Dissertations / Theses on the topic 'Parameterizations'
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1
Brück, Heiner Matthias. "Evaluation of statistical cloud parameterizations." Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-212714.
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This work is motivated by the question: how much complexity is appropriate for a cloud parameterization used in general circulation models (GCM).
To approach this question, cloud parameterizations across the complexity range are explored using general circulation models and theoretical Monte-Carlo simulations. Their results are compared with high-resolution satellite observations and simulations that resolve the GCM subgrid-scale variability explicitly.
A process-orientated evaluation is facilitated by GCM forecast simulations which reproduce the synoptic state.
For this purpose novel methods were develop to
a) conceptually relate the underlying saturation deficit probability density function (PDF) with its saturated cloudy part,
b) analytically compute the vertical integrated liquid water path (LWP) variability,
c) diagnose the relevant PDF-moments from cloud parameterizations,
d) derive high-resolution LWP from satellite observations
and e) deduce the LWP statistics by aggregating the LWP onto boxes equivalent to the GCM grid size. On this basis, this work shows that it is possible to evaluate the sub-grid scale variability of cloud parameterizations in terms of cloud variables.
Differences among the PDF types increase with complexity, in particular the more advanced cloud parameterizations can make use of their double Gaussian PDF in conditions, where cumulus convection forms a separate mode with respect to the remainder of the grid-box. Therefore, it is concluded that the difference between unimodal and bimodal PDFs is more important, than the shape within each mode.
However, the simulations and their evaluation reveals that the advanced parameterizations do not take full advantage of their abilities and their statistical relationships are broadly similar to less complex PDF shapes, while the results from observations and cloud resolving simulations indicate even more complex distributions.
Therefore, this work suggests that the use of less complex PDF shapes might yield a better trade-off.
With increasing model resolution initial weaknesses of simpler, e.g. unimodal PDFs, will be diminished. While cloud schemes for coarse-resolved models need to parameterize multiple cloud regimes per grid-box, higher spatial resolution of future GCMs will separate them better, so that the unimodal approximation improves.
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Zagoruyko, Sergey. "Weight parameterizations in deep neural networks." Thesis, Paris Est, 2018. http://www.theses.fr/2018PESC1129/document.
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Les réseaux de neurones multicouches ont été proposés pour la première fois il y a plus de trois décennies, et diverses architectures et paramétrages ont été explorés depuis. Récemment, les unités de traitement graphique ont permis une formation très efficace sur les réseaux neuronaux et ont permis de former des réseaux beaucoup plus grands sur des ensembles de données plus importants, ce qui a considérablement amélioré le rendement dans diverses tâches d'apprentissage supervisé. Cependant, la généralisation est encore loin du niveau humain, et il est difficile de comprendre sur quoi sont basées les décisions prises. Pour améliorer la généralisation et la compréhension, nous réexaminons les problèmes de paramétrage du poids dans les réseaux neuronaux profonds. Nous identifions les problèmes les plus importants, à notre avis, dans les architectures modernes : la profondeur du réseau, l'efficacité des paramètres et l'apprentissage de tâches multiples en même temps, et nous essayons de les aborder dans cette thèse. Nous commençons par l'un des problèmes fondamentaux de la vision par ordinateur, le patch matching, et proposons d'utiliser des réseaux neuronaux convolutifs de différentes architectures pour le résoudre, au lieu de descripteurs manuels. Ensuite, nous abordons la tâche de détection d'objets, où un réseau devrait apprendre simultanément à prédire à la fois la classe de l'objet et l'emplacement. Dans les deux tâches, nous constatons que le nombre de paramètres dans le réseau est le principal facteur déterminant sa performance, et nous explorons ce phénomène dans les réseaux résiduels. Nos résultats montrent que leur motivation initiale, la formation de réseaux plus profonds pour de meilleures représentations, ne tient pas entièrement, et des réseaux plus larges avec moins de couches peuvent être aussi efficaces que des réseaux plus profonds avec le même nombre de paramètres. Dans l'ensemble, nous présentons une étude approfondie sur les architectures et les paramétrages de poids, ainsi que sur les moyens de transférer les connaissances entre ellesMultilayer neural networks were first proposed more than three decades ago, and various architectures and parameterizations were explored since. Recently, graphics processing units enabled very efficient neural network training, and allowed training much larger networks on larger datasets, dramatically improving performance on various supervised learning tasks. However, the generalization is still far from human level, and it is difficult to understand on what the decisions made are based. To improve on generalization and understanding we revisit the problems of weight parameterizations in deep neural networks. We identify the most important, to our mind, problems in modern architectures: network depth, parameter efficiency, and learning multiple tasks at the same time, and try to address them in this thesis. We start with one of the core problems of computer vision, patch matching, and propose to use convolutional neural networks of various architectures to solve it, instead of manual hand-crafting descriptors. Then, we address the task of object detection, where a network should simultaneously learn to both predict class of the object and the location. In both tasks we find that the number of parameters in the network is the major factor determining it's performance, and explore this phenomena in residual networks. Our findings show that their original motivation, training deeper networks for better representations, does not fully hold, and wider networks with less layers can be as effective as deeper with the same number of parameters. Overall, we present an extensive study on architectures and weight parameterizations, and ways of transferring knowledge between them
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Moon, Todd K., and Krishna Kishor Noru. "WAVEFORM SIGNAL SHAPING USING WAVELET PARAMETERIZATIONS." International Foundation for Telemetering, 2001. http://hdl.handle.net/10150/607582.
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International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, NevadaWe explore the idea of matching a scaling function - the basic building block of a wavelet function - to a desired spectrum. This would allow the scaling function to be used as the signal pulse for a digital communication system that is matched to the channel, avoiding problems such as energy loss or noise amplification due to spectral nulls. An unconstrained parameterization of the scaling function coefficients represents the scaling functions. This parameterization is adapted using gradient descent. Tests indicate that the adaptation is able to capture major features of a desired spectrum, including spectral nulls and major lobes.
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Hales, Jonathan Reid. "Divisors of Modular Parameterizations of Elliptic Curves." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8472.
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The modularity theorem implies that for every elliptic curve E /Q there exist rational maps from the modular curve X_0(N) to E, where N is the conductor of E. These maps may be expressed in terms of pairs of modular functions X(z) and Y(z) that satisfy the Weierstrass equation for E as well as a certain differential equation. Using these two relations, a recursive algorithm can be constructed to calculate the q - expansions of these parameterizations at any cusp. These functions are algebraic over Q(j(z)) and satisfy modular polynomials where each of the coefficient functions are rational functions in j(z). Using these functions, we determine the divisor of the parameterization and the preimage of rational points on E. We give a sufficient condition for when these preimages correspond to CM points on X_0(N). We also examine a connection between the algebras generated by these functions for related elliptic curves, and describe sufficient conditions to determine congruences in the q-expansions of these objects.
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Katz, Jeremy. "Evaluation of Surface Layer Parameterizations Using In-Situ Observations." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2604.
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Appropriate calculation of surface turbulent fluxes between the atmosphere and the underlying surface is one of the major challenges in geosciences. In practice, the surface turbulent fluxes are estimated from the mean surface meteorological variables based on the bulk transfer model combined with Monnin-Obukhov Similarity (MOS) theory. Few studies have been done to examine the extent that to which this flux parameterization framework can be applied to different weather and surface conditions. A novel validation method is developed in this thesis research, which is applied to evaluate the surface flux parameterization using in-situ observations. The main findings are: (a) the theoretical prediction that uses MOS theory does not match well with those directly computed from the observations collected in the coastal region. (b) Large spread in exchange coefficients mainly occurs in the calm wind regime with strong stability. (c) Large turbulent eddies, which depend largely on the mean flow and surface conditions, tend to break the constant flux assumption in the surface layer.
