High-resolution Numerical Model Research Articles

Numerical modeling for particulate flow through realistic microporous structure of microfiltration membrane: Direct numerical simulation coordinated with focused ion beam scanning electron microscopy

In this study, the focused ion beam scanning electron microscope (FIB-SEM) technique is utilized to obtain a realistic microstructure geometry of mullite and α-alumina membranes, which are commercially available microfiltration (MF) membranes, for implementation in a high-resolution numerical simulation model based on coupled direct numerical simulation (DNS) and the discrete element method (DEM). The flow and particle permeation through the membrane pores are evaluated for different particle sizes. The developed simulation model is a powerful tool for enhancing our understanding of the MF process because it introduces the realistic microporous structure of an actual MF membrane rather than the simplified membrane model structures such as straight cylindrical pores and particle packing structures that have been used in previous numerical studies. The application of the developed model is discussed for the prediction of the rejection curve, which shows the importance of considering a realistic microporous structure for the accurate prediction of the MF process. The results showed different rejection curves for the mullite and α-alumina membranes, which mainly contributed to the difference in the local pore size distributions of the two membranes. Furthermore, detailed particle permeation through the membrane is evaluated, which is not feasible in experimental analyses for realistic MF membranes. • Realistic microfiltration geometry was obtained using FIB-SEM technique. • High resolution DNS-DEM was developed for detailed particle permeation analysis. • Different rejection curve for mullite and α-alumina membranes was obtained. • Membrane microstructure affected the particle permeation behavior and rejection. • Image analysis of microstructure supported the DNS-DEM results.

The Response of a Baroclinic Anticyclonic Eddy to Relative Wind Stress Forcing

Abstract Including the ocean surface current in the calculation of wind stress is known to damp mesoscale eddies through a negative wind power input and have potential ramifications for eddy longevity. Here, we study the spindown of a baroclinic anticyclonic eddy subject to absolute (no ocean surface current) and relative (including ocean surface current) wind stress forcing by employing an idealized high-resolution numerical model. Results from this study demonstrate that relative wind stress dissipates surface mean kinetic energy (MKE) and also generates additional vertical motions throughout the whole water column via Ekman pumping. Wind stress curl–induced Ekman pumping generates additional baroclinic conversion (mean potential to mean kinetic energy) that is found to offset the damping of surface MKE by increasing deep MKE. A scaling analysis of relative wind stress–induced baroclinic conversion and relative wind stress damping confirms these numerical findings, showing that additional energy conversion counteracts relative wind stress damping. What is more, wind stress curl–induced Ekman pumping is found to modify surface potential vorticity gradients that lead to an earlier destabilization of the eddy. Therefore, the onset of eddy instabilities and eventual eddy decay takes place on a shorter time scale in the simulation with relative wind stress.

The Use of Sentinel-3 Altimetry Data to Assess Wind Speed from the Weather Research and Forecasting (WRF) Model: Application over the Gulf of Cadiz

This work presents the quality performance and the capabilities of altimetry derived wind speed (WS) retrievals from the altimeters on-board Copernicus satellites Sentinel-3A/B (S3A/B) for the spatial assessment of WS outputs from the weather research and forecasting (WRF) model over the complex area of the Gulf of Cádiz (GoC), Spain. In order to assess the applicability of the altimetry data for this purpose, comparisons between three different WS data sources over the area were evaluated: in situ measurements, S3A/B 20 Hz altimetry data, and WRF model outputs. Sentinel-3A/B WS data were compared against two different moored buoys to guarantee the quality of the data over the GoC, resulting in satisfying scores (average results: RMSE = 1.21 m/s, r = 0.93 for S3A and RMSE = 1.36 m/s, r = 0.89 for S3B). Second, the WRF model was validated with in situ data from four different stations to ensure the correct performance over the area. Finally, the spatial variability of the WS derived from the WRF model was compared with the along-track altimetry-derived WS. The analysis was carried out under different wind synoptic conditions. Qualitative and quantitative results (average RMSE < 1.0 m/s) show agreement between both data sets under low/high wind regimes, proving that the spatial coverage of satellite altimetry enables the spatial assessment of high-resolution numerical weather prediction models in complex water-covered zones.

