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Using fine-scale measurements in the northwestern Sea of Japan, we estimated the vertical mixing parameters in the sea water column extended from the lower part of the thermocline downward to the near-bottom layer above the continental slope. The vertical scales of the turbulent patches were determined together with the turbulent dissipation rate and diapycnal diffusivity based on the conductivity, temperature, and depth data obtained by an Aqualog moored profiler from April through October 2015. The Thorpe-scale method was used to estimate the vertical mixing parameters as well as the vertical heat and salt fluxes. The enhanced vertical mixing, as well as enhanced downward heat flux and upward salt flux, occurred below the mixed layer despite strong density stratification. By comparing the turbulent dissipation rate and diapycnal diffusivity estimates derived via the Thorpe-scale method and the estimates of the same parameters obtained earlier by applying the finescale parameterization method to the same dataset in addition to the collocates of the current velocity measurements, the comparative accuracy evaluation of both methods was carried out. Finally, by compiling the vertical mixing data obtained by the Thorpe-scale method and the finescale parameterization approach, the generalized depth profile for the diapycnal diffusivity is presented for the depth range from 70 to 350 m. [ABSTRACT FROM AUTHOR]

On 8 April 2024, a rare total solar eclipse (TSE) passed over western New York State (NYS), the first since 1925 and the last one until 2079. The NYS Mesonet (NYSM) consisting of 126 weather stations with 55 on the totality path provides unprecedented surface, profile, and flux data and camera images during the TSE. Here we use NYSM observations to characterize the TSE's impacts at the surface, in the planetary boundary layer (PBL), and on surface fluxes and CO2 concentrations. The TSE‐induced peak surface cooling occurs 17 min after the totality and is 2.8°C on average with a maximum of 6.8°C. It results in night‐like surface inversion, calm winds, and reduced vertical motion and mixing, leading to the shallowing of the PBL and its moistening. Surface sensible, latent and ground heat fluxes all decrease whereas near‐surface CO2 concentration rises as photosynthesis slows down. Plain Language Summary: On 8 April 2024, a rare total solar eclipse (TSE) passed over western New York State (NYS), the first one since 1925 and the last one until 2079. The entire NYS witnessed at least 88% obscuration at the peak of the eclipse. It provides an excellent opportunity to study the impacts of the TSE. The NYS Mesonet (NYSM), an advanced statewide weather network, has 55 stations on the totality path and provides unprecedented measurements of surface meteorological variables, atmospheric vertical profiles, the heat exchange between the atmosphere and the surface and carbon dioxide (CO2) concentration. It enables one to study the TSE in greater details on a regional scale for the first time. This study found that the moon shadow cools the surface by as much as 6.8°C and creates a surface inversion layer. The cooling calms down winds and vertical mixing, leading to less escape of the water vapor and moistening of the air. It also reduces the heat exchange between the surface and the air. Without sunlight, the photosynthesis shuts down, causing a robust rise in near‐surface CO2 concentration. One‐minute camera images provide a fantastic view of the darkening of the sky during the TSE. Key Points: The New York State Mesonet provided unprecedented surface, profile, flux and image data during the 8 April 2024 total solar eclipse across New York StateThe eclipse resulted in significant cooling and moistening near the surface and in the boundary layer, leading to a surface inversion layerIt also weakened surface winds, turbulent mixing, heat fluxes, but caused a robust rise in near‐surface CO2 concentrations [ABSTRACT FROM AUTHOR]

Freshwater inputs originating from terrestrial streams and gullies that discharge into quiescent, semi-enclosed coastal regions (such as estuaries, tidal inlets or lagoons), typically provide point sources of nutrients (e.g. nitrates, phosphates) and/or contaminants (e.g. pesticides, pathogens) that may have a deleterious impact on water quality. Many of these sheltered coastal regions also increasingly support aquaculture operations (e.g. finfish, shellfish, or seaweed farms), which can therefore be directly impacted by nutrient and contaminant inputs. Dynamically, these terrestrial freshwater inflows behave as surface buoyant jets or plumes within the coastal saline or brackish receiving waters, due to the salinity-induced density gradients. As such, the presence of infrastructure associated with aquaculture operations in sheltered coastal waters can provide obstruction to the propagation characteristics and residence times for these surface freshwater flows. Consequently, an improved physical understanding of the flow-structure interaction is clearly crucial to assessing the potential contamination risk of aquaculture products. The aim of the current study is therefore to explore, through scaled laboratory experiments within a channel-basin facility, the impact of physical obstruction induced by a vertical grid structure on the flow evolution of a 2D – 3D expanding, surface buoyant jet. Two grid obstructions with different solidity ratios are tested, along with surface gravity currents of different density excesses and freshwater inflows to infer the influence of different parametric conditions on the propagation, blockage and mixing characteristics of the surface current in the vicinity of the grid obstruction. Measurements of the velocity structure and thickness of the expanding surface plume are obtained by ultrasonic velocity profilers, while the density excess in the evolving plume is measured by micro-conductivity probes. Dye visualization results also show that, in the presence of the grid obstruction, the generation of shear-induced billows at the lower interface of the expanding surface current is largely blocked and a local deepening of the fresh-salt water interface in the immediate vicinity of the grid obstruction is observed. In this sense, the obstruction imposed by aquaculture infrastructure in coastal domains can have a considerable influence of the local turbulent mixing and vertical transfer of substances (e.g. nutrients and contaminants), but is likely to have relatively minimal impact in the final dispersion of the surface plume. [ABSTRACT FROM AUTHOR]

This study utilizes the wealth of observational data collected during the recent Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) drift experiment to constrain and evaluate close to two‐hundred daily Large‐Eddy Simulations (LES) of Arctic boundary layers and clouds at high resolutions. A standardized approach is adopted to tightly integrate field measurements into the experimental configuration. Covering the full drift represents a step forward from single‐case LES studies, and allows for a robust assessment of model performance against independent data under a range of atmospheric conditions. A homogeneously forced domain is simulated in a Lagrangian frame of reference, initialized with radiosonde and value‐added cloud profiles. Prescribed boundary conditions include various measured surface characteristics. Time‐constant composite forcing is applied, primarily consisting of subsidence rates sampled from reanalysis data. The simulations run for 3 hours, allowing turbulence and clouds to spin up while still facilitating direct comparison to MOSAiC data. Key aspects such as the vertical thermodynamic structure, cloud properties, and surface energy fluxes are well reproduced and maintained. The model captures the bimodal distribution of atmospheric states that is typical of Arctic climate. Selected days are investigated more closely to assess the model's skill in maintaining the observed boundary layer structure. The sensitivity to various aspects of the experimental configuration and model physics is tested. The model input and output are available to the scientific community, supplementing the MOSAiC data archive. The close agreement with observed meteorology justifies the use of LES for gaining further insight into Arctic boundary layer processes and their role in Arctic climate change. Plain Language Summary: The Arctic is one of the regions most affected by global climate change, warming up to four times as fast as the rest of the globe. It is also a particularly inaccessible region to conduct measurements. Fortunately, between 2019 and 2020 the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign collected an unprecedented amount of data in the Arctic. In this study, numerous of these measurements are incorporated into high‐resolution computer simulations of the lowest part of the Arctic atmosphere. This simulation data complements and contextualizes the observations and enables insight into complex physical processes, for example, cloud formation, cloud ice production, or turbulent mixing. The Arctic is an extreme place, and models often struggle to represent the atmosphere accurately. Therefore, the main achievement of this study is to successfully simulate 190 atmospheric situations as measured during the campaign. The generated data set performs well when compared to independent observations. Single cases deliver information about individual atmospheric conditions, and the collection gives insight into how key climate variables behaved throughout the MOSAiC year. Key Points: A standardized LES setup based on campaign data is developed with an aim to supplement the local measurements during the Multidisciplinary drifting Observatory for the Study of Arctic Climate driftIndependent drift‐long statistics on key aspects of the surface energy budget, thermodynamic structure, and clouds are reproducedSensitivity tests indicate microphysics, ice‐radiation interaction and surface representation are critical for successful daily simulations [ABSTRACT FROM AUTHOR]

