Engineering topics

Fritz, T. A.

Publications and source records attributed to Fritz, T. A..

At least 19 records

NASA NTRS2016

Density Variations in the Earth's Magnetospheric Cusps

Seven years of measurements from the Polar spacecraft are surveyed to monitor the variations of plasma density within the magnetospheric cusps. The spacecraft's orbital precession from 1998 through 2005 allows for coverage of both the northern and southern cusps from low altitude out to the magnetopause. In the mid- and high- altitude cusps, plasma density scales well with the solar wind density (n(sub cusp)∕n(sub sw) approximately 0.8). This trend is fairly steady for radial distances greater then 4 R(sub E). At low altitudes (r less than 4R(sub E)) the density increases with decreasing altitude and even exceeds the solar wind density due to contributions from the ionosphere. The density of high charge state oxygen (O(greater +2) also displays a positive trend with solar wind density within the cusp. A multifluid simulation with the Block-Adaptive-Tree Solar Wind Roe-Type Upwind Scheme MHD model was run to monitor the relative contributions of the ionosphere and solar wind plasma within the cusp. The simulation provides similar results to the statistical measurements from Polar and confirms the presence of ionospheric plasma at low altitudes.

Walsh, B. M.↗

NASA NTRS1999

CUSP: A New Acceleration Region of the Magnetosphere

A new magnetospheric phenomenon called a cusp energetic particle (CEP) event has been discovered by the POLAR spacecraft in 1996. The events were detected in the dayside polar cusp near the apogee of POLAR and could last for hours, in which the measured helium ions had energies up to 8 MeV. All of these events were associated with a dramatic decrease in the magnitude of the local magnetic field. A fundamental question is where do the cusp MeV ions come from? To answer this question, we have compared the ion flux in the September 18, 1996 CEP events with that in the upstream from the bow shock and found that bow shock acceleration cannot explain the measured ion flux in the CEP events. We have further determined the parallel power spectra of the local magnetic field turbulence calculated over the CEP event periods for fluctuations in the ultra-low frequency (ULF) ranges, corresponding to periods of about 0.33-500s. It is found that the mirror parameter, defined as the ratio of the square root of the integration of the parallel turbulent spectral component over the ULF ranges to the local mean field, is correlated with the intensity of the MeV helium flux. These new results represent a discovery that the high-altitude dayside cusp is a new acceleration region of the magnetosphere.

Chen, J.↗

NASA NTRS1995

PULSAUR 2: A sounding rocket project to study pulsating aurora and related phenomena

The second pulsating aurora (PULSAUR 2) rocket was a comprehensively instrumented rocket for the study of the generating mechanisms of pulsating auroras and their related atmospheric and ionospheric effects. It carried instruments to measure electrons and ions over a wide range of energies and pitch angles, optical emissions and X-rays, direct currents and alternating currents, magnetic fields, electron densities and temperatures. The rocket was flown from Andoeya, Norway on 9 February 1994, during good auroral and optical conditions, and reached an altitude of 291.5 km. Coordinated measurements were made from the rocket range by television cameras, photometers, magnetometers, riometers and very low frequency receivers. Ionospheric parameters were measured by the EISCAT radar. The main objectives and performance of the project are discussed, and some of the data obtained are mentioned.

Maaseide, K.↗

NASA NTRS1993

Structured plasma sheet thinning observed by Galileo and 1984-129

On December 8, 1990, the Galileo spacecraft used the Earth for a gravity assist on its way to Jupiter. Its trajectory was such that it crossed geosynchronous orbit at approximately local midnight between 1900 and 2000 UT. At the same time, spacecraft 1984-129 was also located at geosynchronous orbit near local midnight. Several flux dropout events were observed when the two spacecraft were in the near-Earth plasma sheet in the same local time sector. Flux dropout events are associated with plasma sheet thinning in the near-profile of the near-Earth plasma sheet while 1984-129 provided an azimuthal profile. With measurements from these two spacecraft we can distinguish between spatial structures and temporal change. Our observations confirm that the geosynchronous flux dropout events are consistent with plasma sheet thinning which changes the spacecraft's magnetic connection from the trapping region to the more distant plasma sheet. However, for this period, thinning occurred on two spatial and temporal scales. The geosynchronous dropouts were highly localized phenomena of 30 min duration superimposed on a more global reconfiguration of the tail lasting approximately 4 hours.

Reeves, G. D.↗

NASA NTRS1993

RAPID: The imaging energetic particle spectrometer on Cluster

The RAPID spectrometer for the Cluster mission, an advanced particle detector for the analysis of suprathermal plasma distributions in the energy range from 20 to 400 keV and from 2 keV/nuc to 1500 keV for electrons and ions, respectively, is presented. Novel detector concepts in combination with pinhole acceptance permit the measurement of angular distributions over a range of 180 deg in polar angle for either species. The detection principle for the ionic component is based on a two dimensional analysis of a particle's velocity and energy. Electrons are identified by the well known energy range relationship. The detection techniques are described and selected areas in geospace are used to highlight the scientific objectives of this investigation.

