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Accurate simulation of atmospheric circulation, particularly in the lower stratosphere, is challenging due to unresolved wave-mean flow interactions and limited high-resolution observations for validation. Gravity-induced pressure gradients lead to a small but measurable separation of heavy and light gases by molecular diffusion in the stratosphere. Because the relative abundance of Ar to N2 is exclusively controlled by physical transport, the argon-to-nitrogen ratio (Ar/N2) provides an additional constraint on circulation and the age of air (AoA), i.e. the time elapsed since entry of an air parcel into the stratosphere. Here we use airborne measurements of N2O and Ar/N2 from nine campaigns with global coverage spanning 2008–2018 to calculate AoA and to quantify gravitational separation in the lowermost stratosphere. To this end, we develop a new N2O-AoA relationship using a Markov Chain Monte Carlo algorithm. We observe that gravitational separation increases systematically with increasing AoA for samples with AoA between 0 to 3 years. These observations are compared to a simulation of the TOMCAT/SLIMCAT 3-D chemical transport model, which has been updated to include gravitational fractionation of gases. We demonstrate that although AoA at old ages is slightly underestimated in the model, the relationship between Ar/N2 and AoA is robust and agrees with the observations. This highlights the potential of Ar/N2 to become a new AoA tracer that is subject only to physical transport phenomena and can supplement the suite of available AoA indicators.

The AirCore is a long coiled tube that acts as a “tape recorder” of the composition of air as it is slowly filled or flushed. When launched by balloon with one end of the tube open and the other closed, the initial fill air flows out during ascent as the outside air pressure drops. During descent atmospheric air flows back in. We describe how we can associate the position of an air parcel in the tube with the altitude it came from by modeling the dynamics of the fill process. The conditions that need to be satisfied for the model to be accurate are derived. The extent of mixing of air parcels that enter at different times is calculated, so that we know how many independent samples are in the tube upon landing, and later when the AirCore is analyzed.

We analyze the solvability of a system of ordinary differential equations modeling a warm cloud. A unique feature of this model is the automatic onset of nucleation when the moist air parcel become...

Base on January and July 4-times daily ECMWF Interim data from 2009 to 2018 over the Northeast Sphere (0–180E,0–90N), the condensed moisture profile of experiential methods and that of ECMWF analysis are compared. The result shows that, the meridional-height distribution of mean cloud condensed moisture has a maximum slab spreading near ground in the Arctic region in July, and the maximum takes a circular shape at 700 hPa above 30N latitude in January. The distribution feature unlike the universal profile, it distributes in a single or double peak function manner, instead of a constant value. The quick decreasing level height and thickness varies with latitude, especially in January. The second experiential profile concerning warm cloud assumes air parcel lifting adiabatically, the liquid water path (LWP) is compared for general information. The result shows that the experiential LWP is much larger than that of the reanalysis by 1 to 2 order, decreasing with latitudes. The possible reason of LWP difference is from the critic water content value of cloud boundary identification. If the value is small, the thickness of warm cloud will be large, temperature and pressure at the cloud base are both large too, results in a larger LWP. These results will enrich the knowledge of the condensed moisture characteristics of ECMWF reanalysis and the experiential moisture profile methods.

We present a Lagrangian convective transport scheme developed for global chemistry and transport models, which considers the variable residence time that an air parcel spends in convection. This is particularly important for accurately simulating the tropospheric chemistry of short-lived species, e.g., for determining the time available for heterogeneous chemical processes on the surface of cloud droplets. In current Lagrangian convective transport schemes air parcels are stochastically redistributed within a fixed time step according to estimated probabilities for convective entrainment as well as the altitude of detrainment. We introduce a new scheme that extends this approach by modeling the variable time that an air parcel spends in convection by estimating vertical updraft velocities. Vertical updraft velocities are obtained by combining convective mass fluxes from meteorological analysis data with a parameterization of convective area fraction profiles. We implement two different parameterizations: a parameterization using an observed constant convective area fraction profile and a parameterization that uses randomly drawn profiles to allow for variability. Our scheme is driven by convective mass fluxes and detrainment rates that originate from an external convective parameterization, which can be obtained from meteorological analysis data or from general circulation models. We study the effect of allowing for a variable time that an air parcel spends in convection by performing simulations in which our scheme is implemented into the trajectory module of the ATLAS chemistry and transport model and is driven by the ECMWF ERA-Interim reanalysis data. In particular, we show that the redistribution of air parcels in our scheme conserves the vertical mass distribution and that the scheme is able to reproduce the convective mass fluxes and detrainment rates of ERA-Interim. We further show that the estimated vertical updraft velocities of our scheme are able to reproduce wind profiler measurements performed in Darwin, Australia, for velocities larger than 0.6 m s−1. SO2 is used as an example to show that there is a significant effect on species mixing ratios when modeling the time spent in convective updrafts compared to a redistribution of air parcels in a fixed time step. Furthermore, we perform long-time global trajectory simulations of radon-222 and compare with aircraft measurements of radon activity.

