Vertical Dispersion Research Articles

Spurious heating of stellar motions in simulated galactic discs by dark matter halo particles

ABSTRACT We use idealized N-body simulations of equilibrium stellar discs embedded within course-grained dark matter (DM) haloes to study the effects of spurious collisional heating on disc structure and kinematics. Collisional heating artificially increases the vertical and radial velocity dispersions of disc stars, as well as the thickness and size of discs; the effects are felt at all galacto-centric radii. The integrated effects of collisional heating are determined by the mass of DM halo particles (or equivalently, by the number of particles at fixed halo mass), their local density and characteristic velocity dispersion, but are largely insensitive to the stellar particle mass. The effects can therefore be reduced by increasing the mass resolution of DM in cosmological simulations, with limited benefits from increasing the baryonic (or stellar) mass resolution. We provide a simple empirical model that accurately captures the effects of spurious collisional heating on the structure and kinematics of simulated discs, and use it to assess the importance of disc heating for simulations of galaxy formation. We find that the majority of state-of-the-art zoom simulations, and a few of the highest-resolution, smallest-volume cosmological runs, are in principle able to resolve thin stellar discs in Milky Way-mass haloes, but most large-volume cosmological simulations cannot. For example, DM haloes resolved with fewer than ≈106 particles will collisionally heat stars near the stellar half-mass radius such that their vertical velocity dispersion increases by ≳ 10 per cent of the halo’s virial velocity in approximately one Hubble time.

Analysis of aerosol production and aerosol dispersion during otologic surgery.

BackgroundAs a respiratory disease, the transmission of Coronavirus disease (COVID-19) is mainly caused by small droplets and aerosols. Healthcare personnel are particularly exposed during otologic surgery given the continuity with the nasopharynx, where the viral load is high, and the use of high-speed instruments. The purpose of the present study is to test a model of droplet dispersion produced in the performance of a drilling procedure on human bone to provide information about its distribution and size of the deposit in similar conditions to those of an operating theatre, to design different preventive measures.Material and methodA mastoidectomy and trans-labyrinthine approach were performed on an embalmed human corpse using for irrigation during drilling methylene blue dye in physiological saline solution (pss) at a concentration of 0.324 mg/mL. The distribution of the drops was stablished using semi-absorbent papers of size 52 cm × 42 cm covering the area around the dissection field to a radius of 150 cm and on the corpse at different heights to check vertical dispersion. The collected deposit material was analysed with the microscope at different magnification objectives.ResultsDroplets between 2 μm and 2.6 cm were obtained. The visualization of the coloured droplets in the horizontal plane at a magnification of 1.5 was detected at 150 cm from the focus of emission of milling particles.DiscussionAccording to our study, bone drilling with high speed motors under continuous saline irrigation in a haemorrhagic surgical field increases the amount of aerosols exposing healthcare personnel to additional airbone particles. This risk does not end in the operating rooms as particles smaller than 2 μm can be suspended in the air for hours and could exit the operating theatre due to the use of positive pressure systems. Thus, the use of N95, FFP2, FFP3 or PAPRS should be considered and the development of hood systems to prevent the dispersion of aerosols during these procedures should be considered.

Effect of the aspect ratio on the dynamics of air bubbles within Rayleigh–Bénard convection

Laboratory experiments and numerical simulations were performed to quantify the effect of the aspect ratio, Γ, in the dynamics of air bubbles within turbulent Rayleigh–Bénard (RB) convection. We explored four scenarios defined by Γ=1.25, 1.5, 2, and 2.5 under Rayleigh numbers ranging from 2.0×109 to 1.6×1010. Continuous 1-mm bubbles were released at two locations from the bottom along the roll path. Three-dimensional particle tracking velocimetry was used to track a large number of bubbles and determine features of the trajectories and pair dispersion, R2(t), for various initial separations, rp within H/10≤rp≤5H/10; here, H is the height. The R2(t) of the bubbles within a quiescent medium was included for reference. Characterization of the bubble streams, namely, the center of mass (Lc), mean deviation (Rc) to Lc, vertical (vz) and lateral (vL) velocities, and their ratios reveal the strong modulation of the roll structure and Γ. In particular, Lc exhibited an approximately symmetric distribution around the maximum, which occurred at the middle height only in the Γ=1.25 case. Maximum Lc was near the wall top with the highest aspect ratio. However, Rc did not vary substantially among the cases. Bubbles' lateral pair dispersion RL2 shows correlated trends with Γ, particularly at large initial separations and times, whereas the vertical pair dispersion is mainly dominated by buoyancy. The RL2 decreased as Γ increased. It indicates the effect of different-sized roll structures modulated by Γ. In general, R2 embodies distinct features of Γ-modulated bubble dynamics in RB convection.

