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NASA NTRS1978

Energetic protons associated with interplanetary active regions 1-5 AU from the sun

Pioneer 11 has yielded data on approximately 100 energetic proton events at heliocentric distances between 1 and 2 AU. Measurements of absolute intensities, anisotropies, and crude energy spectra are studied in connection with interplanetary active regions (IAR's). It is found that in close vicinity to IAR's, the number of events observed per unit time interval is 10 times greater than in other areas of interplanetary space, and that the frequency of events has a maximum at plus or minus 5 hours of the time IAR edges are crossed. It is also noted that events in IAR vicinity have greater particle densities, softer energy spectra, and smaller time widths than other events. For many events associated with IAR's, particle anisotropies correspond to the net flow of particles along the interplanetary magnetic field toward the sun. This suggests that a mechanism in MHD shocks is responsible for local acceleration in the interplanetary medium.

Pesses, M. E.↗

NASA NTRS1978

Nitric oxide production by Tunguska meteor

The nonequilibrium chemical processes of nitric oxide formation are computed for the wake of the Tunguska meteor of 1908. The wake characteristics are derived by carrying out an optically-thick radiation field analysis for ablation of the meteoroid. The wake flow field is approximated by a one-dimensional, well-stirred reactor model. Known characteristics of the Tunguska event are imposed as constraints, and three controlling parameters - chemical composition, density, and velocity - are varied over a range around the values derived by Korobeinikov et al. (1976) and Petrov and Stulov (1975). The calculation shows that at least 19 million tons of nitric oxide is produced between the altitudes of 10 and 50 km. The anomalous atmospheric phenomena following the event are attributed to the reactions involving nitric oxide thus produced and atmospheric ozone. It is speculated that the nitric oxide produced by the event fertilized the area near the fall, causing the observed rapid plant growth.

Park, C.↗

NASA NTRS1981

Propagating substorm injection fronts

It is argued that a series of two-satellite observations leads to a clarification of substorm plasma injection, in which boundary motion plays a major role. Emphasis is put on a type of event characterized by abrupt, dispersionless changes in electron intensity and a coincident perturbation that consists of both a field magnitude increase and a small rotation toward more dipolar orientation. Comparing plasma observations at two points, it is found that in active, preinjection conditions the two most important features of the plasma sheet are: (1) the low-energy convection boundary for near-zero energy particles, determined by the magnitude of the large-scale convection electric field; and (2) the precipitation-flow boundary layer between the hot plasma sheet and the atmospherically contaminated inner plasma sheet.

Moore, T. E.↗

NASA NTRS1981

The role of magnetic helicity in cosmic ray transport theory

It has been found that the computed values of the mean free path for pitch angle scattering of low rigidity cosmic rays computed from weak turbulence theory are systematically larger than the values inferred from analyses of solar particle events. Reasons for this discrepancy are considered, taking into account components of the spectral tensor of the magnetic field fluctuations which can contribute to pitch angle scattering. The contributions of the additional terms can be estimated from the interplanetary magnetic field. It is shown that these additional contributions can be significant. A description is given of a formalism which includes the possibility that the field magnitude is constant. The formalism provides a formal basis for the heuristic arguments made by Goldstein (1980).

Goldstein, M. L.↗

NASA NTRS1984

Ionosphere-magnetosphere coupling and convection

The following international Magnetospheric Study quantitative models of observed ionosphere-magnetosphere events are reviewed: (1) a theoretical model of convection; (2) algorithms for deducing ionospheric current and electric-field patterns from sets of ground magnetograms and ionospheric conductivity information; and (3) empirical models of ionospheric conductances and polar cap potential drop. Research into magnetic-field-aligned electric fields is reviewed, particularly magnetic-mirror effects and double layers.

