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A new computational fluid dynamics code for Large-Eddy Simulation (LES) of the atmospheric boundary layer and convection is presented and made available. A key novelty is that moist thermodynamics is formulated in terms of thermodynamic potentials, ensuring thermodynamic consistency. Despite the apparent complexity of the thermodynamic potential approach, the model's performance demonstrates that it is feasible and effective at reasonable computational cost for three-dimensional simulations. Semi-implicit semi-Lagrangian numerical methods are used; such methods are unusual for simulating boundary layer and convective flows and are more typical of global atmospheric models. Moreover, the model includes no explicit scheme to represent subgrid-scale fluxes of scalars and momentum but relies instead on the mixing and dissipation resulting from the numerical methods used; in other words, it employs Implicit LES (ILES). Sample results from several standard LES test cases show that the model's ability to capture the main aspects of the flows is comparable to other LES models. At the same time, the results highlight limitations of the ILES approach near the bottom boundary and suggest that ILES might need to be augmented in some way, for example, by distributing the convergence of surface fluxes over several model layers. Also, results for a marine stratocumulus case show a significant sensitivity to different options for the numerical methods and parameters used. Further development and application of the code would benefit from a deeper understanding of both the bottom boundary behaviour and the sensitivities to numerics. [ABSTRACT FROM AUTHOR]

We present the first analysis of frame‐indifferent (objective) fluxes and material vortices in Large Eddy Simulations of atmospheric boundary layer turbulence. We extract rotating fluid features that maintain structural coherence over time for near‐neutral, transitional, and convective boundary layers. In contrast to traditional analysis of coherent structures in turbulent boundary layers, we provide the first identification of vortex boundaries that are mathematically defined to behave as tracer transport barriers. Furthermore, these vortices are indifferent to the choice of observer reference frame and can be identified without user‐dependent velocity field decompositions. We find a strong agreement between the geometric qualities of the coherent structures we extract using our new method and classical descriptions of horizontal rolls and convective cells arising from decades of observational studies. We also quantify trends in individual vortex contributions to turbulent and advective fluxes of heat under varying atmospheric stability. Using recently developed tools from the theory of transport barrier fields, we compare diffusive momentum and heat barrier fields with the presence of rolls and cells, and determine a strong connection between heat and momentum orthogonality with the physical drivers of roll‐cell transformation. This newly employed frame‐indifferent characterization of coherent turbulent structures can be directly applied to numerical model output, and thus provides a new Lagrangian approach to understand complex scale‐dependent processes and their associated dynamics. Plain Language Summary: As uniform temperature wind flows over flat terrain that is the same temperature as the air, special eddies, called horizontal rolls, begin to appear in the wind and organize the flow into quasi‐recurrent patterns. When air flows over terrain that is much hotter than the air, the air warms and begins to rise and subsequently cool. This gives rise to a different kind of organizing structure, the convective cell, much like you see in fluids on a warm stove. The physics of the transition from roll structures to cell structures in the atmosphere is poorly understood, but important for quantifying exchanges of energy and moisture between the land, ocean, and atmosphere. In the present research, we utilize recent advances from nonlinear dynamical systems to explicitly identify the boundaries of individual coherent fluid structures, and quantify their role in the transport of momentum and heat. This gives us a new way to objectively quantify atmospheric fluxes and determine how much a certain eddy is behaving like a roll or a cell. Key Points: Lagrangian‐Averaged Vorticity Deviation (LAVD) identifies eddy boundaries in large eddy simulations of near‐neutral and convective atmospheresLAVD contour eddies exhibit specific frame‐indifferent momentum and heat transport characteristics for different atmospheric stabilitiesDifferentiating roll and convective cell type coherent structures is possible via the orthogonality of momentum and heat barrier fields [ABSTRACT FROM AUTHOR]

A vigorous development process of the deep convective boundary layer (CBL) was observed at the southern edge of the Taklimakan Desert on 6 June 2022. Based on coherent Doppler wind lidar and ERA5 data, the formation mechanism of the deep CBL exceeding 5 km was analyzed, which was mainly driven by the low-level jet (LLJ) and thermal effects. During the stage of the LLJ preceding the formation of the deep CBL, the LLJ had adequately prepared the conditions for the development of the deep CBL in terms of momentum, energy, and material. Firstly, the cold downhill airflow from the Tibetan Plateau, which leads to the formation of the LLJ, weakens the height and intensity of the temperature inversion layer, thereby reducing the energy demand for the breakdown of this layer. Secondly, the LLJ not only supplements the material and energy in the residual layer but also suppresses the exchange with the lower atmosphere. In addition, the LLJ provides a driving force for the development of the deep CBL. During the stage of thermal effects, the sensible-heat-driven air pump from the Tibetan Plateau and the passage of a cold front provide additional impetus for the development of the deep CBL. Finally, the formation of the deep CBL was catalyzed by extreme thermal effects of the underlying surface, such as the furnace effect and the atmospheric superadiabatic expansion process. The study of the development of the deep CBL is important for revealing the land–air exchange process of momentum, energy, and material between the Taklimakan Desert and the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

This study investigates analytically the stability analysis of a nonlinear convective boundary layer (BL) flow of the nanofluids GO-EG and GO-W on a shrinking surface in the presence of a magnetic field and viscous dissipation. We provide a second-order nonlinear ordinary differential equation (NODE) for temperature distribution (TD) and a third-order NODE for velocity profile (VP) coupling based on the thermophysical characteristics of the base fluid and nanofluid as well as similarity transformations (STs) in the fundamental governing equations of momentum and energy. The analytical method HAM is used to answer the equations that have been gathered. In many different industries, such as manufacturing, automotive, microelectronics, and defense, cooling of various types of equipment and devices has very important challenges. To fulfill the demands of the engineering and industrial industries, it is hoped that this issue would significantly improve the heat transformation ratio. [ABSTRACT FROM AUTHOR]

We investigated the stability of the bottom boundary layer (BBL) beneath periodic internal solitary waves (ISWs) of depression over a flat bottom through two-dimensional direct numerical simulations. We explored the convective versus absolute/global nature of the BBL instability in response to changes in Reynolds number, and the sensitivity of the instability to seeding noise in the front of the ISW – spanning laboratory to geophysical scales. The BBL was laminar at $Re_{ISW}=90$ and convectively unstable at $Re_{ISW}=300$. At laboratory-scale $Re_{ISW}=300$ , the convective wave packet was periodically amplified by each successive ISW, until vortex shedding occurred. The associated noise-amplification behaviour potentially explains the discrepancies of the critical $Re_{ISW}$ between the lock–release laboratory experiments and our Dubreil–Jacotin–Long-initialized numerical simulations as the result of the difference in background noise. Instability energy decreased under the front shoulder of the ISW, analogous to flow relaminarization under a favourable pressure gradient. At geophysical-scale $Re_{ISW}=900$ , the BBL was initially convectively unstable, and then the instability tracked with the ISW, appearing phenomenologically similar to a global instability. The simulated initial convective instability at both $Re_{ISW}=300$ and $Re_{ISW}=900$ is in agreement with local linear stability analysis which predicts that the instability group speed is always lower than the ISW celerity. Increased free stream perturbations in front of the ISW and larger $Re_{ISW}$ shift the location of vortex shedding (and enhanced bed shear stress) beneath the wave, closer to the ISW trough, thereby potentially changing the location of maximum sediment resuspension, in agreement with field observations at higher $Re_{ISW}$. [ABSTRACT FROM AUTHOR]

The convective boundary layer flow on the external surface of an iso-flux heated horizontal cylinder is investigated in this study. Under the premise of a Prandtl number Pr larger than 1, numerical simulations are conducted over a wide range of flow parameters, including variations in Rayleigh and Prandtl numbers. The present simulations demonstrate that similar to the extensively studied flat-plate boundary layer flows, development of the present curved boundary layer also consists of three states: an initial growth state, a transitional state, and a steady state. Scale laws of the characteristic velocity, boundary layer thickness, and Nusselt number Nu describing the initial and steady states are determined based on the calculated cases. The comparison suggests that the proposed scale laws could satisfactorily quantify the boundary layer flow, and the corresponding regression constants R2 are all above 0.995. The results indicate that the present characteristic velocity of the curved boundary layer depends both on time and streamwise location. Hence, the flow of the curved boundary layer follows a two-dimensional initiation, which is different from the one-dimensional growth of the flat-plate boundary layer in the initial state. The obtained scale law also indicates that the characteristic velocity of the boundary layer flow maximizes at π/2, but its thickness is circumferential location independent. In the steady state, the maximum tangential velocity occurs at approximately the central angle θ = 7π/9, and we show that this value is independent of the governing parameters. [ABSTRACT FROM AUTHOR]

The growing need for industrial development, limited availability of non-renewable energy resources, minimizing energy consumption, and ecosystem concerns has prompted researchers to explore the practical applications of two-phase nanofluid materials processing and electromagnetic energy emitted via the sun. Therefore, using two-phase nanofluids in solar thermal technology systems can enhance system performance by improving heat absorption and transfer efficiency. Owing to its usage, this study examines the magnetized two-phase nanofluid flow on a two-dimensional laminar mixed convective boundary layer with the impact of multiple slips. The flow contains an electrically conducting non-Newtonian nanofluid over a deformable (stretching/shrinking) sheet with a solar radiation effect. Also, the study utilizes a nonlinear Roseland diffusion flux approximation to incorporate the solar radiation effect, which is valid for nanofluid media with high optical density. This work utilizes similarity variables to simplify the partial derivative model into ordinary differential equations. These equations are then solved using the wavelets and Chebyshev wavelets scheme with the help of MATHEMATICA 11.3 software. According to the findings, the nanoparticle volume fraction is increased for high electrical conductivity (M = 2) and decreased for the electrically non-conducting case (M = 0). [ABSTRACT FROM AUTHOR]

