Mesoscale Flow Research Articles

微生物懸濁液内の輸送現象

Microorganisms play a vital role in many biological and medical phenomena. Transport phenomena in a suspension of microorganisms are extremely important, because they dominate the growth and distribution of cells. In terms of fluid mechanics, however, mathematical modeling of a suspension of swimming microorganisms is still under way. In this article, I explain recent developments in modeling a suspension of microorganisms. Macroscopic properties of a suspension are strongly affected by the mesoscale flow structures, and the mesoscale flow structures are affected by the interactions between microorganisms. Thus, a bottom-up strategy, i.e. from a cellular level to a continuum suspension level, represents the natural approach to the study of a suspension of swimming microorganisms.

Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers

AbstractNightside auroral zone localized flow channels, typically associated with auroral poleward boundary intensifications and streamers, are an important component of high‐latitude ionospheric plasma dynamics. We investigate the structure of these flow channels using two‐dimensional line‐of‐sight flow observations from the Super Dual Auroral Radar Network (SuperDARN) radars and auroral images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground‐based all‐sky imager (ASI) array. Radar echoes captured <~500 km horizontal distance from the radars were mainly used to detect small‐scale flow structures that would otherwise be missed or poorly resolved in long‐range radar echoes. After identifying 135 auroral streamers in the ASI images at close‐radar capture locations, we examined the associated ionospheric flow data in the radar echoes. Flow bursts and streamers are invariably correlated in all events. The flow bursts are often directed equatorward and appear simultaneously with the streamers. Equatorward flows are located just to the east of the streamers. Less frequently (~10% of the time), a poleward flow enhancement was detected even when a streamer propagated equatorward, the poleward flow enhancement being located to the west of the auroral streamer, or to the east of the equatorward flow enhancement, consistently with the spatial relationship between flow shear and upward field‐aligned currents in plasma sheet flow bursts. The azimuthal width of the flow channel is, on average, ~75 km, and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is ~57 km eastward. This study demonstrates the capability of radar‐imager pairs for identifying the 2‐D structure of localized flows associated with plasma sheet flow bursts.

The role of sea–land air thermal difference, shape of the coastline and sea surface temperature in the nocturnal offshore convection

ABSTRACTNocturnal precipitation cells and lines occur near the coastline in the whole Mediterranean basin in all seasons. The precipitation events are mainly located in areas where coastal mountain ranges and rivers enhance convergence though the interaction of nocturnal mesoscale and local flows (land breeze, katabatic and drainages winds) with prevailing synoptic wind or with other mesoscale and local flows. The methodology used here to study this phenomenon consists of three stages. First, the Tropical Rainfall Measuring Mission (TRMM) radar satellite database is used to detect nocturnal precipitation near the coastline, from 18 to 09 UTC. An event is included in the study if the 3 hours accumulated precipitation detected by TRMM is stationary near the coast, or has moved slightly onshore or offshore, and has lasted no more than six consecutive hours. Second, the NCEP reanalysis database is used to describe the synoptic conditions and to discard precipitation associated with synoptic events (large low pressure areas, dynamic polar fronts, or troughs, for example). In the final step by using the version 3 of the Weather Research Forecast model, we simulate and analyse some of the selected events to determine the role of the land–sea temperature differences, the curvature of the coastline and the sea surface temperature.The simulations confirm that the nocturnal precipitation studied in the Mediterranean basin near the coastline is formed from the interaction between relatively warm and wet sea-air with the cold air mass from drainage winds, as well as from the convergence of several drainage winds offshore. The mechanism is the same that is used to explain nocturnal precipitation in tropical areas.