For understanding the aerosol characteristics over the Yellow Sea according to the air flow patterns in East Asia, the aerosol volume concentration distribution by particle size (size distribution) of the shipborne samples collected in the KORUS-AQ campaign is examined in conjunction with air quality (AQ) model simulations and air parcel trajectory analyses. Cluster analyses of the air parcel trajectories show that 42% of the collected air samples originated in Korea and Japan, 30% in inland/east-coast China, 16% in the highlands of Inner Mongolia, and 11% in the East China Sea. The aerosol size distribution varies characteristically according to the upstream path of individual trajectory clusters; particles of diameters 2 μm, indicating a mixed industrial-dust aerosol type in which the dust particles from the Inner Mongolia is mixed with fine particles in the industrialized northeast China. Model studies for cases of typical air flow trajectory groups show that the model simulates the spatial distribution of the satellite-observed particulate matter reasonably, but underestimates the observed volume concentration of fine particles

The near-surface environment of the earth remains either in calm or in a turbulent state as per the kinetic force acts, which encourage the growth of disturbance in the atmospheric fluid. In a stable condition, mixing of the air particles at different heights reduces the overall vertical variability of the air particles in the atmosphere while unstable atmospheric condition produces the minimum shear that leads to convective situation and promotes the mixing of its composition. To analyse these types of atmospheric conditions, here two basic parameters temperature lapse rate and aerosol optical depth (AOD), has been taken into consideration. Along with these parameters, a model named hybrid single particle lagrangian integrated trajectory (HYSPLIT) has been utilised to track the air parcel or wind flow pattern. The observations were made over Guwahati (26°N, 92°E), NE region of India. It has been determined from the observations that the wind shear (WS) follows a seasonal pattern. On certain days, the shear is higher than that of the normal condition. In this context, parameters temperature lapse rate and AOD along with WS has been observed and examined to analyse the stability of the atmosphere. It is observed that on the day of high WS value, high AOD and slow decrease of temperature per km (vertically with height) shows a completely different pattern than the normal one.

Despite the existing myriad of tools and models to assess atmospheric source–receptor relationships, their uncertainties remain largely unexplored and arguably stem from the scarcity of observations available for validation. Yet, Lagrangian models are increasingly used to determine the origin of precipitation and atmospheric heat, scrutinizing the changes in moisture and temperature along air parcel trajectories. Here, we present a holistic framework for the process-based evaluation of atmospheric trajectories to infer source–receptor relationships of both moisture and heat. The framework comprises three steps: (i) the diagnosis of moisture and heat from Lagrangian trajectories using multi-objective criteria to evaluate the accuracy and reliability of the fluxes, (ii) the attribution of sources following mass- and energy-conserving algorithms in order to establish source–receptor relationships, and (iii) the bias correction of diagnosed fluxes and the corresponding source–receptor relationships. Applying this framework to simulations from the Lagrangian model FLEXPART, driven with ERA-Interim reanalysis data, allows us to quantify the errors and uncertainties associated with the resulting source–receptor relationships for three cities in different climates (Beijing, Denver and Windhoek). Our results reveal large uncertainties inherent in the estimation of heat and precipitation origin with Lagrangian models, but they also demonstrate the synergistic impacts of source- and sink bias-corrections. The proposed framework paves the way for a cohesive assessment of the dependencies in source–receptor relationships.

The Aral Sea basin is the most active source of salt-dust storms in the central Asian region, while its exposed bottom is acting as a “distributer” of salts and chemicals over the adjoining areas. In this study, the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT-4) is used to identify the trajectories of air parcels from the dried bottom of the Aral Sea region (45.40° N, 61.30° E) that are potentially containing salt-dust and their probability of influencing the downwind area in the period of 2016–2020. The frequency of air parcel trajectory was mapped for six levels: 100, 300, 500, 1000, 2000, and 3000 m agl. The trajectories were categorized by k-means clustering into four clusters that are named by their direction of movement as follows: Cluster 1: E category, Cluster 2: NE category, Cluster 3: W category, and the Cluster 4: S category. The 72 h of forward trajectories showed that salt-dust storms starting from the dried bottom of the Aral Sea had the highest probability of affecting the northeastern region e.g., Siberian Plain, followed by the southern region e.g., Iran Plateau. Total number of trajectories within these two clusters (NE and S) accounts for 90% (or 413 days) of trajectories in examined days. The main area of influence of salt-dust is close to the source area. The potential transport distance of salt-dust particles increases with the height of the starting point. The surface wind, which results from the changes of the Siberian High (SH), has a major role in shaping the surface atmospheric circulation which determines the transport pathway of salt-dust particles over the Aral Sea region. The results of this study could be useful to forecast the potential occurrence of salt-dust storms in downwind affected areas and would also be helpful to understand the possible causes of salt-dust storms which can provide the scientific basis for mitigation of the negative impact of salt-dust storms on the environment and human health. Further research should be conducted by using monitoring data to confirm the deposition of dust and salt particles in those areas mapped by our study.

The main objective of the ACRIDICON-CHUVA (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the Global Precipitation measurements) campaign in September 2014 was the investigation of aerosol-cloud-interactions in the Amazon Basin. Cloud properties near cloud base of growing convective cumuli were characterized by cloud droplet size distribution measurements using a cloud combination probe (CCP) and a cloud and aerosol spectrometer (CAS-DPOL). In the current study, an adiabatic parcel model was used to perform cloud droplet number (Nd) closure studies for several flights in differently polluted air masses. Model input parameters included aerosol size distributions, measured with an ultra-high sensitive aerosol spectrometer (UHSAS), in combination with a condensation particle counter (CPC). Updraft speeds (w) were measured near cloud base using a boom-mounted Rosemount model 858 AJ probe. To compare to model predictions, measured Nd and w were statistically matched based on equal percentiles of occurrence. Reasonable agreement between measured and predicted Nd was achieved when a particle hygroscopicity of κ ~ 0.1 is assumed. Similar closure results were obtained when the variability in the particle number concentration was taken into account. We conclude that Nd can be predicted using a single κ, and measured aerosol particle number concentration below cloud base when w is constrained based on measurements. In accordance with previous adiabatic air parcel model studies, the largest disagreements between predicted and measured Nd were found when updraft speeds were high (w > 2.5 m s−1) or in the presence of a bimodal aerosol size distribution. We show that simplifying assumptions on κ might not be appropriate when the aerosol size distribution is comprised of both distinct Aitken and accumulation modes, as predicted Nd clearly deviate from measured ones at w ≥ 1 m s−1 which points to a contribution of Aitken mode particles to Nd.