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Kim, Youngseob. "Air quality modeling : evaluation of chemical and meteorological parameterizations." Phd thesis, Université Paris-Est, 2011. http://pastel.archives-ouvertes.fr/pastel-00667777.
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The influence of chemical mechanisms and meteorological parameterizations on pollutant concentrations calculated with an air quality model is studied. The influence of the differences between two gas-phase chemical mechanisms on the formation of ozone and aerosols in Europe is low on average. For ozone, the large local differences are mainly due to the uncertainty associated with the kinetics of nitrogen monoxide (NO) oxidation reactions on the one hand and the representation of different pathways for the oxidation of aromatic compounds on the other hand. The aerosol concentrations are mainly influenced by the selection of all major precursors of secondary aerosols and the explicit treatment of chemical regimes corresponding to the nitrogen oxides (NOx) levels. The influence of the meteorological parameterizations on the concentrations of aerosols and their vertical distribution is evaluated over the Paris region in France by comparison to lidar data. The influence of the parameterization of the dynamics in the atmospheric boundary layer is important ; however, it is the use of an urban canopy model that improves significantly the modeling of the pollutant vertical distribution
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Quaas, Johannes, and Philip Stier. "Satellite observations of convection and their implications for parameterizations." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-203263.
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Parameterization development and evaluation ideally takes a two-step approach (Lohmann et al., 2007). Insight into new processes, and initial parameterization formulation should be guided by theory, process-level observations (laboratory experiments or field studies) or, if these are unavailable, by high-resolution modelling. However, once implemented into large-scale atmospheric models, a thorough testing and evaluation is required in order to assure that the parameterization works satisfactorily for all weather situations and at the scales the model is applied to. Satellite observations are probably the most valuable source
of information for this purpose, since they offer a large range of parameters over comparatively long time series and with a very large, to global, coverage. However, satellites usually retrieve parameters in a rather indirect way, and some quantities (e.g., vertical wind velocities) are unavailable. It is thus essential for model evaluation
1. to assure comparability; and,
2. to develop and apply metrics that circumvent the limitations of satellite
observations and help to learn about parameterizations.
In terms of comparability, the implementation of so-called \"satellite simulators\" has emerged as the approach of choice, in which satellite retrievals are emulated, making use of model information about the subgrid-scale variability of clouds, and creating summary statistics (Bodas-Salcedo et al., 2011; Nam and Quaas, 2012; Nam et al., 2014). In terms of process-oriented metrics, a large range of approaches has been developed, e.g. investigating the life cycle of cirrus from convective detrainment (Gehlot and Quaas, 2012), or focusing on the details of microphysical processes (Suzuki et al., 2011). Besides such techniques
focusing on individual parameterizations, the data assimilation technique might be exploited, by objectively adjusting convection parameters and learning about parameter choices and parameterizations in this way (Schirber et al., 2013).In this chapter, we will first introduce the available satellite data, consider their limitations and the approaches to account for these, and then discuss observations-based process-oriented metrics that have been developed so far.
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Griffin, Joshua Thomas. "Characterization of errors in various moisture roughness length parameterizations." Tallahassee, Florida : Florida State University, 2009. http://etd.lib.fsu.edu/theses/available/etd-11092009-112425/.
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Thesis (M.A.)--Florida State University, 2009.Advisor: Mark A. Bourassa, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed on Apr. 8, 2010). Document formatted into pages; contains viii, 30 pages. Includes bibliographical references.
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Wilkinson, Jonathan Mark. "Evaluating numerical model cloud parameterizations using radar and lidar simulation." Thesis, University of Reading, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440441.
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Solovev, Mikhail A. "Assessment of mesoscale eddy parameterizations for coarse resolution ocean models." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/58517.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999.Includes bibliographical references (p. 248-253).
Climate simulation with numerical oceanic models requires a proper parameterization scheme in order to represent the effects of unresolved mesoscale eddies. Even though a munber of schemes have been proposed and some have led to improvements in the simulation of the bulk climatological properties, the success of the parameterizations in representing the mesoscale eddies has not been investigated in detail. This thesis examines the role of eddies in a 105-years long basin scale eddy resolving simulation with the MIT General Circulation Model (GCM) forced by idealized wind stress and relaxation to prescribed meridional temperature; this thesis also evaluates the Fickian diffusive, the diabatic Green-Stone (GS) and the quasi-adiabatic Gent-McWilliams (GM) parameterizations in a diagnostic study and a series of coarse resolution experiments with the same model in the same configuration. The mesoscale eddies in the reference experiment provide a significant contribution to the thermal balance in limited areas of the domain associated with the upper 1000M of the boundary regions. Specifically designed diagnostic tests of the schemes show that the horizontal and vertical components of the parameterized flux are not simultaneously downgradient to the eddy heat flux. The transfer vectors are more closely aligned with the isopycnal surfaces for deeper layers, thus demonstrating the adiabatic nature of the eddy heat flux for deeper layers. The magnitude of the coefficients is estimated to be consistent with traditionally used values. However, the transfer of heat associated with timedependent motions is identified as a complicated process that cannot be fully explained with any of the local parameterization schemes considered. The eddy parameterization schemes are implemented in the coarse resolution configuration with the same model. A series of experiments exploring the schemes' parameter space demonstrate that Fickian diffusion has the least skill in the climatological simulations because it overestimates the temperature of the deep ocean and underestimates the total heat transport. The GS and GM schemes perform better in the simulation of the bulk climatological properties of the reference solution, although the GM scheme in particular produces an ocean that is consistently colder than the reference state. Comparison of the eddy heat flux divergence with the parameterized divergences for typical parameter values demonstrates that the success of the schemes in the climatological simulation is not related to the representation of the eddy heat flux but to the representation of the overall internal mixing processes.
by Mikhail A. Solovev.
Ph.D.
11
Martinazzo, Michele. "Cloud optical properties parameterizations for infrared high spectral resolution fast codes." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21747/.
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Lo scopo principale di questo lavoro di tesi è quello di produrre un set di parametrizzazioni analitiche per le proprietà ottiche delle nubi e degli aerosoli, utili per essere implementate in un codice veloce di trasferimento radiativo. Il codice veloce da noi preso in considerazione è sigma-IASI-as. Allo stato attuale, questo modello incorpora delle routines di Mie, le quali vengono sfruttate per il calcolo dello spessore ottico in presenza di nubi o aerosoli. Inoltre il codice sfrutta l'approssimazione di Chou allo scopo di tener conto dello scattering della radiazione infrarossa da parte delle particelle di nube o aerosol. La parametrizzazione prodotta potrà essere sfruttata allo scopo di creare un set di tabelle consultabili dal codice,
che potranno essere usate per sostituire le routine di Mie. Lo studio sugli effetti indotti dalla implementazione della approssimazione di Chou è stata investigata considerando diversi scenari atmosferici. Il modello sfruttato per calcolare le radianze è LBLDIS. Per ogni scenario sono quindi calcolate e confrontate le due soluzioni, implementando o non implementando l’approssimazione di Chou. Una parametrizzazione in funzione del raggio della distribuzione è trovata per: l’efficienza di estinzione, l’albedo si singolo scattering, il parametro di asimmetria, e il parametro di backscattering di Chou. L’impatto e le differenze nelle radianze introdotte dall'utilizzo dell’approssimazione di Chou e della parametrizzazione delle proprietà ottiche, è valutato per diversi scenari atmosferici.
