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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

A DE-1/whistler study of the thermal plasma structure and dynamics in the dusk bulge sector of the magnetosphere

The objective of this research was to obtain new understanding of the thermal plasma structure and dynamics of the plasmasphere bulge region of the magnetosphere, with special emphasis on the erosion process that results in a reduction in plasmasphere size and on the manner in which erosion leads to the presence of patches of dense plasma in the middle and outer afternoon-dusk magnetosphere. Case studies involving data from the DE 1, GEOS 2, and ISEE 1 satellites and from ground whistler stations Siple, Halley, and Kerguelen were used. A copy of the published paper entitled 'A case study of plasma structure in the dusk sector associated with enhanced magnetospheric convection,' is included.

Carpenter, D. L.↗
NASA NTRS1993

Research relative to the heavy isotope spectrometer telescope experiment

The Heavy Isotope Spectrometer Telescope (HIST) was launched during August 1978 on ISEE-3 (ICE). HIST was designed to measure the isotopic composition of solar, galactic, and interplanetary cosmic ray nuclei for the elements from H to Ni (1 less than or equal to Z less than or equal to 28) in the energy range from approximately 5 to approximately 200 MeV/nucleon. The results of these measurements have been used in studies of the composition of solar matter and galactic cosmic ray sources, the study of nucleosynthesis processes, studies of particle acceleration and propagation, and studies of the life-history of cosmic rays in the heliosphere and in the galaxy. On December 1, 1978, after 110 days in orbit, HIST suffered an electronic failure in its readout system. After that point, only one-half of the telemetry bits associated with the pulse heights measured by HIST were transmitted to Earth. As a result, the resolution of HIST was significantly degraded, and it served as an element rather than an isotope spectrometer. Fortunately, HIST was able to measure the isotopic composition of heavy nuclei in the 9/23/78 solar event (the largest solar energetic particle event since 1972) during the brief period that it operated at full resolution. This grant funded the analysis of data from the HIST instrument over the period from 12/1/85 to 11/30/92. In section 2 of this final report, we summarize the scientific accomplishments that have resulted from HIST measurements during this time period. A bibliography of tasks and papers that resulted is attached.

Stone, Edward C.↗
NASA NTRS1992

A proposed neutral line signature

An identifying signature is proposed for the existence and location of the neutral line in the magnetotail. The signature, abrupt density, and temperature changes in the Earthtail direction, was first discovered in test particle simulations. Such temperature variations have been observed in ISEE data (Huang et. al. 1992), but their connection to the possible existence of a neutral line in the tail has not yet been established. The proposed signature develops earlier than the ion velocity space ridge of Martin and Speiser (1988), but can only be seen by spacecraft in the vicinity of the neutral line, while the latter can locate a neutral line remotely.

Doxas, I.↗
NASA NTRS1992

Anomalous aspects of magnetosheath flow and of the shape and oscillations of the magnetopause during an interval of strongly northward interplanetary magnetic field

On 15 Feb. 1978, the orientation of the interplanetary magnetic field (IMF) remained steadily northward for more than 12 hours. The ISEE 1 and 2 spacecraft were located near apogee on the dawn side flank of the magnetotail. IMP 8 was almost symmetrically located in the magnetosheath on the dusk flank and IMP 7 was upstream in the solar wind. Using plasma and magnetic field data, we show the following: (1) the magnetosheath flow speed on the flanks of the magnetotail steadily exceeded the solar wind speed by 20 percent; (2) surface waves with approximately a 5-min period and very non-sinusoidal waveform were persistently present on the dawn magnetopause and waves of similar period were present in the dusk magnetosheath; and (3) the magnetotail ceased to flare at an antisunward distance of 15 R(sub E). We propose that the acceleration of the magnetosheath flow is achieved by magnetic tension in the draped field configuration for northward IMF and that the reduction of tail flaring is consistent with a decreased amount of open magnetic flux and a larger standoff distance of the subsolar magnetopause. Results of a three-dimensional magnetohydrodynamic simulation support this phenomenological model.