A new assessment of the circulation of Atlantic and Intermediate Waters in the Eastern Mediterranean

A simulation of the Mediterranean circulation between 2011 and 2020 at a resolution of 3–4 km in the Eastern basin was compared to vertical profiles and horizontal distributions of temperature and salinity from Argo profilers distributed throughout the basin. The comparison is marked by high temporal (∼0.9) and spatial (0.6–0.8) correlations and low biases. Comparisons of SST with satellite imagery have also shown strong similarities for numerous structures over a wide range of spatial scales. The simulation is used to describe the mean circulation of surface Atlantic Waters and Intermediate Waters in winter and summer.The surface circulation is cyclonic alongslope, stronger and more stable in winter. In summer, the current veins are sometimes interrupted and replaced by trains of eddies like in the South Ionian. In other cases, the current becomes very narrow and stuck to the coast as along the Ionian east coast or the Middle East coast. In winter, surface and Levantine Intermediate Waters exit from the Levantine mainly through the Aegean, while in summer, they exit westward south of Crete. The Aegean tends in summer to be isolated by eddies that develop on both sides of the Cretan Arc. The juxtaposition of Ierapetra, the Rhodes Gyre and the Mersa-Matruh Eddies produces a southward path across the Levantine basin at about 27 − 28°E which delimits a large cyclonic circulation to the east which tends to separate the two parts of the basin (west and east Levantine). Concerning the Levantine Intermediate Waters, the alongslope cyclonic circulation all around the Levantine basin in winter is no longer maintained in summer as a large anticyclonic circulation occupies the southeast of the basin. The intermediate waters entering the Ionian either through southern Crete in summer or through the Aegean in winter, are submitted to a strong northward, southward and even westward dispersion by Pelops and the nearby anticyclonic areas. The presence of recurrent anticyclones between 35 and 37°N along a band extending from west to east of the Ionian also produces a vertical dispersion of intermediate water. Finally, the circulation of intermediate water in the South Ionian is marked by an important seasonality with the presence in summer of a large anticyclonic circulation that seems to be wind induced and finally drives a secondary branch to the Sicily Channel. A climatology for the transport through the different straits is discussed and simplified representations of the circulation are proposed.

Particle behaviours of biomass gasification in a bubbling fluidized bed

Biomass gasification in a bubbling fluidized bed (BFB) reactor is numerically studied based on a particle-scale computational fluid dynamics-discrete element method (CFD-DEM), with thermochemical and polydispersity effects featuring. After model validation, the particle-scale information (e.g., particle motions, particle mixing, solid dispersion, and heat transfer contribution) are thoroughly explored with the discussion of the effects of several critical operating parameters on particle behaviours. The results show that the middle dense region has the highest biomass pyrolysis reaction rate due to the vigorous particle motion. Sand and biomass particles show synchronous horizontal motions, and the solid vertical dispersion coefficients are much higher than the solid horizontal ones, denoting that the vertically introduced gas flow dominates bed hydrodynamics. A higher operating temperature causes a higher solid dispersion coefficient. Elevating temperature and steam to biomass ratio (S/B) first increases and then decreases the particle mixing index. Convection plays a dominant role during the biomass gasification process, followed by the radiation and heat of reaction. The conduction accounts for the smallest proportion and can be neglected. Increasing operating temperature promotes chemical reactions, biomass temperature, and all heat transfer modes. Increasing S/B promotes biomass motions and gasification reactions, leading to more heat consumed and biomass temperature decrease. Decreasing biomass temperature results in a larger temperature difference between biomass particles and bed material, which enhances the conduction, convection, and radiation.

