Engineering topics

Scholer, M.

Publications and source records attributed to Scholer, M..

At least 19 records

NASA NTRS2000

Solar Cycle Dynamics of Solar, Magnetospheric, and Heliospheric Particles, and Long-Term Atmospheric Coupling: SAMPEX

This final technical report summarizes science analysis activities by the SAMPEX mission science team during the period July 1, 1995 through September 30, 2000. Bibliographic entries for 1995 to date (October 2000) are included. The SAMPEX science team was extremely active, with 72 articles published or submitted to referred journals, 38 papers published in their entirety in Conference Proceedings, and 260 contributed papers, seminars, and miscellaneous presentations. The bibliography at the end of this report constitutes the primary description of the research activity. Science highlights are given under the major activity headings, as well as other activities of the team. One Ph.D. student, Mr. Daniel Williams, completed his thesis at California Institute of Technology based on data from the MAST instrument.

Mason, G. M.↗

NASA NTRS1998

Recent Advances, Open Questions and Future Directions in Solar-Terrestrial Research

Solar-terrestrial research deserves the special attention of the scientific community, both because of the attractive physics underlying the various phenomena associated with them, as well as because of the applied aspect of the sometimes destructive effects of solar-terrestrial coupling on a wide variety of technological systems.

International Symposium on solar-terrestrial coupl↗

NASA NTRS1997

Solar Cycle Dynamics of Solar, Magnetospheric, and Heliospheric Particles, and Long-Term Atmospheric Coupling: SAMPEX

This report summarizes science analysis activities by the SAMPEX mission science team during the period during the period July 1, 1997 through July 1, 1997. Bibliographic entries for 1996 and 1997 to date (July 1997) are included. The SAMPEX science team was extremely active, with 27 articles published or submitted to refereed journals, 17 papers published in their entirety in Conference Proceedings, and 74 contributed papers, seminars, and miscellaneous presentations. The bibliography at the end of this report constitutes the primary description of the research activity. Science highlights are given under the major activity headings, as well as other activities of the team.

Mason, G. M.↗

NASA NTRS1996

Solar cycle dynamics of solar, magnetospheric, and heliospheric particles, and long-term atmospheric coupling: SAMPLEX

This report summarizes science analysis activities by the SAMPEX mission science team during the period during the period July 1, 1995 through July 1, 1996. Bibliographic entries for 1995 and 1996 to date (July 1996) are included. The SAMPEX science team was extremely active, with 20 articles published or submitted to refereed journals, 18 papers published in their entirety in Conference Proceedings, and 53 contributed papers, seminars, and miscellaneous presentations. The bibliography at the end of this report constitutes the primary description of the research activity. Science highlights are given under the major activity headings of anomalous cosmic rays, solar energetic particles, magnetospheric precipitating electrons, trapped H and He isotopes, and data analysis activities.

Mason, G. M.↗

NASA NTRS1995

Charge state of anomalous cosmic-ray nitrogen, oxygen, and neon: SAMPEX observations

We report observations of the ionization state of anomalous cosmic-ray (ACR) nitrogen, oxygen, and neon during the period 1992 October to 1993 May, carried out with instrumentation on the Solar, Anomalous & Magnetospheric Particle Explorer (SAMPEX) spacecraft. The low-altitude (510 x 675 km) and high-inclination (82 deg) orbit enables SAMPEX to sample the interplanetary ACR fluxes on each polar pass and then to observe the cutoff of these fluxes by the geomagnetic field at lower latitudes. The arrival time and direction of each ion is recorded by the instruments, allowing detailed calculations of the particle's trajectory through the Earth's magnetic field and thereby placing upper limits on the ionization state of the particles. We find (a) that ACR nitrogen, oxygen, and neon each contain singly ionized particles and (b) that ACR oxygen is predominantly singly ionized with an upper limit of 10% for higher ionization states. These ionization states confirm theories of ACR origin as neutral interstellar material that is singly ionized near the Sun by UV or charge exchange with the solar wind, and is subsequently accelerated in the outer heliosphere.

Klecker, B.↗

NASA NTRS1994

Statistical analysis of diffuse ion events upstream of the Earth's bow shock

A statistical study of diffuse energetic ion events and their related waves upstream of the Earth's bow shock was performed using data from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) satellite over two 5-month periods in 1984 and 1985. The data set was used to test the assumption in the self-consistent model of the upstream wave and particle populations by Lee (1982) that the particle acceleration through hydromagnetic waves and the wave generation are directly coupled. The comparison between the observed wave power and the wave power predicted on the observed energetic particle energy density and solar wind parameters results in a high correlation coefficient of about 0.89. The intensity of diffuse ions falls off approximately exponentially with the distance upstream from the bow shock parallel to the magnetic field with e-folding distances which vary from approximately 3.3 R(sub E) to approximately 11.7 R(sub E) over the energy range from 10 keV/e to 67.3 keV/e for both protons and alpha particles. After normalizing the upstream particle densities to zero bow shock distance by using these exponential variations, a good correlation (0.7) of the density of the diffuse ions with the solar wind density was found. This supports the suggestion that the solar wind is the source of the diffuse ions. Furthermore, the spectral slope of the diffuse ions correlates well with the solar wind velocity component in the direction of the interplanetary magnetic field (0.68 and 0.66 for protons and alpha particles) which concurs with the notion that the solar wind plays an important role in the acceleration of the upstream particles.

