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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Synoptic observations of coronal transients and their interplanetary consequences

Conclusions reached to date after 5 yr of pooled, extensive monitoring of the solar coronal mass ejection (CME) at the Hawaiian High Altitude Observatory, Skylab and with the SMM are reported. Additional white light data have been gathered with the OSO-7 and P78-1 spacecraft. CME provides 5 percent of the solar wind mass flux and was the dominant driving force in interplanetary shocks in the last solar maximum phase. Both bubble and cloud shapes have been observed in CME events, which are nearly ubiquitous in proton events. Each of the CME shapes possesses distinctive dynamical characteristics. Finally, steady emissions of soft X-rays have been identified as precursors to CMEs, which display some latitudinal confinement.

Michels, D. J.↗
NASA NTRS1985

Theoretical investigation of the interstellar CH3NC/CH3CN ratio

Calculations have been performed to determine the abundance ratio of the metastable isomer CH3NC to the stable isomer CH3CN in dense interstellar clouds. According to gas phase, ion-molecule treatments, these molecules are both synthesized via protonated ion precursors. A calculation has been made of the ratio of the formation rates of the protonated precursor ions, CH3NCH(+) and CH3CNH(+), synthesized via the radiative association reaction between CH3(+) and HCN, which is thought to be the dominant formation process of the two isomeric ions. The calculations, which involve both ab initio quantum chemistry and equilibrium determinations, lead to a predicted CH3NCH(+)/CH3CNH(+) formation rate ratio between 0.1 and 0.4. If this ratio is maintained in the neutral species formed from the precursor ions, theory predicts a sizable abundance for methyl isocyanide (CH3NC) and lends credence to its tentative observation.

Defrees, D. J.↗
NASA NTRS1986

Plasma waves observed by the IRM and UKS spacecraft during the AMPTE solar wind lithium releases - Overview

The wave measurements from the Ion Release Module and the United Kingdom Satellite in the diamagnetic cavity, the transition region, and the upstream region are examined. Solar wind conditions during the releases on September 11 and 20, 1984 are described. The quasi-static electric field, wideband, high-frequency waves, and medium and VLF waves observations are analyzed. The data reveal that extremely low levels of wave activity are observed in the boundary between the diamagnetic cavity and external magnetic field, medium and VLF waves in the ion acoustic electrostatic cyclotron harmonic modes are detected in the transition region from the diamagnetic cavity to the solar wind, and decay in the magnetic field strength and density, and an increase in the quasi-static electric field is seen in the upstream edge of the transition region. The emissions observed are related to the different phases of the Li cloud development and different spatial regimes of the Li plasma-solar wind interaction.

Haeusler, B.↗
NASA NTRS1987

Composition, structure, and chemistry of interstellar dust

Different dust components present in the interstellar medium (IM) such as amorphous carbon, polycyclic aromatic hydrocarbons, and those IM components which are organic refractory grains and icy grain mantles are discussed as well as their relative importance. The physical properties of grain surface chemistry are discussed with attention given to the surface structure of materials, the adsorption energy and residence time of species on a grain surface, and the sticking probability. Consideration is also given to the contribution of grains to the gas-phase composition of molecular clouds.

Tielens, A. G. G. M.↗
NASA NTRS1989

Cold atomic gas in the inner Galaxy

A new set of 21 cm H I absorption spectra were obtained toward 21 compact continuum sources in the Galactic plane is presented. The 21 cm line velocity-averaged absorption coefficient as a function of Galactocentric distance is calculated. The result for distances within 2 kpc of the sun agrees with the local value found from absorption toward pulsars of 5-7 km/s/kpc. Overall, the absorption coefficient decreases to about half of its local value inside a Galactocentric radius of about 4 kpc. This decrease is shown to be primarily due to an increase in the mean line-of-sight distance between absorbing atomic clouds. Thus, the cool phase of the atomic gas is less abundant in the inner Galaxy than at the solar circle. The absorption spectra are similar in appearance to existing (C-12)O spectra. The spectral regions which show H I absorption also show CO emission.

