Horizontal Diffusion Coefficient Research Articles

Impact of different approaches to computing rotating stellar models. I. The case of solar metallicity

The physics of stellar rotation plays a crucial role in the evolution of stars, in their final fates, and for the properties of compact remnants. Diverse approaches have been adopted to incorporate the effects of rotation in stellar evolution models. This study seeks to explore the consequences that these various prescriptions for rotation have for the essential outputs of massive star models. We computed a grid of 15 and 60 M$_ odot $ stellar evolution models with the Geneva Stellar Evolution Code that accounted for both hydrodynamical and magnetic instabilities induced by rotation. In the 15 and 60 M$_ odot $ models, the choice of the vertical and horizontal diffusion coefficients for the nonmagnetic models strongly impacts the evolution of the chemical structure, but has a weak impact on the angular momentum transport and the rotational velocity of the core. In the 15 M$_ odot $ models, the choice of the diffusion coefficient impacts the convective core size during the core H-burning phase, regardless of whether the model begins core He-burning as a blue or red supergiant and regardless of the core mass at the end of He-burning. In the 60 M$_ odot $ models, the evolution is dominated by mass loss and is less strongly affected by the choice of the diffusion coefficient. In the magnetic models, magnetic instability dominates the angular momentum transport, and these models are found to be less strongly mixed than their rotating nonmagnetic counterparts. Stellar models with the same initial mass, chemical composition, and rotation may exhibit diverse characteristics depending on the physics applied. By conducting thorough comparisons with observational features, we can ascertain which method(s) produce the most accurate results in different cases.

Analysis of the calibration and validation of hydrodynamic simulations with TELEMAC-3D model of the Patos Lagoon

This work presents the analysis of the calibration and validation of the computational model for two configurations of the Jetties of the Rio Grande Barra for hydrodynamic studies of the Patos Lagoon and the continental shelf of southern Brazil. The model used was TELEMAC-3D, which solves the three-dimensional Navier-Stokes equations, considering the hydrostatic hypothesis, to describe the dynamics of free surface geophysical fluids. We developed two finite element triangular meshes, with about 75.000 elements and seven sigma levels. The numerical domain reaches depths up to 2.427 m, with fluvial and oceanic liquid boundaries. The horizontal turbulence model adopted was Smagorinsky and the vertical model of mixing length. Current velocity data obtained from December 2005 were used for calibration, varying the coefficient of wind friction, horizontal and vertical velocity diffusion, and the salinity tracer. The coefficient of wind influence was the factor that most influenced the model results. The calculated Relative Mean Absolute Error was 0.383 dn. for surface and 0.167 dn. for depth, rated good and excellent, respectively. For validation, we evaluated the model performance on reproducing the salinity behavior, related to the depth of the environment, in January 2017. The calculated Root Mean Square Error was 7.37 dn. and the Relative Mean Absolute Error was 0.228 dn., rating the model performance as good. These variances between metrics is uniformly acceptable for real models. Salt transport is a complex phenomenon and depends on both advective and diffusive transport. Thus, it is possible to conclude that he proposed computational model is able to reproduce a complex phenomenon reliably.

The Experience in Drone Use to Evaluate the Coefficients of Turbulent Diffusion in Small Water Bodies

Small lakes and reservoirs located in the zone of active technogenesis are subject to the risk of various emergency situations. The present-day computer technologies, including hydrodynamic computation modules, can be used to effectively estimate and forecast their consequences with the aim to minimize the adverse effect. These models require evaluating the coefficients of horizontal diffusion. The theoretical analysis of such processes is very difficult because of their specifics. Studies aimed at evaluating these coefficients in Russia and other countries are very few, even under the assumption of their homogeneity and isotropy. The modern measurement technologies involving the use of pilotless vehicles, make such studies much simpler. The article discusses the significance of such studies, the technology of their performance, and the results obtained for the Verkhne-Zyryansk Reservoir. A field experiment with the use of eight floats yielded an average estimate of the coefficient of horizontal turbulent diffusion equal to 0.012 m2/s. The specific features of the obtained results are discussed.