Effect of hydrodynamic conditions on seagrass ecosystems during Cyclone Lehar in the South Andaman Islands, India

The physical disturbances of hydrodynamic conditions in shaping the seagrass meadows were studied in the vicinity of seagrass meadows over the south of Port Blair in the Andaman and Nicobar Islands (ANI) during the lifetime of Cyclone Lehar using spatial and temporal metrological - oceanic parameters and in-situ measurements. A cyclonic depression formed on 23 November 2013 over the west coast of the Malay Peninsula and then transformed into a severe cyclone named Lehar on 25th November 2013. It made its first landfall south of Port Blair in the ANI and caused extensive damage to life and properties. The present study made an attempt to investigate the hydrodynamic condition and their impact on the seagrass meadows during the lifetime of the cyclone. The results revealed that the floristic composition of seagrass species such as Thalassia hemperichii, Halodule pinnifolia and Halodule uninervis was badly damaged due to the effect of the high gradient of velocities in the vertical direction, turbulence, high energetic waves, and storm surge. Approximately 32.4% of the seagrass meadows were uprooted in Haddo Bay and 68% in Sesostris Bay of the South Andaman Islands. A year after the cyclone passage (December 2014), 13% (∼0.70 ha) of the seagrass meadow in Haddo Bay and 44.5% (∼0.30 ha) of the seagrass in Sesostris Bay had recovered. This study emphasises that the morphometric features of the most dominant species, T. hemperichii, were regulated by the physical hydrodynamic mechanisms and led to substantial destruction in the study sites. This study is very useful to understand the impact of hydrodynamic conditions on seagrass ecosystems during a cyclone and brings attention to the real-time monitoring of seagrass ecosystems. Monitoring of the seagrass ecosystem can be further improved by predicting the behavioural dynamics of the marine ecosystem under the various scenarios of extreme weather conditions using high-resolution numerical models. It also helps to determine the appropriate management policy during extreme natural events.

Orographic Effects on Landfalling Lake-Effect Systems

Abstract Landfalling lake- and sea-effect (hereafter lake-effect) systems often interact with orography, altering the distribution and intensity of precipitation, which frequently falls as snow. In this study, we examine the influence of orography on two modes of lake-effect systems: long-lake-axis-parallel (LLAP) bands and broad-coverage, open-cell convection. Specifically, we generate idealized large-eddy simulations of a LLAP band produced by an oval lake and broad-coverage, open-cell convection produced by an open lake (i.e., without flanking shorelines) with a downstream coastal plain, 500-m peak, and 2000-m ridge. Without terrain, the LLAP band intersects a coastal baroclinic zone over which ascent and hydrometeor mass growth are maximized, with transport and fallout producing an inland precipitation maximum. The 500-m peak does not significantly alter this structure, but slightly enhances precipitation due to orographic ascent, increased hydrometeor mass growth, and reduced subcloud sublimation. In contrast, a 2000-m ridge disrupts the band by blocking the continental flow that flanks the coastlines. This, combined with differential surface heating between the lake and land, leads to low-level flow reversal, shifting the coastal baroclinic zone and precipitation maximum offshore. In contrast, the flow moves over the terrain in open lake, open-cell simulations. Over the 500-m peak, this yields an increase in the frequency of weaker (<1 m s−1) updrafts and weak precipitation enhancement, although stronger updrafts decline. Over the 2000-m ridge, however, buoyancy and convective vigor increase dramatically, contributing to an eightfold increase in precipitation. Overall, these results highlight differences in the influence of orography on two common lake-effect modes. Significance Statement Landfalling lake- and sea-effect snowstorms frequently interact with hills, mountains, and upland regions, altering the distribution and intensity of snowfall. Using high-resolution numerical modeling with simplified lake shapes and terrain features, we illustrate how terrain features affect two common types of lake-effect storms and why long-lake-axis-parallel (LLAP) bands can feature high precipitation rates but weaker orographic enhancement than broad-coverage, open-cell convection.

