Abstract: A general circulation model (GCM) study is presented in which cloud radiative properties are computed from cloud liquid water content inferred from the GCM hydrological cycle. Model-generated and satellite albedos are in rough agreement. Analysis of the cloud radiative forcing indicates that cloud albedo effects overcome cloud infrared opacity effects in most regions. Both computed and observed albedo of clouds decrease from low to high altitudes. The model with variable cloud optics produces significantly different regional albedos from the same one with fixed cloud optics, especially over the tropics. The cloud droplet size distribution also has a significant impact on the model albedos. The temperature of the tropical upper troposphere is somewhat sensitive to the microphysical characteristics of the model cirrus clouds.

Abstract: The analysis of Paluch suggests that some cumuli contain cloudy air from only two sources: cloud base and cloud top A framework is presented for the investigation of droplet spectral evolution in clouds composed of air from only these two sources The key is the investigation of the dependence of droplet concentration N on the fraction of cloud base air F in a sample of cloudy air This N-vs-F analysis is coupled with an investigation of droplet spectral parameters to infer the types and scales of entrainment and mixing events The technique is used in a case study of a small, nonprecipitating continental cumulus cloud which was sampled during the 1981 CCOPE project in eastern Montana The mixing between cloudy and entrained air in this cloud often appears to occur without total removal of droplets, although there is evidence that total evaporation occurs in some regions with low liquid water content The observed droplet spectra are compared with those calculated from an adiabatic parcel model

Abstract: Observational and modeling studies dealing with different aspects of convective clouds are reviewed and interpreted to construct a generalized description of the structure, dynamics, and thermodynamics of convective cloud downdrafts. Observational studies reveal that downdraft speeds and sizes range from typical values of several meters per second and several hundred meters in nonprecipitating cumulus congestus clouds to typical values of 5–10 m s−1 and several kilometers in precipitating cumulonimbi. Maximum measured downdraft speeds appear to be limited to ∼20 m s−1. Different types of downdrafts appear to exist within precipitating convective clouds. Penetrative downdrafts common to nonprecipitating convective clouds and upper regions of precipitating convective clouds exhibit maximum horizontal dimensions of ∼1 km. These downdrafts emerge when subsaturated environmental air is entrained or mixed into the cloud. A second type, cloud edge downdrafts, appear in both observations and in cloud model results. Although their driving mechanisms are not fully understood, such downdrafts may be forced by cloud edge evaporational cooling and localized updraft mass flux compensation. Overshooting downdrafts comprise a third type and are typically associated with intense convection in which updraft air surpasses an equilibrium level of neutral buoyancy, cools upon further ascent, and then descends but remains within a few kilometers of cloud top. Finally, the precipitation-associated downdraft is one forced at low levels by precipitation loading, evaporation, and melting. This downdraft may attain relatively large scales, of the order of the horizontal dimension of precipitating regions within the lowest several kilometers. Such large scales provide a clear distinction from (penetrative-type) downdrafts of ∼1 km maximum scale within nonprecipitating convection. There is evidence from both observational and modeling studies that downdraft dynamical and thermodynamical processes are strongly influenced by static stability, wind shear profiles, cloud microphysical processes, and precipitation characteristics. However, the degree to which downdraft structure depends on such interrelated controlling factors has not yet been determined.

Abstract: We have analyzed small-scale fluctuations in microphysical, dynamical and thermodynamical parameters measured in two warm cumulus clouds during the Cooperative Convective Precipitation Experiment (CCOPE) project (1981) in light of predictions of several recent models. The measurements show the existence at all levels throughout the sampling period of two statistically distinct kinds of cloudy regions, termed “variable” and “steady,” often separated by transition zones of less than ten meters. There is some evidence for microphysical variability induced by local fluctuations in thermodynamic and dynamic parameters; however, the predominant variations are of a nature consistent with laboratory evidence suggesting that mixing is dominated by large structures. Entrainment appears to occur largely near cloud top but the data presented here do not permit identification of a mechanism for transport of the entrained air throughout the cloud.

Abstract: An algorithm has been developed for using the reflection of solar radiation in the oxygen A-band to determine cloud-top altitude. Because of multiple scattering and molecular absorption inside the cloud, the reflection of clouds is substantially modified in comparison with a mirror cloud, which is assumed to have a 100 percent reflection. To infer true cloud-top altitude, therefore, it is necessary to accurately estimate the amount of 'photon penetration'. Theoretical calculations indicate that the amount of photon penetration depends on the altitude, the scaled volume scattering coefficient, and the scaled optical thickness of the cloud. Algorithms using the reflection in the oxygen A-band to determine the cloud-top pressure have been applied to an aircraft field experiment in conjunction with CCOPE, 1981. Results of this study are very encouraging, especially for extended clouds.

