Engineering topics

Fritz, T. A.

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

At least 37 records · Page 2

NASA NTRS1982

Overview of the IMS July 29, 1977, magnetic storm analysis

The physical characteristics and temporal development of a significant IMS magnetospheric event - the sudden commencement and multiple substorms of July 29, 1977 - are reviewed. It is pointed out that the ring current showed a maximum at 0600 UT and a major perturbation at 1230 UT, corresponding to the last substorm. The computerized coordinated data analysis workshop (CDAW 2) conducted in October 1979 is described. Attention is given to the solar wind conditions and magnetospheric response.

Manka, R. H.↗

NASA NTRS1982

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

In the 12 hours immediately after a worldwide storm sudden commencement at 0027 UT on July 29, 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) are examined, and vector magnetic field data and energetic electron and ion data from approximately 15 keV to more than 2MeV are employed. Four primary types of studies are carried out: (1) timing and morphology of energetic particle injections; (2) variation of particle phase space densities, using local magnetic field and particle flux data; (3) measurement of boundary motions, using high-energy ion gradient anisotropies; and (4) adiabatic modeling, which included injection, large-scale convection, corotation, and gradient drifts. For the 1200 UT substorms, it is concluded that there was a substantial flux dropout in a broad sector near local midnight because of a large-scale boundary motion, followed by a recovery to a predropout configuration.

Baker, D. N.↗

NASA NTRS1982

Pitch angle distributions of geomagnetically trapped MeV helium ions during quiet times

It is noted that during geomagnetically quiet conditions, energetic radiation belt helium ion fluxes at MeV energies have been found to exhibit characteristic radial profiles and large pitch angle anisotropies. Compiling data from many experiments, a systematic dependence of this anisotropy with helium ion energy is deduced. Provided a certain approximation holds for the observed pitch angle distributions, an empirical relation is deduced involving the helium ion energy. The range of the total ion energy here is 0.59-9 MeV (148-2250 keV per nucleon). These values are obtained for L shells in the range where L is approximately 2 to 5. The results are compared with theoretical expectations, and a qualitative explanation for the observed trend is suggested.

Fritz, T. A.↗

NASA NTRS1982

High temporal resolution energetic particle soundings at the magnetopause on November 8, 1977, using ISEE 2

An inbound crossing of the magnetopause on November 8, 1977, was analyzed using the greater spatial resolution obtained by the ISEE 2 instrument at high bit rate. A technique is described, which was used to obtain trapping boundary parameters for five energy channels in the energy range from 24-70 keV, and the location of the trapping boundary with respect to the boundary layer plasma is identified in addition to the waves on the trapping boundary consistent with the soundings in all energy channels. It is found that the trapping boundary for energetic ions is sharp and well defined for about 35 keV ions, corresponding most of the time to the earthward edge of the plasma boundary layer. Magnetosheath-like plasma is sometimes observed up to 800 km inside the trapping boundary, and it is argued that the wave nature of the trapping boundary is the cause of the slight difference between the higher and lower energy ion trapping boundary locations.

Fritz, T. A.↗

NASA NTRS1982

The magnetopause as sensed by energetic particles, magnetic field, and plasma measurements on November 20, 1977

The position of the trapping boundary for ions not less than 24 keV in the vicinity of the magnetopause was determined using energetic particle three-dimensional distributions observed by ISEE 1 and 2. For a short period of time on November 20, 1977, definite periods were observed when the subsolar magnetopause current and magnetosheath plasma penetration layers were not overlapping the trapping region for energetic particles whose outer edge is the trapping boundary. The trapping boundary was found to be in rapid continual motion, representing a sharp, well-defined boundary, and the penetration of the magnetosheath plasma inside this boundary can be limited to a distance comparable to the plasma ion gyroradius of not greater than about 100 km, although plasma penetration was seen up to 200 km earthward of the trapping boundary.

Fritz, T. A.↗

NASA NTRS1981

Preserved signatures of ion flux modulations observed by ATS 6

The considered investigation is concerned with a detailed analysis of the event of August 13, 1974. The considered day was a geomagnetically quiet day, and ATS 6 was stationed at 94 deg W longitude. On the basis of the conducted analysis it is found that the observed flux oscillations may be a fossil signature of flux modulations which have occurred in ions at an earlier time and at a region away from the spot of observation. In conclusion, it is pointed out that the August 13, 1974, and the January 23, 1975, events of proton flux oscillations observed by ATS 6 are of great importance. They reveal another unique capability of the drifting particles for preserving small modulation signatures imposed upon them during earlier wave-particle interactions. At the present, no conclusions are drawn as to what kind of the wave-particle interaction process was responsible for the observation.

