Dissertations / Theses on the topic 'Cloud microphysic'
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BHOWMICK, TARAPRASAD. "A numerical investigation of a few problems in cloud microphysics." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2868592.
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Ovtchinnikov, Mikhail. "An investigation of ice production mechanisms using a 3-D cloud model with explicit microphysics /." Full-text version available from OU Domain via ProQuest Digital Dissertations, 1997.
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David, 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.
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Orographically-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.
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Williams, Robyn D. "Studies of Mixed-Phase Cloud Microphysics Using An In-Situ Unmanned Aerial Vehicle (UAV) Platform." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7252.
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Cirrus clouds cover between 20% - 50% of the globe and are an essential
component in the climate. The improved understanding of ice cloud
microphysical properties is contingent on acquiring and analyzing in-situ and
remote sensing data from cirrus clouds. In ??u observations of microphysical
properties of ice and mixed-phase clouds using the mini-Video Ice Particle Sizer
(mini-VIPS) aboard robotic unmanned aerial vehicles (UAVs) provide a promising
and powerful platform for obtaining valuable data in a cost-effective, safe, and
long-term manner.
The purpose of this study is to better understand cirrus microphysical
properties by analyzing the effectiveness of the mini-VIPS/UAV in-situ platform.
The specific goals include:
(1) To validate the mini-VIPS performance by comparing the mini-VIPS data
retrieved during an Artic UAV mission with data retrieved from the millimeterwavelength
cloud radar (MMCR) at the Barrow ARM/CART site.
(2) To analyze mini-VIPS data to survey the properties of high latitude mixedphase
clouds
The intercomparison between in-situ and remote sensing measurements
was carried out by comparing reflectivity values calculated from in-situ
measurements with observations from the MMCR facility. Good agreement
between observations and measurements is obtained during the time frame
where the sampled volume was saturated with respect to ice. We also have
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shown that the degree of closure between calculated and observed reflectivity
strongly correlates with the assumption of ice crystal geometry observed in the
mini-VIPS images. The good correlation increases the confidence in mini-VIPS
and MMCR measurements. Finally, the size distribution and ice crystal geometry
obtained from the data analysis is consistent with published literature for similar
conditions of temperature and ice supersaturation.
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Young, Gillian. "Understanding the nucleation of ice particles in polar clouds." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/understanding-the-nucleation-of-ice-particles-in-polar-clouds(4f80f81b-ed06-480a-944b-6e3594ba8471).html.
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Arctic clouds are poorly represented in numerical models due to the complex, small-scale interactions which occur within them. Modelled cloud fractions are often significantly less than observed in this region; therefore, the radiative budget is not accurately simulated and forecasts of the melting cryosphere are fraught with uncertainty. Our ability to accurately model Arctic clouds can be improved through observational studies. Recent in situ airborne measurements from the springtime Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign are presented in this thesis to improve our understanding of the cloud microphysical interactions unique to this region. Aerosol-cloud interactions - where aerosol particles act as ice nucleating particles (INPs) or cloud condensation nuclei (CCN) - are integral to the understanding of clouds on a global scale. In the Arctic, uncertainties caused by our poor understanding of these interactions are enhanced by strong feedbacks between clouds, the boundary layer, and the sea ice. In the Arctic spring, aerosol-cloud interactions are affected by the Arctic haze, where a stable boundary layer allows aerosol particles to remain in the atmosphere for long periods of time. This leads to a heightened state of mixing in the aerosol population, which affects the ability of particles to act as INPs or CCN. Aerosol particle compositional data are presented to indicate which particles are present during the ACCACIA campaign, and infer how they may participate in aerosol-cloud interactions. Mineral dusts (known INPs) are identified in all flights considered, and the dominating particle classes in each case vary with changing air mass history. Mixed particles, and an enhanced aerosol loading, are identified in the final case. Evidence is presented which suggests these characteristics may be attributed to biomass burning activities in Siberia and Scandinavia. Additionally, in situ airborne observations are presented to investigate the relationship between the Arctic atmosphere and the mixed-phase clouds - containing both liquid cloud droplets and ice crystals - common to this region. Cloud microphysical structure responds strongly to changing surface conditions, as strong heat and moisture fluxes from the comparatively-warm ocean promote more turbulent motion in the boundary layer than the minimal heat fluxes from the frozen sea ice. Observations over the transition from sea ice to ocean show that the cloud liquid water content increases four-fold, whilst ice crystal number concentrations, N_ice, remain consistent at ~0.5/L. Following from this study, large eddy simulations are used to illustrate the sensitivity of cloud structure, evolution, and lifetime to N_ice. To accurately model mixed-phase conditions over sea ice, marginal ice, and ocean, ice nucleation must occur under water-saturated conditions. Ocean-based clouds are found to be particularly sensitive to N_ice, as small decreases in N_ice allow glaciating clouds to be sustained, with mixed-phase conditions, for longer. Modelled N_ice also influences precipitation development over the ocean, with either snow or rain depleting the liquid phase of the simulated cloud.
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Mineart, Gary M. "Multispectral satellite analysis of marine stratocumulus cloud microphysics." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/23321.
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Variations in marine stratocumulus cloud microphysics during FIRE IFO 1987 are observed and analyzed through the use of NOAA-9/10 AVHRR satellite data and aircraft in-cloud measurements. The relationships between channel 3 reflectance and cloud microphysical properties are examined through model reflectances based on Mie theory and the delta-Eddington approximation, and reveal a channel 3 reflectance dependence on cloud droplet size distribution. Satellite observations show significant regions of continental influence over the ocean through higher channel 3 reflectances resulting from the injection of continental aerosols and the associated modification of cloud droplet characteristics. Channel 3 reflectance gradients across individual cloud elements correspond to radially varying cloud droplet size distributions within the elements. Various mesoscale and microscale features such as ship stack effluent tracks and pollution sources are observed in the data. Correlations between reflectance values and aircraft measurements illustrate the potential of estimating cloud droplet size distribution and marine atmospheric boundary layer aerosol composition and concentration through use of satellite data. Such an estimation technique may prove useful in determining climatic implications of cloud reflectance changes due to the influence of natural and man-made aerosol sources, and provide a means to assess the performance of boundary layer electro-optic systems. Keywords: Radiometry; Cloud physics. Theses. (edc) 24u
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Petch, Jonathan. "Modelling the interaction of clouds and radiation using bulk microphysical schemes." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308098.
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Pringle, Kirsty Jane. "Aerosol - cloud interactions in a global model of aerosol microphysics." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431991.
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Zuberi, 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.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.Vita.
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.
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Nichman, Leonid. "Optical measurements of the microphysical properties of aerosol and small cloud particles in the CLOUD project." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/optical-measurements-of-the-microphysical-properties-of-aerosol-and-small-cloud-particles-in-the-cloud-project(ad792d0c-90d1-4704-b666-b75d284b40fe).html.
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Clouds play an important role in precipitation, solar radiation budget and electrification of Earth's atmosphere. The presence of small ice crystals in clouds and their morphology can complicate parametrisation and climate modelling, consequently leading to a net cooling feedback on climate. In situ airborne measurements provide single particle characterisation with high temporal and spatial resolution allowing better understanding of atmosphericprocesses of ice nucleation and growth. Simulations of the preindustrial clouds and accurate characterisation and comparison of the instruments require a well-controlled and often pristine environment. The experimental chamber setup allows simulations of these and other conditions. The microphysical features of the micrometric ice particles in clouds were examined in a laboratory setup, at numerous sub-zero temperatures [-10 to -50 ⁰C]. The following instruments were sampling the content of the CLOUD chamber air volume: Cloud and Aerosol Spectrometer with Polarisation (CASPOL), Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition), 3-View Cloud Particle Imager (3V-CPI), and the Scattering-Intensity-Measurements-for-the-Optical-detectioN-of-icE (SIMONE-Junior). Cluster analysis was applied to the data collected with CASPOL and compared with results from the other probes. We were able to discriminate and map the aerosol and cloud particles in the pristine chamber environment using polarisation ratios (Dpol/Backscatter and Dpol/Forwardscatter) of the scattered light. We demonstrate the sensitivity of the instruments in detecting secondary organic aerosol (SOA) phase transitions. Then, we show the ability of the viscous SOA to nucleate ice in a series of SPectrometer for Ice Nuclei (SPIN) measurements. The detected viscous SOA ice nucleation efficiency may affect global modelling and estimations of ice water content in the atmosphere. Subsequently, the analysis and discrimination technique used in the CLOUD chamber was applied to airborne measurements to test its efficiency and to retrieve the composition of clouds. Data from four flight campaigns on board of the FAAM BAe-146 were analysed: Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA), COnvective-Precipitation-Experiment (COPE) in south England, CIRrus Coupled Cloud-Radiation EXperiment (CIRCCREX), and PIKNMIX in Scotland. In these and other flights, we were able to identify unique clusters such as salts, minerals, organics, volcanic ash, water and ice, confirming some of the offline laboratory elemental analysis results, and providing complementary information. Single particle polarisation measurements were compared with bulk depolarisation, diffraction patterns, and imaging. Most of the optical instruments still suffer from ambiguity in phase derivation (i.e. water/ice) of optically spherical small shapes. We discuss some of the limitations of optical cloud particle discrimination in different ambient conditions and offer possible solutions to reduce the uncertainty, e.g., surface complexity derivation from scatteringpatterns. Our findings will help to develop better instruments and improve the models which are used for weather forecasts and climate change predictions.