Toward Multiscale Simulation of Moist Flows with Soundproof Equations

Abstract This paper discusses the incorporation of phase changes of the water substance that accompany moist atmospheric flows into the all-scale atmospheric model based on soundproof equations. A specific issue involves developing a theoretical basis and practical implementation to include pressure perturbations associated with atmospheric circulations, from small scale to global, into representations of moist thermodynamics. In small-scale modeling using soundproof equations, pressure perturbations are obtained from the elliptic pressure solver and are typically excluded from the moist thermodynamics. This paper argues that in larger-scale flows, at least the hydrostatic component of the pressure perturbation needs to be included because pressure variation in synoptic weather systems may affect moist thermodynamics in a way comparable to the temperature variations. As an illustration, two idealized test problems are considered: the small-scale moist thermal rising in a stratified environment and the moist mesoscale flow over idealized topography. The paper compares numerical solutions obtained with a fully compressible acoustic mode–resolving model and with two versions of the anelastic model, either including or excluding anelastic pressure perturbations in moist thermodynamics. The two versions of the anelastic model are referred to as the generalized and standard anelastic. In agreement with the scaling arguments, only negligible differences between anelastic and compressible solutions are simulated. Incorporation of the anelastic pressure perturbations into moist thermodynamics paves the way for future studies where larger-scale moist dynamics will be considered.

An online trajectory module (version 1.0) for the nonhydrostatic numerical weather prediction model COSMO

Abstract. A module to calculate online trajectories has been implemented into the nonhydrostatic limited-area weather prediction and climate model COSMO. Whereas offline trajectories are calculated with wind fields from model output, which is typically available every one to six hours, online trajectories use the simulated resolved wind field at every model time step (typically less than a minute) to solve the trajectory equation. As a consequence, online trajectories much better capture the short-term temporal fluctuations of the wind field, which is particularly important for mesoscale flows near topography and convective clouds, and they do not suffer from temporal interpolation errors between model output times. The numerical implementation of online trajectories in the COSMO-model is based upon an established offline trajectory tool and takes full account of the horizontal domain decomposition that is used for parallelization of the COSMO-model. Although a perfect workload balance cannot be achieved for the trajectory module (due to the fact that trajectory positions are not necessarily equally distributed over the model domain), the additional computational costs are found to be fairly small for the high-resolution simulations described in this paper. The computational costs may, however, vary strongly depending on the number of trajectories and trace variables. Various options have been implemented to initialize online trajectories at different locations and times during the model simulation. As a first application of the new COSMO-model module, an Alpine north foehn event in summer 1987 has been simulated with horizontal resolutions of 2.2, 7 and 14 km. It is shown that low-tropospheric trajectories calculated offline with one- to six-hourly wind fields can significantly deviate from trajectories calculated online. Deviations increase with decreasing model grid spacing and are particularly large in regions of deep convection and strong orographic flow distortion. On average, for this particular case study, horizontal and vertical positions between online and offline trajectories differed by 50–190 km and 150–750 m, respectively, after 24 h. This first application illustrates the potential for Lagrangian studies of mesoscale flows in high-resolution convection-resolving simulations using online trajectories.

Bottom-up construction of interaction models of non-Markovian dissipative particle dynamics

We derive the equation of motion for non-Markovian dissipative particle dynamics (NMDPD) by introducing the history effects on the time evolution of the system. Our formulation is based on the generalized Langevin equation, which describes the motions of the centers of mass of clusters comprising microscopic particles. The mean, friction, and fluctuating forces in the NMDPD model are directly constructed from an underlying molecular dynamics (MD) system without any scaling procedure. For the validation of our formulation, we construct NMDPD models from high-density Lennard-Jones systems, in which the typical time scales of the coarse-grained particle motions and the fluctuating forces are not fully separable. The NMDPD models reproduce the temperatures, diffusion coefficients, and viscosities of the corresponding MD systems more accurately than the dissipative particle dynamics models based on a Markovian approximation. Our results suggest that the NMDPD method is a promising alternative for simulating mesoscale flows where a Markovian approximation is not valid.

Submesoscale impacts on horizontal and vertical transport in the Gulf of Mexico

[1] Impacts of submesoscale processes on transport are investigated numerically in an energetic mesoscale flow with an ocean model run at two horizontal resolutions, 1 and 5 km. The focus is the northwestern Gulf of Mexico, where the Loop Current eddies are surrounded by smaller vortices. By increasing the horizontal resolution, the number and strength of submesoscale eddies and vorticity filaments within the mixed layer increase dramatically and with them the vertical velocities. Inside the coherent eddies and at their peripheries, increased vertical velocities for increasing resolution are associated to near-inertial motions and they are not limited to the mixed layer, but are found at all depths. Horizontal velocities, on the contrary, are similar. Lagrangian isobaric tracers are deployed close to the surface and at 100 m, and three-dimensional, neutrally buoyant particles are released close to the surface, at the base of the mixed layer and at 100 m. The modeled horizontal dispersion curves for each deployment depth are independent of the kind of particles and of horizontal resolution. Close to the ocean surface, however, convergence zones, generated by submesoscale ageostrophic motions and resolved at 1 km resolution, influence the details of the tracer distributions. Vertical dispersion increases by several folds for increasing resolution at all depths explored, with the largest differences found close to the surface. Therefore, submesoscales processes play a fundamental role in driving vertical transport in eddy-dominated flows, both within and below the mixed layer, for times comparable to the Eulerian time scale.