Su, S.-Y.↗

NASA NTRS1981

Steady-state observations of geomagnetically trapped energetic heavy ions and their implications for theory

Data from the Heavy Ion Telescope on board Explorer 45 and the heavy ion channels on the ATS-6 spacecraft are used to describe the equatorial radial profiles of protons and He ions in the energy range of 0.1-1 MeV/nucleon. Measurements during a quiet period in June 1972 revealed that: fluxes of energetic protons and heavy ions inside L equals 4.5 are stable, with no observed decay; He ions of a given level are confined to the equatorial plane in a narrow L-range centered at Lmax; the equatorial differential flux ratio, compared on the basis of equal energy/ion, can exceed unity, indicating that He ion fluxes can be greater than equivalent energy proton fluxes; radial diffusion driven by variations of the magnetic field adequately models processes occurring in the inner magnetosphere for ion energies over 200 keV. The ATS-6 data from GEO found energetic heavy ions always present at L equals 6.6 and enhanced during magnetospheric substorms.

Fritz, T. A.↗

NASA NTRS1981

Discovery of ions with nuclear charge Z greater than or equal to 9 stability trapped in the earth's radiation belts

Observations of MeV heavy ions obtained by Explorer 45 in an equatorial earth orbit during a 7 month period in 1972 are presented, including data from four major magnetic storms. The spacecraft contained a heavy ion detector telescope and heavy ion discriminator electronics. Heavy ions were distinguished from protons and electrons, and He ions and ions heavier than F were recorded on separate data channels. The L equals 2.25 to L equals 4 zones were probed, and it was found that the relative enhancement in heavy ion fluxes in the radiation belts over the prestorm ion flux intensities tends to increase with increasing ion mass and/or increasing ion energy in the MeV range. The radial profiles of ions with nucleon number greater than nine peak at L equals 2.9, and MeV ions in this class decay on time scales from 23 days at L equals 3.25 to 55 days at L equals 2.25. Indirect evidence indicated a solar source for the very heavy ions in the magnetosphere.

Spjeldvik, W. N.↗

NASA NTRS1981

Observations of ions with nuclear charge Z greater than or equal to 9 in the inner magnetosphere

The Explorer 45 heavy ion data analysis is extended to ions heavier than fluorine, that is, ions with nuclear charge Z greater than about 9 during and after a major magnetic storm on August 4, 1972. Although the heavy ion detector telescope does not permit a precise identification of these ions, it is pointed out that if they are, for example, magnesium ions, then an equatorially mirroring peak trapped flux of 0.02 ions/sq cm-s-sr-keV is derived on L shells just below L = 3 at energies 12.8-51.2 MeV per ion (533-2133 keV per nucleon). It is noted that other possible ion contributions include silicon and iron. The fluxes of these ions are found to decay on time scales typically several tens of days; this is substantially faster than that of helium ions and slightly faster than that of oxygen ions in the lower MeV range.

Spjeldvik, W. N.↗

NASA NTRS1981

Observations of energetic helium ions in the earth's radiation belts during a sequence of geomagnetic storms

Observations of energetic (MeV) helium ions made with Explorer 45 during a sequence of magnetic storms during June through December of 1972 are presented. It is noted that the first of these storms started on June 17 and had a Dst index excursion to -190 gamma and that the MeV helium ions were perturbed primarily beyond 3 earth radii in the equatorial radiation belts with a typical flux increase of an order of magnitude at L equal to 4. The second storm period was in August and was associated with very major solar flare activity. While the Dst extremum was at best 35 gamma less than the June storm, this period can be characterized as irregular (or multi-storm) with strong compression of the magnetosphere and very large (order of magnitude) MeV helium ion flux enhancements down to L approximately equal to 2. After this injection, the trapped helium ion fluxes showed positive spherical slope with the peak beyond 3.15 MeV at L equal to 2.5; at the lowest observable L shells, little flux decay was seen during the remainder of the year.

Spjeldvik, W. N.↗

NASA NTRS1981

Energetic heavy ions with nuclear charge Z greater than or equal to 4 in the equatorial radiation belts of the earth - Magnetic storms

Direct in situ observations of trapped energetic heavy ions with nuclear charge Z greater than or equal to 4 at energies in the lower MeV range made with Explorer 45 during the period June-December 1972 are presented. It is noted that all measurements were carried out in the vicinity of the geomagnetic equatorial plane and that the data show the varying effects of four major magnetic storm periods. Orders of magnitude increases in the trapped heavy ion population are seen deep within the radiation belts following the August 1972 solar flare and magnetic storm events. Fluxes of the Z greater than or equal to 4 ions are found to decay faster than those of helium ions of comparable energies; typical decay times for these ions are found to be 24-40 days at L less than or equal to 4 and shorter at higher L shells. The observations are compared with the expected post-injection long-term behavior of atomic oxygen ions deduced from charge exhange, radial diffusive transport, and Coulomb collisions. Good agreement is found between theory and observations.

Spjeldvik, W. N.↗

NASA NTRS1981

Energetic ion and electron observations of the geomagnetic plasma sheet boundary layer - Three-dimensional results from ISEE 1

A description of energetic ion and electron behavior in the geomagnetic plasma sheet boundary layer is presented based on observations made by the medium-energy particle experiment on board ISEE 1. Three-dimensional observations of ions of energies 24-2081 keV and electrons of energies 22.5-1200 keV were obtained by the NOAA/WAPS instrument near the center of the magnetotail at a distance of approximately 15 earth radii. Large-scale motions of plasma sheet energetic particles are observed as an apparent result of a series of magnetospheric disturbances (substorms), which are characterized by substantial contractions and expansions. Ion flow velocity in a distinct boundary layer in energetic ions has been found to be in the earthward direction in each of the five ISEE 1 boundary crossings. Boundary layer motion during one of these crossings is interpreted as large-amplitude boundary waves with periodicities of a few minutes superimposed on the general plasma sheet behavior associated with the substorm process.

