Terms Of Energy Budget Research Articles

Efficiency Versus Accuracy: A Review of Design Techniques for DNN Hardware Accelerators

Deep neural networks (DNNs) have surpassed other algorithms in analyzing today's abundant data. Due to the security and delay requirements of the given applications, analytical data extraction should happen on edge devices. Edge devices, however, struggle to support the increasingly complex DNNs because of the models' high computational load and number of employed parameters. Thus, edge devices need support by efficient accelerators to process DNNs. However, the design of DNN accelerators remains challenging, as there is a lack of established design techniques directed towards a specific design point in terms of energy budget, area, time-to-solution, and classification accuracy. This article fills this gap by providing a quantitative, large-scale, state-of-the-art comparison of DNN accelerators building on published data subjected to technology scaling and benchmark normalization. The leveled comparison stimulates learning from previous designs by considering the impact of each technique on energy, area, and time-to-solution. Furthermore, the key design techniques used in the DNN accelerators are classified according to their influence on the classification accuracy. Finally, we provide a discussion of hardware accelerators to support future designers in considering the trade-off between efficiency and accuracy in order to identify the most suitable techniques for certain benchmarks.

Measuring the Impact of a New Snow Model Using Surface Energy Budget Process Relationships

AbstractEnergy exchange at the snow‐atmosphere interface in winter is important for the evolution of temperature at the surface and within the snow, preconditioning the snowpack for melt during spring. This study illustrates a set of diagnostic tools that are useful for evaluating the energy exchange at the Earth's surface in an Earth System Model, from a process‐based perspective, using in situ observations. In particular, a new way to measure model improvement using the response of the surface temperature and other surface energy budget (SEB) terms to radiative forcing is presented. These process‐oriented diagnostics also provide a measure of the coupling strength between the incoming radiation and the various terms in the SEB, which can be used to ensure that improvements in predictions of user‐relevant properties, such as 2 m temperature, are happening for the right reasons. Correctly capturing such process relationships is a necessary step toward achieving more skilful weather forecasts and climate projections. These diagnostic techniques are applied to assess the impact of a new multi‐layer snow scheme in the European Centre for Medium‐Range Weather Forecasts'‐Integrated Forecast System at two high‐Arctic sites (Summit, Greenland and Sodankylä, Finland). A previous study showed that it will enhance 2 m temperature forecast skill across the Northern Hemisphere in boreal winter compared to forecasts with the single layer model, reducing a warm bias. In this study we use the diagnostics to show that the bias is improved for the right reasons.

Effect of Permeable Ribs on Thermal-Flow Characteristics in an Internal Cooling Duct

Abstract This study aims to understand the effect of flow structures within the inter-rib regions of a novel permeable rib configuration in vertical and horizontal streamwise planes upon surface heat transfer parameters. In this investigation, the liquid crystal thermography (LCT) and particle image velocimetry (PIV) are used to extract the local heat transfer and flow-field information, respectively. The effect of slit-converging angle (ϕ = 0 deg, 5 deg, 10 deg, and 15 deg) are examined at a typical Reynolds number of 42,500 and relative rib pitch ratio of 10. Surface- and spanwise-average and overall augmentation Nusselt numbers are obtained along with the pressure drop measurements. Flow-field experiments are performed in both vertical and horizontal streamwise planes, and the results are expressed in terms of mean velocities, stream traces, turbulent statistics, coherent structures, and turbulent kinetic energy budgets. Critical points are also identified on the basis of critical point theory, which provides evidences of the different flow phenomena accountable for enhance mixing between the ribs. The secondary flow coming from the slit shows three-dimensionality in the flow resulting to higher turbulence intensity and rotational motion (say higher turbulent mixing), and thereby leading to high heat transfer just behind the permeable rib. The permeable ribs are also helpful in the reduction of friction factor by 32% with a typical ϕ value of 5 deg, compared to solid ribs, while the thermohydraulic performance increases with increasing ϕ from 0 deg to 15 deg up to 21%. The pentagonal ribs with convergent slit provide comparable or better performance among the permeable rib geometries used in the pertinent literature.

