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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Energetic ion and electron phase space densities in the magnetosphere of Uranus

Proton and electron phase space density profiles are constructed from an analysis of Voyager 2 low-energy charged particle data from the magnetosphere of Uranus. The Uranus proton profiles reveal an approximately exponential decline with decreasing radius for L less than about 9 in a relatively dense thermal plasma region with intense plasma wave activity. Among the distributed loss mechanisms at Uranus are satellite sweeping, wave-particle interactions, and charge exchange of protons with an extended hydrogen corona.

Cheng, Andrew F.↗
NASA NTRS2021

Aerosol–Ice Formation Closure: A Southern Great Plains Field Campaign

Prediction of ice formation in clouds presents one of the grand challenges in the atmospheric sciences. Immersion freezing initiated by ice-nucleating particles (INPs) is the dominant pathway of primary ice crystal formation in mixed-phase clouds, where supercooled water droplets and ice crystals coexist, with important implications for the hydrological cycle and climate. However, derivation of INP number concentrations from an ambient aerosol population in cloud-resolving and climate models remains highly uncertain. We conducted an aerosol-ice formation closure pilot study using a field-observational approach to evaluate the predictive capability of immersion freezing INPs. The closure study relies on co-located measurements of the ambient size-resolved and single-particle composition and INP number concentrations. The acquired particle data serve as input in several immersion freezing parameterizations, that are employed in cloud-resolving and climate models, for prediction of INP number concentrations. We discuss in detail one closure case study in which a front passed through the measurement site, resulting in a change of ambient particle and INP populations. We achieved closure in some circumstances within uncertainties, but we emphasize the need for freezing parameterization of potentially missing INP types and evaluation of the choice of parameterization to be employed. Overall, this closure pilot study aims to assess the level of parameter details and measurement strategies needed to achieve aerosol-ice formation closure. The closure approach is designed to accurately guide immersion freezing schemes in models, and ultimately identify the leading causes for climate model bias in INP predictions.

ice formation↗
NASA NTRS2005

Interplanetary Radiation and Internal Charging Environment Models for Solar Sails

A Solar Sail Radiation Environment (SSRE) model has been developed for defining charged particle environments over an energy range from 0.01 keV to 1 MeV for hydrogen ions, helium ions, and electrons. The SSRE model provides the free field charged particle environment required for characterizing energy deposition per unit mass, charge deposition, and dose rate dependent conductivity processes required to evaluate radiation dose and internal (bulk) charging processes in the solar sail membrane in interplanetary space. Solar wind and energetic particle measurements from instruments aboard the Ulysses spacecraft in a solar, near-polar orbit provide the particle data over a range of heliospheric latitudes used to derive the environment that can be used for radiation and charging environments for both high inclination 0.5 AU Solar Polar Imager mission and the 1.0 AU L1 solar missions. This paper describes the techniques used to model comprehensive electron, proton, and helium spectra over the range of particle energies of significance to energy and charge deposition in thin (less than 25 micrometers) solar sail materials.

Minow, Joseph I.↗
NASA NTRS2010

Simulation and 'TWINS Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 is the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly -80nT at 7:00 and 10:00 UT. During the main phase and at the peak of the storm, TWINS 1 and 2 were near apogee and moving from pre-dawn to post-dawn local time. The energetic neutral atom (ENA) imagers on the 2 spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the ENA emissions was seen in the midnight-to-dawn local-time sector. The development of this storm has been simulated using the Comprehensive Ring Current Model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in-situ ion data from THEMIS satellites. Simulation with static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always eastward than those in the observed TWINS images. On the other hand, simulation with a dynamic magnetic field gives better spatial agreements with both ENA and insitu particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, Mei-Ching↗
NASA NTRS1995

Neural Networks Analyze Data In Particle-Impact-Noise Tests

Electronic neural networks and computers put to use in analyzing data acquired in particle-impact-noise-detection (PIND) tests of packaged electronic components. PIND tests detect loose particles in packages that cause failures during subsequent operation of packages in presence of accelerations or other effects - for example, loose electrically conductive particles that bounce into positions in which they cause short circuits. Interpretation of test data more objective and accurate. Preliminary results suggest use of neural networks result in significant improvement in quality and reliability and decrease in cost of PIND testing.

