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Burch, J. L.

Publications and source records attributed to Burch, J. L..

At least 127 records · Page 7
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NASA NTRS1985

Near-conjugate observations of inverted-V electron precipitation using DE 1 and DE 2

A major focus of auroral research has been related to the inverted-V electron precipitation event, distinguished by the 'inverted-V' variation of peak energy flux in an energy-time spectrogram. Thieman and Hoffman (1984), in an examination of plasma data from near-conjugate DE 1/2 passes in the southern hemisphere, have found that some inverted-V events remain reasonably stable over a time span of up to 18 min, while other events change over shorter time periods. The present investigation has the objective to study quantitatively the energization of inverted-V electron fluxes and to compare the results with predictions from adiabatic acceleration by an electrostatic field. The obtained results suggest that the turbulent processes might contirbute minimally to the energy flux of secondary electrons for some events, but significantly for others.

Lin, C. S.↗
NASA NTRS1985

Remote sensing of plasma injection and acceleration phenomena

Dynamics Explorer-1 High Altitude Plasma Instrument data have been used to investigate the injection of magnetosheath plasma into the polar cusp, the injection of auroral ion beams into the magnetosphere, and the acceleration of electrons transverse to the magnetic field direction, and the results are discussed. In the case of polar cusp plasmas, it is found that injection occurs at the high-latitude magnetopause, at geocentric distances near eight earth radii. In the case of auroral ion beams it is determined that ion bands are not produced by equatorial injection from the plasma sheet, but by the upward acceleration of ions from auroral acceleration regions. Finally, conical electron distributions are found to be consistent with transverse acceleration at altitudes of a thousand or more km, within or below the magnetic-field-aligned potential drops of the auroral acceleration regions.

Burch, J. L.↗
NASA NTRS1985

Composition of the polar wind - Not just H(+) and He(+)

In their paper 'First measurements of the supersonic polar wind', Nagai et al. (1984) make the point that, because the ion measurements presented in the earlier publication on the polar wind (Gurgiolo and Burch, 1982) were probably of oxygen, the observations were not of the polar wind but of an unspecified alternate ion upflow. The impression is given that oxygen is not considered a polar wind constituent. Allusions are also made to the energy range of the measurements indicating that it is too high to measure the polar wind. Such arguments are not consistent with the current work being done on the supersonic polar wind.

Gurgiolo, C.↗
NASA NTRS1985

Field-aligned currents and ion convection at high altitudes

Hot plasma observations from Dynamics Explorer 1 have been used to investigate solar-wind ion injection, Birkeland currents, and plasma convection at altitudes above 2 earth-radii in the morning sector. The results of the study, along with the antiparallel merging hypothesis, have been used to construct a By-dependent global convection model. A significant element of the model is the coexistence of three types of convection cells (merging cells, viscous cells, and lobe cells). As the IMF direction varies, the model accounts for the changing roles of viscous and merging processes and makes testable predictions about several magnetospheric phenomena, including the newly-observed theta aurora in the polar cap.

Burch, J. L.↗
NASA NTRS1985

Introduction to the Dynamics Explorer mission

The NASA Dynamics Explorer (DE) mission has the objective to investigate the physical processes which control interactions among the earth's upper atmosphere, ionosphere, and magnetosphere. The DE 1 and the DE 2 spacecraft were launched together on a Delta 3913 launch vehicle from the Western Test Range on Aug. 3, 1981. It is pointed out that the science objectives of the Dynamics Explorer mission required a comprehensive set of measurements of plasma and electric and magnetic fields simultaneously at high and low altitudes along with neutral-gas measurements in the thermosphere. Attention is given to the various instruments employed on the spacecraft, the primary measurement objectives, and a summary of science results.

Burch, J. L.↗
NASA NTRS1985

Space plasma physics results from Spacelab 1

The Spacelab 1 payload carried several instrument systems which together investigated a number of space plasma phenomena. These experiments used the Space Shuttle Orbiter as a platform for making controlled particle-beam, plasma and neutral gas inputs to the ionosphere and magnetosphere and for observing the outputs produced. Spacelab 1 space-plasma investigations included the Space Experiments with Particle Accelerators (SEPAC), Phenomena Induced by Charged Particle Beams (PICPAB), Atmospheric Emissions Photometric Imaging (AEPI) and the Low Energy Electron Spectrometer and Magnetometer. Among the major phenomena investigated both singly and jointly by these experiments are vehicle charging and neutralization, beam-plasma and wave-particle interactions, anomalous ionization phenomena produced by neutral-gas and plasma injections and several phenomena induced by modulated particle beam injections.