Spjeldvik, W. N.↗

NASA NTRS1980

Time-average fluxes of heavy ions at the geostationary orbit

Measurements of average proton, helium, carbon, and oxygen fluxes at 6.6 earth radii are reported. The data represent averages obtained on ATS 6 between June 15 and Oct. 3, 1974. The energy range covered was 0.36-1.1 MeV for protons and approximately 1-4 MeV for the heavier ions. The results indicate that above about 1 MeV the heavier ion fluxes dominate over the proton flux on the energy/ion scale. Using two different spectral dependencies to fit the data, the carbon to oxygen concentration ratio for energies above 1 MeV was found to be 0.43 for the power law spectrum and 0.44 for the exponential spectrum. Thus in either case the abundance ratio is consistent with the solar origin of the particles. Similarly, the helium to oxygen concentration ratio is found to be 0.17 for the power law spectrum and 0.28 for the exponential spectrum. This is inconsistent with the solar wind ratio, which is about 10. The results quoted above are based on a very small portion of the distribution function above 1 MeV.

Konradi, A.↗

NASA NTRS1980

Observations of ULF oscillations in the ion fluxes at small pitch angles with ATS 6

The ultra-low-frequency modulation of ion flux densities at small pitch angles observed by ATS 6 is examined, with particular attention given to a detailed analysis of a representative event. ULF modulation events with maximum modulation at small pitch angles were identified 14 times during the first eight months of operation of the NOAA low-energy particle detector on ATS 6. For the event of October 23, 1974, maximum flux modulation, with a maximum/minimum intensity ratio of 3.7, was observed in the 100 to 150 keV detector at an angle of 32 deg to the ambient field. Spectral analysis of magnetic field data reveals a right elliptically polarized magnetic perturbation with a 96-sec period and a 5-gamma rms amplitude, propagating in the dipole meridian at an angle of about 15 deg to the ambient field and the dipole axis. Proton flux modulation is found to lag the field by up to 180 deg for the lowest-energy channel. Observations are compared with the drift wave, MHD slow wave, and bounce resonant interaction associated with transverse wave models, and it is found that none of the wave models can adequately account for all of the correlated particle and field oscillations.

Su, S.-Y.↗

NASA NTRS1979

An energetic particle perspective of the magnetopause

The present analysis deals with energetic (above 24 keV) particle data from the Isee satellites during a series of magnetopause crossings. The primary energetic particle data employed in the analysis are the three-dimensional distributions from the Isee A satellite. Correlative magnetic field measurements are used to relate the particle behavior to magnetic field characteristics at and earthward of the magnetopause. It is shown that, to first order, the magnetopause may be regarded as a perfectly absorbing boundary for the trapped energetic particles, that it is nearly always in motion, and that boundary waves are often present. The observed dayside magnetopause motion is consistent with a large-scale radial motion having an approximately 10-min period plus superimposed boundary waves with a 90- to 150-sec period.

Williams, D. J.↗

NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗

NASA NTRS1979

Simultaneous quiet time observations of energetic radiation belt protons and helium ions - The equatorial alpha/p ratio near 1 MeV

Simultaneous monitoring of energetic helium ions and protons in the earth's radiation belts has been conducted with Explorer 45 in the immediate vicinity of the equatorial plane. Protons were measured from less than 1 keV to 1.6 MeV and also above 3.3 MeV in a channel responsive up to 22 MeV; helium ions were monitored in three passbands: 910 keV to 3.15 MeV, 590 to 910 keV, and 2.0 to 3.99 MeV. Alpha/proton flux ratios were found to vary significantly with energy and location in the radiation belts. At equal energy per nucleon a range of variability for alpha/p from 0.0001 to well above 0.001 was found, and at equal energy per ion the corresponding variability was from 0.001 to above 10. The latter findings emphasize the relative importance of the very energetic helium ions in the overall radiation belt ion populations.

Fritz, T. A.↗

NASA NTRS1978

Quiet time observations of equatorially trapped megaelectronvolt radiation belt ions with nuclear charge Z greater than or equal to 4

Data from the equatorial satellite Explorer 45 were used to study ion fluxes during the geomagnetically quiescent period June 1-15, 1972. A heavy-ion solid-state ion detector system obtained count rates close to the equatorial plane in the energy passband 1.82-4.8 MeV per ion during a single satellite pass through the radiation belts. Fluxes of these ions are interpreted as oxygen ions and are found to maximize in the L shell range 3-3.5 with peak equatorially mirroring flux of 0.38 ions/(sq cm s sr keV). This peak is not as sharply confined in L shell as is the helium ion peak.

Spjeldvik, W. N.↗