Scaglione, Lois J.↗
NASA NTRS2011

Simulation and Twins Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 was at the time the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly .80 nT at 0700 and 1000 UT. During the main phase, and at the peak of the storm, TWINS 1 and 2 were near apogee and moving between predawn and postdawn local time. The energetic neutral atom (ENA) imagers on the two spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the high-altitude ENA emissions was seen in the midnight-to-dawn local time sector. The development of this storm has been simulated using the comprehensive ring current model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in situ ion data from a THEMIS satellite. Simulation with a static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always more eastward than those in the observed TWINS images. On the other hand, the simulation with a dynamic magnetic field gives better spatial agreement with both ENA and in situ particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, M.-C.↗
NASA NTRS2004

Interplanetary Radiation and Internal Charging Environment Models for Solar Sails

A Solar Sail Radiation Environment (SSRE) model has been developed for characterizing the radiation dose and internal charging environments in the solar wind. The SSRE model defines the 0.01 keV to 1 MeV charged particle environment for use in testing the radiation dose vulnerability of candidate solar sail materials and for use in evaluating the internal charging effects in the interplanetary environment. Solar wind and energetic particle instruments aboard the Ulysses spacecraft provide the particle data used to derive the environments for the high inclination 0.5 AU Solar Polar Imager mission and the 1.0 AU L1 solar sail missions. Ulysses is the only spacecraft to sample high latitude solar wind environments far from the ecliptic plane and is therefore uniquely capable of providing the information necessary for defining radiation environments for the Solar Polar Imager spacecraft. Cold plasma moments are used to derive differential flux spectra based on Kappa distribution functions. Energetic particle flux measurements are used to constrain the high energy, non-thermal tails of the distribution functions providing a comprehensive electron, proton, and helium spectra from less than 0.01 keV to a few MeV.

Minow, Joseph I.↗
NASA NTRS1981

Multiple crossings of a very thin plasma sheet in the earth's magnetotail

High resolution magnetic field, thermal plasma, and energetic particle data measured on the IMP 8 spacecraft are used to demonstrate that a thin plasma sheet with rapidly flowing plasma undergoes violent oscillatory motion that causes the entire thickness of the plasma sheet to pass over the spacecraft in times which are sometimes as short as 10 s. Ions with 50 and 290 keV energy are investigated since their gyroradii are comparable to the plasma sheet thickness. As the spacecraft moves from the plasma sheet into the lobe, the energetic particle intensities decrease, but the 290 keV ions are relatively more numerous than 50 keV ions on field lines located deeper in the lobe.

Fairfield, D. H.↗
NASA NTRS1975

Cosmic ray intensity variations during 0200-0700 UT, August 5, 1972

The cosmic ray intensity variations over the energy range of about 0.5 MeV to 1 GeV during the early part of August 5 are discussed in relation to the intensity changes during the entire period of activity (August 2 to 11). Measurements of the interplanetary magnetic field and particle data from ground-based neutron monitors, lunar sensors, and detectors in board Explorers 41 and 43 are used in the investigation. Analysis is made of intensity changes during the period from 0200 to 0700 UT on August 5, the north-south asymmetry in neutron monitor intensities, changes in the alpha particle/proton flux ratios, the lag in onset times as recorded by the two Explorers, and observations of flux enhancement by the lunar detectors. The results indicate that the enhanced particle fluxes (about 1 GeV) were due to a leakage of galactic cosmic rays into a low-intensity region of the interplanetary magnetic field bounded by tangential discontinuities, which connected to different particle sources both near the sun and in the outer solar system.

Venkatesan, D.↗
NASA NTRS1985

ISEE particle observations of surface waves at the magnetopause boundary layer

The dual-spacecraft ISEE mission provides a unique opportunity to study the motions of the magnetopause and adjacent boundary layer. By comparing high-time-resolution energetic particle data from ISEE 1 to those of ISEE 2, the velocity and orientation of the inner boundary of the boundary layer can be determined. Two cases are presented. In one, tailward propagating sinusoidally shaped surface waves with a wavelength in excess of 42,000 km and an amplitude of approximately 5000 km are found. In the other, surface waves are indicated with a wavelength of approximately 40,000 km and an amplitude of approximately 11,000 km having steepened nonsinusoidal shapes. The existence of such large-amplitude waves suggests that the particle dynamics near the magnetopause support nonlinear processes.