Wolf, R. A.↗

NASA NTRS1987

Nimbus 7 earth radiation budget wide field of view climate data set improvement. I - The earth albedo from deconvolution of shortwave measurements

A deconvolution method for extracting the top of the atmosphere (TOA) mean, daily albedo field from a set of wide-FOV (WFOV) shortwave radiometer measurements is proposed. The method is based on constructing a synthetic measurement for each satellite observation. The albedo field is represented as a truncated series of spherical harmonic functions, and these linear equations are presented. Simulation studies were conducted to determine the sensitivity of the method. It is observed that a maximum of about 289 pieces of data can be extracted from a set of Nimbus 7 WFOV satellite measurements. The albedos derived using the deconvolution method are compared with albedos derived using the WFOV archival method; the developed albedo field achieved a 20 percent reduction in the global rms regional reflected flux density errors. The deconvolution method is applied to estimate the mean, daily average TOA albedo field for January 1983. A strong and extensive albedo maximum (0.42), which corresponds to the El Nino/Southern Oscillation event of 1982-1983, is detected over the south central Pacific Ocean.

Hucek, Richard R.↗

NASA NTRS1984

Ocean surface wind stress

The need for improved surface wind and wind stress data is discussed. The collection of wind data using ship reports, research buoys, and cloud motion vectors is examined. The need for data on surface-wind stress fields is emphasized. Accurate stress data are required for studying: (1) the normal seasonal cycle and the intraannual events; (2) wind stress curls and the forcing of ocean circulation; (3) El Nino events; and (4) the low response of the midlatitude ocean circulation.

Harrison, D. E.↗

NASA NTRS1989

Properties of whistler mode wave packets at the leading edge of steepened magnetosonic waves - Comet Giacobini-Zinner

The physical characteristics of high-frequency wave packets detected at the steepened edge of magnetosonic waves near Comet Giacobini-Zinner are explored, based on an examination of over 45 well-defined events. The results suggest that the wave packets play an important role in the reorientation and reduction in field magnitude from the steepened magnetosonic waves to the upstream ambient field. The observed properties of the wave packets are shown to be consistent with anomalously Doppler-shifted right-hand polarized waves.

Tsurutani, Bruce T.↗

NASA NTRS1992

Data analysis of the COMPTEL instrument on the NASA gamma ray observatory

The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied.

Diehl, R.↗

NASA NTRS1992

Ulysses particle observations of the March 1991 solar flare events

Observations of energetic ions from the COSPIN instrument on the Ulysses spacecraft at 2.5 AU during the March 1991 series of solar flare events arae presented. The intensity profiles observed during this sequence of events were affected both by the presence of interplanetary shocks and large-scale discontinuities in the magnetic field, the low-energy (about 1 MeV) protons being influenced mainly by the shocks and the discontinuities, and the high-energy (about 100 MeV) protons by the discontinuities. The first shock observed at Ulysses was followed by several discontinuities and a Coronal Mass Ejection (CME) which were probably moving with the shock. Particles following this shock were prevented from propagating freely into the heliosphere by the structure moving with the shock, and were carried along with it. A second shock was followed by a region containing bi-directional particle anisotropies. A subsequent enhancement of low-energy particles suggests the passage of another shock. This was followed by a slow intensity decay which coincided with a second CME and where bi-directional particle anisotropies were again observed.

Sanderson, T. R.↗

NASA NTRS1994

Statistical study of ULF wave occurrence in the dayside magnetosphere

Ultralow-frequency (ULF) waves are observed almost everywhere in the dayside magnetosphere. The mechanism by which these waves are generated and transformed in the dayside magnetosphere is still not understood. Here we report a statistical study of these waves based on magnetic field data from the International Sun-Earth Explorer 1 (ISEE 1) spacecraft. Data from the first traversal of the spacecraft through the entire dayside magnetosphere have been examined to determine the spatial distribution of wave occurrence. Successive 20-min segments of data were transformed to a field-aligned coordinate system. The parallel component was detrended and all three components of the field spectrally analyzed. Wave occurrence was defined by the presence of significant peaks in the power spectra. Wave events were categorized by three wave frequency bands: Pc 3 with T approximately 10-45 s; Pc 4 with T approximately 45-150 s; the short-period part of the Pc 5 wave band with T approximately 150-324 s. Properties of the spectral peaks were then entered into a data base. The data base was next sorted to determine the spatial occurrence pattern for the waves. Our results show that Pc 3 waves most frequently occur just outside synchronous orbit and are approximately centered on local noon. Pc 4 waves have a similar distribution with its peak further out. Pc 5 waves have high occurrence rate at the two flanks of the magnetosphere. Peaks in spectra obtained near the magnetopause are less clearly defined than those deeper in the magnetosphere.

