Tesis sobre el tema "Atmospheric cloud"
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Barahona, Donifan. "On the representation of aerosol-cloud interactions in atmospheric models". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41169.
Texto completoPaunova, Irena T. "Explicit numerical study of aerosol-cloud interactions in boundary layer clouds". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100670.
Texto completoThree summertime cases have been evaluated: a marine stratus and a cold frontal system over the Bay of Fundy near Nova Scotia, formed on 1 Sep 1995 and extensively sampled as a part of the Radiation, Aerosol, and Cloud Experiment (RACE); and a continental stratocumulus, formed over the southern coast of Lake Erie on 11 July 2001. The marine stratus and the frontal system have been examined for the effects of aerosol on cloud properties and thoroughly evaluated against the available observations. The frontal system and the continental stratocumulus have been evaluated for the effects of cloud processing on the aerosol spectrum.
The marine stratus simulations suggest a significant impact of the aerosol on cloud properties. A simulation with mechanistic activation and a uni-modal aerosol showed the best agreement with observations in regards to cloud-base and cloud-top height, droplet concentration, and liquid water content. A simulation with a simple activation parameterization failed to simulate essential bulk cloud properties: droplet concentration was significantly underpredicted and the vertical structure of the cloud was inconsistent with the observations. A simulation with a mechanistic parameterization and a bi-modal aerosol, including a coarse mode observed in particle spectra below cloud, showed high sensitivity of droplet concentration to the inclusion of the coarse mode. There was a significant reduction in droplet number relative to the simulation without the coarse mode. A similar change occurred in the precipitating system preceding the stratus formation, resulting in an enhancement of precipitation in the weaker (upstream) part of the system while the precipitation in the more vigorous (downstream) part of the system remained almost unaffected.
Aerosol processing via collision-coalescence and aqueous chemistry in the non-drizzling stratocumulus case suggests that impact of the two mechanisms is of similar magnitude and can be as large as a 3-5 % increase in particle mean radius. A more detailed analysis reveals that the impact of chemical processing is oxidant-limited; beyond times when the oxidant (H 2O2) is depleted (∼ 40 minutes), the extent of processing is determined by supply of fresh oxidant from large-scale advection (fresh gaseous emissions are not considered). Aerosol processing via drop collision-coalescence alone suggests, as expected, sensitivity to the strength of the collection process in clouds. Larger particle growth, up to 5-10 %, is observed in the case of the frontal clouds, which exhibit stronger drop collection compared to that in the stratocumulus case. The processed aerosol exerted a measurable impact on droplet concentrations and precipitation production in the frontal clouds. For the case modeled here, contrary to expectations, the processed spectrum (via physical processing) produced higher droplet concentration than the unprocessed spectrum. The reasons explaining this phenomenon and the resulting impact on precipitation production are discussed.
The current work illustrates the complexity of the coupled system at the cloud system scales, revealed earlier at much smaller large eddy scales. If future parameterizations of the regional effect of aerosols on clouds are to be developed, careful consideration is required of the many of feedbacks in the boundary layer.
Nugent, Paul Winston. "Wide-angle infrared cloud imaging for cloud cover statistics". Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/nugent/NugentP0508.pdf.
Texto completoBrösamlen, Gerd. "Radiative transfer in lognormal multifractal clouds and analysis of cloud liquid water data". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68158.
Texto completoDavid, Robert O. "Cloud Dynamics and Microphysics during CAMPS| A Comparison between Airborne and Mountaintop Cloud Microphysics". Thesis, University of Nevada, Reno, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1591334.
Texto completoOrographically-enhanced clouds are essential for global hydrological cycles. To better understand the structure and microphysics of orographically-enhanced clouds, an airborne study, the Colorado Airborne Mixed-Phase Cloud Study (CAMPS), and a ground-based field campaign, the Storm Peak Lab (SPL) Cloud Property Validation Experiment (StormVEx) were conducted in the Park Range of the Colorado Rockies. The CAMPS study utilized the University of Wyoming King Air (UWKA) to provide airborne cloud microphysical and meteorological data on 29 flights totaling 98 flight hours over the Park Range from December 15, 2010 to February 28, 2011. The UWKA was equipped with instruments that measured cloud droplet and ice crystal size distributions, liquid water content, and 3-dimensional wind speed and direction. The Wyoming Cloud Radar and LiDAR were also deployed during the campaign. These measurements are used to characterize cloud structure upwind and above the Park Range. StormVEx measured temperature and cloud droplet and ice crystal size distributions at SPL. The observations from SPL are used to determine mountain top cloud microphysical properties at elevations lower than the UWKA was able to sample in-situ. To assess terrain flow effects on cloud microphysics and structure, vertical profiles of temperature, humidity and wind were obtained from balloon borne soundings and verified with high resolution modeling. Comparisons showed that cloud microphysics aloft and at the surface were consistent with respect to snow growth processes and previous studies on terrain flow effects. Small ice crystal concentrations were routinely higher at the surface and a relationship between small ice crystal concentrations, large cloud droplet concentrations and temperature was observed, suggesting liquid-dependent ice nucleation near cloud base.
Miller, Daniel J. "Satellite Simulator Studies of the Impact of Cloud Inhomogeneity on Passive Cloud Remote Sensing Retrievals". Thesis, University of Maryland, Baltimore County, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10642202.
