Engineering topics

Scholer, M.

Publications and source records attributed to Scholer, M..

At least 37 records · Page 2

NASA NTRS1986

ISEE 3 observations during a plasma sheet encounter at 140 earth radii - Evidence for enhancement of reconnection at the distant neutral line

A plasma sheet encounter of the ISEE-3 spacecraft in the distant tail at 140 earth radii on March 20, 1983 is studied using magnetic field, energetic particle, and plasma electron data sets. The H-component magnetograms from auroral magnetometer stations, intensity-time profiles, high resolution magnetic field measurements, and electron and proton angular distributions are analyzed. The dynamics of the plasma sheet displayed by the strong tailward and earthward directed ion beams, large northward and southward magnetic fields excursions, and short tailward and earthward plasma flows are described.

Scholer, M.↗

NASA NTRS1985

Spatial dependence of the local diffusion coefficient measured upstream of the November 12, 1978 interplanetary traveling shock

Characteristics of wuprathermal particles accelerated by quasi-parallel interplanetary traveling shocks have been generally explained in terms of a first order Fermi mechanism. Such models require diffusive scattering of particles upstream of the shock. This scattering is characterized by a local diffusion coefficient, kappa, which is determined by the local power density of waves in the upstream region. The dependence of the diffusion coefficient of suprathermal upstream protons on distance from the November 12, 1978 interplanetary traveling shock using a different approach is studied. Unlike previous studies this method, which is based on measurements of particle streaming and intensity gradients, does not rely on predictions. The local spatial variations of Kappa upstream of the November 12, 1978 shock have been chosen for study because the characteristics of this quasi-parallel shock have been extensively studied, and also because of its favorable geometry (i.e. B field nearly radial).

Gloeckler, G.↗

NASA NTRS1985

The mean ionic charges of N, Ne, MG, SI and S in solar energetic particle events

The mean ionic charges of nitrogen, neon, magnesium, silicon, and sulfur in solar flare particle events were determined for 12 flares during the time interval from September 1978 to September 1979. The observations were carried out with the MPI/UoMd ULEZEQ Sensor on the ISEE-3 satellite comparing the results with mean charge states established in a hot coronal plasma under equilibrium conditions, different temperatures for different elements are discussed. These range from approx. 2 million K to 7 million K in a single flare. From flare to flare the variation in temperature for each element is less than the variation between different ion species.

Luhn, A.↗

NASA NTRS1985

Observation of pick-up ions in the solar wind: Evidence for the source of the anomalous cosmic ray component?

Singly ionized energetic helium has been observed in the solar wind by using the time of flight spectrometer SULEICA on the AMPTE/IRM satellite between September and December, 1984. The energy density spectrum shows a sharp cut off which is strongly correlated with the four fold solar wind bulk energy. The absolute flux of the He(+)ions of about 10000 ion/sq cm.s is present independent of the IPL magnetic field orientation. The most likely source is the neutral helium of the interstellar wind which is ionized by solar UV radiation. It is suggested that these particles represent the source of the anomalous cosmic ray component.

Hovestadt, D.↗

NASA NTRS1985

Particles upstream of the pre-dawn bow shock - ISEE-3 observations

The first observations of energetic ions (equal to or greater than 30 keV) in the region upstream of the pre-dawn bow shock (X between 0 and -60 Re inclusively) are presented. The intensity in this region is controlled by the direction of the interplanetary magnetic field (IMF) and is maximized when the IMF is around the spiral direction. The particle distributions are highly anisotropic with the anisotropy directed perpendicular to the magnetic field. In the E x B frame this perpendicular anisotropy is conserved and it is argued that the distribution is pancake-like. This indicates that the energetic particles in the pre-dawn upstream region have their origin in the near-earth upstream region, from where they are convected by the solar wind perpendicular to the magnetic field. It is therefore concluded that acceleration occurs mainly near the nose of the bow shock, and particle acceleration at the distant bow shock is weak.

Terasawa, T.↗

NASA NTRS1985

Correlated observations of substorm effects in the near-earth region and the deep magnetotail

Simultaneous observations of energetic particle measurements from the geosynchronous satellite 1982-019 and magnetic field, electron plasma, and energetic proton and electron measurements obtained with ISEE 3 in the deep tail are presented. The data are supplemented by ground magnetograms. A substorm occurred on March 22, 1983, close to 0300 UT as identified in the ground magnetograms and by a particle injection at geosynchronous orbit. About 10 min later, ISEE 3 observed (at a distance of approximately 130 RE in the deep tail) magnetic field, plasma, and energetic particle signatures consistent with the passage of a plasmoid. After the passage of the plasmoid the satellite enters shortly into a lobelike environment, in which an energetic proton beam is observed. High-resolution magnetic field data are indicative of small-scale structures in the postplasmoid plasma sheet. From the plasma sheet flow speed during the plasmoid's passage it is concluded that the 0300 UT substorm is responsible for its origin. This allows an approximate timing of the plasmoid release at a near-earth neutral line and of the plasma sheet recovery after substorm onset, and it indicates a close relationship between processes in the near-earth plasma sheet and the deep tail during substorms.