Trattner, K. J.↗

NASA NTRS1993

The return of the anomalous cosmic rays to 1 Au in 1992

New observations of low energy (approximately 1 to 200 MeV/nuc) cosmic rays measured by three newly launched experiments on Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) during 1992 and 1993 show the strong presence of anomalous cosmic ray (ACR) nitrogen and oxygen, well before the approaching solar minimum. When compared with ACR temporal variations over the past two solar cycles we find that the 1992-1993 fluxes are approximately 5 to 10 times their level at corresponding neutron monitor counting rates in 1969-1970 and 1985.

Mewaldt, R. A.↗

NASA NTRS1993

HILT - A heavy ion large area proportional counter telescope for solar and anomalous cosmic rays

The HILT sensor has been designed to measure heavy ion elemental abundances, energy spectra, and direction of incidence in the mass range from He to Fe and in the energy range 4 to 250 MeV/nucleon. With its large geometric factor of 60 sq cm sr the sensor is optimized to provide compositional and spectral measurements for low intensity cosmic rays (i.e. for small solar energetic particle events and for the anomalous component of cosmic rays). The instrument combines a large area ion drift chamber-proportional counter system with two arrays of 16 Li-drift solid state detectors and 16 CsI crystals. The multi dE/dx-E technique provides a low background mass and energy determination. The sensor also measures particle direction. Combining these measurements with the information on the spacecraft position and attitude in the low-altitude polar orbit, it will be possible to infer the ionic charge of the ions from the local cutoff of the Earth's magnetic field. The ionic charge in this energy range is of particular interest because it provides unique clues to the origin of these particles and has not been investigated systematically so far. Together with the other instruments on board SAMPEX (LEICA, MAST, and PET), a comprehensive measurement of the entire solar and anomalous particle population will be achieved.

Klecker, Berndt↗

NASA NTRS1990

SAMPEX mission overview

The Solar, Anomalous, and Magnetospheric Particle Explorer SAMPEX will carry out energetic particle studies of outstanding scientific questions in the fields of space plasma physics, solar physics, magnetospheric and middle atmospheric physics, and cosmic ray physics. SAMPEX will measure the electron and ion composition of energetic particle populations from about 0.4 MeV/nucleon to hundreds of MeV/nucleon from a zenith-pointing small satellite in near-polar orbit. While over the magnetic poles, the instruments will study the composition of anomalous cosmic rays, solar energetic particles, and Galactic cosmic rays. At lower magnetic latitudes, geomagnetic cutoff effects will allow determination of the ionization state of these particles at energies much higher than can be studied from interplanetary spacecraft. At subauroral latitudes, SAMPEX will also observe precipitating relativistic magnetospheric electrons, which undergo important intertactions within the middle atmosphere.

Mason, G. M.↗

NASA NTRS1989

ISEE 3 observations during the CDAW 8 intervals - Case studies of the distant geomagnetic tail covering a wide range of geomagnetic activity

Observations made by the ISEE 3 spacecraft in the distant geomagnetic tail during the eight CDAW 8 intervals are discussed, along with their relation to concurrent geomagnetic activity. This extensive multiinstrument case study of distant tail data covers a wide range of geomagnetic conditions from extended intervals of magnetic quiet with isolated substorms to prolonged periods of intense disturbance. Plasmoids are observed in the distant tail following disturbance enhancements, the time of their appearance being generally consistent with disconnection from the near-earth region at the time of the enhancement. Their structure is entirely consistent with the neutral line model. However, not all enhancements in geomagnetic activity result in the observation of plasmoids. In particular, the CDAW 8 data suggest that, during extended intervals of strong activity, a continuous neutral line may reside in the near-earth tail and some disturbance enhancements may then relate to an increase in the reconnection rate at a preexisting neutral line, rather than to new neutral line and plasmoid formation.

Richardson, I. G.↗

NASA NTRS1989

Multispacecraft observations of energetic ions upstream and downstream of the bow shock

Simultaneous measurements of energetic protons and alpha particles were obtained inside and outside of the magnetopause and upstream and downstream of the bow shock. In the magnetosheath, no gradient or streaming is found in the upstream direction. The present results are consistent with first-order Fermi acceleration at the bow shock and subsequent downstream convection, and exclude the possibility of a magnetospheric source for these particles.

Scholer, M.↗

NASA NTRS1988

Asessment of the boundary layer model of the magnetospheric substorm

Data on energetic protons, thermal electrons, and magnetic field characteristics obtained by the ISEE 3 in the magnetotail at the distance of 80 R(E) from the earth were analyzed. Many features were found that were present in the ISEE 1 and 2 data. In particular, flow directions of the plasma observed at 80 R(E) were found to be quite consistent with the formation of the near-earth neutral line during the expansion phase, giving further support to the near-earth reconnection model of the magnetospheric substorm described by Eastman et al. (1985).