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Jerg, Matthias. "Solar radiative transfer parameterizations for three-dimensional effects in cloudy atmospheres." Diss., lmu, 2006. http://nbn-resolving.de/urn:nbn:de:bvb:19-62898.
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Zidikheri, Meelis Juma, and m. zidikheri@bom gov au. "Dynamical Subgrid-scale Parameterizations for Quasigeostrophic Flows using Direct Numerical Simulations." The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20090108.112027.
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In this thesis, parameterizations of non-linear interactions in quasigeostrophic (QG) flows for severely truncated models (STM) and Large Eddy Simulations (LES) are studied.
Firstly, using Direct Numerical Simulations (DNS), atmospheric barotropic flows over topography
are examined, and it is established that such flows exhibit multiple equilibrium states for a wide range of parameters. A STM is then constructed, consisting of the large
scale zonal flow and a topographic mode. It is shown that, qualitatively, this system behaves similarly to the DNS as far as the interaction between the zonal flow and topography
is concerned, and, in particular, exhibits multiple equilibrium states. By fitting the analytical form of the topographic stationary wave amplitude, obtained from the STM,
to the results obtained from DNS, renormalized dissipation and rotation parameters are obtained. The usage of renormalized parameters in the STM results in better quantitative
agreement with the DNS.¶
In the second type of problem, subgrid-scale parameterizations in LES are investigated with both atmospheric and oceanic parameters. This is in the context of two-level QG flows on the sphere, mostly, but not exclusively, employing a spherical harmonic triangular truncation at wavenumber 63 (T63) or higher. The methodology that is used is spectral, and is motivated by the stochastic representation of statistical closure theory, with the damping and forcing covariance, representing backscatter, determined from the statistics
of DNS. The damping and forcing covariance are formulated as 2 × 2 matrices for each wavenumber. As well as the transient subgrid tendency, the mean subgrid tendency is needed in the LES when the energy injection region is unresolved; this is also calculated from the statistics of the DNS. For comparison, a deterministic parameterization scheme consisting of 2×2 damping parameters, which are calculated from the statistics of DNS,
has been constructed. The main difference between atmospheric and oceanic flows, in this thesis, is that the atmospheric LES completely resolves the deformation scale, the energy and enstrophy injection region, and the truncation scale is spectrally distant from it, being well in the enstrophy cascade inertial range. In oceanic flows, however, the truncation scale is in the vicinity of the injection scale, at least for the parameters chosen, and is therefore not in an inertial range. A lower resolution oceanic LES at T15 is also examined, in which case the injection region is not resolved at all.¶
For atmospheric flows, it is found that, at T63, the matrix parameters are practically diagonal so that stratified atmospheric flows at these resolutions may be treated as uncoupled
layers as far as subgrid-scale parameterizations are concerned. It is also found that the damping parameters are relatively independent of the (vertical) level, but the
backscatter parameters are proportional to the subgrid flux in a given level. The stochastic
and deterministic parameterization schemes give comparably good results relative to the DNS. For oceanic flows, it is found that the full matrix structure of the parameters must be used. Furthermore, it is found that there is a strong injection of barotropic energy
from the subgrid scales, due to the unresolved, or partially resolved, baroclinic instability injection scales. It is found that the deterministic parameterization is too numerically unstable to be of use in the LES, and instead the stochastic parameterization must be used to obtain good agreement with the DNS. The subgrid tendency of the ensemble mean flow is also needed in some problems, and is found to reduce the available potential energy of
the flow.
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PeÌrez, PeÌrez Edgar. "Heat transport by baroclinic eddies : evaluating eddy parameterizations for numerical models." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442945.
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Antritter, Felix [Verfasser]. "Tracking Controller Design for Nonlinear Dynamics using Differential Parameterizations / Felix Antritter." Aachen : Shaker, 2007. http://d-nb.info/1166511219/34.
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Komacek, Thaddeus D., and Dorian S. Abbot. "EFFECT OF SURFACE-MANTLE WATER EXCHANGE PARAMETERIZATIONS ON EXOPLANET OCEAN DEPTHS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622455.
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Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to random volatile delivery by planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a "waterworld." On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. Here we explore how the incorporation of different mechanisms for the degassing and regassing of water changes the volatile evolution of a planet. For all of the models considered, volatile cycling reaches an approximate steady state after similar to 2 Gyr. Using these steady. states, we find that if volatile cycling is either solely dependent on temperature or seafloor pressure, exoplanets require a high abundance (greater than or similar to 0.3% of total mass) of water to have fully inundated surfaces. However, if degassing is more dependent on seafloor pressure and regassing mainly dependent on mantle temperature, the degassing rate is relatively large at late times and a steady. state between degassing and regassing is reached with a substantial surface water fraction. If this hybrid model is physical, super-Earths with a total water fraction similar to that of the Earth can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.
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Whisenhant, Michelle K. "Turbulence parameterizations for convective boundary layers in high-resolution mesoscale models." Diss., Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FWhisenhant%5FPhD.pdf.
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Zidikheri, Meelis Juma. "Dynamical subgrid-scale parameterizations for quasigeostrophic flows using direct numerical simulations /." View thesis entry in Australian Digital Theses, 2007. http://thesis.anu.edu.au/public/adt-ANU20090108.112027/index.html.
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Atariah, Dror [Verfasser]. "Parameterizations in the Configuration Space and Approximations of Related Surfaces / Dror Atariah." Berlin : Freie Universität Berlin, 2014. http://d-nb.info/1051812410/34.
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Kwok, Wilfred. "Automating Radiotherapy: Parameterizations of Sensor Time Delay Compensators and the Separation Principle." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/954.
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Motivated by recent research to automate radiotherapy, this thesis looks into feedback control problems where the feedback sensor imposes considerable time delay. The use of an asymptotic estimator is considered as a method to compensate for the time delay. Properties and parameterizations of asymptotic estimators are analyzed. It is shown that if such a delay compensation scheme is adopted, a separation principle holds, which allows for independent design of the feedback controller and the time delay compensator. The radiotherapy problem is used as a case study to show how asymptotic estimators may be designed, exploiting the separation principle. Lastly, the thesis considers multivariable versions of asymptotic estimators.
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Schemann, Vera, Bjorn Stevens, Verena Grützun, and Johannes Quaas. "Scale dependency of total water variance and its implication for cloud parameterizations." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177479.
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The scale dependency of variance of total water mixing ratio is explored by analyzing data from a general circulation model (GCM), a numerical weather prediction model (NWP), and large-eddy simulations (LESs). For clarification, direct numerical simulation (DNS) data are additionally included, but the focus is placed on defining a general scaling behavior for scales ranging from global down to cloud resolving. For this, appropriate power-law exponents are determined by calculating and approximating the power density spectrum.
The large-scale models (GCM and NWP) show a consistent scaling with a power-law exponent of approximately 22. For the high-resolution LESs, the slope of the power density spectrum shows evidence of being somewhat steeper, although the estimates are more uncertain. Also the transition between resolved and parameterized scales in a current GCM is investigated. Neither a spectral gap nor a strong scale break is found, but a weak scale break at high wavenumbers cannot be excluded. The evaluation of the parameterized total water variance of a state-of-the-art statistical scheme shows that the scale dependency is underestimated by this parameterization. This study and the discovered general scaling behavior emphasize the need for
a development of scale-dependent parameterizations.