Texto completoSatellite cloud remote sensing provides us the opportunity to study the spatial and temporal distributions of marine boundary layer clouds, as well as their connections with environments on a global scale. However, cloud remote sensing is not without difficulties; retrievals require numerous simplifying assumptions, placing limits on our understanding of cloud processes. Passive remote sensing retrievals often assume that clouds are homogeneous slabs, when in reality, these clouds often have complex inhomogeneous vertical and horizontal structures. Enhancing our understanding of how cloud inhomogeneity influences passive cloud remote sensing requires comparison between cloud retrievals and the underlying cloud properties. In observational data-sets this can become problematic, as it is difficult to compare satellite and airborne measurements because they have both different observed spatial scales and sensitivities to cloud properties. To avoid these complications, this work is based on a satellite retrieval simulator – a Large-Eddy Simulation (LES) cloud model coupled to radiative transfer and retrieval algorithms. The LES-satellite simulator can be used to study the source of retrieval biases. It provides the underlying realistic cloud structure as a reference, informing conclusions about its impact on various cloud retrieval methods. In the first step we focus on cloud vertical profile, finding that the selection of appropriate vertical profile assumptions for the retrieval of cloud liquid water path. Confirming previous studies, drizzle and cloud top entrainment of dry air are identified as physical features that bias liquid water path retrievals away from adiabatic and toward homogeneous profile assumptions. The mean bias induced by drizzle-influenced profiles was shown to be on the order of 5–10 grams per meter squared. In contrast, the influence of cloud top entrainment was found to be smaller by about a factor of 2. A theoretical framework is also developed to explain variability in LWP retrievals by introducing modifications to the adiabatic effective radius profile. The second step focuses on horizontal inhomogeneity and exploring a comparison of both the bispectral and polarimetric cloud retrieval techniques. Using the satellite retrieval simulator we are able to verify that at high spatial resolution (50 meters) the bispectral and polarimetric retrievals are indeed highly correlated with one another. The small differences at high spatial resolution can be attributed to different sensitivity limitations of the two retrievals. In contrast, a systematic difference between the two effective radius retrievals emerges at coarser resolution. This bias largely stems from differences related to sensitivity of the two retrievals to unresolved inhomogeneities in effective variance and optical thickness. The influence of coarse angular resolution is found to increase uncertainty in the polarimetric effective radius retrieval, but generally maintains a constant mean value. The third study focuses on 3-D radiative effects influencing both total and polarized reflectances and retrievals. Comparisons between the 1-D and 3-D reflectances are made in order to study horizontal photon transfer and radiative smoothing. We find noticeable differences between the total and polarized reflectance 3-D effects, with radiative smoothing and roughening occurring at different scales as well as viewing geometry dependence. Despite these apparently strong 3-D effects on polarized reflectances, the polarimetric retrieval is robust to the influence of 3-D effects – with only sub-micron biases in the retrieval of effective radius.
Duane, William John. "Correcting middle infrared cloud reflectances for atmospheric effects". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324809.
Texto completoGrandey, Benjamin Stephen. "Investigating aerosol-cloud interactions". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:8b48c02b-3d43-4b04-ae55-d9885960103d.
Texto completoVaillancourt, Paul. "Numerical experiments on entrainment, mixing and their effect on cloud dropsize distributions in a cumulus cloud". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61085.
Texto completoResults show that vortex circulations and penetrative downdrafts are responsible for entrainment of clear air into the cloud structure. Entrainment and mixing are more severe on the downshear side of the cloud leading to a more fragmented structure and often to total dissipation of cloudy air rather than partial dilution as is the case on the upshear side. Mixing followed by uplifting leads to fresh activation of cloud droplets and results in multimodal spectra. In areas where mixing has occurred, the spectra exhibit smaller average radius and larger standard deviation.
Zhong, Weiguo. "Characteristics of the Pinatubo aerosol cloud". Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290573.
Texto completoMaroon, Elizabeth A. "The impact of Arctic cloud water and ice on cloud radiative forcing during the Arctic Summer Cloud-Ocean Study in August 2008". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/114379.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (pages 49-52).
The Arctic atmosphere is especially sensitive to changes in climate forcing; however, Arctic processes and feedbacks are not understood well enough to accurately predict how the Arctic environment might change under anthropogenic forcing. Further study of the basic atmospheric processes is needed, especially due to uncertainties in modeling cloud feedbacks. August and September are the months when the Arctic sea surfaces begin to freeze; clouds play an important role in determining when this process begins. In this study, the radiative properties of Arctic stratocumulus are studied by comparing measurements for two days in August 2008 during the Arctic Surface Cloud Ocean Study (ASCOS) with simulations using the Rapid Radiative Transfer Model (RRTM). Cloud radiative forcing for both days is examined, and the modeled radiative fluxes were found to compare well to observations. Sensitivity studies are conducted on single and multi-level stratocumulus clouds to study their radiative interactions with each other. Cloud-top cooling in upper clouds is found to radiatively turn off cloud-top cooling in clouds below it. The RRTM and the surface radiative observations are used together to constrain estimates of liquid droplet radius; constraining these radii shows the sensitivity of shortwave cloud radiative forcing and the insensitivity of long wave cloud forcing to changes in drop size.
by Elizabeth A. Maroon.
S.B.
Lathem, Terry Lee. "On the water uptake of atmospheric aerosol particles". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50112.
Texto completoSong, Qingyuan. "A parameterization of in-cloud sulphate production /". Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35622.
Texto completoPreliminary application in a regional climate model confirms that the parameterization is able to improve the agreement of the mass budget and spectrum distribution of sulphate aerosol with observations.
Hohenegger, Cathy. "Dynamical analysis of atmospheric predictability in cloud-resolving models /". Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16871.
Texto completoNyman, Oscar. "Towards a quality control for cloud top pressure and cloud top height products". Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-61977.
Texto completoDiao, Minghui. "Ice supersaturation and cirrus cloud formation from global in-situ observations". Thesis, Princeton University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3597474.
Texto completoWater vapor, clouds and aerosols are three major components in the atmosphere that largely influence the Earth's climate and weather systems. However, there is still a lack of understanding on the distribution and interaction of these components. Large uncertainties still remain in estimating the magnitude and direction of the aerosol indirect effect on cloud radiative forcing, which potentially can either double or cancel out all anthropogenic greenhouse gas effect. In particular, a small variation in water vapor mixing ratio and cloud distribution in the upper troposphere and lower stratosphere (UT/LS) can generate large impacts on the Earth's surface temperature. Yet the understanding of water vapor and clouds in the UT/LS is still limited due to difficulties in observations. To improve our understanding of these components, observations are needed from the microscale (~100 m) to the global scale. The first part of my PhD work is to provide quality-controlled, high resolution (~200 m), in situ water vapor observations using an open-path, aircraft-based laser hygrometer. The laboratory calibrations of the laser hygrometer were conducted using complementary experimental systems. The second part is to compare the NASA AIRS/AMSU-A water vapor and temperature retrievals with aircraft-based observations from the surface to the UT/LS at 87°N-67°S in order to understand the accuracy and uncertainties in remote sensing measurements. The third part of my research analyzes the spatial characteristics and formation condition of ice supersaturation (ISS), the birthplace of cirrus clouds, and shows that water vapor horizontal heterogeneities play a key role in determining the spatial distribution of ISS. The fourth part is to understand the formation and evolution of ice crystal regions (ICRs) in a quasi-Lagrangian view. Finally, to help estimate the hemispheric differences in ice nucleation, the ISS distribution and ICR evolution are compared between the two hemispheres. Overall, these analyses provided a microphysical scale yet global perspective of the formation of ISS and cirrus clouds. Ultimately, these efforts will help to improve the understanding of human activities' influences on clouds, water vapor and relative humidity in the UT/LS and provide more accurate representations of these components in future climate prediction.
