Abstract: To provide a background for ARM's activities at the North Slope of Alaska/Adjacent Arctic Ocean sites, an overview is given of our current state of knowledge of Arctic cloud and radiation properties and processes. The authors describe the Arctic temperature and humidity characteristics, cloud properties and processes, radiative characteristics of the atmosphere and surface, direct and indirect radiative effects of aerosols, and the modeling and satellite remote sensing of cloud and radiative characteristics. An assessment is given of the current performance of satellite remote sensing and climate modeling in the Arctic as related to cloud and radiation issues. Radiation-climate feedback processes are discussed, and estimates are made of the sign and magnitude of the individual feedback components. Future plans to address these issues are described.

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.

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 ...

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.

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 ...

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.

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

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.

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.

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.

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.

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

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 ...

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.

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...

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.

Abstract: The split-window facility offered by the AVHRR instrument is used to good purpose in an advanced cloud detection and analysis package called APOLLO. This is based on threshold tests to distinguish between cloud-free, fully-cloudy and partially-cloudy pixels over land and sea surfaces. If necessary, a further test to distinguish between cloud, snow and ice is applied. The final result is a cloud mask which enables users to use only those pixels which are most appropriate for their desired application, i.e. fully-cloudy pixels for cloud products, cloud-free pixels for surface products and both partially-cloudy and fully-cloudy pixels for cloud cover amount estimation. In this chapter we present the design of the algorithms included in the scheme, and also discuss validation of the derived products which has been performed in several case studies and shows reasonable results.

Abstract: Some 70% of powders handled in industry are combustible and, if dispersed into a cloud and ignited, can cause a dust explosion. Methods for control of dust explosions exist but important problems remain unresolved. A consensus view from European industry and research associations on the 23 topics requiring further study is presented. Reacting to this review, the E.U. Environment Programme has supported research on measurement dust cloud characteristics in plant, characterisation of smouldering in powders, burning characteristics of dust clouds, measurement of blast effects and fireball sizes from vented explosions and modelling these effects. The results from the research are summarised.

Abstract: We present a practical approach for detecting and localizing clouds in satellite remote sensing images. Cloud detection is useful in improving the accuracy of land cover classification when there are clouds present in the images. After detection and removal of clouds we can selectively merge classification results from two temporally separate images of the same area to minimize the cloud effect. We emphasize the ease of implementation of the algorithm so that practitioners can easily adapt the method for their own use

Abstract: A new method based upon high-spatial-resolution imagery is presented that matches cloud and shadow regions to estimate cirrus and stratus cloud heights. The distance between the cloud and the matching shadow pattern is accomplished using the 2D cross-correlation function from which the cloud height is derived. The distance between the matching cloud-shadow patterns is verified manually. The derived heights also are validated through comparison with a temperature-based retrieval of cloud height. It is also demonstrated that an estimate of cloud thickness can be retrieved if both the sunside and antisunside of the cloud-shadow pair are apparent. The technique requires some intepretation to determine the cloud height level retrieved (i.e., the top, base, or mid-level). It is concluded that the method is accurate to within several pixels, equivalent to cloud height variations of about ±250 m. The results show that precise placement of the templates is unnecessary, so that the development of a semiaut...

Abstract: This paper describes an application of the intelligent system (IS) combining an expert system (ES) and an artificial neural network (ANN) for the evaluation of the short time thermal rating and temperature rise of overhead power transmission lines The IS was developed as a rule-based system using the Leonardo expert system shell in conjunction with a neural network and database The ANN and regression best-fitting techniques were employed to determine the hourly solar irradiance The neural network was trained for the prediction of maximum hourly values of the direct and diffuse solar radiation dependent on astronomic and meteor-climatic conditions The developed IS can be used to assist operators in loading of transmission lines in different operating, ambient, geographic latitude, cloud and ground reflection conditions It also assists the operators to determine the permissible duration of the conductor overload

Abstract: Gaining a better understanding of the influence of clouds on the earth's energy budget requires a cloud classification that takes into account cloud height, thickness, and cloud cover. The radiometer ScaRaB (scanner for radiation balance), which was launched in January 1994, has two narrowband channels (0.5–0.7 and 10.5–12.5 µm) in addition to the two broadband channels (0.2–4 and 0.2–50 µm) necessary for earth radiation budget (ERB) measurements in order to improve cloud detection. Most automatic cloud classifications were developed with measurements of very good spatial resolution (200 m to 5 km). Earth radiation budget experiments (ERBE), on the hand, work at a spatial resolution of about 50 km (at nadir), and therefore a cloud field classification adapted to this scale must be investigated. For this study, ScaRaB measurements are simulated by collocated Advanced Very High Resolution Radiometer (AVHRR) ERBE data. The best-suited variables for a global cloud classification are chosen using as a...