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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Effects of spacecraft potential on three-dimensional electron measurements in the solar wind

Using the three-dimensional, low-energy electron spectrometer aboard the Ulysses spacecraft, we have measured the gyrotropicity of electron distributions in the solar wind. In order to make these observations, we have developed a new technique for correcting spacecraft charging effects in three-dimensional, low-energy particle measurements. Comparisons of ion and electron number and current densities, and the alignment of electron temperature anisotropies with the local magnetic field, are presented as evidence of the improvement in the accuracy of the electron moments resulting from the spacecraft charging corrections. The implications of our charging correction technique go beyond simple scalar corrections to the Ulysses measurements. We discuss the effects of our charging correction upon the measurements of temporal and radial gradients in a plasma environment and for two-dimensionally obtained low-energy particle data.

Scime, Earl E.↗
NASA NTRS1995

The heliospheric sector boundary as a distented magnetic cloud

A magnetic cloud was detected both near Earth and by Pioneer 11 located 43 deg east of Earth at 4.8 AU. The magnetic field within the cloud rotated smoothly from toward to away polarity, marking sector boundary passage. Interpreted as a flux rope, the cloud had a vertical axis, implying that its cylindrical cross-section in the ecliptic plane was distended along the sector boundary by at least 43, forming an extensive occlusion in the heliospheric current sheet. At 1 AU the cloud had plasma signatures typical of a fast coronal mass ejection with low temperature and a leading shock. In contrast, at 4.8 AU, only the cloud signature remained. Its radial dimension was the same at both locations, consistent with little expansion beyond 1 AU. Energetic particle data at 4.8 AU show high fluxes preceding the cloud but not extending forward to the corotating shock that marked entry into the interaction region containing the cloud. The streaming direction was antisunward, consistent with possible acceleration in a low-beta region of field line draping around the cloud's western (upstream) end. The fluxes dropped upon entry into the cloud and became essentially isotropic one third of the way through it. On the basis of sector boundary characteristics published in the past, we suggest that distended clouds may be common heliospheric current sheet occlusions.

Crooker, N. U.↗
NASA NTRS1997

Elemental composition before, during and after the January 6, 1997, CME event measured by CELIAS/SOHO

Using solar wind particle data from the charge, element and isotope analysis system (CELIAS) experiment on the SOHO mission, densities of the elements O, Ne, Mg, Si, S, Ca, and Fe are derived, and their abundance is analyzed before, during and after the 6 Janaury 1997 coronal mass ejection event (CME). In the interstream and coronal hole regions before and after this event, typical solar wind abundances for the elements investigated were found. However, during the passage of the coronal mass ejection and during the passage of the erupted filament, the elemental composition differed markedly from typical solar wind. For the passage of the CME and for the passage of the erupted filament, a mass-dependent enhancement of the elements was found, with a monotonic increase towards heavier elements. Si/O and Fe/O ratios of the order of one during these time periods were observed.

Wurz, P.↗
NASA NTRS1997

The Relationship of Subvisible Cirrus Clouds Observed During NASA's Tropical Ozone

Thin, subvisible cirrus (SVC) clouds at the tropical tropopause have been observed by a number of methods in a variety of observational programs, including in situ sampling and aircraft and space-based lidar. Modeling studies suggest that these clouds play an important role in dehydrating tropospheric air as it enters the stratosphere. This is because particles large enough to have significant fall speeds can form under the conditions of slow cooling that are implied by the large horizontal extent of the SVC sheets. The IRA radiation that these clouds absorb, and the upward vertical motion this implies, also make them candidates for a tropical troposphere-to-stratosphere mass transfer mechanism. These sheets were observed on five flights during the Tropical Ozone Transport Experiment (TOTE) by the NASA Langley DIAL lidar aboard NASA's DC-8 research aircraft, operating during December 1995 and February 1996 south of Hawaii (12 S to 21 N). This experiment provided a unique look at these clouds since temperature profiles were available for all the SVC observations. Thus, the observed distributions of SVC's can be compared with the position of the tropopause to establish whether the SVC's are tropospheric or stratospheric. It also allows comparison of TOTE observations with in situ experiments, where water and cloud particle data is available as a function of temperature and potential temperature.