Burch, J. L.↗
NASA NTRS1984

DE 1 observations of type 1 counterstreaming electrons and field-aligned currents

Dynamics Explorer 1 satellite observations of plasma and magnetic fields during type one counterstreaming electron events are presented. Counterstreaming electrons are observed at high altitudes in the region of field-aligned current. The total current density computed from the plasma data in the 18-10,000 eV energy range is generally about 1-2 micro-A/sq m. For the downward current, low-energy electrons contribute more than 40 percent of the total plasma current density integrated above 18 eV. For the upward current, such electrons contribute less than 50 percent of that current density. Electron beams in the field-aligned direction are occasionally detected. The pitch angle distributions of counterstreaming electrons are generally enhanced at both small and large pitch angles. STARE simultaneous observations for one DE 1 pass indicated that the field-aligned current was closed through Pedersen currents in the ionosphere. The directions of the ionospheric current systems are consistent with the DE 1 observations at high altitudes.

Lin, C. S.↗
NASA NTRS1984

Correlated low-frequency electric and magnetic noise along the auroral field lines

Dynamics Explorer 1 measurements of intense low-frequency electric and magnetic noise observed at low altitudes over the auroral zone are described. The intensity of both the electric and magnetic fields decreases rapidly with increasing frequency. Most of the energy is at frequencies below the O(+) cyclotron frequency, and some evidence is found for a cutoff or change in spectral slope near that frequency. The magnetic to electric field ratio decreases rapidly with increasing radial distance and also decreases with increasing frequency. The polarization of the electric field in a plane perpendicular to the earth's magnetic field is essentially random. The transverse electric and magnetic fields are closely correlated, with the average Poynting flux directed toward the earth. The total electromagnetic power flow associated with the noise is substantial. Two general models are discussed to interpret these observations, one based on static electric and magnetic fields imbedded in the ionosphere and the other based on Alfven waves propagating along the auroral field lines.

Gurnett, D. A.↗
NASA NTRS1984

Bands of ions and angular V's - A conjugate manifestation of ionospheric ion acceleration

Data from the hot plasma instruments on Dynamics Explorer 1 and 2 spacecraft have been used to study the injection, drift, and subsequent precipitation of suprathermal positive ions in the auroral zone. The observation at both high and low altitudes of electron inverted 'V' events in the boundary plasma sheet (BPS) and of ion 'bands' (energy decreasing with decreasing latitude) in the adjacent central plasma sheet (CPS) leads to the following ion injection model: upward-moving energetic ion beams are injected onto BPS magnetic field lines by the electrostatic potential drops associated with electron inverted V's. As the ion beams move toward the equator and into the conjugate hemisphere they are convected to lower latitudes and into the CPS. The energy-latitude dependence of the ion bands, coupled with concurrent ion convection measurements, indicate that the ion distributions are primarily O(+), in agreement with their postulated ionospheric source.

Winningham, J. D.↗
NASA NTRS1984

Correlation of auroral hiss and upward electron beams near the polar cusp

Data were obtained from the DE-1 high-altitude plasma instrument (HAPI) and plasma wave instrument (PWI) during outbound passes through the polar cusp near local noon. The observed distribution functions of electron beams are fitted by drifting Maxwellian functions and the observed distribution functions of hot background electrons by isotropic Maxwellian functions. In addition, the cold plasma density is inferred from knowledge of the electron plasma frequency and the measured density of the warm plasma, including the electron beam distribution. The empirically fitted plasma parameters, including density, temperature and drifting energy, are used to solve the linear dispersion equation for the resulting whistler mode emissions. Because the whistler mode becomes quasi-electrostatic for wave-normal angles near the resonance cone, the electrostatic approximation is used for the whistler mode dispersion relation. The results of wave instability analyses are then compared with the wave observations. A ray tracing of cusp hiss emission is conducted to locate the wave source region (at about one earth-radius).