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Painemal, David. "Investigation of the Cloud Microphysics and Albedo Susceptibility of the Southeast Pacific Stratocumulus Cloud Deck." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/581.
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Marine stratocumulus cloud regimes exert a strong climatic influence through their high solar reflectivity. Human-induced changes in stratocumulus clouds, attributed to an increase of the aerosol burden (indirect effects), can be significant given the cloud decks proximity to the continents; nevertheless, the magnitude and the final climatic consequences of these changes are uncertain. This thesis investigates further the interactions between aerosols, cloud microphysics, regional circulation, and radiative response in the Southeast Pacific stratocumulus cloud deck, one of the largest and most persistent cloud regimes in the planet. Specifically, three different aspects are addressed by this thesis: The importance of the synoptic atmospheric variability in controlling cloud microphysical and radiative changes, a validation analysis of satellite retrievals of cloud microphysics from MOderate Resolution Imaging Spectroradiometer (MODIS), and the quantitative assessments of cloud aerosol interactions along with their associated radiative forcing using primarily aircraft remote sensing data. Synoptic and satellite-derived cloud property variations for the Southeast Pacific region associated with changes in coastal satellite-derived cloud droplet number concentration (Nd) are analyzed through a composite technique. MAX and MIN Nd composites are defined by the top and bottom terciles of daily area-mean Nd values over the Arica Bight, the region with the largest mean oceanic Nd, for the five October months of 2001, 2005, 2006, 2007, and 2008. The MAX-Nd composite is characterized by a weaker subtropical anticyclone and weaker winds than the MIN-Nd composite. Additionally, the MAX-Nd composite clouds over the Arica Bight are thinner than the MIN-Nd composite clouds, have lower cloud tops, lower near-coastal cloud albedos, and occur below warmer and drier free tropospheres. At 85˚W, the top-of-atmosphere shortwave fluxes are significantly higher (50%) for the MAX-Nd, with thicker, lower clouds and higher cloud fractions than for the MIN-Nd. The change in Nd at this location is small, suggesting that the MAX-MIN Nd composite differences in radiative properties primarily reflects synoptic changes. The ability of MODIS level 2 retrievals to represent the cloud microphysics is assessed with in-situ measurements of droplet size distributions, collected during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). The MODIS cloud optical thickness (t) correlates well with the in-situ values with a positive bias (1.42). In contrast, the standard 2.1 micron-derived MODIS cloud effective radius (r_e) is found to systematically exceed the in-situ cloud-top r_e, with a mean bias of 2.08 um. Three sources of errors that could contribute to the MODIS r_e positive bias are investigated further: the spread of the cloud droplet size distribution, the presence of a separate drizzle mode, and the sensor viewing angles. The sensor zenith viewing angles were found to have little impact, while the algorithm assumption about the cloud droplet spectra and presence of a precipitation mode could affect the retrievals but not by enough to fully explain the positive MODIS r_e bias. The droplet spectra effects account for r_e offsets smaller than 0.6 um, 0.9 um, and 1.6 um for non-drizzling, light-drizzling, and heavy-drizzling clouds respectively. An explanation for the observed MODIS bias is lacking although three-dimensional radiative effects were not considered. This investigation supports earlier studies documenting a similar bias, this time using data from newer probes. MODIS r_e and t were also combined to estimate a liquid water path (LWP) and Nd. A positive bias was also apparent in LWP, and attributed to r_e. However, when selected appropriate parameters a priori, the MODIS Nd estimate was found to agree the best with the insitu aircraft observations of the four MODIS variables. Lastly, the first aerosol indirect effect (Twomey effect) is explicitly investigated with VOCALS-REx observations, collected during three daytime research flights (Nov 9, 11, and 13), utilizing an aerosol-cloud interactions metric, and defined as ACI=dln(t)/dln(Na), with Na corresponding to the accumulation mode aerosol concentration, t derived from a broadband pyranometer, and ACI binned by cloud LWP derived from a millimeter-wavelength radiometer. Aircraft remote sensing estimates of the ACI, during sub-cloud transects, show that the cloud aerosol-interactions are strong and close to the maximum theoretical value for thin clouds, with a decrease of ACI with LWP. Although an explanation for the dependence of ACI on LWP is lacking, we found that a decrease in ACI with LWP is associated with decreases in both surface meridional winds and Nd. Similar to ACI, albedo fractional changes due to Nd fractional changes also tended to be smaller for higher LWPs, but with an overall radiative forcing larger than conservative global estimates obtained in global circulation models. The findings of this thesis emphasize the strong stratocumulus albedo response to an aerosol perturbation and its dependence on the regional scale atmospheric configuration. The results presented here can be used as a benchmark for testing regional and climate models, as well as helping to improve the current parameterizations of the first aerosol indirect effect.
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Morales, 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.
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This thesis addresses a series of questions related to the problem of achieving reliable and physically consistent representations of aerosol-cloud interaction in global circulation models (GCM). In-situ data and modeling tools are used to develop and evaluate novel parameterization schemes for the process of aerosol activation for applications in GCM simulations. Atmospheric models of different complexity were utilized, ranging from detailed Lagrangian parcel model simulations of the condensational growth of droplets, to one-dimensional single column model with aerosol and cloud microphysics, and finally GCM simulations performed with the Community Atmosphere Model (CAM). A scheme for mapping the sub-grid scale variability of cloud droplet number concentrations (CDNC) to a number of microphysical process rates in a GCM was tested, finding that neglecting this impact can have substantial influences in the integrated cloud properties. A comprehensive comparison and evaluation of two widely used, physically-based activation parameterizations was performed in the framework of CAM5.1. This was achieved by utilizing a numerical adjoint sensitivity approach to comprehensively investigate their response under the wide range of aerosol and dynamical conditions encountered in GCM simulations. As a result of this, the specific variables responsible for the observed differences in the physical response across parameterizations are encountered, leading to further parameterization improvement.
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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.
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Despite their importance in Earth's radiation budget and atmospheric models, Arctic clouds remain poorly documented and understood. The deployment of a cloud radar and a high spectral resolution lidar at Eureka (80°N) in August 2005 offers a unique data set for the study of Arctic clouds. In this project, synergetic retrievals were developed and applied to two years of data in order to provide a first climatology of the clouds and their microphysics at this remote location. Results show an annual cycle in cloud coverage. They are mostly detected in the low levels or in single-layer, especially in winter due to a temperature inversion and cloud top radiative cooling. An analysis of the winds also demonstrated that different wind directions relate to different cloudiness conditions, while a strong channelling from the topography is present in the low levels. Moreover, liquid phase particles were detected all year round, with a minimum occurrence in winter due to colder temperatures. Turbulence and high relative humidity seem to maintain supercooled liquid, especially when ice crystals were also present. Precipitation was mostly identified during summer months, often in the form of virga, although falling snow might have been missed due to the difficulty to distinguish it from glaciated clouds. Finally, results show that satellite validation is possible using Eureka's data, but only under homogeneous conditions and when the instruments characteristics (like the sampling and sensitivity) are taken into account.Malgré 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
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Raabe, Armin, and Nicole Mölders. "Evaluation of cloudiness and snowfall simulated by a semi-spectral and a bulk-parameterization scheme of cloud microphysics for the passage of a Baltic heat cyclone." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-213950.