Pfister, L.↗
NASA NTRS2003

Reply to Comment on “Coronal Mass Ejections, Interplanetary Ejecta and Geomagnetic Storms” by Gopalswamy Et Al.

The comment of Gopalswamy et al. (thereafter GMY) relates to a letter discussing coronal mass ejections (CMEs), interplanetary ejecta and geomagnetic storms. GMY contend that Cane et al. incorrectly identified ejecta (interplanetary CMEs) and hypothesize that this is because Cane et al. fail to understand how to separate ejecta from "shock sheaths" when interpreting solar wind and energetic particle data sets. They (GMY) are wrong be cause the relevant section of the paper was concerned with the propagation time to 1 AU of any potentially geoeffective structures caused by CMEs, i.e. upstream compression regions with or without shocks, or ejecta. In other words, the travel times used by Cane et al. were purposefully and deliberately distinct from ejecta travel times (except for those slow ejecta, approx. 30% of their events, which generated no upstream features), and no error in identification was involved. The confusion of GMY stems from the description did not characterize the observations sufficiently clearly.

Cane, H. V.↗
NASA NTRS2004

First Terrestrial Soft X-ray Aurora Observations by Chandra

Northern polar "auroral" regions of Earth was observed by High-Resolution Camera in imaging mode (T32C-I) aboard Chandra X-Ray Observatory (CXO) during mid December 2003 - mid April 2004. Ten CXO observations, each approximately 20 min duration, were made in a non-conventional method (due to CXO technical issues), such that Chandra was aimed at a fixed point in sky and the Earth's polar cusp was allowed to drift through the HRC-I field-of-view. The observations were performed when CXO was near apogee and timed during northern winter mostly near midnight (6 hr), except two observations which occurred around 1200 UT, so that northern polar region is entirely in dark and solar fluoresced x-ray contamination can be avoided. These observations were aimed at searching the Earth's soft x-ray aurora and to do a comparative study with Jupiter's x-ray aurora, where a pulsating x-ray hot-spot near the northern magnetic pole has been observed by Chandra that implies a particle source region near Jupiter's magnetopause, and entry of heavy solar wind ions due to high-latitude reconnection as a viable explanation for the soft x-ray emissions. The first Chandra soft (0.1-2 keV) x-ray observations of Earth's aurora show that it is highly variable (intense arc, multiple arcs, diffuse, at times almost absent). In at least one of the observations an isolated blob of emission is observed where we expect cusp to be: giving indication of solar wind charge-exchange signature in x-rays. We are comparing the Chandra x-ray observations with observations at other wavelengths and particle data from Earth-orbiting satellites and solar wind measurements from near-Earth ACE and SOH0 spacecraft. Preliminary results from these unique CXO-Earth observations will be presented and discussed.

Bhardwaj, Anil↗
NASA NTRS2004

MARIE Dose and Flux Measurements in Mars Orbit

We present results from the Martian Radiation Environment Experiment (MARIE), aboard the 2001 Mars Odyssey spacecraft in orbit around Mars. MARIE operated successfully from March 2002 through October 2003. At the time of this writing, the instrument is off due to a loss of communications during an extremely intense Solar Particle Event. Efforts to revive MARIE are planned for Spring 2004, when Odyssey's role as a communications relay for the MER rovers is completed. During the period of successful operation, MARIE returned the first detailed energetic charged particle data from Mars. Due to limitations of the instrument, normalizing MARIE data to flux or dose is not straightforward - several large corrections are needed. Thus normalized results (like dose or flux) have large uncertainties and/or significant model-dependence. The problems in normalization are mainly due to inefficiency in detecting high-energy protons (signal-to-noise problems force the trigger threshold to be higher than optimal), to the excessively high gains employed in the signal processing electronics (many ions deposit energy sufficient to saturate the electronics, and dE/dx information is lost), and to artifacts associated with the two trigger detectors (incomplete registration of dE/dx). Despite these problems, MARIE is efficient for detecting helium ions with kinetic energies above about 30 MeV/nucleon, and for detecting high-energy ions (energies above about 400 MeV/nucleon) with charges from 5 to 10. Fluxes of these heavier ions can be compared to fluxes obtained from the ACE/CRIS instrument, providing at least one area of direct comparison between data obtained at Earth and at Mars; this analysis will be presented as a work in progress. We will also present dose-rate data, with a detailed explanation of the many sources of uncertainty in normalization. The results for both flux and dose will be compared to predictions of the HZETRN model of the GCR.