Chen, Sheng-Hsien↗
NASA NTRS1993

Mars aqueous chemistry experiment

The Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. Progress for the first year MACE PIDDP is reported in two major areas of effort: (1) fluids handling concepts, definition, and breadboard fabrication and (2) aqueous chemistry ion sensing technology and test facility integration. A fluids handling breadboard was designed, fabricated, and tested at Mars ambient pressure. The breadboard allows fluid manipulation scenarios to be tested under the reduced pressure conditions expected in the Martian atmosphere in order to validate valve operations, orchestrate analysis sequences, investigate sealing integrity, and to demonstrate efficacy of the fluid handling concept. Additional fluid manipulation concepts have also been developed based on updated MESUR spacecraft definition. The Mars Aqueous Chemistry Experiment Ion Selective Electrode (ISE) facility was designed as a test bed to develop a multifunction interface for measurements of chemical ion concentrations in aqueous solution. The interface allows acquisition of real time data concerning the kinetics and heats of salt dissolution, and transient response to calibration and solubility events. An array of ion selective electrodes has been interfaced and preliminary calibration studies performed.

Clark, Benton C.↗
NASA NTRS1992

Plasmoid observations in the distant plasma sheet boundary layer

Substorm associated large amplitude bipolar magnetic events occurred when ISEE 3 was in the distant geotail's plasma sheet boundary layer (PSBL). The characteristics of these events, their substorm association and their possible source mechanisms are examined. We propose that these PSBL events are signatures of a passing plasmoid in the plasma sheet, analogous to the traveling compression region model in the geomagnetic lobes.

Moldwin, Mark B.↗
NASA NTRS1992

Waves in the inner magnetosheath - A case study

We study the waves within, and upstream of, the density enhancements in front of the magnetopause using magnetic field and plasma measurements from ISEE 1 and 2. The waves upstream of the density enhancements are most likely to be mirror modes and are convected with the magnetosheath flow. Within the density enhancements there is additional wave power at lower frequencies. These low frequency waves appear to be slow modes propagating sunward and quasi-standing in the flow. These observations lend support to the contention that the outer edge of the density enhancement is a slow mode wave front which marks the greatest distance that slow modes can propagate upstream into the solar wind.

Song, P.↗
NASA NTRS1992

The susceptibility critical exponent for a nonaqueous ionic binary mixture near a consolute point

We report turbidity measurements of a nonaqueous ionic solution of triethyl n-hexylammonium triethyl n-hexylboride in diphenyl ether. A classical susceptibility critical exponent gamma = 1.01 +/- 0.01 is obtained over the reduced temperature range t between values of 0.1 and 0.0001. The best fits of the sample transmission had a standard deviation of 0.39 percent over this range. Ising and spherical model critical exponents are firmly excluded. The correlation length amplitude xi sub 0 from fitting is 1.0 +/- 0.2 nm which is much larger than values found in neutral fluids and some aqueous binary mixtures.

Zhang, Kai C.↗
NASA NTRS1992

A two satellite study of nightside flux transfer events in the plasma sheet

The short-term (about 1 min) events during two consecutive substorms on March 23 1979 have been studied using high time resolution measurements of magnetic and electric fields and of the kiloelectronvolt electron flux at X about -21 R(e). Data obtained make it possible to describe the localized magnetic structures transported or propagated within the plasma sheet and to identify these events as plasma sheet nightside magnetic flux transfer events (NFTEs). The best examples of the NFTEs found so far are all observed in a thin portion of plasma sheet where the contraction of the reconnected field lines dominates over the oppositely directed pressure gradient force. Systematic differences in the magnetic variations observed at ISEE-1 and 2 indicate current concentration at the outer plasma sheet boundary during the passage of a NFTE.

Sergeev, V. A.↗
NASA NTRS1993

Geomagnetic substorm association of plasmoids

The relationship of geomagnetic substorms and plasmoids is examined by determining the correlation of the 366 plasmoids identified by Moldwin and Hughes (1992) with ground auroral zone magnetograms and geosynchronous particle data signatures of substorm onsets. Over 84 percent of the plasmoid events occurred between 5 and 60 min after the substorm onsets. We also find near one-to-one correlation between large isolated substorm signatures in the near-earth region and signatures consistent with a passing plasmoid in the distant tail. However, there does not appear to be an absolute correspondence of every substorm onset to a plasmoid signature in the deep tail especially for periods of prolonged disturbance that have multiple substorm onsets. A correlation of interplanetary magnetic field Bz south with plasmoid observations was also found. The locations of the near- and far-earth reconnection sites are estimated using the time of flight of the plasmoids from substorm onset to their observation at ISEE 3. The estimates of the near- and far-earth reconnection sites are highly variable and range from 10 to 140 R(E).

