Engineering topics

Williams, D. J.

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

At least 73 records · Page 4

NASA NTRS1980

Variability of plasma sheet dynamics

IMP 7 observations of plasma sheet structure and dynamics made during a 24-h period in which the satellite traversed the tail plasma sheet at a radial distance of 35 earth radii and remained within 2 earth radii of the expected position at the neutral sheet and in which at least five substorms occured on the ground are presented. High-time-resolution measurements of the magnetic field, plasma flow and greater than 50-keV protons obtained by the satellite and ground-based magnetic measurements are discussed for a 4-hr interval in which two small substorms occurred, a 6-hr geomagnetically quiet interval in which moderate variable plasma flows were observed, a very rapid, smooth neutral sheet crossing and earthward plasma flow during the expansion phase of a small substorm, a moderate-size substorm in which a prolonged interval of field-aligned tailward flow commenced at onset, a strong tailward and dawnward flow burst in an interval between substorms and a large substorm in which strong tailward flow was observed. Observations indicate the significant distortion of the tail field, possibly by plasma flow stresses, a neutral sheet structure occasionally resembling the hydromagnetic rotational discontinuity and a high level of magnetic turbulence during an earthward plasma flow which may contribute towards plasma sheet dissipation.

Coroniti, F. V.↗

NASA NTRS1980

ISEE 1 charged particle observations indicative of open magnetospheric field lines near the subsolar region

On November 20, 1977, at 0230-0300 UT, ISEE 1 encountered unusual charged particle distributions within the magnetosphere. The three-dimensional distribution observations for energetic (greater than 24 keV) ions and plasma show the development of field-aligned asymmetries in the energetic ion distributions simultaneously with a marked change in plasma flow. It is concluded that the most likely explanation for these observations is that ISEE 1 encountered open magnetospheric field lines at its position within the magnetosphere (1030 LT and 1200 plus or minus 300 km from the magnetopause). Field lines were open near the geomagnetic equator, and the geometry was spatially or temporally variable. Other features of the field line topology are presented.

Williams, D. J.↗

NASA NTRS1980

A source for the geomagnetic storm main phase ring current

The paper considers a proposed source for the geomagnetic storm main phase ring current. It is shown that the flux increases of trapped ions and electrons observed by Explorer 45 at L below 4 during two large geomagnetic storms can be explained by inward radial displacement of the preexisting trapped particle distribution. The proposed source requires only the acceleration of the previously entrapped particle population by inward displacement under conservation of the first two adiabatic invariants. It is suggested that a significant difference between large geomagnetic storms and typical substorm activity may be the inward convection occurring over a large longitude range during storms, but only over a small longitude range during typical substorms.

Lyons, L. R.↗

NASA NTRS1979

Short term magnetospheric particle variations (1 minute T 1 day), appendix 1

A schematic representation of the generation and propagation processes for energetic particles of concern in solar terrestrial predictions is given. Particle precipitation at low, mid, and high altitudes is discussed with emphasis on prediction techniques. Methods given for testing of such techniques include traditional collaborations, enhanced collaborations, simulated prediction schemes, and field tests.

Higbie, P. R.↗

NASA NTRS1979

An energetic particle perspective of the magnetopause

The present analysis deals with energetic (above 24 keV) particle data from the Isee satellites during a series of magnetopause crossings. The primary energetic particle data employed in the analysis are the three-dimensional distributions from the Isee A satellite. Correlative magnetic field measurements are used to relate the particle behavior to magnetic field characteristics at and earthward of the magnetopause. It is shown that, to first order, the magnetopause may be regarded as a perfectly absorbing boundary for the trapped energetic particles, that it is nearly always in motion, and that boundary waves are often present. The observed dayside magnetopause motion is consistent with a large-scale radial motion having an approximately 10-min period plus superimposed boundary waves with a 90- to 150-sec period.

Williams, D. J.↗

NASA NTRS1979

Time structure of postmidnight energetic electron precipitation and the limit of stable trapping

The paper examines the detailed time structure of high-energy (over 30 keV) electron precipitation along the morningside and dayside of the auroral zone. To this end, available high time resolution data from the Ogo 6 energetic electron experiment are analyzed. The relationship between trapped flux levels and degree of precipitation observed is studied from an observational standpoint and compared with the critical flux levels estimated by Kennel and Petschek (1966). A possible explanation within the general framework of the Kennel-Petschek theory of the observed burstlike precipitation episodes is presented, and the implications of these features for the average lifetime of electrons in drifting clouds are discussed.