The diurnal cycle of dust aerosols on Mars is studied by analyzing lidar observations at the Phoenix landing site under cloud‐ and fog‐free conditions and in the absence of elevated, long‐range transported dust layers. There is a pronounced diurnal cycle in the dust‐layer height with minimum heights of 4–6 km occurring between 11:00 and 17:00 local time. The ratio of the aerosol optical depth (AOD) within the lowermost 2 km to the total AOD reaches peak values at the same time. This can be explained by local dust emissions driven by the diurnal cycle of heating and cooling in the boundary layer. Analysis of wind and pressure measurements show that the gustiness of surface winds and the frequency of convective vortices undergo diurnal variations resembling those of AOD, indicating that these processes are the main drivers for local dust emissions. Plain Language Summary: Dust particles suspended in air are important for the radiative energy budget of Mars. By interacting with solar radiation, these aerosols impact the temperature, dynamics, and composition of the atmosphere, as well as the surface temperature of Mars. Dust aerosols are produced by wind‐lifting processes ranging from small‐scale eddies to planetary‐scale dust storms, resulting in spatially and temporally varying concentrations. Here the focus is on the diurnal cycle of dust emissions as observed by the Phoenix lander. By jointly analyzing light‐scattering observations by a lidar instrument and measurements of wind speed and air pressure, one can correlate the concentration of aerosols in air in proximity to the ground to meteorological processes. The results reveal distinct maxima in aerosol loads, the intensity of wind gusts, and the frequency of dust devils around local noon and early afternoon, and corresponding minima around midnight. This indicates that gustiness and dust devils, both fueled by solar heating during the day, are among the main causes for local dust emissions. During daytime the aerosols are concentrated at altitudes of 4–6 km. This can provide us with an indication for the degree of vertical mixing in the planetary boundary layer of Mars. Key Points: Diurnal variation of local dust emissions, wind gustiness, and convective vortices are analyzed for the entire Phoenix missionPeak values are observed in early afternoon, indicating that gustiness and convective vortices are main drivers for local dust emissionsTypical dust‐layer heights in early afternoon are 4–6 km, consistent with typical boundary‐layer heights [ABSTRACT FROM AUTHOR]

This study investigates the behavior of a mixed convective boundary layer flowing around a rigid spherical shape with non-isothermal wall temperature. The fluid assumed in this examination exhibits both incompressibility and viscosity. The major purpose is to examine the impact of the non-uniform surface temperature on the flow patterns, including velocity outlines and temperature outlines. An examination is conducted on the modified conservation equations of the boundary layer flow utilizing the local non-similarity method. The MATLAB built-in code bvp4c is used to find computational solutions. The outcomes are then shown for both air and water, specifically at a temperature of 21°C. The influence of several factors, such as the mixed convective variable λ and the exponent γ in the wall temperature function G(x), is shown in velocity and temperature profiles. In addition, the study computes the local frictional force factor and local wall heat transport factor and compares these values with results from earlier research. Significantly, the study expands upon data made around the lower stagnating point to include other sites within the sphere, thereby offering a thorough comprehension of the whole flowing field. [ABSTRACT FROM AUTHOR]

An inclined plate is being approached by a mixed convective boundary layer nanofluid flow of titanium dioxide–water through a porous medium. A numerical analysis has been done to investigate the effects of chemical reactions on the considered nanofluid flow. With the aid of a system of governing partial differential equations, a set of nonlinear ordinary differential equations for taking into consideration nanofluid flow have been derived using appropriate matching transformations. The Runge–Kutta method, as well as the Nachtsheim and Swigert Shooting method, is applied to numerically resolve the group of subsequent nondimensionalized equations. The associated numerical result was then successfully compared with the available published literature in a few unique, limited circumstances. Based on the considered nanofluid flow characteristics for heat as well as mass transfer, the effects of the Schmidt number, the permeability, and the chemical reaction parameters of the titanium dioxide–water nanofluid flow have been examined, assessed, and presented for velocity in conjunction with the local skin friction coefficient, temperature in conjunction with the local Nusselt number, as well as concentration in conjunction with the local Sherwood number. Numerical results reveal that the local Sherwood number Sh, as well as the local Nusselt number Nux, increase, whereas the local skin friction coefficient Cf decreases due to the increase in the chemical reaction parameter Krp. [ABSTRACT FROM AUTHOR]

This study emphasizes the dual exposition of the impact of convective condition and the significant effects of magnetic field, heat source and velocity slip on hybrid nanofluid flow over the exponentially shrinking sheet. The hybrid nanofluid is regarded as a contemporary variety of nanofluid; consequently, it is utilized to enhance the efficiency of heat transfer. By applying the Tiwari–Das model, the key objective of the current research is to investigate the impact of involving factors Biot number, Eckert number, volume fraction, magnetohydrodynamic (MHD), slip and suction on the temperature and velocity profiles. In addition, the Nusselt number and skin friction variations have been explored against the suction effect on the solid volume fraction of copper ϕ 2 ∈ [1–3%] and the Biot number Bi ∈ [1–3%]. The nonlinear partial differential equations are converted to a set of an ordinary differential equations by incorporating exponential similarity vectors. Eventually, ordinary differential equations are rectified utilizing MATLAB bvp4c solver. The results demonstrate the presence of dual exposition for suction with varying values of copper volume fraction and the Biot number. The heat transmission rate is observed to escalate in both cases as the strength of the Biot and Eckert numbers intensifies in the range of 1–3%. In summary, the results show that duality and non-unique solutions occur in the aiding flow situation when the suction S ≥ S ci , while there is no flow and unique solutions of hybrid nanofluid feasible when S < S ci . [ABSTRACT FROM AUTHOR]

This research study concerns an experimental, budget-friendly, electricity-powered apparatus for bench-scale fire testing. The apparatus consists of various elements, of which the most important are ceramic heating pads, used to impose heat fluxes on exposed surfaces of specimens. The test method allows to control the heating pads' temperature and to adjust the distance between the heating pads and the specimen to obtain well-defined heat fluxes up to 50–60 kW/m2. Higher heat fluxes and temperatures can be obtained by setting the heating pads in full power mode, with or without the use of a thermal shield, which can lead to heat fluxes up to 150 kW/m2. The heating and thermal boundary conditions imposed by the apparatus are characterised and discussed, and the thickness of the convective boundary layer at the heating pads' surface is estimated significantly lower than in the case of gas-fired radiant panels. The performance of the apparatus is analysed for various conditions: controlling the temperature of the heating pads, in an open environment or with the presence of thermal shields, and in full power mode. A few examples of application of the apparatus to fire test typical construction materials (steel and glass) are also presented. These results emphasise the well-defined heating conditions in temperature-controlled mode. The study finally discusses the advantages and limitations of the apparatus, as well as many possibilities of future applications and improvement for future research studies. [ABSTRACT FROM AUTHOR]

A semi-numeric study is presented to explore the nonlinear, radiative, mixed convective boundary layer flow of non-Newtonian Eyring-Powell fluid (EPF) over a porous stretching wedge in the existence of suction/injection, viscous dissipation, activated energy, and ohmic heating. The governing coupled partial differential equations (PDEs) in the flow regime are transformed into coupled ordinary differential equations (ODEs) under suitable boundary conditions (BCs). Computations are performed for variations of various pertinent parameters on velocity, temperature distribution, surface drag force, and heat transfer rate number. It is noted that with increasing Eyring Powell parameter velocity increases for stretching parameter greater than free stream velocity, but decreases when wedge stretches slowly than free stream velocity. An increase in the local non-Newtonian fluid parameter decreases velocity when the wedge stretches faster as compared to free stream velocity. However, velocity increases when the wedge stretches faster. Temperature velocity decreases for both cases of wedge stretches faster or slower as the local non-Newtonian fluid parameter increases. Similar behavior is seen in the case of Eyring Powell parameter. Increasing heat generation or absorption decreases the momentum as well as thermal boundary layer thickness. When the suction/injection parameter is enhanced the velocity shows a declines behavior for both the cases of stretching parameter as it increases. Temperature profiles decline as the mass transfer parameter is enhanced for both the case's velocity ratio parameters, respectively. Excellent agreement is achieved with the differential transform method and numerical result. [ABSTRACT FROM AUTHOR]

We investigated the combined impact of convective boundary conditions, thermal conductivity, and magnetohydrodynamic on the flow of a tangent hyperbolic nanofluid across the stratified surface. Furthermore, the ramifications of Brownian motion, thermophoresis, and activation energy were considered. Heat generation, chemical reactions, mixed convection, thermal conductivity, and other elements were considered when analyzing heat transfer phenomena. The governing equations were converted via similarity transformations into non-dimensional ordinary differential equations in order to analyze the system. Using the shooting method, the problem’s solution was determined. We showed the mathematical significance of the temperature, concentration profiles, and velocity of each fluid parameter. These profiles were thoroughly described and shown graphically. The findings demonstrated that as the Weissenberg number and magnetic number increased, the fluid velocity profile decreased. Higher heat generation and thermophoresis parameters resulted in an increase in the temperature profile. Higher Brownian motion and Schmidt parameter values resulted in a drop in the concentration profile. Tables were used to discuss the numerical values of skin friction (Cfx), Nusselt number (Nux), and Sherwood number (Shx). For the greater values of Weissenberg number and mixed convection parameters, skin friction numerical values fell while Nusselt numbers rose. [ABSTRACT FROM AUTHOR]