Abstract: The detection of clouds by satellite-borne sensors, especially those operating in the visible wavelengths, is plagued by an easily recognized but not readily eliminated problem, namely, the overestimation of cloud amount at viewing angles other than zero. An idealized cloud field is used in Figure 1 to illustrate the problem. The fraction of a fixed area which is assessed as “cloudy” increases markedly as the viewing angle £ increases, in spite of the fact that the cloud amount is uni-form. Involved is the reality that clouds have vertical as well as horizontal dimension, and at £>0, the sides as well as the tops of clouds are detected from a satellite.

Abstract: Two one-dimensional steady-state models of cumulus convection in common use in weather modification research, the NOAA Experimental Meteorology Branch model (EMB) and the Great Plains Cumulus Model (GPCM), differ in their formulations in several ways. Some of the differences arise from the conceptualization of the convective phenomenon which is modeled in each and some from the physical parameterizations utilized. Predictions of cloud top and dynamic modification potential (seedability) by the two models for 57 midday radiosondes in the Midwest, differed significantly, with the EMB values consistently higher. GPCM simulations provided a better overall estimate of observed radar echo tops, while EMB consistently overestimated, by largest amounts when tops were below 12 km. Study of the impact of temporal and/or spatial separation between sounding and cloud area emphasizes the need, in the Midwest, to consider factors other than thermodynamic stratification (e.g. forced lifting, convergence) on the...

Abstract: In order to develop the remote sensing techniques to infer cloud physical parameters, a multispectral cloud radiometer (MCR) was mounted on a NASA high-altitude aircraft in conjunction with the Cooperative Convective Precipitation Experiment in 1981. The MCR has seven spectral channels, of which three are centered near windows associated with water vapor bands in the near infrared, two are centered near the oxygen A band at 0.76 microns, one is centered at the 1.14-micron water vapor band, and one is centered in the thermal infrared. The reflectance and temperature measured on May 31, 1981, are presented together with theoretical calculations. The results indicate that the MCR produces quality measurements. Therefore several cloud parameters can be derived with good accuracy. The parameters are the cloud-scaled optical thickness, cloud top pressure, volume scattering coefficient, particle thermodynamic phase, effective mean particle size, and cloud-top temperature.

Abstract: Light coming from a cloud to the detector of a multispectral satellite (Landsat) consists of light reflected from the cloud and light scattered by the layer of atmosphere between the cloud and satellite. Because of the strong wavelength dependence of Rayleigh scattering, the comparison of the signals in two spectral channels allows one to find the thickness of the scattering layer and hence the height of the cloud top.

Abstract: : Objectives of this research are: (1) to critically evaluate the Kuo and Arakawa Schubert (A-S) cumulus parameterization schemes for numerical weather prediction; and (2) to improve these parameterization schemes to improve precipitation forecasts on the global scale. Major improvements to the Kuo scheme include prediction of cloud top height and incorporation of the effect of entrainment on cloud temperature and mixing ratio profiles. This enables the Kuo scheme to parameterize shallow to medium clouds as well as deep clouds. Tests of the Kuo scheme using a semi-prognostic approach and a cloud cluster model indicate that the improved version verifies better with observation during weaker convective periods. Experimental predictions were made and the results clearly demonstrated the ability of the AFGL model to predict large-scale stratiform precipitation. With incorporation of the modified Kuo scheme, the area of convective precipitation can also be well predicted. However, the predicted convective precipitation area is generally broader and the amount of rainfall smaller than observed which may be attributed to the resolution of the AFGL model in that it cannot resolve the narrow band of the cold front, ther major mesoscale rain-producing system. Implementation of the A-S scheme in the AFGL model also produced a reasonable distribution of convective precipitation but the precipitation area is more concentrated and sometimes is produced in an observed clear area. This result may be caused by the current implementation of the A-S scheme in the AFGL model, in which the cloud base is assumed to be 500 m above the ground surface.

Abstract: A global cloud cover data set, derived from the USAF 3D NEPH Analysis, was developed for use in climate studies and for Earth viewing applications. This data set contains a single parameter - total sky cover - separated in time by 3 or 6 hr intervals and in space by approximately 50 n.mi. Cloud cover amount is recorded for each grid point (of a square grid) by a single alphanumeric character representing each 5 percent increment of sky cover. The data are arranged in both quarterly and monthly formats. The data base currently provides daily, 3-hr observed total sky cover for the Northern Hemisphere from 1972 through 1977 less 1976. For the Southern Hemisphere, there are data at 6-hr intervals for 1976 through 1978 and at 3-hr intervals for 1979 and 1980. More years of data are being added. To validate the data base, the percent frequency of or = 0.3 and or = 0.8 cloud cover was compared with ground observed cloud amounts at several locations with generally good agreement. Mean or other desired cloud amounts can be calculated for any time period and any size area from a single grid point to a hemisphere. The data base is especially useful in evaluating the consequence of cloud cover on Earth viewing space missions. The temporal and spatial frequency of the data allow simulations that closely approximate any projected viewing mission. No adjustments are required to account for cloud continuity.