Trefall, H.↗

NASA NTRS1979

Observations of significant magnetosheath antisolar energy flow

Results from the Imp 7 satellite reveal antisolar magnetosheath ion flows of 10 to the 18th to 10 to the 20th ergs/sec when they are integrated over the observed flow cross-sectional area. These results extend, in energy and spatial regions sampled, the earlier work of West and Buck (1976). The results show the existence of energized protons in the downstream magnetosheath which at energies above 50 keV carry an energy flow of the same magnitude as the extrapolated (above 1 keV) results of Baker and Stone (1977). Possible sources of the energy flow include dissipation processes due to a magnetopause electric field, leakage of magnetospheric particles through the magnetopause into the magnetosheath, bow shock acceleration, and magnetosheath acceleration.

Williams, D. J.↗

NASA NTRS1979

Magnetopause characteristics inferred from three-dimensional energetic particle distributions

Three-dimensional distributions for 24- to 44.5 KeV protons (ions) are presented from the ISEE 1 medium-energy particles instrument during a magnetopause traversal at about 0145:00 hours UT on November 20, 1977. The use of these data and simple particle orbit geometry makes it possible to infer magnetopause boundary location, orientation, and velocity. The results are consistent with both overall boundary motions toward and away from the earth at velocities of 10-20 km/s and the presence of a surface wave on the boundary. For the case analyzed, the boundary appears stable and well defined, being capable of supporting trapped type distributions (conservation of the first and second adiabatic invariants) within a fraction of a gyroradius from the magnetosheath field where no trapping is observed.

Williams, D. J.↗

NASA NTRS1978

Observations of counterstreaming between plasma and energetic particles in the magnetotail

The paper presents fast time resolution (10-20 sec) angular distribution and energy spectrum measurements of energetic particles (protons and electrons) during a period of three magnetospheric bursts in the distant (32 earth radii) magnetotail on October 16, 1973. Attention is given to particle measurements in the plasma sheet during the onset of a magnetospheric substorm where the plasma is flowing earthward, and the energetic protons (Ep no less than 290 keV) and the electrons (Ee no less than 220 keV) are streaming tailward. Particle observations in the distant magnetotail during a magnetospheric substorm reveal the presence of two distinct particle populations: an earthward-flowing hot plasma, and tailward streaming energetic particles in the energy range 50 keV to 1 MeV. Separation of the ambient thermal and nonthermal particle populations in the magnetotail is emphasized.

Sarris, E. T.↗

NASA NTRS1978

The ISEE 1 and 2 Medium Energy Particles Experiment

The Medium Energy Particles Experiment (MEPE) on board ISEE 1 and 2 consists of the WIM instrument on ISEE 1 and the KED instrument on ISEE 2. Both instruments employ solid-state detectors and magnetic analysis to measure the angular, energy, and intensity distributions of protons (ions) above 24 keV and electrons above 20 keV. The WIM instrument also includes a composition measurement employing Delta E-by-E and time-of-flight techniques. Three-parameter analysis is performed above 250 keV/nucleon, and single parameter analysis is performed above 125 keV/nucleon for helium through oxygen. Three-dimensional angular distributions are obtained through the use of a scan platform in the WIM instrument and multiple detector heads in the KED instrument. A variety of operational modes are used to optimize data collection from both instruments. Resolutions up to 128 channels in energy, 192 samples over the unit sphere in angle, and 0.095 sec in time are available.

Williams, D. J.↗

NASA NTRS1977

Simultaneous observations of substorm electrons - Explorer 45 and ATS 5

Simultaneous observations of substorm-associated electron flux variations made on the satellites Explorer 45 and ATS 5 are used to infer the value of the dawn-dusk electric field present during a substorm. The observations were made during a substorm which occurred on December 17, 1971, while the two satellites were in the evening local time sector, within the plasma sheet. It is found that a dawn-dusk electric field of about 11 kV/R-E (about 2 mV/m) was present during the substorm. It is shown that the observations made at the two satellites are compatible with the model of a uniform enhanced dawn-dusk electric field acting upon a particle source which is spatially uniform in the region from which particles are convected to synchronous orbit.

Barfield, J. N.↗

NASA NTRS1976

Magnetometer networks during the International Magnetosphere Study

The paper describes the geographical layout of the planned North American IMS magnetometer network and outlines some plans regarding instrumentation and data transmission services. The network consists of three meridional high-latitude chains, an east-west chain along the auroral zone, and a network of stations at mid-latitudes. In addition, the Air Force Cambridge Research Laboratories will have their own network with an east-west chain along geomagnetic latitude 54 N and some other mid-latitude stations. The preliminary magnetometer specifications require that the three-component flux gate magnetometer be accurate to within 0.25 gamma and that each axis be sampled every 10 sec. A block diagram is presented showing the proposed magnetometer station, of which the most complex piece of equipment will be the interface controller. The SMS-GOES satellite telemetry relay capability will be used for transmission of data from a selected network of magnetic stations to the Space Environment Laboratory in Boulder.