The culmination of the implications of the Ideal Gas Law, hydrostatic balance, and humidity leads naturally to an ability to describe the path of a hypothetical blob of air—called an air parcel—as it is forced to rise in the atmosphere. This tendency to rise is a measure of atmospheric stability. Stability is assessed by comparing the temperature of the air parcel to that which occurs in its surrounding environment; the former is described by the unsaturated adiabatic lapse rate, or the saturated adiabatic lapse rate for saturated conditions. A stable atmosphere is one in which the parcel resists further upward motion once the lifting force is removed because the parcel is cooler than the surrounding environment at that level; this generally leads to fair skies but also stagnant conditions that can be associated with poor air quality. An unstable atmosphere is one in which the parcel continues to ascend even after the lifting force is removed, because the parcel is warmer than its surrounding environment at that level; this generally leads to enhanced vertical cloud growth. A neutral atmosphere is one in which the parcel shows neither a tendency to continue to rise nor to sink, after the lifting force is removed. Stability conditions may depend on whether the parcel is saturated, and stability is inherently related to the amount of turbulence in the near-surface atmosphere. Potential temperature is helpful in describing stability because a positive gradient of potential temperature with height (i.e., increasing potential temperature with increasing height) identifies a stable condition, and a negative gradient of potential temperature with height (i.e., decreasing potential temperature with increasing height) represents an unstable condition.

Rising motion is important in meteorology because it allows air to cool to its dew point temperature, condense, form clouds, and enlarge droplets by either the collision-coalescence process or the Wegener-Bergeron-Findeisen process before precipitation is possible. This chapter covers the four basic ways that air can rise. The first mechanism follows naturally from the theme of thermal turbulence and atmospheric stability/instability; convectional lifting, or free convection, involves surface heating that causes an air parcel to rise because it is convectively unstable. The other three mechanisms are known as forced convection because the rising occurs regardless of whether the parcel is convectively unstable. Two parcels of air that are near the surface and converging cause forced rising. This convergence is particularly common in the coastal zone where relative humidity is likely to be high. Orographic lifting occurs when an air parcel is lifted upslope as it is pushed against a mountain or hill on the windward slope. Finally, when an air mass with cold air is pushed up against another air mass containing warmer air, there is an enhancement to the precipitation potential beyond that caused by the horizontal convergence that would produce lifting; specifically, the warmer air will get pushed up over the cold air because it is less dense in frontal lifting.

In addition to obeying the Ideal Gas Law and principles of adiabatic motion, air moves vertically based on the principles described in the hydrostatic equation, which relates height differences in a static atmosphere to the vertical pressure change over those differences. In addition, the First Law of Thermodynamics—the postulate that energy can be neither created nor destroyed, but only changed from one form to another—applies by ensuring that air has some combination of gaining or losing internal energy and doing work (or having work done) on its surrounding environment as it moves vertically. These principles are important in modeling and predicting atmospheric motion. Specifically, if air is assumed to move adiabatically in its vertical motion and is not saturated, then these principles dictate that it will always cool by 0.9753 K (or approximately 1 C°) per 100 m. As will be shown in the subsequent chapters, this unsaturated adiabatic lapse rate becomes very important in determining whether an imaginary blob of air known as an air parcel will have a tendency to rise (and perhaps generate tall clouds) or sink.

The Lagrangian and Eulerian structure and dynamics of a strong wind event in the Tokar Gap region are described using a Weather Research and Forecasting (WRF) model hindcast for 2008. Winds in the Tokar Gap reach 25 m s&minus, 1 and remain coherent as a jet far out over the Red Sea, whereas equally strong wind jets occurring in neighboring gaps are attenuated abruptly by jump-like hydraulic transitions that occur just offshore of the Sudan coast. The transition is made possible by the supercritical nature of the jets, which are fed by air that spills down from passes at relatively high elevation. By contrast, the spilling flow in the ravine-like Tokar Gap does not become substantially supercritical and therefore does not undergo a jump, and also carries more total horizontal momentum. The Tokar Wind Jet carries some air parcels across the Red Sea and into Saudi Arabia, whereas air parcel trajectories in the neighboring jets ascend as they cross through the jumps, then veer sharply to the southeast and do not cross the Red Sea. The mountain parameter Nh/U is estimated to lie in the range of 1.0&ndash, 4.0 for the general region, a result roughly consistent with a gap jet having a long extension, and supercritical flows spilling down from higher elevation passes. The strong event is marked by the formation of a feature with a vertical cellular structure in the upstream entrance region of the Tokar Gap, a feature absent from the more moderate events that occur throughout the summer. The cell contains descending air parcels that are fed into the Tokar Gap and one of the neighboring gaps. An analysis of the Bernoulli function along air parcel trajectories reveals an approximate balance between the loss of potential energy and gain of internal energy and pressure, with surprisingly little contribution from kinetic energy, along the path of the descending flow. The winds in all gaps attain the critical wind speed nominally required to loft dust into the atmosphere, though only the Tokar Gap has a broad, silty delta region capable of supplying particulate matter for dust storms.