Abstract: : A satellite-derived cloud and precipitation analysis program has been developed for an interactive mini-computer system. The program utilizes geostationary infrared and visual data with operational upper air and surface temperature analyses to specify cloud-type, cloud amount, cloud-top temperature, cloud-top height and estimated precipitation intensity. Five cases of GOES-East data ( 2 x 2 n mi visual and 2 x 4 n mi infrared) for an approximately 1600 x 1600 n mi area over the eastern United States and western North Atlantic Ocean are used in evaluating the model's performance. Each satellite-derived, cloud and precipitation analysis is evaluated subjectively, using conventional synoptic data, radar measurements and manual nephanalysis for verification, and objectively, using surface synoptic observations for verification. Successful estimates of cloud amount for overcast and clear skies were obtained; howeverm broken and scattered conditions were underestimated. The majority of stratiform cloud tupes and multi-layered clouds were analyzed correctly by the model. Classification errors occurred with cumuliform clouds and thin cirrus. Reasonable precipitation intensity and cloud-top temperature/height analyses were produced by the NPS model. Keywords: GOES(Geostationary Operational Environmental Satellite).

Abstract: An observational study of convective motion in the cumulus subcloud layer was made by remote sensing from the ground. The vertical distributions of three-dimensional wind components are observed by a Doppler acoustic sounder (Sodar); the cloud base temperature is detected by a radiation thermometer; and cloud form was recorded by a fish-eye camera. Three cases of cumulus cloud passage were observed during the period of August and September 1981. In the case of a small developing cumulus cloud, an updraft in the boundary layer preceded the cloud passage. However, in the case of a little larger and more mature cloud, an updraft area trails from the cloud. This trailing updraft area consists of a horizontally rotating wind system in the boundary layer. In the case of a roll cloud, no systematic relation between cloud and boundary layer air flow was found. In all three cases no evidence of cloud passage was seen in the surface meteorological parameters.

Abstract: : Satellite and surface data are used to analyze mesoscale and subsynoptic cloud and precipitation patterns Digital GOES (Geostationary Operational Environment Satellite) visible and infrared data are used to produce high resolution (4 n mi) satellite analyses of cloud amount, cloud type, cloud-top temperature and height, and precipitation intensity for an approximate 1600 x 1600 n mi area over the northeastern United States and the western North Atlantic Ocean Conventional surface observations, the Automated Radar Summary chart and manual analysis of the imagery are used to evaluate the satellite-derived analyses for nine cases during the winger and spring 1985 The majority of cloud amount estimates for clear and overcast sky conditions are analyzed correctly; however, broken and scattered skies are underestimated The general cloud type patterns are depicted accurately More success occurs with uniform-textured clouds (ie nimbostraus, stratocumulus) and multi-layered clouds than with nonuniform-textured clouds (ie cirrus, cumulus) The majority of cloud-top temperature/height analyses are representative of the cloud types and patterns Most atmospheric precipitation areas are identified correctly; however, the intensity of the precipitation is underestimated Keywords: Cloud cover; and Thresholds

Abstract: Irregular small-scale motions, which are introduced into a one-dimensional entraining jet lead to a random cloud with additive stochastic forcing. These clouds are characterized by probability distributions of the thermodynamic cloud properties. Applying a first-passage analysis, probability distributions for maximum cloud top heights can be deduced. In the disturbed tropical atmosphere, random clouds reveal a bimodal probability distribution of cloud top heights, which is essentially due to the mid-tropospheric minimum of the moist static energy. They represent deep and shallow convection. If separated, each scale may be approximated by a log-normal distribution. Some aspects of the competition between these two cloud scales are evaluated.

Abstract: The deep Dwingeloo survey for high-velocity clouds is now nearing completion. This survey consists of more than 28 000 positions in a 1° grid for δ>−18°. The velocity coverage is −1000 to + 1000 km/s and the detection limit (4 σ) in Tb about 0.05 K, corresponding to ∫Tadv = 1.0 K km/s or 10 Jy km/s or 2.2 r2M⊙ (r the distance in kpc) if we assume an average profile width of 25 km/s.

Abstract: A simple method for reducing the effect of cloud on satellite thermal imagery, while preserving full temperature and spatial resolution, is presented. The method makes use of the correlation between apparent thermal and visible radiances in an area contaminated by thin or patchy (subpixel) cloud. The method was developed for ocean images where the cloud is present over an area of low uniform albedo in the visible spectral region, but advantages are also demonstrated in processing Arctic images containing some sea ice cover.