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Larson, Brady M. "Exploring the Common Design Space of Dissimilar Assembly Parameterizations for Interdisciplinary Design." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2368.pdf.
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Pieroth, Martin [Verfasser], Ulrich [Gutachter] Achatz, and Andrey [Gutachter] Gritsun. "On the climate dependence of subgrid-scale parameterizations / Martin Pieroth ; Gutachter: Ulrich Achatz, Andrey Gritsun." Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2019. http://d-nb.info/1197127992/34.
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Pollmann, Friederike [Verfasser], and Carsten [Akademischer Betreuer] Eden. "Oceanic internal gravity waves and turbulent mixing : observations and parameterizations / Friederike Pollmann ; Betreuer: Carsten Eden." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1151322423/34.
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Nam, Christine C. W., and Johannes Quaas. "Geographically versus dynamically defined boundary layer cloud regimes and their use to evaluate general circulation model cloud parameterizations: Geographically versus dynamically defined boundary layer cloudregimes and their use to evaluate general circulation model cloud parameterizations." American Geophysical Union (AGU), 2013. https://ul.qucosa.de/id/qucosa%3A13460.
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Regimes of tropical low-level clouds are commonly identified according to large-scale subsidence and lower tropospheric
stability (LTS). This definition alone is insufficient for the distinction between regimes and limits the comparison of low-level clouds from CloudSat radar observations and the ECHAM5 GCM run with the COSP radar simulator. Comparisons of CloudSat radar cloud altitude-reflectivity histograms for stratocumulus and shallow cumulus regimes,
as defined above, show nearly identical reflectivity profiles,
because the distinction between the two regimes is dependent
upon atmospheric stability below 700 hPa and observations above 1.5 km. Regional subsets, near California and Hawaii, for example, have large differences in reflectivity profiles than the dynamically defined domain; indicating different reflectivity profiles exist under a given
large-scale environment. Regional subsets are better for the
evaluation of low-level clouds in CloudSat and ECHAM5 as there is less contamination between 2.5 km and 7.5 km from precipitating hydrometeors which obscured cloud reflectivities.
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Iotti, Marcello. "Urban boundary layer modeling with WRF: assessment of different urban parameterizations over the city of Bologna." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Urbanization affects all the components of the Earth system, clearly including the atmosphere. It is therefore important the understanding of cities-related processes and their representation in modeling terms. Many different spatial scales pertain urban modeling: processes linked to a single building or to an
urban district are well represented with microscale methods, but the city as a whole has influences traceable at the mesoscale, a domain traditionally linked to numerical weather prediction (NWP) models. It is evident the discontinuity of these approaches and the advantage that one would have in connecting them, so that buildings-atmosphere interactions are properly considered in mesoscale atmospheric simulations.
Within the Weather Research and Forecasting Model (WRF) community various urban parameterizations, with different degree of sophistication, have been developed. In recent years they have found notable applications, but literature focuses mainly on large cities. The purpose of this work is a comparative evaluation of these parameterizations, applied to a medium-sized city such as Bologna.
Their accuracy was evaluated using temperature, wind speed and wind direction data recorded by a set of measurement stations. Finally the spatial structure of 2 m-air temperature and 10 m-wind fields was examined, highlighting the different behavior of urban parameterizations on the city area of Bologna.
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Martin, Michiko J. "An investigation of momentum exchange parameterizations and atmospheric forcing for the Coastal Mixing and Optics Program." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/55324.
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Thesis (S.M.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998.Includes bibliographic references (p. 77-83).
This thesis presents an investigation of the influence of surface waves on momentum exchange. A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved flux estimates, modifications to the traditional flux parameterizations are explored. Modification to the bulk aerodynamic method involves incorporating sea state dependence into the roughness length calculation. For the inertial dissipation method, a new parameterization for the dimensionless dissipation rate is proposed. The modifications lead to improved momentum flux estimates for both methods.
by Michiko J. Martin.
S.M.
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Kawai, Hideaki. "Study on Marine Boundary Layer Clouds and Their Environment for Cloud Parameterizations in Global Climate Models." Kyoto University, 2017. http://hdl.handle.net/2433/226008.
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Brück, Heiner Matthias [Verfasser], Johannes [Akademischer Betreuer] Quaas, Johannes [Gutachter] Quaas, and A. Pier [Gutachter] Siebesma. "Evaluation of statistical cloud parameterizations / Heiner Matthias Brück ; Gutachter: Johannes Quaas, A. Pier Siebesma ; Betreuer: Johannes Quaas." Leipzig : Universitätsbibliothek Leipzig, 2016. http://d-nb.info/1240629699/34.
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Menon, Surabo, Jean-Louis Brenguier, Olivier Boucher, Paul Davison, Genio Anthony D. Del, Johann Feichter, Steven Ghan, et al. "Evaluating aerosol/cloud/radiation process parameterizations with single-column models and Second Aerosol Characterization Experiment (ACE-2) cloudy column observations: Evaluating aerosol/cloud/radiation process parameterizations withsingle-column models and Second Aerosol Characterization Experiment (ACE-2) cloudy column observations." Wiley, 2003. https://ul.qucosa.de/id/qucosa%3A13455.
Full textAbstract:
The Second Aerosol Characterization Experiment (ACE-2) data set along with ECMWF reanalysis meteorological fields provided the basis for the single column model (SCM) simulations, performed as part of the PACE (Parameterization of the Aerosol Indirect Climatic Effect) project. Six different SCMs were used to simulate ACE-2 case
studies of clean and polluted cloudy boundary layers, with the objective being to identify limitations of the aerosol/cloud/radiation interaction schemes within the range of uncertainty in in situ, reanalysis and satellite retrieved data. The exercise proceeds in three
steps. First, SCMs are configured with the same fine vertical resolution as the ACE-2 in situ data base to evaluate the numerical schemes for prediction of aerosol activation, radiative transfer and precipitation formation. Second, the same test is performed at the coarser vertical resolution of GCMs to evaluate its impact on the performance of the
parameterizations. Finally, SCMs are run for a 24–48 hr period to examine predictions of boundary layer clouds when initialized with large-scale meteorological fields. Several schemes were tested for the prediction of cloud droplet number concentration (N). Physically based activation schemes using vertical velocity show noticeable discrepancies compared to empirical schemes due to biases in the diagnosed cloud base vertical velocity. Prognostic schemes exhibit a larger variability than the diagnostic ones, due to a coupling between aerosol activation and drizzle scavenging in the calculation of N. When
SCMs are initialized at a fine vertical resolution with locally observed vertical profiles of liquid water, predicted optical properties are comparable to observations. Predictions however degrade at coarser vertical resolution and are more sensitive to the mean liquid
water path than to its spatial heterogeneity. Predicted precipitation fluxes are severely underestimated and improve when accounting for sub-grid liquid water variability. Results from the 24–48 hr runs suggest that most models have problems in simulating boundary
layer cloud morphology, since the large-scale initialization fields do not accurately reproduce observed meteorological conditions. As a result, models significantly overestimate optical properties. Improved cloud morphologies were obtained for models with subgrid inversions and subgrid cloud thickness schemes. This may be a result of
representing subgrid scale effects though we do not rule out the possibility that better large-forcing data may also improve cloud morphology predictions.
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Nam, Christine C. W., and Johannes Quaas. "Geographically versus dynamically defined boundary layer cloud regimes and their use to evaluate general circulation model cloud parameterizations." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177436.