대류가 유도하는 중규모 흐름에 미치는 비정역학 효과

대류가 유도하는 중규모 흐름에 미치는 비정역학 효과를 조사하기 위하여 기존의 무차원화된 정역학 모형을 바탕으로 무차원화된 비정역학 모형을 개발하였다. 모형을 검증하기 위하여 정역학 방정식 계의 해석해와 비정역학성이 아주 작은 경우의 수치 실험 결과를 비교하였고, 두 결과가 거의 같음을 확인하였다. 무차원화된 비정역학 모형을 이용하여 선형 계와 비선형 계에서 대류가 유도하는 중규모 흐름에 미치는 비정역학 효과를 조사하였다. 선형 계와 비선형 계 모두에서 비정역학성 인자가 작은 경우 열원 꼭대기 위에서 연직 방향으로, 비정역학성 인자가 상대적으로 큰 경우 주 상승 기류의 풍하측에서 수평 방향으로 상승 운동과 하강 운동이 교대하는 파동 형태의 섭동장이 나타났다. 풍하측에서 나타나는 상승 운동과 하강 운동을 분석하기 위하여 선형, 정상 상태, 비점성 흐름에 대한 Taylor-Goldstein 방정식을 구하였다. 주 상승기류의 풍하측에서 교대로 나타나는 상승 하강 기류세포는 전파파의 수평 방향 전파 성분과 에바네센트파, 즉 비정역학성 인자에 의해 결정되는 임계 파장보다 파장이 짧아 연직 방향으로 전파되지 못하고 수평 방향으로만 전파되는 중력파의 중첩으로 설명할 수 있다. 선형 계에 대한 수치 실험 결과에서 나타난 상승 하강 기류 세포의 수평 방향 길이는 선형 계에 대한 방정식에서 얻은 에바네센트 파의 임계 파장 길이의 절반과 일치하였으나, 약한 비선형 계에 대한 수치 실험 결과에서 나타난 상승 하강 기류 세포의 수평 방향 길이는 선형 계에 대한 방정식에서 얻은 에바네센트 파의 임계 파장 길이의 절반보다 다소 길었다. 주 상승 기류 지역 내에서 최대 상승 기류의 위치는 비선형성과 비정역학성 정도에 따라 다르게 나타났다. Nonhydrostatic effects on convectively forced mesoscale flows in two dimensions are numerically investigated using a nondimensional model. An elevated heating that represents convective heating due to deep cumulus convection is specified in a uniform basic flow with constant stability, and numerical experiments are performed with different values of the nonlinearity factor and nonhydrostaticity factor. The simulation result in a linear system is first compared to the analytic solution. The simulated vertical velocity field is very similar to the analytic one, confirming the high accuracy of nondimensional model's solutions. When the nonhydrostaticity factor is small, alternating regions of upward and downward motion above the heating top appear. On the other hand, when the nonhydrostaticity factor is relatively large, alternating updraft and downdraft cells appear downwind of the main updraft region. These features according to the nonhydrostaticity factor appear in both linear and nonlinear flow systems. The location of the maximum vertical velocity in the main updraft region differs depending on the degrees of nonlinearity and nonhydrostaticity. Using the Taylor-Goldstein equation in a linear, steady-state, invscid system, it is analyzed that evanescent waves exist for a given nonhydrostaticity factor. The critical wavelength of an evanescent wave is given by <TEX>${\lambda}_c=2{\pi}{\beta}$</TEX>, where <TEX>${\beta}$</TEX> is the nonhydrostaticity factor. Waves whose wavelengths are smaller than the critical wavelength become evanescent. The alternating updraft and downdraft cells are formed by the superposition of evanescent waves and horizontally propagating parts of propagating waves. Simulation results show that the horizontal length of the updraft and downdraft cells is the half of the critical wavelength (<TEX>${\pi}{\beta}$</TEX>) in a linear flow system and larger than <TEX>${\pi}{\beta}$</TEX> in a weakly nonlinear flow system.

