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1
GOTOH, Hitoshi, Tetsuo SAKAI, and Tomoki SHIBAHARA. "LAGRANGIAN FLOW SIMULATION WITH SUB-PARTICLE-SCALE TURBULENCE MODEL." PROCEEDINGS OF HYDRAULIC ENGINEERING 44 (2000): 575–80. http://dx.doi.org/10.2208/prohe.44.575.
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Ganshin, A., T. Oda, M. Saito, S. Maksyutov, V. Valsala, R. J. Andres, R. E. Fisher, et al. "A global coupled Eulerian-Lagrangian model and 1 × 1 km CO<sub>2</sub> surface flux dataset for high-resolution atmospheric CO<sub>2</sub> transport simulations." Geoscientific Model Development 5, no. 1 (February 15, 2012): 231–43. http://dx.doi.org/10.5194/gmd-5-231-2012.
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Abstract. We designed a method to simulate atmospheric CO2 concentrations at several continuous observation sites around the globe using surface fluxes at a very high spatial resolution. The simulations presented in this study were performed using the Global Eulerian-Lagrangian Coupled Atmospheric model (GELCA), comprising a Lagrangian particle dispersion model coupled to a global atmospheric tracer transport model with prescribed global surface CO2 flux maps at a 1 × 1 km resolution. The surface fluxes used in the simulations were prepared by assembling the individual components of terrestrial, oceanic and fossil fuel CO2 fluxes. This experimental setup (i.e. a transport model running at a medium resolution, coupled to a high-resolution Lagrangian particle dispersion model together with global surface fluxes at a very high resolution), which was designed to represent high-frequency variations in atmospheric CO2 concentration, has not been reported at a global scale previously. Two sensitivity experiments were performed: (a) using the global transport model without coupling to the Lagrangian dispersion model, and (b) using the coupled model with a reduced resolution of surface fluxes, in order to evaluate the performance of Eulerian-Lagrangian coupling and the role of high-resolution fluxes in simulating high-frequency variations in atmospheric CO2 concentrations. A correlation analysis between observed and simulated atmospheric CO2 concentrations at selected locations revealed that the inclusion of both Eulerian-Lagrangian coupling and high-resolution fluxes improves the high-frequency simulations of the model. The results highlight the potential of a coupled Eulerian-Lagrangian model in simulating high-frequency atmospheric CO2 concentrations at many locations worldwide. The model performs well in representing observations of atmospheric CO2 concentrations at high spatial and temporal resolutions, especially for coastal sites and sites located close to sources of large anthropogenic emissions. While this study focused on simulations of CO2 concentrations, the model could be used for other atmospheric compounds with known estimated emissions.
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Ganshin, A., T. Oda, M. Saito, S. Maksyutov, V. Valsala, R. J. Andres, R. Fischer, et al. "A global coupled Eulerian-Lagrangian model and 1 × 1 km CO<sub>2</sub> surface flux dataset for high-resolution atmospheric CO<sub>2</sub> transport simulations." Geoscientific Model Development Discussions 4, no. 3 (August 24, 2011): 2047–80. http://dx.doi.org/10.5194/gmdd-4-2047-2011.
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Abstract. We designed a method to simulate atmospheric CO2 concentrations at several continuous observation sites around the globe using surface fluxes at a very high spatial resolution. The simulations presented in this study were performed using a Lagrangian particle dispersion model coupled to a global atmospheric tracer transport model with prescribed global surface CO2 flux maps at a 1 × 1 km resolution. The surface fluxes used in the simulations were prepared by assembling the individual components of terrestrial, oceanic and fossil fuel CO2 fluxes. This experimental setup (i.e., a transport model running at a medium resolution, coupled to a high-resolution Lagrangian particle dispersion model together with global surface fluxes at a very high resolution), which was designed to represent high-frequency variations in atmospheric CO2 concentration, has not been reported at a global scale previously. Two sensitivity experiments were performed: (a) using the global transport model without coupling to the Lagrangian dispersion model, and (b) using the coupled model with a reduced resolution of surface fluxes, in order to evaluate the performance of Eulerian-Lagrangian coupling and the role of high-resolution fluxes in simulating high-frequency variations in atmospheric CO2 concentrations. A correlation analysis between observed and simulated atmospheric CO2 concentrations at selected locations revealed that the inclusion of both Eulerian-Lagrangian coupling and high-resolution fluxes improves the high-frequency simulations of the model. The results highlight the potential of a coupled Eulerian-Lagrangian model in simulating high-frequency atmospheric CO2 concentrations at many locations worldwide. The model performs well in representing observations of atmospheric CO2 concentrations at high spatial and temporal resolutions, especially for coastal sites and sites located close to sources of large anthropogenic emissions. While this study focused on simulations of CO2 concentrations, the model could be used for other atmospheric compounds with known estimated emissions.
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Turner, Adrian K., Kara J. Peterson, and Dan Bolintineanu. "Geometric remapping of particle distributions in the Discrete Element Model for Sea Ice (DEMSI v0.0)." Geoscientific Model Development 15, no. 5 (March 9, 2022): 1953–70. http://dx.doi.org/10.5194/gmd-15-1953-2022.
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Abstract. A new sea ice dynamical core, the Discrete Element Model for Sea Ice (DEMSI), is under development for use in coupled Earth system models. DEMSI is based on the discrete element method, which models collections of ice floes as interacting Lagrangian particles. In basin-scale sea ice simulations the Lagrangian motion results in significant convergence and ridging, which requires periodic remapping of sea ice variables from a deformed particle configuration back to an undeformed initial distribution. At the resolution required for Earth system models we cannot resolve individual sea ice floes, so we adopt the sub-grid-scale thickness distribution used in continuum sea ice models. This choice leads to a series of hierarchical tracers depending on ice fractional area or concentration that must be remapped consistently. The circular discrete elements employed in DEMSI help improve the computational efficiency at the cost of increased complexity in the effective element area definitions for sea ice cover that are required for the accurate enforcement of conservation. An additional challenge is the accurate remapping of element values along the ice edge, the location of which varies due to the Lagrangian motion of the particles. In this paper we describe a particle-to-particle remapping approach based on well-established geometric remapping ideas that enforces conservation, bounds preservation, and compatibility between associated tracer quantities, while also robustly managing remapping at the ice edge. One element of the remapping algorithm is a novel optimization-based flux correction that enforces concentration bounds in the case of nonuniform motion. We demonstrate the accuracy and utility of the algorithm in a series of numerical test cases.
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Rutherford, B., and M. T. Montgomery. "A Lagrangian analysis of a developing and non-developing disturbance observed during the PREDICT experiment." Atmospheric Chemistry and Physics Discussions 11, no. 12 (December 19, 2011): 33273–323. http://dx.doi.org/10.5194/acpd-11-33273-2011.
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Abstract. The problem of tropical cyclone formation requires among other things an improved understanding of recirculating flow regions on sub-synoptic scales in a time evolving flow with typically sparse real-time data. This recirculation problem has previously been approached assuming as a first approximation both a layer-wise two-dimensional and nearly steady flow in a co-moving frame with the parent tropical wave or disturbance. This paper provides an introduction of new Lagrangian techniques for locating flow boundaries that encompass regions of recirculation in time-dependent flows that relax the steady flow approximation. Lagrangian methods detect recirculating regions from time-dependent data and offer a more complete methodology than the approximate steady framework. The Lagrangian reference frame follows particle trajectories so that flow boundaries which constrain particle transport can be viewed objectively. Finite-time Lagrangian scalar field methods from dynamical systems theory offer a way to compute boundaries from grids of particles seeded in and near a disturbance. The methods are applied to both a developing and non-developing disturbance observed during the recent pre-depression investigation of cloud systems in the tropics (PREDICT) experiment. The data for this analysis is derived from global forecast model output that assimilated the dropsonde observations as they were being collected by research aircraft. Since Lagrangian methods require trajectory integrations, we address some practical issues of using Lagrangian methods in the tropical cyclogenesis problem. Lagrangian diagnostics developed here are used to evaluate the previously hypothesized import of dry air into ex-Gaston, which did not re-develop into a tropical cyclone, and the exclusion of dry air from pre-Karl, which did become a tropical cyclone and later a major hurricane.
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Rutherford, B., and M. T. Montgomery. "A Lagrangian analysis of a developing and non-developing disturbance observed during the PREDICT experiment." Atmospheric Chemistry and Physics 12, no. 23 (December 3, 2012): 11355–81. http://dx.doi.org/10.5194/acp-12-11355-2012.
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Abstract. The problem of tropical cyclone formation requires among other things an improved understanding of recirculating flow regions on sub-synoptic scales in a time evolving flow with typically sparse real-time data. This recirculation problem has previously been approached assuming as a first approximation both a layer-wise two-dimensional and nearly steady flow in a co-moving frame with the parent tropical wave or disturbance. This paper provides an introduction of Lagrangian techniques for locating flow boundaries that encompass regions of recirculation in time-dependent flows that relax the steady flow approximation. Lagrangian methods detect recirculating regions from time-dependent data and offer a more complete methodology than the approximate steady framework. The Lagrangian reference frame follows particle trajectories so that flow boundaries which constrain particle transport can be viewed in a frame-independent setting. Finite-time Lagrangian scalar field methods from dynamical systems theory offer a way to compute boundaries from grids of particles seeded in and near a disturbance. The methods are applied to both a developing and non-developing disturbance observed during the recent pre-depression investigation of cloud systems in the tropics (PREDICT) experiment. The data for this analysis is derived from global forecast model output that assimilated the dropsonde observations as they were being collected by research aircraft. Since Lagrangian methods require trajectory integrations, we address some practical issues of using Lagrangian methods in the tropical cyclogenesis problem. Lagrangian diagnostics are used to evaluate the previously hypothesized import of dry air into ex-Gaston, which did not re-develop into a tropical cyclone, and the exclusion of dry air from pre-Karl, which did become a tropical cyclone and later a major hurricane.
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Sanchez, Kevin J., Bo Zhang, Hongyu Liu, Matthew D. Brown, Ewan C. Crosbie, Francesca Gallo, Johnathan W. Hair, et al. "North Atlantic Ocean SST-gradient-driven variations in aerosol and cloud evolution along Lagrangian cold-air outbreak trajectories." Atmospheric Chemistry and Physics 22, no. 4 (March 2, 2022): 2795–815. http://dx.doi.org/10.5194/acp-22-2795-2022.
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Abstract. Atmospheric marine particle concentrations impact cloud properties, which strongly impact the amount of solar radiation reflected back into space or absorbed by the ocean surface. While satellites can provide a snapshot of current conditions at the overpass time, models are necessary to simulate temporal variations in both particle and cloud properties. However, poor model accuracy limits the reliability with which these tools can be used to predict future climate. Here, we leverage the comprehensive ocean ecosystem and atmospheric aerosol–cloud dataset obtained during the third deployment of the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES3). Airborne and ship-based measurements were collected in and around a cold-air outbreak during a 3 d (where d stands for day) intensive operations period from 17–19 September 2017. Cold-air outbreaks are of keen interest for model validation because they are challenging to accurately simulate, which is due, in part, to the numerous feedbacks and sub-grid-scale processes that influence aerosol and cloud evolution. The NAAMES observations are particularly valuable because the flight plans were tailored to lie along Lagrangian trajectories, making it possible to spatiotemporally connect upwind and downwind measurements with the state-of-the-art FLEXible PARTicle (FLEXPART) Lagrangian particle dispersion model and then calculate a rate of change in particle properties. Initial aerosol conditions spanning an east–west, closed-cell-to-clear-air transition region of the cold-air outbreak indicate similar particle concentrations and properties. However, despite the similarities in the aerosol fields, the cloud properties downwind of each region evolved quite differently. One trajectory carried particles through a cold-air outbreak, resulting in a decrease in accumulation mode particle concentration (−42 %) and cloud droplet concentrations, while the other remained outside of the cold-air outbreak and experienced an increase in accumulation mode particle concentrations (+62 %). The variable meteorological conditions between these two adjacent trajectories result from differences in the local sea surface temperature in the Labrador Current and surrounding waters, altering the stability of the marine atmospheric boundary layer. Further comparisons of historical satellite observations indicate that the observed pattern occurs annually in the region, making it an ideal location for future airborne Lagrangian studies tracking the evolution of aerosols and clouds over time under cold-air outbreak conditions.