Zeitlin, C.↗
NASA NTRS2007

Space Environment (Natural and Induced)

Considerable effort and improvement have been made in the study of ionizing radiation exposure occurring in various regions of space. Satellites and spacecrafts equipped with innovative instruments are continually refining particle data and providing more accurate information on the ionizing radiation environment. The major problem in accurate spectral definition of ionizing radiation appears to be the detailed energy spectra, especially at high energies, which is important parameter for accurate radiation risk assessment. Magnitude of risks posed by exposure to radiation in future space missions is subject to the accuracies of predictive forecast of event size of SPE, GCR environment, geomagnetic fields, and atmospheric radiation environment. Although heavy ion fragmentations and interactions are adequately resolved through laboratory study and model development, improvements in fragmentation cross sections for the light nuclei produced from HZE nuclei and their laboratory validation are still required to achieve the principal goal of planetary GCR simulation at a critical exposure site. More accurate prediction procedure for ionizing radiation environment can be made with a better understanding of the solar and space physics, fulfillment of required measurements for nuclear/atomic processes, and their validation and verification with spaceflights and heavy ion accelerators experiments. It is certainly true that the continued advancements in solar and space physics combining with physical measurements will strengthen the confidence of future manned exploration of solar system. Advancements in radiobiology will surely give the meaningful radiation hazard assessments for short and long term effects, by which appropriate and effective mitigation measures can be placed to ensure that humans safely live and work in the space, anywhere, anytime.

Kim, Myung-Hee Y.↗
NASA NTRS2015

New Horizons Successful Completes the Historic First Flyby of Pluto and Its Moons

On July 14, 2015, after a 9.5 year trek across the solar system, NASA's New Horizons spacecraft flew by the dwarf planet Pluto and its system of moons, taking imagery, spectra and in-situ particle data. Data from New Horizons will address numerous outstanding questions on the geology and composition of Pluto and Charon, plus measurements of Pluto's atmosphere, and provide revised understanding of the formation and evolution of Pluto and Charon and its smaller moons. This data set is an invaluable glimpse into the outer Third Zone of the solar system. Data from the intense July 14th fly-by sequence will be downlinked to Earth over a period of 16 months, the duration set by the large data set (over 60 GBits) and the limited transmitted bandwidth rates (approx. 1-2 kbps) and sharing the three 70 m DSN assets with our missions. The small fraction (approx. 1%) of data downlinked during the early phase of the flyby has already revealed Pluto and Charon to be very different worlds, with increasing and dynamic complexity.

Pluto↗
NASA NTRS2018

Production of Negative Hydrogen Ions Within the MMS Fast Plasma Investigation Due to Solar Wind Bombardment

The particle data delivered by the Fast Plasma Investigation instrument aboard National Aeronautics and Space Administration's Magnetospheric Multiscale (MMS) mission allow for exceptionally high-resolution examination of the electron and ion phase space in the near-Earth plasma environment. It is necessary to identify populations which originate from instrumental effects. Using Fast Plasma Investigation's Dual Electron Spectrometers, we isolate a high-energy (approximately kiloelectron volt) beam, present while the spacecraft are in the solar wind, which exhibits an azimuthal drift with period associated with the spacecraft spin. We show that this population is consistent with negative hydrogen ions H− generated by a double charge exchange interaction between the incident solar wind H+ ions and the metallic surfaces within the instrument. This interaction is likely to occur at the deflector plates close to the instrument aperture. The H− density is shown to be approximately 0.2-0.4% of the solar wind ion density, and the energy of the negative ion population is shown to be 70% of the incident solar wind energy. These negative ions may introduce errors in electron velocity moments on the order of 0.2-0.4% of the solar wind velocity and significantly higher errors in the electron temperature.