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The differences in the concepts of two different parameterizations of cloud microphysics are analyzed. Simulations alternatively applying these parameterizations are performed for a Baltic heat cyclone event. The results of the simulations are compared to each other as well as to observed distributions of cloudiness and snowfall. The main differences between the simulated distributions result from the assumptions on ice, the ice classes, and size distributions of the cloud and precipitating particles. Both schemes succeeded in predicting the position and the main structure of the main cloud and snowfall fields. Nevertheless, the more convective type parameterization overestimates, while the other one underestimates snowfallDie Unterschiede in den Konzepten zweier unterschiedlicher Parametrisierungen der Wolkenmikrophysik werden analysiert. Die Ergebnisse der Simulationen werden miteinander und mit den beobachteten Wolken- und Schneeverteilungen für eine Baltische Wärmezyklone verglichen. Die wesentlichen Unterschiede in den berechneten Verteilungen resultieren aus den verschiedenen Annahmen über Wolkeneis, die Eisklassen und die Größenverteilungen der Wolken- und Niederschlagspartikel. Beide Schemata sagen die Position und die wesentlichen Strukturen der Wolken- und Schneeverteilungen erfolgreich vorher. Dennoch überschätzt das eher konvektive Schema den Schneefall, während das andere ihn unterschätzt
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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.
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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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Schmidt, Jörg. "Dual-field-of-view Raman lidar measurements of cloud microphysical properties." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-150408.
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Im Rahmen der vorliegenden Arbeit wurde eine neuartige Lidartechnik in ein leistungsstarkes Lidar-System implementiert. Mit Hilfe des realisierten Aufbaus wurden Aerosol-Wolken-Wechselwirkungen in Flüssigwasserwolken über Leipzig untersucht.
Die angewandte Messmethode beruht auf der Detektion von Licht, das an Wolkentröpfchen mehrfach in Vorwärtsrichtung gestreut und an Stickstoffmolekülen inelastisch zurückgestreut wurde. Dabei werden zwei Gesichtsfelder unterschiedlicher Größe verwendet. Ein Vorwärtsiterations-Algorithmus nutzt die gewonnenen Informationen zur Ermittlung von Profilen wolkenmikrophysikalischer Eigenschaften. Es können der Extinktionskoeffizient, der effektive Tröpfchenradius, der Flüssigwassergehalt sowie die Tröpfchenanzahlkonzentration bestimmt werden. Weiterhin wird die exakte Erfassung der Wolkenunterkantenhöhe durchdie eingesetzte Messtechnik ermöglicht. Darüber hinaus ist die Bestimmung von Aerosoleigenschaften mit dem eingesetzten Lidargerät möglich.
Die Qualität des realisierten Messaufbaus wurde geprüft und eine Fehleranalyse durchgeführt. Unter anderem wurde der aus einer Wolkenmessung bestimmte Flüssigwassergehalt mit einem Mikrowellen-Radiometer bestätigt.
Anhand von Fallbeispielen konnte das Potential dieser Messtechnik demonstriert werden. Die Bedeutung von Profilinformationen von Wolkeneigenschaften für die Untersuchung von Aerosol-Wolken-Wechselwirkungen wurde gezeigt. Weiterhin wurde mit Hilfe eines Doppler-Windlidars der Einfluss der Vertikalwindgeschwindigkeit auf Wolkeneigenschaften und damit Aerosol-Wolken-Wechselwirkungen verdeutlicht.
Neunundzwanzig Wolkenmessungen wurden für eine statistische Auswertung bezüglich Aerosol-Wolken-Wechselwirkungen genutzt. Dabei konnte erstmalig die Abhängigkeit von Aerosol-Wolken-Wechselwirkungen von der Wolkeneindringtiefe untersucht werden. Es wurde festgestellt, dass diese auf die untersten 70m von Wolken beschränkt sind. Weiterhin wurden deutlich stärkere Aerosol-Wolken-Wechselwirkungen in Wolkengebieten festgestellt, die von Aufwinden dominiert werden.
Für der Quantifizierung der Stärke von Aerosol-Wolken-Wechselwirkungen wurden ACIN-Werte genutzt, welche den Zusammenhang zwischen der Tröpfchenanzahlkonzentration und dem Aerosol-Extinktionskoeffizienten beschreiben. Dabei wurde zwischen der Untersuchung der entsprechenden mikrophysikalischen Prozesse und deren Bedeutung für die Wolkenalbedo und damit dem Strahlungsantrieb der Wolken unterschieden. Für die erstgenannte Zielstellung wurde ein ACIN-Wert von 0.80 +/- 0.40 ermittelt, für Letztere 0.13 +/- 0.07.
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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.
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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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Taylor, Jonathan P. "The remote retrieval of stratiform water cloud radiative and microphysical properties." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357173.
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Sheyko, Benjamin Andrew. "The development and application of sensitivity tools for investigating microphysical processes in atmospheric models." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54248.
Full textAbstract:
We present the development of the adjoint of a physically based cirrus formation parameterization that computes the sensitivity of formed crystal number concentration to numerous model variables (e.g., updraft velocity, soluble aerosol geometric mean diameter and number concentration, insoluble aerosol geometric mean diameter and number concentration, and ice deposition coefficient). The adjoint is demonstrated in the CESM Community Atmosphere Model Version 5.1, where sensitivity information is computed and used to quantify which variables are most responsible for modeled variability in formed crystal number concentration. The sensitivity of formed crystal number concentration to updraft velocity is positive and largest over the tropics where regions of deep convection are collocated with large sulfate number concentrations. Sensitivity to sulfate number concentration is largest over the tropics where updraft cooling is sufficient and sulfate number concentration is low, pointing to a sulfate limited regime. Outside of the tropics, crystal production is dominated by heterogeneous freezing; unexpectedly, sensitivities to insoluble aerosol number concentration for accumulation and coarse mode dust, black carbon, and organic carbon are negative in sign here. This is a result of infrequent, anomalously high updraft velocity events causing shifts in the dominant modes of freezing which act to bias sensitivity information when annually averaged. Updraft velocity is responsible for ~95% of the variability in formed crystal number concentration in the high latitudes of the Northern Hemisphere. In the tropics, sulfate number concentration controls variability in formed crystal number concentration since crystal production here is sulfate limited. Insoluble aerosol species play a secondary role in influencing the variability of crystal concentrations; coarse mode dust is the largest contributor to crystal number variability at nearly 60%, although the spatial extent of this influence is small and concentrated over highly localized dust events. When globally averaged, nearly 90% of the variability in crystal number concentration can be described by only updraft velocity, sulfate number, temperature, and coarse mode dust number concentration. Although these results depend on parameter assumptions, the robustness of the underlying physics of the cirrus formation parameterization used throughout this work suggests that this approach can be a powerful method for efficiently identifying the origin of microphysical dependencies within large scale atmospheric simulations.
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Small, Jennifer D. "Observational studies of the microphysics and dynamics of warm cumulus clouds /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2009. http://uclibs.org/PID/11984.
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Khairoutdinov, Marat. "Large-eddy simulation of stratocumulus-topped boundary layer with an explicit and a new bulk microphysics scheme /." Full-text version available from OU Domain via ProQuest Digital Dissertations, 1997.
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Rémillard, 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.
Full textAbstract:
Low-level stratiform clouds remain one of the wildcards in future climate simulations. Despite their important role in the earth's radiation budget and the large number of dedicated field campaigns, several cloud-scale processes in marine stratocumulus clouds remain misrepresented. The 19-month-long deployment of the Atmospheric Radiation Measurement Program Mobile Facility in the Azores provided the longest and most comprehensive ground-based observational dataset of marine boundary layer clouds to date. The first objective of this project was the documentation of the frequency of occurrence of different cloud and precipitation systems in the Azores using a combination of passive and active measurements. The analysis indicates that, even though clouds were often observed (close to 80 % of the time), especially in the boundary layer (~50 %), a single-layer stratocumulus coverage rarely persisted more than a day. In fact, many stratocumulus clouds were observed to have cumulus clouds underneath them. This is linked to the nearly constant decoupled state of the boundary layer in the Azores, contrary to what has been observed in the Pacific decks. 35 cases of mostly single-layer persisting stratocumulus coverage were selected for further analysis. Results include similarities with other studies (e.g., maximum coverage at night, thicker clouds needed to drizzle, and importance of cloud-top radiative cooling at night), as well as differences (e.g., coherent structures account for a smaller fraction of the updraft mass flux). The second objective of this project was to revisit the detection of drizzle-size particles in stratocumulus clouds using radar observations. First, the cloud and drizzle size distributions are related theoretically to the radar measurements, including the effects of the dynamics. Then, a forward radar Doppler spectra model was developed to test the sensitivity of the radar measurements to modifications of the drizzle contribution. Finally, a simple 1-D steady-state model was exploited to simulate drizzle growth as it falls in a cloud, using the forward model to link the output back to the radar observations. Using that combination of models, some observed features of the drizzle evolution inside continental and maritime stratocumulus clouds were successfully investigated. Overall, it was found that the skewness of a radar Doppler spectrum is a good indicator of the presence of early drizzle droplets, while a reflectivity or Doppler velocity threshold indicates the change in dominance in the Doppler spectrum occurring when drizzle is well developed. The third and final objective of this project was to revisit another long-standing challenge: the retrieval of cloud microphysical properties using a combination of radar-radiometer measurements. A new technique was developed to retrieve the cloud particle size distribution in stratocumulus clouds, adding a microphysical condensational model under steady-state supersaturation conditions to a common retrieval method. The results appear reasonable in two nondrizzling marine stratocumulus clouds, and the derived cloud optical depth compares well with the one derived independently with another instrument. The errors of the retrievals were also estimated, demonstrating the added value of the new technique.Les 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.