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Wu, Dien, John C. Lin, Benjamin Fasoli, Tomohiro Oda, Xinxin Ye, Thomas Lauvaux, Emily G. Yang, and Eric A. Kort. "A Lagrangian approach towards extracting signals of urban CO<sub>2</sub> emissions from satellite observations of atmospheric column CO<sub>2</sub> (XCO<sub>2</sub>): X-Stochastic Time-Inverted Lagrangian Transport model (“X-STILT v1”)." Geoscientific Model Development 11, no. 12 (December 4, 2018): 4843–71. http://dx.doi.org/10.5194/gmd-11-4843-2018.
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Abstract. Urban regions are responsible for emitting significant amounts of fossil fuel carbon dioxide (FFCO2), and emissions at the finer, city scales are more uncertain than those aggregated at the global scale. Carbon-observing satellites may provide independent top-down emission evaluations and compensate for the sparseness of surface CO2 observing networks in urban areas. Although some previous studies have attempted to derive urban CO2 signals from satellite column-averaged CO2 data (XCO2) using simple statistical measures, less work has been carried out to link upwind emission sources to downwind atmospheric columns using atmospheric models. In addition to Eulerian atmospheric models that have been customized for emission estimates over specific cities, the Lagrangian modeling approach – in particular, the Lagrangian particle dispersion model (LPDM) approach – has the potential to efficiently determine the sensitivity of downwind concentration changes to upwind sources. However, when applying LPDMs to interpret satellite XCO2, several issues have yet to be addressed, including quantifying uncertainties in urban XCO2 signals due to receptor configurations and errors in atmospheric transport and background XCO2. In this study, we present a modified version of the Stochastic Time-Inverted Lagrangian Transport (STILT) model, “X-STILT”, for extracting urban XCO2 signals from NASA's Orbiting Carbon Observatory 2 (OCO-2) XCO2 data. X-STILT incorporates satellite profiles and provides comprehensive uncertainty estimates of urban XCO2 enhancements on a per sounding basis. Several methods to initialize receptor/particle setups and determine background XCO2 are presented and discussed via sensitivity analyses and comparisons. To illustrate X-STILT's utilities and applications, we examined five OCO-2 overpasses over Riyadh, Saudi Arabia, during a 2-year time period and performed a simple scaling factor-based inverse analysis. As a result, the model is able to reproduce most observed XCO2 enhancements. Error estimates show that the 68 % confidence limit of XCO2 uncertainties due to transport (horizontal wind plus vertical mixing) and emission uncertainties contribute to ∼33 % and ∼20 % of the mean latitudinally integrated urban signals, respectively, over the five overpasses, using meteorological fields from the Global Data Assimilation System (GDAS). In addition, a sizeable mean difference of −0.55 ppm in background derived from a previous study employing simple statistics (regional daily median) leads to a ∼39 % higher mean observed urban signal and a larger posterior scaling factor. Based on our signal estimates and associated error impacts, we foresee X-STILT serving as a tool for interpreting column measurements, estimating urban enhancement signals, and carrying out inverse modeling to improve quantification of urban emissions.
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Olin, M., T. Rönkkö, and M. Dal Maso. "CFD modeling of a vehicle exhaust laboratory sampling system: sulfur driven nucleation and growth in diluting diesel exhaust." Atmospheric Chemistry and Physics Discussions 15, no. 2 (January 29, 2015): 2905–56. http://dx.doi.org/10.5194/acpd-15-2905-2015.
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Abstract. A new exhaust aerosol model CFD-TUTEAM (Tampere University of Technology Exhaust Aerosol Model for Computational Fluid Dynamics) was developed. The model can be used to simulate particle formation and evolution in diesel exhaust. The model has an Eulerian sub-model that provides spatial information within the computational domain, and a computationally less expensive Lagrangian sub-model that can be used to examine particle formation in a high temporal resolution. Particle formation in a laboratory sampling system that includes a porous tube type diluter and an aging chamber was modeled with CFD-TUTEAM. The simulation results imply that over 99% of new particles are formed in the aging chamber region, because nucleation rate remains at high level in the aging chamber due to low dilution ratio and low nucleation exponents. The nucleation exponents for sulfuric acid in sulfuric acid-water nucleation ranging from 0.25 to 1 appeared to fit best with measurement data, which are the same values as the slopes of volatile nucleation mode number concentration vs. raw exhaust sulfuric acid concentration obtained from the measurement data. These nucleation exponents are very low compared to the nucleation exponents obtained from the classical nucleation theory of binary sulfuric acid-water nucleation. The values of nucleation exponent lower than unity suggest that other compounds, such as hydrocarbons, might have a significant role in the nucleation process.
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Emmerson, K. M., A. R. MacKenzie, S. M. Owen, M. J. Evans, and D. E. Shallcross. "A Lagrangian model with simple primary and secondary aerosol scheme 1: comparison with UK PM<sub>10</sub> data." Atmospheric Chemistry and Physics Discussions 4, no. 3 (June 15, 2004): 3127–57. http://dx.doi.org/10.5194/acpd-4-3127-2004.
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Abstract. A Lagrangian trajectory model used to simulate photochemistry has been extended to include a simple parameterisation of primary and secondary aerosol particles. The model uses emission inventories of primary particles for the UK from the NAEI (National Atmospheric Emissions Inventory for the UK), and for Europe from the TNO (Institute of Environmental Sciences, Energy Research and Process Innovation, the Netherlands) respectively, to transport tracers representing PM10. One biogenic and two anthropogenic organic compounds were chosen as surrogates to model the formation of condensable material suitable for the production of secondary organic aerosol (SOA). The SOA is added to the primary PM10 and compared to measured PM10 at one urban and two rural UK receptor sites. The results show an average under-prediction by factors of 4.5 and 8.9 in the urban and rural cases respectively. The model is also used to simulate production of two secondary inorganic species, H2SO4 and HNO3, which are assumed, as a limiting case, to be present in the particle phase. The relationships between modelled and measured total PM10 improved with the addition of secondary inorganic compounds, and the overall model under-prediction factors are reduced to 3.5 and 3.9 in the urban and rural cases respectively. Nevertheless, our conclusion is that current emissions and chemistry do not appear to provide sufficient information to model PM10 well (i.e. to within a factor of two). There is a need for further process studies to inform global climate modelling that includes climate forcing by aerosol.
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Emmerson, K. M., A. R. MacKenzie, S. M. Owen, M. J. Evans, and D. E. Shallcross. "A Lagrangian model with simple primary and secondary aerosol scheme 1: comparison with UK PM<sub>10</sub> data." Atmospheric Chemistry and Physics 4, no. 8 (November 9, 2004): 2161–70. http://dx.doi.org/10.5194/acp-4-2161-2004.
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Abstract. A Lagrangian trajectory model used to simulate photochemistry has been extended to include a simple parameterisation of primary and secondary aerosol particles. The model uses emission inventories of primary particles for the UK from the NAEI (National Atmospheric Emissions Inventory for the UK), and for Europe from the TNO (Institute of Environmental Sciences, Energy Research and Process Innovation, the Netherlands) respectively, to transport tracers representing PM10. One biogenic and two anthropogenic organic compounds were chosen as surrogates to model the formation of condensable material suitable for the production of secondary organic aerosol (SOA). The SOA is added to the primary PM10 and compared to measured PM10 at one urban and two rural UK receptor sites. The results show an average under-prediction by factors of 4.5 and 8.9 in the urban and rural cases respectively. The model is also used to simulate production of two secondary inorganic species, H2SO4 and HNO3, which are assumed, as a limiting case, to be present in the particle phase. The relationships between modelled and measured total PM10 improved with the addition of secondary inorganic compounds, and the overall model under-prediction factors are reduced to 3.5 and 3.9 in the urban and rural cases respectively. Nevertheless, our conclusion is that current emissions and chemistry do not appear to provide sufficient information to model PM10 well (i.e. to within a factor of two). There is a need for further process studies to inform global climate modelling that includes climate forcing by aerosol.
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Olin, M., T. Rönkkö, and M. Dal Maso. "CFD modeling of a vehicle exhaust laboratory sampling system: sulfur-driven nucleation and growth in diluting diesel exhaust." Atmospheric Chemistry and Physics 15, no. 9 (May 13, 2015): 5305–23. http://dx.doi.org/10.5194/acp-15-5305-2015.
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Abstract. A new exhaust aerosol model CFD-TUTEAM (Tampere University of Technology Exhaust Aerosol Model for Computational Fluid Dynamics) was developed. It is based on modal aerosol dynamics modeling with log-normal assumption of particle distributions. The model has an Eulerian sub-model providing detailed spatial information within the computational domain and a computationally less expensive, but spatial-information-lacking, Lagrangian sub-model. Particle formation in a laboratory sampling system that includes a porous tube-type diluter and an aging chamber was modeled with CFD-TUTEAM. The simulation results imply that over 99% of new particles are formed in the aging chamber region because the nucleation rate remains at a high level in the aging chamber due to low dilution ratio and low nucleation exponents. The nucleation exponents for sulfuric acid in sulfuric-acid–water nucleation ranging from 0.25 to 1 appeared to fit best with measurement data, which are the same values as obtained from the slopes of the measured volatile nucleation mode number concentration vs. the measured raw exhaust sulfuric acid concentration. These nucleation exponents are very low compared to the nucleation exponents obtained from the classical nucleation theory of binary sulfuric-acid–water nucleation. The values of nucleation exponent lower than unity suggest that other compounds, such as hydrocarbons, might have a significant role in the nucleation process.
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Field, P. R., A. J. Heymsfield, and A. Bansemer. "A Test of Ice Self-Collection Kernels Using Aircraft Data." Journal of the Atmospheric Sciences 63, no. 2 (February 1, 2006): 651–66. http://dx.doi.org/10.1175/jas3653.1.
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Abstract Aircraft observations from the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL)–Florida Area Cirrus Experiment (FACE) campaign obtained in the anvil of a large convective storm from 26 July 2002 are presented. During this flight a Lagrangian spiral descent was made, allowing the evolution of the ice particle size distribution to be followed. Relative humidities during ∼1 km (from −11° to −3°C) of the descent were within 4% of ice saturation. It was assumed that the ice particle size distribution was evolving through the process of aggregation alone. Three idealized ice–ice collection kernels were used in a model of ice aggregation and compared to the observed ice particle size distribution evolution: a geometric sweep-out kernel, a Golovin (sum of particle masses) kernel, and a modified-Golovin kernel (sum of particle masses raised to a power). The Golovin kernel performed worst. The sweep-out kernel produced good agreement with the observations when a constant aggregation efficiency of 0.09 was used. The modified-Golovin kernel performed the best and implied that the aggregation efficiency of sub-300-μm particles was greater than unity when compared with a geometric sweep-out kernel.
