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Winningham, J. D.

Publications and source records attributed to Winningham, J. D..

At least 91 records · Page 5
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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.↗
NASA NTRS1982

Observation of a heated electron population associated with the 6300 A SAR arc emission

Conjunctive observations of the Dynamics Explorer satellite pair and the Pacific Northwest Laboratory scanning photometer unit at Richland, WA have allowed identification of the low energy, heated, electron population associated with the 6300 A Stable Auroral Red (SAR) arc emission. Measurements over the SAR arc on day 296 of 1981 show an enhanced flux in the low altitude 5-12 eV electrons. Analysis of this electron population shows them to be fairly Maxwellian, with temperatures on the order of 9900 + or - 1100 K and an earthward field aligned velocity of approximately 275 + or - 60 km/sec. The electrons are not accompanied by ion precipitation. The ion loss cone is empty at least as high as 6000 km. This fact may cast some doubt as to the role of the ring current ions in the SAR arc production.

Gurgiolo, C.↗
NASA NTRS1982

DE-2 photoelectron measurements consistent with a large scale parallel electric field over the polar cap

Winningham and Heikkila (1974) presented observations of various polar cap particle morphologies. They interpreted observations of 'anomalous' photoelectron angular distribution over the polar caps to be indicative of a large scale, outwardly directed, parallel electric field over the polar cap. The parallel field was observed to be spatially and/or temporarily variable. However, results obtained by Winningham and Heikkila have one weakness, which is related to the lack of simultaneous observations at many pitch angles. The present investigation is, therefore, concerned with the presentation of results from Dynamics Explorer 2 (DE-2) which confirm the experimental results of Winningham and Heikkila. It is concluded that the earth's polar caps act much like any conductor immersed in a plasma and illuminated by sunlight. DE-1 and DE-2 would then represent tiny point probes examining the internal details in the sheath region of the polar cap.

Winningham, J. D.↗
NASA NTRS1982

DE-2 cusp observations - Role of plasma instabilities in topside ionospheric heating and density fluctuations

Observations by the low altitude Dynamics Explorer satellite (DE-2) in the polar cusp show the ionospheric plasma electron temperature and the ratio of electron to ion temperature to be increased, and the electron density fluctuations to be enhanced. Also, downward fluxes of energetic eletrons and ions increase in the cusp, and the magnetic field structure are consistent with the existence of a field-aligned current. Simultaneously, there is characteristic broadband electrostatic noise (BEN) with amplitudes of 1-10 mV/m, peaking in the cusp but extending into the polar cap. These emissions range from far below the local 0(+) gyrofrequency F sub O(+) to the vicinity of the proton gyrofrequency, but below the oxygen lower hybrid frequency. The BEN observations are compared to the predictions of several theories. The amplitude of these waves is shown to be far too small to contribute significantly to the observed ionospheric heating or density fluctuations by local wave-particle interactions. Rather, the observed spatial variations are attributed to nonlocal field aligned heating processes and reflect the nonuniformity of the magnetosheath plasma's penetration into the ionosphere.

Curtis, S. A.↗
NASA NTRS1982

Polar views of the earth's aurora with Dynamics Explorer

Preliminary examination of the first global auroral images gained with the vacuum-ultraviolet imaging photometer on board DE 1 reveals a remarkable spatial configuration of auroral luminosities. Frequently the northern auroral oval is bifurcated by a sun-aligned arc extending from the midday auroral zone to the nighttime sector of the oval. Simultaneous plasma measurements with the low-altitude DE-2 spacecraft are used to show that the character of plasmas above the polar arc is similar to those found over the poleward zones of the auroral oval. The spatial distribution of auroral luminosities is suggestive of a two-cell structure of current systems and convection electric fields over the earth's polar cap and a similar division of the corresponding lobe in the magnetotail.

Frank, L. A.↗
NASA NTRS1982

Satellite observations of suprathermal electron bursts

Data from the ISIS 2 satellite are used to study the spatial distribution of the suprathermal electron bursts discovered by high-altitude sounding rockets. It is found that the bursts form an integral part of the boundary plasma sheet and are linked with the formation of discrete auroral arcs. The maximum energy of the bursts is always below the peak energy in neighboring discrete forms, and it appears that if the bursts fail to reach the minimum energy found to be necessary to sustain a discrete arc they collapse within a few seconds. It is suggested that in a pass across the auroral oval the overall envelope of the maximum energy in bursts and the peak energy in discrete auroral forms reflect the variation of the available acceleration (perhaps a parallel electric potential) across the auroral oval while the energy structure in individual forms is a function of the nonlinear processes which sustain them. This explanation appears to resolve the apparent discrepancy in scale thickness between rocket and satellite inverted V's.

Johnstone, A. D.↗
NASA NTRS1981

High-Altitude Plasma Instrument for Dynamics Explorer-A

The Dynamics Explorer A High-Altitude Plasma Instrument (HAPI) will make differential measurements of the velocity-space distributions of electrons and positive ions over the energy/charge range of 5 eV to 32 keV. Five identical analyzers, each making simultaneous measurements of electrons and positive ions at 64 possible energy levels, will have viewing angles of 45, 78, 90, 102, and 135 deg relative to the spacecraft spin axis. The HAPI data will contribute to the overall Dynamics Explorer science objectives, particularly by providing information on the hot-plasma effects of the coupling of energy, mass, and momentum within the earth's atmosphere, ionosphere, and magnetosphere.