The GAMIL3: Model Description and Evaluation

AbstractThe Grid‐point Atmospheric Model of the IAP LASG version 3 (GAMIL3) has been developed by upgrading the horizontal resolution, methods of parallel computation, boundary layer scheme, aerosol parameterization, convective parameterization, stratocumulus cloud fraction scheme, land component, and coupler, as well as tuning some moist physical parameters with large uncertainties. Its performance is evaluated, and the results show significant improvements compared with the previous version, GAMIL2. The simulated performance of mean states is notably enhanced, including the energy budget terms at the top of the atmosphere (TOA) and surface, shortwave/longwave cloud radiative forcing (SWCF/LWCF), precipitation, zonal wind, low‐level temperature, 500‐hPa geopotential height, and snow cover fraction in the Northern Hemisphere. The characteristics of internal variability are captured well, such as the frequency band and active areas of quasi‐biweekly (QBW) oscillation, spectral power of convectively coupled equatorial waves (CCEWs), Madden‐Julian Oscillation (MJO) eastward propagation, and heat flux response to El Niño‐Southern Oscillation (ENSO), and these variabilities are generally strengthened in GAMIL3. In addition, the anthropogenic aerosol climate effects are weakened when using the forcings recommended by CMIP6.

Deep Learning Emulation of Subgrid‐Scale Processes in Turbulent Shear Flows

AbstractDeep neural networks (DNNs) are developed from a data set obtained from the dynamic Smagorinsky model to emulate the subgrid‐scale (SGS) viscosity (νsgs) and diffusivity (κsgs) for turbulent stratified shear flows encountered in the oceans and the atmosphere. These DNNs predict νsgs and κsgs from velocities, strain rates, and density gradients such that the evolution of the kinetic energy budget and density variance budget terms is similar to the corresponding values obtained from the original dynamic Smagorinsky model. These DNNs also compute νsgs and κsgs ∼2–4 times quicker than the dynamic Smagorinsky model resulting in a ∼2–2.5 times acceleration of the entire simulation. This study demonstrates the feasibility of deep learning in emulating the subgrid‐scale (SGS) phenomenon in geophysical flows accurately in a cost‐effective manner. In a broader perspective, deep learning‐based surrogate models can present a promising alternative to the traditional parameterizations of the subgrid‐scale processes in climate models.

Direct numerical simulation of supersonic flow and acoustics over a compression ramp

We present direct numerical simulations of the shock wave boundary layer interaction (SBLI) at Mach number 2.9 over a 24° ramp. We study both the numerical accuracy and flow physics. Two classes of spatial reconstruction schemes are employed: the monotonic upstream-centered scheme for conservation laws and the Weighted Essentially Non-Oscillatory (WENO) scheme, of accuracy ranging from 2nd- to 11th-order. Using the canonical Taylor–Green vortex test-case, a simple and computationally inexpensive rescaling of the candidate stencil values—within the context of the high-order WENO scheme—is proposed for reducing the numerical dissipation, particularly in under-resolved simulations. For the compression ramp case, higher-order schemes are shown to capture the size of the SBLI separation zone more accurately, a consequence of resolving much finer turbulence structures. For second- and fifth-order schemes, the energy of the unresolved small scale turbulence shifts the cascade of the turbulence kinetic energy (TKE) spectrum, thus resulting in more energetic large scale turbulent structures. Consequently, the λ-shock foot shifts further downstream, leading to a smaller separation bubble size. Nonetheless, other statistical quantities, such as the turbulence anisotropy invariant map and the turbulence kinetic energy budget terms, show little dependence on the type and order of the spatial reconstruction scheme. Finally, using the more accurate ninth-order WENO results, it is reasoned that the interaction of the λ-shock with the post-shock relaxation region drives the low-frequency oscillation of the λ-shock.