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De Padova, Diana, Lucas Calvo, Paolo Michele Carbone, Domenico Maraglino, and Michele Mossa. "Comparison between the Lagrangian and Eulerian Approach for Simulating Regular and Solitary Waves Propagation, Breaking and Run-Up." Applied Sciences 11, no. 20 (October 11, 2021): 9421. http://dx.doi.org/10.3390/app11209421.
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The present paper places emphasis on the most widely used Computational Fluid Dynamics (CFD) approaches, namely the Eulerian and Lagrangian methods each of which is characterized by specific advantages and disadvantages. In particular, a weakly compressible smoothed particle (WCSPH) model, coupled with a sub-particle scale (SPS) approach for turbulent stresses and a new depth-integrated non-hydrostatic finite element model were employed for the simulation of regular breaking waves on a plane slope and solitary waves transformation, breaking and run-up. The validation of the numerical schemes was performed through the comparison between numerical and experimental data. The aim of this study is to compare the two modeling methods with an emphasis on their performance in the simulation of hydraulic engineering problems.
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Paris, J. D., A. Stohl, P. Ciais, P. Nédélec, B. D. Belan, M. Y. Arshinov, and M. Ramonet. "Source-receptor relationships for airborne measurements of CO<sub>2</sub>, CO and O<sub>3</sub> above Siberia: a cluster-based approach." Atmospheric Chemistry and Physics Discussions 9, no. 2 (March 9, 2009): 6207–45. http://dx.doi.org/10.5194/acpd-9-6207-2009.
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Abstract. We analysed three intensive campaigns above Siberia resulting in a total of ~70 h of continuous CO2, CO and O3 measurements. The flight route consists of consecutive ascents and descents between Novosibirsk (55° N, 82° E) and Yakutsk (62° N, 129° E). Our data analysis uses clustering of footprints obtained with the Lagrangian particle dispersion model FLEXPART. The model-based technique was found to be able to separate efficiently tracers' concentrations. High CO and O3 concentrations (median values 121 ppb and 54.5 pb respectively) were found in clusters associated with fires in Kazakhstan in September 2006. High correlation (as high as R2=0.68) and robust linear relationships with regression slope between −0.10 and 0.24 ppb ppb−1 were found in individual plumes. Summer (August 2007, September 2006) uptake of CO2 was found to be largely (~50% of variance) explained by exposure to boreal and sub-arctic ecosystems, most likely by photosynthesis. This results in an average 5 to 10 ppm gradient in the August 2007 campaign. European emissions seem to contribute to high O3 concentrations above Siberia in altitude were it is also near stratospheric inputs. Large-scale deposition processes reduce O3 in the boreal and sub-arctic BL, resulting in a ~20 ppb gradient. This first attempt of Lagrangian footprint clustering is very promising and could also be advantageously applied to the interpretation of ground based measurements including calculation of tracers' sources and sinks.
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Jadidi, Mehdi, Sara Moghtadernejad, and Jack Hanson. "Numerical Study of the Effects of Twin-Fluid Atomization on the Suspension Plasma Spraying Process." Fluids 5, no. 4 (November 28, 2020): 224. http://dx.doi.org/10.3390/fluids5040224.
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Suspension plasma spraying (SPS) is an effective technique to enhance the quality of the thermal barrier, wear-resistant, corrosion-resistant, and superhydrophobic coatings. To create the suspension in the SPS technique, nano and sub-micron solid particles are added to a base liquid (typically water or ethanol). Subsequently, by using either a mechanical injection system with a plain orifice or a twin-fluid atomizer (e.g., air-blast or effervescent), the suspension is injected into the high-velocity high-temperature plasma flow. In the present work, we simulate the interactions between the air-blast suspension spray and the plasma crossflow by using a three-dimensional two-way coupled Eulerian–Lagrangian model. Here, the suspension consists of ethanol (85 wt.%) and nickel (15 wt.%). Furthermore, at the standoff distance of 40 mm, a flat substrate is placed. To model the turbulence and the droplet breakup, Reynolds Stress Model (RSM) and Kelvin-Helmholtz Rayleigh-Taylor breakup model are used, respectively. Tracking of the fine particles is continued after suspension’s fragmentation and evaporation, until their deposition on the substrate. In addition, the effects of several parameters such as suspension mass flow rate, spray angle, and injector location on the in-flight behavior of droplets/particles as well as the particle velocity and temperature upon impact are investigated. It is shown that the injector location and the spray angle have a significant influence on the droplet/particle in-flight behavior. If the injector is far from the plasma or the spray angle is too wide, the particle temperature and velocity upon impact decrease considerably.
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Fiedler, V., R. Nau, S. Ludmann, F. Arnold, H. Schlager, and A. Stohl. "East Asian SO<sub>2</sub> pollution plume over Europe – Part 1: Airborne trace gas measurements and source identification by particle dispersion model simulations." Atmospheric Chemistry and Physics 9, no. 14 (July 20, 2009): 4717–28. http://dx.doi.org/10.5194/acp-9-4717-2009.
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Abstract. A large SO2-rich pollution plume of East Asian origin was detected by aircraft based CIMS (Chemical Ionization Mass Spectrometry) measurements at 3–7.5 km altitude over the North Atlantic. The measurements, which took place on 3 May 2006 aboard of the German research aircraft Falcon, were part of the INTEX-B (Intercontinental Chemical Transport Experiment-B) campaign. Additional trace gases (NO, NOy, CO, H2O) were measured and used for comparison and source identification. The atmospheric SO2 mole fraction was markedly increased inside the plume and reached up to 900 pmol/mol. Accompanying lagrangian FLEXPART particle dispersion model simulations indicate that the probed pollution plume originated at low altitudes from densely populated and industrialized regions of East Asia, primarily China, about 8–12 days prior to the measurements.
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Uhlmann, Markus, and Agathe Chouippe. "Clustering and preferential concentration of finite-size particles in forced homogeneous-isotropic turbulence." Journal of Fluid Mechanics 812 (January 11, 2017): 991–1023. http://dx.doi.org/10.1017/jfm.2016.826.
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We have performed interface-resolved direct numerical simulations of forced homogeneous-isotropic turbulence in a dilute suspension of spherical particles in the Reynolds number range $Re_{\unicode[STIX]{x1D706}}=115{-}140$. The solid–fluid density ratio was set to $1.5$, gravity was set to zero and two particle diameters were investigated corresponding to approximately $5$ and $11$ Kolmogorov lengths. Note that these particle sizes are clearly outside the range of validity of the point-particle approximation, as has been shown by Homann & Bec (J. Fluid Mech., vol. 651, 2010, pp. 81–91). At the present parameter points the global effect of the particles upon the fluid flow is weak. We observe that the dispersed phase exhibits clustering with moderate intensity. The tendency to cluster, which was quantified in terms of the standard deviation of Voronoï cell volumes, decreases with the particle diameter. We have analysed the relation between particle locations and the location of intense vortical flow structures. The results do not reveal any significant statistical correlation. Contrarily, we have detected a small but statistically significant preferential location of particles with respect to the ‘sticky points’ proposed by Goto & Vassilicos (Phys. Rev. Lett., vol. 100 (5), 2008, 054503), i.e. points where the fluid acceleration field is acting such as to increase the local particle concentration in one-way coupled point-particle models under Stokes drag. The presently found statistical correlation between the ‘sticky points’ and the particle locations further increases when focusing on regions with high local concentration. Our results suggest that small finite-size particles can be brought together along the expansive directions of the fluid acceleration field, as previously observed only for the simplest model for sub-Kolmogorov particles. We further discuss the effect of density ratio and collective particle motion upon the basic Eulerian and Lagrangian statistics.
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Hittmeir, Sabine, Anne Philipp, and Petra Seibert. "A conservative reconstruction scheme for the interpolation of extensive quantities in the Lagrangian particle dispersion model FLEXPART." Geoscientific Model Development 11, no. 6 (June 22, 2018): 2503–23. http://dx.doi.org/10.5194/gmd-11-2503-2018.
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Abstract. Lagrangian particle dispersion models require interpolation of all meteorological input variables to the position in space and time of computational particles. The widely used model FLEXPART uses linear interpolation for this purpose, implying that the discrete input fields contain point values. As this is not the case for precipitation (and other fluxes) which represent cell averages or integrals, a preprocessing scheme is applied which ensures the conservation of the integral quantity with the linear interpolation in FLEXPART, at least for the temporal dimension. However, this mass conservation is not ensured per grid cell, and the scheme thus has undesirable properties such as temporal smoothing of the precipitation rates. Therefore, a new reconstruction algorithm was developed, in two variants. It introduces additional supporting grid points in each time interval and is to be used with a piecewise linear interpolation to reconstruct the precipitation time series in FLEXPART. It fulfils the desired requirements by preserving the integral precipitation in each time interval, guaranteeing continuity at interval boundaries, and maintaining non-negativity. The function values of the reconstruction algorithm at the sub-grid and boundary grid points constitute the degrees of freedom, which can be prescribed in various ways. With the requirements mentioned it was possible to derive a suitable piecewise linear reconstruction. To improve the monotonicity behaviour, two versions of a filter were also developed that form a part of the final algorithm. Currently, the algorithm is meant primarily for the temporal dimension. It was shown to significantly improve the reconstruction of hourly precipitation time series from 3-hourly input data. Preliminary considerations for the extension to additional dimensions are also included as well as suggestions for a range of possible applications beyond the case of precipitation in a Lagrangian particle model.
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Carcano, S., L. Bonaventura, T. Esposti Ongaro, and A. Neri. "A semi-implicit, second-order-accurate numerical model for multiphase underexpanded volcanic jets." Geoscientific Model Development 6, no. 6 (November 4, 2013): 1905–24. http://dx.doi.org/10.5194/gmd-6-1905-2013.
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Abstract. An improved version of the PDAC (Pyroclastic Dispersal Analysis Code, Esposti Ongaro et al., 2007) numerical model for the simulation of multiphase volcanic flows is presented and validated for the simulation of multiphase volcanic jets in supersonic regimes. The present version of PDAC includes second-order time- and space discretizations and fully multidimensional advection discretizations in order to reduce numerical diffusion and enhance the accuracy of the original model. The model is tested on the problem of jet decompression in both two and three dimensions. For homogeneous jets, numerical results are consistent with experimental results at the laboratory scale (Lewis and Carlson, 1964). For nonequilibrium gas–particle jets, we consider monodisperse and bidisperse mixtures, and we quantify nonequilibrium effects in terms of the ratio between the particle relaxation time and a characteristic jet timescale. For coarse particles and low particle load, numerical simulations well reproduce laboratory experiments and numerical simulations carried out with an Eulerian–Lagrangian model (Sommerfeld, 1993). At the volcanic scale, we consider steady-state conditions associated with the development of Vulcanian and sub-Plinian eruptions. For the finest particles produced in these regimes, we demonstrate that the solid phase is in mechanical and thermal equilibrium with the gas phase and that the jet decompression structure is well described by a pseudogas model (Ogden et al., 2008). Coarse particles, on the other hand, display significant nonequilibrium effects, which associated with their larger relaxation time. Deviations from the equilibrium regime, with maximum velocity and temperature differences on the order of 150 m s−1 and 80 K across shock waves, occur especially during the rapid acceleration phases, and are able to modify substantially the jet dynamics with respect to the homogeneous case.