Effects of wind direction and building array arrangement on airflow and contaminant distributions in the central space of buildings

Buildings are physical obstacles that diminish the benefits of wind by creating turbulence and reducing airflow velocities in urban settings. Particularly in the inner garden or amenities situated at the pedestrian level in the central space of a group of buildings, the efficiency of pollutant dispersion determines air quality and outdoor health. In this study, the effects of incident wind angles on wind velocity and pollutant distribution inside the central space of two building arrays arranged in ‘L’ and ‘U’ shapes were examined using computational fluid dynamics simulations. The ‘L’-shaped array performed better than the ‘U’-shaped array by forming a smaller low-wind-velocity (LWV) zone in the central space of the buildings (34.9%–76.11 % of the total space). The ‘L’-shaped array performed best at an incident wind angle of 225°, in which the LWV zone covered only 34.52 % of the central space. A 90° incident angle produced the largest LWV zone (81.80 %) for the ‘U’-shaped array. The ‘L’-shaped array generally distributed pollutants better than the ‘U’-shaped array. However, the ‘U’-shaped array with a 180° wind angle had a smaller high pollutant concentration area than the ‘L’-shaped array with a wind angle of 225° (Kc > 218.5 covering only 0.37 %). The worst vertical dispersion corresponded to a 135° wind angle for the ‘L’-shaped array, which recorded the highest Kc at the mid-level of the building. In conclusion, the appropriate selection of building array designs and their orientations allows for the most effective use of wind flow to enhance ventilation and pollutant dispersion.

Understanding Vertical Pay Dispersion in the Public Sector: The Role of Publicness

This study introduces vertical pay dispersion into public management research, a prevailing equity issue in discussions in organizations and society. Bridging tournament and equity theory with the publicness debate, the study analyses how manager-to-worker pay ratios of state-owned enterprises (SOEs) are affected by the dimensions of publicness – ownership, funding, and control. For a unique, hand-collected, five-year data set, the study finds that ownership publicness partly affects vertical pay dispersion, and the effects are moderated by city and SOE size. It enhances the understanding of vertical pay dispersion in the public sector and offers a research agenda for the determinants.

Gentle Topography Increases Vertical Transport of Coarse Dust by Orders of Magnitude

AbstractThe presence of coarse mineral dust in the atmosphere has been substantiated in several recent measurement campaigns, which include observations of particles up to and above 100 μm in diameter. Yet, atmospheric dust models either do not include particles larger than 20 μm or severely underestimate their concentrations. One possibility for the underestimated concentrations is that models do not represent enhancements of particle transport due to subgrid‐scale topography. Here, large‐eddy simulations are used in combination with Lagrangian particle tracking to assess the impact of gentle two‐dimensional topography with 50 and 100 m elevation on the vertical transport of coarse dust in neutrally stratified conditions. The presence of topography significantly increases the likelihood that 5 and 20 μm particles reach several hundred meters in altitude. Further, topography increases this likelihood by orders of magnitude for larger 60 μm particles. Three mechanisms are observed to contribute to the increased vertical transport: a strong upward mean flow region on the uphill side of the topography, ejection of particles downwind of the topography crest, and enhanced vertical dispersion in the wake of the crest. The compounding effects of these mechanisms provide a pathway for coarse dust emitted from the surface to reach elevations where they can be further transported into the free atmosphere by large‐scale motions such as convective plumes. While these findings are motivated by mineral dust observations, they are generally applicable to other heavy aerosols such as pollen.

Impacts of synoptic forcing and topography on aerosol pollution during winter in Shenyang, Northeast China

Northeast China frequently experiences aerosol pollution episodes in winter. In addition to the pollutant emissions, synoptic pattern and topography can impact the air quality in complex ways, which are still not well understood in Northeast China. Therefore, the impacts of synoptic forcing and topography on aerosol pollution in Shenyang were investigated combining surface observations, sounding measurements, and three-dimensional air quality simulations. The studied pollution episode occurred from January 1 to 5, 2020, along with poor meteorological dispersion conditions characterized by weak winds, strong thermal stabilities, and shallow planetary boundary layers (PBLs). During the formation of pollution, strong elevated thermal inversion layers were observed over Shenyang, induced by the large-scale synoptic pattern, which suppressed the PBL growth and the vertical dispersion of aerosols. Moreover, the blocking effect of mountains to the east of Shenyang further worsened the pollution when northwesterly/westerly flows prevailed in shallow PBLs. Numerical sensitive experiment was conducted to estimate the contribution of blocking effect of mountains to the near-surface PM2.5 concentration in Shenyang, and it was found that around one third of PM2.5 concentration during January 1–4 was relevant to the terrain effect. These findings can facilitate a comprehensive understanding of the physical formation of aerosol pollution in Northeast China and helpful for the pollution controls.

Seasonal and vertical characteristics of particulate and elemental concentrations along diverse street canyons in South India.