Garwood, Robert W.↗
NASA NTRS1994

Measurements of stratospheric odd nitrogen at Arrival Heights, Antarctica, in 1991

An FTIR spectrometer was installed at Arrival Heights, Antarctica (78 deg S, 167 deg E) in February 1991 to measure the evolution of stratospheric HNO3 during the year. In particular, it was the intention to make the first observations of HNO3 trends during autumn, concurrently with ongoing measurements of column NO2 made with a grating spectrometer. The time-series of NO2 in the Antarctic shows a rapid decline in the column amount during autumn, and a slow recovery in spring, as the photochemical conditions move the species to and from higher storage reservoirs. The new nitric acid data show for the first time that during autumn the vertical column increases from approximately 1.9 x 10(exp 16) molecule cm(exp -2) at day 30 to approximately 3.1 x 10(exp 16) molecule cm(exp -2) by day 100. When the sun returns in spring, it is found that the column amount has fallen to about half the value at the end of autumn. Spring amounts are variable, but as found in the data from previous years remain low inside the vortex. The autumn increase is attributed to the heterogeneous conversion of N2O5 to gas-phase HNO3 on background aerosols. Low nitric acid column amounts at the start of spring suggest that the HNO3 has moved from the gas to the condensed phase on polar stratospheric clouds with the advent of low temperatures during the polar night.

Keys, J. Gordon↗
NASA NTRS1997

A Study of the Role of Clouds in the Relationship Between Land Use/Land Cover and the Climate and Air Quality of the Atlanta Area

The goal of Project ATLANTA is to derive a better scientific understanding of how land cover changes associated with urbanization affect local and regional climate and air quality. Clouds play a significant role in this relationship. Using GOES images, we found that in a 63-day period (5 July-5 September 1996) there were zero days which were clear for the entire daylight period. Days which are cloud-free in the morning become partly cloudy with small cumulus clouds in the afternoon in response to solar heating. This result casts doubt on the applicability of California-style air quality models which run in perpetual clear skies. Days which are clear in the morning have higher ozone than those which are cloudy in the morning. Using the RAMS model, we found that urbanization increases the skin surface temperature by about 1.0-1.5 C on average under cloudy conditions, with an extreme of +3.5 C. Clouds cool the surface due to their shading effect by 1.5-2.0 C on average, with an extreme of 5.0 C. RAMS simulates well the building stage of the cumulus cloud field, but does poorly in the decaying phase. Next year's work: doing a detailed cloud climatology and developing improved RAMS cloud simulations.

Kidder, Stanley Q.↗
NASA NTRS1999

Lightning and 85-GHz MCSs in the Global Tropics

Numerous observations of tropical convection show that tropical continental mesoscale convective systems (MCSs) are much more prolific lightning producers than their oceanic counterparts. Satellite-based climatologies using 85-GHz passive microwave ice-scattering signatures from the Special Sensor Microwave/Imager (SSM/I) indicate that MCSs of various size and intensity are found throughout the global tropics. In contrast, global lightning distributions show a strong land bias with an order of magnitude difference between land and ocean lightning. This is somewhat puzzling, since 85-GHz ice-scattering and the charge separation processes that lead to lightning are both thought to depend upon the existence of large graupel particles. The fact that low 85-GHz brightness temperatures are observed in tropical oceanic MCSs containing virtually no lightning leads to the postulate that tropical oceanic and tropical continental MCSs have fundamentally different hydrometeor profiles through the mixed phase region of the cloud (0 C <= T <= 20 C). Until recently, validation of this postulate has not been practicable on a global scale. Recent deployment of the Tropical Rainfall Measuring Mission (TRMM) satellite presents a unique opportunity for MCS studies. The multi-sensor instrument ensemble aboard TRMM, including a multi-channel microwave radiometer, the Lightning Imaging Sensor (LIS), and the first space-borne radar, facilitates high-resolution case studies of MCS structure throughout the global tropics. An important precursor, however, is to better understand the distribution of MCSs and lightning in the tropics. With that objective in mind, this research undertakes a systematic comparison of 85-GHz-defined MCSs and lightning over the global tropics for a full year, as an initial step toward quantifying differences between land and ocean convective systems.

Toracinta, E. Richard↗
NASA NTRS1999

The Infrared Spectral Imaging Radiometer and Laser Altimeter on STS-85 (an Aircraft Style Experiment Flown in Space)

Improvements in the remote sensing of clouds from space in the future will come from instruments with higher spatial and spectral resolution on more platforms and supported by active sounding. The space shuttle hitchhiker system allows new measurements to be prototyped in space with costs, operating flexibility and data volumes similar to aircraft experiments. The Infrared Spectral Imaging Radiometer and Shuttle Laser Altimeter hitchhiker experiment was flown in 1997. The experiment tested the use of uncooled thermal infrared imaging, laser cloud altitude measurements and high spatial resolution, tri-spectral sensing of cloud particle size and phase. A 1/4 km resolution, fifty orbit data set was obtained from STS-85. The presentation will focus on the use of the shuttle as an experiment platform and cover possible transition to the space station in the future.

