Cloud Dissipation Research Articles

Liquid and Ice Cloud Microphysics in the CSU General Circulation Model. Part 1: Model Description and Simulated Microphysical Processes

Abstract Microphysical processes responsible for the formation and dissipation of water and ice clouds have been incorporated into the Colorado State University General Circulation Model in order to 1) yield a more physically based representation of the components of the atmospheric moisture budget, 2) link the distribution and optical properties of the model-generated clouds to the predicted cloud water and ice amounts, and 3) produce more realistic simulations of cloudiness and the earth's radiation budget. The bulk cloud microphysics scheme encompasses five prognostic variables for the mass of water vapor, cloud water, cloud ice, rain, and snow. Graupel and hail are neglected. Cloud water and cloud ice are predicted to form through large-scale condensation and deposition processes and also through detrainment at the tops of cumulus towers. The production of rain and snow occur through autoconversion of cloud water and cloud ice. Rain drops falling through clouds can grow by collecting cloud water, and ...

A Sensitivity Study of Convective Cloud Formation by Vegetation Forcing with Different Atmospheric Conditions

Variable vegetation cover is a possible trigger for convection, especially in semiarid areas due to differential surface forcing. A two-dimensional numerical model with explicit cloud physics and a detailed vegetation parameterization scheme is used to investigate the role of vegetation differences in triggering convective cloud formation. The ground surface in all simulations includes two irrigated vegetation areas with a dry steppe in the center of the domain. The effects of atmospheric stability, ambient moisture profile, and horizontal heating scale are investigated. Atmospheric stability controls the growth of convective circulations. Thermal circulations form at the interfaces between the vegetated areas and the dry steppe. In the more stable environment, two distinct convective cells persist; they merge into one cell in the less stable cases. The existence of low-level moisture controls the timing and persistence of clouds that form. An interesting result is the earlier dissipation of clouds in less stable cases, as greater mixing with drier air from aloft leads to the dilution of the cloud water. Since the largest thermal forcing exists at the interfaces, length of the steppe interacts with the stability to control the merger of the cells. The two cells merge quickly into one for narrow horizontal heating. For the widest heating scale studied, no merger occurs.

Simulation of climate change over europe using a nested regional‐climate model. I: Assessment of control climate, including sensitivity to location of lateral boundaries

AbstractPresent‐day climate simulations for Europe are presented, based on a 50 km regional‐climate model (RCM) driven by output from a global general‐circulation model (GCM) using a one‐way nesting approach. Both models are components of the Meteorological Office Unified Forecast/Climate Model and use the same subgrid‐scale physics. the relationship between the RCM circulation and that of the driving GCM was assessed in seasonal RCM integrations using domains of different sizes. In the larger domains, both the mean flow and the day‐to‐day variability in the RCM diverge from that of the GCM on the synoptic scale, rendering the RCM solution physically inconsistent with the GCM solution external to the RCM domain. At the grid‐point scale the RCM freely generates its own features, even in the smaller domains—only at points adjacent to the boundary buffer zone is there evidence of significant distortion by the lateral boundary forcing from the GCM.Using one of the smaller domains, a 10‐year RCM simulation was carried out, driven by a coupled atmosphere/mixed‐layer‐ocean version of the GCM. Over the region of interest the general circulation and daily synoptic variability is realistically simulated by the GCM and, therefore, also by the RCM (see above). Stronger vertical motions in the RCM lead to a general increase in dynamical precipitation relative to the GCM, and thus a drier and warmer troposphere and reduced convective cloud and precipitation. Layer‐cloud cover is also reduced in the RCM, due to a time‐step dependence in the treatment of the dissipation of ice cloud. Significant changes occur in the surface heat balance. the spatial patterns of surface air temperature and precipitation over Europe are well simulated by both the GCM and the RCM on scales resolved by the former. At finer scales the RCM contains a strong signal which is related to orographic height. Validation against a detailed observed climatology for Great Britain demonstrates that this signal contains considerable skill.