Full textAbstract:
Regimes of tropical low-level clouds are commonly identified according to large-scale subsidence and lower tropospheric
stability (LTS). This definition alone is insufficient for the distinction between regimes and limits the comparison of low-level clouds from CloudSat radar observations and the ECHAM5 GCM run with the COSP radar simulator. Comparisons of CloudSat radar cloud altitude-reflectivity histograms for stratocumulus and shallow cumulus regimes,
as defined above, show nearly identical reflectivity profiles,
because the distinction between the two regimes is dependent
upon atmospheric stability below 700 hPa and observations above 1.5 km. Regional subsets, near California and Hawaii, for example, have large differences in reflectivity profiles than the dynamically defined domain; indicating different reflectivity profiles exist under a given
large-scale environment. Regional subsets are better for the
evaluation of low-level clouds in CloudSat and ECHAM5 as there is less contamination between 2.5 km and 7.5 km from precipitating hydrometeors which obscured cloud reflectivities.
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Nam, Christine C. W., Johannes Quaas, Roel Neggers, Drian Colombe Siegenthaler-Le, and Francesco Isotta. "Evaluation of boundary layer cloud parameterizations in the ECHAM5 general circulation model using CALIPSO and CloudSat satellite data." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177343.
Full textAbstract:
Three different boundary layer cloud models are incorporated into the ECHAM5 general circulation model (GCM) and compared to CloudSat and CALIPSO satellite observations. The first boundary layer model builds upon the standard Tiedtke (1989) parameterization for shallow convection with an adapted convective trigger; the second is a bulk parameterization of the effects of transient shallow cumulus clouds;
and lastly the Dual Mass Flux (DMF) scheme adjusted to better represent shallow convection. The three schemes improved (Sub)Tropical oceanic low-level cloud cover, however, the fraction of low-level cloud cover remains underestimated compared to CALIPSO observations. The representation of precipitation was improved by all schemes as they reduced the frequency of light intensity events <0.01 mm d-1, which were found to dominate the radar reflectivity histograms as well as be the greatest source of differences
between ECHAM5 and CloudSat radar reflectivity histograms. For both lidar and radar diagnostics, the differences amongst the schemes are smaller than the differences compared to observations. While the DMF
approach remains experimental, as its top-of-atmosphere radiative balance has not been retuned, it shows the most promise in producing nonprecipitating boundary layer clouds. With its internally consistent
boundary layer scheme that uses the same bimodal joint distribution with a diffusive and an updraft component for clouds and turbulent transport, the ECHAM5_DMF produces the most realistic boundary layer depth as indicated by the cloud field. In addition, it reduced the frequency of large-scale precipitation intensities of <0.01 mm d-1 the greatest.
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Börker, Janine [Verfasser], and Jens [Akademischer Betreuer] Hartmann. "Quantifications of global chemical weathering fluxes applying new lithological maps and new parameterizations / Janine Börker ; Betreuer: Jens Hartmann." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1192913116/34.
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Nam, Christine C. W., Johannes Quaas, Roel Neggers, Drian Colombe Siegenthaler-Le, and Francesco Isotta. "Evaluation of boundary layer cloud parameterizations in the ECHAM5 general circulation model using CALIPSO and CloudSat satellite data." American Geophysical Union (AGU), 2014. https://ul.qucosa.de/id/qucosa%3A13458.
Full textAbstract:
Three different boundary layer cloud models are incorporated into the ECHAM5 general circulation model (GCM) and compared to CloudSat and CALIPSO satellite observations. The first boundary layer model builds upon the standard Tiedtke (1989) parameterization for shallow convection with an adapted convective trigger; the second is a bulk parameterization of the effects of transient shallow cumulus clouds;
and lastly the Dual Mass Flux (DMF) scheme adjusted to better represent shallow convection. The three schemes improved (Sub)Tropical oceanic low-level cloud cover, however, the fraction of low-level cloud cover remains underestimated compared to CALIPSO observations. The representation of precipitation was improved by all schemes as they reduced the frequency of light intensity events <0.01 mm d-1, which were found to dominate the radar reflectivity histograms as well as be the greatest source of differences
between ECHAM5 and CloudSat radar reflectivity histograms. For both lidar and radar diagnostics, the differences amongst the schemes are smaller than the differences compared to observations. While the DMF
approach remains experimental, as its top-of-atmosphere radiative balance has not been retuned, it shows the most promise in producing nonprecipitating boundary layer clouds. With its internally consistent
boundary layer scheme that uses the same bimodal joint distribution with a diffusive and an updraft component for clouds and turbulent transport, the ECHAM5_DMF produces the most realistic boundary layer depth as indicated by the cloud field. In addition, it reduced the frequency of large-scale precipitation intensities of <0.01 mm d-1 the greatest.
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Menon, Surabo, Jean-Louis Brenguier, Olivier Boucher, Paul Davison, Genio Anthony D. Del, Johann Feichter, Steven Ghan, et al. "Evaluating aerosol/cloud/radiation process parameterizations with single-column models and Second Aerosol Characterization Experiment (ACE-2) cloudy column observations." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177303.
Full textAbstract:
The Second Aerosol Characterization Experiment (ACE-2) data set along with ECMWF reanalysis meteorological fields provided the basis for the single column model (SCM) simulations, performed as part of the PACE (Parameterization of the Aerosol Indirect Climatic Effect) project. Six different SCMs were used to simulate ACE-2 case
studies of clean and polluted cloudy boundary layers, with the objective being to identify limitations of the aerosol/cloud/radiation interaction schemes within the range of uncertainty in in situ, reanalysis and satellite retrieved data. The exercise proceeds in three
steps. First, SCMs are configured with the same fine vertical resolution as the ACE-2 in situ data base to evaluate the numerical schemes for prediction of aerosol activation, radiative transfer and precipitation formation. Second, the same test is performed at the coarser vertical resolution of GCMs to evaluate its impact on the performance of the
parameterizations. Finally, SCMs are run for a 24–48 hr period to examine predictions of boundary layer clouds when initialized with large-scale meteorological fields. Several schemes were tested for the prediction of cloud droplet number concentration (N). Physically based activation schemes using vertical velocity show noticeable discrepancies compared to empirical schemes due to biases in the diagnosed cloud base vertical velocity. Prognostic schemes exhibit a larger variability than the diagnostic ones, due to a coupling between aerosol activation and drizzle scavenging in the calculation of N. When
SCMs are initialized at a fine vertical resolution with locally observed vertical profiles of liquid water, predicted optical properties are comparable to observations. Predictions however degrade at coarser vertical resolution and are more sensitive to the mean liquid
water path than to its spatial heterogeneity. Predicted precipitation fluxes are severely underestimated and improve when accounting for sub-grid liquid water variability. Results from the 24–48 hr runs suggest that most models have problems in simulating boundary
layer cloud morphology, since the large-scale initialization fields do not accurately reproduce observed meteorological conditions. As a result, models significantly overestimate optical properties. Improved cloud morphologies were obtained for models with subgrid inversions and subgrid cloud thickness schemes. This may be a result of
representing subgrid scale effects though we do not rule out the possibility that better large-forcing data may also improve cloud morphology predictions.
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Friedrich, Stefan Roland [Verfasser], Martin [Akademischer Betreuer] Buss, Jürgen [Gutachter] Adamy, and Martin [Gutachter] Buss. "Learning and Feedback in Robotics with Stabilizing Controller Parameterizations / Stefan Roland Friedrich ; Gutachter: Jürgen Adamy, Martin Buss ; Betreuer: Martin Buss." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1237413222/34.
