Engineering topics

Hovestadt, D.

Publications and source records attributed to Hovestadt, D..

At least 109 records · Page 6

NASA NTRS1981

Time and energy dependence of heavy ion abundances in solar flare energetic particle events

Data from a survey of solar flare events undertaken by the UMD/MPI ULET telescope on the IMP-8 satellite during the period 1973-1977 yields examples of time and energy dependence of the abundances and spectra of the He, C, O and Fe heavy ions. Time variations are found in the O/He, O/C and Fe/O ratios which appear to be inconsistent with models based entirely on rigidity-dependent propagation in the interplanetary medium. It is speculated that such other factors as the abundance differences at the flare site on the sun, or features of the acceleration and release mechanisms, may play an important role in the variations discussed.

Mason, G. M.↗

NASA NTRS1981

Observations of the ionization states of energetic particles accelerated in solar flares

The ionization states and spectra of 0.3 to 2.4 MeV/nuc He, C, O and Fe are measured in a survey of ten solar flare particle events. He(plus) is found to be present in all events, which indicates the common presence of energetic He(plus) in the source material from which solar particles are accelerated. The distribution functions of He(plus), He(plus plus) and heavier elements are represented by simple exponentials of the particle speed times its rigidity to a power n, where n is between 0 and 1, and equal e-folding values. Results are consistent with a model where ions are accelerated in the corona by multi-dimensional shocks out of a population taken from both hot and cold coronal regions.

Gloeckler, G.↗

NASA NTRS1981

A comparison of helium and heavy ion spectra in He/3/ rich solar flares with a model calculation

He isotopes, O and Fe in He(3) rich solar flares are studied during the 1977 to 1979 period with the MPI/UoMd particle experiment on ISEE-1 and ISEE-3. The study revealed that the He(3) spectrum is generally harder than that of He(4), and the O spectrum is harder than that of Fe. The spectra are compared with a stationary model based on stochastic Fermi acceleration in Alfven turbulence including a rigidity dependent particle loss. Model calculations fit the He(3) and He(4) spectra between 0.4 and 4.0 MeV/nucleon, with discrepancies at lower and higher energies, and the O and Fe spectra cannot be fitted simultaneously.

Mobius, E.↗

NASA NTRS1980

On the charge state of the anomalous oxygen component

Observations of a phase lag between the intensity variations of high-energy galactic cosmic rays and the quiet-time oxygen flux in the energy region 7.6-24 MeV/nucleon during the time period 1974-1975 are reported. Phase lag or hysteresis effects have been observed during the 11-year solar cycle for low-energy galactic cosmic rays and several authors have shown that this hysteresis effect is a function of the velocity and rigidity (and therefore of the ionic charge) of the particles. Assuming a similar rigidity dependence of the phase lag during the transient intensity decrease of both galactic cosmic rays and the anomalous oxygen component in the time period 1974-1975, and comparing the phase lag as observed for protons and helium during the same period with the oxygen measurements, an upper limit of approximately 4 is derived for the ionic charge of the anomalous oxygen component.

Klecker, 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 NTRS1980

Observations of a nonthermal ion layer at the plasma sheet boundary during substorm recovery

Measurements of the energy and angular distributions of energetic protons and alpha particles (not less than 30 keV/charge) in the geomagnetic tail are presented. The measurements were made during the recovery phase of a geomagnetic substorm on Apr. 19, 1978, with the Max-Planck-Institut/University of Maryland sensor system on the Isee 1 satellite. The measurements were also correlated with plasma observations made by the LASL/MPE instrument on Isee 1. The data reveal the presence of a thin nonthermal layer of protons and alpha particles at the plasma sheet boundary. The particles have their maximum flux at 60 keV/charge and are streaming highly collimated in the earthward direction. The alpha particle layer is confined within the proton layer. Many aspects of the observations are in agreement with an acceleration model near the neutral line proposed by Jaeger and Speiser (1974)

Moebius, E.↗

NASA NTRS1980

Conditions for acceleration of energetic ions greater than 30 keV associated with the earth's bow shock

A statistical analysis of particles (greater than 30 keV/charge) upstream of the earth's bow shock is conducted and shows that the rate of occurrence of upstream particle events is relative to the angle between the magnetic field and the shock normal at the shock intersection point as well as relative to the angle between the magnetic field and the radial direction (i.e., the sun-earth line). In addition, the occurrence rate of upstream particle events relative to the bow shock connection time of a field line convected with the solar wind is presented for a model bow shock. A linear dependence of the diffusion coefficient on energy per charge is apparent with the value of the mean free path of a 30-keV proton found to be about 4 earth radii, and the free escape boundary to be at about 30 earth radii in front of the bow shock.