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Carcano, S., L. Bonaventura, T. Esposti Ongaro, and A. Neri. "A semi-implicit, second order accurate numerical model for multiphase underexpanded volcanic jets." Geoscientific Model Development Discussions 6, no. 1 (January 22, 2013): 399–452. http://dx.doi.org/10.5194/gmdd-6-399-2013.
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Abstract. An improved version of the PDAC (Pyroclastic Dispersal Analysis Code, Esposti Ongaro et al., 2007) numerical model for the simulation of multiphase volcanic flows is presented and validated for the simulation of multiphase volcanic jets in supersonic regimes. The present version of PDAC includes second-order time and space discretizations and fully multidimensional advection discretizations, in order to reduce numerical diffusion and enhance the accuracy of the original model. The model is tested on the problem of jet decompression, in both two and three dimensions. For homogeneous jets, numerical results are consistent with experimental results at the laboratory scale (Lewis and Carlson, 1964). For non-equilibrium gas-particle jets, we consider monodisperse and bidisperse mixtures and we quantify non-equilibrium effects in terms of the ratio between the particle relaxation time and a characteristic jet time scale. For coarse particles and low particle load, numerical simulations well reproduce laboratory experiments and numerical simulations carried out with an Eulerian-Lagrangian model (Sommerfeld, 1993). At the volcanic scale, we consider steady-state conditions associated to the development of Vulcanian and sub-Plinian eruptions. For the finest particles produced in these regimes, we demonstrate that the solid phase is in mechanical and thermal equilibrium with the gas phase and that the jet decompression structure is well described by a pseudogas model (Ogden et al., 2008). Coarse particles, on the contrary, display significant non-equilibrium effects, associated to their larger relaxation time. Deviations from the equilibrium regime occur especially during the rapid acceleration phases and are able to appreciably modify the average jet dynamics, with maximum velocity and temperature differences of the order of 150 m s−1 and 80 K across shock waves.
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Hedelius, Jacob K., Junjie Liu, Tomohiro Oda, Shamil Maksyutov, Coleen M. Roehl, Laura T. Iraci, James R. Podolske, et al. "Southern California megacity CO<sub>2</sub>, CH<sub>4</sub>, and CO flux estimates using ground- and space-based remote sensing and a Lagrangian model." Atmospheric Chemistry and Physics 18, no. 22 (November 16, 2018): 16271–91. http://dx.doi.org/10.5194/acp-18-16271-2018.
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Abstract. We estimate the overall CO2, CH4, and CO flux from the South Coast Air Basin using an inversion that couples Total Carbon Column Observing Network (TCCON) and Orbiting Carbon Observatory-2 (OCO-2) observations, with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the Open-source Data Inventory for Anthropogenic CO2 (ODIAC). Using TCCON data we estimate the direct net CO2 flux from the SoCAB to be 104 ± 26 Tg CO2 yr−1 for the study period of July 2013–August 2016. We obtain a slightly higher estimate of 120 ± 30 Tg CO2 yr−1 using OCO-2 data. These CO2 emission estimates are on the low end of previous work. Our net CH4 (360 ± 90 Gg CH4 yr−1) flux estimate is in agreement with central values from previous top-down studies going back to 2010 (342–440 Gg CH4 yr−1). CO emissions are estimated at 487 ± 122 Gg CO yr−1, much lower than previous top-down estimates (1440 Gg CO yr−1). Given the decreasing emissions of CO, this finding is not unexpected. We perform sensitivity tests to estimate how much errors in the prior, errors in the covariance, different inversion schemes, or a coarser dynamical model influence the emission estimates. Overall, the uncertainty is estimated to be 25 %, with the largest contribution from the dynamical model. Lessons learned here may help in future inversions of satellite data over urban areas.
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Temisanren, B. U., and A. I. Igbafe. "Modelling the Transport and Dispersion of Atmospheric Aerosols over Warri Area of the Niger Delta Subregion of Nigeria." Advanced Materials Research 824 (September 2013): 643–49. http://dx.doi.org/10.4028/www.scientific.net/amr.824.643.
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This study investigates the transport profile and source-sink system for atmospheric aerosols over Warri area of the Niger Delta subregion of Nigeria. The study utilized GPS information of the study locations to simulate meteorological variables over the area from the Air Resource Laboratory (ARL) website. The ARL/GFS model was used to determine the wind-field information between 1stand 8thMarch 2012 over sub region. In addition backward air mass trajectories were determined at various heights of 5m, 1000m and 2000m AGL for aerosol transport pattern, as well as concentration dispersion using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. During the study period, aerosols were noticed to evolve from the sea of the Atlantic Ocean, hence are likely of sea salt origin. Winds over the sub region ranged between 4 and 6 m/s and predominantly in the south and south westerly directions. The maximum pollutant concentration observed was about 1.0 x 10-12μg/m3while the minimum was about 1.5 x 10-24μg/m3.
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Nguyen, Quynh T., Marianne Glasius, Lise L. Sørensen, Bjarne Jensen, Henrik Skov, Wolfram Birmili, Alfred Wiedensohler, Adam Kristensson, Jacob K. Nøjgaard, and Andreas Massling. "Seasonal variation of atmospheric particle number concentrations, new particle formation and atmospheric oxidation capacity at the high Arctic site Villum Research Station, Station Nord." Atmospheric Chemistry and Physics 16, no. 17 (September 13, 2016): 11319–36. http://dx.doi.org/10.5194/acp-16-11319-2016.
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Abstract. This work presents an analysis of the physical properties of sub-micrometer aerosol particles measured at the high Arctic site Villum Research Station, Station Nord (VRS), northeast Greenland, between July 2010 and February 2013. The study focuses on particle number concentrations, particle number size distributions and the occurrence of new particle formation (NPF) events and their seasonality in the high Arctic, where observations and characterization of such aerosol particle properties and corresponding events are rare and understanding of related processes is lacking.A clear accumulation mode was observed during the darker months from October until mid-May, which became considerably more pronounced during the prominent Arctic haze months from March to mid-May. In contrast, nucleation- and Aitken-mode particles were predominantly observed during the summer months. Analysis of wind direction and wind speed indicated possible contributions of marine sources from the easterly side of the station to the observed summertime particle number concentrations, while southwesterly to westerly winds dominated during the darker months. NPF events lasting from hours to days were mostly observed from June until August, with fewer events observed during the months with less sunlight, i.e., March, April, September and October. The results tend to indicate that ozone (O3) might be weakly anti-correlated with particle number concentrations of the nucleation-mode range (10–30 nm) in almost half of the NPF events, while no positive correlation was observed. Calculations of air mass back trajectories using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model for the NPF event days suggested that the onset or interruption of events could possibly be explained by changes in air mass origin. A map of event occurrence probability was computed, indicating that southerly air masses from over the Greenland Sea were more likely linked to those events.
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Paris, J. D., A. Stohl, P. Ciais, P. Nédélec, B. D. Belan, M. Yu Arshinov, and M. Ramonet. "Source-receptor relationships for airborne measurements of CO<sub>2</sub>, CO and O<sub>3</sub> above Siberia: a cluster-based approach." Atmospheric Chemistry and Physics 10, no. 4 (February 15, 2010): 1671–87. http://dx.doi.org/10.5194/acp-10-1671-2010.
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Abstract. We analysed results of three intensive aircraft campaigns above Siberia (April and September 2006, August 2007) with a total of ~70 h of continuous CO2, CO and O3 measurements. The flight route consists of consecutive ascents and descents between Novosibirsk (55° N, 82° E) and Yakutsk (62° N, 129° E). We performed retroplume calculations with the Lagrangian particle dispersion model FLEXPART for many short segments along the flight tracks. To reduce the extremely rich information on source regions provided by the model calculation into a small number of distinct cases, we performed a statistical clustering – to our knowledge for the first time – into potential source regions of the footprint emission sensitivities obtained from the model calculations. This technique not only worked well to separate source region influences but also resulted in clearly distinct tracer concentrations for the various clusters obtained. High CO and O3 concentrations were found associated with agricultural fire plumes originating from Kazakhstan in September 2006. A statistical analysis indicates that summer uptake of CO2 is largely explained (~50% of variance) by air mass exposure to uptake by Siberian and sub-arctic ecosystems. This resulted in an average 5 to 10 ppm difference with overlaying air masses. Stratosphere-troposphere exchange is found to strongly influence the observed O3 mixing ratios in spring, but not in summer. European emissions contributed to high O3 concentrations above Siberia in April 2006 and August 2007, while emissions from North Eastern China also contributed to higher O3 mixing ratios in summer, but tend to lower mixing ratios in spring, when the airmass aerosol burden is important. In the lower troposphere, large-scale deposition processes in the boreal and sub-arctic boundary layer is a large O3 sink, resulting in a ~20 ppb difference with overlaying air masses. Lagrangian footprint clustering is very promising and could also be advantageously applied to the interpretation of ground based measurements including calculation of tracers' sources and sinks.
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Dash, S. M., T. S. Lee, and H. Huang. "Particle Sedimentation in a Constricted Passage Using a Flexible Forcing IB-LBM Scheme." International Journal of Computational Methods 12, no. 01 (January 23, 2015): 1350095. http://dx.doi.org/10.1142/s0219876213500953.
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A novel flexible forcing hybrid immersed boundary-lattice Boltzmann model (IB-LBM) is introduced in the present paper for solving moving boundary problems. In conventional IB-LBM schemes, explicit formulations of force density term may not ensure no-slip boundary condition accurately, which leads to inaccurate force and torque calculations for moving object. Following an implicit force density calculation, a single Lagrangian velocity correction term is advised in this study. The formula for this correction term is much simpler and with the help of flexible number of sub-iteration/forcing, the computational time is significantly saved. The no-slip boundary condition is achieved accurately within a convergence limit. The proposed algorithm shows advantages for unsteady and moving boundary problem, where boundary convergence is satisfied consistently at every time step. In particular, a 2D particulate flow case is simulated in a constricted channel. Interesting observations and results are discussed in this article.
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Maksyutov, Shamil, Tomohiro Oda, Makoto Saito, Rajesh Janardanan, Dmitry Belikov, Johannes W. Kaiser, Ruslan Zhuravlev, et al. "Technical note: A high-resolution inverse modelling technique for estimating surface CO<sub>2</sub> fluxes based on the NIES-TM–FLEXPART coupled transport model and its adjoint." Atmospheric Chemistry and Physics 21, no. 2 (January 29, 2021): 1245–66. http://dx.doi.org/10.5194/acp-21-1245-2021.