The Tokara Strait is a mixing hotspot due to the coexistence of complex bottom topographies and strong composite flow including both the Kuroshio and tidal currents. Although previous studies have revealed several mechanisms from the view of Kuroshio‐Topography interaction, the role of tides in driving mixing is still not clear. Given that it is located at the M2 critical latitude (29°N), parametric subharmonic instability (PSI) is expected as an important process responsible for the mixing. Here, we study PSI of the M2 internal tides in the Tokara Strait based on a high‐resolution model. Our model results indicate that intense near‐inertial waves are generated via PSI, which exhibit a horizontally layered structure and have much larger vertical wavenumbers than the M2 internal tides. Energy is transferred from the M2 internal tides to the near‐inertial waves around the generation sites, and most of the near‐inertial energy is dissipated locally. The dissipation rates of near‐inertial waves are comparable to those of the M2 internal tides. Simulations with and without the Kuroshio Current revealed the suppression of PSI along the Kuroshio path, which could be attributed to two mechanisms. First, the Kuroshio Current modifies the local minimum internal wave frequency by its horizontal and vertical shear, making the condition for PSI not satisfied. Second, the Kuroshio Current advects the near‐inertial waves downstream in the Okinawa Trough, which inhibits the accumulation of near‐inertial energy there. However, in most of the areas outside the Kuroshio path, PSI majorly contributes to mixing in and around the Tokara Strait. Plain Language Summary: The Tokara Strait is the passage of the Kuroshio Current from the East China Sea to the Western Pacific, which is characterized by complex bottom topographies and strong turbulent mixing. By conducting numerical simulations, we find that intense nonlinear wave‐wave interaction occurs in the Tokara Strait, since it is exactly located at the M2 critical latitude where the local inertial frequency is equal to half of the M2 tidal frequency. Such nonlinear wave‐wave interaction gives rise to high‐wavenumber internal waves at inertial frequency, causing elevated energy dissipation. By performing the sensitivity experiment without the Kuroshio Current, we further reveal that the Kuroshio Current suppresses the above nonlinear energy transfer process specifically along its path because it changes the lower limit of internal wave frequency via sheared currents and advects the near‐inertial energy downstream in a shorter time scale. Our results reveal an important process responsible for mixing in and around the Tokara Strait and help us understand the energy cascade of internal tides in the ocean. Key Points: Parametric subharmonic instability (PSI) of the M2 internal tides in the Tokara Strait generates small‐scale near‐inertial wavesInternal tidal energy is transferred to near‐inertial waves around generation sites via PSI and most of it is dissipated locallyThe Kuroshio Current weakens PSI by changing the minimum wave frequency, causing an advection effect [ABSTRACT FROM AUTHOR]

We study two sea surface temperature (SST) warming events and upper ocean stratification changes in the northern South China Sea in 2022 using data from an EM‐APEX float and satellite observations. The diurnal warm layers (DWLs) and the increasing buoyancy frequency N2 above the top of the thermocline can restrict the penetration depth of nighttime convection and wind‐driven mixing, which prevents cooler water from mixing upward, allowing solar heating to increase the SST by more than 1°C in a few days. The stratification budget approach is used to reproduce observations below 40 m despite some uncertainties in estimating variables such as horizontal gradient. After the first SST warming event, the stratification changes in the subsurface layers constituted by an increase in N2 above 70 m and a decrease below this depth can be attributed to the combined effects of turbulent diffusion and vertical advection rather than to horizontal advection or penetrative solar radiation. This ocean interior mixing is likely caused by the shear of near‐inertial waves at ∼50 m, when the nighttime convection could not penetrate through the DWL's base around 20 m. The stratification budget approach fails to simulate the changes above 40 m after the second SST warming event partly due to the presence of a near‐surface freshwater layer. Our observations offer insights into the effect of inertial wave‐induced mixing in the ocean interior when near‐surface stratified layers are present, which can lead to changes in upper ocean stratification and SST. Plain Language Summary: The formation of near‐surface stratified layers, such as a diurnal warm layer (DWL), can restrict the penetration depth of the turbulent mixing caused by atmospheric forcing and prevent cooler subsurface water from mixing upward; as a result, the sea surface temperature (SST) remains warm. Strong shear from oceanic dynamics, such as inertial waves, can induce mixing in the ocean interior. Our observations show that when the nighttime convection cannot penetrate through the base of a DWL under low wind conditions, inertial wave‐induced mixing may influence the stratification near the top of the thermocline. The resulting restratification within the ocean surface boundary layer can then counteract the destratification forces from wind and nighttime convection. Solar heating can thus rapidly increase the SST by more than 1°C within a few days. Studying the effects of the DWL and inertial wave shear could improve climate and weather model forecasts in the future. Key Points: The presence of diurnal warm layers and stratification changes near the top of the thermocline can suppress nighttime convectionStrong shear of inertial waves enhances the vertical turbulent diffusion in the thermoclineThe increase of stratification in the ocean surface boundary layer warms the sea surface temperature by 1° within 5 days [ABSTRACT FROM AUTHOR]

Coral reef roughness produces turbulent boundary layers and bottom stresses that are important for reef metabolism monitoring and reef circulation modeling. However, there is some uncertainty as to whether field methods for estimating bottom stress are applicable in shallow canopy environments as found on coral reefs. Friction velocities (u∗ ${u}_{\ast }$) and drag coefficients (CD ${C}_{D}$) were estimated using five independent methods and compared across 14 sites on a shallow forereef (2–9 m deep) in Palau with large and spatially variable coral roughness elements (0.4–1 m tall). The methods included the following: (a) momentum balance closure, (b) log‐fitting to velocity profiles, (c) Reynolds stresses, (d) turbulence dissipation, and (e) roughness characterization from digital elevation models (DEMs). Both velocity profiles and point turbulence measurements indicated good agreement with log‐layer scaling, suggesting that measurements were taken within a well‐developed turbulent boundary layer and that canopy effects were minimal. However, u∗ ${u}_{\ast }$ estimated from the DEMs, momentum budget and log‐profile fitting were consistently larger than those estimated from direct turbulence measurements. Near‐bed Reynolds stresses only contributed about 1/3 of the total bottom stress and drag produced by the reef. Thus, effects of topographical heterogeneity that induce mean velocity fluxes, dispersive stresses, and form drag are expected to be important. This decoupling of total drag and local turbulence implies that both rates of mass transfer as well as values of fluxes inferred from concentration measurements may be proportional to smaller, turbulence‐derived values of u∗ ${u}_{\ast }$ rather than to those based on larger‐scale flow structure. Plain Language Summary: Bottom stress plays a primary role in the dynamics of coral reef flows and is therefore critical to parameterize correctly in reef circulation models. These models are often used to examine transport of the larvae of reef biota, for example. Bottom stress is also important for coral metabolism, as turbulent mixing enhances nutrient uptake and potentially alleviates coral bleaching severity. However, it is difficult to measure directly in the field and there is some uncertainty as to whether commonly used methods are applicable in shallow, canopy environments as might be found on coral reefs. We estimated bottom stress on a shallow forereef with high coral cover in Palau using five common methods at 14 different locations. The methods included point‐measurements of near‐bed turbulence, velocity profile fitting to expected boundary layer scaling, large‐scale momentum budgets, and roughness characterization from digital elevation models of the reef. Estimates of bottom stress derived from "local" measurements of turbulence were consistently smaller than those from more "spatially distributed" methods such as momentum balance closure. Care should be taken in choosing the appropriate measurement of bottom stress to use in circulation modeling or reef health studies. Key Points: Bottom stress was estimated using 5 methods and compared across 14 sites on a shallow forereef in Palau with large coral roughness elementsMeasurements indicate that Reynolds stresses contributed only about 1/3 of the total bottom stress and drag produced by the reefCirculation models should use drag coefficients from momentum budgets; reef metabolism studies should use direct turbulence measurements [ABSTRACT FROM AUTHOR]

In this paper, the importance of model horizontal resolution in mixing and dispersion is investigated by comparing two data‐assimilative high‐resolution simulations (4 and 1 km), one of which is submesoscale‐permitting. By employing both Eulerian and Lagrangian metrics, upper‐ocean differences between the mesoscale‐resolving and submesoscale‐permitting simulations are examined in the northeastern Gulf of Mexico, a region of high mesoscale and submesoscale activity. Mixing in both simulations is explored by conducting Lagrangian experiments to track the generation of Lagrangian coherent structures (LCSs) and their associated transport barriers. Finite‐time Lyapunov exponent (FTLE) fields show higher separation rates of fluid particles in the submesoscale‐permitting case, which indicate more vigorous mixing with differences being more pronounced in the shelf regions (depths ≤ 500 m). The extent of the mixing homogeneity is examined using probability density functions (PDFs) of FTLEs with results suggesting that mixing is heterogeneous in both simulations, but some homogeneity is exhibited in the submesoscale‐permitting case. The FTLE fields also indicate that chaotic advection dominates turbulent mixing in both simulations regardless of the horizontal resolution. In the submesoscale‐permitting experiment, however, smaller scale LCSs emerge as noise‐like filaments that suggest a larger turbulent mixing component than in the mesoscale‐resolving experiment. The impact of resolution is then explored by investigating the spread of oil particles at the location of the Deepwater Horizon oil spill. Plain Language Summary: Small‐scale processes (0.1–50 km) play a critical role in upper‐ocean water transport and mixing. Thus, the added value from resolving these finer scales in numerical models is evaluated by comparing two high‐resolution numerical simulations in the northeastern Gulf of Mexico: one at 1 km horizontal resolution that truly resolves features on the order of 10 km and one at 4 km that only resolves features greater than 50 km. Passive fluid particle experiments are conducted to document the mixing and identify structures that act as barriers to transport between fluids with different properties and determine the fate of dispersants in the ocean. In both simulations, the particles' distribution is spatially heterogeneous, which indicates that mixing is largely controlled by these structures. Results also show that neighboring fluid particles separate faster from one another in the 1 km simulation than in the 4 km simulation, meaning that mixing of fluids is more intense. Lastly, we find that the 1 km simulation is more realistic when applied to oil particle dispersion at the location of the Deepwater Horizon oil spill. Key Points: Resolving submesoscale motions leads to increased Lagrangian transport and mixing as well as the generation of more intricate LCSsChaotic advection dominates turbulent mixing regardless of the horizontal model resolution (either 4 km or 1 km)Submesoscale‐permitting simulation yields reduced error against drifter observations compared to mesoscale‐resolving counterpart [ABSTRACT FROM AUTHOR]