Couzens, D.↗
NASA NTRS1986

Subcritical and supercritical interplanetary shocks - Magnetic field and energetic particle observations

A study of 34 forward interplanetary shocks observed by ISEE 3 during 1978 and 1979 has been conducted. Magnetic field and high-energy particle data have been used, and for each shock the first critical Mach number has been determined. The first surprising result is that the majority of the observed shocks appear to be supercritical, and consistent with their supercritical character, many shocks have a foot and/or an overshoot in the magnetic field structure. Large-amplitude low-frequency waves (period of about 20 s in the spacecraft frame) are commonly observed upstream of all supercritical shocks (except for a few quasi-perpendicular shocks) and also upstream of the few subcritical shocks. Intense particle events are frequently observed at many shocks: spikes at quasi-perpendicular shocks and energetic storm particle events associated with quasi-parallel shocks can be comparably intense. The correlation of the high-energy particle peak flux with various shock parameters is in agreement with the acceleration mechanisms proposed by previous studies.

Bavassano-Cattaneo, M. B.↗
NASA NTRS1980

Observations of the mean ionization states of energetic particles in the vicinity of the earth's magnetosphere

The mean ionization states of 44-260 keV per charge ions observed as bursts in and near the earth's magnetosphere have been determined by using the particle data collected by the University of Maryland experiment on Imp 8. We find that during the period from October 1973 to December 1976 (1) the abundance ratio of heavy ions (Z greater than 2) to alphas ranges from 0.04 to 0.10, with a mean value of 0.08 plus or minus 0.02; (2) the energy spectra of alphas and Z greater than 2 ions in these bursts are adequately represented as exponentials in energy per charge with e-folding energies of 30-50 keV/Q; (3) the e-folding energies of both alpha particles and heavier ions are generally harder upstream from the bow shock than in the magnetotail and magnetosheath; and (4) the elemental abundances and ionization state distribution of the heavy ions are consistent with those of the corona at an equilibrium coronal temperature of 1-2 x 10 to the 6th K, which tends to support a solar wind origin for these particles.

Ma Sung, L. S.↗
NASA NTRS1993

Cosmic ray decreases and magnetic clouds

A study has been made of energetic particle data, obtained from IMP 8, in conjunction with solar wind field and plasma data at the times of reported magnetic clouds. It is shown that magnetic clouds can cause a depression of the cosmic ray flux but high fields are required. A depression of 3 percent in a neutron monitor requires a field of about 25 nT. Such high fields are found only in a subset of coronal ejecta. The principal cause for Forbush decreases associated with energetic shocks is probably turbulence in the postshock region, although some shocks will be followed by an ejecta with a high field. Each event is different. The lower-energy particles can help in identifying the dominant processes in individual events.

Cane, H. V.↗
NASA NTRS1992

Cosmic ray decreases and magnetic clouds

Energetic particle data, obtained from IMP 8, in conjunction with solar wind field and plasma data at the times of reported magnetic clouds was studied. It is shown that magnetic clouds can cause a depression of the cosmic ray flux but high fields are required. A depression of 3 percent in a neutron monitor requires a field of about 25 nT. Such high fields are found only in a subset of coronal ejecta. The principal cause for Forbush decreases associated with energetic shocks is probably turbulence in the post-shock region although some shocks will be followed by an ejecta with a high field. Each event is different. The lower energy particles can help in identifying the dominant processes in individual events.