Se presenta el análisis preliminar de cuencas atmosféricas con origen en el Valle de Sogamoso, Boyacá, Colombia, mediante la modelación del comportamiento de las parcelas de aire como herramienta para la planificación territorial. El estudio de caso se sitúa en uno de los corredores industriales de mayor emisión de contaminantes en Colombia, por tanto, es importante conocer el comportamiento de las variables meteorológicas, la topografía de la zona y la dinámica atmosférica que allí se desarrolla como consecuencia de relacionar las dos variables, para lograr la conformación y delimitación de la cuenca atmosférica. Se calculó por medio del modelo HYSPLIT, las trayectorias de parcelas de aire hacia adelante durante los meses de febrero y abril, estableciendo las temporadas secas y húmedas del año 2015. Se observó la circulación de parcelas de aire provenientes del Valle, hacia territorios que han presentado altos índices en contaminación atmosférica para el contaminante PM10 y se evidenció la relación de las variables meteorológicas y topográficas para delimitar la cuenca. Se proponen criterios para la planificación y ordenamiento territorial desde el enfoque de cuencas atmosféricas como unidad de gestión regional y apoyo a los sistemas de monitoreo de calidad del aire, con el fin de establecer una variable ambiental como eje principal para la toma de decisiones territoriales.

Exact and approximate relations have been obtained to describe the evolution of the following parameters of heated air parcels during their convective uplifting in the atmosphere: the altitude and temporal dependences of the speed of the parcel center, the parcel characteristic size (radius), and the excess relative temperature. Cases of moderate and strong heating have been considered. The original equations include relations for the rate of uplifting thermals, the mass of entrained cool air, and the complete integral of thermal buoyancy. It has been shown that during uplifting the radius of the heated air parcel increases, the excess temperature decreases, and the uplift rate varies nonmonotonically: first, it increases from zero and reaches a maximum; then it gradually decreases to zero. Numerical estimates for characteristic situations have been performed.

The US National Oceanic and Atmospheric Administration Air Research Laboratorys HYSPLIT (HYbrid Single Particle Lagrangian Integrated Trajectory) model uses a hybrid Lagrangian and Eulerian calculation method to compute particle dispersion and deposition simulations as well as air parcel paths (trajectories), forward or backward in time. This model is used worldwide in a variety of scientific contexts. The author presents the first Python package designed from the ground up to facilitate and expedite HYSPLIT trajectory analysis workflows by providing an intuitive and efficient API for generating, inspecting, and plotting trajectory paths and data. PySPLIT enables fully reproducible workflows, with orders of magnitude superior efficiency compared to what was previously possible with HYSPLIT alone, and leverages the capabilities of the scientific Python ecosystem and matplotlib to generate reproducible, publication-quality figures.

The initiation processes of one of the initial convective cells near and on the east side of a dryline on 19 June 2002 during the IHOP_2002 field experiment in the central United States is analyzed in detail based on a high-resolution numerical simulation. Prominent horizontal convective rolls and associated near-surface moisture convergence bands [called roll convergence bands (RCBs) here] develop within the convective boundary layer (CBL) due to surface heating, in the hours leading to convective initiation (CI). The RCBs east of the dryline are advected toward the primary dryline convergence boundary (PDCB) by the southerly moist flow as the CBL deepens with time. Backward trajectories of air parcels forming the initial precipitating updraft of the convective cell are found to primarily originate at about 1-1.5 km above ground, within the upper portion of the shallower CBL earlier on. The representative air parcel is found to follow and stay on top of a surface RCB as the RCB moves toward the PDCB, but the RCB forcing alone is not enough to initiate convection. As this RCB gets close to the PDCB, it moves into a zone of mesoscale convergence and a deeper CBL that exhibits an upward moisture bulge associated with the PDCB. The combined upward forcing of the RCB and the mesoscale PDCB convergence quickly lifts the representative air parcel above its level of free convection to initiate convection. A conceptual model summarizing the CI processes is proposed.

The exchange of reactive pollutants (NO, NO2, and O3) at the top (roof level) of a street canyon are investigated using the parallelized large-eddy simulation model (PALM). The transport equations of NO, NO2, and O3 with simple photochemical reactions are combined within the LES model for this study. NO and NO2 are emitted from an area source located near the canyon floor, and O3 is included within the ambient air and inflow. A clockwise-rotating vortex appears in the street canyon and transports NO, NO2, and O3. NO and NO2 are transported along the ground and leeward wall and escape from the canyon at the roof level. O3 enters the canyon at the roof level and is transported along the windward wall. The mean O3 production rate is generally negative with large magnitudes at and near the roof level and near the windward wall. The chemical reactions reduce the mean NO and O3 concentrations in the canyon by 31% and 84%, respectively, and increase the mean NO2 concentration in the canyon by 318%. The exchange of reactive pollutants at the roof level is significantly affected by small-scale eddies at the roof level and low- or high-speed streaks above the canyon. Air in the canyon with high NO and NO2 concentrations escapes from the canyon when low-speed air parcel appears due to small-scale eddies at the roof level or low-speed streak above the canyon. In contrast, air outside the canyon with a high O3 concentration enters the canyon when high-speed air parcel appears because of small-scale eddies at the roof level or high-speed streak above the canyon. The time-lagged correlation analysis reveals that NO, NO2, and O3 concentrations near the ground are affected by low- or high-speed streaks above the canyon but not significantly affected by small-scale eddies at the roof level.