Satellite-derived estimations of the clear-air turbulence in the upper troposphere

The paper presents the results of a study of turbulence zones in the upper troposphere of the Northern Hemisphere based on measurements from European geostationary meteorological satellites in 2007 - 2018. The essence of the method for determining the zones of turbulence is the use of inhomogeneity’s of concentration of water vapor as tracers and the use of correlation-extremal algorithms. Turbulence zones with a horizontal mesoscale turbulent diffusion coefficient Ked ≥ 104 m2 / s can occupy up to 50% of the Northern Hemisphere area visible from satellites. It is shown that in analyzed time interval there is a significant (by 60-120%) increase in areas occupied by relatively weak and moderate turbulence and a slight decrease (by 6-33%) in areas with strong and very strong turbulence. The temporal variability of these zones and their relationship with the characteristics of jet streams and some climatic parameters are analyzed. A statistical model of the temporal variability of the turbulence zone areas has been built. It is shown that the multiple linear regression model with jet stream characteristics as predictors describes up to 68% of variability of zones of strong turbulence. The use of climatic parameters as predictors makes it possible to describe up to 74% of the temporal variability of strong turbulence zones.

A Stochastic Parameter Perturbation Method to Represent Uncertainty in a Microphysics Scheme

AbstractCurrent state-of-the art regional numerical weather forecasts are run at horizontal grid spacings of a few kilometers, which permits medium- to large-scale convective systems to be represented explicitly in the model. With the convection parameterization no longer active, much uncertainty in the formulation of subgrid-scale processes moves to other areas such as the cloud microphysical, turbulence, and land surface parameterizations. The goal of this study is to investigate experiments with stochastically perturbed parameters (SPP) within a microphysics parameterization and the model’s horizontal diffusion coefficients. To estimate the “true” uncertainty due to parameter uncertainty, the magnitudes of the perturbations are chosen as realistically as possible and not with a purposeful intent of maximal forecast impact as some prior work has done. Spatial inhomogeneities and temporal persistence are represented using a random perturbation pattern with spatial and temporal correlations. The impact on the distributions of various hydrometeors, precipitation characteristics, and solar and longwave radiation are quantified for a winter case and a summer case. In terms of upscale error growth, the impact is relatively small and consists primarily of triggering atmospheric instabilities in convectively unstable regions. In addition, small in situ changes with potentially large socioeconomic impacts are observed in the precipitation characteristics such as maximum hail size. Albeit the impact of introducing physically based parameter uncertainties within the bounds of aerosol uncertainties is small, their influence on the solar and longwave radiation balances may still have important implications for global model simulations of future climate scenarios.

Reconstruction of Diffusion Coefficients and Power Exponents from Single Lagrangian Trajectories

Using discrete wavelets, a novel technique is developed to estimate turbulent diffusion coefficients and power exponents from single Lagrangian particle trajectories. The technique differs from the classical approach (Davis (1991)’s technique) because averaging over a statistical ensemble of the mean square displacement (<X2>) is replaced by averaging along a single Lagrangian trajectory X(t) = {X(t), Y(t)}. Metzler et al. (2014) have demonstrated that for an ergodic (for example, normal diffusion) flow, the mean square displacement is <X2> = limT→∞τX2(T,s), where τX2 (T, s) = 1/(T − s) ∫0T−s(X(t+Δt) − X(t))2 dt, T and s are observational and lag times but for weak non-ergodic (such as super-diffusion and sub-diffusion) flows <X2> = limT→∞≪τX2(T,s)≫, where ≪…≫ is some additional averaging. Numerical calculations for surface drifters in the Black Sea and isobaric RAFOS floats deployed at mid depths in the California Current system demonstrated that the reconstructed diffusion coefficients were smaller than those calculated by Davis (1991)’s technique. This difference is caused by the choice of the Lagrangian mean. The technique proposed here is applied to the analysis of Lagrangian motions in the Black Sea (horizontal diffusion coefficients varied from 105 to 106 cm2/s) and for the sub-diffusion of two RAFOS floats in the California Current system where power exponents varied from 0.65 to 0.72. RAFOS float motions were found to be strongly non-ergodic and non-Gaussian.