Flow Heck Reactions Using Extremely Low Loadings of Phosphine-Free Palladium Acetate

High-yielding Heck reactions are demonstrated using 0.05 mol % Pd(OAc)2 without phosphine ligands. These reactions are run in a mesoscale flow reactor which allows precise control of reaction times and temperatures. Profiling yield and selectivity versus Pd loading shows 500 ppm to be optimal for aryl iodides; higher loadings favor side reactions caused by Pd(II) species. Aryl halides are examined via concise Design of Experiment to expand the scope and optimize conditions.

The circulation dynamics associated with a northern Benguela upwelling filament during October 2010

Upwelling filaments, a common feature in all the major upwelling systems, are also regularly observed in the Benguela upwelling system and are thought to provide an effective mechanism for the exchange of matter between the shelf and the open ocean. The mesoscale dynamics of a northern Benguela upwelling filament located at approximately 18.5°S were examined and the associated transport was quantified. The development of the filament was tracked using optimal interpolated SST satellite data and two transects were consequently sampled across the feature using a towed undulating CTD (ScanFish). Additional hydrographic, nutrient and biological parameters were investigated at several stations along each transect. Following 7 days of strong upwelling favorable winds, sampling coincided with a period of relative wind relaxation and the filament was presumably in a decaying state. The basic mesoscale structure of the investigated filament corresponded well to what had previously been described for filaments from other eastern boundary current systems. The cross-shore transport associated with the filament was found to be significantly greater than the integrated Ekman transport in the region. With the combination of the high resolution dataset and a MOM-4 ecosystem model the complex mesoscale flow field associated with the feature could be observed and the counterbalancing onshore transport, associated with subsurface dipole eddies, was revealed within the filament. The results further suggest that an interaction between the offshore bending of flow at the Angola-Benguela Front (ABF), the detachment of the strong poleward flow from the coast as the thermal front meanders and the observed dipole eddies may be driving filament occurrence in the region off Cape Frio.

Studies of a Diastereoselective Electrophilic Fluorination Reaction Employing a Cryo-Flow Reactor

The application of meso-scale flow chemistry in research laboratories continues to increase. Here, we report on the use of a modular cryo-flow device as applied to a diastereoselective fluorination process. The reactor can be incorporated into existing flow chemistry setups to permit continuous processing at low temperatures without recourse to cryogenic consumables.

A new observationally motivated Richardson number based mixing parametrization for oceanic mesoscale flow

AbstractOcean models require subgrid‐scale parametrizations of vertical mixing expressed in terms of a quantity that is easily diagnosable from model output, such as the Richardson number. To date parametrizing mixing for low (&lt;1) Richardson number flows, such as the Equatorial Undercurrent, has received the most attention. Here a new Richardson number parametrization is proposed that provides estimates of vertical turbulent diffusivity in the high Richardson number stratified shear flow that is associated with mesoscale ocean features such as eddies and fronts. This parametrization is based on direct observations of vertical turbulent diffusivity from three separate ocean regions in the North Atlantic and Southern Ocean and is found to be robust for values of the Richardson number greater than 1 at depths below the ocean surface boundary layer. The new parametrization gives substantially improved agreement with the observed mixing in the presence of mesoscale ocean features compared to existing Richardson number parametrizations.