Spinhirne, James D.↗
NASA NTRS2001

Remote Sensing of Cloud, Aerosol, and Water Vapor Properties from MODIS

MODIS is an earth-viewing cross-track scanning spectroradiometer launched on the Terra satellite in December 1999. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar orbiting, sun-synchronous, platform at an altitude of 705 kilometers, and provides images in 36 spectral bands between 0.415 and 14.235 micrometers with spatial resolutions of 250 meters (2 bands), 500 meters (5 bands) and 1000 meters (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this presentation we review the comprehensive set of remote sensing algorithms that have been developed for the remote sensing of atmospheric properties using MODIS data, placing primary emphasis on the principal atmospheric applications of (i) developing a cloud mask for distinguishing clear sky from clouds, (ii) retrieving global cloud radiative and microphysical properties, including cloud top pressure and temperature, effective emissivity, cloud optical thickness, thermodynamic phase, and effective radius, (iii) monitoring tropospheric aerosol optical thickness over the land and ocean and aerosol size distribution over the ocean, (iv) determining atmospheric profiles of moisture and temperature, and (v) estimating column water amount. The physical principles behind the determination of each of these atmospheric products will be described, together with an example of their application using MODIS observations. All products are archived into two categories: pixel-level retrievals (referred to as Level-2 products) and global gridded products at a latitude and longitude resolution of 1 degree (Level-3 products). An overview of the MODIS atmosphere algorithms and products, status, validation activities, and early level-2 and -3 results will be presented.

King, Michael D.↗
NASA NTRS2001

Remote Sensing of Cloud, Aerosol, and Land Properties from MODIS: Applications to the East Asia Region

MODIS is an earth-viewing cross-track scanning spectroradiometer launched on the Terra satellite in December 1999. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar-orbiting, sun-synchronous platform at an altitude of 705 km, and provides images in 36 spectral bands between 0.415 and 14.235 microns with spatial resolutions of 250 m (two bands), 500 m (five bands) and 1000 m (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this presentation we review the comprehensive set of remote sensing algorithms that have been developed for the remote sensing of atmospheric properties using MODIS data, placing primary emphasis on the principal atmospheric applications of (i) developing a cloud mask for distinguishing clear sky from clouds, (ii) retrieving global cloud radiative and microphysical properties, including cloud top pressure and temperature, effective emissivity, cloud optical thickness, thermodynamic phase, and effective radius, (iii) monitoring tropospheric aerosol optical thickness over the land and ocean and aerosol size distribution over the ocean, (iv) determining atmospheric profiles of moisture and temperature, and (v) estimating column water amount. The physical principles behind the determination of each of these atmospheric products will be described, together with an example of their application using MODIS observations to the east Asian region in Spring 2001. All products are archived into two categories: pixel-level retrievals (referred to as Level-2 products) and global gridded products at a latitude and longitude resolution of 1 degree (Level-3 products). An overview of the MODIS atmosphere algorithms and products, status, validation activities, and early level-2 and -3 results will be presented.

King, Michael D.↗
NASA NTRS2001

TRMM Precipitation Radar and Microwave Imager Observations of Convective and Stratiform Rain and Their Theoretical Implications

Theoretical models of radiative transfer are developed to simulate the 85 GHz brightness temperature, T85, observed by the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer as a function of rain rate. These simulations are performed separately over regions of convective and stratiform rain. For the purpose of constructing vertical profiles of hydrometeors in these regions, guidance is taken from TRMM Precipitation Radar (PR) observations, and from recent investigations of LDR and Z(sub DR) measurements made by land-based polarimetric radars. We find that for a given rain rate, the extinction in 85 GHz due to hydrometeors above the freezing level is relatively weak in convective regions compared to that in stratiform regions. The hydrometeor profile above the freezing level responsible for this weak extinction in convective regions is inferred, from LDR and Z(sub DR) observations and theoretical considerations, to contain two layers: 1) a layer of two km thickness with mixed phase particles, liquid drops and graupel, directly above the freezing level, and 2) a layer of graupel extending from the top of the mixed-phase layer to the cloud top. Strong extinction in the stratiform regions is inferred to result from slowly-falling, low-density ice aggregates (snow) above the freezing level. These theoretical results are consistent with T85 measured by TMI and the rain rate deduced from PR for convective and stratiform rain regions. On the basis of this study we infer that the accuracy of the rain rate sensed by TMI depends critically on the specification of the convective or stratiform nature of the rain.

