ABSTRACT Using a cloud model with explicit microphysics and radiation, we evaluate the microphysi... more ABSTRACT Using a cloud model with explicit microphysics and radiation, we evaluate the microphysical changes in a supercooled liquid altocumulus cloud with increasing ice content, until glaciation occurs. The properties of the ice and water particle constituents are resolved independently, revealing the relative radiative contributions from the water phase source cloud versus the ice phase virga. Cloud contents are also converted to millimeter-wave radar reflectivities to shed light on the ability of such radars to study these ubiquitous clouds. The results show that the radiative and radar backscattering properties of mixed-phase clouds are dominated by the cloud droplets and ice crystals they contain, respectively.
[1] A unique and extensive data set of cirrus properties collected on 13 July 2002 during CRYSTAL... more [1] A unique and extensive data set of cirrus properties collected on 13 July 2002 during CRYSTAL-FACE provides the framework for simulations using cloud models to interpret the observations and to develop recommendations for microphysical parameterizations in large-scale models. Several outstanding issues in the simulations of cirrus clouds are addressed using detailed bin-resolving and bulk microphysics models. A new heterogeneous ice nucleation formulation based on extended classical theory with simultaneous dependence on temperature and saturation ratio is applied for the first time to thin tropopause cirrus. The simulated cloud microphysical properties are similar to observations, suggesting that tropopause cirrus may potentially form as a result of heterogeneous immersion freezing of internally mixed aerosols serving as ice nuclei (IN). The potential for mixed aerosols to serve as IN in tropopause cirrus is consistent with measurements of comparable amounts of soluble and insoluble material in cirrus residues and aerosols during CRYSTAL-FACE. Simulations using homogeneous nucleation theory are also able to produce comparable microphysical properties if the heterogeneous mode is turned off; hence the homogeneous mode cannot be excluded if insoluble material capable of serving as IN is not available. The calculated critical ice supersaturation for the onset of heterogeneous nucleation at these cold temperatures (∼200 K) was 70–80% (for the assumed aerosol nucleation parameters) and 15–20% higher for homogeneous nucleation. The calculated supersaturation relaxation time ranged from ∼1–2 hours in the center of the cloud to 3–6 hours near the boundaries, which may explain the high values of ice supersaturation (30–80%) observed in this cloud. Analysis of the supersaturation budget showed that supersaturation was generally nonequilibrium, and relaxation from the initial critical values to near equilibrium occurred only after several hours. The bulk model was able to simulate this case and in particular the slow crystal growth and large supersaturation because of its detailed treatment of ice nucleation and supersaturation. The fraction of condensed ice relative to excess vapor predicted by both models was 40–60% for several hours, indicating that bulk models with zero supersaturation (instantaneous condensation of all excess vapor) would substantially overpredict the ice water path and optical thickness.
ABSTRACT Using a cloud model with explicit microphysics and radiation, we evaluate the microphysi... more ABSTRACT Using a cloud model with explicit microphysics and radiation, we evaluate the microphysical changes in a supercooled liquid altocumulus cloud with increasing ice content, until glaciation occurs. The properties of the ice and water particle constituents are resolved independently, revealing the relative radiative contributions from the water phase source cloud versus the ice phase virga. Cloud contents are also converted to millimeter-wave radar reflectivities to shed light on the ability of such radars to study these ubiquitous clouds. The results show that the radiative and radar backscattering properties of mixed-phase clouds are dominated by the cloud droplets and ice crystals they contain, respectively.