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Sehili, Aissa Mounir. "Coupling between complex multiphase chemistry and detailed microphysics in a size resolved cloud model." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=979424763.
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Nogherotto, Rita. "A numerical framework for multiple phase cloud microphysics in regional and global atmospheric models." Doctoral thesis, Università degli studi di Trieste, 2015. http://hdl.handle.net/10077/11140.
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2012/2013The Regional Climate Model RegCM4 (Giorgi et al., 2012) treats nonconvective clouds and precipitation following the Subgrid Explicit SUBEX param- eterization (Pal et al., 2000). This scheme includes a simple representation for the formation of raindrops and solves diagnostically the precipitation: rain forms when the cloud water content exceeds the autoconversion threshold, that is an increasing function of the temperature and assumes different values over the land and over the ocean to account for the difference in number of the cloud condensation nuclei over continental and oceanic regions. The SUBEX scheme does not account for the presence of clouds ice, and the fraction of ice is diagnosed as a function of temperature in the radiation scheme. Due to the increasing emphasis on cloud representations in the climate community and the forthcoming increasing resolution due to the inclusion, in the close future, of a non-hydrostatic compressible core, the treatment of the ice microphysics and a prognostic representation of the precipitation is required in RegCM4. This thesis presents the new parameterization for stratiform cloud microphysics and precipitation implemented in RegCM4. The approach of the new parameterization is based on an implicit numerical framework recently developed and implemented into the ECMWF operational forecasting model (Tiedtke, 1993). The new parameterization solves 5 prognostic equations for the water vapour, the liquid water, the rain, the ice and the snow mixing ratios. It allows a proper treatment of mixed-phase clouds and a more physically realistic representation of the precipitation as it is no more an instantaneous response to the microphysical processes occurring in clouds and is subjected to the horizontal advection. A first discussion of the results contains an evaluation of the vertical distributions of the main microphysical quantities, such as the liquid and ice water mixing ratios and the relative fractions. It also presents a series of sensitivity tests to understand how the moisture and radiation quantities respond to the variation of the microphysical parameters used in the scheme, such as the fall speeds of the falling categories, the autoconversion scheme and the evaporation coefficient. Cloud properties are afterwards evaluated through the implementation for RegCM4 of the new cloud evaluation COSP tool (Bodas-Salcedo et al., 2011), developed by the Cloud Feedback Model In- tercomparison Project (CFMIP), that facilitates the comparison of simulated clouds with observations from passive and active remote sensing by diagnosing from model outputs the quantities that would be observed from satellites if they were flying above an atmosphere similar to that predicted by the model. Different hypothesis are presented to explain the reasons for RegCM4 biases in representing different types of clouds over the tropical band and new prospectives for the future investigations designed to answer to the open questions are outlined.
XXVI Ciclo
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Dearden, Christopher. "Exploring the effects of microphysical complexity in numerical simulations of liquid and mixed-phase clouds." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/exploring-the-effects-of-microphysical-complexity-in-numerical-simulations-of-liquid-and-mixedphase-clouds(abe4b249-a608-4a42-819c-962e2114d1ba).html.
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This thesis forms a NERC funded CASE studentship with the Met Office, whose aim is to investigate the treatment of cloud microphysical processes in numerical models, with a particular focus on exploring the impacts and possible benefits of microphysical complexity for the purpose of simulating clouds and precipitation. The issue of complexity is an important one in numerical modelling in order to maintain computational efficiency, particularly in the case of operational models. The latest numerical modelling tools are utilised to perform simulations of cloud types including idealised trade wind cumulus, orographic wave cloud and wintertime shallow convective cloud. Where appropriate, the modelling results are also validated against observations from recent field campaigns. The Factorial Method is employed as the main analysis tool to quantify the effect of microphysical variables in terms of their impact on a chosen metric. Ultimately it is expected that the techniques and results from this thesis will be used to help inform the future development of cloud microphysics schemes for use in both cloud resolving and operational models. This is timely given the current plans to upgrade the microphysics options available for use within the Met Office Unified Model. For an idealised warm cloud, it is shown that different bin microphysics schemes can produce different results, and therefore additional microphysical complexity does not necessarily ensure a more consistent simulation. An intercomparison of bin microphysics schemes in a 1-D column framework is recommended to isolate the origin of the discrepancies. In relation to the mixed-phase wave cloud, model simulations based on an adaptive treatment of ice density and habit struggled to reproduce the observed ice crystal growth rates, highlighting the need for further laboratory work to improve the parameterization of ice growth by diffusion within the sampled temperature regime. The simulations were also found to be largely insensitive to values of the deposition coefficient within the range of 0.1 to 1.0. Results from a mesoscale modelling study of shallow wintertime convection demonstrate the importance of the representation of dynamical factors that control cloud macrostructure, and how this has the potential to overshadow any concerns of microphysical complexity. Collectively, the results of this thesis place emphasis on the need to encourage more synergy between the dynamics and microphysics research communities in order to improve the future performance of numerical models, and to help optimise the balance between model complexity and computational efficiency.
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Koch, Dorothy, Yves Balkanski, Susanne E. Bauer, Richard C. Easter, Sylvaine Ferrachat, Steven J. Ghan, Corinna Hoose, et al. "Soot microphysical effects on liquid clouds, a multi-model investigation." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184919.
Full textAbstract:
We use global models to explore the microphysical effects of carbonaceous aerosols on liquid clouds. Although absorption of solar radiation by soot warms the atmosphere, soot may cause climate cooling due to its contribution to cloud condensation nuclei (CCN) and therefore cloud brightness. Six global models conducted three soot experiments;
four of the models had detailed aerosol microphysical schemes. The average cloud radiative response to biofuel soot (black and organic carbon), including both indirect and semi-direct effects, is −0.11Wm−2, comparable in size but opposite in sign to the respective direct effect. In a more idealized fossil fuel black carbon experiment, some models
calculated a positive cloud response because soot provides a deposition sink for sulfuric and nitric acids and secondary organics, decreasing nucleation and evolution of viable CCN. Biofuel soot particles were also typically assumed to be larger and more hygroscopic than for fossil fuel soot and therefore caused more negative forcing, as also found in previous studies. Diesel soot (black and organic carbon) experiments had relatively smaller cloud impacts with five of the models <±0.06Wm−2 from clouds. The results are subject to the caveats that variability among models, and regional and interrannual variability for each model, are large.
This comparison together with previously published results stresses the need to further constrain aerosol microphysical schemes. The non-linearities resulting from the competition of opposing effects on the CCN population make it difficult to extrapolate from idealized experiments to likely impacts of realistic potential emission changes.
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Koch, Dorothy, Yves Balkanski, Susanne E. Bauer, Richard C. Easter, Sylvaine Ferrachat, Steven J. Ghan, Corinna Hoose, et al. "Soot microphysical effects on liquid clouds, a multi-model investigation." Copernicus Publication, 2011. https://ul.qucosa.de/id/qucosa%3A13767.
Full textAbstract:
We use global models to explore the microphysical effects of carbonaceous aerosols on liquid clouds. Although absorption of solar radiation by soot warms the atmosphere, soot may cause climate cooling due to its contribution to cloud condensation nuclei (CCN) and therefore cloud brightness. Six global models conducted three soot experiments;
four of the models had detailed aerosol microphysical schemes. The average cloud radiative response to biofuel soot (black and organic carbon), including both indirect and semi-direct effects, is −0.11Wm−2, comparable in size but opposite in sign to the respective direct effect. In a more idealized fossil fuel black carbon experiment, some models
calculated a positive cloud response because soot provides a deposition sink for sulfuric and nitric acids and secondary organics, decreasing nucleation and evolution of viable CCN. Biofuel soot particles were also typically assumed to be larger and more hygroscopic than for fossil fuel soot and therefore caused more negative forcing, as also found in previous studies. Diesel soot (black and organic carbon) experiments had relatively smaller cloud impacts with five of the models <±0.06Wm−2 from clouds. The results are subject to the caveats that variability among models, and regional and interrannual variability for each model, are large.
This comparison together with previously published results stresses the need to further constrain aerosol microphysical schemes. The non-linearities resulting from the competition of opposing effects on the CCN population make it difficult to extrapolate from idealized experiments to likely impacts of realistic potential emission changes.