Dynamics of Subsiding Shells in Actively Growing Clouds with Vertical Updrafts

Abstract The dynamics of a subsiding shell at the edges of actively growing shallow cumulus clouds with updrafts is analyzed using direct numerical simulation. The actively growing clouds have a fixed in-cloud buoyancy and velocity. Turbulent mixing and evaporative cooling at the cloud edges generate a subsiding shell that grows with time. A self-similar regime is observed for first- and second-order moments when normalized with respective maximum values. Internal scales derived from integral properties of the flow problem are identified. A self-similarity analysis using these scales reveals that contrary to classical self-similar flows, the turbulent kinetic energy budget terms and velocity moments scale according to the buoyancy and not with the mean velocity. The shell thickness is observed to increase linearly with time. The buoyancy scale remains time invariant and is set by the initial cloud–environment thermodynamics. The shell accelerates ballistically with a magnitude set by the saturation value of the buoyancy of the cloud–environment mixture. In this regime, the shell is buoyancy driven and independent of the in-cloud velocity. Relations are obtained for predicting the shell thickness and minimum velocities by linking the internal scales with external flow parameters. The values thus calculated are consistent with the thickness and velocities observed in typical shallow cumulus clouds. The entrainment coefficient is a function of the initial state of the cloud and the environment, and is shown to be on the same order of magnitude as fractional entrainment rates calculated for large-scale models.

Roles of Irrigation and Reservoir Operations in Modulating Terrestrial Water and Energy Budgets in the Indian Subcontinental River Basins

AbstractWater management activities affect the terrestrial water cycle by increasing water supply and redistributing the water and energy budgets over irrigated agricultural land. However, the dynamics of how water management activities interact with the terrestrial water and energy budgets have not been sufficiently studied over Indian subcontinental Basins. In this study, we applied a well‐evaluated water management model, coupled with a large‐scale land surface hydrological model with irrigation and reservoir operation schemes to examine the impacts of irrigation and reservoir operations on terrestrial water and energy budgets over the Indian subcontinental basins. We conducted two simulations: NATURAL (i.e., no irrigation and no reservoirs) and water management scenario (i.e., with irrigation and with reservoir regulations, referred to as MANAGED) over 18 basins from 1951 to 2012. The water management impacts were evaluated by comparing a number of key water and energy budget terms such as evapotranspiration (ET), total runoff, land surface temperature (LST), latent heat flux (LHF), sensible heat flux (SHF), reservoir storage, and discharge. Our results show that water management activities have significant (pvalue <0.05) impacts on ET, LHF, and LST in most of the river basins during the pre‐monsoon season (February–May). Comparing to the NATURAL scenario, ET and LHF under the MANAGED scenario are significantly increased in most basins during pre‐monsoon and post‐monsoon seasons, especially in semiarid regions. Therefore, the influence of irrigation on water and energy budget can be an overestimation in comparison to the constrained irrigation, which is a more realistic scenario.

An Improved Estimate of the Coupled Arctic Energy Budget

Abstract This study combines state-of-the-art reanalyses such as the fifth-generation European Re-Analysis (ERA5) and the Ocean Reanalysis System 5 (ORAS5) with novel observational products to present an updated estimate of the coupled atmosphere–ocean–sea ice Arctic energy budget, including flux and storage terms covering 2001–17. Observational products provide independent estimates of crucial budget terms, including oceanic heat transport from unique mooring-derived data, radiative fluxes from satellites, and sea ice volume from merged satellite data. Results show that the time averages of independent estimates of radiative, atmospheric, and oceanic energy fluxes into the Arctic Ocean domain are remarkably consistent in the sense that their sum closely matches the observed rate of regional long-term oceanic heat accumulation of ~1 W m−2. Atmospheric and oceanic heat transports are found to be stronger compared to earlier assessments (~100 and ~16 W m−2, respectively). Data inconsistencies are larger when considering the mean annual cycle of the coupled energy budget, with RMS values of the monthly budget residual between 7 and 15 W m−2, depending on the employed datasets. This nevertheless represents an average reduction of ~72% of the residual compared to earlier work and demonstrates the progress made in data quality and diagnostic techniques. Finally, the budget residual is eliminated using a variational approach to provide a best estimate of the mean annual cycle. The largest remaining sources of uncertainty are ocean heat content and latent heat associated with sea ice melt and freeze, which both suffer from the lack of observational constraints. More ocean in situ observations and reliable sea ice thickness observations and their routinely assimilation into reanalyses are needed to further reduce uncertainty.

