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Author: Benjamin H. Cole Publisher: ISBN: Category : Languages : en Pages : 112
Book Description
The energy balance of the Earth is regulated in part by ice clouds, which both reflect shortwave solar radiation and absorb infrared radiation from the Earth. These clouds appear frequently worldwide, with up to 70% coverage in tropical regions. The microphysics of ice clouds determines their radiative properties, and is important for accurately predicting the role of ice clouds in Earth's energy balance. However, describing the microphysics of ice clouds remains a challenging problem, especially with regard to the shape of ice particles and the degree of ice particle surface roughening. In-situ studies have found evidence for ice surface roughness and have found many complex ice geometries; however, these studies are limited spatially and temporally. An approach which allows large-scale analysis is to retrieve these properties via theoretical modeling using satellite observations of polarized reflectance from ice clouds, since polarized reflectance is sensitive to the shape and roughness of ice particles. The theoretical model requires the scattering properties of simulated ice particles. These properties are obtained for 10 different ice shapes and 17 different levels of surface roughness. Simulations are performed for 3 different effective ice particle diameters: 30, 60 and 90 [mu]m. Overall, the retrieved shape is dominated by the compact aggregate of columns. Although the exact composition of shapes varies from month to month, the compact aggregate of columns remains the most commonly retrieved shape. The retrieved roughness varies from moderately rough at [delta] = 0.1 to severely rough at [delta] = 0.5. Retrieved roughness varies more than shape, and smooth surfaced ice is most prominent in January. Tropical regions tend to have ice particles that are more roughened, while the midlatitudes and polar regions tend to have more smooth ice. In almost all cases, roughened ice represents > 60% of the total retrievals. The asymmetry parameter inferred from the retrieval of ice particle shape and roughness has a mean value near 0.77, with only small differences based on assumed ice effective diameter. The median value of the asymmetry parameter has a nearly constant value of approximately 0.75. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151196
Author: Benjamin H. Cole Publisher: ISBN: Category : Languages : en Pages : 112
Book Description
The energy balance of the Earth is regulated in part by ice clouds, which both reflect shortwave solar radiation and absorb infrared radiation from the Earth. These clouds appear frequently worldwide, with up to 70% coverage in tropical regions. The microphysics of ice clouds determines their radiative properties, and is important for accurately predicting the role of ice clouds in Earth's energy balance. However, describing the microphysics of ice clouds remains a challenging problem, especially with regard to the shape of ice particles and the degree of ice particle surface roughening. In-situ studies have found evidence for ice surface roughness and have found many complex ice geometries; however, these studies are limited spatially and temporally. An approach which allows large-scale analysis is to retrieve these properties via theoretical modeling using satellite observations of polarized reflectance from ice clouds, since polarized reflectance is sensitive to the shape and roughness of ice particles. The theoretical model requires the scattering properties of simulated ice particles. These properties are obtained for 10 different ice shapes and 17 different levels of surface roughness. Simulations are performed for 3 different effective ice particle diameters: 30, 60 and 90 [mu]m. Overall, the retrieved shape is dominated by the compact aggregate of columns. Although the exact composition of shapes varies from month to month, the compact aggregate of columns remains the most commonly retrieved shape. The retrieved roughness varies from moderately rough at [delta] = 0.1 to severely rough at [delta] = 0.5. Retrieved roughness varies more than shape, and smooth surfaced ice is most prominent in January. Tropical regions tend to have ice particles that are more roughened, while the midlatitudes and polar regions tend to have more smooth ice. In almost all cases, roughened ice represents > 60% of the total retrievals. The asymmetry parameter inferred from the retrieval of ice particle shape and roughness has a mean value near 0.77, with only small differences based on assumed ice effective diameter. The median value of the asymmetry parameter has a nearly constant value of approximately 0.75. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151196
Author: Benjamin Cole Publisher: ISBN: Category : Languages : en Pages :
Book Description
Uncertainties associated with the microphysical and radiative properties of ice clouds remain an active research area because of the importance these clouds have in atmospheric radiative transfer problems and the energy balance of the Earth. In this study, an adding/doubling model is used to simulate the top of atmosphere (TOA) radiance and full Stokes vector from an ice cloud at the wavelength lambda = 865 nm with many different combinations of assumed ice habits (shapes) and different degrees of ice surface roughness, and the polarized radiance at a wide range of scattering angles is derived. Simulated results are compared with polarized radiance data from the POLDER (POLarization and Directionality of the Earth's Reflectances) instrument on board the PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) satellite. Bulk ice scattering properties are obtained by using five different size distributions collected during field campaigns ranging in effective diameter from 10 micrometers to 90 micrometers. Bulk scattering properties for the MODIS Collection 5 ice cloud product are used in this study, along with properties for two mid-latitude ice cloud models, a polar/mid-latitude ice model, and a model built for ice clouds over deep convection. Solid columns and hollow columns are used as well. The polarized radiance simulation results for the moderate surface roughness level best fit the satellite measurements for all ice models, though severely roughened ice crystals do fare well in a few cases. Hollow columns are the best fit to the satellite polarization measurements, but of the ensemble ice models, the polar/mid-latitude model at an effective diameter of 90 micrometers best fits the polarized radiance measurements for the one day of PARASOL data considered. This model should be the best to simulate ice cloud properties on a global scale.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD). Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D