Shear instability is a dominant mechanism for mixing in the stratified oceans and coastal seas. For the first time, we present fine‐scale, direct measurements of shear instabilities in the bottom front generated by the Kuroshio intrusion into the Changjiang (Yangtze) river plume. Shear instabilities were identified using a shipboard echo‐sounder and the resulting turbulent mixing was quantified using a turbulence microstructure profiler. The shear instabilities generate vigorous turbulent mixing with dissipation rate and vertical diffusivity up to O (10−4 m2 s−3) and O (10−1 m2 s−1), respectively, comparable to values associated with shear instabilities observed in river plumes and western boundary currents but several orders of magnitude larger than typical values in the open ocean. The enhanced turbulence may contribute significantly to mixing between the Kuroshio water and coastal water and thereby alter the coastal biogeochemistry cycles. Plain Language Summary: Strong velocity shear across a density interface can produce instability, causing the interface to roll up to form a train of vortices ("billows") that subsequently break down into turbulence. This process is important in the vertical mixing of the oceanic interior and coastal seas. Using acoustic images, we find that this flow instability is induced by the interaction between the Kuroshio current and the Yangtze river plume. We also quantify the resulting turbulent mixing using high‐resolution measurements. The turbulence efficiently mixes the Kuroshio and river plume‐influence water and can change biogeochemistry cycles in the coastal seas. Key Points: Interaction between Kuroshio and river plume‐influenced coastal waters generates shear instabilityShear instability elevates turbulence level by 2–3 orders of magnitude compared to the fluid above and belowThe enhanced turbulence effectively mixes oceanic and coastal waters [ABSTRACT FROM AUTHOR]

The horizontal turbulence parameterization is vital for the intensity and structure forecasting of tropical cyclone (TC) in numerical weather prediction (NWP) models. The default two‐dimensional (2D) standard Smagorinsky model with a single universal constant in Weather and Research Forecasting (WRF) model has been proven to be over dissipative for TC, leading to underprediction of TC intensity. This study provides the first attempt to implement the physically based 2D dynamic Smagorinsky model (DSM) for horizontal turbulence parameterization in WRF model for TC forecasts. The DSM dynamically computes the Smagorinsky coefficient as a function of the resolved flow during the simulation, avoiding the need to prescribe the coefficient a prior. The test results of the DSM in a TC NWP model show that the DSM can significantly improve the wind intensity forecasts compared to the standard Smagorinsky model. Plain Language Summary: The representation of horizontal turbulent mixing in numerical models is important for the tropical cyclone (TC) forecasting. However, existing horizontal turbulence models (i.e., traditional Smagorinsky model with a constant coefficient) in numerical models underpredict the observed maximum surface wind speed. A dynamic Smagorinsky model with dynamically calculated coefficient according to the state of flow avoids the need for case‐by‐case tuning of the coefficient. The simulations of five TC cases using the dynamic Smagorinsky model present the improved wind intensity forecasts compared to the traditional Smagorinsky model. Key Points: Standard Smagorinsky model with default constant coefficient is overly dissipative for tropical cyclone (TC), underpredicting TC intensityWe are the first to attempt to implement the dynamic Smagorinsky model for horizontal turbulence parameterization in TC mesoscale numerical weather prediction modelDynamic Smagorinsky model significantly reduces the bias in TC intensity forecasts [ABSTRACT FROM AUTHOR]

The article delves into the scaling of vertical coherence and energy profiles for wall-attached eddies during sand and dust storms, using high-frequency observation data. It highlights self-similar features for velocity, temperature, and particulate matter at lower heights during these storms. The research aims to improve near-wall models by enhancing understanding of wall-attached eddies in sand and dust storms, focusing on turbulence characteristics and energy profiles. The study also examines the logarithmic behavior of turbulence intensity for different components, considering factors like buoyancy and dust field effects. [Extracted from the article]

The parameterization of fluxes associated with representing unresolved dynamics in turbulent flows, especially in the atmosphere and ocean (which have a vast range of scales), remains a challenging task. This is especially true for Earth system models including complex biogeochemistry and requiring very long simulations. The problem of representing the dependence of the mean flux of a passive tracer in terms of the mean has a very long history; in this study, we take a somewhat different approach. We use a formalism showing that the mean flux will be a functional of the mean gradients, a formalism that can be used to calculate the structure of the functional which is non-local in both space and time. Two-dimensional turbulent simulations are used to explore the weight of nearby (in space or time) gradients. We also use stochastic velocities and iterated maps to show that the results are similar. The functional formalism provides an understanding of when non-locality needs to be considered and when a local eddy diffusivity can be a reasonably good approximation. Furthermore, the formalism provides guidance for the development of data-driven parameterizations. [ABSTRACT FROM AUTHOR]

The response of the Black Sea upper layer and, in particular, of the cold intermediate layer (CIL) to intense wind forcing during cold air intrusions (CAIs) in winter is considered. Using data of the ERA5 atmospheric reanalysis and Copernicus marine reanalysis, joint distributions of surface wind speed and water temperature differences at different depths for the period of 2000–2020 have been obtained. It is shown that the time scale of the sea response to such extreme phenomena is about two days and that the CAI influence extends to rather great depths, down to 60–70 m. Using the coupled mesoscale sea–atmosphere model, the cooling mechanisms in the sea upper layer during the CAI case in January 23–25, 2010, are investigated. Two numerical experiments with suppressed air–sea interaction have been performed. In the first experiment, sensible and latent heat fluxes from the sea surface into the atmosphere were turned off; in the second experiment, wind shear stress at the sea surface was turned off. It is shown that the main cause of the temperature decrease in the upper mixed layer is sea surface cooling due to sensible and latent heat fluxes. And the mechanism of deep cooling that penetrates into the pycnocline is vertical turbulent mixing caused by breaking of wind waves and shear instability. In the first experiment, the temperature decrease was insignificant; it was caused mainly by the entrainment of colder water from the CIL through the lower boundary of the mixed layer. In the second experiment, the temperature decrease was almost the same as in the control run. It is shown that turning off the wind shear stress changes the character of turbulent mixing in the upper quasihomogeneous layer: in order to compensate the considerable decrease in the intensity of turbulent eddies and provide the same vertical heat flux as in the main calculation, the vertical scale of the turbulent eddies increases. [ABSTRACT FROM AUTHOR]

Results of a laboratory experiment performed to test the fundamental mechanism of fine-structure stratification of a stratified fluid during turbulent mixing are described and analyzed [14-15]. A series of experiments were carried out with mixing of aquatic environment with initially linear vertical salinity gradient using oscillating vertical rods, inducing uniform turbulent effect throughout the entire thickness of the water layer. At the same time, in each experiment, regular measurements of electrical conductivity (salinity) profiles were carried out and calculations of the vertical salt flux (mass) were performed. Under the condition of sufficiently strong density (salinity) gradient, the mass flux is described by a decreasing function of the density gradient, and this is the main condition for the formation of the fine structure, according to the proposed mechanism. The experimental results confirmed its realism and feasibility. The dependence of the vertical scale of the fine structure on the parameters of stratification and turbulent influence has also been established. [ABSTRACT FROM AUTHOR]

Riblets can be potentially employed to passively reduce the turbulent friction drag. However, the drag reduction performance of riblets does not currently meet expectations, which could assist in emission reduction and energy conservation in green transportation. This study proposes and validates a topological form of hierarchical nested riblets (HNR) that significantly enhances the drag reduction performance. To explore the drag reduction enhancement mechanism, direct numerical simulations are performed for flow simulation on the riblet surface under different Reynolds numbers. The results show that under the riblet dimensionless spacing of the riblet s + ≈ 21 , the drag reduction performance of the HNR surface improves by about 70% compared to that of the uniform riblet surface, which is inspired by shark skin. From the perspective of turbulence statistics, the HNR surface reduces the turbulent mixing near the wall, weakening the momentum transfer. Furthermore, the transient flow field shows that the secondary riblet in HNR prevents some turbulent flow and streamwise vortices from entering the groove, considerably weakening the dispersive stress induced by the secondary flow. Moreover, owing to the influence of the secondary riblet, small-scale turbulence develops and strengthens into large-scale turbulent motion, which is advantageous to the boundary layer flow and results in drag reduction improvement. [ABSTRACT FROM AUTHOR]

Large eddy simulations (LES) with flamelet and presumed filtered density function closure are used to simulate turbulent premixed and partially premixed hydrogen flames. Different approaches to model differential diffusion are investigated and compared. In particular, two existing models are extended to the LES framework to correct the resolved diffusive flux of the controlling variables due to differential diffusion. A lean premixed turbulent hydrogen flame in a slotted burner configuration is simulated first to compare the capability of the considered models in capturing local mixture fraction redistribution, super-adiabatic temperatures and thermo-diffusive instabilities. Results show that both models describe the formation of cellular burning structures. Next, a partially premixed lifted hydrogen flame in vitiated hot coflow is simulated to gain insight on the relevance of differential diffusion modelling at a higher turbulence level, a different combustion mode and in the presence of a complex stabilisation mechanism. Good predictions of the turbulent mixing and temperature fields are observed. Moreover, results show that the flame lift-off height has an appreciable sensitivity to the differential diffusion model. When differential diffusion is included only in the thermochemistry database, only mild effects on the predicted temperature fields, mixing and flame height are observed. On the contrary, a considerable shift of the flame base is observed when corrections are applied in the LES at the resolved level, depending on what controlling variables are considered. Further analyses reveal how the corrections of diffusive fluxes in the thermochemistry and at the LES level affect differently the flame burning mode, whose details are given throughout the paper. [ABSTRACT FROM AUTHOR]