Moldwin, Mark B.↗
NASA NTRS1993

Energetic ion anisotropies in the geomagnetic tail. I - A statistical survey. II - Magnetic field and substorm characteristics

A comprehensive data set from the ISEE 2 spacecraft is used here to perform a statistical study of events in the earth's central magnetotail that are characterized by high anisotropies of energetic ions. In about 75 percent of the cases the anisotropy vector deviates no more than 45 deg from the tidal axis. High-anisotropy samples within 45 deg of the tidal axis are dominated by the earthward fraction. High ion anisotropies are observed continuously for longer than 1 min only in a few cases. The probability of observing high ion anisotropies is significantly enhanced beyond about 16 R(E) downtail distance within a few earth radii of the neutral sheet and on the duskside of the magnetotail. The analysis is extended with respect to the local magnetic field and to the relationship between energetic ion anisotropies and substorm phases. It is found that the events can be well organized in terms of substorm expansion phase and substorm recovery. These relations and the magnetic field characteristics during the events support the notion that the near-earth source of tailward streaming ions is identical with a substorm neutral line.

Kettmann, Georg↗
NASA NTRS1993

Wave properties near the subsolar magnetopause - Pc 3-4 energy coupling for northward interplanetary magnetic field

Strong slow mode waves in the Pc 3-4 frequency range are found in the magnetosheath close to the magnetopause. We have studied these waves at one of the ISEE subsolar magnetopause crossings using the magnetic field, electric field, and plasma measurements. We use the pressure balance at the magnetopause to calibrate the Fast Plasma Experiment data versus the magnetometer data. When we perform such a calibration and renormalization, we find that the slow mode structures are not in pressure balance and small scale fluctuations in the total pressure still remain in the Pc 3-4 range. Energy in the total pressure fluctuations can be transmitted through the magnetopause by boundary motions. The Poynting flux calculated from the electric and magnetic field measurements suggests that a net Poynting flux is transmitted into the magnetopause. The two independent measurements show a similar energy transmission coefficient. The transmitted energy flux is about 18 percent of the magnetic energy flux of the waves in the magnetosheath. Part of this transmitted energy is lost in the sheath transition layer before it enters the closed field line region. The waves reaching the boundary layer decay rapidly. Little wave power is transmitted into the magnetosphere.

Song, P.↗
NASA NTRS1993

Ion temperature profiles in the horns of the plasma sheet

The plasma sheet horns are the low-altitude extensions of the plasma sheet that lie poleward of the plasmasphere and equatorward of the tail lobes. Within the horns, magnetic field lines of increasing geomagnetic latitudes map to increasing distances into the downtail plasma sheet. Plasma data from the fast plasma experiment on ISEE 2 have been analyzed for 11 outbound crossings of the horns in the premidnight sector of the magnetosphere at typical altitudes of 2-4 R(E). These crossings typically occurred on time scales of less than 1 hour, providing almost instantaneous snapshots of plasma gradients within the horns. Ion temperatures observed during these crossings generally decreased by a factor of four to eight as magnetic field lines of increasing geomagnetic latitude were traversed. If we make the reasonable assumption that the ion temperatures are constant along the field lines within the plasma sheet, then this result implies that the ion temperatures in the downtail plasma sheet also commonly decrease by this same factor over the radial range extending from the inner edge of the plasma sheet at the plasmapause boundary to the outer edge at a neutral line in the distant tail.

Suszcynsky, D. M.↗
NASA NTRS1993

The abundances of hydrogen, helium, oxygen, and iron accelerated in large solar particle events

Energy spectra measured in 10 large flares with the University of Maryland/Max-Planck-Institut sensors on ISEE I and Goddard Space Flight Center sensors on IMP 8 allowed us to determine the average H, He, O, and Fe abundances as functions of energy in the range of about 0.3-80 MeV/nucleon. Model fits to the spectra of individual events using the predictions of a steady state stochastic acceleration model with rigidity-dependent diffusion provided a means of interpolating small portions of the energy spectra not measured with the instrumentation. Particles with larger mass-to-charge ratios were relatively less abundant at higher energies in the flare-averaged composition. The Fe/O enhancement at low SEP energies was less than the Fe/O ratios observed in He-3-rich flares. Unlike the SEP composition averaged above 5 MeV/nucleon, the average SEP abundances above 0.3 MeV/nucleon were similar to the average solar wind.