Author: Kerry Glynne Meyer Publisher: ISBN: Category : Languages : en Pages :
Book Description
Ice clouds occur quite frequently, yet so much about these clouds is unknown. In recent years, numerous investigations and field campaigns have been focused on the study of ice clouds, all with the ultimate goal of gaining a better understanding of microphysical and optical properties, as well as determining the radiative impact. Perhaps one of the most recognized instruments used for such research is the Moderate-resolution Imaging Spectroradiometer (MODIS), carried aboard the NASA EOS satellites Terra and Aqua. The present research aims to support ongoing efforts in the field of ice cloud research by use of observations obtained from Terra and Aqua MODIS. First, a technique is developed to infer ice cloud optical depth from the MODIS cirrus reflectance parameter. This technique is based on a previous method developed by Meyer et al. (2004). The applicability of the algorithm is demonstrated with retrievals from level-2 and -3 MODIS data. The technique is also evaluated with the operational MODIS cloud retrieval product and a method based on airborne ice cloud observations. From this technique, an archive of daily optical depth retrievals is constructed. Using simple statistics, the global spatial and temporal distributions of ice clouds are determined. Research has found that Aqua MODIS observes more frequent ice clouds and larger optical depths and ice water paths than does Terra MODIS. Finally, an analysis of the time series of daily optical depth values revealed that ice clouds at high latitudes, which are most likely associated with synoptic scale weather sytems, persist long enough to move with the upper level winds. Tropical ice clouds, however, dissipate more rapidly, and are in all likelihood associated with deep convective cells.
Author: Edwin Lee Dunnavan Publisher: ISBN: Category : Languages : en Pages :
Book Description
This dissertation develops methodological and mathematical techniques for describing the distribution of various ice particle geometries and their 2D observations. It is common for models and observations to integrate both types of distributions when estimating key microphysical properties related to growth and depletion of ice particles. However, much of what is known about the actual 3D ice particle shapes is derived from 2D images or projections of each particle. Ice particle orientations therefore can distort the observed 2D geometry in a way that obscures the underlying 3D structure. A major discovery of this dissertation is that various transformations of ice particle distributions and their projections are represented in closed-form as univariate and bivariate H-functions. The properties of H-functions are based heavily on the Mellin integral transform. The concepts, notations, and properties of these functions might seem foreign to many in the meteorology and atmospheric science community. Therefore, chapter 2 of this dissertation provides an overview of the relevant math that surrounds H-functions as well as their various properties. Chapter 3 develops an integral transform method for projecting distributions of ice particle habits (approximated as spheroids) onto a 2D plane. This projection process is geometrically analogous to how in situ observations capture ice particle shapes as well as how projected areas are used in microphysical fall speed calculations. Distribution transformations using mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientation parameters. This shape uncertainty is maximized for distributions of highly eccentric particles and for particles like aggregates that are thought to fall with large canting-angle deviations. The integral transform methodology is used to propose an in situ approach for estimating model parameters that govern ice particle shape from distribution moments of observed in situ ellipse fit eccentricity or second eccentricity.Chapter 4 utilizes two separate datasets of best-fit ellipsoid estimates derived from Multi-Angle Snowflake Camera (MASC) observations to construct a bivariate beta distribution for capturing snow aggregate shapes. This mathematical model is used along with Monte Carlo simulated aggregates to study how combinations of monomer properties affect aggregate shape evolution. Plate aggregates of any aspect ratio produce a consistent ellipsoid shape evolution, whereas thin column aggregates evolve to become more spherical. However, thin column aggregates yield fractal dimensions much less than the often assumed value of 2.0. This discovery suggests that aggregates formed in cirrus clouds could exhibit significantly different physical properties than those formed in mixed-phase clouds. Simulated aggregate ellipsoid densities and fractal analogs of density (lacunarity) are much more variable depending on combinations of monomer size and shape. The inconsistent relationship between shape and density suggests that mass-dimensional prefactors should be rescaled in a more physical manner. Both simulations and observations prove aggregates are rarely oblate. These results therefore contradict much of the current literature on snow aggregate shapes, since many models and radar forward simulators assume homogeneous oblate spheroids. Chapter 5 investigates the effect of convolving particle property distributions when using the bivariate beta distribution from chapter 4. Idealized tests show that the number weighted mean fallspeed for ellipsoidal aggregates is more than 90% less than that of sphere/fractal aggregates, while mass-weighted fallspeeds for ellipsoid aggregates are approximately 60% of sphere/fractal aggregates. The distribution ranges produced by ellipsoidal aggregates is shown to be much more consistent with observed fall speed ranges than using a mass-dimensional relationship alone. This implies that current microphysics models systematically overestimate mass and number sedimentation fluxes but underestimate size sorting anywhere from 8% to 20%. Properties of the H-function are used to develop a spectral bulk modeling methodology that can utilize any number of distribution moments in the estimation of distribution parameters. The use of this spectral bulk microphysics methodology in numerical weather prediction models can therefore provide the computational simplicity of bulk microphysics models while still exhibiting the numerical complexity of bin microphysics models.
