Showing papers on "Cloud computing published in 1996"

Computer Architecture: A Quantitative Approach, 2nd Edition

Abstract: The computing world today is in the middle of a revolution: mobile clients and cloud computing have emerged as the dominant paradigms driving programming and hardware innovation today. The Fifth Edition of Computer Architecture focuses on this dramatic shift, exploring the ways in which software and technology in the cloud are accessed by cell phones, tablets, laptops, and other mobile computing devices. Each chapter includes two real-world examples, one mobile and one datacenter, to illustrate this revolutionary change. Updated to cover the mobile computing revolution Emphasizes the two most important topics in architecture today: memory hierarchy and parallelism in all its forms. Develops common themes throughout each chapter: power, performance, cost, dependability, protection, programming models, and emerging trends ("What's Next") Includes three review appendices in the printed text. Additional reference appendices are available online. Includes updated Case Studies and completely new exercises.

Two-Time-Level Semi-Lagrangian Modeling of Precipitating Clouds

Abstract: This paper discusses two-time-level semi-Lagrangian approximations for the bulk warm-rain microphysics embedded in the framework of an anelastic cloud model. The central theoretical issue is a semi-Lagrangian integration of the rain-evolution equation. Because departure points of rain trajectories differ from those of flow trajectories and the terminal velocity of the precipitation depends on the concentration of the precipitation itself, effective semi-Lagrangian approximations are not necessarily straightforward. Some simplifying assumptions are adopted that compromise formal accuracy and computational efficiency of the method. Theoretical considerations are illustrated with idealized simulations of precipitating thermal convection and orographically forced clouds. Comparisons with corresponding results obtained using a more traditional, flux-form Eulerian cloud model document highly competitive performance of the semi-Lagrangian approach. Although derived for the warm-rain parameterization, th...

Edited synoptic cloud reports from ships and land stations over the globe, 1982--1991

Abstract: Surface synoptic weather reports for the entire globe for the 10-year period from December 1981 through November 1991 have been processed, edited, and rewritten to provide a data set designed for use in cloud analyses. The information in these reports relating to clouds, including the present weather information, was extracted and put through a series of quality control checks. Correctable inconsistencies within reports were edited for consistency, so that the ``edited cloud report`` can be used for cloud analysis. Cases of ``sky obscured`` were interpreted by reference to the present weather code as to whether they indicated fog, rain or snow and were given appropriate cloud type designations. Nimbostratus clouds were also given a special designation. Changes made to an original report are indicated in the edited report so that the original report can be reconstructed if desired. While low cloud amount is normally given directly in the synoptic report, the edited cloud report also includes the amounts, either directly reported or inferred, of middle and high clouds, both the non-overlapped amounts and the ``actual`` amounts. Since illumination from the moon is important for the adequate detection of clouds at night, both the relative lunar illuminance and the solar altitude are given; well as a parameter that indicates whether our recommended illuminance criterion was satisfied. This data set contains 124 million reports from land stations and 15 million reports from ships. Each report is 56 characters in length. The archive consists of 240 files, one file for each month of data for land and ocean separately. With this data set a user can develop a climatology for any particular cloud type or group of types, for any geographical region and any spatial and temporal resolution desired.

On the Global Variation of Precipitating Layer Clouds

Abstract: The aim of the Global Energy and Water Cycle Experiment Cloud System Study (GCSS) is to promote the description and understanding of key cloud system processes, with the aim of developing and improving the representation of cloud processes in general circulation models. The GCSS Science Panel identified a need to document important observational gaps in the structure of cloud systems inhibiting the development of cloud-resolving models as a tool for parameterizing cloud systems in general circulation models. The nature of precipitating layer clouds around the world is not well documented. To better quantify this, a synthesis of observations of these types of clouds made during field experiments conducted around the world has been developed. The synthesis draws on observations made in Australia, Canada, China, Israel, Japan, Russia, the Ukraine, the United States, and several European countries. The survey examines the global variation of the horizontal scales of cloud and precipitation, embedded ...