The role of turbulence in strong submesoscale fronts of the Bay of Bengal

The evolution of turbulence in a shallow submesoscale front is investigated using high-resolution large-eddy simulations (LES). The model front has uniquely large cross-front temperature and salinity differences motivated by recent observations in the Bay of Bengal. The temperature and salinity differences are increased in a parametric study to examine their effects on the evolution of turbulence. Shear turbulence induced by the initially geostrophic jet causes the front to slump and an ageostrophic secondary circulation (ASC) develops. The ASC is composed of two rotating currents: a surface gravity current (SGC) with cold fresh water above a counter-current (CC) jet with warm saline water. Virtual moorings on the two sides of the front are used to depict the evolution of stratification, shear, turbulent stresses, turbulent heat and salt fluxes, as well as turbulent kinetic energy (TKE) budget terms. A barrier layer with thermal inversion develops on both sides of the front while the mixed layer depth becomes shallower across the front. Turbulent production driven by vertical shear is the dominant source of TKE on both sides of the front and horizontal shear production also contributes significantly to the TKE generation. The turbulent stresses, heat and salt fluxes are enhanced on both sides of the front with subsurface warming in the thermal inversion layers. As the cross-front temperature and salinity differences increase among the cases, the ASC intensifies, and the currents and the turbulence become stronger.

Population‐level consequences of seismic surveys on fishes: An interdisciplinary challenge

AbstractOffshore activities elevate ambient sound levels at sea, which may affect marine fauna. We reviewed the literature about impact of airgun acoustic exposure on fish in terms of damage, disturbance and detection and explored the nature of impact assessment at population level. We provided a conceptual framework for how to address this interdisciplinary challenge, and we listed potential tools for investigation. We focused on limitations in data currently available, and we stressed the potential benefits from cross‐species comparisons. Well‐replicated and controlled studies do not exist for hearing thresholds and dose–response curves for airgun acoustic exposure. We especially lack insight into behavioural changes for free‐ranging fish to actual seismic surveys and on lasting effects of behavioural changes in terms of time and energy budgets, missed feeding or mating opportunities, decreased performance in predator‐prey interactions, and chronic stress effects on growth, development and reproduction. We also lack insight into whether any of these effects could have population‐level consequences. General “population consequences of acoustic disturbance” (PCAD) models have been developed for marine mammals, but there has been little progress so far in other taxa. The acoustic world of fishes is quite different from human perception and imagination as fish perceive particle motion and sound pressure. Progress is therefore also required in understanding the nature and extent to which fishes extract acoustic information from their environment. We addressed the challenges and opportunities for upscaling individual impact to the population, community and ecosystem level and provided a guide to critical gaps in our knowledge.

The Madden‐Julian Oscillation in an Aquaplanet‐Like General Circulation Model With and Without Continents

AbstractWe have conducted experiments with the Community Atmospheric Model version 5.1 configured as an aquaplanet, with the sun at March equinox, in order to study how the model Madden‐Julian oscillation (MJO) responds to (i) the introduction of continents and (ii) realistic sea surface temperature (SST) distribution. Model results are compared with ERA‐Interim reanalysis and analyzed in terms of the moist static energy (MSE) budget to study the growth and propagation of MJO. With idealized zonally symmetric SST, the aquaplanet model produces a double Intertropical Convergence Zone (ITCZ) and an MJO‐like mode with variance at intraseasonal (30‐ to 96‐day) periods and zonal wave number 1. When we introduce continents with realistic orography and interactive surface temperature, soil moisture, and albedo, the variance of MJO is mainly confined to zonal wave numbers 1 and 2 but reduced by a factor of 3 due to weaker boundary layer moisture convergence. With prescribed climatological January SST boundary condition (which includes Indo‐west Pacific warm pool) in the presence of continents, model MJO variance is enhanced and distributed across zonal wave numbers 1 to 5, in closer agreement with observation. Thus, the presence of land by itself is not enough, but realistic SST distribution is necessary for improved space‐time characteristics of model MJO. Both in simulations and ERA‐Interim data, meridional and vertical advection of MSE promotes eastward movement of MJO. In the model experiments, meridional advection of low‐level MSE anomaly is most significant in the vicinity of the ITCZ, indicating the importance of processes that determine the location of (single or double) ITCZ.