[1] A unique and extensive data set of cirrus properties collected on 13 July 2002 during CRYSTAL... more [1] A unique and extensive data set of cirrus properties collected on 13 July 2002 during CRYSTAL-FACE provides the framework for simulations using cloud models to interpret the observations and to develop recommendations for microphysical parameterizations in large-scale models. Several outstanding issues in the simulations of cirrus clouds are addressed using detailed bin-resolving and bulk microphysics models. A new heterogeneous ice nucleation formulation based on extended classical theory with simultaneous dependence on temperature and saturation ratio is applied for the first time to thin tropopause cirrus. The simulated cloud microphysical properties are similar to observations, suggesting that tropopause cirrus may potentially form as a result of heterogeneous immersion freezing of internally mixed aerosols serving as ice nuclei (IN). The potential for mixed aerosols to serve as IN in tropopause cirrus is consistent with measurements of comparable amounts of soluble and insoluble material in cirrus residues and aerosols during CRYSTAL-FACE. Simulations using homogeneous nucleation theory are also able to produce comparable microphysical properties if the heterogeneous mode is turned off; hence the homogeneous mode cannot be excluded if insoluble material capable of serving as IN is not available. The calculated critical ice supersaturation for the onset of heterogeneous nucleation at these cold temperatures (∼200 K) was 70–80% (for the assumed aerosol nucleation parameters) and 15–20% higher for homogeneous nucleation. The calculated supersaturation relaxation time ranged from ∼1–2 hours in the center of the cloud to 3–6 hours near the boundaries, which may explain the high values of ice supersaturation (30–80%) observed in this cloud. Analysis of the supersaturation budget showed that supersaturation was generally nonequilibrium, and relaxation from the initial critical values to near equilibrium occurred only after several hours. The bulk model was able to simulate this case and in particular the slow crystal growth and large supersaturation because of its detailed treatment of ice nucleation and supersaturation. The fraction of condensed ice relative to excess vapor predicted by both models was 40–60% for several hours, indicating that bulk models with zero supersaturation (instantaneous condensation of all excess vapor) would substantially overpredict the ice water path and optical thickness.
Thermodynamics, Kinetics, And Microphysics of Clouds
Climate change has provided a new impetus... more Thermodynamics, Kinetics, And Microphysics of Clouds
Climate change has provided a new impetus for research on clouds and precipitation. One of the greatest uncertainties in current global climate models is cloud feedback, arising from uncertainties in the parameterization of cloud processes and their impact on the global radiation balance. In the past two decades, substantial progress has been made in the simulation of clouds using cloud resolving models. However,
most of the parameterizations employed in these models have been empirically based. New theoretical descriptions of cloud processes are now being incorporated into cloud models, using spectral microphysics based on the kinetic equations for the drop and crystal size spectra along with the supersaturation equation,
and newer parameterizations of drop activation and ice nucleation based on the further development of the classical nucleation theory. From these models, cloud microphysics parameterizations are being developed for use in global weather and climate models.
Thermodynamics, Kinetics, and Microphysics of Clouds reflects this shift to an increasingly theoretical basis for the simulation and parameterization of cloud processes. The book presents a unified theoretical foundation that provides the basis for incorporating cloud microphysical processes in cloud and climate
models in a manner that represents interactions and feedback processes over the relevant range of environmental and parametric conditions. In particular, this book provides:
• the closed system of equations of spectral cloud microphysics that includes kinetic equations for the drop and crystal size spectra for regular and stochastic condensation/deposition and coagulation/accretion along with the supersaturation equations;
• the latest theories and theoretical parameterizations of aerosol hygroscopic growth, drop activation, and ice homogeneous and heterogeneous nucleation, derived from the general principles of thermodynamics and kinetics and suitable for cloud and climate models;
• a theoretical basis for understanding the processes of cloud particle formation, evolution, and precipitation, based on numerical cloud simulations and analytical solutions to the kinetic equations and supersaturation equation;
• a platform for advanced parameterizations of clouds in weather prediction and climate models using these solutions;
• the scientific foundation for weather and climate modification by cloud seeding.
This book will be invaluable for researchers and advanced students engaged in cloud and aerosol physics, and air pollution and climate research.
Vitaly I. Khvorostyanov is Professor of Physics of the Atmosphere and Hydrosphere, Central Aerological Observatory (CAO ), Russian Federation. His research interests are in cloud physics, cloud numerical modeling, atmospheric radiation, and cloud-aerosol and cloud-radiation interactions, with applications for climate studies and weather modification. He has served as Head of the Laboratory of Numerical Modeling of Cloud Seeding at CAO , Coordinator of the Cloud Modeling Programs on Weather Modification by Cloud Seeding in the USSR and Russia, Member of the International GEWEX Radiation Panel of the World Climate
Research Program, and Member of the International Working Group on Cloud-Aerosol Interactions. Dr. Khvorostyanov has worked as a visiting scientist and Research Professor in the United States, United Kingdom, France, Germany, and Israel. He has co-authored nearly 200 journal articles and four books:
Numerical Simulation of Clouds (1984), Clouds and Climate (1986), Energy-Active Zones: Conceptual Foundations (1989), and Cirrus (2002). Dr. Khvorostyanov is a member of the American Geophysical Union and the American Meteorological Society.