Vaillancourt, Paul. "Microscopic approach to cloud droplet growth by condensation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0021/NQ44614.pdf.
Texto completoPflug, Karen. "Generalized scale invariance, differential rotation and cloud texture". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61076.
Texto completoUsing a two-dimensional representation of GSI and three new analysis techniques, we test the following relation for each picture: $ langle vert F( lambda sp{ tilde G} vec k) vert sp2 rangle = lambda sp{-s} langle vert F( vec k) vert sp2 rangle$, where $F( vec k)$ is the Fourier amplitude at wavenumber $ vec k$, $ lambda$ is the scale ratio and $ tilde G$ is the generator of the semi-group of scale changes in Fourier space. Since we test only the linear approximation to GSI, $ tilde G$ is approximated here as a matrix.
For the three texturally--and meteorologically--very different images analyzed, we find three different generators that generally well reproduce the Fourier space anisotropy. These results show that linear GSI is a workable approximation for studying the atmosphere and that GSI can be used for cloud classification and modeling over this important mesoscale range.
Tremblay, André 1948. "A three dimensional cloud chemistry model /". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=73980.
Texto completoGlazer, Anna. "Evaluation of the ADOM cloud module". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61213.
Texto completoComparisons of results for a variety of initial conditions show that wet-deposition of sulphate, nitrate and ammonium ions tend to be underpredicted by the cloud module and that the pH of the rain is overpredicted. However, the differences are for the most part not large. Concentrations of hydrogen peroxide deposited at the surface are significantly smaller in the ADOM module than in the cloud chemistry model. The results of the cloud module do seem to be sensitive to the model cloud top height.
Slater, Daniel. "Predicting the impacts of cloud processing on aerosol properties /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10175.
Texto completoJakob, Christian. "The representation of cloud cover in atmospheric general circulation models". Diss., lmu, 2001. http://nbn-resolving.de/urn:nbn:de:bvb:19-3281.
Texto completoGérard, Violaine. "Surfactants in atmospheric aerosols and their role on cloud formation". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1216/document.
Texto completoClouds are essential components of the Earth’s hydrological system and climate but some aspects of their formation are still not completely understood. In particular, although Köhler theory predicts that surfactants should enhance cloud droplet activation, current models consider this role negligible. At the time of this PhD work, a few studies had started to demonstrate the contrary but atmospheric evidence for the role of these compounds was still missing and very little was known about their atmospheric concentrations, sources, and mechanism of action. The objective of this PhD work was to investigate these aspects. A method was developed to quantify surfactant concentrations in aerosols. Its application led to the first absolute atmospheric surfactants’ surface tension curves, in coastal PM2.5 aerosols in Sweden, and to the identification of the ratio C/CMC as the key parameter controlling the cloud-forming efficiency of aerosols. A second study revealed strong correlations between cloud occurrence and intrinsic surfactant properties in boreal PM1 aerosols in Finland, demonstrating for the first time the role of surfactants in cloud formation from direct atmospheric observations. The results predicted Cloud Condensation Nuclei numbers four times larger on average than when neglecting surfactant effects, showing the importance of including surfactant effects in cloud predictions models. The role of surfactants inferred from macroscopic measurements was confirmed by laboratory experiments on individual micron-sized droplets showing an increase of droplet growth in the presence of surfactants. Finally, observations from the different field studies indicated a biological origin for the surfactants present in atmospheric aerosols
Good, Nicholas. "Measuring the hygroscopic properties and cloud activation of atmospheric aerosols". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508525.
Texto completoHorseman, Andrew Mark. "Modelling cirrus cloud fields for climate and atmospheric chemistry studies". Thesis, Lancaster University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.652029.
Texto completoZuberi, Bilal 1976. "Microphysics of atmospheric aerosols : phase transitions and cloud formation mechanisms". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17654.
Texto completoVita.
Includes bibliographical references (leaves 134-148).
Clouds play an extremely important role in our atmosphere, from controlling the local weather, air pollution and chemical balance in the atmosphere to affecting long-term climatic changes at local, regional and global scales. The mechanisms through which tropospheric clouds form are still not fully understood, leading to gross uncertainties in understanding the effect of atmospheric aerosols on the environment. Using laboratory measurements, microphysical properties of typical micro-meter size atmospheric aerosols are investigated in this study. Upper tropospheric ice clouds (cirrus) form when ice is nucleated either homogeneously or heterogeneously in aqueous aerosols. We have investigated the homogeneous and heterogeneous ice nucleation in aqueous particles. Our results for homogeneous nucleation in aqueous ammonium nitrate particles show that the current thermodynamic models do not correctly predict water activities in these particles under super-saturated conditions. High super-saturations are required for ice to nucleate homogeneously in aqueous ammonium nitrate particles. We have also investigated the role of crystallized salt cores, such as solid ammonium sulfate and letovicite, in the heterogeneous nucleation of ice in saturated aqueous ammonium sulfate particles. Our results show that the surface morphology and defects on microcrystals could result in the creation of active sites, leaving the crystallized salt cores as potent ice nuclei under certain conditions. We have also investigated the role of mineral dust and soot, major components of insoluble particulates in the atmosphere, as ice-nuclei. We have found mineral dust to be an effective ice nuclei but both fresh and aged soot do not promote ice nucleation in aqueous particles.
(cont.) Soot is the most ubiquitous aerosol in the atmosphere. The lifetime and microphysics of nano-porous soot has a large impact on earth's radiative budget, heterogeneous chemistry, urban and regional air pollution and human health. We have investigated the hydrophilic properties of both fresh and aged soot as a function of relative humidity. Our results show that fresh hydrophobic soot oxidized (aged) by OH/0₃/UV in the presence of water vapor or by exposure to concentrated HNO₃ becomes hydrophilic and exhibits a greater affinity for water. Due to this increased hydrophilicity, aged soot can be easily entrained inside existing liquid cloud droplets, and even activate as cloud condensation nuclei at high super-saturations, thus influencing its heterogeneous chemistry, radiative properties and atmospheric lifetime.
by Bilal Zuberi.