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Riley, Emily Marie. "A Global Survey of Clouds by CloudSat." Scholarly Repository, 2009. http://scholarlyrepository.miami.edu/oa_theses/198.
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With the launch of CloudSat, direct observations of cloud vertical structure became possible on the global scale. This thesis utilizes over two years of CloudSat data to study large-scale variations of clouds. We compose a global data set of contiguous clouds (echo objects, EOs) and the individual pixels comprising each EO. For each EO many attributes are recorded. EOs are categorized according to cloud type, time of day, season, surface type, and region. From the categorization we first look at gross global climatology of clouds. Maps of cloud cover are subdivided by EO (cloud) type, and results compare well with previous CloudSat work. The seasonality of cloud cover is also examined. Focus topics studied in this thesis include: (1) mid-level clouds, (2) stratocumulus clouds, and (3) clouds across the Madden-Julian Oscillation (MJO). The mid-level cloud work found an unexpected frequency peak in EO top heights between 7-8 km in the tropics, further shown to correspond to a global peak in EO top temperature between -15°C ? -20°C. Hypotheses are discussed regarding cause of this feature. Stratocumulus clouds are defined as low-level (tops < 4.5 km), wide (width > 11 km) EOs. Stratocumulus cloud cover agrees (with understandable differences) with other estimates (ISCCP and CALIPSO). The seasonal cycle of stratocumulus over the main stratocumulus decks is examined. The Peruvian and Namibian decks have increased cloud cover in austral spring in 2007 vs. 2006, corresponding sensibly to sea surface temperature differences and changes in lower static stability. Looking at rain and drizzle statistics, wider EOs are found to drizzle more. Clouds across the MJO are defined relative to temporally filtered OLR data. Cloud cover (volume) doubles (triples) from suppressed to active MJO phases, with some shifts of the relative contributions of different EO types from the front to back of the MJO. Pixel statistics in dBZ-height space correspond to these cloud-type shifts. High anvils and low clouds in front lead deep convection followed by relatively lower anvils in the back.
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Swann, Hugh. "The development and validation of a microphysics scheme for cloud resolving model simulations of deep convection." Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339515.
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Vant-Hull, Brian. "Radiative and cloud microphysical effects of forest fire smoke over North America and Siberia." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7423.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Atmospheric and Oceanic Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Kinney, Jacqueline Anne. "Retrieval of optical and microphysical properties of ice clouds using Atmospheric Radiation Measurement (ARM) data." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2524.
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The research presented here retrieves the cloud optical thickness and particle
effective size of cirrus clouds using surface radiation measurements obtained during the
Atmospheric Radiation Measurement (ARM) field campaign. The algorithm used is
based on a method proposed by Yang et al. (2005). The research examines single-layer
ice clouds in the midlatitude and polar regions. The retrieved information in the
midlatitudes is then verified using retrievals from the Moderate-resolution Imaging
Spectroradiometer (MODIS) onboard the Terra and Aqua satellites.
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McGouldrick, Kevin Bartholomew. "Microphysics and radiative-dynamical feedback in the near infrared brightness features in the Venus clouds." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3273820.
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Nachbar, Mario Alexander [Verfasser], and Thomas [Akademischer Betreuer] Leisner. "The microphysics of mesospheric cloud formation on Earth and Mars - Laboratory experiments / Mario Alexander Nachbar ; Betreuer: Thomas Leisner." Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177252538/34.
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Nachbar, Mario [Verfasser], and Thomas [Akademischer Betreuer] Leisner. "The microphysics of mesospheric cloud formation on Earth and Mars - Laboratory experiments / Mario Alexander Nachbar ; Betreuer: Thomas Leisner." Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177252538/34.
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Raabe, Armin, and Nicole Mölders. "Evaluation of cloudiness and snowfall simulated by a semi-spectral and a bulk-parameterization scheme of cloud microphysics for the passage of a Baltic heat cyclone." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 12 = Meteorologische Arbeiten aus Leipzig ; 4 (1999), S. 59-70, 1999. https://ul.qucosa.de/id/qucosa%3A15107.
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The differences in the concepts of two different parameterizations of cloud microphysics are analyzed. Simulations alternatively applying these parameterizations are performed for a Baltic heat cyclone event. The results of the simulations are compared to each other as well as to observed distributions of cloudiness and snowfall. The main differences between the simulated distributions result from the assumptions on ice, the ice classes, and size distributions of the cloud and precipitating particles. Both schemes succeeded in predicting the position and the main structure of the main cloud and snowfall fields. Nevertheless, the more convective type parameterization overestimates, while the other one underestimates snowfall.Die Unterschiede in den Konzepten zweier unterschiedlicher Parametrisierungen der Wolkenmikrophysik werden analysiert. Die Ergebnisse der Simulationen werden miteinander und mit den beobachteten Wolken- und Schneeverteilungen für eine Baltische Wärmezyklone verglichen. Die wesentlichen Unterschiede in den berechneten Verteilungen resultieren aus den verschiedenen Annahmen über Wolkeneis, die Eisklassen und die Größenverteilungen der Wolken- und Niederschlagspartikel. Beide Schemata sagen die Position und die wesentlichen Strukturen der Wolken- und Schneeverteilungen erfolgreich vorher. Dennoch überschätzt das eher konvektive Schema den Schneefall, während das andere ihn unterschätzt.
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Lawless, Ryan Lee. "Sensitivity of the Mueller matrix to the optical and microphysical properties of cirrus clouds." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4323.
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An adding-doubling method is employed to calculate the reflected Stokes
parameters for cirrus cloud layers composed of different habits and effective sizes. The
elements of the Mueller matrix are determined from the reflected Stokes parameters by
considering four different incident polarization states. The sensitivity of these elements is
observed by comparing different ice crystal habits, effective sizes, and optical depth. The
Mueller elements are strongly dependent on habit. The three habits, aggregate, bullet
rosette, and plate, are observed and the
M12/M11,M43/M11 and M44/M11 elements are discussed. The wavelength used is 0.532õm, which is the lidar wavelength used on
the CALIPSO satellite. The linear depolarization ratio is also discussed. The method of
subtracting the two depolarization ratios, is noted as another way to possibly better distinguish ice crystal habits.
The sensitivity of the Mueller matrix to effective size is also observed. For three
size distributions, the Mueller elements indicate no strong dependence. This may be due
to the assumption of randomly oriented ice. Also, using an absorbing wavelength might
provide dependence. Finally, the Mueller elements are dependent on optical depth. For a
greater optical depth, the strength of reflection increases while the polarization decreases.
As the optical depth increases, any peak-like features become non-existent.
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Taufour, Marie. "Validation et amélioration du schéma microphysique à deux moments LIMA à partir des observations de la campagne de mesures HyMeX." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30325/document.