Horizontal spreading of planetary debris accreted by white dwarfs

ABSTRACT White dwarfs with metal-polluted atmospheres have been studied widely in the context of the accretion of rocky debris from evolved planetary systems. One open question is the geometry of accretion and how material arrives and mixes in the white dwarf surface layers. Using the three-dimensional (3D) radiation hydrodynamics code co5bold, we present the first transport coefficients in degenerate star atmospheres that describe the advection–diffusion of a passive scalar across the surface plane. We couple newly derived horizontal diffusion coefficients with previously published vertical diffusion coefficients to provide theoretical constraints on surface spreading of metals in white dwarfs. Our grid of 3D simulations probes the vast majority of the parameter space of convective white dwarfs, with pure-hydrogen atmospheres in the effective temperature range of 6000–18 000 K and pure-helium atmospheres in the range of 12 000–34 000 K. Our results suggest that warm hydrogen-rich atmospheres (DA; ${\gtrsim} 13\, 000$ K) and helium-rich atmospheres (DB and DBA; ${\gtrsim} 30\, 000$ K) are unable to efficiently spread the accreted metals across their surface, regardless of the time dependence of accretion. This result may be at odds with the current non-detection of surface abundance variations in white dwarfs with debris discs. For cooler hydrogen- and helium-rich atmospheres, we predict a largely homogeneous distribution of metals across the surface within a vertical diffusion time-scale. This is typically less than 0.1 per cent of disc lifetime estimates, a quantity that is revisited in this paper using the overshoot results. These results have relevance for studies of the bulk composition of evolved planetary systems and models of accretion disc physics.

Оценка эффектов усвоения данных наблюдений в модели общей циркуляции океана с помощью ансамблевого фильтра Калмана: численные эксперименты с имитацией наблюдений

The quality of simulation of model fields is analyzed depending on the assimilation of various types of data using the PDAF software product assimilating synthetic data into the NEMO global ocean model. Several numerical experiments are performed to simulate the ocean–sea ice system. Initially, free model was run with different values of the coefficients of horizontal turbulent viscosity and diffusion, but with the same atmospheric forcing. The model output obtained with higher values of these coefficients was used to determine the first guess fields in subsequent experiments with data assimilation, while the model results with lower values of the coefficients were assumed to be true states, and a part of these results was used as synthetic observations. The results are analyzed that are assimilation of various types of observational data using the Kalman filter included through the PDAF to the NEMO model with real bottom topography. It is shown that a degree of improving model fields in the process of data assimilation is highly dependent on the structure of data at the input of the assimilation procedure.

Response of water-exchange capacity to human interventions in Jiaozhou Bay, China

Intensive anthropogenic activities, land reclamation, a cross-bay bridge construction, and the correction of Red Island have significantly changed the topography of Jiaozhou Bay (JZB) in northern China over the last decades. To quantify the effects of these modifications on the water-exchange capacity of the bay, the Finite Volume Community Ocean Model was used to calculate basin, regional and local residence time (RT) in the years 1935, 1966, 1986, 2000, 2008, and 2013, covering the periods of significant land reclamation. The bridge construction and a government plan to restore Red Island were also included in additional modelling scenarios. The regional RT increased significantly between 1935 and 1986, by 77% in the northeast, 40% in the west and 56% in the north-bridge regions, concurrent with the largest land reclamation. The regional RT continued to increase from 1986 to 2000 in the northeast and north-bridge regions but decreased slightly from 2000. These patterns can be explained by the general decreasing trend of the tidal prism from 1935 to 2000, up to 66% in the northeast region. A significant decrease in residual currents from 1935 to 1966 probably also contributed to explain this trend. The bridge construction had only a limited effect on regional RT. The restoration of Red Island would have reduced the regional RT in the northeast region from 83 to 60 days. The simulation of tracer transport, and therefore calculation of local RT, was found to be sensitive to the scheme used to formulate the horizontal diffusion coefficient, which should be taking into account when comparing results from different model configurations.