Measurements of ground and near surface atmospheric temperatures at Jezero obtained during 700 sols by the Mars Environmental Dynamics Analyzer (MEDA) characterize the thermal behavior of the near surface Martian atmosphere during a full Martian Year. The seasonal evolution of MEDA measurements is compared with predictions from the Mars Climate Database and the solar irradiance at the surface. Thermal tides observed in the daily cycle of temperatures follow a seasonal cycle with additional variations greater than 2 K on time‐scales of tens of sols. We also observe sol‐to‐sol variations of about 1 K in mean daily air temperatures in autumn and winter with periodicities of 4–7 sols that might be related to baroclinic disturbances that are frequent in those seasons at high latitudes. We examine the evolution of the vertical thermal gradient and temperature fluctuations without finding a seasonal response to irradiance and dust load. We find that the convective boundary layer becomes isothermal and collapses 1 hr before sunset except during northern hemisphere winter, when the collapse occurs closer to sunset, implying a longer duration of the daytime convective instability. Around this period, the rover was located in the delta front in a location of complex topography where we observed stronger thermal gradients and intense daytime air temperature fluctuations. We also find in this place a nighttime event of gravity waves on near‐surface air temperatures, with amplitudes of 2 K and periods of 10 min. These waves possibly propagate downward through a near isothermal stable layer. Plain Language Summary: The Perseverance rover on Mars is carrying a meteorological station that among other measurements obtains air temperatures at three heights near the surface as well as ground temperatures. We analyze seasonal and local changes in temperatures measured over one Martian year (687 Earth days) in which Perseverance moved several kilometers across Jezero crater, comparing in situ observations with the output from a Global Climate Model of the atmosphere of Mars. Our results show that the diurnal cycle of temperatures is modulated by the solar irradiance on the surface, the amount of dust in the atmosphere, local dynamics and large‐scale weather systems. The temperature difference between the ground and the atmosphere greatly determines the meteorology in the lower atmosphere. Neither this temperature difference, nor temperature fluctuations, which during daytime are a proxy of atmospheric convection driven by the heating of the surface, show seasonal variations in line with the seasonal solar irradiance or dust load. Instead, the rover path toward a more complex topography led to the highest surface‐to‐air temperature difference during the northern hemisphere winter, despite the solar irradiance being minimum at that time. Close to this complex topography, the meteorological station recorded oscillations in near‐surface temperature related to gravity waves. Key Points: Seasonal variations in irradiance at Mars' surface drive observed daily mean near‐surface air temperatures with some differences from modelsThermal tides and long‐period traveling waves present a clear seasonal cycle with autumn and winter seasons more prone to variabilityAir temperatures underwent non‐seasonal changes near Jezero's delta, with strong daytime convection and nighttime gravity waves [ABSTRACT FROM AUTHOR]

Over the past century, rapid urbanization has greatly altered landscapes and affected atmospheric conditions causing impacts across a wide range of sectors including human welfare, infrastructure, and ecosystems. As a result, there is a growing imperative to improve understanding of urbanization impacts on local and regional weather events and hydroclimates. This study investigates how urbanization affects precipitation and cloud fraction (CF) in the vicinity of Indianapolis. We employ multi‐month simulations using the Weather Research and Forecasting model to: (a) assess the impact of an urban area on precipitation and CF, (b) quantify how this impact varies with urban growth, and (c) examine the main mechanisms through which the city alters the local hydroclimate. Specifically, two perturbed simulations, where the urban land cover is either replaced by croplands or is increased in size, are also performed for the two rainiest months. Comparisons of the control run with no city against the perturbed runs indicate statistically significant impacts of the urban area in enhancing precipitation amounts, frequency and low‐level CF, particularly within the first 100 km radius downwind of the city boarder. The urban environment is found to increase precipitation efficiency over the city and in downwind regions. Temperature at 2 m height, planetary boundary layer height, turbulent kinetic energy, and convective available potential energy, are also enhanced in the perturbed runs and drive changes in vertical mixing, downwind precipitation amounts, frequency and low‐level height CF. All these changes appear to be a non‐linear function of the city size. Plain Language Summary: Over the past century, rapid urbanization has reshaped landscapes, influencing atmospheric circulation, and leaving profound impacts on human welfare, infrastructure, and ecosystems. Recognizing the urgency to comprehend these effects, this study contributes to an improved understanding of the influence of urbanization on precipitation amounts and cloud fraction (CF) in the surrounding areas of a metropolitan area in the United States. This work utilizes a modeling approach based on an ensemble of simulations of the Weather Research and Forecasting model. The design of our modeling experiment allows us to investigate the role of different degrees of urbanization and to decouple the urban signature from the background climate in terms of precipitation and cloud properties. Our findings reveal a statistically significant increase in low‐level CF and precipitation, particularly within the first 100 km radius downwind of the city border. Further, we identify a non‐linear relationship between size of the urban area and the associated changes in precipitation amounts, frequency, and CF. Key Points: Urban areas may modify the regional climate by altering cloud fraction (CF), rainfall patterns, and rain efficiencyStatistically significant increases in downwind low‐level CF, precipitation amounts, intensity, and frequency are identifiedUrban areas enhance turbulent mixing, convective available potential energy and rain efficiency, over the city, and in downwind regions [ABSTRACT FROM AUTHOR]

The planetary boundary layer height (PBLH) is a crucial indicator reflecting the region of the atmosphere characterized by continuous turbulence. Here, we use radiosonde and surface meteorological observations (4–7 times per day, year‐round measurements) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition to derive the PBLH (PBLHMOSAiC), and further evaluate the PBLH from the ERA5 reanalysis (PBLHERA5). Comparisons between PBLHMOSAiC and PBLHERA5 from different perspectives reveal that: (a) The overestimation of PBLHERA5 when the sea ice concentration is >90% is significant with the centered root mean squared error reaching up to 201 m; (b) The difference between the two products is notably pronounced in cold seasons, while it is comparatively diminished in warm seasons; (c) In neutral boundary layers, differences in PBLHERA5 are larger compared with stable and convective boundary layers. In addition, the analysis of error sources indicates that the bias of PBLHERA5 is sensitive to the bias of vertical thermal structure and wind speed profiles in ERA5 data sets in all conditions. Finally, we find a Random Forest model effectively reduces the bias of PBLHERA5 with the index of agreement reaching up to 0.71 in the test data set, while a multiple linear regression demonstrates comparable performance to the Random Forest model. Plain Language Summary: The planetary boundary layer (PBL) is a crucial component in the interactions between the atmosphere and the surface, especially for the shallow PBL in the Arctic. However, the scarcity of observations over the central Arctic limits our understanding of physical characteristics of the Arctic boundary layer, and current research relies heavily on atmospheric reanalysis. This study focuses on evaluating the planetary boundary layer height (PBLH) of ERA5 over the Arctic sea‐ice surface using observations collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. We find the PBLHERA5 is often overestimated, especially with high sea ice concentrations and in cold seasons. Additionally, the PBLHERA5 performs comparatively worse against observations in neutral boundary layers when contrasted with stable and convective boundary layers. Analysis of error sources reveals the PBLHERA5 bias is sensitive to vertical thermal structure and wind speed profiles in ERA5 data sets under all conditions. To rectify the errors in the PBLHERA5, we employ a Random Forest model, significantly improving PBLHERA5's accuracy. Our model‐corrected PBLHERA5 shows strong agreement with observations, providing a more reliable representation of PBLH. This study highly enhances our understanding of the performance of the Arctic atmospheric boundary layer structure in ERA5 data sets. Key Points: The MOSAiC observations are employed to comprehensively assess the ERA5 planetary boundary layer height (PBLH) performance in the ArcticThe bias of the ERA5 PBLH is more sensitive to biases in temperature and wind speed profiles than to biases in specific humidity profileThe random forest model can reduce the ERA5 PBLH bias with the index of agreement reaching up to 0.71 in the test data set [ABSTRACT FROM AUTHOR]

AbstractThe nanofluids exclusively enhance the thermal significance of many engineering and industrial processes including the manufacturing processes, chemical reactions, polymers, thermal devices, heating systems, solar energy etc. The presence of porous medium and suction/injection phenomenon incorporates key importance in the petroleum engineering and plasma physics. The objective of current work is to present a theoretical analysis for investigating the bioconvective flow of Maxwell nanofluid with applications of suction/injection effects. The flow is causing by porous moving surface. The radiative phenomenon with nonlinear expressions is adopted. The chemical reaction features are used for analysis of concentration phenomenon. Modified Cattaneo–Christov approach is followed to model the problem. A set of dimensionless variables are used for simplifying the modeled equations. The solution procedure is subject to implementation of shooting scheme. Graphical explanation of problems is presented in order to evaluates the role of different parameters. Physical behavior of problem is focused and justified in details. It is noted that heat and mass transfer enhances due to suction/injection parameter. The temperature profile reduces due to thermal relaxation parameter. Current results reveal significance in the ehat exchangers, improving the sustainability of thermal systems, controlling the cooling processes, fertilizes, biofuels etc. [ABSTRACT FROM AUTHOR]

The present study introduces "WindAware", a wind and turbulence prediction system that provides nowcasts of wind and turbulence parameters every 5 min up to 6 h over a predetermined airway over Chicago, Illinois, USA, based on 100 m high-resolution simulations (HRSs). This system is a long short-term memory-based recurrent neural network (LSTM-RNN) that uses existing ground-based wind data to provide nowcasts (forecasts up to 6 h every 5 min) of wind speed, wind direction, wind gust, and eddy dissipation rate to support the Uncrewed Aircraft Systems (UASs) safe integration into the National Airspace System (NAS). These HRSs are validated using both ground-based measurements over airports and upper-air radiosonde observations and their skill is illustrated during lake-breeze events. A reasonable agreement is found between measured and simulated winds especially when the boundary layer is convective, but the timing and inland penetration of lake-breeze events are overall slightly misrepresented. The WindAware model is compared with the classic multilayer perceptron (MLP) and the eXtreme Gradient Boosting (XGBoost) models. It is demonstrated by comparison to high-resolution simulations that WindAware provides more accurate predictions than the MLP over the 6 h lead times and has almost similar performance as the XGBoost model although the XGBoost's training is the fastest using its parallelized implementation. WindAware also has higher prediction errors when validated against lake-breeze events data due to their under-representation in the training dataset. [ABSTRACT FROM AUTHOR]

