354 research outputs found
Direct and semi-direct aerosol effects on the southern African regional climate during the austral winter season
No full textIncludes abstract.Includes bibliographical references (p. 195-219).The regional climate model RegCM3 is used to investigate the direct and semi-direct aerosol effects on the southern African climate during the austral winter season (June-September). The sensitivity of simulated aerosol-climate effects to different biomass burning inventories, boundary conditions and sea surface temperature (SST) feedbacks is tested to assess the range of uncertainty associated with these parameters
Radiative Forcing of Carbonaceous Aerosols over Two Urban Environments in Northern India Abhilash S. Panicker , Rathod Aditi, Gufran Beig, Kaushar Ali, Fabien Solmon
No full textThe radiative forcing of elemental carbon (EC) and organic carbon (OC) has been estimated over two urban environments in Northern India (Jabalpur [JBL] and Udaipur [UDPR]) from November 2011 till November 2012 (till September 2012 over Jabalpur). The elemental carbon concentrations reached 7.36 ± 1.99 µg m–3 over JBL and were as high as 10.78 ± 4.85 µg m–3 over UDPR, whereas the corresponding OC concentrations were much higher in different months (as high as 19.37 ± 12.6 µg m–3 over JBL and 39.71 ± 13.05 µg m–3 over UDPR). The radiative forcing for OC and EC has been estimated using an optical model along with a radiative transfer model. The surface OC radiative forcing was found to range from –2.19 ± 1.93 W m–2 to –3.083 ± 2.29 W m–2 over JBL and –1.97 ± 1.37 to –5.89 ± 2.17 W m–2 over UDPR, whereas the estimated top of the atmosphere (TOA) forcing ranged from –0.87 ± 0.49 to –1.87 ± 0.90 W m–2 over JBL and from –1.23 ± 0.31 to –3.44 ± 1.51 W m–2 over UDPR. However, the effect of EC forcing (as high as –21.75 W m–2 at the surface of and +6.3 W m–2 at TOA over JBL and –38.21 W m–2 at the surface of and +5.05 W m–2 at TOA over UDPR) was found to be more than tenfold higher than OC forcing due to its strong atmospheric absorption, in spite of much lower concentrations compared to OC
Chile Niño/Niña processes across a hierarchy of models
No full textLa région d'upwelling de frontière Est du Pacifique Sud-Est (SEP) est l'une des zones océaniques les plus productives sur le plan biologique à l'échelle mondiale, ce qui lui confère une grande importance pour la sécurité alimentaire et les activités socio-économiques. Ces dernières années, les vagues de chaleur marine ont attiré l'attention de la communauté scientifique en raison de leurs effets délétères, qui devraient être exacerbés par le changement climatique, un problème auquel le SEP est particulièrement vulnérable. Récemment, de nouveaux modes climatiques couplés air-mer ont été identifiés dans tous les principaux systèmes d'upwelling côtière et ont été baptisés Niños côtiers. Au large du Chili central, un tel mode, appelé Chile Niño/Niña, se produit et détermine une part substantielle de la variabilité locale de la température de surface de la mer. Améliorer notre capacité à prévoir de tels événements est un défi important qui a des implications sociétales claires pour les pays proches de la côte ouest de l'Amérique du Sud. Dans cette thèse, nous avons étudié les mécanismes sous-jacents de Chile Niño/Niña et ses changements prévus dans le cadre du changement climatique. Pour ce faire, nous avons utilisé des observations, des produits de réanalyse et un ensemble de modèles d'une grande complexité, allant de modèles conceptuels simples et de modèles basés sur des données, à des modèles climatiques complets. Un modèle régional couplé de complexité intermédiaire a également été développé. Nous constatons que l'oscillation du Pacifique Sud (SPO) et El Niño-Oscillation australe (ENSO) sont des précurseurs de Chile Niño/Niña, tandis que le mode méridien du Pacifique Sud (SPMM) y est étroitement lié. En outre, nous montrons que la variabilité quasi-annuelle de Chile Niño/Niña peut être interprétée comme résultant d'un processus de tonalité combinée entre ENSO et le cycle annuel, tandis que sa variabilité décennale découle en partie du rougissement océanique du bruit atmosphérique lié à la variabilité décennale du Pacifique tropical. Ensuite, en utilisant un ensemble de 62 modèles, nous démontrons que les modèles CMIP5 et 6 sont capables de simuler les principales caractéristiques spatio-temporelles de Chile Niño/Niña. Les modèles ont également tendance à simuler trop de Chile Niñas, ce qui se traduit par une asymétrie plus faible que dans