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Abstract. We developed a high-resolution surface flux inversion system based on the global Eulerian–Lagrangian coupled tracer transport model composed of the National Institute for Environmental Studies (NIES) transport model (TM; collectively NIES-TM) and the FLEXible PARTicle dispersion model (FLEXPART). The inversion system is named NTFVAR (NIES-TM–FLEXPART-variational) as it applies a variational optimization to estimate surface fluxes. We tested the system by estimating optimized corrections to natural surface CO2 fluxes to achieve the best fit to atmospheric CO2 data collected by the global in situ network as a necessary step towards the capability of estimating anthropogenic CO2 emissions. We employed the Lagrangian particle dispersion model (LPDM) FLEXPART to calculate surface flux footprints of CO2 observations at a spatial resolution of 0.1∘×0.1∘. The LPDM is coupled with a global atmospheric tracer transport model (NIES-TM). Our inversion technique uses an adjoint of the coupled transport model in an iterative optimization procedure. The flux error covariance operator was implemented via implicit diffusion. Biweekly flux corrections to prior flux fields were estimated for the years 2010–2012 from in situ CO2 data included in the Observation Package (ObsPack) data set. High-resolution prior flux fields were prepared using the Open-Data Inventory for Anthropogenic Carbon dioxide (ODIAC) for fossil fuel combustion, the Global Fire Assimilation System (GFAS) for biomass burning, the Vegetation Integrative SImulator for Trace gases (VISIT) model for terrestrial biosphere exchange, and the Ocean Tracer Transport Model (OTTM) for oceanic exchange. The terrestrial biospheric flux field was constructed using a vegetation mosaic map and a separate simulation of CO2 fluxes at a daily time step by the VISIT model for each vegetation type. The prior flux uncertainty for the terrestrial biosphere was scaled proportionally to the monthly mean gross primary production (GPP) by the Moderate Resolution Imaging Spectroradiometer (MODIS) MOD17 product. The inverse system calculates flux corrections to the prior fluxes in the form of a relatively smooth field multiplied by high-resolution patterns of the prior flux uncertainties for land and ocean, following the coastlines and fine-scale vegetation productivity gradients. The resulting flux estimates improved the fit to the observations taken at continuous observation sites, reproducing both the seasonal and short-term concentration variabilities including high CO2 concentration events associated with anthropogenic emissions. The use of a high-resolution atmospheric transport in global CO2 flux inversions has the advantage of better resolving the transported mixed signals from the anthropogenic and biospheric sources in densely populated continental regions. Thus, it has the potential to achieve better separation between fluxes from terrestrial ecosystems and strong localized sources, such as anthropogenic emissions and forest fires. Further improvements in the modelling system are needed as our posterior fit was better than that of the National Oceanic and Atmospheric Administration (NOAA)'s CarbonTracker for only a fraction of the monitoring sites, i.e. mostly at coastal and island locations where background and local flux signals are mixed.
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Ghazanfarian, Jafar, Roozbeh Saghatchi, and Mofid Gorji-Bandpy. "Turbulent fluid-structure interaction of water-entry/exit of a rotating circular cylinder using SPH method." International Journal of Modern Physics C 26, no. 08 (May 3, 2015): 1550088. http://dx.doi.org/10.1142/s0129183115500886.
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This paper studies the two-dimensional (2D) water-entry and exit of a rotating circular cylinder using the Sub-Particle Scale (SPS) turbulence model of a Lagrangian particle-based Smoothed-Particle Hydrodynamics (SPH) method. The full Navier–Stokes (NS) equations along with the continuity have been solved as the governing equations of the problem. The accuracy of the numerical code is verified using the case of water-entry and exit of a nonrotating circular cylinder. The numerical simulations of water-entry and exit of the rotating circular cylinder are performed at Froude numbers of 2, 5, 8, and specific gravities of 0.25, 0.5, 0.75, 1, 1.75, rotating at the dimensionless rates of 0, 0.25, 0.5, 0.75. The effect of governing parameters and vortex shedding behind the cylinder on the trajectory curves, velocity components in the flow field, and the deformation of free surface for both cases have been investigated in detail. It is seen that the rotation has a great effect on the curvature of the trajectory path and velocity components in water-entry and exit cases due to the interaction of imposed lift and drag forces with the inertia force.
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Tomlin, A. S., T. Ziehn, P. Goodman, J. E. Tate, and N. S. Dixon. "The treatment of uncertainties in reactive pollution dispersion models at urban scales." Faraday Discussions 189 (2016): 567–87. http://dx.doi.org/10.1039/c5fd00159e.
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The ability to predict NO2 concentrations ([NO2]) within urban street networks is important for the evaluation of strategies to reduce exposure to NO2. However, models aiming to make such predictions involve the coupling of several complex processes: traffic emissions under different levels of congestion; dispersion via turbulent mixing; chemical processes of relevance at the street-scale. Parameterisations of these processes are challenging to quantify with precision. Predictions are therefore subject to uncertainties which should be taken into account when using models within decision making. This paper presents an analysis of mean [NO2] predictions from such a complex modelling system applied to a street canyon within the city of York, UK including the treatment of model uncertainties and their causes. The model system consists of a micro-scale traffic simulation and emissions model, and a Reynolds averaged turbulent flow model coupled to a reactive Lagrangian particle dispersion model. The analysis focuses on the sensitivity of predicted in-street increments of [NO2] at different locations in the street to uncertainties in the model inputs. These include physical characteristics such as background wind direction, temperature and background ozone concentrations; traffic parameters such as overall demand and primary NO2 fraction; as well as model parameterisations such as roughness lengths, turbulent time- and length-scales and chemical reaction rate coefficients. Predicted [NO2] is shown to be relatively robust with respect to model parameterisations, although there are significant sensitivities to the activation energy for the reaction NO + O3 as well as the canyon wall roughness length. Under off-peak traffic conditions, demand is the key traffic parameter. Under peak conditions where the network saturates, road-side [NO2] is relatively insensitive to changes in demand and more sensitive to the primary NO2 fraction. The most important physical parameter was found to be the background wind direction. The study highlights the key parameters required for reliable [NO2] estimations suggesting that accurate reference measurements for wind direction should be a critical part of air quality assessments for in-street locations. It also highlights the importance of street scale chemical processes in forming road-side [NO2], particularly for regions of high NOx emissions such as close to traffic queues.
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Uglietti, C., M. Leuenberger, and D. Brunner. "European source and sink areas of CO<sub>2</sub> retrieved from Lagrangian transport model interpretation of combined O<sub>2</sub> and CO<sub>2</sub> measurements at the high alpine research station Jungfraujoch." Atmospheric Chemistry and Physics 11, no. 15 (August 8, 2011): 8017–36. http://dx.doi.org/10.5194/acp-11-8017-2011.
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Abstract. The University of Bern monitors carbon dioxide (CO2) and oxygen (O2) at the High Altitude Research Station Jungfraujoch since the year 2000 by means of flasks sampling and since 2005 using a continuous in situ measurement system. This study investigates the transport of CO2 and O2 towards Jungfraujoch using backward Lagrangian Particle Dispersion Model (LPDM) simulations and utilizes CO2 and O2 signatures to classify air masses. By investigating the simulated transport patterns associated with distinct CO2 concentrations it is possible to decipher different source and sink areas over Europe. The highest CO2 concentrations, for example, were observed in winter during pollution episodes when air was transported from Northeastern Europe towards the Alps, or during south Foehn events with rapid uplift of polluted air from Northern Italy, as demonstrated in two case studies. To study the importance of air-sea exchange for variations in O2 concentrations at Jungfraujoch the correlation between CO2 and APO (Atmospheric Potential Oxygen) deviations from a seasonally varying background was analyzed. Anomalously high APO concentrations were clearly associated with air masses originating from the Atlantic Ocean, whereas low APO concentrations were found in air masses advected either from the east from the Eurasian continent in summer, or from the Eastern Mediterranean in winter. Those air masses with low APO in summer were also strongly depleted in CO2 suggesting a combination of CO2 uptake by vegetation and O2 uptake by dry summer soils. Other subsets of points in the APO-CO2 scatter plot investigated with respect to air mass origin included CO2 and APO background values and points with regular APO but anomalous CO2 concentrations. Background values were associated with free tropospheric air masses with little contact with the boundary layer during the last few days, while high or low CO2 concentrations reflect the various levels of influence of anthropogenic emissions and the biosphere. The pronounced cycles of CO2 and O2 exchanges with the biosphere and the ocean cause clusters of points and lead to a seasonal pattern.
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Unterstrasser, Simon, Fabian Hoffmann, and Marion Lerch. "Collisional growth in a particle-based cloud microphysical model: insights from column model simulations using LCM1D (v1.0)." Geoscientific Model Development 13, no. 11 (October 30, 2020): 5119–45. http://dx.doi.org/10.5194/gmd-13-5119-2020.
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Abstract. Lagrangian cloud models (LCMs) are considered the future of cloud microphysical modelling. Compared to bulk models, however, LCMs are computationally expensive due to the typically high number of simulation particles (SIPs) necessary to represent microphysical processes such as collisional growth of hydrometeors successfully. In this study, the representation of collisional growth is explored in one-dimensional column simulations, allowing for the explicit consideration of sedimentation, complementing the authors' previous study on zero-dimensional collection in a single grid box. Two variants of the Lagrangian probabilistic all-or-nothing (AON) collection algorithm are tested that mainly differ in the assumed spatial distribution of the droplet ensemble: the first variant assumes the droplet ensemble to be well-mixed in a predefined three-dimensional grid box (WM3D), while the second variant considers the (sub-grid) vertical position of the SIPs, reducing the well-mixed assumption to a two-dimensional, horizontal plane (WM2D). Since the number of calculations in AON depends quadratically on the number of SIPs, an established approach is tested that reduces the number of calculations to a linear dependence (so-called linear sampling). All variants are compared to established Eulerian bin model solutions. Generally, all methods approach the same solutions and agree well if the methods are applied with sufficiently high resolution (foremost is the number of SIPs, and to a lesser extent time step and vertical grid spacing). Converging results were found for fairly large time steps, larger than those typically used in the numerical solution of diffusional growth. The dependence on the vertical grid spacing can be reduced if AON-WM2D is applied. The study also shows that AON-WM3D simulations with linear sampling, a common speed-up measure, converge only slightly slower compared to simulations with a quadratic SIP sampling. Hence, AON with linear sampling is the preferred choice when computation time is a limiting factor. Most importantly, the study highlights that results generally require a smaller number of SIPs per grid box for convergence than previous one-dimensional box simulations indicated. The reason is the ability of sedimenting SIPs to interact with a larger ensemble of particles when they are not restricted to a single grid box. Since sedimentation is considered in most commonly applied three-dimensional models, the results indicate smaller computational requirements for successful simulations, encouraging a wider use of LCMs in the future.
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Cassiani, Massimo, Andreas Stohl, Dirk Olivié, Øyvind Seland, Ingo Bethke, Ignacio Pisso, and Trond Iversen. "The offline Lagrangian particle model FLEXPART–NorESM/CAM (v1): model description and comparisons with the online NorESM transport scheme and with the reference FLEXPART model." Geoscientific Model Development 9, no. 11 (November 11, 2016): 4029–48. http://dx.doi.org/10.5194/gmd-9-4029-2016.
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Abstract. The offline FLEXible PARTicle (FLEXPART) stochastic dispersion model is currently a community model used by many scientists. Here, an alternative FLEXPART model version has been developed and tailored to use with the meteorological output data generated by the CMIP5-version of the Norwegian Earth System Model (NorESM1-M). The atmospheric component of the NorESM1-M is based on the Community Atmosphere Model (CAM4); hence, this FLEXPART version could be widely applicable and it provides a new advanced tool to directly analyse and diagnose atmospheric transport properties of the state-of-the-art climate model NorESM in a reliable way. The adaptation of FLEXPART to NorESM required new routines to read meteorological fields, new post-processing routines to obtain the vertical velocity in the FLEXPART coordinate system, and other changes. These are described in detail in this paper. To validate the model, several tests were performed that offered the possibility to investigate some aspects of offline global dispersion modelling. First, a comprehensive comparison was made between the tracer transport from several point sources around the globe calculated online by the transport scheme embedded in CAM4 and the FLEXPART model applied offline on output data. The comparison allowed investigating several aspects of the transport schemes including the approximation introduced by using an offline dispersion model with the need to transform the vertical coordinate system, the influence on the model results of the sub-grid-scale parameterisations of convection and boundary layer height and the possible advantage entailed in using a numerically non-diffusive Lagrangian particle solver. Subsequently, a comparison between the reference FLEXPART model and the FLEXPART–NorESM/CAM version was performed to compare the well-mixed state of the atmosphere in a 1-year global simulation. The two model versions use different methods to obtain the vertical velocity but no significant difference in the results was found. However, for both model versions there was some degradation in the well-mixed state after 1 year of simulation with the build-up of a bias and an increased scatter. Finally, the capability of the new combined modelling system in producing realistic, backward-in-time transport statistics was evaluated calculating the average footprint over a 5-year period for several measurement locations and by comparing the results with those obtained with the reference FLEXPART model driven by re-analysis fields. This comparison confirmed the effectiveness of the combined modelling system FLEXPART with NorESM in producing realistic transport statistics.