AbstractNon-Newtonian flow from wedges is a vital problem in coatings, polymer processing etc. Hence the main aim is to investigate the convective boundary layer flow of micropolar hybrid nanofluid (MHN)from a wedge. It is assumed that the wedge surface is isothermal. The Eringen model is employed to define micropolar fluid. Nanoscale Tiwari–Das formulations are used to study the specific effects of nanoparticles and volume fractions. The dimensionless boundary value problem arises by suitable coordinate transformations as a system of nonlinearly coupled ordinary differential equations. The so-called Falkner Skan flow case is resolved. Dimensionless, transformed, coupled momentum, microrotation, boundary layer equations are resolved using the numerical scheme MATLAB bvp4c. The parameteric investigations are performed on hybrid nanofluids using water as the basis liquid and varying volume fractions from 0 to 8%. Affirmation with previous work is done. The consequence of Eringen micropolar parameter, Hartree pressure gradient parameter, nanoparticle volume fraction, Eckert number, heat absorption (sink) parameter, on the flow and physical characteristics are visualized graphically and in tables. With rising material factor and volume fraction of nanoparticle, temperature is markedly enhanced. Increases in volume fraction dampen angular velocity close to the wedge surface, while farther from the wall, the opposite effect is seen. Temperature and thermal boundary layer thickness are both greatly enhanced by increasing Eckert number. With an increase in the volume proportion of nanoparticles, velocity decreases. Heat generation raises temperatures while a heat sink lowers them. The pressure gradient parameter increases skin friction while decreasing Nusselt number. Nusselt number for hybrid nanofluid is higher than for nanofluid. [ABSTRACT FROM AUTHOR]

A mathematical model is presented for magnetohydrodynamic viscous incompressible flow of an electrically conducting Newtonian polymeric fluid from a moving permeable horizontal stretching sheet with variable magnetic field, momentum and thermal slip boundary conditions. The emerging nonlinear ordinary differential boundary value problem is solved numerically by the Runge-Kutta-Fehlberg fourth-fifth order numerical method in Maple symbolic software. The effects of the governing parameters on the dimensionless stream function, dimensionless flow velocity and the dimensionless temperature have been investigated, displayed graphically and discussed. It is found that greater momentum slip and magnetic field parameters reduce the dimensionless velocity. It is further observed that higher values of Prandtl number, thermal slip, and conductionradiation parameter (weaker radiation contribution) reduce the dimensionless temperature whilst stronger magnetic field increases the temperature due to the supplementary work expended in dragging the polymer against the action of the magnetic field which is dissipated as heat. Comparisons of numerical results with previous published results show an excellent agreement. The study finds applications in electro-conductive polymer (ECP) processing systems. [ABSTRACT FROM AUTHOR]

AbstractThe mixed convective transport in a vertically shear-driven square cavity with a rotating circular porous cylinder is investigated numerically in two dimensions. This study aims to enhance the understanding of heat distribution within a closed environment containing intricate electronic systems and heat exchangers by employing a porous media modeling approach. The vertical walls of the enclosure are kept isothermal, while both the horizontal walls are assumed to be adiabatic. Upward progress is being made by the left wall at a constant translational speed. The porous circular cylinder is inserted within the square cavity concentrically, which is then rotated both clockwise and counter-clockwise. While the Reynolds number based on the motion of the lid is maintained constant at Re = 100, the porosity of the cylinder fluctuates in accordance with the Darcy number range 10−6 ≤ Da ≤ 10−2 The streamline and the isotherm patterns for a range of controlling factors, including the Richardson number (0.5 ≤ Ri ≤ 10) and the dimensionless rotational speed (−5≤Ω≤5) are used to show how the flow and the thermal fields within the enclosure evolve. Additionally, the entropy generation is calculated and compared for the above mentioned parameters. The irreversibility generation as well as the flow and the heat transfer phenomena are observed to be significantly influenced by the rotation and the porosity of the cylinder. [ABSTRACT FROM AUTHOR]

Industry and space technology have significant issues managing heat energy and controlling mass dispersion. The purpose of this study is to develop motion caused by boundary layer thickness sheets that are increasingly being used in various engineering fields (civil engineering, mechanical, aeronautical, maritime processes and constructions). The activation energy is a critical factor in chemical reactions due to the existence of many applications in gas-cooled reactors, nuclear thermal rockets and liquid-fluoride reactors. This study presents the numerical analysis of activation energy on three dimensional (3D) nanofluid (NFs) motion via Stretching Surface (SS) with nonlinear thermal radiation effect. This is in contrast to the conventional slip condition, convective condition applied at surface. The governing basic equations are translated into nonlinear ODEs by suitable similarity transformations. The relevant boundary value problem was explored for a numerical solution for applying the MATLAB based on Runge–Kutta–Fehlberg (RKF) scheme via shooting technique. The major outcomes of current work have more concentration (ϕ (η 1)) and Mass Transfer Rate ( Sh x Re x − 1 ∕ 2 ) for various numerical values of Activation Energy ( E A ). The present solutions determine very good correlation with the previously studied ones in a special case as predicted in the tables. [ABSTRACT FROM AUTHOR]

We study the stability of a zero-pressure gradient boundary layer subjected to free-stream disturbances by means of local stability analysis. The dataset under study corresponds to a direct numerical simulation (DNS) of a flat plate with a sharp leading edge in realistic wind tunnel conditions, with a turbulence level of 3.45% at the leading edge. We present a method to track the convective evolution of the secondary instabilities of streaks by performing sequential stability calculations following the wave packet, connecting successive unstable eigenfunctions. A scattered nature, in time and space, of secondary instabilities is seen in the stability calculations. These instabilities can be detected before they reach finite amplitude in the DNS, preceding the nucleation of turbulent spots, and whose appearance is well correlated to the transition onset. This represents further evidence regarding the relevance of secondary instabilities of streaks in the bypass transition in realistic flow conditions. Consistent with the spatio-temporal nature of this problem, our approach allows us to integrate directly the local growth rates to obtain the spatial amplification ratio of the individual instabilities, where it is shown that instabilities reaching an N-factor in the range [2.5,4] can be directly correlated to more than 65% of the nucleation events. Interestingly, it is found that high amplification is not only attained by modes with high growth rates, but also by instabilities with sustained low growth rates for a long time. [ABSTRACT FROM AUTHOR]

A global transient linear stability analysis of the three-dimensional time-dependent flow around an aerofoil undergoing small-amplitude pitching motion is performed using the optimally time-dependent (OTD) framework. The most salient linear instabilities associated with the instantaneous basic state are computed and tracked over time. The resulting OTD modes reflect the variations in the basic state and can be used as predictors of its spatial and temporal evolution, including the formation of a laminar separation bubble and its gradual spanwise modulation via primary global instability, leading to secondary instability and finally rapid breakdown to turbulence. The study confirms and expands upon earlier stability analyses of the same case based on the local properties of spanwise averaged velocity profiles in the bubble that predicted the onset of absolute instability soon followed by rapid breakdown of the separation bubble. The three-dimensional structure of the most unstable OTD mode is extracted, which compares well with both the locally absolutely unstable mode and the evolution of the basic state itself. [ABSTRACT FROM AUTHOR]

Large-eddy simulations are used to evaluate mean profile similarity in the convective boundary layer (CBL). Particular care is taken regarding the grid sensitivity of the profiles and the mitigation of inertial oscillations in the simulation spin-up. The nondimensional gradients ϕ for wind speed and air temperature generally align with Monin–Obukhov similarity across cases but have a steeper slope than predicted within each profile. The same trend has been noted in several other recent studies. The Businger-Dyer relations are modified here with an exponential cutoff term to account for the decay in ϕ to first-order approximation, yielding improved similarity from approximately 0.05 z i to above 0.3 z i , where z i is the CBL depth. The necessity for the exponential correction is attributed to an extended transition from surface scaling to zero gradient in the mixed layer, where the departure from Monin–Obukhov similarity may be negligible at the surface but becomes substantial well below the conventional surface layer height of 0.1 z i . [ABSTRACT FROM AUTHOR]

Efficient heat transfer technologies are critical in a wide range of industrial applications, including air conditioning, chemical reactors, and heat exchangers. One method for improving heat transfer performance is to use twisted tape inserts in heat exchanger tubes. Heat transmission is aided by the disturbance of fluid flow caused by these inserts, although research is still ongoing to establish the specific design components that maximize their efficacy. The research focuses on heat transfer optimization in practical applications by exploring hexagonal perforated twisted tape inserts with varied cut orientations (horizontal, vertical, and alternate) and a pitch ratio of 4. The problem becomes more complex without a complete numerical prediction model. The study seeks to construct a hybrid deep neural network based on a gannet optimization algorithm (DNN-GOA) model in order to estimate heat transfer performance accurately. According to the experimental results, the TTA's specific design with alternate cuts produces a thinner thermal boundary layer and a higher convective heat transfer coefficient for Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). The Hybrid DNN-GOA model has the best predictive performance, with a high R2 indicating a tight match between anticipated and real Nu, f, and TPF values. It also exhibits the lowest Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), and Mean Squared Error (MSE), confirming its exceptional accuracy. [ABSTRACT FROM AUTHOR]