Wilken, B.↗

NASA NTRS1991

Energetic particles at Venus - Galileo results

At Venus the Energetic Particles Detector (EPD) on the Galileo spacecraft measured the differential energy spectra and angular distributions of ions above about 22 keV and electrons above about 15 keV in energy. The only time particles were observed by EPD was in a series of episodic events near closest approach (0559:03 UT). Angular distributions were highly anisotropic, ordered by the magnetic field, and showed ions arriving from the hemisphere containing Venus and its bow shock. The spectra showed a power law form with intensities observed into the 120- to 280-keV range. Comparisons with model bow shock calculations show that these energetic ions are associated with the Venusian foreshock-bow shock region. Shock-drift acceleration in the Venusian bow shock seems the most likely process responsible for the observed ions.

Williams, D. J.↗

NASA NTRS1990

CDAW 7 revisited - Further evidence for the creation of a near-earth substorm neutral line

Eastman et al. (1988) have interpreted the CDAW 7 substorm of April 24, 1979, previously taken as unambiguously supporting the near-earth neutral line model of magnetospheric substorms, in terms of spatial movements of a preexisting plasma-sheet boundary layer (PSBL) and its associated current sheets across the observing ISEE 1 and 2 spacercraft. It is presently noted that, by contrast, a reinvestigation of ISEE 1 and 2 energetic particle measurements around substorm onset on short time-scales shows the observed flux pattern to require the formation of a particle source eastward of the ISEE spacecraft, well within the plasma sheet, associated with the substorm onset. Strong flows were absent prior to substorm onset, indicating the temporal nature of the event, as opposed to an encounter with a preexisting PSBL containing large flows.

Kettmann, G.↗

NASA NTRS1989

A small-scale plasmoid formed during the May 13, 1985, AMPTE magnetotail barium release

Plasmoids are closed magnetic-loop structures with entrained hot plasma which are inferred to occur on large spatial scales in space plasma systems. A model is proposed here to explain the brightening and rapid tailward movement of the barium cloud released by the AMPTE IRM spacecraft on May 13, 1985. The model suggests that a small-scale plasmoid was formed due to a predicted development of heavy-ion-induced tearing in the thinned near-tail plasma sheet. Thus, a plasmoid may actually have been imaged due to the emissions of the entrained plasma ions within the plasma bubble.

Baker, D. N.↗

NASA NTRS1989

Energetic electron components at geosynchronous orbit

Energy distribution functions have been derived from energetic (30-2000 keV) electron fluxes observed simultaneously by three geosynchronous orbit satellites throughout the year 1986. These distributions, as well as others derived from empirical models of outer magnetospheric electron fluxes, can be resolved into two distinct relativistic Maxwellian components which are each fully parameterized by a density and a temperature. A four-parameter characterization is presented which provides a new, simplified procedure for the interpretation of energetic electron data in the outer magnetosphere.

Cayton, T. E.↗

NASA NTRS1988

Simultaneous energetic particle observations at geostationary orbit and in the upstream solar wind - Evidence for leakage during the magnetospheric compression event of November 1, 1984

The issue of accelertion and transport of particles in the upstream solar wind was investigated using the energetic ion and electron observations obtained simultaneously by three fortuitously positioned geostationary spececraft during a strong magnetospheric compression event of November 1, 1984. This compression event brought the subsolar magnetopause inward of the synchronous orbit. Data obtained indicate that, in the November 1 event, the process of magnetospheric ion escape was a very likely source for energetic particles both in the magnetosheath and the upstream solar wind.

Baker, D. N.↗

NASA NTRS1988

Multi-point measurements of ULF wave phases using a multi-channel energetic ion detector

The oscillation of differential fluxes of energetic ions modulated by a ULF wave often shows a phase shift between measurements in back-to-back detectors with look directions perpendicular to the ambient magnetic field. In a plasma of a single ion species, the phase difference is caused by displacement of the effective measurement positions by one ion gyroradius to each side of the detector. As the wave phase is periodic, the observed phase shift can correspond to a family of possible wavelengths. Simultaneous measurements of the flux modulations in different energy channels, which are equivalent to measurements of the wave phase at different positions, may make it possible to single out a unique wavelength consistent with all the measurements. Using the medium-energy-particle experiments ISEE-1 and 2, each of which may serve as a back-to-back detector, the above method was applied to a compressional Pc 5 wave observed near the equatorial plane at L between about 7 and 11. The transverse propagation properties of the wave were determined unambiguously.

Lin, N.↗

NASA NTRS1987

Do flux transfer events cause long-period micropulsations in the dayside magnetosphere?