Comparisons of Salinity Adaptation in Terms of Growth, Body Composition, and Energy Budget in Juveniles of Rainbow and Steelhead Trouts (Oncorhynchus mykiss)

This study examined the effect of different salinities (0, 5, 10, 15, 20, 25 and 30) on the growth performance and energy budget of juveniles of two different ecotypes of Oncorhynchus mykiss, landlocked rainbow trout and anadromous steelhead trout. In the 42 d experiment, fish were cultured in three replicate tanks per salinity treatment (eight fish per tank). At the end of the experiment, the growth of rainbow and steelhead trouts was significantly higher at salinities of 5 and 10, respectively, than at all other salinities. The protein, lipid and energy content of both ecotypes declined with the increase of salinity. Based on their energy budgets, the percentage of energy consumed for growth by rainbow and steelhead trouts were significantly higher at salinities of 5 (34.00% ± 1.69%) and 10 (43.76% ± 1.29%), respectively, than at all other salinities. The percentage of energy consumed for respiration by rainbow and steelhead trouts was lower at salinities of 5 (54.90% ± 1.77%) and 10 (46.73% ± 0.62%), respectively, than at all other salinities. Our results indicated that the salinity adaptation ability of juvenile steelhead trout was slightly better than that of juvenile rainbow trout, and salinities of 10 and 5, respectively, were most suitable for growth of these two fishes.

Turbulence kinetic energy budget and conditional sampling of momentum, scalar, and intermittency fluxes in thermally stratified wind farms

ABSTRACTA description of the turbulence kinetic energy budget is investigated to understand the dynamics and turbulence energy transfer between the atmospheric boundary layer and large wind farms. The turbulence kinetic energy budget terms are a dominant factor in explaining the energy supply process in wind farms. Large eddy simulations are used to generate the thermally stratified wind turbine array boundary layer, where stable and unstable conditions are considered. The wakes represent a sink of mean kinetic energy, and turbulence transport redistributes energy in the wake region. The energy balance between the budget terms is dependent on the physical location in the wind farm. During the unstable scenario, turbulence is driven by the production, transport, and buoyancy terms. Further, the contribution of the turbulence kinetic energy budget terms is reduced with increasing atmospheric stability, especially above the shear layer, where the mechanical production is the dominant term. Pressure diffusion redistributes the turbulent energy from the streamwise direction into the other components of the normal Reynolds stresses. This distinctive feature of the changing thermal stratification is presented through the quadrant analysis. The momentum ejection and sweep frequencies are both comparable and dominant. The scalar flux shows an increase in the contribution of the negative correlation in the quadrants. The quadrant analysis is extended to account for intermittency based on the pointwise Hölder exponents. Positive correlations are dominant in the wake and in higher layers of the domain for both considered cases.