The purpose of this study is to provide a mathematical model of the process of entropy formation that occurs during the MHD convective transport of Carreau fluid across a curved stretched surface with soret and dufour effects. The energy equation is explored with the combined characteristics of joule heating, viscous dissipation and heat absorption/generation. The modeled governing equations are converted into nonlinear ordinary differential equations using similarity variables, and the results are acquired through the utilization of the built-in command NDSolve. It is revealed that entropy generation and Bejan number increase for higher values of Brinkman number. The impact of the Hartman number increase the entropy generation and reduced the Bejan behavior. The curvature parameter reduced the flow and temperature of fluid but increased the concentration profile. A small change in the heat absorption parameter strengthens the temperature profile. Graphical representations are used to discuss the behavior of Bejan number, entropy generation, velocity, temperature, and concentration profiles for the different values of physical parameters. The results of computations of drag force, the local nusselt number, and the Sherwood number are shown in tabular form for numerous values of the parameters. [ABSTRACT FROM AUTHOR]

Turbulence parametrizations will remain a necessary building block in kilometer‐scale Earth system models. In convective boundary layers, where the mean vertical gradients of conserved properties such as potential temperature and moisture are approximately zero, the standard ansatz which relates turbulent fluxes to mean vertical gradients via an eddy diffusivity has to be extended by mass‐flux parametrizations for the typically asymmetric up‐ and downdrafts in the atmospheric boundary layer. We present a parametrization for a dry and transiently growing convective boundary layer based on a generative adversarial network. The training and test data are obtained from three‐dimensional high‐resolution direct numerical simulations. The model incorporates the physics of self‐similar layer growth following from the classical mixed layer theory of Deardorff by a renormalization. This enhances the training data base of the generative machine learning algorithm and thus significantly improves the predicted statistics of the synthetically generated turbulence fields at different heights inside the boundary layer, above the surface layer. Differently to stochastic parametrizations, our model is able to predict the highly non‐Gaussian and transient statistics of buoyancy fluctuations, vertical velocity, and buoyancy flux at different heights thus also capturing the fastest thermals penetrating into the stabilized top region. The results of our generative algorithm agree with standard two‐equation mass‐flux schemes. The present parametrization provides additionally the granule‐type horizontal organization of the turbulent convection which cannot be obtained in any of the other model closures. Our proof of concept‐study also paves the way to efficient data‐driven convective parametrizations in other natural flows. Plain Language Summary: Even though global simulations of the Earth system on monthly timescales reach now resolutions of 2.5 km, essential turbulent transport processes in the lowest part of the atmosphere still have to be modeled. Here, we implement a machine learning‐based mass‐flux parametrization of the subgrid‐scale heat flux for a shear‐free dry atmospheric boundary layer by a generative adversarial network. Training data and prediction capability of the algorithm are increased by incorporating the physics of boundary layer growth following from classical mixed layer similarity theory. Our model is compared successfully to standard mass‐flux parametrizations based on an equation model. It is additionally found to reproduce the intermittent fluctuations of the convective buoyancy flux and the horizontal organization of the transiently evolving turbulence correctly. Key Points: A generative adversarial network produces the subgrid‐scale buoyancy flux for a transiently growing dry convective boundary layerThe training data are enhanced by renormalizing simulation snapshots in correspondence with the self‐similar growth by mixed‐layer theoryThe algorithm generates data with the right spatial patterns and non‐Gaussian statistics, and agrees with standard parametrizations [ABSTRACT FROM AUTHOR]

Deserts play an important role in the climate system, which is closely associated with the emission and transport of dust aerosols. Based on the intensive observation experiment in the Taklimakan Desert, the potential physical processes between the deep convective boundary layer (CBL) and dust emission are revealed in this study. Deep CBL enables the formation of clouds in the late afternoon, leading to significant cooling of surface. Large‐scale buoyant coherent structures thereby transform into the mechanical coherent structures confined near the surface. The responses promote the earlier occurrence of low‐level jet (LLJ) than in cloudless conditions, which allows the downward transport of LLJ momentum and substantially increases surface wind. Therefore, dust emission is initiated by strong wind at dusk and lasts for several hours. The results are useful to predict dust emissions and improve our understanding of distinctive boundary‐layer processes in desert regions. Plain Language Summary: Desert is a key component of regional/global climate system, which is closely associated with the emission and transport of dust aerosols. A better understanding of dust emission mechanisms and their interaction with atmospheric physical processes is of great significance for improving numerical weather and climate models. This study investigates possible physical mechanisms of the dust emission related to deep atmosphere boundary layer, based on the field experiment in the Taklimakan Desert. It is found that the formation of late‐afternoon clouds and the occurrence of wind maxima at 400–600 m are crucial during the processes. Initially, the formation of clouds is enabled by deep atmosphere boundary layer that developed in the late afternoon. After cloud formation, surface becomes cooling, and then the upper part of the boundary layer is gradually released from the surface frictional restraint, which promotes the development of wind maxima at 400–600 m. As the momentum of the wind maxima is transported downwards, surface wind substantially increases, which systematically blows dust particles up. Consequently, dust emission happens at dusk in desert regions. Key Points: Deep convective boundary layer enables the lifting condensation of moisture and the formation of boundary‐layer clouds in desert regionsThe emergence of late‐afternoon clouds strengthens the surface cooling and thus advances the development of low‐level jetDownward momentum transfer from low‐level jet to near‐surface wind is crucial to initiate dust emission at dusk [ABSTRACT FROM AUTHOR]

Doppler lidar (DL) applications with a focus on turbulence measurements sometimes require measurement settings with a relatively small number of accumulated pulses per ray in order to achieve high sampling rates. Low pulse accumulation comes at the cost of the quality of DL radial velocity estimates and increases the probability of outliers, also referred to as "bad" estimates or noise. Careful filtering is therefore the first important step in a data processing chain that begins with radial velocity measurements as DL output variables and ends with turbulence variables as the target variable after applying an appropriate retrieval method. It is shown that commonly applied filtering techniques have weaknesses in distinguishing between "good" and "bad" estimates with the sensitivity needed for a turbulence retrieval. For that reason, new ways of noise filtering have been explored, taking into account that the DL background noise can differ from generally assumed white noise. It is shown that the introduction of a new coordinate frame for a graphical representation of DL radial velocities from conical scans offers a different perspective on the data when compared to the well-known velocity–azimuth display (VAD) and thus opens up new possibilities for data analysis and filtering. This new way of displaying DL radial velocities builds on the use of a phase-space perspective. Following the mathematical formalism used to explain a harmonic oscillator, the VAD's sinusoidal representation of the DL radial velocities is transformed into a circular arrangement. Using this kind of representation of DL measurements, bad estimates can be identified in two different ways: either in a direct way by singular point detection in subsets of radial velocity data grouped in circular rings or indirectly by localizing circular rings with mostly good radial velocity estimates by means of the autocorrelation function. The improved performance of the new filter techniques compared to conventional approaches is demonstrated through both a direct comparison of unfiltered with filtered datasets and a comparison of retrieved turbulence variables with independent measurements. [ABSTRACT FROM AUTHOR]

A computational analysis is performed to scrutinize the stimulus of an aligned magnetized force and radiative flux on the unsteady magneto-flow of ZnO + H2O nanoliquid across a varied thickness extending surface in the attendance of convective edge constraints. The prime motive of this exploration is to confer the best thermal transfer enactment nanomodel among Maxwell and Xue nanomodels. The arising system of PDE's are exercised by adopting suitable similarities to attain the no-dimension ODE's and the solutions are attained by implementing the built-in bvp5c MATLAB package. The energy equation is encompassed by Buongiorno slip mechanism, viscous dissipation, and radiative flux. Further, the flow, thermal, and concentration gradients are illustrated graphically. The major upshots imply that the radiative flux and thermal Biot number efficiently augment the Nusselt number in both situations. Also, the energy transport rate is noticeably 4% large in the Maxwell nanomodel when equated to Xue nanomodel. [ABSTRACT FROM AUTHOR]

The atmospheric boundary layer is a key region for human activities and the interaction of various layers and is an important channel for the transportation of momentum, heat, and various substances between the free atmosphere and the surface, which has a significant impact on the development of weather and climate change. During the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) in June 2022, utilizing the comprehensive stereoscopic observation experiment of the "Plateau Low Vortex Network", this study analyzed the variation characteristics and influencing factors of the atmospheric boundary layer height (ABLH) at three stations with different underlying surface types on the Qinghai–Tibet Plateau (QTP): Qumalai Station (grassland), Southeast Tibet Observation and Research Station for the Alpine Environment (SETORS, forest), and Sieshan Station (cropland). The analysis utilized sounding observation data, microwave radiometer data, and ERA5 reanalysis data. The results revealed that the temperature differences between the sounding observation data and microwave radiometer data were minor at the three stations, with a notable temperature inversion phenomenon observed at Sieshan Station. Regarding water vapor density, the differences between the sounding observation data and microwave radiometer data were relatively small at Sieshan Station. The relative humidity increased with height at Sieshan Station, whereas it increased and then decreased with height at SETORS and Qumalai Station. The ABLH at all sites reached its maximum value around noon, approximately 1500 m, and exhibited mostly convective boundary layer (CBL) characteristics. During the night, the ABLH mostly showed a stable boundary layer (SBL) pattern, with heights around 250 m. In summer, latent heat flux (LE) and sensible heat flux (H) in the eastern plateau were generally lower than those in the western plateau except at 20:00, where they were higher. Vertical velocity (w) in the eastern plateau was greater than in the western plateau. Among Sieshan Station and SETORS, LE, and H had the most significant impact on ABLH, while at Qumalai Station, ABLH was more influenced by surface long-wave radiation (Rlu). These four influencing factors showed a positive correlation with ABLH. The impact of different underlying surface types on ABLH primarily manifests in surface temperature variations, solar radiation intensity, vegetation cover, and terrain. Grasslands typically exhibit a larger range of ABLH variations, while the ABLH in forests and mountainous cropland areas is relatively stable. [ABSTRACT FROM AUTHOR]

