Search NASA⌕ Search

SEARCH · Search NASA

Results for “cumulus,”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Cloud interactions and merging - Numerical simulations

A total of 48 numerical experiments have been performed to study cloud interactions adn merging by means of a two-dimensional multi-cell model. Two soundings of deep convection during GATE and two different magnitudes of large-scale lifting have been used as the initial conditions and as the main forcing on the model. Over two hundred groups of cloud systems with a life history of over sixty minutes have been generated under the influence of different combinations of the stratification and large-scale lifting. The results demonstrate the increase in convective activity and in amount of precipitation with increased intensity of large-scale lifting. The results also show increased occurrence of cloud merger with increased intensity of large-scale lifting. The most unfavorable environmental conditions for cloud merging are (1) less unstable stratification of the atmosphere and (2) weaker large-scale lifting. A total of fourteen cloud systems qualify as mergers. Two selected cases will be described dynamically and thermodynamically in this paper. Although these cloud mergers have been simulated under the influence of different synoptic-scale conditions, the major physical mechanism related to the cloud merging process is the same as that proposed by Simpson. Cumulus downdrafts and associated cold outflows play a dominant role in the merging process in all cases studied.

Tao, W.-K.↗
NASA NTRS1984

The role of an apparent mesoscale frontogenetic circulation in squall line initiation

The present investigation is concerned with the nature and apparent origin of a mesoscale clear zone and associated frontal line convection (a line of cumulus congestus clouds along an intensifying cold front) which appeared just prior to the explosive development of a line of severe thunderstorms at the cold front. It is pointed out that the clear zone formed immediately behind the cold front in southeastern Kansas and northeastern Oklahoma during the afternoon of April 16, 1982. Sequential displays of GOES-East satellite imagery are considered. The mechanism which seems to explain best the observations is a thermally direct frontogenetic circulation resulting from the combined effects of the synoptic-scale wind deformation field and mesoscale differential sensible heating.

Koch, S. E.↗
NASA NTRS1983

The sensitivity of a general circulation model to Saharan dust heating

Evidence is accumulating that tropospheric aerosols, such as Saharan dust, can significantly influence weather and climate. The Climate Model of the Goddard Laboratory for Atmospheric Sciences is presently used to assess the possible effects of Saharan dust on the weather and climate of North Africa and the tropical Atlantic Ocean. The three-dimensional model solves the conservation equations for the horizontal wind vector, potential temperature, water vapor mixing ratio, and surface pressure. Parameterizations are included for turbulent exchange at the earth surface, cumulus convection, large scale saturation, diurnally varying solar radiation, and terrestrial radiation. Realistic simulations are thereby produced for many aspects of the observed climate.

Randall, D.↗
NASA NTRS1983

Stratocumulus simulation with a general circulation model

Stratus and stratocumulus cloud sheets which are among the most common cloud types over the world are discussed. They are characteristic of the undisturbed subtropical marine boundary layer over the eastern oceans, where cool water and large scale sinking motion suppress penetrative cumulus convection. They also occur over the Arctic Ocean, particularly in summer, and behind cold outbreaks over the western oceans in winter. Observational studies were conducted and further observations are planned.

Randall, D. A.↗
NASA NTRS1984

A new technique to infer convective rainfall from satellite infrared cloud observations

GLAS-2, a modified version of the GLAS-1 technique developed by Negri et al. (1984) for estimating convective precipitation from GEO-satellite IR data, is introduced and demonstrated on the data set for the Florida Area Cumulus Experiment in 1980. In GLAS-2, rain cells are located by identification of all local blackbody-temperature minima below 253 K in an array of GOES digital data, and rain parameters are assigned on the basis of the one-dimensional cloud model of Adler and Mack (1984). The demonstration results are presented in graphs and tables and compared with those of GLAS-1 and a number of other methods as well as radar and rain-gage measurements. The false-alarm rate for GLAS-2 is found to be 0.54, somewhat better than that of other satellihte methods; further improvements are suggested.