Mazur, J. E.↗
NASA NTRS1993

Ion and electron heating at the low-Mach-number, quasi-parallel bow shock

The study examines the magnetic structure and energy dissipation at low-Mach-number, quasi-parallel collisionless shocks on the basis of observations obtained by the ISEE 1 and 2 spacecraft at seven crossings of the earth's dayside bow shock. All the shocks exhibit a fairly short-scale-length ramp where the principal jumps in the electron temperature, ion temperature, and magnetic field strength take place. Large-amplitude LF transverse waves in the magnetic field are present in and downstream from the ramp, with more modest waves upstream. The amplitude of the downstream waves is typically larger than can be accounted for by shock compression of the upstream waves. The electron heating represents about 6 percent of the dissipated bulk flow energy, consistent with observations in other parameter regimes, and suggesting that the dominant electron heating process is the same. It is suggested that the low-Mach-number shocks are reforming but do not exhibit downstream variability because of the relatively low levels of reflected ions.

Thomsen, M. F.↗
NASA NTRS1993

Anomalous aspects of magnetosheath flow and of the shape and oscillations of the magnetopause during an interval of strongly northward interplanetary magnetic field

On February 15, 1978, the orientation of the IMF remained steadily northward for more than 12 hours. Using plasma and magnetic field data from ISEE 1 and 2, IMP 8, and IMP 7, we show that (1) the magnetosheath flow speed on the flanks of the magnetotail steadily exceeded the solar wind speed by 20 percent, (2) surface waves of about 5-min period and very nonsinusoidal waveform were persistently present on the dawn magnetopause and waves of similar period were present in the dusk magnetosheath, and (3) the magnetotail ceased to flare at an antisunward distance of 15 earth radii. We propose that the acceleration of the magnetosheath flow is achieved by magnetic tension in the draped field configuration for northward IMP; the reduction of tail flaring is consistent with a decreased amount of open magnetic flux and a larger standoff distance of the subsolar magnetopause. Results of a 3D MHD simulation support this phenomenological model.

Chen, Sheng-Hsien↗
NASA NTRS1993

Wave properties near the subsolar magnetopause - Pc 1 waves in the sheath transition layer

We study the waves in the frequency range of Pc 1 in the sheath transition layer of the magnetopause from the ISEE 1 and 2 observations. The waves are enhanced in the sheath transition layer, although they are scattered into the magnetosheath when the outer edge of the sheath transition layer is not sharp. The wave frequency is proportional to, and equal to, about 44 percent of the ion gyrofrequency. The waves are left-handed polarized for southward IMF, but linearly polarized for northward IMF. The direction of maximum variation is perpendicular to both the background field and the gradients of the field and density for northward IMF; for southward IMF, the waves are more turbulent. Wave generation mechanisms may depend on IMF orientations rather than the shock geometry. To investigate the free energy generating the waves for northward IMF, a method is developed combining the measurements from the fast plasma experiment and Lepedea to obtain a high time resolution estimate of the temperature anisotropy for strongly northward IMF. The estimated ion temperature anisotropy is enhanced, up to a factor of 2, within the sheath transition layer for northward IMF.

Song, P.↗
NASA NTRS1993

Comment on 'Observations of reconnection of interplanetary and lobe magnetic field lines at the high-latitude magnetopause' by J.T. Gosling, M.F. Thomsen, S.J. Bame, R.C. Elphic, and C.T. Russell

Comment is presented on the results of measurements, reported by Gosling et al. (1991), that were made on ISEE in the vicinity of the high-latitude dusk magnetopause near the terminator plane, at a time when the local magnetosheath and tail lobe magnetic fields were nearly oppositely directed. The character of the observed plasma flowing both tailward and sunward within the high-latitude magnetopause current layer presented real evidence for the local reconnection process. Gosling et al. argued that this process may be a manifestation of different global magnetospheric topology structures. In the comment, a global magnetospheric convection pattern is constructed for the northward IMF and for the case of a large azimuthal component of the IMF with small Bz, irrespective of its sign. The suggested scheme provides a simple explanation for the observed sunward convection in the polar caps both for the northward and for strong By with small Bz. According to the present model, for the magnetosheath field at 2300 UT on June 11, 1978, the reconnection between the open field lines appears at the northern neutral point.

Belen'kaia, Elena↗