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La formation des systèmes convectifs est un processus complexe qui s'étend de l'échelle synoptique, avec la mise en place de circulations favorisant la convection, à la micro-échelle, avec les processus de formation et de croissance des hydrométéores. C'est aux échelles les plus fines que se concentre cette thèse dont l'objectif est d'étudier l'apport d'une microphysique complexe sur l'occurrence et la morphologie d'évènements fortement précipitants. La microphysique évaluée est celle du schéma LIMA, de type bulk à deux moments, capable de prendre en compte l'évolution d'une population d'aérosols multimodale et le traitement pronostique de son interaction avec les nuages et les précipitations. Dans un premier temps, l'apport de la microphysique de LIMA est évalué en comparaison à la microphysique bulk à un moment du schéma ICE3, moins sophistiqué et actuellement opérationnel à Météo-France dans le modèle AROME. Afin de mesurer l'apport de ce nouveau schéma sur la simulation de cas fortement précipitants tels que ceux qui touchent régulièrement le sud-est de la France à l'automne, deux cas d'étude de la campagne HyMeX ont été simulés avec Meso-NH et comparés aux nombreuses observations disponibles. Si l'évaluation des cumuls de précipitations montre un impact modéré de l'un ou l'autre des schémas microphysiques, l'écart est plus marqué en terme de composition et de structure des systèmes convectifs : la microphysique à 2 moments développe une structure verticale plus réaliste et introduit plus de variabilité sur les champs microphysiques. L'évaluation a aussi identifié des biais dans le schéma, notamment une surestimation des diamètres de gouttes de pluie. Des pistes d'amélioration de la microphysique de LIMA ont alors été proposées et évaluées sur les mêmes cas. Des tests de sensibilité à l'initialisation de la population d'aérosols ont ensuite été menés. Il s'avère que les aérosols n'affectent pas uniquement les hydrométéores primaires (gouttelettes d'eau nuageuse et cristaux de glace) mais aussi les autres hydrométéores, engendrant des impacts sur le développement des systèmes convectifs simulés, en termes de composition nuageuse et de précipitations. Les simulations avec une population d'aérosols réaliste initialisée à partir des analyses CAMS ont montré un impact modéré sur les cumuls de précipitations mais une amélioration plus significative de l'évolution temporelle du système (intensification, dissipation) et de la composition nuageuse, réduisant le diamètre des gouttes de pluie sur les cas d'étudeThe triggering and growth of Convective systems is a complex process that extends from the synoptic scale, with the establishment of atmospheric circulations promoting convection, to the microscale, with the formation and growth processes of hydrometeors. This PhD focuses on these finest scales and investigates the contribution of complex cloud-microphysics to the occurrence and morphology of heavy precipitation events. The two-moment microphysical scheme LIMA evaluated in this study takes into account the evolution of a multimodal aerosol population and the prognostic treatment of its interaction with liquid and ice clouds and precipitation. First, the contribution of LIMA is evaluated in comparison to the ICE3 one-moment bulk microphysical scheme, which is less sophisticated and currently operational in the AROME model at Météo-France. In order to measure the performance of this new scheme, two case studies of the HyMeX campaign were simulated with the Meso-NH model and compared to a wide variety of available measurements. The assessment of cumulative precipitation shows a moderate impact of each of these microphysical schemes, but the difference is more pronounced in terms of convective systems composition and structure: the two moment microphysics develops a more realistic vertical structure and introduces more microphysical variability. The evaluation also identified biases in the scheme (such as an overestimation of rain drop diameters). Some improvements to the implementation of LIMA were proposed and evaluated on the same cases. Then, the scheme is used to perform a sensitivity test to the aerosol population on the same case studies. Tests on the concentration of idealized populations have shown that aerosols do not only affect primary production of cloud droplets and ice crystals but also precipitating hydrometeors, causing impacts on the development of simulated convective systems in terms of cloud composition and generated precipitation. Simulations based on a realistic aerosol population initialized from CAMS analyses also showed a moderate impact on cumulative precipitation, but a more significant improvement on the temporal evolution of the system (intensification, dissipation) and cloud composition, leading to a reduction of rain drop diameters in the studied cases
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Targino, Admir Créso. "Regional studies of the optical, chemical and microphysical properties of atmospheric aerosols : Radiative impacts and cloud formation." Doctoral thesis, Stockholm University, Department of Meteorology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-740.
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Atmospheric particles are ubiquitous in the Earth’s atmosphere and have potential to influence atmospheric chemistry, visibility, global climate and human health, particularly downwind from major pollution sources. The main objective of this thesis was to investigate questions pertaining to the microphysical, chemical and optical properties of aerosol particles by using in situ data collected during four experiments carried out in different regions of the Northern Hemisphere.
The first two papers of this thesis reports on airborne measurements of the aerosol optical properties performed over the North Atlantic and the Los Angeles basin. Airmasses from Europe and North Africa are usually advected in over the North Atlantic, alternating with the background marine conditions. The results showed that the aerosols are not uniformly distributed in the area and variability in the aerosol fields occurs at sub-synoptic scales. It was also observed that the single scattering coefficient varied as the polluted plumes aged, suggesting a relationship between this quantity and transport time. The measurements performed around the Los Angeles basin showed that the area’s complex topography and local meteorological circulations exert a strong control on the distribution of the aerosol in the basin. Large spatio-temporal gradients in the aerosol optical properties were observed along a transect flown from the shore towards the mountains. Profiles flown over sites located on the mountains displayed a stratified configuration with elevated aerosol layers.
Airborne data of residual particles collected in orographic wave clouds over Scandinavia were analyzed using a single particle analysis technique. Mineral dust, organic aerosols and sea salt were the main group of particles identified. Residuals composed predominantly of mineral dust were found in glaciated clouds while organic residuals were found in liquid clouds. The results suggest that organic material may inhibit freezing and have considerable influence on supercooled clouds that form through heterogeneous pathways.
The partitioning of the aerosol particles between cloud droplets and interstitial air has been addressed in terms of their microphysical properties using data obtained at a mountain-top site in Sweden during a stratocumulus event. The results showed that the scavenging efficiency varied during the cloud event, and Aitken-mode particles were also efficiently scavenged in addition to accumulation-mode particles. It is hypothesized that alterations of the aerosol chemical composition occurred during the measurement period, modifying the hygroscopic nature of the particles and decreasing their activation diameter.
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Xie, Yu. "The effect of ice crystal surface roughness on the retrieval of ice cloud microphysical and optical properties." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5970.
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The effect of the surface roughness of ice crystals is not routinely accounted for in
current cloud retrieval algorithms that are based on pre-computed lookup libraries. In this
study, we investigate the effect of ice crystal surface roughness on the retrieval of ice
cloud effective particle size, optical thickness and cloud-top temperature. Three particle
surface conditions, smooth, moderately rough and deeply rough, are considered in the
visible and near-infrared channels (0.65 and 3.75 õm). The discrete ordinates radiative
transfer (DISORT) model is used to compute the radiances for a set of optical
thicknesses, particle effective sizes, viewing and illumination angles, and cloud
temperatures. A parameterization of cloud bi-directional reflectances and effective
emittances is then developed from a variety of particle surface conditions. This
parameterization is applied in a 3-channel retrieval method for Moderate Resolution
Imaging Spectroradiometer (MODIS) data at 0.65, 3.75, and 10.8 õm. Cloud optical
properties are derived iteratively for each pixel that contains ice clouds. The impact of ice
crystal surface roughness on the cloud parameter retrievals is examined by comparing the
results for particles with smooth surfaces and rough surfaces. Retrieval results from two
granules of MODIS data indicate that the retrieved cloud optical thickness is significantly reduced if the parameterization for roughened particles is used, as compared with the case
of smooth particles. For the retrieval of cloud effective particle size, the inclusion of the
effect of surface roughness tends to decrease the retrieved effective particle size if ice
crystals are small. The reversed result is noticed for large ice crystals. It is also found that
surface roughness has a very minor effect on the retrieval of cloud-top temperatures.
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Targino, Admir Creso. "Regional studies of the optical, chemical and microphysical properties of atmospheric aerosols : radiative impacts and cloud formation /." Stockholm : Dept. of meteorology, Stockholm university, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-740.
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Brückner, Marlen. "Retrieval of optical and microphysical cloud properties using shipbased spectral solar radiation measurements over the Atlantic ocean." Universität Leipzig, 2015. https://ul.qucosa.de/id/qucosa%3A16653.
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In this paper spectral solar zenith radiances are analyzed which were obtained from ship–based measurements over the Atlantic ocean. In combination with high–resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity–based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds.In dem vorliegenden Artikel werden abwärtsgerichtete spektrale Strahldichten analysiert, die mithilfe schiffsgebundener Beobachtungen über dem Atlantischen Ozean gemessen wurden. In Verbindung mit hochauflösenden Lidar und Mikrowellenradiometer Fernerkundungsverfahren werden optische und mikrophysikalische Wolkeneigenschaften aus spektralen Daten abgeleitet. Um Probleme bereits existierender Verfahren, die auf Transmissionen basieren, zu beseitigen, wird ein neuer Fernerkundungsalgorithmus vorgestellt, der nicht nur Zweideutigkeiten in der Bestimmung der Parameter umgeht, sondern auch den Einfluss von Messunsicherheiten verringert. Die Methode vergleicht gemessene spektrale Transmissionsverhältnisse bei sechs Wellenlängen mit modellierten Verhältnissen. Die neue Fernerkundungsmethode ist schnell und exakt, sodass sie für operative Zwecke geeignet ist. Sie wird für homogene und inhomogene Wasserwolken als auch für Cirren angewendet. Die Ergebnisse des neuen Ableitungsverfahrens werden mit Beobachtungen des Flüssigwasserpfades eines Mikrowellenradiometers verglichen. Daraus ergibt sich eine Überschätzung des Flüssigwasserpfades unter dicken Wolken, jedoch eine leichte Unterschätzung für dünne Wolken.
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Loewe, Katharina [Verfasser]. "Arctic mixed-phase clouds : Macro- and microphysical insights with a numerical model / Katharina Loewe." Karlsruhe : KIT Scientific Publishing, 2017. http://www.ksp.kit.edu.
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Thornton, Jenna Louise. "Ice particle size and roughness from novel techniques : in situ measurements and validation." Thesis, University of Hertfordshire, 2016. http://hdl.handle.net/2299/17644.