A methodology study of the validation of clouds in GCMs using ISCCP satellite observations

Abstract: The cloudiness fields simulated by a general circulation model and a validation using the International Satellite Cloud Climatology Project (ISCCP) satellite observations are presented. An adapted methodology is developed, in which the issue of the sub-grid scale variability of the cloud fields, and how it may affect the comparison exercise, is considered carefully. In particular different assumptions about the vertical overlap of cloud layers are made, allowing us to reconstruct the cloud distribution inside a model grid column. Carrying out an analysis directly comparable to that of ISCCP then becomes possible. The relevance of this method is demonstrated by its application to the evaluation of the cloud schemes used in Laboratoire de Meteoroligie Dynamique (LMD) general circulation model. We compare cloud properties, such as cloud-top height and cloud optical thickness, analysed by ISCCP and simulated by the LMD GCM. The results show that a direct comparison of simulated low cloudiness and that shown from satellites is not possible. They also reveal some model deficiencies concerning the cloud vertical distribution. Some of these features depend little on the cloud overlap assumption and may reveal inadequate parameterisation of the boundary layer mixing or the cloud water precipitation rate. High convective clouds also appear to be too thick.

The Link between Summertime Cloud Radiative Forcing and Extratropical Cyclones in the North Pacific

Abstract: This paper examines the role of extratropical cyclones in determining the cloud radiative forcing over the North Pacific during summer. Specifically, this study uses daily and monthly ERBE cloud radiative forcing, monthly ISCCP cloud-type distributions and optical depth, daily ECMWF meteorological analyses, and a climatology of cloud-type distributions based on surface observations. The geographic correspondence between monthly mean fields of cloud radiative forcing, cloud type and optical depth, and quantities such as baroclinicity and transient eddy flux suggests that large-scale, stratiform cloud systems associated with traveling cyclones are largely responsible for the band of strongly negative shortwave cloud forcing (Cs) over the Pacific between 40° and 60°N. Analysis of daily ERBE cloud forcing for July 1985, in conjunction with daily ECMWF geopotential, demonstrates the evolution of highly reflective cloud systems associated with several traveling, closed lows. The southwest to northeast ...

The impacts of SO2 oxidation in cloud drops and in haze particles on aerosol light scattering and CCN activity

Abstract: Calculations with an explicit microphysical model show significant sulfate production in both clouds and unactivated haze but significant impact on particle light scattering and CCN production only for the cloud scenarios.

Atmospheric Scene Simulation Modeling and Visualization.

Abstract: : This report provides a review of the Cloud Scene Simulation Model (CSSM), an empirical cloud model developed to support high-fidelity training and simulation applications. TASC and the U.S. Air Force Phillips Laboratory have developed the CSSM to simulate realistic high-resolution cloud and precipitation features within domains defined by larger-scale weather conditions. The current version of the cloud model is built upon the CSSM developed previously for the Smart Weapons Operability Enhancement Program. It contains several key additions and enhancements to satisfy modeling and simulation requirements of the Distributed Interactive Simulation (DIS) community. The model generates four-dimensional (three spatial and time) cloud and precipitation fields using a combination of stochastic field generation techniques and a simple convection model. Internal model parameters have been tuned to fit observed cloud data.

Automated cloud cover assessment for Landsat TM images

Abstract: This paper describes a method for cloud cover assessment using computer-based analysis of multi-band Landsat images. The objective is to accurately determine the percentage of cloud cover in an efficient manner. The 'correct' value is determined by an expert's visual assessment. Acceptable error rates are +/- 10 percent from the visually determined coverage. This research improves upon an existing algorithm developed for use by the EROS data center several years ago. The existing algorithm uses threshold values in bands, 3, 5 and 6 based on the expected frequency response for clouds in each band. While this algorithm is reasonably fast, the accuracy is often unsatisfactory. The dataset used in developing the new method contained 329 subsampled, 7-band Landsat browse images with wide geographic coverage and a variety of cloud types. This dataset, provided by the EROS Data Center, also specifies the visual cloud cover assessment and the cloud cover assessment using the current automated algorithm. Mask images, separating cloud and non- cloud pixels, were developed for a subset of these images. The new approach is statistically based, developed forma multi-dimensional histogram analysis of a training subset. Images from a disjoint test set wee then classified. Initial results are significantly more accurate than the existing automated algorithm.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Semi-prognostic tests of a new cumulus parameterization scheme for mesoscale modeling