Diagnosing Forecast Errors in Tropical Cyclone Motion

Abstract This paper reports on the development of a diagnostic approach that can be used to examine the sources of numerical model forecast error that contribute to degraded tropical cyclone (TC) motion forecasts. Tropical cyclone motion forecasts depend upon skillful prediction of the environment wind field, and by extension, the synoptic-scale weather systems nearby the TC. While previous research suggests that the deep-layer mean (DLM) steering flow typically approximates the actual TC motion, it is shown that the motion of even mature TCs can depart from the DLM steering flow. An optimal environmental steering flow is defined, which varies the vertical extent of the steering layer and the radius over which TC vorticity and divergence are removed. Errors in predicted TC motion are quantified using a diagnostic equation that accounts for not only differences in the synoptic-scale flow, but also differences in the depth and radius used to define the steering flow. Differences in the latter two parameters are interpreted in terms of errors in predicted TC structure or errors in proximate mesoscale flow features. Results from an analysis of 24-h forecasts from the Advanced Hurricane Weather Research and Forecasting Model during the 2008–10 North Atlantic TC seasons show that forecast motion errors are dominated by errors in the environment wind field. Contributions from other terms are occasionally large and are interpreted from a vorticity perspective. The utility of this new diagnostic equation is that it can be used to assess TC motion forecasts from any numerical modeling system.

Mesoscale flow variability and its impact on connectivity for the island of Hawai`i

Understanding population connectivity is a contemporary challenge in marine ecology. Connectivity results from a combination of biological traits and physical mechanisms, at different life stages. We focus on the transport of particles around an oceanic island, simulating transport at early life stages of marine organisms. We aim to investigate through case studies how mesoscale features influence particle transport, recruitment, and connectivity. We determine particle dispersion by using an individual‐based model and the flow fields derived from a regional implementation of an ocean circulation model. To understand the underlying physical processes of transport, we locate coherent structures in the flow field, identify recurrent physical features, and observe how particle transport is related to them. Our results show that the varying eddying flow increases connectivity among populations located on different sides of the island. Both the flow field and dispersal patterns are highly variable. In this scenario, eddy events influence transport in distinct ways, and the timing of release plays an important role in dispersal. Our results highlight the need for modeling studies to use hydrodynamical model flows that represent the scales of variability affecting transport and dispersion.

Implicit-Explicit Formulations of a Three-Dimensional Nonhydrostatic Unified Model of the Atmosphere (NUMA)

We derive an implicit-explicit (IMEX) formalism for the three-dimensional (3D) Euler equations that allow a unified representation of various nonhydrostatic flow regimes, including cloud resolving and mesoscale (flow in a 3D Cartesian domain) as well as global regimes (flow in spherical geometries). This general IMEX formalism admits numerous types of methods including single-stage multistep methods (e.g., Adams methods and backward difference formulas) and multistage single-step methods (e.g., additive Runge--Kutta methods). The significance of this result is that it allows a numerical model to reuse the same machinery for all classes of time-integration methods described in this work. We also derive two classes of IMEX methods, one-dimensional and 3D, and show that they achieve their expected theoretical rates of convergence regardless of the geometry (e.g., 3D box or sphere) and introduce a new second-order IMEX Runge--Kutta method that performs better than the other second-order methods considered. We then compare all the IMEX methods in terms of accuracy and efficiency for two types of geophysical fluid dynamics problems: buoyant convection and inertia-gravity waves. These results show that the high-order time-integration methods yield better efficiency particularly when high levels of accuracy are desired.

Meso-scale microwave-assisted continuous flow reactions utilizing a selective heating matrix

Convergence of two powerful synthetic tools, microwave heating and flow chemistry, is described herein. Utilizing a selectively heated, microwave absorbing material as part of a packed reactor bed, several chemistries such as N-Boc pyrolysis, Michael additions, and Diels–Alder cycloadditions were performed at elevated temperatures. Scale-up from microwave batch to flow was readily accomplished and results showed that flow greatly increased product output while maintaining high yields. Product quantities of over 150 grams per hour were synthesized in this manner.

Performance of a Biologically Inspired Heat Exchanger with Hierarchical Bifurcating Flow Passages

The performance of a heat exchanger with tree-like flow passages has been examined. The hierarchical bifurcating flow passages in the heat exchanger mimic those seen in the vascular systems of plants and animals. Overall system performance was examined computationally. The results, cast in terms of commonly defined dimensionless parameters, show that system performance can be characterized in a manner similar to traditional compact heat exchanger designs. Previous use of hierarchical bifurcating flow passages for heat exchanger applications has typically been limited to microscale flow networks. The mesoscale flow network examined in this paper resulted in pressure and wall temperature distributions similar to previously studied microscale networks. The mesoscale flow network resulted in a total pressure drop two orders of magnitude smaller and a bulk fluid temperature increase an order of magnitude larger than the microscale flow network under the conditions studied.

