ◽

Surface Winds ◽

Wind Fields ◽

Near Surface ◽

Wind Speeds ◽

Wide Range ◽

Ocean Surface Winds ◽

The Tropics ◽

Global Surface

Abstract The quality of MERRA-2 surface wind fields was assessed by comparing them with 10 years of measurements from a wide range of surface wind observing platforms. This assessment includes a comparison of MERRA-2 global surface wind fields with the ones from its predecessor, MERRA, to assess if GMAO’s latest reanalyses improved the representation of the global surface winds. At the same time, surface wind fields from other modern reanalyses—NCEP-CFSR, ERA-Interim, and JRA-55—were also included in the comparisons to evaluate MERRA-2 global surface wind fields in the context of its contemporary reanalyses. Results show that MERRA-2, CFSR, ERA-Interim, and JRA-55 show similar error metrics while MERRA consistently shows the highest errors. Thus, when compared with wind observations, the accuracy of MERRA-2 surface wind fields represents a clear improvement over its predecessor MERRA and is in line with the other contemporary reanalyses in terms of the representation of global near-surface wind fields. All reanalyses showed a tendency to underestimate ocean surface winds (particularly in the tropics) and, oppositely, to overestimate inland surface winds (except JRA-55, which showed a global tendency to underestimate the wind speeds); to represent the wind direction rotated clockwise in the Northern Hemisphere (positive bias) and anticlockwise in the Southern Hemisphere (negative bias), with the exception of JRA-55; and to show higher errors near the poles and in the ITCZ, particularly in the equatorial western coasts of Central America and Africa. However, MERRA-2 showed substantially lower wind errors in the poles when compared with the other reanalyses.

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