les observations. Nous avons également étudié les changements des propriétés de Chile Niño/Niña dans le cadre du changement climatique en nous basant sur un ensemble de 36 modèles CMIP5/6. Nous constatons une augmentation modeste de sa variabilité, qui est due à une augmentation de l'amplitude plutôt qu'à une augmentation du nombre d'événements. Ces changements résultent d'une interaction entre des processus locaux et lointains, y compris une augmentation (diminution) de la variabilité ENSO (SPO) et des changements dans les processus locaux avec des effets opposés. Ensuite, en réalisant une série d'expériences avec un modèle atmosphérique régional couplé à une configuration océanique en dalle, nous constatons que les événements Chile Niño/Niña peuvent se produire en l'absence de dynamique océanique et peuvent résulter d'une dynamique purement interne. Les bilans thermiques de la couche de mélange révèlent que, si le rayonnement d'ondes courtes est un processus clé pour induire le développement de Chile Niño/Niña, il existe une diversité dans l'équilibre entre les processus de flux de chaleur et que le changement de la profondeur de la couche de mélange n'est pas nécessaire au développement de l'événement. Certains événements ont également besoin de la dynamique des océans pour atteindre une amplitude réaliste. Nous démontrons également son lien étroit avec le SPMM, ce qui suggère qu'il pourrait faire partie d'un mécanisme reliant la variabilité tropicale et celle des moyennes et hautes latitudes à des échelles de temps interannuelles à décennales.The eastern boundary upwelling region of the southeastern Pacific (SEP) is one of the most biologically productive oceanic areas on a global scale, which makes it highly important for food security and socio economic activities. Over recent years, marine heat waves have attracted the attention of the scientific community due to their deleterious impacts, which are projected to be exacerbated by climate change, an issue to which the SEP is particularly vulnerable to. Recently, new air-sea coupled climate modes have been identified in all major coastal upwelling systems and have been named Coastal Niños. They are thought to interact with basin-scale climate variability although it is not clear the extent to which current generation of global climate models realistically account for their statistical properties. Off Central Chile, such a mode, called Chile Niño/Niña, takes place and drives a substantial share of the local sea surface temperature variability. Improving our ability to predict these events is a significant challenge with clear societal implications for the countries close to the west coast of South America. In this thesis we investigated the underlying mechanisms of Chile Niño/Niña and its projected changes under climate change. For this we made use of observations, reanalysis products and a set of models of a wide range of complexities, from simple conceptual models and data-driven models, to full-physics climate models. A regional coupled model of intermediate complexity was also developed. We find that the South Pacific Oscillation (SPO) and the El Niño-Southern Oscillation (ENSO) are precursors of Chile Niño/Niña, while the South Pacific Meridional Mode (SPMM) has a close connection with it. Further, we show that Chile Niño/Niña near-annual variability can be interpreted as resulting from a combination tone process between ENSO and the annual cycle, while its decadal variability partly stems from oceanic reddening of atmospheric noise linked to Tropical Pacific Decadal Variability. Following, using an ensemble of 62 models, we demonstrate that CMIP5 and 6 models are skillful in simulating the main spatio-temporal characteristics of Chile Niño/Niña. Models also tend to simulate too much Chile Niñas resulting in a weaker asymmetry than in the observations. We also investigated the changes of Chile Niño/Niña properties under climate change based on an ensemble of 36 CMIP5/6 models. We find a modest increase in its variability, which is shown to be due to an increase in amplitude rather than an increase in the number of events. These changes result from an interplay of local and remote processes, including an increase (decrease) in ENSO (SPO) variability and changes in local processes with opposite effects. Amongst the local processes investigated, only the changes on the thermocline feedback show a high correlation with the change in Chile Niño/Niña variability amongst the models, emphasizing the key role of mean stratification