Magnetospheric Multiscale↗
NASA NTRS2016

Pluto Revealed: First Results from the Historic 1st Fly-By Space Mission.

On July 14, 2015, after a 9.5 year trek across the solar system, NASAs New Horizons spacecraft successfully flew by the dwarf planet Pluto and its system of moons, taking imagery, spectra and in-situ particle data. In this internet-information age, this historic first fly-by was shared across planet Earth, everyone witnessing first-hand the transformation of distant point of lights into real worlds. The New Horizons dataset has become an invaluable first glimpse into the outer Third Zone of the Solar System. Pluto has revealed itself to be a complex, beautiful place, with a variety of geophysical and surface-atmosphere interactions. Charon has been unmasked; its surface features implying a complicated, enigmatic history. The smaller moons, origins still unknown, are uniquely different in their own right. This presentation summarizes NASAs New Horizons mission and its early science results, and touches on the future of further exploring the outer Third Zone.

Pluto↗
NASA NTRSDate not supplied

The Spacecraft Potential of Wind Over Time

In a space plasma, exposed to ionizing radiation, a conducting object like a spacecraft will generate a net charge as the relevant currents from the plasma and photoelectrons attempt to reach equilibrium over time. This net charging is measured (or inferred from particle measurements) as an electrostatic potential, called the spacecraft potential. The Wind spacecraft will be 30 years old on November 1, 2023 and as such, has one of the longest baselines of continuous spacecraft potential measurements of any space mission. We determine the spacecraft potential from observations of photoelectrons in the thermal particle data. We examine the variations over time finding oscillations that correlate with solar rotation. This preliminary study examines for other effects but is ultimately for the purpose of generating a properly calibrated velocity moment dataset for the entire Wind mission.

Lynn B. Wilson III↗
DOE OSTI2024

A Measurement of the Eta Meson Radiative Decay Width via the Primakoff Effect

The ? meson is an interesting tool to study fundamental symmetries in Quantum Chromodynamics (QCD). In particular, its radiative decay width, ? p? Ñ ??q, is an important quantity that can be predicted in the framework of Chiral Perturbation Theory. A precision measurement of this quantity would provide critical inputs to understanding the mixing of the ? and ?1 mesons and extracting constants with wide-ranging applications in low-energy QCD. This decay width has been measured in the past using two different experimental techniques. The more popular technique utilized e`e´ collisions to produce ? mesons through electromagnetic interactions. Today, the Particle Data Group (PDG) averages the results of five such experiments to obtain their currently-accepted value of the decay width as: 0.515?0.018 keV. However the first measurement of this quantity was obtained from a fixed-target experiment that measured the cross section for photoproduction of ? mesons on a nuclear target via the Primakoff effect. Their result of 0.324?0.046 keV shows strong tension with the average of the collider measurements, motivating a new, high precision measurement using the Primakoff method. For this purpose, the PrimEx-eta experiment was conducted in Hall D of the Thomas Jefferson National Accelerator Facility (Jefferson Lab or JLab). The data is currently being analyzed to measure the differential cross section for the photoproduction of ? mesons on a liquid, 4He target. Preliminary results obtained from the analysis of the first phase of the PrimEx-eta experiment show reasonable agreement with the currently-accepted PDG value of the radiative decay width. However, as will be discussed, there are many challenges to this precision measurement which must be studied before any results can be finalized and compared with previous measurements. In parallel to the ? decay width measurement, the PrimEx-eta experiment measured the total cross section for the fundamental, Quantum Electrodynamics (QED) process of Compton scattering from the atomic electrons inside the target. The results obtained from this measurement are in strong agreement with the next-to-leading order QED calculations, and the total combined uncertainties are below 3% for incident photon energies between 7-10 GeV. In addition to providing the first precision measurement of the total Compton scattering cross section within this beam energy range, this measurement verifies the capability of the PrimEx-eta experimental setup to perform absolute cross section measurements at forward angles, and serves as a reference process for the calibration of systematic uncertainties.

