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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Fragmentation of elongated cylindrical clouds. IV - Clouds with solid-body rotation about an arbitrary axis

Results of 3D hydrodynamic collapse calculations of elongated isothermal clouds with solid-body rotation about an arbitrary axis are presented. Four different modes of fragmentation are identified. In all evolutions that formed more than one fragment, a structural fragmentation mode occurred first, forming condensations on each side of the cylinder. It is shown that gravitational torques and tidal effects control most of the fragmentation and coalescence which occur. The fragmentation processes and gravitational torques can also reduce the fragment's specific angular momentum by up to two orders of magnitude compared to that of the parent cloud. This is consistent with the inferred value of the specific angular momentum of the initial protosolar nebula.

Bonnell, Ian↗
NASA NTRS1994

Cloud condensation nucleus-sulfate mass relationship and cloud albedo

Analysis of previously published, simultaneous measurements of cloud condensation nucleus number concentration and sulfate mass concentration suggest a nonlinear relationship between the two variables. This nonlinearity reduces the sensitivity of cloud albedo to changes in the sulfur cycle.

Hegg, Dean A.↗
NASA NTRS1999

Global Studies of Molecular Clouds in the Galaxy, The Magellanic Clouds, and M31

Over the course of this grant we used various spacecraft surveys of the Galaxy and M31 in conjunction with our extensive CO spectral line surveys to address central problems in galactic structure and the astrophysics of molecular clouds. These problems included the nature of the molecular ring and its relation to the spiral arms and central bar, the cosmic ray distribution, the origin of the diffuse X-ray background, the distribution and properties of x-ray sources and supernova remnants, and the Galactic stellar mass distribution. For many of these problems, the nearby spiral M31 provided an important complementary perspective. Our CO surveys of GMCs (Galactic Molecular Clouds) were crucial for interpreting Galactic continuum surveys from satellites such as GRO (Gamma Ray Observatory), ROSAT (Roentgen Satellite), IRAS (Infrared Astronomy Satellite), and COBE (Cosmic Background Explorer Satellite) because they provided the missing dimension of velocity or kinematic distance. GMCs are a well-defined and widespread population of objects whose velocities we could readily measure throughout the Galaxy. Through various emission and absorption mechanisms involving their gas, dust, or associated Population I objects, GMCs modulate the galactic emission in virtually every major wavelength band. Furthermore, the visibility. of GMCs at so many wavelengths provided various methods of resolving the kinematic distance ambiguity for these objects in the inner Galaxy. Summaries of our accomplishments in each of the major wavelength bands discussed in our original proposal are given

Thaddeus, Patrick↗
NASA NTRS1996

Comparisons Between the Formation of Polar Stratospheric Clouds and Cirrus Clouds

Analyses of lidar data taken during the 1989 AASE I program show that polar stratospheric clouds most often contain frozen particles, but sometimes contain spherical, presumably liquid, particles. In this paper the mechanisms that lead to the freezing of particles, and to the formation of liquid particles will be discussed based largely upon analyses of existing data. For example, trajectory studies help shed light on the conditions that lead to particle freezing. During April of 1996 an experiment using the NASA DC-8 and ER-2 aircraft will be conducted over the central U.S. Some of the goals of the project are to better understand the mechanisms of cirrus cloud formation, and to investigate the properties of freezing nuclei in the upper troposphere. Results from this field program will be presented as they apply to the topic of ice crystal nucleation. Comparisons will be drawn between the mechanisms that lead to new particle formation in the polar stratosphere, and the mechanisms that lead to new particles formation in the upper troposphere.

Toon, Owen B.↗
NASA NTRS2008

On the Sensitivity of Atmospheric Ensembles to Cloud Microphysics in Long-Term Cloud-Resolving Model Simulations

Month-long large-scale forcing data from two field campaigns are used to drive a cloud-resolving model (CRM) and produce ensemble simulations of clouds and precipitation. Observational data are then used to evaluate the model results. To improve the model results, a new parameterization of the Bergeron process is proposed that incorporates the number concentration of ice nuclei (IN). Numerical simulations reveal that atmospheric ensembles are sensitive to IN concentration and ice crystal multiplication. Two- (2D) and three-dimensional (3D) simulations are carried out to address the sensitivity of atmospheric ensembles to model dimensionality. It is found that the ensembles with high IN concentration are more sensitive to dimensionality than those with low IN concentration. Both the analytic solutions of linear dry models and the CRM output show that there are more convective cores with stronger updrafts in 3D simulations than in 2D, which explains the differing sensitivity of the ensembles to dimensionality at different IN concentrations.