This study presents a simpler procedure for grouping air parcel back trajectories than others previously applied. Two-day air parcel back trajectories reaching an unpolluted site in the centre of the northern plateau of the Iberian Peninsula were calculated over a three-year period using the METEX model. A procedure based on the kernel density calculation was applied to the direction of each trajectory centroid to determine groups of trajectories. This method is much faster than the cluster procedure when it comes to retaining the directional details of groups. Seasonal analysis of six groups of trajectories revealed that the Atlantic origin prevailed against displacement from northern Europe. Moreover, Mediterranean and particularly African trajectories were infrequent, probably due to the rough peninsular orography in these directions. The location of air trajectories reaching the study site was described using a surface classification below the air parcels with improved spatial resolution compared to previous analyses. Local contribution was very marked, particularly in summer. Mean trajectories were calculated for each group together with meteorological features and CO2 and CH4 concentrations. Groups may be identified by their mean temperature, wind speed, elevation and distance values. However, only two groups should be considered when analysing the two trace gases, one for trajectories from the Atlantic Ocean and the second for trajectories from the continent. Contrasts of about 4 ppm for CO2 in summer and 0.023 ppm for CH4 in winter were observed, revealing that air trajectories from the Atlantic Ocean were cleaner than those arriving from the continent. These differences were attributed to higher air stagnation over land.

This paper proposes a selection model of candidate nodes and an air parcel network hub location model to estimate the efficiency of the parcel network when adding pure freighters. Using the data on real demands among airports in practice, this article analyzes the hub location problem of the parcel network for DHL Express in the Asia-Pacific region. We find that Beijing, Hong Kong, Singapore, and Mascot are potential choices to be hub airports. The four hubs have parcel production of 10.1, 5.36, 2.75 and 0.84 million tons in the planning horizon, respectively. A sensitivity analysis is conducted to analyze the influence of different numbers of pure freighters on the air parcel network and the results indicate that the number of pure freighters can alleviate parcel pressure.

Lagrangian air parcel tracking is a powerful tool for estimating vapor source locations, particularly for isotope hydrology applications. Identified vapor source regions may be sensitive to the distribution of altitudes at which back trajectories are initiated. Ideally, those initial altitudes should reflect the altitudes where precipitation forms. This paper introduces a novel method for estimating these heights from reanalysis data and an air parcel lofting routine, which is referred to as the “Reanalysis” method. Using Barrow, Alaska (now known as Utqiaġvik), as a test site, the study compares the distribution of air parcel initiation heights and vapor source conditions from back trajectories initiated at 1) heights determined by the Reanalysis method and 2) heights acquired from 35-GHz vertically resolved cloud radar, termed the “Cloud Radar” method. Only 2 of the 70 events failed to produce condensation at any elevation. The distribution of air parcels generated by each method was compared on the basis of the median height and the median-adjusted overlap, and yielded excellent (n = 28), good (n = 20), fair (n = 6), and poor (n = 14) matches between the two methods. The excellent and good category events tended to produce condensation profiles with lower median heights, which translated to more similar vapor source characteristics. Poorly matched events tended to result from rain events where the Reanalysis method yielded much higher median heights than the Cloud Radar method.

Air quality forecasters, emergency responders, aviation interests, government agencies, and the atmospheric research community are among those who require access to tools to analyze and predict the transport and dispersion of pollutants in the atmosphere. Because of this need, the unique web-based Real-time Environmental Applications and Display sYstem (READY) has been under continuous development since 1997 to provide access to a suite of tools for producing air parcel trajectory and dispersion model results and displaying meteorological data. READY provides a “quasi-operational” portal to run the HYSPLIT atmospheric transport and dispersion model and interpret its results. Typical user applications include modeling the release of hazardous pollutants and volcanic ash, forest fire and prescribed burn smoke forecasting, poor air quality events, and various climatological studies. In addition, READY provides the user with quick access to meteorological data interpolated to the location of interest, helping in the interpretation of the HYSPLIT model results.

The MHD peristaltic motion of a compressible and electrically conducting Jeffrey fluid induced by a surface acoustic wave in a confined parallel-plane microchannel through a porous medium is analytically investigated. A proper attention is given to the combined effects of physical parameters and magnetic field on the rheological aspects of the considered flow. The slip velocity is considered and the problem is discussed for free pumping case. The wave amplitude is related to the power output of an acoustic source. A perturbation technique is employed to analyze the problem in terms of a small amplitude ratio. In the second order approximation, the net axial velocity is calculated for various values of the fluid parameters. Finally, the effects of the parameters of interest on the mean axial velocity, the reversal flow, and the perturbation function are discussed and shown graphically. The critical value of the magnetic parameter M is discussed such that an optimum M is shown where some physical variables are obtained maximum. It is noticed that, for the Jeffrey fluid, oscillations decay rapidly as we move from the hydrodynamic to the hydromagnetic fluid, and the effect of retardation time becomes weak. It is inferred that increasing the magnetic parameter makes the fluid less prone to nonlinear effects. Several results of other fluid models are deduced as the limiting cases of our problem. This work is the most general model of peristalsis created to date with wide-ranging applications in biological microfluidic networks.