Negri, A. J.↗
NASA NTRS1984

Diagnosing the severe thunderstorm environment by mesoscale cloud tracking - A new approach and new information

A new method for cloud tracking and observing storm development using satellite imagery in a cloud relative mode is presented. This method changes the analyst's function to one of monitoring cloud growth and changes over a finite time period and identifying portions of the cloud that are suitable for use as trackers. It is shown how many problems previously encountered by meteorologists in mesoscale cloud tracking can be overcome by using the cloud relative technique to determine mesoscale flow fields whose heights are determined using stereographic techniques. By separating growth and decay from cloud motion in a cumulus field using the method and accurately defining cloud heights, vertical wind shears within mesoscale domains may be defined. When this information is used to study the relative velocity of flows at different levels with respect to a developing or mature storm, improved insight into storm behavior can be achieved.

Purdom, J. F. W.↗
NASA NTRS1985

Computer image processing of up-draft flow motion and severe storm formation observed from satellite

Special rapid-scan satellite visible and infrared observations have been used to study the life cycle of the clouds from the initiation of updraft flow motion in the atmosphere, the condensation of humid air, the formation of clouds, the development of towering cumulus, the penetration of the tropopause, the collapsing of an overshooting turret, and the dissipation of cloud. The infrared image provides an indication of the equivalent blackbody temperature of the observed cloud tops. By referencing the temperature, height and humidity profiles from rawinsonde observations as the background meteorological data for the instability of the air mass to the satellite infrared data sets at different time periods, the development of convective clouds can be studied in detail.

Hung, R. J.↗
NASA NTRS1985

Severe Storms Branch research report (April 1984 April 1985)

The Mesoscale Atmospheric Processes Research Program is a program of integrated studies which are to achieve an improved understanding of the basic behavior of the atmosphere through the use of remotely sensed data and space technology. The program consist of four elements: (1) special observations and analysis of mesoscale systems; (20 the development of quanitative algorithms to use remotely sensed observations; (3) the development of new observing systems; and (4) numerical modeling. The Severe Storms Branch objectives are the improvement of the understanding, diagnosis, and prediction of a wide range of atmospheric storms, which includes severe thunderstorms, tornadoes, flash floods, tropical cyclones, and winter snowstorms. The research often shed light upon various aspects of local weather, such as fog, sea breezes, air pollution, showers, and other products of nonsevere cumulus cloud clusters. The part of the program devoted to boundary layer processes, gust front interactions, and soil moisture detection from satellites gives insights into storm growth and behavior.

Dubach, L.↗
NASA NTRS1985

A monthly forecast experiment: Preliminary report

An experiment on monthly forecasts with eight winter cases is being carried out, using a 1980 general circulation model (GCM), which incorporates a set of dubgrid-scale physics characterized by the Mellon-Yamada turbulence closure (hierarchy level 2.5), the Monin-Obukhov parameterization for the layer next to the ground surface, Manabe's cumulus parameterization, and the soil heat conduction. The sample cases adopted are for the month of January in the years from 1977 to 1983, which include the extraordinarily severe winter of 1977 and the most pronounced E1 Nino year of 1983. Each case is predicted by prescribing the climatologically normal sea surface temperature as the lower boundary conditions and by using an ensemble means of three individual integrations. These integrations start with three different initial conditions based on the Level data generated separately at the Geophysical Fluid Dynamics Laboratory, the National Meteorological Center, and the European Centre for Medium Range Weather Forecasts.

Miyakoda, K.↗
NASA NTRS1985

Mixing line analysis of clouds and cloudy boundary layers

The diagnostic study of the thermodynamic structure of nonprecipitating clouds and cloudy boundary layers is formulated using a mixing line and saturation point approach. A parametric model for the mean structure is developed as a tool for diagnostic and prognostic modeling. Cloud-scale mixing processes are analyzed in the same framework, together with the energies of the evaporative instability in cumulus clouds. A velocity scale emerges for this evaporative instability. The statistical study of saturation level distribution in partially cloudy boundary layers is proposed to related cloud fraction to the mean thermodynamic mixing processes.