Deficiencies in upper ocean vertical mixing parameterizations contribute to tropical upper ocean biases in global coupled general circulation models, affecting their simulated ocean heat uptake and ENSO variability. To better understand these deficiencies, we develop a suite of ocean model experiments including both idealized single column models and realistic global simulations. The vertical mixing parameterizations are first evaluated using large eddy simulations as a baseline to assess uncertainties and evaluate their implied turbulent mixing. Global models are then developed following NOAA/GFDL's 0.25° nominal horizontal grid spacing OM4 (uncoupled) configuration of the MOM6 ocean model, with various modifications that target biases in the original model. We test several enhancements to the existing mixing schemes and evaluate them against observational constraints from Tropical Atmosphere Ocean moorings and Argo floats. In particular, we find that we can improve the diurnal variability of mixing in OM4 via modifications to its surface boundary layer mixing scheme, and can improve the net mixing in the upper thermocline by reducing the background vertical viscosity, allowing for more realistic, less diffuse currents. The improved OM4 model better represents the mixing, leading to improved diurnal deep‐cycle variability, a more realistic time‐mean tropical thermocline structure, and a better Pacific Equatorial Undercurrent. Plain Language Summary: Computational models of the oceanic and atmospheric circulation are critical tools for understanding and projecting changes in the Earth's climate. These models have errors that can arise from many sources, including model formulation or the choices in applying the model. One of the more well known sources of error is the representation of turbulent mixing. In this work we consider specially designed small‐scale models that simulate turbulent mixing, and use their results to improve the representation of turbulence and its induced mixing in large‐scale models. In particular, we investigate how the intensity of mixing varies throughout the day, considering the progression from deep mixing during cooler nighttime surface conditions to shallower mixing in the presence of strong solar heating during the day. We find some modifications to the mixing scheme in the ocean climate model that can improve the model solutions when compared to the real ocean. Key Points: Large eddy simulation results are used to evaluate the diurnal cycle of equatorial turbulent mixing in the OM4 ocean modelReducing vertical viscosity in an ocean model increases shear near the Equatorial Undercurrent (EUC) and can result in increased vertical mixingVertical grid spacing of a few meters helps to resolve shear mixing events within and below the EUC in ocean models [ABSTRACT FROM AUTHOR]

The parameterization of subgrid‐scale processes such as boundary layer (PBL) turbulence introduces uncertainty in Earth System Model (ESM) results. This uncertainty can contribute to or exacerbate existing biases in representing key physical processes. This study analyzes the influence of tunable parameters in an experimental version of the Cloud Layers Unified by Binormals (CLUBBX) scheme. CLUBB is the operational PBL parameterization in the Community Atmosphere Model version 6 (CAM6), the atmospheric component of the Community ESM version 2 (CESM2). We perform the Morris one‐at‐a‐time (MOAT) parameter sensitivity analysis using short‐term (3‐day), initialized hindcasts of CAM6‐CLUBBX with 24 unique initial conditions. Several input parameters modulating vertical momentum flux appear most influential for various regionally‐averaged quantities, namely surface stress and shortwave cloud forcing (SWCF). These parameter sensitivities have a spatial dependence, with parameters governing momentum flux most influential in regions of high vertical wind shear (e.g., the mid‐latitude storm tracks). We next evaluate several experimental 20‐year simulations of CAM6‐CLUBBX with targeted parameter perturbations. We find that parameter perturbations produce similar physical mechanisms in both short‐term and long‐term simulations, but these physical responses can be muted due to nonlinear feedbacks manifesting over time scales longer than 3 days, thus causing differences in how output metrics respond in the long‐term simulations. Analysis of turbulent fluxes in CLUBBX indicates that the influential parameters affect vertical fluxes of heat, moisture, and momentum, providing physical pathways for the sensitivities identified in this study. Plain Language Summary: Models struggle with certain aspects of predicting the Earth's current and future climate. To achieve better predictions in the future, it is important to understand which parts of the model need to be improved. This study explores how changing certain model characteristics influences what the model outputs. We find that changing how the model estimates small‐scale motions in the atmosphere improves the model's accuracy. Furthermore, these changes affect both short‐term (several days) and long‐term (several decades) model simulations. The results of this study can help scientists understand the physical behavior of climate models and help inform future improvements to enhance model accuracy. Key Points: A computationally‐efficient sensitivity analysis identifies key parameters and physical mechanisms for global climate propertiesCertain parameter sensitivities in short‐term, initialized hindcasts are consistent with those seen in multidecadal climate simulationsParameters governing the degree of turbulent mixing in the presence of vertical wind shear are influential for surface stress representation [ABSTRACT FROM AUTHOR]

A grid spacer with a vane is an influential segment in reactor fuel channels. A vane produces significant effects on flow mixing and augmentation of heat transfer in subchannnels. The purpose of this work was to do a computational fluid dynamics (CFD) analysis on the effects of a grid spacer vane on the thermal-hydraulic performance of fluid in a 5×5 fuel channel. A square array of a 5×5 fuel channel was used for this analysis with a pitch–to–rod diameter ratio of 1.33 and a blockage ratio of the grid spacer of 0.16. The relative study was made for the thermal-hydraulic performance among a grid spacer with a vane, a grid spacer (without a vane), and without a grid spacer (bare bundle). Analyses were made for fluid pressure of 15.5 MPa, inlet temperature of 583 K, and velocity of 4.74 m/s. The SST k-ω and RNG k-ε turbulence models were used to analyze flow phenomena and thermal performance. CFD results were validated with experiment data and were also compared with correlations proposed by researchers. The results were analyzed by different methods such as data curves, streamlines, and vector and contour plots. The results show that the strong characteristics of swirl flow in subchannels cause a greater mixing rate of turbulent flow, which hence improves heat transfer performance. The swirl ratio was observed maximum close downstream to a grid spacer with a vane. Grid spacer effects on heat transfer were noticed from z/Dh = 0 to 20 in downstream. [ABSTRACT FROM AUTHOR]

Black carbon (BC) in the Tibetan Plateau (TP) region has distinct climate effects that strongly depend on its mixing state. The aging processes of BC in the TP are subject to emissions from various regions, resulting in considerable variability of its mixing state and physicochemical properties. However, the mechanism and magnitude of this effect are not yet clear. In this study, field observations on physicochemical properties of BC-containing particles (PM BC) were conducted in the northeast (Xihai) and southeast (Lulang) regions of the TP to investigate the impacts of transported emissions from lower-altitude areas on BC characteristics in the TP. Large spatial discrepancies were found in the chemical composition of PM BC. Both sites showed higher concentrations of PM BC when they were affected by transported air masses outside the TP but with diverse chemical composition. Source apportionment for organic aerosol (OA) suggested that primary OA in the northeastern TP was attributed to hydrocarbon OA (HOA) from anthropogenic emissions, while it was dominated by biomass burning OA (BBOA) in the southeastern TP. Regarding secondary aerosol, a marked enhancement in nitrate fraction was observed on aged BC coating in Xihai when the air masses were brought by updrafts and easterly winds from lower-altitude areas. With the development of boundary layer, the enhanced turbulent mixing promoted the elevation of anthropogenic pollutants. In contrast to Xihai, the thickly coated BC in Lulang was mainly caused by elevation and transportation of biomass burning plumes from south Asia, showing a large contribution of secondary organic aerosol (SOA). The distinct transported emissions lead to substantial variations of both chemical composition and light absorption ability of BC across the TP. The thicker coating and higher mass absorption cross-section (MAC) of PM BC in air masses elevated from lower-altitude regions reveal the promoted BC aging processes and their impacts on the mixing state and light absorption of BC in the TP. These findings emphasize the vulnerability of plateau regions to influences of elevated emissions, leading to significant changes in BC concentration, mixing states and light absorption across the TP, all of which need to be considered in the evaluation of BC radiative effects for the TP region. [ABSTRACT FROM AUTHOR]

SATAKE MultiMix Corporation developed a new type of pitched paddle impeller for low power consumption turbulent mixing for wastewater treatment and its performance was evaluated by measuring power consumption, mixing time, and particle suspension. The power number of the new impeller was lower than that of the existing pitched paddle, which could be constructed by modifying the correlation equation. For the same power consumption per unit volume, the mixing performance was almost the same as that of other axial flow impellers. The particle suspension performance was also the same as that of other axial flow impellers. [ABSTRACT FROM AUTHOR]

This paper describes the use of a phenomenological model of anisotropic turbulence for studying the development of turbulence in the gravity field on the plane interface between two incompressible fluids (gases) with density ratio of ρ2/ρ1 = 3. The case, when at some time the acceleration changes its sign, is considered. The calculated results are compared to the 3D results of the direct numerical simulation with the CFD code and the corresponding experimental data. [ABSTRACT FROM AUTHOR]