The seafloor heat flux driven by bottom water temperature variation in the Yellow and Bohai Seas

The Yellow and Bohai Seas (YBS) are shallow marginal seas located at the temperate latitudes of the western North Pacific. The seasonal bottom water temperature variation in the YBS can be greater than 20 °C and therefore generates significant seafloor heat flux, which significantly changes both the sediment temperature profile and heat content of the overlying water column. In this study, we investigated the seafloor heat flux driven by bottom water temperature variation in the YBS using a high-resolution numerical ocean model and a one-dimensional sediment temperature model. The results showed that seafloor heat flux in the area shallower than 50 m was on the order of 10 W/m2. The seafloor heat flux was larger than the lateral heat flux driven by circulation and ranked second only to surface net heat flux accounting for the most important forcing mechanism of ocean heat content variation in the coastal YBS. The accumulated seafloor heat flux during the sediment cooling/warming season could warm/cool the overlying water column by about 1 °C in the coastal YBS where the depth is shallower than 30 m. The depth of sediment affected by seafloor heat flux (seasonal sediment temperature variation >0.1 °C) could be as deep as 10 m. The complex spatial–temporal distribution of seafloor heat flux generated a complex distribution of sediment temperature and sound speed, which may have an important effect on acoustic wave propagation in the YBS.

High-resolution offshore wind resource assessment at turbine hub height with Sentinel-1 synthetic aperture radar (SAR) data and machine learning

Abstract. This paper presents a method for estimating offshore extractable wind power at hub height using Sentinel-1 synthetic aperture radar (SAR) data and machine learning. The method was tested in two areas off the Dutch coast, where measurements from Doppler wind lidars installed at the sea surface were available and could be used as a reference. A first machine learning algorithm improved the accuracy of SAR sea surface wind speeds by using geometrical characteristics of the sensor and metadata. This algorithm was trained with wind data measured by a large network of weather buoys at 4 m above sea level. After correction, the bias in SAR wind speed at 4 m versus buoys was 0.02 m s−1, with a standard deviation of error of 0.74 m s−1. Corrected surface wind speeds were then extrapolated to hub height with a second machine learning algorithm, which used meteorological parameters extracted from a high-resolution numerical model. This algorithm was trained with lidar vertical wind profiles and was able to extrapolate sea surface wind speeds at various altitudes up to 200 m. Once wind speeds at hub height were obtained, the Weibull parameters of their distribution were estimated, taking into account the satellites' irregular temporal sampling. Finally, we assumed the presence of a 10 MW turbine and obtained extractable wind power with a 1 km spatial resolution by multiplying the Weibull distribution point by point by its power curve. Accuracy for extractable wind power versus lidars was ± 3 %. Wind power maps at hub height were presented and compared with the outputs of the numerical model. The maps based on SAR data had a much higher level of detail, especially regarding coastal wind gradient. We concluded that SAR data combined with machine learning can improve the estimation of extractable wind power at hub height and provide useful insights to optimize siting and risk management. The algorithms presented in this study are independent and can also be used in a more general context to correct SAR surface winds, extrapolate surface winds to higher altitudes, and produce instantaneous SAR wind fields at hub height.

Formation mechanism of ground fissure at Beijing Capital International Airport revealed by high-resolution InSAR and numerical modelling