Quantitative analysis of the factors influencing the dispersion of thermal pollution caused by coastal power plants

In recent years, to meet the needs of economic development, an increasing number of coastal nuclear power plants and thermal power plants (CNATPPs) have used seawater as the source and sink of cooling water. Considering six CNATPPs along the coast of China, based on the model of conservation of mass and energy for an environmental fluid medium, this study quantitatively evaluates the thermal diffusion capacity (TDC) and contribution rate of factors influencing the thermal plume. The results showed that (1) the current velocity, shoreline topography and horizontal diffusion coefficient are linearly correlated with the TDC. The former two variables were the same and the largest and are highly sensitive parameters; (2) the average contribution rates of the current velocity and shoreline topography were the largest at 0.32, and that of the water depth ranged from 0 to 0.28; (3) the shoreline topography close to the outfall affects the TDC of the emitting source of CNATPPs, rather than the geographical location; and (4) this study can provide a comprehensive measurement tool for the planning, site selection and layout of CNATPPs to reduce the impact of their thermal pollution on aquatic organisms in the receiving water. Considering the TDC and thermal sensitivity of marine organisms, it might be assumed that the same heat and the same volume of thermal pollution may have smaller impacts on marine organisms in the East China Sea than in the South China Sea.

Estimation of submarine groundwater discharge and nutrient loading using radium isotopes quartet in Kuwait

The water resources in the arid region like Kuwait are a scarce commodity. With the increasing population, industry and urbanization have lead to the demand of water resources with respect to both in quantity and quality. Therefore, quantification of submarine groundwater discharge is essential for sustainable groundwater management. Moreover, submarine groundwater discharge plays a vital role in delivering nutrients, dissolved carbon, and trace elements to the sea. This study used the naturally occurring radioactive isotopes to identify and estimate the SGD in the coastal strip of Kuwait along the Arabian Gulf. The study gains its significance in determining the loss of brackish groundwater from inland, in the arid region. The groundwater samples were collected from wells along the coast. Seawater samples were collected from Kuwait bay and open sea in transects. Samples were analyzed for major ions, nutrients, and 223Ra, 224Ra, 226Ra, and 228Ra. Box model and offshore gradient model approaches were used to estimate the SGD. The variation of 223Ra, 224Ra, 226Ra, and 228Ra concentrations was studied in different transects, and it was inferred to be influenced by the Kuwait coastal jet in the territorial waters. The water mass residence time calculated for the Kuwait Bay and the open sea ranged from 10 to 58 and 12 to 64 days, respectively. The 223Ra-based horizontal eddy diffusion coefficients for the Kuwait Bay and the south Arabian Gulf were 205.1 and 827.5 m2/s, respectively. The estimation of SGD fluxes in the Kuwait Bay using box model approach based on the spatial distribution of 226Ra and 228Ra were 3.05 × 106 and 5.46 × 106 m3/day, respectively. Similarly, the estimated SGD fluxes for the south Arabian Gulf by offshore gradient model using 226Ra and 228Ra concentrations were 2.92 × 108 and 3.0 × 107 m3/day, respectively. The nutrient fluxes from groundwater to Kuwait Bay and open sea were estimated for PO43−-P, SiO2-Si, and NO3−-N using box model and offshore gradient model approach.