This paper examines the impacts of a nonlinearly expanding sheet on velocity, heat and mass transport for a Suttery hybrid nanoliquid (mixture of Sutterby fluid and Al 2 O 3 and Cu). The zero-mass flux concentration and convective boundary conditions are considered. Nondimensionalization of governing equations may be achieved through similarity conversions. The governing equations are solved utilizing the Optimal Homotopy Analysis Method. Graphs and tables were used to document the effects of different variables. The numerical values for skin friction, Sherwood number and Nusselt number are provided in a table for diverse relevant factors. Comparisons were made to a previous study's findings. The results obtained are in agreement with the findings of the prior study. The outcome is that the occurrence of hybrid nanoparticles ( Al 2 O 3 and Cu) in ethylene glycol liquid enhances its thermal conductivity thereby increasing the thermal boundary layer thickness. The presence of hybrid nanoparticles ( Al 2 O 3 and Cu) in ethylene glycol liquid also increases the momentum boundary layer thickness. [ABSTRACT FROM AUTHOR]

Dust devils are vertically oriented, columnar vortices that form within the atmospheric convective boundary layer (CBL) of dry regions. They are able to lift a sufficient amount of soil particles including dust to become visible and are considered as a potentially important dust source for the atmosphere. Mineral dust, a key component of atmospheric aerosols, influences the climate by affecting the radiation budget and cloud formation. Current estimates of the contribution of dust devils to the global, regional, and local dust release vary considerably from less than 1% to more than 50%. To address this uncertainty, we perform the highest resolved large‐eddy simulation (LES) study on dust emission in the CBL to date, using the PALM model system and the saltation‐based Air Force Weather Agency (AFWA) dust emission scheme. Our results show that under desert‐like conditions, dust devils are responsible for an average of 5% of regional dust emissions, with temporary maxima of up to 15%. This contrasts with previous measurement‐based (>35%) and LES‐based estimates (∼0.1%). Local emissions of dust devils (up to 10 mg m−2 s−1) are 1–3 orders of magnitude higher than the emission in the surroundings. This makes dust devils important for air quality and visibility. Additionally, our study reveals previously unknown large‐scale convective dust emission patterns. These patterns are tied to the CBL's cellular flow structure and are the main cause of dust release. Contrary to other studies, our findings clarify the important role of saltation‐induced dust emission. Plain Language Summary: Dust devils, vertically oriented convective vortices frequently observed in arid and semi‐arid regions, are potential contributors to the atmospheric dust. This airborne dust has significant implications for climate, as it can alter the radiation budget and influence cloud formation. The exact proportion of atmospheric dust originating from dust devils is currently under debate, with widely varying estimates. To address this uncertainty, we used an advanced turbulence‐resolving large‐eddy simulation model, the PALM model system, combined with the saltation‐based Air Force Weather Agency's dust emission scheme. Our results showed that under desert‐like conditions, dust devils account for an average of 5% of regional dust emissions. Peaks can reach up to 15%. Notably, these figures challenge both previous measurement and simulation‐based assessments. Additionally, our study found that dust devils produce local dust emission fluxes up to 1–3 orders of magnitude higher than ambient values. This suggests a notable effect on air quality and visibility. Moreover, we identified large‐scale patterns of dust emission linked to the flow structure of the convective boundary layer. These patterns emerge as the primary contributors to the regional dust release. Our study underscored the importance of understanding saltation‐induced dust emission and the role of dust devils in the atmosphere. Key Points: Dust devils cause peak dust emission fluxes of 46.7 mg m−2 s−1, which is 1–2 orders of magnitude larger than previous numerical estimatesDust devils contribute an average of 5% to the total dust emission of the simulated domain, with instantaneous contributions of up to 15%Saltation‐induced dust emission is arranged in large‐scale patterns that are related to the polygonal convection cells of the boundary layer [ABSTRACT FROM AUTHOR]

The radiative effects of biomass burning aerosols (BBAs) on low-level atmospheric circulation over southern Africa are investigated on 5 September 2017 during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) field campaign. This is conducted using a variety of in situ and remote sensing observations, as well as two 5 d ensemble simulations made with the Meso-NH mesoscale model, one including the direct and semi-direct radiative effects of aerosols and one in which these effects are not included. We show that the radiative impact of BBA building up over a period of 5 d in the Meso-NH simulations can lead to significantly different circulations at low and middle levels, thereby affecting dust emissions over southern Namibia and northwestern South Africa as well as the transport of BBA in a so-called "river of smoke". While most of the regional-scale dynamics, thermodynamics and composition features are convincingly represented in the simulation with BBA radiative effects, neglecting the radiative impact of BBA leads to unrealistic representations of (i) the low-level jet (LLJ) over the plateau, which is the main low-level dynamic feature fostering dust emission, and (ii) the mid-level dynamics pertaining to the transport of BBA from the fire-prone regions in the tropics to the mid-latitudes. For instance, when the BBA radiative impacts are not included, the LLJ is too weak and not well established over night, and the developing convective planetary boundary layer (PBL) is too deep compared to observations. The deeper convective PBL over Etosha and surrounding areas is related to the enhanced anomalous upward motion caused by the eastern displacement of the river of smoke. This eastern displacement is, in turn, related to the weaker southerly African easterly jet. Both ensemble simulations provide clear evidence that the enhanced near-surface extinction coefficient values detected from observations over Etosha are related to the downward mixing of BBA in the developing convective boundary layer rather than dust being emitted as a result of the LLJ breakdown after sunrise. This study suggests that the radiative effect of BBAs needs to be taken into account to properly forecast dust emissions in Namibia. [ABSTRACT FROM AUTHOR]

Many real‐world devices, such as heat exchangers, geothermal reservoirs, and cooling systems, utilize the concept of boundary layer flow across a cone geometry. The current study presents and analyses the mathematical formulation for the mixed convection flow of a hybrid nanofluid over a permeable stationary cone. The heat transfer analysis considers the effects of thermal radiation and convective boundary condition. Numerical and statistical analyses of this flow problem yield new, physically significant results. The numerical analysis is carried out using the bvp4c solver in Matlab. Similarity transformations are performed to obtain a system of nonlinear ordinary differential equations from the governing partial differential equations and boundary conditions. In both assisting and opposing flows, spherical‐ and platelet‐shaped nanoparticles are observed to produce the lowest and highest local skin friction coefficient, respectively. The spherical‐ and blade‐shaped nanoparticles also offer the highest and lowest local Nusselt number, respectively, with a difference of 6.4% (assisting) and 6.03% (opposing). Meanwhile, the increase in the mixed convection parameter raised the velocity profile but diminished the temperature profile of the hybrid nanofluid. Then, the relationship of the Biot number (Bi)$({Bi})$, suction (S)$(S)$, and thermal radiation (R$(R$) parameters with the local Nusselt number is investigated through the response surface methodology (RSM). The local Nusselt number for the current flow problem is estimated to be maximized at 0.814323 (assisting) and 0.814629 (opposing) when these parameters are at the highest range of S=2.0$S\ = \ 2.0$, R=1.0$R\ = \ 1.0$, and Bi=0.5$Bi\ = \ 0.5$. Several researchers had presented experimental studies conducted at different temperatures (15, 25, 35°C), mass flow rates (ranging from 0.00076 to 0.041 kg/s), and nanoparticle concentrations (0.387, 0.992, 3.12, 4.71 mass%). [ABSTRACT FROM AUTHOR]

The present analysis intends predominantly to explore the multiple behaviors of radiating ethylene glycol‐based titanium dioxide nanofluids during their steady boundary layer flows near a vertical permeable surface under the prominent impacts of uniform blowing and nonuniform internal heating processes. By incorporating the dynamical contribution of Lorentz and buoyancy forces in the momentum equation and adopting the single‐phase nanofluid approach along with the constitutive equations of the second‐grade rheological model and Corcione's correlations, the governing partial differential equations and their appropriate boundary conditions are derived mathematically based on the boundary layer theory and other admissible physical approximations. After several simplifications, the aforesaid differential formulation is converted into a set of ordinary differential equations and realistic boundary conditions, which are solved thereafter numerically using GDQ's‐NT method. Moreover, it is demonstrated that the strengthening in the blowing and internal heating processes has a boosting effect on the velocity and temperature profiles. However, the other influencing parameters show dissimilar dynamical and thermal trends. Furthermore, it is witnessed that the mixed convective heat transfer, the viscoelasticity trend of the nanofluidic medium, and the nanoparticles' loading exhibit an enhancing impression on the surface heat transfer rate. [ABSTRACT FROM AUTHOR]

This research examines the flow of 2D micropolar fluid across an inclined linear shrinking/stretching surface with suction, convective, slip and thermal radiation impact. The governing partial differential equations (PDEs) are transformed into an ordinary differential equations (ODEs) system using a linear similarity transformation, and the bvp4c technique is then used to solve the ODEs system in MATLAB. Comparisons of both solutions are presented. The effects of regulating flow parameters on dimensionless temperature profiles, angular velocity, velocity, skin friction, wall couple stress and heat transfer are shown graphically. Stable velocity profiles are inversely related to velocity slip and material parameter. For a given suction and stretching/shrinking parameter value, graphs show double solutions. The couple stress and skin friction in the first solution, drop then increase as the material parameter K increases. Critical points of the stretching/shrinking parameter, λ c i ≥ λ where both solutions occur, are indicated by the symbols λ c i (i.e., i = 1 , 2 , 3) , and that there is no solution when λ c i > λ. A table summarizes the stability study's results and highlights. [ABSTRACT FROM AUTHOR]