A NE-SW trending ground fissure that extends for 13 km was first discovered at Beijing Capital International Airport (BCIA) in 1985. There are many factors that influenced its formation mechanism, including the activity of the Shunyi-Liangxiang (SL) fault, land subsidence and human engineering activities. Fine-scale surface deformation at BCIA was obtained by interferometric synthetic aperture radar (InSAR), using 27 TerraSAR-X data with a 3 m resolution, to better understand the failure phenomenon and formation mechanism of the ground fissure. Spatially, the SL fault intersects runway 36R obliquely at the airport, and the fissure forms along the fault. A zone of subsidence was observed on the footwall (northwest side) of the SL fault; however, the ground fissure along the SL fault dips towards the southeast. The InSAR subsidence rate profiles show a rate difference of 9–17 mm/yr across the ground fissure, consistent with the deformation characteristics of concrete surface fractures at BCIA. Constrained by the subsidence rate obtained by InSAR, the discrete element method (DEM) was applied to simulate the failure process of runway 36R. The formation mechanism of the ground fissure was revealed: the SE-dipping SL normal fault is the most important geological factor controlling the boundary of subsidence and extension of the ground fissure; the regional subsidence on the footwall of the SL fault is the main triggering factor in the development of the ground fissure; the damage of the concrete surface induced localized uplift; and the decrease in soil strength in the fault zone has led to localized subsidence along the ground fissure.

Submesoscale processes-induced vertical heat transport modulated by oceanic mesoscale eddies

Oceanic submesoscale processes mainly arise from phenomena such as jets, density fronts, and mesoscale eddies. Previous studies suggest that the overall submesoscale processes transport heat vertically upgradient, i.e. from cold to warm. However, it is not clear whether the submesoscale processes-induced vertical heat transport (VHT) in mesoscale eddies remains upgradient. Therefore, the present study focuses on submesoscale-induced VHT modulated by mesoscale eddies. A high-resolution oceanic numerical model product is applied to examine the VHT induced by submesoscale processes associated with a pair of cyclonic and anticyclonic mesoscale eddies in the Kuroshio Extension (KE) region. Eddies at different time steps are collocated in terms of the eddy centers to reconstruct a time series of a new eddy dataset that presents eddy-modulated submesoscale processes. The frequency-wavenumber spectra, Rossby numbers, and strain rates in the pair of eddies reveal the existence of submesoscale motions surrounding mesoscale eddies. The variables are decomposed into monthly mean mesoscale and submesoscale components to calculate submesoscale VHT at low-frequency (LF) and high-frequency (HF). The results indicate that submesoscale VHT is modulated by mesoscale eddies mainly along the eddy boundaries. The LF submesoscale VHT (upward in both cyclonic and anticyclonic eddies) dominates the monthly-averaged submesoscale VHT. The magnitude of the hourly HF submesoscale VHT is larger than the LF component, while its monthly average becomes negligible because it is caused by periodical internal waves. The submesoscale VHT along the eddy edges is related to strong frontogenesis which develops the vertical flux.

An extreme warm event of the Yellow Sea Cold Water Mass in the summer of 2007 and its causes

A high-resolution numerical model based on the Regional Ocean Modeling System (ROMS) was used to simulate the Yellow Sea Cold Water Mass (YSCWM) and revealed an extreme warm event of the YSCWM in the summer of 2007. This event was also captured by in situ observations. In August 2007, the average temperature of the YSCWM was above 1 °C higher than its climatological mean. The unusually-high temperature anomaly of the YSCWM could trace back to the winter 2006–07. Heat budget of the Yellow Sea deep water (YSDW) below 50 m depth, indicated that vertical mixing, rather than advection, in the winter 2006–07 played a crucial role in the generation of the warm event. With the seasonal thermocline disappearing in the winter 2006–07, a weak vertical mixing effect due to weak wind speeds and high heat content in the Yellow Sea upper water (YSUW) above the YSDW, together with strong advection effect, caused the YSDW to become quite warmer than its climatological mean. After that, the seasonal thermocline above the YSDW formed again and the warm YSDW persisted until the summer of 2007, resulting in the extreme warm event of the YSCWM.