Mesoscale eddies and their dispersive environmental impacts in the Persian Gulf

As the mesoscale eddies in oceans and semi-enclosed seas are significant in horizontal dispersion of pollutants, we investigate the seasonal variations of these eddies in the Persian Gulf (PG) that are usually generated due to seasonal winds and baroclinic instability. The sea surface height (SSH) data from 2010 to 2014 of AVISO are used to identify and track eddies, using the SSH-based method. Then seasonal horizontal dispersion coefficients are estimated for the PG, using the properties of eddies. The results show an annual mean of 78 eddies with a minimum lifetime of one week. Most of the eddies are predominantly cyclonic (59.1%) and have longer lifetimes and higher diffusion coefficients than the anti-cyclonic eddies. The eddy activity is higher in warm seasons, compared to that of cold seasons. As locations with high eddy diffusion coefficients are high-risk areas by using maps of horizontal eddy diffusion coefficients, perilous times and locations of the release of pollutants are specified to be within the longitude from 51.38°E to 55.28°E. The mentioned areas are located from the Strait of Hormuz towards the northeast of the PG, closer to Iranian coast. Moreover, July can be considered as the most dangerous time of pollution release.

Near-field hydrothermal plume dynamics at Brothers Volcano (Kermadec Arc): A short-lived radium isotope study

The naturally occurring radium (Ra) isotope quartet was measured for the first time at an intraoceanic arc hydrothermal setting along the Kermadec Island Arc (SW Pacific). 224Ra (3.7 d half life) and 223Ra (11.4 d half life) are assumed to be tracers solely originating from hydrothermal discharge and have been used to resolve near-field hydrothermal plume dynamics by applying both advection and eddy diffusion-based dispersion models. Assuming dominant advective processes, we identified different horizontal plume age structures at Brothers volcano, with a slow moving plume inside the caldera (0.060 cm/s) and a faster moving plume outside the caldera (0.323 cm/s), indicating a longer plume residence time within the caldera structure. The decreasing trend in Ra activity also allows the calculation of horizontal eddy diffusion coefficients inside and outside of the caldera, with 0.164 m2/s and 3.545 m2/s for 224Ra, respectively. These trends are in accordance with the radial horizontal eddy diffusion model. Our results reveal that net advection might not necessarily play a major role at Brothers, as radial horizontal eddy diffusion reproduces the observed Ra activity distribution to the same degree. Additional model simulations based on a combination of advection and diffusion, favor slow net advection to explain the Ra activity distribution. Within the rising non-buoyant plume, Ra isotopes suggested constant dilution along the first 170 m of the vertical water column and a vertical transport velocity on the order of 0.156 cm/s for altitudes up to 150 m above the vent and around 0.004 cm/s for altitudes above 150 m. When a common source of diffuse and focused venting is assumed and only small amounts of Ra are added to the ascending plume, due to recoil originating from high water to rock ratios, fluids from diffuse vents show a slower migration rate through the subsurface than fluids from focused vents. Our data imply that the fluids from diffuse vents needed approximately five days longer to percolate through the underlying subsurface to reach the water column plume, compared to the fluids from direct vents which emanate through chimney structures. This study demonstrates the potential of short-lived Ra isotopes as tracers of near-field plume dynamics, which will improve our understanding of hydrothermal vents as sources for various trace elements to the global ocean.

Stochastic Lagrangian particle simulation of air pollution dynamic at mountain base and vicinity

In this work, we investigated the effect of horizontal turbulent diffusion coefficients on the pollution accumulation and distribution near the mountain. The diffusion coefficients, corresponding to variation of wind and particle flow, were considered in three different functions, which are constant, linear decay, and exponential decay function, in governing main simplified cases. In the calculation, the transport of pollution was performed using Lagrangian particle models. The results show that the characteristics of pollution distribution were given by how diffusion coefficients are functioned. Specifically, the non-variant of turbulent diffusion coefficient causes the pollution concentration to get highly accumulated close to the mountain boundary. However, the higher magnitude in non-variant diffusion coefficients allows more turbulences and reflect the highest pollution concentration to step away from the mountain base. Nevertheless, for diffusion coefficient in variant version, the pollution distribution characteristic lies between the low and high non-variant limits, caused by the decay of the diffusion coefficients away from the mountain. However, the exponential decay tends to spread the pollution further out than that of the linear decay due to the abrupt drop of the diffusion coefficients.

