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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.

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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Characterization of the aerosol vertical distributions and their impacts on warm clouds based on multi-year ARM observations

Aerosol vertical distribution plays a crucial role in cloud development and thus precipitation since both aerosol indirect and semi-direct effects significantly depend on the relative position of aerosol layer in reference to cloud, but its precise influence on cloud remains unclear. In this study, we integrated multi-year Raman Lidar measurements of aerosol vertical profiles from the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) facility with available Value-Added Products of cloud features to characterize aerosol vertical distributions and their impacts on warm clouds over the continental and marine ARM atmospheric observatories, i.e., Southern Great Plains (SGP) and Eastern North Atlantic (ENA). A unimodal seasonal distribution of aerosol optical depths (AODs) with a peak in summer is found at upper boundary layer over SGP, while a bimodal distribution is observed at ENA for the AODs at lower levels with a major winter-spring maximum. The diurnal mean of upper-level AOD at SGP shows a maximum in the early evening. According to the relative positions of aerosol layers to clouds we further identify three primary types of aerosol vertical distribution, including Random, Decreasing, and Bottom. It is found that the impacts of aerosols on cloud may or may not vary with aerosol vertical distribution depending on environmental conditions, as reflected by the wide variations of the relations between AOD and cloud properties. For example, as AOD increases, the liquid water paths (LWPs) tend to be reduced at SGP but enhanced at ENA. The relations of cloud droplet effective radius with AOD largely depend on aerosol vertical distributions, particularly showing positive values in the Random type under low-LWP condition (<50gm -2 ). In conclusion, the distinct features of aerosol-cloud interactions in relation to aerosol vertical distribution are likely attributed to the continental-marine contrast in thermodynamic environments and aerosol conditions between SGP and ENA.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1981

On the formation of protostellar disks

An analysis is presented of the hydrodynamic aspects of the growth of protostellar disks from the accretion of a rotating gas cloud. Streamline equations for the flow onto the disk are derived, including the special case where the disk is very thin. For the radial structure of the disk, detailed equations of conservation of mass, momentum, angular momentum, and energy are given. Exact solutions are found for the case of no internal viscosity. For the more general case where there is viscous stress, hypotheses are formulated with the objective of discovering the main qualitative characteristics of a turbulent system and to estimate the magnitude of the turbulent stress. Solutions are also found for boundary conditions, and the large and small viscosity limits. The relation of energy balance to disk thermal structure is detailed. Finally, trends in the collapse of the dust cloud are discussed in the light of the solutions given.

Cassen, P.↗
DOE OSTI2022

Combined Effect of the Wegener–Bergeron–Findeisen Mechanism and Large Eddies on Microphysics of Mixed-Phase Stratiform Clouds

Abstract The process of glaciation in mixed-phase stratiform clouds was investigated by a novel Lagrangian–Eulerian model (LEM) in which thousands of adjoining Lagrangian parcels moved within a turbulent-like velocity field with statistical parameters typical of the Arctic boundary layer. We used detailed bin microphysics to describe the condensation/evaporation processes in each parcel, in which droplets, aerosols, and ice particles were described using size distributions of 500 mass bins. The model also calculated aerosol mass inside droplets and ice particles. Gravitational sedimentation of droplets and ice particles was also accounted for. Assuming that droplet freezing is the primary source of ice particles, the Arctic clouds observed in Indirect and Semi-Direct Aerosol Campaign (ISDAC) were successfully simulated. The model showed that at a low ice particle concentration typical of ISDAC, large vortices (eddies) led to a quasi-stationary regime, in which mixed-phase St existed for a long time. The large eddies controlled the water partitioning in the mixed-phase clouds. Droplets formed and grew in updrafts, typically reaching the cloud top, and evaporated in downdrafts. Ice particles grew in updrafts and downdrafts. The Wegener–Bergeron–Findeisen (WBF) mechanism was efficient in downdrafts and some parts of updrafts, depending on ice concentration and vertical velocity. At low ice concentrations, the effect of ice on the phase partitioning was negligible. In this regime, liquid droplets were found near the cloud top, whereas ice particles precipitated through the cloud base. When ice concentration exceeded about 10 L −1 , the WBF mechanism led to glaciation of almost the entire cloud, with the exception of narrow cloud regions associated with strong updrafts. At ice particle concentrations of a few tens per liter, the oscillatory regime took place due to the ice–liquid interaction. The microphysical structure of mixed-phase St forms as a combined effect of cloud dynamics (large eddies) and the WBF mechanism.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