Abstract: A new cumulus parameterization scheme is developed, discussed, and tested. 3 sizes of clouds: small, medium and large are allowed by this scheme; they crudely represent a spectrum of clouds and all 3 sizes of cloud may exist at any given time. All clouds are based on a quasi-one-dimensional cloud model that has been shown to deliver mass, moisture and heat fluxes comparable to those calculated by a 3-dimensional convective cloud model at the mature stage of a modeled convective storm. The radus of the largest cloud is twice that of the medium-sized cloud which is, in turn, twice that of the smallest cloud. The largest cloud may also have a saturated downdraft that can penetrate to the ground. In order to close the relation between the cloud and grid scales, 3 closure relations are imposed. Together, they yield a unique solution of the cloud population at any given time. In the first 2 constraints, both the convective and grid scale mass and moisture budgets are linked. Of the possible cloud sets that satisfy both the mass and moisture constraints, we choose the one that produces the fastest rate of heating from integrating the individual cloud heating rates over the possible cloud sets and over the cloud depths. The scheme is tested semi-prognostically with Sesame V storm-scale analyses during a period in which the precipitation was almost exclusively convective in nature (2000 GMT to 2300 GMT on 20 May 1979). The comparison between observed grid scale and cumulus parameterization diagnosed heating and drying rates is quite good. This is true for both individual grid points and the convectively active area as a whole. DOI: 10.1034/j.1600-0870.1996.t01-1-00006.x

Rainfall estimation from cold cloud duration : experience of the TAMSAT group in West Africa

Abstract: It is now more than ten years since the initiation of rainfall estimates over West Africa which use the duration of cold Cloud as the main observed variable. Since then, these estimates have been put to a number of operational uses, and the results of several different algorithms have been compared, for example during the 1993 workshop held in Niamey (AGRHYMET, 1994). However, there has been little advance in the scientific basis for the methods used, and their empirical nature means that they have not improved systematically over the years. It is appropriate at this stage to review the results, and consider the way forward. This paper presents a contribution to this process based on the experience of the TAMSAT group. The obvious gains in the last few years have included the increasing amount of data which is available to provide calibrations, and these are now based on a variety of wetter and drier years. The stability of the calibrations is discussed in section 5. Another major advance has been in understanding the limitations of the rainfall estimates which result from any of the regressions, and hence the realism with which they can be used in operational decision making. In spite of the substantial scatter which is inherent in the methods, the estimates can indeed be relied upon for a number of important purposes, and some of these are outlined in section 7. First, however, a brief account is given of the detailed procedures which have been used by TAMSAT, knowing that these can have a substantial effect on the outputs from apparently similar processing systems. Some attempts to elaborate and improve the algorithms are reviewed. Compared with the original, simplistic version none of these has yet provided a significant increase in the accuracy of the estimates when tested in an operational mode.