Smith, Andrew↗
NASA NTRS2012

Laser Diffraction Techniques Replace Sieving for Lunar Soil Particle Size Distribution Data

Sieving was used extensively until 1999 to determine the particle size distribution of lunar samples. This method is time-consuming, and requires more than a gram of material in order to obtain a result in which one may have confidence. This is demonstrated by the difference in geometric mean and median for samples measured by [1], in which a 14-gram sample produced a geometric mean of approx.52 micrometers, whereas two other samples of ~1.5 grams resulted in gave means of approx.63 and approx.69 micrometers. Sample allocations for sieving are typically much smaller than a gram, and many of the sample allocations received by our lab are 0.5 to 0.25 grams in mass. Basu [2] has described how the finest fraction of the soil is easily lost in the sieving process, and this effect is compounded when sample sizes are small.

Cooper, Bonnie L.↗
NASA NTRS1987

Particle field holography data reduction by Fourier transform analysis

The size distribution of a particle field hologram is obtained with a Fourier transformation of the Fraunhofer diffraction pattern of the reconstructed hologram. Off-axis absorption holograms of particle fields with known characteristics were obtained and analyzed with a commercially available instrument. The mean particle size of the reconstructed hologram was measured with an error of + or - 5 percent, while the distribution broadening was estimated within + or - 15 percent. Small sections of a pulsed laser hologram of a synthetic fuel spray were analyzed with this method thus yielding a spatially resolved size distribution. The method yields fast and accurate automated analysis of particle field holograms.

Hess, Cecil F.↗
NASA NTRS1987

Holographic, particle imaging and data reduction at Spectron Development Laboratores

Spectron has been deeply involved in the development and use of a wide variety of particle and flow diagnostic, electro optical instruments. Holography and imaging systems have played an important role in this work, but the extraction of data from images and holograms have always presented a limit to their use. Systems and techniques were devised to speed up and automate the extraction of data from holographic and conventional interferograms, particle images and holograms, and other types of optical flow visualization techniques. An IBM/AI based image analyzer was developed that is capable of automatically analyzing many useful image types including interferograms. A key feature of this system is the low total cost of the required hardware. In the particle field work, a commercial diffraction field analyzer was adopted to the image reconstructed from a hologram. This could expand the use of holography in particle diagnostics greatly.

Trolinger, James D.↗
NASA NTRS1995

Interactive data exploration and particle tracking for general circulation models

The SCENE environment for interactive visualization of complex data sets is discussed. This environment is used to create tools for graphical exploration of atmospheric flow models. These tools may be extended by the user in a seamless manner, so that no programming is required. A module for accurately tracing field lines and particle trajectories in SCENE is presented. This is used to examine the flowfield qualitatively with streamlines and pathlines and to identify critical points in the velocity field. The paper also describes a visualization tool for general circulation models on which the primary features of the environment are demonstrated.

Rosenbaum, R. I.↗
NASA NTRS1991

A global data set of soil particle size properties

A standardized global data set of soil horizon thicknesses and textures (particle size distributions) was compiled. This data set will be used by the improved ground hydrology parameterization designed for the Goddard Institute for Space Studies General Circulation Model (GISS GCM) Model 3. The data set specifies the top and bottom depths and the percent abundance of sand, silt, and clay of individual soil horizons in each of the 106 soil types cataloged for nine continental divisions. When combined with the World Soil Data File, the result is a global data set of variations in physical properties throughout the soil profile. These properties are important in the determination of water storage in individual soil horizons and exchange of water with the lower atmosphere. The incorporation of this data set into the GISS GCM should improve model performance by including more realistic variability in land-surface properties.

Webb, Robert S.↗