Betts, A. K.↗
NASA NTRS1986

Remote sensing of cloud distributions over the Bayanhar Mountains - Watershed of the Yangtze and Yellow rivers

Although the two largest rivers in China originate in the same region separated only by the Bayanhar Mountains as a watershed, the Yangtze and Yellow rivers behave in quite different ways. Most of the warm and humid air currents from the Arabian sea and the Bay of Bengal are blocked by the Bayanhar Mountains. As a result the amount of water in the Yellow River is only 5 percent of that in the Yangtze river. Based on the cloud coverage area and the cloud volumetric distributions, and also the thickness above 9.4 km of the cumulus clouds located north and south of the Bayanhar Mountains from the geosynchronous satellite infrared imagery, the results suggest that a more detailed investigation is warranted in the hope that the proper modification of cumuli north of the Bayanhar Mountains would enhance the rainfall over the fountainhead of the Yellow River.

Hung, R. J.↗
NASA NTRS1986

The parental magma of the Nakhla achondrite - Ultrabasic volcanism on the shergottite parent body

An examination of chemical and mineral chemical data available for the cumulate and the intercumulus magma of the Nakhla meteorite is presented. The composition of the intercumulus magma, calculated by mass balance, is found to be ultrabasic (SiO2 is less than 45 percent), and the magma is enriched in incompatible elements (La/Lu=6 x Cl). The cumulus augite and intercumulus magma are in chemical equilibrium, implying that the intercumulus magma is a sample of Nakhla's parental magma. The possibility of Nakhla's Martian origin is discussed.

Treiman, A. H.↗
NASA NTRS1986

Further studies with data collected by NASA's airborne Doppler lidar in Oklahoma in 1981

Continued study of the lidar data collected in 1981 has resulted in significant new improvements in the analysis techniques reported by Bluestein et al. (1985) and McCaul (1985). Through comparison of fore- and aft-derived scalar fields of intensity and spectral width, the self-consistency of the lidar moment estimates was assessed. Reflectivity estimates were found to be quite stable and reliable, while spectral widths were prone to become noisy if signal to noise ratio (SNR) fell below 12 dB. In addition, spectral widths contained a significant component due to radial velocity gradients in areas along gust fronts, and these components were different along the fore and aft lines of sight. Significant improvement in agreement between the fore and aft fields of spectral width was obtained by estimating the radial velocity gradient component and then removing it from the raw measured widths to yield only the turbulent portion of the contribution to width. Additional analyses showed that lidar-derived vorticity estimates were consistent with several approximate models of vorticity growth along gust front zones, and with the hypothesis that Helmholtz instability could have been responsible for vortices seen along part of the gust front of 30 June 1981. Computations of divergence transverse to axes through an isolated cumulus congestus indicated that the strongest convergence tended to lie along an axis parallel to the congestus. This and the results of other additional analyses seem to suggest that the lidar winds do indeed accurately reflected the basic features of the real wind field.

Bluestein, H. B.↗
NASA NTRS1986

T-28 data acquisition during COHMEX 1986

As part of the 1986 Cooperative Huntsville Meteorological Experiment (COHMEX) a cloud physics instrumented T-28 aircraft was used in conjunction with multiple ground based Doppler radars to characterize hydrometeors and updraft structure within developing summertime cumulus and cumulonimbus cloud systems near Huntsville, Alabama. Instrumentation aboard the aircraft included a Particle Measuring Systems (PMS) Forward Scattering Spectrometer Probe (FSSP), a PMS 2D Cloud Probe and a PMS 2D Precipitation Probe, as well as a hail spectrometer and a foil impactor. Hydrometeor spectra were obtained in the interior of mature thunderstorms over the size range from cloud droplets through hailstones. In addition, vertical wind speed, temperature, Johnson-Williams (JW) liquid water content and electric field measurements were made. Significant microphysical differences exist between these clouds and summertime cumulonimbus clouds which develop over the Central Plains. One notable difference in clouds displaying similar radar reflectivities is that COHMEX hydrometeors are typically smaller and more numerous than those observed in the Central Plains. The COHMEX cloud microphysical measurements represent ground truth values for the remote sensing instrumentation which was flown over the cloud tops at altitudes between 60,000 and 70,000 ft aboard NASA U-2 and ER-2 aircraft. They are also being used jointly with a numerical cloud model to assist in understanding the development of summertime subtropical clouds.