Ph.D.
Caya, Alain. "Assimilation of radar observations into a cloud-resolving model". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38165.
Texto completoExperiments with synthetic data from model outputs at 1 km horizontal resolution show that the method is able to retrieve unobserved variables. An assimilation period of 10 minutes is shown to be optimal for the analysis of clouds. All the other variables of the model are rather insensitive to the assimilation period. Here the model time step has been varied from 1 to 5 minutes. Most of the a posteriori residual distributions have a high kurtosis while the velocity and the near-surface refractivity index residual distributions are nearly Gaussian. The data assimilation for the case of a shallow hailstorm suggests that the model used for the assimilation is able to forecast the system for 30 minutes within the estimated observational errors. Application of the method to the initialization of the MC2 model leads to a better forecast of a convective system over 40 minutes than the nowcasting technique based on Lagrangian persistence.
Wilson, Jean. "Physically based stochastic modelling of rain and cloud fields". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60551.
Texto completoGuan, Hong. "The effects of longwave radiation in a small cumulus cloud". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39916.
Texto completoA longwave radiation model was developed. The model was first applied to the case of an isolated cumuliform cloud in the form of a cylinder, the results of which illustrate the importance of cloud side cooling. We proposed that the radiatively forced sinking of air at the sides of cumuliform clouds would lead to lower-level convergence and thereby enhances the upward motion in the interior of the cloud.
A study of cloud top cooling rate in stratiform clouds with positive (lifting) or negative (sinking), axially symmetric perturbations shows that a lifting of the cloud top does not increase cooling rate, whereas the peak cooling rate decreases rapidly in depressions. For small perturbation, $ approx$10 m, this may tend to inhibit the growth of negative perturbations. For larger perturbations, $ approx$100 m, changes to the radiative cooling rates within the positive perturbations and next to the negative perturbations may act to sustain the perturbation and promote its growth.
Using a three-dimensional longwave radiation model and a slab-symmetric cloud dynamics model, we demonstrated that longwave radiative cooling substantially enhances the maximum cloud water content. The maximum increase reaches 96%. The total cloud water was also increased somewhat (maximum 20%).
In the initial stage of the development, the augmentation of cloud water content near the cloud top and sides is traced mainly to the direct effect of longwave radiative cooling on cloud microphysics (i.e. radiative cooling reduces the local temperature and hence the saturation water vapor pressure, which leads to additional condensation).
In the mature stage of cloud, the increase of total cloud water content comes from a combination of the effects of radiation on microphysics and dynamics. The cooling from radiation and evaporation produces additional downward motion at the sides of the cloud. The enhanced low-level convergence invigorates the updraft promoting further cloud development.
In the decaying stage, the negative buoyancy produced by cloud top radiative cooling and a higher liquid water load speeds up the decay process in the LW run.
In a sheared environment, shear suppresses convection. In conjunction with horizontal momentum transport, radiative cooling also results in a more negative temperature perturbation and a stronger downdraft on the downshear flank relative to the upshear side.
In an axially symmetric simulation, longwave cooling produces a weaker updraft in the cloud core. This phenomena was attributed to the shorter lifetime of the axially symmetric cloud, and the fact that the cloud side sinking motion can spread around the cloud core instead of being confined to a vertical plane. As a result, a weaker secondary circulation develops which is offset by the negative effects of the cloud top radiative cooling and the higher liquid water load.
Greene, Heather. "Drought and associated cloud fields over the Canadian Prairies". Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32404.
Texto completoTrès peu est connu a propos des nuages durant une sècheresse. Entre 1999 et 2005, les Prairies canadiennes ont vécu une des sècheresses les plus sévères et les plus longues dans ses registres climatologiques. L'objectif de cette étude est de caractériser et de mieux comprendre les nuages et leurs propriétés radiatives durant les sècheresses dans les provinces des Prairies canadiennes. Une attention particulière a été donnée à cette récente sècheresse. La sévérité de la sècheresse a été déterminée avec l'index standardise de précipitations. Les propriétés des nuages obtenues de la base de données du Budget Radiatif de Surface de NASA/GEWEX ont été utilisées pour examiner l'ensemble de la quantité de nuage, l'épaisseur optique et l'albédo du haut de l'atmosphère. Les résultats ont démontré que malgré une légère différence dans la quantité de nuage entre des périodes sèches et humide (une augmentation d'environ 10% dans la couverture nuageuse de 63% durant des conditions extrêmement sèches a 73% pendant des périodes extrêmement humide), la corrélation avec la précipitation est faible. Les nuages minces augmentent lorsque la sévérité de la sècheresse augmente, alors que les nuages d'épaisseur moyenne ou épaisse diminuent. Les résultats ont aussi démontré que des tendances similaires se rapportent à plus petite échelle.
Menon, Surabi. "Role of Sulfates in Regional Cloud-Climate Interactions". NCSU, 1998. http://www.lib.ncsu.edu/theses/available/etd-19981102-133647.