Atmospheric heat advection in the Kara Sea region under main synoptic processes

Atmospheric studies document both a periodic variability in the winter temperatures in the Kara Sea region related to internal Arctic climate variability and a recent trend of winter warming—one of the strongest warming trends in the whole Arctic. This study aims to analyse side by side with other energy budget terms the contribution of horizontal heat and moisture advection to the observed recent warming. The atmospheric energy budget terms vertically integrated from the surface up to 500 hPa are estimated using the ERA‐Interim reanalysis for the period 1979–2014. The core of this study is to relate variability and changes in heat fluxes in the Kara Sea region to synoptic‐scale processes using the Russian weather‐type classification system. Singular spectrum analysis is applied to the heat flux data which were previously stratified into changes due to changes in frequency and due to changes in amplitude. We have shown that the multi‐decadal variations in the horizontal heat advection (now on a rising phase) are comparable to the positive trend in the turbulent heat fluxes due to sea ice reduction, although relatively weaker. We have also found that the changes in sensible heat flux (a constant increase in the first principal component since 1999) is a general regional feature and not related to any weather pattern, while the changes in horizontal heat advection are clearly related to the changes in frequency of the weather type A (characterized by a low‐pressure system in the central Arctic surrounded by high pressure in the continents, winds of S, S‐W direction and a positive horizontal heat advection and surface temperature anomaly over the Kara Sea) which are periodic in nature with a period of about 22 years. In recent years (at least until 2012) not only is warm air advection, associated with A type, more frequent, but it also brings much more energy from the continent to the Kara Sea compared to the reference period (1980–1990). This is most probably related to the increase in the radiatively forced surface air temperature at the source.

Turbulence kinetic energy budget in the stable boundary layer over a heterogeneous surface

This study presents turbulence kinetic energy (TKE) budget terms above tall, deciduous walnut canopy in the wintertime stable boundary layer (SBL) and makes a comparison to well‐known results of horizontally homogeneous and flat (HHF) terrain. Turbulence measurements performed at five levels above the canopy height (approximately h=18 m) enable the investigation of joint effect of the roughness sublayer (RSL) and the transition layer on the TKE budget terms. Each term of the TKE budget is investigated within the framework of local similarity theory. Kolomogorov's similarity hypothesis assumes local isotropy within the inertial subrange. Thoroughly testing the local isotropy hypothesis for the present dataset results in a ratio of the horizontal spectral densities (Sv/Su) approaching 4/3, while the ratio of the vertical to the longitudinal spectral density (Sw/Su) is less than the canonical value of 4/3 (even less than 1) for all levels indicating anisotropic turbulence even at very small scales above the canopy. As a consequence, estimated values of TKE dissipation rate (ε) from the vertical component are smaller than those obtained from the horizontal velocity components. This finding has a direct influence on the applicability of classical Kansas spectral models valid for HHF terrain as well as on the budget of wind variances. Additionally, the behavior of the non‐dimensional gradient of mean wind speed is tested with regard to conformity to z‐less scaling requirements (i.e. linear dependence on stability). It is confirmed that a stability threshold (such as Rf > 0.25, where Rf is the flux Richardson number) is a stronger determinant of z‐less behavior than the existence of a well‐defined inertial subrange ‐ opposite to observations in the SBL over ideal flat surfaces. Finally, the local equilibrium between the production and destruction of TKE within the RSL and transition layer is analyzed.

A thermodynamic paradigm for using satellite based geophysical measurements in public health applications

A thermodynamic paradigm for studying disease vector’s habitats & life cycles using NASA’s remote sensing data is being proposed. NASA’s current and planned satellite missions provide measurements of the critical environmental measures environmental state functions important to vector & disease life cycles such as precipitation, soil moisture, temperature, vapor pressure deficits, wet/dry edges, and solar radiation. Satellite data provide landscape scale process functions represented by land use/cover mapping and actual measurements of ecological functions/structure: canopy cover, species, phenology, and aquatic plant coverage. These measurements are taken in a spatial context and provide a time series of data to track changes in time. Global public health is entering a new informational age through the use of spatial models of disease vector/host ecologies driven by the use of remotely sensed data to measure environmental and structural factors critical in determining disease vector habitats, distributions, life cycles, and host interactions. The vector habitat microclimates can be quantified in terms of the surface energy budget measured by satellites. The epidemiological equations (processes) can be adapted and modified to explicitly incorporate environmental factors and interfaces required by a specific disease and its vector/host cycle. Remote sensing can be used to measure or evaluate or estimate both environment (state functions) and interface (process functions). It is critical that the products of remote sensing must be expressed in a way they can be integrated directly into the epidemiological equations.