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Inghilesi, R., L. Ottolenghi, A. Orasi, C. Pizzi, F. Bignami, and R. Santoleri. "Fate of river Tiber discharge investigated through numerical simulation and satellite monitoring." Ocean Science 8, no. 5 (September 18, 2012): 773–86. http://dx.doi.org/10.5194/os-8-773-2012.
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Abstract. The aim of this study was to determine the dispersion of passive pollutants associated with the Tiber discharge into the Tyrrhenian Sea using numerical marine dispersion models and satellite data. Numerical results obtained in the simulation of realistic discharge episodes were compared with the corresponding evolution of the spatial distributions of MODIS diffuse light attenuation coefficient at 490 nm (K490), and the results were discussed with reference to the local climate and the seasonal sub-regional circulation regime. The numerical model used for the simulation of the sub-tidal circulation was a Mediterranean sub-regional scale implementation of the Princeton Ocean Model (POM), nested in the large-scale Mediterranean Forecasting System. The nesting method enabled the model to be applied to almost every area in the Mediterranean Sea and also to be used in seasons for which imposing climatological boundary conditions would have been questionable. Dynamical effects on coastal circulation and on water density due to the Tiber discharge were additionally accounted for in the oceanographic model by implementing the river estuary as a point source of a buoyant jet. A Lagrangian particle dispersion model fed with the POM current fields was then run in order to reproduce the effect of the turbulent transport of passive tracers mixed in the plume with the coastal flow. Two significant episodes of river discharge in both winter and summer conditions were discussed in this paper. It was found that the winter regime was characterized by the presence of a strong coastal jet flowing with the ambient current. In summer the prevailing wind regime induced coastal downwelling conditions, which tended to confine the riverine waters close to the shore. In such conditions sudden wind reversals due to local weather perturbations, causing moderate local upwelling, proved to be the only effective way to disperse the tracers offshore, moving the plume from the coast and detaching large pools of freshwater.
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Inghilesi, R., L. Ottolenghi, A. Orasi, C. Pizzi, F. Bignami, and R. Santoleri. "Fate of river Tiber discharge investigated through numerical simulation and satellite monitoring." Ocean Science Discussions 9, no. 2 (April 12, 2012): 1599–649. http://dx.doi.org/10.5194/osd-9-1599-2012.
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Abstract. The aim of this study was to determine the dispersion of passive pollutants associated with the Tiber discharge into the Tyrrhenian Sea using numerical marine dispersion models and satellite data. Numerical results obtained in the simulation of realistic discharge episodes were compared with the corresponding evolution of the spatial distributions of MODIS diffuse light attenuation coefficient at 490 nm (K490), and the results were discussed with reference to the local climate and the seasonal sub-regional circulation regime. The numerical model used for the simulation of the sub-tidal circulation was a Mediterranean sub-regional scale implementation of the Princeton Ocean Model (POM), nested in the large-scale Mediterranean Forecasting System. The nesting method enabled the model to be applied to almost every area in the Mediterranean Sea and also to be used in seasons for which imposing climatological boundary conditions would have been questionable. Dynamical effects on coastal circulation and on water density due to the Tiber discharge were additionally accounted for in the oceanographic model by implementing the river estuary as a point source of a buoyant jet. A Lagrangian particle dispersion model fed with the POM current fields was then run, in order to reproduce the effect of the turbulent transport of passive tracers mixed in the plume with the coastal flow. Two significant episodes of river discharge in both Winter and Summer conditions were discussed in this paper. It was found that the Winter regime was characterized by the presence of a strong coastal jet flowing with the ambient current. In Summer the prevailing wind regime induces coastal downwelling conditions, which tend to confine the riverine waters close to the shore. In such conditions sudden wind reversals due to local weather perturbations, causing strong local upwelling, proved to be an effective way to disperse the tracers offshore, moving the plume from the coast and detaching large pools of freshwater.
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Ghazanfarian, Jafar, Roozbeh Saghatchi, and Mofid Gorji-Bandpy. "SPH simulation of turbulent flow past a high-frequency in-line oscillating cylinder near free-surface." International Journal of Modern Physics C 27, no. 12 (November 23, 2016): 1650152. http://dx.doi.org/10.1142/s0129183116501527.
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This paper studies a two-dimensional incompressible viscous flow past a circular cylinder with in-line oscillation close to a free-surface. The sub-particle scale (SPS) turbulence model of a Lagrangian particle-based smoothed-particle hydrodynamics (SPH) method has been used to solve the full Navier–Stokes equations together with the continuity equation. The accuracy of numerical code has been verified using two cases consisting of an oscillating cylinder placed in the stationary fluid, and flow over a fixed cylinder close to a free-surface. Simulations are conducted for the Froude number of 0.3, the Reynolds numbers of 40 and 80, various gap ratios for fully-submerged and half-submerge cylinders. The dimensionless frequency and amplitude of oscillating have been chosen as 0.5, 0.8 and 10, 15, respectively. The selection of such a high oscillating frequency causes the flow regime to become turbulent. It is seen that the gap ratio defined as the ratio of cylinder distance from free-surface and its diameter, strongly affects the flow pattern and the magnitude of the drag and lift coefficients. The jet-like flow (the region above the cylinder and beneath the free-surface) creation is discussed in detail and showed that the strength of this jet-like flow is weakened when the gap ratio shrinks. It is seen that by decreasing the gap ratio, the lift and drag coefficients increase and decrease, respectively. It is found that the Reynolds number has an inverse effect on the drag and lift coefficients. Also, it is concluded that by increasing the amplitude of oscillation the drag coefficient increases.
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Dayalu, Archana, J. William Munger, Steven C. Wofsy, Yuxuan Wang, Thomas Nehrkorn, Yu Zhao, Michael B. McElroy, Chris P. Nielsen, and Kristina Luus. "Assessing biotic contributions to CO<sub>2</sub> fluxes in northern China using the Vegetation, Photosynthesis and Respiration Model (VPRM-CHINA) and observations from 2005 to 2009." Biogeosciences 15, no. 21 (November 12, 2018): 6713–29. http://dx.doi.org/10.5194/bg-15-6713-2018.
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Abstract. Accurately quantifying the spatiotemporal distribution of the biological component of CO2 surface–atmosphere exchange is necessary to improve top-down constraints on China's anthropogenic CO2 emissions. We provide hourly fluxes of CO2 as net ecosystem exchange (NEE; µmol CO2 m−2 s−1) on a 0.25∘×0.25∘ grid by adapting the Vegetation, Photosynthesis, and Respiration Model (VPRM) to the eastern half of China for the time period from 2005 to 2009; the minimal empirical parameterization of the VPRM-CHINA makes it well suited for inverse modeling approaches. This study diverges from previous VPRM applications in that it is applied at a large scale to China's ecosystems for the first time, incorporating a novel processing framework not previously applied to existing VPRM versions. In addition, the VPRM-CHINA model prescribes methods for addressing dual-cropping regions that have two separate growing-season modes applied to the same model grid cell. We evaluate the VPRM-CHINA performance during the growing season and compare to other biospheric models. We calibrate the VPRM-CHINA with ChinaFlux and FluxNet data and scale up regionally using Weather Research and Forecasting (WRF) Model v3.6.1 meteorology and MODIS surface reflectances. When combined with an anthropogenic emissions model in a Lagrangian particle transport framework, we compare the ability of VPRM-CHINA relative to an ensemble mean of global hourly flux models (NASA CMS – Carbon Monitoring System) to reproduce observations made at a site in northern China. The measurements are heavily influenced by the northern China administrative region. Modeled hourly time series using vegetation fluxes prescribed by VPRM-CHINA exhibit low bias relative to measurements during the May–September growing season. Compared to NASA CMS subset over the study region, VPRM-CHINA agrees significantly better with measurements. NASA CMS consistently underestimates regional uptake in the growing season. We find that during the peak growing season, when the heavily cropped North China Plain significantly influences measurements, VPRM-CHINA models a CO2 uptake signal comparable in magnitude to the modeled anthropogenic signal. In addition to demonstrating efficacy as a low-bias prior for top-down CO2 inventory optimization studies using ground-based measurements, high spatiotemporal resolution models such as the VPRM are critical for interpreting retrievals from global CO2 remote-sensing platforms such as OCO-2 and OCO-3 (planned). Depending on the satellite time of day and season of crossover, efforts to interpret the relative contribution of the vegetation and anthropogenic components to the measured signal are critical in key emitting regions such as northern China – where the magnitude of the vegetation CO2 signal is shown to be equivalent to the anthropogenic signal.
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Meyer, M., L. Burgin, M. C. Hort, D. P. Hodson, and C. A. Gilligan. "Large-Scale Atmospheric Dispersal Simulations Identify Likely Airborne Incursion Routes of Wheat Stem Rust Into Ethiopia." Phytopathology® 107, no. 10 (October 2017): 1175–86. http://dx.doi.org/10.1094/phyto-01-17-0035-fi.
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In recent years, severe wheat stem rust epidemics hit Ethiopia, sub-Saharan Africa’s largest wheat-producing country. These were caused by race TKTTF (Digalu race) of the pathogen Puccinia graminis f. sp. tritici, which, in Ethiopia, was first detected at the beginning of August 2012. We use the incursion of this new pathogen race as a case study to determine likely airborne origins of fungal spores on regional and continental scales by means of a Lagrangian particle dispersion model (LPDM). Two different techniques, LPDM simulations forward and backward in time, are compared. The effects of release altitudes in time-backward simulations and P. graminis f. sp. tritici urediniospore viability functions in time-forward simulations are analyzed. Results suggest Yemen as the most likely origin but, also, point to other possible sources in the Middle East and the East African Rift Valley. This is plausible in light of available field surveys and phylogenetic data on TKTTF isolates from Ethiopia and other countries. Independent of the case involving TKTTF, we assess long-term dispersal trends (>10 years) to obtain quantitative estimates of the risk of exotic P. graminis f. sp. tritici spore transport (of any race) into Ethiopia for different ‘what-if’ scenarios of disease outbreaks in potential source countries in different months of the wheat season.
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Gallot-Lavallée, S., W. P. Jones, and A. J. Marquis. "Large Eddy Simulation of an Ethanol Spray Flame with Secondary Droplet Breakup." Flow, Turbulence and Combustion 107, no. 3 (April 1, 2021): 709–43. http://dx.doi.org/10.1007/s10494-021-00248-z.