Texto completoAerosols affect the radiation budget of the earth-atmosphere system by directly reflecting or absorbing solar radiation and also indirectly, by altering the cloud albedo through changes in the cloud condensation nuclei concentration (CCN). Increases in CCN concentrations result in an increase in the cloud droplet number concentration (N). Assuming the cloud liquid water content (LWC) stays the same, this will result in smaller cloud droplet sizes. Thus, this will increase cloud reflectance and cloud lifetime as cloud cover also increases. An accurate quantification of the aerosol forcing effect is still not possible due to the complexity involved in understanding aerosol processes and their effects on climate. There has also been a lack of a coordinated effort toward linking surface and in situ observations, as well climate model results and satellite data. Due to the spatial and temporal heterogeneity in aerosol forcing, regional effects are important. In this dissertation, the direct and indirect radiative forcing effects of aerosols - primarily sulfates and to lesser extent soot aerosols at a site located in the southeastern U.S. are investigated by means of surface observations, modeling results and satellite data.During the summers of 1993-96, field experiments were conducted at Mt. Mitchell, North Carolina, at a site representative of the southeastern U.S. to determine the effect of pollutants on the cloud microphysical and optical properties. Analyses of the results from empirical relationships are used to obtain an estimate of the contribution of sulfates to indirect radiative forcing. Concurrent measurements of size resolved chemical concentrations, light scattering and absorption coefficients, aerosol size distribution and optical depth measurements were obtained during the winter of 1997 for cloud-free skies. Data from these measurements are used to investigate the chemical-physical-optical interaction between aerosols and to determine the direct forcing effect of aerosols by means of a column forcing model. Cloud water sulfate concentration is used as a measure of anthropogenic pollution. Back-trajectory analysis is used to identify the source of the air masses classified as polluted continental, continental and marine. The effect of anthropogenic pollution on cloud microphysical properties such as LWC, N, effective radii (Reff), CCN activation spectrum, cloud optical depth and reflectivity are investigated. The relationship between Reff and sulfate for different air masses, as well as the N-sulfate mass relationship, suggests that the counteracting effect of sulfates on greenhouse warming for the southeastern U.S. would be of a magnitude greater than -4.0 W m-2 obtained by previous modeling studies. Acidity variations between cloud droplets of different sizes indicated that on an average, smaller drops are enriched in sulfates, nitrates and ammonium, whereas, larger droplets have higher concentrations of sodium, calcium and magnesium. As part of a closure experiment cloud albedo calculated from in situ measurements was compared to that retrieved from the Advanced Very High Resolution Radiometer data for four years (1993-96). The nonlinear relationships between the cloud microphysical/optical properties and the sulfate content imply the existence of an optimum level for the sulfate concentration that would affect cloud albedo. In terms of the direct forcing effect, wintertime forcing obtained for an internal mixture of sulfate and soot aerosols is much lower than that obtained during summer, due to reduced sulfate concentrations in winter. A quantitative measure of the direct forcing indicates higher magnitudes both for summer and winter than is obtained from previous modeling results. Analyses of the direct and indirect radiative forcing effect of sulfates for the southeastern U.S. indicate that the negative forcing effect is of greater magnitude than is predicted by modeling results. Thus, reduction in sulfate emissions would have a significant impact on climate for the southeastern U.S.
Lauzon, Louise. "Evaluation of a three dimensional cloud chemistry model". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56995.
Texto completoIn general, the simulated concentrations of NO$ sbsp{3}{-},$ NH$ sbsp{4}{+},$H$ sp+$, H$ sb2O sb2$ and the concentrations of SO$ sbsp{4}{2-}$ calculated with the perfect nucleation condition concur with the observed concentrations. For the four polluted cases, more than 80% of the cloud water SO$ sbsp{4}{2-}$ comes from nucleation, whereas for the clean case, it is mostly created by SO$ sb2$ oxidation. The relative importance of $ rm H sb2O sb2$ and O$ sb3$ in SO$ sb2$ oxidation, as well as the relative importance of nucleation and NH$ sb3$ absorption on the cloud water NH$ sbsp{4}{+}$ budget vary according to the chemical state of the atmosphere.
Pyykkö, Joakim. "Improving Short-Range Cloud Forecasts in Harmonie-Arome Through Cloud Initialization Using Mesan Cloud Data". Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-380151.
Texto completoI en operationell vädermodell inkluderas olika mätdata, såsom temperatur och atmosfärstryck, i ett regelbundet intervall. Molnighet är inte vanligtvis en del av dessa cykler; istället bildas molnen av modellen utifrån balanser i de andra fysikaliska fälten. Detta projekt gick ut på att direkt införa molnmätningar från väderanalyssystemet MESAN i vädermodellsystemet HARMONIE-AROME genom en metod som kallas molninitialisering. Specifikt förbättringar för korttidsprognoser var av i ntresse. MESAN är ett system vars produkter är en sammanslagning av ett bakgrundsfält från en vädermodellkörning med olika mätdata. I MESAN kommer molndata från tre källor: bakgrundsfältet, satellitdata och synoptisk väderstationsdata (SYNOP-data). Undersökningar av indata till MESAN samt molninitialiseringsmetoden har utförts. Analyser av indata till MESAN visade på överskattningar av moln i satellitdata över hav och underskattningar av moln i SYNOP-data över land. För satellitdatat berodde detta på medtagande av moln på liten skala eller väldigt tunna moln, medan det för SYNOP berodde på begränsningar i mätmetoderna. Det fanns även en skillnad i kvalitet i SYNOP-data i Sverige och Finland gentemot Norge, vilket kan bero på att de flesta mätstationer i Norge är manuella medan de flesta i Sverige och Finland är automatiska. Molninitialiseringsmetoden bestod i att extrahera data om molnbashöjd och molntopphöjd från MESAN, och sedan modifiera fuktighet, temperatur och hydrometeorer (såsom molndroppar och iskristaller) i HARMONIE-AROME utifrån molnens position. Brister i metoden hittades. Initialiseringsprocessen upprepades ett suboptimalt antal gånger. En begränsning i hur mycket fuktigheten tillåts modifieras förändras under initialiseringsprocessen och fungerade inte som avsett. Dessutom, jämförese med radiosonddata pekar på att relativa fuktighetsgränserna för villket moln bildas inledningsvis inte ansattes korrekt. Effekterna av metoden kunde vara i över 12 timmar, men denna studie pekar på ytterligare troliga förbättringsmöjligheter i HARMONIE-AROME genom införande av reviderad version av metoden samt förbättrade satellitprodukter.
Ahern, Helen. "Cloud bourne bacteria : community composition and potential impact on atmospheric nucleation". Thesis, University of East London, 2008. http://roar.uel.ac.uk/3385/.
Texto completoVec̆ei, Danijela. "Detection of supercooled cloud by radar : algorithm comparisons with aircraft data". Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79151.
Texto completoFor the analyzed cases, the results of the two algorithms agreed well with each other. Furthermore, these results matched radiometric and aircraft measurements overall. Both algorithms demonstrated some limitations. Possible solutions to reduce some of the observed limitations include employing an algorithm for resolving trail patterns, and an algorithm for separating the drizzle from the snow echo.
Song, Shi. "The Spectral Signature of Cloud Spatial Structure in Shortwave Radiation". Thesis, University of Colorado at Boulder, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10151129.