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The roughness of ice crystals, defined by small-scale surface roughness and large scale complexity, in high-altitude cloud, has been studied due to its important influence on the radiative properties of ice cloud. The Small Ice Detector 3 (SID-3) created at the University of Hertfordshire was used to measure the characteristics of individual ice crystals in situ. These are supplemented by a range of meteorological in situ measurements, including temperature, relative humidity, and wind velocity to investigate the influence of atmospheric conditions on ice crystal roughness/complexity. Since the method of roughness retrieval was novel, for atmospheric ice particles, laboratory experiments were setup to test and improve the characterization techniques. Criteria were set as a result of the laboratory experiments which data was expected to meet for it to be deemed reliable. These criteria and techniques were applied to data collected in situ on research aircraft. A range of degrees of ice crystal roughness were observed over five flights from two campaigns based out of Scotland in 2012 and 2015 (PIKNMIX and CIRCCREX). When all the flights were combined the majority of particles (51%) were categorised as lightly rough; the second most common roughness type was moderately rough (39%). Smooth particles made up 10% of the total particles, and < 0.02% were classed as severely rough. When considering a wave-cloud case separately, a similar range of roughness values were seen, however, smooth particles were only observed at the cloud leading-edge where nucleation was expected to occur during the only straight level run of the aircraft to probe this region. During the same wave-cloud flight smooth particles were more common in supersaturated regions and moderately rough crystals were more common in subsaturated regions, suggesting that crystals are more likely to tend towards rougher values when observed in subsaturated environments (a statistical T-test showed this hypothesis to be statistically significant). It was found that due to limitations associated with instantaneous measurements, it was challenging to observe how ice particle roughness evolved in situ, since the history of the individual crystals was unknown in most cases. Orographic cloud, however, was found to provide a more robust estimation of crystal evolution as a consequence of having sharp-leading edges where nucleation events were expected to occur, and since crystals then follow streamlines, the distance from the sharp-leading edge can act as a proxy for time since nucleation.
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Shrestha, Rudra Kumar. "Towards an improved understanding of regional scale climate change in the Nepal Himalayas." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/towards-an-improved-understanding-of-regional-scale-climate-change-in-the-nepal-himalayas(e2fe4192-a0ef-4d4e-be16-107b5c572d47).html.
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The effects of enhanced greenhouse gas concentrations on Earth’s climate are well understood. However, the impacts of anthropogenic aerosol particles, in particular due to the many aerosol-cloud indirect feedback mechanisms are not fully or even explicitly quantified as yet. This PhD seeks to contribute to improve our knowledge and understanding of aerosol – precipitation interactions over the Nepal Himalayas region and their consequences for precipitation patterns there. The research was carried out using the cloud-resolving Weather Research and Forecasting (WRF) model through a series of sensitivity studies and supported by literature reviews of satellite and field observations, although the latter are sparse. To complement the modelling studies, from March to December 2011, aerosols and surface meteorology were also continuously measured at Nagarkot (Lat: 27.7°N, Lon: 85.5° E, Alt: 1900m), Nepal, located in the eastern flank of a bowl shaped Kathmandu valley. The location was chosen to provide a representative vertical profile of aerosol and the impact on topographical flows. Our results showed a unique pattern of diurnal pollution circulation within the valley with a morning and evening peak. The evening peak, which is higher than the morning peak is attributed to the light wind blowing through the valley carrying locally generated fresh evening pollution, further enhanced by re-circulations of aged pollutants through suppression of the mixing layers as suggested by a previous study at a different location. The morning peak is caused by calm wind conditions followed by the transitional growth of the nocturnal boundary layer. It is found that the thermally driven mountain – valley wind circulations are responsible for ventilation of pollutants. The WRF simulations showed that a sophisticated double moment bulk microphysics parameterization scheme performed best, which did not show any statistically significant difference compared to the observed data at 80% confidence interval using a Chi-squared goodness of best fit test. A sensitivity analysis of aerosol and temperature perturbations on the monsoon precipitation was conducted. We found that the model represented the first indirect effect reasonably well however, rainfall was not particularly sensitive to the aerosol perturbations used, due to the poorly documented role of the ice phase processes which assume a greater importance in this region due to the influence of topography and diurnal heating cycle. Further model studies focusing on chemical properties of aerosol and sensitivity of Ice Nuclei (IN) to precipitation in this region are recommended. In contrast, the effects of temperature perturbation were found to be significant, more so than the currently modelled aerosol indirect effects, suggesting that reduced frequency but intense rain events are likely over the Himalayas as the climate warms.
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Schmidt, Jörg [Verfasser], Andreas [Akademischer Betreuer] Macke, Andreas [Gutachter] Macke, and Herman [Gutachter] Russchenberg. "Dual-field-of-view Raman lidar measurements of cloud microphysical properties : Investigation of aerosol-cloud interactions / Jörg Schmidt ; Gutachter: Andreas Macke, Herman Russchenberg ; Betreuer: Andreas Macke." Leipzig : Universitätsbibliothek Leipzig, 2014. http://d-nb.info/123878867X/34.
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Brückner, Marlen. "Retrieval of Optical and Microphysical Cloud Properties Using Ship-based Spectral Solar Radiation Measurements over the Atlantic Ocean." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-164322.
Full textAbstract:
In this thesis spectral solar zenith radiances are analyzed which were obtained from ship-based measurements over the Atlantic ocean. In combination with high-resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity-based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds. A statistical analysis of retrieved cloud properties during three Atlantic transects is introduced. Similar characteristics of cloud properties are found in the mid latitudes and northern subtropics but the large variability of meridional distribution in the remaining regions imply the prevailing influence of weather systems compared to typical cloud distributions. With about 63% homogeneous stratocumulus clouds are found to be the prevailing cloud type over ocean, while scattered and inhomogeneous liquid water clouds amount to 16% and 21%, respectively. All analyzed distributions are affected by an increased frequency of small values of cloud properties caused by 3D radiative effects. The comparison with satellite-based and ship-based cloud retrievals along the cruise track show comparable results for the cloud optical thickness with limitations for thick liquid water clouds. The meridional distribution of effective radius agreed within the uncertainties of both methods, however, the satellite-derived values are biased toward larger mean values.
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Albrecht, Rachel Ifanger. "Eletrificação dos sistemas precipitantes na região Amazônica: processos físicos e dinâmicos do desenvolvimento de tempestades." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/14/14133/tde-24102008-154430/.