Judith A. Curry is Professor and Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. She previously held faculty positions at the University of Colorado, Penn State University, and Purdue University. Dr. Curry’s research interests span a variety of topics in the atmospheric and climate sciences. Current interests include cloud microphysics, air and sea interactions, and climate
feedback processes associated with clouds and sea ice. Dr. Curry is co-author of Thermodynamics of Atmospheres and Oceans (1999) and editor of the Encyclopedia of Atmospheric Sciences (2003). She has published more than 190 refereed journal articles. Dr. Curry is a Fellow of the American Meteorological Society, the American Association for the Advancement of Science, and the American Geophysical Union.
In 1992, she received the Henry Houghton Award from the American Meteorological Society
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Papers by Vitaly Khvorostyanov
Climate change has provided a new impetus for research on clouds and precipitation. One of the greatest uncertainties in current global climate models is cloud feedback, arising from uncertainties in the parameterization of cloud processes and their impact on the global radiation balance. In the past two decades, substantial progress has been made in the simulation of clouds using cloud resolving models. However,
most of the parameterizations employed in these models have been empirically based. New theoretical descriptions of cloud processes are now being incorporated into cloud models, using spectral microphysics based on the kinetic equations for the drop and crystal size spectra along with the supersaturation equation,
and newer parameterizations of drop activation and ice nucleation based on the further development of the classical nucleation theory. From these models, cloud microphysics parameterizations are being developed for use in global weather and climate models.
Thermodynamics, Kinetics, and Microphysics of Clouds reflects this shift to an increasingly theoretical basis for the simulation and parameterization of cloud processes. The book presents a unified theoretical foundation that provides the basis for incorporating cloud microphysical processes in cloud and climate
models in a manner that represents interactions and feedback processes over the relevant range of environmental and parametric conditions. In particular, this book provides:
• the closed system of equations of spectral cloud microphysics that includes kinetic equations for the drop and crystal size spectra for regular and stochastic condensation/deposition and coagulation/accretion along with the supersaturation equations;
• the latest theories and theoretical parameterizations of aerosol hygroscopic growth, drop activation, and ice homogeneous and heterogeneous nucleation, derived from the general principles of thermodynamics and kinetics and suitable for cloud and climate models;
• a theoretical basis for understanding the processes of cloud particle formation, evolution, and precipitation, based on numerical cloud simulations and analytical solutions to the kinetic equations and supersaturation equation;
• a platform for advanced parameterizations of clouds in weather prediction and climate models using these solutions;
• the scientific foundation for weather and climate modification by cloud seeding.
This book will be invaluable for researchers and advanced students engaged in cloud and aerosol physics, and air pollution and climate research.
Vitaly I. Khvorostyanov is Professor of Physics of the Atmosphere and Hydrosphere, Central Aerological Observatory (CAO ), Russian Federation. His research interests are in cloud physics, cloud numerical modeling, atmospheric radiation, and cloud-aerosol and cloud-radiation interactions, with applications for climate studies and weather modification. He has served as Head of the Laboratory of Numerical Modeling of Cloud Seeding at CAO , Coordinator of the Cloud Modeling Programs on Weather Modification by Cloud Seeding in the USSR and Russia, Member of the International GEWEX Radiation Panel of the World Climate
Research Program, and Member of the International Working Group on Cloud-Aerosol Interactions. Dr. Khvorostyanov has worked as a visiting scientist and Research Professor in the United States, United Kingdom, France, Germany, and Israel. He has co-authored nearly 200 journal articles and four books:
Numerical Simulation of Clouds (1984), Clouds and Climate (1986), Energy-Active Zones: Conceptual Foundations (1989), and Cirrus (2002). Dr. Khvorostyanov is a member of the American Geophysical Union and the American Meteorological Society.
Judith A. Curry is Professor and Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. She previously held faculty positions at the University of Colorado, Penn State University, and Purdue University. Dr. Curry’s research interests span a variety of topics in the atmospheric and climate sciences. Current interests include cloud microphysics, air and sea interactions, and climate
feedback processes associated with clouds and sea ice. Dr. Curry is co-author of Thermodynamics of Atmospheres and Oceans (1999) and editor of the Encyclopedia of Atmospheric Sciences (2003). She has published more than 190 refereed journal articles. Dr. Curry is a Fellow of the American Meteorological Society, the American Association for the Advancement of Science, and the American Geophysical Union.
In 1992, she received the Henry Houghton Award from the American Meteorological Society