This paper introduces a newly compiled set of feature-based climatologies identified from ERA-Interim (1979–2014). Two categories of flow features are considered: (i) Eulerian climatologies of jet streams, tropopause folds, surface fronts, cyclones and anticyclones, blocks, and potential vorticity streamers and cutoffs and (ii) Lagrangian climatologies, based on a large ensemble of air parcel trajectories, of stratosphere–troposphere exchange, warm conveyor belts, and tropical moisture exports. Monthly means of these feature climatologies are openly available at the ETH Zürich web page (http://eraiclim.ethz.ch) and are annually updated. Datasets at higher resolution can be obtained from the authors on request. These feature climatologies allow studying the frequency, variability, and trend of atmospheric phenomena and their interrelationships across temporal scales. To illustrate the potential of this dataset, boreal winter climatologies of selected features are presented and, as a first application, the very unusual Northern Hemispheric winter of 2009/10 is identified as the season when most of the considered features show maximum deviations from climatology. The second application considers dry winters in the western United States and reveals fairly localized anomalies in the eastern North Pacific of enhanced blocking and surface anticyclones and reduced cyclones.

An approach for analysis and modeling of global atmospheric chemistry is developed for application to measurements that provide a tropospheric climatology of those heterogeneously distributed, reactive species that control the loss of methane and the production and loss of ozone. We identify key species (e.g., O3, NOx, HNO3, HNO4, C2H3NO5, H2O, HOOH, CH3OOH, HCHO, CO, CH4, C2H6, acetaldehyde, acetone) and presume that they can be measured simultaneously in air parcels on the scale of a few km horizontally and a few tenths of a km vertically. As a first step, six global models have prepared such climatologies sampled at the modeled resolution for August with emphasis on the vast central Pacific Ocean basin. Objectives of this paper are to identify and characterize differences in model-generated reactivities as well as species covariances that could readily be discriminated with an unbiased climatology. A primary tool is comparison of multidimensional probability densities of key species weighted by the mass of such parcels or frequency of occurrence as well as by the reactivity of the parcels with respect to methane and ozone. The reactivity-weighted probabilities tell us which parcels matter in this case, and this method shows skill in differentiating among the models' chemistry. Testing 100 km scale models with 2 km measurements using these tools also addresses a core question about model resolution and whether fine-scale atmospheric structures matter to the overall ozone and methane budget. A new method enabling these six global chemistry–climate models to ingest an externally sourced climatology and then compute air parcel reactivity is demonstrated. Such an objective climatology containing these key species is anticipated from the NASA Atmospheric Tomography (ATom) aircraft mission (2015–2020), executing profiles over the Pacific and Atlantic Ocean basins. This modeling study addresses a core part of the design of ATom.

Dynamic of particles in annular fluid flow is a very relevant subject for many industrial applications, especially for the oil and gas industry. Successful drilling is, to a large extent, dependent upon the ability of the drilling fluid to clean the hole by conveying the cuttings to the surface. The aim of this work was to evaluate experimentally and through numerical simulations, the helical path and the axial mean velocity developed by glass beads with diameter of 2.7 mm flowing with a non-Newtonian fluid through a partially obstructed annulus. Experimental data are reported for flow of 1 m3/h of an aqueous solution with 0.5% Xanthan gum through concentric annulus with partial obstruction of 6 mm and a 183 rpm rotation of the inner cylinder. Techniques of computational fluid dynamics (CFD) were applied to obtain detailed information about the flow field, allowing to estimate the radial position of launching of particles in the range of 35.5 mm to 39.1 mm. Comparisons between numerical calculations and the flow data indicated, in general, a very good agreement.

International audience; Flow-induced vibration in square cylinder arrangement under viscous fluid incompressible cross-flow is investigated in the present work. The purpose is to contribute to better mod-eling and understanding external fluid loads exerted on long thin cylinders inducing flow perturbations. Due to high flow confinement, thin cylinders may be subjected to strong vibrations, which may lead to dynamic instability development. A theoretical approach is developed to determine a stability criterion of the dynamical system. The influence of geometric, mechanical and flow parameters such as reduced velocity and pitch ratio is investigated. The proposed model is derived from the potential flow theory and enhanced through an algebraic phase lag model in order to predict the critical limit of the reduced velocity for a square cylinder arrangement submitted to an external in-line cross flow. A theoretical formulation of the total damping, including added damping in still fluid, the damping due to fluid flow and the damping derived from the phase shift between the fluid load and the tube displacement, is expressed. A function depending on fluid and structure parameters, such as reduced velocity, pitch ratio and Scruton number is thus obtained. It is shown that this function provides a prediction of the dynamic stability limit of the system for several ranges of the major parameters to be considered. The results are compared to experimental reference solutions and to those provided by other theoretical models. This work proposes a consistent original model based on a potential flow theory enriched by using an algebraic formulation based on standard physical assumptions from literature. The major advantage of this model is due to the fact that it is in the same time robust and very user-friendly from a computational point of view thanks to the potential framework. In order to describe fluid and solid dynamics in the domain, terms coming from the potential flow theory are estimated by using a finite element method and complementary terms acting on damping are obtained through an algebraic formulation. Therefore this is a convenient way to propose a hybrid numerical / algebraic model for predicting dynamic instability limit in cylinder arrangements.

It is widely presumed that the convective stability and enormous kinematic viscosity of Earth's upper thermosphere hinders development of both horizontal and vertical wind shears and other gradients. Any strong local structure (over scale sizes of several hundreds of kilometers) that might somehow form would be expected to dissipate rapidly. Air flow in such an atmosphere should be relatively simple and transport effects only slowly disperse and mix air masses. However, our observations show that wind fields in Earth's thermosphere have much more local-scale structure than usually predicated by current modeling techniques, at least at auroral latitudes; they complicate air parcel trajectories enormously, relative to typical expectations. For tracing air parcels, we used wind measurements of an all-sky Scanning Doppler Fabry-Perot interferometer and reconstructed time-resolved two-dimensional maps of the horizontal vector wind field to infer forward and backward air parcel trajectories over time. This is the first comprehensive study to visualize the complex motions of thermospheric air parcels carried through the actual observed local-scale structures in the high-latitude winds. Results show that thermospheric air parcel transport is a very difficult observational problem, because the trajectories followed are very sensitive to the detailed features of the driving wind field. To reconstruct the actual motion of a given air parcel requires wind measurements everywhere along the trajectory followed, with spatial resolutions of 100 km or less, and temporal resolutions of a few minutes or better. Understanding such transport is important, for example in predicting the global-scale impacts of aurorally generated composition perturbations.