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Juricke, Stephan [Verfasser], Thomas [Akademischer Betreuer] Jung, and Peter [Akademischer Betreuer] Lemke. "Representing uncertainty in global climate models using stochastic sea ice parameterizations / Stephan Juricke. Gutachter: Thomas Jung ; Peter Lemke. Betreuer: Thomas Jung." Bremen : Staats- und Universitätsbibliothek Bremen, 2014. http://d-nb.info/1072225980/34.
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Schemann, Vera, Bjorn Stevens, Verena Grützun, and Johannes Quaas. "Scale dependency of total water variance and its implication for cloud parameterizations: Scale dependency of total water variance and its implication for cloudparameterizations." American Meteorological Society, 2013. https://ul.qucosa.de/id/qucosa%3A13462.
Full textAbstract:
The scale dependency of variance of total water mixing ratio is explored by analyzing data from a general circulation model (GCM), a numerical weather prediction model (NWP), and large-eddy simulations (LESs). For clarification, direct numerical simulation (DNS) data are additionally included, but the focus is placed on defining a general scaling behavior for scales ranging from global down to cloud resolving. For this, appropriate power-law exponents are determined by calculating and approximating the power density spectrum.
The large-scale models (GCM and NWP) show a consistent scaling with a power-law exponent of approximately 22. For the high-resolution LESs, the slope of the power density spectrum shows evidence of being somewhat steeper, although the estimates are more uncertain. Also the transition between resolved and parameterized scales in a current GCM is investigated. Neither a spectral gap nor a strong scale break is found, but a weak scale break at high wavenumbers cannot be excluded. The evaluation of the parameterized total water variance of a state-of-the-art statistical scheme shows that the scale dependency is underestimated by this parameterization. This study and the discovered general scaling behavior emphasize the need for
a development of scale-dependent parameterizations.
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Quaas, Johannes. "Evaluating the “critical relative humidity” as a measure of subgrid-scale variability of humidity in general circulation model cloud cover parameterizations using satellite data." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177265.
Full textAbstract:
A simple way to diagnose fractional cloud cover in general circulation models is to relate it to the simulated relative humidity, and allowing for fractional cloud cover above a “critical relative humidity” of less than 100%. In the formulation chosen here, this is equivalent to assuming a uniform “top-hat” distribution of subgrid-scale total water content with a variance related to saturation. Critical relative humidity has frequently been treated as a “tunable” constant, yet it is an observable. Here, this parameter, and its spatial distribution, is examined from Atmospheric Infrared Sounder (AIRS) satellite retrievals, and from a combination of relative humidity from the ECMWF Re-Analyses (ERA-Interim) and cloud fraction obtained from CALIPSO lidar satellite data. These observational data are used to evaluate results from different simulations with the ECHAM general circulation model (GCM). In sensitivity studies, a cloud feedback parameter is analyzed from simulations applying the original parameter choice, and applying parameter choices guided by the satellite data. Model sensitivity studies applying parameters adjusted to match the observations show larger positive cloud-climate feedbacks, increasing by up to 30% compared to the standard simulation.
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Pelletier, Charles. "Etude mathématique du problème de couplage océan-atmosphère incluant les échelles turbulentes." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAM014/document.
Full textAbstract:
Cette thèse s'intéresse à la modélisation numérique du couplage entre l'océan et l'atmosphère. Bien que présentant un certain nombre de caractéristiques communes, ces deux milieux physiques sont suffisamment dissemblables pour être numériquement simulés par des modèles distincts, incluant chacun des spécificités propres. Par conséquent, leurs interactions sont prises en compte via des algorithmes de couplage multiphysique.La mise en place de tels algorithmes nécessite une bonne compréhension des modélisations des milieux océanique et atmosphérique, en particulier au voisinage de leur interface commune. C'est pourquoi une partie conséquente de la présente thèse dissèque, analyse et complète les paramétrisations turbulentes, qui sont des mécanismes numériques définis au niveau continu, traitant la couche limite turbulente au voisinage de la surface océanique. Les travaux entrepris ont permis d'identifier deux sources d'erreurs, théoriquement et numériquement significatives, dans la modélisation numérique standard de l'interface océan-atmosphère.La première source d'erreur se manifeste dans les formulations continues des paramétrisations turbulentes: celles-ci sont actuellement utilisées de manière incomplète, ce qui se traduit par le caractère mathématiquement irrégulier des solutions qu'elles génèrent. En revenant aux fondements de la théorie dont les paramétrisations découlent, la présente thèse étend leur domaine d'application, permettant de générer des profils de solution réguliers, dans un cadre théorique uniforme et bi-domaine. Les effets d'une telle extension sont numériquement évalués sur des cas tests physiquement réalistes: celle-ci peut mener à des biais considérables (de l'ordre de 20%) dans les flux échangés entre océan et atmosphère. D'un point de vue théorique, cette extension permet de définir des critères simples sous lesquels le couplage océan-atmosphère peut être considéré comme cohérent par rapport aux deux domaines physiques, et surtout aux paramétrisations turbulentes.La seconde source d'erreur est de nature algorithmique: elle concerne la discrétisation temporelle des mécanismes de couplage. Les méthodes actuelles, dites ad hoc, ne garantissent pas une complète cohérence des flux d'un modèle à l'autre. Les algorithmes de Schwarz globaux en temps, issus de thématiques liées à la décomposition de domaine, constituent une piste intéressante pour traiter ces aspects. La mise en place de tels algorithmes sur des modèles physiquement réalistes représente un défi considérable. Leur impact numérique sur des cas tests simplifiés est évalué. L'étude préalable des paramétrisations turbulentes permet de donner des pistes quant au développement d'algorithmes de couplage, concernant à la fois la cohérence du couplage précédemment introduite, et l'incorporation graduelle d'effets physiques plus complexesThis thesis focuses on the numerical modelling of the air-sea coupling. Although they share some common features, these two physical environments are sufficiently dissimilar for their numerical treatment to be carried out by distinct models, each including their own specificities. The interactions between these two components are thus taken into account through coupling algorithms.Implementing such algorithms requires proper understanding of the oceanic and atmospheric modelling, most importantly in the vicinity of their common interface. Therefore a substantial part of this thesis dissects, analyzes and completes turbulent parameterization schemes, which are the numerical mechanisms, defined at a continuous level, through which the turbulent surface layer at the vicinity of the sea surface is treated. Two theoretically and numerically meaningful sources of errors in the standard numerical modelling of the air-sea interface have been isolated.The first source of error lies in the continuous formulation of the turbulent parameterizations, which are currently used in an incomplete manner, leading to mathematically irregular solution profiles. By carefully studying their theoretical bases, this thesis extends the parameterizations, allowing them to generate regular profiles within a standardized, bi-domain framework. Numerical investigations on physically relevant test cases show that including such an extension can result in considerable bias (of the order of 20%) in air-sea fluxes evaluations. From a theoretical perspective, carrying this extension leads to establishing simple criteria under which the air-sea coupling can be considered as coherent with respect to the two physical environments, and more importantly, to the turbulent parameterizations.The second source of error is algorithmic in essence: it is linked to the temporal discretization of the coupling mechanisms. Existing ad hoc methods do not guarantee perfect coherence of the air-sea fluxes from one model to the other. Global in time Schwarz algorithms, which have first been developed as domain decomposition methods, are good candidates for correcting these flaws, although their implementation to the air-sea context is a considerable challenge, given the complexity of this problem. Investigations on the numerical impact of such algorithms are carried out on simplified test cases. Thanks to the undertaken work on turbulent parameterizations, perspectives on the development of coupling algorithms are given, regarding both their coherence as per the aforementioned conditions, and the gradually increasing complexity of physical effects that are accounted for
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Schomburg, Annika [Verfasser]. "Improving the simulation of small-scale variability in radiation and land-surface parameterizations in a mesoscale numerical weather prediction model / Annika Schomburg. Mathematisch-Naturwissenschaftliche Fakultät." Bonn : Universitäts- und Landesbibliothek Bonn, 2011. http://d-nb.info/1016198094/34.