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AbstractA computational investigation of three configurations of the Delft Spray in Hot-diluted Co-flow (DSHC) is presented. The selected burner comprises a hollow cone pressure swirl atomiser, injecting an ethanol spray, located in the centre of a hot co-flow generator, with the conditions studied corresponding to Moderate or Intense Low-oxygen Dilution (MILD) combustion. The simulations are performed in the context of Large Eddy Simulation (LES) in combination with a transport equation for the joint probability density function (pdf) of the scalars, solved using the Eulerian stochastic field method. The liquid phase is simulated by the use of a Lagrangian point particle approach, where the sub-grid-scale interactions are modelled with a stochastic approach. Droplet breakup is represented by a simple primary breakup model in combination with a stochastic secondary breakup formulation. The approach requires only a minimal knowledge of the fuel injector and avoids the need to specify droplet size and velocity distributions at the injection point. The method produces satisfactory agreement with the experimental data and the velocity fields of the gas and liquid phase both averaged and ‘size-class by size-class’ are well depicted. Two widely accepted evaporation models, utilising a phase equilibrium assumption, are used to investigate the influence of evaporation on the evolution of the liquid phase and the effects on the flame. An analysis on the dynamics of stabilisation sheds light on the importance of droplet size in the three spray flames; different size droplets play different roles in the stabilisation of the flames.
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Olsen, Karen Pardos, Blakesley Burkhart, Mordecai-Mark Mac Low, Robin G. Treß, Thomas R. Greve, David Vizgan, Jay Motka, et al. "sígame v3: Gas Fragmentation in Postprocessing of Cosmological Simulations for More Accurate Infrared Line Emission Modeling." Astrophysical Journal 922, no. 1 (November 1, 2021): 88. http://dx.doi.org/10.3847/1538-4357/ac20d4.
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Abstract We present an update to the framework called Simulator of Galaxy Millimeter/submillimeter Emission (sígame). sígame derives line emission in the far-infrared (FIR) for galaxies in particle-based cosmological hydrodynamics simulations by applying radiative transfer and physics recipes via a postprocessing step after completion of the simulation. In this version, a new technique is developed to model higher gas densities by parameterizing the probability distribution function (PDF) of the gas density in higher-resolution simulations run with the pseudo-Lagrangian, Voronoi mesh code arepo. The parameterized PDFs are used as a look-up table, and reach higher densities than in previous work. sígame v3 is tested on redshift z = 0 galaxies drawn from the simba cosmological simulation for eight FIR emission lines tracing vastly different phases of the interstellar medium. This version of sígame includes dust radiative transfer with Skirt and high-resolution photoionization models with Cloudy, the latter sampled according to the density PDF of the arepo simulations to augment the densities in the cosmological simulation. The quartile distributions of the predicted line luminosities overlap with the observed range for nearby galaxies of similar star formation rate (SFR) for all but two emission lines: [O i]63 and CO(3–2), which are overestimated by median factors of 1.3 and 1.0 dex, respectively, compared to the observed line–SFR relation of mixed-type galaxies. We attribute the remaining disagreement with observations to the lack of precise attenuation of the interstellar light on sub-grid scales (≲200 pc) and differences in sample selection.
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Colberg, C. A., B. P. Luo, H. Wernli, T. Koop, and Th Peter. "A novel model to predict the physical state of atmospheric H<sub>2</sub>SO<sub>4</sub>/NH<sub>3</sub>/H<sub>2</sub>O aerosol particles." Atmospheric Chemistry and Physics Discussions 2, no. 6 (December 16, 2002): 2449–87. http://dx.doi.org/10.5194/acpd-2-2449-2002.
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Abstract. The physical state of tropospheric aerosol particles is largely unknown despite its importance for cloud formation and for the aerosols' radiative properties. Here we show the first systematic global modelling study of the physical state of the H2SO4/NH3/H2O aerosol, which constitutes an important class of aerosols in the free troposphere. The Aerosol Physical State Model (APSM) developed here is based on Lagrangian trajectories computed from ECMWF (European Centre for Medium Range Weather Forecasts) analyses, taking full account of the deliquescence/efflorescence hysteresis. As input APSM requires three data sets: (i) deliquescence and efflorescence relative humidities from laboratory measurements, (ii) ammonia-to-sulfate ratios (ASR) calculated by a global circulation model, and (iii) relative humidities determined from the ECMWF analyses. APSM results indicate that globally averaged a significant fraction (17-57%) of the ammoniated sulfate aerosol particles contain solids with the ratio of solid-containing to purely liquid particles increasing with altitude (between 2 and 10 km). In our calculations the most abundant solid is letovicite, (NH4)3H(SO4)2, while there is only little ammonium sulfate, (NH4)2SO4. Since ammonium bisulfate, NH4HSO4, does not nucleate homogeneously, it can only form via heterogeneous crystallization. As the ammonia-to-sulfate ratios of the atmospheric aerosol usually do not correspond to the stoichiometries of known crystalline substances, all solids are expected to occur in mixed-phase aerosol particles. This work highlights the global importance of letovicite, whose role as cloud condensation nucleus (CCN) and as scatterer of solar radiation remains to be scrutinized.
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Colberg, C. A., B. P. Luo, H. Wernli, T. Koop, and Th Peter. "A novel model to predict the physical state of atmospheric H<sub>2</sub>SO<sub>4</sub>/NH<sub>3</sub>/H<sub>2</sub>O aerosol particles." Atmospheric Chemistry and Physics 3, no. 4 (July 2, 2003): 909–24. http://dx.doi.org/10.5194/acp-3-909-2003.
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Abstract. The physical state of the tropospheric aerosol is largely unknown despite its importance for cloud formation and for the aerosol's radiative properties. Here we use detailed microphysical laboratory measurements to perform a systematic global modelling study of the physical state of the H2SO4/NH3/H2O aerosol, which constitutes an important class of aerosols in the free troposphere. The Aerosol Physical State Model (APSM) developed here is based on Lagrangian trajectories computed from ECMWF (European Centre for Medium Range Weather Forecasts) analyses, taking full account of the deliquescence/efflorescence hysteresis. As input APSM requires three data sets: (i) deliquescence and efflorescence relative humidities from laboratory measurements, (ii) ammonia-to-sulfate ratios (ASR) calculated by a global circulation model, and (iii) relative humidities determined from the ECMWF analyses. APSM results indicate that globally averaged a significant fraction (17-57%) of the ammoniated sulfate aerosol particles contain solids with the ratio of solid-containing to purely liquid particles increasing with altitude (between 2 and 10 km). In our calculations the most abundant solid is letovicite, (NH4)3H(SO4)2, while there is only little ammonium sulfate, (NH4)2SO4. Since ammonium bisulfate, NH4HSO4, does not nucleate homogeneously, it can only form via heterogeneous crystallization. As the ammonia-to-sulfate ratios of the atmospheric H2SO4/NH3/H2O aerosol usually do not correspond to the stoichiometries of known crystalline substances, all solids are expected to occur in mixed-phase aerosol particles. This work highlights the potential importance of letovicite, whose role as cloud condensation nucleus (CCN) and as scatterer of solar radiation remains to be scrutinized.
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Cong, Xiao Chun, Xu Jie Sun, Wen Jiang Xiang, and Shu Li Yang. "Study of Parametric Effects on Aqueous Ammonia Process for Removal of SO2." Advanced Materials Research 236-238 (May 2011): 1836–40. http://dx.doi.org/10.4028/www.scientific.net/amr.236-238.1836.
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A three-dimension computational fluid dynamics study on spray tower of aqueous ammonia process is presented. The gas flow is described using standard turbulence model ,and the motion of the liquid droples is described in a Lagrangian way, using the stochastic discrete particle mode. The influence of parameters including ammonia concentration, liquid gas ratio and porosity of air distributor on the efficiency of FGD was studied. When liquid-gas ratio is about 2.2, the concentration of NH3 is about 0.09% and the porosity of air distributor is between 70% and 80%, the SO2 removal efficiency of spray tower will be higher from the result. It can be taken as a reference for process design, optimization and intensive study of desulfurization by aqueous ammonia process.
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Granados-Muñoz, Maria Jose, and Thierry Leblanc. "Tropospheric ozone seasonal and long-term variability as seen by lidar and surface measurements at the JPL-Table Mountain Facility, California." Atmospheric Chemistry and Physics 16, no. 14 (July 28, 2016): 9299–319. http://dx.doi.org/10.5194/acp-16-9299-2016.
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Abstract. A combined surface and tropospheric ozone climatology and interannual variability study was performed for the first time using co-located ozone photometer measurements (2013–2015) and tropospheric ozone differential absorption lidar measurements (2000–2015) at the Jet Propulsion Laboratory Table Mountain Facility (TMF; elev. 2285 m), in California. The surface time series were investigated both in terms of seasonal and diurnal variability. The observed surface ozone is typical of high-elevation remote sites, with small amplitude of the seasonal and diurnal cycles, and high ozone values, compared to neighboring lower altitude stations representative of urban boundary layer conditions. The ozone mixing ratio ranges from 45 ppbv in the winter morning hours to 65 ppbv in the spring and summer afternoon hours. At the time of the lidar measurements (early night), the seasonal cycle observed at the surface is similar to that observed by lidar between 3.5 and 9 km. Above 9 km, the local tropopause height variation with time and season impacts significantly the ozone lidar observations. The frequent tropopause folds found in the vicinity of TMF (27 % of the time, mostly in winter and spring) produce a dual-peak vertical structure in ozone within the fold layer, characterized by higher-than-average values in the bottom half of the fold (12–14 km), and lower-than-averaged values in the top half of the fold (14–18 km). This structure is consistent with the expected origin of the air parcels within the fold, i.e., mid-latitude stratospheric air folding down below the upper tropospheric sub-tropical air. The influence of the tropopause folds extends down to 5 km, increasing the ozone content in the troposphere. No significant signature of interannual variability could be observed on the 2000–2015 de-seasonalized lidar time series, with only a statistically non-significant positive anomaly during the years 2003–2007. Our trend analysis reveals however an overall statistically significant positive trend of 0.3 ppbv year−1 (0.6 %) in the free troposphere (7–10 km) for the period 2000–2015. A classification of the air parcels sampled by lidar was made at 1 km intervals between 5 and 14 km altitude, using 12-day backward trajectories (HYSPLIT, Hybrid Single Particle Lagrangian Integrated Trajectory Model). Our classification revealed the influence of the Pacific Ocean, with air parcels of low ozone content (43–60 ppbv below 9 km), and significant influence of the stratosphere leading to ozone values of 57–83 ppbv down to 8–9 km. In summer, enhanced ozone values (76 ppbv at 9 km) were found in air parcels originating from Central America, probably due to the enhanced thunderstorm activity during the North American Monsoon. Influence from Asia was observed throughout the year, with more frequent episodes during spring, associated with ozone values from 53 to 63 ppbv at 9 km.
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Hirsch, A. I. "On using radon-222 and CO<sub>2</sub> to calculate regional-scale CO<sub>2</sub> fluxes." Atmospheric Chemistry and Physics Discussions 6, no. 6 (November 2, 2006): 10929–58. http://dx.doi.org/10.5194/acpd-6-10929-2006.
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Abstract. Because of its ubiquitous release on land and well-characterized atmospheric loss, radon-222 has been very useful for deducing fluxes of greenhouse gases such as CO2, CH4, and N2O. It is shown here that the radon-tracer method, used in previous studies to calculate regional-scale greenhouse gas fluxes, returns a weighted-average flux (the flux field F weighted by the sensitivity of the measurements to that flux field, f) rather than an evenly-weighted spatial average flux. A synthetic data study using a Lagrangian particle dispersion model and modeled CO2 fluxes suggests that the discrepancy between the sensitivity-weighted average flux and evenly-weighted spatial average flux can be significant in the case of CO2, due to covariance between F and f for biospheric CO2 fluxes during the growing season and also for anthropogenic CO2 fluxes in general. A technique is presented to correct the radon-tracer derived fluxes to yield an estimate of evenly-weighted spatial average CO2 fluxes. A new method is also introduced for correcting the CO2 flux estimates for the effects of radon-222 radioactive decay in the radon-tracer method.