Long time series of observations of atmospheric dynamics and composition are collected at the French Pyrenean Platform for Observation of the Atmosphere (P2OA). Planetary boundary layer depth is a key variable of the climate system, but it remains difficult to estimate and analyse statistically. In order to obtain reliable estimates of the convective boundary layer height (Zi) and to allow long-term series analyses, a new restitution algorithm, named CALOTRITON, has been developed. It is based on the observations of an ultra-high-frequency (UHF) radar wind profiler (RWP) from P2OA with the help of other instruments for evaluation. Estimates of Zi are based on the principle that the top of the convective boundary layer is associated with both a marked inversion and a decrease in turbulence. Those two criteria are respectively manifested by larger RWP reflectivity and smaller vertical-velocity Doppler spectral width. With this in mind, we introduce a new UHF-deduced dimensionless parameter which weighs the air refractive index structure coefficient with the inverse of vertical velocity standard deviation to the power of x. We then search for the most appropriate local maxima of this parameter for Zi estimates with defined criteria and constraints such as temporal continuity. Given that Zi should correspond to fair-weather cloud base height, we use ceilometer data to optimize our choice of the power x and find that x=3 provides the best comparisons. The estimates of Zi by CALOTRITON are evaluated using different Zi estimates deduced from radiosounding according to different definitions. The comparison shows excellent results with a regression coefficient of up to 0.96 and a root-mean-square error of 71 m, which is close to the vertical resolution of the UHF RWP of 75 m, when conditions are optimal. In more complex situations, that is when the atmospheric vertical structure is itself particularly ambiguous, secondary retrievals allow us to identify potential thermal internal boundary layers or residual layers and help to qualify the Zi estimations. Frequent estimate errors are observed nevertheless; for example, when Zi is below the UHF RWP first reliable gate or when the boundary layer begins its transition to a stable nocturnal boundary layer. [ABSTRACT FROM AUTHOR]

The concept of heat transport over a flat stretching surface for the inclusion of two unlike types of metal and oxide nanoparticles in a solvent water to investigate the role of hybrid nanofluid. The inclusion of Darcy–Forchheimer inertial drag over an elongating surface embedding in a porous medium enriches the flow behavior. However, the main attraction of the proposed investigation is the implementation of the Mintsa model conductivity combined with convective boundary condition that boosts up the thermophysical model. The suitable choice of similarity rules is useful for the transformation of governing equations into its non-dimensional form, and further traditional Runge–Kutta fourth-order method associated with shooting is employed to solve the flow profiles. The characteristics of controlling parameters on the flow phenomena along with the rate coefficients are deployed via graphs and tables. This investigation gives comparative results with earlier studies in particular cases. The important outcomes of the proposed investigation are: The augmented particle concentration favors in enhancing the fluid temperature in the permeable medium, whereas drag opposes the velocity profile significantly. [ABSTRACT FROM AUTHOR]

This study evaluates the methods of identifying the height zi of the top of the convective boundary layer (CBL) during winter (December and January) over the Great Lakes and nearby land areas using observations taken by the University of Wyoming King Air research aircraft during the Lake-Induced Convection Experiment (1997/98) and Ontario Winter Lake-effect Systems (2013/14) field campaigns. Since CBLs facilitate vertical mixing near the surface, the most direct measurement of zi is that above which the vertical velocity turbulent fluctuations are weak or absent. Thus, we use zi from the turbulence method as the "reference value" to which zi from other methods, based on bulk Richardson number (Rib), liquid water content, and vertical gradients of potential temperature, relative humidity, and water vapor mixing ratio, are compared. The potential temperature gradient method using a threshold value of 0.015 K m−1 for soundings over land and 0.011 K m−1 for soundings over lake provided the estimates of zi that are most consistent with the turbulence method. The Rib threshold-based method, commonly used in numerical simulation studies, underestimated zi. Analyzing the methods' performance on the averaging window zavg we recommend using zavg = 20 or 50 m for zi estimations for lake-effect boundary layers. The present dataset consists of both cloudy and cloud-free boundary layers, some having decoupled boundary layers above the inversion top. Because cases of decoupled boundary layers appear to be formed by nearby synoptic storms, we recommend use of the more general term, elevated mixed layers. Significance Statement: The depth zi of the convective atmospheric boundary layer (CBL) strongly influences precipitation rates during lake-effect snowstorms (LES). However, various zi approximation methods produce significantly different results. This study utilizes extensive concurrently collected observations by project aircraft during two LES field studies [Lake-Induced Convection Experiment (Lake-ICE) and OWLeS] to assess how zi from common estimation methods compare with "reference" zi derived from turbulent fluctuations, a direct measure of CBL mixing. For soundings taken both over land and lake; with cloudy or cloud-free conditions, potential temperature gradient (PTG) methods provided the best agreement with the reference zi. A method commonly employed in numerical simulations performed relatively poorly. Interestingly, the PTG method worked equally well for "coupled" and elevated decoupled CBLs, commonly associated with nearby cyclones. [ABSTRACT FROM AUTHOR]

To investigate the consequence of thermophoresis and Brownian diffusion on convective boundary layer micropolar fluid flow over a stretching wedge-shaped surface. The effects of non-dimensional parameters namely coupling constant parameter (0.01 ≤ B1 ≤ 0.05), magnetic parameter (1.0 ≤ M ≤ 15.0), Grashof number (0.3 ≤ Gr ≤ 0.9), modified Grashof number (0.3 ≤ Gm ≤ 0.8), micropolar parameter (2.0 ≤ G2 ≤ 7.5), vortex viscosity constraint (0.02 ≤ G1 ≤ 0.2), Prandtl number (7.0 ≤ Pr ≤ 15.0), thermal radiation parameter (0.25 ≤ R ≤ 0.50), Brownian motion parameter (0.2 ≤ Nb ≤ 0.62), thermophoresis parameter (0.04 ≤ Nt ≤ 0.10), heat generation parameter (0.1 ≤ Q ≤ 0.5), Biot number (0.65 ≤ Bi ≤ 1.0), stretching parameter (0.2 ≤ A ≤ 0.5), Lewis number (3.0 ≤ Le ≤ 7.0), and chemical reaction parameter (0.2 ≤ K ≤ 0.7) on the steady MHD heat and mass transfer is investigated in the present study. The coupled non-linear partial differential equations are reduced into a set of non-linear ordinary differential equations employing similarity transformation. Furthermore, by using the Runge-Kutta method followed by the shooting technique, the transformed equations are solved. The main goal of this study is to investigate the numerical analysis of nanofluid flow within the boundary layer region with the effects of the microrotation parameter and velocity ratio parameter. The novelty of this paper is to propose a numerical method for solving third-order ordinary differential equations that include both linear and nonlinear terms. To understand the physical significance of this work, numerical analyses and tabular displays of the skin friction coefficient, Nusselt number, and Sherwood number are shown. The new approach of the present study contributes significantly to the understanding of numerical solutions to nonlinear differential equations in fluid mechanics and micropolar fluid flow. Micropolar fluids are becoming even more of a focus due to the desire for engineering applications in various fields of medical, mechanical engineering, and chemical processing. [ABSTRACT FROM AUTHOR]

The effect of radiation evolved from fluids and particles on a convective balanced boundary layer dusty fluid flow model has been analyzed over a vertical stretching surface. Models are available with the consideration of radiation and viscous dissipation in fluid phase only. However, an equal and opposite reaction/force is also developed in the particle/dust phase, which was not taken into account in the previous literature. So, this paper investigates a model where the radiation and viscous dissipation are coupled through both the fluid and particle phase equations. A linear stretching of surface generates the boundary layer flow. By the help of suitable similar transformation, the prevailing equations are transferred to ordinary non-linear differential equations of order three and are solved numerically by the bvp4c method of MATLAB. An analysis has been performed to show the effectiveness of different thermophysical parameters on different boundary layer characteristics. The numerical results are in good agreement with the past literature, validating the present method and result. Graphs are plotted for different flow characteristics to explore the physics of problem. [ABSTRACT FROM AUTHOR]

The effects of atmospheric thermal structure on the surface energy flux are poorly understood over the Arctic sea‐ice surface. Here, we explore the mechanism of sensible heat exchange under different types of thermal structures over the Arctic sea‐ice surface by using data collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition. The quadrant analysis indicates that strong surface temperature inversions below 100 m enhance non‐local effects on the positive (upward) sensible heat flux (w′θ′‾ $\overline{{w}^{\prime }{\theta }^{\prime }}$) through entrainment of large eddies from the convective boundary layer aloft. However, strong surface inversions restrict the contributions of large eddies to the negative (downward) w′θ′‾ $\overline{{w}^{\prime }{\theta }^{\prime }}$ due to intensified surface stability. By inspecting the existing parameterization schemes, we found that the European Center for Medium‐Range Weather Forecasts Integrated Forecasting System scheme fails to predict the impacts of non‐local processes on the positive w′θ′‾ $\overline{{w}^{\prime }{\theta }^{\prime }}$, and an adjustment term to correct the bias of parameterized w′θ′‾ $\overline{{w}^{\prime }{\theta }^{\prime }}$ is proposed. Plain Language Summary: Since pre‐industrial times, the increase of Arctic near‐surface air temperature has been 2–3 times larger than the global average, known as the Arctic amplification. The atmospheric physical processes occurring in the boundary layer are essential for understanding the ongoing climate changes because they modulate the surface energy budget over the Arctic. However, scarce observations limit our understanding of surface heat flux exchange in this area. Recently, the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition was conducted in the central Arctic to support the urgent need for understanding and modeling the rapidly changing Arctic atmosphere‐ice‐ocean system. Based on the MOSAiC observations, we investigate the role of non‐local effects on sensible heat flux under different types of atmospheric thermal structures over the Arctic sea‐ice surface. To the best of our knowledge, this study represents the first time that the effects of strong surface inversions on negative and positive sensible heat fluxes over the Arctic sea‐ice surface are found to be opposite. In addition, we propose a method for taking non‐local effects into account, which can be applied in the European Center for Medium‐Range Weather Forecasts Integrated Forecasting System flux parameterization or other numerical models to correct the bias in parameterized positive sensible heat flux. Key Points: The characteristics of thermal structure during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition are presentedThe effects of strong surface inversions on the negative and positive sensible heat flux are contrastingWe propose an improved solution to predict the impacts of non‐local processes on the positive sensible heat flux [ABSTRACT FROM AUTHOR]