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Sič, Bojan. "Amélioration de la représentation des aérosols dans un modèle de chimie-transport : modélisation et assimilation de données." Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2667/.
Full textAbstract:
L'objectif général de cette thèse est d'améliorer la représentation des aérosols dans le modèle MOCAGE. Pour se faire, nous avons modifié directement la représentation des aérosols en réexaminant et améliorant les différents processus déjà présents via la prise en compte de schémas et de paramétrisations plus détaillés et implémenté l'assimilation de données des aérosols dans le modèle. Les processus ayant subi les améliorations les plus importantes sont les émissions des aérosols du type sel marin, poussière désertique et cendre volcanique, le dépôt humide et la sédimentation. Nous avons évalué les impacts de ces changements et comparé les champs modélisés avec des observations. Les modifications implémentées ont permis d'améliorer significativement l'accord entre modèle et observations. Comme approche complémentaire pour répondre à l'objectif de cette thèse, nous avons également implémenté dans le CTM MOCAGE l'assimilation de données des aérosols. Le système d'assimilation de données des aérosols est implémenté et il est capable d'assimiler l'épaisseur optique des aérosols (AOD) et les mesures lidar. L'assimilation des observations d'AOD est un outil efficace pour améliorer les performances du modèle en terme d'AOD et de concentration. L'assimilation de mesures lidar sur le signal ainsi que les coefficients de rétrodiffusion et d'extinction, ont montré un impact efficace sur les profils verticauxThe main goal of this thesis is to improve the aerosol representation in the CTM MOCAGE. The work may be divided into: the direct improvement of aerosol physical parameterizations, and the development of a data assimilation system able to assimilate aerosol optical depth (AOD) and lidar profiles. On the modelling side, the processes that underwent the important improvements were sea salt, desert dust and volcanic aerosol emissions, wet deposition and sedimentation. The ambition is related to improve the model biases compared to observations, and to implement more physically detailed schemes in the model. We evaluated the impacts of these changes and compared the modelled fields to observations. The implemented updates significantly enhanced the model agreement with the observations and the inter-model comparison data. The results also confirmed that large uncertainties in models can come from the use of different parameterizations. The aerosol data assimilation is implemented to further reduce the model uncertainties. The set of observation operators and their tangent linear and adjoint operators for AOD and lidar profile observations are developed to link the model and the observation space. Aerosol assimilation proved to be very efficient to reduce the differences between the model and the observations. The assimilated AOD observations were able to significantly improve the model performance in terms of AOD and concentrations. Assimilation of lidar measurements: the backscatter signal, the extinction and backscatter coefficients, also showed an efficient influence on the vertical profiles
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Havel, Jiří. "Zobrazení bodů na přímky a jiné parametrizace přímek nejen pro Houghovu transformaci." Doctoral thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2012. http://www.nusl.cz/ntk/nusl-261256.
Full textAbstract:
Tato práce se zabývá Houghovou transformací (HT). HT je nejčastěji používána pro detekci přímek nebo křivek, ale byla zobecněna i pro detekci libovolných tvarů. Hlavní téma této práce jsou parametrizace přímek, speciálně PTLM - zobrazení bodů na přímky. Tyto parametrizace mají tu vlastnost, že bodům v obrázku odpovídají přímky v parametrickém prostoru. Tato práce poskytuje důkazy některých vlastností PTLM. Za zmínku stojí existence páru PTLM vhodného pro detekci a efekt konvoluce v obrázku na obsah parametrického prostoru. V práci jsou prezentovány dvě implementace HT. Obě využívají k akceleraci grafický hardware. Jedna využívá GPGPU API CUDA a druhá zobrazovací API OpenGL. Jako aplikace detekce přímek je uvedena část detekce šachovnicových markerů použitelných pro rozšířenou realitu.
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Agar, Christopher D. "Dynamic parameterization of IPSEC." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA401378.
Full textAbstract:
Thesis (M.S. in Computer Science) Naval Postgraduate School, December 2001.Thesis Advisor (s): Irvine, Cynthia E. "December 2001." Includes bibliographical references (p. 311-313). Also available online.
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Oliveira, Erikson Magno Gomes de. "PARAMETRIZAÇÕES CONVECTIVAS NO MODELO WRF E SUA RELAÇÃO COM A PRECIPITAÇÃO DURANTE CICLOGÊNESES NO SUDESTE DA AMÉRICA DO SUL." Universidade Federal de Santa Maria, 2014. http://repositorio.ufsm.br/handle/1/10274.
Full textAbstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe Weather Research and Forecasting (WRF) model is used in the simulation of 26 cases of cyclogenesis in southeastern South America, on the cyclogenetic region near the La Plata River mouth. The simulations comprised 26 cases of cyclogenesis in which rainfall was observed over the region, especially on the state of Rio Grande do Sul. Given the important role of convective parameterization in the production of precipitation into a numerical weather prediction model, this study aims to evaluate the precipitation produced in the simulations of cases of cyclogenesis using three different convection parameterization schemes: Betts-Miller-Janjic (BMJ), Grell-Dévényi (GD) e Kain-Fritsch (KF), keeping the other physical options, to isolate the impact of using different parameterizations for convection. For the evaluation of simulated rainfall, verification skill scores were used in order to make an objective assessment of simulated rain field from the observed data set (TRMM and MERGE), also allowing a comparison between simulations with different schemes. The results of the skill scores showed that, in general, the WRF best represents the rain of lower thresholds, with indexes based positioning (ETS, POD and RAF) with values closer to the ideal. The BIAS score indicated that the area of light rain is usually overestimated, while moderate and heavy rain showed greater differences between simulations with KF and BMJ schemes and verified with the two sets of observed data. Differences in the verification scores showed that the way how the convective flows are treated by schemes exert great influence on the precipitation produced, with the largest differences being observed between the BMJ and KF schemes. The simulations with the BMJ, wich is a convective adjustment based scheme, produced clearly smaller areal coverage and rainfall volume, especially if compared to the simulations with the KF scheme. Along with lower production of precipitation, the simulations with the BMJ showed, on average, smaller partition of convective rainfall compared to others. The sea level pressure field showed no significant differences, with the WRF simulating consistently with the GFS-FNL analysis, the position and central pressure of the cyclones.