Texto completoIn this thesis, we aim to systematically understand the relationship between cloud spatial structure and its radiation imprints, i.e., three-dimensional (3D) cloud effects, with the ultimate goal of deriving accurate radiative energy budget estimates from space, aircraft, or ground-based observations under spatially inhomogeneous conditions. By studying the full spectral information in the measured and modeled shortwave radiation fields of heterogeneous cloud scenes sampled during aircraft field experiments, we find evidence that cloud spatial structure reveals itself through spectral signatures in the associated irradiance and radiance fields in the near-ultraviolet and visible spectral range.
The spectral signature of 3D cloud effects in irradiances is apparent as a domain- wide, consistent correlation between the magnitude and spectral dependence of net horizontal photon transport. The physical mechanism of this phenomenon is molecular scattering in conjunction with cloud heterogeneity. A simple parameterization with a single parameter ϵ is developed, which holds for individual pixels and the domain as a whole. We then investigate the impact of scene parameters on the discovered correlation and find that it is upheld for a wide range of scene conditions, although the value of ϵ varies from scene to scene.
The spectral signature of 3D cloud effects in radiances manifests itself as a distinct relationship between the magnitude and spectral dependence of reflectance, which cannot be reproduced in the one-dimensional (1D) radiative transfer framework. Using the spectral signature in radiances and irradiances, it is possible to infer information on net horizontal photon transport from spectral radiance perturbations on the basis of pixel populations in sub-domains of a cloud scene.
We show that two different biases need to be considered when attempting radiative closure between measured and modeled irradiance fields below inhomogeneous cloud fields: the remote sensing bias (affecting cloud radiances and thus retrieved properties of the inhomogeneous scene) and the irradiance bias (ignoring 3D effects in the calculation of irradiance fields from imagery-based cloud retrievals). The newly established relationships between spatial and spectral structure lay the foundation for first-order corrections for these 3D biases within a 1D framework, once the correlations are explored on a more statistical basis.
Trahan, Adam J. "Acoustic Attenuation in the Lower Cloud Layer of Venus". Thesis, University of Louisiana at Lafayette, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13419931.
Texto completoGeneric predictions for the acoustic wavenumber at low frequencies in the condensational cloud layers of Venus are presented, based on and adapted from the terrestrial model of Baudoin et al. (J. Acoust. Soc. Am. 130. 1142 (2011)). While the general thermodynamics of Earth clouds is well understood, that of Venusian clouds is still a matter of debate. Venus’ clouds are primarily formed of H2O and H2SO4 vapors and aqueous sulfuric acid droplets, the fluxes of which are not fully constrained due to the few in situ observations. Inside the clouds, the Navier-Stokes-Fourier equations of continuum fluid mechanics are used for the gaseous (dry + vapor) and liquid phases of H 2O andH2SO4, combined with equations describing the evaporation/condensation processes; the gaseous phase is treated as an ideal gas and the liquid droplets are considered polydisperse. Thermophysical parameters are interpolated at the ambient conditions pertaining to an altitude of 50 km, a level where balloon platforms (e.g., European Space Agency’s EVE) and manned airships (e.g., NASA’s HAVOC) may be deployed in the future. At low frequencies, the dominant source of absorption is caused by the evaporation/condensation of the liquid phase. At higher frequencies, absorption is dominated by momentum transfers between the wave and the ambient gas and liquid droplets. The intrinsic dispersion is negligible. Sensitivity studies of the attenuation coefficient and the sound speed on the cloud physical parameters is performed, namely, the mean cloud particle size and the cloud density. The attenuation coefficient is sensitive to changes in both mean cloud particle size and cloud density, while the intrinsic dispersion changes negligibly.
Berlin, Shaena R. (Shaena Rochel). "An electrodynamic balance (EDB) for extraterrestrial cloud formation studies". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90650.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (pages 42-48).
Ice clouds scatter and absorb solar radiation, affecting atmospheric and surface temperatures (Gettelman et al., 2012). On Mars, where ice contained in clouds makes up a large portion of total atmospheric water vapor, ice clouds also alter the planetary water budget (Maltagliati et al., 2011; Rafkin et al., 2013). Thus, it is important for climate models to be able to accurately predict the conditions under which ice clouds can form. Typical Martian temperatures at cloud-formation height range from -150-200 K (Trainer, Toon, & Tolbert, 2009). Heterogeneous deposition nucleation is thought to be the dominant freezing mechanism on Mars due to the abundance of mineral dust to serve as ice nuclei (IN) (Mdittanen et al., 2005). The parameters for such nucleation are not well characterized at such low temperatures (Trainer et al., 2009). Previous experimental studies have investigated the relative humidity required for deposition nucleation within the Martian temperature range. However, most studies took place on bulk aerosol samples, did not use mineral dusts analogous to Martian dust, or were constrained by particle lifetime and temperature limits. In this project, we re-purpose a single-particle instrument and set it up to perform experiments for more precise ice nucleation data under Martian atmospheric conditions. We use an electrodynamic balance (EDB) to levitate individual particles with diameters around 10 pm. We calculate the size of the particle and changes in size based on the holding voltages. The system can be cooled to 200 K in its current configuration, and the relative humidity and atmospheric constituents can be controlled by adding gas. To test the EDB, we perform validation experiments. We investigate deliquescence and efflorescence on salts at room temperature and 0 'C. We modify the cooling system, thermocouples, and relative humidity sensors and begin freezing experiments with Arizona Test Dust (ATD) and with Mojave Mars Simulant (MMS) dust. We investigate water uptake on MMS particles and find it to be non-hygroscopic but wettable, uptaking monolayers of water between 65-95% relative humidity. From 200 K to 220 K, MMS does not nucleate up to 115% RHice, suggesting that higher supersaturations are needed for ice clouds to form; some Martian cloud modelers should revisit the critical supersaturation parameterization. Future work will improve the EDB and use it to examine phase functions and light scattering.
by Shaena R. Berlin.
S.M. in Atmospheric Sciences
Gunturu, Udaya Bhaskar. "Aerosol-Cloud interactions : a new perspective in precipitation enhancement". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/58462.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (p. 171-184).