Prabhakara, C.↗
NASA NTRS2001

Remote Sensing of Cloud, Aerosol, and Water Vapor Properties from MODIS

MODIS is an earth-viewing cross-track scanning spectroradiometer launched on the Terra satellite in December 1999. MODIS scans a swath width sufficient to provide nearly complete global coverage every two days from a polar-orbiting, sun-synchronous, platform at an altitude of 705 km, and provides images in 36 spectral bands from 0.415 to 14.235 microns with spatial resolutions of 250 m (2 bands), 500 m (5 bands) and 1000 m (29 bands). These bands have been carefully selected to enable advanced studies of land, ocean, and atmospheric processes. In this presentation I will review the comprehensive set of remote sensing algorithms that have been developed for the remote sensing of atmospheric properties using MODIS data, placing primary emphasis on the principal atmospheric applications of: (1) developing a cloud mask for distinguishing clear sky from clouds, (2) retrieving global cloud radiative and microphysical properties, including cloud top pressure and temperature, effective emissivity, cloud optical thickness, thermodynamic phase, and effective radius, (3) monitoring tropospheric aerosol optical thickness over the land and ocean and aerosol size distribution over the ocean, (4) determining atmospheric profiles of moisture and temperature, and (5) estimating column water amount. The physical principles behind the determination of each of these atmospheric products will be described, together with an example of their application using MODIS observations. All products are archived into two categories: pixel-level retrievals (referred to as Level-2 products) and global gridded products at a latitude and longitude resolution of 1 deg (Level-3 products). An overview of the MODIS atmosphere algorithms and products, status, validation activities, and early level-2 and -3 results will be presented. Finally, I will present some highlights from the land and ocean algorithms developed for processing global MODIS observations, including: (1) surface reflectance, (2) vegetation indices, leaf area index, and FPAR, (3) albedo and nadir BRDF-adjusted reflectance, (4) normalized water-leaving radiance, (5) chlorophyll-a concentration, and (6) sea surface temperature.

King, Michael D.↗
NASA NTRS2006

Laboratory Studies of Stabilities of Heterocyclic Aromatic Molecules: Suggested Gas Phase Ion-Molecule Routes to Production in Interstellar Gas Clouds

Several ring compounds have been detected in interstellar gas clouds, ISC, including the aromatic, benzene. Polycyclic aromatic hydrocarbons, PAHs, have been implicated as carriers of diffuse interstellar bands (DIBs) and unidentified infrared (UIR) bands. Heterocyclic aromatic rings of intermediate size containing nitrogen, possibly PreLife molecules, were included in early searches but were not detected and a recent search for Pyrimidine was unsuccessful. Our laboratory investigations of routes to such molecules could establish their existence in ISC and suggest conditions under which their concentrations would be maximized thus aiding the searches. The stability of such ring compounds (C5H5N, C4H4N2, C5H11N and C4H8O2) has been tested in the laboratory using charge transfer excitation in ion-molecule reactions. The fragmentation paths, including production of C4H4(+), C3H3N(+) and HCN, suggest reverse routes to the parent molecules, which are presently under laboratory investigation as production sources.

Adams, Nigel G.↗
NASA NTRS2006

Vibrational Spectroscopy after OSU - From C2- to Interstellar Polycyclic Aromatic Hydrocarbons

The composition of interstellar ice and dust provides insight into the chemical history of the interstellar medium and early solar system. It is now possible to probe this unique and unusual chemistry and determine the composition of these microscopic interstellar particles which are hundreds to many thousands of light years away thanks to substantial progress in two areas: astronomical spectroscopic techniques in the middle-infrared, the spectral region most diagnostic of chemical composition, and laboratory simulations which realistically reproduce the critical conditions in various interstellar environments. High quality infrared spectra of many different astronomical sources, some associated with giant, dark molecular clouds -the birthplace of stars and planets- and others in more tenuous, UV radiation rich regions are now available. The fundamentals of IR spectroscopy and what comparisons of astronomical IR spectra with laboratory spectra of materials prepared under realistic simulated interstellar conditions tell us about the components of these materials is the subject of this talk. These observations have shown that mixed molecular ices comprised of H2O, CH3OH, CO, NH3 and H2CO contain most of the molecular material in molecular clouds and that gas phase, ionized polycyclic aromatic hydrocarbons (PAHs) are widespread and surprisingly abundant throughout most of the interstellar medium.