Boundary Conditions for the Paleoenvironment: Chemical and Physical Processes in the Pre-Solar Nebula

The basic theme of this program is the study of molecular complexity and evolution in interstellar clouds and in primitive solar system objects. Research has included the detection and study of a number of new interstellar molecules and investigation of reaction pathways for astrochemistry from a comparison of theory and observed molecular abundances. The latter includes studies of cold, dark clouds in which ion-molecule chemistry should predominate, searches for the effects of interchange of material between the gas and solid phases in interstellar clouds, unbiased spectral surveys of particular sources, and systematic investigation of the interlinked chemistry and physics of dense interstellar clouds. In addition, the study of comets has allowed a comparison between the chemistry of such minimally thermally processed objects and that of interstellar clouds, shedding light on the evolution of the biogenic elements during the process of solar system formation.

Irvine, William M.↗
DOE OSTI2021

Observations of Clouds, Aerosols, Precipitation, and Surface Radiation over the Southern Ocean: An Overview of CAPRICORN, MARCUS, MICRE, and SOCRATES

Weather and climate models are challenged by uncertainties and biases in simulating Southern Ocean (SO) radiative fluxes that trace to a poor understanding of cloud, aerosol, precipitation, and radiative processes, and their interactions. Projects between 2016 and 2018 used in situ probes, radar, lidar, and other instruments to make comprehensive measurements of thermodynamics, surface radiation, cloud, precipitation, aerosol, cloud condensation nuclei (CCN), and ice nucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase clouds common to this pristine environment. Data including soundings were collected from the NSF–NCAR G-V aircraft flying north–south gradients south of Tasmania, at Macquarie Island, and on the R/V Investigator and RSV Aurora Australis. Synergistically these data characterize boundary layer and free troposphere environmental properties, and represent the most comprehensive data of this type available south of the oceanic polar front, in the cold sector of SO cyclones, and across seasons. Results show largely pristine environments with numerous small and few large aerosols above cloud, suggesting new particle formation and limited long-range transport from continents, high variability in CCN and cloud droplet concentrations, and ubiquitous supercooled water in thin, multilayered clouds, often with small-scale generating cells near cloud top. These observations demonstrate how cloud properties depend on aerosols while highlighting the importance of dynamics and turbulence that likely drive heterogeneity of cloud phase. Satellite retrievals confirmed low clouds were responsible for radiation biases. Furthermore, the combination of models and observations is examining how aerosols and meteorology couple to control SO water and energy budgets.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Dimensionless parameters for cloudy Rayleigh-Bénard convection: Supersaturation, Damköhler, and Nusselt numbers

In steady-state Rayleigh-Bénard convection, heat is transported by turbulent thermal convection from the bottom, hot surface to the top, cold surface, leading to a height-independent sensible heat flux. When water vapor is present and cloud formation occurs, there is also an additional latent heat flux. Heat transport in cloudy Rayleigh-Bénard convection depends on turbulent flow as well as the microphysical state of the clouds: specifically, whether substantial supersaturations exist and whether cloud liquid water is removed through sedimentation/precipitation. In this article we bridge between the Rayleigh-Bénard convection literature and the atmospheric literature. We express the governing equations for cloudy convection in dimensionless form, thereby explicitly identifying the governing parameters relevant to the cloudy case, including Schmidt, Damköhler, supersaturation, and sedimentation numbers. We further connect to the atmospheric literature by obtaining a Nusselt number (dimensionless heat flux) for a cloud-convection system, directly from the conservation equations for temperature and water vapor. This flux has the same form as that identified by Zhang et al. [L. Zhang, K. L. Chong, and K.-Q. Xia, J. Fluid Mech. 874, 1041 (2019)] for convection with water vapor, but is extended to the cloudy case. For equal thermal and water vapor diffusivities, the flux corresponds to the widely used atmospheric quantities equivalent temperature and moist static energy. Using large eddy simulation (LES) of an idealized cloudy Rayleigh-Bénard convection system with fixed boundary conditions, we find that the equivalent heat flux (Nusselt number) is only weakly dependent on the microphysical details of the system, such as liquid water mixing ratio and cloud droplet number concentration. Finally, from the results, we show the vertical profiles of sensible and latent heat fluxes depend on the liquid water content, whereas the equivalent heat flux remains a constant throughout the height of the chamber.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

A Survey of Precipitation-Induced Atmospheric Cold Pools over Oceans and Their Interactions with the Larger-Scale Environment