Cao, M.↗

NASA NTRS1994

Filamentary current structures in the postnoon sector: Observations from UARS

During an intense geomagentic storm (Kp 7+) that began at approximately 1830 UT on October 1, 1991, the Upper Atmosphere Research Satellite (UARS) satellite encountered the dayside postnoon auroral oval. On two consecutive crossings of the northern hemisphere between 2040 and 2240 UT, the vector magnetometer detected region 1 and 2 Birkeland and ionospheric currents in the postnoon sector. Low-energy electron events were observed near 1400 MLT within a narrow portion of the region 1 current system. Simultaneous magnetic field measurements revealed the presence of intense (approximately 20 microA/sq m) bipolar filament current structures embedded in the auroral oval. The upward-directed currents were associated with the more concentrated region of precipitating electrons. Ions associated with the more intense flux of low-energy electrons exhibited a dispersion signature typical of an ion velocity filter. The dispersion, aligned along the orbit, exhibited higher-energy ions at lower latitudes and earlier local times. The colocation of filament currents and ion dispersion signatures at such late postnoon local times is not consistent with typical E x B 'cusp' dispersions. These features more likely result from dayside boundary wave phenomena.

Bythrow, P. F.↗

NASA NTRS2001

Chandra ACIS Observations of Jovian X-Ray Emission

On November 25 and 26, 1999, the Chandra X-ray spacecraft conducted a set of four 19,000 sec observations of Jupiter. The ACIS-S instrument configuration was used for its good low energy efficiency and spatial resolution. An anomalous response was obtained which was subsequently attributed to strong jovian infrared radiation penetrating the detector and piling up spurious events across the entire X-ray range. However, the pre-observation establishment of an offsetting bias field has allowed the recovery of data from that portion of Jupiter's disc which remained within the elevated portion of the bias field during the observation. This ranges from fewer than 3000 sec to the entire observing time for about 10% of the planet. Auroral emission is seen near both poles in each observation. The northern aurora ia overall more intense than the southern, consistent with prior Einstein and ROSAT Observatory results. The southern aurora shows more modulation with Jupiter's rotation than the northern. Spatial resolution has been improved by at least a factor of two over prior measurements but convincing evidence of structure has not been seen. Lower latitude emission, first observed by ROSAT, is confirmed with flux levels averaging more than a factor of five below peak auroral values. Pronounced variation in the observed emission has occurred over the observing period. The spectral response extends from 0.24 keV, below which noise dominates, to about 1.2 keV. For all four observations the spectrum is clearly enhanced between 0.45 and 0.85 keV. This is apparently unequivocal evidence that Jupiter's X-ray emission is the result of oxygen and perhaps sulfur ions precipitating into the planet's atmosphere, where they undergo charge exchange interactions. The identification of specific transitions lines in the spectrum is among the ongoing efforts. A bremsstrahlung component has not yet been identified.

Garmire, Gordon↗

NASA NTRS2003

Parametric Transformation Analysis

Because twisted coronal features are important proxies for predicting solar eruptive events, and, yet not clearly understood, we present new results to resolve the complex, non-potential magnetic field configurations of active regions. This research uses free-form deformation mathematics to generate the associated coronal magnetic field. We use a parametric representation of the magnetic field lines such that the field lines can be manipulated to match the structure of EUV and SXR coronal loops. The objective is to derive sigmoidal magnetic field solutions which allows the beta greater than 1 regions to be included, aligned and non-aligned electric currents to be calculated, and the Lorentz force to be determined. The advantage of our technique is that the solution is independent of the unknown upper and side boundary conditions, allows non-vanishing magnetic forces, and provides a global magnetic field solution, which contains high- and low-beta regimes and is consistent with all the coronal images of the region. We show that the mathematical description is unique and physical.