Scholer, M.↗

NASA NTRS1980

A survey of approximately 1 MeV/nucleon solar flare particle abundances, in the Z ? 1-26 range, during the 1973-1977 solar minimum period

The abundances of the major elements over the range H-Fe in solar flare energetic particles near 1 MeV/nucleon were surveyed for a large number of flares during the period 1973-1977; observations were carried out by the IMP 8 spacecraft in interplanetary space. The survey considered two types of solar flare events: (1) large events from which the average boundaries were deduced, and (2) events which have significant abundance differences from average. In addition, two He-3-rich events with abundance features that are different from previous examples are reported: one case with no enhancements of heavy ions, and a second case in which, compared to O, the heavy-ion enhancements are confined to the charge range Si-Fe rather than the usual case in which all elements Ne-Fe are enriched.

Mason, G. M.↗

NASA NTRS1980

Comment on 'magnetosheath burst of predominantly medium nuclei observed with Imp 8 on February 16, 1974' by T. P. Armstrong, S. M. Krimigis, and R. P. Lepping

Armstrong et al. (1978) have observed a unique series of bursts with an unusually high content of Z greater than 2 particles and a high degree of collimation from the direction of the sun. The bursts were observed only with the CPME (Charged Particle Measurement Instrument) on Imp 8, but not with the CPME on Imp 7 nor with the ULET (Ultralow Energy Telescope) on Imp 8, whose response characteristics matched those of the CPME on Imp 7. The present comparison of the measurements made with the CPME and ULET cast doubt on the correctness of the reported observations.

Hovestadt, D.↗

NASA NTRS1980

Energy dependence and temporal evolution of the He-3/He-4 ratios in heavy-ion-rich energetic particle events

A study is presented of the energy dependence of the He-3/He-4 between 0.44 and 4.1 MeV per nucleon for six heavy-ion-rich events observed in 1974 and 1976. The observations were made using the low-energy dE/dx vs E Ultralow-Energy Particle telescope on IMP 8. It was found that all selected heavy-ion-rich events are also enriched in He-3: that the He-3/He-4 ratio decreases with decreasing energies; and that a rapid temporal evolution of the He-3/He-4 and the Fe/(H + He) ratios is strongly correlated during one event with the maximum value at the onset. These results are analyzed in terms of a model based on the preferential injection of He-3 and Fe resulting from turbulent ion heating and subsequent Fermi acceleration.

Moebius, E.↗

NASA NTRS1980

Upstream particle events close to the bow shock and 200 earth radii upstream - ISEE-1 and ISEE-3 observations

Two energetic particle events (28 keV - 145 keV) upstream of the earth's bow shock have been investigated with two identical experiments of the Max-Planck-Institut/University of Maryland on ISEE-1 and ISEE-3. Close to the bow shock the particle distribution is more or less isotropic and indicates strong scattering of these particles in the upstream wave field. At ISEE-3 the particles move essentially scatter-free from the general bow shock direction. The temporal evolution of the particle bursts is discussed in terms of the interplanetary magnetic field topology and the scattering conditions.

Scholer, M.↗

NASA NTRS1980

Search for characteristic features of low-energy quiet-time H, He and heavy nuclei fluxes, 1973-1977

Results of a survey of the 0.5-10 MeV/nucleon fluxes of H, He and heavier ions during interplanetary 'quiet-times' over the period 1973-1977 using the ULET telescope on IMP-8 are reported. It is found that in this energy range no characteristic flux level, or, e.g., proton/alpha ratio emerges during quiet periods in any year, thus precluding systematic long-term studies of the time behavior of the quiet-time component at these energies. Spectra for a uniquely quiet period in May 1977 and a less restrictively chosen set of quiet periods in 1976-1977 are presented and compared with previous results.