changes along the coast. Thereafter, by performing a set of experiments with a regional atmospheric model coupled to a slab ocean configuration, we find that Chile Niño/Niña events can take place in the absence of ocean dynamics and can arise from purely internal dynamics. Mixed-layer heat budgets reveal that, while shortwave radiation is a key process to induce Chile Nino/Nina development, there is a diversity in the balance between heat flux processes and that change in mixed layer depth is not necessary for its development. Some events also need ocean dynamics to reach realistic amplitudes. Overall, we show that Chile Niño/Niña variability involves a wide diversity of local processes, and can be sustained under varied forcing conditions. We also demonstrate its tight connection with the SPMM, which suggests it could be part of a mechanism linking tropical and mid-to-high latitude variability at interannual to decadal timescales
Modeling dust and soluble iron deposition to the South Atlantic Ocean
Full text linkThe global chemical transport model GEOS-Chem, implemented with a dust-iron dissolution scheme, was used to analyze the magnitude and spatial distribution of mineral dust and soluble-iron (sol-Fe) deposition to the South Atlantic Ocean (SAO). The comparison of model results with remotely sensed data shows that GEOS-Chem can capture dust source regions in Patagonia and characterize the temporal variability of dust outflow. For a year-long model simulation, 22 Tg of mineral dust and 4 Gg of sol-Fe were deposited to the surface waters of the entire SAO region, with roughly 30% of this dust and sol-Fe predicted to be deposited to possible high nitrate low chlorophyll oceanic regions. Model-predicted dissolved iron fraction of mineral dust over the SAO was small, on average only accounting for 0.57% of total iron. Simulations suggest that the primary reason for such a small fraction of sol-Fe is the low ambient concentrations of acidic trace gases available for mixing with dust plumes. Overall, the amount of acid added to the deliquesced aerosol solution was not enough to overcome the alkalinity buffer of Patagonian dust and initiate considerable acid dissolution of mineral-iron. Sensitivity studies show that the amount of sol-Fe deposited to the SAO was largely controlled by the initial amount of sol-Fe at the source region, with limited contribution from the spatial variability of Patagonian-desert topsoil mineralogy and natural sources of acidic trace gases. Simulations suggest that Patagonian dust should have a minor effect on biological productivity in the SAO.Fil: Johnson, Matthew S.. North Carolina Sate University; Estados UnidosFil: Meskhidze, Nicholas. North Carolina Sate University; Estados UnidosFil: Solmon, Fabien. French National Center for Scientific Research; FranciaFil: Gassó, Santiago. University of Maryland; Estados UnidosFil: Chuang, Patrick Y.. California State University; Estados UnidosFil: Gaiero, Diego Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Yantosca, Robert M.. Harvard University; Estados UnidosFil: Wu, Shiliang. Michigan Technological University; Estados UnidosFil: Wang, Yuxuan. Tsinghua University Beijing; ChinaFil: Carouge, Claire. Harvard University; Estados Unido
particleShear: Discrete Python particle simulation with digital rheology and stress tensor evaluation
No full textparticleShear: Python package for particle shear simulation
This package provides a discrete particle simulation kit for having multiple spheres interacting. The spheres (i.e. 2D circles) interact by mutual elastic repulsion and tangential friction upon contact, but can also be crosslinked together. In addition to the elementary implementation of the interacting particles, it is also possible to define rheological experiments where the spheres are exposed to sinusoidally varying displacement conditions on the boundaries. We paid particular attention to avoid pitfalls that generate asymmetric stress tensors.
Acknowledgement: Thanks from the author go to Fabien Bonini and Joé Brefie-Guth for package testing, and to Daniel Lyobenov for initial help with simulation setup.
This repository archives the releases of the source code hosted at https://github.com/tbgitoo/particleShear. The package is available through the Python package server (see https://pypi.org/project/particleShear/1.0.2/). It can be installed automatically in python via
pip3 install particleShear
In some installations, the command may also be pip install particleShear; the minimal version of Python is 3.