Burch, J. L.↗
NASA NTRS1981

The Low Altitude Plasma Instrument /LAPI/

The Low Altitude Plasma Instrument on the Dynamics Explorer-B spacecraft provides high resolution velocity space measurements of positive ions and electrons from 5 eV to 32 keV and a monitor of electrons with energies above 35 keV. It consists of an array of 15 parabolic electrostatic analyzers spanning 180 deg in angle and two Geiger-Mueller counters mounted on a one-degree of freedom scan platform. The platform is controlled by a magnetometer that allows placement of the array to selected angles with respect to the magnetic field. Each parabolic analyzer simultaneously measures electrons and positive ions. The temporal resolution and energy range of the measurements and the detector complement to be sampled are programmable by ground command

Winningham, J. D.↗
NASA NTRS1980

Magnetospheric multiprobes: Investigations and instrumentation

The multiprobe scientific objectives are to: (1) determine the spatial structure of plasma phenomena such as the aurora, convection reversals, and ion troughs; (2) separate spatial and temporal variations in these phenomena; (3) determine field aligned current densities; (4) perform multiple point analysis of particle beams, wave fields, and plasma clouds that are injected into the ionosphere and magnetosphere by Spacelab active experiment facilities. Trade studies described include: instrument accommodations, power, attitude determination, electric field antennas, storage and ejection, thermal control, tracking communications, command and data management, payload and mission specialist support, functional objectives, and orbital analysis.

Burch, J. L.↗
NASA NTRS1980

The relationships between high-latitude convection reversals and the energetic particle morphology observed by Atmosphere Explorer

A statistical investigation and a case study of simultaneous particle and ion convection velocity measurements from Atmosphere Explorer are presented. They show that at all local times between 1800 and 0600 hours the gross convection reversal boundary lies equatorward of the boundary between the discrete, highly structured boundary plasma sheet precipitation and the polar rain. This study indicates the existence of shear and rotational convection reversals on closed field lines; the observed morphology is consistent with a partially closed magnetosphere in which some portion of convection electric field is generated in the low-latitude boundary layer.

Heelis, R. A.↗
NASA NTRS1980

An empirical determination of the production efficiency for auroral 6300-A emission by energetic electrons

Auroral data from the soft particle spectrometer and the red line photometer on board the Isis satellite are presented as a data base for electron energy flux and optical auroral emission and are used to derive production efficiencies for 6300 A emission. Data obtained during a single orbit in which an aurora was observed is corrected by integrating the precipitating flux observed in four energy bands over the loss cone and eliminating the effects of airglow and albedo in the optical emission measurements. A regression analysis of the corrected data from 12 orbits is used to determine 6300 A production coefficients for the 5-60 eV, 60-300 eV, 0.3-1 keV and 1-15 keV electron energy bands. Production coefficients are shown to be in good agreement with theoretical calculations and rocket measurements in conjugate photoelectrons, and applications of the method to other data sets are discussed.

Shepherd, G. G.↗
NASA NTRS1980

The relationships between high latitude convection reversals and the energetic particle morphology observed by the Atmosphere Explorer

Simultaneous measurements of the auroral zone particle precipitation and the ion convection velocity by Atmosphere Explorer show a consistent difference between the location of the poleward boundary of the auroral particle precipitation and the ion convection reversal. The difference of about 1.5 degrees of invariant latitude is such that some part of the antisunward convection lies wholly within the auroral particle precipitation region. The nature of the convection reversals within the precipitation region suggests that in this region the convection electric field is generated on closed field lines that connect in the magnetosphere to the low latitude boundary layer.

Heelis, R. A.↗
NASA NTRS1979

Energetic particle precipitation into the high-latitude ionosphere and the auroral electrojets. I - Definition of electrojet boundaries using energetic electron spectra and ground-based magnetometer data

Magnetometric data are used to define the poleward and equatorward borders of the eastward electrojet in the evening sector. The relationship between central plasma sheet (cps) and boundary plasma sheet (bps) and the auroral electrojet region is explored. This relationship is used to infer the electric field configuration in the cps and bps regions. It is shown that in the evening sector the cps is threaded by field lines carrying current flowing into the ionosphere, while the bps is threaded by field lines carrying current flowing out of the ionosphere.

Winningham, J. D.↗
NASA NTRS1978

A case study of the aurora, high-latitude ionosphere, and particle precipitation during near-steady state conditions

An Isis 2 pass studied in related experiments was singled out for a detailed examination of the particle fluxes, optical emissions, and ionospheric parameters observed during a quiescent period (late recovery) between two substorms. Since both long-duration measurements (aircraft) and transient snapshot (spacecraft) data are available, space and time effects can, on a macroscopic level, be separated. The latitudinal morphology observed by the satellite is found to be basically spatial in nature. It is suggested that the observed particle fluxes can be explained in terms of precipitation from the quiet time plasma sheet without intervening acceleration. The agreement of the observed optical emissions and ionospheric parameters with the electron fluxes is discussed.

Winningham, J. D.↗
NASA NTRS1978

Relationships between particle precipitation and auroral forms

The paper discusses recent measurements pertaining to the relationship between high-latitude particle (electron) precipitation and auroras. The discussion covers three topics: the large-scale relationships between auroral forms and the particle populations of the magnetosphere as determined from satellite measurements; (2) the relationship between satellite and sounding-rocket observations, particularly field-aligned pitch-angle distributions and upward field-aligned currents measured in the vicinity of auroral forms; and (3) recent results on the interaction of auroral electrons with the atmosphere.

Burch, J. L.↗