Parameter sensitivity to concentrations and transport distance of odorous compounds from solid waste facilities

Treatment facilities dealing with municipal solid waste (MSW) are typical pollution sources of urban odor nuisance which threatens public health and environmental safety. Dispersion simulation with specialized models is an important approach for simulating the concentration distribution and estimating the transport distances of the released odorous compounds. Given that the temporal and spatial distribution are affected by many factors with different variations and functions. This study investigated the influence of key parameters on the dispersion of odor compounds on the basis of a numerical atmospheric dispersion model. The sensitivity analysis was applied to quantitatively identify their influence on the concentration distributions and transport distances. The results reveal that source intensity is a sensitive parameter in the whole domain under the specified dispersion conditions, with the sensitivity ratios around 1 to concentrations and of 1.5–2.5 to transport distances. Wind speed possesses higher sensitivity ratios at the upwind direction than the downwind direction. Horizontal diffusion coefficient is sensitive to concentrations only in the area of a typical radius of 500 m from the source. Degradation reaction constant and wet deposition are not sensitive in either concentration distribution or transport distances. The most sensitive parameters present respective importance to the transport distances when different olfactory thresholds of compounds are applied to determine the protection area of odor pollution. This study thus provides important information to the application of dispersion models and the data collection of the most sensitive parameters in odor pollution evaluation and management.

Radium-228 as a tracer of dissolved trace element inputs from the Peruvian continental margin

Abstract Continental margins play a central role in the composition of seawater by being an important source of trace element essentials to the functioning of the ocean ecosystems. Here, we measured long-lived radium isotopes ( 226 Ra, 228 Ra) along a zonal transect at 12°S (US GEOTRACES GP16) in the eastern tropical South Pacific Ocean. We used 228 Ra to quantify the trace element and isotope (TEI) fluxes (DMn, DFe, and DCo) delivered from the Peruvian continental i) shelf and ii) slope. First, elevated 228 Ra activities were measured in surface water over the entire transect (~ 8500 km), evidence that the continental shelf is an important source of sediment-derived TEIs not only to coastal areas, but to central Pacific Ocean waters. Modeled 228 Ra shelf fluxes combined with water column dissolved TEI/ 228 Ra ratios were used to quantify the shelf-ocean input rates (normalized to shelf-area) for DMn (3.3 × 10 3 μmol m − 2 y − 1 ), DFe (1.5 × 10 3 μmol m − 2 y − 1 ), and DCo (1.0 × 10 2 μmol m − 2 y − 1 ). Second, co-occurring plumes of 228 Ra, DFe, and DMn extended over 1800 km from the margin at 1000–2500 m depth, indicative of a continental slope sediment TEI input to the intermediate water column. The 228 Ra gradient allowed us to derive an effective horizontal eddy diffusion coefficient (K h ) of 46 m 2 s − 1 , which in turn permitted the calculation of slope sediment DMn (6.4 μmol m − 2 y − 1 ) and DFe (5.9 × 10 2 μmol m − 2 y − 1 ) fluxes based on their offshore concentration gradients. On the scale of the South Pacific continental margin between 0–20°S, the DMn shelf flux is approximately 2–3 orders of magnitude higher than the slope flux, while the DFe shelf/slope flux is ~ 3:1. Both shelf and slope sediment derived DMn was transported over a significant distance towards the ocean interior, while DFe concentration gradients were steep, consistent with longer water column residence time for DMn as compared to DFe in marine systems. These findings highlight the importance of considering the continental slope-ocean boundary in the oceanic budgets of biologically-important trace elements.