Deterministic chaos, fractals, and quantumlike mechanics in atmospheric flows

The complex spatiotemporal patterns of atmospheric flows that result from the cooperative existence of fluctuations ranging in size from millimetres to thousands of kilometres are found to exhibit long-range spatial and temporal correlations. These correlations are manifested as the self-similar fractal geometry of the global cloud cover pattern and the inverse power-law form for the atmospheric eddy energy spectrum. Such long-range spatiotemporal correlations are ubiquitous in extended natural dynamical systems and are signatures of deterministic chaos or self-organized criticality. In this paper, a cell dynamical system model for atmospheric flows is developed by consideration of microscopic domain eddy dynamical processes. This nondeterministic model enables formulation of a simple closed set of governing equations for the prediction and description of observed atmospheric flow structure characteristics as follows. The strange-attractor design of the field of deterministic chaos in atmospheric flows consists of a nested continuum of logarithmic spiral circulations that trace out the quasi-periodic Penrose tiling pattern, identified as the quasi-crystalline structure in condensed matter physics. The atmospheric eddy energy structure follows laws similar to quantum mechanical laws. The apparent waveparticle duality that characterizes quantum mechanical laws is attributed to the bimodal phenomenological form of energy display in the bidirectional energy flow that is intrinsic to eddy circulations, e.g., formation of clouds in updrafts and dissipation of clouds in downdrafts that result in the observed discrete cellular geometry of cloud structure.

Satellite observation and mesoscale cloud modeling of St. Anthony, Minnesota storm clouds

Both rawinsonde data and geosynchronous satellite imagery were used to study the life cycles of St. Anthony, Minnesota's severe convective storms. Cloud modeling, with input sounding data from Saint Cloud, Minnesota, and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation. Comparisons were made among the seven groups of severe storms which produced an outbreak of 30 tornadoes across the United States.

Observations of Marine Stratocumulus Clouds During FIRE

The First International Satellite Cloud Climatology Project Regional Experiment (FIRE) to study extensive fields of stratocumulus clouds off the coast of California is presented. Measurements on the regional and detailed local scales were taken, allowing for a wide interpretation of the mean, turbulent, microphysical, radiative, and chemical characteristics of stratocumulus. Multiple aircraft and ground-based remote-sensing systems were used to study the time evolution of the boundary layer structure over a three-week period, and probes from tethered balloons were used to measure turbulence and to collect cloud-microphysical and cloud-radiative data. The observations provide a base for studying the generation maintenance and dissipation of stratocumulus clouds, and could aid in developing numerical models and improved methods for retrieving cloud properties by satellite.

Transverse deflection and dissipation of small plasma beams and clouds in magnetized media

Propagation of a quasi‐neutral plasma beam or cloud across a magnetic field is considered for the case where the transverse dimension of the beam or cloud is sufficiently small compared to ion gyroradii. This situation commonly arises for active experiments in near‐earth space. Two mechanisms are presented for transverse deflection of a beam or cloud in the ‐ v0 × B0 direction where v0 is the velocity relative to the ambient medium. In the first, asymmetric escape of ions from an electrically polarized beam or cloud causes transverse deflection by means of a rocket effect. The transverse deflection distance is estimated to be a few times the initial transverse dimension of the beam or cloud. Dissipation occurs within a few times the thermal ion transverse crossing time. In the second mechanism, asymmetric charging results from localized accumulation of incident ions from the ambient medium. This excess positive charge distorts electric equipotentials and drives electron Hall currents that maintain an asymmetric compressed magnetic field region. The asymmetry of the magnetic stress contributes to transverse deflection with the same sign as the rocket effect. The asymmetric magnetic field also focuses incident ions to yield the localized charge accumulation. These ideas are qualitatively consistent with observations of the Active Magnetospheric Particle Tracer Explorers artificial comet releases.

Interstellar planetesimals – I. Dissipation of a primordial cloud of comets by tidal encounters with massive nebulae

The Oort cometary cloud is subject to tidal disruption during close encounters with massive nebulae. The process is studied by numerical integration of ∼ 33 000 comet orbits, using realistic models of the Oort cloud and the interstellar medium. It is found that the cloud is rapidly cleared of long period comets, and it is concluded that such comets are probably interstellar in origin. A capture event or tidal disturbance may have taken place ≾ a few 107 yr ago.

Infrared (106-μm) scattering and extinction in laboratory water and ice clouds

Measurements of the angular scattering and extinction of IR (10.6-mum) laser radiation in laboratory water and ice clouds are reported and compared to theoretical predictions for spheres and visible (0.633-mum) light scattering data. Randomly oriented cloud particles with dimensions ranging from several times smaller to larger than the incident wavelength generated phase functions span the Rayleigh and Mie scattering domains and illustrate the effects caused by strong internal energy absorption. Dual-wavelength extinction measurements reveal information on the growth and dissipation of laboratory water clouds and the effects of cloud seeding. The remote sensing significance of the findings is discussed.