A High-Resolution Quantitative Precipitation Estimate over Alaska through Kriging-Based Merging of Rain Gauges and Short-Range Regional Precipitation Forecasts

Abstract A method is presented to generate quantitative precipitation estimates over Alaska using kriging to merge sparse, unevenly distributed rain gauge observations with quantitative precipitation forecasts from a three-member ensemble of high-resolution numerical weather prediction models. The estimated error variance of the analysis is computed by starting with the estimated error variance from kriging and then refining the variance in k-fold cross validation by an empirically derived inflation factor. The method combines dynamical model forecast information with observational data to deliver a best linear unbiased estimate of precipitation, along with an analysis uncertainty estimate, that provides a much-needed precipitation analysis in a region where sparse in situ observations, poor coverage by remote sensing platforms, and complex terrain introduce large uncertainties that need to be quantified. For 6-hourly accumulation estimates produced four times daily from 1 August 2019 to 31 July 2020, three analysis configurations are tested to measure the value added by including model forecast data and how those data are best utilized in the analysis. Several directions for further improvement and validation of the analysis product are provided.

Impacts of urban canyon aspect ratio and roof albedo on heat fluxes and temperatures in four urban centers

The impacts of urban canyon aspect ratio (UCAR defined as the ratio of buildings height to street width) and roof albedo on the heat fluxes and temperatures in four North America urban centers are investigated using a high-resolution numerical model coupled with the Town Energy Balance scheme. Analytical results show that UCAR affects the sensible heat flux over urban centers in a nonlinear way. While the increase of UCAR leads to the reduction of sensible heat fluxes from roads and walls during the daytime, the nonlinearity can lead to the enhancement of sensible heat flux over urban centers under certain condition. The comparisons between benchmark and three scenario model simulation results show that the the increase/decrease of UCAR leads to the increase/decrease of heat fluxes and over urban centers at temperature at 1.5 m in the early morning and nighttime. During the daytime, only very large UCAR can cause the decrease of heat flux and temperature. The increase of UCAR leads to the increase of urban heat island intensity, but there is no obvious correlation between UCAR and the temperature at each grid cell. The comparison between the benchmark simulation and the simulation with a double roof albedo suggests that the increase of roof albedo in the four North America urban areas leads to 0.1 °C-0.2 °C decrease in temperature at 1.5 m.

Drying of mortar at ambient temperature studied using high resolution neutron tomography and numerical modeling

The drying of cement-based materials, naturally occurring in most civil engineering contexts, affects their thermal, hydraulic and mechanical properties and is a leading contributor to the loss of their durability potential. The techniques conventionally employed to study this moisture transfer, such as gravimetry weight loss and point-wise sensor-based measurements, are often destructive and cannot characterize the local driving phenomena in 4D (3D+time), essential given the highly heterogeneous nature of the involved processes. Conversely, full-field techniques, and notably neutron tomography, are non-invasive and ideal for measuring the moisture transport process due to the high attenuation of neutron by hydrogen.In this study, the moisture distribution of a set of cylindrical mortar samples was characterized at different hydric states, as imposed through drying in a thermo-hydrically controlled environment (T=20 °C, RH=35%). The lateral surfaces of the samples were sealed to impose a unidirectional moisture flow. The main phases of the mortar (aggregates, cement paste and voids), visible at the 30μm resolution adopted, were separated, and saturation profiles were deduced and validated against the mortar mixture ratios and weight loss measurements.Besides the intrinsic interest of the spatio-temporal evolution of the local extracted saturation, these hydric gradients are essential to calibrate numerical models, as the commonly used Finite Element model presented here. A minimization algorithm was developed for this purpose to automate, optimize and ensure a more objective numerical–experimental calibration procedure. This has allowed the identification of key hydric parameters such as the convective exchange coefficient and the intrinsic permeability.

Impacts of Climate Change on a Coastal Wetland from Model Simulation Combining Satellite and Gauge Observations: A Case Study of Jiangsu, China

Coastal wetlands are affected by both natural processes and human activities. In the present study, the impacts of natural processes on wetland area variations along the Jiangsu coast in the East China Sea were investigated using a long-term high-resolution numerical model (55 years from 1955 to 2010) validated by satellite and gauge observations. In our 55-year simulation, a 1.33 km2 yr−1 decreasing trend of wetland area as a result of global warming was identified. It was found that the wetland area varied depending on the following temporal scales: intra-seasonal, seasonal, interannual, and decadal. Tides and steric sea level changes are responsible for the intra-seasonal and seasonal wetland variations, respectively. The long-term variations are attributable to the El Niño-Southern Oscillation and Pacific Decadal Oscillation. These basin-scale phenomena cause changes in the local wind patterns along the Jiangsu coast and impact the wetland variation on long-term scales.