Lanzerotti, L. J.↗

NASA NTRS1976

Field-aligned precipitation of greater than 30-keV electrons

A search through 2-3 months of data from Ogo 6 has revealed about 10 cases of field-aligned precipitation of electrons at energies greater than 30 keV. Brief descriptions are given of the four most spectacular of these events, in which the ratio between precipitated and trapped fluxes reached about 100 in one case. Preliminary indications are that such events occur mainly in the evening and midnight sectors and at high geomagnetic latitudes (usually at or above the trapping boundary for electrons with energies greater than 30 keV).

Williams, D. J.↗

NASA NTRS1976

Fluxes of protons above 50 keV and electrons above 30 keV at approximately 35 earth radii. I - Velocity anisotropies and plasma flow in the magnetotail. II Morphology and flow patterns in the magnetotail

Imp-7 data were used to study the morphology and flow patterns of energetic proton and electron events in the magnetotail and magnetosheath at 35 earth radii. The patterns are deduced from the probability of occurrence and the spatial distribution of the events. The distribution of 50 to 200 keV proton and 30 to 90 keV electron fluxes shows that in the magnetotail (i.e., inside the magnetopause) the proton and electron events occur primarily in the plasma sheet region within plus or minus 10 earth radii of the neutral sheet; fluxes of 50- to 200-keV protons are also found in the magnetosheath, along with occasional fluxes of 30- to 90-keV electrons; the plasma sheet is well defined (at 35 earth radii) by both the proton and electron probabilities; the frequency of the electron events in the magnetotail shows a positive correlation with the geomagnetic Kp index in the dawn and dusk sectors.

Roelof, E. C.↗

NASA NTRS1976

Simultaneous observations of the proton ring current and stable auroral red arcs

Explorer 45 observed the equatorial proton ring current in the plasmapause region and Fritz Peak Observatory observed stable auroral red (SAR) arcs on Dec. 17, 1971 during a geomagnetic storm. An estimate of energy lost from the ring current was obtained by using Explorer 45 observations of pitch angle distribution transitions which are probably due to pitch angle diffusion-driven resonant interactions with ion cyclotron waves. Estimates of the equatorial loss rate yield values greater than the required SAR arc energy input rate, and the location of the peaks in these loss rates agrees with the observed location of the arcs. It is thus concluded that this energy loss is sufficient to sustain the SAR arcs.

Williams, D. J.↗

NASA NTRS1976

Storm-associated variations of equatorially mirroring ring current protons, 1-800 keV, at constant first adiabatic invariant

Explorer 45 observations of ring current protons mirroring near the equator, 1-800 keV, are presented at constant first adiabatic invariant mu throughout the period of the December 17, 1971, geomagnetic storm. The parameter mu is obtained from simultaneous magnetic field and particle observations. Particle deceleration in response to the storm time magnetic field decrease causes ring current measurements viewed at constant energy to underestimate the storm time increase in proton intensities at energies not exceeding 200 keV. This adiabatic deceleration also accounts for the large flux decreases observed at energies above 200 keV during the storm, in contradiction with previous results (Soraas and Davis, 1968) obtained using a model for the storm time magnetic field.

Lyons, L. R.↗

NASA NTRS1975

Explorer 45 /S3-A/ observations of the magnetosphere and magnetopause during the August 4-6, 1972, magnetic storm period

The Explorer 45 (S3-A) satellite performed extensive field and particle measurements in the heart of the magnetosphere during the double magnetic storm period of August 4-6, 1972. Both the ground level magnetic records and the magnetic field deformations measured along the orbit by the satellite indicated the existence of only a moderate ring current. This was confirmed by the measurements of the total proton energy density by the on-board particle detectors, which showed a maximum energy density less than the densities observed during the December 1971 and June 1972 magnetic storms. The plasmapause in the noon quadrant was eroded continuously from the onset of the first storm at the beginning of August 4 to an altitude below L = 2.07 at about 1800 hours on August 5. Throughout the entire orbit during which the second sudden commencement occurred, a large amount of low-frequency electric and magnetic field noise was encountered. The most remarkable observation during this orbit was the contraction of the magnetopause to distances inside the satellite location at L = 5.2.

Hoffman, R. A.↗

NASA NTRS1975

The storm and poststorm evolution of energetic /35-560 keV/ radiation belt electron distributions

Detailed Explorer 45 equatorial observations of the storm and poststorm structure of radiation-belt electrons (35 to 560 keV) for L values between 1.7 and 5.2 are presented. Injection during major storms results in electron pitch-angle distributions and radial profiles that are greatly distorted from their quiet-time equilibrium structure. Following storms, the pitch-angle distributions return to their prestorm shape over a period of several days. This shape is maintained as electron fluxes decay back to the quiet-time levels. The equatorial radial profiles slowly return to their prestorm equilibrium structure over a period of a few weeks and then maintain that structure.

Lyons, L. R.↗