Eddy Formation near San Simeon

A unique example of early morning and noontime very high resolution (0.62 km) visual satellite imagery is presented depicting a well-defined eddy over California coastal waters west of San Simeon. In addition to the low cloud vortex, the pictures vividly display the dissipation or movement of stratoform clouds. The synoptic situation during the occurrence of this eddy formation and cloud dissipation is also presented as a source of possible explanations of the cloud pattern.

The Collection Efficiencies of Highly Charged Water Drops for Uncharged Cloud Droplets

Abstract Experiments have been conducted to investigate the collection efficiencies of highly charged drops with radii from 60 to 120 μm for relatively uncharged droplets of about 20 μm radius. The measurements indicate that, for drop charges approaching the Rayleigh limit value, the collection efficiencies are increased by a factor of around 20–30 over those for uncharged drops. The high collection efficiencies imply that a highly charged drop is capable of collecting uncharged droplets initially situated at distances of several drop radii from the fall trajectory of the drop. Calculations utilizing a simple numerical model for the interaction of a drop and droplet pair demonstrate that these high values of collection efficiency are due to the electrical forces of attraction arising between the drop charge and the dipole induced within the uncharged droplet. The implications of this work for the modification and dissipation of warm clouds and fogs are briefly discussed.

Polar meteorology: a review of some recent research

The general large-scale circulation of the global atmosphere has its basic driving mechanism in the equator-poleward temperature gradients in both hemispheres. It has become increasingly obvious over the last few decades that to understand and predict the behaviour of the atmosphere at any point, it is essential to understand the behaviour of the total global fluid system. The Global Atmospheric Research Project (GARP) is an outcome of this recognition. Studies of the heat sinks (the polar regions) are therefore just as important as studies of the heat source (the equatorial regions) to understand the meteorology of the planet. Interest in polar meteorology has undergone many cyclic fluctuations, peaking during the various international polar years and, more recently, during the International Geophysical Year, 1957–58. At the present, the focus of GARP's first objective (improved extended weather forecasts) is on the tropical heat source, where convection and cloud formation and dissipation are still relatively little understood processes. However, the second GARP objective (better understanding of the physical basis of climate) requires more attention to be devoted to the cryosphere, its long-term interaction with oceans and atmosphere, and its role as an indicator of climatic change. The idea of a polar experiment (POLEX) was initially introduced by Treshnikov and others (1968) and by Borisenkov and Treshnikov (1971). A summary of the early history of POLEX was recently given by Weller and Bierly (1973). The two closely related objectives of POLEX that most directly pertain to GARP may be restated in their simplest terms as (1) a better understanding of energy transfer processes and the heat budgets of the polar regions for the purpose of parameterizing them properly in general circulation models and climate models, and (2) provision of adequate data from the polar regions during the First GARP Global Experiment (FGGE) in 1978.

Survey of Weather Modification in the Soviet Union

On the basis of a review of abstracts of articles published mostly since 1969, a summary has been prepared of Soviet research in weather modification. A wide spectrum of problems is being studied. Hail suppression and precipitation stimulation still are major areas of activity in the USSR. In recent years, Soviet scientists have begun research on the lightning suppression, the dissipation of convective clouds, and the use of heat for the dissipation of warm fog and stratus. The articles surveyed show little evidence that Soviet scientists, unlike their American counterparts, are convinced of the value of randomized experiments in the evaluation of cloud-seeding hypotheses. There is no evidence in this literature that the modification of large scale weather phenomena is being actively investigated in the Soviet Union.

The 1968–69 Winter as an Outgrowth of Sea and Air Coupling During Antecedent Seasons

Abstract North Pacific sea surface temperature variations are analyzed as a result of and a controlling factor for the general atmospheric circulation during the period from May 1968 through the subsequent winter, when heavy rains in California, snows in Washington and Oregon, and disappearance of the Hawaiian trade winds occurred. The data indicate that a vast pool of abnormally warm water developed rapidly over southern portions of the North Pacific in June because of an abrupt May-to-June change in atmospheric circulation. This change favored strong subsidence in a deep Pacific anticyclone, dissipation of cloud, and greatly increased insolation. The climatologically stable Pacific anticyclone with its subsidence permitted the warm pool to remain through the subsequent fall. Penetration into the area of the pool by fronts and cold air masses during winter appears to have excited abnormal low-latitude cyclonic developments which transported deep moist air currents from the intertropical convergence zone ...

