Cloud Dynamics

During recent decades a new field of study in atmospheric science has made its appearance - the dynamics of clouds. As the name implies, the subject matter of cloud dynamics includes the causes of cloud formation and the temporal development of clouds. At first, effort was concentrated mainly on devising models of the structure and development of convective clouds, and thus there exists considerable literature on this [9, 69, 88, 330, 411]. Although convective clouds are of great significance (thunder­ storm formation and very intense turbulence are associated with these clouds), they are observed much less frequently than other cloud types. For instance, the frequency of occurrence of strati­ form (frontal) clouds and wave clouds over the U.S.S.R. and Western Europe is more than 90% [2-4]. During the last 20 or 30 years there has been considerable success in studying the dynamics of stratiform clouds. Fundamental laws (equations) describing the formation, development, and dis­ sipation of these clouds (and also of fog) have been formulated, and also laws describing the formation of humidity and temperature fields in a turbulent medium. Hydrodynamic models of clouds and fog constructed on the basis of these equations have made it pos­ sible to formulate the fundamental regularities in the formation and evolution of large-scale cloud fields, and also to ascertain the structural features of clouds of various kinds. These topics are covered in Chapters 1-4 of this monograph.

Contenu

1. Equations of Heat and Moisture Transfer in a Turbulent Atmosphere.- 1.1. Water-vapor influx (balance).- 1.2. Heat influx (balance).- 1.3. Influxes of heat and water vapor in moist saturated air (in a cloud).- 1.4. Equations for temperature and condensation rate of water vapor.- 1.5. Cloud-droplet distribution functions.- 1.5.1. Droplet growth by condensation in a turbulent medium.- 1.5.2. Droplet growth by coalescence in a turbulent medium.- 1.6. Equations of stochastic condensation.- 2. Models of Stratiform-Cloud Formation.- 2.1. Solution of the system of equations for heat and moisture exchange in a turbulent atmosphere.- 2.1.1. Taking into account the fall of cloud elements and the fallout of precipitation.- 2.2. Formation and evolution of stratiform clouds.- 2.3. Precipitation modeling and the microphysical quantities of a stratus cloud.- 2.3.1. Droplet clouds.- 2.3.2. Mixed clouds.- 2.3.3. Formation of a stratus cloud in the boundary layer of the atmosphere.- 2.4. Modeling of frontal cloudiness.- 2.5. The lower cloud boundary.- 2.6. The role of turbulence and radiation in the formation of stratus clouds in the Arctic.- 3. Models of Fog Formation.- 3.1. Radiation fogs.- 3.2. Evaporation fogs.- 3.3. Advection fogs.- 3.4. On urban fogs.- 4. Atmospheric Moisture Content and Cloud Water Reserves.- 4.1. Modeling fields of atmospheric moisture content and cloud water reserves.- 4.2. The water-vapor in an air column and cloud water reserves according to data of radio and aircraft sounding.- 4.3. The atmospheric moisture content and cloud water reserves according to radiometric data.- 5. The Hydrodynamic Prediction of Cloudiness and Precipitation.- 5.1. The first models of precipitation prediction.- 5.2. A hydrodynamic five-level model for predicting humidity and cloudiness.- 5.3. A ten-level model for predicting frontal precipitation.- 5.4. A numerical model for predicting the formation of stratus in the atmospheric boundary layer.- 5.5. A numerical model for predicting cloudiness and precipitation.- 5.6. A synoptic-hydrodynamic method for predicting precipitation.- 6. Mesoscale Atmospheric Motions and Cloudiness.- 6.1. Some experimental data on mesoscale clouds.- 6.2. A numerical model of convection in an unstable layer.- 6.3. Ensembles of cumulus clouds.- 6.4. The albedo of a cumulus field.- 6.5. Cloud formation in a mountainous region.- 7. The Vertical Structure of a Cloud Field.- 7.1. Correlations between cloudiness characteristics.- 7.1.1. The vertical structure of the temperature field.- 7.1.2. The height of the cloud boundaries.- 7.1.3. The humidity field.- 7.1.4. Double-layer cloudiness.- 7.2. Statistical methods for determining cloud boundaries and temperatures.- 7.3. The statistical correlation between temperature increments in time.- 7.4. Conditions preceding and accompanying cloud formation.- 7.5. Frontal clouds; precipitation and cloud water content.- 8. Statistical Data of Clouds and Cloud Behavior.- 8.1. Cloud boundaries and depth; amount of cloud cover.- 8.2. Air humidity in clouds.- 8.3. Cloud water content.- 8.4. Phase states of clouds.- 8.5. Horizontal dimensions and fluctuations of cloud fields.- 9. The Global Cloudiness Field.- 9.1. Seasonal average of the zonal cloudiness field.- 9.2. Cloud-field averages over large areas.- 9.3. Cloud-cover distribution density and distribution functions and their approximation.- 9.3.1. Effect of averaging area on the cloud-cover distribution density.- 9.3.2. Approximating cloud-cover distributions.- 9.3.3. Approximating cloud-cover distribution functions using squares of different sizes.- 9.3.4. Cloud-cover distribution functions averaged over latitude circles and seasons, and their approximation.- 9.4. Cloud-cover correlation functions.- 9.5. Parametrization of the global cloudiness field using complete systems of spectral functions.- 10. The Statistical Structure of the Humiduty Field in the Atmosphere.- 10.1. Expansion in natural orthogonal functions.- 10.2. The effect of cloudiness on the vertical profiles of temperature and humidity.- 10.3. Correlations between variations of specific humidity.- Conclusion.- References.