Aerothermal Characteristics of Solid and Slitted Pentagonal Rib Turbulators

This work is an experimental study of detailed aerothermal characteristics inside a duct carrying an array of solid and permeable pentagonal ribs with a parallel and inclined slit, mounted on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, and the open area ratio fixed during experiments are 0.125%, 12%, and 25%, respectively. The heat transfer coefficient (HTC) distribution is mapped by using transient liquid crystal thermography (LCT), while the detailed flow measurements are performed by using particle image velocimetry (PIV). The primary focus of the study is to assess the influence of inter-rib region flow characteristics on the local heat transfer fields. The heat transfer and friction factor measurements are evaluated along with thermohydraulic performances at different Reynolds numbers, i.e., 26,160, 42,500, and 58,850. Performance indexes show that the pentagonal ribs with the inclined-slit are superior to other configurations from both perspective. Aerothermal features within inter-rib region were elucidated by analyzing the time-averaged streamlines, mean velocities, fluctuation statistics, vorticity, turbulent kinetic energy (TKE) budget terms, and local and spanwise-averaged Nusselt number as well as augmentation Nusselt numbers. Critical flow structures and coherent structures were identified, which illustrate about different flow dynamic processes. The flow emanating out of the inclined-slit pentagonal rib significantly affects the magnitude of streamwise velocity, fluctuation statistics, vorticity, and TKE budget terms at the downstream corner, whereas the dissipation term of TKE budget correlates well with the surface heat transfer distribution.

Experimental investigation of vertical-axis wind-turbine wakes in boundary layer flow

In this experiment, a small scale vertical-axis wind-turbine (VAWT) is immersed in a boundary-layer in a wind tunnel and stereo particle image velocimetry is employed to quantify the 3D characteristics of the wake. The measurements show that the wake is strongest behind the sector of the rotor which turns into the wind. Two counter-rotating vortex pairs in the wake induce crosswind motion which reintroduces streamwise momentum into the wake. Terms of the mean kinetic energy budget are computed and demonstrate that this crosswind flow has a significant influence on the redistribution of momentum in the wake. A similar analysis of the turbulence kinetic energy budget identifies shearing at the boundary of the wake as the primary contributor to the production of turbulence. An analytical model is developed in order to obtain a theoretical basis from which to understand how the aerodynamic behavior of VAWTs induces crosswind motion consistent with the production of counter-rotating vortex pairs.

A Case Study of Observed and Modeled Barrier Flow in the Denmark Strait in May 2015

Abstract Mesoscale barrier jets in the Denmark Strait are common in winter months and have the capability to influence open ocean convection. This paper presents the first detailed observational study of a summertime (21 May 2015) barrier wind event in the Denmark Strait using dropsondes and observations from an airborne Doppler wind lidar (DWL). The DWL profiles agree well with dropsonde observations and show a vertically narrow (~250–400 m) barrier jet of 23–28 m s−1 near the Greenland coast that broadens (~300–1000 m) and strengthens farther off coast. In addition, otherwise identical regional high-resolution Weather Research and Forecasting (WRF) Model simulations of the event are analyzed at four horizontal grid spacings (5, 10, 25, and 50 km), two vertical resolutions (40 and 60 levels), and two planetary boundary layer (PBL) parameterizations [Mellor–Yamada–Nakanishi–Niino, version 2.5 (MYNN2.5) and University of Washington (UW)] to determine what model configurations best simulate the observed jet structure. Comparison of the WRF simulations with wind observations from satellites, dropsondes, and the airborne DWL scans indicate that the combination of both high horizontal resolution (5 km) and vertical resolution (60 levels) best captures observed barrier jet structure and speeds as well as the observed cloud field, including some convective clouds. Both WRF PBL schemes produced reasonable barrier jets with the UW scheme slightly outperforming the MYNN2.5 scheme. However, further investigation at high horizontal and vertical resolution is needed to determine the impact of the WRF PBL scheme on surface energy budget terms, particularly in the high-latitude maritime environment around Greenland.