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Os sistemas convectivos da região Amazônica possuem características microfísicas peculiares, que variam de um caráter convectivo marítimo (estação chuvosa) a continental (estação de transição seca-chuvosa). Essas características modulam a eletrificação desses sistemas, porém ainda não se sabe quais são os processos dominantes que intensificam o número de descargas elétricas de uma estação para outra: efeito dos aerossóis, termodinâmico, grande-escala ou topografia? Para responder à essa pergunta, o objetivo deste trabalho foi identificar e quantificar a importância de cada um desses efeitos na eletrificação dos sistemas convectivos da Amazônia. A metodologia foi baseada em análises de dados observacionais do experimento de campo DRYTOWET e em um modelo numérico com parametrizações de transferências de cargas e descargas elétricas. A análise do ciclo anual das descargas elétricas do tipo nuvem-solo (CGs) mostrou que a atividade elétrica dos sistemas precipitantes da região sudoeste da Amazônia aumenta durante a transição da estação seca para a estação chuvosa (Agosto a Setembro), associada aos sistemas convectivos com maior desenvolvimento vertical que acontecem nesse período. Com o estabelecimento da estação chuvosa (Novembro a Março), o número de CGs diminui porém a atividade elétrica ainda se mantêm. A porcentagem desses totais de CGs que tinham polaridade positiva (+CGs) tem média de 12% durante todo o ano, aumentando drasticamente para até 25% em Setembro, durante a transição entre as estações secas e chuvosa. Esse aumento da %+CGs ocorreu simultaneamente ao aumento da poluição atmosférica provocada pela queima de biomassa das pastagens realizada pelos fazendeiros locais, que as preparam para a agricultura e pecuária durante o início das primeiras chuvas. Por outro lado, o aumento da %+CGs das tempestades também ocorreu preferencialmente sobre a área de pastagem do estado de Rondônia. Através da análise de dados de radar dos sistemas precipitantes que ocorreram durante o experimento DRYTOWET, foi constatado que as tempestades positivas (tempestades que produzem mais de 50% de +CGs em 50% de seu tempo de vida) se formaram em ambientes mais secos e com alturas do nível de convecção por levantamento (NCL, altura da base da nuvem) maiores do que as demais tempestades (tempestades negativas), durante todo o experimento mas com maiores diferenças durante o final da estação seca (Setembro-Outubro). Com altura da base da nuvem mais elevada, a espessura da camada quente (ECQ - base da nuvem até a isoterma de 0oC) diminui, aumentando assim a velocidade das correntes ascendentes através de um melhor processamento da energia potencial disponível para convecção (CAPE) devido a um menor entranhamento. O aumento da velocidade das correntes ascendentes dentro da nuvem resulta em tempestades mais profundas e mais intensas. O efeito do aumento do NCL é uma característica das regiões com vegetação de pastagem, onde a razão entre o calor sensível e latente na superfície é maior do que as áreas florestadas, aumentando a altura da camada limite planetária. As diferenças de concentração total e distribuição de tamanho dos aerossóis devido ao aumento da poluição durante a transição entre as estações seca e chuvosa não foram conclusivas quanto a um possível efeito na distribuição de hidrometeoros das tempestade positivas e negativas, uma vez que o ciclo diurno da concentração dos aerossóis acompanha o ciclo diurno da camada limite planetária, que também regula o efeito da ECQ. Simulações numéricas com um modelo 1D de nuvem, acoplado à parametrizações de transferências de cargas elétricas entre hidrometeoros e raios, mostraram que a estrutura termodinâmica da atmosfera foi a maior responsável pela eletrificação das tempestades simuladas, aumentando a velocidade das correntes ascendentes. O efeito do aumento do número de aerossóis, que inibe da fase quente da nuvem e conseqüentemente fortalece a da fase fria da nuvem fornecendo mais vapor e gotículas de nuvem para essa região, provocou a diminuição da quantidade de granizo nas tempestades simuladas e o aumento de partículas agregadas menores, como os flocos de neve e graupel, diminuindo a freqüência de raios.Amazonian convective systems have unique microphysical characteristics, varying from a maritime convective behavior (rainy season) to a continental behavior (wet-dry transition season). These characteristics modulate the electrification of these systems, however it is still not well understood which are the dominant processes that intensify the frequency of lightning from one season to another: aerosol effect, thermodynamics, large-scale variability, landscape or topography? To answer this question, the objective of this study was to identify and quantify the importance of each one of these effects on the electrification of convective systems over the Amazon. The methodology was based on the analysis of observational data from the field experiment DRYTOWET and a numerical model with charge transfer parameterizations and lightning discharges. The cloud-to-ground (CG) lightning discharges annual cycle presented that the electrical activity of the southwestern Amazonian precipitating systems increased during the transition between the dry and wet seasons (August to September), in association with the convective systems deepening. With the establishment of the wet season (November to March), the number of CGs decreased but the electrical activity continued. The mean annual percentage of cloud-to-ground lightning of positive polarity (+CGs) was 12%, increasing drastically to 25% in September during the transition between the dry and wet seasons. This percentage of +CGs raise happened simultaneously with the increase in the atmospheric pollution due to the pasture biomass burning, held by local farmers to prepare the soil for agriculture and livestock during the begging of first rains. On the other hand, the increase in %+CGs also occurred preferentially over pasture areas of Rondonia state. Through the analysis of radar precipitating systems that occurred during the field campaign DRYTOWET, it was noted that positive thunderstorms (storms that produced more than 50% of +CGs over 50% of their life time) were initiated in drier and higher lift condensation levels (cloud base height) environments than other storms (negative thunderstorms) during all the field experiment, especially in the end of the dry season (September-October). A higher cloud base height is associated with a shallower warm cloud depth (cloud base height to the 0oC isotherm) and consequently less entrainment, increasing the updrafts due to a more efficient processing of the convective available potential energy (CAPE). This increase in updrafts inside the clouds results in deeper and stronger thunderstorms. The higher cloud base heights is a characteristic from pasture regions, where the ratio between sensible and latent heats at surface is greater than forested areas, which increases the top of the planetary boundary layer. The differences in the aerosol total concentration and size distribution, due to the increase in the atmospheric pollution during the transition between the dry and wet seasons, were inconclusive in a possible aerosol effect in the strength of positive and negative thunderstorms, once the aerosol concentration diurnal cycle follows the cycle of the planetary boundary layer, that also regulates the warm cloud depth effect. Numerical simulation of an 1D cloud model, coupled with charge transfer between the hydrometeors, showed that the thermodynamic structure was the main responsible feature for cloud electrification, increasing the updraft velocities. The pollution effect was masked in simulations, which inhibit the warm precipitation and consequently strength the the mixed and cold regions of the cloud, was responsible for an increase in the number of smaller aggregated particles, like snow flakes and graupel, decreasing the electrification and lightning frequency.
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Michael, Ryan A. "Fate of volatile chemicals during accretion on wet-growing hail." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002796.
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MARTINS, Rafael Castelo Guedes. "Estudo da sensibilidade do modelo WRF às parametrizações de microfísica de nuvens e à assimilação de dados observados." Universidade Federal de Campina Grande, 2014. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1466.
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RAFAEL CASTELO GUEDES MARTINS – TESE (PPGMet) 2014.pdf: 3362803 bytes, checksum: 5a99c28e73f6a95fef76f82f96d2edc4 (MD5)Made available in DSpace on 2018-08-15T19:02:39Z (GMT). No. of bitstreams: 1 RAFAEL CASTELO GUEDES MARTINS – TESE (PPGMet) 2014.pdf: 3362803 bytes, checksum: 5a99c28e73f6a95fef76f82f96d2edc4 (MD5) Previous issue date: 2014-12-12
Um dos principais desafios atuais da modelagem numérica da atmosfera trata da previsão quantitativa da precipitação e do posicionamento das nuvens de chuva. Este trabalho tem com o principal objetivo avaliar o desempenho das arametrizações de microfísicas na modelagem regional com ênfase no papel da informação de grande escala e sua influência sobre as simulações, e no uso de dados observados de radiossondagens como forma de acrescentar informação à modelagem . Inicialmente, duas reanálises (NCEP2 e ERAI) foram estatisticamente comparadas com dados de PCDs do Estado do Ceará. Verificou - se qu e a ERAI apresentou maior semelhança com as observações, principalmente para as variáveis diretamente ligadas à convecção. Em seguida, a ERAI foi utilizada como forçamento de grande escala em simulações com o modelo WRF. Observou- se que o uso de microfísica detalhada não melhora necessariamente a previsão do modelo, caso não sejam utilizados dados observados no local de estudo. Por último, duas simulações de alta resolução foram realizadas. Uma forçada pela reanálise sem modificação e outra forçada pela reanálise modificada utilizando o método de análise objetiva do WRF, para incluir as séries temporais de radiossondagens coletadas durante campanha experimental do Projeto CHUVA, em Fortaleza- CE. As duas simulações foram comparadas com dados observados pelo radiômetro para o mesmo local e período das radiossondagens . Observou - se que a inclusão das observações de sondagens na modelagem possibilita melhor modelagem de um sistema convectivo ocorrido em abril de 2011, principalmente para as variáveis ligadas à convecção. Este trabalho aponta, utilizando análises comparativas e estatísticas, que a utilização de uma maior densidade de dados observacionais válidos no modelo pode melhorar de forma muito mais eficiente o resultado da modelagem, do que mesmo a utilização do downscaling dinâmico do dado de grande escala ou a utilização de esquemas de microfísica detalhada, que, em algumas situações, pode inclusive inserir mais erros nos sistema s modelados.
The quantitative prediction of precipitation and the positioning of the rain clouds is one of the main challenges of numerical modeling of the atmosphere in present days. This work aims to evaluate the performance of the microphysical parameterizations in regional modeling, with emphasis on the role of large- scale information and its influence on the simulations, and the use of observational data from radiosondes as a way to add information to modeling. Initially, two reanalysis (NCEP2 and ERAI) were statistically compared with data from PCDs from the Ceará State. It was found that the ERAI showed similarity to the observations, especially for variables directly linked to convection. Then, the ERAI is used as large scale forcing in simulations with the WRF model. It was observed that the use of detailed microphysics does not necessarily improve the model performance, if in situ data were not used. Finally, two high resolution simulations were performed. The first f orced by reanalysis without modification and other forced by reanalysis using the modified method of objective analysis of the WRF, to include the time series of radiosonde observations collected during the experimental campaign of the CHUVA Project in Fortaleza- CE. The two simulations were compared with data observed by the radiometer to the same place and period of the radiosonde. It was observed that the inclusion of radiosonde observations in to the model leads to a better simulation of a convective system that occurred in April 2011, mostly for the variables related to convection. Using comparative statistical analysis, t his work points that the use of a higher density of valid observational data in the model can improve much more efficiently the model results than the use of a dynamic downscal ing of large- scale data or the use of schemes with detailed microphysics, which in some circumstances may even introduce more errors into the modeled system s.