Electrostatic haring and Dissipation of Dust Clouds in Enclosed Rooms

Experimental results are presented on a method of cleaning the particles in suspension in the air of a working area, without circulating the air. Only a small percentage of the particles are charged directly by means of a light carriage supporting a grid of alternate corona and ground potential wires and traveling back and forth through the smoke and dust cloud.

A simplified model for the formation, movement, and dissipation of fair weather cumulus clouds

Certain patches of ground are favorable to the formation of fair weather cumulus clouds. These are patches which reflect rather than absorb solar heat. As the air above these patches is warmed, it will rise and, if the humidity is sufficient, the cooling effect of higher elevation will cause formation of a cloud of the type known as the fair weather cumulus. This fact is used in the present paper to develop a stochastic model for the temporal evolution of the contribution to cloud cover by fair weather cumuli.

A simplified model for the formation, movement, and dissipation of fair weather cumulus clouds

Certain patches of ground are favorable to the formation of fair weather cumulus clouds. These are patches which reflect rather than absorb solar heat. As the air above these patches is warmed, it will rise and, if the humidity is sufficient, the cooling effect of higher elevation will cause formation of a cloud of the type known as the fair weather cumulus. This fact is used in the present paper to develop a stochastic model for the temporal evolution of the contribution to cloud cover by fair weather cumuli.

SCATTERING OF SOLAR ENERGY BY CLOUDS OF “LARGE DROPS”

For the case when absorption is negligible, the direct and scattered solar beams have been followed down into clouds of “large” spherical waterdrops, to calculate the distribution of the generation of diffuse energy in the cloud. The generated diffuse energy is considered to obey a simple diffusion equation, from which the cloud albedo has been computed as a function of the cloud thickness, the mean free path, and the sun's zenith distance. One of the main results is the marked variation of albedo with zenith distance, especially for “thin” clouds. The results are compared with observations, and it appears that the dissipation of stratus clouds is often accompanied by a reduction in the effective scattering radius of the cloud drops.

The dissipation of scattered and broken cloud

AbstractShaw's early work on the dissipation of scattered and broken cloud is outlined and the loss of heat by cloud resulting from terrestrial radiation is indicated. The process of cloud dissipation is described and various criteria are given.The implications of these concepts in evaluating the significance of the slice method for studying cumulus clouds are then considered.A method of calculating the time required for a specified system of scattered and broken cloud to dissipate as a result of radiational cooling is described and the assumptions involved are discussed. The influence of the turbulent transfer of heat and water vapour under various conditions is indicated in a general manner and the effect of the absorption of solar radiation by the cloud is evaluated.Widespread vertical motion of the atmosphere may have a marked influence on cloud dissipation, depending on whether ascent or subsidence of the whole air mass is occurring. A method of calculating the amount of subsidence required to cause a given system of cloud to dissipate is described. For a particular case, the effects of ascent of the air mass and of radiation are combined, and useful criteria thereby obtained.

Journal of Meteorology

ONE result of the War has been such an increase in the number of meteorologists in the United States that the American Meteorological Society has decided that the moment has arrived when a financial success can be made in America of what is described as "a technical journal of the highest caliber in the field of meteorology". The recently reorganized Society has recognized the need to serve both the professional and amateur meteorologist, and it is for the professional that the new journal under the title The Journal of Meteorology is mainly intended (American Meteorological Society, Milton 86, Mass.). It is to be a quarterly journal eventually, but owing to the difficulty of starting a new publication, especially in war-time, it was considered best to have only two issues in the first volume, dated 1944, and the copy of the first issue that we have received, dated September 1944, is accordingly described as vol. 1, Nos. 1 and 2. The journal is edited by Prof. Victor P. Starr, of the University of Chicago, and there are four associate editors, among whom is J. Bjerknes. The print is larger than that usually used in scientific journals at the present time, and both it and the diagrams are very clear; the paper cover is a bright yellowish-orange. There are four articles, dealing respectively with the theory of the genesis and movement of cyclones, the determination of normal regions of atmospheric heating and cooling, the changes of temperature during the formation and dissipation of stratus cloud on the Californian coast, and lastly, the relationship between the major changes in the paths of tropical storms and the upper wind-field. The journal has certainly made a very promising start, and we wish its editors every success.