Evaluation of future estuarine floods in a sea level rise context

Reliable predictions of future inundation extent within estuaries require a precise evaluation of future extreme sea levels and the application of accurate numerical models that account for the physical processes driving estuarine hydrodynamics. In this study, a methodology that integrates the estimation of local extreme sea levels with high-resolution numerical modeling was applied to assess the future inundation extent in five estuarine systems located on the Portuguese Coast. The main findings obtained were compared with available results from the popular bathtub approach, that disregards the physical processes driving estuarine hydrodynamics and therefore provide imprecise predictions of inundation extent and associated socio-economic impacts. The inundation extent is revealed to be highly dependent on the extreme sea levels and on the estuarine geomorphology, which controls the propagating long-wave. As the long-wave height is highly attenuated within estuaries that have adjacent low-lying areas, restricted inlets, or extensive tidal flats, the results of this study revealed that the extent of inundation is considerably smaller than that obtained by the bathtub approach. The uncertainties associated with mean sea level rise and the estuarine geomorphological evolution constitute the greatest difficulty in assessing the extent of flooding, posing major challenges to the efficient and sustainable management of estuaries.

Modeling the seasonal circulation and connectivity in the North Patagonian Gulfs, Argentina

The coastal region surrounding the North Patagonian Gulfs is considered one of the most productive areas of the Patagonian Shelf ecosystem. Despite its ecological and economical importance the physical processes that contribute to their fertilization are poorly understood. Here we expand previous studies performing a detailed analysis of the Nuevo (NG) and San José (SJG) gulfs seasonal circulation using a high-resolution numerical model. The circulation patterns in NG are characterized by two distinct modes corresponding to the summer and winter seasons. During summer, stratification decouples the upper and deeper layers of the NG, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. Differential tidal mixing in coastal and deep areas induces the subsurface circulation. As stratification weakens during fall and winter, the circulation patterns are replaced by a large wind-driven anticyclonic gyre in the south and a small cyclonic loop in the north. The western sector of SJG is dominated by two counterrotating gyres generated by tidal rectification while the eastern portion shows sluggish circulation patterns. Consequently, a meridional thermal front develops in summer and winter. Particle tracking experiments indicate that the inner portion of the southern Patagonian shelf replenish the surface layers of the NG and SJG. The deeper layer in NG is mostly renovated by local winter convection. Residence times are very different for NG and SJG; while NG is highly retentive, SJG exchanges with the San Matías Gulf are very effective. There is more connectivity between NG and the coastal region of Valdés Peninsula and the Valdés Front in summer than in winter and a weak seasonal connection between NG and SJG. The connectivity of particles released in SJG with coastal regions of San Matías Gulf are quite important in summer but declines substantially in winter.

Instabilities in the Bottom Boundary Layer Reduce Boundary Layer Arrest and Stir Boundary Layer Water Into the Stratified Interior

AbstractAn along‐isobath current in stratified waters leads to a bottom boundary layer. In models with no alongshore variation, cross‐isobath density transport in this bottom boundary layer reduce the velocity in the bottom boundary layer via thermal wind, and thus the bottom friction experienced by the current above the boundary layer—this is bottom‐boundary‐layer arrest. If, however, alongshore variation of the flow is allowed, the bottom boundary layer is baroclinically unstable. We show with high resolution numerical models that these instabilities reduce this arrest and allow bottom friction to decelerate the flow above the bottom boundary layer when the flow is in the Kelvin wave direction (so that the bottom Ekman transport is downwelling). Both the arrest of the bottom boundary layer and the release from this arrest are asymmetric; the friction experienced by flows in the direction of Kelvin‐wave propagation (downwave) is much greater than flows in the opposite direction. The strength of the near bottom currents, and thus the magnitude of bottom friction, is found to be governed by the destruction of potential vorticity near the bottom balanced by the offshore along‐isopycnal transport of this anomalous potential vorticity. A simple model of this process is created and used to quantify the magnitude of this effect and the resulting reduction of arrest of the bottom boundary layer.