Gas and Aerosol Exchange Between Terrestrial Ecosystems and the Atmosphere: Advancing Our Understanding of Vegetation-Climate Couplings
Full text linkThis dissertation attempts to improve knowledge of the complex interactions of vegetation and climate by addressing two vegetation-atmosphere mass exchanges that are or might be critical to climate: photosynthetic carbon uptake, and biological aerosol emissions. First, a prognostic model of Pollen Emissions for Climate Models (PECM) for use within regional and global climate models is developed to simulate pollen counts over the seasonal cycle based on geography, vegetation type and meteorological parameters. An observation-based parameterization of pollen season phenology is determined using pollen count data to estimate the linear relationship between start and end dates and prior-year annual average temperature. This regression model explains as much as 57% of the variance in pollen phenological dates for many taxa common to the U.S., and it is used to create a “climate-flexible” phenology that can be used to study the response of wind-driven pollen emissions to climate change. The simulated surface pollen concentrations from coupling PECM with a regional climate model are evaluated against observations, and simulated pollen counts are within an order of magnitude of the observed concentrations. Second, the first model of atmospheric pollen grain rupture is developed and implemented in regional climate model simulations over spring pollen season in the United States with a CCN-dependent moisture scheme. The source of SPPs (surface or in- atmosphere) is compared and found to depend on region and sometimes season, due to the distribution of relative humidity and rain. It is shown that upper-bound estimated SPP concentrations can suppress average seasonal precipitation over the continental U.S. by 32% in clean background aerosol conditions, though this effect is smaller (~2%) for polluted air. Finally, the impact of a vertically complex canopy and its microenvironment on carbon uptake is assessed for deciduous broadleaved forests using different model representations of the canopy. Simulations of a multilayer version of Community Land Model (CLM-ml) are compared with CLM4.5 “big-leaf” simulations for the month of July (peak growing season), and evaluated with observed eddy covariance tower fluxes at five FLUXNET deciduous broadleaf forest sites. Four abiotic environmental drivers – air temperature, relative humidity, incoming shortwave radiation
and soil moisture – are correlated with GPP inter-annual variations at each site to determine the strength of their influence and the overall sensitivity of GPP to local climate variability. It is found that, even though the models all underestimate GPP and its inter-annual variability, the patterns of GPP IAV and its drivers loosely resemble observed patterns. When using Ball-Berry stomatal conductance and a uniformly applied soil moisture stress factor in CLM-ml, vertical variation in the sensitivity of leaf-level carbon assimilation rate to climate variability is small, and therefore the canopy-scale GPP and its response to climate variability at all five sites are similar between CLM-ml and CLM4.5 simulations. However, using CLM-ml with plant hydraulics with non-uniform water stress, the sensitivity of carbon assimilation rate to climate variability varies with height and canopy-scale GPP is dampened from CLM4.5. Both reduced dependence on soil moisture and opposing climatic forcings on different leaf layers cause such dampening. This research highlights several unknowns in the climate system stemming from vegetation-climate interactions, as well as the importance of model-data integration for solving these unknowns. The results can be used to further the development of more accurate climate prediction to prepare society for the impacts of climate change.PhDAtmospheric, Oceanic & Space ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/151516/1/mcwoz_1.pd
The (uncertain) future of air quality
No full textInternational audienceThe assessment of the future evolution of air quality requires accounting for both climate projections and the development of environmental policies. In the context of climate change adaptation, the geophysical changes to be expected in the decades to come will have an impact on chronic and extreme air pollution events (Jacob and Winner, 2009). But air quality is also sensitive to climate mitigation strategies: the social and technological changes required to reduce greenhouse gases emissions will also be accompanied by changes in the emission of air pollutants and precursors thereof. There are potentially large co-benefits between air quality and climate change mitigation that could help in leveraging efforts to engage in win-win strategies. But mitigating climate change can also potentially induce collateral damages to air quality. It is thus very important to precisely identify what are the co-benefits and the possible collateral damages in order to maximize the former while minimizing the later. Here we briefly review recent results on climate change impacts on Mediterranean regional air quality in terms of ozone and particles, and list identified positive and negative feedbacks of climate change on air quality
Optimizing construction of scheduled data flow graph for on-line testability
Full text linkThe objective of this work is to develop a new methodology for behavioural synthesis using a flow of synthesis, better suited to the scheduling of independent calculations and non-concurrent online testing. The traditional behavioural synthesis process can be defined as the compilation of an algorithmic specification into an architecture composed of a data path and a controller. This stream of synthesis generally involves scheduling, resource allocation, generation of the data path and controller synthesis. Experiments showed that optimization started at the high level synthesis improves the performance of the result, yet the current tools do not offer synthesis optimizations that from the RTL level. This justifies the development of an optimization methodology which takes effect from the behavioural specification and accompanying the synthesis process in its various stages. In this paper we propose the use of algebraic properties (commutativity, associativity and distributivity) to transform readable mathematical formulas of algorithmic specifications into mathematical formulas evaluated efficiently. This will effectively reduce the execution time of scheduling calculations and increase the possibilities of testability
Dataset: Stability of hemicarbonate under cement paste-like conditions
No full textData, and scripts (analysis, plots) to go with the publication:
Stability of hemicarbonate under cement paste-like conditions
Fabien Georget (a,1,∗), Barbara Lothenbach (b) , William Wilson (a,c) , Franco Zunino (a) Karen L. Scrivener (a)
a: aboratory of Construction Materials, LMC, EPFL-STI-IMX, Station 12, CH-1015
Lausanne, Switzerland
b: Empa, Concrete & Asphalt Laboratory, Dübendorf, Switzerland
c: Sherbrooke University, Sherbrooke, Quebec, Canada
1: current address: Institute of Building Materials Research, RWTH Aachen, Aachen, Germany
* corresponding author
To be submitted to Cement and Concrete Researc
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