Two trapped lee-wave events dominated by the transverse mode downstream of the island of Oahu in Hawaii—27 January 2010 and 24 January 2003—are simulated using the Weather Research Forecasting (WRF) Model with a horizontal grid size of 1 km in conjunction with the analyses of soundings, weather maps, and satellite images. The common factors for the occurrences of these transverse trapped mountain-wave events are 1) Froude number [Fr = U/(Nh)] > 1, where U is the upstream speed of the cross-barrier flow, N is stability, and h is the mountain height; 2) insufficient convective available potential energy for the air parcel to become positively buoyant after being lifted to the top of the stable trade wind inversion layer; and 3) increasing cross-barrier wind speed with respect to height through the stable inversion layer, satisfying Scorer’s criteria between the inversion layer and the layer aloft. Within the inversion layer, where the Scorer parameter has a maximum, the wave amplitudes are the greatest. The two trapped mountain waves in winter occurred under strong prefrontal stably stratified southwesterly flow. On the other islands in Hawaii, where the mountaintops are below the base of the inversion, transverse trapped lee waves can occur under similar large-scale settings if the mountain height is lower than U/N. The high-spatial-and-temporal-resolution WRF Model successfully simulates the onset, development, and dissipation of these two events. Sensitivity tests for the 27 January 2010 case are performed with reduced relative humidity (RH). With a lower RH and less-significant latent heating, trapped lee waves have smaller amplitudes and shorter wavelengths.

The energy available in a solar energy powered grid is uncertain due to the weather conditions at the time of generation. Forecasting global solar irradiance could address this problem by providing the power grid with the capability of scheduling the storage and dispatch of energy. The occlusion of the Sun by clouds is the main cause of instabilities in the generation of solar energy. This investigation proposes a method to visualize the wind velocity field in sequences of longwave infrared images of clouds when there are multiple wind velocity fields in an image. This method can be used to forecast the occlusion of the Sun by clouds, providing stability in the generation of solar energy. Unsupervised learning is implemented to infer the distribution of the clouds’ velocity vectors and heights in multiple wind velocity fields in an infrared image. A multi-output weighted support vector machine with flow constraints is used to extrapolate the wind velocity fields to the entire frame, visualizing the path of the clouds. The proposed method is capable of approximating the wind velocity field in a small air parcel using the velocity vectors and physical features of clouds extracted from infrared images. Assuming that the streamlines are pathlines, the visualization of the wind velocity field can be used for forecasting cloud occlusions of the Sun. This is of importance when considering ways of increasing the stability of solar energy generation.

In this paper we have investigated the steady plane Couette flow of viscous incompressible fluid between two porous parallel plates in magnetic field. We have studied the velocity, average velocity, shearing stress, skin frictions, the volumetric flow, drag coefficients and stream lines. Keywords: Steady Couette flow, viscous parallel plates, incompressible fluid and magnetic field. NOMENCLATURE u = velocity component along x - axis v = velocity component along y - axis t = the time = the density of fluid P = the fluid pressure K= the thermal conductivity of the fluid

The helical flows of couple-stress fluids in a straight circular cylinder are studied in the framework of the newly developed, fully determinate linear couple-stress theory. The fluid flow is generated by the helical motion of the cylinder with time-dependent velocity. Also, the couple-stress vector is given on the cylindrical surface and the nonslip condition is considered. Using the integral transform method, analytical solutions to the axial velocity, azimuthal velocity, nonsymmetric force-stress tensor, and couple-stress vector are obtained. The obtained solutions incorporate the characteristic material length scale, which is essential to understand the fluid behavior at microscales. If characteristic length of the couple-stress fluid is zero, the results to the classical fluid are recovered. The influence of the scale parameter on the fluid velocity, axial flow rate, force-stress tensor, and couple-stress vector is analyzed by numerical calculus and graphical illustrations. It is found that the small values of the scale parameter have a significant influence on the flow parameters.

The method of molecular dynamics simulation is applied in order to study the behavior of liquid Argon flow within oscillatory Couette flows, in both smooth and rough nanochannels. To accomplish this study, the fluid velocity and the fluid slip in oscillatory Couette flows were used to assess the effects of: oscillatory velocity amplitude, speed frequency rate, channel height, wall density, and the amount of interaction between fluid and wall particles. Both smooth and rough walls were modelled in order to investigate the effect on the fluid patterns as well. Rectangular and triangular wall roughnesses in different dimensions were used to study this effect. The results indicate that an increase in the velocity amplitude increases the fluid slip, and decreases the fluid velocity fluctuations near the walls. Similar to the steady-state Couette flow, in oscillatory flow we observe a decrease in fluid slip by reducing the wall density. Moreover, by reducing the energy parameter between the fluid and wall, the fluid slip increases, and by reducing the length parameter the fluid slip decreases. Implementing the rectangular and triangular roughness to the bottom wall in the oscillatory flow results in a decrease in fluid slip, which is also similar to the usual non-oscillating flows.