Zeng, Xiping↗
NASA NTRSDate not supplied

LAADS DAAC Migrates to the Cloud: Lessons Learned from Communicating About Earth Science Data on the Cloud

The Level-1 and Atmosphere Archive Distribution System (LAADS) Distributed Active Archive Center (DAAC) is migrating data to the cloud. As one of twelve DAACS supported by NASA’s Earth Science Data and Information System (ESDIS), LAADS is using moving away from on premise data storage facilities to migrating to Amazon Web Services, where the massive archive of data from the Moderate Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) will be available for download and post-processing transformations online. The migration is happening in three phases and LAADS is concluding its beta testing period. This poster shows the lessons learned from communicating with a select group of users about how to effectively educate data users on using data in the cloud.

Tassia Owen↗
DOE OSTI2024

To Exascale and Beyond—The Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM), a Performance Portable Global Atmosphere Model for Cloud-Resolving Scales

The new generation of heterogeneous CPU/GPU computer systems offer much greater computational performance but are not yet widely used for climate modeling. One reason for this is that traditional climate models were written before GPUs were available and would require an extensive overhaul to run on these new machines. In addition, even conventional “high–resolution” simulations don't currently provide enough parallel work to keep GPUs busy, so the benefits of such overhaul would be limited for the types of simulations climate scientists are accustomed to. The vision of the Simple Cloud-Resolving Energy Exascale Earth System (E3SM) Atmosphere Model (SCREAM) project is to create a global atmospheric model with the architecture to efficiently use GPUs and horizontal resolution sufficient to fully take advantage of GPU parallelism. After 5 years of model development, SCREAM is finally ready for use. In this paper, we describe the design of this new code, its performance on both CPU and heterogeneous machines, and its ability to simulate real-world climate via a set of four 40 day simulations covering all 4 seasons of the year.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

The intrinsic reddening of the Magellanic Clouds as traced by background galaxies – III. The Large Magellanic Cloud

ABSTRACT We present a map of the total intrinsic reddening across ≃ 90 deg2 of the Large Magellanic Cloud (LMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created from a sample of 222 752 early-type galaxies based on the lephareχ2 minimization SED-fitting routine. We find excellent agreement between the regions of enhanced intrinsic reddening across the central (4 × 4 deg2) region of the LMC and the morphology of the low-level pervasive dust emission as traced by far-IR emission. In addition, we are able to distinguish smaller, isolated enhancements that are coincident with known star-forming regions and the clustering of young stars observed in morphology maps. The level of reddening associated with the molecular ridge south of 30 Doradus is, however, smaller than in the literature reddening maps. The reduced number of galaxies detected in this region, due to high extinction and crowding, may bias our results towards lower reddening values. Our map is consistent with maps derived from red clump stars and from the analysis of the star formation history across the LMC. This study represents one of the first large-scale categorizations of extragalactic sources behind the LMC and as such we provide the lephare outputs for our full sample of ∼ 2.5 million sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Giant Cloud Condensation Nuclei Facilitate Drizzle Formation in Stratocumulus—Insights From a Combined Observation‐Modeling Framework

The mechanism for initiating drizzle drop remains a gap in the current understanding of warm rain formation. One prevalent hypothesis suggests that the presence of Giant Cloud Condensation Nuclei (GCCN) generates drizzle‐sized drops necessary to trigger the Collision‐Coalescence (C‐C) process. Here, in this study, this hypothesis is investigated using a novel framework that integrates in situ observations, remote sensing measurements, and idealized models. Results show that GCCN can efficiently generate drizzle drops through condensation, producing a broad Droplet Size Distribution (DSD) comparable to in situ observations. The large drizzle drop and broad DSD strongly facilitate C‐C, further accelerating drizzle initiation. To compare with observation, the model‐generated DSDs are used to generate radar Doppler spectra where radar reflectivity and Doppler skewness is estimated. The simulated radar quantities correspond well with radar observations, providing critical evidence for the GCCN‐induced drizzle initiation mechanism.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1974

Jupiter's clouds - Equatorial plumes and other cloud forms in the Pioneer 10 images

The imaging photopolarimeter experiment aboard the Pioneer 10 spacecraft produced two-dimensional maps of intensity and polarization in red and blue light at high resolution during flyby of Jupiter in December 1973. The present article describes cloud forms seen in the equatorial zone and compares them with rotational periods as a function of latitude derived from earth-based observations of features on Jupiter. A striking new feature consists of a bright, well-defined nucleus in the equatorial zone, with a plume apparently drawn out from the core of the nucleus.