Allamandola, Louis J.↗
NASA NTRS2009

Multilayer Cloud Detection with the MODIS Near-Infrared Water Vapor Absorption Band

Data Collection 5 processing for the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the NASA Earth Observing System EOS Terra and Aqua spacecraft includes an algorithm for detecting multilayered clouds in daytime. The main objective of this algorithm is to detect multilayered cloud scenes, specifically optically thin ice cloud overlying a lower-level water cloud, that presents difficulties for retrieving cloud effective radius using single layer plane-parallel cloud models. The algorithm uses the MODIS 0.94 micron water vapor band along with CO2 bands to obtain two above-cloud precipitable water retrievals, the difference of which, in conjunction with additional tests, provides a map of where multilayered clouds might potentially exist. The presence of a multilayered cloud results in a large difference in retrievals of above-cloud properties between the CO2 and the 0.94 micron methods. In this paper the MODIS multilayered cloud algorithm is described, results of using the algorithm over example scenes are shown, and global statistics for multilayered clouds as observed by MODIS are discussed. A theoretical study of the algorithm behavior for simulated multilayered clouds is also given. Results are compared to two other comparable passive imager methods. A set of standard cloudy atmospheric profiles developed during the course of this investigation is also presented. The results lead to the conclusion that the MODIS multilayer cloud detection algorithm has some skill in identifying multilayered clouds with different thermodynamic phases

Wind, Galina↗
NASA NTRS2011

Laser Altimetry Sampling Strategies over Sea Ice

With the conclusion of the science phase of the Ice, Cloud and land Elevation Satellite (ICESat) mission in late 2009, and the planned launch of ICESat-2 in late 2015, NASA has recently established the IceBridge program to provide continuity between missions. A major goal of IceBridge is to obtain a sea-ice thickness time series via airborne surveys over the Arctic and Southern Oceans. Typically two laser altimeters, the Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS), are utilized during IceBridge flights. Using laser altimetry simulations of conventional analogue systems such as ICESat, LVIS and ATM, with the multi-beam system proposed for ICESat-2, we investigate differences in measurements gathered at varying spatial resolutions and the impact on sea-ice freeboard. We assess the ability of each system to reproduce the elevation distributions of two seaice models and discuss potential biases in lead detection and sea-surface elevation, arising from variable footprint size and spacing. The conventional systems accurately reproduce mean freeboard over 25km length scales, while ICESat-2 offers considerable improvements over its predecessor ICESat. In particular, its dense along-track sampling of the surface will allow flexibility in the algorithmic approaches taken to optimize the signal-to-noise ratio for accurate and precise freeboard retrieval.

Farrell, Sinead L.↗
NASA NTRS2009

Molecular Cooling as a Probe of Star Formation: Spitzer Looking Forward to Herschel

We explore here the question of how cloud physics can be more directly probed when one observes the majority of cooling emissions from molecular gas. For this purpose we use results from a recent Spitzer Space Telescope study of the young cluster of embedded objects in NGC1333. For this study we mapped the emission from eight pure H2 rotational lines, from S(0) to S(7). The H2 emission appears to be associated with the warm gas shocked by the multiple outflows present in the region. The H2 lines are found to contribute to 25 - 50% of the total outflow luminosity, and can be used to more directly ascertain the importance of star formation feedback on the natal cloud. From these lines, we determine the outflow mass loss rate and, indirectly, the stellar infall rate, the outflow momentum and the kinetic energy injected into the cloud over the embedded phase. The latter is found to exceed the binding energy of individual cores, suggesting that outflows could be the main mechanism for cores disruption. Given the recent launch of Herschel and the upcoming operational lifetime of SOFIA we discuss how studies of molecular cooling can take a step beyond understanding thermal balance to exploring the origin, receipt, and transfer of energy in atomic and molecular gas in a wide range of physical situations.

Bergin, Edwin A.↗