The impact of street geometries on vertical dispersion of PMs (PM2.5 and PM10) in (1) non-street canyon (NSC), (2) street canyon (SC), and (3) street canyon with viaduct (SCV) was studied during four seasons. The chemical composition of the species was analysed for source apportionment. The mass concentration of PMs in canyons was in the order of SCV > SC > NSC, implicating the canyon effect. Independent of height, most of the PM concentrations in SC and SCV violated the National Ambient Air Quality Standards (NAAQS) and exceeded the World Health Organization (WHO) guidelines in all three street geometries. The vertical concentration trend of PMs was significant during winter and summer seasons in NSC and SC. The vertical trend of both PMs was significant during summer and monsoon seasons in SCV. The seasonal change in PMs' vertical trend was influenced by atmospheric stability, wind velocities associated with street morphology, and emission sources. The ratio of PM2.5/PM10 indicated the dominance of PM10 in all three locations. Among the estimated species, Fe (crustal and vehicle) and Na (sea salt and crustal) were abundant in PM2.5 and PM10, respectively. Estimation of enrichment factor (EF) revealed that most of the emission sources were anthropogenic in PM2.5 and natural in PM10. Principal component analysis (PCA) showed crustal/soil dust, vehicular emission, and sea salt to the common source profile for PMs. Specific contribution of smoking activity contributed to Be and Tl in PM2.5, which may be considered a site-specific source.

Simulation of vertical dispersion of oil droplets by Langmuir supercells through a Reynolds-averaged Eulerian formulation combined with Lagrangian particle tracking

Langmuir supercells (LS) are full-depth Langmuir circulations in unstratified shallow shelves. A Reynolds-averaged Eulerian formulation is developed resolving LS as a secondary component to the wind-driven mean shear current. This formulation is combined with Lagrangian particle tracking to investigate oil droplet entrainment induced by LS as a function of wind stress. Two cases are simulated, one in which 500-μm oil droplets are released into a steady field of LS generated by a wind stress of 0.1 N m−2 and waves of intermediate wavelength λ=6H where H=15 m is the water column depth, significant amplitude of 0.6 m and period of 8 s. In the second case, the 500-μm oil droplets are released into a steady field of LS generated by the same wave forcing but with a weaker wind stress of 0.025 N m−2. It is found that the greater wind stress leads to LS able to spread the droplets throughout upwelling and downwelling limbs of the cells within the first 80 minutes after release. The weaker wind leads to weaker LS that, within the same time after release, limit the dispersion of the droplets to the downwelling limbs of the cells forming Stommel retention zones for a prolonged time.

Estimation of Macrodispersivity in Bounded Formations by Circulant Embedding and Analysis of Variance

AbstractWe present a new method to estimate the displacement covariance and macrodispersivity for solute transport in bounded formations. Here we use circulant embedding, which is based on fast Fourier transform and is much more efficient than eigen‐decomposition, for the factorization of random spatial fields. We compute the displacement covariances by the analysis of variance approach, and introduce an interpolation process to significantly reduce the number of forward simulations. Once the effect of each eigenvector on the displacement covariance is obtained, it is unnecessary to rerun the simulator for different spatial covariance functions or anisotropy ratios, which saves a large amount of computational effort. The proposed method is validated in various tests in two‐dimensional and three‐dimensional examples and accurately matches the results from the Monte Carlo simulation. It is found that the longitudinal dispersivity is less sensitive to the impervious boundaries, while the transverse and vertical dispersivities are greatly affected. The method is applied to the Borden site and provides a better explanation of the observed data after considering the effect of vertical boundaries. These results show that our method could serve as a promising tool for studying and predicting the characteristics of solute transport in heterogeneous media.

Effects of a rooftop wind turbine on the dispersion of air pollutant behind a cube-shaped building

The concentration distribution of urban air pollutants is closely related to people's health. As an important utilization form of urban wind power, rooftop wind turbines have been widely used in cities. The wake effect of the rooftop wind turbines will change the flow behind buildings and then affect the pollutant dispersion. To this end, the pollutant dispersion behind the building is studied via the computational fluid dynamics method. The actuator disk model and idealized cube are adopted to model the wind turbine and the building, respectively. The study shows that the rooftop wind turbine can reduce the pollutant mass fraction near the ground and the pedestrian level. Due to the wake effect of the rooftop wind turbine, the turbulent fluctuation behind the building is weakened, and the spanwise pollutant dispersion is suppressed. Besides, the rooftop wind turbine weakens the downwash movement of the building, which enhances the vertical pollutant dispersion.

