Showing papers on "Cloud computing published in 1978"

Numerical study of cloud electrification in an axisymmetric, time-dependent cloud model

Abstract: An axisymmetric, time-dependent, numerical cloud model has been applied to study how an isolated convective cloud can be electrified when rain and cloud particles are allowed to be charged by two particle charging mechanisms: ion attachment and polarization. Charge transports by electrical conduction, air convection, turbulent mixing, and the particle terminal velocities are all simulated. The close tie-in of the electrical development with the evolutions of the cloud growth is one of the distinctive features of the study. The full dynamical-microphysical-electrical interactions are allowed in the simulation. The results of numerical experiments make it appear likely that the polarization charging mechanism is an important one for the electrification of warm clouds. The results also show that with the inclusion of the polarization charging mechanism and depending on the growth stage of the cloud the cloud can be electrified into various charge center structures, which have been observed and reported in the literature for many years. The numerical results show that the cloud cannot be rapidly electrified until rainwater forms and the polarization charging mechanism operates. Initially, the cloud is charged into a ‘positive dipole’ structure with a positive charge center in the upper part of the cloud and a negative one below. As the cloud grows further, another positive charge center forms below the main negative one. This weaker positive center is closely associated with the positively charged rain formed in that region. As the rain falls out of the cloud, this positive center extends below the cloud base. When the cloud top reaches its maximum level, the cloud base starts to rise and the cloud grows weaker thereafter. In the later stage of the development the charge distribution patterns of the rain field dominate the whole electrical structure of the model. The electrical pattern thereafter is greatly affected by the downward movement of the rain. With the fallout of the rain the cloud charge centers exhibit successfully a positive dipole structure and then a ‘negative dipole’ structure consisting of a negative charge center in the upper part of the cloud and a positive one below. The electrical force effects on the terminal velocities of the rain and cloud particles are also included in the study. The results show that the rain particle terminal velocities start to decrease by a few meters per second in a region where the electric field strength grows beyond 2 × 105 or 3 × 105 V/m. The cloud particle terminal velocities reach only several centimeters per second, even in the thunderstorm electrical state. As a result of the levitation effect on rain, the simulated cloud in the present study develops double maxima in the cloud water content, giving it a more irregular appearance than the weakly electrified or nonelectrified cloud.

Dynamic Classification of Mesoscale Cloud Patterns.

Abstract: Cumulative histograms taken from eight consecutive infrared pictures of GOES 1 are used to study the spatio-temporal evolution of mesoscale cloud patterns. A model is proposed to approximate the volume of cloud lying in a particular area. Then, the cloud volume variation between successive pictures in the same area is deduced. This volume variation is used to define a cloud development index. Development or dissipation of cloud formations can be distinguished using this index.

Cloud Analysis from Bi Spectral Satellite Data

Abstract: : A horizontal differencing bi-spectral technique has been developed which includes an iteration scheme for reducing errors in computed cloud amount. The technique requires that cloud surfaces over the area of application be horizontally homogeneous, and as developed, assumes that the observed maximum and minimum brightness counts represent cloud and clear filled resolution points respectively. These values are then used to normalize the data in computing total cloud amount. The computed results of the horizontal differencing bi-spectral method, as applied to real data sets, have been compared to the results obtained from a modified frequency distribution method and the general bi-spectral method. The results of this comparative analysis indicate that the computed cloud amounts of the horizontal differencing method are less variable than for the frequency distribution and general bi-spectral methods, and are thus better suited for objective analyses. The computed cloud temperatures of the horizontal differencing method were also shown to be more realistic than those computed by the general bi-spectral method.