Increased industrialization and human activity modified the atmospheric aerosol composition and size-distribution during the last several decades. This has affected the structure and evolution of clouds, and precipitation from them. The processes and mechanisms by which clouds and precipitation are modified by changes in aerosol composition and size-distribution are very intricate. The objective of this thesis is to improve the understanding of the processes and mechanisms through which the changes in aerosol concentrations impact the evolution of deep convective clouds and precipitation formation. We develop a new coupled model in which a very detailed model of aerosol activation is coupled to a three-dimensional cloud resolving model. This coupled model can accurately represent different kinds of aerosol populations. This coupled model is used to investigate the impact of changing aerosol concentrations on the dynamics, microphysical evolution and precipitation formation in deep convective clouds. We examine the theories of aerosol activation, and the representation of aerosol activation in cloud models. The limitations of the extant methods of representation of aerosol activation in cloud models are evaluated. Then we descibe the components of the coupled model - Modified Eulerian and Lagrangian Aerosol Model (MELAM) and the Cloud Resolving Model (CRM). The features of these two component models with respect to aersol activation and cloud formation are discussed. The evaluation of the coupled model by simulation of a deep convertive event observed during the INDian Ocean EXperiment (INDOEX) by statistcal comparison of observed and simulated cloud fields shows that the coupled model can simulate deep convective events reasonably well. We present a study of the senstivity of the model to initial thermodynamic conditions (CAPE). Different initial thermodynamic conditons sampled during the INDOEX are used to initialize the coupled model and, the structure and evolution of the deep convective event are discussed. The study sheds new light on the respone of deep convection to CAPE. It is found that when the atmosphere has moderate CAPE, the precipitation forming processes are very active and when the CAPE is (cont.) low or high, they are comparatively less efficient.
As the most important part of our study, we examine the response of deep convection to changing initial aerosol concentration. Different aerosol concentrations from those representing pristine to polluted atmospheres are considered. We look at the buoyancy of the cloud and the microphysical evolution. It is found that the dynamics and microphysics are tightly coupled and we infer that to understand aerosol-cloud interactions in deep convective clouds, both - dynamics and microphysics - and their interaction have to be taken into consideration. Our results show that the response of a deep convective cloud to changing aerosol concentration is very different from the much well understood reponse of shallow clouds or small cumulus clouds. In general, increase in aerosol concentratin is seen to invigorate convection and lead to greater condensate. Although the cloud droplet size decreases, collision-coalescence is not completely inefficient. The precipitation in high aerosol regime is seen to occure in short spells of intense rain. A very interesting anomalous response of deep convection to initial aerosol concentration is observed at intermediate aerosol concentrations. The cloud lifetime, and precipitation are seen to increase in this regime. A possible mechanism to explain this anomalous behavior is proposed and the available circumstantial support for the mechanism from extant observations is presented. It is proposed that the efficient collection of rain and cloud droplets by ice and graupel particles in the middle troposphere is primarily responsible for this increased cloud lifetime and precipitation.
by Udaya Bhaskar Gunturu.
Ph.D.
Hoffman, Paul M. S. B. Massachusetts Institute of Technology. "Spontaneous tropical cyclogenesis in a cloud revolving numerical model". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/114341.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (page 24).
In this thesis, spontaneous tropical cyclogenesis occurring in a cloud-resolving numerical model is studied. The model environment is one of radiative convective-equilibrium on an f-plane with doubly periodic boundary conditions and constant sea surface temperature. While a variety of initial conditions may exhibit spontaneous tropical cyclogenesis, this study focuses on one. Using assumptions of axisymmetry for the growing disturbance and focusing on the large scale processes, fields were created for a number of thermodynamic variables along constant height surfaces and as azimuthal means plotted against height. The tropical cyclone is hypothesized to develop in three steps. First, convective aggregation creates regions of high moist static energy, and regions of cold dry air. Importantly, a deep moist column is created which provides a perfect environment the developing storm. In the second step, mid-level cyclone intensification, a mid-level cold core cyclone develops in the deep moist region, and benefits from moist static energy and potential vorticity fluxes from the upper troposphere. Exhibiting anticyclonic convergent flow, the upper troposphere is an unlikely source for the mid-level disturbance, while convective downdrafts and divergent surface flow hinder energy transport from the ocean to the growing system. In fact, a cold surface anticyclone exists near the center for much of the second step. It is not until potential vorticity anomalies advect down to the surface that the final step, low-level cyclone intensification, creates a classical hurricane structure. Potential vorticity advection stimulates cyclonic flow at the surface, extinguishing the surface anticyclone, and thereby linking the mid-level disturbance to the oceanic energy source. While like some cold core cyclones previously studied, the anticyclone as an energy source is unique to this spontaneous case.
by Paul M. Hoffman.
S.B.
Kipling, Zak. "Cloud cycling, scavenging and aerosol vertical profiles : process sensitivity and observational constraints". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:16f442be-dac6-40d2-b1fa-4c5a2ff69e9c.
Texto completoKoziol, Anna S. (Anna Sophia). "The effect of turbulence on the collision rates of small cloud drops". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28802.
Texto completoWe developed a method to calculate collision rates of small hydrodynamically interacting drops embedded in an external flow field; we call it the flux method. Then, the method was tested for simple cases of laminar flows such as linear shear and a two-dimensional deformation field. The tests were designed not only to validate the method but also to examine the mechanisms associated with the simplified types of external flows which may be equally important for real turbulent flows.
In order to obtain estimates of collision rates for turbulent flows, the flux method was used in conjunction with a probabilistic approach. Numerous simulations of trajectories of two hydrodynamically interacting droplets in a turbulent field were carried out. The ratio of the number of collisions to the total number of simulations gave the probability of collision for different relative positions of the drops. Because the Reynolds number of the flow around droplets (based on the drop radius and terminal velocity) is small, the trajectories were calculated with the help of a model based on the linear Stokes hydrodynamics. Turbulence was modelled in the form of random Fourier modes with both the space and the time spectrum prescribed. Both spectra were characterized by Kolmogorov scaling. The space spectrum was modelled in the inertial and dissipation subranges. On the basis of scale analysis, only small scale time variations were allowed, and, the so called Eulerian-Lagrangrian time spectrum was applied.
The results show that most collision rates increase moderately in a turbulent flow characterized by a rate of energy dissipation of the order of 1, 10, and 100 cm$ sp2$ sec$ sp{-3}.$ The estimated increase in collision efficiencies, however, is not uniform, and a rather complicated relation between the increase in the collision efficiency and the parameters--the drop radii, and the rate of energy dissipation--can be observed.