Pools of air cooled by partial rain evaporation span up to several hundreds of kilometers in nature and typically last less than 1 day, ultimately losing their identity to the large-scale flow. These fundamentally differ in character from the radiatively-driven dry pools defining convective aggregation. Advancement in remote sensing and in computer capabilities has promoted exploration of how precipitation-induced cold pool processes modify the convective spectrum and life cycle. This contribution surveys current understanding of such cold pools over the tropical and subtropical oceans. In shallow convection with low rain rates, the cold pools moisten, preserving the near-surface equivalent potential temperature or increasing it if the surface moisture fluxes cannot ventilate beyond the new surface layer; both conditions indicate downdraft origin air from within the boundary layer. When rain rates exceed ~2 mm h –1, convective-scale downdrafts can bring down drier air of lower equivalent potential temperature from above the boundary layer. The resulting density currents facilitate the lifting of locally thermodynamically favorable air and can impose an arc-shaped mesoscale cloud organization. This organization allows clouds capable of reaching 4–5 km within otherwise dry environments. These are more commonly observed in the northern hemisphere trade wind regime, where the flow to the intertropical convergence zone is unimpeded by the equator. Here their near-surface air properties share much with those shown from cold pools sampled in the equatorial Indian Ocean. Cold pools are most effective at influencing the mesoscale organization when the atmosphere is moist in the lower free troposphere and dry above, suggesting an optimal range of water vapor paths. Outstanding questions on the relationship between cold pools, their accompanying moisture distribution and cloud cover are detailed further. Near-surface water vapor rings are documented in one model inside but near the cold pool edge; these are not consistent with observations, but do improve with smaller horizontal grid spacings.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Ceilometer (CEIL) Instrument Handbook

The Vaisala Laser Ceilometer (CEIL) is a self-contained, ground-based, active, remote-sensing device designed to measure cloud-base height, vertical visibility, and potential backscatter signals by aerosols. It detects up to three cloud layers simultaneously. Model CL31 has a maximum vertical range of 7700 meters (m). The laser ceilometer transmits near-infrared pulses of light, and the receiver detects the light scattered back by clouds and precipitation.

47 OTHER INSTRUMENTATION↗
NASA NTRS1983

Diagnosing convective instability using VAS data

The utility of combining visible and various infrared images from the VAS to produce a forecasting tool, that can be available on a near real time basis, to predict severe weather development is shown. Areas where dry air in the midtroposphere overlays substantial moisture at low levels are used to diagnose mesoscale regions that have the potential for being convectively unstable before the onset of severe convection. Specifically, 6.7 micron water vapor imagery, used for isolating regions of substantial midlevel dryness, are combined with images of low level clouds or with split-window low level moisture images to delineate regions that have the potential for convective instability. In areas where scattered low level clouds are present, computer generated, color image combinations are used to isolate those warm, low level clouds that are in potential convectively unstable environments from clouds that exist under a deeply moist atmosphere. In clear regions, the split window technique is used for delineating areas of substantial boundary layer moisture. These images are again computer overlayed by the midlevel dryness to produce a color coded image of potential convective instability.

Petersen, R. A.↗
NASA NTRS1985

A shadowed flow in the stem of the Crab nebula?

The faint radio and emission line 'jet' outward from the northern boundary of the Crab Nebula which appears as a neat right cylinder is modelled here as the convected margin of a gas cloud that accidentially cast its shallow across the nearly ballistic flow of the stellar envelope ejected in the supernova explosion. It is shown that this model is consistent with known data on the jet, and that it accounts for the strikingly regular geometrical features in a natural way. In contrast, flow instability models do not easily result in so neat a cylinder.

Morrison, P.↗
NASA NTRS1990

Are periodic bombardments real?

Consideration is given to the hypothesis that showers of comets or asteroids strike the earth every 26 m yrs, causing climatic castastrophes and mass extinctions (Raup and Sepkoski, 1984). Possible explanations for the alleged periodicity are discussed, including the possibility that the sun has a small faint companion star and perturbations of the Oort cloud as the solar system passes through the Galactic plane. Also, the possible causes of the extinction at the K-T boundary are examined. The implications of these theories are noted and evidence suggesting that impacts do not have periodicity is presented.