The document delves into the entrainment of ambient fluid into variable-density jets and challenges existing scaling theories. Large-eddy simulations suggest that the entrainment coefficient is not significantly affected by density ratio variations. The collection of research articles covers various aspects of fluid mechanics, including temperature and velocity fluctuations, entrainment in plumes, and turbulent transport in fluid flows, offering valuable insights for researchers interested in these topics. Further experimental and numerical work is recommended to enhance our understanding of variable-density releases and related phenomena. [Extracted from the article]

The study of upper ocean mixing processes, including their dynamics and thermodynamics, has been a primary focus for oceanographers and meteorologists. Wave breaking in deep water is believed to play a significant role in these processes, affecting air–sea interactions and contributing to the energy dissipation of surface waves. This, in turn, enhances the transfer of gas, heat, and mass at the ocean surface. In this paper, we use the FVCOM-SWAVE coupled wave and current model, which is based on the MY-2.5 turbulent closure model, to examine the response of upper ocean turbulent kinetic energy (TKE) and temperature to various wave breaking parametric schemes. We propose a new parametric scheme for wave breaking energy at the sea surface, which is based on the correlation between breaking wave parameter R B and whitecap coverage. The impact of this new wave breaking parametric scheme on the upper ocean under typhoon conditions is analyzed by comparing it with the original parametric scheme that is primarily influenced by wave age. The wave field simulated by SWAVE was verified using Jason-3 satellite altimeter data, confirming the effectiveness of the simulation. The simulation results for upper ocean temperature were also validated using OISST data and Argo float observational data. Our findings indicate that, under the influence of Typhoon Nanmadol, both parametric schemes can transfer the energy of sea surface wave breaking into the seawater. The new wave breaking parameter R B scheme effectively enhances turbulent mixing at the ocean surface, leading to a decrease in sea surface temperature (SST) and an increase in mixed layer depth (MLD). This further improves upon the issue of uneven mixing of seawater at the air–sea interface in the MY-2.5 turbulent closure model. However, it is important to note that wave breaking under typhoon conditions is only one aspect of wave impact on ocean disturbances. Therefore, further research is needed to fully understand the impact of waves on upper ocean mixing, including the consideration of other wave mechanisms. [ABSTRACT FROM AUTHOR]

Validating the theoretical work on Rayleigh–Taylor instability (RTI) through experiments with an exceptionally clean and well-characterized initial condition has been a long-standing challenge. Experiments were conducted to study the three-dimensional RTI of an SF $_6$ –air interface at moderate Atwood numbers. A novel soap film technique was developed to create a discontinuous gaseous interface with controllable initial conditions. Spectrum analysis revealed that the initial perturbation of the soap film interface is half the size of an entire single-mode perturbation. The correlation between the initial interface perturbation and Atwood numbers was determined. Due to the steep and highly curved feature of the initial soap film interface, the early-time evolution of RTI exhibits significant nonlinearity. In the quasi-steady regime, various potential flow models accurately predict the late-time bubble velocities by considering the channel width as the perturbation wavelength. Differently, the late-time spike velocities are described by these potential flow models using the wavelength of the entire single-mode perturbation. These findings indicate that the bubble evolution is influenced primarily by the spatial constraint imposed by walls, while the spike evolution is influenced mainly by the initial curvature of the spike tip. Consequently, a recent potential flow model was adopted to describe the time-varying amplitude growth induced by RTI. Furthermore, the self-similar growth factors for bubbles and spikes were determined from experiments and compared with existing studies, revealing that a large amplitude in the initial soap film interface promotes the spike development. [ABSTRACT FROM AUTHOR]

The background potential energy (BPE) is the only reservoir that double diffusive instabilities can tap their energy from when developing from an unforced motionless state with no available potential energy (APE). Recently, Middleton and Taylor linked the extraction of BPE into APE to the sign of the diapycnal component of the buoyancy flux, but their criterion can predict only diffusive convection instability, not salt finger instability. Here, we show that the problem can be corrected if the sign of the APE dissipation rate is used instead, making it emerge as the most fundamental criterion for double diffusive instabilities. A theory for the APE dissipation rate for a two-component fluid relative to its single-component counterpart is developed as a function of three parameters: the diffusivity ratio, the density ratio, and a spiciness parameter. The theory correctly predicts the occurrence of both salt finger and diffusive convection instabilities in the laminar unforced regime, while more generally predicting that the APE dissipation rate for a two-component fluid can be enhanced, suppressed, or even have the opposite sign compared to that for a single-component fluid, with important implications for the study of ocean mixing. Because negative APE dissipation can also occur in stably stratified single-component and doubly stable two-component stratified fluids, we speculate that only the thermodynamic theory of exergy can explain its physics; however, this necessitates accepting that APE dissipation is a conversion between APE and the internal energy component of BPE, in contrast to prevailing assumptions. [ABSTRACT FROM AUTHOR]

Wind‐generated near‐inertial internal waves (NIWs) are characterized by dominant long‐range equatorward radiation due to the gradient of the planetary vorticity, known as the β‐refraction effect. In this study, we analyze the effects of horizontal model resolution on the long‐range equatorward radiation of NIWs. In a high‐resolution Community Earth System Model (CESM‐HR) with a 0.1° oceanic resolution, about 25% (15%) of NIW energy flux injected downward the surface boundary layer base poleward of 30°N (30°S) radiates into the lower‐latitude region. This ratio decreases to about 15% (8%) in a low‐resolution CESM (CESM‐LR) with a 1° oceanic resolution. The higher long‐range equatorward radiation efficiency in the CESM‐HR than the CESM‐LR is directly attributed to the faster equatorward group velocity of the NIWs of the first three vertical modes, which reflects the better representation of equatorward propagation and beta‐refraction of smaller scale NIWs in the CESM‐HR. The enhancement of equatorward wavenumber induced by the β‐refraction is inhibited in the CESM‐LR, which underrepresent the long‐range equatorward radiation of NIWs. These results underscore the necessity of high‐resolution ocean models in accurately simulating the spatial variabilities of NIWs and their induced turbulent diapycnal mixing in the global ocean. Plain Language Summary: Generated by variable winds like synoptic storms, hurricanes, and typhoons, near‐inertial internal waves (NIWs) are ubiquitous in the upper ocean with frequency close to the inertial frequency. Although NIWs have been extensively studied using numerical modeling, there remains a question on how fine the model horizontal resolution needs to be for their reliable simulations. In this study, we investigate the effect of model horizontal resolution on the long‐range equatorward radiation of NIWs induced by the gradient of planetary vorticity. It is found that the long‐range equatorward radiation of NIWs is significantly weaker in a climate model with a 1° oceanic resolution than in one with a 0.1° oceanic resolution. This finding emphasizes the importance of fine model resolution in accurately simulating the geographical distribution of NIWs and their induced turbulent mixing. Key Points: Long‐range equatorward radiation efficiency of near‐inertial waves (NIWs) is enhanced in high‐resolution models than in low‐resolution modelsEquatorward group velocity of the NIWs of the first three modes is essential in determining the long‐range radiation efficiencyThe beta refraction of NIWs is inhibited in the low‐resolution model [ABSTRACT FROM AUTHOR]

To investigate the stratosphere-troposphere exchange (STE) process induced by the gravity waves (GWs) caused by Typhoon Molave (2020) in the upper troposphere and lower stratosphere, we analyzed the ERA5 reanalysis data provided by the European Centre for Medium-Range Weather Forecasts and the CMA Tropical Cyclone Best Track Dataset. We also adopted the mesoscale forecast model Weather Research and Forecasting model V4.3 for numerical simulation. Most of the previous studies were about typhoon-induced STE and typhoon-induced GWs, while our research focused on the STE caused by typhoon-induced gravity waves. Our analysis shows that most of the time, the gravity wave signal of Typhoon Molave appeared below the tropopause. It was stronger on the east side of the typhoon center (10°-20°N, 110°-120°E) than on the west side, suggesting an eastward tilted structure with height increase. When the GWs in the upper troposphere and lower stratosphere region on the west side of the typhoon center broke up, it produced strong turbulence, resulting in stratosphere-troposphere exchange. At this time, the average potential vorticity vertical flux increased with the average ozone mass mixing ratio. The gravity wave events and STE process simulated by the WRF model were basically consistent with the results of ERA5 reanalysis data, but the time of gravity wave breaking was different. This study indicates that after the breaking of the GWs induced by typhoons, turbulent mixing will also be generated, and thus the STE. [ABSTRACT FROM AUTHOR]