Review of Debris-Cloud Modeling Techniques

Abstract: The state of the art in debris-cloud modeling is examined. The simulation of the debris-generating breakup event is discussed, including how the distributions of fragment number and velocity can be utilized in a parametric cloud model. The various methods available for fragment, and hence cloud, propagation are described, and the different techniques employed to calculate collision probabilities for spacecraft encountering the cloud are also discussed. It is concluded that the method of probabilistic continuum dynamics, which inherently couples cloud evolution and collision hazard assessment, offers the greatest combination of versatility and simulation accuracy among the models developed to date. danger to orbiting spacecraft comes from objects in the millimeter- to-centimeter size range. These objects are both numerous and large enough to be able to penetrate all but the most heavily shielded space structures. The most common source of such particles is on-orbit fragmentation events, and so the modeling of such events is impor- tant when trying to determine the risk they pose to current and future space missions. Modeling the evolution of a space debris cloud and the collision risk associated with it is essentially a two-stage process. First, there is the necessity to simulate the fragmentation event itself. This takes the form of a quantitative description of the event with regard to the distributions of fragments produced and the processing of these dis- tributions to yield a set of parameters that describe the breakup in a form that can serve as input to the second stage of the overall sim- ulation. On receipt of the output from the fragmentation model, the debris-cloud propagator can then evolve the cloud forward in time, and the desired analysis of the spread of fragments produced can be performed. This analysis may take the form of an investigation into the size, shape, and general behavior of the cloud itself, or al- ternatively may concentrate on the cloud's interaction and possible collision with other orbiting objects. This paper examines the state of the art in debris-cloud mod- eling, looking at both the simulation of the breakup event and the subsequent evolution of the fragments produced. The different tech- niques employed to calculate collision probabilities for spacecraft encountering the cloud are also discussed.

Neural network-based cloud detection/classification using textural and spectral features

Abstract: An efficient and robust neural network-based scheme is introduced in this paper to perform automatic cloud detection and classification. An unsupervised Kohonen neutral network was used to classify, the cloud contents of a 8/spl times/8 blocks in an image into ten different cloud classes. Inputs to the network consisted of textural features of each block obtained using an efficient feature extraction scheme namely, the wavelet transform (WT). This scheme not only reduces the dimensionality of the data but also extracts useful features of the data. To improve the detection rate and reduce the false positive rate, especially for low clouds and thin high clouds, a multi-channel fusion system was constructed to combine the results of different optical bands. All alternative approach for automatic cloud detection/classification based on multi-spectral features was also studied to analyze and compare the effectiveness of multi-spectral-based scheme vs textural-based scheme. The results using high resolution GOES 8 data show the promise of the Kohonen neural network when used in conjunction with WT as feature extractor for cloud detection/classification.

A new approach to land-based cloud classification

Abstract: Land-based cloud-classification resolves details which are unavailable in operational satellite imagery. In this study, the emphasis is on single-channel image processing employing convolution masks and statistical measures. Experimental results of classification are examined as a means of deriving simplified cloud amount and class encoding similar to the internationally accepted practice.

Validation of modelled cloudiness using satellite-estimated cloud climatologies

Abstract: A method to evaluate forecasts of total fractional cloud cover using satellite measurements is demonstrated. Cloud analyses in the form of monthly cloud climatologies are extracted from NOAA AVHRR data which are compared to corresponding cloud forecast information from the HIRLAM and ECMWF numerical weather prediction models. The satellite-based cloud information is extracted for a summer month in 1994 and a winter month in 1995 by use of the SMHI cloud classification model SCANDIA. Cloud analyses are conducted for an area covering a substantial part of northern Europe. Deficiencies in forecasted cloud amounts are found for both models, especially the underestimation of cloudiness for short forecast lengths with the HIRLAM model. Forecast improvements using the HIRLAM model are indicated when introducing a cloud initialisation technique using cloud fields from initial 6-hour forecasts (first-guess fields). Future systematic validations using this technique are, however, needed to make firm conclusions on the general model behaviour. SCANDIA-derived cloud information is proposed as a valuable complement to other datasets used for cloud forecast validation (e.g., the SSM/I- and ISCCP data sets). DOI: 10.1034/j.1600-0870.1996.t01-1-00015.x

Cloud Field Identification for Earth Radiation Budget Studies. Part I: Cloud Field Classification Using HIRS-MSU Sounder Measurements

Abstract: Onboard the NOAA satellites, the High-Resolution Infrared Sounder (HIRS) with its 20 channels, combined with the Microwave Sounding Unit (MSU), provides a powerful tool for cloud field classification at a spatial resolution of about 100 km. The 3I (improved initialization inversion) algorithm-developed to obtain atmospheric temperature and water vapor profiles as well as cloud and surface properties-has been modified in order to extract more reliable information on cloud-top pressure and effective cloud amount. These cloud parameters have been compared to cloud types identified by an operationally working threshold algorithm based on Advanced Very High Resolution Radiometer measurements over the North Atlantic. The improved 3I cloud algorithm provides cloud parameters not only for high clouds but also greatly improves the determination of low clouds. The algorithm has also been extended to give cloud information over partly cloudy situations. The 3I cloud field classification yields 11 different ...