Rémillard, Jasmine. "Cloud climatology and microphysics at Eureka using synergetic radar/lidar measurements". Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32392.
Texto completoMalgré leur importance dans le budget radiatif terrestre et les modèles atmosphériques, les nuages arctiques restent mal documentés et incompris. Le déploiement d'un radar millimétrique et d'un lidar à haute résolution spectrale à Eureka (80°N) en août 2005 offre un ensemble unique de données pour l'étude des nuages arctiques. Dans ce projet, des algorithmes synergétiques furent développés et appliqués à deux ans de données pour fournir une première climatologie des nuages et de leur microphysique à cet emplacement éloigné. Les résultats montrent un cycle annuel dans l'étendue des nuages. Ils sont surtout détectés dans les bas niveaux ou en une couche, particulièrement en hiver à cause de l'inversion thermique et du refroidissement radiatif du haut des nuages. Une analyse des vents a démontré que différentes directions sont reliées à différentes conditions nuageuses, alors qu'une forte canalisation des vents due à la topographie est présente dans les bas niveaux. De plus, la phase liquide fut détectée à l'année longue, avec une occurrence minimale en hiver causée par des températures plus froides. De la turbulence et un haut taux d'humidité semblent maintenir les particules liquides surfondues, particulièrement quand des cristaux de glace sont aussi présents. Les précipitations furent principalement identifiées durant l'été, surtout sous forme de virga, bien que la difficulté à distinguer la neige des nuages glacés a pu influencer les résultats. Finalement, la validation d'un satellite est possible grâce aux données d'Eureka, mais seulement sous des conditions homogènes et si les caractéristiques instrumentales
Gryspeerdt, Edward. "Aerosol-cloud-precipitation interactions". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:3d1210b0-2ada-403c-8fdf-2bef1724fcd8.
Texto completoAyala, Orlando. "Effects of turbulence on the collision rate of cloud droplets". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 6.00 Mb , 236 p, 2005. http://wwwlib.umi.com/dissertations/fullcit/3181864.
Texto completoSchmidt, Eric Otto. "Cloud properties as inferred from HIRS/2 multi-spectral data". Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/26817.
Texto completoXu, Liming 1958. "Estimating rainfall from satellite infrared imagery: Cloud patch analysis". Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282573.
Texto completoRémillard, Jasmine. "Remote sensing of drizzle onset and cloud microphysical properties in marine stratocumulus". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114395.
Texto completoLes nuages stratiformes de basse altitude restent un des facteurs imprévisibles dans les simulations du climat futur. Malgré leur rôle important dans le budget radiatif terrestre et le grand nombre de campagnes de terrain dédiées, plusieurs procédés à l'échelle nuageuse dans les stratocumulus marins demeurent mal représentés. Le déploiement dans les Açores d'un laboratoire mobile du programme « Atmospheric Radiation Measurement » pendant 19 mois a fourni l'ensemble de données d'observation au sol sur les nuages de couche limite marine le plus long et le plus complet à ce jour. Le premier objectif de ce projet fut la documentation de la fréquence d'apparition de différents systèmes de nuages et de précipitations dans les Açores en utilisant une combinaison de mesures passives et actives. L'analyse indique que, même si des nuages étaient souvent observés (près de 80 % du temps), en particulier dans la couche limite (~50 %), une couverture de stratocumulus seul persistait rarement plus d'une journée. En fait, de nombreux stratocumulus furent observés avec des cumulus en dessous. Ceci est lié à l'état découplé de la couche limite quasi-constant dans les Açores, contrairement à ce qui a été observé dans les stratocumulus du Pacifique. 35 cas de couverture d'un stratocumulus persistant principalement seul furent sélectionnés pour une analyse approfondie. Les résultats incluent des similarités avec d'autres études (par exemple, une couverture maximale durant la nuit, un besoin de nuages plus épais pour bruiner et l'importance du refroidissement radiatif au haut des nuages durant la nuit), ainsi que des différences (par exemple, les structures cohérentes représentent une plus petite fraction du flux ascendant de masse). Le deuxième objectif de ce projet fut de revisiter la détection des particules de bruine dans les stratocumulus en utilisant les observations radar. Tout d'abord, les distributions de tailles des gouttelettes de nuage et de bruine sont liées théoriquement aux mesures radar, en incluant les effects dynamiques. Ensuite, un modèle direct de spectres Doppler radar fut développé pour tester la sensibilité des mesures radar à des modifications de la contribution de la bruine. Finalement, un simple modèle 1-D à l'état d'équilibre fut exploité pour simuler la croissance de la bruine pendant sa descente dans un nuage, en utilisant le modèle direct pour relier de nouveau les données sortantes avec les observations radar. En utilisant cette combinaison de modèles, quelques caractéristiques de l'évolution de la bruine observées à l'intérieur de nuages stratocumulus continental et maritime furent examinées avec succès. Dans l'ensemble, il fut déterminé que l'asymétrie d'un spectre Doppler radar est un bon indicateur de la présence de jeunes gouttelettes de bruine, alors qu'un seuil de réflectivité ou de vitesse Doppler indique le changement de domination dans le spectre Doppler se produisant quand la bruine est bien développée. Le troisième et final objectif de ce projet fut de revisiter un autre défi de longue date : le recouvrement de propriétés microphysiques des nuages en utilisant une combinaison de mesures radar et radiométriques. Une nouvelle technique fut développée pour retrouver la distribution de tailles des particules nuageuses, en ajoutant un modèle microphysique de condensation dans des conditions de supersaturation en équilibre à une méthode populaire de recouvrement. Les résultats semblent raisonnables pour deux stratocumulus marins ne bruinant pas et la profondeur optique dérivée pour ces nuages se compare bien avec celle dérivée indépendamment avec un autre instrument. Les erreurs de recouvrement furent également estimées, démontrant la valeur ajoutée de la nouvelle technique.
Wang, Zhen y Zhen Wang. "Interactions Between Atmospheric Aerosols and Marine Boundary Layer Clouds on Regional and Global Scales". Diss., The University of Arizona, 2018. http://hdl.handle.net/10150/626640.
Texto completoMorales, Betancourt Ricardo. "On the representation of sub-grid scale phenomena and its impact on clouds properties and climate". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50373.
Texto completo