The exchange of momentum, heat and trace gases between atmosphere and surface is mainly controlled by turbulent fluxes. Turbulent mixing is usually parametrized using Monin–Obukhov similarity theory (MOST), which was derived for steady turbulence over homogeneous and flat surfaces, but is nevertheless routinely applied to unsteady turbulence over non-homogeneous surfaces. We study four years of eddy-covariance measurements at a highly heterogeneous alpine valley site in Finse, Norway, to gain insights into the validity of MOST, the turbulent transport mechanisms and the contributing coherent structures. The site exhibits a bimodal topography-following flux footprint, with the two dominant wind sectors characterized by organized and strongly negative momentum flux, but different anisotropy and contributions of submeso-scale motions, leading to a failure of eddy-diffusivity closures and different transfer efficiencies for different scalars. The quadrant analysis of the momentum flux reveals that under stable conditions sweeps transport more momentum than the more frequently occurring ejections, while the opposite is observed under unstable stratification. From quadrant analysis, we derive the ratio of the amount of disorganized to organized structures, that we refer to as organization ratio (OR). We find an invertible relation between transfer efficiency and corresponding organization ratio with an algebraic sigmoid function. The organization ratio further explains the scatter around scaling functions used in MOST and thus indicates that coherent structures modify MOST. Our results highlight the critical role of coherent structures in turbulent transport in heterogeneous tundra environments and may help to find new parametrizations for numerical weather prediction or climate models. [ABSTRACT FROM AUTHOR]

There are few studies on the effects of spatial distribution of hydrodynamics on the micro-mixing in stirred reactors. In this work, a statistical approach is introduced to quantitatively assess the spatial distributions of hydrodynamic parameters, using the turbulent dissipation rate as an example. According to the results, the effects of impeller geometry and angular velocity on the turbulent dissipation rate can be well described in terms of the volume-averaged values and spatial distribution functions. In the present study, a more uniform distribution of the turbulent dissipation rate is achieved by the multiple impellers with an inclinational angle of 15° at the same rotational speed. However, increasing the inclinational angle can decrease the volume-averaged value. The cumulative percentage of area-averaged turbulent dissipation rate is well modeled by an exponential function. The effects of impeller types on the meso- and micro-mixing processes are also investigated. It is found that the micro-mixing process has more significant influences than the meso-mixing process in the bottom region and near the free surface. The effects of impeller types on the micro-mixing performance are further investigated using the Villermaux–Dushman reaction system, both experimentally and numerically. An empirical correlation that considers the spatial distribution of turbulent parameters for the reaction rate of I2 synthesis is proposed. The results show that the predictions of segregation index, which represents micro-mixing performance, are improved by a numerical model coupled with the new reaction rate model. [ABSTRACT FROM AUTHOR]

An understanding of turbulence and mixing is essential to the knowledge of turbulent dissipation, sediment transport, advection of nutrient-rich and organic effluents, and stormwater runoff in prototype water systems, as well as in laboratory channels used for physical modeling of geometrically-scaled full-scale water bodies and for validation of computational models. The acoustic Doppler velocimeter (ADV) system is a robust instrument well suited for such turbulence measurements in open channel flows. The application of acoustic Doppler velocimeter to transient free-surface flows is reviewed in this paper. Based upon field applications and laboratory experiments, the intricacy and inherent difficulties are discussed. The experience and expertise in transient flows highlighted the importance of the signal processing and precise synchronization. Finally, we stress a major benefit of the acoustic Doppler velocimetry for its capability to be used in both field and laboratory, in turn providing some level of confidence in the comparison between full-scale and laboratory data. [ABSTRACT FROM AUTHOR]

Large‐eddy simulations (LES) of the Marine Atmospheric Boundary Layer (MABL) commonly utilize roughness length to parameterize wave effects on the sea surface. However, this method might not adequately capture the intricacies of wind‐wave interactions, especially in swell‐dominated conditions. In this study, we integrated a wave‐induced stress parameterization method into the open‐source LES code, PArallel Large‐eddy simulation Model (PALM), and assessed its performance under low wind conditions with varying wave ages and directions. Our method treats windsea effects as surface friction while employing an exponentially decaying profile to represent swell‐induced stress. We examined the model's sensitivity to wind and wave parameters and calibrated the wave damping rate values across various scenarios, leveraging data from wave‐phase‐resolved simulations and field measurements. The enhanced LES model with the proposed wave parameterization effectively reproduces wave‐influenced wind characteristics such as upward momentum flux, low‐level wind maximum, and negative wind gradients, showing good agreement with previous numerical and observational data. Moreover, our model accounts for wind‐wave misalignment scenarios by calculating each directional and spectral wave stress component individually and integrating them over the wave spectrum. We found that the swell‐induced stress is the dominant force in the wave boundary layer (WBL) with low wind speed, with its magnitude significantly varying with the wave direction relative to the wind. This variation influences the dynamic equilibrium within the WBL, modifying both wind shear and wind veer, and these effects persist up to the top of the boundary layer flow. Plain Language Summary: Ocean waves significantly impact the atmospheric boundary layer flow by modulating the momentum and energy exchange at the wind‐wave interface. Understanding these effects is crucial for an accurate modeling of the atmosphere and ocean systems. We incorporated the wave‐induced stress into the conventional logarithmic wind profile near the sea surface to improve the presentation of the wind‐wave interaction in the numerical simulation. The enhanced model can reproduce complex processes such as the wind‐wave misalignment effects, energy transfer from wave to wind field, and wave‐induced jet flows. Our findings show that the wave stress is the dominant force in the wave boundary layer and its influence on wind varies with their direction relative to the wind. Swells that follow the wind reduce friction and accelerate wind speed, while opposing swells increase drag, potentially causing slower or even reversed near‐surface winds. These wave impacts can extend to the top of the atmospheric boundary layer through turbulent mixing. Incorporating wave‐induced stress into large‐eddy simulations significantly enhances the representation of offshore wind fields and contributes to research on atmosphere‐ocean interactions and offshore meteorology. Key Points: Parameterization of wave‐induced stress is integrated into a large‐eddy simulation model and verified for the first timeThe wave growth/damping rate for the proposed parameterization is calibrated by comparison with numerical and observational dataWind‐wave misalignment impacts the wind and turbulence by modifying the dynamic equilibrium in the wave boundary layer [ABSTRACT FROM AUTHOR]

The inverse temperature layer (ITL) beneath water‐atmosphere interface within which temperature increases with depth has been observed from measurement of water temperature profile at an inland lake. Strong solar radiation combined with moderate wind‐driven near‐surface turbulence leads to the formation of a pronounced diurnal cycle of the ITL predicted by a physical heat transfer model. The ITL only forms during daytime when solar radiation intensity exceeds a threshold while consistently occurs during nighttime. The largest depth of the ITL is comparable to the e‐fold penetration depth of solar radiation during daytime and at least one order of magnitude deeper during nighttime. The dynamics of the ITL depth variation simulated by a physical model forced by observed water surface solar radiation and temperature is confirmed by the observed water temperature profile in the lake. Plain Language Summary: An idealized one‐dimensional heat transfer equation reveals the physical mechanisms of water temperature increasing with depth beneath the water‐atmosphere interface known as inverse temperature layer (ITL). Solar radiation is the dominant forcing of water temperature profile while wind‐driven turbulent mixing is a critical process determining whether the ITL forms. The limited depth of the ITL poses a constraint on the rate of heat transfer from the water body into the atmosphere. The dynamics of the ITL plays an important role in the water and energy cycle of large water bodies such as lakes and oceans. Key Points: The formation of inverse temperature layer (ITL) is driven by strong solar radiation and moderate wind‐driven turbulenceThe ITL depth has pronounced diurnal cycle shallower during daytime than during nighttimeA physical model using observed solar radiation and water surface temperature captures the ITL dynamics [ABSTRACT FROM AUTHOR]

Hydrogen-fueled gas turbines play one of the key roles in future carbon-neutral energy structure. Due to hydrogen's high flame speed and extreme flame temperature, design of burners applying hydrogen as fuel is of challenge. In this work, we conduct direct numerical simulations to investigate a non-premixed steam-diluted oxygen/hydrogen combustion, which is formed by inclined impinging fuel and oxidizer jets injected by sub-millimeter nozzles. This configuration inherently prevent flashback and has a higher mixing efficiency enhanced by jet impingement, thereby leveraging advantages of both conventional premixed and non-premixed configurations. The flame is lifted flame held at the jet impinging position far away from the wall boundary. The most intensive mixing process occurs at the outer sides of the two branches of hydrogen jet after impinging, forming the flame base and resulting in an edge-flame configuration. A larger jet inclination angle leads to more effective bulk turbulence mixing because of the increased mixing volume, thereby enhancing combustion completeness. Simultaneously, it results in lower wall heat flux due to gentler upstream recirculation of burnt products. Chemical explosive mode analysis is conducted to analyze the combustion procedure from ignition to burnt out. The flame is held by the recirculation of high-temperature burnt products upstream of the impingement position, and its structure is primarily formed by the simultaneous ignition of a widespread explosive mixture enhanced by intense turbulence. • DNSs are conducted to investigate the combustion of impinging fuel and oxidizer jets. • Edge-flame configuration is formed by impinging fuel and oxidizer jets. • Fuel and Oxidizer are intensively mixed near the oxidizer jet branches. • Inclination angle of jets affects the statistical thermophysical performance. • Flame is held by hot product recirculation. [ABSTRACT FROM AUTHOR]