O modelo Weather Research and Forecasting (WRF) é utilizado na simulação de 26 casos de ciclogênese no sudeste da América do Sul, na região ciclogenética próxima da foz do Rio da Prata. As simulações compreenderam 26 casos de ciclogênese nos quais foi observada precipitação sobre a região, especialmente sobre o estado do Rio Grande do Sul. Tendo em vista o importante papel das parametrizações convectivas na produção de precipitação em um modelo numérico de previsão de tempo, este estudo visa avaliar a precipitação produzida nas simulações dos casos de ciclogênese utilizando três diferentes esquemas de parametrização da convecção: Betts-Miller-Janjic (BMJ), Grell-Dévényi (GD) e Kain-Fritsch (KF), mantendo as outras opções físicas constantes, de modo a isolar o impacto do uso das diferentes parametrizações para a convecção. Para a avaliação da precipitação simulada foram utilizados índices estatísticos, com o objetivo de avaliar objetivamente o campo de chuva simulado a partir do conjunto de dados observados (TRMM e MERGE), possibilitando também uma comparação entre as simulações com os diferentes esquemas. Os resultados dos índices mostraram que em geral, o WRF representa melhor a chuva dos limiares mais fracos, com índices baseados no posicionamento (ETS, POD e RAF) tendo valores mais próximos dos ideais. O índice BIAS indicou que a área de chuva fraca é, em geral, superestimada enquanto que a de chuva moderada a forte apresentou diferenças maiores entre as simulações com os esquemas KF e BMJ e na verificação com os dois conjuntos de dados observados. As diferenças nos índices mostraram que a forma como os fluxos convectivos são tratados pelos esquemas exerce grande influência na precipitação produzida, com as maiores diferenças sendo observadas entre os esquemas KF e BMJ. As simulações com o esquema BMJ, que é baseado no ajuste convectivo dos perfis, claramente produziram menor área e volume de chuva, principalmente se comparadas às simulações com o KF. Juntamente com menor produção de precipitação, as simulações com o BMJ apresentaram, em média, menor partição de precipitação convectiva se comparada às outras. O campo de pressão ao nível do mar não apresentou diferenças muito significativas, com o WRF simulando de forma consistente com as análises FNL-GFS, o posicionamento e pressão central do ciclone.
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Brunton, Alan P. "Multi-scale Methods for Omnidirectional Stereo with Application to Real-time Virtual Walkthroughs." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23552.
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This thesis addresses a number of problems in computer vision, image processing, and geometry processing, and presents novel solutions to these problems. The overarching theme of the techniques presented here is a multi-scale approach, leveraging mathematical tools to represent images and surfaces at different scales, and methods that can be adapted from one type of domain (eg., the plane) to another (eg., the sphere). The main problem addressed in this thesis is known as stereo reconstruction: reconstructing the geometry of a scene or object from two or more images of that scene. We develop novel algorithms to do this, which work for both planar and spherical images. By developing a novel way to formulate the notion of disparity for spherical images, we are able effectively adapt our algorithms from planar to spherical images. Our stereo reconstruction algorithm is based on a novel application of distance transforms to multi-scale matching. We use matching information aggregated over multiple scales, and enforce consistency between these scales using distance transforms. We then show how multiple spherical disparity maps can be efficiently and robustly fused using visibility and other geometric constraints. We then show how the reconstructed point clouds can be used to synthesize a realistic sequence of novel views, images from points of view not captured in the input images, in real-time. Along the way to this result, we address some related problems. For example, multi-scale features can be detected in spherical images by convolving those images with a filterbank, generating an overcomplete spherical wavelet representation of the image from which the multiscale features can be extracted. Convolution of spherical images is much more efficient in the spherical harmonic domain than in the spatial domain. Thus, we develop a GPU implementation for fast spherical harmonic transforms and frequency domain convolutions of spherical images. This tool can also be used to detect multi-scale features on geometric surfaces. When we have a point cloud of a surface of a particular class of object, whether generated by stereo reconstruction or by some other modality, we can use statistics and machine learning to more robustly estimate the surface. If we have at our disposal a database of surfaces of a particular type of object, such as the human face, we can compute statistics over this database to constrain the possible shape a new surface of this type can take. We show how a statistical spherical wavelet shape prior can be used to efficiently and robustly reconstruct a face shape from noisy point cloud data, including stereo data.
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Touzé-Peiffer, Ludovic. "Paramétrisation de la convection atmosphérique dans les modèles numériques de climat - Pratiques et enjeux épistémologiques." Electronic Thesis or Diss., Sorbonne université, 2021. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2021SORUS539.pdf.
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Historiquement, les modèles de circulation générale ont joué un rôle crucial pour avertir les décideurs et le grand public des changements climatiques à venir. Pourtant, depuis quelques années, des débats agitent la communauté scientifique sur le paradigme dominant sur lequel ont été développés de tels modèles: en particulier, les paramétrisations, censées représentées l'ensemble des processus pertinents pour le climat qui ne sont pas résolus à l'échelle de la grille des modèles, sont parfois remises en cause. L'objectif de notre travail de thèse est de mener une analyse épistémologique des paramétrisations, en nous centrant tout particulièrement sur les paramétrisations utilisées pour modéliser la convection atmosphérique. Ces dernières reposent parfois sur la distinction entre un environnement et certaines structures atmosphériques cohérentes que nous appellerons “objets”. Nous nous intéressons tout d'abord à l'utilisation de tels objets en sciences de l'atmosphère et à leur rôle dans notre compréhension de la convection. Nous étudions ensuite les paramétrisations en elles-mêmes, et expliquons dans quel contexte elles sont apparues, quelles furent leurs motivations historiques, et comment il est possible de justifier et d'interpréter aujourd'hui leur formalisme. Nous nous interrogeons également sur le statut et le rôle de l'ajustement des paramètres libres contenus dans les paramétrisations. Nous étendons enfin notre réflexion à la comparaison de plusieurs modèles de circulation générale dans le cadre du projet d'intercomparaison de modèles couplés CMIP. Le rôle historique et les effets structurels que CMIP a eu sur les recherches en sciences du climat sont analysésHistorically, general circulation models have played a crucial role in warning policy makers and the general public of future climate change. However, in recent years, there has been a growing debate in the scientific community about the dominant paradigm on which these models have been developed: in particular, parameterizations, which are supposed to represent climate-relevant processes that are not resolved at the scale of the model grid, are sometimes questioned. The objective of our thesis is to conduct an epistemological analysis of parameterizations, focusing on the parameterizations used to represent atmospheric convection. The latter are sometimes based on the distinction between an environment and certain coherent atmospheric structures that we will call ``objects". We first look at the use of such objects in atmospheric science and at their role in our understanding of convection. We then focus on parametrizations themselves, and explain in which context convective parameterizations emerged, what were their historical motivations and how their formalism can be interpreted and justified today. We also question the status and the role of the tuning of free parameters contained in parameterizations. Finally, we expand our reflection to the comparison of several general circulation models in the Coupled Model Intercomparison Project (CMIP). The historical role and structural effects CMIP has had on climate research are analyzed
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Valle, G. Raul del. "Model parameterization in refraction seismology." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66057.
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Litke, Nathan Jacob Schröder Peter. "Variational methods in surface parameterization /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05312005-224704.
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Larsson, Oscar. "Empirical parameterization of organic electrochemical transistors." Thesis, Linköping University, Department of Science and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1503.
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In this diploma work, organic electrochemical transistors based on PEDOT:PSS have been studied, focusing on the influence of the geometry and physical dimensions on the transistor characteristics. The geometrical parameters studied are the area ratio between the gate and channel, the channel width and the channel length. Each parameter has been varied in five steps with each step containing three identical transistors. Results concerning the geometrical influence of the linear region resistance, the saturation current (density) and the on/off ratio are presented and discussed. Also, empirical curve-fits of the geometrical influence on the linear region resistance and the saturation current have been performed. In addition, tentative results of the locus of the saturation current versus saturation voltage for specific transistors have been obtained.