A simultaneous deployment of Doppler, temperature, and water-vapor lidars is able to provide profiles of molecular destruction rates and turbulent kinetic energy (TKE) dissipation in the convective boundary layer (CBL). Horizontal wind profiles and profiles of vertical wind, temperature, and moisture fluctuations are combined, and transversal temporal autocovariance functions (ACFs) are determined for deriving the dissipation and molecular destruction rates. These are fundamental loss terms in the TKE as well as the potential temperature and mixing ratio variance equations. These ACFs are fitted to their theoretical shapes and coefficients in the inertial subrange. Error bars are estimated by a propagation of noise errors. Sophisticated analyses of the ACFs are performed in order to choose the correct range of lags of the fits for fitting their theoretical shapes in the inertial subrange as well as for minimizing systematic errors due to temporal and spatial averaging and micro- and mesoscale circulations. We demonstrate that we achieve very consistent results of the derived profiles of turbulent variables regardless of whether 1 or 10 s time resolutions are used. We also show that the temporal and spatial length scales of the fluctuations in vertical wind, moisture, and potential temperature are similar with a spatial integral scale of ≈160 m at least in the mixed layer (ML). The profiles of the molecular destruction rates show a maximum in the interfacial layer (IL) and reach values of ϵm≃7×10-4 g 2 kg -2 s -1 for mixing ratio and ϵθ≃1.6×10-3 K 2 s -1 for potential temperature. In contrast, the maximum of the TKE dissipation is reached in the ML and amounts to ≃10-2 m 2 s -3. We also demonstrate that the vertical wind ACF coefficient kw∝w′2‾ and the TKE dissipation ϵ∝w′2‾3/2. For the molecular destruction rates, we show that ϵm∝m′2‾w′2‾1/2 and ϵθ∝θ′2‾w′2‾1/2. These equations can be used for parameterizations of ϵ , ϵm , and ϵθ. All noise error bars are derived by error propagation and are small enough to compare the results with previous observations and large-eddy simulations. The results agree well with previous observations but show more detailed structures in the IL. Consequently, the synergy resulting from this new combination of active remote sensors enables the profiling of turbulent variables such as integral scales, variances, TKE dissipation, and the molecular destruction rates as well as deriving relationships between them. The results can be used for the parameterization of turbulent variables, TKE budget analyses, and the verification of large-eddy simulations. [ABSTRACT FROM AUTHOR]

The surface and air temperature gradient (TS00 − Tair) drives the development of the convective boundary layer and the occurrence of clouds and precipitation. However, its variability is still poorly understood due to the lack of high-quality observations. This study fills in this gap by investigating the diurnal to decadal variability in TS00 − Tair from 2002 to 2022 based on hourly observations collected at over 100 stations of the U.S. Climate Reference Network. It is found that TS00 − Tair reaches its maximum at noon with an average of 6.85°C over the contiguous United States, which decreases to 4.28°C when the soil moisture exceeds 30%. The daily minimum of TS00 − Tair has an average of −2.08°C, which generally occurs in the early evening but is postponed as the cloud fraction decreases. Moreover, while existing studies have used the near-surface soil temperature, such as the 5-cm soil temperature (TS05), to calculate TS05 − Tair, we find that TS00 − Tair and TS05 − Tair have opposite diurnal cycles, and their amplitudes differed drastically. The daily minimum of TS00 − Tair has a significant decreasing trend (−0.50° ± 0.007°C decade−1) from 2002 to 2022 due to Tair increasing at a higher rate than TS00 during the nighttime. The occurrence frequency of near-surface stable conditions (TS00 − Tair < 0) increases significantly, and the frequency of unstable conditions (TS00 − Tair > 0) decreases notably throughout the year except for winter. When it is stable, the magnitude of TS00 − Tair tends to decrease while the TS00 − Tair tends to increase when it is unstable, which is consistent with the drying condition caused by the precipitation deficit. This study provides the first observational evidence on how TS00 − Tair responds to warming. Significance Statement: The impact of global warming on surface-air temperature gradients is a crucial scientific issue that needs to be addressed. These gradients determine changes in cloud and precipitation, affecting water resources. However, traditional surface temperature measurements from weather stations are of high uncertainty due to direct exposure to the insolation. Satellite retrieval of surface temperature is limited by the availability of clear sky conditions, with low accuracy for temperature gradient calculations. Despite their importance, high-accuracy data of land surface temperature are still lacking. To address this issue, the U.S. Climate Reference Network (USCRN) uses infrared radiometers to continuously monitor surface temperature with high accuracy and sampling frequency. This study reports on surface-air temperature gradients at more than 100 U.S. stations, providing insight into diurnal to decadal variability over the contiguous United States. The study also highlights the significant difference between the land surface temperature–air temperature gradient and soil temperature–air temperature gradient. [ABSTRACT FROM AUTHOR]

The Jintsu-oroshi refers to Japan's south foehn, which blows over the Toyama Plain in the Hokuriku region. This region faces the Sea of Japan to the north and the central mountain range to the south. The Jintsu-oroshi occurs more frequently at night than during the day. In this study, we determined the primary factors causing this feature using the Weather Research and Forecasting (WRF) Model. We selected a typical Jintsu-oroshi case in May 2016 for analysis. An extratropical cyclone traversed the Sea of Japan during the event, leading to a temporal change in the synoptic-scale pressure pattern. The observations and numerical simulation results showed that the collapse of the mixed layer over the mountains and the end of the sea breeze are key factors for the nighttime onset of the Jintsu-oroshi. Indeed, mountain waves and their resulting downslope winds did not occur under near-neutral atmospheric stability conditions over the mountains during the daytime. After sunset, the atmospheric stability changed to stable conditions, which caused the downslope winds to blow. However, the downslope winds did not reach the plains because of the sea breeze. After several hours, the sea breeze disappeared, and the downslope winds reached the leeward plains and increased the temperature there. Similar features were confirmed in August 2013 for another typical Jintsu-oroshi case under atmospheric conditions, without temporal changes in the synoptic-scale pressure pattern. We expect the results obtained in this study to advance our understanding of foehn occurrence in regions where mountains adjoin seas, similar to the coastal areas adjacent to the Sea of Japan. Significance Statement: The Jintsu-oroshi refers to Japan's south foehn, which blows over the Toyama Plain in the Hokuriku region. This foehn occurs more frequently at night than during the day. Strong foehns enhance the risk of fire. Nocturnal high temperatures due to foehns can cause sleeplessness in people. Nighttime foehns cause damage to paddy rice. Analyses of observations and numerical simulations for the two typical cases showed that Jintsu-oroshi did not tend to occur during the daytime because the development of a convective boundary layer over the mountains and sea breezes in the leeward plain inhibited the occurrence of the downslope winds. We expect the results obtained in this study to advance our understanding of foehn occurrence in regions where mountains adjoin seas, similar to the coastal areas adjacent to the Sea of Japan. [ABSTRACT FROM AUTHOR]

An approximation of the turbulent moments of the atmospheric convective layer is based on a variant of the local similarity theory using the concepts of the semiempirical theory of Prandtl turbulence. In the proposed variant of the local similarity theory, the second moment of vertical velocity and the "spectral" Prandtl mixing length are used as basic parameters. This approach allows us to extend Prandtl's theory to turbulent moments of vertical velocity and buoyancy and additionally offer more than ten new approximations. A comparison of the proposed approximation with other variants of the theory of local similarity is considered. It is shown that the selected basic parameters significantly improve the agreement between the local similarity approximations and experimental data. The approximations are consistent with observations in the turbulent convective layer of the atmosphere, the upper boundary of which nearly corresponds to the lower boundary of the temperature inversion. Analytical approximations of local similarity can find applications in the construction of high-order moment closures in the vortex of resolving numerical turbulence models, as well as in the construction of "mass-flux" parametrization. [ABSTRACT FROM AUTHOR]

Many applications rely on a correct estimation of the convective boundary layer (CBL) depth over mountainous terrain, but often these applications use numerical model simulations. Although models inevitably smooth terrain, the amount of smoothing depends on grid spacing. We investigate the behavior of the CBL in coarse- and fine-grid models applied to mountainous terrain by using output from an operational mesoscale modeling system and by performing quasi-idealized simulations. We investigate different areas in different climate zones using different CBL top derivation methods, grid spacing ratios, planetary boundary layer (PBL) schemes, and terrain smoothing. We find that when compared to fine-grid simulations, CBL depths are systematically larger in coarse domains over mountaintops, and to a lesser extent in valleys. On average, differences between coarse- and fine-domains over mountaintops could reach around 10%. In certain locations, differences could be as high as 25%. We attribute the result to terrain smoothing. Similarly, when using a coarse-grid CBL height (relative to mean sea level) interpolated using fine-grid terrain information, there is good agreement with fine-grid CBL depths over mountaintops and less agreement in valleys. Our results have implications for applications that use output from coarse model grids in mountainous terrain. These include inverse modeling studies (e.g., greenhouse gas budget estimations or integrated water vapor transport), PBL evaluation studies, climate research, air quality applications, planning and executing prescribed burns, and studies associated with precipitation over mountainous terrain. [ABSTRACT FROM AUTHOR]