Recent theoretical progress using multiscale asymptotic analysis has revealed various possible regimes of stratified turbulence. Notably, buoyancy transport can either be dominated by advection or diffusion, depending on the effective Péclet number of the flow. Two types of asymptotic models have been proposed, which yield measurably different predictions for the characteristic vertical velocity and length scale of the turbulent eddies in both diffusive and non-diffusive regimes. The first, termed a 'single-scale model', is designed to describe flow structures having large horizontal and small vertical scales, while the second, termed a 'multiscale model', additionally incorporates flow features with small horizontal scales, and reduces to the single-scale model in their absence. By comparing predicted vertical velocity scaling laws with direct numerical simulation data, we show that the multiscale model correctly captures the properties of strongly stratified turbulence within regions dominated by small-scale isotropic motions, whose volume fraction decreases as the stratification increases. Meanwhile its single-scale reduction accurately describes the more orderly, layer-like, quiescent flow outside those regions. [ABSTRACT FROM AUTHOR]

This study demonstrates that temporally developing lobed jets can qualitatively reproduce the diffusion performance in the fully developed states of spatially developing lobed jets in laboratory experiments. The jet exit geometries, Reynolds number (= 70 , 000) , and turbulence intensity (3% of mean velocity) were set to be the same across the temporally and spatially developing jets. Four types of jet flows were tested, one being a round jet and three being lobed jets with different numbers or curvatures of lobes, referred to as 6L, 6S, and 3L, respectively. The half-width of the mean streamwise velocity distributions and centerline mean streamwise velocity of the four jets in the developed states were consistent between the numerical simulations and experiments. The round jet displayed the highest diffusion performance, followed by 3L, while 6L and 6S were the smallest and were comparable with each other. Despite such consistency in the developed states, the diffusion performance and formation of the streamwise swirling flows did not agree between the numerical and experimental results. These results suggest that unique large-scale structures corresponding to the initial conditions are reproduced in temporally developing jets, which is in good agreement with the spatially developing lobed jets. Therefore, the current study demonstrated that the temporally developing simulations can reproduce similar diffusion processes to those of the spatially developing ones. [ABSTRACT FROM AUTHOR]

The Indonesian seas, with their complex passages and vigorous mixing, constitute the only route and are critical in regulating Pacific–Indian Ocean interchange, air–sea interaction, and global climate events. Previous research employing remote sensing and numerical simulations strongly suggested that this mixing is tidally driven and localized in narrow channels and straits, with only a few direct observations to validate it. The current study offers the first comprehensive temporal microstructure observations in the south of Lombok Strait with a radius of 0.05° and centered on 115.54oE and 9.02oS. Fifteen days of tidal mixing observations measured potential temperature and density, salinity, and turbulent energy dissipation rate. The results revealed significant mixing and verified the remotely sensed technique. The south Lombok temporal and depth averaged of the turbulent kinetic energy dissipation rate, and the diapycnal diffusivity from 20 to 250 m are ε = 4.15 ± 15.9) × 10–6 W kg–1 and K ρ = (1.44 ± 10.7) × 10–2 m2s–1, respectively. This K ρ is up to 104 times larger than the Banda Sea [ K ρ = (9.2 ± 0.55) × 10–6 m2s–1] (Alford et al. Geophys Res Lett 26:2741–2744, 1999) or the "open ocean" K ρ = 0.03 × 10–4 m2s−1 within 2° of the equator to (0.4–0.5) × 10–4 m2s−1 at 50°–70° (Kunze et al. J Phys Oceanogr 36:1553–1576, 2006). Therefore, nonlinear interactions between internal tides, tidally induced mixing, and ITF plays a critical role regulating water mass transformation and have strong implications to longer-term variations and change of Pacific–Indian Ocean water circulation and climate. [ABSTRACT FROM AUTHOR]

This paper focuses on the numerical modelling of the autoignition process in an ethanol-air mixture within a turbulent droplet-laden temporally evolving mixing layer, utilising the Large Eddy Simulation (LES) method. We compare results obtained by implementing two notably distinct discretisation methods (second-order Total Variation Diminishing – TVD, and fifth-order Weighted Essentially Non-Oscillatory – WENO) in the species and energy transport equations. Additionally, we examine three widely recognised evaporation models (the ' $ D^2 $ D 2 ' model, the Abramzon–Sirignano model, and a non-equilibrium model based on the Langmuir-Knudsen law). For modelling the combustion process, we employ the Eulerian Stochastic Field method and a laminar chemistry model. The simulations encompass two droplet diameter distributions, one with low and the other with significant diameter non-uniformity. Furthermore, nine distinct initial conditions are considered. Our findings indicate that adjusting the discretisation scheme or the evaporation model can yield simulation outcomes differing to a substantial degree, similar to the impact of modifying the actual properties of the spray droplets or their initial distribution. This is particularly pronounced in the case of sprays featuring a narrowed droplet diameter distribution. We found that the Abramzon–Sirignano model results in the most rapid autoignition. The TVD scheme contributes to a more even spatial distribution of the evaporated fuel, consequently facilitating quicker evaporation and faster autoignition. Using the WENO scheme generates higher fuel vapor gradients near the droplets, leading to less intense evaporation and slower fuel transport in space. [ABSTRACT FROM AUTHOR]

Supercritical CO2 (s-CO2) is a natural eco-friendly refrigerant finding global acceptance in energy systems. Supersonic ejectors are passive gasdynamic devices where a motive flow energizes and compresses a secondary stream in a varying area duct having energy applications. Mathematically modeling ejectors, including real gas effects present in CO2, is challenging. We develop a comprehensive physics-based hybrid model of the ejector operating in the critical flow regime where both the primary and secondary mass flow rates are choked. The method of characteristics is used to model the primary supersonic flow and is concurrently solved with a discrete quasi-1D model for the secondary flow with appropriate pressure-matching interface conditions and boundary conditions. The compressible turbulent mixing layer growth between the primary and secondary flow is modeled, and the location of choking is evaluated without any prior assumptions. We introduce empirical fits of the non-mixed length in the ejector to ascertain the length of the mixing duct, and the shock location in the mixed flow is estimated using an entropy minimization principle. Real gas thermodynamic properties are fetched from thermophysical database at each discrete point. The overall model exhibits remarkable fidelity and robustness in the prediction of previous experimental results of air ejectors. Comparisons between numerical results and the physics-based model with s-CO2 as working fluid confirm the accuracy of prediction of the current model (<5% difference in entrainment ratio) compared with conventional modeling approaches (10%–15% difference in entrainment ratio). The computationally effective model developed in this study is invaluable for optimization of ejectors. [ABSTRACT FROM AUTHOR]

In this work, an artificial neural network (ANN) aided vapor–liquid equilibrium (VLE) model is developed and coupled with a fully compressible computational fluid dynamics (CFD) solver to simulate the transcritical processes occurring in high-pressure liquid-fueled propulsion systems. The ANN is trained in Python using TensorFlow, optimized for inference using Open Neural Network Exchange Runtime, and coupled with a C++ based CFD solver. This plug-and-play model/methodology can be used to convert any multi-component CFD solver to simulate transcritical processes using only open-source packages, without the need of in-house VLE model development. The solver is then used to study high-pressure transcritical shock-droplet interaction in both two- and four-component systems and a turbulent temporal mixing layer (TML), where both qualitative and quantitative agreement (maximum relative error less than 5%) is shown with respect to results based on both direct evaluation and the state-of-the-art in situ adaptive tabulation (ISAT) method. The ANN method showed a 6 times speed-up over the direct evaluation and a 2.2-time speed-up over the ISAT method for the two-component shock-droplet interaction case. The ANN method is faster than the ISAT method by 12 times for the four-component shock-droplet interaction. A 7 times speed-up is observed for the TML case for the ANN method compared to the ISAT method while achieving a data compression factor of 2881. The ANN method also shows intrinsic load balancing, unlike traditional VLE solvers. A strong parallel scalability of this ANN method with the number of processors was observed for all the three test cases. Code repository for 0D VLE solvers, and C++ ANN interface—https://github.com/UMN-CRFEL/ANN_VLE.git. [ABSTRACT FROM AUTHOR]

A new high-flow, compact aerosol concentrator, using rapid, turbulent mixing to grow aerosol particles into droplets for dry spot sample collection, has been designed and tested. The "TCAC (Turbulent-mixing, Condensation Aerosol Concentrator)" is composed of a saturator for generating hot vapor, a mixing section where the hot vapor mixes with the cold aerosol flow, a growth tube where condensational droplet growth primarily occurs, and a converging nozzle that focuses the droplets into a beam. The prototype concentrator utilizes an aerosol sample flow rate of 4 L min−1. The TCAC was optimized by varying the operating conditions, such as relative humidity of the aerosol flow, mixing flow ratio, vapor temperature, and impaction characteristics. The results showed that particles with a diameter ≥ 25 nm can be grown to a droplet diameter > 1400 nm with near 100% efficiency. Complete activation and growth were observed at relative humidity ≥ 25% of the aerosol sample flow. A consistent spot sample with a diameter of D90 = 1.4 mm (the diameter of a circle containing 90% of the deposited particles) was obtained regardless of the aerosol particle diameter (dp = 20–1900 nm). For fiber counting applications using phase contrast microscopy, the TCAC can reduce the sampling time, or counting uncertainty, by two to three orders of magnitude, compared to the 25-mm-filter collection. The study shows that the proposed mixing-flow scheme enables a compact spot sample collector suitable for handheld or portable applications, while still allowing for high flow rates. [ABSTRACT FROM AUTHOR]