Lin, C. S.↗
NASA NTRS1984

Relationships between field-aligned currents, electric fields, and particle precipitation as observed by Dynamics Explorer-2

The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

Sugiura, M.↗
NASA NTRS1983

Upward electron beams measured by DE-1 - A primary source of dayside region-1 Birkeland currents

Measurements made by the High Altitude Plasma Instrument on DE-1 have shown that intense upward electron beams with energies from about 20 eV to about 200 eV are a common feature of the region just equatorward of the morning-side polar cusp. Computations of the currents carried by these beams and by the precipitating cusp electrons show excellent agreement with the simultaneous DE-1 magnetometer measurements for both upward and downward Birkeland currents. The data indicate that cold ionospheric electrons, which carry the downward region-1 Birkeland currents on the morning side, are accelerated upward by potential drops of a few tens of eV at altitudes of several thousand kilometers. This acceleration process allows spacecraft above those altitudes to measure routinely the charge carriers of both downward and upward current systems.

Burch, J. L.↗
NASA NTRS1983

Relationships between field-aligned currents, electric fields and particle precipitation as observed by dynamics Explorer-2

The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

Sugiura, M.↗
NASA NTRS1983

Energy transfer in the quiet and disturbed magnetosphere

Progress on magnetospheric energy transfer reported during the 1979-1982 quadrennium is reviewed. A discussion of the macroscopic control of magnetospheric phenomena by solar-wind electric and magnetic fields and kinetic pressure is followed by sections on energy transfer processes at the dayside magnetopause, in the magnetotail, near geosynchronous orbit, and at altitudes of about 1 earth radius above the auroral oval. Rapid progress in these areas has been stimulated primarily by ISEE and S3-3 observations and by the development of techniques for the large-scale computer simulation of plasma phenomena.

Burch, J. L.↗
NASA NTRS1983

Design and development of a fast ion mass spectrometer

Two Fast Ion Mass Spectrometers (FIMS A and FIMS B) were developed. The design, development, construction, calibration, integration, and flight of these instruments, along with early results from the data analysis efforts are summarized. A medium energy ion mass spectrometer that covers mass velocity space with significantly higher time resolution, improved mass resolution, (particularly for heavier ions), and wider energy range than existing instruments had achieved was completed. The initial design consisted of a dual channel cylindrical electrostatic analyzer followed by a dual channel cylindrical velocity filter. The gain versus count rate characteristics of the high current channel electron multipliers (CEM's), which were chosen for ion detection, revealed a systematic behavior that can be used as a criterion for selection of CEM's for long counting lifetimes.

Burch, J. L.↗
NASA NTRS1982

Plasma injection and transport in the mid-altitude polar cusp

DE-1 hot plasma observations in the mid-altitude polar cusp have shown evidence of a significant velocity filtering phenomenon which is consistent with a latitudinally narrow region of plasma injection located at a geocentric distance of about eight earth radii (in a dipole approximation). Plasma convection from the injection region into the polar cap results in a V-shaped log E vs. observed pitch angle relation at geocentric distances near 4 earth radii. This velocity filtering effect allows the measurement of much smaller flow velocities (about 10 km/sec) than have heretofore been possible with hot plasma measurements. The flows thus determined are consistent with ionospheric flows measured nearly simultaneously by the DE-2 spacecraft, although the magnitudes of the higher altitude flows are higher by a factor of 2 or more than an approximately r to the 3/2 power dipole-field mapping would predict.

Burch, J. L.↗
NASA NTRS1982

DE-1 observations of counterstreaming electrons at high altitudes

Observations of plasma at altitudes of 2-3 earth radii with the High Altitude Plasma Instrument (HAPI) on DE-1 indicate two distinct types of counterstreaming electron events. The type 1 event is characterized by two Maxwellian distribution functions, an isotropic high-temperature component and a field-aligned low temperature component. The type 2 event is distinguished by beams parallel and antiparallel to the magnetic field direction. The observations suggest two distinct mechanisms for accelerating counterstreaming electrons. Type 1 events appear to involve wave-particle interactions while type 2 events imply direct acceleration by oppositely-directed electric fields pointing toward the satellite along magnetic field lines.

Lin, C. S.↗