Fountain, J. W.↗
NASA NTRS1957

Impingement of Cloud Droplets on 36.5-Percent-Thick Joukowski Airfoil at Zero Angle of Attack and Discussion of Use as Cloud Measuring Instrument in Dye-Tracer Technique

The trajectories of droplets i n the air flowing past a 36.5-percent-thick Joukowski airfoil at zero angle of attack were determined. The amount of water i n droplet form impinging on the airfoil, the area of droplet impingement, and the rate of droplet impingement per unit area on the airfoil surface were calculated from the trajectories and cover a large range of flight and atmospheric conditions. With the detailed impingement information available, the 36.5-percent-thick Joukowski airfoil can serve the dual purpose of use as the principal element in instruments for making measurements in clouds and of a basic shape for estimating impingement on a thick streamlined body. Methods and examples are presented for illustrating some limitations when the airfoil is used as the principal element in the dye-tracer technique.

Brun, R. J.↗
NASA NTRS1985

Ultraviolet interstellar absorption toward stars in the Small Magellanic Cloud. IV - Highly ionized gas associated with the Small Magellanic Cloud

High-dispersion International Ultraviolet Explorer satellite spectra of seven stars in the Small Magellanic Cloud (SMC) are examined to study the properties of interstellar C IV and Si IV absorption in the SMC. Absorption by C IV or Si IV or both is found near 160 km/s for all the stars. The velocity and the relative C IV and Si IV strengths suggest UV-photoionized nebular gas as the origin of this absorption. In addition, the stars show absorption by C IV and, sometimes, Si IV in the velocity range 100-130 km/s. This velocity is 30-60 km/s more negative than that expected for normal nebular gas, and the relative C IV and Si IV strengths indicate an ionization source other than stellar UV photoionization by normal Population I stars. Possible global origins are considered for this absorption, including a hot phase of the SMC interstellar medium and a circum-SMC distribution of highly ionized gas. The only detection of interstellar N V toward a SMC star is for HD 5980. The line is broad, possibly complex, and spans the velocity range of the nebular absorption and the 100-130 km/s absorption.

Fitzpatrick, E. L.↗
NASA NTRS1986

Observational discrimination between modes of shock propagation in interstellar clouds: Predictions of CH+ and SH+ column densities in diffuse clouds

Considerable effort in recent years has been devoted to the study of shocks in the diffuse interstellar medium. This work has been motivated partly by the observations of rotationally excited states of H2, and partly by the realization that species such as CH(+), OH and H2O might be formed preferentially in hot, post-shock gas. The problem of CH(+) and the difficulties encountered when trying to explain the high column densities, observed along lines of sight to certain hot stars, have been reviewed earlier. The importance of a transverse magnetic field on the structure of an interstellar shock was also demonstrated earlier. Transverse magnetic fields above a critical strength give rise to an acceleration zone or precursor, in which the parameters on the flow vary continuously. Chemical reactions, which change the degree of ionization of the gas, also modify the structure of the shock considerably. Recent work has shown that large column densities of CH(+) can be produced in magnetohydrodynamic shock models. Shock speeds U sub s approx. = 10 km/s and initial magnetic field strengths of a few micro G are sufficient to produce ion-neutral drift velocities which can drive the endothermic C(+)(H2,H)CH(+) reaction. It was also shown that single-fluid hydrodynamic models do not generate sufficiently large column densities of CH(+) unless unacceptably high shock velocities (u sub s approx. 20 km/s) are assumed in the models. Thus, the observed column densities of CH(+) provide a constraint on the mode of shock propagation in diffuse clouds. More precisely, they determine a lower limit to the ion-neutral drift velocity.

Flower, D. R.↗
NASA NTRS1986

Thunderstorm cloud top dynamics as inferred from satellite observations and a cloud top parcel model

Thunderstorm top temperature-height structure and temperature-height conversion relations in the convective overshooting top region are examined using data from GOES IR, AVHRR, and aircraft overflights, and GOES stereoscopic observations. Using a Lagrangian one-dimensional cloud parcel model applied in the overshooting region, three classes of storm tops are described and the causes of their unique temperature-height structures are explored. Although the parcel model used does not fully reproduce the three-dimensional structure and dynamics of an evolving thunderstorm top, it is shown to crudely reproduce the parcel dynamics of updraft core parcels. The locations of cold points, high points, warm points, and the magnitude of cold-high offsets compare favorably between the model and the satellite observations.

Adler, Robert F.↗