Nishida, A.↗

NASA NTRS1987

Simultaneous observations of the near-earth and distant geomagnetic tail during a substorm by ISEE-1, ISEE-3 and geostationary spacecraft

The structure of the geomagnetic tail during a substorm is investigated by combining plasma, magnetic field, and energetic particle data from the ISEE-3 spacecraft in the deep tail with similar near-earth observations from ISEE-1 and geostationary spacecraft. The observations can be interpreted in terms of the neutral-line model of substorms and indicate the formation of a closed-loop field region (plasmoid) following substorm onset, which is ejected down the tail. The plasmoid is observed to have a double-loop field strucure. This may be the result of a second substorm onset occurring about 25 min after the first, producing a further near-earth neutral line and closed field loop. During the substorm recovery phase, the substorm neutral line moves tailward to beyond 130 earth radii from earth by some 3 h after substorm onset.

Richardson, I. G.↗

NASA NTRS1987

Energetic ion and electron beams at the plasma-sheet boundary in the distant tail

Several energetic particle bursts observed by ISEE 3 in the distant tail are analyzed. The energetic particle data are supplemented by the electron plasma and magnetic field measurements. These bursts are characterized by large velocity-dispersion effects, with energetic electrons observed first, followed by ions with continuously lower velocities. Both ions and electrons stream in the tailward direction. Protons and alpha particles of the same energy per nucleon are observed at the same time. The dispersion effects are observed in reverse order when the spacecraft leaves from the boundary layer into the lobe. No obvious signature indicating the passage of a plasmoid has been observed in the particle or magnetic field data during or immediately following these bursts. It is concluded that these beams at the plasma-sheet boundary originate at a steady source, presumably close to a neutral line, and not at a time varying source. The velocity filter effect in a dawn-dusk electric field arranges particles with progressively lower velocity further inside the wedge-shaped region of reconnected field lines. The plasma electron distribution exhibits a tailward directed heat flux within this layer.

Scholer, M.↗

NASA NTRS1986

Quasi-stagnant plasmoid in the middle tail - A new preexpansion phase phenomenon

From the analysis of ISEE 3 data it is found that a plasmoid is sometimes formed in the middle tail outside the intervals of the substorm expansion phase. This plasmoid is produced by reconnection at the X-type neutral line, which is located earthward of the distant neutral line but beyond the substorm-associated near-tail neutral line, and it is almost stagnant in that the associated flow speed is less than 300 km/s. The blocking effect of the distant neutral line is the most probable reason for the slow movement. The quasi-stagnant plasmoid is observed at x = -60 to - 100 earth radii for a duration of a few tens of minutes, and in about one half of the cases it is followed by the fast tailward streaming. The onset of this streaming tends to coincide with the onset of the substorm expansion phase, and this probably occurs when the reconnection at the middle-tail neutral line comes close to processing the last closed field line. Intensification of the dawn-to-dusk electric field that causes the mantle plasma to reach the plasma sheet boundary closer to the earth is suggested as the reason for the formation of the middle-tail neutral line earthward of the distant neutral line. The effects on the energetic particle flux and relation to the near-tail reconnection are also discussed.

Nishida, A.↗

NASA NTRS1986

Energetic particle beams in the plasma sheet boundary layer following substorm expansion - Simultaneous near-earth and distant tail observations

Simultaneous observations of ions and electron beams in the near-earth and deep magnetotail following the onset of substorm are analyzed in terms of the substorm neutral line model. The observations were collected on March 20, 1983 with ISSE 1 and 3. Energy fluxes and intensity-time profiles of protons and electrons are studied. The data reveal that the reconnection at the near-earth neutral line produces ions and electrons for the plasma sheet boundary layer. The maximum electric potential along the neutral line is evaluated.

Scholer, M.↗

NASA NTRS1986

Cometary pick-up ions observed near Giacobini-Zinner

The number and energy density of cometary water-group ions observed near Comet Giacobini-Zinner are derived using the rest-frame distribution functions. The data reveal that density profiles of inbound and outbound passes and their shape correlate with pick-up ion production model predictions. The lose rate and production rate of water-group cometary molecules calculated from predicted and measured density profiles are 2 x 10 to the -6th/sec and 2.6 x 10 to the 28th/sec respectively. The shapes of the distribution functions are examined to study the solar wind/cometary ions interaction process.

Gloeckler, G.↗

NASA NTRS1986

Observations of shock acceleration processes in the solar wind

Substantial evidence was accumulated over more than two decades that ion acceleration occurs at all collisionless shocks sampled directly in the solar system. The various shock waves in the heliosphere and the associated energetic particle phenomena are shown schematically. Three shocks have attracted considerable attention in recent years: corotating shocks due to the interaction of fast and slow solar wind streams during solar minimum, travelling interplanetary shocks due to coronal mass ejections, and planetary bow shocks. The signatures of these shocks and of their energetic particles are briefly reviewed. The most prominent theoretical models for shock acceleration are also reviewed. Recent observations at the earth's bow shock and at quasi-parallel interplanetary shocks are discussed in detail.

Scholer, M.↗