Mixing Inferred from an Ocean Climatology and Surface Fluxes

AbstractThis study provides observation-based estimates, determined by inverse methods, of horizontal and isopycnal eddy diffusion coefficients KH and KI, respectively, the small-scale mixing coefficient D, and the diathermohaline streamfunction Ψ. The inverse solution of Ψ represents the ocean circulation in Absolute Salinity SA and Conservative Temperature Θ coordinates. The authors suggest that the observation-based estimate of Ψ will be useful for comparison with equivalent diagnostics from numerical climate models. The estimates of KH and KI represent horizontal eddy mixing in the mixed layer and isopycnal eddy mixing in the ocean interior, respectively. This study finds that the solution for D and KH are comparable to existing estimates. The solution for KI is one of the first observation-based global and full-depth constrained estimates of isopycnal mixing and indicates that KI is an order of magnitude smaller than KH. This suggests that there is a large vertical variation in the eddy mixing coefficient, which is generally not included in ocean models. With ocean models being very sensitive to the choice of isopycnal mixing, this result suggests that further investigation of the spatial structure of isopycnal eddy mixing from observations is required.

Modulation of wave–current interactions by horizontal mixing and spatial resolution

The mechanics of rip currents are complex, involving interactions between waves, currents, water levels and bathymetry that pose particular challenges for numerical modeling. Horizontal turbulent diffusion in a rip system is difficult to measure using dye dilution or surfzone drifters, as shown by the range of published values for the horizontal diffusion coefficient. Here, we studied the effects of horizontal mixing on wave–current interactions by testing several diffusivity estimates in a fully coupled 3D wave–current model run at two different spatial resolutions. Published results using very low diffusion have found that near the shore the wave rays converge towards the rip channel because of refraction by the currents. We showed that this process is modulated by both horizontal mixing and spatial resolution. We found that, without the feedback of currents on waves, the flow is more sensitive to horizontal mixing, with large alterations, especially offshore, and generally lower velocities. These modifications ascribed to mixing are similar to those induced by the feedback mechanism. When a large mixing coefficient is used: (i) the behavior of the rip system is similar for both coupling modes (i.e., with and without the feedback of currents on waves) and for each resolution; and (ii) the evolution of the flow is more stable over time. Lastly, we show that the horizontal mixing strongly decreases the intensity of the 3D rip velocity, but not its vertical shear, which is mainly dependent on the vertical mixing scheme and on the forcing terms.

Using 224Ra to estimate eddy diffusivity and submarine groundwater discharge in Laizhou Bay, China

The short-lived 224Ra isotope was measured in coastal water samples from Laizhou Bay, China using a radium delayed coincidence counting system. Based on the horizontal distribution of 224Ra and a mixing model, the horizontal eddy diffusion coefficient was estimated to be 253.1 × 106 and 56.5 × 106 m2/d for the surface and middle layers, respectively. The submarine groundwater discharge (SGD) into the bay was estimated on the basis of the 224Ra mass balance model. The estimate of the SGD into the bay is 4.2 × 108 m3/d, approximately six times the annual average flux of the Yellow River.

226Ra and 228Ra tracer study on nutrient transport in east coastal waters of Hainan Island, China

Material fluxes (e.g., nutrients) from coastal waters to offshore areas play an important role in controlling the water quality of the adjacent sea areas not only by increasing nutrient concentration but also by changing nutrient structures. In this study, naturally occurring isotopes, 226Ra and 228Ra, were measured with the alpha spectrometry in the Wenjiao-Wenchang and Wanquan estuaries and adjacent sea areas along the east coast of Hainan Island. The excess 226Ra and 228Ra activities were observed by comparison with the values derived from the conservative mixing of freshwater and seawater end-members in both estuaries. Using a one-dimensional diffusion model, the horizontal eddy diffusion coefficient of 3.16 x 105 cm2/s, for nutrients diffusing from their sources, was derived from 228Ra activities. Consequently, the corresponding nutrient fluxes flowing into the coastal waters were assessed. The results can provide useful information for the study of the mixing and exchange processes of coastal waters as well as dissoluble pollutant transport in this sea area.