Different theoretical and laboratory studies on the propagation of elastic waves in layered hydrocarbon reservoir have shown characteristic velocity dispersion and attenuation of seismic waves. The wave-induced fluid flow between mesoscopic-scale heterogeneities (larger than the pore size but smaller than the predominant wavelengths) is the most important cause of attenuation for frequencies below 1 kHz. Most studies on mesoscopic wave-induced fluid flow in the seismic frequency band are based on the representative elementary volume, which does not consider interaction of fluid flow due to the symmetrical structure of representative elementary volume. However, in strongly heterogeneous media with unsymmetrical structures, different courses of wave-induced fluid flow may lead to the interaction of the fluid flux in the seismic band; this has not yet been explored. This paper analyses the interaction of different courses of wave-induced fluid flow in layered porous media. We apply a one-dimensional finite-element numerical creep test based on Biot's theory of consolidation to obtain the fluid flux in the frequency domain. The characteristic frequency of the fluid flux and the strain rate tensor are introduced to characterise the interaction of different courses of fluid flux. We also compare the behaviours of characteristic frequencies and the strain rate tensor on two scales: the local scale and the global scale. It is shown that, at the local scale, the interaction between different courses of fluid flux is a dynamic process, and the weak fluid flux and corresponding characteristic frequencies contain detailed information about the interaction of the fluid flux. At the global scale, the averaged strain rate tensor can facilitate the identification of the interaction degree of the fluid flux for the porous medium with a random distribution of mesoscopic heterogeneities, and the characteristic frequency of the fluid flux is potentially related to that of the peak attenuation. The results are helpful for the prediction of the distribution of oil–gas patches based on the statistical properties of phase velocities and attenuation in layered porous media with random disorder.

The results of linearization of the basic equations describing a compressible viscous fluid in which low-amplitude oscillations occur or solids move or that interacts with elastic bodies in which small perturbations propagate are discussed. The general solutions of the linearized equations are presented. The results of studying wave processes in hydroelastic systems using the three-dimensional linearized theory of finite deformations and theory of compressible viscous fluid are discussed. The results of studying the propagation of acoustic waves of various types in waveguides with plane and circular cylindrical interfaces between elastic and liquid media and the influence of large (finite) initial deformations, viscosity and compressibility of the fluid on acoustic waves are presented. Studies of the motion of objects in compressible ideal and viscous fluids under the action of radiation forces due to the acoustic field are reviewed. The emphasis is placed on the studies that use a method involving the solution of hydrodynamic problems for a compressible fluid with solid particles and the evaluation of the forces acting on these particles. The radiation force is determined as the constant component of the hydrodynamic force. The numerical results are presented in the form of plots, which are then analyzed

A two-type classification of ice clouds (cirrus) is introduced, based on the liquid and ice water content, LWC and IWC, along air parcel backward trajectories from the clouds. In situ cirrus has no LWC along the trajectory segment containing IWC; it forms via nucleation from the gas phase. In contrast, liquid-origin cirrus has both LWC and IWC along their backward trajectories; it forms via lifting from the lower troposphere and freezing of mixed-phase clouds. This classification is applied to 12 years of ERA-Interim ice clouds in the North Atlantic region. Between 400 and 500 hPa more than 50% are liquid-origin cirrus, whereas this frequency decreases strongly with altitude (

The present paper deals with the unsteady laminar flow of an incompressible, electrically conducting dusty visco-elastic fluid between two parallel stationary plates. The flow is caused by an exponentially decaying pressure gradient .A uniform magnetic field is applied on the lower plate at different inclinations. We observe that the motions of the fluid and dust particles are affected by the variation of some significant physical parameters of the visco-elastic fluid. Mass concentration number, time-relaxation parameter, visco-elastic parameter, intensity of the applied magnetic field and time are some of indispensable physical parameters of fluid flow. The governing equations of motion have been solved by analytical method and the results have been discussed with the help of graphs. The velocity is observed to be symmetrical with the centre of the channel of fluid flow as well as of dust particles. The velocity of the fluid particles and that of the dust particles go on decreasing with an increase in the values of mass concentration number, magnetic field intensity, visco-elastic parameter and time whereas the velocity profiles of fluid and dust particles are observed to be increasing with an increase in the time- relaxation parameter.

Dispersion of backward air parcel trajectories that are initially tightly grouped near the tropical tropopause is examined using three ensemble approaches: “RANWIND,” in which different ensemble members use identical resolved wind fluctuations but different realizations of stochastic, multifractal simulations of unresolved winds; “PERTLOC,” in which members use identical resolved wind fields but initial locations are perturbed 2° in latitude and longitude; and a multimodel ensemble (“MULTIMODEL”) that uses identical initial conditions but different resolved wind fields and/or trajectory formulations. Comparisons among the approaches distinguish, to some degree, physical dispersion from that due to data uncertainty and the impacts of unresolved wind fluctuations from those of resolved variability. Dispersion rates are robust properties of trajectories near the tropical tropopause. Horizontal dispersion rates are typically ~3°/d, which is large enough to spread parcels throughout the tropics within typical tropical tropopause layer transport times (30–60 days) and underscores the importance of averaging large collections of trajectories to obtain reliable parcel source and pathway distributions. Vertical dispersion rates away from convection are ~2–3 hPa/d. Dispersion is primarily carried out by the resolved flow, and the RANWIND approach provides a plausible representation of actual trajectory dispersion rates, while PERTLOC provides a reasonable and inexpensive alternative to RANWIND. In contrast, dispersion from the MULTIMODEL calculations is important because it reflects systematic differences in resolved wind fields from different reanalysis data sets.