An observational testbed for cosmological zoom-in simulations: constraining stellar migration in the solar cylinder using asteroseismology

ABSTRACT Large-scale stellar surveys coupled with recent developments in magneto-hydrodynamical simulations of the formation of Milky Way-mass galaxies provide an unparalleled opportunity to unveil the physical processes driving the evolution of the Galaxy. We developed a framework to compare a variety of parameters with their corresponding predictions from simulations in an unbiased manner, taking into account the selection function of a stellar survey. We applied this framework to a sample of over 7000 stars with asteroseismic, spectroscopic, and astrometric data available, together with six simulations from the Auriga project. We found that some simulations are able to produce abundance dichotomies in the [Fe/H]−[α/Fe] plane which look qualitatively similar to observations. The peak of their velocity distributions match the observed data reasonably well; however, they predict hotter kinematics in terms of the tails of the distributions and the vertical velocity dispersion. Assuming our simulation sample is representative of Milky Way-like galaxies, we put upper limits of 2.21 and 3.70 kpc on radial migration for young (<4 Gyr) and old (∈[4, 8] Gyr) stellar populations in the solar cylinder. Comparison between the observed and simulated metallicity dispersion as a function of age further constrains migration to about 1.97 and 2.91 kpc for the young and old populations. These results demonstrate the power of our technique to compare numerical simulations with high-dimensional data sets, and paves the way for using the wider field TESS asteroseismic data together with the future generations of simulations to constrain the sub-grid models for turbulence, star formation, and feedback processes.

Fundamental relations for the velocity dispersion of stars in the Milky Way

ABSTRACT We explore the fundamental relations governing the radial and vertical velocity dispersions of stars in the Milky Way, from combined studies of complementary surveys including GALAH, LAMOST, APOGEE, the NASA Kepler and K2 missions, and Gaia DR2. We find that different stellar samples, even though they target different tracer populations and employ a variety of age estimation techniques, follow the same set of fundamental relations. We provide the clearest evidence to date that, in addition to the well-known dependence on stellar age, the velocity dispersions of stars depend on orbital angular momentum Lz, metallicity, and height above the plane |z|, and are well described by a multiplicatively separable functional form. The dispersions have a power-law dependence on age with exponents of 0.441 ± 0.007 and 0.251 ± 0.006 for σz and σR, respectively, and the power law is valid even for the oldest stars. For the solar neighbourhood stars, the apparent break in the power law for older stars, as seen in previous studies, is due to the anticorrelation of Lz with age. The dispersions decrease with increasing Lz until we reach the Sun’s orbital angular momentum, after which σz increases (implying flaring in the outer disc) while σR flattens. For a given age, the dispersions increase with decreasing metallicity, suggesting that the dispersions increase with birth radius. The dispersions also increase linearly with |z|. The same set of relations that work in the solar neighbourhood also work for stars between 3 < R/kpc < 20. Finally, the high-[α/Fe] stars follow the same relations as the low-[α/Fe] stars.

Study of vertical line source dispersion in a turbulent channel flow

Turbulent dispersion of passive concentration released from a vertical line source in a fully-developed channel flow is studied using direct numerical simulation (DNS). The investigation into the turbulent transport processes of the momentum and concentration is conducted in both physical and spectral spaces, based on a systematic analysis of the statistical moments of the velocity and concentration fields, probability density functions (PDFs) of the concentration fluctuations, and the characteristic wavelengths of energetic eddies that dominate turbulent mixing processes. It is observed that the plume development experiences turbulent convective- and diffusive-stages through a comparative study of the spatial and temporal scales of the velocity and concentration fields. It is also observed that the meandering ratio is small near the ground and within the turbulent diffusive stage, and PDFs of concentration fluctuations are sensitive to both the wall-normal distance and the downstream distance from the concentrated line source.

Recolonization by Slugs: Vertical and Horizontal Dispersal by the Field Slug, Deroceras reticulatum.

Simple SummarySlugs are persistent pests. Following control treatments, the numbers of slugs can rapidly return to pre-treatment levels and it is often assumed they are migrating in to the site from adjacent areas. By comparing plots with restricted access to those with open access over a 32-month period we were able to compare the importance of migration from adjacent areas with migration from the soil below the plots. For Deroceras reticulatum, which is a major pest species, a large proportion of immigration came from soil below the undisturbed grassland plots. The importance of this inactive subpopulation, below the soil surface, needs further study.Following treatment with molluscicides or other controls, slugs can recolonize a site very quickly, but the proportion of the colonizing slugs moving from adjacent areas (horizontal dispersal) and the proportion from within the soil (vertical dispersal) has not previously been established. At a grassland site, barriers were used to exclude and trap slugs in order to estimate horizontal and vertical movement over a period of 32 months. For the first 15 months vertical movement made a significant contribution to the slugs recolonizing a grassland area. The ecological mechanisms occurring and the implications for the control of slugs are discussed.