Mason, G. M.↗

NASA NTRS1980

Composition and energy spectra of low energy ions observed upstream of the earth's bow shock on ISEE-1

The characteristics of eleven locally accelerated particle events in the energy range from 30 to 125 keV/Q observed upstream of the earth's bow shock have been determined, including composition, energy spectra, and intensity versus time profiles. The measurements were made with the Ultra Low Energy Charge Analyzer sensor on ISEE-1. The composition in these events is similar to that of the solar wind, with a He to proton ratio of 8% and a CNO to He ratio of 6%. The composition is reasonably constant only when evaluated at equal energy per charge. The energy spectra cannot be adequately fit by a single power law in energy; an exponential or Maxwellian in energy per charge gives a satisfactory representation of the spectra. The time-intensity profiles of these upstream events show an inverse velocity dispersion, which may provide clues to the responsible acceleration mechanism.

Ipavich, F. M.↗

NASA NTRS1980

Ion and electron pulses observed in the earth's magnetospheric environment

Pulses of about 100 keV ions and electrons of time duration of several minutes are frequently detected in the earth's magnetotail and in the upstream region from the earth's bow shock. The distribution of the locations of the IMP 7 satellite where the particles were observed over the period from Sept. 29, 1972 to Oct. 6, 1973 is presented. The physical implications of these findings as related to (1) the source locations and (2) the dynamic nature of the acceleration and propagation of these particles are discussed.

Lin, Y. C.↗

NASA NTRS1980

Temporal variations of the anomalous oxygen /1974-1979/ and disappearance in 1978

The temporal changes in the differential intensity and energy spectra of anomalous oxygen, and in the O/C ratios of the anomalous cosmic ray component during the 1974-79 time period were examined using data from the IMP-8 and ISEE-3 spacecrafts. In addition to the solar modulation of the intensity of anomalous oxygen, the strength of the source of this component varies, and in 1978 the anomalous component disappeared almost completely. The results disagree with the existence of a purely galactic source but are consistent with expectations based on an heliospheric origin hypothesis as formulated by Fisk et al., (1974).

Hovestadt, D.↗

NASA NTRS1980

Heavy ion composition in solar flares at low energies, 1973-1977

The composition of solar flare particles near 1 MeV/nucleon has been surveyed for the major species between H and Fe over a four-year period using the IMP-8 ULET instrument. The average composition for the larger flares is found to be remarkably similar to that found by previous studies at energies greater than 10 MeV/nucleon. Variations in abundance are found to be well ordered by atomic number. It is suggested that such a smooth variation in abundances is due to an acceleration mechanism which preserves the main features of the ambient composition of the accelerated material, at least in the larger flares.

Mason, G. M.↗

NASA NTRS1980

Composition anomalies in solar flares

Flares with anomalies in He-3 and Fe enrichment and unusual abundances of heavy ions are discussed. Enrichment in heavy elements including O, Ne, Mg, Si, S-Ca group, and Fe is found in small flares enriched in He-3 and Fe; the flares enriched in He-3 and all heavy elements through Fe show depletion of the carbon abundance. An extreme case of the carbon abundance depletion with the C/O ratio of 0.01 contrasting with the normal solar flare C/O ratio of 0.5 indicates new constraints on acceleration models for small Fe-rich events.

Mason, G. M.↗

NASA NTRS1980

Distribution function representation of energy spectra of H, He, C, O and Fe in corotating particle streams

From an analysis of nine corotating events observed near 1 AU during the 1974-1976 solar minimum, the spectral parameters for H, He, C, O and Fe and relative abundances of these elements and of Ne, Mg, Si, and S-Ca were determined. The distribution functions of H, He, O and Fe are well represented by an exponential in particle speed over the energy range of the measurements from 0.3 to 5 MeV/nucleon. The composition resembles that of the solar corona, particularly in the O/C ratio which is 0.95 + or - 0.19, and the He/H and He/Ne ratios are similar to the respective ratios in the solar wind. The results are consistent with interplanetary statistical acceleration of these particles out of the high-energy tail of the high-speed solar wind.

Gloeckler, G.↗