Gary, G. Allan↗

NASA NTRS2004

The Chemistry of Early Self-Replicating Systems

On June 10, 2003, a symposium 'Celebrating 50 Years of Prebiotic Chemistry' honoring the 50th Anniversary of the 1953 publication of the Miller Experiment in SCIENCE was held at the University of California, San Diego. This event was organized and hosted by the NASA Specialized Center of Research and Training in Exobiology. It was sponsored by NASA, the Dean of Physical Sciences and the Department of Chemistry and Biochemistry at the University of California, San Diego (UCSD). The following events were held: 1) For the symposium, public lectures and a reception were held at UCSD on June 10, 2003 in honor of the 50th Anniversary of the Miller Experiment. The speakers were the NSCORT/Exobiology Principal Investigators Dr. Jeffrey L. Bada and Dr. Gerald F. Joyce and the moderator, Dr. Leslie Orgel; 2) A evening discussion seminar and dinner was held at UCSD with invited scientists, NSCORT investigators, NASA Headquarters Officials and the Chancellor and Officials of the University of California, San Diego. Stanley Miller has had a long history of support from the NASA Exobiology Section. This event commemorated the anniversary of his classic experiment and was a small recognition of his contributions to the field.

Bada, Jeffrey L.↗

NASA NTRS2005

Diamond-Coated Carbon Nanotubes for Efficient Field Emission

Field-emission cathodes containing arrays of carbon nanotubes coated with diamond or diamondlike carbon (DLC) are undergoing development. Multiwalled carbon nanotubes have been shown to perform well as electron field emitters. The idea underlying the present development is that by coating carbon nanotubes with wideband- gap materials like diamond or DLC, one could reduce effective work functions, thereby reducing threshold electric-field levels for field emission of electrons and, hence, improving cathode performance. To demonstrate feasibility, experimental cathodes were fabricated by (1) covering metal bases with carbon nanotubes bound to the bases by an electrically conductive binder and (2) coating the nanotubes, variously, with diamond or DLC by plasma-assisted chemical vapor deposition. In tests, the threshold electric-field levels for emission of electrons were reduced by as much as 40 percent, relative to those of uncoated- nanotube cathodes. Coating with diamond or DLC could also make field emission-cathodes operate more stably by helping to prevent evaporation of carbon from nanotubes in the event of overheating of the cathodes. Cathodes of this type are expected to be useful principally as electron sources for cathode-ray tubes and flat-panel displays.

Dimitrijevic, Stevan↗

NASA NTRS2015

Trajectory Simulation of Meteors Assuming Mass Loss and Fragmentation

Program used to simulate atmospheric flight trajectories of entry capsules [1] Includes models of atmospheres of different planetary destinations - Earth, Mars, Venus, Jupiter, Saturn, Uranus, Titan, ... Solves 3-‐degrees of freedom (3DoF) equations for a single body treated as a point mass. Also supports 6-DoF trajectory simula4on and Monte Carlo analyses. Uses Fehlberg-‐Runge-‐Kuna (4th-5th order) time integraion with automaic step size control. Includes rotating spheroidal planet with gravitational field having a J2 harmonic. Includes a variety of engineering aerodynamic and heat flux models. Capable of specifying events - heatshield jettison, parachute deployment, etc. - at predefined altitudes or Mach number. Has material thermal response models of typical aerospace materials integrated.

Atmospheric Entry↗

NASA NTRS2016

Simulations of Solar Jets Confined by Coronal Loops

Coronal jets are collimated, dynamic events that occur over a broad range of spatial scales in the solar corona. In the open magnetic field of coronal holes, jets form quasi-radial spires that can extend far out into the heliosphere, while in closed-field regions the jet outflows are confined to the corona. We explore the application of the embedded-bipole model to jets occurring in closed coronal loops. In this model, magnetic free energy is injected slowly by footpoint motions that introduce twist within the closed dome of the jet source region, and is released rapidly by the onset of an ideal kink-like instability. Two length scales characterize the system: the width (N) of the jet source region and the footpoint separation (L) of the coronal loop that envelops the jet source. We find that both the conditions for initiation and the subsequent dynamics are highly sensitive to the ratio L/N. The longest-lasting and most energetic jets occur along long coronal loops with large L/N ratios, and share many of the features of open-field jets, while smaller L/N ratios produce shorter-duration, less energetic jets that are affected by reflections from the far-loop footpoint. We quantify the transition between these behaviors and show that our model replicates key qualitative and quantitative aspects of both quiet Sun and active-region loop jets. We also find that there connection between the closed dome and surrounding coronal loop is very extensive: the cumulative reconnected flux at least matches the total flux beneath the dome for small L/N, and is more than double that value for large L/N.

Wyper, P. F.↗