Spectral Observations of Superthin Galaxies

Abstract We conduct spectral observations of 138 superthin galaxies (STGs) with high radial-to-vertical stellar disk scale ratios with the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory (APO) to obtain the ionized gas rotation curves with R ∼5000 resolution. We also performed near-infrared (NIR) H and Ks photometry for 18 galaxies with the NICFPS camera on the 3.5 m telescope. The spectra, the NIR photometry, and published optical and NIR photometry are used for modeling that utilizes the thickness of the stellar disk and rotation curves simultaneously. The projection and dust extinction effects are taken into account. We evaluate eight models that differ in their free parameters and constraints. As a result, we estimated the masses and scale lengths of the galactic dark halos. We find systematic differences between the properties of our red and blue STGs. The blue STGs have a large fraction of dynamically underevolved galaxies whose vertical velocity dispersion is low in both gas and stellar disks. The dark halo-to-disk scale ratio is shorter in the red STGs than in the blue ones, but in a majority of all STGs, this ratio is under 2. The optical color (r − i) of the STGs correlates with their rotation curve maximum, vertical velocity dispersion in stellar disks, and mass of the dark halo. We conclude that there is a threshold central surface density of 50 M ⊙ pc−2 below which we do not observe very thin, rotationally supported galactic disks.

Angle-resolved photoemission spectroscopy study of rare-earth tritelluride charge density wave compounds: RTe3 (R = Pr, Er)

The electronic structures of layered rare-earth tritelluride RTe3 (R = Pr, Er) charge density wave (CDW) compounds have been investigated by performing R 4d → 4f resonant photoemission spectroscopy (RPES) and angle-resolved photoemission spectroscopy (ARPES) measurements for high-quality single crystals. R 4d → 4f RPES measurements reveal that the R 4f states do not contribute directly to the CDW formation in RTe3 but that the R 4f-Te 5p hybridization in PrTe3 is significantly larger than that in ErTe3. In the photon-energy maps for the Fermi-edge (E F)-crossing states in RTe3, straight vertical dispersions are observed along k c , demonstrating the 2D character for the near-E F states in both R = Pr and Er. This finding implies the weak interlayer interaction between R-Te(1) and Te(2)–Te(3) layers, which is supported by the similar linear dichroism in ARPES for PrTe3 and ErTe3. The CDW-induced Fermi surface of PrTe3 exhibits two-fold symmetric features while that of ErTe3 exhibits four-fold symmetric features. This finding reveals different CDW distortions in PrTe3 and ErTe3, the origin of which is likely to be different ionic sizes of R ions and different R 4f-Te 5p hybridization.

Vertical location of ephemeral resources by adult Diptera: Implications for the colonization of cadavers in high-rise buildings

Sarcosaprophagous flies (Diptera) rank among the most common insects associated with human-transformed environments all over the world. Synanthropic species of the families Calliphoridae, Muscidae, Sarcophagidae and Phoridae, in particular, have tremendous forensic importance due to their ability to colonize human cadavers and thus provide information on minimum post-mortem interval. Recently, cases of flies colonizing cadavers inside buildings of different heights drew attention to the vertical dispersal abilities of these flies, a subject that has received little attention. We investigated the vertical distribution of sarcosaprophagous flies in an urban environment, using uninhabited buildings as experimental models in Northeastern Brazil. To assess the vertical stratification of flies, one in every three floors of nine buildings was sampled using traps baited with bovine spleen, from the ground to the 27th floor. Calliphoridae was the most abundant family (52.9%), followed by Muscidae (41.2%), Sarcophagidae (3.2%) and Phoridae (2.7%). Most of the insects were collected at ground level (78.8%), with a decreasing abundance registered on the higher floors. Nevertheless, adults of the four families tested here were able to reach substrates as high as the 15th floor, which corresponds to approximately 48 m in height. Regarding calliphorids, seven species were identified, of which Chrysomya albiceps (30.4%) and C. megacephala (68.3%) were the most abundant. This is, to our knowledge, the first detailed, replicated study on vertical resource localization of sarcosaprophagous flies.