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Hirsch, A. I. "On using radon-222 and CO<sub>2</sub> to calculate regional-scale CO<sub>2</sub> fluxes." Atmospheric Chemistry and Physics 7, no. 14 (July 17, 2007): 3737–47. http://dx.doi.org/10.5194/acp-7-3737-2007.
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Abstract. Because of its ubiquitous release on land and well-characterized atmospheric loss, radon-222 has been very useful for deducing fluxes of greenhouse gases such as CO2, CH4, and N2O. It is shown here that the radon-tracer method, used in previous studies to calculate regional-scale greenhouse gas fluxes, returns a weighted-average flux (the flux field F weighted by the sensitivity of the measurements to that flux field, f) rather than an evenly-weighted spatial average flux. A synthetic data study using a Lagrangian particle dispersion model and modeled CO2 fluxes suggests that the discrepancy between the sensitivity-weighted average flux and evenly-weighted spatial average flux can be significant in the case of CO2, due to covariance between F and f for biospheric CO2 fluxes during the growing season and also for anthropogenic CO2 fluxes in general. A technique is presented to correct the radon-tracer derived fluxes to yield an estimate of evenly-weighted spatial average CO2 fluxes. A new method is also introduced for correcting the CO2 flux estimates for the effects of radon-222 radioactive decay in the radon-tracer method.
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Kretschmer, R., C. Gerbig, U. Karstens, G. Biavati, A. Vermeulen, F. Vogel, S. Hammer, and K. U. Totsche. "Impact of optimized mixing heights on simulated regional atmospheric transport of CO<sub>2</sub>." Atmospheric Chemistry and Physics 14, no. 14 (July 16, 2014): 7149–72. http://dx.doi.org/10.5194/acp-14-7149-2014.
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Abstract. The mixing height (MH) is a crucial parameter in commonly used transport models that proportionally affects air concentrations of trace gases with sources/sinks near the ground and on diurnal scales. Past synthetic data experiments indicated the possibility to improve tracer transport by minimizing errors of simulated MHs. In this paper we evaluate a method to constrain the Lagrangian particle dispersion model STILT (Stochastic Time-Inverted Lagrangian Transport) with MH diagnosed from radiosonde profiles using a bulk Richardson method. The same method was used to obtain hourly MHs for the period September/October 2009 from the Weather Research and Forecasting (WRF) model, which covers the European continent at 10 km horizontal resolution. Kriging with external drift (KED) was applied to estimate optimized MHs from observed and modelled MHs, which were used as input for STILT to assess the impact on CO2 transport. Special care has been taken to account for uncertainty in MH retrieval in this estimation process. MHs and CO2 concentrations were compared to vertical profiles from aircraft in situ data. We put an emphasis on testing the consistency of estimated MHs to observed vertical mixing of CO2. Modelled CO2 was also compared with continuous measurements made at Cabauw and Heidelberg stations. WRF MHs were significantly biased by ~10–20% during day and ~40–60% during night. Optimized MHs reduced this bias to ~5% with additional slight improvements in random errors. The KED MHs were generally more consistent with observed CO2 mixing. The use of optimized MHs had in general a favourable impact on CO2 transport, with bias reductions of 5–45% (day) and 60–90% (night). This indicates that a large part of the found CO2 model–data mismatch was indeed due to MH errors. Other causes for CO2 mismatch are discussed. Applicability of our method is discussed in the context of CO2 inversions at regional scales.
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Bouzaiene, Maher, Milena Menna, Dalila Elhmaidi, Ahmad Fehmi Dilmahamod, and Pierre-Marie Poulain. "Spreading of Lagrangian Particles in the Black Sea: A Comparison between Drifters and a High-Resolution Ocean Model." Remote Sensing 13, no. 13 (July 2, 2021): 2603. http://dx.doi.org/10.3390/rs13132603.
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The Lagrangian dispersion statistics of the Black Sea are estimated using satellite-tracked drifters, satellite altimeter data and a high-resolution ocean model. Comparison between the in-situ measurements and the model reveals good agreement in terms of the surface dispersion. The mean sub-basin coherent structures and currents of the Black Sea are well reproduced by the model. Seasonal variability of the dispersion in the upper (15 m), intermediate (150 m) and deep (750 m) layers are discussed with a special focus of the role of sub-basin scale structures and currents on the turbulent dispersion regimes. In terms of the surface relative dispersion, the results show the presence of the three known turbulent exponential, Richardson and diffusive-like regimes. The non-local exponential regime is only detected by the model for scales <10 km, while the local Richardson regime occurs between 10 and 100 km in all cases due to the presence of an inverse energy cascade range, and the diffusive-like regime is well detected for the largest distance by drifters (100–300 km) in winter/spring. Regarding the surface absolute dispersion, it reflects the occurrence of both quasi-ballistic and random-walk regimes at small and large times, respectively, while the two anomalous hyperbolic (5/4) and elliptic (5/3) regimes, which are related to the topology of the Black Sea, are detected at intermediate times. At depth, the signatures of the relative and absolute dispersion regimes shown in the surface layer are still valid in most cases. The absolute dispersion is anisotropic; the zonal component grows faster than the meridional component in any scenario.
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Belikov, Dmitry A., Shamil Maksyutov, Alexander Ganshin, Ruslan Zhuravlev, Nicholas M. Deutscher, Debra Wunch, Dietrich G. Feist, et al. "Study of the footprints of short-term variation in XCO<sub>2</sub> observed by TCCON sites using NIES and FLEXPART atmospheric transport models." Atmospheric Chemistry and Physics 17, no. 1 (January 3, 2017): 143–57. http://dx.doi.org/10.5194/acp-17-143-2017.
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Abstract. The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier transform spectrometers (FTSs) that record near-infrared (NIR) spectra of the sun. From these spectra, accurate and precise observations of CO2 column-averaged dry-air mole fractions (denoted XCO2) are retrieved. TCCON FTS observations have previously been used to validate satellite estimations of XCO2; however, our knowledge of the short-term spatial and temporal variations in XCO2 surrounding the TCCON sites is limited. In this work, we use the National Institute for Environmental Studies (NIES) Eulerian three-dimensional transport model and the FLEXPART (FLEXible PARTicle dispersion model) Lagrangian particle dispersion model (LPDM) to determine the footprints of short-term variations in XCO2 observed by operational, past, future and possible TCCON sites. We propose a footprint-based method for the collocation of satellite and TCCON XCO2 observations and estimate the performance of the method using the NIES model and five GOSAT (Greenhouse Gases Observing Satellite) XCO2 product data sets. Comparison of the proposed approach with a standard geographic method shows a higher number of collocation points and an average bias reduction up to 0.15 ppm for a subset of 16 stations for the period from January 2010 to January 2014. Case studies of the Darwin and Reunion Island sites reveal that when the footprint area is rather curved, non-uniform and significantly different from a geographical rectangular area, the differences between these approaches are more noticeable. This emphasises that the collocation is sensitive to local meteorological conditions and flux distributions.
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Tohjima, Y., M. Kubo, C. Minejima, H. Mukai, H. Tanimoto, A. Ganshin, S. Maksyutov, K. Katsumata, T. Machida, and K. Kita. "Temporal changes in the emissions of CH<sub>4</sub> and CO from China estimated from CH<sub>4</sub> / CO<sub>2</sub> and CO / CO<sub>2</sub> correlations observed at Hateruma Island." Atmospheric Chemistry and Physics Discussions 13, no. 8 (August 30, 2013): 22893–930. http://dx.doi.org/10.5194/acpd-13-22893-2013.
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Abstract. In-situ observation of the atmospheric CO2, CH4, and CO mixing ratios at Hateruma Island (HAT, 24.05° N, 123.80° E) often show synoptic-scale variations with correlative elevations during winter, associated with air transport from the East Asian countries. We examine winter (November–March) trends in ΔCH4 / ΔCO2, ΔCO / ΔCO2, and ΔCO / ΔCH4 observed at Hateruma over the period 1999 to 2010. Although the ratios ΔCH4 / ΔCO2 and ΔCO / ΔCO2 both show an overall gradual decrease over the study period due to a recent rapid increase in fossil fuel consumption in China, we note that ΔCH4 / ΔCO2 and ΔCO / ΔCO2 remains relatively flat (no trend) during 2005–2010 and 1999–2004, respectively. The CO/CH4 slope on the other hand shows an increasing trend during 1999–2004 but a decrease during 2005–2010. Calculation of the concentration footprint for the atmospheric observation at HAT by using the FLEXPART Lagrangian particle dispersion model indicates that most of the short-term variations are caused by emission variations from North and East China. Combined with a set of reported emission maps, we have estimated the temporal changes in the annual CH4 and CO emissions from China under the assumption that the estimate of the fossil fuel-derived CO2 emissions based on the energy statistics is accurate. The estimated annual CH4 emissions, corresponding to non-seasonal sources or anthropogenic sources without rice fields, show a nearly constant value of 39 ± 6 TgCH4 yr−1 during 1998–2002, and then gradually increases to 46 ± 7 TgCH4 yr−1 in 2009/2010. The estimated annual CO emissions increase from 134 ± 26 TgCO yr−1 in 1998/1999 to 182 ± 33 TgCO yr−1 in 2004/2005, level off after 2005, and then slightly decrease to less than 160 TgCO yr−1 in 2008–2010.
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Biferale, L., C. Meneveau, and R. Verzicco. "Deformation statistics of sub-Kolmogorov-scale ellipsoidal neutrally buoyant drops in isotropic turbulence." Journal of Fluid Mechanics 754 (July 30, 2014): 184–207. http://dx.doi.org/10.1017/jfm.2014.366.
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AbstractSmall droplets in turbulent flows can undergo highly variable deformations and orientational dynamics. For neutrally buoyant droplets smaller than the Kolmogorov scale, the dominant effects from the surrounding turbulent flow arise through Lagrangian time histories of the velocity gradient tensor. Here we study the evolution of representative droplets using a model that includes rotation and stretching effects from the surrounding fluid, and restoration effects from surface tension including a constant droplet volume constraint, while assuming that the droplets maintain an ellipsoidal shape. The model is combined with Lagrangian time histories of the velocity gradient tensor extracted from direct numerical simulations (DNS) of turbulence to obtain simulated droplet evolutions. These are used to characterize the size, shape and orientation statistics of small droplets in turbulence. A critical capillary number is identified associated with unbounded growth of one or two of the droplet’s semi-axes. Exploiting analogies with dynamics of polymers in turbulence, the critical capillary number can be predicted based on the large deviation theory for the largest finite-time Lyapunov exponent quantifying the chaotic separation of particle trajectories. Also, for subcritical capillary numbers near the critical value, the theory enables predictions of the slope of the power-law tails of droplet size distributions in turbulence. For cases when the viscosities of droplet and outer fluid differ in a way that enables vorticity to decorrelate the shape from the straining directions, the large deviation formalism based on the stretching properties of the velocity gradient tensor loses validity and its predictions fail. Even considering the limitations of the assumed ellipsoidal droplet shape, the results highlight the complex coupling between droplet deformation, orientation and the local fluid velocity gradient tensor to be expected when small viscous drops interact with turbulent flows. The results also underscore the usefulness of large deviation theory to model these highly complex couplings and fluctuations in turbulence that result from time integrated effects of fluid deformations.