Cane, H. V.↗
NASA NTRS1994

Effects of the intense solar activity of March/June 1991 observed in the outer heliosphere

The properties of the large-scale global merged interaction region (GMIR) generated by the intense solar events of March and June 1991 are studied using the available solar wind, interplanetary magnetic field, and energetic particle data from the observing network of Pioneer 10 and Voyagers 1 and 2 in the outer heliosphere. At heliocentric distances extending to 55 AU the delayed effects of this enhanced solar activity are observed in the form of large inceases in the solar wind velocity and interplanetary magnetic field and significant decreases in the galactic cosmic ray intensity. For low-energy ions (5-MeV protons) there was a single long-lived event extending over a period of some 6 months. Near the strongest interplanetary disturbances the H and He spectra are best represented by similar exponentials in momentum/nucleon (i.e., particle velocity at these at these energies). Over the rest of the event the characteristic momentum for He, (P(sub 0))(sub He) is generally approximately 0.66 for hydrogen. These spectra and the consistently low H/He ratio (25.3) at 2 MeV/nucleon closely resemble that observed in corrotating interaction regions events. Despite the strong north/south asymmetry in the solar activity, the interplanetary disturbances produced the same net decrease in the galactic cosmic ray intensity of ions greater than 70 MeV at the three widely separated spacecraft when the effects of the long-term recovery are taken into account. A comparison of the relative intensity of MeV ions at these three spacecraft suggest that the most intense solar events occurred on the back side of the Sun in time periods adjacent to the March and June episodes of solar activity. It is argued that this GMIR as a system is responsible for the low-frequency radio emission observed by the Voyager Plasma Wave experiment some 1.46 years after the onset of the March 1991 activity.

Mcdonald, F. B.↗
NASA NTRS1986

Pionener 11 observations of effects of Ganymede and Callisto on Jupiter's trapped radiation

Charged particle data for low-energy protons and electrons from the Pioneer 11 high-latitude flyby of Jupiter in 1974 are reviewed in the light of the Voyager 1 magnetic field model of Connerney et al. (1981). It is found that if the trajectory of Pioneer 11 is mapped to the equatorial plane along the model magnetic field lines, significant features in the time-intensity profiles of trapped protons and electrons, including one microsignaturelike feature, are found to correspond to shells of closed field lines crossed by the orbits of Ganymede and Callisto. It is suggested that these features are signatures of interaction of the trapped particles with Ganymede and Callisto.

Mckibben, R. B.↗
NASA NTRS1987

High latitude currents in the 0600 to 0900 MLT sector - Observations from Viking and DMSP-F7

High-resolution magnetic field and charged-particle data acquired on March 25, 1986 by the Viking and DMSP-F7 satellites, as they traversed the dawn sector auroral zone on nearly antiparallel trajectories within 40 min of each oher, are analyzed. Magnetic field measurements by Viking at 0850 MLT and by DMSP at 0630 MLT indicate the presence of a large-scale earthward-directed region 1 Birkeland current and an upward-flowing region 2 current. Both satellites also observed a third Birkeland current adjacent to and poleward of the region 1 system with opposite flow. This poleward system is about 0.5 deg invariant latitude wide and has a current density comparable to the region 1 and 2 systems. The highest-latitude current is identified as region 0. Its charged-particle signatures were used to infer field line mapping to the equatorial plane.

Bythrow, P. F.↗
NASA NTRS1989

Investigation of the Saturn dust environment from the analysis of energetic charged particle measurements

In order to assist the Cassini project in evaluating risks of collisions with particulate matter in the rotational equatorial plane, available Pioneer 11 and Voyager energetic charged particle data were reinvestigated to constrain the column mass density of absorbing material within several radial ranges. Within the orbit of Mimas, CRAND proton phase space densities maximize near 2.67 R sub s and exhibit secondary maximum at 2.43 R sub s. From the condition that sources must exceed losses near these maxima and using available theoretical models for CRAND proton production rates, upper bounds on the column mass density at these two radial locations are calculated. Detailed fits of radial diffusion models to the observed flux maxima yield somewhat more restrictive upper limits. The upper limits compare to a lower limit on the column mass density, estimated from previous model calculations by Van Allen. Aside from continuous rings, longitudinally limited, low optical depth clouds of particulates may exist in orbit with several of the inner satellites including Mimas and Enceladus. A brief review of Voyager energetic particle microsignatures that suggest the presence of material co-orbiting with these two satellites is presented. Finally, Pioneer 11 and Voyager measurements of low energy electron fluxes exhibit minima near the location of the tenuous E Ring centered on approx. 4 R sub s. Pioneer 11 pitch angle distributions appear to support the possibility that direct absorption by Ring E particulates produced the observed flux decreases.

Hood, L. L.↗