Author: Kuo-Nan Liou Publisher: Cambridge University Press ISBN: 0521889162 Category : Science Languages : en Pages : 461
Book Description
This volume outlines the fundamentals and applications of light scattering, absorption and polarization processes involving ice crystals.
Author: Yu Xie Publisher: ISBN: Category : Languages : en Pages :
Book Description
The dissertation first investigates the single-scattering properties of inhomogeneous ice crystals containing air bubbles. Specifically, a combination of the ray-tracing technique and the Monte Carlo method is used to simulate the scattering of light by randomly oriented large hexagonal ice crystals containing spherical or spheroidal air bubbles. The effect of the air bubbles within ice crystals is to smooth the phase functions, diminish the 22° and 46° halo peaks, and reduce the backscatter in comparison with the case of bubble-free ice crystals. Cloud reflectance look-up tables were generated at the wavelengths of 0.65 um and 2.13 um to examine the impact of accounting for air bubbles in ice crystal morphology on the retrieval of ice cloud optical thickness and effective particle size. To investigate the effect of the representation of aggregates on electromagnetic scattering calculations, an algorithm is developed to efficiently specify the geometries of aggregates and to compute some of their geometric parameters such as the projected area. Based on in situ observations, aggregates are defined as clusters of hexagonal plates with a chain-like overall shape. An aggregate model is developed with 10 ensemble members, each consisting of between 4-12 hexagonal plates. The scattering properties of an individual aggregate ice particle are computed using the discrete dipole approximation or an Improved Geometric Optics Method, depending upon the size parameter. The aggregate model provides an accurate and computationally efficient way to represent all aggregates occurring within ice clouds. We developed an algorithm to determine an appropriate ice cloud model for application to satellite-based retrieval of ice cloud properties. Collocated Moderate Resolution Imaging Spectroradiometer and Multi-angle Imaging SpectroRadiometer (MISR) data are used to retrieve the optical thicknesses of ice clouds as a function of scattering angle in the nine MISR viewing directions. The difference between cloud optical thickness and its averaged value over the nine viewing angles can be used to validate the ice cloud models. Using the data obtained on 2 July 2009, an appropriate ice cloud model is determined. With the presence of all the uncertainties in the current operational satellite-based retrievals of ice cloud properties, this ice cloud model has excellent performance in terms of consistency in cloud property retrievals with the nine MISR viewing angles.
Author: Constantin Andronache Publisher: Elsevier ISBN: 012810550X Category : Science Languages : en Pages : 302
Book Description
Mixed-Phase Clouds: Observations and Modeling presents advanced research topics on mixed-phase clouds. As the societal impacts of extreme weather and its forecasting grow, there is a continuous need to refine atmospheric observations, techniques and numerical models. Understanding the role of clouds in the atmosphere is increasingly vital for current applications, such as prediction and prevention of aircraft icing, weather modification, and the assessment of the effects of cloud phase partition in climate models. This book provides the essential information needed to address these problems with a focus on current observations, simulations and applications. Provides in-depth knowledge and simulation of mixed-phase clouds over many regions of Earth, explaining their role in weather and climate Features current research examples and case studies, including those on advanced research methods from authors with experience in both academia and the industry Discusses the latest advances in this subject area, providing the reader with access to best practices for remote sensing and numerical modeling
Author: Benjamin H. Cole
Author: Benjamin H. Cole
Author: Benjamin Cole
Author: 
Author: 
Author: Kerry Glynne Meyer
Author: Edwin Lee Dunnavan
Author: Kuo-Nan Liou
Author: 
Author: Yu Xie
Author: Constantin Andronache