Russell and Elphic (1979) suggested the possibility that flux transfer events (FTEs) generate long-period micropulsations in the outer, dayside magnetosphere. The reasons for this hypothesis are examined and results are presented for two pulsation surveys designed to test it. In the first survey, observations of micropulsations by GOES 2 are compared with ISEE 3 and IMP observations of interplanetary magnetic field (IMF) direction; since FTEs are highly correlated with southward IMF, a similar correlation between pulsations and southward IMF was sought. In the second survey, a catalog of ISEE 1 and 2 magnetopause crossings is compared with magnetometer readings from GOES 2 and 3 to determine whether Pc 4 and Pc 5 pulsations are more likely to occur after FTEs have taken place. Results indicate that there is a correlation between FTEs and transversely polarized Pc 4 pulsations with periods between 60 and 120 s, but not between FTEs and Pc pulsations with periods greater than 120 s. This suggests that the generating (or driving) frequency associated with FTEs lies between 60 and 120

Gillis, E. J.↗

NASA NTRS1986

Detailed observations of the plasma sheet during a substorm on April 24, 1979

Plasma, magnetic field, and energetic particle data obtained by ISEE 1 and 2 satellites for the April 24, 1979 substorm are studied in relation to the neutral line model and the boundary layer model. The ISEE 1 and 2 instruments and experiments utilized to collect the data are discussed. The major reconfiguration of the tail plasma and magnetic field plasma region, and the plasma ion flows observed support the neutral line model for interpreting substorms. The plasma ion distribution function and plasma flow are examined. The region of lobe-plasma sheet interface referred to as the separatrix layer is identified. The differences in times of plasma sheet dropout and recovery, and absence or presence of flux anisotropies are investigated. Energetic particle measurements are analyzed to study the relationship between energetic ions and plasma ions, and the velocity distributions. The data support the application of the neutral line model to the evaluation of substorms; however, the data are inconsistent with the boundary layer dynamics model.

Hones, E. W., Jr.↗

NASA NTRS1985

Magnetotail energy storage and release during the CDAW 6 substorm analysis intervals

The concept of the Coordinated Data Analysis Workshop (CDAW) grew out of the International Magnetospheric Study (IMS) program. According to this concept, data are to be pooled from a wide variety of spacecraft and ground-based sources for limited time intervals. These data are to provide the basis for the performance of very detailed correlative analyses, usually with fairly limited physical problems in mind. However, in the case of the CDAW 6 truly global goals are involved. The primary goal is to trace the flow of energy from the solar wind through the magnetosphere to its ultimate dissipation by substorm processes. The present investigation has the specific goal to examine the evidence for the storage of solar wind energy in the magnetotail prior to substorm expansion phase onsets. Of particular interest is the determination, in individual substorm cases, of the time delays between the loading of energy into the magnetospheric system and the subsequent unloading of this energy.

Baker, D. N.↗

NASA NTRS1984

Energetic particle sounding at the magnetopause and implications for magnetic reconnection

Measurements of energetic particle three dimensional distributions used to infer the structure of the region of the subsolar magnetopause obtained from the Medium Energy Particle Experiment onboard the ISEE-1 and 2 satellites are reviewed. Although initial interpretations of two types of energetic particle signatures argued against the topology predicted by magnetic reconnection at the magnetopause, subsequent understanding of the meaning of these observations demonstrate that the energetic particle data are uniformly consistent with the theory.

Fritz, T. A.↗

NASA NTRS1983

Hydromagnetic vortices. I - The 11 December 1977 event

Through a synthesis of magnetometer, plasma, energetic particle and electric field data from the ISEE satellite pair, the characteristics of the initial (11 December 1977) magnetotail plasma vortex event reported by Hones et al. (1978), are described. The event is associated with a hot (beta is approximately unity) compressional hydromagnetic wave and apparent vortical motion is seen because at two points in the flow cycle the flow is field-aligned. The behavior of the energetic ions receives special study: when combined with the thermal flow measurements energy dispersion is evident in the field-aligned flow, while the large pitch angle energetic ions reveal the presence of gradients. It is argued that these gradients are wave-induced, and the data are used to determine the perpendicular wave wavelength together with the speed and direction of transverse wave propagation.

Saunders, M. A.↗

NASA NTRS1983

Experimental determination of geomagnetically trapped energetic heavy ion fluxes

The observed spatial, directional and spectral characteristics of geomagnetically trapped heavy ions are reviewed. It is found that ions heavier than protons are significantly abundant in the earth's radiation belts, not only at low (ring-current) energies, but also at multi-MeV energies. Observations both at the geomagnetic equator and at low altitudes on the corresponding L-shell show the important roles played by the heavy ions. The heavy ion-to-proton flux ratio can exceed unity when compared at equal total ion energy. This is particularly the case at several MeV energies and in the outer radiation zone. In contrast, comparisons at equal energy per nucleon generally favor protons. The trapped fluxes of helium ions, of carbon, nitrogen and oxygen (CNO) ions, and of ions heavier than fluorine all exhibit high degrees of pitch angle anisotropy. Many of the observed radiation belt particle distribution characteristics are in agreement with first-order (quiet time) theoretical predictions, although some of the finer details await further research.

Spjeldvik, W. N.↗

NASA NTRS1982

Observation and modeling of energetic particles at synchronous orbit on July 29, 1977

In the twelve hours following a worldwide storm, there was a series of at least four magnetospheric substorms, the last and largest of which exhibited an expansion phase onset at approximately 1200 UT. Data from six spacecraft in three general local time groupings (0300, 0700, and 1300 LT) were examined and vector magnetic field data and energetic electron and ion data from approximately 15 keV to 2 MeV were employed.

Baker, D. N.↗