Scholer, M.↗

NASA NTRS1985

Energetic particle characteristics of magnetotail flux ropes

During the recent ISEE-3 Geotail Mission three events have been identified from the magnetometer data which are consistent with a spacecraft crossing of a magnetotail flux rope. Energetic electron and proton observations obtained by the Max-Planck-Institut/University of Maryland sensor system during two of the possible flux rope events are presented. During one event remote sensing of the flux rope with energetic protons reveals that the flux rope is crossed by the spacecraft from south to north. This allows determination of the bandedness of the magnetic field twist and of the flux rope velocity relative to the spacecraft. A minimal flux rope radius of 3 earth radii is derived. Energetic proton intensity is highest just inside of the flux rope and decreases towards the core. Energetic electrons are streaming tailward near the outer boundary, indicating openness of the field lines, and are isotropic through the inner part of the flux rope.

Scholer, M.↗

NASA NTRS1985

Suprathermal O(+) and H(+) ion behavior during the March 22, 1979 (CDAW 6), substorms

The present investigation has the objective to report on the behavior of energetic (approximately 130 keV) O(+) ions in the earth's plasma sheet, taking into account observations by the ISEE 1 spacecraft during a magnetically active time interval encompassing two major substorms on March 22, 1979. Attention is also given to suprathermal H(+) and He(++) ions. ISEE 1 plasma sheet observations of the proton and alpha particle phase space densities as a function of energy per charge during the time interval 0933-1000 UT on March 22, 1979 are considered along with the proton phase space density versus energy in the energy interval approximately 10 to 70 keV for the selected time periods 0933-1000 UT (presubstorm) and 1230-1243 UT (recovery phase) during the 1055 substorm on March 22, 1979. A table listing the proton energy density for presubstorm and recovery periods is also provided.

Ipavich, F. M.↗

NASA NTRS1984

Characteristics of suprathermal H(+) and He(++) in plasmoids in the distant magnetotail

Rest frame distribution functions were obtained for suprathermal H(+) and He(2+) ions during 20 particle intensity increases that were observed in the distant magnetotail by ISEE-3. All of these increases were characterized by isotropic, approximately 100-keV electrons, preceded by beaming electrons and velocity-dispersed protons distributions whose signatures are typically associated with plasmoids. In each of the plasmoids, both H(+) and He(2+) are found to be convected tailward, with speeds that range from 200 to 1000 km/sec. The acceleration mechanism is found to depend on particle velocity, and it is established that the solar wind is a dominant plasma source. The plasmoids appear to be expanding at about 100 km/sec during their tailward propagation.

Gloeckler, G.↗

NASA NTRS1984

Simultaneous observation of the plasma sheet in the near earth and distant magnetotail - ISEE-1 and ISEE-3

Particle data have been acquired by the 1981-025 and 1982-019 spacecraft at geosynchronous orbit, as well as ISEE-1 in the near earth geomagnetic tail, and ISEE-3 in the distant geomagnetic tail. These observations are supplemented by ground-based magnetograms from near local midnight stations. Attention is given to a substorm recovery phase, and to observations of ion beams at the plasma sheet boundary in the near earth and distant tail, respectively, which are found to flow in opposite directions.

Scholer, M.↗

NASA NTRS1984

Correlation between proton anisotropy and magnetic field direction in the distant geotail

A statistical analysis has been conducted of the anisotropy of suprathermal protons and the polarity of the magnetic field during April 10-16, 1983. At this time, ISEE-3 was at lunar distances in the geomagnetic tail of the earth, and well within the nominal magnetopause. The first-order anisotropy is presently correlated with the latitude angle and the z-component of the magnetic field. The anisotropy direction's frequency distribution is strongly peaked in the earthward and tailward direction, indicating fast earthward and tailward flows. For large anisotropies, and within 5 earth radii of the nominal neutral sheet position, a strong correlation is found between the earthward-streaming suprathermal protons and the northward polarity of the magnetic field; large tailward anisotropies are generally correlated with southward magnetic field polarity. This correlation is most simply interpreted in terms of a neutral line or reconnection model.

Klecker, B.↗

NASA NTRS1984

Magnetospheric ions and electrons in the distant magnetosheath at about 50 and 180 earth radii - ISEE-3 observations

Energetic particle data were obtained in the dawn magnetosheath at about 50 earth radii (ER), analyzed, and compared with data taken at 180 ER. Both data sets were acquired during the ISEE-3 geotail mission. The results of analyses of the 16 sec time profiles of 32 and 130 keV protons, 75-115 keV electrons, and some of the 30-36 keV proton angular distributions (PAD) are presented. No temporal dispersions were detected in the particle bursts, implying instead a spatial dispersion. The particles filled flux tubes of 6 ER, with the energetic electrons being beamed along magnetic field lines. PADs displayed anisotropy symmetric relative to the magnetic field. The electrons were not detected at 180 ER. The phenomena are modeled as flux tubes connected to the magnetotail magnetic field in the near-earth magnetopause. The particles leak out along connected field lines. Lion roars scatter the electrons, which escape into interplanetary space. Ions, however, may carry their intensity out to 200 ER, a factor which awaits verification by further data.