Visualization of flow behavior during bioleaching of waste rock dumps under saturated and unsaturated conditions

A simulation framework is outlined for the analysis of the saturated and unsaturated flow behaviors within a waste rock dump. The traditional inherent “black-box” approach for treating waste rock dumps has resulted in generalizations that sometimes prove inaccurate. The hydrodynamics play an important role in terms of leaching reaction kinetics, heat and solute transport. The coexistence of saturated and unsaturated flows within the dump makes the flow behavior complicated. In this study, X-ray CT (SOMATOM Sensation 16) was used to obtain the real pore structure of the packed waste rocks. The meso-scale saturated flow process was visualized through solving the governing equation by the COMSOL Multiphysics software. The velocity field depends strongly on the distribution of channels, pore connectivity and curvature. The macro-scale unsaturated velocity field within the dump was obtained. The information drawn from this model can be used to improve the understanding of the hydrodynamics within waste rock dumps.

Nonlinear Effects on Convectively Forced Two-Dimensional Mesoscale Flows

Abstract One of the important problems in mesoscale atmospheric dynamics is how the atmosphere responds to convective heating or cooling. Here, the authors examine nonlinear effects on convectively forced mesoscale flows in the context of the nonlinear response of a stably stratified flow to elevated steady heating in two dimensions using a nondimensional numerical model. Results of two-dimensional numerical experiments in a uniform flow show that even without vertical wind shear, a separation of an upwind cellular updraft from the steady heating-induced main updraft occurs in a highly nonlinear flow system. This separation occurs as the compensating cellular downdraft associated with a secondary maximum in the main updraft develops. As the nonlinearity of the flow system increases, the upwind cellular updraft is separated earlier and becomes stronger. Smaller viscous terms result in the separation of more cellular updrafts, which become stronger and move farther away from the main updraft region. In particular, in an inviscid flow, cellular updrafts are periodically separated from the main updraft, and the first cellular updraft and downdraft have intensities comparable to the intensity of the main updraft. In a viscid flow with a constant vertical wind shear up to a certain height, the propagating cellular updraft and downdraft are produced when the nonlinearity is large, as in a uniform flow. Stronger vertical wind shear leads to the earlier formation of the cellular updraft and its stronger intensity, faster propagating speed, and longer lifetime. Results of numerical experiments with squall line–type forcing imply that the highly nonlinear state is necessary for the development of cellular updrafts.

Ageostrophic instability in a rotating stratified interior jet

AbstractOceanic large- and meso-scale flows are nearly balanced in forces between Earth’s rotation and density stratification effects (i.e. geostrophic, hydrostatic balance associated with small Rossby and Froude numbers). In this regime advective cross-scale interactions mostly drive energy toward larger scales (i.e. inverse cascade). However, viscous energy dissipation occurs at small scales. So how does the energy reservoir at larger scales leak toward small-scale dissipation to arrive at climate equilibrium? Here we solve the linear instability problem of a balanced flow in a rotating and continuously stratified fluid far away from any boundaries (i.e. an interior jet). The basic flow is unstable not only to geostrophic baroclinic and barotropic instabilities, but also to ageostrophic instabilities, leading to the growth of small-scale motions that we hypothesize are less constrained by geostrophic cascade behaviours in a nonlinear regime and thus could escape from the inverse energy cascade. This instability is investigated in the parameter regime of moderate Rossby and Froude numbers, below the well-known regimes of gravitational, centrifugal, and Kelvin–Helmholtz instability. The ageostrophic instability modes arise with increasing Rossby number through a near-degeneracy of two unstable modes with coincident phase speeds. The near-degeneracy occurs in the neighbourhood of an identified criterion for the non-integrability of the ‘isentropic balance equations’ (namely $A\ensuremath{-} S= 0$ with $A$ the absolute vertical vorticity and $S$ the horizontal strain rate associated with the basic flow), beyond which development of an unbalanced component of the flow is expected. These modes extract energy from the basic state with large vertical Reynolds stress work (unlike geostrophic instabilities) and act locally to modify the basic flow by reducing the isopycnal Ertel potential vorticity gradient near both its zero surface and its critical surface (phase speed equal to basic flow speed).