Musil, Dennis J.↗
NASA NTRS1987

Spectral radiometry and tropospheric aerosols: Report of panel

The term aerosols, as used here, refers to the haze, smoke, and dust that appear in the troposphere. The term does not refer to the hydrometeors in cumulus and stratus clouds but does include the sulfuric acid-water droplets which are assumed to predominate in the stratospheric aerosol layer. The aerosol properties that were measured from satellites and those which can be made in the near term (up to 1992) will be reviewed. The capabilities that will exist in the years 1992 to 2000, with implementation of EOS, are then discussed. Finally, a few words will be said concerning the potential for aerosol measurements for the decade after 2000.

Fraser, Robert S.↗
NASA NTRS1987

Convective heating and precipitation estimates for the tropical South Pacific during FGGE, 10-18 January 1979

Heat and moisture budgets are computed during part of the FGGE Special Observing Period-1 for an area containing the South Pacific convergence zone, deriving 12-hour precipitation rate estimates as residuals and comparing them with those derived from a GOES IR technique. Heat budget estimates are generally in good agreement with the IR estimates; the axis of maximum precipitation derived from tne heat budget is well aligned with the lowest values of outgoing long wave excitation, which represent high, cold cloud tops resulting from deep cumulus convection. The vertical advection term is found to be the dominant term in the heat budget; this, together with radiative cooling, yields the approximate balance between adiabatic cooling and diabatic heating.

Miller, Bernard L.↗
NASA NTRS1986

Small-scale motions observed by aircraft in the tropical lower stratosphere - Evidence for mixing and its relationship to large-scale flows

Measurements of temperature and ozone from instrumented aircraft in the tropical lower stratosphere show the presence of small-scale disturbances generated by underlying cumulus convection and Kelvin-Helmholtz instability. The disturbances associated with underlying convection have peak-to-peak vertical parcel excursions of about 300 m. Flying conditions were smooth, suggesting an ensemble of gravity waves and little or no turbulent mixing. It is nevertheless possible that these waves break at other altitudes, leading to turbulent mixing and net fluxes of vertically stratified tracers. Disturbances attributed to KH instability implied vertical parcel excursions of 300-400 m. The disturbances coincided with rough flying conditions, suggesting turbulent mixing. A linear stability analysis of the atmospheric basic state defined by high-resolution radiosondes shows fastest growing waves with horizontal wavelengths of 1.4-1.8 km, consistent with the aircraft observations. The strong shears responsible for the KH instability are due to large-scale waves propagating into a region of small intrinsic frequency. Radiosonde observations show that the zonal length scale of these waves is about 1000 km.

Pfister, Leonhard↗
NASA NTRS1987

The role of convective parameterization in the simulation of a Gulf Coast precipitation system

Three simulations were performed with the Limited Area Mesoscale Prediction System (LAMPS) model in order to examine the role of convective parameterization in the simulation of the Gulf Coast precipitation system of March 6-7, 1982. The first simulation neglected moist processes, the second used the representation for moist physics of Orlanksi and Ross (1984) and Rosenthal (1978, 1979), and the third simulation incorporated the LAMPS sequential plume cumulus cloud model as convective parameterization for the model. The effects of various representations of moist physics on the evolution of the model's precipitation, kinematic and diabatic heating, and mass and wind fields are investigated. It is determined that the representation of moist thermodynamics in the meso-alpha-scale model influences the manner in which the model describes the mesoscale structures.

Kalb, Michael W.↗