Weissman, Paul R.↗
NASA NTRS1992

STS-48 case study, 17-18 September 1991

Weather conditions are documented prior to and during the STS-48 attempted landing at the Shuttle Landing Facility at KSC on 18 Sep. 1991. Trends in meteorological data during 17 and 18 Sep. are examined along with their relationship to the overall weather pattern observed over the KSC region. The primary weather problems during the landing were the formation of showers within 10 nautical miles of the SLF and any ceiling less than 10,000 ft. The controlling factor of the weather was a high pressure ridge that was gradually weakening and moving off the northeast. As this occurred, the low level flow was switching from a easterly to a southeasterly direction. This change in wind direction was reflected by shower movement on the McGill radar and by trends in rawinsondes launched from the Cape. These rawinsondes also indicated that the boundary layers was becoming slightly more unstable several hours prior to the attempted landing which may have aided in the development of clouds and small isolated showers. Also, analyses of Doppler wind profiler and rawinsondes indicated a possible midlevel disturbance in the easterly flow pattern near 700 mb. This weak disturbance may have made the atmosphere a little more unstable early on 18 Sep. Finally, embedded within the southeasterly flow were several bands of low clouds. These clouds were rather difficult to see in unenhanced IR satellite imagery available to forecasters in real time. However, post analyses using several different enhancement curves, adapted from NESDIS, clearly reveals the presence of these clouds.

Atchison, Michael K.↗
NASA NTRS1995

Vertical transport by convective clouds: Comparisons of three modeling approaches

A preliminary comparison of the GEOS-1 (Goddard Earth Observing System) data assimilation system convective cloud mass fluxes with fluxes from a cloud-resolving model (the Goddard Cumulus Ensemble Model, GCE) is reported. A squall line case study (10-11 June 1985 Oklahoma PRESTORM episode) is the basis of the comparison. Regional (central U. S.) monthly total convective mass flux for June 1985 from GEOS-1 compares favorably with estimates from a statistical/dynamical approach using GCE simulations and satellite-derived cloud observations. The GEOS-1 convective mass fluxes produce reasonable estimates of monthly-averaged regional convective venting of CO from the boundary layer at least in an urban-influenced continental region, suggesting that they can be used in tracer transport simulations.

Pickering, Kenneth E.↗
NASA NTRS1998

Effects of Ice Accretion on Aircraft Aerodynamics

The primary objective of this research was to support the development of a new ice accretion model by improving our physical understanding of the ice accretion process through experimental measurements. The focus was on the effect of the initial ice roughness (smooth/rough boundary) on the accretion process. This includes understanding the boundary-layer development over the roughness and especially its effect on the heat transfer which is fundamental to the ice accretion process. The research focused on acquiring the experimental data needed to formulate a new ice accretion physical model. Research was conducted to analyze boundary-layer data taken on a NACA 0012 airfoil with roughness to simulate the smooth/rough boundary. The effect of isolated roughness on boundary-layer transition was studied experimentally to determine if the classical critical roughness Reynolds number criteria could be applied to transition in the airfoil leading-edge area. The effect of simulated smooth/rough boundary roughness on convective heat transfer was studied to complete the study. During the course of this research the effect of free-stream wind tunnel turbulence on the boundary layer was measured. Since this quantity was not well known, research to accurately measure the wind tunnel turbulence in an icing cloud was undertaken. Preliminary results were attained and the final data were acquired, reduced and presented under a subsequent grant.

Bragg, Michael B.↗
NASA NTRS1995

Observing Tropospheric Water Vapor by Radio Occultation using the Global Positioning System

Given the importance of water vapor to weather, climate and hydrology, global humidity observations from satellites are critical. At low latitudes, radio occultation observations of Earth's atmosphere using the Global Positioning System (GPS) satellites allow water vapor profiles to be retrieved with accuracies of 10 to 20% below 6 to 7 km altitude and approx. 5% or better within the boundary layer. GPS observations provide a unique combination of accuracy, vertical resolution (less than or equal to 1 km) and insensitivity to cloud and aerosol particles that is well suited to observations of the lower troposphere. These characteristics combined with the inherent stability of radio occultation observations make it an excellent candidate for the measurement of long term trends.

Kursinski, E. R.↗
NASA NTRS1998

Modulation of Cosmic Ray Precipitation Related to Climate

High energy cosmic rays may influence the formation of clouds, and thus can have an impact on weather and climate. Cosmic rays in the solar wind are incident on the magnetosphere boundary and are then transmitted through the magnetosphere and atmosphere to reach the upper troposphere.

cosmic rays climate weather solar wind upper tropo↗
NASA NTRSDate not supplied

Remote Marine Aerosol Properties over the Western North Atlantic Ocean during NAAMES

The overarching goal of this postdoctoral project is: quantitatively assess and constrain the aerosol budgets in the remote North Atlantic marine boundary layer, under a wide range of aerosol emission sources, meteorological states to improve process-level understanding of marine aerosol-cloud interactions critical to adequately link observations and climate modelling.

Aerosol NAAMES↗