Scholer, M.↗

NASA NTRS1984

Characteristics of plasmoidlike structures in the distant magnetotail

A statistical analysis is presented of energetic particle burst events in the distant geomagnetic tail which have the particle characteristics of plasmoids as described by Hanes et al. (1984) and Scholer et al. (1984). The average velocities of the plasmoids are more or less evenly distributed between about 300 km/s and about 1000 km/s, with a mean value of about 600 km/s. Most plasmoids have a length between about 50 and 100 earth radii, with a mean value of about 80 earth radii. The proton energy spectra are always steeper than power law. The proton differential intensity at 30 keV varies between 100 and 1000 protons/sq cm/s/sr/keV, with an average value of about 500 protons/sq cm/s/sr/keV. This value is about one order of magnitude smaller than typical values in the near-earth plasma sheet.

Scholer, M.↗

NASA NTRS1984

Fast moving plasma structures in the distant magnetotail

The paper reports for the first time the detailed time behavior of the intensities and the angular distributions of energetic protons and electrons in the distant magnetotail of the earth at 220 earth radii and 110 earth radii. The data have been obtained by the Max-Planck-Institut/University of Maryland sensor system on ISEE 3 during the spacecraft's first deep tail passage. Three energetic particle bursts are studied in detail. It is suggested that the satellite encounters detached plasma structures evidenced by the isotropic electrons. These structures, probably plasmoids, move with high velocities (about 800 km/s) down the tail. The energetic electrons and protons stream ahead of these fast tailward moving plasma structures, which leads to the various time dispersion effects. This allows, in principle, a determination of the source distance from the satellite.

Scholer, M.↗

NASA NTRS1984

Survey of He(+)/He(2+) abundance ratios in energetic particle events

First results of a systematic study of the helium ionic charge distribution in the energy range 0.4-0.62 MeV per nucleon in energetic particle events are reported. Large fluctuations of the He(+)/He(2+) ratios are found, especially at low interplanetary particle fluxes. The ratios exceeded a value of 0.3 for 41 days and a value of 1.0 for 11 days out of the 216 days analyzed. The median of the distribution is He(+)/He(2+) = 0.11. No obvious association with optical flare events could be observed for the events richest in He(+). No significant differences were found between the proton energy spectra and the elemental abundances of helium relative to hydrogen and heavy ions for He(+)-rich events versus events low in He(+). However, it has been found that generally He(+)-rich events are predominantly low in energetic particle intensity.

Hovestadt, D.↗

NASA NTRS1984

Direct determination of the ionic charge distribution of helium and iron in He-3-rich solar energetic particle events

The first direct measurement of the ionic charge distribution of the helium isotopes and of iron in (He-3)-Fe-rich solar energetic particle events is reported. No significant contribution of singly ionized helium to the events is found. The two-sigma upper limits for the He-3(+)/He-3(2+) and He-4(+)/He-4(2+) ratios are 0.02 and 0.03, respectively. The mean charge state of iron found by averaging five (He-3)-Fe-rich solar energetic particle events is 19 + or -2, significantly larger than the iron charge state for energetic solar particles in normal composition events. These results appear to favor the resonant heating model proposed by Fisk (1978). It is concluded that temperatures in the source region exceed 5 million K in the events under study.

Klecker, B.↗

NASA NTRS1984

Ionic charge state measurements during He(+)-rich solar particle events

Ionic charge state measurements of carbon, oxygen, and iron in He(+)-rich energetic particle events are presented. The data have been obtained with the Max-Planck-Institut/University of Maryland sensor system on the ISEE 3 spacecraft. The ionic charge states cannot be explained in terms of a model in which the coronal temperature determines a charge equilibrium which is subsequently frozen-in nor in terms of charge exchange during transition through coronal matter after acceleration. It is concluded that the acceleration and probably also the injection process is biased against particles with high mass-to-charge ratios. The plasma injected into the acceleration process must consist of material of cold (not greater than 8.5 x 10 to the 4th K) as well as hot (2.5 x 10 to the 6th K) origin. The cold material must be more abundant than the hot material.

Hovestadt, D.↗

NASA NTRS1984

Abundances and spectra of superathermal H(+), He(++) and heavy ions in a fast moving plasma structure (plasmoid) in the distant geotail

An ISEE-3 Geotail Mission sensor has furnished data on a 16-min particle intensity increase in the distant magnetotail from which rest frame distribution functions have been deduced for 3-150 keV/amu H(+), He(++), and ions with a charge state greater than 3. The event was characterized by isotropic electron distributions and is identified as a tailward-moving plasmoid. These suprathermal ions are convected nearly tailward at an average speed of 1000 + or - 50 km/sec and have an energy density of 150 eV/cu cm. A crosstail expansion speed of about 80 km/sec is indicated.

Gloeckler, G.↗