The turbulence mixing initiated by the Rayleigh–Taylor instability has been reported in a two-dimensional (2D) strongly coupled dusty plasma system using classical molecular dynamics simulation. The entire evolution cycle, including the initial equilibrium, the instability, turbulent mixing, and, finally, a new equilibrium through the thermalization process, has been demonstrated via the respective energy spectra. The fully developed spectrum follows the Bolgiano-Obukho k − 11 / 5 scaling at smaller wavenumbers, a characteristic 2D buoyancy-driven turbulent flow feature. At higher wavenumbers, the energy spectrum E (k) ∝ k represents the thermalization of the system and is a characteristic feature of 2D Euler turbulence. At longer timescales, the system reflects the Kolmogorov scale of k − 3 . Moreover, strong coupling slows the turbulent mixing process, though the final state is a complete thermalized system. Our results also help us to understand the thermalization process in Yukawa fluids, other strongly coupled plasma families, and turbulent mixing in low Reynolds number fluids. [ABSTRACT FROM AUTHOR]

The diurnal cycles of near‐surface velocity and temperature, also known as diurnal jet and diurnal warm layer (DWL), are ubiquitous in the tropical oceans, affecting the heat and momentum budget of the ocean surface layer, air‐sea interactions, and vertical mixing. Here, we analyze the presence and descent of near‐surface diurnal shear and stratification in the upper 20 m of the equatorial Atlantic as a function of wind speed using ocean current velocity and hydrographic data taken during two trans‐Atlantic cruises along the equator in October 2019 and May 2022, data from three types of surface drifters, and data from Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) moorings along the equator. The observations during two seasons with similar mean wind speeds but varying surface heat fluxes reveal similar diurnal jets with an amplitude of about 0.11 m s−1 and similar DWLs when averaging along the equator. We find that higher wind speeds lead to earlier diurnal peaks, deeper penetration depths, and faster descent rates of DWL and diurnal jet. While the diurnal amplitude of stratification is maximum for minimal wind speeds, the diurnal amplitude of shear is maximum at 6 m depth for moderate wind speeds of about 5 m s−1. The inferred wind dependence of the descent rates of DWL and diurnal jet is consistent with the earlier onset of deep‐cycle turbulence for higher wind speeds. The DWL and the diurnal jet not only trigger deep‐cycle turbulence but are also observed to modify the wind power input and thus the amount of energy available for mixing. Plain Language Summary: During daytime, solar radiation leads to the formation of a thin warm layer at the ocean surface which can trap heat and wind‐forced momentum. Both heat and momentum are transported in the deeper ocean during the evening and night by turbulent mixing. The associated diurnal variation of temperature, current velocity, and their vertical gradients, stratification and velocity shear, are thus relevant for understanding ocean‐atmosphere interactions. This study investigates how the diurnal variation in stratification and velocity shear is influenced by the wind speed. For that, basin‐scale observations of velocity and temperature, which were collected in the equatorial Atlantic during two trans‐Atlantic equatorial cruises and by instruments installed at long‐term moorings along the equator, are analyzed. These observations reveal that the wind speed influences the amplitude, the timing, and the vertical structure of the diurnal variation in stratification and velocity shear. Wind speed also influences how deep and how fast this variation propagates from the surface downward. The study concludes that the diurnal variation of stratification and velocity shear impacts first the input of mechanical energy from the atmosphere into the ocean and second the process of turbulent mixing below the night‐time mixed layer. Key Points: Basin‐scale in‐situ data show the evolution of diurnal warm layer and diurnal jet in the upper 15 m of the equatorial Atlantic OceanHigher wind speeds lead to earlier diurnal peaks, deeper penetration depths, and faster descent rates of the diurnal jetWind speed dependence of descent rates of diurnal shear and stratification can explain the varying onset of deep‐cycle turbulence [ABSTRACT FROM AUTHOR]

This study uses large eddy simulations to investigate nutrient transport and uptake in suspended macroalgal farms. Various farm configurations and oceanic forcing conditions are examined, with the farm base located near the nutricline depth. We introduce the Damkohler number Da to quantify the balance between nutrient consumption by macroalgae uptake and supply by farm‐enhanced nutrient transport. Most cases exhibit low Da, indicating that farm‐generated turbulence drives sufficient upward nutrient fluxes, supporting macroalgae growth. High Da and starvation may occur in fully grown farm blocks, a configuration that generates the weakest turbulence, particularly when combined with densely planted macroalgae or weak flow conditions. Flow stagnation within the farm due to macroalgae drag may constrain the uptake efficiency and further increase the starvation risk. Mitigation strategies involve timely harvesting, avoiding dense macroalgae canopies, and selecting farm locations with robust ocean currents and waves. This study provides insights for sustainable macroalgal farm planning. Plain Language Summary: Offshore macroalgal farming has been proposed as a sustainable strategy for carbon sequestration, biofuel production, food supply, and bioremediation. However, challenges arise as macroalgal farms are typically suspended above the nutricline and may thus deplete the existing nutrient inventory near the sea surface. In this study, large eddy simulations reveal that suspended farms can generate intense turbulence and drive upward nutrient fluxes from below the farm base. Various farm simulations are conducted, and in most cases the farm‐generated turbulence is indicated to provide sufficient nutrient fluxes to support macroalgae growth. This presents a self‐sustaining solution for nutrient supply through passive entrainment. To mitigate the risk of farm starvation, we propose strategies such as timely harvesting, avoiding dense macroalgae canopies, and selecting farm locations with robust ocean currents and waves. Key Points: Suspended macroalgal farms can enhance turbulence and drive upward nutrient fluxes from below the farm base to prevent starvationThe Damkohler number, comparing nutrient transport with uptake by macroalgae, can be used to predict nutrient availability in the farmFarming strategies are proposed such as timely harvesting and selecting locations with a shallow nutricline and robust currents and waves [ABSTRACT FROM AUTHOR]

Lipid nanoparticles often contain a phosphatidylcholine with a long chain fatty acid, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). However, their preparation often encounters difficulties such as the inability to yield <20 nm nanoparticles due to the aggregation-prone behavior of DSPC. High-density lipoproteins (HDLs) are ∼10 nm protein-bound lipid nanoparticles in our body, and microfluidic preparations of HDL-mimicking nanoparticles (μHDL) have been reported. Herein, we report a new microfluidic mixing mode that enables preparation of μHDL with DSPC in high yield (≥90% on a protein basis). The critical mechanism of this mode is a spontaneous asymmetric distribution of the ethanol flow injected in a symmetric manner followed by turbulent mixing in a simple rectangular parallelepiped-shaped chip. [ABSTRACT FROM AUTHOR]

Transparent exopolymer particles (TEP), a major component of coral mucus, are responsible for particle aggregation. These particles contribute substantially to the carbon cycle in coral reefs, and serve as an energy source for bacteria and other microorganisms. Water flows and induced turbulent mixing control material exchange between the coral canopy and the surrounding water, which is critical for coral health. However, how these factors affect TEP release by coral colonies has yet to be evaluated. Using a recirculating flume, we assessed TEP release by branching Acropora coral colonies and associated bacterial growth in the water column under different unidirectional flows. Changes in TEP and bacterial concentrations after 24-h incubation were quantified for flow speeds of 0, 5, 10, and 30 cm/s. Particle image velocimetry (PIV) measurements provided an estimate of turbulent mixing efficiency above the coral canopy. TEP and bacterial concentrations in the water column increased after 24 h of incubation. The increase in TEP and bacterial concentrations were 6.2-9.3 times and 3.4-5.1 times higher in the absence of flows, respectively, than mean values under water flows. Although mixing efficiency increased linearly with mean flow speeds, TEP release and bacterial growth differed only marginally at flows ranging from 5-30 cm/s. Detailed flow measurements combined with evaluation of TEP release suggest that the complex geometry of corals facilitates efficient material exchange at a range of flow speeds, and highlight the importance of considering these factors when estimating coral reef biogeochemistry. [ABSTRACT FROM AUTHOR]

Turbulent mixing in the ocean exerts an important control on the rate and structure of the overturning circulation. However, the balance of processes underpinning this mixing is subject to significant uncertainties, limiting our understanding of the overturning's deep upwelling limb. Here, we investigate the hitherto primarily neglected role of tens of thousands of seamounts in sustaining deep-ocean upwelling. Dynamical theory indicates that seamounts may stir and mix deep waters by generating lee waves and topographic wake vortices. At low latitudes, stirring and mixing are predicted to be enhanced by a layered vortex regime in the wakes. Using three realistic regional simulations spanning equatorial to middle latitudes, we show that layered wake vortices and elevated mixing are widespread around seamounts. We identify scalings that relate mixing rate within seamount wakes to topographic and hydrographic parameters. We then apply such scalings to a global seamount dataset and an ocean climatology to show that seamount-generated mixing makes an important contribution to the upwelling of deep waters. Our work thus brings seamounts to the fore of the deep-ocean mixing problem and urges observational, theoretical, and modeling efforts toward incorporating the seamounts' mixing effects in conceptual and numerical ocean circulation models. [ABSTRACT FROM AUTHOR]