Effects of a polydisperse cloud on tropospheric chemistry

Abstract: Effects of a polydisperse cloud on tropospheric chemistry have been studied in the framework of a two-dimensional model where dynamical, microphysical, and chemical processes are fully interactive. The chemical module describes the tropospheric photochemistry of ozone precursors in both gaseous and aqueous phases for a remote atmosphere. Impacts of the cloud polydisperse feature have been obtained by comparing the results in the case of a monodisperse cloud created under the same meteorological conditions. The [NO]/[NO•] ratio decreases more sharply in the case of the polydisperse cloud. The partitioning of ihe most soluble species does not follow the Henry's law equilibrium except in the middle of the cloud. This result has implications for airborne measurements made within clouds. Deviations from Henry's law found in samples are usually explained only by the effect of variations of the liquid water content with time, assuming that no real deviations exist in the real cloud. Here, it is shown that deviations from Henry's law equilibrium may exist even for clouds consisting of small droplets.

Global Modeling of Cloud Radiative Effects Using ISCCP Cloud Data

Abstract: Cloud radiative effects are represented in simulations with the general circulation model of the Navy Operational Global Atmospheric Prediction System (NOCAPS) using ingested cloud field data from the ISCCP dataset rather than model-diagnosed cloud fields. The primary objective is to investigate the extent to which the high temporal resolution ISCCP data can be used to improve the simulation of cloud radiative effects on the general circulation in GCM simulations much as observed sea surface temperatures (SSTs) have been used to avoid simulation errors resulting from inaccurately modeled SSTs. Experiments are described that examine the degree to which uncertainties in cloud field vertical structure impair the utility of the observed cloud data in this regard, as well as the extent to which unrealistic combinations of cloud radiative forcing and other physical processes may affect GCM simulations. The potential for such unrealistic combinations stems from the lack of feedback to the cloud fields i...

Automated cloud-drift winds from GOES images

Abstract: Estimation of the atmospheric wind field based on cloud tracking using a time sequence of satellite imagery is an extremely challenging problem due to the complex dynamics of the imaging instruments and the underlying non-linear phenomena of cloud formation and weather. Cloud motion may involve both partial fluid motion and partial solid motion, which we model as semi-fluid motion. Motion algorithm with subpixel accuracy using differential geometry invariants of surfaces was developed to track clouds. The motion model is general enough to include both physical and geometrical constraints. Typically, a polynomial displacement function is used to model the local deformation behavior of a surface patch undergoing semi-fluid motion. The cloud tracking algorithm recovers local cloud surface deformations using a sequence of dense depth maps and corresponding intensity imagery, that captures the time evolution of cloud-top heights. Either intensity or depth information can be used by the semi-fluid motion analysis algorithm. A dense disparity or depth map that can be related to cloud-top heights is provided by the Goddard Automatic Stereo Analysis module for input to the motion analysis module. The results of the automatic cloud tracking algorithm are extremely promising with errors comparable to manually tracked winds. Experiments were performed on GOES images of Hurricanes Frederic, Gilbert and Luis, and a temporally dense 1.5 minute time interval thunderstorm sequence covering Florida region. Future work involves using multispectral information, incorporating robustness, cloud motion segmentation and adaptive searching for improving operational cloud-tracking performance.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

What do we Really Know about Cloud Formation

Abstract: Four processes of molecular cloud formation are discussed: formation in swept-up shells, coagulation of smaller clouds, condensation in larger clouds, and compression in a supersonically turbulent medium. Examples and constraints for each process are given.