Modelling the Oceanic Advection of Pollutants Spilt Along with the Northwest Passage

ABSTRACT The Arctic sea ice is dramatically retreating in concentration, thickness, and duration. The larger and longer-lasting periods of open water will likely lead to increase trans-Arctic ship traffic, which then increases the risk of accidents and of pollutant spills. In this study, we focus on the potential oceanic circulation pathways of pollutants that may be spilt along with the Northwest Passage in the Canadian Arctic. We used a high-resolution numerical model and a Lagrangian particle tracking tool to simulate the advection of pollutants released in and within proximity to the Canadian Arctic Archipelago. We released 5000 virtual particles over 24 main release sites every 10 days during the operating season (June–October) for 12 years (2004–2015). For each simulation, we examined the circulation pathway and computed particles’ spreading area, distances travelled, subsurface spread, and the variability and uncertainty of their distribution during the two-year simulation duration. We analysed these factors with respect to the dominant oceanic circulation of where the particles were initially seeded and the role of atmospheric circulation and were able to identify three main circulation regimes and eight small-scale regimes. This study highlights the role of oceanic advection in the spreading of particles and determines that particles released in the eastern study area exhibited the largest spreading area as the majority propagated into the North Atlantic Ocean rapidly.

Transport Structure of the South Atlantic Ocean Derived From a High-Resolution Numerical Model and Observations

The South Atlantic Ocean plays an important role in the Atlantic meridional overturning circulation (AMOC), connecting it to the Indian and Pacific Oceans as part of the global overturning circulation system. Yet, there are still open questions regarding the relative importance of the warm water versus cold water sources in the upper limb of the AMOC and on the detailed circulation pathways of the North Atlantic Deep Water (NADW) in the lower limb. These questions are addressed using model outputs from a 60-year, eddying global ocean-sea ice simulation that are validated against observations. We find that the Pacific Antarctic Intermediate Water (AAIW) plays a role in setting the temperature and salinity properties of the water in the subtropical South Atlantic, but that the upper limb of the AMOC originates primarily from the warm Indian water through the Agulhas leakage (9.8 Sv of surface water + 3.5 of AAIW) and that only a relatively small contribution of 1.5 Sv colder, fresher AAIW originates from the Pacific Ocean. In the lower limb, the NADW flows southward as a deep western boundary current all the way to 45°S and then turns eastward to flow across the Mid-Atlantic Ridge near 42°S before leaving the Atlantic Ocean, although there is clockwise recirculation in the Brazil, Angola, and Cape Basins.

Hydrokinetic Power Resource Assessment in a Combined Estuarine and River Region

The worldwide river and tidal hydrokinetic power potential is considerable. Harnessing such potential could allow the generation of a significant amount of sustainable electricity for local uses. To the present, most studies on hydrokinetic power have focused on large-scale commercial technology development, large tidal farms planning, and high-intensity resources assessment. Reduced attention was oriented towards investigating possibilities for small to medium-size hydrokinetic plants. However, given the characteristics of rivers and estuaries, in most cases, relevant hydrokinetic power exploitation possibilities exist regardless of the dimensions of the region considered. The planning of small to medium-size hydrokinetic plants for various aspects differs from larger developments. In the present work, a method for assessing the hydrokinetic resource is proposed and applied to the case study of the Douro waterway, which is characterized by moderate flow speeds and limited water depths. A high-resolution shallow-water numerical model is set up using ocean and river inflow boundary conditions. The flow velocities are estimated for the neap-spring period for different freshwater discharges. The spots presenting the highest annual hydrokinetic power average were identified, maximum flow speeds of about 1 m/s were found, and an annual mean power of 0.4 kW/m2 was estimated, indicating that prospects for hydrokinetic energy harvesting exist.